Bin Hu,Qiang Lu,Xiao-yan Jiang,Xiao-chen Dong,Min-shu Cui,Chang-qing Dong,Yong-ping Yang
Fast pyrolysis of glucose/cellulose will produce abundant 1,6-anhydro-β-d-glucopyranose (known as levoglucosan, LG) as the predominant anhydrosugar product, together with certain amounts of other anhydrosugars, mainly including 1,6-anhydro-β-d-glucofuranose (AGF), 1,4:3,6-dianhydro-α-d-glucopyranose (DGP), 1,5-anhydro-4-deoxy-d-glycero-hex-1-en-3-ulose (APP), 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one (LAC). The formation mechanisms of the latter four anhydrosugar products are not well-known at present. Substantiated by analytical pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) experiments, quantum chemistry calculations are employed to give a deep insight into their formation mechanisms in this study. The anomeric effect of glucopyranose has a distinct effect to their formation. DGP is mainly derived from α-d-glucopyranose which plays a vital role in the formation of 1,4-acetal ring. On the contrary, APP and LAC can merely derive from β-d-glucopyranose due to the dehydration at 1-OH + 2-H site. APP is important but not necessary to form LAC, and their formation pathways also compete with each other. Moreover, AGF is not influenced by the anomeric effect of the two anomers, because its formation relies on the acyclic d-glucose.
Non-enzymatic browning of vinegar soaked-soybean residual solution was investigated using a model solution. A glycine-fructose-gallic acid model system was proposed by analyzing reducing sugars, amino acids, total phenolics, and pH value of the vinegar soaked-soybean residual solution. Based on the proposed model, the kinetics of 5-hydroxymethylfurfural (5-HMF) formation was also studied. The results showed that Maillard reaction and sugar pyrolysis might be the accurate mechanisms of non-enzymatic browning in vinegar soaked-soybean residual solution. The formation of 5-HMF in the model solution exhibited characteristics of the first-order kinetic model at temperature from 60 to 140 °C. The frequency constant k f was 450.65 /h, and the apparent activation energy E a was 20.15 kJ/mol. Acetic acid, Fe 2+ , and Fe 3+ significantly enhanced the browning rate and 5-HMF formation; whereas Ca 2+ , Mg 2+ , Na + , glucose oxidase, and H 2 O 2 inhibited the browning rate.
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