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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.
- Peach polyphenol and carotenoid content as affected by frozen storage and pasteurizationPublication . Oliveira, Ana L.; Alexandre, Elisabete M. C.; Coelho, Marta; Barros, Rui M.; Almeida, Domingos P. F.; Pintado, ManuelaThe profile of polyphenol and carotenoid of peach were analysed on fresh fruits, immediately after freezing or after pasteurization, and during frozen storage at -20 ºC for 360 days. Freezing did not affect the concentration of polyphenols or carotenoids. Pasteurization of fresh and frozen samples induced an increase in the extractability of chlorogenic acid (38% and 24%) and of zeaxanthin (336% and 127%) and a decrease of lutein (22% and 56%) and b-cryptoxanthin (32 and 51%). Total antioxidant capacity and total phenolic content changed by less than 20% after frozen storage for 360 d. However, total carotenoid content decreased 41% and 48% in unpasteurized and pasteurized samples, after the same storage period. Long term storage induced an increase in the extractability of (+)-catechin (47%) and zeaxanthin (90%) and a decrease in neochlorogenic acid (59%), chlorogenic acid (39%), quercetin-3-glucoside (21%), lutein (24%) and b-cryptoxanthin (40%). Pasteurization of frozen samples promoted a decrease in the concentration of neochlorogenic acid (91%), chlorogenic acid (87%) and quercetin-3-rutinoside (71%) and increase in lutein (16%), b-cryptoxanthin (42%) and b-carotene (31%). Peach should be stored for periods no longer than 230 d, since pasteurization after that, induced a higher decrease in neochlorogenic, chlorogenic acids and quercetin-3-rutinoside content.
- 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.