Antibacterial effect of plantaricin LP84 on foodborne pathogenic bacteria occurring as contaminants during idli batter fermentation

Idli, a traditional cereal/legume-based naturally fermented steamed product with soft and spongy texture is highly popular and widely consumed in India. The inherent viable bacterial populations of mesophilic aerobes and lactics in idli batter increased in their numbers with time at 35 °C, reaching numbers in the range of 13 to 15 log₁₀ CFU g^–1. Simultaneously, the pH level decreased from 6.2 to 4.4. Strains of Bacillus cereus F 4810, Escherichia coli D 21 and Staphylococcus aureus FRI 722 (foodborne pathogens) introduced into the idli batter at an initial level of 4.3 log₁₀ CFU g^–1 was able to survive and grow well in an initial period of 6 h. However, the strain of S. aureus showed a constant increase in its numbers reaching 9.3 log₁₀ CFU g^–1 in 12 h. The addition of plantaricin LP84, a bacteriocin produced by Lactobacillus plantarum NCIM 2084 to idli batter at 1% (v/w) level was able to retard the growth of the inoculated cultures during fermentation. Two aspects were established from this study, (i) that foodborne pathogens occurring as contaminants in idli batter can survive and grow under conditions of natural fermentation and (ii) the efficacy of a lactic bacteriocin as a potential food biopreservative.     

Flavour profile of idli batter prepared from defined microbial starter cultures

Idli is a traditional cereal/legume-based naturally fermented steamed product with a soft and spongy texture which is highly popular and widely consumed as a snack food item in India. The predominant fermentation microflora comprises lactic acid bacteria and yeasts and causes an improvement in the nutritional, textural and flavour characteristics of the final product. The flavour profile of idli batter prepared with initial levels of 2 × 10⁴ c.f.u. g⁻¹ of Candida versatilis CFR 505 and 2 × 10¹ c.f.u. g⁻¹ of Pediococcus pentosaceus CFR 2123 in 500 g idli batter, packed in polyester polylaminate pouches and stored at 30 ± 2 °C was periodically analysed by GC-MS. The desirable flavour compounds such as ketones, diols and acids were found to be present upto 8 days of storage, whereas undesirable flavours like sulphurous and oxazolidone compounds, ethanone and thiazole appeared in the batter subsequent to 6 days of storage. The sensory attributes of idlis (final product) prepared from the stored batter related well to the determined flavour profile. The present study appeared to indicate that the flavour profile of traditional fermented foods can be a reliable qualitative and quantitative parameter for objective assessment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterisation of the bacteriocins produced by two probiotic Lactobacillus isolates from idli batter

Lactobacillus plantarum JJ18 and Lactobacillus plantarum subsp. plantarum JJ60, probiotics from idli batter, produce bacteriocins JJ18 and JJ60 having a wide spectrum of activity. After optimising the environmental conditions for bacteriocin production the effect of various media components was determined. Maximum bacteriocin production was observed in MRS broth, pH 6.4 at 37 °C after 36 h. Tryptone (as nitrogen source) and glucose (as carbon source) are required for optimal production of bacteriocins JJ18 and JJ60. Activity was not affected by surfactants like Triton X-100, Tween 80 and Tween 20 or by treatment with NaCl, urea and EDTA. Protease treatment resulted in complete loss of activity of the partially purified bacteriocins JJ18 and JJ60, while lipase and α-amylase had no effect, indicating that the bacteriocin is a simple protein. Tris tricine SDS-PAGE electrophoresis depicted a single band of less than 3.5 kDa. However, the strain Lactobacillus plantarum JJ18 was inhibited by bacteriocin JJ60 and Lactobacillus plantarum JJ60 by bacteriocin JJ18, whereas no inhibition was observed against the respective producer strains, indicating that the two bacteriocins are different. The bacteriocins remained active over a wide range of pH and temperature. The bacteriocins were able to adsorb onto producer and target cells, Lactobacillus plantarum and Listeria monocytogenes and differentially in the presence of various surfactants, salts and solvents. A bactericidal mode of action was observed against Listeria monocytogenes. Given their wide spectrum of activity against various pathogens, the bacteriocins JJ18 and JJ60 can be applied as bio-preservatives in the food industry.     

Optimization of physicochemical parameters for IndianDosa batter fermentation

Summary Dosa batter fermentation was optimized by employing a variable set of different physicochemical conditions for further raising the nutritional levels. The best combination of these parameters was incubation at 28°C, with initial pH 4.5 and supplementation of the batter with free sugar (sucrose, I-2%).     

Broth recycle in a yeast fermentation

Fermentation is a water-intensive process requiring treatment of large amounts of effluent broth. It is desirable to increase the ratio of product produced to the volume of effluent by minimizing the discharge of effluent from the fermentation process. A study of recycling spent fermentation process. A study of recycling spent fermentation broth for the subsequent fermentation was carried out with Apiotrichum curvatum an oleaginous yeast, as the working culture. Spent broth from a defined medium was recycled t replace as much as 75% of the water and salts for subsequent batches and this was repeated for seven sequential batches without affecting cell mass and lipid production. A 64% vlume reduction of wastewater was achieved in this manner. However, when using whey permeate as the medium, lipid production dropped after three consecutive recycle operations at 50% recycle, and after two consecutive recycle operations at 75% and 100% recycle. Accumulation of ions in the broth appeared to be responsible for the inhibition. An ion exchange step was able to eliminate the ion buildup and restore fermentation performance. (c) 1994 John Wiley & Sons, Inc.     

发酵抑制物对絮凝酵母戊糖发酵的影响

将絮凝剂加入酵母溶液中,使酵母絮凝成颗粒以此作为固定化酵母进行戊糖发酵。研究了常见发酵抑制物(甲酸、乙酸、糠醛和乳酸等)对絮凝酵母发酵木糖的影响。结果表明:在60.0g/L木糖发酵液中,经过24h发酵,木糖利用率达94.6%,当分别添加抑制物甲酸、乙酸、糠醛、乙醇和乳酸时,聚氧乙烯絮凝酵母分别对其的耐受浓度为0.5、0.5、1.0、30.0和8.0g/L。当抑制物添加量超过各自的耐受浓度后,对絮凝酵母发酵会产生明显的抑制作用。     

Sugar utilization by yeast during fermentation

Summary When glucose and fructose are fermented separately, the uptake profiles indicate that both sugars are utilized at similar rates. However, when fermentations are conducted in media containing an equal concentration of glucose and fructose, glucose is utilized at approximately twice the rate of fructose. The preferential uptake of glucose also occurred when sucrose, which was first rapidly hydrolyzed into glucose and fructose by the action of the enzyme invertase, was employed as a substrate. Similar results were observed in the fermentation of brewer's wort and wort containing 30% sucrose and 30% glucose as adjuncts. In addition, the high levels of glucose in the wort exerted severe catabolite repression on maltose utilization in theSaccharmyces uvarum (carlsbergensis) brewing strain. Kinetic analysis of glucose and fructose uptake inSaccharomyces cerevisiae revealed aK _m of 1.6 mM for glucose and 20 mM for fructose. Thus, the yeast strain has a higher affinity for glucose than fructose. Growth on glucose or fructose had no repressible effect on the uptake of either sugar. In addition, glucose inhibited fructose uptake by 60% and likewise fructose inhibited, glucose uptake by 40%. These results indicate that glucose and fructose share the same membrane transport components.     

Continuous secondary fermentation using immobilised yeast

An immobilised yeast, two-stage reactor system was applied to laboratory fermentations of wort. The first stage, the primary fermentation process was carried out in an up-flow gas-lift bioreactor, and in the second stage, fermentation was processed in column reactors consisting of eight packed-beds filled with both yeasts entrapped in three different polysaccharide hydrogels (calcium alginate, calcium pectate, sodium carrageenan) and with free yeast in parallel. The residence time for the two-stage immobilised system varied from 74 to 108 h. © Rapid Science Ltd. 1998     

Alcoholic fermentation by agar-immobilized yeast cells

Immobilized yeast cells in agar gel beads were used in a packed bed reactor for the production of ethanol from cane molasses at 30°C, pH 4.5. The maximum productivity, 79.5g ethanol/l.h was obtained with 195g/l reducing sugar as feed. Substrate (64.2%) was utilized at a dilution of 1.33h^-1. The immobilized cell reactor was operated continuously at a constant dilution rate of 0.67h^-1 for 100 days. The maximum specific ethanol productivity and specific sugar uptake rate were 0.610g ethanol/g cell.h and 1.275g sugar/g cell.h, respectively.     

Viricidal effects of Lactobacillus and yeast fermentation

The survival of selected viruses in Lactobacillus- and yeast-fermented edible waste material was studied to determine the feasibility of using this material as a livestock feed ingredient. Five viruses, including Newcastle disease virus, infectious canine hepatitis virus, a porcine picornavirus, frog virus 3, and bovine virus diarrhea, were inoculated into a mixture of ground food waste (collected from a school lunch program) containing Lactobacillus acidophilus. Mixtures were incubated at 20, 30, and 40 degrees C for 216 h. In a second trial, four viruses, including Newcastle disease virus, infectious canine hepatitis virus, frog virus 3, and a porcine picornavirus, were inoculated into similar edible waste material containing Saccharomyces cerevisiae. Mixtures were incubated at 20 and 30 degrees C for 216 h. Samples were obtained daily for quantitative (trial 1) and qualitative (trial 2) virus isolation. Temperature, pH, and redox potential were monitored. Controlled pH and temperature studies were also done and compared with the inactivation rates in the fermentation processes. In trial 1 (Lactobacillus fermentation), infectious canine hepatitis virus survived the entire test period in the fermentation process but was inactivated below pH 4.5 in the controlled studies. Newcastle disease virus was inactivated by day 8 in the fermentation process and appeared to be primarily heat sensitive and secondarily pH sensitive in the controlled studies. The porcine picornavirus survived the fermentation process for 8 days at 20 degrees C but was inactivated more rapidly at 30 and 40 degrees C. The controlled studies verified these findings. Frog virus 3 was inactivated by day 3 in the fermentation process and appeared to be sensitive to low pH in the controlled studies. Bovine virus diarrhea was rapidly inactivated in the fermentation process (less than 2 h) and was pH and temperature sensitive. In trial 2 (yeast fermentation), infectious hepatitis virus survived the entire test period in the fermentation process. Newcastle disease virus was inactivated by day 7 at 20 degrees C and day 6 at 30 degrees C. The porcine picornavirus was inactivated by day 7 at 30 degrees C but survived the entire test period at 20 degrees C. Frog virus 3 was inactivated by day 3 at 20 degrees C and day 2 at 30 degrees C.     

Intracellular pH of yeast during brewery fermentation

The intracellular pH value of Saccharomyces cerevisiae NCYC 1681 was measured using radiolabelled [¹⁴C]-propionic acid. Errors, due to the binding of radioactive material to trub, were eliminated using silicone oil centrifugation. Replication of analyses reduced the variations associated with low cell counts during fermentation. Whilst fermenting brewer's wort, yeast intracellular pH values were maintained within a narrow range (5.9–6.4). Cellular ATP concentrations were highly conserved in spite of the fact that the cells were exposed to an increasing concentration of ethanol as the fermentation progressed.     

Histone deacetylases in sake yeast affect fermentation characteristics

ABSTRACT

Yeast histone deacetylases (HDAC) affect the production of alcoholic beverages. In this study, we evaluated the sake fermentation characteristics when using HDAC gene-disrupted yeast strain Kyokai No. 701. Flavor components of the sake product were significantly changed. RPD3 or HDA1 disruption increased twofold the amount of isoamyl acetate, and isoamyl alcohol levels also increased in the rpd3Δ strain. To determine the contribution of Rpd3L and Rpd3S complexes to sake characteristics, a gene responsible for Rpd3L and/or Rpd3S formation was also disrupted. Disruption of DEP1 or SDS3 that is an essential component of Rpd3L led to increased isoamyl alcohol production similar to that of the rpd3Δ strain, but the efficiency of isoamyl alcohol esterification was not affected. In addition, Rpd3 and Hda1 may regulate the responsiveness to oxygen in isoamyl acetate production. We conclude that HDAC genes regulate the production of flavor components during sake fermentation.

Abbreviations: HDAC: Histone deacetylase; HAT: histone acetyltransferase; K701: sake yeast Kyokai No. 701; PCR: polymerase chain reaction; HPLC: high performance liquid chromatography; E/A: Ester/Alcohol; BCAA: branched chain-amino acid; Atf: alcohol acetyltransferase.     

Ethanol fermentation in a yeast immobilized tubular fermentor

In this article, a mathematical model describing the kinetics of ethanol fermentation in a whole cell immobilized tubular fermentor is proposed. Experimental results show reasonable agreement with the proposed model. A procedure for treating the fermentation data for determining the ethanol inhibition constants k(1) and k(2) is described. The ethanol productivity of the immobilized cell fermentor is compared with those of traditional fermentors. Experimental studies indicate that with Saccharomyces cerevisiae (NRRL Y132) culture, ethanol productivity in the range 21.2-83.7 g ethanol L(-1) h(-1) at ethanol concentration of 76-60 g/L can be achieved. This is comparable to or higher than those reported in the literature for yeast. The product yield factor of 0.5 g ethanol/g glucose was obtained. The immobilized cell fermentor does not show washout at dilution rates of 7 h(-1) and shows good stability over a 650-h operating period.     

Behaviour of yeast fermentation in the presence of zeolite

Summary The catalytic effect on the acceleration of yeast fermentation by the presence of natural and homoionic zeolites was tested. The addition of 10–5 g/L of zeolite to the fermentation after inoculation increases the alcoholic fermentation rate both in laboratory and large scale processes.     

The speed-controlling reactions in fermentation of quickly dried yeast

Several factors which influence the speed of fermentation of quickly dried yeast are investigated. If the yeast is washed and the bulk of coenzymes and phosphate is removed, addition of 0.5 μmole diphosphopyridine nucleotide (DPN) and 0.5 μmole adenosine triphosphate (ATP) per cc. is necessary for maximal speed. In the optimal pH range, which lies between 6.6 and 6.2, and with optimal amounts of cofactors, there is no influence of nicotinamide mononucleotide (NMN), but with suboptimal amounts of DPN, the speed is raised by synthesis to DPN.The dialyzate of boiled juice contains factors which raise the speed of washed yeast by 20–30% of the maximum obtained in the presence of the usual cofactors. A phosphate concentration of 0.01–0.02 M is likewise necessary even if the phosphate is only partly esterified. At pH 6.0 to 5.9 the speed is less than half that at pH 6.5.Fermentation is completely absent without either K⁺ or NH₄⁺ and without Mg. The optimal amount of the monovalent ions is 5 × 10^?2M. Sodium alone is unable to allow fermentation but is only slightly harmful if enough K⁺ or NH₄⁺ is present.Addition of small amounts of phosphoglycerate at optimal potassium phosphate concentration and pH increases the rate of sugar fermentation and gives rise to an extra CO₂ formation during the time of phosphoglycerate decomposition of about 3 to 5 times the amount added.     

Monitoring of Saccharomyces cerevisiae in commercial bakers' yeast fermentation

In the highly competitive market of commercial bakers' yeast, fermentations are operated for maximum efficiency and minimum production cost. In order to maintain competitiveness, the fermentations must be highly consistent with minimum variation in yeast performance, maximum yield on raw materials, and minimum production of undesirable side products. The use of advanced instrumentation is of critical importance to achieving these goals by the production engineer. An in situ optical density probe was used to determine the yeast cell density in full-scale commercial bakers' yeast fermentations. The optical density probe results were compared with oxygen uptake rate analyses, packed cell volume, and off-line measured cell dry weights. The most accurate measurement of cell density was found to be the optical density probe. This instrument allowed the on-line determination of cell density with highly consistent results from fermentation batch to batch and with out the need for intermittent recalibration. (c) 1995 John Wiley & Sons, Inc.