Effect of Chitosan Coating with Different Degrees of Deacetylation on the Shelf Life of Button Mushroom (Agaricus bisporus)

IntroductionWith the growth of the population and increasing demand for obtaining food and supplying the required food, the interest in the cultivation and consumption of edible mushrooms has increased. Since 1990, the world has focused on the mushroom production industry. In recent years, mushrooms have become one of the most important food and medicinal sources. One of the largest species of edible mushroom is button mushroom (Agaricus bisporus), which has high nutritional value due to the presence of fiber, carbohydrates, protein, amino acids, minerals, vitamins, etc., and also its antioxidant, anti-cancer, and anti-diabetic properties. This commodity has shown good health benefit for humans. The quality of button mushrooms is determined by their color, texture, and taste. Color is the first characteristic that is perceived by consumers. Browning is one of the main reasons for the loss of mushroom quality, which reduces the commercial value of mushrooms. Edible coating is considered as the best method for maintaining quality of perishable foods, these coatings almost prevent the penetration of oxygen, depending on the type of coating used, and reduce the loss of moisture during storage. Chitosan has functional characteristics such as antimicrobial and antioxidant properties. The purpose of this research was to find a suitable chitosan coating for button mushrooms that can maintain its characteristics such as color, texture hardness, and moisture during the storage period and increase the shelf life of  mushroom. Materials and MethodsTo make chitosan solutions, first, each type of chitosan (70% deacetylated, 80% deacetylated, 90% deacetylated, and 100% deacetylated) was weighed in amounts of 0.5g, 1g, and 2g., then it was dissolved in 100 ml of 0.5% acetic acid  and stirred for 12 hours at a speed of 1000 rpm at room temperature to dissolve uniformly. After 12 hours, each sample was centrifuged for 15 minutes at 6000 rpm at 25°C to separate undissolved materials. Mushrooms were prepared freshly harvested, washed with water, and then excess water was removed. After sorting and screening in terms of size and approximate weight, the mushrooms were added to 0.5%, 1%, and 2% chitosan solutions without being sliced and were immersed in the solution for one minute. The control sample was immersed in 0.5% acetic acid solution for one minute. After that, the mushrooms were air-dried at room temperature for one hour, and at the end, their excess water was removed with a tissue. The mushrooms were placed in 18*14 size polyethylene zip lock bags and stored in a refrigerator at 4°C. The effects of chitosan coating on weight loss, color and browning index, enzyme activity, texture, and total phenolic compounds of mushroom were studied. Results and DiscussionThe spoilage of edible mushrooms happens in a short time, and the storage of mushrooms has become one of the most important challenges in mushroom marketing. Coating edible mushrooms is one of the suitable methods to increase the shelf life of edible mushrooms. In this research, chitosan with four degrees of deacetylation and three different concentrations was used as a coating for button mushroom. The results indicated that coating the mushroom with chitosan could delay the occurrence of spoilage and change its color or texture. Due to the very strong antimicrobial properties of chitosan, it is suggested to investigate the microbial load of edible button mushrooms ans other tissue factors of the mushroom, such as gumminess, adhesive properties and cohesieveness. ConclusionThe spoilage of edible mushrooms happens in a short time, and the storage of mushrooms has become one of the most important things in mushroom production. Coating edible mushrooms is one of the suitable methods to increase the shelf life of edible mushrooms. In this research, chitosan with four degrees of deacetylation and three different concentrations was used as a coating for button mushroom. The results indicated that coating the mushroom with chitosan could delay the occurrence of spoilage and change its color or texture. Due to the very strong antimicrobial properties of chitosan, it is suggested to investigate the microbial load of edible button mushrooms, also other tissue factors of the mushroom, such as gumminess, adhesive properties and cohesieveness can be studied.