Immobilized cell systems for batch and continuous winemaking

The major challenges in the food industry are the development of healthier, safer and environmental friendly products. To achieve these objectives, it is essential to develop advanced technologies to make the production processes economically attractive. The use of immobilized cell systems has been widely applied in the production of several products. However, in winemaking, it has only been studied to prove its applicability. The studies targeting the production of wine using these innovative fermentation systems aim to overcome limitations related to the product quality, the operational costs associated with the material used as support and the immobilization process itself.Zlatina Genisheva gratefully acknowledges FCT (Contract/grant number: SFRH/BD/48186/2009) and the Project "BioInd - Biotechnology and Bioengineering for improved Industrial and Agro-Food processes", REF. NORTE-07-0124-FEDER-000028 Co-funded by the Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER, for the financial support of this work

Wine production with immobilized yeasts on grape pomace

The alcoholic fermentation is one of the most important stages in the winemaking process and contributes decisively for the quality of the final product, particularly aromatic characteristics. The immobilization of yeast cells in fermentation processes presents several technological and economic advantages when compared with free cells systems, such as increased productivity and greater tolerance of the cells to inhibitory substances. In this context, the objective of this work consisted in using immobilized yeasts for driving and controlling the alcoholic fermentation process in winemaking. The immobilization of Saccharomyces cerevisiae took place on grape pomace by natural adsorption. The evolution of the alcoholic fermentation was followed daily by measuring must density until a value lower than 1000 kg/m3 was reached. Physical-chemical and sensorial characterization of the wines, produced with free and immobilized cells, were carried out. The immobilized yeasts were able to effectively conduct the alcoholic fermentation and therefore, to produce wine. Sensory analysis demonstrated the existence of perceptible olfactory differences in wines produced by free cells and immobilized cells. Moreover, the produced wines presented significant differences respecting color attributes.A fermentação alcoólica é uma das etapas mais importantes no processo de produção de vinho e contribui decisivamente para a qualidade final do produto, particularmente o aroma. A imobilização de células de levedura em processos fermentativos apresenta diversas vantagens tecnológicas e económicas quando comparada com sistemas de células livres, tais como incremento da produtividade e maior tolerância das células a substâncias inibitórias. Neste contexto, o objectivo do trabalho consistiu na utilização de leveduras imobilizadas para para a condução e controlo do processo de fermentação alcoólica em vinificação. A imobilização de Saccharomyces cerevisiae foi realizada por adsorção natural num suporte natural constituído por bagaço de uva. A evolução da fermentação foi seguida diariamente pela medição da massa volúmica, sendo dada por terminada para valores inferiores a 1000 kg/m3 . Os vinhos produzidos, quer com células livres quer com células imobilizadas, foram avaliados por caracterização físico-química e por análise sensorial. As leveduras imobilizadas foram capazes de conduzir eficazmente as fermentações alcoólicas e, por conseguinte, de produzir vinho. A análise sensorial dos vinhos demonstrou a existência de diferenças olfactivas perceptíveis nos vinhos produzidos a partir de células livres e de células imobilizadas. Além disso, as análises de cor demonstraram que os vinhos produzidos apresentaram diferenças significativas

Malolactic fermentation with Oenococcus oeni immobilized on natural materials

Bioprocesses with immobilized cells is a fast expanding field of investigation due to the various advantages of this system when compared to conventional free cells fermentations. One of the advantages of this system is the easier control of the fermentation process, which is of great importance especially for processes that are complex and difficult to control, like the malolactic fermentation (MLF) in winemaking. The implementation of MLF is very important for wines produced in cold regions as it reduces the acidity, brings biological stability and may improve the organoleptic characteristics of the product. MLF normally occurs spontaneously during storage of a new wine and is usually a very slow process that can undergo for weeks and even months, and not always give a satisfactory result. The use of immobilized lactic acid bacteria during MLF helps to accelerate the process and also simplifies the control of its extension. However, the material to be used as immobilization support must be carefully chosen in order to not negatively affect the final product, and should also be cheap, abundant in nature, and of food grade purity. The aim of the present work was to find low cost natural materials of food grade purity, suitable for immobilization of Oenococcus oeni for use on MLF. Four natural materials, including corn cobs, grape stems, grape seeds and grape skins were evaluated. Immobilization and fermentation occurred simultaneously in 500 mL Erlenmeyer flasks containing 2 g of support material and 200 mL of synthetic medium inoculated with 1 g/L cells of O. oeni. Fermentations were carried out in duplicate, and samples were taken every 2 h for estimation of free biomass, glucose, fructose and malic acid consumption, and lactic acid production. For comparison, free cells assays under the same conditions described above were also performed. Fermentations with immobilized cells gave better results than the assays containing only free cells in suspension. Among the support materials, corn cobs, grape skins and grape stems proportioned the best results. Grape skins immobilized the highest amount of cells (40.3 mg/g) followed by corn cobs (31.9 mg/g) and grape stems (30.9 mg/g). Fermentations with cells immobilized in corn cobs and grape stems achieved the highest lactic acid productivities [4.06 g/(L h) and 4.03 g/(L h), respectively]. It was concluded that such materials are suitable for use as support for immobilization of Oenococcus oeni during malolactic fermentation

Malolactic fermentation of wines with immobilised lactic acid bacteria : Influence of concentration, type of support material and storage conditions

Corn cobs, grape skins and grape stems were evaluated as support materials for immobilization of the lactic acid bacteria Oenococcus oeni. The support materials with immobilized cells were further used in malolactic fermentation (MLF) of white wine. Viability of using the immobilized supports was evaluated in consecutive batch fermentations under different conditions of temperature, ethanol and SO2. Additionally, the possibility of storage and operational stability of the immobilized supports was also studied. All the three supports presented large potential for immobilization of O. oeni cells. The consecutive batches of MLF were successfully conducted for a total period of around 5 months with the possibility of storage of the biocatalyst for 30 d in wine at 25 °C.Zlatina Genisheva gratefully acknowledges FCT (Contract/Grant No. SFRH/BD/48186/2009) for financial support of this work. The authors would like to thank to Divisao de Vitivinicultura e Fruticultura do Direccao Regional de Agricultura de Entre Douro e Minho for providing the grape pomace for yeast immobilization and must to conduct alcoholic fermentations

Selection of natural materials for Saccharomyces cerevisiae immobilization

Immobilized cells systems have been considered as a promising alternative to improve the performance of biotechnological processes, since in these systems, immobilized cells completely maintain their biological functions with increased stability that may often lead to increased cell productivity. However, the correct selection of immobilization carrier is essential to design an effective system to each particular purpose. The objective of the present study was to find a cheap and abundant natural material suitable for immobilization of Saccharomyces cerevisiae yeast, which is usually used in fermentation processes for wine production. Four different carriers were evaluated, namely grape seeds, grape skin, grape stems and corn cobs. To be used in the experiments, the carriers were washed with water and dried to constant weight. The inoculum was prepared by cultivating the yeast in YPD medium under static conditions for 24 h and 30 ºC. Fermentation runs were performed in semi-defined medium composed by: glucose (120 g/L), yeast extract (4 g/L), (NH4)2SO4 (1 g/L), KH2PO4 (1 g/L), and MgSO4 (5 g/L). The assays were carried out in 500 mL Erlenmeyer flasks containing 200 mL of medium and 2 g of material carrier, statically incubated at 30 C for 24 h. Samples were taken periodically for estimation of biomass, glucose consumption and ethanol production. Corn cobs and grape skins were the best material carriers for S. cerevisiae immobilization, since they immobilized the highest amount of cells (22.2 ± 0.9 mg/g and 25.1± 10.8 mg/g, respectively) and fermentation with these immobilized cells gave elevated ethanol yield (YP/S = 0.51 and 0.49 g/g, respectively) and productivity (QP = 3.35 and 3.41 g/(Lh), respectively). These results are of great interest since the material did not require any pre-treatment to be used as immobilization carrier

Effect of the support material and storage conditions of immobilized lactic acid bacteria on malolactic fermentation of white wine

In this work, the lactic acid bacterium Oenococcus oeni was immobilized on three different natural materials (namely corn cobs, grape skins and grape stems) and used to induce malolactic fermentation in white wine. Additionally, the biocatalyst reuse after different periods of storage in cold or in hot environments was also evaluated. The resistance of the immobilized lactic acid bacterium against inhibitors was determined by performing the MLF in presence of high SO2 concentration. Immobilization occurred in situ during the fermentation, which was performed in 500 mL Erlenmeyer flasks containing 6 g of support material, 1 g/L cells of O. oeni and 200 mL of complex medium. Fermentations were carried out in duplicate, and samples were taken periodically for the estimation of glucose, fructose and malic acid consumption, and lactic acid production. At the end of the fermentation (16 h), since all the assays presented similar results, different strategies were adopted. One of them consisted on the recovery of the corn cobs with immobilized cells, and subsequent storage of this biocatalyst at 5 ºC during 31 d. The flasks containing grape skins and stems were directly stored at 25 ºC during 27 d and 37 d, respectively. After these periods, the support materials with immobilized cells were recovered, washed with sterilized distilled water and added to 200 mL of white wine for conducting MLF, which was performed during 18 d. Subsequently, the biocatalysts were recovered, washed and added to 200 mL of white wine for conducting MLF in presence of 32 mg/L of free SO2, which was maintained during 17 d. Malic acid consumption and lactic acid production was observed during all the MLF, independently of the used support material. However, fermentation runs with cells immobilized on grape skins gave the best results, providing the highest lactic acid concentration and also high conversion of malic acid. The presence of high SO2 concentration (32 mg/L) did not affect the conversion of malic acid for cells immobilized in grape skins and stems, and gave similar results of produced lactic acid (3.60 g/L and 2.90 g/L, for grape skins and stems, respectively). The presence of high SO2 concentration strongly affected the conversion of malic acid by cells immobilized on corn cobs. Oenococcus oeni immobilized on grape skins and grape stems can be successfully used on MLF even after long periods of storage at 25 oC, and in the presence of high SO2 concentration

Influence of concentration and type of support material on the immobilization of Oenococcus oeni

The malolactic fermentation (MLF) in winemaking is a complex and difficult to control biological process . The implementation of MLF is very important for wines produced in cold regions as it reduces the acidity, brings biological stability and may improve the organolept ic characteristics of the product. MLF normally occurs spontaneously during storage of a new wine and is usually a very slow process that can undergo for we eks and even months, and not always give a satisfactory result. The use of immobilized lactic acid bacteria during MLF helps to accelerate the process and also simplifies the control of its extension. However, t he material to be used as immobilization support must be carefully chosen in order to not negatively affect the final product, and should also be cheap, abundant i n nature, and of food grade purity. The aim of the present work was to evaluate differe nt low cost natural materials of food grade purity (na mely corn cobs, grape stems and grape skins) and their concentration, for immobilization of Oenococcus oeni for use on MLF

Electron mobility in surface- and buried- channel flatband In_0.53Ga_0.47As MOSFETs with ALD Al₂O₃ gate dielectric.

In this paper, we investigate the scaling potential of flatband III-V MOSFETs by comparing the mobility of surface and buried In<sub>0.53</sub>Ga<sub>0.47</sub>As channel devices employing an Atomic Layer Deposited (ALD) Al<sub>2</sub>O<sub>3</sub> gate dielectric and a delta-doped InGaAs/InAlAs/InP heterostructure. Peak electron mobilities of 4300 cm<sup>2</sup>/V·s and 6600 cm<sup>2</sup>/V·s at a carrier density of 3×1012 cm<sup>-2</sup> for the surface and buried channel structures respectively were determined. In contrast to similarly scaled inversion-channel devices, we find that mobility in surface channel flatband structures does not drop rapidly with electron density, but rather high mobility is maintained up to carrier concentrations around 4x10<sup>12</sup> cm<sup>-2</sup> before slowly dropping to around 2000 cm<sup>2</sup>/V·s at 1x10M<sup>13</sup> cm<sup>-2</sup>. We believe these to be world leading metrics for this material system and an important development in informing the III-V MOSFET device architecture selection process for future low power, highly scaled CM