Integration of ultrasonic treatment in biorefinery of tea residue: protein structural characteristics and functionality, and the generation of by-products

摘要

The effect of integrating ultrasonic pretreatment with ethanol and Viscozyme in the alkaline extraction of protein from tea residue and the generation of possible by-products such as polyphenols and galacturonic acid was assessed. Four extraction pathways: ethanol, Viscozyme, ultrasound (EVU); water, Viscozyme, ultrasound (WVU); ethanol, water, ultrasound (EWU); and ethanol, Viscozyme, heat (EVH) were employed. EVU pretreatment together with alkaline extraction resulted in the highest protein recovery yield of 80.95% with a purification factor of 8.5. EVU enhanced the functionality of extracted proteins in terms of solubility, foam capacity and stability, and emulsion capacity and stability. Surface hydrophobicity of EVU extracted proteins increased compared to the other treatments. There was an increase in free sulfhydryl and a decrease in disulfide bond contents in all the treatments except EVH. Analysis of Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, non-protein nitrogen content and amino acid content revealed slight modification in the protein advance structure in terms of pretreatment, however, the main peptide chain and amino acid composition were not altered. Yield of 79.25 +/- 0.75, 54.7 +/- 0.98, and 116.50 +/- 6.36mg/g of polyphenols, galacturonic acid, and total sugars were respectively extracted along the extraction protocol as by-products.