DRYING CHARACTERISTICS OF SOME OYSTER MUSHROOM SPICIES AND EFFECTS ON THEIR ANTISIABETIC AND ANTIHYPERTENSIVE PROPERTIES

Abstract

This study was undertaken to assess the properties of three species of Oyster mushroom namely; Pleurotus ostreatus, Pleurotus sajur-caju (PSC) and Pleurotus florida as a functional food and determine the best model to describe their drying characteristics, the development of mushroom biscuit and the determination of their antidiabetic and antihypertensive properties. Fresh oyster mushroom species (Pleurotus oestreatus, Pleurotus sajur-caju and Pleurotus florida) were cultivated using wheat bran and saw dust. The fresh Oyster mushroom was dried at 60oC for 8h. The proximate compositions, minerals, vitamins, phytochemicals, antinutrients and amino acid compositions were determined. The storage stability test was conducted to determine the effect of storage temperature on the moisture content, the TBA, free fatty acids and microbial studies on the oyster mushroom species packaged in a High density polyethylene (HDPE). The samples were removed and analysed at two weeks intervals. The other portion of the dried oyster mushroom species (Pleurotus oestreatus, Pleurotus sajur-caju (PSC) and Pleurotus florida) were used for sorption isotherm study using the static gravimetric method and drying kinetics. The three species were also analysed for their antidiabetic and antihypertensive properties. Based on the result of the above mentioned analysis the best oyster mushroom species Pleurotus sajur-caju (PSC) were picked for the production of mushroom composite biscuit. Pleurotus sajur-caju (PSC) mushroom was dried, processed into flour and used to substitute wheat flour as composite flour at 0, 5, 10, 20 and 30% level of addition, the resulting composite flour were then used to produce biscuit. Physicochemical, antidiabetic and antihypertensive properties, starch and sugar content, in vitro starch and protein digestibilities, amylose and amylopectin content, glycemic index and sensory evaluation of the biscuit samples were carried out. The results showed that the fresh mushrooms had the higher moisture content than the dried samples. The protein, fat, fibre and ash contents of the dried samples were higher than those of the fresh samples. The mineral element also increased with drying, while drying reduced the vitamin content of the antinutritional constituents of the fresh samples. There was also a decline in the DPPH, FRAP, ABTS, total phenol and flavonoid composition as a result of drying. Eighteen amino acids were found in varying proportions in the species of oyster mushroom with the three predominant amino acids being glutamic acid, aspartic acid and lysine. All the samples inhibited the starch hydrolysing enzymes (α-amylase and α-glucosidase) and angiotensin converting enzyme (ACE) in dose dependent manner in the following order; Pleurotus sajur-caju> Pleurotus ostreatus > Pleurotus florida. The moisture sorption curves were sigmoid in shape which conforms to the type II classification characteristic of agricultural products. The sorption capacity of the oyster mushroom species followed the order; Pleurotus florida> Pleurotus ostreatus> Pleurotus sajur-caju. The drying kinetics of the samples showed that drying took place in the falling rate period, while the best fit model that described the drying kinetics was the Logarithmic model. The result of the physical property of the biscuit samples showed that as the ratio of mushroom level increased, the mean thickness, diameter, weight as well as the spread ratio improved. Furthermore, 5% level of PSC mushroom flour inclusion had the highest α-amylase, α-glucosidase and ACE inhibitory activity while control had the least. It can be concluded based on the the low sugar, GI, amylose, and amylopectin contents of the biscuit as well as their α-amylase and α-glucosidase inhibitory activities could be possible mechanisms and justification for their recommendation in the management of type-2 diabetes.