Efficient production of fungal chitosan utilizing an advanced freeze-thawing method; quality and activity studies

Fungal chitosan was produced from brown Agaricus bisporus, white Agaricus bisporus, and Pleurotus ostreatus mushrooms (commercially known as brown portobello, white protobello, and oyster mushrooms, respectively) by utilizing a classic alkali deacetylation protocol (PI), as well as a new protocol (PII) that involves a freeze-thawing cycle. The new protocol (PII) has led up to a twofold increase in the obtained chitosan's yield, a more efficient deacetylation process that resulted in up to a threefold decrease in its acetylated units, and a whiter color. For instance, using the PII protocol, 1 g of dry Pleurotus ostreatus mushrooms yielded 44.3 mg of chitosan that contained only 14.8% acetylated units, and had a whiteness index of 80.3. For comparison, using the classic PI protocol, 1 g of dry Pleurotus ostreatus mushrooms yielded only 22.4 mg of chitosan with 44.1% acetylated units, and a whiteness index of 75.7. Gel permeation chromatography, FTIR, NMR, UV, elemental analysis, X-ray diffractometry, and thermogravimetric analysis were all used to characterize the prepared fungal chitosan samples and examine their physical properties (viscosity, color, hydrophobicity, and solubility). Microbiological studies have revealed the yielded chitosan samples have demonstrated biological activity against Gram-positive Bacillus subtilis, Gram-negative Escherichia coli bacteria, and Saccharomyces cerevisiae yeast. The prepared fungal-sourced chitosan samples were also compared with the crustacean-sourced commercial chitosan all throughout this paper studies. It can be concluded that the PII protocol allows for the formation of fungal chitosan with quality and properties that do not fall short of those found in the crustacean-sourced chitosan. This study therefore presents an efficient method for the production of non-animal sourced chitosan, which is extremely desired in the food industry because it overcomes the limitations of animal-sourced chitosan and allows to expand this material use. In addition, the presented freeze-thaw cycle technique can also be used to yield and modify other edible hydrocolloids. (C) 2018 Elsevier Ltd. All rights reserved.