Carotenoid value addition to distillers dried grain with solubles by red yeast fermentation

Abstract

Distillers Dried grain with Solubles (DDGS) is a co-product of grain-based ethanol and is primarily used as livestock feed. With increasing production of DDGS, it is imperative to produce value-added products and/or find new applications of DDGS to help sustain the biofuel industry. Carotenoids are expensive yet essential feed additives. Since animals cannot synthesize carotenoids and animal feeds including DDGS are generally poor in carotenoids, about 30-120 ppm of total carotenoids is added to animal feed to improve animal health. The objectives of this study were to 1) produce carotenoid (astaxanthin and β-carotene)-enriched DDGS by Phaffia rhodozyma and Sporobolomyces roseus monoculture and mixed culture submerged fermentation of whole stillage, 2) optimize fermentation media by response surface methodology (RSM) and mixture design followed by validation, 3) evaluate the nutritional profile of carotenoid-enriched DDGS, 4) improve carotenoid production by the use of precursors, and 5) develop carotenoid-enriched feeds namely, wheat bran, rice bran and soybean products. Carotenoid-enriched DDGS was produced from both monoculture and mixed culture fermentation with yields ranging from 17-233 µg/g. Upon media optimization, astaxanthin and β-carotene yields, especially in P. rhodozyma were enhanced by 177% and 164% to yield 98 and 275 µg/g respectively. Nutrition profiling of the carotenoid-enriched DDGS showed that the secondary fermentation resulted in low fiber, protein and %N and enhanced fat. Fiber was reduced by 77% and 66% by P. rhodozyma and S. roseus respectively, whereas the crude fat increased by 80% in mixed culture fermentation. Additionally, abundant vaccenic acid, a monounsaturated fatty acid was seen in S. roseus and mixed culture fermented DDGS. Vaccenic acid is a precursor of conjugated linolenic acid which is known to confer numerous health benefits. Fermentation of milo DDGS, wheat bran, rice bran and soybean products also resulted in carotenoid enrichment, with the best astaxanthin yield of 80 µg/g in rice bran, and best β-carotene yield of 837 µg/ g in soy flour. Precursors like mevalonic acid, apple pomace and tomato pomace increased carotenoid yield in DDGS and other substrates, with the yield increment depending on the substrate. Mevalonic acid resulted in the best astaxanthin and β-carotene yield increment by 140% and 236% resulting in 220 µg/g and 904 µg/g respectively in corn DDGS. Apple pomace and tomato pomace resulted in 29% carotenoid yield increment. Numerous studies thus far have used cheap agricultural substrates to produce carotenoids especially astaxanthin using P. rhodozyma with the intent of extracting the carotenoids for use in animal feed. However, by fermenting the animal feed directly, carotenoid-enriched feed can be produced without the need for extraction. By this simple yet novel carotenoid value addition, premium feeds or feed blends can be developed. Apart from carotenoid enrichment, low-fiber DDGS can help expand the market base of DDGS for use in non-ruminant feeds. Carotenoid value addition of DDGS can not only help sustain the biofuel industry but can also capture the aquaculture feed base which heavily relies on astaxanthin supplementation.