Effects of Freezing Methods and Storage Temperature on Flavor Stability and Ester Contents of Frozen Strawberries

Abstract

Berries of three strawberry cultivars, Hoko-wase, Toyonaka, and Nyoho, were quick-frozen and stored at -20 °, -40 0, and -80 °C, for 6 months. Strawberries were also frozen slowly or dipped into a sugar solution before freezing and stored at -20 °C.
1. Berries kept at -40° and -80 °C for 6 months retained their flavor comparable to fresh raw berries. The flavor of strawberries stored at -20 °C deteriorated quickly. The deterioration at -20 °C was slightly retarded by quick-freezing or coating the berries with sugar prior to freezing.
2. The sugar (Brix), acid and vitamin C content of strawberries did not change much during storage, whereas the anthocyanin content was reduced to less than half after 6 months at each storage temperature.
3. The total ester content of the strawberries stored at -40 ° and -80 °C remained unchanged, whereas that in berries stored at -20 °C disappeared quickly. The disappearance is attributed to the rapid decomposition and diffusion of esters which led to lower sensory scores. Quick-freezing and dipping in a sugar solution followed by storage at -20 °C were effective in retaining the ester content only for a short period.