210 Produce Degradation: Reaction Pathways and their Prevention
(cyanidin-3-glucoside and pelargonidin-3-glucoside), and flavonoids (kaempferol,
quercetin, and myricetin). Ellagic acid in the green stage, pelargonidin-3-glucoside
and p-coumaric acid in the pink stage, and pelargonidin-3-glucoside and p-coumaric
acid in the ripe stage were determined to be the major constituents. Significant
changes in phenolic compounds were observed during maturation, including a large
increase in p-coumaric acid.
7.4.6 POSTHARVEST AND PROCESSING CHANGES OF FLAVONOIDS
Significant amounts of fruits and vegetables are subjected to various postharvest
operations before consumption. Different stages of handling include storage, indus-
trial processing, distribution, and preparation for consumption. All of these steps
affect physical and chemical characteristics of produce. One of the concerns is the
possible loss of nutritionally important and health-protecting ingredients. Scientists
and the food industry are continuously making attempts to reduce processing losses
of beneficial bioactive compounds present in fruits and vegetables.
Spanos et al. (1990) reported that diffusion extraction at various temperatures
leads to a significant increase of phenolic compounds in apple juice compared to
traditional straught pressing.
Van der Sluis et al. (2002) reported that using conventional methods of processing
apples into juice causes a significant degradation of flavonoids and 90 to 97% loss of
the fruit’s antioxidant activity. The same authors (Van der Sluis et al., 2004) proposed
a novel production method for apple juice that includes alcohol extraction of pulp or
pomace and evaporating the alcohol and enriching the juice with the extracted polyphe-
nols. The enriched juice showed five times higher antioxidant activity compared to
conventionally obtained juice. The triangle sensory test showed a significant taste
difference between enriched and conventional juice samples at 0.1% level.
Traditional methods applied to decide the optimal time for harvesting grapes for
wine production include determination of weight, sugar content, and acidity (Gonza-
lez-Sanjose et al., 1991). Recently, more attention is being paid to the content of
polyphenols due to their influence on color, bitterness, and astringency. Perez-
Magarino and Gonzalez-San Jose (2004) investigated the influence of degree of
grape ripening on wine composition, quality, and changes during aging. Two varieties
of grapes were used (Tinto Fino and Cabernet Sauvignon). The grapes were harvested
at three stages of ripening (the first stage was based mainly on sugar content, and
the second and third stages were 1 and 2 weeks after the first stage). The aging was
conducted for 1 year in American oak barrels and followed for 6 months in bottles.
The results show that the delay in harvesting grapes between 1 and 2 weeks under
the conditions of these particular experiments led to production of wines that con-
tained higher levels of anthocyanin derivatives and to better color quality and sta-
bility. The results also showed that if grapes are allowed to ripen too much the wine’s
quality benefits are lost.
Numerous studies in the past showed significant losses of color and nutrients
during thermal processing of fruits and vegetables. Recently, it was reported that in
some instances thermal processing might have beneficial effects. Total antioxidant