Appropriate water blanching treatment to keep quality and color of Agaricus bisporus slices

Abstract: Button mushroom (Agaricus bisporus) is one of the most popular and valuable mushrooms in the world, and it is usually processed for long-time storage. Button mushrooms are a good source of vitamins, protein, phenolics, polysaccharose and many mineral elements. However, they are highly perishable commodities due to browning, water loss, senescence, and microbial attack, in which, browning reactions limit their shelf life to a few days. The enzyme polyphenoloxidase (PPO) is the responsible cause of this deteriorative process. In view of their highly perishable nature, button mushrooms must be processed to extend their commercial shelf life for off-season use.The production of heat-sterilized preserves represents most usual long-term preservation. Sterilization accounts for more than 60 percent of industrially processed mushrooms. In the preparation process of sterilized mushrooms, blanching is an important pre-treatment, which objectives may be: (i) to reduce enzymatic browning through thermal inactivation of PPO; (ii) to induce volume contraction (shrinkage) to avoid this occurrence at the sterilization stage; (iii) to make the product more pliable to facilitate filling operations. However, some negative features of blanching are the loss of valuable nutritious components, partial biochemical conversions of components resulting in changes in aroma and - in general - deteriorative effects on sensory properties like texture and color, which are the main features taken into account by consumers.To maintain the quality and color of button mushrooms, the content of ascorbic acid and total phenolic, antioxidant capacity, and color of button mushroom slices blanched between 85℃ and 100℃with an increment of 5℃ for different times were investigated. Results showed that blanching significantly reduced the content of ascorbic acid and total phenolic, antioxidant capacity, and color. Ascorbic acid and total phenolic content decreased by 66.67 percent -93.33 percent and 12.33 percent -59.49 percent, respectively. Moreover, heavy losses in the antioxidant capacity of 16.86 percent -42.75 percent also occurred as a result of blanching. Compared with unblanched samples, blanching caused a reduction in L value of 11.23 percent -30.63 percent, low chroma change, and total color difference from 10.12±0.55 to 22.86±0.21. At the blanching temperature of 100℃, the loss of quality and color was the biggest and had significant difference with the treatments of blanching under 95℃ within two minutes. In consideration of the effects on ascorbic acid, total phenols contents, color, and antioxidant activity of mushroom slices during blanching, the results showed that that temperature between 85℃ and 95℃ and the processing time one minute to two minutes were the optimal blanching conditions，Under these blanching conditions, the better quality and color were obtained.