CHANGES IN GLUCOSE, AMYLASE AND SOLUBLE PROTEINS LEVELS IN SOLID STATE FERMENTED YAM (DIOSCOREA SPP.) PEELS BY RHIZOPUS OLIGOSPORUS

Abstract

Solid-state fermentation (SSF) of yam peels was carried out by Rhizopus oligosporus under acidic and basic conditions, to optimize the production of soluble proteins, glucose and α-amylase activity. Cultures were prepared with dried, grounded yam peels as substrate . The substrate was inoculated with spores of R. oligosporus after pH adjustment using citrate and phosphate buffer solutions. Five sets of samples with pH range of 3 – 7 (citrate cultures), and 7 – 11 (phosphate cultures) were obtained. Each
sample set had a control at pH 6; all samples were left at room temperature and allowed to ferment for four days. Post fermentation, there was noticeable decrease in acidity in the citrate cultures and increase in acidity for the phosphate cultures; this in turn had an effect on α-amylase activity and the production of glucose and total soluble proteins. Decreased acidity resulted in increased production of soluble proteins and amylase activity (247.47 ± 3.00 mg g-1 and 420.09 ± 21.45 μg g-1 min-1
respectively), compared to the control (118.13 ±13.30 mg g-1 and 312.42 ± 14.04 μg g-1 min-1 respectively). Changes observed in both parameters were significant (p < 0.05); by contrast, glucose level reduced with rise in pH by 4.7 units but peaked after a rise by 1.8 units. The best initial pH for optimum amylase and soluble proteins production using citrate as buffer is 3, while that for glucose production is 6. With phosphate buffer, the highest glucose content was obtained in the sample at initial pH 11 after a decrease in pH by 3.1 units (increase in acidity to pH 7.9). The highest yield for soluble proteins (222.13 ± 20.41 mg g-1 ) and amylase (377.96 ± 21.45 μg g-1min-1 )was observed at initial pH 8; this increase was significant compared to control (p < 0.05). Overall, for both buffer solutions, increases in glucose yield was not significant compared to control (p > 0.05). However, the
results confirm that R. oligosporus could be used for amylase and soluble proteins production by SSF on yam peels. Citrate buffer is recommended as the most suitable for pH control using yam peels as solid medium material