Edible coatings as a means to improve the quality and shelf-life of Agaricus bisporus (white button) mushroom

Mushrooms are highly perishable products that tend to lose their unique organoleptic properties immediately after harvesting. Their short shelf-life is mainly explained by the water loss, high respiration raters high (200-500 mgkgh at 20 ± 1oC) and microbial colonization by bacteria or fungi. Furthermore, also enzymatic activity and biochemical alterations lead to mushrooms changes after harvesting. Active edible coatings have been applied in the last years as an alternative method for the control of microbial contamination in food products, and the decrease of enzymatic browning. The incorporation of antimicrobial and anti-browning compounds showed potential for maintaining food quality and safety of foods during storage. Aiming at developing an active edible coating to increase the shelf-life of Agaricus bisporus mushrooms, polysaccharide-based coatings were developed using chitosan, alginate and guar gum, glycerol (as plasticizer) and Tween 80 (as surfactant). Coating formulations were evaluated and an optimal formulation was selected. Two coatings were selected, one containing 0.5% (w/v) of chitosan, 0.125% (v/v) of glycerol and 0.15% (v/v) of Tween 80 and other with 0.5% (w/v) of alginate, 0.125% (v/v) of glycerol and 0.05% (v/v) of Tween 80. Different concentrations (0-1%, v/v) of eugenol and carvacrol and a combination of both (1:1) were added to chitosan and alginate coatings and their antimicrobial activity was evaluated against E. coli and P. fluorescens. The best results of inhibition were obtained for eugenol with a concentration of 0.05%. Also, different concentrations (0-0.8 mM) of cinnamic acid (enzymatic inhibitor) were used and the effect of this compound on the enzymatic activity of mushroom tyrosinase was determined. A concentration of 0.6 mM of cinnamic acid was selected. After the application of the coatings on mushrooms the effect of the coating in the mushroom colour was evaluated, and it was found that the application of chitosan coating on mushroom lead to a degradation of the mushrooms, so it was excluded. Therefore, only the Agaricus bisporus (white button) mushrooms coated with sodium alginate-based coating with incorporation of eugenol and cinnamic acid were used during the shelf-life evaluation. The coated and uncoated mushrooms were stored at 90-95% RH and at 6-8 oC during 10 days. Shelf-life analyses were performed in coated and uncoated mushrooms in terms of colour, bacterial growth, weight loss, moisture, content of total solids, total soluble solids (TSS), pH, titratable acidity and enzymatic analyses. The results showed that the coating prolongs the shelf life of mushrooms, decreasing weight loss, reducing changes in colour (confirmed by the decrease of FCUP/FCNAUP Edible coatings as a means to improve the quality and shelf-life of Agaricus bisporus (white button) mushroom v polyphenol oxydase activity), titratable acidity, pH and TSS during refrigerated storage. The coated mushrooms showed to be more effective in reducing the mesophilic and psychrophilic counts and was totally effective against the fungi, avoiding their presence. These results show that the edible coating used in this work may be a promising method of maintaining the quality of the button mushrooms and increase their shelf-life during refrigerated storage. FCUP/FCNAUP Edible coatings as a means to improve the quality and shelf-life of Agaricus bisporus (white button) mushroom vi