Mathematical modeling of maize starch liquefaction catalyzed by α-amylases from Bacillus licheniformis: effect of calcium, pH and temperature

Investigation of γ-polyglutamic acid production via asynchronous saccharification and fermentation of raw corn starch

Starch, a crucial raw material, has been extensively investigated for biotechnological applications. However, its application in γ-polyglutamic acid (γ-PGA) production remains unexplored. Based on γ-PGA output of Bacillus subtilis SCP010-1, a novel asynchronous saccharification and fermentation process for γ-PGA synthesis was implemented. The results revealed that a starch concentration of 20%, α-amylase dosage of 75 U/g, liquefaction temperature of 72℃, and γ-PGA yield of 36.31 g/L was achieved. At a glucoamylase dosage of 100 U/g, saccharification 38 h at 60℃, the yield of γ-PGA increased to 48.88 g/L. The contents of total sugar, glucose, maltose and oligosaccharide in saccharified liquid were determined. Through batch fermentation of saccharified liquid in fermentor, the γ-PGA output was elevated to 116.08 g/L. This study can offer a potential cost reduction of 40%, which can be a promising advancement in industrial γ-PGA production. Moreover, our approach can be applied in other starch-based fermentation industries.

Analysis of the action pattern of sequential α-amylases from B. stearothermophilus and B. amyloliquefaciens on highly concentrated soluble starch

Hydrolysis of highly concentrated soluble starch (60%, w/w) was performed using sequential α-amylases from Bacillus stearothermophilus (T, 0.2%, w/w) and Bacillus amyloliquefaciens (B, 0.1%, w/w) to identify their possible action patterns. We found that T reduced the average molecular weight (Mw) of soluble starch from 52,827 Da to 31,914 Da and significantly affected its branched chain length. Compared with soluble starch, the chains with DP 6-12 and DP ≥ 13 in the T samples were diminished by 46% and 96%, respectively. This resulted in an attenuation in the proportions of exterior and inner chains, as well as low iodine binding capacity of the hydrolysates. In contrast, a slower decrease in the average Mw of soluble starch occurred after TB incubation, and the level of DP 6-12 further lowered, causing a gradual decline in the iodine binding capacity of the hydrolysates. Gathered data revealed an unusual action pattern of sequential α-amylase treatment at high substrate concentrations. Bacillus stearothermophilus α-amylase exhibited more pronounced endo-hydrolysis of amylopectin, whereas the attack of Bacillus amyloliquefaciens α-amylase on the exterior chains was enhanced in amylopectin residues. These findings suggest that the synergy of various α-amylases is an effective strategy to promote the dextrinization of highly concentrated starch and finely modify the molecular structure of starch.

Modelling of icodextrin hydrolysis and kinetics during peritoneal dialysis

In peritoneal dialysis, ultrafiltration is achieved by adding an osmotic agent into the dialysis fluid. During an exchange with icodextrin-based solution, polysaccharide chains are degraded by α-amylase activity in dialysate, influencing its osmotic properties. We modelled water and solute removal taking into account degradation by α-amylase and absorption of icodextrin from the peritoneal cavity. Data from 16 h dwells with icodextrin-based solution in 11 patients (3 icodextrin-exposed, 8 icodextrin-naïve at the start of the study) on dialysate volume, dialysate concentrations of glucose, urea, creatinine and α-amylase, and dialysate and blood concentrations of seven molecular weight fractions of icodextrin were analysed. The three-pore model was extended to describe hydrolysis of icodextrin by α-amylase. The extended model accurately predicted kinetics of ultrafiltration, small solutes and icodextrin fractions in dialysate, indicating differences in degradation kinetics between icodextrin-naïve and icodextrin-exposed patients. In addition, the model provided information on the patterns of icodextrin degradation caused by α-amylase. Modelling of icodextrin kinetics using an extended three-pore model that takes into account absorption of icodextrin and changes in α-amylase activity in the dialysate provided accurate description of peritoneal transport and information on patterns of icodextrin hydrolysis during long icodextrin dwells.

Modeling cereal starch hydrolysis during simultaneous saccharification and lactic acid fermentation; case of a sorghum-based fermented beverage, gowé

Gowé is an acidic beverage obtained after simultaneous saccharification and fermentation (SSF) of sorghum. A previous paper focused on modeling the growth of lactic acid bacteria during gowé processing. This paper focuses on modeling starch amylolysis to build an aggregated SSF model. The activity of α-amylase was modeled as a function of temperature and pH, and the hydrolysis rates of both native and soluble starch were modeled via a Michaelis-Menten equation taking into account the maltose and glucose inhibition constants. The robustness of the parameter estimators was ensured by step by step identification in sets of experiments conducted with different proportions of native and gelatinized starch by modifying the pre-cooking temperature. The aggregated model was validated on experimental data and showed that both the pre-cooking and fermentation parameters, particularly temperature, are significant levers for controlling not only acid and sugar contents but also the expected viscosity of the final product. This generic approach could be used as a tool to optimize the sanitary and sensory quality of fermentation of other starchy products.