Argyro Bekatorou

Whey valorisation: a complete and novel technology development for dairy industry starter culture production.

Whey is the major by-product of the dairy industry, produced in large quantities and usually disposed off causing major environmental pollution, due to its high organic load that makes treatment cost prohibitive. This paper comprises a contribution on the valorisation of this high polluting liquid waste of the dairy industry, based on research for the production of novel dairy starter cultures using whey as raw material. Starter cultures are used for cheese ripening in order to: (i) accelerate ripening, (ii) improve quality and (iii) increase shelf-life. The developed technology involves biomass production from whey followed by thermal drying of cultures. Specifically, Kluyveromyces marxianus, Lactobacillus bulgaricus and kefir yeasts were thermally dried, and their efficiency in lactose and milk whey fermentations was studied. The most suitable culture regarding its technological properties was kefir, which was used for cheese ripening in freeze-dried and thermally dried form. Besides the reduction of production cost, which is an essential requirement for the food industry, the use of thermally dried kefir displayed several other advantages such as acceleration of ripening, increase of shelf-life, and improvement of hard-type cheese quality.

Solid state fermentation of food waste mixtures for single cell protein, aroma volatiles and fat production

Growth of selected microorganisms of industrial interest (Saccharomyces cerevisiae, Kluyveromyces marxianus and kefir) by solid state fermentation (SSF) of various food industry waste mixtures was studied. The fermented products were analysed for protein, and nutrient minerals content, as well as for aroma volatile compounds by GC/MS. The substrate fermented by K. marxianus contained the highest sum of fat and protein concentration (59.2% w/w dm) and therefore it could be considered for utilisation of its fat content and for livestock feed enrichment. Regarding volatiles, the formation of high amounts of ε-pinene was observed only in the SSF product of kefir at a yield estimated to be 4 kg/tn of SSF product. A preliminary design of a biorefinery-type process flow sheet and its economic analysis, indicated potential production of products (enriched livestock feed, fat and ε-pinene) of significant added value.

Scale-up of extremely low temperature fermentations of grape must by wheat supported yeast cells.

A new biocatalyst was prepared by immobilization of Saccharomyces cerevisiae AXAZ-1 yeast cells on whole wheat grains. This biocatalyst was used for 30 repeated batch fermentations of glucose and grape must at various temperatures. The biocatalyst retained its operational stability for a long period and it was proved capable to produce dry wines of fine clarity even at extremely low temperatures (5 degrees C). After the completion of these fermentations the new biocatalyst was used in a scale-up system of 80 L for wine making at ambient (20 degrees C) and extremely low temperatures (2 degrees C). The scale-up process did not affect the fermentative ability of biocatalyst, even at low temperatures, while the produced wines had almost the same improved aromatic profile compare to free cells as revealed by GC and GC-MS analyses. More specifically the results showed that both systems with immobilized cells (laboratory scale and 80 L bioreactor) increased the formation of esters and produced wines with improved aromatic profile compared to those with free cells. Finally an increase in the percentages of total esters and a decrease in those of higher alcohols was observed in lower fermentation temperatures.

Nano-tubular cellulose for bioprocess technology development.

Delignified cellulosic material has shown a significant promotional effect on the alcoholic fermentation as yeast immobilization support. However, its potential for further biotechnological development is unexploited. This study reports the characterization of this tubular/porous cellulosic material, which was done by SEM, porosimetry and X-ray powder diffractometry. The results showed that the structure of nano-tubular cellulose (NC) justifies its suitability for use in “cold pasteurization” processes and its promoting activity in bioprocessing (fermentation). The last was explained by a glucose pump theory. Also, it was demonstrated that crystallization of viscous invert sugar solutions during freeze drying could not be otherwise achieved unless NC was present. This effect as well as the feasibility of extremely low temperature fermentation are due to reduction of the activation energy, and have facilitated the development of technologies such as wine fermentations at home scale (in a domestic refrigerator). Moreover, NC may lead to new perspectives in research such as the development of new composites, templates for cylindrical nano-particles, etc.

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.

Effect of pressure and temperature on alcoholic fermentation by Saccharomyces cerevisiae immobilized on γ-alumina pellets

Saccharomyces cerevisiae was immobilized on γ-alumina pellets and used for repeated batch fermentations in glucose medium (16.5 g/100 mL) at various temperatures and pressures. An increase in pressure from 3 to 7 atm and a decrease in temperature from 30 to 20 °C reduced the ethanol productivity by about 50% and 70%, respectively. Increasing concentrations of volatile by-products were observed at lower fermentation temperatures, while the pressure influence on the concentrations of these by-products was proved to be more complex. Mathematical expressions were established to allow the calculation of the fermentation rate at various pressures and sugar concentrations when the corresponding rate at atmospheric pressure is known. The study showed that the height of bioreactors has to be limited to 19.5 m due to hydrostatic pressure shock at higher fill levels.

Red Wine Making by Immobilized Cells and Influence on Volatile Composition

Red wine making using yeast cells immobilized in two types of raisin berries, at various temperatures (6-30 degrees C), was studied. A modification of the batch bioreactor was used to separate the grape skins used for color extraction from the biocatalyst and the fermenting grape must. The evaluation of the immobilized biocatalysts was made on terms of productivity and organoleptic quality, including color intensity and formation of volatiles. The immobilized cells were found capable of low-temperature wine making, producing red wines containing more than 11% v/v alcohol in 8 days at 6 degrees C. The quality of wines was examined by gas chromatography (GC) and GC-MS analysis and sensory evaluation. Higher alcohol concentrations were decreased, and ethyl acetate concentrations increased by the drop of temperature. Many esters, alcohols, carbonyls, and miscellaneous compounds were identified in wines produced by immobilized cells, revealing no significant qualitative differences as compared to wines produced by free cells. The sensory evaluation showed that the best red wine was produced at 6 degrees C.

Lead(II) uptake during baker's yeast production by aerobic fermentation of molasses

Lead(II) removal through biosorption on bakers yeast during biomass production was studied to estimate the level of uptake from contaminated molasses medium and to monitor its impact on cell growth. Lead(II) additions had significant negative effects on growth. Concentrations above 50 mgl(-1) resulted in a 50% reduction in growth rate and 60% lower overall biomass yields compared to controls. Nevertheless, the decrease in yeast biomass did not lead to decreased lead(II) uptake, on the contrary the biosorption ability was higher at higher initial lead(II) concentrations

Lactic acid fermentation by Lactobacillus casei in free cell form and immobilised on gluten pellets

A comparative study of the fermentation of a range of carbohydrate substrates, at various temperatures, was carried out using a commercial Lactobacillus casei strain in a free cell form and immobilised on gluten pellets. This strain required yeast extract, l-cysteine ⋅ HCl and Mn2+ at 5, 0.5 and 0.1 g l−1, respectively, for maximum growth and lactic acid production. Sugar fermentation using free cells showed preference in the order glucose, sucrose, fructose while lactose was poorly utilised. Optimum temperature for growth and lactic acid production over (18–30 h) was 43 °C. L. casei was successfully immobilised on gluten pellets and fermented glucose and sucrose in a shorter time (18 h) with increased lactic acid production (42 and 41 g l−1 on glucose and sucrose, respectively).

Lactic acid fermentation by cells immobilised on various porous cellulosic materials and their alginate/poly-lactic acid composites

Porous delignified cellulose (or tubular cellulose, abbr. TC) from Indian Mango (Mangifera indica) and Sal (Shorea robusta) wood and Rice husk, and TC/Ca-alginate/polylactic acid composites, were used as Lactobacillus bulgaricus immobilisation carriers leading to improvements in lactic acid fermentation of cheese whey and synthetic lactose media, compared to free cells. Specifically, shorter fermentation rates, higher lactic acid yields (g/g sugar utilised) and productivities (g/Ld), and higher amounts of volatile by-products were achieved, while no significant differences were observed on the performance of the different immobilised biocatalysts. The proposed biocatalysts are of food grade purity, cheap and easy to prepare, and they are attractive for bioprocess development based on immobilised cells. Such composite biocatalysts may be used for the co-immobilisation of different microorganisms or enzymes (in separate layers of the biocatalyst), to efficiently conduct different types of fermentations in the same bioreactor, avoiding inhibition problems of chemical or biological (competition) nature.