Batch xanthan fermentations by Xanthomonas campestris NRRL B-1459 at various temperatures ranging between 22 degrees C and 35 degrees C were studied. At 24 degrees C or lower, xanthan formation lagged significantly behind cell growth, resembling typical secondary metabolism. However, at 27 degrees C and higher, xanthan biosynthesis followed cell growth from the beginning of the exponential phase and continued into the stationary phase. Cell growth at 35 degrees C was very slow; the specific growth rate was near zero. The specific growth rate had a maximum value of 0.26 h(-1) at temperatures between 27 degrees C and 31 degrees C. Cell yield decreased from 0.53 g/g glucose at 22 degrees C to 0.28 g/g glucose at 33 degrees C, whereas xanthan yield increased from 54% at 22 degrees C to 90% at 33 degrees C. The specific xanthan formation rate also increased with increasing temperature. The pyruvate content of xanthan produced at various temperatures ranged between 1.9% and 4.5%, with the maximum occurring between 27 degrees C and 30 degrees C. These results suggest that the optimal temperatures for cell growth are between 24 degrees C and 27 degrees C, whereas those for xanthan formation are between 30 degrees C and 33 degrees C. For single-stage batch fermentation, the optimal temperature for xanthan fermentation is thus dependent on the design criteria (i. e., fermentation rate, xanthan yield, and gum qualities). However, a two-stage fermentation process with temperature shift-up from 27 degrees C to 32 degrees C is suggested to optimize both cell growth and xanthan formation, respectively, at each stage, and thus to improve overall xanthan fermentation.

BACKGROUND 2‐Phenylethanol (PEA) is an important aromatic compound produced mainly by chemical synthesis. PEA production by biotechnological approach has gained popularity in recent years. However, biological synthesis of PEA is limited by microorganisms and product inhibition. The influence of culture temperature on the bioconversion of L‐phenylalanine (L‐Phe) into PEA is investigated in this study. A novel strategy to enhance PEA using two‐stage fermentation with in situ product recovery also is proposed. RESULTS Batch culture at 25 °C with aeration rate of 1.3 vvm was optimal for high cell density, whereas cultivation at 35 °C with aeration rate 2 vvm was favorable for high product yield. Then, a two‐stage batch fermentation with switch time at 72 h was performed resulting in an increase in PEA concentration by 19.0% as compared to a single‐stage fermentation at 35 °C with a 2.0 vvm aeration rate. A semicontinuous fermentation with in situ product recovery was conducted, yielding a total PEA concentration of 4.5 g L−1. CONCLUSIONS The influence of culture temperature on bioconversion of L‐Phe is significant. Cell growth favors a lower temperature at 25 °C, but product formation favors a higher temperature at 35 °C. A two‐stage fermentation strategy was successful in batch culture, but not in fed‐batch culture due to the product inhibition from the accumulation of PEA. Therefore, employment of two‐stage semicontinuous culture with in situ product removal was successfully demonstrated in this study.

Batch fermentation kinetics of xanthan gum production from glucose by Xanthomonas campestris at temperatures between 22 degrees C and 35 degrees C were studied to evaluate temperature effects on cell growth and xanthan formation. These batch xanthan fermentations were modeled by the logistic equation for cell growth, the Luedeking-Piret equation for xanthan production, and a modified Luedeking-Piret equation for glucose consumption. Temperature dependence of the parameters in this model was evaluated. Growth-associated rate constants increased to a maximum at approximately 30 degrees C and then decreased to zero at approximately 35 degrees C. This temperature effect can be modeled using a square-root model. On the contrary, non-growth-associated rate constants increased with increasing temperature, following the Arrhenius relationship, in the entire temperature range studied. The model developed in this work fits the experimental data very well and can be used in a simulation study. However, due to the empirical nature of the model, the parameter values need to be reevaluated if the model is to be applied to different growth conditions.

BACKGROUND The use of commercially available ferulic acid (FA) as a precursor for vanillin production is costly. The utilization of agro‐waste as a starting material provides an alternative to obtain FA at a low cost and establish an economically profitable production system. In this work, optimization of ultrasound‐assisted extraction conditions for releasing FA from corn cobs using alkaline treatment was conducted. Further, bioconversion of FA from the crude hydrolysate of corn cobs to vanillin using Amycolatopsis thermoflava was performed. RESULTS Since autoclaved hydrolysate was unfavorable for cell growth and vanillin formation, pasteurization was proposed. However, the presence of contaminants limited the entire process. Aiming to suppress the growth of contaminants and increase vanillin yield, novel strategies of limiting and controlling the nutrients for the strain were developed. Optimal hydrolysis conditions (NaOH concentration = 0.5 M, solid loading = 10% for 30 min) produced hydrolysate with relatively high titers of FA (715 mg L−1) and p‐coumaric acid (1025 mg L−1). To improve vanillin production from FA, four parameters (including the effects of sterilization method, nutrient limitation, initial biomass concentration, and reducing sugar control) were investigated. By adopting these strategies and performing bioconversion of FA to vanillin with an initial biomass concentration of 1.5 g L−1, the yield of vanillin was significantly increased by 29.5‐fold to 477.4 mg g−1, compared to bioconversion using autoclaved hydrolysate. CONCLUSION This approach represents a relatively economical method for vanillin production from agro‐waste because it uses crude hydrolysate, requires minimum nutrients, and involves non‐modified organisms with a relatively short bioconversion time (17 h). © 2022 Society of Chemical Industry (SCI).

Management of spent mushroom substrate (SMS) is causing a global environmental concern due to tremendous increase in mushroom production globally. Therefore, in this research, the performance of a two-stage anaerobic co-digestion (TS-AD) of spent mushroom substrate and chicken manure was evaluated in terms of methane and biogas production and process stability with respect to single stage anaerobic digestion (SS-AD). Activation of anaerobic sludge using aeration or heat treatment in the first stage at mesophilic temperature followed by thermophilic co-digestion with chicken manure in the second stage was investigated. TS-AD exhibited better performance and enhanced methane generation over SS-AD. The optimal temperatures were determined as 35°C and 50°C for the first and the second stage of TS-AD, respectively. C/N ratio of 10 was the most suitable for biogas and methane production. TS-AD with C/N ratio of 10 and mesophilic digestion of SMS and sludge for 3 days at 35°C followed by co-digestion of the first stage effluent with chicken manure at 50°C was the optimized state producing 1359 mL of biogas of which 614.42 mL was methane, showing an increment by 59.44% in methane production as compared to SS-AD. TS-AD might be promising approach for utilization of SMS as feed stocks for biogas and methane production.