Evaluation of the effects of different freezing and thawing methods on color, polyphenol and ascorbic acid retention in strawberries (Fragaria × ananassa Duch.)

Abstract

Strawberries were frozen conventionally (−20°C) and using liquid nitrogen, respectively, and subsequently thawed at various temperatures (+4, +20 and +37°C, respectively) and in a microwave oven. Drip loss was determined by weighing the exudates, color measurements were carried out applying the CIE L*a*b* system, ascorbic acid was monitored spectrophotometrically, and individual anthocyanins and non-anthocyanin phenolics were assessed by HPLC-DAD-MSn.While anthocyanin and ascorbic acid retentions after thawing were independent of the freezing technology, different thawing procedures significantly affected fruit quality. Anthocyanins were best retained when strawberries were thawed at 20°C and in a microwave oven, respectively. Maximum ascorbic acid retention was observed when strawberries were thawed in a microwave oven (10min). Usual thawing at 4°C (24h) caused the most pronounced pigment and ascorbic acid losses. Thus, the thawing regime proved to be the key parameter for color and vitamin C retention of strawberry products.