Improvement of protein extraction from sunflower meal using ultrafiltration and isoelectric precipitation techniques

The objective of the research was to add value to deoiled sunflower meal by fractionation into functionalized food ingredients. The experiments were carried out with sunflower meal obtained after husking and deoiling by extraction with supercritical carbon dioxide. Two fractions of interest were analyzed 1. sunflower protein-rich fraction with > 75% protein content and 2. sunflower fiber concentrate, both reduced in polyphenols. The reduction in the formation of colored pigments was achieved by depleting chlorogenic acid through acidic pretreatment with the addition of sodium bisulfite. The extracts were further processed using membrane filtration technologies. Thus, the molecular weight limit of the membrane modules, as well as pH and oxygen exclusion under nitrogen gassing and degassing of the water used, were varied and the effect of ultrafiltration and combinations with diafiltration was optimized. The products obtained were compared to the ones produced after classical isoelectric protein precipitation process. The protein-rich fraction and fiber concentrate were characterized for protein content, amino acid profile, chemical score, protein digestibility, dietary fiber and, only for fiber-rich fraction, also probiotic properties. In conclusion, using sodium bisulfite, an exceptional light color was achieved for both, the protein-rich fraction and fiber-rich concentrate (L* = 81 and 84). Direct extraction at pH 7.3 and subsequent ultrafiltration resulted in promising protein-rich fractions with protein yield of 21%, protein content of 73% and protein solubility of 69%. The protein-rich fraction showed adequate balance of essential amino acids, except for the amino acid lysine. The chemical score indicated lysine as being the limiting amino acid (CS= 0,6). In vitro digestibility showed high values for both samples (above 83.13%) where the fiber concentrate had lower protein digestibility. The acidic pretreatment using sodium bisulfite was effective in the overall functionalization of the protein-rich fraction obtained by ultrafiltration (protein content: 87%) in terms of protein solubility (38%), emulsifying capacity (590 mL/g), and brightness (L* = 81). This highlights the advantage of aqueous fractionation to obtain food ingredients with specific properties, which can be used for targeted food applications.