Optimization of bacterial cellulose production by Komagataeibacter sucrofermentans in synthetic media and agrifood side streams supplemented with organic acids and vitamins

The effect of thiamine (TA), ascorbic acid (AA), citric acid, and gallic acid (GA) on bacterial cellulose (BC) production by Komagataeibacter sucrofermentans, in synthetic (Hestrin and Schramm, HS) and natural substrates (industrial raisins finishing side stream extract, FSSE; orange juice, OJ; green tea extract, GTE), was investigated. The Response Surface Methodology was found reliable for BC yield prediction and optimization. Higher yields were achieved in the FSSE substrates, especially those supplemented with AA, TA, and GA (up to 19.4 g BC/L). The yield in the non-fortified substrates was 1.1-5.4 and 11.6-15.7 g/L, in HS and FSSE, respectively. The best yield in the natural non-fortified substrate FSSE-OJ-GTE (50-20-30 %), was 5.9 g/L. The porosity, crystallinity, and antioxidant properties of the produced BC films were affected by both the substrate and the drying method (freeze- or oven-drying). The natural substrates and the process wastewaters can be further exploited towards added value and sustainability. Take Home Message Sentence: Raisin and citrus side-streams can be efficiently combined for bacterial cellulose production, enhanced by other vitamin- and phenolic-rich substrates such as green tea.

Tubular Cellulose Composite as a Vehicle for the Development of Meat Products with Low Nitrite Content

Research background

Nitrite salts are among the most used preservatives in meat products as they ensure their safe consumption. Despite their positive effects on food safety and stability, many side effects on human health have been reported, leading to the need to reduce their use. Therefore, the aim of this study is to produce veal products with low nitrite content through low diffusion of potassium nitrite and to study their microbiological characteristics.

Experimental approach

Edible tubular cellulose from leaf celery was produced and KNO2 was encapsulated in this material. This was achieved in two ways: by impregnation of tubular cellulose in a KNO2 solution under stirring and using starch gel as a stabilizer. Two samples of impregnated cellulose were applied on the surface of two veal samples of which one was stored at room temperature and the other at 3 °C. Similarly, two samples of cellulose with starch gel were applied on the surface of two veal samples of which one was stored at room temperature and the other at 3 °C. The KNO2 diffusion in different depths of the meat was measured and its effect on the microbiological characteristics of the meat was evaluated. Τhe experiment was carried out in duplicate.

Results and conclusions

A satisfactory percentage of about 70 % of the initially encapsulated amount of KNO2 was diffused in the meat, while the rest remained in the pores of the delignified leaf celery. The migrating amount of KNO2 proved to be effective in preserving meat, as the microbiological load decreased significantly (especially within the first 12 h, from a decrease of 0.6 log CFU/g up to 2.4 log CFU/g).

Novelty and scientific contribution

The demand for meat products with low nitrite content is constantly increasing and the results of the present study are promising for the development of this technology in scale-up systems and on an industrial scale. This innovative approach could lead to products with controlled diffusion of the preservatives.

Effect of cellulose crystallinity modification by starch gel treatment for improvement in ethanol fermentation rate by non-GM yeast cell factories

This paper studies the reduction of crystallinity degree (CD) of cellulose treated with starch gel (SG), and the correlation of CD with the fermentation efficiency of cellulose to fuel-grade ethanol. Cellulose bioconversion from wood sawdust, consisting of three processes, was conducted in the same batch (one-step). The XRD and TEM analysis revealed 11% reduction in cellulose CD after its treatment with SG. One-step bioconversion process was performed employing two cell factories (CF) of non-engineered S. cerevisiae. CFs contained non- engineered S. cerevisiae cells covered with either SG entrapping Trichoderma reesei or cellulases prepared in the laboratory and immobilized in SG. The consolidated fermentation of treated cellulose resulted in an increase of bioethanol concentration (60-90%) in 2-day fermentation and the maximum ethanol concentration reached was approximately 5 mL/L (3.95 g/L). The fermentation efficiency for grade-fuel ethanol production was improved by cellulose pretreatment using SG to achieve reduced CD.

Consolidated bioprocessing of lactose into lactic acid and ethanol using non-engineered cell factories

The aim of this study is the consolidated bioprocessing of lactose into lactic acid and ethanol using non-engineered Cell Factories (CFs). Therefore, two different types of composite biocatalysts (CF1-CF2) based on Saccharomyces cerevisiae with immobilized microorganism or enzyme on starch gel (SG) were prepared for 5% w/v lactose fermentation. In CF1, S. cerevisiae was covered with SG containing Lactobacillus casei, Lactobacillus bulgaricus, Kluyveromyces marxianus CF1a-c. S. cerevisiae/SG-β-galactosidase (CF1d) was also used for simultaneous saccharification and fermentation (SSF) of lactose. In CF2, S. cerevisiae immobilized on tubular cellulose (TC) was covered with SG containing the aforementioned microorganisms (CF2a-c). The wet CF1d resulted in 96% of the theoretical ethanol yield while the wet CF1b and freeze-dried CF2b resulted in 89% of the theoretical lactic acid yield. The repeated batches using the CF2a-c exhibited better results than using CF1a-c. Subsequently, the freeze-dried CF2 as preservative and more manageable were verified for future exploitation of whey.

Vinegar Production from Corinthian Currants Finishing Side-Stream: Development and Comparison of Methods Based on Immobilized Acetic Acid Bacteria

Fruit wastes and side-streams can be used for vinegar production to create added value for the agri-food sector and enhance farmer incomes and local economies. In this study, methods for vinegar production by wild and selected acetic acid bacteria (the quick starter Acetobacter aceti and the acid-resistant Komagataeibacter europaeus), free (FC) and immobilized (IC) on a natural cellulosic carrier, are proposed using sweet wine made from the industrial finishing side-stream (FSS) of Corinthian currants as raw material. The results showed all cultures can produce vinegar with 46.65 ± 5.43 g/L acidity, from sweet FSS wine containing 5.08 ± 1.19% alcohol. The effect of immobilization was more obvious in the case of the selected culture, presenting better acetification efficiency, both fresh and after cold storage for 2 months. The vinegars had an antioxidant capacity of 263.5 ± 8.4 and 277.1 ± 6.7 mg/L (as ascorbic acid) and phenolic content 333.1 ± 12.0 and 222.2 ± 2.9 mg/L (as gallic acid) (for FC and IC, respectively). They also had a rich volatilome (140 compounds identified by SPME GC-MS), with higher percentages of esters identified in vinegars made by IC. The results are encouraging for vinegar production with IC of a mixed A. aceti and K. europaeus culture.

Cell factory models of non-engineered S. cerevisiae containing lactase in a second layer for lactose fermentation in one batch

The objective of this project was to ferment lactose and whey to ethanol in one-step process. Models of cell factory of non-engineered S.cerevisiae have been proposed to ferment lactose. The cell factory of non-engineered S. cerevisiae/SG-lactase was prepared by the addition, of a starch gel solution containing lactase on non-engineered S. cerevisiae, and freeze drying of it. The 2-layer non engineered S.cerevisiae-TC/SG-lactase factory was prepared by immobilizing S. cerevisiae on the internal layer of tubular cellulose (TC), and the lactase enzyme was contained in the upper layer of starch gel (SG) covering cells of S. cerevisiae. Using such cell factory for the fermentation of lactose, alcohol yield of 23-32 mL/L at lactose conversion of 71-100%. The improvement in alcohol yield by cell factory versus co-immobilization of lactase enzyme and S. cerevisiae on alginates, was found in the range of 28-78%. Likewise, the cell factories are more effective than engineered S. cerevisiae. The fermentation of whey instead of lactose resulted in a significant reduction of the fermentation time. Freeze-dried cell factories led to improved results as compared with non-freeze dried. When lactase was substituted with L. casei, ethanol and lactic acid were produced simultaneously at high concentrations, but in a much longer fermentation time. The cell factories can be considered as models for white biotechnology using lactose containing raw materials. This suggested cell factory model can be applied for other bioconversions using the appropriate enzymes and cells, in the frame of White Biotechnology without genetic modification.

Entrapped Psychrotolerant Yeast Cells within Pine Sawdust for Low Temperature Wine Making: Impact on Wine Quality

An alternative methodology is proposed for low temperature winemaking using freeze-dried raw materials. Pine sawdust was delignified and the received porous cellulosic material was applied as immobilization carrier of the psychrotolerant yeast strain Saccharomyces cerevisiae AXAZ-1. The immobilization of yeast cells was examined and verified by scanning electron microscopy (SEM). The immobilized biocatalyst and high-gravity grape must were separately freeze-dried without cryoprotectants and stored at room temperature (20–22 °C) for 3 months. The effect of storage on the fermentation efficiency of the immobilized biocatalyst at low temperatures (1–10 °C), as well as on the aromatic characteristics of the produced wines was evaluated. Storage time had no significant effect on the fermentation efficiency of the biocatalyst resulting in most cases in high ethanol production 13.8–14.8% v/v. The volatile fraction of the produced wines was examined using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography mass spectrometry (GC/MS). GC-MS/SPME analysis along with the organoleptic evaluation revealed in all produced wines a plethora of fresh and fruit aromatic notes. To conclude, fermentation kinetics and aromatic profile evaluation encourages the production of high-quality sweet wines at low temperatures using pine sawdust (Pinus halepensis) entrapped yeast cells as a promoter.

Food waste from restaurant sector - Characterization for biorefinery approach

The aim of this study is the analysis of food waste (FW) composition from local catering services to assess potential biorefinery development. Moisture content of different FW samples showed that 27-47% (w/w) was organic material. Main components were lipids (25.7-33.2, w/w), starch (16.2-29.4%, w/w) and proteins (23.5-18.3%, w/w) on a dry basis. A metal profile with Na and Mg as main components, followed by trace elements, i.e. Zn or Fe, was also found in food waste samples. Statistical tests in combination with principal component analysis provides an efficient methodology to establish specific composition variations between FW from different catering services, while relating them to FW typology. The combination of chemical characterization with statistical study constitutes a promising decision-making tool for FW processing and valorization. The innovative methodology presented in this study provides systematic evaluation of FW composition and variability to allow selection of the most appropriate valorization paths.

Production of a Potentially Synbiotic Pomegranate Beverage by Fermentation with Lactobacillus plantarum ATCC 14917 Adsorbed on a Prebiotic Carrier

A probiotic biocatalyst was prepared through Lactobacillus plantarum ATCC 14917 immobilization on a prebiotic carrier (delignified wheat bran) and was used for fermentations of pomegranate juice. Initially, pomegranate juice was fermented for 24 h and then was stored for 28 days at 4 °C. The obtained results regarding sugar and organic acid analysis revealed that the probiotic biocatalyst was effective. Ethanol was produced in small amounts (0.4-1% v/v). Total phenolic content and antioxidant activity was greater in the fermented pomegranate juice than in unfermented juice after 24 h of fermentation and over the time span of 28 days. Viability of probiotic cells was well maintained (above 8.65 log cfu/mL) after 24 h of fermentation and during 4 weeks of storage at 4 °C, and it is noteworthy that no pathogens were observed. The strength of viability of probiotic cells can be attributed to the immobilization carrier (delignified wheat bran) that exhibits prebiotic properties providing a protective effect to the cells. Finally, the proposed bioprocess of employing the proposed synbiotic biocatalyst for pomegranate juice fermentation shows great potential for commercialization while sensory evaluation highlights the degree of quality of the produced functional pomegranate beverages.

Employment of L. paracasei K5 as a Novel Potentially Probiotic Freeze-Dried Starter for Feta-Type Cheese Production

In the present study, a novel potentially probiotic Lactobacillus paracasei strain, previously isolated from dairy products, was evaluated as a starter culture of Feta-type cheese production. Targeting industrial applications, the starter culture was applied as a ready-to-use freeze-dried culture that was either free or immobilized. The immobilized biocatalyst composed of Lactobacillus paracasei K5 cells absorbed within delignified wheat bran prebiotic carrier. All produced cheeses were compared with cheese manufactured by renin enzyme. Several parameters that affect acceptability, quality and shelf-life of Feta-type cheese were investigated, including microbial populations, physicochemical characteristics and cheese volatiles through 90 days of ripening and storage. Survival of L. paracasei K5 remained in high levels (≥6.0 log cfu/g) after the 90th day of cheese production, as recorded by combining microbiological enumeration and strain-specific multiplex PCR analysis. The use of the freeze-dried novel starter culture (free or immobilized) enhanced the aromatic profile of Feta-type cheeses. Finally, the use of the potentially synbiotic immobilized biocatalyst further improved aromatic characteristics of produced cheese and decrease of possible spoilage or pathogenic microorganisms. These findings indicate the potential industrial use of freeze-dried L. paracasei K5 as starter culture for the production of good-quality functional Feta-type cheese.

Growth Capacity of a Novel Potential Probiotic Lactobacillus paracasei K5 Strain Incorporated in Industrial White Brined Cheese as an Adjunct Culture

In this study, a novel potential probiotic strain Lactobacillus paracasei K5, previously isolated from traditional Greek Feta cheese and kefir grains, was evaluated as an adjunct culture for industrial white brined cheese production. Targeting industrial applications, apart from free cell cultures, a novel ready-to-use freeze-dried immobilized biocatalyst was prepared. The biocatalyst composed of L. paracasei K5 cells immobilized on delignified wheat bran prebiotic carrier and was freeze-dried without cryoprotectants. The adjunct free or immobilized culture was added separately without prior adaptation during white brined cheese manufacture and the produced cheeses were compared with commercial white brined cheeses. Several parameters that affect the acceptability and quality of the cheeses, including microbial populations, physicochemical parameters, volatile by-products and organoleptic characteristics, were analyzed through 70 days of storage. Results showed that the viability of the adjunct culture added either free or immobilized remained in high levels (7 to 8 log cfu/g) during maturation and storage. In addition, all white brined cheeses with the adjunct probiotic culture showed a sharp decrease in spoilage and pathogenic microorganisms such as enterobacteria, salmonella, staphylococci and coliforms during cheese maturation, especially when compared with the commercial white brined cheeses. Finally, after maturation time exceeded, all cheeses were characterized as safe for human consumption. Cheeses volatile compounds were significantly enhanced by the incorporated immobilized biocatalysts. These findings indicate the potential industrial use of freeze-dried ready-to-use immobilized lactobacilli as reinforcement adjunct cultures for the production of good-quality functional cheese products.

PRACTICAL APPLICATION

The launch on market of novel foods developed by the incorporation of functional ingredients provides potential benefits to consumers' diet and new business opportunities for producers. Probiotic food products are one significant category of functional foods. Thus, this study focused on the development of a novel ready-to-use freeze-dried potential probiotic biocatalyst for functional white brined cheese production. The potential industrial application of such biocatalysts is highlighted by their incorporation as adjunct cultures that resulted in good-quality functional cheeses.

Lipid production and characterization by Mortierella (Umbelopsis) isabellina cultivated on lignocellulosic sugars

AIMS

To study and characterize the lipids produced by Mortierella (Umbelopsis) isabellina, during its growth on mixtures of glucose and xylose.

METHODS AND RESULTS

Glucose and xylose were utilized as carbon sources, solely or in blends, under nitrogen-limited conditions, in batch-flask trials (initial sugars at 80 g l^-1 ). Significant lipid production (maximum lipid 17·8 g l^-1 ; lipid in DCW 61·0% w/w; lipid on glucose consumed 0·23 g g^-1 ) occurred on glucose employed solely, while xylose concentration in the growth medium was conversely correlated with lipid accumulation. With increasing xylose concentrations into the blend, lipid storage decreased while xylitol in significant concentrations (up to 24 g l^-1 ) was produced. Irrespective of the sugar blend employed, significant quantities of endopolysaccharides were detected in the first growth steps (in the presence of nitrogen into the medium or barely after its disappearance) while lipids were stored thereafter. Neutral lipids, mainly composed of triacylglycerols, were the main microbial lipid fraction. Phospholipids were quantified both through fractionation and subsequent gravimetric determination and also through determination of phosphorus, and it seemed that the second method was more accurate. Phospholipids were mainly composed of phosphatidylcholine and another nonidentified compound presumably being phosphatidyldimethylethanolamine.

CONCLUSIONS

Mortierella isabellina is suitable to convert lignocellulosic sugars into lipids.

SIGNIFICANCE AND IMPACT OF THE STUDY

Differentiations between metabolism on xylose and glucose were reported. Moreover, this is one of the first reports indicating extensive analysis of microbial lipids produced by M. isabellina.

Technological Development of Brewing in Domestic Refrigerator Using Freeze-Dried Raw Materials

Development of a novel directly marketable beer brewed at low temperature in a domestic refrigerator combined with yeast immobilization technology is presented in this study. Separately, freeze-dried wort and immobilized cells of the cryotolerant yeast strain Saccharomyces cerevisiae AXAZ-1 on tubular cellulose were used in low-temperature fermentation (2, 5 and 7 °C). The positive effect of tubular cellulose during low-temperature brewing was examined, revealing that freeze-dried immobilized yeast cells on tubular cellulose significantly reduced the fermentation rates in contrast to freeze-dried free cells, although they are recommended for home-made beer production. Immobilization also enhanced the yeast resistance at low-temperature fermentation, reducing the minimum brewing temperature value from 5 to 2 °C. In the case of high-quality beer production, the effect of temperature and initial sugar concentration on the fermentation kinetics were assessed. Sensory enrichment of the produced beer was confirmed by the analysis of the final products, revealing a low diacetyl concentration, together with improved polyphenol content, aroma profile and clarity. The proposed process for beer production in a domestic refrigerator can easily be commercialized and applied by dissolving the content of two separate packages in tap water; one package containing dried wort and the other dried immobilized cells on tubular cellulose suspended in tap water.

Porous cellulose as promoter of oil production by the oleaginous yeast Lipomyces starkeyi using mixed agroindustrial wastes

Enhanced single cell oil (SCO) production by the oleaginous yeast Lipomyces starkeyi DSM 70296, immobilised on delignified porous cellulose, is reported. Pure glucose media were initially used. The effects of substrate pH and treatment temperature were evaluated, showing that 30°C and pH 5.0 were the optimum conditions for SCO production by the immobilised yeast. The immobilisation technique led to increased lipid accumulation and cell growth by 44% and 8%, respectively, in the glucose media, compared to free cells in suspension. This positive effect was also shown when low concentration mixed agro-industrial waste suspensions were used as substrates, leading to 85% enhanced SCO production in comparison with free cells. Higher fatty acid (HFA) analysis showed that yeast immobilisation led to increased formation of unsaturated HFAs (6%) and reduced saturated HFAs (5%) compared to free cells.

Scale-up for esters production from straw whiskers for biofuel applications

Delignified wheat straw was fermented by a mixed bacterial anaerobic culture obtained from a UASB reactor to produce organic acids (OAs). Kissiris was used as immobilization carrier in a 2-compartment 82L bioreactor filled with 17L of fermentation broth for the first 7 fermentation batches and up to 40L for the subsequent batches. The amount of straw used was 30g/L and the temperature was set at 37°C for all experiments. The total OAs reached concentrations up to 17.53g/L and the produced ethanol ranged from 0.3 to 1mL/L. The main OAs produced was acetic acid (6-8g/L) and butyric acid (3-8g/L). The OAs were recovered from the fermentation broth by a downstream process using 1-butanol, which was the solvent with the best recovery yields and also served as the esterification alcohol. The enzymatic esterification of OAs resulted to 90% yield.

Downstream extraction process development for recovery of organic acids from a fermentation broth

The present study focused on organic acids (OAs) recovery from an acidogenic fermentation broth, which is the main problem regarding the use of OAs for production of ester-based new generation biofuels or other applications. Specifically, 10 solvents were evaluated for OAs recovery from aqueous media and fermentation broths. The effects of pH, solvent/OAs solution ratios and application of successive extractions were studied. The 1:1 solvent/OAs ratio showed the best recovery rates in most cases. Butyric and isobutyric acids showed the highest recovery rates (80-90%), while lactic, succinic, and acetic acids were poorly recovered (up to 45%). The OAs recovery was significantly improved by successive 10-min extractions. Alcohols presented the best extraction performance. The process using repeated extractions with 3-methyl-1-butanol led to the highest OAs recovery. However, 1-butanol can be considered as the most cost-effective option taking into account its price and availability.

Biorefining of by-product streams from sunflower-based biodiesel production plants for integrated synthesis of microbial oil and value-added co-products

This study focuses on the valorisation of crude glycerol and sunflower meal (SFM) from conventional biodiesel production plants for the separation of value-added co-products (antioxidant-rich extracts and protein isolate) and for enhancing biodiesel production through microbial oil synthesis. Microbial oil production was evaluated using three oleaginous yeast strains (Rhodosporidium toruloides, Lipomyces starkeyi and Cryptococcus curvatus) cultivated on crude glycerol and nutrient-rich hydrolysates derived from either whole SFM or SFM fractions that remained after separation of value-added co-products. Fed-batch bioreactor cultures with R. toruloides led to the production of 37.4gL(-1) of total dry weight with a microbial oil content of 51.3% (ww(-1)) when a biorefinery concept based on SFM fractionation was employed. The estimated biodiesel properties conformed with the limits set by the EN 14214 and ASTM D 6751 standards. The estimated cold filter plugging point (7.3-8.6°C) of the lipids produced by R. toruloides is closer to that of biodiesel derived from palm oil.

New generation biofuel: continuous acidogenesis of sucrose-raffinose mixture simulating vinasse is promoted by γ-alumina pellets

BACKGROUND

This investigation comprises a contribution on the production of a new generation biofuel using the industrial liquid waste of bioethanol distilleries, known as vinasse. This study focuses on the exploitation of vinasse as an acidogenesis substrate for volatile fatty acids and simultaneous ethanol production. These products can be used for ester production, which is the new generation biofuel. Therefore, the aims of the present study are (i) to examine any promotional effect of γ-alumina on acidogenesis of a sucrose-raffinose mixture simulating vinasse, (ii) to study the operational stability of the continuous acidogenesis of sucrose and raffinose and subsequently of vinasse, and (iii) to determine the volatile fatty acid chemical composition and ethanol formation.

RESULTS

Batch acidogenesis of sucrose and raffinose mixtures showed that γ-alumina promoted fermentation leading to an increase in the volatile fatty acid yield factor from 40% to 95% compared to free cells. The application of the system in continuous mode for more than 3 months showed that the continuous volatile fatty acid productivity obtained was higher than 7 g/L/day. Lactic acid was the predominant acid when sucrose and raffinose were used while butyric acid in the case of vinasse. The highest volatile fatty acid concentration reached was 19 g/L for vinasse.

CONCLUSIONS

A promoting effect of γ-alumina in acidogenic fermentation of sucrose-raffinose and vinasse is reported. Continuous acidogenesis of sucrose-raffinose mixtures and vinasse using γ-alumina with immobilized cells showed high operational stability (more than 3 months). These findings result in easy scale up of the process that will produce a high annual added value of $11,000,000 in a daily bioethanol production plant of 50,000 L.

Continuous acidogenesis of sucrose, raffinose and vinasse using mineral kissiris as promoter

The use of kissiris as promoter (culture immobilization carrier) in anaerobic acidogenesis of sucrose, raffinose and vinasse is reported. Initially, the effect of pH (4-8) and fermentation temperature (18-52 °C) on the accumulation of low molecular weight organic acids (OAs) during sucrose acidogenesis, was evaluated. The promoting effect of kissiris was confirmed compared to free cells, resulting in 80% increased OAs production. The optimum conditions (pH 8; 37 °C) were used during acidogenesis of sucrose/raffinose mixtures. A continuous system was also operated for more than 2 months. When sucrose and sucrose/raffinose mixtures were used, lactic acid type fermentation prevailed, while when vinasse was used, butyric acid type fermentation occurred. Total OAs concentrations were more than 14 g/L and ethanol concentrations were 0.5-1 mL/L. Culture adaptation in vinasse was necessary to avoid poor results. The proposed process is promising for new generation ester-based biofuel production from industrial wastes.

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.

Free and immobilized Lactobacillus casei ATCC 393 on whey protein as starter cultures for probiotic Feta-type cheese production

The use of free and immobilized Lactobacillus casei ATCC 393 on whey protein as starter culture in probiotic Feta-type cheese production was evaluated. The probiotic cultures resulted in significantly higher acidity; lower pH; reduced counts of coliforms, enterobacteria, and staphylococci; and improved quality characteristics compared with cheese with no culture. Microbiological and strain-specific multiplex PCR analysis showed that both free and immobilized L. casei ATCC 393 were detected in the novel products at levels required for conferring a probiotic effect at the end of the ripening. The effect of starter culture on production of volatile compounds was investigated by the solid-phase microextraction gas chromatography-mass spectrometry analysis technique. The immobilized cells resulted in an improved profile of aroma-related compounds and the overall high quality of the novel products was ascertained by the preliminary sensory test. Finally, the high added value produced by exploitation of whey, which is an extremely polluting industrial waste, was highlighted and assessed.

Favouring butyrate production for a new generation biofuel by acidogenic glucose fermentation using cells immobilised on γ-alumina

The effect of γ-alumina as a fermentation advancing tool and as carrier for culture immobilisation, regarding VFAs and ethanol production during acidogenic fermentation of glucose, was examined at various process conditions (sugar concentration, pH) and operation modes (continuous with and without effluent recirculation and batch). The results showed that at high initial pH (8.9) the continuous acidogenic fermentation of glucose led to high yields of VFAs and favoured the accumulation of butyric acid. The batch process on the other hand at pH 6.5, favoured the ethanol-type fermentation. The results indicate that in the frame of technology development for new generation biofuels, using γ-alumina as a process advancing tool at optimum process conditions (pH, initial glucose concentration and mode of operation), the produced VFAs profile and ethanol concentration may be manipulated.

Study of whey fermentation by kefir immobilized on low cost supports using 14C-labelled lactose

Brewer's Spent Grains (BSG) and Malt Spent Rootlets (MSR) were used as supports for kefir cells immobilization and the role of lactose uptake rate by kefir in the positive activity of produced biocatalysts during whey fermentation was investigated. Lactose uptake rate by the immobilized cells was recorded using (14)C-labelled lactose and the effect of various conditions (pH, temperature and kind of support) on it and consequently on fermentation time and ethanol production was examined. The results showed that lactose uptake rate was correlated to fermentation rate and increased as temperature was increased up to 30°C at pH 5.5. The same results have been recently noticed by using biocatalysts with Delignified Cellulosic Materials (DCM) and Gluten Pellets (GP), but fermentation time of about 7h by kefir immobilized on DCM and BSG resulted to two fold lower than that on GP and MSR. The highest alcohol concentration was observed by MSR.

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.

γ-Alumina as a process advancing tool for a new generation biofuel

The production of volatile fatty acids (VFAs) in a continuous process using a synthetic glucose medium as model substrate in the presence of γ-alumina as promoter is described. The results showed formation of acetic, propionic, isobutyric, butyric, isovaleric and valeric acids, with acetic acid being more than 90% of the total VFAs produced. It is also highlighted that γ-alumina enhanced the simultaneous production of acetic acid and ethanol, which in some cases was formed at concentrations able to esterify about 85% of the produced VFAs. Since most agro-industrial effluents can be treated by anaerobic acidogenic digestion, while lignocellulosic biomass can be converted to VFAs after hydrolysis, this contribution can lead to a breakthrough in the research of biofuel production from renewable waste sources.

Evaluation of by-products from the biodiesel industry as fermentation feedstock for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production by Cupriavidus necator

Utilization of by-products from oilseed-based biodiesel production (crude glycerol, rapeseed meal hydrolysates) for microbial polyhydroxyalkanoate (PHA) production could lead to the replacement of expensive carbon sources, nutrient supplements and precursors for co-polymer production. Batch fermentations in shake flasks with varying amounts of free amino nitrogen led to the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) with a 2.8-8% 3HV content. Fed-batch fermentations in shake flasks led to the production of 10.9g/L P(3HB-co-3HV) and a 55.6% P(3HB-co-3HV) content. NaCl concentrations between 2 and 6g/L gradually became inhibitory to bacterial growth and PHA formation, whereas in the case of K(2)SO(4), the inhibitory effect was observed only at concentrations higher than 20g/L. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and nuclear magnetic resonance ((13)C NMR) demonstrated that the incorporation of 3HV into the obtained P(3HB-co-3HV) lowered glass transition temperature, crystallinity and melting point as compared to polyhydroxybutyrate. Integrating PHA production in existing oilseed-based biodiesel plants could enhance the viability and sustainability of this first generation biorefinery.

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.

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.

Volatiles formation from grape must fermentation using a cryophilic and thermotolerant yeast

Grape must fermentation performance and volatiles formation by simultaneously cryophilic and thermotolerant yeast (strain AXAZ-1), isolated from grapes in Greece, was evaluated in a wide temperature range (5-40°C). Yeast strain was immobilized on brewer's spent grains (BSG) and the formed biocatalyst was introduced into a Multi-Stage Fixed Bed Tower (MFBT) bioreactor. Almost complete sugar utilization from the aforementioned biocatalyst was observed in a wide temperature spectrum, ranging from 5 °C to 37 °C, while at 40 °C residual sugar was up to 29 g/l. Time to complete fermentation with the immobilized yeast ranged from 290 h at 5 °C and 120 h at 40 °C to 25 h at 33 °C. The daily ethanol productivity reached maximum (88.6 g/l) and minimum (5.6 g/l) levels at 33 °C and 5 °C, respectively. The aroma-related compounds' profiles of immobilized cells at different fermentation temperatures were evaluated by using solid phase microextraction (SPME) gas chromatography/mass spectrometry (GC/MS). Must fermentation resulted in a high-quality fermentation product due to the low concentrations of higher and amyl alcohols at all temperatures tested. AXAZ-1 is a very promising strain for quality wine production, as it is capable of performing fermentations of high ethanol concentration and productivities in both low and high temperatures.

Research perspectives and role of lactose uptake rate revealed by its study using 14C-labelled lactose in whey fermentation

The present investigation examines the effect of pH, temperature and cell concentration on lactose uptake rate, in relation with kinetics of whey fermentation using kefir and determines the optimum conditions of these parameters. Lactose uptake rate was measured by adding (14)C-labelled lactose in whey. The results reveal the role of lactose uptake rate, being the main factor that affects the rate of fermentation, in contrast to the activity of the enzymes involved in lactose bioconversion process. Lactose uptake rate results discussion showed that mainly Ca(2+) is responsible for the reduced whey fermentation rate in comparison with fermentations using synthetic media containing lactose. Likewise, the results draw up perspectives on whey fermentation research to improve whey fermentation rate. Those perspectives are research to remove Ca(2+) from whey, the use of nano and microtubular biopolymers and promoters such as γ-alumina pellets and volcan foaming rock kissiris in order to accelerate whey fermentation.

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.

Lactose uptake rate by kefir yeast using 14C-labelled lactose to explain kinetic aspects in its fermentation

Tauhe present work shows the relation between kefir fermentation ability and carbohydrate uptake rate. This was examined in a model system containing kefir co-culture and lactose in order to study fermentation induced by yeasts and bacteria at the same time. Lactose uptake rate was recorded by using (14)C-labelled lactose. The effect of lactose, cell concentration and pH on lactose fermentation was examined. Results have shown increase of lactose uptake rate at lower cell concentrations and specifically the maximum values of lactose uptake rate were obtained at 30 degrees C, 5.5 pH value and initial lactose and cell concentration 10% w/v and 16 g/L, respectively. Likewise, lighten that the increase of the fermentation rate by immobilized cells can be attributed also, in addition to other factors, to lower cell concentration on the surface of the support or of the promoter. Besides, it is shown that the effect of pH value on the biochemical reactions, carried out by intracellular enzymes can be attributed, except to the effect of pH on enzyme ability, in addition to the effect of pH on carbohydrate uptake rate.

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.