Dextransucrase production using cashew apple juice as substrate: effect of phosphate and yeast extract addition

Cashew apples are considered agriculture excess in the Brazilian Northeast because cashew trees are cultivated primarily with the aim of cashew nut production. In this work, the use of cashew apple juice as a substrate for Leuconostoc mesenteroides cultivation was investigated. The effect of yeast extract and phosphate addition was evaluated using factorial planning tools. Both phosphate and yeast extract addition were significant factors for biomass growth, but had no significant effect on maximum enzyme activity. The enzyme activities found in cashew apple juice assays were at least 3.5 times higher than the activity found in the synthetic medium. Assays with pH control (pH = 6.5) were also carried out. The pH-controlled fermentation enhanced biomass growth, but decreased the enzyme activity. Crude enzyme free of cells produced using cashew apple juice was stable for 16 h at 30°C at a pH of 5.0.     

Continuous fermentation of apple juice by immobilized yeast cells

Summary The sugar content of an apple juice was continuously converted into ethanol bySaccharomyces cerevisiae entrapped in Ca-alginate gel. The average values characterizing the process were: fermentation efficiency, 84.7±4.2%, ethanol concentration in the mash, 38.9–1.9 g·l^–1 and volumetric productivity, 6.3±0.5 g·l^–1·h^–1.     

Ethanolic fermentation of cane molasses by a highly flocculent yeast

Summary A study of the comparative kinetics of standardS.uvarum ATCC 26602 withS.cerevisiae Y-10 (an isolate) and a highly flocculent strain ofS.uvarum in batch mode has shown that both the isolate and the highly flocculentS. uvarum strain have more desirable characteristics than the standard strains for ethanol production from cane molasses.     

The effect of temperature,pH, and initial glucose concentration on the kinetics of ethanol production by Zymomonas mobilis in batch fermentation

Summary Zymomonas mobilis, strain ATCC 10988, was used to evaluate the effects of pH (5.0 to 8.0), temperature (30°C to 40°C), and initial glucose concentration (75 g/l to 150 g/l) on the kinetics of ethanol production from glucose using batch fermentation. Specific ethanol production rate was maximum and nearly constant over a pH range of 6.0 to 7.5. End-of-batch ethanol yield and specific growth rate were insensitive to pH in the range of 5.0 to 7.5. End-of-batch ethanol yield was maximum and nearly constant between 30°C and 37°C but decreased by 24% between 37°C and 40°C. All other kinetic parameters are greatest at 34°C. End-of-batch ethanol yield is maximum at an initial glucose concentration of 100 g/l. Specific growth rate reaches a maximum at 75 g/l, but specific ethanol production rate decreases throughout the range. The optimum initial glucose concentration of 100 g/l gives the highest ethanol yield at a specific ethanol production rate less than 10% below the maximum observed.     

Effects of inoculum concentration,temperature, and carbon sources on tannase production during solid state fermentation of cashew apple bagasse

In this study, the optimization of tannase production by solid state fermentation was investigated using cashew apple bagasse (CAB), an inexpensive residue produced by the cashew apple agroindustry, as a substrate. To accomplish this, CAB was enriched with 2.5% (w/w) tannic acid and 2.5% (w/w) ammonium sulphate and then moistened with water (60 mL/100 g of dry CAB). The influence of inoculum concentration (10⁴ to 10⁷ spores/g), temperature (20, 25, 30, and 35°C) and several additional carbon sources (glucose, starch, sucrose, maltose, analytical grade glycerol, and glycerol produced during biodiesel production) on enzyme production by Aspergillus oryzae was then evaluated. Supplementation with maltose and glycerol inhibited tannase synthesis, which resulted in lower enzyme activity. Starch and sucrose supplementation increased enzyme production, but decreased the enzyme productivity. The maximum tannase activity (4.63 units/g of dry substrate) was obtained at 30°C, using 10⁷ spores/g and 1.0% (w/v) sucrose as an additional carbon source.     

Mathematical modelization of a packed-bed reactor performance with immobilized yeast for ethanol fermentation

The performance of a continuous vertical packed-bed reactor with yeast immobilized in carrageenan gel beads is reported. The study focuses on the mathematical modelling of the steady-state fermentor behavior by means of a tanks-in-series model which includes the intrinsic kinetic model and the external mass transfer and internal diffusion-reaction conditions in the beads.     

Inhibition of alcoholic fermentation by substrate and ethanol

The effect of ethanol and sugars on rates of fermentation was studied. We used a strain of Canadida pseudotropicalis. The specific rate of fermentation was determined by using the Warburg manometer. The effect of ethanol was formulated as an exponential function of ethanol concentration, but the empirical constant was different when glucose or lactose was used as a substrate. The effects of both ethanol and substrate were formulated. It was demonstrate that when lactose and glucose were present in the medium with a small amount of alcohol, a synergistic effect on the rate of fermentation appeard. This phenomenon considerably limits the rate of fermentation.     

The effect of temperature on the growth of strains of Kloeckera apiculata and Saccharomyces cerevisiae in apple juice fermentation

The influence of temperature (10°C and 25°C) on the survival and growth of Saccharomyces cerevisiae and Kloeckera apiculata was examined in mixed and pure cultures during fermentation in apple juice. The growth reached by S. cerevisiae did not seem to be affected by temperature and the presence of K. apiculata . However, the growth and survival of K. apiculata , both in single and mixed cultures, were substantially enhanced at 10°C. The highest amount of ethyl acetate was produced by K. apiculata in pure culture at 10°C. Nevertheless, this concentration was lowest when both yeasts were fermented together at 10°C and 25°C.     

Batch ethanol fermentation of molasses: a correlation between the time necessary to complete the fermentation and the initial concentrations of sugar and yeast cells

Batch fermentations of sugar-cane blackstrap molasses to ethanol, using pressed yeast as inoculum, demonstrated an exponential relationship between the time necessary to complete the fermentation and the initial concentrations of sugar and yeast cells. The parameters of the derived exponential equations depended on the experimental conditions.     

Effects of ethanol concentration and stripping temperature on continuous fermentation rate

The operation of a pilot plant consisting of a 14-l fermentor, 10-cm packed column and condenser for continuous fermentation and stripping of ethanol was stable for more than 100 days. The feed consisted of a non-sterile solution of 560 g/l glucose with 100 g/l corn steep water. Fouling of the packing in the column with attached growth of yeast cells was controlled by in situ washing at intervals of 3–6 days. A computer simulation of the pilot plant was developed and used to analyze the data. The productivity of the continuous fermentor varied from 14 g ethanol to 17 g ethanol l⁻¹ h⁻¹. The yield was equal to the maximum theoretically possible: 0.51 g ethanol/g glucose consumed. Results are fit to linear models for the effects of ethanol concentration on specific growth rate and cell yield, and for the effect of stripping temperature on specific growth rate. Received: 16 October 1996 / Received revision: 3 January 1997 / Accepted: 24 January 1997     

Xylose fermentation by Candida shehatae and Pichia stipitis: effects of pH,temperature and substrate concentration

The effects of temperature, pH and xylose concentration on the fermentation parameters of Candida shehatae and Pichia stipitis were evaluated. The optimum pH was in the region of pH 4–5.5, with an optimum fermentation temperature of 30°C. Maximum fermentation rates were reached at 50 g l⁻¹ xylose. A maximum volumetric ethanol productivity of about 0.9 g (l h)⁻¹ was obtained with both yeast strains. The ethanol yield of C. shehatae decreased considerably when cultivated above 30°C or when the xylose concentration was increased. Xylitol accumulated concomitantly. Xylitol production by P. stipitis was observed only during cultivation at 36°C. Whereas the ethanol yield of C. shehatae was usually about 75% of the theoretical maximum, it was 85–90% with P. stipitis.     

Fermentation-based biotransformation of bioactive phenolics and volatile compounds from cashew apple juice by select lactic acid bacteria

Select lactic acid bacteria (LAB); Lactobacillus plantarum, L. casei and L. acidophilus were targeted for enhancing bioactives and flavor volatiles of cashew apple juice (CAJ) that is an underutilized byproduct from cashew nut processing in Tropical countries. Results indicated the vitamin C and phenolic metabolites such as condensed tannin can be increased at certain stages such as at 12 h over the 48 h fermentation period. Whereas antioxidant activity based on DPPH and ABTS radical scavenging activity generally decreased from initial unfermented stage range of (75%–95%) to consistently in the 50% range by 48 h of fermentation and this follows the decrease in viable counts. The fermentation process increased the condensed tannin contents in CAJ whereas hydrolysable tannins decreased. In this study the changes in flavor volatile types were also analyzed over the course of CAJ fermentation. The results indicated that LAB changed the flavor profiles of fermented CAJ and overall the fruity odor decreased, but the whiskey and acid odor increased. These results provide the foundation to further target the functional benefits of LAB-induced fermented CAJ for further human, animal, and plant health applications.     

The effect of pH,temperature and sucrose concentration on high productivity continuous ethanol fermentation using Zymomonas mobilis

Summary A flocculent strain of Zymomonas mobilis was used for ethanol production from sucrose. Using a fermentor with cell recycle (internal and external settler) high sugar conversion and ethanol productivity were obtained. At a dilution rate of 0.5 h^-1 (giving 96% sugar conversion) the ethanol productivity, yield and concentrations respectively were 20 g/l/h, 0.45 g/g and 40 g/l using a medium containing 100 g/l sucrose. At a sucrose concentration of 150 g/l, the ethanol concentration reached 60 g/l. The ethanol yield was 80% theoretical due to levan and fructo-oligomer formation. No sorbitol was detected. This fermentation was conducted at a range of conditions from 30 to 36°C and from pH 4.0 to 5.5.     

The effect of start wort on the initial period of Baker's yeast fermentation

В лабораторных ферментационных танках, в условиях, как можно больше отвечающих производственным, исследовалось влияние субстрата на период взбраживания при дрожжевом брожении. Исследовались влияние концентрации инвертного сахара на ход\(Q_{CO_2 }^{N_2 } \) на мальтозе и глюкозе, а также динамика содержания РНК и ДНК. Далее исследовалась также динамика фосфатных фракций и некоторых других составных частей клеток (трегелёза, полисахариды, белки, свободные аминокислоты). Было установлено, что субстрат быстро метаболизируется и немедленно протекает синтез РНК, всех углеводов и белков, что сопровождается регулярным понижением содержания 7-минутного фосфора. Синтез ДНК осущест-вляется позднее. Изменения составных частей клетки находятся в корреляции с морфологическими изменениями клетки, с процессом роста и деления дрожжей. Из результатов опытов очевидно, что процессы, протекающие в этот период брожения, можно сравнить с кратким циклом роста. С точки зрения технологии дрожжевого брожения констатируется, что 1-часовый период взбраживания слишком долог и что клетки в указанных усповиях страдают от недостатка сахарного субстрата и бывают принуждены с углеводного субстрата перейти на алкоголь.     

Stillage backset and its impact on ethanol fermentation by the flocculating yeast

The second largest cost in fuel ethanol production is from energy consumption with ethanol distillation and stillage treatment, particularly when stillage is treated by the multi-evaporation process. Therefore, stillage backset is the most economically competitive strategy for reducing discharge and saving energy consumption. In this article, continuous ethanol fermentation was performed by the flocculating yeast under stillage backset conditions. Compared to regular yeast, immobilized yeast within the fermentor through flocculation reduced byproducts formation in the stillage, since heat lysis of yeast during ethanol distillation was prevented, and many side reactions were thus eliminated, making more stillage backset within the fermentation system possible. Although pyruvic acid, succinic acid, citric acid, α-ketoglutaric acid, fumaric acid and glycerol from yeast metabolism, furfural and 5-hydroxymethyl furfural from process operations, and acetic acid and lactic acid from slight contamination were accumulated with the stillage backset, they had no significant impact on yeast growth and ethanol fermentation due to low concentrations accumulated within the fermentation system. However, propionic acid that was generated mainly during hydrolysate sterilization and distillation of the fermentation broth was detected as the major inhibitor, but this byproduct would be significantly reduced under industrial conditions without hydrolysate sterilization, making the stillage backset more reliable for industrial application.     

Breeding of flocculent industrial alcohol yeast strains by self-cloning of the flocculation gene FLO1 and repeated-batch fermentation by transformants

A nonflocculent industrial polyploid yeast strain, Saccharomyces cerevisiae 396-9-6V, was converted to a flocculent one by introducing a functional FLO1 gene at the URA3 locus. The flocculent strain FSC27 obtained was a so-called self-cloned strain, having no bacterial DNA. FSC27 cells could be easily recovered for reuse from fermentation mash without any physical energy. The strain produced a concentration of alcohol as high as 396-9-6V, although the fermentation rate of FSC27 was slightly lower than that of 396-9-6V. When uracil was added to the medium or when URA3 was reintroduced into FSC27 (named FSCU-L18), the fermentation rate and the growth rate increased, and the ethanol concentration produced was higher than that produced by the parent strain. The stable flocculation and high ethanol productivity were observed by using FSCU-L18 during 10 cycles of repeated-batch fermentation test.