Differences in the functionality and characterization of kafirins extracted from decorticated sorghum flour or gluten meal treated with protease

Enzymatic production and physicochemical and functional properties of sorghum protein isolates

Grain sorghum has emerged as a promising source for producing alternative proteins, yet current extraction methods lack efficiency. In this study, a novel enzymatic approach using α-amylase and cellulase on sorghum materials was developed to address this challenge. Comparisons were made among the proteins isolated from dry-milled sorghum flours, wet-milled sorghum gluten meals, and sorghum dried distiller's grains (DDG). Remarkably, proteins obtained from sorghum gluten meals demonstrated the highest protein purity (83-85 %) and recovery rate (92-93 %), followed by those from sorghum flour (purity 75-76 %) and DDG (purity 45-50 %). Physicochemical properties and functionalities of the isolated sorghum proteins were analyzed and compared with common commercial plant proteins (e.g., soy protein isolate, pea protein isolate, and wheat gluten). Sorghum proteins exhibited higher levels of crude fat content, α-helix, and random coil structures, along with higher surface hydrophobicity and oil holding capacity (OHC) compared to the commercial plant protein isolates. Notably, proteins extracted from sorghum flours displayed slightly higher α-helix and random coil structures, total sulfhydryl content, water holding capacity (WHC), OHC, and protein digestibility compared to proteins isolated from sorghum gluten meals. Overall, this study demonstrates that enzymatic processing is feasible in producing sorghum proteins and provides insights into their basic properties and functionalities.

Evaluation of nutritional and functional properties of anatomical parts of two sorghum (Sorghum bicolor) varieties

Compositional differences exist among grain varieties as well as in the content of respective fractions. The proximate composition, amino acids, mineral contents, and functional properties of white and brown sorghum and its anatomical parts (dehulled and bran) were studied. The results showed that the bran had higher crude protein, crude fat, crude fibre, and ash contents for both sorghum varieties than the whole grain and dehulled samples. Likewise, significantly (p ≤ 0.05) higher essential and non-essential amino acids and minerals, particularly calcium, zinc, potassium were recorded for the bran samples compared to the whole grains or dehulled ones. With regard to the functional properties, the hydration capacity, hydration index, water, and oil absorption capacities of the dehulled samples were significantly (p ≤ 0.05) lower than the other investigated samples, except for bulk density, which was significantly (p ≤ 0.05) higher. In contrast, none of the swelling capacities differed significantly in any of the samples. In conclusion, sorghum bran has significant potential in the food industry and could be an excellent material for formulating high-fibre foods and serving as a nutritionally-rich food ingredient.

Effect of wet and dry milling on the functional properties of whole sorghum grain flour and kafirin

The effect of wet and dry milling on the functional properties of whole sorghum grain flour (SF) and extracted kafirin were assessed. White sorghum landrace was used to prepare two SFs by wet milling (SF1) or dry milling (SF2) and to extract their respective kafirins SK1 and SK2. Protein contents of SK1 and SK2 were 90.07 and 94.23%. Wet milling of SF allowed increasing the oil binding capacity, the least gelling concentration and the instant foam capacity and decreasing the water binding capacity and foam stability. The emulsifying activity index of SF1 and SF2 were in the same range, while emulsion stability was two time higher in SF2. Functional properties of SK1 and SK2 showed an appropriate water binding capacity of 2.20 ± 0.10 and 1.82 ± 0.22 (g water/g dry mater), respectively. Both SK1 and SK2 showed higher oil binding capacity than SF1 and SF2 with no gel and foam formation. The wet milling improved water and oil binding capacities of SK1 by 17 and 5%. The emulsifying activity indexes were approximately similar for SK1 and SK2 with emulsion stability exceeding 60%. Fourier transform infrared spectroscopy of SK1 and SK2 showed that wet milling induced a decrease of α-helical structure and an increase of intermolecular β-sheet and β-turns and no change in the anti parallel β-sheet. This study showed that wet milling could allow extracting kafirin with preserving the most important functional properties of SF and kafirin and could constitute an interesting method for protein recovery and starch isolation.