Studies on the variables and kinetics of SCP production from nopal fruit juice

Summary Submerged batch cultivation under controlled environmental conditions of pH 3.8, temperature 30°C, and K_La200 h^–1 (above 180 mMO₂ l ^–1 h^–1 oxygen supply rate) produced a maximum (12.0 g·l ^–1) SCP (Candida utilis) yield on the deseeded nopal fruit juice medium containing C/N ratio of 7.0 (initial sugar concentration 25 g·l ^–1) with a yield coefficient of 0.52 g cells/g sugar. In continuous cultivation, 19.9 g·l ^–1 cell mass could be obtained at a dilution rate (D) of 0.36 h^–1 under identical environmental conditions, showing a productivity of 7.2 g·l ^–1·h^–1. This corresponded to a gain of 9.0 in productivity in continuous culture over batch culture. Starting with steady state values of state variables, cell mass (C_X–19.9 g·l ^–1), limiting nutrient concentration (C_ln–2.5 g·l ^–1) and sugar concentration (C_S–1.5 g·l ^–1) at control variable conditions of pH 3.8, 30°C, and K_La 200 h^–1 keeping D=0.36 h^–1 as reference, transient response studies by step changes of these control variables also showed that this pH, temperature and K_La conditions are most suitable for SCP cultivation on nopal fruit juice. Kinetic equations obtained from experimental data were analysed and kinetic parameters determined graphically. Results of SCP production from nopal fruit juice are described.Nomenclature C_ln concentration of ammonium sulfate (g·l ^–1) - C_S concentration of total sugar (g·l ^–1) - C_X cell concentration (g·l ^–1) - D dilution rate (h^–1) - K_ln Monod's constant (g·l ^–1) - m maintenance coefficient (g ammonium sulfate cell^–1 h^–1) - m_(S) maintenance coefficient (g sugar g cell^–1 h^–1) - t time, h - Y yield coefficient (g cells/g ammonium sulfate) - Y_m maximum of Y - Y_S yield coefficient based on sugar consumed (g cells · g sugar^–1) - Y_S(m) maximum value of Y_S - ^µm maximum specific growth rate constant (h^–1)     

Fermentation behaviour and volatile compound production by agave and grape must yeasts in high sugar Agave tequilana and grape must fermentations

Few studies have been performed on the characterization of yeasts involved in the production of agave distilled beverages and their individual fermentation properties. In this study, a comparison and evaluation of yeasts of different origins in the tequila and wine industries were carried out for technological traits. Fermentations were carried out in high (300 g l⁻¹) and low (30 g l⁻¹) sugar concentrations of Agave tequilana juice, in musts obtained from Fiano (white) and Aglianico (red) grapes and in YPD medium (with 270 g l⁻¹ of glucose added) as a control. Grape yeasts exhibited a reduced performance in high-sugar agave fermentation, while both agave and grape yeasts showed similar fermentation behaviour in grape musts. Production levels of volatile compounds by grape and agave yeasts differed in both fermentations.     

An optimization study of carotenoid production by Rhodotorula glutinis DBVPG 3853 from substrates containing concentrated rectified grape must as the sole carbohydrate source

A multivariate statistical approach was employed for the optimization of conditions for carotenoid production by Rhodotorula glutinis DBVPG 3853 from a substrate containing concentrated rectified grape must as the sole carbohydrate source. Several experimental parameters (carbohydrate, yeast autolysate and salt concentrations, and pH) were tested at two levels by following a fractional factorial design. Carotenogenesis was most sensitive to both initial pH and yeast autolysate concentration. A Central Composite Design experiment was then performed by obtaining both second-order polynomial models and isoresponse diagrams where initial pH and yeast autolysate concentration were considered as variables. In this way it was possible to determine the conditions (pH = 5.78, yeast autolysate = 4.67 g L⁻¹) which maximize both the concentration of total carotenoids and that of β-carotene (6.9 mg L⁻¹ and 1100 μg L⁻¹ of culture fluid, respectively, after 120 h of fermentation). Journal of Industrial Microbiology & Biotechnology (2000) 24, 41–45. Received 23 February 1999/ Accepted in revised form 14 September 1999     

Use of the crossflow-microscreen technique for SCP production from dilute substrates

Summary A crossflow-microscreen cultivation technique was successfully used to select and maintain an easily harvestable microbial culture with a limited number of species under non-aseptic conditions in diluted cheese whey. The microbial selective pressure exerted by the system could be manipulated by varying the hydraulic () and mean cell () residence times. The optimum system parameters were =1 h and =10 h, resulting in a selected microbial population comprising three species only, namely Geotrichum candidum, Streptococcus cremoris and Leuconostoc lactophilum. The amino acid profile of the SCP produced compared favourably with other types of protein. The crossflow-microscreen technique makes SCP production possible from dilute, waste organic effluents.     

Bioconversion of grape must into modulated gluconic acid production by Aspergillus niger ORS-4.410

AIMS: Analysis of regulators for modulated gluconic acid production under surface fermentation (SF) condition using grape must as the cheap carbohydrate source, by mutant Aspergillus niger ORS-4.410. Replacement of conventional fermentation condition by solid-state surface fermentation (SSF) for semi-continuous production of gluconic acid by pseudo-immobilization of A. niger ORS-4.410. METHODS AND RESULTS: Grape must after rectification was utilized for gluconic acid production in batch fermentation in SF and SSF processes using mutant strain of A. niger ORS-4.410. Use of rectified grape must led to the improved levels of gluconic acid production (80-85 g l(-1)) in the fermentation medium containing 0.075% (NH4)2HPO4; 0.1% KH2PO4 and 0.015% MgSO4.7H2O at an initial pH 6.6 (+/-0.1) under surface fermentation. Gluconic acid production was modulated by incorporating the 2% soybean oil, 2% starch and 1% H2O2 in fermentation medium at continuously high aeration rate (2.0 l min(-1)). Interestingly, 95.8% yield of gluconic acid was obtained when A. niger ORS-4.410 was pseudo-immobilized on cellulose fibres (bagasse) under SSF. Four consecutive fermentation cycles were achieved with a conversion rate of 0.752-0.804 g g(-1) of substrate into gluconic acid under SSF. CONCLUSIONS: Use of additives modulated the gluconic acid production under SF condition. Semi-continuous production of gluconic acid was achieved with pseudo-immobilized mycelia of A. niger ORS-4.410 having a promising yield (95.8%) under SSF condition. SIGNIFICANCE AND IMPACT OF THE STUDY: The bioconversion of grape must into modulated gluconic acid production under SSF conditions can further be employed in fermentation industries by replacing the conventional carbohydrate sources and expensive, energy consuming fermentation processes.     

Yeast production from virgin grape marc

An alternative utilization of virgin grape marc (VGM) to produce SCP from S. ceretisiae is reported. A simple extraction method of fresh grape marc produces a sugar-rich solution: through fed-batch fermentation, a high-value yeast biomass instead of a low-value product like ethanol can be produced. Productivity and quality of yeast are similar to these obtainable from molasses. The convenience of yeast production from VGM is briefly discussed; it appears of great interest in south Italy and generally in grape-producing countries, specially if these lack relevant sources of fermentable sugars.     

Semi-continuous and continuous riboflavin production by calcium-alginate-immobilized Candida tropicalis in concentrated rectified grape must

Candida tropicalis cells were immobilized in calcium alginate. Gel beads were used to inoculate a medium containing concentrated rectified grape must as the sole carbohydrate source for both semi-continuous and continuous riboflavin production, in a 1litre glass stirred-tank fermenter. In semi-continuous mode, vitamin B₂ concentrations in culture broth ranged from approximately 350 to 650mg.l^-1 in successive runs. In continuous mode, concentrations of about 400–600mg.l^-1 were observed in the effluent for more than 1monthwithout significant loss of flavinogenic activity. The highest value of both vitamin B₂ production and sugar bioconversion occurred at the lowest dilution rate (0.008h^-1).     

Utilization of grape must and concentrated rectified grape must to produce gluconic acid by Aspergillus niger,in batch fermentations

Summary Grape must and concentrated rectified grape must were used for the gluconic acid synthesis using Aspergillus niger batch cultures. The latter substrate was the better, with a production, at 72 h, of 67.43 g/l and a yield (calculated on converted glucose) of 0.96. Citric acid was also observed as a by-product. In order to decrease the residual fructose content, at the end of the gluconate production cycle, an experimental model of sequential fermentation A. niger — Rhizopus arrhizus was proposed for the synthesis of gluconic and fumaric acid. The use of Glucose-isomerase (EC 5.3.1.5) to convert fructose to glucose was also tested.     

Effect of operating variables on back-extraction characteristics of succinic acid from organic phase

Tri-n-octylamine (TOA) is an effective extractant for the recovery of succinic acid from fermentation broth. The recovery of succinic acid from organic phase depends on the operating variables such as temperature, pH, volume of aqueous phase, and use of displacer. In thermal recovery of succinic acid, 34% of succinic acid was recovered at 90°C. More than 90% of succinic acid was back-extracted by pH-swing. Efficiency of back-extraction was increased 23% as increasing volume of aqueous phase. Use of oleic acid as a displacer increased efficiency of back-extraction to 76%. Aqueous phase volume and concentration of oleic acid were controlled simultaneously to increase the efficiency of back-extraction and percent recovery of succinic acid reached to 90.     

Effect of some operating variables on citrate recovery from model solutions by electrodialysis

The effect of pH and temperature (straight theta) on the overall performance indicators (i.e., solute recovery, rho, and Faraday, eta, efficiencies; specific energy consumption, epsilon, solute, JS, and water, JW, fluxes) of batch electrodialytic recovery of citric acid from model solutions was assessed at different values of feed solute concentration (cSf) and electric current density (j). Regardless of the initial feed concentration used, rho and JS were found to be independent of straight theta; eta and JW exhibited a positive trend with respect to straight theta, while epsilon a negative one. At the maximum temperature tested (33 degrees C), as the pH of the feed solution was varied from 3 to 7, rho increased from 0.90 +/- 0.08 to 0.97 +/- 0.02, eta grew from 0.09 +/- 0.02 to 0.50 +/- 0.01, JS practically doubled, epsilon reduced about 8 times, but JW increased from 3 to 4 times. So, the optimal conditions for this technique are to be determined by balancing the savings in the investment and maintenance costs against the energy costs. Copyright John Wiley & Sons, Inc.     

Characterization of Saccharomyces cerevisiae strains isolated from must of grape grown in experimental vineyard

AIMS: Isolation and characterization of indigenous Saccharomyces cerevisiae strains from 12 grape varieties grown in an experimental vineyard of Apulia. METHODS AND RESULTS: Thirty to 40 colonies from each of the 12 fermentations were obtained at the end stage of spontaneous fermentation. By using morphological and physiological methods and by the PCR analysis of internal transcribed ITS1-5,8S-ITS2, the isolates belonging to Saccharomyces genus were identified. These isolates were further characterized by amplification with S. cerevisiae species- and delta element-specific primers, thus allowing the identification of S. cerevisiae strains selected from each of the 12 fermentations. By means of RFLP analysis of mtDNA, each S. cerevisiae population isolated from a single fermentation appeared to constitute a genetically homogenous group. The comparison of the 12 cultivar-specific mtDNA RFLP patterns, allowed classifying the 12 S. cerevisiae populations into three genetically homogenous groups. The isolated strains fermented vigorously in synthetic and grape juice medium and showed high alcohol and sulphur dioxide (SO(2)) resistance and low hydrogen sulphite (H(2)S) production. CONCLUSIONS: The molecular analysis, in conjunction with the traditional morphological and physiological methods, was useful in discriminating at strain level the indigenous population of S. cerevisiae present in a vineyard of Apulia. The dominant S. cerevisiae strains identified in the 12 fermented musts showed potentially important oenological characteristics. SIGNIFICANCE AND IMPACT OF THE STUDY: The characterization of natural S. cerevisiae strains from several typical Italian grapes grown in a restricted experimental vineyard is an important step towards the preservation and exploitation of yeast biodiversity of Apulia, a relevant wine-producing region. The close relationship between the S. cerevisiae strains from different grapes grown in the same vineyard indicated that the occurrence of native strains is representative of the area rather than of the variety of grapes.     

Biochemical aspects of stuck and sluggish fermentation in grape must

Recently a number of studies have focused on the factors responsible for the occurrence of stuck and sluggish fermentations. Results from these studies indicate that together with nutritional deficiencies and inhibitory substances, technological practices could lead to such situations. This review explains, from a biochemical point of view, the influence of nutritional deficiencies, inhibitory substances and technological practices on yeast cell development and physiology and the fermentation process. Received 07 February 1997/ Accepted in revised form 01 July 1997     

Evaluation of the SCP from Opuntia juice

Summary In deseeded opuntia juice medium batch and continuous cultivation ofCandida utilis produced 12 and 19.9gl^–1 yield of the SCP respectively. Its biological value(72), digestibility coefficient(70) and protein score(58) indicated it to be a good protein.     

Ethyl esterification of long-chain unsaturated fatty acids derived from grape must by yeast during alcoholic fermentation

The composition of total fatty acid ethyl ester (FAEE) in yeast cells and the liquid phase separated from grape must during alcoholic fermentation at different temperatures was investigated by using the solid-phase extraction method. Thirteen FAEE from butyric to linolenic acids were detected during fermentation. Significant amounts of long-chain unsaturated FAEE, including linoleic and linolenic acids derived from grape material, had already accumulated in the yeast cells by day 3 during fermentation.     

SCP production and removal of organic load from cassava starch industry waste by yeasts

Wastewater obtained from the cassava processing industry was used to produce single cell protein (SCP). A few selected strains of yeasts were analysed for the SCP production based on the criteria of best biomass yield and high reduction in Chemical Oxygen Demand (COD) under nitrogen limitation. The monoculturing of Candida tropicalis gave the highest μmax with a protein enhancement of 4 fold and 50% decrease in COD. The performance of cocultures have shown an improvement in the COD removal of the wastewater and in the percent increase of protein. The effects of coculturing were better in a lab fermentor under controlled conditions.     

Contribution of winery-resident Saccharomyces cerevisiae strains to spontaneous grape must fermentation

The origin of the Saccharomyces cerevisiae strains that are responsible for spontaneous grape must fermentation was investigated in a long-established industrial winery by means of two different approaches. First, seven selected components of the analytical profiles of the wines produced by 58 strains of S. cerevisiae isolated from different sites and phases of the production cycle of a Grechetto wine were subjected to Principal Components Analysis. Secondly, the same S. cerevisiae isolates underwent PCR fingerprinting by means of delta primers. The results obtained by both methods demonstrate unequivocally that under real vinification conditions, the S. cerevisiae strains colonising the winery surfaces are the ones that carry out the natural must fermentation.