A. A. Koutinas

Room temperature and low temperature wine making using yeast immobilized on gluten pellets

Abstract A cryotolerant and alcohol tolerant strain of Saccharomyces cerevisiae was immobilized on gluten pellets and examined by electron microscopy. The biocatalyst was used for repeated batch fermentations in glucose and must for wine making at 30, 15, 10, 5 and 0°C, without any loss of activity. This biocatalyst produced at least a three-fold increase in the fermentation rate when compared with free cells and reduced the activation energy, E a . Wine and ethanol productivities obtained at 15°C were about half those obtained at 30°C. At 10°C the average wine productivity was about 30% of that obtained at 30°C. For each temperature, ethanol and wine productivities for immobilized cells were higher than those for free cells and the improvement increased as the temperature was decreased. At temperatures lower than 10°C, wine productivities were four to seven times higher than those of the free cells.

Continuous Wine Making by γ-Alumina-Supported Biocatalyst

The main objective of the present work was the removal of aluminum from wines produced by γ-alumina-supported yeast cells. Reagents such as Na2CO3, NH4OH, albumin, and Ca(OH)2 were used. Calcium in the presence of albumin was effective, whereas other reagents were not so effective. Because of the improved aroma and taste of distillates produced by γ-alumina-supported biocatalyst, volatile byproducts of distillates were analyzed. They were also assessed by sensory tests. Methanol, acetaldehyde, ethyl acetate, propanol-1, isobutyl alcohol, and amyl alcohols were determined in distillates. It was noted that the amounts of higher alcohols and amyl alcohols decreased as the temperature of fermentation dropped, leading to a product of improved quality and reduced toxicity.

Wine production using yeast immobilized on quince biocatalyst at temperatures between 30 and 0 °C

A biocatalyst was prepared by immobilization of Saccharomyces cerevisiae, strain AXAZ-1, yeast cells on quince pieces and its suitability for fermentation of glucose and grape must was investigated. The immobilized yeast showed operational stability and no decrease in activity, even at low temperatures (0-10 degreesC). Total and volatile acidities in the wines produced were similar to dry wines. The concentrations of higher alcohols (propan-1nol and isobutyl alcohol) were low. The production of amyl alcohols proved to be temperature-dependent and decreased with lower temperatures. Ethyl acetate concentrations were relatively high, up to 113 mg/l. This probably contributes to the fruity aroma and high quality taste of the wines. GGMS analysis of wines produced using the immobilized biocatalyst and free cell fermentations showed no significant differences in the qualitative composition of aroma-related constituents

Volatile by-products formed in low-temperature wine-making using immobilized yeast cells

Abstract The formation of acetaldehyde, ethyl acetate, propanol-1, isobutanol, amyl alcohols and methanol in repeated batch and continuous fermentations of must using a cryotolerant and alcohol-resistant yeast immobilized on delignified cellulosic material (DCM) and gluten pellets was studied. The fine and fruity aroma of the wines prepared may be attributed to the high content of ethyl acetate in the total volatiles. Immobilization of yeast cells increased ethyl acetate production and, in the case of the DCM, decreased amyl alcohol production at low temperatures compared with free cells. With the DCM-supported biocatalyst, the percentage ethyl acetate of total volatiles minus methanol remained constant as the temperature was reduced, while the amyl alcohol content was reduced. Amyl alcohols are thought to be correlated with improvement of the aroma and the decrease in toxicity of the wine.

Continuous winemaking fermentation using quince-immobilized yeast at room and low temperatures

Quince-supported biocatalyst, prepared by the immobilization of an alcohol resistant psychrophilic yeast Saccharomyces cerevisiae AXAZ-1 on quince pieces, was suitable for room and low-temperature continuous winemaking. Continuous fermentation was carried out for 46 days without diminution of wine and ethanol productivity (up to 750 and 71 g/l, respectively) which at 5 degreesC was equal to that usually obtained by traditional fermentation at 22-25 degreesC. The total and volatile acidities were similar to those in dry wines. Methanol, ethyl acetate propanol-1, isobutanol and amyl alcohols (2-methylbutanol-1 and 3-methylbutanol-1) were monitored. The concentrations of ethyl acetate, amyl alcohols and methanol were < 100 mg/l in all cases, indicating an improvement in the product. Preliminary sensory tests established the fruity aroma, fine taste and the overall improved quality of the produced wines

New alcohol resistant strains ofSaccharomyces cerevisiae species for potable alcohol production using molasse

Two alcohol resistant strains ofSaccharomyces cerevisiae species were isolated from a Greek vineyard plantation. The strain AXAZ-1 gave a concentration of 17.6% v/v alcohol and AXAZ-2 16.5%, when musts from raisin and sultana grapes, respectively, were employed in alcoholic fermentations. They were found to be more alcohol tolerant and fermentative in the fermentation of molasse than the traditional baker’s yeast. Specifically, using an initial {fx153-1}Be density of 16{fx153-2}Be at the repeated batch fermentation process, in the first as well as fourth batch, the better AXAZ-1 gave final {fx153-3}Be densities of 6.0 and 10.5 respectively, and the baker’s yeast 11.6 and 14.5.

Thermally-dried immobilized kefir on casein as starter culture in dried whey cheese production

The aim of the present study was to evaluate the use of thermally-dried immobilized kefir on casein as a starter culture for protein-enriched dried whey cheese. For comparison reasons, dried whey cheese with thermally-dried free kefir culture and with no starter culture were also produced. The effect of the nature of the culture, the ripening temperature and the ripening process on quality characteristics of the whey cheese was studied. The association of microbial groups during cheese maturation suggested repression of spoilage and protection from pathogens due to the thermally-dried kefir, as counts of coliforms, enterobacteria and staphylococci were significantly reduced in cheeses produced using thermally-dried kefir starter cultures. The effect of the starter culture on production of volatile compounds responsible for cheese flavor was also studied using the SPME GC/MS technique. Thermally-dried immobilized kefir starter culture resulted in an improved profile of aroma-related compounds. The preliminary sensory evaluation ascertained the soft, fine taste and the overall improved quality of cheese produced with the thermally-dried immobilized kefir. The potential of protein-based thermally-dried starter cultures in dairy products is finally highlighted and assessed.

Freeze-dried Saccharomyces cerevisiae cells immobilized on gluten pellets for glucose fermentation

No protecting medium was used for the freeze-drying of Saccharomyces cerevisiae free cells and those immobilized on gluten pellets to form an immobilized biocatalyst. The use of these for glucose fermentations at various initial glucose concentrations, temperatures and initial pH values showed that the fermentation time for the first batch with freeze-dried immobilized cells was 1.5- to 3-fold less than that with free freeze-dried cells. In the second repeated batch, the fermentation time of freeze-dried immobilized cells was less, in some cases up to three times less than the first batch and reached the fermentation time of fresh immobilized cells. After storage for 16 months at 4°C, freeze-dried immobilized biocatalyst was used for five repeated batch fermentations of glucose. The fermentation time decreased continuously until 18 h, which was less than the half of the fermentation time of the first batch.

A catalytic multistage fixed-bed tower bioreactor in an industrial-scale pilot plant for alcohol production.

This article describes the development of an industrial‐scale, multistage fixed‐bed tower (MFBT) bioreactor using the promoter mineral kissiris for industrial alcohol production using free cells. Specifically, we examined the parameters needed to maintain operational stability from batch to batch for long periods. Pilot plant operations used one‐ and two‐stage fixed‐bed, 7000‐L bioreactors. Likewise a 100,000‐L, multistage fixed‐bed tower system containing layered kissiris confirmed the laboratory results. Compared with a continuous stirred tank fermentor (CSTF) with recycle, a 30% reduction of energy demand and 10%–20% of the production costs are obtained. The latter are attributed to the increased ethanol concentration and alcohol productivity.

Immobilization of Saccharomyces cerevisiae on γ-alumina pellets and its ethanol production in glucose and raisin extract fermentation

Abstract The immobilization of Saccharomyces cerevisiae cells on γ-alumina pellets was examined by electron microscope and by measurement of the electrokinetic charge of the cells and the γ-alumina pellets. Repeated batch fermentations (about 20) were done for glucose and raisin extract, separately, with an average ethanol production of 80 g/ l ·d and 52 g/ l ·d respectively.