3.2. Effect of storage and pasteurization on total antioxidant activity, total phenolic and total carotenoids content of frozen peach
Total antioxidant activity increased 19% after freezing for 360 d. The pasteurization promoted a decrease of 20% when day 1 and 360 were compared (Fig. 3A). However, besides the variations no significant differences were observed between samples pasteurized and unpasteurized and within storage time (Table 1). The 12-month storage at -20 ̊C induced a 42% decrease in the antioxidant activity
of cauliflower but storage at -30 ̊C improved the antioxidant activity by 9%.
Total phenolic content increased between 60 and 180 d of storage and then after 360 d decreased to a similar value obtained the beginning of storage (Fig. 3B). However, during all the storage period no significant differences were detected between samples pasteurized and unpasteurized (Table 1). found
a 30% increase in the total phenolics of clingstone peaches after 3 months storage at -12 ̊C. Freezing process may result in disruption of the cellular matrix and more facilitated extraction of the phenolics. studied the effects of freezing on phenolic compounds of peas, carrots, cauliflower, cabbage and
potatoes and they reported an average loss of 20-30% of total phenolics in most vegetables, although no change was observed in most carrot samples and a 26% increasewas observed in cabbage. In the process of freeze-drying higher extraction efficiency of the total phenolics can be obtained because it can lead to the development of ice crystals within the plant matrix. Ice crystals can result in a greater rupturing of plant cell structure, allowing better solvent access and extraction.
In total carotenoids content time factor was significant since it decreased 41% after 360 d at -20 ̊C and 48% after pasteurization (Fig. 3C) while the process was not significative (Table 1). After 12 months of storage at -18 ̊C, an important decrease of total carotenoid occurred in papaya, although the carotenoid profile was unchanged. A decrease in total carotenoids (36%) as well β-carotene (51%) and lycopene (48%) was reported for tomato cubes stored 12 months at -20 ̊C. Cauliflower stored for 12-months at -20 ̊C had an insignificant (10-11%) decrease in carotenoids and polyphenols while storage at -30 ̊C improved the preservation of carotenoids by 10% and of polyphenols by 6%.
Most of studies reported results on a wet weight basis, and the majority found carotenoid losses from 5% to 48% for freezing.