Physicochemical And Cholesterol-lowering Properties Of Soy Peptides

The main objective of this research was to explore the possibility of hydrophobic lowmolecular weight peptides in lowering cholesterol as well as their functional properties. Soyprotein isolate was enzymatically hydrolyzed to 15.44% degree of hydrolysis (DH) usingalcalase 2.4L (EC 3.21.62) enzyme. DH was monitored by pH-stat technique and the enzymeinactivated to pH 4 using 4M HCl. Its hydrolysate was fractionated with 60, 70 and 80 percentethanol concentrations. The different ethanol concentrations yielded 87.04%, 83.87% and77.74% ethanol-soluble peptides, and 9.50%, 13.37% and 17.76% of their correspondingprecipitates, with increase in ethanol concentration. The ethanol soluble peptides(supernatants) had low proportions of hydrophilic amino acids (~34 % w/w total amino acids)to hydrophobic amino acids (~55% w/w total amino acids) whereas the insoluble(precipitates) had high proportions of hydrophilic amino acids (~80% w/w total amino acids)to hydrophobic amino acids (~12% w/w total amino acids). In both cases, the proportionsincreased with increase in alcohol concentration. The supernatants had higher amounts ofessential amino acids, 36.77 – 42.42% than the precipitated ones, 33.57 - 35.94%. The molecular weight (Mw) profiles of the fractions were characterized by HPLC.The supernatants comprised of more than 85% low molecular weight species of less than 2000Da and less than 10% of Mw >2000 Da. Mw species greater than 2000 Da were mostlyabundant in precipitates (49 - 64%). With increase in ethanol concentration, low molecularweight species increased while high molecular ones decreased in supernatants. Theprecipitates showed a decrease in high Mw species and an increase in low ones as ethanolconcentration increased, with almost equal proportions at 80% ethanol fractionation. An in vivo test of cholesterol-lowering potency of supernatants with soy protein as areference was done on Kunming mice. Cholesterol lowering effect was not observed at 5%diet concentrations whereas at 15 % diet concentration, the supernatants showed a slightlowering (p < 0.05) of cholesterol with a high effect at 70 and 80% ethanol concentrations.Soy protein resulted in a marked difference with respect to supernatants. However, differencesamong means of all samples irrespective of concentrations showed no significant differences(p < 0.05) among samples. High density lipoprotein (HDL) and triglyceride concentrations didnot differ much among samples at both concentrations (p < 0.05). The supernatants at a high diet dosage showed a decreased amounts of low-densitylipoproteins (LDL) with respect to control (hypercholesterolemic diet). At 5% concentration,only an 80% ethanol fraction exhibited a lower LDL concentration.The protein content of the fractions irrespective of their alcohol fractionation concentrationwere 20-25 % lower than the parent material hence having a fairly high protein content. vM.Sc DissertationEthanol fractions had low moisture contents with respect to soy protein. Compared to soyprotein isolate, addition of base during hydrolysis increased the ash contents in ethanolfractions by approximately 5-fold. Solubility, emulsifying properties and oil holding capacity were studied. Bothprecipitates and supernatants were soluble at all pH values including the isoelectric pH of soyproteins. A slight significant difference (p < 0.05) as pH increased was observed mainly withthe precipitates. Oil holding capacity of the fractions was poor in reference to soy proteinisolate. Poor emulsion properties of supernatants were exhibited by their low emulsificationactivity index (<20) -except supernatant at 80% concentration (pH 8.5) -and stability atdifferent salt concentrations (distilled water and 0.1M NaCL). Increase in pH increased theemulsification activity index in soy protein except at pH 4.5 whereas the supernatants werenot greatly affected. This trend correlated with the oil co...