Chemical degradation and enzymatic degradation are the common methods for the preparation of oligosaccharides by polysaccharide degradation. The products prepared by chemical methods are often complicated and difficult to obtain oligosaccharides with a single degree of polymerization. The enzymatic method has become an important issue in recent years because of its high specificity and high uniformity of target products. In this study, the technological conditions for producing gellan oligosaccharides by acid hydrolysis were optimized first, and the optimum acid hydrolysis conditions were as follows: substrate concentration 0.5%, HCl concentration 0.5 mol/L, and hydrolysis for 3 h. A strategy for one-step production of gellan oligosaccharides by Pichia pastoris fermentation coupled with polysaccharides degradation was proposed. The results showed that the optimal fermentation conditions for gellan lyase were 20 g/L yeast powder, 1% methanol, and pH 6.0; the optimal enzymatic degradation conditions were 2 g/L gellan gum at the initial fermentation and hydrolysis for 96 h. Finally, the products of the two degradation methods were compared by Fourier transform infrared spectrometer (FTIR) and matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). Gellan oligosaccharides with polymerization degrees of 5, 8, and 12 were obtained after acid hydrolysis, and gellan oligosaccharide with a polymerization degree of four was obtained after enzymatic degradation. The structure of the acid hydrolysis product was not changed, and the CC could be observed in the enzymatic degradation product. This study provides a feasible way to prepare gellan oligosaccharides with a single degree of polymerization and explore their functional activities.
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