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Ame r J of Pota to Res (2005) 82:163-172 163

nvi ted Review

n t i o x i d a n t s i n P o t a t o

C. R. Brown*USDA/ARS, 24106 N. Bunn Road, Prosser, WA 99350, USA

*Corresponding author: Tel: 509.786.9252; Fax: 509.786.9277; Email: cbrown@pars.ars.usda.gov

B S T R C TThe conte nt of compounds in potato that may act as

antio xidan ts in the hu man diet is not widely appreciated.Carotenoi ds are prese nt in the f lesh of al l potatoes. Thecontents ment ion ed in the l i te ra ture range f rom 50 to100 pg per 100 g fresh weight (FW) in white-fleshed vari-etie s to 2000 ~g per 100 g FW in deepl y yellow to orange-f leshed cult ivars. The carotenoid s in potato are p r imarilylutein, zexanthi n, and vio laxanthin , al l of which arexanthophylls. There is jus t a trace of ei ther alpha- orbeta-caroten e, meaning that p otato is not a source ofpro-vi tami n A carotenes . In pota toes wi th to t a lcaro teno ids ran ging from 35 to 795 pg per 100 g FW, thelipophilic extract of potato f lesh presented oxygen radi-cal absorbance capacity (ORAC) values ranging from 4.6to 15.3 umoles ~-toc opherol eq uiva lent s per 100 g FW.Potatoes contai n phenolic compounds and the predomi-nant one is chlorogenic acid, which consti tutes about80 of the tot al phenolic acids. Up to 30 ~g per 100 g FWof f lavonoids are pres ent in the f lesh of white-f leshedpota toes wi th roughly twice the amount present inred- and purple - f leshed pota toes . The predominantf lavonoids are catechin and epicatechin. Red and purp lepotato es der ive their color f rom anthocyanins. The skinalone may be pigmented, or the f lesh may be par t ial ly orentirel y pigmented. Whole unpe eled with complete pig-ment ati on in the f lesh may have up to 40 mg per 100 gFW of total antho cyanins. Red-f leshed potatoes haveacylated glucosides of pelargonidi n while purple po ta-toes have, in addit ion, acylated glucosides of malvidin,

Accepted for publication 25 August 2004.ADDITIONALKEY WORDS: anthocyanins, carotenoids, phenolic acids,flavonoids,Solanum tuberosum L.

petunidin, peonidin, and delphinidin. The hydrophil icantio xidan t activi ty of solidly pigmen ted red or purplepotatoes is comparable to brussels sprouts or spinach.In red and purp le potat oes with solidly pigment ed f leshwith levels of total ant hocya nin ranging from 9 to 38 mgper 100 g FW, ORAC ranged from 7.6 and 14.2 umole pe rg FW of Trolox equivalents. Potato contain s on average20 mg per 100 g FW of vitam in C, which may acco unt forup to 13 of the total antiox idant capacity. Potatoesshould be considered vegetables that may have highantiox idant capacity depending on the f lesh composit ion.

I N T R O D U C T I O NThe potato tuber is an underground stem providing an

opportunity for the potato plant to propagate itself vegeta-tively. Domest ication by hum an beings and selection as a food-stuff provided for higher yield and ch aracteristics suitable forfresh market and processing. As a result the potato hasbecome an exceptionally high-yielding carbohydrate-rich crop.Other notabl e features are a high-quality prot ein an d a signifi-cant level of vitamin C (Woolfe 1987). Less well kno wn are thecarotenoids and phenolics found in potato, which are po tentantioxidants. The pm]0ose of this review is to place the antiox-idant status of potato into perspective in terms of genetic vari-ation available in germplas m and in relati on to its place in thehum an diet.

Diets rich in antioxida nt flavonoids and caroteno ids havebeen associated with a lower incidence of atheroscleroticheart disease, certain cancers, macular degeneration andseverity of cat aract s (Cao et al. 1998a, 1999; Hertog e t al. 1993;

ABBREVIATIONS:AAPH, 2,2'-azobis(2-amidmopropane) ihydrochlo-ride; DPPH,2 2-Diphenyl-l-pieryhydrazyl; FRAP ferric reducing abilityof plasma; ORAC, oxygen radical absorbance capacity

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1 64 A M E R I C A N J O U R N A L O F P O T A T O R E S E A R C H V o l. 8 2

K n e k t e t a l . 1 9 9 6 ; K r u e z e r 2 0 01 ; W a n g e t a l . 19 9 9) . A r g u m e n t sf o r t h e h e a l t h b e n e f i t s o f a n t i o x i d a n t s a r e l a r g e l y c o r r e l a t e d t od i e t c o m p o s i t i o n v s d i s e a s e a n d m o r b i d i t y in p o p u l a t i o u s . T h ec o n s u m p t i o n o f a n t i o x i d a n t - r i c h f o o d s r e s u l t s i n t h e m a i n t e -n a n c e o f h i g h e r a n t i o x i d a n t l e v e l s in b l o o d s e r u m ( C a o e t a l .1998a , 1998b ; Ma zza e t a l . 2002; P r i o r and C ao 2000) . Re du c t io no f a t h e r o s c l e r o t i c h e a r t d i s e a s e i n a s s o c i a t i o n w i t h a n t i o x i d a n tr i c h d i e t s i s h y p o t h e s i z e d t o b e r e l a t e d t o a r e d u c t i o n i n t h eo x i d a t i v e p o l y m e r i z a t io n o f l o w - d e n s i ty l i p o p r o t e i n s a n d c o n -s e q u e n t l e s i o n fo r m a t i o n a n d p l a q u e b u i ld u p i n k e y c o r o n a r ya r t e r i e s ( B u r i n g a n d H e n n e k e u s 1 99 7) . C a n c e r r e d u c t i o n i s t i mt h e r h y p o t h e s i z e d t o b e d u e t o p r o t e c t i o n o f D N A f r o md e s t r u c t i o n b y r e a c t i v e o x i d a t i v e s p e c i e s ( W a r g o v i c h 2 0 0 0 ) .L u t e in s u p p l e m e n t a t i o n i n t h e d i e t h a s b e e n c o r r e l a t e d w i t hi m p r o v e m e n t i n v i s u a l f u n c t i o n i n p a t i e n t s s u f f e r i n g f r o m m a c -u l a r d e g e n e r a t i o n a n d c a t a r a c t s ( O l m e d i l l a e t a l . 2 0 01 ) . C o n -s u m p t i o n o f d i e t s h ig h i n f r u i t s a n d v e g e t a b l e s i n c r e a s e d t h ea n t i o x i d a n t le v e l s i n b l o o d s e r u m i n h u m a n s u b j e c t s ( C a o e t a l .1 9 98 a , 1 99 8 b) . A l t h o u g h n o s t u d i e s h a v e y e t m e a s u r e db i o a v a i la b i l it y o f a n t i o x i d a n t s f r o m p o t a t o s o u r c e s , t h e r e i sl i m i t e d in f o r m a t i o n f r o m s m a l l f r u i t c o n s u m p t i o n s t u d i e s .A n t h o c y a n i n s f r o m e l d e r b e r r y ju i c e w e r e d e t e c t e d i n b l o o ds e r u m a n d u r i n e o f s u b j e c t s w h o c o n s u m e d j u i c e c o n t a i n i n g5 0 0 m g o f a n t h o c y a n i n s . T h e y i e l d i n t h e u r i n e w a s 0 .0 3 o f t h ei n g e s t e d a m o u n t s u g g e s ti n g a v e r y l o w a b s o r p t i o n t h r o u g h t h eg a s t r o in t e s t in a l t r a c t a n d e x c r e t i o n a s t h e i n t a c t f o r m ( M u r -c o v i c e t a l . 2 0 01 ). M a z z a e t a l . ( 2 0 0 2) f o u n d t h a t a n t h o c y a n i n sf r o m a b l u e b e r r y e x t r a c t w e r e a b s o r b e d i n t h e i r i n t a c t g l yc o -s y l a t e d an d a c y l a t e d f o r m s a n d w e r e a s s o c i a t e d w i t h a ni n c r e a s e i n s e r u m a n t i o x i d a n t s ta t u s .

G E N E T I C S O F N T H O C Y N I N SN D C R O T E N O I D S IN P O T T O

T h e n a t u r a l v a r i a t io n o f c u l t iv a t e d p o t a t o g e r m p l a s mi n c l u d e s t y p e s t h a t a r e r e d a n d p u r p l e p i g m e n t e d d u e t o t h ep r e s e n c e o f fl a v o n o i d s in t h e s l d n a n d / o r f l e s h. A n t h o c y a n i n sa r e a m o n g t h e m a n y f l a v o n o i d s th a t m a y b e f o u n d i n p o t a t ot u b e r s . A s e r i e s o f si n g l e g e n e s c o n t r o l s p r e s e n c e a n d a b s e n c eo f r e d a n d b l u e p i g m e n t s . D i f f e r e n t g e n e t i c s y s t e m s c o n t r o l l i n gp i g m e n t e x p r e s s i o n h a v e b e e n i d e n t i f i e d f o r d i p l o i d c u l ti v a t e dv s t e t r a p l o i d c u l t i v a t e d p o t a t o e s ( D o d d s a n d L o n g 1 9 5 5, 1 9 56 ;L u n d e n 1 9 60 ). D e J o n g ( 1 9 9 1 ) a n d V a n E c k e t a l . ( 1 9 94 ) h a v ea r g u e d t h a t t h e g e n e s a p p e a r t o b e s y n t e n i c a n d s h o u l d b e

r e g a r d e d a s b e l o n g i n g t o t h e s a m e g e n o m e . I n o t h e r w o r d s , t h eg e n e s c o d i n g f o r s i m i l a r p h e n o t y p e s i n d i p l o i d s a n d t e t r a p l o i d sa r e t h e s a m e g e n e s . T h e s y m b o l D d e n o t e s a s i n g le g e n e c o n -t r o ll i n g s y n t h e s i s o f r e d p i g m e n t , l o c a t e d o n c h r o m o s o m e 2 ;t h e s y m b o l P s t a n d s f o r a s i n g l e g e n e o n c h r o m o s o m e 1 1 c o n -t r o ll i n g b l u e p i g m e n t s y n t h e si s ; w h i l e / , o f u n d e t e r m i n e d l o c a -t i o n, e p i s t a t i c a l l y c o n t r o l s p r e s e n c e a n d a b s e n c e o f t u b e r s l d na n d f l e s h p i g m e n t a t i o n e v e n w h e n P a n d D a r e p r e s e n t . G e b -h a r d t e t a l . (1 9 8 9) r e p o r t e d a l o c u s c o n t r o l l i n g p u r p l e s k i nco lo r , P s c o n c h r o m o s o m e 4 . T h e s i n g l e g e n e P~ , l i n k e d t o / ,d e t e r m i n e s w h e t h e r p i g m e n t is p r e s e n t b e y o n d t h e p e r i d e r mi n t h e i n t e r i o r t i s s u e s o f t h e t u b e r ( D e J o n g 1 98 7, 1 9 91 ; V a n E c ke t a l. 1 99 4) . T h e p i g m e n t s h a v e b e e n d e t e r m i n e d t o b e v a r i o u st y p e s o f a c y l a t e d a n t h o c y a n i d i n g l u c o s i d e s ( H a r b o u r n e 1 96 0;R o d r i g u e z - S a o n a e t a l . 19 9 8) . T h e g e n e A c i s i m p u t e d t o c o n -t r o l a c y l a t i o n o f a n t h o c y a n i n s . D i p l o i d c u l t iv a t e d p o t a t o e s d i s -p l a y b o t h a c y l a t e d a n d n o n - a c y l a t e d f o r m s w h i l e o n l y a c y l a t e da n t h o c y a n i n s a r e p r e s e n t i n t h e t e t r a p l o i d c u l ti v a r s ( S w a m i -n a t h a n a n d H o w a r d 1 9 53 ). P o t a t o e s h a v e a c y l a t e d g l u c o s i d e so f s e v e r a l a g l y c o u s ( p e l a r g o n i d i n , p e t u n i d i n , m a l v i d i n , a n dp e o n i d i n ) a n d m o s t l y x a n t h o p h y l l t y p e c a r o t e n o i d s , i n c l u d i n gp r e d o m i n a n t l y l u te i n , v i o l a x a n t h i n a n d z e a x a n t h i n Browne t a l .2 00 3; F o s s e n a n d A n d e r s e n 2 00 0; F o s s e n e t a l . 2 00 3; I w a n z i k e ta l . 1 98 3 ; M a z z a a n d M i n i a t i 1 9 9 3 ; R o d r i g u e z - S a o n a e t a l . 1 9 9 8) .

O u t s i d e o f t h e c e n t e r o f o r i g i n o f c u l t i v a t e d p o t a t o i n t h eA n d e s o f S o u t h A m e r i c a , it i s r a r e t o f m d v a r i e ti e s w i t h a n t h o -c y a n i n p i g m e n t s c o n f e r r i n g r e d o r p u r p l e f l e s h . H o w e v e r ,m u c h o f t h e w o r l d ' s p r o d u c t i o n i s o c c u p i e d b y y e l l o w - f l e s h e dp o t a t o e s , w h i c h h a v e h i g h e r to t a l c a r o t e n o i d t h a n t h e w h i t e-f l e s h e d v a r i e t i e s o f N o r t h A m e r i c a a n d G r e a t B r i t a in . A l t h o u g hg e n e t ic c o n t r o l o f p r e s e n c e a n d a b s e n c e o f a n t h o c y a u ln s i sm o n o g e n i c , t h e c o m p l e t e n e s s o f a n t h o c y a n i n d i s t r i b u ti o n i np i g m e n t e d f l e sh m a y b e u n d e r c o m p l e x g e n e t i c c o n t r o l( B r o w n e t a l . 2 0 03 ; D e J o n g 1 9 91 ). W h i t e v s y e l l o w f l e s h i st h o u g h t t o b e u n d e r s i n g l e g e n e c o n t r o l , w h i l e g e n e m a p sa g r e e o n t h e p l a c e m e n t o f th i s y e l l o w - f l e s h f a c t o r ( Y / y ) o nh o m o l o g 3 ( B o n l e r b a l e e t a l . 19 8 8; G e b h a r d t e t a l . 1 98 9 ). W h i t e -a n d y e l l o w - f l e s h e d p o t a t o e s h a v e s i m i l a r c o m p o s i t i o n o fc a r o t e n o i d s ; h o w e v e r , t h e y e l l o w c o l o r o f t h e l a t t e r g r o u p i sd u e t o h i g h e r c o n c e n t r a t i o n s o f c e r t a i n x a n t h o p h y l l s ( B r o w ne t a l . 1993 ; Gro ss 1991).

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2005 BROWN: ANTIOXIDANTS IN POTATO 165

N T I O X I D N TM E S U R E M E N T M E T H O D S

There are numer ous antiox idant s assays in the literature.A description of three in some detail will provide a base ofknowledge. Antioxidants are compounds that, w hen in thepresence of an oxidizable substrate and an oxidizing agent,delay the oxidation of the substrate. Oxygen radicalabsorb ance capacity (ORAC) is a measure of the capacity of anantioxid ant to delay oxidation of a target molecule. In ORACthis is meas ured by detecti ng the loss of luminescence of ~-Phy-coeryth rin (PE) due to oxidation. The loss of PE fluoresc ence inthe pre sence of free radicals is an index of oxidative damage tothe protein. The assay us es 2,2 -azobis(2-amidlnopropane)dihydrochloride (AAPH) as a free-rad ical-generating syste mand an area-under-curve technique for quantitation of antioxi-dan t capacity. AAPH under goes spon tane ous decomposition andproduces peroxyl radicals with a rate dependent on temperature.Thus, the ORAC assay measures the capacity of an anti oxidantto di rectly quench free radicals. The ORAC method is cons ideredto have the advantage of combining both inhibition percent ageand the length of inhibition time of free radical action by anantio xidan t into a single quantity (Cao an d Prior 1998).

The ferric reducing ability of plasma (FRAP) assay (Ben-zie and Strain 1996) is a me asure of the ferric-to-ferrous ironreduction followed by the formation of colored ferrous-tripyridyltriazine complex in the presen ce of antioxidant s. It iseasier and less expen sive to carry o ut than ORAC, but pr esentsonly a single time point percentage inhibiti on of oxidation.

The 2,2-Diphenyl-l-picryhydrazyl (DPPH) assay for totalantioxidant activity determines antioxidant activity based onthe analysis described by Brand-Wi lliams et al. (1995). DPPH,a stable radical, absorbs at 515 run, and upon reducti on by anantio xidan t species, a decrease in absorb ance is observed. Thechange in color (from purple to yellow) provides an easy andrapid way to evaluate the antiradical activities of extracts.DPPH can be used as a broad screen to identify the ranges ofant iox ida nt activity.

Prior and Cao (1999) reviewed antio xidant meas urem enttechniques. They emphasized the difficulty of comparing stud-ies due to the large numbe r of different techniques. However,they favored the ORAC assay because it takes the reactionbetween substrate and free radicals to completion using anarea-under-the-curve technique compared to single measure-

men t during the lag phase. Ideally several different measure-ments should be used.

N T H O C Y N I N SAnthocyanin contents of potatoes with pigmented flesh

have been studied recently by several workers. Rodriguez~Saona et al. (1998) repo rted an thocy anin contents of partiallyand solidly red-fleshed potatoes ranging from 3 to 40 mg per100 g fresh weight (FW). The major pig ments were identifiedby HPLC and mass spectroscopy analysis to be acylated glu-cosides of pelargonidin. The potential commercial value ofpelargonidin derivatives intended as natural colorants fromred-fleshed radish and red-fleshed potato were compared byWrolstad et al. (2001) and found to be promising from thestandpoint of stability relative to artificial colorants, attrac-tiveness, intensit y of red hue, a nd stability.

Lewis et al. (1998a) found much higher co ncentra tions ofantho cyani ns in certain cultivars extendin g up to 368 mg per100 g FW in the purple-fleshed cv Urenika and up to 22 mg per100 g FW in red-fleshed types. Concentrations are consider-ably higher in sldn, approa ching 900 mg in purple-fleshed and500 mg in red-fleshed types per 100 g FW (of the s kin alone).Red- and pro-pie-fleshed potatoes always have red- and purple-pigment ed skin, respectively. Pelargonldin and peon idin werein nearly equal amounts in the red flesh, while petuni din andmalvidin were p redo mina nt in the pu rple flesh. Wild specieshad no antho cyani ns in the flesh but up to 27 mg per 100 g FWin the skin (Lewis et al. 1998b). The cv Urehika, thought tohave been directly transferred to the Maori by 18th centuryEuropean visitors to New Zealand was identified by Cambieand Ferg uson (2003) as an import ant functional food in theMaori diet due to the presence of anthocyanius. Fossen andAnders on (2000) det ermined the an thocy anin s of the purple-fleshed cv Congo to consist of ferulyl gluco- and rhamno-pyra-nosides of malvidin and petunidin, novel anthocyanins. Fossenet al. (2003) f urther rep orted the n ew fmdin g of acylation withcaffeic acid in extracts from an u nna med purple-fleshed Nor-wegia n cultivar. Naito et al. (1997) simi larly identi fied acylatedglucopyranosides of pelargonidin as the primary anthocyaninsin a red-fleshed potato prod uced from hybri dization betwee nS tuberosum ssp tuberosum and S tuberosum ssp. andigenaAlcalde-E on et al. (2003) reported ac ylat ed glucosides ofanthocyanidins. The aglycons were pelargonidin, maldvidin,

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petunidin, peonidin, and delphinidin acylated with hydrocin-nami c acids in the skin and flesh of pigmented cv Pinta Boca,a variety in the taxon o l a r iu m s t e ~ m t o m u m from Bolivia.Anthoc yanin conte nt of red- and purple-fleshed potato derivedfrom a breeding program conducted by the USDA/ARS atProsser, WA, ranged from 7 to 35 mg in red-fleshed and 6 to 17mg in purple-fleshed potato (Brown et al. 2003).

Anthocyanins were predominantly acylated glucosides ofpelargonid in in the red-fleshed potato and acylated glucosid esof predominantly petuni din and peonidln with smalleramounts of delphinidin and malvidin in the purple-fleshedpotato. Antioxi dant values (ORAC) for red-fleshed typesranged as high as 300/5 of the white flesh, wh ile for purple-fleshed antioxi dant values reached 250/5 of the white flesh.Hale (2003) fo und a range of 104 to 565 ~tg per 100 g FW (DPPHtest) among highly diverse materials. The purple-fleshedclones were among the top, presuma bly due to the high antho-cyanins. One of the more inte resting outcomes of this work isthe measurement of high antioxidant values in cv NorkotahRusset (NR) and a series of intraclo nal variants derived fromNR. The DPPH test values ran ged from 161 to 452 span ning sig-nificant differences statistically. This kind of result in a white-fleshed variety and its variants suggests that colorlesscompounds that are probably either flavonoids or phenolicacids are potentially very pot ent as antioxidants. Brown et al.(2004a) surveyed a nu mb er of breedin g lines with solidly pig-ment ed flesh reporting levels of the an thocya nin ranging from9 to 38 mg pe r 100 g FW. ORAC values ranged from 7.6 and 14.2umole per g FW of Trolox equivalents. The highest anti oxidan tvalue, a red-fleshed breeding line, was approximately 330/5that of the average of the white-fleshed breeding lines and vari-eties tested. Pietta (2000) p resen ted evidence that cyanid in isup to th ree times more effective than pelarg onidin as anantioxidant. Ka-hkSnen and Heionan (2003) have determ inedthat malvidin is the most potent antioxidant of the antho-cyanidins. Reyes and Cisneros-Zevallos (2003) fo und t hat thelocation of cultivation of the potato crop affected anth ocya ninconcen tratio n of a purple-fleshed cultivar. Also they found t hatcertain storage conditions simulating stress increased antho-cyania co ncentrat ion by 60/5 n tub ers harvested from environ-ment s that resulted in the lowest out-of-field concentration s. Ametho d to extract red pigm ent from red-fleshed potato for useas a natural colorant was developed by Wrolstad andRodriguez-Saona (2001).

O T H E R P H E N O L I C C O M P O U N D SLewis et al. (1998a) found that cultivated potato tu ber

skin co ntain ed 2000-5000 pg per g FW pheno lic acids and 200-300 ~g of flavonoids. Purple- and red- sldnn ed tubers contain edtwice the concentration of phenolic acids as white-skinnedtubers. Tuber flesh contained lower co ncentrations rangingfrom 100-600 ~g of phenol ic acids a nd 0 to 30 ~tg of flavonoids.They also found that purple- or red-fleshed cultivars had twicethe flavonoid concentration of white-fleshed cultivars andthree to four tim es the con centra tion of phenoli c acids. Exam-ples of flavonoids in order of abundance were catechin, epi-catechin, erodictyol, kaempeferol, and n aringenin. Thepred omi nant phenolic acids were chorogenic acid, protocate-chic acid, vanillic acid, an d p-coumaric acid. In wild o l a n u mspecies (Lewis et al. 1998b) phenolic acids ranged from 600 to2700 in ski n and 100 to 600 ~g per 100 g FW in the flesh. Simi-lar types of phenolics acids were found with the exception ofthat caffeic acid concentrations increased to be the secondmost ab und ant after top-ranking chlorogenic acid. Flavonoid sranged from 20 to 170 Itg in the skin and 0 to 25 ~g per 100 gFW in the flesh, with the identities basically following the pat-tern found in cultivated potato. Pietta (2000) has shown thatflavonoids differ greatly in their antixoxidant capacity.Quercetin is, for instance, more than three times more effec-tive as an antioxidant than kaempferol and eridictyol, and istwice as effective as catec hin. Inte restingly , Lewis et al. (1999)found that the total anthocyanin , phenol ic acids, and flavonoidcontent increased during cold storage (at 4 C) in the skin andflesh of purple-fleshed New Zealand variety Urenika. Chu et al.(2000) found th at the flavonoids and fl avone extracts had highscavenging activities toward oxygen radicals. Potatoesshowed 94 scavenging activity towards hydroxyl radicals,and, along with onions , almost complete inhibiti on of super-oxide radicals.

V I T M I N CPotatoes have levels of vitanfin C that con tribute substan -

tially to th e Recom mended Dally Allowance (in the USA) of 60mg for adult s (Augustin 1975). In two r ecent surveys of potatogenotypes, concen tratio ns varied betwe en 11 and 30 mg per100 g FW in North Am erican varieties and bree ding lines (Loveet at. 2003) and 18 to 36 mg in six E urop ean varieties and 27breeding lin es (Dale et al. 2003). Recent reports of genetic vari-

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ability report a high heritability for vitami n C content, h 2 = 0.96,and measured progeny clones from crosses that had 40 mgvitam in C per 100 g FW (Pavek and Corsini 2003). The p res-ence of high vitamin C in the South American cultivatedspecies Solanum phureja has been noted. In crosses ofS. phureja a diploid, with tetraploid parents relatively highlevels of vitamin were no ted in th e progeny (Davies et al.2002). Dale et al. (2003) also documented the large reductionin vitamin C cont ent that occurs during storage, averaging 45%.Vitamin C was found to decrease more rapidly at 1 C storagecompared to 20 C in two Japanese varieties, Danshaku andKataaka ri (Kawakami et al. 2000). Relatively little is kn ow n ofthe contribution of vitamin C in potato to antioxidant value.However, one study (Chu et al. 2002) has estimated that vita-min C extracted from an unidentified potato obtained from agrocery store contrib utes 13.3% of the total a ntioxi dant activ-ity. Although a modest value, it remain s to be det ermine d whatthe higher concentrations available in breeding materialsmight contribute to total antioxid ant value.

Relatively little is know n of th e affects o f handling, stor-age, and processing of carotenoids, anthocyanins, phenolics,or flavonoids. There is, however, a body of knowledge sur-roun ding the fate of vitami n C. Besides the decrease duringstorage already noted, vitamin C conten t is known to rise dur-ing crop development, but decrease during late season matu-ration of the crop (Shekhar et al. 1978). Bruising of potatoesduring hand ling results in an initial increase in vitamin C fol-lowe d by a 30/5 o 40/5 educ tion relative to unbrui sed pot atoesafter 12 weeks in storage regardless of the storage tempera-ture (Mondy et al. 1987). Vitamin C was in greater co ncentra -tion in the pith than i n the co rtex In this study. Sweeney et al.(1969) noted higher concentrations in the apical end ( budend ) vs the basal end ( stem end ) of tubers of cvs Pungo,Rosemount Cobbler, and Russet Burbank over 5 mont hs stor-age at 55 F (12.8 C) and 70 F (21.1 C). The apical-basal differ-ences persisted while whole tuber assays showed an overalldecline in concen trati on of betwe en 40/5 and 55%. Zinc fertil-ization (using zinc sulfate) result ed in a 40/5 ncrease in vita-min C cont ent in the variety Katahdin (Mondy et al. 1993).

A numb er of studies have charted the loss of vitamin Cduring diverse cooking and processing steps. The processingof potato into flakes almost totally eradicated vit amin C (Sulli-van et al. 1985). An importan t part of pre-cooked Fre nch fryproduction involves a blanching step. It has been found that20/5 o 45% of vitamin C is lost due to diffusion into th e w ate r

bath during this process and that losses are mitigated best byreducing time of bl anching at higher tempera tures (Artz et al.1983; Luna and Garrote 1987). Retention of vit amin C in pro-cessed com mercial products, which inclu ded a blanching step,was 69%, 61%, and 53% in large-sized frenc h fries, small-sizedfrench fries, and pre-formed patties, respectively (Augustin etal. 1979). Vitamin C may decrease during chilling and briefrefrigerated storage followed by microwave reheating; how-ever, these decreases are smaller than reductions caused byextended storage or those due to the bl anchin g step in com-mercial processing (Augustin et al. 1979). In experimentsdesigned to mimic home preparation, vitamin C losses werebetwee n 20/5 and 25%. The leas t loss was found in u npeeledboiled potato. Unpeeled and boiled Russet Burbank lost muchless vi tamin C (5%) tha n Katahdin (34%) (Augu stin et al. 1978).Cooking by boiling decreased vitamin C by 300/5 in Europe ancvs Bintje, Van Gogh, and Nicola and ke eping the po tatoes hotfor 1 h af ter c ook ing redu ced it a fiLrther 10/5 Hfigg et al. 1998).

N T I O X I D N T C T I V IT Y D U ET O P H E N O L I C N D O T H E R

C O M P O U N D SThe antioxidant capacity of tuber com ponents was exam-

ine d by A1-Saikhan et al. (1995). Pata tin, the major tub er stor-age protein, and chlorogenic acid were the most potentantioxidants. Antioxidant activity appeared to be correlatedwith total phenol ic acids. Of four potato cultiv ars tested (twowhite flesh and two yellow flesh), Norkotah Russet presente dthe highest total phenolic acid content and was among the twohighest in antioxidant activity. As mentioned above Hale(2003) also fou nd Norkotah Russet and intraclo nal variants tobe among the highest in antioxidant values.

Velioglu et al. (1998) compared a large group of fruits andvegetables as well as plant-derived products for antioxidantactivity of the phenolic acid extracts. White-fleshed potato(Russet Burbank) was ranked among the top in antioxidantvalues of the pheno lic acid fraction while harbori ng a compar-atively low am oun t of total phenol ic acids, 437 9g per 100 gFW. Dao and Freidman (1992) reported a range of 10 to 19 mgper 100 g FW of chlorogenic acid in different white-fleshedpotato genotypes. In the ran king of different phenoli c acids foroxidation potential, caffeic acid, and chlorogenic acid werethe lowest with values at one-third of those com pounds withthe highest oxi dation poten tial (e.g., 4-hydroxybenzoic acid).

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Hale (2003) reported total phenolic acid concentrations ofwhite-fleshed varieties ranging betw een 60 and 394 pg per 100grams FW. Most of the variation was ex plained by differencesin chlorogenic acid, which va ried betwee n 26 and 329 ~g. Oneaberrat ion was the pres ence of more t han 300 ~tg per 100 g FWof rutin hydrate in cv Ranger Russet. This is a good example o fpossible genetic variation in phenolic acid composition inpotato. An examination of hydrophilic extracts of white-fleshed wild species revealed a range as great as that fou nd incultivars and breeding lines including those with pigmentedflesh. Although not clear which compounds were responsiblefor the high values, two wild species were cousist antly high, S.james ii and S. pinnatisectum (Hale 2003). In addition, Hale(2003) found that the concentration of phenolic acidsaccou nted for relatively little of the an tioxid ant activity (R2 =0.18). Reyes and Cisneros-Zevallos (2003) found tha t slic ingincreas ed the total phenolic acids cont ent in the flesh of a pur-ple-fleshed potato in storage while it did not increase theanthocyanin content. Clearly, however, the phenolic acids ingreatest abundance in potato (chlorogenic being foremost onthis list as 80 of total) are potent antiox idants in raw flesh(Dao and Friedm an 1992).

C R O T E N O I D SWhite- and yellow-fleshed potatoes are very familiar to

people aroun d the world. The inten sity of yellow color variesgreatly and those at the far end of the continuu m may bedescribed as orange. Despite the common belief in earlierstudies that the most intensely colored yenow-fleshed pota-toes contained beta-carotene it may be true that there is nobeta-carotene, or just a trace (Gross 1991). Rather, Solanumpotato, in contrast to the sweet potato Ipomoea spp.), con-talns xanthoph ylls of various sorts. Total carotenoid measure-men ts from mid-20th century exist in the literature. Caldwell etal. (1945) repor ted 14 to 54 and 110 to 187 ~g per 100 g FW forwhite- and yellow-fleshed potatoes, respectively. Brunstetterand Wiseman (1947) reported 60 ~g and included beta-carotene as a minor com ponent of the total carotenoid mix-ture. It is likely that the specific extraction methods, e xposu reto light during the process, rapidity of completion of each step,and oxidation intervene to change the carotenoid spectrumoriginally present in the tub er flesh. Kasim (1967) reported val-ues for total caroteno id be tween 199 and 560 p~g, identifyinglutein, violaxanthin, and l utein 5,6 epoxide as the compon ents.

Granado et al. (1992) repo rted 17 and 65 pg in raw an d cookedpotato, respectively. Tevini et al. (1984) and Tev in and Scho-necker (1986) reported a range of 102 to 219 ~tg in yellow-fleshed potato, listing lutein, beta-carotene, neoxanthin,violaxanthin, and lutein 5,6 epoxide as compon ents. Iwanzik etal. (1983), in one of the most complete studies, compared pota-toes with va rious degrees of yenow in tensi ty fmding a range oftotal caroteno ids from 27 to 329 pg. They listed lutein, neox-anthin, violaxanthin, and lutein 5,6 epoxide as componentsand found a strong correlation between carotenoid concentra-tion and colorimetric measurements of yellowness. Heinonanet al. (1989) reported 13 and 60 pg from summer and spnngpotatoes, respectively, identifying he xanthop hyll as lutein. Anumber of studies have measured levels in potato withintense ly yellow flesh that derive these high levels from S.phureja, a diploid cultivated species endemic to the AndeanCordillera. Brow n et al. (1993) fou nd levels exce eding 2000 ~gin breeding materials segregating for orange-, yellow-, andwhite-fleshed phenotypes derived from a diploid populationoriginating from S. phureja and S. stenotomum originallydeveloped by F rank Haynes, North Carolina State University,NC, USA. The orange-fleshed types contained predominantlyzeaxanthin, which is redder in color than lutein, conferring adark yellow to orange appearance depending on concentrationin the flesh. Hale (2003) fo und a range o f 97 to 536 ~g per 100g FW in a series of cultivars and breeding lines. Carotenoidconte nt did not appear to be related to c olor of flesh. Brown etal. (2004a) divided cultivars into white, yellow, and dark yel-low categories on the basis of color which corresp onded to 50to 100, 150 to 250, and 500 to 700 ~tg per 100 g FW groupings.The last category, dark yellow, is not commerciall y availableexcept as Papa Amarilla in South America; however, it is pre-sent in br eeding lines in North America at this writing. RSmeret al. (2002) produced an increase of zeaxanthin in yellow-fleshed potato by txansformation of sense and antisense con-structs of neox anthin epoxidase. This inhibited conversion ofzeaxanthin into violaxanthin. Increases in zeaxanthin overwild type ranged betwe en four- and 130-fold. The highest lev-els of zeaxanthin reached 40 ~g per g dry weight (approxi-mately 1000 9g per 100 g FW). Lu et al. (2001) found highlevels, in thei r mo st highly pigme nted materials, 1435 and 2200of total carotenoids, respectively, listing lutein, zeaxanthin,neoxanthin, violaxanthin, and lutein 5,6 epoxide as compo-nents. Bre ithaupt a nd Bamedi (2002) reported values of 58-175and 38-62 ~g for yellow and white flesh, respectively, indicat-

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i n g t h a t e s t e r i f i e d x a n t h o p h y l l s m a d e u p a s u b s t a n t i a l p o r t i o no f t h e t o t a l c a r o t e n o i d c o n t e n t . N e s t e r e n k o a n d S i n k ( 20 0 3 )r e p o r t e d t h e c a r o t e n o i d l e v e ls a n d x a n t h o p h y l l id e n t i t ie s o fw h i t e - , y el l o w - , a n d o r a n g e - f l e s h e d p o t a t o . T h e y r e p o r t e d v a l -u e s r a n g i n g 4 8 t o 8 7 9 ~ g . O f t h e y e l l o w - f l e s h e d t y p e s , t h e h i g h -e s t v a l u e s w e r e 2 6 5 ~ g w h i l e t h e s i n g l e o r a n g e - f l e s h e d t y p eh a d 8 7 9 p g . In t e r e s t in g l y , t h e o r a n g e - f l e s h e d t y p e ( d e r i v e df r o m g e n e t i c m a t e r i a l s d e s c r i b e d i n B r o w n e t a l . [1 99 3] ) w a st h e o n l y o n e c o n t a in i n g m o r e t h a n a t r a c e o f z e a x a n th i n , w h i c hc o n s t i t u t e d a b o u t o n e - h a l f o f t h e t o t a l c a r o t e n o i d . B e s i d e t h eu b i q u i t o u s l u t e i n , w h i c h i s a l w a y s p r e s e n t i n w h i t e - f l e s h e dp o t a t o , v i o l a x a n th i n w a s t h e s e c o n d m o s t c o m m o n x a n t h o -p h y l l r e p o r t e d i n a b u n d a n c e i n y e l l o w - f l e sh e d p o t a t o e s .B r o w n e t a l . (2 0 0 4 a) i s t h e o n l y p u b l i s h e d s t u d y t o d a t e t or e p o r t a n t i o x i d a n t v a l u e s a t t r i b u t a b l e t o a c h l o r o f o r m s o l u b l ef r a c t i o n o f t h e t u b e r f l e s h . T h e O R A C v a l u e s r a n g e d f r o m 2 t o7 ~ g p e r 1 00 g F W a - t o c o p h e r o l e q u i v a l e n ts . T o t a l c a r o t e n o i dc o n c e n t r a t i o n w a s c o r r e l a t e d w i t h t h e O R A C v a l u e s , r = 0 .7 7,a n d a l s o h a d a s t a t i s t i c a l l y s i g n i f i c a n t p o s i t i v e r e g r e s s i o n c o e f -f i c i e n t . V a r i o u s s t u d i e s h a v e c o m p a r e d p u r i f i e d s a m p l e s o fc a r o t e n o i d s f o r a n t i o x i d a n t v a l ue s . T h e r e i s a g r e e m e n t t h a tl y c o p e n e , th e r e d c a r o t e n o i d a b u n d a n t i n to m a t o , d i s p l a y s t h eh i g h e s t v a l u e w h i le l u t e in a n d z e a x a n t h i n a r e a p p r o x i m a t e l yh a f t a s e f f e c t i v e ( B o h m e t a l . 2 00 2 ; M i l l e r e t a l. 1 9 96 ) . C l e v i -d e n c e e t a l . ( 2 00 0 ) d e t e r m i n e d i n t h e i r r e v i e w a r t i c l e t h a t c o n -s u m p t i o n o f d i e t a r il y r e a l i s ti c a m o u n t s o f c a r o t e n o i d - r ic hv e g e t a b l e s r a i s e d p l a s m a a n d c o l o n c e l l le v e l s o f s e v e r a lc a r o t e n o i d s b y s i g n if i c an t a m o u n t s .

E F F E T S O F O O K I N GT h e r e i s a l m o s t n o p u b l i s h e d i n f o r m a t i o n o n t h e e f f e c t s o f

c o o k i n g o n t h e f u n c t i o n a l p r o p e r t i e s o f c o n s t i tu e n t s o f p o t a t oo t h e r t h a n v i t a m i n C . O n e s t u d y f o u n d t h a t t h e a n t h o c y a n i n i nr e d - a n d p u r p l e -f l e s h e d p o t a t o e s s u r v i v es i n l a r g e p a r t v a r i o u sc o o k i n g m e t h o d s i n c l u d i n g f r y i n g i n o i l . F u r t h e r t h e a n t i o x i -d a n t p r o p e r t i e s o f t h e a n t h o c y a n i n s p e r s i s t a t l e v e l s eq u a l t o o rg r e a t e r t h a n 7 5 o f t h e r a w p o t a t o ( B r o w n e t a l . 2 0 0 4 b) . B l e s s -i n g t o n e t a l . (2 0 04 ) r e p o r t e d t h a t f r y i n g a n d m i c r o w a v i n gi n c r e a s e d a n t i o x i d a n t a c t i v it y a s m e a s u r e d i n a h y d r o p h i l i ce x t r a c t u s i n g t h e D P P H a s s a y . I n t er e s t i n g ly , in t h i s s t u d y , i r r a -d i a t i o n i n c r e a s e d b o t h c a r o t e n o i d c o n c e n t r a t i o n a n d D P P Ha n t i o x i d a n t a c t iv i t y.

O N L U S I O N SP o t a t o i s n o t o r d i n a r i l y c o n s i d e r e d a f o o d r i c h i n a n t i o x i -

d a n t s . H o w e v e r , a c o n s i d e r a t i o n o f t h e g e n e t i c v a r i a b i l i t y i nc o n c e n t r a t i o n s o f a n t h o c y a n i n s , p h e n o l i c a c i d s , f l a v o n o i d s ,a n d c a r o t e n o i d s , i n c l u d i n g c u l t i v a r s f r o m t h e c e n t e r o f o r ig i ni n S o u t h A m e r i c a i n v i t e s r e - o r i e n t a t i o n o f p r e c o n c e p t i o n s .F r i e d m a n ( 1 9 9 7 ) l i s t e d i m p u t e d h e a l t h b e n e f i t s o f d i e t s ri c h inp h e n o l i c a c i d s a s a n t i m u t a g e n i c , a n t i c a r c i n o g e n i c , g l u c o s e -l o w e r i n g , a n d c h o l e s t e r o l - l o w e r i n g . M a n y s t u d i e s s u g g e s t b e n -e f ic i al e f f ec t s i n h u m a n h e a l t h b a s e d o n c o n s u m p t i o n o fa n t i o x i d a n t s a s s u p p l e m e n t s o r i n t h e d i e t. H o w e v e r , i n f o r m a -t i o n i s s t il l t o o p r e l i m i n a r y t o s p e a k w i t h u n g u a r d e d a u t h o r it y .A t l e a s t o n e p o p u l a r b o o k a d v o c a t e s v e r y d e l i b e r a t e l y c h o o s-i n g d i e ts w i t h h i g h l y p i g m e n t e d f o o d s b a s e d p r i m a r i l y o n t h es a l u t a r y e f f e c t s o f a n t i o x i d a n t s a n d i n c l u d e s r e d - , p u r p l e - , a n dy e l l o w - f l e s h e d p o t a t o e s i n t h e l i s t o f e s p e c i a l l y h e a l t h y f o o d s( J o s e p h e t a l . 2 0 02 ) . O f f ic i a l d i e t a r y r e c o m m e n d a t i o n s o na n t i o x i d a n t s d o n o t y e t e x i st . N o n e t h e l e s s , s t u d i e s i n t h eb i o a v a il a b i li t y a n d p h y s i o l o g ic a l p a r a m e t e r s a s s o c i a t e d w i t ht h e p r o t e c t i v e f u n c t i o n o f a n t i o x i d a n t s c o n t r ib u t e d b y p o t a t ot o t h e d i e t w o u l d b e v e r y u s e f l fi t o t h e p o t a t o i n d u s t ry .

F u r t h e r m o r e , t h e g e n e t ic v a r i a b i l i t y r e p o r t e d i n t h i sr e v i e w p r o v i d e s i m p e t u s f o r f u t u r e b r e e d i n g w o r k d i r e c t e ds p e c i f i c a l l y a t e n h a n c i n g t h e a n t i o x i d a t i v e m a t r i x b y d i r e c t e ds e l e c t io n f o r h i g h e r c o n c e n t r a t io n s o f c o m p o u n d s h a v in gt h e s e p r o p e r t i e s . T h e i d e n t i f i c a t i o n a n d q u a n t i f i c a t i o n o f c o m -p o u n d s i n t h e p o t a t o t u b e r a n d a t t r ib u t i o n o f a n t i o x i d a t iv e va l -u e s a s w e l l a s o t h e r p r o p e r t i e s i s s t i ll i n i t s in f a n c y. E v e n m o r et a n t a l i z in g is t h e l a c k o f k n o w l e d g e i n t e r m s o f i d e n t i f i c a t i o no f n e w c o m p o u n d s a n d t h e d i f f e r e nc e s b e t w e e n g e n o t y p e s i nt e r m s o f p r e d o m i n a t i n g t y p e s i n e a c h c l a s s . T h er e i s a m p l er o o m f o r m u c h e x p e r i m e n t a t i o n o n t h e e f f e c t o f c u l tu r a l a n ds t o r a g e c o n d i t i o n s o n t h e c o n c e n t r a t i o n s o f a l l c l a s se s o f c o m -p o u n d s . L a s tl y , t h e e f f e c t o f d i f f e r e n t m o d e s o f c o o k i n g o n s t a -b i l it y o f t h e s e c o m p o u n d s h a s h a r d l y b e e n t o u c h e d , d e s p i t et h e o b v i o u s i m p o r t a n c e o f th i s . P r e l i m i n a r y re s u l t s , h o w e v e r ,a p p e a r t o i n d i c a t e t h a t m a j o r c a t e g o r i e s o f a n t i o x i d a n t s( a n t h o c y a n i n s a n d c a r o t e n o i d s ) w i t h s t a n d t h e u s u a l m o d e s o fc o o l d n g a n d r e t a i n t h e i r a n t i o x i d a n t c a p a c i t y a f te r c o o k i n g i nl a rg e p a rt . P o t a t o i s a l w a y s c o o k e d b e f o r e c o n s u m p t i o n i n t h eh u m a n d i e t. T h e r e i s r e a s o n t o e x p e c t t h a t c a r o t e n o i d s s u r v iv ec o o k i n g t o a c o n s i d e r a b l e e x t e n t b a s e d o n s t u d i e s in o t h e rf o o d s ( C l e v i d e n c e e t a l . 20 00 ). T h e p e r s i s t e n c e o f v i t a m i n C i sd o c u m e n t e d a f t e r d i v e r s e c o o k i n g m e t h o d s , y e t t h e r e i s

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always some loss . I t would appe ar that the ant ioxidat ive valueof phenolic acids is mostly null i fied by cooking (Fr iedman1997). The effects of cooldng on th e propert ies of antioxida ntsin potato is therefore a f ield deserving of considerab le effort inthe future . The anthocyani n pigments of potato may be ofinteres t as natural foo d colorants . The intensi ty of hue and thes tabil i ty would be at t ract ive in natural proc essed foods or forhomeopa thic medicines . The co-elut ion of anthocyanins andgtycoalkaloids would be a technical problem requiring specialseparat ion s teps to avoid the presen ce of glycoalkaloids in nat-ural pigme nt produc t (Rodrigue z-Saona et al. 1998). A met ho dto extract red anthocyanin pigment f rom red-f leshed potatofor use as a natural colorant was developed and paten ted byWrolstad an d Rodriguez-Saon a (2001).

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Shaw, and RM Deutsch. 1978. Changes in the composition ofpotato during home preparation: lI. Vitamins. Am Potato J55:653-661.

Augustin J, GI Marousek, LA Thoein, and B Bertelli. 1980. Vitaminrentent ion in cooked, chilled, and rehea ted potatoes. J Fo od Sci45:814-816.

Augustin J, BG Swanson, C Teitzel, SR Johnson, SF Pometto , WE Artz,CP Huang, and C Schomaker. 1979. Changes in the nuitrientcomposition during commercial processing of frozen potatoprodu cts. J Food Sci 44:807-809.

Benzie IFE, and JJ Strain. 1996. The ferric reducing ability of plasma(FRAP) as a measu re of antioxidant power : the FRAP assay.Anal Biochem 239:70-76.

Bless ingr on T, AL Hale, DC Schetwing, a nd JC Miller Jr. 2004. Effect ofcooking, storage, and ga mma irradiation on antioxida nt activityin potato Solanum tuberosum L.). Abstr Presented at the 88thAnn Mtg Potato As soc of Amer. p 35.

Bonierbale MW, RL Plaisted, and SD Tanksley. 1988. RFLP maps basedon a common set of clones reveal modes of chromosomal evo-lution in potato and tomato. Genetics 120:1095-1103.

BrandLWilliams w, ME Cuvelier, and C Berset. 1995. Use of free radicalmeth od to evaluate antiox idant activity. Lebensm Wiss Technol28:25-30.

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