Qualitative changes in Pleurotus ostreatus (Jacq.: Fr.) Kumm. mushrooms resulting from different methods of preliminary processing and periods of frozen storage

BACKGROUND: The aim of this study was to investigate the effect of different methods of preliminary processing and periods of frozen storage on the quality of Pleurotus ostreatus (Jacq.: Fr.) Kumm. mushrooms. In pre-processing, mushrooms were blanched or soaked and blanched in water as well as in aqueous solutions of citric acid, L-ascorbic acid and/or lactic acid. During 12 months of storage at -25 degrees C, sensory evaluations, instrumental colour measurements and chemical analyses of the frozen products were carried out every 4 months. RESULTS: The greatest changes resulting from technological treatment were found in flavour. At the end of the storage period the content of thiamine and riboflavin decreased by 14-65% and 3-13% respectively compared with the raw material. This was accompanied by changes in total acidity and vitamin C content within the ranges -56 to +61% and -97 to +5% respectively. CONCLUSION: Based on the results of the sensory evaluation, a maximum storage period of 4 months was set for the frozen product obtained from unblanched mushrooms. Mushroom products pre-processed in aqueous solutions with added substances may be stored for 8 months and those blanched in water for 12 months. (c) 2009 Society of Chemical Industry