A superior approach for production of protein isolates from de-oiled soy meal and its comparison with conventional method

Protein isolates were prepared from de-oiled soy meal by a superior approach, i.e. biological precipitation using two lactic acid bacterial strains and a conventional acid precipitation method. The isolates were characterised for physico-chemical, functional, anti-nutritional and structural properties and compared with isolates prepared using the conventional method. The purity, yield, lightness, whiteness index and degree of hydrolysis were higher (P = 0.05) for biologically precipitated soy protein isolates (BPSPIs). The functional properties of BPSPI samples were also superior. BPSPIs showed 1.85 mg g(-1) and 1.44 TIU mL(-1), whereas acid-precipitated soy protein isolates (APSPIs) showed 3.65 mg g(-1) and 3.16 TIU mL(-1) of phytic acid and trypsin inhibition activity respectively. A sharp bend in the wavelength ranges from 3700 to 3900 cm(-1) was observed in BPSPI samples, which depicts structural changes owing to fermentation by lactic acid bacteria. Two characteristic peaks at 2O = 20 degrees and 2O = 15 degrees were observed in both the samples; however, intensity and crystallinity were higher in BPSPIs. Hexagonal-shaped particles of different sizes were displayed by field emission scanning electron microscopy images. The results thus confirm that the soy protein samples prepared through the biological precipitation process had better properties over conventionally prepared soy protein samples, which can be further used as novel ingredients in protein-based functional products.