Improvement of the Solubility of Protein Isolate from Glandless Cottonseed

Cottonseed is classified as glanded or glandless, depending on the gossypol glands. The toxic gossypol in glanded seed limits this vast protein resource primarily feeding ruminants. Glandless seeds may be useful as food and feed sources due to trace levels of gossypol. However, the low solubility of seed protein is a major factor affecting its food and beverage applications. The current objective was to improve the solubility of the protein isolate from glandless cottonseed. Protein isolate (91.71% of protein by weight) 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 10–10.6 and the lowest solubility at pH 6. Protein solubility was significantly (p ≤ 0.05) increased by 0.01–1 N NaOH, reaching 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 in the compounds 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 the temperature change from 22 to 37 °C and by protein size reduction. Our data provide useful results for increasing the solubility of glandless cottonseed protein for developing acidic juices and drinks and suggest that the food-compatible ethyl lauroyl arginate may be used to improve glandless cottonseed protein isolate for food purposes.