Improvement of the solubility of protein isolate from glandless cottonseed

Authors: Cao, Heping; Sethumadhavan, Kandan; Pelitire, Scott; He, Zhongqi; Cheng, Huai; Klasson, K Thomas

Submitted to: ACS Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2024
Publication Date: 4/16/2024
Citation: Cao, H., Sethumadhavan, K., Pelitire, S.M., He, Z., Cheng, H.N., Klasson, K.T. 2024. Improvement of the solubility of protein isolate from glandless cottonseed. ACS Food Science and Technology. 4(5):1121-1129. https://doi.org/10.1021/acsfoodscitech.3c00692.
DOI: https://doi.org/10.1021/acsfoodscitech.3c00692

Interpretive Summary: Cotton industry produces approximately 50 million metric tons of seed annually. Cottonseed is a sustainable resource but sells as a low-value commodity at approximately $250/ton. It accounts for approximately 20% of the crop value. Cottonseed industry can generate approximately 10 million metric tons of protein annually. This protein resource from cottonseed could potentially meet the needs of half a billion people. Efforts have been made to make use of cottonseed protein as a source of food for humans and feed for animals. In addition, cottonseed protein has been explored for added value as wood adhesives and as a commercial ingredient for fermentation media and as plant fertilizer or growth substrate. However, the commercial cottonseed meal contains approximately 1% of toxic gossypol, which binds to protein and causes difficulties to produce proteins free of gossypol. Therefore, cottonseed has been used primarily to feed ruminants. Less cultivated glandless cottonseed lacks gossypol glands and has only trace levels of gossypol. The protein is potentially applicable as a food and feed source for non-ruminant animals and humans. However, low solubility of seed protein is a major factor affecting its food and beverage applications. The current objective was to improve the solubility of protein isolate from glandless cottonseed. Protein isolate was treated with various buffers with pH 2-10.6, a range of NaOH concentrations and different types of detergents. Our data provide useful information for increasing the solubility of glandless cottonseed protein for developing acidic juices and drink and suggest that the food-compatible ethyl lauroyl arginate may be used to improve glandless cottonseed protein isolate for food purposes.

Technical Abstract: Cottonseed is classified as glanded or glandless depending on gossypol glands. The toxic gossypol in glanded seed limits this vast protein resource to use primarily for feeding ruminants. Glandless seed may be useful as a food and feed source due to trace levels of gossypol. However, low solubility of seed protein is a major factor affecting its food and beverage applications. The current objective was to improve the solubility of protein isolate from glandless cottonseed. Protein isolate (91.71% of protein of weight basis) was obtained from glandless cottonseed by NaOH solubilization and precipitation with HCl neutralization. The protein was treated with various buffers with pH 2-10.6, a range of NaOH concentrations and different types of detergents. Protein isolate had the highest solubility at pH 2 and pH 10-10.6, and the lowest solubility at pH 6. Protein solubility was significantly (p = 0.05) increased by 0.01-1 N NaOH and at a maximum with 0.1 N NaOH. Most detergents especially cationic detergents (CTAB and ethyl lauroyl arginate) increased the solubility of the protein isolate but anionic detergents (deoxycholic acid and SDS) decreased the solubility. The order of solubility was CTAB > ethyl lauroyl arginate > BRIJ 35 > Triton X-100 > NP40 > CHAPS > Tween-20 > Tween-80 > Water > DMSO > deoxycholic acid > SDS. The protein solubility was significantly (p = 0.05) increased by temperature change from 22 to 37°C and by protein size reduction. SDS-PAGE analyses confirmed the effects of various treatments on protein solubility and revealed that high molecular mass polypeptide were extracted by alkali buffers and cationic detergents. Our data provide useful information for increasing the solubility of glandless cottonseed protein for developing acidic juices and drink and suggest that the food-compatible ethyl lauroyl arginate may be used to improve glandless cottonseed protein isolate for food purposes.