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The aroma-active compounds of Beijing roast duck were investigated by using aroma extract dilution analysis (AEDA), dynamic headspace dilution analysis (DHDA), gas chromatography-olfactometry-mass spectrometry (GC-O-MS) and odour activity values (OAVs; ratio of concentration to odour threshold). The following volatile components are the predominant odorants of Beijing roast duck: 3-methylbutanal, hexanal, dimethyl trisulphide, methional, 2-methylbutanal, octanal, heptanal, 2-methyl-3-furanthiol, 2-furfurylthiol, 2-ethyl-3,5-dimethylpyrazine, (E,E)-2,4-nonadienal, 1-octen-3-ol, nonanal, decanal, (E)-2-decenal, (E,E)-2,4-decadienal, (E)-2-nonenal, (E,Z)-2,6-nonadienal, (E,E)-2,4-octadienal (fatty, fried), etc. Due to abundant flavour precursors of Beijing crammed duck (raw material of Beijing roast duck), such as amino acids, esters, vitamins and carbohydrates, and the special process (e.g. roasting, drying, etc.), the identified compounds above were likely derived from different kinds of reactions, such as degradation of fatty acids and amino acids, Maillard/Strecker and other associated reactions, which were considered to account for the typical aroma of Beijing roast duck.

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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.

There has been a growing interest in developing natural antioxidants with high efficiency and low cost. Bioactive protein hydrolysates could be a potential source of natural and safer antioxidants. The objectives of this study were to hydrolyze corn gluten meal using three plant-derived proteases, namely papain, ficin, and bromelain, to produce antioxidative hydrolysates and peptides and to characterize the antioxidant performances using both chemical assays and a ground meat model. The optimum hydrolysis time for papain was 3 h, and for ficin and bromelain was 4 h. The hydrolysates were further separated by sequential ultrafiltration to 5 hydrolysate fractions named F1 to F5 from low molecular weight (MW) (<1 kDa) to high MW range (>10 kDa), which were further characterized for TPC, free radical scavenging capacity against DPPH and ABTS, and metal chelating activity. The fraction F4 produced by papain (CH-P4), F1 produced by ficin (CH-F1), and F3 produced by bromelain (CH-B3) showed the strongest antioxidant activity and yield, respectively. These three fractions were incorporated into ground pork to determine their inhibition effects on lipid oxidation during a 16-day storage period. The inhibition effect was enhanced with the addition of higher amount of hydrolysate (e.g., 1000 vs. 500 mg/kg). The CH-P4 reduced lipid oxidation in ground meat by as much as 30.45%, and CH-B3 reduced oxidation by 27.2% at the same level, but the inhibition was only 13.83% with 1000 mg/kg of CH-F1. The study demonstrated that CGM protein hydrolysates and peptides could be used as naturally derived antioxidant in retarding lipid oxidation and improving product storage stability.

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