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Fermentation of raffinose by lactose-fermenting strains of Yersinia enterocolitica and by sucrose-fermenting strains of Escherichia coli.

Introduction of plasmids carrying the lacY gene (lactose permease gene) into Yersinia enterocolitica results in cells being able to ferment both lactose and raffinose. Transfer of such plasmids into Escherichia coli C600 (lacY) confers ability to ferment lactose but not raffinose. Derivatives of C600 that ferment both lactose and sucrose (Lac+ Scr+ strains) are able to ferment raffinose, but do not grow well on raffinose minimal medium. Fermentation of raffinose by Lac+ strains of Y. enterocolitica, and by Lac+ Scr+ strains of E. coli, is explained in terms of transport of raffinose via the lac permease and subsequent breakdown catalyzed by invertase.

Conjugation, Genetic↗

Antimycin A fermentation. II. Fermentation in aerated-agitated fermenters.

Fermentation characteristics, previously studied in shake flasks, were reproduced in aerated-agitated fermenters, using three strains of Streptomyces sp. which had been selected for their high antimycin A productivity in shake flasks. Fermentation in fermenters was run in three stages. The medium consisted of soy flour, glucose, ammonium sulfate and calcium carbonate; initial pH was 7.2 approximately 7.5, and temperature 25 degrees C. The course of fermentation was then modified to encourage maximal growth and eliminate the intermediate lag period observed in shake flasks. Useful corrections included continuous addition of soybean oil at 1.25 %/day and maintenance of pH at 6 by addition of ammonium hydroxide on demand. The ammonium hydroxide added also served as a rapidly utilized nitrogen source and could not be replace by NaOH or KOH. Under optimal conditions antimycin A was produced at constant rate from the second to the sixth day, when maximum yields of more than 9 g/liter were attained. A procedure for antimycin A extraction is described.

Antimycin A↗

A comparison of the effects of dietary cellulose and fermentable galacto-oligosaccharide, in a rat model of colorectal carcinogenesis: fermentable fibre confers greater protection than non-fermentable fibre in both high and low fat backgrounds.

The objective of this experiment was to compare the effects of diets with either a non-fermentable fibre source (cellulose) or a fermentable fibre source [galacto-oligosaccharide (GOS)], combined with different levels of dietary fat, on the development of colorectal cancer. Male Wistar rats were fed AIN76-based diets with either a low or high level of cellulose, or a low or high level of GOS, for 9 months. The fat content of the diets was low, medium or high. All rats were treated with 1,2-dimethylhydrazine to induce colorectal tumours. Generally, the tumour incidence increased with increasing fat content in the diet. Despite marked faeces bulking, dietary cellulose either had no effect or an enhancing effect on the formation of colorectal tumours in general, although the development of carcinomas was decreased. GOS appeared to be highly protective against the development of colorectal tumours, as was demonstrated by an inhibitory effect on tumour incidence, multiplicity and size, regardless of the fat content of the diet. Neither fibre source influenced the bromodeoxyuridine labelling index determined in colon crypts or tumours. In animals fed high-GOS diets, the caecal content was significantly increased in weight and significantly decreased in pH. It was concluded that tumorigenesis was enhanced by increased fat content of the diet, and that the diets containing fermentable GOS conferred a greater protection against colorectal cancer than did the diets containing non-fermentable cellulose.

1,2-Dimethylhydrazine↗

Cornstarch fermentation by the colonic microbial community yields more butyrate than does cabbage fiber fermentation; cornstarch fermentation rates correlate negatively with methanogenesis.

Fermentations of cornstarch and a cabbage-fiber preparation by human fecal suspensions were studied. The molar percent of butyrate of total short-chain fatty acid products was significantly higher when cornstarch was the substrate. Higher molar percents of butyrate were also produced from cornstarch as compared with endogenous substrate when rat fecal suspensions were used. A range of cornstarch fermentation rates was found with suspensions from 20 human subjects. Rapid fermentaion was associated with the absence of methane production. Methane-negative rat fecal suspensions also fermented cornstarch more rapidly than did methane-positive suspensions. High butyrate production may be important because butyrate provides energy to colonocytes and it regulates differentiation of cultured cells.

Analysis of Variance↗

Characterization of lactic acid bacteria isolated from a Thai low-salt fermented fish product and the role of garlic as substrate for fermentation.

Lactic acid bacteria (LAB) isolated from raw materials (fish, rice, garlic and banana leaves) and processed som-fak (a Thai low-salt fermented fish product) were characterized by API 50-CH and other phenotypic criteria. Lactococcus lactis subsp. lactis and Leuconostoc citreum were specifically associated with fish fillet and minced fish, Lactobacillus paracasei subsp. paracasei with boiled rice and Weisella confusa with garlic mix and banana leaves. In addition, Lactobacillus plantarum, Lactobacillus pentosus and Pediococcus pentosaceus were isolated from raw materials. A succession of aciduric, homofermentative lactobacillus species, dominated by Lb. plantarum/pentosus, was found during fermentation. In total, 9% of the strains fermented starch and 19% fermented garlic, the two main carbohydrate components in som-fak. The ability to ferment garlic was paralleled by a capacity to ferment inulin. An increased percentage of garlic fermenting strains was found during fermentation of som-fak, from 8% at day 1 to 40% at day 5. No starch fermenting strains were isolated during fermentation. Three mixed LAB cultures, composed of either starch fermenting Lc. lactis subsp. lactis and Lb. paracasei subsp. paracasei, or garlic fermenting Lb. plantarum and Pd. pentosaceus, or a combination of these strains were inoculated into laboratory prepared som-fak with or without garlic. In som-fak without garlic, pH was above 4.8 after three days, irrespective of addition of mixed LAB cultures. The starch fermenting LAB were unable to ferment som-fak and sensory spoilage occurred after three days. Fermentation with the combined mix of starch and garlic fermenting strains led to production of 2.5% acid and a decrease in pH to 4.5 in two days. The fermentation was slightly slower with the garlic fermenting strains alone. This is the first report describing the role of garlic as carbohydrate source for LAB in fermented fish products.

Animals↗

Integrated electronic nose, GC-MS, and metagenomic analyses reveal volatile flavor and microbial community differences in heap-fermented grains of Jiangxiangxing Baijiu across different fermentation degrees.

The fermentation degree of heap-fermented grains in Jiangxiangxing Baijiu production is a critical factor influencing base Baijiu quality. However, conventional assessment methods largely rely on empirical experience and therefore suffer from limited objectivity and accuracy. In this study, integrated volatile profiling and metagenomic approaches were employed to investigate volatile characteristics and microbial functional potential differentiation in fermented grains with different fermentation degrees (under-fermented, normally fermented, and over-fermented). Significant differences in physicochemical properties were observed among fermentation degrees, particularly in acidity and reducing sugar content. Electronic nose analysis revealed distinct sensor response patterns among different fermentation degrees, indicating differences in overall volatile odor fingerprint patterns. A total of 81 volatile compounds were identified by HS-SPME-GC-MS, with aldehydes, ketones, and pyrazines showing pronounced variations among fermentation degrees, and acetaldehyde exhibiting strong discriminatory potential. LEfSe analysis identified 18 microbial taxa as potential biomarkers associated with different fermentation degrees, including Pichia kudriavzevii, Lentibacillus daiqui, and Acetobacter pasteurianus. Correlation analysis revealed significant positive associations between acetaldehyde levels and Acetobacter abundance. Furthermore, KEGG, CAZy, and eggNOG analyses revealed differentiated functional potentials among fermentation degrees, providing insights into the potential metabolic basis associated with flavor differentiation. Overall, these findings highlight that fermentation degree differentiation is closely associated with coordinated changes in physicochemical conditions, microbial communities, and functional potentials, providing ecological insights into flavor differentiation and theoretical support for objective fermentation degree evaluation and quality control of Jiangxiangxing Baijiu production.

Fermentation↗

Studies on the interaction of fermentation and microfiltration operations: erythromycin recovery from Saccharopolyspora erythraea fermentation broths.

Changes in fermentation media not only affect the performance of the fermentation itself (with regard to the kinetics of biomass and product formation and the yields obtained) but also the initial product-recovery operations downstream of the fermentor. In this work, microfiltration experiments to remove Saccharopolyspora erythraea biomass from fermentation broth and to recover erythromycin were carried out using two fundamentally different media; a soluble complex medium (SCM) and an oil-based process medium (OBM). Small-scale batch fermentations of 14-L working volume were carried out in triplicate using both media. Broth samples were taken from each fermentation at regular intervals from the end of the exponential-growth phase onwards. These were then processed using a Minitan II (acrylic), tangential crossflow-filtration module, fitted with a single 60 cm(2) Durapore hydrophilic 0.2 microm membrane, operated in concentration mode. The OBM fermentations produced higher titers of erythromycin but required longer fermentation times due to increased lag phases and slower maximum-growth rates. The OBM also increased the loading on the membrane; at maximum product titers residual oil concentrations of 3 g. L(-1), antifoam concentrations of 2 g. L(-1) and flour concentrations estimated at approximately 10 g/L(-1) were typical. It was found that both the permeate flux and erythromycin transmission were affected by the choice of medium. The OBM had significantly lower values for both parameters (12.8 Lm(-2) h(-1) and 89.6% respectively) than the SCM (35.9 Lm(-2) h(-1) and 96.7% respectively) when the fermentations were harvested at maximum erythromycin titers. Transmission of erythromycin stayed approximately constant as a function of fermentation time for both media, however, for the OBM the permeate flux decreased with time which correlated with an increase in broth viscosity. The relatively poor microfiltration performance of the OBM medium was, however, offset by the higher titers of erythromycin that were achieved during the fermentation. The filtration characteristics of the SCM broth did not show any correlation with either broth viscosity or fermentation time. Image-analysis data suggested that there was a correlation between hyphal morphology (main hyphal length) and permeate flux (no such correlation was found for the OBM broth). Moreover, it has been shown for the OBM broth that the residual flour had a profound effect on the microfiltration characteristics. The influence of the residual flour was greater than that imposed by the morphology and concentration of the biomass. The understanding of the factors governing the interaction of the fermentation and microfiltration operations obtained in this work provides a first step towards optimization of the overall process sequence.

Biomass↗

Fermentation in human subjects of nonstarch polysaccharides in mixed diets, but not in a barley fiber concentrate, could be predicted by in vitro fermentation using human fecal inocula.

The fermentation of nonstarch polysaccharides (NSP) contained in a low fiber diet, two high fiber diets high or low in protein, and a barley fiber concentrate was determined in balance experiments in six women and in an in vitro batch system using fecal inocula obtained from these same women. In vitro fermentations were performed with fiber residues prepared from duplicates of the fiber-containing foods consumed during the balance trials. Fermentation of total NSP in humans was 83.8 +/- 0.9% (low fiber diet), 61.8 +/- 3.6% (high fiber diet high in protein), 59.2 +/- 3. 9% (high fiber diet low in protein) and 31.2 +/- 7.4% (barley fiber concentrate). Fermentation in vitro differed from fermentation in humans by -4.0 +/- 1.6% (low fiber diet, P < 0.05,), 4.9 +/- 3.7% (high fiber diet high in protein), 8.8 +/- 3.0% (high fiber diet low in protein, P < 0.01) and 19.7 +/- 8.0% (barley fiber concentrate, P < 0.05). Differences between in vivo and in vitro fermentation were most pronounced for NSP-glucose, i.e., cellulose. Production of short-chain fatty acids in vitro corresponded to the fermentability of NSP. The yield of short-chain fatty acids per gram of fermented NSP was similar for the diets (8.8-9.4 mmol) but lower for the barley fiber concentrate (7.4 mmol, P < 0.05). Although differences between the fermentation measured in humans and in vitro were significant for two diets, the magnitude of the differences was such that fermentation of NSP in mixed diets could be predicted with sufficient accuracy in vitro, whereas agreement between the fermentation in vivo and in vitro of NSP in the barley fiber concentrate was not satisfactory.

Adult↗

In vitro fermentation of swine ileal digesta containing oat bran dietary fiber by rat cecal inocula adapted to the test fiber increases propionate production but fermentation of wheat bran ileal digesta does not produce more butyrate.

This experiment evaluated three hypotheses: i) production of propionate is increased during fermentation of substrate containing oat bran (OB)(6); ii) production of butyrate is increased during fermentation of substrate containing wheat bran (WB) and iii) results of in vitro fermentations using physiological substrates and inocula agree with in vivo data. Ileal digesta collected from swine fed OB and WB were the substrates. Digesta was fermented for 0-96 h in an anaerobic in vitro system using inocula prepared from ceca of rats fed the same fiber sources. Carbohydrate and short-chain fatty acid (SCFA) contents in the fermentations were measured by gas chromatography. Fermentation of WB digesta did not produce more n-butyrate (P > 0.05) and was significantly slower (P < 0.05) than fermentation of OB digesta. OB digesta fermentation produced a significantly greater (P < 0.05) molar proportion of SCFA as propionate. Bacterial mass increased more and was maintained longer during fermentation of OB digesta than the WB digesta. Our results indicate that dilution of undigested WB fiber and not n-butyrate production is one mechanism by which WB may protect colonic mucosa; propionate production is increased during fermentation of beta-glucan in OB; and an in vitro system using physiological sources of inoculum and substrate containing WB and OB yields results that agree with in vivo findings in humans and rats.

Analysis of Variance↗

Effect of soy-fortification method on the fermentation characteristics and nutritional quality of fermented maize meal.

Studies were conducted to develop an appropriate household/small-scale enterprise level technique for the production of soy-fortified fermented maize dough (or meal) by comparing different treatments, processing methods and fortification levels. The effects of fortification method of the Ghanaian traditional fermented maize dough with raw or heat-treated whole soybeans and full-fat soyflour at 0%, 10% and 20% replacement levels, on the rate of fermentation and product quality were investigated. Sensory characteristics, trypsin inhibitor activity, amino acid pattern, proximate composition and hot paste viscosity were used as the indices of quality. Addition of whole soybeans to maize before milling and fermentation reduced the fermentation time by 60% while increasing the protein content by 24% and 70% respectively for 10% and 20% levels of fortification. A significant improvement was also achieved in the amino acids pattern of the fortified dough. However, raw whole soybeans imparted an undesirable color and beany flavor and an appreciable concentration of trypsin inhibitor activity (TIA) to the dough. Boiling soybeans for 20 min before incorporation into the maize for milling and fermentation was found necessary for desirable flavor and low levels of TIA. Little or no changes in the pasting viscosity characteristics occurred in samples containing boiled soybeans, while the usual method of fortifying maize meal with soy flour was found to severely depress the pasting viscosity characteristics and drastically reduced the acidity of the fermented dough. Based on the findings of the study, the most appropriate technique for the production of soy-fortified high protein fermented maize dough has been suggested to involve incorporation of boiled whole soybeans in soaked maize before milling and fermentation for improved sensory characteristics, enhanced nutritive value and optimal functional properties.

Amino Acids↗

Fermentation, fermented foods and lactose intolerance.

Lactose (milk sugar) is a fermentable substrate. It can be fermented outside of the body to produce cheeses, yoghurts and acidified milks. It can be fermented within the large intestine in those people who have insufficient expression of lactase enzyme on the intestinal mucosa to ferment this disaccharide to its absorbable, simple hexose sugars: glucose and galactose. In this way, the issues of lactose intolerance and of fermented foods are joined. It is only at the extremes of life, in infancy and old age, in which severe and life-threatening consequences from lactose maldigestion may occur. Fermentation as part of food processing can be used for preservation, for liberation of pre-digested nutrients, or to create ethanolic beverages. Almost all cultures and ethnic groups have developed some typical forms of fermented foods. Lessons from fermentation of non-dairy items may be applicable to fermentation of milk, and vice versa.

Dairy Products↗

Fermentation--a traditional anti-diarrhoeal practice lost? The use of fermented foods in urban and rural Kenya.

Whereas modern dietary advice emphasizes the importance of freshly preparing food, many African communities leave food to ferment. Fermentation of cereals is a traditional method of reducing the microbial contamination of porridges. Beliefs and consumption patterns of fermented food were examined among mothers of children aged under five and health workers in a rural and urban community in Kenya. The majority (83%) of rural mothers reported that their families regularly consumed fermented food and over half (66%) gave their young children fermented food. In the urban area, fewer mothers (56%) reported that their families ate fermented food and only (40%) gave their children some kind of fermented food. Several reasons for the declining uses of fermented food were given including education by health workers that fermented foods were bad, declining production and availability, and substitution of traditional foods by commercial products such as soft drinks. Health educators need to consider that mothers may be missing out on a potentially useful means of preventing diarrhoea in their children.

Attitude↗

Food fermentation: a safety and nutritional assessment. Joint FAO/WHO Workshop on Assessment of Fermentation as a Household Technology for Improving Food Safety.

An assessment of the food-safety and nutritional aspects of lactic acid fermentation for the preparation of weaning food at the household level was carried out during a Joint FAO/WHO Workshop held in Pretoria, South Africa, in December 1995. In particular, lactic acid fermentation was evaluated as a part of food preparation processes involving other operations such as soaking, cooking, and the germination of cereal grains. The use of germinated cereals is of particular interest since they can be used to prepare semi-liquid porridges of high nutrient density. After reviewing the present state of knowledge concerning the antimicrobial effects of the lactic acid in fermented foods, and the nutritional benefits of fermentation and the use of germinated cereals, the Workshop made an inventory of gaps in current knowledge and priorities for further research. High priority areas for research include the following: the effect of lactic acid fermentation on viruses, parasites, certain bacteria, and mycotoxins; certain physiological and nutritional effects of the consumption of fermented foods; the characterization and optimization of fermentation processes and the development of appropriate fermentation starters; and risk mitigation using the Hazard Analysis Critical Control Point system, the health education of food handlers, and efforts to change the consumer perception of fermented foods.

Bacteria↗

Alcoholic fermentation by 'non-fermentative' yeasts.

All type strains of 'non-fermentative' yeasts, available in the culture collection of the Centraalbureau voor Schimmelcultures, were reinvestigated for their capacity to ferment glucose in the classical Durham tube test. Although visible gas production was absent, nearly all strains produced significant amounts of ethanol under the test conditions. Under conditions of oxygen-limited growth, even strong alcoholic fermentation may occur in a number of yeasts hitherto considered as non-fermentative. Thus, shake-flask cultures of Hansenula nonfermentans and Candida silvae fermented more than half of the available sugar to ethanol. It is concluded that the taxonomic test for fermentation capacity, which relies on detection of gas formation in Durham tubes, is not reliable for a physiological classification of yeasts as fermentative and non-fermentative species.

Candida↗

Vegetable fiber fermentation by human fecal bacteria: cell wall polysaccharide disappearance and short-chain fatty acid production during in vitro fermentation and water-holding capacity of unfermented residues.

Dietary fiber from eight vegetables (broccoli, carrot, cauliflower, celery, cucumber, lettuce, onion and radish) was analyzed for chemical composition and potential in vitro fermentation by human fecal bacteria. Total dietary fiber concentration of substrates ranged from 34.9 (broccoli) to 5.8 (cucumber) g/kg edible matter. Substrate fiber fractions were composed primarily of pectic substances and cellulose with smaller concentrations of hemicelluloses and lignin. Total dietary fiber residues isolated from substrates were fermented in vitro for 24 h with fecal bacteria obtained from each of three human volunteers. Substrate dry matter disappearance during fermentation was highest for carrot (63.7%) and lowest for cucumber (49.4%). Averaged across all substrates, disappearances of arabinose, galactose, glucose, mannose, xylose and uronic acids during fermentation were 96, 90, 54, 68, 51 and 97%, respectively. Short-chain fatty acid (SCFA) production during substrate fermentation averaged 10.5 mmol SCFA/g dry matter fermented. Averaged across all substrates, production of the major SCFA, acetate, propionate and butyrate, occurred in the molar ratio 76:14:10. Potential water-holding capacity of substrates was not influenced by fiber source and averaged 2.04 g H2O/g original substrate dry matter. Extent of substrate fermentation, SCFA production and substrate potential water-holding capacity were significantly different among inoculum donors, indicating that considerable inter-individual variation exists in the potential in vivo fermentation of vegetable fiber.

Adult↗

Nitrogen availability of grape juice limits killer yeast growth and fermentation activity during mixed-culture fermentation with sensitive commercial yeast strains.

The competition between selected or commercial killer strains of type K2 and sensitive commercial strains of Saccharomyces cerevisiae was studied under various conditions in sterile grape juice fermentations. The focus of this study was the effect of yeast inoculation levels and the role of assimilable nitrogen nutrition on killer activity. A study of the consumption of free amino nitrogen (FAN) by pure and mixed cultures of killer and sensitive cells showed no differences between the profiles of nitrogen assimilation in all cases, and FAN was practically depleted in the first 2 days of fermentation. The effect of the addition of assimilable nitrogen and the size of inoculum was examined in mixed killer and sensitive strain competitions. Stuck and sluggish wine fermentations were observed to depend on nitrogen availability when the ratio of killer to sensitive cells was low (1:10 to 1:100). A relationship between the initial assimilable nitrogen content of must and the proportion of killer cells during fermentation was shown. An indirect relationship was found between inoculum size and the percentage of killer cells: a smaller inoculum resulted in a higher proportion of killer cells in grape juice fermentations. In all cases, wines obtained with pure-culture fermentations were preferred to mixed-culture fermentations by sensory analysis. The reasons why killer cells do not finish fermentation under competitive conditions with sensitive cells are discussed.

Antibiosis↗

Characterization of anaerobic fermentative growth of Bacillus subtilis: identification of fermentation end products and genes required for growth.

Bacillus subtilis can grow anaerobically by respiration with nitrate as a terminal electron acceptor. In the absence of external electron acceptors, it grows by fermentation. Identification of fermentation products by using in vivo nuclear magnetic resonance scans of whole cultures indicated that B. subtilis grows by mixed acid-butanediol fermentation but that no formate is produced. An ace mutant that lacks pyruvate dehydrogenase (PDH) activity was unable to grow anaerobically and produced hardly any fermentation product. These results suggest that PDH is involved in most or all acetyl coenzyme A production in B. subtilis under anaerobic conditions, unlike Escherichia coli, which uses pyruvate formate lyase. Nitrate respiration was previously shown to require the ResDE two-component signal transduction system and an anaerobic gene regulator, FNR. Also required are respiratory nitrate reductase, encoded by the narGHJI operon, and moaA, involved in biosynthesis of a molybdopterin cofactor of nitrate reductase. The resD and resDE mutations were shown to moderately affect fermentation, but nitrate reductase activity and fnr are dispensable for fermentative growth. A search for genes involved in fermentation indicated that ftsH is required, and is also needed to a lesser extent for nitrate respiration. These results show that nitrate respiration and fermentation of B. subtilis are governed by divergent regulatory pathways.

ATP-Dependent Proteases↗

Toward consistent and productive complex media for industrial fermentations: studies on yeast extract for a recombinant yeast fermentation process.

Yeast extract (YE) is commonly used as a key component in the complex media for industrial fermentations. However, the lot-to-lot variation of this raw material frequently requires extensive "use testing" of many lots to identify only the few that support desired fermentation performance. Through extensive fermentation studies and chemical analyses, we have identified adenine and two metabolizable carbon sources, trehalose and lactate, as the principle components in YE that affect the production of a recombinant protein antigen by a yeast strain. Adenine is required for culture growth and the relationship between biomass and measured adenine can be expressed by a Michaelis-Menten model, while the slowly metabolized trehalose serves to maintain the energy supply to the continued antigen synthesis. The rapidly utilized lactate exerts an indirect positive effect by sparing some of the accumulated ethanol from being consumed for growth to being utilized in the product formation. The effects of these YE components are mutually dependent. Based on the database generated from 40 lots at laboratory scale, a relatively high level of carbon sources in YE (trehalose plus lactate, >9.5% w/w) and an intermediate level of adenine (0.14-0.24% w/w) appear to be the minimal requirement of a good lot for this recombinant yeast fermentation. Many poor lots were improved in lab fermenters by rational supplementation of trehalose, lactate, or adenine to compensate for their insufficiencies. At the large production scale, predictions based on adenine and trehalose/lactate contents in various YE lots used correlated reasonably well with culture growth and antigen yield, illustrating the feasibility of such a simple chemical/biochemical analysis as a rapid and reliable initial screening tool. Without incurring any compositional change to an established manufacturing medium, this study demonstrates an effective approach to achieve consistency in fermentations employing complex nutrients and to improve fermentation productivities supported by suboptimal lots of raw material.

Adenine↗