Food Chemistry 133 (2012) 1138–1154

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Food Chemistry

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Acrylamide formation in fried potato products – Present and future, a criticalreview on mitigation strategies

Raquel Medeiros Vinci, Frédéric Mestdagh, Bruno De Meulenaer ⇑NutriFOODchem Unit, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium

a r t i c l e i n f o a b s t r a c t

Article history:Available online 6 August 2011

Keywords:AcrylamideFried potato productsFrench friesMitigation strategiesLab scale testsIndustrial productionRisk management

0308-8146/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.foodchem.2011.08.001

⇑ Corresponding author. Tel.: +32 9 264 61 66; fax:E-mail address: Bruno.DeMeulenaer@UGent.be (B.

Acrylamide is proven to be carcinogenic in rodents and a ‘probable’ human carcinogen, with increasingevidence of positive associations with human cancers. Thus, authorities and industry urge to find solu-tions for acrylamide formation, while no legal limits have yet been established for this contaminant infoods. Most of the acrylamide dietary exposure results from potato products, coffee, bakery productsand chocolate. Acrylamide is formed in potato products during industrial processing, retail, cateringand home preparation. This review summarizes the research to date on acrylamide levels, mechanismsof formation, assessment of acrylamide intake and health risk, and possible mitigation strategies fromfarm to fork in fried potato products. Furthermore, relevant issues regarding the implementation of mit-igation strategies on an industrial scale are discussed and evolution of risk management summarized. Inconclusion, ‘lab scale studies’ in acrylamide mitigation research should be interpreted with utmost care.This leads to the pertinent question ‘‘What is the next step to reduce acrylamide exposure while main-taining the expected product quality for the consumer?’’

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Acrylamide is used in the chemical industry since the 1950s asan intermediate in the production of polyacrylamide polymers andcopolymers in order to improve adhesion and cross-link of poly-mers. Polymerized acrylamide is widely used as a flocculant inwastewater treatment and paper and textile manufacturing. Itsapplication is also extended as grouting agents for the constructionof dam foundations, sewers and tunnels, in cosmetics and in elec-trophoresis gels. Incomplete polymerization may result in residualamounts of the acrylamide monomer in final products (Shipp et al.,2006) with a maximum concentration permitted up to of 5 mg/kg(Cosmetic Ingredient Review, 2009). In addition, acrylamide is alsofound in filtered cigarette mainstream smoke (Smith, Perfetti,Rumple, Rodgman, & Doolittle, 2000).

After the leakage of acrylamide that occurred at the Hallandsåstunnel construction in Sweden (Reynolds, 2002), unexpected highlevels of acrylamide were found in the blood of a control groupof subjects (non-smokers) without occupational exposure. Thesefindings led to the hypothesis that acrylamide might be presentvia dietary exposure (Tareke, Rydberg, Karlsson, Eriksson, &Törnqvist, 2000). The Swedish National Food Administration re-ported in 2002 the presence of relevant amounts of acrylamidein several carbohydrates rich foods baked at high temperatures

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+32 9 264 62 15.De Meulenaer).

(Swedish National Food Administration, 2002). These findingswere soon confirmed by other research groups and together withstakeholders, efforts were carried out to build greater understand-ing of acrylamide, concerning the mechanism of its formation infoods, the risks associated for consumers and possible strategiesto lower acrylamide levels in foodstuffs.

1.1. Pathways for acrylamide formation

Soon after its discovery in heat processed foods, scientists re-ported that acrylamide was formed during the Maillard reaction(Mottram, Wedzicha, & Dodson, 2002; Stadler et al., 2002)(Fig. 1). This non-enzymatic browning reaction influences severalaspects of food quality such as, flavor, color and aroma formation.Mass spectral studies using 15N-labeled asparagine and 13C-labeledglucose confirmed that the three carbon atoms and the nitrogen ofthe amide group are derived from asparagine. Although asparaginealone may release acrylamide by thermally initiated decarboxyl-ation and deamination, in the presence of reducing sugars acrylam-ide formation from asparagine is significantly increased (Yaylayan,Wnorowski, & Locas, 2003). The major mechanism of acrylamideformation therefore involves the reaction of a carbonyl compound(preferably an a-hydroxycarbonyl) with asparagine, resulting inthe corresponding N-glycosyl conjugation and the formation of adecarboxylated Schiff base (after dehydration under high temper-atures) (Stadler et al., 2004; Zyzak et al., 2003). This reactioninvolves a cascade of reactions with different highly reactive

Fig. 1. Proposed mechanism for acrylamide formation as a side reaction of the Maillard reaction. Based on Mottram et al. (2002), Stadler et al. (2004) and Granvogl andSchieberle (2006).

R. Medeiros Vinci et al. / Food Chemistry 133 (2012) 1138–1154 1139

intermediates resulting in acrylamide formation in food. The fol-lowing intermediates have been proposed (Fig. 1): (a) the decar-boxylation of the Schiff base which may lead after decompositiondirectly to acrylamide and an imine or followed by hydrolysis to3-aminopropamide (3-APA) and carbonyl compounds. In this re-spect, it should be noted that 3-APA may also occur in potatoesas such (Granvogl & Schieberle, 2006); (b) subsequent eliminationof ammonia from 3-APA can yield acrylamide (Granvogl & Schi-eberle, 2006); (c) alternatively, the hydrolysis of the imine whichfurnishes the Strecker aldehyde of asparagine (3-oxopropanamide)may also yield acrylamide, although to a limited extent (Blanket al., 2005; Stadler & Scholz, 2004).

Other minor reaction routes have been proposed for acrylamideformation, such as from ammonia and acrolein in the absence ofasparagine, a pathway that was suggested to play a role in lipidrich foods (Yasuhara, Tanaka, Hengel, & Shibamoto, 2003). Acroleincan be formed by oxidative lipid degradation or from glycerol,leading to acrylic acid. Acrylic acid can react with ammonia to formacrylamide (Yaylayan, Locas, Wnorowski, & O’Brien, 2005). How-ever, this pathway does not seem to be involved in acrylamide for-mation in fried potatoes (Becalski, Lau, Lewis, & Seaman, 2003). Itwas also reported that oil degradation products, such as glycerol,

mono-, and diacylglycerols had no significant impact on acrylam-ide formation in a potato model system and French fries(Mestdagh, De Meulenaer, & Van Peteghem, 2007). Nonetheless,recent studies have demonstrated that some oxidized lipids maypotentially promote the decarboxylation of asparaginase and thelater deamination of the produced 3-APA (Hidalgo, Delgado,Navarro, & Zamora, 2010; Zamora, Delgado, & Hidalgo, 2009;Zamora & Hidalgo, 2008). Acrylamide formation has also been pro-posed from protein pyrolysis in dry heated wheat gluten (Claus,Weisz, Schieber, & Carle, 2006).

Nevertheless, a general consensus has been achieved upon thatthe major route for acrylamide formation in potato productsremains the route via asparagine and reducing sugars.

1.2. Occurrence of acrylamide in foods and dietary exposureassessment

Acrylamide is present in several carbohydrate rich foods whencooked at high temperatures (>120 �C) upon frying, baking androasting. The European Union recommended in 2007 that MemberStates perform annually the monitoring of acrylamide in certainfoodstuffs (EC, 2007). The results from 2007 to 2009 have been

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recently published (EFSA, 2011) and are summarized in Table 1.The data of the three monitoring years was statistically evaluatedin order to determine possible trends of acrylamide contents infoodstuffs. Based on the available data, it could be identified thatacrylamide levels decreased in ‘crackers’, ‘infant biscuits’ and ‘gin-gerbread’ over the 3 years, whilst it increased in ‘crisp bread’ and‘instant coffee’. No significant changes were observed for ‘potatocrisps’, ‘oven fried potatoes’, ‘bread not specified’, ‘breakfast cere-als’, ‘jarred baby foods’ and ‘processed cereal-based baby foods.Nonetheless, EFSA concluded that a three-year food samplingwas too short to distinguish random fluctuations from real trends.Also recently, the Joint FAO/WHO Expert Committee has reporteddata regarding acrylamide levels in foodstuffs analyzed between2004 and 2009 from 31 countries (12,582 analytical results fromsingle or composite samples). Mean concentrations of acrylamidein major foods were found to range from 399 to 1202 lg/kg for po-tato chips; from 159 to 963 lg/kg for French fries; from 169 to518 lg/kg for cookies; from 87 to 459 lg/kg for crispbread andcrackers; and from 3 to 68 lg/l for coffee (ready to drink) (FAO/WHO, 2011).

A great variability in acrylamide levels can be observed withineach food category as shown in Table 1. Moreover, such variationhas also been reported within the same batch (Roach, Andrzejew-ski, Gay, Nortrup, & Musser, 2003; Sanny, Luning, Marcelis, Jinap, &van Boekel, 2010). Factors such as variability of acrylamide precur-sors in the raw material, difference in food composition, differencein process parameters and final baking conditions could be sourcesof fluctuations. Furthermore, concentrations of acrylamide presentin heated foods are the result of simultaneously occurring forma-tion and elimination mechanisms (Claeys, De Vleeschouwer, &Hendrickx, 2005a; Gökmen & Senyuva, 2006a). This big variabilityof acrylamide levels in foods becomes important when consideringdietary exposure to acrylamide and moreover when evaluatingpossible mitigation strategies, as will be discussed ahead.

The Joint FAO/WHO Expert Committee on Food Additives (JEC-FA) estimated the mean dietary acrylamide intake for general pop-ulation including children, between 1 and 4 lg/kg bw/day. It wasnoted that children have dietary acrylamide exposures at least

Table 1Acrylamide levels (lg/kg) of foodstuffs monitored from 2007 to 2009 reported by EFSA. A

2007

Nb Meana SDc M

Biscuits crackers 66 284 315 15Biscuits infant 97 204 352 23Biscuits not specified 291 303 433 42Wafers 38 210 256 13Bread crisp 153 228 328 24Bread soft 123 70 116 9Bread non specified 54 190 424 25Coffee instant 51 357 327 10Coffee non specified 41 261 268 11Coffee roasted 151 253 203 9Gingerbread 357 425 494 36Muesli and porridge 47 215 183 8Other products not specified 378 271 355 25Substitute coffee 59 800 1062 47Breakfast cereals 132 152 184 16Cereal-based baby food 92 69 72 3Jarred baby food 87 44 35 1Home cooked potato products deep fried 54 354 413 16Home cooked potato products not specified 82 277 392 21Home cooked potato products oven fried 8 385 342 9French fries 647 357 382 26Potato crisps 273 565 259 41

a Values based on an upper bond scenario (values below LOD and values between LOb Number of individual samples analyzed for each food category.c Standard deviation of the upper bond scenario. Standard deviation not available for

twice as high as for adult consumers when expressed on a bodyweight basis (FAO/WHO, 2011). EFSA also recently performed anexposure assessment based on acrylamide monitoring results from2007 to 2008. The 95th percentile of acrylamide intake for adults(>18 years) and for children (3–10 years) were estimated to rangebetween 0.6–2.3 lg/kg bw/day and 1.5–4.2 lg/kg bw/day, foradults and children, respectively (EFSA, 2011). Foods contributingthe most to dietary intake will differ from country to country,according to different dietary patterns and the way how foodstuffsare processed and prepared. However, several acrylamide intakestudies indicate that fried potato products (French fries and potatocrisps), bread and bakery products, coffee and breakfast cereals arethe food commodities that contribute the most for dietary acryl-amide exposure. Other food items contribute less than 10% of thetotal dietary intake (Boon et al., 2005; Claeys et al., 2010; Dybinget al., 2005; EFSA, 2011; FAO/WHO, 2011; Konings et al., 2003;Mestdagh et al., 2007; Mojska, Gielecinska, Szponar, & Oltarzewski,2010; Svensson et al., 2003; Wilson, Rimm, Thompson, & Mucci,2006).

1.3. Health risks and risk assessment

Acrylamide contains an electrophilic double bond which can re-act with nucleophilic groups, hence covalently interacting in vivowith cellular nucleophiles such as the sulphydryl groups in re-duced glutathione and in proteins, and to a lesser extent proteinamino groups (Dybing et al., 2005). Acrylamide is known to be neu-rotoxic and several toxicological studies have demonstrated itsgenotoxic carcinogenicity in animals and thus indicating potentialhuman health risks (Friedman, Dulak, & Stedham, 1995; Johnsonet al., 1986; Rice, 2005). In 1994 the International Agency for Re-search on Cancer classified acrylamide as a possible carcinogenfor humans (Group 2A), based on its carcinogenicity in rodents(IARC, 1994).

According to data derived from animal studies, acrylamide isquickly absorbed by the skin and by the mucosa if inhaled. If takenby the oral route, acrylamide is well absorbed and widely distrib-uted to the tissues as well as to the fetus (Friedman, 2003). It has

dapted from (EFSA, 2011).

2008 2009

ax. Nb Meana SDc Max. Nb Meana Max.

26 131 204 178 1042 99 208 132000 88 110 147 1200 51 108 43000 260 209 247 1940 330 140 264078 48 252 416 2353 90 246 72530 90 235 273 1538 130 223 86010 191 49 56 528 110 37 36465 17 23 19 86 84 76 146047 58 502 285 1373 46 595 147058 10 241 215 720 14 551 292958 253 208 182 1524 172 231 222315 246 437 545 3307 302 384 409505 18 43 27 112 92 82 48429 445 198 309 2592 249 204 165000 73 1124 1138 7095 34 1504 430000 120 170 247 2072 153 142 143553 96 45 81 660 99 70 71062 128 35 39 297 118 47 67761 39 228 253 1220 49 241 123875 100 192 402 3025 136 265 276241 94 235 268 1439 72 317 166568 521 280 279 2466 469 328 338080 435 616 634 4382 388 693 4804

D and LOQ were set to the LOD or the LOQ value, respectively).

the 2009 data.

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been postulated that acrylamide is carcinogenic through a geno-toxic pathway (Dybing et al., 2005), after conversion to glycida-mide, a DNA-reactive epoxide. However, studies indicate thatacrylamide-induced carcinogenicity, might also be modulated byhormonal systems (Besaratinia & Pfeifer, 2007; Pedersen et al.,2010; Wilson, Mucci, Rosner, & Willett, 2010). This and otherrelative risks determined in epidemiological studies turned out tobe 10–100 fold higher than expected from animal studies (Dybing& Sanner, 2003; Hogervorst, Schouten, Konings, Goldbohm, & vanden Brandt, 2007; Wilson et al., 2010). Thus suggesting thatrodents might not be good models for all types of cancer(Hogervorst et al., 2010). Numerous case-control and prospectivecohort studies have investigated possible associations betweendietary acrylamide intake and risk for several types of human can-cers. Yet, most of breast cancer research done to date has not foundan association with dietary acrylamide exposure (Burley et al.,2010; Hogervorst et al., 2007; Larsson, Akesson, & Wolk, 2009;Mucci et al., 2005; Pedersen et al., 2010; Pelucchi et al., 2006;Wilson, Mucci et al., 2009; Wilson et al., 2010). Burley et al.(2010) however reported a weak correlation for premenopausalbreast cancer and acrylamide intake. A cell culture study recentlypublished demonstrated the effect of acrylamide on early molecu-lar changes known to be linked to the development of breast can-cer (Lyn-Cook et al., 2011), therefore, further investigation is stillwarranted. So far, there is no evidence either that acrylamide in-take could influence brain, bladder, prostate, lung, thyroid andgastrointestinal cancers (Hogervorst, Schouten, Konings,Goldbohm, & van den Brandt, 2008; Hogervorst, Schouten,Konings, Goldbohm, & van den Brandt, 2008; Hogervorst,Schouten, Konings, Goldbohm, & van den Brandt, 2009;Hogervorst, Schouten, Konings, Goldbohm, & van den Brandt,2009; Larsson, Akesson, & Wolk, 2009; Pelucchi et al., 2006;Schouten, Hogervorst, Konings, Goldbohm, & van den Brandt,2009; Wilson, Balter et al., 2009). On the other hand, increasedrisks were reported for ovarian and endometrial cancers(Hogervorst et al., 2007; Wilson et al., 2010), although otherauthors found no association between these cancers and acrylam-ide intake (Larsson, Akesson, & Wolk, 2009; Larsson, Hakansson,Akesson, & Wolk, 2009; Pelucchi et al., 2006). Other positive asso-ciations were reported for renal (Hogervorst, Schouten et al., 2008),oral cavity (Schouten et al., 2009) and esophageal (Lin, Lagergren, &Lu, 2011) cancers. A recent review paper summarizes animal andepidemiological studies up to 2010 on the carcinogenicity ofdietary acrylamide intake (Hogervorst et al., 2010). Many of thehuman cancer studies present certain uncertainties related toimprecise estimates of acrylamide intake based on calculationsfrom food consumption databases or from the use of food fre-quency questionnaires (FFQs). Moreover, the large variability be-tween individual foods is a further limitation in these studies,leading to a relatively small difference between high – and low –level intake and therefore lacking sufficient power to detect effectson cancer incidence (Mills, Mottram, & Wedzicha, 2009).

Genotoxic carcinogens are often considered to have no thresh-old limit of exposure, meaning that a single exposure to one mol-ecule of carcinogen could trigger the biological process leading tocancer (FAO/WHO, 2005). Since acrylamide is present at quite highlevels in many food products consumed daily, EFSA and the JointFAO/WHO Committee recommend the MOE ‘margin of exposure’approach as the preferred method of risk assessment for this con-taminant (EFSA, 2005; FAO/WHO, 2005). The value of the MOE isrepresented by the ratio between a particular point on the dose–response curve leading to tumors in experimental animals andthe human dietary intake. Thus, this value indicates the level ofconcern to assist risk managers in setting priorities for implement-ing measures to protect public health. The higher the MOE, thelower the risk of exposure to the component concerned. The

MOE values reported for acrylamide range from 200 to 50, forthe general population and consumers with high exposure, respec-tively. These low MOE values not only reveal that this contaminant,being genotoxic and carcinogenic, indeed presents a human healthconcern (FAO/WHO, 2011), but also indicates that acrylamide is amuch more ‘‘severe’’ process contaminant compared to others(e.g. benzo(a)pyrene with MOE values ranging from 10,000 to25,000). Thus, authorities and industry urge to find a solution foracrylamide formation in foods. This review will focus on acrylam-ide formation and mitigation in fried potato products, since theseare so important on the total intake of dietary acrylamide.

2. Different aspects affecting acrylamide formation in friedpotato products and possible mitigation strategies

Potato products are strongly susceptible to acrylamide forma-tion. On one hand, this food commodity contains the acrylamideprecursors (asparagine and reducing sugars) and, on the otherhand, the traditional applied baking conditions (tempera-tures > 120 �C), such as frying and roasting favor the Maillard reac-tion to occur, which is linked to acrylamide formation (Fig. 1).Thus, all potential strategies to prevent acrylamide formationmay be resumed in two major approaches, removal of the acrylam-ide precursors or interference with the Maillard reaction (Table 2).However, since the Maillard reaction is essential for the desiredand characteristic flavor and color formation of potato products,this constitutes the first challenge for food scientists on how toreduce acrylamide formation without affecting final product spec-ifications and quality. Research performed to date, and described inthis section, demonstrates the necessity of a farm-to-fork approachin order to reduce acrylamide in fried potato products. Severalrelevant aspects regarding acrylamide formation at different stagesof commercial production of French fries and other potatoproducts, are presented in Table 2 and discussed in the followingsections.

2.1. Potato cultivar

Potato composition varies greatly between different cultivarsbut generally comprises 63–87% water, 13–37% dry matter, 13–30% carbohydrates, 0.7–4.6% proteins, 0.02–0.96% lipids, 0.2–3.5 fi-ber, and 0.4–2% ash (Torres & Parreño, 2009). In potatoes, aspara-gine concentrations are relatively in excess compared to reducingsugar contents. Thus, it is the latest which represents the limitingfactor in acrylamide formation and therefore will largely deter-mine acrylamide formation in potato products (Amrein et al.,2003; Amrein et al., 2004; Becalski et al., 2004; De Wilde et al.,2005).

Some varieties are therefore more suitable than others forFrench fries production. These generally consist of cultivars withlarge, long, oval tubers containing moderately high dry matterand low reducing sugar contents. Regarding crisps production, cul-tivars with even lower reducing sugar contents, higher dry matterand moderate sized oval tubers are preferred (Torres & Parreño,2009). De Wilde, De Meulenaer, Mestdagh, Govaert, Ooghe et al.(2006) reported that acrylamide levels in fried potatoes derivedfrom 16 different varieties correlated to reducing sugar contentof the potatoes (R2 = 0.82, n = 96). The correlation between reduc-ing sugars and acrylamide formation has been demonstrated inseveral other studies, whereas sucrose and asparagine presentedno correlation (Amrein et al., 2003; Amrein et al., 2004;Biedermann, Noti, Beidermann-Brem, Mozzetti, & Grob, 2002; DeWilde et al., 2005; Mestdagh, De Wilde, Delporte, Van Peteghem,& De Meulenaer, 2008; Medeiros Vinci, Mestdagh, De Muer, VanPeteghem, & De Meulenaer, 2010).

Table 2Industrial production process of French fries and other potato products and possible variables influencing acrylamide formation in the final product,with reference to the main mechanism of action on acrylamide formation (effect on precursors or the Maillard reaction).

Industrial production process for French fries and potato crisps Precursors Maillard reaction

Raw material production Pre-harvestCultivar XFertilization XClimate XMaturity X

Post-harvestStorage (time and temperature) X

Processing Quality control of raw material X related to colorSorting (size) XPeeling/washingCutting X surface-volume ratioBlanching (time and temperature) XDip (dextrose and SAPP, and other additives) XDrying XPar-fryinga XFreezinga

PackagingFinal frying X color formation

a Not applicable for potato crisps.

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2.2. Soil properties and fertilization

Soil type may influence the specific gravity of tubers due to itswater holding capacity, drainage, aeration, structure, temperatureand fertility (Torres & Parreño, 2009). However, only minor differ-ences in acrylamide formation from 16 different varieties grown ina sandy loam soil vs a clay soil were reported by De Wilde, De Meu-lenaer, Mestdagh, Govaert, Ooghe et al. (2006). A recent studyexamined the effect of tuber mineral composition (influenced byboth the mineral content and pH of the soil), on the expressionof asparagine and reducing sugars in tubers (Whittaker et al.,2010). The authors concluded that the cultivation location had asignificant effect on the mineral composition of the tubers, andsubsequently reducing sugar contents were negatively correlatedwith potassium and calcium, and positively correlated with zincand copper contents.

Nitrogen fertilization has been reported in literature to have animpact on asparagine and reducing sugars concentrations. A de-crease in nitrogen fertilization enhanced reducing sugars expres-sion resulting in an increase of acrylamide formation (De Wilde,De Meulenaer, Mestdagh, Govaert, Vandeburie et al., 2006). Moder-ate nitrogen fertilization combined with a good provision of potas-sium may result in low levels of free asparagine and reducingsugars in tubers (Heuser, Gerendás, & Sattelmacher, 2005). Thecombination of high phosphorous and low potassium supply hasbeen reported to increase asparagine and reducing sugars in pota-toes (Gerendas, Heuser, & Sattelmacher, 2007). These studiesclearly indicate that the mineral composition involved in the pota-to tubers development, either due to the soil composition or to fer-tilization, may have an impact on concentrations of acrylamideprecursors in potato products. An appropriate balance betweenthe levels of fertilizers therefore should be considered in order toobtain tubers less prone to acrylamide formation, while taking intoaccount possible environment impacts and legal fertilization limits(De Wilde, De Meulenaer, Mestdagh, Govaert, Vandeburie et al.,2006).

2.3. Climatological conditions and maturity of the tuber

Climatological conditions during tuber development and nearto harvest period may affect the susceptibility of acrylamide for-mation in potatoes. The effect of seasonal variation on the chemicalcomposition of four potato varieties (used in the French fries and

crisp production) over a period of 9 months storage has been stud-ied (De Meulenaer et al., 2008). Results showed a significant im-pact of variable climatological conditions on reducing sugar, drymatter, total free amino acid, and free asparagine contents of tu-bers. Lower reducing sugar contents were observed on exception-ally warm summers which resulted in lower acrylamide generationin fried potatoes.

Throughout tuber maturation, nutrients are transported fromthe leaves to the tuber, and during vine senescence prior to har-vesting, a drop of sugar levels in the tuber is normally observed.This drop in sugar concentration is therefore an indication ofchemical maturity and suggests that harvesting can proceed withthe maximum likelihood of quality being maintained in storage(Torres & Parreño, 2009). The harvest of immature and thus smal-ler tubers is related to higher reducing sugar contents in the tuberand therefore increased acrylamide formation upon final frying (DeWilde, De Meulenaer, Mestdagh, Govaert, Ooghe et al., 2006). How-ever, the maturity of the tuber upon harvest not only influencesreducing sugar levels in the tubers but also the enzymatic systemresponsible for cold induced sweetening (Hertog, Putz, & Tijskens,1997). Accordingly, this agronomical aspect is strongly related tothe tuber storage behavior which is discussed below.

2.4. Potato storage

Generally after harvest, tubers are stored up to several monthsin order to maintain supplies of potatoes throughout the year.Nonetheless, certain storage conditions can cause potatoes to accu-mulate unacceptable quantities of sugars, even though levels wereacceptable at harvest. Senescent sweetening and cold tempera-tures are the main causes of sugar accumulation during storage.Senescent sweetening results from an enzymatic process which oc-curs more rapidly at higher storage temperature (>8 �C) and is re-lated to the start of sprout growth (Amrein et al., 2004). Chemicalsprout suppressing agents may be used to avoid tuber sprouting,although this is not always an option due to customer demands.An alternative solution for avoiding tubers to sprout in additionto making tubers less susceptible to diseases, is cold temperaturestorage (<8 �C) (Blenkinsop, Copp, Yada, & Marangoni, 2002; Bur-ton & Wilson, 1978). This alternative however, has a major impacton reducing sugar accumulation (Fig. 2) and subsequently in acryl-amide formation in fried potato products (Biedermann et al., 2002;De Wilde et al., 2005; Knutsen et al., 2009; Matsuura-Endo et al.,

Fig. 2. Influence of storage time and temperature on acrylamide formation duringfrying of three varieties (Bintje, Ramos, Saturna) stored at 4 and 8 �C over 24 weeks,expressed in lg/kg (� = Bintje, 4 �C; j = Ramos, 4 �C; N = Saturna, 4 �C; } = Bintje,8 �C; h = Ramos, 8 �C; 4 = Saturna, 8 �C). Reprinted from (De Wilde et al., 2005)with kind permission from the American Chemical Society (� 2005).

R. Medeiros Vinci et al. / Food Chemistry 133 (2012) 1138–1154 1143

2006; Noti et al., 2003; Ohara-Takada et al., 2005; Olsson, Svens-son, & Roslund, 2004; Viklund, Olsson, Sjoholm, & Skog, 2008; Vikl-und, Olsson, Sjoholm, & Skog, 2010). Thus, cold inducedsweetening is presumably a defense mechanism of tubers to pro-tect themselves from frost, and therefore start mobilizing sugarsfrom starch at temperatures <8 �C (Blenkinsop et al., 2002). Aspar-agine contents appear to be not susceptible to different storagetemperatures and long storage time (De Wilde et al., 2005). Reduc-ing sugar content is not significantly influenced when potatoes arestored at 8 �C (Biedermann et al., 2002; De Wilde et al., 2005; DeWilde, De Meulenaer, Mestdagh, Govaert, Ooghe et al., 2006; Notiet al., 2003) (Fig. 2). Therefore potato tubers should be ideallystored at intermediate temperature of approximately 8 �C (Kumar,Singh, & Kumar, 2004). On the other hand, cold conditions aresometimes unavoidable during winter periods. While senescentsweetening is a permanent condition and only gets worse withtime, cold induced sweetening may be partially reversible (Burton,1989). Submission of cold-stored tubers at 15 �C for a period of3 weeks may result in a reversible reduction of the reducing sugarlevels (Biedermann et al., 2002; Blenkinsop et al., 2002; De Wildeet al., 2005). This solution however may affect the production yield,due to changes in dry matter content. In the case of sugar accumu-lation due to senescence sweetening, it is critical that no attempt ismade to recondition the potatoes, since warm temperatures willonly speed up the aging process, therefore incrementing the prob-lem (Torres & Parreño, 2009).

2.5. Quality control of incoming potatoes

All the above mentioned agronomical aspects unavoidably leadto great variability of the raw material between different seasonsand even within the same storage season. Reducing sugars are animportant parameter in the quality control of potatoes for process-ing given their influence not only on acrylamide formation (Amreinet al., 2004; Biedermann et al., 2002; De Wilde et al., 2005) but alsoon the final color of fried potato products (Mestdagh, De Wilde,Castelein et al., 2008; Márquez & Añón, 1986; Pedreschi, Moyano,Kaack, & Granby, 2005; Pedreschi, Kaack et al., 2007). Current qual-ity control criteria before accepting potato lots for production,comprise size grading (as mentioned above smaller tubers tendto accumulate more reducing sugars), dry matter determinationand color evaluation with a USDA (US Department of Agricul-ture)/Munsell color chart (after a short frying test, typically180 �C for 3 min) (EUPPA, 2007). The later relates raw material tocolor specifications of final product (customer demand) and,

accordingly, either the raw material is rejected for processing orappropriate adjustments are taken (e.g. optimized blanching con-ditions). Thus, an effective entrance control of the raw potato tu-bers could identify batches of potatoes prone to acrylamideformation and therefore prevent the problem of acrylamide forma-tion at the start of the production process. A recent study evaluatedwhether alternative color measurements (Agtron process analyzerand with CIE L⁄a⁄b⁄ color parameters) and/or reducing sugar con-tent determination would correlate better with acrylamide levelsof French fries upon final frying (Medeiros Vinci et al., 2010). Toinvestigate whether seasonal variation would influence the data,the authors repeated the study in the following potato storage sea-son (Medeiros Vinci et al., submitted for publication). It was dem-onstrated that a more effective entrance control for incomingpotatoes was indeed possible and differences in the raw materialdue to season variability did not affect overall conclusions. Colordetermination by means of the Agtron methodology and reducingsugar contents in the raw material allows a better identification ofpotatoes prone to acrylamide formation when compared to thecurrent entrance control. This potentially enables industry to implypreventive measures in order to minimize the acrylamide risk intheir products. From an implementation point of view, measuringcolor with an Agtron process analyzer as an acrylamide predictorin raw material is probably more practical than analyzing sugarcontent. Moreover, color is one of the most important quality spec-ifications demanded by customers.

2.6. Cutting

Acrylamide is formed in the surface layer of the potato productand therefore, size and cut shape of the product (surface-to-vol-ume ratio) will also influence final acrylamide contents. Accord-ingly, thinner and smaller cut sizes result in increasedacrylamide formation upon final frying (Matthäus, Haase, & Vos-mann, 2004). Moreover, since the peripheral region of tubers havehigher reducing sugar contents, these fine cuts from the outersphere of tubers tend to overheat upon frying. Therefore, removingthese fines may contribute to an acrylamide reduction (Foot,Haase, Grob, & Gondé, 2007).

2.7. Blanching process

Blanching is an important unit operation in the industrial pro-cess of French fries production and its complexity may differ be-tween production lines (e.g. the use of 1, 2 or 3 blanchers).During this step enzymes are inactivated and a layer of gelatinizedstarch is formed which limits oil absorption and improves texture(Moreira, Castell-Perez, & Barrufet, 1999). In addition, blanchingalso contributes for an uniform color of the product after final fry-ing. Moreover, during this step, acrylamide precursors are leachedout, resulting in the reduction of acrylamide content in the finalproduct (Medeiros Vinci et al., 2010; Mestdagh, De Wilde, Fraselleet al., 2008; Pedreschi, Kaack, Granby, & Troncoso, 2007; Pedreschi,Kaack, & Granby, 2004; Pedreschi, Travisany, Reyes, Troncoso, &Pedreschi, 2009; Viklund et al., 2010). Blanching conditions (timeand temperature) therefore can be manipulated until an optimizedreducing sugar extraction is reached. In order to maintain the finalproduct specifications constant, potato processors typically in-crease the intensity of blanching conditions towards the end ofthe potato season due to senescent sweetening. However, extremeblanching conditions result in textural and nutrient loss issues andtherefore blanching can only be adapted within certain limitations.Mestdagh, De Wilde, Fraselle et al. (2008), reported an acrylamidereduction of 65% and 96% for French fries and potato crisps, respec-tively, after blanching (70 �C, 10–15 min). Besides time and tem-perature, the concentration of soluble components extracted

1144 R. Medeiros Vinci et al. / Food Chemistry 133 (2012) 1138–1154

from the potato cuts during this continuous process will also influ-ence the efficiency of sugar extractability and therefore affectingacrylamide formation in potato products. A decrease of sugarextraction of 10% was ascribed to the concentration of solublecomponents in the blanching water when compared to extractionrates in fresh water (Mestdagh, De Wilde, Fraselle et al., 2008).On the other hand, the continuous replacement of the blanchingwater with fresh water is however not feasible, both from environ-mental and economical point of view. Moreover, since in generaldextrose is added in the subsequent step (as discussed below), thisaspect becomes less relevant on the acrylamide content of the finalproduct.

2.8. Use of additives or processing aids

Two common substances used in the potato processing industry(e.g. French fries) are sodium acid pyrophosphate (SAPP, E450) anddextrose (glucose). SAPP is added (pH level �4.7) to reduce thedarkening of the blanched potato cuts (caused by the ferri-dichlor-ogenic acid complex formation during potato cooking and air expo-sure) while dextrose contributes to a uniform and standardizedcolor of the final product (according to customers demands). Dex-trose dip treatments may affect acrylamide formation in potatoproducts as shown on Fig. 3. In North America, the use of coloradditives such as caramel and annatto are permitted for use in po-tato processing instead of dextrose. Two US patent applicationsclaim that these color agents in replacement of dextrose, preventacrylamide formation in potato products (up to 86% and 93%reduction with caramel and annatto, respectively) (US, 2005; US,2010). However the use of these additives is still restricted in Eur-ope for this particular food commodity. Besides these, other foodadditives have been described in literature to influence acrylamideformation in model systems (Table 3A) and in potato products (Ta-ble 3B). Organic acids are known for their mitigating effect due tothe protonation of asparagine amino groups at low pH. This wouldblock the nucleophilic addition of asparagine with a carbonyl com-pound, preventing the formation of the corresponding Schiff base,a key intermediate in the Maillard reaction and in the formation ofacrylamide (Gama-Baumgartner, Grob, & Biedermann, 2004; Jung,Choi, & Ju, 2003; Kita, Brathen, Knutsen, & Wicklund, 2004; Lowet al., 2006; Pedreschi et al., 2004; Rydberg et al., 2003; Pedreschi,Kaack et al., 2007; Mestdagh, De Wilde, Delporte et al., 2008; Mest-dagh, Maertens et al., 2008).

Mono- and divalent cations (e.g. Na+ and Ca2+) were indicated toefficiently reduce acrylamide formation. It was postulated thatthese ions could interact with asparagine so that the Schiff baseformation was again prevented (Gökmen & Senyuva, 2007; Lindsay

Fig. 3. Changes in acrylamide content of lab-scaled produced 3/8 French fries as afunction of glucose dip concentration and reconstitution temperature (-j- 180 �C, -N- 160 �C, -s- 140 �C). Reprinted from (Taeymans et al., 2004) with kind permissionfrom the Taylor and Francis (� 2004).

& Jang, 2005; Mestdagh, De Wilde, Delporte et al., 2008; Mestdagh,Maertens et al., 2008; Ou et al., 2008; Park et al., 2005; Pedreschi,Granby, & Risum, 2010; Pedreschi, Bustos et al., 2007). The additionof calcium ions has also been related to a pH decrease of the foodmatrices and accordingly associated to acrylamide reductions (Le-vine & Ryan, 2009; Mestdagh, Maertens et al., 2008). The pH de-crease may be explained by the competitive displacement ofprotons from ionizable functional groups, containing oxygen,nitrogen, or sulfur atoms that share electrons with hydrogen atoms(Clydesdale, 1988). NaCl has also been proposed to accelerateacrylamide elimination via polymerization in a model food matrix(Kolek, Simko, & Simon, 2006).

Free amino acids such as glycine, cysteine and lysine have alsobeen suggested for reducing acrylamide formation, either by pro-moting competitive reactions and /or by covalently binding acryl-amide which is formed through Michael type addition reactions(Anese et al., 2009; Brathen, Kita, Knutsen, & Wicklund, 2005; Cla-eys, De Vleeschouwer, & Hendrickx, 2005b; Hanley et al., 2005;Kim, Hwang, & Lee, 2005; Low et al., 2006; Mestdagh, De Wilde,Delporte et al., 2008; Mestdagh, Maertens et al., 2008; Ou et al.,2008; Rydberg et al., 2003) resulting in adducts formation (Fried-man, 2003). Thus, the presence of amino acids other than aspara-gine can have an effect on the formation and/or eliminationkinetics of acrylamide (Claeys, De Vleeschouwer, & Hendrickx,2005a, 2005b).

Hydrocolloids are described to efficiently reduce fat uptakewhen used as coating agents for fried potato products and snacks(Garcia et al., 2004; Khalil, 1999; Kowalczyk & Gustaw, 2009).More recently, Zeng et al. (2010) studied the effect of severalhydrocolloid coatings on acrylamide formation in potato strips.Coating treatments with alginic acid and pectin reduced acrylam-ide contents of the final product, whereas carob gum, carrageenan,hydroxypropyl distarch phosphate and xanthan gum enhancedacrylamide formation (Zeng et al., 2010).

Antioxidants have been reported to influence the Maillard reac-tion and therefore affecting positively and negatively acrylamideformation (Bassama, Brat, Bohuon, Boulanger, & Gunata, 2010;Becalski et al., 2003; Cheng, Shi, Ou, Wang, & Jiang, 2010; Fernan-dez, Kurppa, & Hyvönen, in press; Ou et al., 2010; Zhang, Chen,Zhang, Wu, & Zhang, 2007; Zhu, Cai, Ke, & Corke, 2009; Zhu, Cai,Ke, & Corke, 2010). The mechanism of antioxidants on acrylamideformation is however not yet fully understood. Acrylamide reduc-tions were reported in potatoes cuts when treated with extract ofbamboo leaves (Zhang et al., 2007) and oregano phenolic extract(Kotsiou, Tasioula-Margari, Kukurova, & Ciesarova, 2010). Kotsiouet al. (2010) concluded that phenolic compounds without aldehy-dic groups in their structures are more effective in acrylamidereduction. Moreover, higher levels of phenolic compounds were re-lated to lower acrylamide contents in potato powders from 16commercial potato varieties when submitted at 185 �C for 25 min(Zhu et al., 2010). These experimental conditions however do notrepresent realistic baking conditions applied to potato products.In contrast, other studies either described positive correlations be-tween acrylamide and antioxidants or no correlations were found(Bassama et al., 2010; Becalski et al., 2010; Ehling & Shibamoto,2005; Rydberg et al., 2003; Serpen & Gokmen, 2009). Supplemen-tary factors associated to the addition of antioxidants, such as pHdecrease or the presence of amino acids present in the extractscould influence acrylamide contents and therefore hinder the com-parison of results between different studies (Mestdagh, Van Peteg-hem, & De Meulenaer, 2009).

Asparaginase, an enzyme that hydrolyzes asparagine to asparticacid and ammonia, can reduce acrylamide formation in foods byremoval of the precursor asparagine (Ciesarova, Kiss, & Boegl,2006; Hendriksen, Kornbrust, Ostergaard, & Stringer, 2009; Pedre-schi, Kaack, & Granby, 2008; Pedreschi, Mariotti, Granby, & Risum,

Table 3Summary of studies and findings on mitigation strategies of acrylamide formation tested in (A) potato model systems; (B) potato products on laboratory scale and (C) potato products in industrial settings.

Matrix Additive Control sample conditions Results Sensorial aspects References

A-Potato model systemsPotato cake Glutamine, glycine, 4-

aminobutyric acid, lysine,sodium glutamate, alanineand sodium ascorbate (pH5.72–6.16)

-pH 5.7–5.9-Acrylamide concentration439–488 lg/kg

92%, 91%, 86%, 88%, 54%, 50% and 46%acrylamide reduction for the differentadditives tested, respectively

N/A Rydberg et al. (2003)

Potato cake Citric acid and glycine – 20% and 70% acrylamide reduction forcitric acid and glycine

N/A Low et al. (2006)

Potato cake Asparaginase – Up to 97% acrylamide reduction N/A Ciesarova et al. (2006)Potato powder (fructose and

glucose (0.03 g/100 gpowder) and asparagine(0.9 g/100 g powder))

Citric, acetic and L-lacticacids (pH 4.5–3.7)

-pH 5.4 78%, 46% and 62% acrylamide reduction,respectively

N/A Mestdagh et al. (2008b)

L-cystein, L-, glycine, L-lysinand gluatamine

92%, 24% and 39% acrylamide reductionfor cystein, glycine and lysine,respectively; 50% acrylamide increase forglutamine

NaCl, SAPP, MgCl2 and CaCl2 5%, 10%, 25%, 58% and 82% acrylamidereduction, respectively

Potato cake Virgin olive oil and oreganophenolic compounds

– Up to 45% acrylamide increase for samplestreated with virgin olive oil, and up to 30%acrylamide reduction when treated withoregano phenolic extracts

N/A Kotsiou et al. (2010)

B-Potato products (lab experiments)French fries Citric acid - Dipped in distilled water for 1 h

(pH 6.2)-Acrylamide concentration 645 lg/kg

Up to 75% acrylamide reduction No differences betweencontrol and citric acidsolution 1%; solution at2% resulted in sour andharder in texture fries

Jung et al. (2003)

Crisps Antioxidants - Acrylamide concentration2160 lg/kg

�50% acrylamide reduction – Fernandez et al. (inpress)

French fries Citric acid (pH 4.54) - pH 5.8-Acrylamide concentration 275 lg/kg

46% acrylamide reduction – Rydberg et al. (2003)

French fries Citric acid - Immersed in tap water at 60 �C for15 min- Acrylamide concentration290 lg/kg.

14% acrylamide reduction Treatment affectsensorial properties

Gama-Baumgartneret al. (2004)

Crisps Citric and acetic acid - Blanched in water at 70 �C for 3 min- Acrylamide concentration428 lg/kg.

32% acrylamide reduction for both acidictreatments

Sour taste detected forcitric acid treatment

Kita et al. (2004)

Crisps Citric acid - Rinsed with distilled water- Acrylamide concentration356 lg/kg.

70% acrylamide reduction – Pedreschi et al. (2004)

Crisps Lysine and glycine - Soaked in water at 65 �C for 5 min- Acrylamide concentration�1048 lg/kg

Up to 94% acrylamide reduction – Kim et al. (2005)

Crisps Glycine and glutamine - Blanched in water at 80 �C for 2 min- Acrylamide concentration4127 lg/kg

55% and 25% acrylamide reduction,respectively

– Brathen et al. (2005)

French fries Glycine and glutamine - Blanched in water at 70–90 �C for10–15 min- Acrylamide concentration211–404 lg/kg

No effect on acrylamide contents –

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Table 3 (continued)

Matrix Additive Control sample conditions Results Sensorial aspects References

French fries NaCl and SAPP - Cut, washed and fried immediately- Acrylamide concentration489 lg/kg

71% and 95% acrylamide reduction whensamples were blanched at 80 �C for 4 minand 70 �C for 30 min, respectivelyfollowed by a soaking treatment in NaCland SAPP

– Lindsay and Jang(2005)

French fries Lactic acid fermentation - Blanched in water at 80 �C for 5 min- pH 5.7- Acrylamide concentration�1000 lg/kg

Up to 86% acrylamide reduction whenfermentation lasted 120 min

No difference fromcontrol sample

(Baardseth et al., 2006)

French fries NaCl and CaCl2 - Dipped in distilled water at roomtemperature for 60 min- Acrylamide concentration589 ± 41 lg/kg

49% and 93% acrylamide reduction,respectively

No effect on finalproduct

Gökmen and Senyuva(2007)

Crisps Antioxidant of bambooleaves

- Acrylamide concentration�3743 lg/kg

�74% acrylamide reduction No significantdifferences withcontrol sample

Zhang et al. (2007)

French fries - Commercial French fries, washed toremove fat coating.- Acrylamide concentration�580 lg/kg

�76% acrylamide reduction

French fries Citric acid and SAPP - Rinsed with water- Acrylamide concentrations 1180,3427 and 4028 lg/kg for the threefrying conditions, respectively

53% and 17% acrylamide reduction(average values of three frying conditionstested) for citric acid and SAPP treatments,respectively

– Pedreschi et al. (2007a)

Crisps NaCl - Blanched in distilled water at 85 �Cfor 3.5 min- Acrylamide concentrations, �800,930 and 3860 lg/kg for the threefrying conditions, respectively

97%, 92% and 82% acrylamide reductionfor the three frying conditions,respectively

– (Pedreschi et al.,2007b)

French Fries Asparaginase - Blanched in distilled water at 75 �Cfor 10 min- Acrylamide concentration1264 lg/kg.

Up to 62% acrylamide reduction – Pedreschi et al. (2008)

Crisps Citric, acetic and L-lacticacid

- Blanched in distilled water (65 �Cfor 5 min)

Up to 100% acrylamide reduction with allacids

Crisps treated withcitric acid were sour,while for other acidictreatments crisps werenot significantlydifferent from control

Mestdagh et al. (2008a)

Glycine and L-lysine Up to 68% and 85% acrylamide reduction,respectively

Crisps treated withglycine were notsignificantly differentfrom control, while L-lysine resulted inpopcorn like taste

NaCl, SAPP, CaCl2 and Ca-lactate

Up to 43%, 90%, 93% and 82% acrylamidereduction, respectively

No significant effectsfor treated samplesregarding taste, butdifferences in texture

Crisps NaHSO3 (5 g/L) - Rinsed in distilled water(1 min)- Acrylamide concentration5433 lg/kg

47% acrylamide reduction Unpleasant odor Ou et al. (2008)

CaCl2 (5 g/L) 100% acrylamide reduction Increased brittlenessCystein (5 g/L) 100% acrylamide reduction Unpleasant odor

Potato cubes Glycine, lactic acidfermentation and

- Immersed in distilled water at 37 �Cfor 75 min (pH 5.9)

35, 50 and 70% acrylamide reduction,respectively

No effect of treatmentson taste, lactic acid

Anese et al. (2009)

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combination of both (pH5.32–5.83)

- Acrylamide concentration�5000 lg/kg.

treatment resulted inlighter in color finalproduct

French fries Asparaginase - Blanched by pouring water at 90–95 �C, and holding in water at 70 �Cfor 20 min (pH 6.5–5.5)- Acrylamide concentration 600–1900 lg/kg.

60–85% acrylamide reduction – Hendriksen et al.(2009)

Crisps - Blanched at 80 �C for 1 min- Acrylamide concentration1750 lg/kg.

Up to 60% acrylamide reduction –

Crisps Fruit extracts – Up to 26% acrylamide reduction – Cheng et al. (2010)French fries Hydrocolloids - Immersed in water at room

temperature for 1 and 5 hUp to 60% acrylamide reduction – Zeng et al. (2010)

Crisps NaCl - Blanched at 90 �C for 5 min inwater- Acrylamide concentration�2600 lg/kg

�62% acrylamide reduction - (Pedreschi et al., 2010)

Crisps Asparaginase - Blanched in distilled water at 85 �Cfor 3.5 min followed by soaking inwater at 50 �C for 20 min- Acrylamide concentration�800 lg/kg

Up to 80% acrylamide reduction – Pedreschi et al. (inpress)

Frozen par-fried French fries Acetic, citric, lactic, L-ascorbic and succinic acid(pH 3.4–2.6)

- Potato strips previously blanched,SAPP treated and stored at 4 �C

45%, 64%, 30%, 25% and 7% acrylamidereduction, respectively

Acceptable In supportinginformation MedeirosVinci et al. (2011)

CaCl2, Ca lactate, MgCl2, Mglactate, KCl and NaCl

- Dipped in distilled water at 60 �C for1 min

44, 12, 32, 18, 23 and 49% acrylamidereduction, respectively

Glycine 7% acrylamide reductionAsparaginase - Potato strips previously blanched,

SAPP treated and stored at 4 �C- Dipped in distilled water at 60 �C for5 min

Up to 65% acrylamide reduction

C-Potato products (industrial settings)Crisps CaCl2 (5 g/L) – 85–96% acrylamide reduction – Ou et al. (2008)Frozen par-fried French fries Citric acid (pH 4.0–2.0) - SAPP treated, pH 4,7

- Acrylamide concentration 111 ± 33to 289 ± 36 lg/kg

Up to 39% acrylamide reduction (pH 3.0) Negative impact onsensorial properties

Medeiros Vinci et al.(2011)

Acetic acid (pH 3.6–3.3) No consistent results in three trials (notsignificantly different from controlincreased and decreased acrylamideformation)

Ca lactate (6–36 g/L) Up to 36% acrylamide reduction (pH 3.0)Asparaginase (5000–20,000 ASNU/L)

- SAPP treated, pH 4,7- Acrylamide concentration 247 ± 40to 298 ± 11 lg/kg

Up to 66% acrylamide increase, and inanother trial �14% reduction

Chilled (not par-fried) Frenchfries

Asparaginase (625–2500 ASNU/L)

- SAPP treated, pH 4,7- Acrylamide concentration 90 ± 9.1to 124 ± 21.5 lg/kg

�100% acrylamide reduction No effect detected

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Fig. 4. Influence of reconstitution temperature and frying time on acrylamideformation in 3/8 lab processed French fries. Reprinted from (Taeymans et al., 2004)with kind permission from the Taylor and Francis (� 2004).

1148 R. Medeiros Vinci et al. / Food Chemistry 133 (2012) 1138–1154

in press). Thus, acrylamide formation is successfully reduced uponaddition of the enzyme in dough based products, given that aspar-agine is readily available for the enzyme to be converted to asparticacid. On the other hand, asparaginase application on potato prod-ucts which consist of solid cut pieces reveals to be more complexdue to the less optimal contact between enzyme and substrate(Hendriksen et al., 2009). For that reason, a blanching step priorto enzyme application is required for better asparaginase-asparagine contact (Pedreschi et al., 2008).

Studies regarding lactic acid fermentation with Lactobacillusplantarum have shown to reduce acrylamide formation in friedpotato products upon final frying (Anese et al., 2009; Baardsethet al., 2006). Accordingly, glucose was metabolized in addition toan acidifying effect of lactic acid production (Baardseth et al.,2006).

2.9. Drying

Drying of blanched or soaked potato cuts prior to final frying re-duces fat absorption and oil hydrolysis (Choe & Min, 2007; Krokida,Oreopoulou, Maroulis, & Marinos-Kouris, 2001). In addition, it alsoreduces acrylamide formation in French fries due to the need ofshorter finish frying times to obtain the same product quality interms of color and crispiness (Franke, Sell, & Reimerdes, 2005; Gök-men, Palazoglu, & Senyuva, 2006).

2.10. Frying

Finally but not less important, frying conditions dramatically af-fect acrylamide levels of the products as they are eaten, since it isduring this last step that acrylamide is actually formed. Simulta-neously to acrylamide formation, browning, texture and flavordevelopment caused by the Maillard reaction equally occur duringfrying. And therefore, acrylamide formation is correlated to colordevelopment, given that both are linked to the Maillard reactionand moreover, the applied frying conditions (time and tempera-ture) affect both in similar manner. Intense frying conditions (timeand temperature) lead to darker fries and higher acrylamide con-tents (Gökmen & Mogol, 2010; Gökmen & Senyuva, 2006b; Mest-dagh, De Wilde, Castelein et al., 2008; Pedreschi, Kaack, &Granby, 2006; Pedreschi et al., 2005; Pedreschi, Leon et al., 2007;Viklund, Mendoza, Sjöholm, & Skog, 2007). On the other hand, fry-ing at lower temperatures (below 140 �C) results in increased fry-ing time and enhances fat uptake (Foot et al., 2007). Thus, fryingtime and oil temperature should be controlled in order to avoidhigh acrylamide levels, meaning that they should not exceed170–175 �C (Fig. 4) and lower temperatures towards the end ofthe process may reduce acrylamide formation. Other factors, suchas the product/oil ratio may influence a drop of initial frying tem-perature and therefore longer frying periods would be neededresulting in higher acrylamide contents.

The type of oil used for frying was investigated on acrylamideformation in a potato model system and French fries. Some studiesindicated that palm oil relatively to rapeseed and sunflower oilsgenerated higher acrylamide contents (Gertz & Klostermann,2002) and olive oil in comparison to corn oil (Becalski et al.,2003), while other authors reported that oil type did not influenceacrylamide in the final product (Matthäus et al., 2004; Mestdaghet al., 2005). Moreover, oil oxidation and hydrolysis productswhich have been proposed as possible acrylamide precursors seemto be negligible in acrylamide formation in fried potato products(Becalski et al., 2003; Mestdagh, De Meulenaer et al., 2007; Mest-dagh, Lachat et al., 2007).

Frying under reduced pressure by means of a vacuum fryer mayresult in great acrylamide reductions (up to 94%) (Granda & More-ira, 2005). This decrease in acrylamide content can be attributed to

the lower temperature used during vacuum frying. However, inpractice this frying method is only applicable in the productionof crisps.

A recent study compared the effect of frying vs baking on acryl-amide contents of potato chips (Palazoglu, Savran, & Gokmen,2010). The authors concluded that baking at 170 �C resulted inmore than the double of acrylamide contents when compared tofrying at the same temperature. However, at 180 and 190 �C, acryl-amide levels of chips prepared by baking were lower than theirfried counterparts.

3. Additives or processing aids – From lab tests to industrialscale

Various mitigation recipes have been proposed in literature (Ta-ble 3(A and B)). However, most of them have been only tested on alab scale and therefore it is of crucial importance to perform fur-ther in-depth studies before transposing these possible treatmentsto the factory environment. From a food safety and industrial fea-sibility perspective, the main criteria regarding the successfulnessof any acrylamide mitigation strategy ought to be the efficientreduction of acrylamide formation without affecting overall qual-ity of the final product. Till now, only two studies are describedin literature regarding the application of additives or processingaids on an actual industrial setting of potato processing (Table3C). One of these studies investigated the effect of various addi-tives or processing aids on the industrial production of French fries(Medeiros Vinci et al., 2011). The application of acetic and citricacid, calcium lactate and asparaginase was evaluated on the pro-duction of frozen par-fried French fries regarding their effect onacrylamide reduction and sensorial properties of the final productbesides other parameters. Even though the authors obtained signif-icant acrylamide reductions in preliminary lab experiments, thesetreatments did not translate in consistent acrylamide reductions inthe industrial production of par-fried French fries during four dif-ferent trials. pH reduction treatments were only effective in reduc-ing acrylamide formation (up to 39%) when applied at extremelyexaggerated low pH values (e.g. pH 3 and 2 vs pH 4.7 of the stan-dard production process). This obviously affected negatively thesensorial properties of the fries. An acidic treatment below pH4.7 (standard process conditions) is therefore not realistic and fea-sible in terms of acrylamide mitigation in the industrial productionof French fries. Calcium lactate treatment provided inconsistentresults when tested throughout three trials and only reduced

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acrylamide formation (up to 36%) when exaggerated concentra-tions were used, however, also with negative consequences onthe sensorial properties of the fries. In addition, this additive pre-cipitates in the presence of SAPP, which could represent problemstowards production (e.g. cleaning of the line). Regarding the use ofasparaginase, this treatment was not successful in reducing acryl-amide formation when tested on the production of frozen Frenchfries even at high enzyme concentrations. Crucial factors thatmight have affected the enzyme performance in the productionof frozen French fries are the pH of the standard process not beingoptimal for enzyme activity, temperature of the dip treatment notoptimal either and time allowed for the enzyme to react beforereaching the par-frying step. The effect of pH on enzyme activityin the production of par-fried frozen French fries was also tested(Medeiros Vinci et al., 2011). At pH values (6.0, 5.6 and 5.2) abovestandard operating pH (4.7), the enzyme effectively reduced acryl-amide formation. On the other hand, acrylamide contents of the fi-nal product treated with asparaginase at pH 6.0 were notsignificantly different from the ones of French fries from the stan-dard production process (pH 4.7, without enzyme). This demon-strates that the low pH applied in the standard productionprocess mitigates acrylamide formation in the same order of mag-nitude as the enzyme treatment when applied at higher pH levels.The authors, additionally tested asparaginase in the production ofchilled French fries (not par-fried), which accounts only for a smallsegment of the French fries business. In this type of product, aspar-aginase reduced up to 90% of acrylamide formation after 3 days ofproduct storage at 4 �C. Since for this product, there is no par-fry-ing step or any other process step that would deactivate the en-zyme, asparaginase could remain active throughout the productshelf-life.

The second study reports the addition of an additive for acryl-amide mitigation in an industrial line of potato crisps production(Ou et al., 2008) (Table 3C). These authors describe an acrylamidereduction of 85–96% in potato crisps, when CaCl2 (5 g/L) is added inthe blanching process. This however is the only result Ou et al.(2008) describes and no reference to acrylamide content in controlor treated sample was made. The sensorial properties of the finalproduct were not documented either. Moreover, CaCl2 presentssome disadvantages such as incompatibility with SAPP (as men-tioned above), limitations related to the chloride content of theeffluent and possible 3-MCPD formation upon frying. This lastpoint is merely speculative since it has not yet been investigated.

Although there are many promising acrylamide reducingagents, special care should be given to the interpretation of the re-sults while considering the possibility of implementation in anindustrial setting. In most of reported studies (Table 3(A and B)),the use of additives in potato products do not consider the senso-rial properties of the final product, therefore unrealistic concentra-tions of different additives might have been tested andconsequently resulted in significant acrylamide reductions. Inaddition, the pH employed by potato processors at a certain stageof the production process is generally already acidic (�4.7) due tothe addition of pyrophosphate. This important aspect is frequentlyoverlooked and not considered in the reported lab experiments.Higher acrylamide levels of control samples simply immersed indistilled water therefore correspond to higher reduction yields ob-tained in lab studies. Moreover, laboratory experiments generallyreflect standardized ‘‘process conditions’’ and variability of exper-imental conditions and of raw material is controlled. However, inindustry raw material variability is a daily challenge and may rep-resent an obstacle when accessing implementation of a mitigationstrategy on industrial scale. Model systems based on potato flakesor powder to test the effect of additives on acrylamide formationdeserve special interpretation of the results. In model systems,additives are distributed homogeneously throughout the potato

cake, while standard potato crisps and French fries being solidcut pieces have restricted contact to the surface layers only. Thetime that the surface of a potato slice or stick is exposed to theadditives is limited by the production process, representing an-other constriction in acrylamide reduction in industrial settingswhich is not covered by model systems.

This leads to the conclusion that to date, although many addi-tives demonstrate to prevent acrylamide formation in potato prod-ucts on lab scale, these are still not proven on industrial scale, andtherefore further research is warranted. Very recently, the AtlanticCanada Opportunities Agency (ACOA) released $2.5 million toFunctional Technologies Corp. and Phyterra Yeast Inc. to supportthe development and commercialize the application of a yeast,Acryleast (tm), in the processed potato industry. This yeast is capa-ble of preventing acrylamide formation by reducing asparaginecontents in dough based products and this investment is intendedto extend its application to potato products (Functional Technolo-gies Corp., 2011).

4. Evolution of risk management

To date, there are no legal regulations (worldwide) regardingacrylamide levels in food. Many authorities have therefore adoptedminimization strategies by working closely with industry, with fo-cus on effective mitigation strategies and following up whetherthese strategies are applied. Recommendations given by the JointFAO/WHO Committee highlight the need of further efforts ondeveloping and implementing mitigation methods for acrylamidein foods of major importance for dietary exposure (FAO/WHO,2011). Main initiatives taken so far by governmental agenciesand industry are summarized below.

In 2002, the German Federal State authorities, together with theFederal Office of Consumer Protection and Food Safety (BVF),industry and the Federal Ministry of Food Agriculture and Con-sumer Protection (BMELV) developed a risk management tool foracrylamide in foods (Göbel & Kliemant, 2007). This tool, alsoknown as the German signal values was based on values whichrepresent the lowest 10% of products of each food commodity thathave the highest acrylamide content. Thus, the German FederalState prompts food producers to take adequate actions to lowerthe acrylamide contents whenever these exceed the signal value.These signal values were evaluated from 2002 until 2005, and lat-est update included the values of 530 and 1333 lg/kg for Frenchfries (chips) and potato crisps, respectively (Göbel & Kliemant,2007). However, since 2007 no other German signal values havebeen published. Just recently, the European Commission adopteda somewhat alternative approach and published a Recommenda-tion on the website from the European Commission’s DirectorateGeneral for Health and Consumer Policy (DG SANCO) on investiga-tions into the levels of acrylamide in food (EC, 2011). MemberStates are therefore recommended to investigate cases whereacrylamide contents of foodstuffs after final preparation, exceedprescribed acrylamide indicative values. For French fries and pota-to crisps, these indicative values are 600 and 1000 lg/kg, respec-tively. The Member States are recommended to report the resultsback to the Commission for further assessment by December2012 and decision making for additional measures if necessary.

Other governments have taken action towards consumer infor-mation. The State of California for example, requires that producersor businesses which knowingly expose individuals to significantamounts of acrylamide must provide clear and reasonable warningto those individuals. Based on this, the Californian State settled acourt agreement in 2008 with a number of French fries and crispproducers and some fast-food chains to reduce the acrylamide con-tent of their products significantly, and to place warning labels

1150 R. Medeiros Vinci et al. / Food Chemistry 133 (2012) 1138–1154

regarding the presence of this contaminant on the packaging, inaddition to the payment of monitory fines (Mills et al., 2009).Health Canada informs consumers by making public on their web-site acrylamide monitoring results from 2002 to 2008 including thebrand names of products (Health Canada, 2009).

The Swiss Federal authorities chose to take direct action facecertain food products present in the market which contained highacrylamide levels. In 2005, an infant biscuit exceeding 1000 lg/kgof acrylamide was removed from the market (Grob, 2007), andapproximately 2 years later, ‘‘hard measures’’ were undertakenregarding a brand of potato chips in the Swiss market which con-tained up to 7000 lg/kg of acrylamide (Biedermann et al., 2010).

A Code of Practice for the reduction of acrylamide in foods hasbeen adopted by the Codex Alimentarius Commission (2009). ThisCode intends to provide authorities, manufactures and other rele-vant bodies with guidance to prevent and reduce acrylamide for-mation in potato and cereal products.

Since the discovery of acrylamide in food, industry has volun-tarily taken action in understanding the mechanism of acrylamideformation and possible mitigation strategies in food by supportingand co-funding several research initiatives. The European Food andDrink Federation (CIAA) established a Technical Acrylamide ExpertGroup in 2003 and created the ‘‘Acrylamide Toolbox’’ which isavailable online (http://www.ciaa.be). This toolbox presents a reg-ularly updated description of the possible mitigation strategiesthat could be employed to reduce acrylamide levels in foods con-tributing the most for acrylamide intake (CIAA, 2009). The mitiga-tion strategies covered in the toolbox comprises aspects related toagronomy, recipe, processing and final preparation which contrib-ute for acrylamide formation. Brochures summarizing the mostimportant information of the toolbox related to French fries andcrisps are also published on the European Commission’s websitein 22 different languages (EC, 2009). The toolbox allows an opencommunication and consequently joined efforts are taken to re-duce the acrylamide problem in most relevant food commodities.Accordingly, small and medium enterprises which normally havelimited R&D resources have access to updated information. An up-dated version of the ‘‘Acrylamide toolbox’’ is foreseen for 2011.

5. Future outlook

Acrylamide is formed in potato products during industrial pro-cessing, retail, catering and home preparation. In literature, severalpossibilities are proposed for acrylamide reduction in potato prod-ucts. These have been described throughout this paper and most ofthem are summarized in the Acrylamide toolbox (CIAA, 2009).

Current industrial practices in the potato processing sector al-ready consider the selection of potato varieties with low reducingsugars contents, and storage temperatures of about 8 �C are nor-mally respected. However, retail and consumers might still be una-ware of the importance of cultivar selection and optimal storageconditions for acrylamide formation. Therefore food safety author-ities and the media may play a key role in this by ensuring thatpotatoes available in the retail market for frying and roasting con-tain low reducing sugar contents and by implementing campaignsregarding ideal storage conditions and suitable baking conditions.Nevertheless, from an agronomical point of view, substantialimprovements can still be made in reducing acrylamide formationin potato products by developing varieties which are resistant tolow temperature sweetening and with lower asparagine contentseither by breeding or genetic engineering. Rommens, Ye, Richael,and Swords (2006), Rommens, Yan, Swords, Richael, and Ye(2008) has demonstrated that with genetic engineering it is indeedpossible to improve potato storage conditions of potatoes and con-sequently lower levels of acrylamide. Due to legal constraints and

public acceptability, it is however currently not possible to usethese genetically engineered products within the European Union.

From the process point of view, blanching conditions and theacidifying effect of added pyrophosphate reduces considerablythe acrylamide formation in French fries. Further acrylamidereductions could probably be obtained by avoiding the use of dex-trose as a browning agent and using caramel and annatto colors asreplacement. Important aspects in this respect are the significantlylower acceptable daily intake (ADI) for annatto compared to cara-mel, and the fact that these food additives are not yet regulated inEurope for use in potato processing.

Regarding the use of processing aids in the industrial produc-tion process, although asparaginase treatment was not successfulin reducing acrylamide formation in par-fried French fries, thistreatment reduced acrylamide to levels < LOD in ‘‘chilled’’ Frenchfries (not par-fried). Thus indicating its potential as a mitigationstrategy. However, certain limitations still need to be evaluated be-fore possible implementation. An optimal pH and temperature forenzyme activity, modifications to the process line and clarificationof regulatory status regarding residual enzyme activity in the prod-uct still need to be addressed. Further work is therefore warrantedin possibly finding an enzyme with improved activity (faster ac-tion), with increased resistance to higher temperatures and lowerpH. Or alternatively, explore other process treatment besides dip-ping, such as spraying in an enclosed system.

So far, none of the acrylamide mitigating agents studied on labscale is readably implementable on industrial processing of potatoproducts, therefore further work is necessary in exploring the dif-ferent possibilities studied in the lab on an industrial setting. Anyconcepts established to minimize acrylamide formation must cer-tainly ensure that the sensorial properties of the final product arenot negatively affected. In addition, factors such as seasonal vari-ability of the raw material, raw material characteristics (beforeand after blanching), the complexity of the blanching step (1, 2or 3 blanchers), dip tank parameters (temperature, pH and dura-tion) and other variables should be considered when implementingan acrylamide mitigation strategy on industrial level while main-taining the expected product quality for the consumer. Other con-siderations such as feasibility, food legislation, cost, effluenttreatment, safety and comfort of the employees, ability to controldosage, etc. are equally relevant when considering the implemen-tation of any change to an industrial process. Ultimately, with re-gard to French fries, the success of any acrylamide mitigationstrategy implemented by industry is strongly dependent uponthe final baking conditions adopted by the household consumersor caterers. For lower acrylamide contents, frying temperature of160–170 �C and to fry until the French fries have a light-yellow col-or is suggested. To enable better control over frying temperatures,it is necessary to improve the reliability and accuracy of tempera-ture controls on frying equipment. This is partially possible bychanging technical specifications of the fryers as suggested by Grob(2007), however, it is of crucial importance that consumers/cater-ers are well informed that darker fries correspond to higher acryl-amide contents.

Finally, any promising mitigation strategy and regulatory reso-lutions should be assessed with regard to the possible impact onconsumer exposures as exemplified by several authors (Boonet al., 2005; Claeys et al., 2010; Seal et al., 2008). In this respect,if acrylamide formation in French fries would be reduced to levelsbelow LOD, as referred in Section 3, this would reduce the P50 andP95 acrylamide total intake for the Belgian population up to 12%and 25%, respectively (Claeys, 2011). This example demonstratesthat besides the efforts of potato industry to reduce acrylamidecontents in potato products, it still remains necessary to mitigateacrylamide in other food commodities in order to effectivelyreduce acrylamide intake.

R. Medeiros Vinci et al. / Food Chemistry 133 (2012) 1138–1154 1151

Mitigating acrylamide in potato products while safeguardingother quality aspects and reducing dietary acrylamide intake, stillremains a challenge.

Acknowledgments

The authors thank EUPPA, Flanders’ FOOD and Belgapom, inparticular Nele Cattoor for a good cooperation in all the acrylamideresearch and fruitful discussions. We also thank Dr. Wendie Claeysfrom the Belgian Federal Agency for the Safety of the Food Chainfor her contribution in the re-evaluation of acrylamide dietaryexposure for the Belgian population.

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