在食品中,磷酸、柠檬酸等酸味物质可催化葡萄糖、果糖等甜味物质转化为5-羟甲基糠醛(5-HMF)。本研究中,将糖酸混合溶液放于安瓿瓶中,采用油浴加热,三种反应温度分别为373 K、393 K、413 K,以HPLC测定了加热时间8 h内的糖酸体系中5-HMF浓度随着时间的变化;利用origin 8.0对数据进行拟合,建立动力学模型。最终发现无机三元酸磷酸的催化效率高于有机三元酸柠檬酸,果糖转化程度高于葡萄糖。在葡萄糖磷酸体系(GP)、葡萄糖柠檬酸体系(GL)、果糖磷酸体系(FP)、果糖柠檬酸体系(FL)中,5-HMF的浓度随着时间的延长呈直线上升,符合零级动力学模型。动力学分析得到四种反应体系的反应活化能(Ea)分别为109.16k J/mol、121.09 k J/mol、102.89 k J/mol、112.36 k J/mol,GP体系中Ea最高,FL体系中最低。在糖酸食品热加工过程中,磷酸、果糖的含量对食品中的5-HMF含量影响很大。
Levulinic acid(LA) has been identified as a promising green,biomass derived platform chemical.Response surface analysis(RSA) with a four-factor-five-level central composite design(CCD) was applied to optimize the hydrolysis conditions for the conversion of bamboo(Phyllostachys Praecox f.preveynalis) shoot shell(BSS) to LA catalyzed with ionic liquid [C4mim]HSO4.The effects of four main reaction parameters including temperature,time,C[C4mim]HSO4(initial [C4mim]HSO4 concentration) and XBSS(initial BSS intake) on the hydrolysis reaction for yield of LA were analyzed.A quadratic equation model for yield of LA was established and fitted to the data with an R2 of 0.9868,and effects of main factors and their corresponding relationships were obtained with RSA.Model validation and results of CCD showed good correspondence between actual and predicted values.The analysis of variance(ANOVA) of the results indicated that the yield of LA in the range studied was significantly(P<0.05) affected by the four factors.The optimized reaction conditions were as follows:temperature of 145 ℃,time of 103.8 min,C[C4mim]HSO4 of 0.9 mol.L-1 and XBSS of 2.04%(by mass),respectively.A high yield [(71±0.41)%(by mol),triplicate experiment] was obtained at the optimum conditions of temperature of 145 ℃,time of 104 min,C[C4mim]HSO4 of 0.9 mol.L-1 and XBSS of 2%(by mass),which obtained from the real experiments,concurred with the model prediction [73.8%(by mol) based on available C6 sugars in BSS or 17.9%(by mass) based on the mass of BSS],indicating that the model was adequate for the hydrolysis process.
