Alcoholic fermentation immobilized yeasts

Alcohol Sensor. On-line measurements of ethyl alcohol concentration in culture broth are required in fermentation industries. A microbial electrode consisting of immobilized yeasts or bacteria, a gas permeable Teflon membrane, and an oxygen electrode was prepared for the determination of methyl and ethyl alcohols(7). 

These examples indicate the in situ applicability of enzyme electrodes however, numerous problems have still to be solved. At present, coupling of enzyme sensors for fermentation control in a bypass arrangement appears to be more favorable [412]. Following this concept, an invertase thermistor incorporating a sterilizable filter unit has been developed [413] for the monitoring of alcoholic fermentation by immobilized yeast cells. Another thermistor has been successfully used for on-line glucose measurement under real cultivation conditions of Cephalosporium acremonium [414]. Similar calorimetric devices are suitable for other fermentation processes and in environmental analysis. 

Nano/microporous cellulose (NMC) prepared after removal of lignin from wood cellulose was found suitable for the development of cold pasteurization" processes acting as a biofilter for cell removal. It was also used successfully as biocatalyst in food fermentations acting as both cell immobilization carrier and as promoter of biochemical reactions, even at extremely low temperatures. The cumulative surface area of the NMC pores was found to be 0.8 to 0.89 m g" as indicated by porosimetry analysis. This surface is relatively small compared with other porous materials such as y-alumina however, using a natural organic material is attractive from the point of view that it is safer for bioprocess applications and is better accepted by consumers. The NMC/immobilized yeast biocatalyst increased the fermentation rate and was more effective at lower temperatures compared with free cells. Furthermore, the activation energy E, of fermentation was found to be 28% lower than that of free cells, indicating that it is an excellent material to promote the catalytic action of cells for alcoholic fermentation. 

Beer, on the other hand, is produced by more complex biochemical and technological processes, which all affect its flavor. Yeast amino acid metabolism, a key to the development of beer flavor as described earlier, is affected by process temperature and use of cell immobilization techniqnes. Therefore, technologies based on these features as well as other process conditions and strain selection have been developed to control beer flavor. The combination of immobilized yeast and low-temperature primary fermentation was found to produce beers with low diacetyl amounts, therefore indicating potential of low-cost industrial application since maturation is a high-energy-consuming process. Finally, Perpete and Collin showed that during alcohol-free beer production, the enzymatic reduction of worty flavor (caused by Strecker aldehydes) by brewer s yeast was improved by cold contact fermentation. 

Because the presence of yeasts can represent a logistical bottleneck in postfermentation clarification, an alternative that has been studied is the use of immobilized microorganisms. Here, yeasts are trapped in calcium alginate beads or strands that are collectively packed into a synthetic mesh sleeve that is immersed into the juice/must. Relatively few yeasts (<10V mL) escape the encapsulation matrix (Yokotsuka et al., 1993) but yet conduct an active alcoholic fermentation. Yajima and Yokotsuka (2001) reported that concentrations of some undesirable volatile compounds (methanol, ethyl acetate, and acetaldehyde) were lower in wines made using Saccharomyces immobilized in double-layer beads. Immobilized yeasts... 

Yokotsuka, K., a. Otaki, A. Naitoh, and H. Tanaka. 1993. Controlled simultaneous deacidification and alcohol fermentation of a high-acid grape must using two immobilized yeasts, Schizosaccharomyces pombe and Saccharomyces cerevisiae. Am.]. Enol. Vitic. 44 371-377. 

The flavor of fermented foods depends highly on the metabolic activity of the cnltnre nsed. Especially, the amino acid and the lipid metabolism in yeasts have a cmcial contribution to flavor, because they are linked to the production of flavor-active compounds snch as esters, alcohols, carbonyl compounds, fatty acids, and nonvolatile components. " The increased ester and decreased fusel alcohol (mainly amyl alcohols) formation that has been observed dnring fermentations nsing immobilized cells, or the improved ratios of esters to higher alcohols, especially at low tanpera-tures, is considered to have a great impact on beverage quality and technology. 

Van lersel M.F.M., Brouwer P.E., Rombouts F.M. and Abee T. Influence of yeast immobilization on fermentation and aldehyde reduction during the production of alcohol free beer. Enzyme and Microbial Technology 26 (8) (2000) 602-607. 

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