Long-term frozen storage and pasteurization effects on strawberry polyphenols content

The profile of the strawberry polyphenols was analysed on fresh strawberry, immediately after freezing or after pasteurization and during frozen storage of strawberry at −20 °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 °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 °C for 360 days, while the thermal treatment applied after freezing storage did not induce any significant change.