Determining the Ideal Temperature and Fermentation Duration to Enhance Crude Protein Content and Reduce Crude Fiber in Rice Bran Using Solid-State Fermentation with Aspergillus niger (USM F4)

Abstract

Solid-state fermentation (SSF) offers a sustainable method for enhancing the nutritional quality of agricultural residues such as red rice bran. This study aimed to determine the optimal temperature and duration for SSF of red rice bran, focusing specifically on increasing the crude protein (CP) content and reducing the crude fiber (CF) content. SFF of rice bran with Aspergillus niger (A. niger) USM F4 was conducted over 14 consecutive days at three different temperatures (25°C, 35°C, and 45°C). A total of 63 samples of rice bran were divided into three temperature groups, each containing 21 samples. Three samples per group were collected at 48-hour intervals over the 14-day fermentation period. The fermentation process for the collected samples at 48-hour intervals was halted by oven drying at 60°C for 24 hours. The fermented products were subjected to proximate analysis for crude protein (CP), ash, ether extract (EE), and crude fiber (CF) contents using the methods outlined by the Association of Official Analytical Chemists (AOAC). The results revealed a significant effect of temperature and fermentation duration on CP, ash, EE, and CF content when compared to the unfermented rice bran kept at room temperature (25oC). The peak values of CP and the highest degradation of CF across all temperature levels were observed on day 10 while the maximum increase in ash and EE content occurred on day 8. Among the temperature conditions, the highest CP values and the lowest CF values were recorded at 35°C. Conversely, the lowest improvements in CP and CF degradation were observed at 25°C on day 10. In conclusion, the optimal conditions for SSF of rice bran with A. niger to enhance CP content and degrade CF are a temperature of 35°C and a fermentation duration of 10 days.