Effects of Cysteine on Physicochemical Properties of High-Moisture Extrudates Prepared from Plant Protein

Abstract

The effects of cysteine addition (0%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%) on the physicochemical properties of plant-based extrudates by high-moisture extrusion were investigated. The texturization degree, rheological properties, hardness, springiness and chewiness of the extrudates significantly improved with the addition of cysteine (<0.15%). Analysis of the microstructure showed that the addition of cysteine (<0.15%) improved the formation of the fiber structure in the extrudates. Cysteine (<0.15%) promoted the formation of new disulfide bonds and non-covalent bonds by changing the disulfide bonds of protein molecules and enhanced the cross-linking degree between proteins. However, the excessive addition of cysteine (>0.15%) had a negative impact on the formation of fiber structure. Analysis of secondary structure suggested that the ordered β-sheet structures gradually converted to the disordered β-turn and random coil structures with the addition of cysteine (>0.15%). In addition, analysis of odor properties with the addition of cysteine using an electronic nose showed the difference in volatile components of the extrudates mainly existed in halides, hydrocarbons, sulfides and amines. On the whole, the addition of cysteine could improve the quality of plant-based extrudates.

Cysteine, sodium metabisulfite, and glutathione enhance crosslinking between proteins during high moisture meat analog extrusion processing and may improve the fibrousness of the products

“…In most cases, the addition of reductants initially caused an increase in hardness, which, especially for the inclusion of cysteine and sodium metabisulfite, and particularly at higher temperatures, turned into a stagnation or a decrease. A similar trend was also reported by Dai and An, 16 who included cysteine into a soy-wheat protein blend. For cysteine and sodium metabisulfite, samples obtained at the higher temperatures generally yielded harder products when small amounts were included; at higher inclusion levels, harder samples were obtained for the lower temperatures.…”

“…A decrease in product quality was observed for samples containing cysteine or sodium metabisulfite at levels higher than 5.0 g kg −1 , especially at higher temperatures. Specifically for cysteine, these levels were surprising as earlier studies conducted by Dai and An 16 and Peng et al 15 indicated that levels above 0.15% and 0.09%, respectively, had negative effects on the product. Possible reasons for the different concentrations are the use of other materials and different processing parameters.…”

“…Therefore, the results reject this hypothesis and suggest that reductants initiate or help with the exposure of deprotonated SH groups capable of crosslinking with those from other protein strands. 16 No specific trends were observed with regard to the different reductants and temperatures. However, relatively high standard deviations (not shown here) between the two extrusion replicates demonstrate the variability during extrusion processing.…”

“…Interestingly, levels at which a significant increase in AI was observed, were fairly high compared to results previously published. 15 Peng et al 15 and Dai and An 16 argue that fibrousness of pea and soy-wheat extrudates decreased above 0.09% and 0.15% cysteine inclusion. In the present study, however, concentrations of 2.5 g kg −1 cysteine and 5.0 g kg −1 sodium metabisulfite were required for a noteworthy rise in AI.…”

“…Reductants could potentially help by cleaving existing disulfide bonds and promoting intermolecular crosslinking. Peng et al 15 and Dai and An 16 included cysteine into HMMA prepared from pea protein and a soy-wheat protein blend, respectively. It was concluded by both teams that the addition of low cysteine levels (< 0.12-0.15%) helped to create a fibrous product structure by promoting the formation of intermolecular disulfide bonds.…”