Effect of thermal processing on anthocyanin stability in foods; mechanisms and kinetics of degradation

Trends in Food Science & Technology 21 (2010) 3e11

Review

* Corresponding author.

0924-2244/$ - see front matter � 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.tifs.2009.07.004

Effect of thermal

processing on

anthocyanin stability

in foods; mechanisms

and kinetics of

degradation

Ankit Patrasa,

Colm O’Donnellb andB.K. Tiwarib,*

aTeagasc, Ashtown Food Research Centre,

Dublin 15, IrelandbBiosystems Engineering, UCD School of Agriculture,

Food Science and Veterinary Medicine, University

College Dublin, Dublin 4, Ireland (Tel.: D353 1

7167302; e-mail: [email protected])

Anthocyanins are the most abundant flavonoid constituents of

fruits and vegetables. The conjugated bonds in their structures,

which absorb light at about 500 nm, are the basis for the red,

blue and purple colours of fruits, vegetables and their prod-

ucts. Anthocyanin pigments readily degrade during thermal

processing which can have a dramatic impact on colour qual-

ity and may also affect nutritional properties. This review

attempts to summarize some important aspects of anthocyanin

degradation during thermal processing. Conclusions regarding

the mechanisms and kinetics of anthocyanin degradation dur-

ing heat treatment are postulated based on current findings.

IntroductionAnthocyanins are bioactive compounds present in many

fruits, vegetables and their products. They are responsiblefor the wide array of colours present in flowers, petals,

leaves, fruits and vegetables and are a sub-group withinthe flavanoids characterized by a C6eC3eC6-skeleton.Since anthocyanins impart a characteristic colour to fruitsand vegetables they impact on a key quality parameter byinfluencing consumer sensory acceptance. A significantproperty of anthocyanins is their antioxidant activity, whichplays an important role in the prevention of neuronal andcardiovascular illnesses, cancer and diabetes, among others(Konczak & Zhang, 2004). There are several studies focus-ing on the effect of anthocyanins in cancer treatments (Lule& Xia, 2005), human nutrition (Stintzing & Carle, 2004),and its biological activity (Kong, Chia, Goh, Chia, &Brouillard, 2003).

A number of recent reviews have comprehensivelysummarized and critically evaluated the health benefits ofanthocyanin consumption (Clifford, 2000; Duthie, Duthie,& Kyle, 2000). Many factors can influence intrinsic antho-cyanin content including species, environmental andagronomic factors. Many foods which contain anthocyaninsare thermally processed prior to consumption and thisprocess can greatly influence anthocyanin content in thefinal product (Giusti & Wrolstad, 2003).

Thermal processing of foods involves heating to temper-atures from 50 to 150 �C, depending upon pH of the prod-uct and desired shelf life. Anthocyanins chemical stabilityis the main focus of many recent studies due to their abun-dant potential applications, their beneficial effects and theiruse as alternative to artificial colorants in foods. It wouldappear from these studies that anthocyanin stability is notmerely a function of the final processing temperature butis in turn influenced by the intrinsic properties of theproduct and the process such as pH, storage temperature,chemical structure and concentration of anthocyanins pres-ent, light, oxygen, the presence of enzymes, proteins andmetallic ions (Rein, 2005). The present review will there-fore summarize and critically evaluate recent findings onto the effect of thermal processing on anthocyanin contentin foods. Particular focus will be given to the degradation ofanthocyanins subjected to heat with an emphasis on thekinetics and mechanisms of degradation.

Anthocyanin stability as affected by heatThe predominant anthocyanins present in fruits and veg-

etables are cyanidin-3-O-glucoside, delphinidin-3-O-gluco-side, malvidin-3-O-glucoside, pelargonidin-3-O-glucoside,and petunidin-3-O-glucoside (Table 1). Recently, Rentzsch,

Table 1. Occurrence of anthocyanins in some fruits and vegetables.

Fruits and vegetables Major anthocyanin Minor anthocyanins

Strawberry Pelargonidin-3-glucoside Cyanidin- 3-glucoside, pelargonidin- 3-rutinosideBlackberry Cyanidin- 3-glucoside cyanidin-3-rutinoside, malvidin-3-glucosideRaspberry Cyanidin- 3-glucoside Pelargonidin-3-glucosides, -Pelargonindin-3-rutinosideSweet cherries Cyanidin-3-rutinoside Cyanidin-3-glucoside, Peonidin-3-rutinosideBlackcurrant Cyanindin-3-rutinoside Cyanindin 3-glucoside, Delphinidin-3-glucosideBilberry Delphinidin-3-galactoside Peonindin-3-glucoside, Peonindin-3-galactosideRed onions Cyanidin 3-glucoside Delphinidin 3-glucoside, Petunidin glucosideBlood orange Cyanidin 3-glucoside Delphinidin 3-glucoside, cyanidin 3,5-diglucoside, cyanidin 3-sophoroside,

delphinidin 3-(600-malonylglucoside), peonidin 3-(600-malonylglucoside), andcyanidin 3-(600-dioxalylglucoside) (Dugo, Mondello, Morabito, & Dugo, 2003;Hillebrand, Schwarz, & Winterhalter, 2004)

4 A. Patras et al. / Trends in Food Science & Technology 21 (2010) 3e11

Schwarz, & Winterhalter, (2007) reviewed the occurrenceand nature of anthocyanins. Due to co-pigmentation mech-anisms pyroanthocyanins are stable and intact in flowers,fruits and vegetables (Rein & Heinonen, 2004).

Magnitude and duration of heating has a strong influenceon anthocyanin stability. In an interesting study, Sadilova,Stintzing, and Carle (2006) observed that elderberry antho-cyanin contents were very sensitive to thermal treatment.After 3 h of heating, only 50% of elderberry pigmentswere retained at 95 �C. Several studies reported a logarith-mic course of anthocyanin destruction with an arithmeticincrease in temperature (Drdak & Daucik 1990; Havlikova& Mikova 1985; Rhim, 2002). The high temperatures[blanching(95 �C/3 min) in combination with pasteurisa-tion] involved in processing blueberries into purees resultedin 43% loss in total monomeric anthocyanins, compared tooriginal levels found in fresh fruit (Brownmiller, Howard,& Prior, 2008) whereas polymeric colour values increasedfrom 1% to 12%. This suggests that heat labile factorscan accelerate anthocyanin pigment destruction andstrongly supports the hypothesis that endogenous enzymesin fruits causes pigment destruction in juice processing.

Similar losses in raspberry purees were reported byOchoa, Kesseler, Vullioud, and Lozano (1999). Garcıa-Vig-uera & Zafrilla (2001) reported that jam manufactureresulted in anthocyanin losses ranging from 10% to 80%when boiling time was varied from (10 to 15 min). Gar-cia-Viguera, et al. (1999) reported that storage temperatureplays critical role for anthocyanin loss during storage. Theyobserved much slower degradation at 20 �C compared to37 �C. Thus stability of anthocyanins is strongly influencedby temperature (Jackman and Smith, 1996).

A combination of unit operations involving heat such asblanching, pasteurisation, and duration can also markedlyaffect the anthocyanin content of fruits and vegetables.For example, Volden et al. (2008) recently reported thatblanching, boiling and steaming, resulted in losses of59%, 41% and 29% respectively in anthocyanin contentof red cabbage. Similar results were reported by Lee, Durst,and Wrolstad (2002); Srivastava, Akoh, Fischer, andKrewer (2007) in blueberry products. Kirca, Ozkan, and

Cemeroglu (2006) reported that anthocyanins from blackcarrots were reasonably stable during heating at 70e80 �C,which is in accordance with the kinetic data by Rhim(2002) on the thermal stability of black carrot anthocyaninsbetween 70 and 90 �C. Hager, Howard, Prior, and Brown-miller (2008) found that processing of berries canned inwater or syrup resulted in total anthocyanin losses of42% and 51%, respectively. Recently Patras, Brunton,and Butler (2009) demonstrated that anthocyanins (cyanin-din-3-glucoside & pelargonidin-3-glucoside) in blackberryand strawberry puree were significantly affected by thermalprocess treatments of 70 �C during holding times of 2 min.

In common with other polyphenols, anthocyanins are en-zymatically degraded in the presence of polyphenol oxi-dase. This enzyme can be inactivated by mild heating andtherefore some authors have reported that the inclusion ofa blanching step (heating to approximately 50� C) canhave a positive effect on anthocyanin retention. For exam-ple Skrede, Wrolstad, AuthorAnonymous, and Durst (2000)demonstrated that addition of a blanched blueberry-pulpextract to blueberry juice resulted in no degradation of an-thocyanins, whereas addition of an unblanched extractcaused a 50% loss of anthocyanins, suggesting an enzy-matic role in anthocyanin degradation. Rossi et al. (2003)suggested that an additional blanching step in juice process-ing may be vital, when evaluating fruit products for theirhealth effects as blanching inactivates polyphenol oxidase.Co-pigmentation would also appear to play a role in antho-cyanin stability. For example in a study conducted byDyrby, Westergaard & Stapelfeldt (2001) the authors re-ported greater thermal stability of anthocyanins present inred cabbage compared to blackcurrant, grape skin and el-derberry anthocyanins in soft drink model system (Table2) due to the protection of flavylium system through co-pig-mentation. Kirca, Ozkan, Cemero glu. (2007) reported thatthe stability of monomeric anthocyanins in black carrotjuice and concentrates depended on temperature, solid con-tent and pH. Anthocyanins from black carrot were rela-tively stable to heat and pH change compared toanthocyanins from other sources due to di-acylation of an-thocyanin structure. Acylation of the molecule is believed

Table 2. Kinetic parameters of anthocyanins in a selection of fruit and vegetable products following thermal processing.

S. No Fruit/Vegetable juice Anthocyanins Processing condition Kinetic parameters References

1 Roselle (Hibiscussabdariffa L. cv. ‘Criollo’)

Delphinidin-3-xylosylglucoside

Temperature (60 to 100 �C)and time (20 to 120 min)

Ea ¼ 15.83 kcal mol�1

(66.22 kJ mol�1)Aurelio, Edgardo, andNavarro-Galindo, (2008)

Cyanidin-3-xylosylglucoside Q10 ¼ 1.012 Grape pomace delphinidin Non-isothermal heating (retort) k110 �C ¼ 0.0607/min Mishra, Dolan,

and Yang, (2008).cyanidin C-p ¼ 3600)/kgpetunidin Ea ¼ 65.32 kJ/molpeonidinmalvidin

3 Purple-flesh potato Anthocyanin extract Blanching (Boiling water) Z ¼ 28.4 Reyes and Cisneros-Zevallos, (2007)pH ¼ 3 Q10 ¼ 2.25

Ea ¼ 72.494 Red-flesh potato Anthocyanin extract Blanching (Boiling water) Z ¼ 27.10 Reyes and Cisneros-Zevallos, (2007)

pH ¼ 3 Q10 ¼ 2.38Ea ¼ 74.24

5 Grape Anthocyanin extract Z ¼ 27.51 Reyes and Cisneros-Zevallos, (2007)Q10 ¼ 2.31Ea ¼ 76.61

6 Purple carrot Anthocyanin extract Blanching (Boiling water) Z ¼ 23.06 Reyes and Cisneros-Zevallos, (2007)pH ¼ 3 Q10 ¼ 2.71

Ea ¼ 88.797 black carrots Monomeric anthocyanin

(439 mg/L)70, 80 and 90 �C Ea ¼ 78.1 (2.5), 72.4

(3.0, 4.0), 5.0 (56.8),42.0 (6.0), 47.4 (7.0)

Kırca, Ozkan, and Cemeroglu, (2007)pH ¼ 2.5, 3.0, 4.0, 5.0, 6.0 and 7.0

Q10(70e80 �C)¼(1.7 e 2.8)11, 30, 45, 64 �Brix

Q10(80e90 �C) ¼ (1.9e 2.2)8 Strawberry juice (8 oB) Monomeric ACN Garzon, and Wrolstad (2002)

Concentrate (65 oB)9 Blond orange juice with

anthocyanin-rich black carrotTotal anthocyanin 70e90 �C Ea ¼ 72.0 KJ/mol Kirca et al. (2003)

10 purple corn cob Total anthocyanin 70 �C, 80 �C and 90 �C)at pH 4.0

Ea ¼ 18.3KJ/mol Yang, Han, Gu, Fan and Chen (2008)

11 Model juice(blackcurrant anthocyanin)

Total monomericanthocyanins

4e100 �C: isothermalmethod 110e140 �C: Non-isothermal method

73 � 2 kJ/mol(calculated over therange 21e100 �C)

Harbourne et al. (2008)

91.09 � 0.03 kJ/mol(non isothermal)

12 plum puree Total anthocyanins 50, 60, 70, 80 and 90 �C Ea ¼ 37.48 kJ/mol Ahmed, Shivhare, and Raghavan (2004)0e20 min

13 Red Cabbage Anthocyanin extractin MB and SD

25, 40, 60 and 80 �C.15 min, 30 min, 60 min,120 min, 240 min and 360 min

Dyrby et al., 2001

14 Grape skin Anthocyanin extractin MB and SD

Ea ¼ 69.0 kJ/mol (MB) Dyrby et al., 2001Ea ¼ 50.0 kJ/mol (SD)

15 Blackcurrant pomace Anthocyanin extractin MB and SD

Ea ¼ 58.0 kJ/mol (MB) Dyrby et al., 2001Ea ¼ 77.0 kJ/mol (SD)

16 Elderberry juice concentrate Anthocyanin extractin MB and SD

Ea ¼ 89.0 kJ/mol (MB) Dyrby et al., 2001Ea ¼ 56.0 kJ/mol (SD) 5

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Patras

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(2010)

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6 A. Patras et al. / Trends in Food Science & Technology 21 (2010) 3e11

to improve anthocyanin stability by protecting it from hy-dration (Brouillard, 1981; Goto, Hoshino & Takase,1979). Similarly, Rubinskiene et al. (2005) demonstratedthat cyanidin-3-rutinoside showed the highest stability tothe effect of thermal treatment at 95 �C temperature inblackcurrant.

Sadilova et al. (2006) reported that methoxylation of theacyl moiety improves the structural integrity towards heat.The degradation rates of anthocyanins increased with in-creasing solid content during heating. This could be dueto closeness of reacting molecules in juice with higher sol-uble solid content (Nielsen, Marcy & Sadler, 1993). Instrawberry, anthocyanin degradation occurs as soon asstrawberries are processed into juice or concentrate andcontinues during storage. This degradation of anthocyaninsis greater in concentrates compared to juices (Garzon &Wrolstad, 2002). Similar trends were reported for anthocy-anins in sour cherry (Cemeroglu, Velioglu, & Isxik, 1994).

In summary, inter and intramolecular co-pigmentationwith other moieties, polyglycosylated and polyacylated an-thocyanins provide greater stability towards change in pH,heat and light (Francis, 1992). Some investigations alsodemonstrated that the co-pigmentation of anthocyaninswith other compounds (co-pigments) is the main mecha-nism of stabilisation of colour in plants (Davies & Mazza,1993). From the above recent findings, it truly soundslogical for industry to re-evaluate existing thermal processtreatments based on studies that demonstrate greater degra-dation of anthocyanin pigments.

Anthocyanin stability as affected by storageStudies have shown degradation of anthocyanins during

storage treatments. For example, Brownmiller et al. (2008)studied the effect of prolonged storage on total monomericanthocyanins in blueberries purees. The authors reportedthat >50% of anthocyanins were lost after 6 month of stor-age. Losses of total monomeric anthocyanins were accom-panied by increased polymeric colour values. It isenvisaged that anthocyanins were extensively polymerizedduring storage (Ochoa et al., 1999). The large increase inpolymeric colour values and corresponding loss of mono-meric anthocyanins may be due to several factors, includingresidual enzyme activity or condensation reactions of an-thocyanins with other phenolics (Brownmiller et al.2008). Similarly, Hager et al. (2008) observed that totalmonomeric anthocyanins in non-clarified black raspberryjuices decreased linearly during storage with losses of>60% over 6-month storage. Similar losses were observedfor clarified juices over 1, 3, and 6 months of storage. An-thocyanins present in clarified and non-clarified blueberryjuices behave similarly, when pasteurized. The conditionsselected for thermal processing may have changed mono-meric anthocyanin content of the black raspberry juice sam-ples during storage. Another reason could be due tocondensation reactions of anthocyanins with other phenoliccompounds, including flavan-3-ols or polyflavan-3-ols

(Reed, Krueger, Vestling, 2005). The exact mechanismfor anthocyanin stability is difficult to establish. Phenolicacids such as ferulic and syringic acid have also beenshown to complex with anthocyanins in strawberry andraspberry juices (Rein, 2005).

However it must be noted anthocyanins, and other phe-nolic compounds, are easily oxidized and, thus, susceptibleto oxidative degradation during various steps of processingand storage. In general, several factors are believed to affectthe stability of anthocyanins in fruits and vegetables andtheir products during preparation, processing, and storage,which include pH, temperature, light, oxygen, metal ions,enzymes, and sugars (Rhim, 2002). Some key criticalfactors influencing anthocyanin stability are discussed insection (4 & 5). Ngo, Wrolstad & Zhao (2007) reportedthat total anthocyanins in strawberries canned in 20

�B

syrup declined 69% over 60 day room temperature storage,during which time percent polymeric colour values in-creased from 7.2% to 33.3% and 27.4% in fruit and syrup,respectively. An increase in percent polymeric colour valueis indicative of condensation reactions of anthocyanins withother phenolic compounds such as procyanidins to formcoloured polymer pigments (Monagas, Bartolome, & Go-mez-Cordoves, 2005), reducing anthocyanin content incanned fruits. During storage of canned products, pelargo-nidin-3-glucoside, the main anthocyaninin in strawberries,can be hydrolyzed by acid to pelargonidin and further bro-ken into hydroxybenzoic acid (Stintzing & Carle 2004).

Similarly, Chaovanalikit & Wrolstad (2004) reportedthat anthocyanins in Bing cherries increased slightly aftercanning; the authors observed a major loss in anthocyaninsover 5 month storage, during which time percent polymericcolour values increased markedly in both cherry and syrupfractions. They observed an increase in percent polymericcolour values (13% to 40% in cherries and 13% to 35%in syrup) over the 5 month storage. The authors suggestedthat polymeric colour could also be formed from polyphe-nol oxidase activity before its inhibition.

Consistent with the above results, Srivastava et al. (2007)reported that only 50% of the anthocyanins were retained inblueberry juices stored for 60 day at 23 �C. Piljac-Zegarac,Valek, Martinez, and Bels�cak (2009) also suggested thatfruit juices should be consumed within the initial 48 h afteropening, if one is after making the most out of the potentialhealth benefits of polyphenolic antioxidants. Gossinger et al.(2009) suggested a significant positive effect of pre-freezingstrawberries on the colour stability of nectars from puree,which can be stored for even more than 12 months. Theyreported that cold storage temperature of the nectars at4 �C is also a suitable way to stabilize the colour of straw-berry nectars (redness) which is a direct reflection ofanthocyanins. Kirca, Ozkan & Cemeroglu (2003) reportedthat storage temperature had a strong influence on the stabil-ity of black carrot anthocyanins coloured juices and nectarsof black carrot. They reported a very fast degradation of an-thocyanins in coloured juices and nectars stored at 37 �C,

7A. Patras et al. / Trends in Food Science & Technology 21 (2010) 3e11

whereas refrigerated storage resulted in much lowerdegradation of anthocyanins. Cyanidin and delphinidin-ruti-nosides were the most stable anthocyanins during storage for12 months at 8 �C temperature. Transformations at lowtemperature (4 �C) in an inert atmosphere may inducea slow degradation process of anthocyanins. Under theseconditions, it is also probable that degradation compoundsof sugars and ascorbic acid may be the prevalent cause ofthe transformation of anthocyanins into brown compounds(Krifi & Maurice, 2000). Higher stability of anthocyaninscan be achieved by using lower temperature and short-time heating during processing and storage. From the abovestudies, it is therefore assumed that the thermal burdenduring processing of anthocyanic food may further degradethem during storage. Intelligent selection of appropriateextrinsic storage condition systems based on detailedsequential studies is necessary.

Mechanism of degradation of anthocyaninsAnthocyanins are glycosylated anthocyanidins; sugars

are attached to the 3-hydroxyl position of the anthocyanidin(sometimes to the 5 or 7 position of flavynium ion)(McGhie & Walton, 2007). Variations in chemical structureis mainly due to differences in the number of hydroxylgroups in the molecule, degree of methylation of theseOH groups, nature and number of sugar moiety attachedto phenolic molecule and to some extent the nature andnumber of aliphatic or aromatic acids attached to it. (Mazza& Brouillard, 1987; Mazza & Miniati, 1993; McGhie &Walton, 2007). Sugar moieties are attached as 3- mono-sides, 3- biosides, 3- triosides, 3, 5-diglycosides, 3, 7- di-glycosides consisting mostly of glucose, galactose,rhamnose and xylose (McGhie & Walton, 2007). Degrada-tion is primarily caused by oxidation, cleavage of covalentbonds or enhanced oxidation reactions due to thermal pro-cessing. Thermal degradation of anthocyanins can result ina variety of species depending upon the severity and natureof heating. Fig. 1 shows the degradation of anthocyaninsand formation of various intermediate compounds. Under-standing degradation mechanisms is a prerequisite formaximizing nutritional and visual quality. Relatively littleis known about degradation mechanisms of anthocyaninsbut chemical structure and presence of other organic acidshave a strong influence. For example, the degradation rateof anthocyanins increases during processing and storageas the temperature rises (Palamidis & Markakis, 1978).Markakis, Livingstone, and Fillers (1957) suggested open-ing of the pyrylium ring and chalcone formation as a firstdegradation step for anthocyanins. Adams (1973) proposedhydrolysis of sugar moiety and aglycone formation as ini-tial degradation step possibly due to the formation of cy-clic-adducts. The author also reported that anthocyaninwould decompose upon heating into a chalcone structure,the latter being further transformed into a coumarin gluco-side derivative with a loss of the B-ring. According toAdams (1973), the aglycon-sugar bond is more labile

than other glycoside bonds at pH 2e4. However, at pH 1all glycosidic bonds are accessible to hydrolysis becauseheating cyanidin-3-rutinoside at pH 1 resulted in the forma-tion of rhamnose and glucose, but only traces of rutinose. Astudy carried out by Seeram, Bourquin, and Nair (2001)demonstrated that high temperatures in combination withhigh pH causes degradation of cherry anthocyanins result-ing in three different benzoic acid derivatives (Seeramet al., 2001). However, a separate study conducted by vonElbe and Schwartz (1996) suggested that Coumarin 3, 5-di-glycosides are also common thermal degradation productsof anthocyanin 3, 5-diglycosides.

Oxidative degradationOxygen also plays a vital role in the anthocyanin degra-

dation processes. The presence of oxygen can acceleratethe degradation of anthocyanins either through a direct ox-idative mechanism and/or through the action of oxidisingenzymes (Jackman, Yada & Tung, 1987). In the presenceof oxygen, enzymes such as PPO catalyse the oxidationof chlorogenic acid (CG) into the corresponding o-quinone(chlorogenoquinone, CGQ). This quinone reacts with an-thocyanins to form brown condensation products (Kader,Irmouli, Nicolas, & Metche., 1999). Kader et al. (1999)working with the model solutions of purified substratesalso proposed that Cyanidin 3-glucoside [ortho-diphenolicanthocyanin, (Cy 3-glc)] is degraded by a mechanism ofcoupled oxidation involving the enzymatically generatedo-quinone with partial regeneration of the o-diphenolicco-substrate (CG). These observations confirm that PPOplays a vital role in anthocyanin degradation. Furthermorein a subsequent study the former authors suggested that re-gardless of the reaction conditions used (�CG), no degra-dation of anthocyanins was observed in the H2O2-freecontrol solutions, meaning that blueberry POD is involvedin the process of anthocyanin degradation (Kader, Irmouli,Nicolas, & Metche, 2002). In a separate study Kader, Ir-mouli, Nicolas, & Metche (2001) demonstrated that antho-cyanins, such as pelargonidin-3-glucoside (Pg 3-glc), aredegraded by a mechanism involving a reaction betweenthe o-quinone and/or secondary products of oxidationformed from the quinone and the anthocyanin pigment.

Sarni, Fulcrand, Souillol, Souquet, and Cheynier (1995)reported that the degradation products of Cy-3-glc and Mv3-glc contained both caffeoyltartaric acid and anthocyaninmoieties. Moreover, these degradation products were grad-ually replaced by colourless products as a consequence offurther oxidative degradation. The former authors pointedout that the reaction between Mv 3-glc and caftaric acido-quinone leads to the formation of adducts (Sarni-Man-chado, Cheynier, & Moutounet, 1997). This indicated thatthe hemiacetal form of the pigment is more reactive thanthe flavylium form. Sadilova, Carle, and Stintzing (2007)studied thermal degradation of anthocyanins by HPLC-DAD-MS and assessed degradation patterns of strawberryand elderberry. They found that after 4 h of heating

O+

OH

HO

OHOH

O+

OH

OH

HO

O–Glu

OH

O+

OH

HO

O–Glu

OH

O+

OH

HO

OH

OH

O

OH

OH

HO

HO

OH

OH

CHO

O

OH

HO

A C

B

A C

B

A C

B

A C

B

A

A

B

Pelargonidin-3-glucoside

Cyanidin-3-glucoside

Pelargonidin

Cyanidin

Protocatechuic acid

Phloroglucinaldehyde

4-hydroxybenzoic acid

Deglycosylation

Deglycosylation

Cleavage

Cleavage

Cleavage

Cleavage

OH

Fig. 1. Possible thermal degradation mechanism of two common anthocyanins.

8 A. Patras et al. / Trends in Food Science & Technology 21 (2010) 3e11

strawberry; a degradation product was detected displayingan absorption maximum at 253 nm (Rt ¼ 23.5, m/z 139).Its molecular ion indicated that it was the 3, 4-hydroxyben-zoic acid (also known as protocatechuic acid) a cleavageproduct of the pelargonidin B-ring. The A-ring of theanthocyanin was degraded to phloroglucinaldehyde witha molecular ion at m/z 155. For elderberry concentrate,after heating the extract for 4 h, degradation productswere identified at 280 nm. Phloroglucinaldehyde and proto-catechuic acid were the main peaks in the mass spectra bycomparison of characteristic data with those of a commer-cial reference standards.

Kinetics of degradation of anthocyanins in foodsKinetic models are often used for an objective, fast and

economic assessment of food safety. Kinetic modeling mayalso be employed to predict the influence of processing oncritical quality parameters. Knowledge of degradationkinetics, including reaction order, rate constant and activa-tion energy, is very vital to predict food quality loss duringstorage as well as thermal process treatments. One of theimportant factors to be considered in food processing isthe loss of nutrients. Therefore, kinetic studies are neededin order to minimize the undesired change and to optimizequality of specific foods. Anthocyanins degradation underisothermal heating are reported to follow first order kinetics(Equation 1) for juice and concentrate of sour cherry(Cemeroglu et al., 1994) strawberries (Garzon and Wrol-stad, 2002) and blackberries (Wang and Xu, 2007). Table2 shows some of the examples for degradation kineticsand parameters of food and food products along with modeljuices containing anthocyanins. Degradation kinetics of

anthocyanins or other quality parameters during thermalprocessing are obtained by first determining the rate con-stants at a given temperature against the time. The key pa-rameters of thermal degradation kinetics i.e. half life (T½)and activation energy are calculated using followingequations.

Ct ¼ C0� expð�K� tÞ ð1Þ

T1=2 ¼Loge2

Kor T1=2 ¼

2:303

Kð2Þ

Log

�KT

K0

�¼� Ea

2:303�R

�1

T1

� 1

T2

�ð3Þ

Where, Ct is anthocyanin concentration (mg/100 mL) attime t (min), C0 is initial concentration (t ¼ 0) and K(min�1), Ea is activation energy (KJ mol�1), R is universalgas constant (8.314 KJmol�1�C�1) is first order degradationrate constant.

The majority of studies on the degradation kinetics ofanthocyanins have been carried out under isothermal condi-tions at temperatures up to 100�C. However, anthocyanindegradation in solid or semi solid foods such as fruit orberry pomace, grains, vegetables is not isothermal i.e.therefore kinetic modeling should include time-temperaturehistory (Mishra, Dolan, & Yang, 2008). Recently, Mishra,et al. (2008) and Harbourne, Jacquier, Morgan, and Lyng(2008) studied thermal degradation of anthocyanins ofgrape pomace and blackcurrant anthocyanins in a modeljuice under non-isothermal conditions (Table 2). Prior tothis study Dolan (2003) proposed a one step kinetic model

9A. Patras et al. / Trends in Food Science & Technology 21 (2010) 3e11

for determining kinetic parameters for non isothermal foodprocess (Equations 4 & 5). This model was employed byHarbourne et al. (2008) for non isothermal processing ofmodel blackcurrant juice.

Ct ¼ C0� expð�Kt � bÞ ð4Þ

Where, b is thermal history can be determined by Equation,Kt is rate constant.

b¼Z t

0

exp

��Ea

R

�1

T� 1

Treft

��ð5Þ

Where Tref is the arbitrary reference temperature and T(t) isthe temperature at time (t).

Kinetic parameters for non isothermal heating can beobtained by employing non linear regression analysis tech-niques (Dolan, Yang & Trampel, 2007). The degradationrate constant and activation energy during isothermal andnon isothermal heating systems depends upon stability ofthe anthocyanin in question which in turn is dependent oncomposition, structure, physicochemical properties andpresence of other flavones’ or organic acids present in fruitjuices.

Conclusion and future trendsCurrent knowledge indicates that in general high tem-

perature treatments can affect levels of anthocyanins in fruitand vegetable based food products. However, only limitedinformation is available on the temperature stability of an-thocyanins derived from food. Thermal degradation of an-thocyanins results in the formation of polyphenolicdegradation products; it is not clear if the formation ofthese components results in an overall reduction in antiox-idant activity. This is because the polyphenolic componentsformed may also possess antioxidant properties, furtherstudy is required to clarify this effect especially in wholefoods and not modelled systems which have been exten-sively studied this far. Further studies in this neglectedarea would generate the potential for consumers to gaineven more positive health benefits from foods with highanthocyanin content such as fresh or processed berry fruits.Based on current knowledge it is not possible to predict theaffect of thermal treatment on anthocyanin retention. Theneed to optimize processes in terms of quality and operat-ing costs, demands more research to streamline processesby combinations of technologies, particularly with respectto optimisation of practical applications. Process optimi-sation of thermal processes in combination with non ther-mal technologies such as high pressure, ultrasound foodhas been the focus of research studies in recent years.The food industry is poised to adopt new concepts and tech-nologies that offer advantages over conventional systems.Extensive validation and verification, accuracy and costeffectiveness, controls and monitoring capabilities, aresome of the key elements that will justify the adoption of

developed systems. Thermal degradation should thereforebe assessed on a case by case basis until a consensus canbe reached. Since the degradation mechanism of anthocya-nins is rather complex and perplexing, it is possible thatthermal processing particularly above 50 �C or higher couldinduce some (un)expected and (un)desired chemical reac-tions which (in) directly influence food quality.

AcknowledgementThis project is funded under the Food Institutional Re-

search Measure (FIRM) by the Irish Agriculture and Foodand Fisheries Development Authority.

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