Hydrophobicity, solubility, and emulsifying properties of soy protein peptides prepared by papain modification and ultrafiltration

Abstract

Peptide size control is important for obtaining desirable functional properties so that these peptides can be better utilized. Proteolytic enzymatic modification of soy protein isolates (SPI), followed by ultrafiltration, is an effective way to fractionate these proteins into peptides with controlled molecular size. SPI was predenatured by mild alkali at pH 10 and heated at 50°C for 1 h prior to partial hydrolysis by papain at pH 7.0 and 38°C for 10, 30, and 60 min (PMSPI10, PMSPI30, and PMSPI60). The hydrolysate PMSPI60 was further fractionated by ultrafiltration with a stirred cell and disc membranes (100-, 50-, and 20-kDa molecular weight cut-off) into one retentate (R100) and three permeates (P100, P50, and P20). Molecular weight distribution, surface hydrophobicity (S 0 ), protein solubility (PS), emulsifying activity index (EAI), and emulsion stability index (ESI) of the control SPI (without added papain), hydrolysates, and ultrafiltrates were investigated. Significant increases (P < 0.001) in S 0 , PS, EAI, and ESI were observed in the hydrolysates. Peptides in the permeates had higher PS and EAI but lower S 0 than the peptides in the retentate and hydrolysate. Soy protein peptides that were prepared from SPI by papain modification and ultrafiltration had lower molecular weight, higher solubility, and higher emulsifying properties. They could find use in products that require these properties, especially in the cosmetic and health food industries. JAOCS 75, 845-850 (1998).Proteolytic enzyme modification of proteins is an effective way to improve their functionality. The peptides produced by partial proteolysis of proteins have smaller molecular size and less secondary structure than the original proteins. They contribute to increased solubility, decreased viscosity, and significant changes in the foaming, gelling, and emulsifying properties when compared with those of the original proteins (1). To obtain desirable functional properties in soy protein hydrolysates, hydrolysis must be carried out under strictly controlled conditions to a specified (generally low) degree of hydrolysis (2). A limited degree of hydrolysis usually improves the emulsifying and foaming capacities, whereas excessive hydrolysis often causes loss of some of these functionalities (3). Therefore, peptide size control is essential if optimal and reproducible changes in functional properties are to be achieved (1).Ultrafiltration has been successfully used to separate proteins (peptides) from salts and sugar and to fractionate proteins (peptides) from each other (4). Partial hydrolysis of soy protein isolates (SPI) (5-9) generates soy protein peptides with different molecular weight distributions that can be separated with ultrafiltration membranes of different pore sizes.To understand the basis of peptide functionality, it is essential to know the fundamental properties of the peptide, including protein surface hydrophobicity, solubility, and emulsifying properties. This study investigated these fundamental properties of soy protein pep...

Improvement of techno-functional properties of edible insect protein from migratory locust by enzymatic hydrolysis

“…Enzymatic hydrolysis with Neutrase (Neu2) could not achieve any improvement of the EA in the tested pH range, while treatments including exoproteases (Fla2, OS2, TS2) significantly enhanced the EA at pH 5 and/or pH 7 to a maximum of 40% (pH 5) and 54% (pH 7). The increased emulsifying activity may be due to the decomposition of large protein molecules and the increased surface hydrophobicity by the exposure of previously buried hydrophobic groups [60]. An increase in emulsifying capacity was similarly found after comparable hydrolysis treatments of tropical banded crickets [33].…”

Effects of caseinate deamidation on transglutaminase-induced glucosamine conjugation and cross-linking as well as properties of the treated caseinates

“…Decreased EAI of the cross-linked proteins was mainly due to the formation of protein polymers of lower flexibility (Tang, Sun, Yin, & Ma, 2008). Surface hydrophobicity was also important to protein's emulsifying activity, as those hydrophobic residues would connect oil phase in oil-water emulsion (Wu, Hettiarachchy, & Qi, 1998). Caseinate was not protein polymers (Figure 1) but had the highest surface hydrophobicity than other three caseinates (Table 2) and thus behaved the highest EAI.…”

Protein-rich beverage developed using non-GM soybean (R08-4004) and evaluated for sensory acceptance and shelf-life

“…Bitterness masking study using Box-Behnken statistical design A Box-Behnken design (BBD) from JMP Pro 12.0 (at P value \0.05) was used to minimize the surface hydrophobicity (S 0 ) of SPH solution containing BB, MA, and stevia since the bitterness of proteins is directly proportional to their S 0 values (Wu et al 1998). The concentration of BB, MA, and Stevia in SPH solution were selected as independent variables (coded: X 1 , X 2 , and X 3 respectively) and incorporated in the BBD with S 0 as the dependent variable (Y).…”

“…Optimization to minimize surface hydrophobicity Box-Behnken design was used to find the optimal combination of BB (X 1 ), MA (X 2 ), and Stevia (X 3 ) for minimizing S 0 which is directly proportional to lowering bitterness (Wu et al 1998), particularly in preparing a mixed-berry flavored drink. The experimental values of S 0 were fitted into a full quadratic second-order polynomial equation.…”

“…Clarity is a challenge when formulating high-protein drinks since insolubility of native protein isolate is undesirable to consumers (Cho et al 2008). Previous research has shown that hydrolysates prepared from soy protein have better solubility and applicability in high protein products (Wu et al 1998;Lee 2011;Nguyen et al 2016;Meinlschmidt et al 2016). In addition, interest in protein hydrolysate incorporation in nutritional products has been increasing due to their effective digestion and faster gastrointestinal absorption compared to intact protein or free amino acids (Sun 2011).…”