摘 要：
【Objective】This study was performed to enhance carotenoid yield, to improve nutritional value of fermentation product, and to reduce the production cost of carotenoids through optimizing solid-state fermentation substrate and fermentation conditions of Rhodotorula mucilaginosa.【Method】In this study, Rhodotorula mucilaginosa TZR2014 was used as a inoculant. First, the Mixture-Design of Design-Expert software was used to design the fermentation substrate, and the contents of ingredients as followed: 50%-80% wheat bran, 6%-20% soybean meal, 3%-15% maize flour, 2%-14% rice bran, 2%-10% maize syrup, 0.4%-2.5% ammonium sulfate, 0.05%-0.5% monopotassium phosphate, and 0.03%-0.3% magnesium sulfate. Then the optimal ratio of ingredients in substrate was determined according to the carotenoid yield. Based on this result, an L16(45) orthogonal design was used to optimize the fermentation conditions, including inoculum(5.0%-12.5%), fermentation time(60.0-96.0 h), fermentation temperature(26-32℃), and fermentation p H(60.0%-75.0%). Finally, the number of Rhodotorula mucilaginosa and contents of carotenoids, crude fiber, crude protein, water, crude fat, ash, calcium, phosphorus, and amino acids in fermentation product were determined to evaluate the effects of the optimized fermentation process on the nutritional values of fermentation product. 【Result】The results showed that there was a positive correlation between maize starch content in substrate and carotenoid content in fermentation product(r=0.344, P=0.040) or between rice bran content in fermentation substrate and carotenoid content in fermentation product(r=0.329, P=0.050). There was a significantly negative correlation between carotenoid yield and the content of wheat bran in solid-state fermentation substrate(r=-0.336, P=0.045). There was a positive correlation between the number of live bacteria of Rhodotorula mucilaginosa in fermentation product and the content of soybean meal in fermentation substrate(r=0.510, P=0.001). Inoculum, fermentation temperature, p H, and moisture had extremely significant impacts on the number of Rhodotorula mucilaginosa(P<0.01), thereinto, fermentation temperature had the greatest effect on the number of Rhodotorula mucilaginosa, followed by moisture, inoculum, and p H. Fermentation time, fermentation temperature, and p H had extremely significant influences on the carotenoid content in the fermentention product(P<0.01), and fermentation temperature had the greatest influence on the carotenoid content in the fermented product, followed by p H and fermentation time. After the optimization of the fermentation process, the carotenoid yield by Rhodotorula mucilaginosa TZR2014 was increased to 4 535 μg·kg-1; the bacteria number was increased to 3.79×109 CFU/kg; the contents of crude fiber, crude protein, ash, threonine, glutamate, and proline in fermentation product were significantly increased(P<0.05), meanwhile, the contents of histidine, water, and crude fat was significantly decreased(P<0.05). 【Conclusion】 The optimal ratio of solid-state fermentation substrate for Rhodotorula mucilaginosa was as followed: 52.5% wheat bran, 20.0% soybean meal, 3.0% maize flour, 14.0% rice bran, 10.0% maize syrup, 0.4% ammonium sulfate, 0.05% monopotassium phosphate, and 0.04% magnesium sulfate. The optimal fermentation conditions were as followed: inoculum 5.0%, fermentation time 72 h, fermentation temperature 28.0℃, p H 6.0, and moisture 60.0%. The results suggested that the optimized fermentation process of Rhodotorula mucilaginosa enhanced the yield of carotenoids and improved the nutritional value of fermentation product.
