Date

2022-2-11

Author

Zengin, Kübra

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Soy protein is a low-cost additive with high biological value, unique functional properties, and beneficial effects on health, and it is widely used in the food industry as an important ingredient. When the health and functional properties of soy protein are considered altogether, there are several benefits for consuming and using it in foods. High hydrostatic pressure (HHP) is a non-thermal novel processing technology that has been generally used to destroys vegetative cells, microorganisms and enzymes. Additionally, HHP treatment has an effect on protein structures, resulting changes in the functional properties of proteins. The aim of the study was to examine the effects of high hydrostatic pressure (HHP) treatment on functional properties of soy protein isolate (SPI). The experiments were carried out at different pressure parameters (300, 400 and 500 MPa) with a constant duration of 5 min at 25 oC and 40 oC. Also, the pH of the SPI samples was adjusted to pH 5 and pH 7 to evaluate the pH effect with HHP treatment on the functional properties of SPI prepared at 38% (w/v) concentration. Water holding capacity (WHC), solubility by Lowry method, emulsion activity, and viscosity of untreated and HHP-treated soy protein isolate were analyzed. Following that, characterization experiments including Fourier transform infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance (NMR) relaxometry were performed to determine the changes in secondary structure and hydration behavior of soy protein isolate (SPI), respectively. This study showed that HHP treatment significantly (p<0.05) decreased WHC compared to control, however there was no significant difference between WHC results of pH 5 and pH 7 (p>0.05). Moreover, HHP treatment significantly enhanced solubility of SPI at pH 7 compared to pH 5 and control, and also, at pH 5, the solubility of HHP-treated SPI at ambient temperature was significantly higher than that of SPI treated at 40 °C (p<0.05). Furthermore, although the emulsion activity results revealed no significant difference (p>0.05) between HHP-treated SPI at pH 7 and untreated SPI, providing the appropriate pressure increased emulsion activity at pH 5, but further increase in pressure resulted in reduced emulsion activity. Also, viscosity of SPI significantly reduced due to HHP treatment at pH 5 and pH 7 compared to control (p<0.05). In addition, FTIR results showed that HHP treatment caused remarkable changes in the secondary structure of SPI due to unfolding of protein. Moreover, HHP treatment had no influence on SPI hydration behavior at pH 7 (p>0.05), but T2 values at pH 5 at 40 °C were significantly much higher than those obtained for control and other treated SPI. In conclusion, the results of this study showed that HHP application could be a valuable alternative to modify and improve the functional properties of soy protein, which has an important role in novel product development.

Subject Keywords

Soy protein isolate (SPI), HHP, FTIR, NMR Relaxometry, functional properties

URI

https://hdl.handle.net/11511/96359

Collections

Graduate School of Natural and Applied Sciences, Thesis