| The use of soy proteins has been of increased interest, primarily attributed to its steady supply, high nutritional and low cost. However, the poor functional properties have limited the application of soy protein isolates (SPI) in food industry. Effects of two physical pre-treatment, twin-screw extrusion and power ultrasound, on the enzymatic hydrolysis and hydrolysates functional properties of SPI have been investigated. Various physicochemical properties, surface properties and secondary structural of modified SPI have also been studied in relation to DH and functional properties. The aim of this paper was to explore new methods for functionality modification of soy proteins, and by study the relationship between"processing method structure characteristics ? good functionalities", the underpinning mechanisms of improved functionalities for modified SPI can be clarified, which can give academic and practical guide for the processing of soy protein product.Effects of extrusion pre-treatment with different temperature (120℃, 140℃,160℃) on the enzymatic hydrolysis and functional properties of soy protein isolates (SPI) have been investigated. Results showed that comparing with SPI, the accessibility of the different extrusion pre-treated SPI (ESPI-120?160℃) was improved marked, with the ESPI-140℃showed the best performance. Combined modification of extrusion-enzymatic hydrolysis can markedly improve the protein recovery (PR) of SPI, which showed a much better effect than that of enzymatic hydrolysis alone. ESPIH-140℃-Pan (ESPI hydrolysate-140℃-Pan) had a PR of ca. 90% in the range of DH=8.0–10.0%, and exhibited a stable nitrogen solubility index (NSI) value among pH=3?11. The highest PR of ESPIH-140℃-Pap was 80.6%, but the NSI will decrease markedly around iso-electric point (pH=4.5). Combined modification of extrusion-enzymatic hydrolysis can not improve the heat-induced gelation properties of SPI. In this paper, the emulsifier concentration selected to make emulsions was set to be 1.6% (w/v), and the emulsion formed by SPI at this concentration had a large mean diameter (d43≈30.9μm). Extrusion-Pan hydrolysis can marked improved the emulsifying capability of SPI, with much better effect than that of enzymatic hydrolysis alone. Emulsions formed by ESPIH-140℃-Pan with DH=8.0?9.1% showed a smallest d43 (2.0μm) among all the sample emulsions. However, Extrusion-Pap hydrolysis can not improve the emulsifying capability of SPI.Extrusion pre-treatment caused a marked improvement in the accessibility of SPI to Pan-hydrolysis, resulting in changes in degree of hydrolysis (DH), protein solubility (PS), surface hydrophobicity (H0) and molecular weight distributions (MWD) for ESPIH-140℃-Pan. It was observed that emulsion systems formed by control SPI or SPIH-Pan were unstable over a quiescent storage period of 21days, due to bridging flocculation and creaming. However, ESPIH-140℃-Pan-9.1% was capable of producing a very fine emulsion (d43 = 2.01μm) which remained stable over a long term quiescent storage. As compared with control SPI and SPIH-Pan-1.0%, ESPIH-140℃-Pan-9.1% appeared to be less surface active, but had a much higher Fads (67.6%) and a significantly lowerГsat (2.8 mg/m2). The |ζ|-potential of all SPIH-Pan and ESPIH-140℃-Pan were larger than 25 mV, which showed substantial electrostatic repulsion. It was suggested that significantly increased protein solubility and molecular flexibility could be the main reasons for the greatly improved emulsifying capability of ESPIH-140℃-Pan-9.1%.Effects of ultrasound pre-treatment with different power (200W, 400W, 600W) on the enzymatic hydrolysis and functional properties of SPI have been investigated. Results showed that comparing with SPI, the accessibility of the different ultrasound pre-treated SPI (USPI-200?600W) was improved marked, with the USPI-400W showed the best performance. Combined modification of ultrasound-enzymatic hydrolysis can markedly improve the PR of SPI, which showed a better effect than that of enzymatic hydrolysis alone. USPIH-400W-Pan-11.8% and USPIH-400W-Pap-2.9% had PR of 84.7% and 86.1% respectively. Their NSI increased slightly in basic conditions but decreased markedly at acidic conditions. The iso-electric point of USPIH-400W-Pap-2.9% showed a shift to pH 3?4. Combined modification of Ultrasound-enzymatic hydrolysis exhibited a equivalent improvement on heat-induced gelation properties of SPI to that of enzymatic hydrolysis alone. Ultrasound-enzymatic hydrolysis can marked improved the emulsifying capability of SPI, with much better effect than that of enzymatic hydrolysis alone. Emulsions formed by USPIH-400W-Pap-1.3% showed a smallest d43 (7.2μm) among all the USPIH emulsions.Emulsion formed by SPIH-Pap became unstable over a quiescent storage of 21 days, due to bridging flocculation and creaming. In contrast, USPIH-400W-Pap exhibited much better emulsifying capability and creaming stability under similar conditions. And as compared with control SPI and SPIH-Pap-0.6%, USPIH-400W-Pap-1.3% was capable of forming stable emulsions with small droplet sizes (d43 = 1.8μm) and at a much lower protein concentration (3.0% w/v). The |ζ|-potential of all SPI-Pap and USPIH-400W-Pap were larger than 25 mV, which showed substantial electrostatic repulsion. After ultrasound pre-treatment, the accessibility ofα-7S and A-11S was improved, and the enzymatic hydrolysis of USPI-400W became fast and harmonious. In some DH range, not only USPIH-400W-Pap had good protein solubility, but also had high H0, which indicated that a lot of surface active proteins or peptides were created. As a result, emulsifying capability was improved.
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