Extraction and role of mushroom polyphenols in starch digestion inhibition : A Dissertation submitted in partial fulfilment of the requirements for the Degree of Master of Science in Food Innovation at Lincoln University

Abstract

Mushrooms are becoming attractive as a functional food and good sources of vitamins, minerals, especially bioactive compounds. Mushroom are used as medicines due to their antioxidant, antitumor, and antimicrobial properties. These are becoming very popular due to their high nutritional value, high protein, and low fat content. Mushroom proteins are rich in all the nine amino acids necessary for human body. They are utilized in preventing several diseases like hypertension, diabetes, hypercholesterolemia, and cancer. These are rich sources of bioactive substances like polyphenols, glycoproteins, and polysaccharides. The phenolic compounds are used as supplements in the isolated forms and have positive impact on the human health. The extraction of polyphenols is very complex due to existence of polyphenols in the form of insoluble complexes. There are several methods utilized for polyphenol extraction. Conventional solvent extraction is one of the most significant method for extracting bioactive substances. In this study, three different kinds of mushrooms (Lentinula edodes, Auricularia auricula, and Tremella fuciformis) were used for extracting polyphenols. Extraction was performed by using water and different concentrations of methanol at different temperature and pH. The antioxidant activity and protein content was determined. The results showed that water mushroom extracts showed higher antioxidant activity and higher protein content than methanol mushroom extracts. Nowadays, cereal products with mushroom powder inclusion are trending because mushroom powder enhances the nutritional value of the product. The 1% concentrated mushroom extracts were incorporated in the white sorghum flour to determine the effect on pasting properties and release of reducing sugars as compared to control group. The results revealed that, addition of mushroom extracts showed negative effect on the pasting properties of white sorghum flour than control group. The release of reducing sugars also decreased due to incorporation of mushroom extracts in the white sorghum flour than control group during in vitro starch digestion. The area under curve (AUC) illustrated that mushroom extracts decreased the predicted glycaemic response of the white sorghum flour. Mushroom extracts also elevated the level of antioxidants (Total phenolic contents and Ferric reducing antioxidant power) in the white sorghum flour as compared to that of control. Moreover, the incorporation of mushroom extracts also increased the protein digestibility during in vitro starch digestion. These results suggested that mushroom extracts can be incorporated into the white sorghum flour to provide health benefits to consumers.