Effect of alkali concentration on functionality, lysinoalanine formation, and structural characteristics of tea residue proteins

Abstract

The effect of varying sodium hydroxide concentration on functionality, structural characteristics, and the generation of lysinoalanine from tea protein extraction was explored. The results indicated that increasing alkali molarity from 0.0125 to 0.150 M resulted in an increase in protein yield, solubility, foam capacity, and stability up to 0.1 M, which declined further with an increase in the alkali concentration. Surface hydrophobicity, thiol, and disulfide contents reached a maximum at 0.075 M and continued to decline afterward. The effect of alkaline concentration on lysinoalanine (LAL) formation showed an increase from 6.00 ± 0.32 g/kg at 0.1 M to 29.43 ± 1.10 g/kg at 0.125 M followed by a decline to 7.37 ± 0.01 g/kg at 0.15 M. There was a significant (p < .05) reduction in Cys and Lys contents as alkali concentration increased. The use of alkali in extracting protein from tea and other plant sources should be monitored as higher alkali concentration may pose a nutritional concern. Practical applications Extraction of protein from plant sources is most often facilitated by use of alkali. However, the adverse effect of use of alkali is not considered in most cases. The use of sonication, ethanol, and Viscozyme pretreatments coupled with varying alkali concentration was adopted to extract proteins from tea residue and the generation of lysinoalanine, a toxic substance was quantified. The use of alkali at higher concentrations could pose a nutritional concern as it caused an increase in lysinoalanine content. Improved protein yield and purity can be achieved at moderately lower alkali concentrations.

Inhibition Effect of Ultrasound on the Formation of Lysinoalanine in Rapeseed Protein Isolates during pH Shift Treatment

“…Recently, some researches have carried out some investigation on the formation and inhibition of LAL. Ayim 15 reported that the content of LAL reached a maximum (29.43 ± 1.10 g/kg) at 0.125 M of the alkali concentration and, then, continued to decrease afterward. Karayiannis 13 revealed that the LAL content of different types of proteins was changed under different temperature and pH treatment conditions.…”

Ultrasound‐assisted reverse micelle extraction and characterization of tea protein from tea residue

“…For UARME, 0.10 g mL −1 tea crude protein was first mixed with CTAB-Tween 80 reverse microemulsion. The other conditions were as follows: ultrasonic power (200, 250, 300, 350, 400 W); KCl concentration (0.05, 0.10, 0.15, 0.20, 0.25 mol L −1 ); pH (6)(7)(8)(9)(10); extraction time (20,40,60, 80, 100 min); extraction temperature (25, 35, 45, 55, 65 °C). The extraction liquid was centrifuged at 4000 rpm for 20 min to isolate the protein.…”

“…[3][4][5] In general, the common methods of tea protein extraction are alkali, enzymatic and compound methods. 2,[6][7][8][9] The extraction yield of tea protein extracted by the alkali method was high, 9,10 but the high concentration of alkali can change the functional properties of protein, 11 causing the loss of nutrients and producing a large quantity of waste water. Compared with the alkali method, the conditions of protease extraction are mild, which can retain more nutritional value of protein, and the process of enzymatic hydrolysis extraction is easy to control.…”

“…In general, the common methods of tea protein extraction are alkali, enzymatic and compound methods 2,6‐9 . The extraction yield of tea protein extracted by the alkali method was high, 9,10 but the high concentration of alkali can change the functional properties of protein, 11 causing the loss of nutrients and producing a large quantity of waste water.…”