Optimization and characterization of fermented soyprotein isolate conjugated with pineapple peel extract

Abstract

Agro-industrial wastes are of great interest because they are significant natural resources for bioactive chemicals and sustainable biomaterials with added value. In this work, soy protein isolate (SPI) was extracted from soy sauce residue using an acid-alkali method and polyphenol extract was obtained from pineapple peels by ethanolic extraction. The results showed that protein isolate from soy sauce residue (sSPI) had the total phenolic and flavonoid contents of 15.27±0.47 and 12.78±1.66 mg/g extract whereas the lower amount was detected in the soy protein isolate commercial grade (cSPI) only at 4.23±0.11 and 1.16±0.38 mg/g extract, respectively. The total phenolic and flavonoid contents of pineapple peel were 9.80±0.11 and 3.81±0.16 mg/g extract. This study presented the changes of physicochemical and functional properties of SPI after conjugation with pineapple peel extract. SPI was conjugated with pineapple peel extract using an alkaline treatment (pH 9.0) and followed by air exposure. The conjugation of SPI with different concentrations of pineapple peel polyphenol showed a strong concentration-dependent manner of emulsifying properties. The SPI-pineapple peel polyphenol conjugates showed an improvement of antioxidant activity and protein solubility. The synthesis of SPI-pineapple peel polyphenol conjugate resulted in an increase of the emulsifying ability of the cSPI and sSPI from 9 and 8 m2/g to 24 and 16 m2/g, whereas the emulsifying stability of cSPI and sSPI was increased from 93% and 75% to 97% and 96%, respectively. The current research implies the feasibility and advantages of the usage of SPI-pineapple peel polyphenol conjugates as innovative materials for nutraceutical delivery and a functional ingredient in the food industry in accordance with the Bio-Circular-Green Economic Model of Thailand and the United Nations Sustainable Development Goal 12.

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