Utilization of Sweet Sorghum Juice for the Production of Astaxanthin as a Biorefinery Co-Product by <i>Phaffia rhodozyma</i>

This work investigates cultivating the red-pigmented yeast Phaffia rhodozyma in sweet sorghum juice (SSJ) to assess the production of astaxanthin as a potential biorefinery co-product. Shake flask cultures on defined sugar medium indicated that all three sugars (sucrose, glucose, and fructose) could be consumed with adequate nitrogen and nutrient supplementation. Only modest biomass growth and astaxanthin production could be achieved in SSJ without nitrogen supplementation; however, combining nitrogen supplementation with yeast extract in diluted SSJ could metabolize all sugars present in 168 h. A 2 L bioreactor trial with full strength (i.e., undiluted) SSJ produced up to 29 g/L of biomass, 65.4 mg/L of astaxanthin, an overall cell astaxanthin content of 2.49 mg astaxanthin/g dry cell mass, and a volumetric astaxanthin productivity of 0.389 mg/L/h after 168 h of cultivation. Further process optimization is needed since glucose metabolism was incomplete in undiluted SSJ

A Comparison of Two Milling Strategies To Reduce the Mycotoxin Deoxynivalenol in Barley

Winter barley (Hordeum vulgare L.), a potential feedstock for fuel ethanol production, may be contaminated with the trichothecene mycotoxin deoxynivalenol (DON). DON is a threat to feed and food safety in the United States and may become concentrated during the production of distillers dried grains with solubles (DDGS). DDGS is a coproduct of fuel ethanol production and is increasingly being used as feed for domestic animals. Therefore, new strategies to reduce the threat of DON in DDGS need to be developed and implemented for grain destined for fuel ethanol production. It is known that large concentrations of DON accumulate in the hulls of wheat and barley. Consequently, improved methods are needed to carefully remove the hull from the grain and preserve the starchy endosperm. Whole kernels from five Virginia winter barley genotypes were used to evaluate the abilities of two different milling strategies (roller milling and precision milling (FitzMill)) for their ability to remove the hull-enriched tissue from the kernel while maintaining starch levels and reducing DON levels in the endosperm-enriched tissue. After whole kernels were milled, DON and starch levels were quantified in the hull-enriched fractions and endosperm-enriched fractions. Initial milling experiments demonstrated that the precision mill system (6 min run time) is able to reduce more DON than the roller mill but with higher starch losses. The average percent DON removed from the kernel with the roller mill was 36.7% ± 5.5 and the average percent DON removed from the dehulled kernel with the precision mill was 85.1% ± 9.0. Endosperm-enriched fractions collected from the roller mill and precision mill contained starch levels ranging from 49.0% ± 12.1 to 59.1% ± 0.5 and 58.5% ± 1.6 to 65.3% ± 3.9, respectively. On average, the precision mill removed a mass of 23.1% ± 6.8 and resulted in starch losses of 9.6% ± 6.3, but produced an endosperm-enriched fraction with relatively very little average DON (5.5 ± 2.7 μg g^–1). In contrast, on average, the roller mill removed a mass of 12.2% ± 1.6 and resulted in starch losses of 2.1% ± 0.5, but produced an endosperm-enriched fraction with high average DON (20.7 ± 13.5 μg g^–1). In a time course precision milling experiment, we tested barley genotypes Nomini, Atlantic, and VA96-44-304 and attempted to reduce the starch loss seen in the first experiment while maintaining low DON concentrations. Decreasing the run time of the precision mill from 5 to 2 min, reduced starch loss at the expense of higher DON concentrations. Aspirated fractions revealed that the precision milled hull-enriched fraction contained endosperm-enriched components that were highly contaminated with DON. This work has important implications for the reduction of mycotoxins such as DON in barley fuel ethanol coproducts and barley enriched animal feeds and human foods