Jun-ichi Horiuchi

Selective production of organic acids in anaerobic acid reactor by pH control.

The selective production of organic acids by anaerobic acidogenesis with pH control was examined using a chemostat culture. The results showed that the product spectrum in the acid reactor strongly depended on the culture pH. Under acidic and neutral conditions, the main products were butyric acid, while acetic and propionic acids were the main products under the basic condition. This phenomenon was reversible between the acidic and basic conditions, and was not affected by the dilution rate. The change in the main products was caused by the change in the dominant microbial populations, from butyric acid-producing bacteria to propionic acid-producing bacteria in the acid reactor due to the pH shift. The control of culture pH was considered to be a useful way for controlling the product spectrum in the anaerobic acid reactor.

Effective cell harvesting of the halotolerant microalga Dunaliella tertiolecta with pH control

An effective method for cell harvesting of the halotolerant microalga, Dunaliella tertiolecta ATCC30929, was investigated. By increasing the pH of the culture broth using NaOH solution, suspended D. terfolecta cells rapidly coagulated and settled within a few minutes, which allowed simple harvesting of the concentrated cells from the culture broth. The pHs for successful coagulation were between 8.6 and 10.5 and more than 90% of cells was recovered from the culture broth. Clarified culture broth could be reused for the successive cultivation of D. tertiolecta simply by supplying fresh medium and neutralizing alkali with HCl without the requirement for an additional inoculum.

Microbial xylitol production from corn cobs using Candida magnoliae.

Microbial production of xylitol from corn cobs using Candida magnoliae was experimentally investigated. Approximately 25 g-xylose/l solution was obtained from 100 g-corn cobs/l solution by hydrolysis using 1.0% sulfuric acid at 121 degrees C for 60 min. To remove inhibitors from the hydrolysates, charcoal pellets were found to be effective in selectively removing the inhibitors from the hydrolysates without affecting xylose concentration. C. magnoliae was successfully cultivated using the treated corn cob hydrolysate, resulting in the production of 18.7 g-xylitol/l from 25 g-xylose/l within 36 h.

Dynamic behavior in response to pH shift during anaerobic acidogenesis with a chemostat culture

To clarify the dynamic behavior of the anaerobic acid reactor in response to pH changes, a continuous cultivation was performed. By stepwise shifting the culture pH in the acid reactor from 6.0 to 8.0, the main products were changed from butyric acid to acetic and propionic acids. This phenomenon was reproducible, reversible and was not affected by the dilution rate. It was considered that the dominant microbial populations changed in the acid reactor due to the pH shift.

Fuzzy modeling and control of biological processes

Fuzzy modeling and control based on the fuzzy sets theory have been used in the biotechnology field for the last two decades. Recent studies on fuzzy modeling and control of various biological processes are reviewed. In addition, five applications of fuzzy control to industrial biological processes are summarized, compared and discussed in terms of the system features, control purpose, input and output variables, development of fuzzy rules and effectiveness. Fuzzy modeling and control are regarded as promising methods for automating the bioprocesses in which experienced operators play significant roles in their successful operation.

New vinegar production from onions.

The possibility of producing a new type of vinegar from worthless onions, which fail to meet the quality standards required for marketing, was investigated. Several kinds of onion were initially tested as raw material for vinegar production, and vinegar was successfully produced from the juice of a red onion, the cultivar Kurenai, by batch culture using yeast and Acetobacter aceti. Nutritional analysis revealed that the potassium content of onion vinegar was extremely high, while the amount of sodium was lower than that in conventional vinegars. It was also shown that the total amino acid and total organic acid contents of the onion vinegar were respectively 1.6-6.9 times and 3.5-11.5 times those in other kinds of vinegars.

Application of fuzzy control to industrial bioprocesses in Japan

Applications of fuzzy control to industrial biological processes in Japan were summarized, compared and discussed in terms of the system features, control purpose, input and output variables, development of fuzzy rules and its effectiveness. Fuzzy control was mainly applied to the fed-batch cultures of microorganisms and used for the on-line control of feeding rate of substrate. Most of the control systems were developed based on the knowledge of experienced. Fuzzy control is regarded as a promising method for automating the bioprocesses where the experienced operators play significant roles for their successful operation.

Industrial application of fuzzy control to large-scale recombinant vitamin B2 production.

A fuzzy control system featuring the identification of culture phases by fuzzy logic was applied to the large-scale recombinant vitamin B2 (VB2) production at the Fukuroi factory of Nippon Roche, Fukuroi. Prior to actual operation, the knowledge base for fuzzy control was tuned and verified by a simulation system. Only four rules, formulated as IF approximately THEN instructions and membership functions for state variables, are employed to control the feed rate and pH of the fed-batch culture. By applying fuzzy control, total VB2 production and VB2 yield was increased by 6-16% and 4-11% compared with conventional control, respectively. Operating stability was also improved. The large-scale fermentor used for VB2 production has been successfully operated under the control of the fuzzy system for more than 2 years.

Simplified method for estimation of microbial activity in compost by ATP analysis.

A simplified method using ATP analysis was proposed to estimate the time course of microbial activity during composting. A compost sample was suspended in distilled water and its filtrate was used to estimate the ATP content in the compost by the luciferine-luciferase fluorescence reaction. The method permitted the rapid and simple determination of ATP in the compost and was successfully applied to monitor the time course of the microbial activity in the laboratory-scale composting process. The analytical simplicity in this method greatly improved the field-applicability of the ATP analysis for the composting process monitoring.

Modeling of pH response in continuous anaerobic acidogenesis by an artificial neural network

A simple modeling method for microbial dynamic behavior in a chemostat using a neural network was proposed and applied to the pH response in continuous anaerobic acidogenesis. By step shifting the culture pH in the acid reactor from 6.0 to 8.0, the main products were changed from butyric acid to acetic and propionic acids. This phenomenon was reproducible, reversible and was not affected by the dilution rate. A three-layered neural network with a back-propagation algorithm was then used to model the pH step response of the acid reactor. The artificial neural network could successfully model the change in the product distribution in response to a pH shift, leading to the prediction of the transient behavior from one steady state to another steady state in continuous acidogenesis.