Structural, functional and proteomic differences of proteins extracted from white garlic and Laba garlic

Abstract

Protein is one of the main nutrients in garlic with multiple functions and healthy effects. The aim of this study was to investigate the effects of greening process on the functional and structural properties of garlic protein, and proteomic strategy was applied to analyze the changes of protein compositions as well as their activities. Results showed that the manufacturing process led to a smaller isoelectric point (pI) and larger particle size of garlic protein (Laba garlic protein, LP) compared to the unprocessed one (untreated white garlic protein, WP). Circular dichroism (CD) and fourier-transform infrared spectroscopy (FTIR) spectra showed that the dominant α-helix structure was lost and became random coil in LP. The surface hydrophobicity was also decreased after processing. Sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) revealed that molecular weight distributions of WP varied from 10 to 80 kDa but those of LP were in 10 to 25 kDa. In the functional property analysis, greening process resulted in poor emulsifying ability for WP at pH 7.2, but led to an increase in water holding capacity (WHC). The proteomic analysis indicated that WP had numerous kinds of proteins and the vital alliinase in WP was lost in LP, and only 6 types of proteins were reserved. The proteins in WP were presumably degraded into peptides in LP. This study firstly applied proteomic analysis to investigate the protein differences in garlic processing, and based on the significant properties difference, WP might be a promising agent for additives in food industry, while LP might be a potential source for bioactive peptides extraction and separation.