Kinetic Study of Non-enzymatic Browning of Physalis pubescens L. during Fermentation
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Abstract:
Physalis pubescens L. was used as the raw material and fermentations were carried out at 25 ℃, 30 ℃, and 37 ℃ with inoculation of both yeast and Lactobacillus plantarum. The changes in the non-enzymatic browning indices, -the content of total polyphenols, reducing sugar, vitamin C (Vc), 5-hydroxymethylfurfural (5-HMF), and amino acid nitrogen, browning degree (BD), and the color difference (L*, a*, b*, ?E)-during the fermentation were studied. The zero-order, first-order, and combined kinetic models were employed to fit the data. The results indicated that for the fermentations at 25 ℃, 30 ℃, and 37 ℃, the combined kinetic model was better for describing the dynamic changes of all indices, including the content of 5-HMF, reducing sugar, Vc, total polyphenols, and amino acid nitrogen, BD, and ?E, than the other two models. Furthermore, regression analysis showed that 5-HMF content and BD-the two important quality indices-had a very good linear relationship during the fermentation, which indicated that BD could be predicated by the 5-HMF content at the corresponding temperature. Meanwhile, the activation energies of 5-HMF and non-enzymatic browning material were 36.299 kJ/mol and 12.287 kJ/mol, respectively, which showed that the reaction rate of non-enzymatic browning was very fast and could easily occur during the fermentation of Physalis pubescens L.
