The effect of lipid oxidation on the quality of meat and meat products

Michaela Králová

Department of Milk Hygiene and TechnologyFaculty of Veterinary Hygiene and Ecology

University of Veterinary and Pharmaceutical Sciences in BrnoBrno, Czech Republic

Abstract

Lipid oxidation is currently one of the greatest economic problems facing the meat industry. It is one of the main causes of deterioration in the quality of meat and meat products during their storage and processing. Meat oxidation causes discoloration, the development of off-flavour, the formation of toxic compounds, reduced shelf life and nutrient losses. Meat becomes susceptible to oxidative deterioration due to high concentrations of unsaturated lipids, haem pigments, metal catalysts and a range of oxidising agents contained in the muscle tissue. Autoxidation is of the greatest significance. This takes place in three stages – initiation, propagation and termination. A large variety of volatiles, including alkanes, aldehydes, alcohols, esters and carboxylic acids, arise from this process. The aim of this study is to summarise current knowledge about the effect of lipid oxidation on the quality of meat and meat products and the use of natural antioxidants which are becoming increasingly important.

Lipids, meat, oxidation,rancidity

Introduction

Meat and meat products are susceptible to deterioration in view of their rich nutritional composition (Devatkal et al. 2012). This deterioration occurs as the result of a number of chemical and microbial changes. The most common form of chemical damage is lipid oxidation in meat (Medina-Meza et al. 2014; Shah et al. 2014). Lipid oxidation is an important factor limiting both the quality of meat products and their acceptability to the customer. Food become unacceptable to the consumer once a certain degree of rancidity is attained (Sammet et al. 2006). Lipid oxidation is a complex process that is dependent on the chemical composition of the meat, the presence of light and oxygen, and on the storage temperature (Belitz et al. 2004). It is also influenced by certain technological procedures to which meat is subjected during processing (Falowo et al. 2014; Medina-Meza et al. 2014). During the course of lipid oxidation, a number of compounds are formed that have an influence on the quality of meat and meat products expressed in the form of sensory changes (colour, texture and taste) and a deterioration of nutritional quality (Min and Ahn 2005; Karre et al. 2013). Lipid oxidation in meat and meat products may be reduced or inhibited by antioxidants, thereby ensuring improved product quality and an extended storage period (Shah et al. 2014). The aim of this study is to assess the mechanism and influence of lipid oxidation on the quality of meat and meat products and to evaluate the use of the antioxidants, largely of natural origin, that are currently being used to a continually increasing extent.

Lipid oxidationAll foods that contain lipids, even in extremely small quantities (< 1%), may undergo

oxidation which leads to the onset of rancidity (Wąsowicz et al. 2004).Oxidation involves reactions of the hydrocarbon chains that are common to free fatty acids

and their esters. The carboxyl of free fatty acids, however, speeds up the decomposition of hydroperoxides and may react with certain oxidation products. A number of types of lipid Address for correspondence:MVDr. Michaela Králová, Ph.D.Department of Milk Hygiene and Technology Faculty of Veterinary Hygiene and EcologyUniversity of Veterinary and Pharmaceutical Sciences BrnoPalackého tř. 1946/1, 612 42 Brno, Czech Republic

Phone: +420 541 562 714E-mail: kralovam@vfu.czwww.maso-international.cz

oxidation reaction may take place in foods, such as autoxidation with atmospheric oxygen, oxidation with hydroperoxides or hydrogen peroxide, oxidation with singlet oxygen during photo-oxidation, oxidation catalysed by enzymes (lipoxygenases), oxidation with heavy metals at a higher valence, and oxidation with quinones and related compounds (Velíšek and Hajšlová 2009).The most important mechanisms of oxidation are given in Table 1 with the type of oxidation, precursors and primary products.

The commonest type of oxidation during the processing and storage of meat and meat products (and foodstuffs in general) is the autoxidation of fatty acids (Gandemer 2002; Santos-Fandila et al. 2014). Only unsaturated fatty acids are oxidised by atmospheric oxygen at ordinary temperatures. Saturated fatty acids enter the autoxidation process at higher temperatures associated with processing methods such as boiling, baking, frying, roasting, etc. (Velíšek and Hajšlová 2009; Resconi et al. 2013). This is due to various degrees of bond dissociation energy at various positions in fatty acids (Table 2).

AutooxidationMechanism

The autoxidation of lipids associated with the production of free radicals is a spontaneous reaction of atmospheric oxygen with fatty acids that leads to oxidative damage to meat and meat products and the formation of undesirable sensory properties (Wąsowicz et al. 2004; Dave and Ghaly 2011; Santos-Fandila et al. 2014). Autoxidation takes place as a radical chain reaction characterised by three steps – initiation, propagation and termination (Falowo et al. 2014; Santos-Fandila et al. 2014).

• InitiationDuring initiation, the homolytic cleavage of the covalent bond in the C-H hydrocarbon

chain takes place with the formation of a free hydrogen radical (H•) and fatty acid free radical (R•) (1) (Velíšek and Hajšlová 2009). Catalysts of this reaction include heating, radiation, metal ions and other free radicals (Hájek et al. 1998; Dave and Ghaly 2011).

RH → R• + H• (1)

126

Table 1. Mechanisms of lipid oxidation (Pokorný 2006)

Type of oxidation Precursors Primary products

Catalysed by lipoxygenase Linoleic and linolenic acid Conjugated hydroperoxidesAutoxidation Unsaturated fatty acids HydroperoxidesPhoto-oxidation Unsaturated fatty acids HydroperoxidesIn vivo oxidation Essential fatty acids EicosanoidsHydrogen peroxide oxidation Unsaturated fatty acids Hydroxy acids

Table 2. Bond dissociation energy of hydrogen at various positions in the carbon chain (Belitz et al. 2004; Zuleta et al. 2012)

Position of hydrogen E [kJ·mol-1]

H-CH2- 422CH3-HCH- 410R-HCH-CH=CH- 322 R-CH=CH-HCH-CH=CH- 272

Cleavage also occurs by means of a reaction with another free radical or a reaction with metals with transitory valence (Velíšek and Hajšlová 2009).

• PropagationA reaction occurs in the second step of autoxidation between the highly reactive fatty

acid radical and atmospheric oxygen to form a highly reactive peroxyl radical (ROO•) (2) which is capable of reacting with unsaturated fatty acids to form hydroperoxides (ROOH) (3) (Wąsowicz et al. 2004; Velíšek and Hajšlová 2009).

R• + O2 → ROO• (2)

ROO• + RH → ROOH + R• (3)

The sequence of two given reactions may be repeated a number of times, for which reason autoxidation is known as a chain reaction (Velíšek and Hajšlová 2009). The reaction of a fatty acid free radical with oxygen is far quicker than the reaction between a peroxyl radical and a lipid hydrocarbon chain. The second reaction therefore determines the speed of autoxidation (Wąsowicz et al. 2004; Velíšek and Hajšlová 2009).

• TerminationIn the final phase of autoxidation, i.e. termination, non-radical relatively stable products

are formed if the concentration of free radicals is sufficiently high (4, 5 and 6) (Wąsowicz et al. 2004; Velíšek and Hajšlová 2009; Dave and Ghaly 2011).

R• + R• → R-R (4)

R• + ROO• → ROOR (5)

ROO• + ROO• → ROOR + O2 (6)

If the availability of oxygen is restricted, when the speed of autoxidation depends on its partial pressure, the main radicals in the system are fatty acid radicals and the main termination reaction is their recombination (4). If sufficient oxygen is available, the reaction speed is not dependent on its partial pressure and more peroxyl radicals are formed. The main reactions are then the recombination of fatty acid radicals with peroxyl radicals and the mutual recombination of peroxyl radicals (5, 6) (Vel íšek and Hajšlová 2009).

Products of autoxidationThe oxidation of lipids, and of unsaturated fatty acids in particular, leads to the formation

of hydroperoxides whose cleavage is accompanied by the formation of secondary products such as pentanal, hexanal, 4-hydroxynonenal, malondialdehyde and other oxygen compounds including aldehydes, acids and ketones (Fernández et al. 1997). These secondary products may cause loss of colour and nutritional value and a negative smell and taste (Min and Ahn 2005; Resconi et al. 2013) due to their effect on lipids, pigments, proteins, saccharides and vitamins (Fernández et al. 1997; Dave and Ghaly 2011). They are often associated with toxic effects (the inception of atherosclerosis, carcinogenic and mutagenic properties) (Sammet et al. 2006; Dave and Ghaly 2011; Duthie et al. 2013). In certain cases, oxidation products may contribute to the typical aroma of the given products (Gandemer 2002). An overview of cleavage products formed during lipid oxidation is given in Fig. 1.

127

• Primary productsThe primary products of autoxidation are hydroperoxides (Fernández et al. 1997;

Wąsowicz et al. 2004; Reconi et al. 2013). Hydroperoxides, and hydroperoxides of diene and triene acids in particular, are highly unstable and eliminate either a hydrogen radical to form a peroxyl radical or a hydroxyl radical to form an alkoxyl radical (Velíšek and Hajšlová 2009). Peroxyl and alkoxyl radicals are highly reactive and can therefore act as initiators of autoxidation (Wąsowicz et al. 2004).

• Secondary productsThe decomposition of fatty acid hydroperoxides and their radicals may lead to the

formation of various products in secondary reactions (Santos-Fandila et al. 2014). Three types of reaction can differentiated (Velíšek and Hajšlová 2009).1. Reactions that do not lead to a change in the number of carbon atoms in the molecule

(e.g. the formation of cyclic peroxides and endoperoxides, epoxy acids, hydroxy acids and oxoacids).

2. Reactions in which decomposition of the molecule occurs with the formation of products with a smaller number of carbon atoms (e.g. reactions forming aldehydes, hydrocarbons or oxoacids).

3. Polymerisation reactions (an increase to the number of carbons in the molecule).

Factors influencing the lipid oxidationThe speed of lipid autoxidation depends on a number of factors, e.g. the composition of

fatty acids (polyunsaturated fatty acids are more susceptible), the presence of antioxidants, pro-oxidants, etc. (Dave and Ghaly 2011; Falowo et al. 2014). An overview of the factors influencing the course of autoxidation is given in Table 3.

Min et al. (2008) and Min and Ahn (2005) state that the susceptibility of meat to the oxidation is also influenced by the animal species, the breed, the type of muscle and its anatomical location.

128

Fig. 1. The mechanism of lipid oxidation (Santos-Fandila et al. 2014; amended)

AntioxidantsModified atmospheres and antioxidants are used to prevent or delay lipid oxidation

(Sammet et al. 2006). Antioxidants are substances that extend the durability of foods and protect them against spoilage caused by oxidation that may take the form of fat rancidity or colour changes in foods (Decree No. 4/2008 Coll.).

129

Table 3. Factors influencing the rate and course of lipid oxidation (Belitz et al. 2004; Schaich et al. 2013, amended)

Nature of the lipids Degree of unsaturation, free fatty acids vs esters vs TAGs, trans vs cis, conjugation, phospholipidsSurface effects Dispersion, emulsionPresence of catalysts Pro-oxidants (hydroperoxides, metals, porphyrins, heme compounds), enzymes (lipoxygenase,

cyclooxygenase, xanthine oxidase), amino acids, ascorbic acid (low concentrations)Presence of inhibitors Antioxidants (endogenic and exogenic), polyphenols, metal chelators, synergists, amino acids,

enzymes (glutathione peroxidase), interceptors (proteins, DNA, vitamins, pigments)Environment Temperature, light, partial oxygen pressure, water, pH, packaging

Fig. 2. The interaction between the induction of oxidation and the potential of natural antioxidants to prevent the oxidation of meat (Falowo et al. 2014, amended)

Antioxidants interfere with the process of the oxidation of lipids and other oxylabile compounds by reacting with free radicals (primary antioxidants) or reducing any hydroperoxides formed (secondary antioxidants). They also bind to complexes of transition metals and eliminate oxygen present (Wąsowicz et al. 2004; Velíšek and Hajšlová 2009; Dave and Ghaly 2011).

In view of possible side effects, an effort is being made to reduce the use of synthetic antioxidants in view of their reduced acceptability among customers (Falowo et al. 2014) and to use natural antioxidants (Shah et al. 2014).

130

Table 4. Plant sources used as natural antioxidants in the production of meat and meat products (Falowo et al. 2014 and Shah et al. 2014, amended)

Part of plant Source

Leaves and secondary branches Rosemary, hyssopLeaf Rosemary, nettle, mint, lotus, myrtle, lemon balm, oregano, lemon grass, summer savory, curry, butterbur, Chinese chives/leek, daisy, pumpkin, sesame, soybean, thyme, oliveFlower NettlePeel Pomegranate, potatoRhizome Ginger, lotusFlowering head BroccoliSeed GrapeAerial parts GarlicBulb Garlic, onionBark Cinnamon

Table 5. Commercially available natural antioxidants of plant origin applied in the production of meat and meat products (Falowo et al. 2014; Shah et al. 2014, amended)

Extract Tested meat / meat product

Grape seed extract Ground beef, beef frankfurters, beef and pork meat, beef and pork patties, frozen pork patties, ground goat meat, restructured mutton slicesWhite grape extract Chilled beef pattiesGrape skin extract Pork pattiesPine bark extract Ground beefGreen tea extract (catechins) Pork sausagesGreen tea extract Pork pattiesCoffee extract Pork pattiesGreen coffee antioxidant Pork sausagesOlive leaf extract Beef, pork patties, pork sausagesWater-soluble oregano extract Beef and pork pattiesAdzuki bean extract Pork sausagesRosemary oleoresin Beef and pork patties, ground beefRosemary extract Boerewors-South African fresh sausage, pork sausages, pork pattiesCarob fruit extract Cooked porkBroccoli powder extract Goat meat nuggetAvocado seed extract Pork pattiesGinkgo biloba leaf extract Meat dumplingsHerbal extracts (marjoram, rosemary) Ground beef

The rate and extent of oxidation may be limited, reduced or halted by the use of natural antioxidants (Fig. 2) (Falowo et al. 2014). For example, Sammet et al. (2006) assessed the effect of α-tocopherol supplementation in the diet of pigs whose meat was used for the production of salami. A concentration twice as high was found in these products in comparison with a control group.

Technological strategies include the application of antioxidants directly to meat and meat products and the application of plant extracts to packaging material with the aim of achieving greater product stability (Falowo et al. 2014).

Natural antioxidants are obtained from plant sources such as herbs, roots, vegetables, fruit and oleaginous products (Shahidi and Zhong 2010). Natural antioxidants come from various parts of plants, such as leaves, roots, stems, fruits, seeds, skin and bark (Shah et al. 2014). An overview of plant sources used as natural antioxidants is given in Table 4. Some of these antioxidants are used commercially in the meat industry and their specific applications are given in Table 5. Many natural antioxidants, e.g. rosemary and spice extracts, have been described as being more effective than synthetic antioxidants. It is important that further research will be focused on their use in the production of foodstuffs (Karre et al. 2013). The use of antioxidants in food products is a subject stated in the national legislation and international standards (Decree No. 4/2004; Karre et al. 2013).

The use of natural antioxidants in meat and meat products during processing and storage can be considered multifunctional in view of their antioxidant, antimicrobial and preservative effects. The addition of natural antioxidants stabilises cholesterol levels, inhibits the formation of its oxidation products, and reduces the formation and absorption of malondialdehyde and heterocyclic amines in heat-treated meat (Falowo et al. 2014).

Conclusions

Lipid oxidation in meat and meat products is the main cause of their deterioration. A large number of compounds formed during autoxidation have a negative effect on the taste, aroma and safety of meat products, reduce their nutritional value and shorten their shelf life. Antioxidants can be used to prevent oxidation processes. Efforts are currently being made to restrict the use of synthetic antioxidants in view of their possible toxic effects and to replace them with natural antioxidants which become more and more interesting for the consumer. These natural antioxidants, rich in phenolic substances, are obtained from various parts of plants, such as leaves, roots, stems, seeds, etc. and provide a suitable alternative to synthetic antioxidants.

References

Belitz HD, Grosch W, Schieberle P 2004: Food Chem 3rd revised Ed: Springer-Verlag Berlin Heidelberg, 1070 pDave D, Ghaly AE 2011: Meat spoilage mechanisms and preservation techniques: A critical review.

Am J Agri Biol Sci 6: 486-510Decree No. 4/2008 Coll., stipulating types and conditions of using additives and extraction solvents in foodstuffs

production. Collection of Laws of the Czech Republic 2008, part 3, 258-340 (In Czech)Devatkal SK, Thorat P, Manjunatha M 2012: Effect of vacuum packaging and pomegranate peel extract on quality

aspects of ground goat meat and nuggets. J Food Sci Technol 51: 2685-2691Duthie G, Campbell F, Bestwick C, Stephen S, Russell W 2013: Antioxidant effectiveness of vegetable

powders on the lipid and protein oxidative stability of cooked turkey meat patties: Implications for health. Nutrients 5: 1241-1252

Falowo AB, Fayemi PO, Muchenje V 2014: Natural antioxidants against lipid-protein oxidative deterioration in meat and meat products: A review. Food Res Int 64: 171-181

Fernández J, Pérez-Álvarez JA, Fernández-López JA 1997: Thiobarbituric acid test for monitoring lipid oxidation in meat. Food Chem 59: 345-353

Gandemer G 2002: Lipids in muscles and adipose tissues, changes during processing and sensory properties of meat products. Meat Sci 62: 309-321

131

Hájek J, Machovič V, Křížová O, Sedláčková V, Novotná M 1998: Využití infračervené spektrofotometrie pro sledování změn při oxidaci řepkového oleje. Chem Listy 92: 434-440 (In Czech)

Karre L, Lopez K, Getty KJK 2013: Natural antioxidants in meat and poultry products. Meat Sci 94: 220-227Medina-Meza IG, Barnaba C, Barbosa-Cánovas GV 2014: Effect of high pressure processing on lipid oxidation:

A review. Innov Food Sci Emerg Technol 22: 1-10Min B, Ahn DU 2005: Mechanism of lipid peroxidation in meat and meat products: A review. Food Sci Biotechnol

14: 152-163Min BR, Nam KC, Cordray JC, Ahn DU 2008: Factors affecting oxidative stability of pork, beef, and chicken

meat. Animal Industry Report, AS 654, ASL R2257Pokorný J 2006: Fat and oils: Science and applications. In: Hui YH Handbook of Food Science, Technology, and

Engineering. Vol. 1. 1st Ed. Boca Raton: CRC press and Taylor & Francis Group, 1-21Resconi VC, Escudero A, Campo MM 2013: The development of aroma in ruminant meat. Molecules

18: 6748-6781Sammet K, Duehlmeier R, Sallmann HP, Von Canstein C, Von Mueffling T, Nowak B 2006: Assessment of

the antioxidative potential of dietary supplementation with α-tocopherol in low-nitrite salami-type sausages. Meat Sci 72: 270-279

Santos-Fandila A, Camino-Sánchez FJ, Zafra-Gómez A 2014: Degradation markers in nutritional products: A review. Austin J Anal Pharm Chem 1: 1-7

Shah MA, Bosco SJD, Mir SA 2014: Plant extracts as natural antioxidants in meat and meat products. Meat Sci 98: 21-33

Shahidi F, Zhong Y 2010: Novel antioxidants in food quality preservative and health promotion. Eur J Lipid Sci Technol 112: 930-940

Schaich KM, Shahidi F, Zhong Y, Eskin NAM 2013: Lipid oxidation. In: Eskin NAM, Shahidi F. Biochemistry of Foods. 3rd Ed. London: Elsevier Inc., 419-478

Velíšek J, Hajšlová J 2009: Chemie potravin 1. 3rd Ed. Tábor: OSSIS, 602 p (In Czech)Wąsowicz E, Gramza A, Hęś M, Jeleń HH, Korczak J, Małecka M, Mildner-Szkudlarz S, Rudzińska M, Samotyja

U, Zawirska-Wojtasiak R 2004: Oxidation of lipids in food. Pol J Food Nutr Sci 13/54: 87-100Zuleta EC, Baena L, Rios LA, Calderón JA 2012: The oxidace stability of biodiesel and its impact on the

deterioration of metalic and polymeric materials: A review. J Braz Chem Soc 23: 2159-2175

132