199 Freeze-thaw stability of oil-in-water emulsions stabilized by soy protein isolate-dextran conjugates
This paper, written by researchers from Northeast Agricultural University and others, discusses Freeze-thaw stability of oil-in-water emulsions stabilized by soy protein isolate-dextran conjugates. The paper is published in an important journal < LWT - Food Science and Technology >. IF：3.129.
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The soy protein isolate-dextran (SPI-D) conjugates were prepared by ultrasound (power output 500 W for 40 min) and microwave (power output 800Wfor 2 min) assisted glycosylation to improve the freezethaw stability of soy protein isolate stabilized oil-in-water (o/w) emulsions. Fourier transform infrared and fluorescence emission spectroscopy analyses confirmed that covalent bonds were formed between soy protein isolate (SPI) and dextran molecules through the Maillard reaction. The stability of SPI, SPIþD mixture, ultrasound SPI-D conjugates (SPI-DU) and microwave SPI-D conjugates (SPI-DM) emulsions subjected to from one to three freeze-thaw cycles was investigated. In comparison with SPI and SPIþD emulsions, SPI-DU and SPI-DM emulsions exhibited smaller creaming index, oiling off, droplet diameters, flocculation degree (FD) and coalescence degree (CD) after each freeze-thaw cycle. In addition, the zeta potential and specific surface area (SSA) were greater. Appearance and microstructure indicated that SPIDU and SPI-DM emulsions exhibited a relative stable state after three freeze-thaw cycles.
This study evaluated the freeze-thawstability of SPI, SPIþD, SPIDU and SPI-DM emulsions by creaming index, oiling off, appearance, particle size, flocculation degree, coalescence degree, specific surface area, zeta potential and microstructure. Results showed that the addition of dextran slightly improved its freeze-thaw stability. SPI-DU and SPI-DM emulsions were the most stable subjected to three freeze-thaw cycles, with lower creaming index, oiling off, droplet diameter, flocculation degree and coalescence degree and higher zeta potential, specific surface area compared with SPI and SPIþD emulsions. The ultrasound and microwave assisted glycosylation has proven to be a useful method for the preparation of SPI with high freeze-thaw stability. This method provides a theoretical basis and technical guidance for special soy protein isolate which is more suitable for frozen foods.
SPI (4 g/100 mL) and dextran (6 g/100 mL) were dispersed in phosphate buffer solution (0.01 M, pH 8.0), stirred at room temperature for 2 h, then stored overnight at 4 C to ensure a complete hydration protein and dextran. Then, the dispersions were stirred until reaching room temperature. An ultrasound processor (XH- 2008D, XiangHu Science and Technology Development Co.,Ltd., Beijing, China) equipped with an 8 mm diameter titanium probe was used to treat 100 mL dispersions in a flat bottom conical flask which was immersed in a water bath device at 80 C. Sample was treated at 25 kHz at the power output 500 W for 40 min. A flat bottom conical flask contained 100 mL dispersions was placed in a microwave oven (KD23B-DA, Midea Group, Guangdong, China) and irradiated at 2450 MHz, 800 W power output for 2 min. The dispersions were cooled rapidly in an ice-water for 5 min to stop the reaction, and then the SPIþD mixture, ultrasound and microwave Maillard reaction dispersions were dialysed at 4 C for 24 h. The SPIþD (as the control), SPI-DU and SPI-DM powders were obtained by freeze-drying and stored at 18 C until analyzed.