Dept. of Grain Science and Industry, Kansas State Univ., Manhattan, KS, 66506, U.S.A.
Center for Grain and Animal Health Research, USDA-ARS, Manhattan, KS, 66502, U.S.A.
J Food Sci. 2019 Aug;84(8):2065-2076. doi: 10.1111/1750-3841.14704. Epub 2019 Jul 17.
Grain sorghum is gaining interest for various uses as a highly sustainable crop. Kafirin is the main storage protein in grain sorghum. However, the antioxidant activities of kafirin hydrolysates have not been systematically investigated. The objectives of this study were to characterize the antioxidative hydrolysates and their ultrafiltrated fractions from sorghum kafirin using chemical assays and model systems and to identify the representative peptides. Kafirin Neutrase hydrolysates displayed promising yield and antioxidant capacity among those prepared with several different proteases. The effects of critical variables including protein substrate content, enzyme-to-substrate ratio, and reaction time on antioxidant production were studied. Selected hydrolysates were further fractionated through ultrafiltration and gel filtration chromatography (GFC). Medium-sized fraction (3 to 10 kDa) revealed relatively higher total phenolic content and stronger antioxidative activities with regard to free radical scavenging activity, metal ion chelating activity, reducing power, and oxygen radical absorbance capacity. In an oil-in-water emulsion system, incorporation of selected fraction of hydrolysates 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. Similar oxidation inhibition effect was also observed in a ground meat system. Peptide compositions of the most promising fraction from GFC and reversed-phase high-performance liquid chromatography were identified using matrix-assisted laser desorption ionization-time of flight/time of flight mass spectrometry. PRACTICAL APPLICATION: This study provided a feasible approach to produce peptide antioxidants from sorghum kafirin. The novel naturally derived antioxidants could be potentially used as alternatives or synergetic components to synthetic antioxidants in improving the oxidative stability of various food products.
高粱作为一种高度可持续的作物，因其多种用途而受到关注。高粱醇溶蛋白是高粱中的主要贮藏蛋白。然而，高粱醇溶蛋白水解物的抗氧化活性尚未得到系统研究。本研究的目的是利用化学分析和模型系统对高粱醇溶蛋白的抗氧化水解物及其超滤级分进行表征，并鉴定代表性肽段。与几种不同蛋白酶制备的水解物相比，Neutrase 水解高粱醇溶蛋白的产率和抗氧化能力都很有前景。研究了关键变量（包括蛋白质底物含量、酶与底物的比例和反应时间）对抗氧化产物的影响。选择的水解物进一步通过超滤和凝胶过滤色谱（GFC）进行分级。中分子量级分（3 至 10 kDa）的总酚含量相对较高，对自由基清除活性、金属离子螯合活性、还原能力和氧自由基吸收能力的抗氧化活性较强。在水包油乳液体系中，所选水解物级分在 14 天的孵育期结束时，分别抑制了初级和次级氧化产物的形成，抑制率分别为 83.03%和 65.59%。在绞肉体系中也观察到了类似的氧化抑制效果。使用基质辅助激光解吸电离飞行时间/飞行时间质谱法对 GFC 和反相高效液相色谱中最有前途的级分的肽组成进行了鉴定。
本研究提供了一种从高粱醇溶蛋白中生产肽类抗氧化剂的可行方法。新型天然来源的抗氧化剂可作为合成抗氧化剂的替代品或协同成分，用于提高各种食品的氧化稳定性。
