Effects of Novel Phase Change Coolant on the Postharvest Quality of Shiitake Mushrooms

Edible mushrooms with unique flavor are rich in protein, vitamins, and a variety of bioactive components, such as polysaccharides, phytosterol, etc. China is the major country in the cultivation and consumption of edible mushrooms, among which shiitake mushroom (Lentinula edodes) is the most widely cultivated. The current coolants exhibit low phase change temperature, which may result in chilling injury of shiitake mushrooms.

Based on the freezing temperature of shiitake mushrooms, a novel phase change coolant specially for shiitake mushrooms was developed to maintain the postharvest quality.

The main component of the coolant was screened by differential scanning calorimetry (DSC) based on the phase change latent heat and phase change temperature. Potassium sulfate, nano titanium dioxide, and superabsorbent resin were mixed to prepare the coolant. The effects of coolant on the qualities of shiitake mushrooms were studied by the weight loss rate, color, hardness and other indexes. The activities of enzymes related to glutamate metabolism and energy metabolism were also measured to explore the mechanism of preservation.

The aqueous solution of maltitol was selected as the main component by DSC. The optimal compositions of coolant were 1.85% of maltitol, 2.35% of potassium sulfate, 0.02% of nano titanium dioxide, and 0.80% of super absorbent resin, leading to the phase change latent heat and temperature at 405.26 J·g^-1 and -1.8 ℃, respectively. Compared with the control group, under the low-temperature conditions provided by the refrigerant, the weight loss rate of shiitake mushrooms decreased by 51.92%, and the hardness and brightness increased by 66.67% and 41.94%, respectively. The shelf life of shiitake mushrooms was extended. The low temperature also regulated the activities of enzymes, which were related to glutamate metabolism and energy metabolism, the glutamic acid and energy charge level increased by 36.64% and 54.76%, respectively. Finally the freshness of shiitake mushroom was maintained.

The novel phase change coolant based on the freezing temperature of shiitake mushrooms could maintain the weight, color, hardness and other indexes, regulate the level of glutamic acid and energy, and delay the deterioration of shiitake mushrooms. Therefore, the coolant was effective for the cold-chain preservation of shiitake mushrooms.