Bioconversions of maize residues to value-added coproducts using yeast-like fungi

Abstract

Agricultural residues are abundant potential feedstocks for bioconversions to industrial fuels and chemicals. Every bushel of maize (approximately 25 kg) processed for sweeteners, oil, or ethanol generates nearly 7 kg of protein- and fiber-rich residues. Currently these materials are sold for very low returns as animal feed ingredients. Yeast-like fungi are promising biocatalysts for conversions of agricultural residues. Although corn fiber (pericarp) arabinoxylan is resistant to digestion by commercially available enzymes, a crude mixture of enzymes from the yeast-like fungus Aureobasidium partially saccharifies corn fiber without chemical pretreatment. Sugars derived from corn fiber can be converted to ethanol or other valuable products using a variety of naturally occurring or recombinant yeasts. Examples are presented of Pichia guilliermondii strains for the conversion of corn fiber hydrolysates to the alternative sweetener xylitol. Corn-based fuel ethanol production also generates enormous volumes of low-value stillage residues. These nutritionally rich materials are prospective substrates for numerous yeast fermentations. Strains of Aureobasidium and the red yeast Phaffia rhodozyma utilize stillage residues for production of the polysaccharide pullulan and the carotenoid astaxanthin, respectively.

Ethanolic fermentation of hydrolysates from ammonia fiber expansion (AFEX) treated corn stover and distillers grain without detoxification and external nutrient supplementation

“…Besides xylanase, effective hydrolysis of hemicellulose in DDGS also required several enzymes including pectinase and ferulic esterase (Bals et al, 2006). It is possible that the commercial enzyme cocktails lack of necessary auxiliary enzymes to hydrolyze xylan in DDGS (Leathers, 2003). …”

Maximising high solid loading enzymatic saccharification yield from acid-catalysed hydrothermally-pretreated brewers spent grain

“…Numerous effective chemical and thermal pre-treatments for BSG have been developed that can enhance the subsequent enzymatic saccharification yields (Wilkinson et al, 2014a;Wilkinson, 2014b). However, large doses of expensive commercial enzymes are still usually required to achieve high conversion efficiencies of cellulose to glucose (Leathers, 2003;Chundawat et al, 2008;Qing et al, 2010). Therefore, optimisation of the enzymatic saccharification stage is a key objective in the cost-effective production of lignocellulosic biofuels.…”

Utilization and biodegradation of starch stillage (distillery wastewater)

“…alternan (Leathers, 1998) and pullulan (West and Strohfus, 1996). Furthermore, maize stillage was made use of as the feedstock for the synthesis of astaxanthin carotenoid by Phaffia rhodozyma (Leathers, 2003). Other starch stillage has been used for the synthesis of protease (Morimura et al 1994;Yang and Lin, 1998), chitosan (Yokoi et al 1998) and biodegradable plastics, e.g.…”