In this research, the effect of freezing under the influence of microwave as a new and innovative method of freezing and its effect on the quality characteristics of button mushrooms (Agaricus bisporus) as a widely used Foodstuff with high nutritional value that is highly corruptible was investigated. First, the most appropriate microwave powers were recorded to investigate the effect of microwaves on mushroom samples, by examining the freezing factors of different samples under different microwave powers. Then, the effects of four levels of microwave power (30, 20, 10, 0%) on the freezing of mushroom samples were investigated and the time-temperature diagram of mushroom samples was drawn. The obtained graph showed the decrease in the freezing speed of the samples and the increase in the freezing time of the samples was due to the increase in the microwave power. Then, the effect of different microwave power levels on the quality characteristics of frozen and thawed button mushrooms was investigated. The effects of microwaves on the microstructure of frozen mushroom samples were analyzed by microscopic images using ImageJ software. The study’s results indicate that using microwaves with higher power led to a decrease in the equivalent diameter and relative surface of ice crystals. So that in 4 levels of microwave power (30, 20, 10, 0%), the relative area of the ice crystal surface of the samples was eva‎luated respectively (38, 33, 30, 28%) and the size of the crystals respectively (52, 45, 40, 38 micrometers); Also, the numerical value of the fractal dimension as an indicator of the shape of ice crystals increased due to the increase in microwave power, while no clear procedure was observed in the roundness indicator. Therefore, we found that the nucleation process, as the most important stage of freezing, which determines the number and size of ice crystals, is affected by microwaves. Also, in the continuation of the investigations, a 48% decrease in the temperature of frozen mushroom samples with the highest microwave power (30%) was observed and compared to frozen samples without applying microwave power (0%). Other investigations show the direct effect of increasing microwave power on textural parameters (hardness, cohesion, elasticity, and gumminess) as well as the amount of electrolyte leakage in the way that the values of the above parameters increased with increasing microwave power. Also, although the color change index (color change factor, browning index, and mushroom whiteness index) was positively affected by microwaves; However, due to the increase in freezing time at high powers and intense activity of enzymes, no specific trend was observed in these indices. In the final section, the investigation of freezing under different powers showed that the microwave source consumes little energy compared to the freezing tunnel; Therefore, the use of this method does not create a significant difference in the amount of energy consumption compared to the usual method of frozen moving air. Keywords: Freezing under the microwave, Nucleation, button mushrooms (Agaricus bisporus), ice crystal,Drip loss, Energy Consumption.

ناصر همدمي , اكبر جوكار

مهشيد رهبري

نفيسه سلطاني زاده , مهرنوش جعفري