Emulsifying properties and antioxidant activity of soy protein isolate conjugated with tea polyphenol extracts
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ORIGINAL ARTICLE
Emulsifying properties and antioxidant activity of soy protein isolate conjugated with tea polyphenol extracts Anwika Utami Putri Djuardi1 • Nancy Dewi Yuliana2 • Masahiro Ogawa3 Takashi Akazawa3 • Maggy Thenawidjaja Suhartono2
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Revised: 23 March 2020 / Accepted: 1 April 2020 Ó Association of Food Scientists & Technologists (India) 2020
Abstract Functional properties of proteins, such as emulsification, foam formation and antioxidant activity, can be improved by conjugating the proteins with phenolic substances. We reported here changes in the structural, physicochemical and functional properties of Soy Protein Isolate (SPI) after conjugation with phenolic substances in the green tea and black tea extracts. Conjugation of SPI with tea extracts were conducted using alkaline treatment (pH 9.0) followed by air exposure. The results showed that conjugation of SPI increased the protein molecular size and decreased the protein hydrophobicity. The hydrophobic decreasing effect by the treatment was larger with the black tea extract than by green tea extract. SPI-tea polyphenol conjugates significantly (p \ 0.05) increased the emulsifying ability of SPI up to 43% and the emulsifying stability of SPI up to 59%. SPI-tea polyphenol conjugates which was prepared using 0.75% (w/w SPI) green tea polyphenol extract showed the best emulsifying properties with strong repulsion forces between the droplets, smaller emulsion droplet size and lower polydispersity index of droplets size distribution. Although the conjugation product is still inferior to egg lecithin in emulsion stability, antioxidant activity of SPI was significantly (p \ 0.05) improved in a
& Maggy Thenawidjaja Suhartono [email protected] 1
Food Science Study Program, Graduate School of Bogor Agricultural University, Bogor, West Java 16680, Indonesia
2
Department of Food Science and Technology, Faculty of Agricultural Technology, Bogor Agricultural University, Bogor, West Java 16680, Indonesia
3
Department of Applied Biological Science, Kagawa University, 2393, Ikenobe, Miki-cho, Kita-gun, Kagawa, Japan
concentration dependant manner. SPI-black tea polyphenol conjugates showed greater antioxidant activity than SPIgreen tea polyphenol conjugate. The present study shows the feasibility and benefits of the use of SPI-tea polyphenol conjugates as a food emulsifier. Keywords Soy protein isolate Tea polyphenol Protein– polyphenol conjugate Emulsifying properties Antioxidant activity
Introduction The tendency to use vegan product as protein sources such as soy protein is increasing due to healthy reason, dietary preferences and food sensitivities. Soy bean is a multifaceted legume with enormous economic value; this protein source has been consumed for over 2000 years especially by the Asian, and nowadays are getting more popular among the Westerners as well. Therefore application of these protein in food industries tent to increase in the last decade. Soy protein isolate (SPI) contains approximately 90% of protein which has high dige
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