Color Quality of Fresh and Processed Foods - American Chemical

Chapter 16

Pigment Composition and Stability in Berry Juices and Wines

Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: June 13, 2008 | doi: 10.1021/bk-2008-0983.ch016

Maarit J. Rein 1

1,2

and Marina Heinonen

1

Department of Applied Chemistry and Microbiology, Food Chemistry Division, University of Helsinki, Helsinki FIN00014, Finland Current address: Nestle Research Center, Vers-Chez-Les-Blanc, 1000 Lausanne, Switzerland 2

The color of berry juices and wines was enhanced and stabilized by the addition of different plant extracts and phenolic acids. This enhancement was established also with pure anthocyanins in model solutions. The color quality of black currant wine was improved by the addition of crowberry juice and grape skin extract. Strawberry and raspberry juice color was improved by the addition of black carrot, grape skin, and rosemary extracts. These commercial color enhancers immediately increased the color intensity of these juices, but during storage these improvements were not very stable. Phenolic acids improved and stabilized the colors of strawberry, raspberry, lingonberry, and cranberry juices during storage. Sinapic and ferulic acids enhanced the color of strawberry and raspberry juices the most. Rosmarinic acid intensified and stabilized the color of lingonberry and cranberry juices the most. Novel anthocyanin derivatives were formed between the phenolic acids and juice anthocyanins during storage.

© 2008 American Chemical Society

In Color Quality of Fresh and Processed Foods; Culver, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

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204 Attractive color is one of the most important sensory characteristics and a significant quality parameter of fruit and berry products. The color of red berry products is, however, unstable and easily susceptible to degradation due to the reactivity of anthocyanins, the chromophore present in these products. The stability of anthocyanins is affected by pH, light, storage temperature, presence of enzymes, oxygen, structure and concentration of the anthocyanins, and the presence of other compounds such as minerals and proteins. The stability of anthocyanin color can be improved by copigmentation, where the anthocyanin molecule reacts with other natural plant components directly or through weak interactions, resulting in an enhanced and stabilized color (7, 2). Copigmentation is known to be responsible for the abundant color variability of bluish flowers and for stable wine colors (3-9), through which the phenomenon was first investigated. Anthocyanins are natural pigments widely distributed in nature. Antho cyanin color molecules belong to the group of flavonoids having the typical C C C skeleton, which is polyhydroxylated and polymethoxylated (10). In nature the aglycone skeleton is glycosylated, and the sugar moiety can also be acylated. Anthocyanins are responsible for the reds, purples, and blues in many flowers, fruits and vegetables. They are found in the petals of petunia, stems of rhubarb, and roots of red radish, for example. Fruits and berries are the most ample sources of anthocyanins in nature. In fruits and berries, anthocyanins are mainly located in the peel, like in apples and grapes, but they are also found in the pulp, as in the case of cherries or blueberries. Anthocyanins are considered to contribute to the protective effect of fruits and berries for their antioxidant, anti-carcinogenic, anti-inflammatory, and antiangiogenic properties, for example (11-13). The positive effect of fruit and berry intake on human health has been reported in several studies (14-18). Anthocyanins can also improve the nutritional value of processed foods by preventing oxidation of lipids and proteins in food products (19-21). The stability of anthocyanins becomes most significant in the case of nutritional value, as well as in the case of color quality. 6

3

6

Color enhancement of Berry Wine and Juices In wine and juice making the anthocyanin content and color quality of the product depends mostly on raw materials and processing methods used. Maintaining a strong and stable color in berry wines and juices is problematic during processing and storage. In the study of black currant wine, it was shown that the anthocyanin color can be enhanced by grape skin extract or by crowberry juice addition (22). Black currant wine enriched with crowberry juice had the strongest color, but the most stable color appeared in black currant wine



205 enhanced with grape skin extract. During storage the anthocyanin content declined in all the wines. However, the decline of color intensity did not take place in the same ratio with the decrease of anthocyanin content. This is presumably due to copigmentation reactions where anthocyanins condense with each other and with other organic molecules to form new pigments. Natural plant extracts, black carrot, grape skin, and rosemary extracts, enhanced the color of strawberry and raspberry juices immediately after their addition, but also during a storage period of 100 days. This enhancement is most probably due to the overall increment of anthocyanin content in the berry juices when black carrot and grape skin extracts were added, since these products contain high amounts of anthocyanins. This is also applicable to the case of black currant wine. However, other substances in the plant extracts, such as phenolic acids and other flavonoids, can also take part in the color enhancement reactions. The color of berry juices was also successfully enhanced by the addition of pure phenolic acids (23). The color of four berry juices (strawberry, raspberry, cranberry, and lingonberry) faded quickly during storage, and their anthocyanin content diminished likewise (Figure 1). Phenolic acids (ferulic, sinapic, and rosmarinic acids) improved the color of the juices by stabilizing and enhancing their color.

Figure 1. Changes in the anthocyanin content of berry juices during storage. 1) Strawberry juice, 2) Raspberry juice, 3) Lingonberry juice, and 4) Cranberry juice. The black bars present the initial anthocyanin concentration. Dark gray bars present the anthocyanin content of non-enhanced juices after 100 days of storage; Medium gray bars present juice enhanced with ferulic acid after storage; Light gray bars juiced sinapic acid; White bars juice+rosmarinic acid.

In strawberry juice, sinapic acid enhanced and stabilized the anthocyanin color significantly; by the end of storage the juice color intensity was 104% of


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the original intensity of the non-enhanced juice. Ferulic and rosmarinic acid had similar effects on strawberry juice, although not as vigorous. In raspberry juice the simple cinnamic acids, ferulic and sinapic acids, improved the juice color the most. At the end of the storage period the color intensity in raspberry juice enhanced with ferulic acid was 35%, and with sinapic acid 30%, more intense than in the non-enhanced raspberry juice at the same time point. In raspberry juice rosmarinic acid enhancement started off strong but was not stable throughout the storage period (Figure 2).

Figure 2. The color enhancement of berry juices by phenolic acids during storage detected as a change in the absorbance of / l ^ . Black lines: raspberry juice; Gray lines: strawberry juice. Plain non-enhanced juice enhanced with ferulic acid, enhanced with sinapic acid-k-; enhanced with rosmarinic acid, Within the specific time point values marked by the same letter are not significantly different.

Rosmarinic acid enhanced the color of cranberry and lingonberry juices the most. The color intensity of cranberry juice enhanced with rosmarinic acid at the end of storage was 110% more than the intensity of the non-enhanced juice in the same time point. In lingonberry juice rosmarinic acid intensified the color by 50% compared to the non-enhanced juice at the end of storage. Sinapic and ferulic acids also enhanced the color of these two juices but more moderately (Figure 3). The reactions observed within the four berry juices with added natural phenolic acids differed significantly by their mechanisms and manifestations. Intermolecular copigmentation reactions are most likely responsible for the



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Figure 3. The color enhancement of berry juices by phenolic acids during storage detected as a change in the absorbance of Xm^. Black lines: cranberry juice; Gray lines: lingonberry juice. Plain non-enhanced juice enhanced with ferulic acid-M-; enhanced with sinapic acid-A-; enhanced with rosmarinic acid, At the end of storage values marked by the same letter are not significantly different within a juice.

color enhancement by the conjugated cinnamic acid, rosmarinic acid, which protected lingonberry and cranberry juice anthocyanins. In raspberry and strawberry juices sinapic and ferulic acids formed new anthocyanin derived pigment molecules, pyranoanthocyanins, which possessed more stable and stronger colors compared to the color of the intact berry juices. The new anthocyanin derivatives found in the juices were 4-vinylguaicol and 4vinylsyringol adducts of pelargonidin and cyanidin depending on the used cinnamic acid, linked to 4- carbon and 5-hydroxyl positions of the anthocyanin. This was the first time pelargonidin 3-glucoside based vinylphenol pyranoanthocyanins, but also pyranoanthocyanin of cyanidin aglycone with more complex glycosyl residues were found. This was also the first time these new derivatives were detected in non-fermented strawberry and raspberry juices (24).

Color Enhancement of Pure Anthocyanins The color of pure anthocyanin molecules was intensified by the addition of phenolic acids (25). The immediate copigmentation effect, i.e. the color


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enhancement perceived directly after preparation, differed from the phenomena observed during storage. The copigmentation reactions were studied with five different anthocyanins and five different phenolic acids, and the phenomenon was observed both as a bathochromic shift and as a hyperchromic effect (figure 4).

Figure 4. Change in absorption maximum wavelength (bathochromic shift) and in the color intensity (hyperchromic effect) of an anthocyanin copigmented with a phenolic acid. A) Cyanidin 3-glucoside; B) Cyanidin 3-glucoside + rosmarinic acid

Ferulic and rosmarinic acids induced the strongest color enhancement to the monoglucosidic anthocyanins, malvidin 3-glucoside, pelargonidin 3-glucoside, and cyanidin 3-glucoside immediately after solution preparation. Caffeic acid and chlorogenic acid appeared as moderate color enhancers and gallic acid was the weakest copigment on the day of preparation (Figure 5). During storage the most efficient color enhancement was observed with ferulic and caffeic acids, especially in pelargonidin 3-glucoside solution, where the color intensity was stabilized and intensified 220% by the former and 190% by the latter of the original intensity, respectively (Figure 6). The copigmentation effect was not significant with acylated and trisaccharidic anthocyanins. Most of the copigments reduced the acylated anthocyanin color during storage. It is most probable that the same new pigments, pyranoanthocyanins, which were detected in berry juices, were generated in the course of time in the model solutions of the pure compounds, but since they were not monitored, no distinct elucidation is available to support this assumption.



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Figure 5. Increment of color intensity of anthocyanin monoglucosides due to the addition of different phenolic acids measured immediately after solution preparation. Black bar: Pelargonidin 3-glucoside; Dark gray bar: Cyanidin 3-glucoside; Light gray bar: Malvidin 3-glucoside. Zero level represents the absorption of the plain non-enhanced anthocyanin.

Figure 6. Copigmentation effect of pelargonidin 3-glucoside with phenolic acids during storage, detected as a change in the absorbance of Amax. Plain anthocyanin anthocyanin +gallic acid,-m-; anthocyanin +chlorogenic acid, -• -; anthocyanin ^rosmarinic acid, -O -; anthocyanin +caffeic acid, - A - ; anthocyanin +ferulic acid -A -. Within the specific time point values marked by the same letter are not significantly different.


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Conclusion Anthocyanin colors can be stabilized and enhanced both with different plant extracts and pure phenolic acids. With pure compounds and in berry juices the observed copigmentation reactions differed significantly. Conjugation of a cinnamic acid affected the way the copigment interacted with anthocyanins. Conjugation results in a weaker color stability and enhancement than what was observed with non-conjugated cinnamic acids. The simple cinnamic acids produced stronger and more stable colors and formed new anthocyanin derived molecules, whereas conjugated cinnamic acids did not. The substitution pattern of each anthocyanin affects the chemical behavior of the pigment molecule. It was observed that methoxylation increased the color enhancement reactions and hydroxylation decreased them. Since the attached glycosyl units and acyl groups of an anthocyanin also have a strong effect on the pigment properties, they of course also affected the color enhancement reactions. Monoglucosidic anthocyanins were more susceptible to color enhancement than trisaccharide and acylated anthocyanins. It is most likely that the acylated and trisaccharidic anthocyanins are sterically too compact for further copigmentation reactions to take place. The current results may be of use in improving the color quality of berry products and in the development of foods with anthocyanin-rich ingredients. To fully benefit from these research findings, the physico-chemical characteristics of the new pyranoanthocyanins should be investigated in respect to their other qualitative and sensory aspects for the development of berry food products.

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Color Quality of Fresh and Processed Foods - American Chemical

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