Abstract:
The objectives of this research were to determine the appropriate condition in processing good quality frozen straw mushroom. Firstly, inhibition of browning was done by immersing the mushroom in 1.5% sodium metabisulphite solution under vacuum at 10 inches Hg for 30 minutes. The weight loss of mushroom in processing were feduced by immersing in variable gum solution and concentrations. The 0.75% of xanthan gum solution gave minimum weight loss, minimum shear value and best sensory test. The freezing time of air blast freezng at -32℃ was found to be 52minutes 40 seconds and appropriate cryogenic freezing conditions by liquid nitrogen ; temperatures varying at 4 levels, were at a temperature fo -70℃ and with a time of 11 minutes 40 seconds. Thawing product in refrigerator gave better result than using microwave or immersing in water. The storage product of both freezing methods with different packaging methods were studied. It was obvious that cryogenic freezing resulted in less % thawing loss, shear value but in higher lightness and sensory characteristic scores than air blast freezing (p< 0.05). Vacuum packing gave the product higher lightness, color score and overall preference than normal packing (p< 0.05). The cryogenic freezing product kept for 6 months still had the overall preference score between like slightly and like moderately and the total plate count (TPC) and yeast and mold counts were still less than 300 colonies/g. The mushroom structures were later studied by Scanning Electron Microscope. It was found that the structures were destroyed by cryogenic freezing less than air blast freezing. Moreover adding glycine in cooling water after blanching could not improve mushroom flavor. The reduction of weight loss product by immersing mushroom in xanthan gum and locust bean gum (LBG) were studied. The appropriate condition was immersing mushroom in xanthan gum 0.25% first for 20 minutes and then immersing in LBG 0.25% for 10 minutes. This condition could reduce 4% weign loss more than using xanthan gum alone.