Effect of exogenous metal ions and mechanical stress on rice processed in thermal-solid enzymatic reaction system related to further alcoholic fermentation efficiency

Publication date: 1 February 2018
Source:Food Chemistry, Volume 240
Author(s): Enbo Xu, Zhengzong Wu, Aiquan Jiao, Zhengyu Jin
Metal-rich thermal-solid enzymatic processing of rice combined with yeast fermentation was investigated. 8 Metal ions were exogenously supplied at 0.05, 0.5 and 5mmol/100g (MG) rice prior to static high pressure enzymatic cooking (HPEC) and dynamic enzymatic extrusion cooking (EEC). Treated rice and its fermentation efficiency (FE) were characterized by rapid viscosity analyzer (RVA), UV–Vis, FT-IR and atomic absorption spectrophotometer (AAS). The optimum pH range of enzyme in solid system (>4.9) was broader than in a liquid system (>5.5). Cations decreased enzymatic activity in HPEC probably due to metal-induced aggregation of rice matrix with reduced reacting area as well as strengthened structure of starch/polysaccharides modified by metals. While using the EEC with mechanical mixing/shearing, relative activity was activated to 110 and 120% by Mg²⁺ (0.05–0.5MG) and Ca²⁺ (0.05–5MG), respectively. Furthermore, the effectiveness of residual ions to promote further FE was found to follow the order: Ca²⁺>K⁺>Zn²⁺>Mg²⁺>Mn²⁺>Na⁺≈Control>Fe²⁺>Cu²⁺, individually.



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