Fermentation based value-added utilization of some corn and wheat coproducts and resulting ingredient characterization

Abstract

Agri-food coproducts such as light corn steep, thin stillage, corn bran, and wheat bran are low-value coproducts of cereal processing industries. These coproducts contain valuable components like carbohydrates, fibers, proteins, and bioactive compounds; however, they are currently limited in utilization primarily as low-cost feed supplements. Some specific physical modifications and fermentation were comparatively studied as feasible techniques for enhancing value of these coproducts. Corn light steep liquor (CSL) and thin stillage (TS) were investigated as fermentation media for the recombinant Lactococcus lactis to produce the ocean pout antifreeze protein III. Light corn steep liquor from yellow dent corn and thin stillage from the industrial corn bioethanol process were optimized in Bioscreen as fermentation media with a combination of the following additives and trace elements: disodium-B-glycerophosphate (DG), tryptone (T), ascorbic acid (AA), iron, zinc (Zn), and magnesium. The corn coproducts media consisting of 50% (v/v) light steep in water supplemented with DG-5 g L−1, T-5 g L−1, AA- 0.5 g L−1, and Zn-4 ppm resulted in the best growth and was considered as the best-optimized media. A distinct supercooling effect was observed for the supernatants frozen at −20°C from recombinant strains thus extending the time and temperature of supercooling and freezing. The maximum time of supercooling extension was 17.55 ± 4.45 min for thin stillage followed by 17.25 ± 4.45 min (M17 media), 10.80 ± 2.12 min (an industrial CSL), and 6.9 ± 0.85 min (yellow dent CSL) when fermented with recombinant Lactococcus lactis strains. The fermentation supernatants exhibited longer times to supercool and freeze compared to control supernatants, indicating potential use as antifreeze compounds in frozen food and non-food applications. Fermentation of physically modified corn and wheat bran were studied, and the resulting ingredients were characterized for beneficial changes. The physical modifications of brans at 25 and 35% moisture were 1) grinding to < 500 µm, and 2) extrusion at two die temperature settings (high-140 and low-120°C); they were then fermented at 37°C for 72 h with shaking at 200 rpm using probiotic microorganisms (Lactobacillus plantarum or Bacillus subtilis) to modify the ingredient characteristics and nutritional profile. All the ground and extruded bran supported the growth of probiotic bacteria studied, indicating that the sugars present in corn and wheat bran are metabolized to support their proper growth. For corn bran, the highest growth rate was 0.64 h-1 and the lower population doubling time was 1.1 h for 35% moisture corn bran extruded at 120°C and fermented with Bacillus subtilis. For wheat bran, the highest growth rate was 0.43 h-1, and population doubling time was 1.6 h for 35% moisture wheat bran extruded at 140°C and fermented with Bacillus subtilis when compared to the control. The total phenolic content was in the range of 9-10 g gallic acid equivalent (GAE) kg-1 and 4-16 g GAE kg-1 corn and wheat bran, respectively. Similarly, anti-nutritional compounds such as phytic acid and trypsin inhibitors were reduced by a maximum of 42 and 34% and 10 and 60%, respectively, for corn and wheat bran, when extruded and fermented. Our results showed that extruded or ground bran supported the growth of probiotic bacteria and positively affected the non-nutritive compounds, thereby improving the nutritional quality and usage, making brans favorable for food applications.