Table 813

Effect of Processing on the Stability of Anthocyanins in Food Systems

Model Process Conditions

Blackberry Different temperatures and juice addition of aldehydes

Grape musts Addition of glutathione

Fresh Modified atmosphere using CO2 strawberries

Barley Heating (40-100°C)

Apples Light exposition

Concentrated Fermentation with S. cereviceae extracts of var. Malaga, room temperature, elderberry pH 4.5

Marashino Brined cherries are pigmented cherries with radish anthocyanin extracts (RAE)

Pomace Freeze dried in the presence of extracts DE 20 maltodextrins

Strawberries Addition of sucrose and quick frozen process

Fresh litchi Coated with chitosan (1 to 2%), storage at 4oC/90% relative humidity

DE = Dextrose equivalents.

Source: Adapted from Delgado-Vargas et al. (2000).17

Effects

Aldehyde favors the disappearance of anthocyanins; reaction follows first-order kinetics

The color is more stable indicating that quinones are involved in anthocyanin degradation The external and internal pigments decrease but more in the internal structures; this is associated with peel that has cyanidin as the main pigment, whereas pelargonidin is in the pulp The anthocyanin hordeumin is protected by forming molecular complexes with polyphenols; color is stable Light-exposed apples show improved colorations vs. those under shade conditions The concentrated juice (4% d.w. of anthocyanins) has an improved shelf life

The obtained color is similar to that reached with synthetic FD&C Red No. 40

The shelf life is increased: two months at 50°C/0.5

aw; more than five years with aw < 0.3 Pigment is stabilized and browning reactions reduced; this favorable effect is associated with inhibition of degradative enzymes and with steric interference with condensation reactions Shelf life is increased, associated with inhibition of polyphenoloxidase and peroxidase anthocyanin profiles have been proposed as a marker of GMP; if red raspberry juices are badly processed, higher levels of polymeric color are observed, instead of the monomeric anthocyanin pigments. Thus, polymeric color is a marker of poor quality for some products.35

The use of modified atmosphere is a common strategy to improve shelf life of fruits and vegetables. The employment of CO2 has been assayed with fresh strawberries to preserve their attractive appearance but results are not satisfactory; after the treatment, skin color is better preserved than internal color, which is associated with anthocyanin identity but also with a higher accumulation of phenolic compounds in the external tissue (Table 8.13).62

As previously mentioned, light has deleterious effects on anthocyanin stability and light exposure of natural colored beverages must be avoided. Light stability could be improved by the presence of other flavonoids (flavone, isoflavone, and aurone sulfonates).3 However, it has been observed in apples that light favors better skin colors (Table 8.13); in this model, color and the activity of UFGT (UDPGal:fla-vonoid-3-O-glycosyltransferase) are correlated, suggesting a regulatory activity of UFGT for anthocyanin biosynthesis. This enzymatic activity is also affected by other phytohormones such as jasmonate and ethylene, which also improve apple coloration.63 In these fruits methyl jasmonate is associated with ethylene production, and thus with anthocyanin accumulation; this is the explanation for the application of methyl jasmonate during the initial stages of apple development to produce better colored fruits.64 Fruit bagging is an effective way to promote anthocyanin synthesis and improve fruit coloration, and it has been widely used in practice. Apples have been stored with one-, two-, or three-layered bags; in one- or two-layered bags higher anthocyanin levels are found than in the three-layered samples. Moreover, fruit with three-layered bags show a rapid accumulation of anthocyanins when exposed to light. Thus, this behavior should be considered in the genetic manipulation of apple to improve its quality characteristics.63

Fermentation has been used to produce concentrated elderberry products, which can be used to color spiced wines (Table 8.13). Coating of fruits and vegetables is another strategy used to preserve good coloration. Sucrose addition improves the color characteristics of frozen strawberries and with litchi interesting results are observed after coating the fruit with chitosan (Table 8.13).65 66 Improved stability could be associated with the inhibition of degradative enzymatic activities of polyphenol oxidase and peroxidase; the plastic coating is a barrier that reduces the supply of oxygen required for the enzymes. In addition to these enzymes, glycosi-dases are very important in anthocyanin stability because of a degradation effect producing very unstable anthocyanidins and glycosides. Consequently, in addition to coating, other procedures such as blanching and treatment with 30 ppm SO2 have been proposed to inactivate some of these enzymes; in particular, treatment of sour cherry juice with SO2 or gallotannin inhibits polyphenoloxidase activity. Thus, blanching to inactivate these enzymes may reduce pigment loss. As can be deduced, enzymatic destruction of anthocyanins is an important parameter that must be considered in the design of the processes for foods and perhaps in their final formulation.3

To inhibit degradative enzymatic activity on pomace anthocyanins, methodologies such as gamma irradiation, vacuum packaging, and SO2 application have been evaluated. Gamma irradiation improves shelf life; in the processing of vegetables the application of 2 kGy is common; however, for grape extracts, 6 kGy is the better choice considering stability and level of extraction. It is also important to take into account that gamma irradiation inhibits the growth of bacteria by 3 days and fungi by 4 days. Moreover, packaging in a mixture of air with SO2 improves the color of the product, which has 12% more anthocyanins than that of the control (at vacuum without SO2). Consequently, the suggested process for grape pomace is packaging in air in the presence of sodium metabisulfite and gamma irradiation at 6 kGy.67 Another important factor that must be taken into account for color preservation is the microbiological control. It has been observed that mold contamination has a

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