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- Long-term frozen storage and pasteurization effects on strawberry polyphenols contentPublication . Oliveira, Ana; Coelho, Marta; Alexandre, Elisabete M. C.; Almeida, Domingos P. F.; Pintado, ManuelaThe profile of the strawberry polyphenols was analysed on fresh strawberry, immediately after freezing or after pasteurization and during frozen storage of strawberry at -20 A degrees C for 360 days. Freezing increased the extractability of (-)-epigallocatechin gallate (60 %), (-)-epicatechin (48 %) and ellagic acid (51 %) and decreased the pelargonidin-3-glucoside (18 %). Direct pasteurization of fresh strawberry increased the extractability for (-)-epigallocatechin gallate (73 %), (-)-epicatechin (45 %) and ellagic acid (143 %) and decreased for pelargonidin-3-glucoside (16 %). During storage at -20 A degrees C for 360 days the extractable levels of pelargonidin-3-rutinoside, (-)-epigallocatechin gallate, (+)-catechin, (-)-epicatechin and ellagic acid decreased by 17, 20, 37, 65 and 80 %, respectively, while those of pelargonidin-3-glucoside increased 13 %. Changes in polyphenols content, produced by pasteurization after 360 days frozen storage, were minimal. Polyphenols content decreased during storage of strawberry pieces at -20 A degrees C for 360 days, while the thermal treatment applied after freezing storage did not induce any significant change.
- Changes in phenolic compounds during storage of pasteurized strawberryPublication . Oliveira, Ana; Almeida, Domingos P. F.; Pintado, ManuelaThis study aimed to establish mathematical models to describe changes in phenolics of pasteurized strawberry (Fragaria ×ananassa Duch.) during storage at 23 °C for 90 days. Freshly cut strawberries cubes were pasteurized for 5 min in a water bath at 90 °C following a heating time of 15 min. Antioxidant activity, total phenolics, total anthocyanins, and individual phenolic compounds were assessed immediately before or after pasteurization and at regular time intervals during storage. The results indicated that (1) pasteurization did not affect (P <0.05) the concentrations of total phenolics or total anthocyanins, but significantly reduced the concentrations of quercetin-3-rutinoside, kaempferol, and cyanidin-3- glucoside, and increased the concentrations of (+)-catechin, (−)-epicatechin, epigallocatechin gallate, quercetin-3- galactoside, and ellagic acid; (2) changes in antioxidant capacity, total anthocyanin, and individual compounds during storage were described by a pseudo-first-order model with the exception of total phenolic and specifically kaempferol and ellagic acid which followed zero-order kinetic models. Pelargonidin-3- glucoside degraded at the highest rate (k =0.07 day−1), followed by ellagic acid (k =0.004 day−1) and kaempferol (k = 0.003 day−1). The rate constants can be used to predict phytochemical changes in strawberry products during storage.