Effect of microwave blanching on the quality of frozen Agaricus bisporus

The aim of this work was to determine the effect of microwave blanching on the levels of selected quality parameters in frozen Agaricus bisporus. Before freezing, mushrooms underwent one of the following treatments: blanching in water; blanching in a solution of sodium metabisulphite and citric acid; microwaving for 5 min; and combined blanching (first in water, then in a microwave oven). Products were freeze stored for 8 months at -25 ℃. Frozen storage resulted in decreased levels of vitamin B1, total polyphenols and antioxidant activity of 10-49%, as well as an increase in polyphenol oxidase activity compared with products immediately after freezing. The values for most colour parameters and whiteness intensity decreased, while cream, yellow, brown and grey saturation increased. There was a considerable deterioration in sensory quality, particularly colour. Microwave-blanched products had significantly higher dry matter, ash, vitamin B1 and B2 content than the remaining products as well as half the polyphenol oxidase activity. Total polyphenols and antioxidant activity were highest in the product blanched in the sodium metabisulphite solution, followed by the microwave-blanched product. Compared with the product blanched using sodium metabisulphite, microwave-blanched mushrooms showed slightly greater darkening but were superior in flavour and aroma.