Protein Extraction from Mustard (B. juncea(L.) Czern) Meal using Thin Stillage

by Ratanapariyanuch, Kornsulee

Oilseeds may be processed to yield a number of potentially valuable compounds and fractions including oil, protein and small molecules. However, energy costs associated with industrial processing of oilseeds can be significant. For example, processes that use water to dissolve and separate materials are burdened with the costs associated with concentrating value-added products from dilute solutions. The ethanol industry produces large amounts of an aqueous solution called thin stillage that has little value and is used in animal feed. Thin stillage contains some of the necessary salts used in protein extraction but has a low pH. Protein extraction and protein isolate production is commonly conducted at higher pH. Waste alkali from biodiesel production has a high pH and can be used to adjust the pH of thin stillage to improve its ability to extract protein from oilseed meal. By combining the properties of the waste products of both the ethanol and the biodiesel industries, a complementary process is possible that may have greater economic potential than current practices in industry.

In this study, processes for protein extraction from mustard (Brassica juncea (L.) Czern.) meal using thin stillage from ethanol production and glycerol from biodiesel production were studied. The osmotic potential of thin stillage used in this research was lower than that of water, whereas both the density and the viscosity were higher. The pH was typically 3.7-3.8, and the total Kjeldahl nitrogen was approximately 0.080.10 %, w/w. Organic compounds identified in thin stillage were isopropanol, ethanol, lactic acid, 1,3-propanediol, acetic acid, succinic acid, glycerophosphorylcholine, betaine, glycerol and phenethyl alcohol. In addition, yeasts, bacteria and fungi were also found. Moreover, the salt types and their concentrations in thin stillage were predictable. The salt types present in thin stillage were CaCl2, NaCl, K2SO4, NaNO3, Mg(OH)2, Na2SO4 and KOH. A model thin stillage synthesized for the purposes of this research had components and chemical and physical properties comparable to those of thin stillage from ethanol production. Protein was extracted from ground, defatted meal using thin stillage at different pHs and salt concentrations. The results showed that pH and salt content affected protein extraction efficiency. However, no differences were found in the efficiency of extraction, SDS-PAGE profile, digestibility, lysine availability or amino acid composition of protein extracted with thin stillage, model thin stillage or sodium chloride solution. Moreover, extracted protein did not display significant hydrolysis. The results from peptide sequencing showed that napin and cruciferin were the most prevalent proteins in the extracted fractions. When increasing the scale of the extraction, the efficiency of protein extraction and the percentage of protein in the extracted protein were decreased. Protein recovery achieved with the complementary protocol was higher than that reported for a published protocol. Allyl isothiocyanate was found in protein extracts.