Produce Color and Appearance 211
activity of tomatoes (Dewanto et al., 2002) was increased as a result of thermal
processing. Jiratanan and Liu (2004) studied the influence of typical commercial
canning conditions on antioxidant activity of table beets and green beans. When
heated at 115°C, initially phenolics decreased by 12%, but during further processing
the content raised to the level of unprocessed beets and after 45 min increased further
by 14%. Thermal processing had no effect on total antioxidant activity of beets. In
the case of green beans, after 10 min at 115°C there was a 40% decrease in total
free phenolic compounds. After 20 min no further decrease was noticed, and after
40 min there was some increase in phenolics. The total antioxidant activity of green
beans decreased by 9% after 10 min of processing and remained unchanged after
further heating for 40 min. According to other authors (Price et al., 1998) the
flavonoids in green beans are not degraded but leach into the water during heat
processing. Due to the complex nature of changes in different kinds of produce, no
general conclusions concerning the fate of phenolic compounds during heat pro-
cessing can be made at this time.
The content of procyanidins in frozen and canned Ross clingstone peaches and
in the syrup used for canning over a 3-month period was investigated by Hong et
al. (2004). Optimized analytical methods allowed quantification of oligomers
through octamers. The following amounts of procyanidins were found in frozen
peeled peaches: monomers 19.59 mg/kg, dimers 39.59 mg/kg, trimers 38.82 mg/kg,
and tetramers through octamers 17.81, 12.43, 10.62, 3.94, and 1.75 mg/kg, respec-
tively. Thermal treatment resulted in losses of all oligomers; the highest loss (30%)
was in hexamers and hectamers, and octamers were not detectable. A significant
amount of the oligomers up to the hexamers lost during heating was detected in the
syrup. Previously reported studies did not quantify oligomers larger than tetramers.
During 3 months of storage the losses of procyanidins were time-related, and oli-
gomers larger than tetramers were not detected.
Goncalves et al. (2004) studied the effect of ripeness and storage of cherries on
the content of phenolic compounds. Samples of sweet cherry cultivars Burlat, Saco,
Summit, and Van were randomly harvested by hand in 2001 and 2002 at two stages
of ripeness (partially ripe and ripe). The color of skin was used as the main indicator
of maturity. After harvest, weight, skin color (measured by colorimeter), soluble
solids, titratable acidity, and pH were recorded. The samples were prepared for
analyses after 0, 5, 10, 15, 20, 25, and 30 d of storage at 1 to 2°C and 0, 3, and 6 d
at room temperature (15°C). Total content of phenolics was determined and at the
same time samples were prepared for HPLC analysis. Pitted and freeze-dried cherry
samples were extracted by 60% methanol, filtered, and injected into the HPLC. The
system was equipped with DAD and identification was conducted using spectral and
retention time characteristics. The cultivar Saco contained the highest amount of
phenolics (227 mg/100 g of fruit), whereas the cultivar Van contained the lowest
amount (124 mg/100 g fruit). During storage at a low temperature of 1 to 2°C the
content of phenolic acids decreased, but it increased at 15°C. Anthocyanins in the
cultivar Van increased from 47 to 230 mg/100 g of fresh weight during storage at
15°C. Phenolic acids were higher in all samples from 2001 and anthocyanins were
higher in 2002, indicating an important influence of seasonal conditions.