Antioxidant characteristics and identification of peptides from sorghum kafirin hydrolysates

Authors: XU, SHIWEI - Kansas State University; SHEN, YANTING - Kansas State University; CHEN, GENGJUN - Kansas State University; Bean, Scott; LI, YONGHUI - Kansas State University

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2019
Publication Date: 8/13/2019
Citation: Xu, S., Shen, Y., Chen, G., Bean, S.R., Li, Y. 2019. Antioxidant characteristics and identification of peptides from sorghum kafirin hydrolysates. Journal of Food Science. 84:2065-2076. https://doi.org/10.1111/1750-3841.14704.
DOI: https://doi.org/10.1111/1750-3841.14704

Interpretive Summary: Oxidation of oils and fats in food products results in the deterioration of many quality features such as color, flavor, aroma, and texture, which will ultimately shorten the shelf-life, decrease the sensory and nutritional quality. Antioxidants are widely used to preserve various food products from oxidation and deterioration, hence, maintaining product stability and quality integrity. Chemically synthesized antioxidants have been widely used in food industry during processing and storage of food products, However, due to the potential toxicity and health-related risks as well as consumer’s expectations for clean-label ingredients alternative natural antioxidants are needed. Thus, the objectives of this study were to develop antioxidative hydrolysates from sorghum kafirin, evaluate the antioxidant performances using chemical assays and model systems, isolate fractions with superior antioxidant properties, and identify the peptide compositions. Peptides generated by a commercially available protease showed good yield and anti-oxidant properties, demonstrating that sorghum hydrolyzed proteins could serve as antioxidants in food systems.

Technical Abstract: Grain sorghum is gaining growing interests for various uses as a highly sustainable crop. Kafirin is the main storage protein in grain sorghum. The objectives of this study were to develop antioxidative hydrolysates from sorghum kafirin, evaluate the antioxidant performances using chemical assays and model systems, isolate fractions with superior antioxidant properties, and identify the peptide compositions. Kafirin hydrolysates prepared with Neutrase displayed promising yield and antioxidant capacity among multiple proteases evaluated. Critical variables including protein substrate content, enzyme-to-substrate ratio, and reaction time on the production were studied. Selected hydrolysates were further fractionated through ultrafiltration and gel filtration chromatography (GFC). Medium-sized fraction (3 – 10 kDa) revealed relatively higher total phenolic content and stronger antioxidative activities with regards to free radical scavenging activity, metal ion chelating activity, reducing power, and oxygen radical absorbance capacity. In an oil-in-water emulsion model system, the incorporation of selected fraction of hydrolysates at 50 mg/mL inhibited the formation of primary and secondary oxidation products by 83.03% and 65.59%, respectively, by the end of a 14-day incubation period. In another ground meat model system, the addition of kafirin hydrolysates at 0.5 and 1.0 mg/g decreased the lipid peroxidation by 35.34% and 43.17%, respectively, after 12 day’s storage. Peptide compositions of the most promising fraction from GFC and RP-HPLC were identified using MALDI-TOF/TOF MS.