Microbiological,rheological and aromaticcharacteristics of fermented Uji (an East African Sour Porridge)

Three methods for fermentation of uji were compared in laboratory trials: spontaneous, backslopping (using an inoculum from a previous fermentation) and use of a starter culture of lactic acid bacteria. Spontaneous fermentation resulted in the slowest decrease in pH, while the use of starter culture led to the lowest final pH (3.5). Coliforms were eliminated in less than 8 h using backslopping or starter culture, but increased in numbers during spontaneous fermentation. The viscosity of uji was only marginally affected by the method of fermentation. The aroma profile following spontaneous fermentation contained esters with fruity notes and ethanol and higher alcohols, while mainly organic acids was produced by fermentation with the starter culture. Backslopping led to the lowest production of almost all volatiles identified.     

Functional yeast starter cultures for cocoa fermentation

The quest to develop a performant starter culture mixture to be applied in cocoa fermentation processes started in the 20th century, aiming at achieving high-quality, reproducible chocolates with improved organoleptic properties. Since then, different yeasts have been proposed as candidate starter cultures, as this microbial group plays a key role during fermentation of the cocoa pulp-bean mass. Yeast starter culture-initiated fermentation trials have been performed worldwide through the equatorial zone and the effects of yeast inoculation have been analysed as a function of the cocoa variety (Forastero, Trinitario and hybrids) and fermentation method (farm-, small- and micro-scale) through the application of physicochemical, microbiological and chemical techniques. A thorough screening of candidate yeast starter culture strains is sometimes done to obtain the best performing strains to steer the cocoa fermentation process and/or to enhance specific features, such as pectinolysis, ethanol production, citrate assimilation and flavour production. Besides their effects during cocoa fermentation, a significant influence of the starter culture mixture applied is often found on the cocoa liquors and/or chocolates produced thereof. Thus, starter culture-initiated cocoa fermentation processes constitute a suitable strategy to elaborate improved flavourful chocolate products.     

Plasmid contents of lactic acid bacteria isolated from different types of sour doughs

The plasmid contents of 13 lactic acid bacteria isolated from different types of sour doughs were examined and compared with the plasmid contents of 11 culture collection strains and one commercial pure starter culture for sour doughs. In addition, plasmid analysis was used as a tool to study the stability of a starter culture during sour dough fermentation in a bakery.The tested strains varied in plasmid content from no plasmid up to six plasmids, with molecular weights from 1.5 to 43 MDal. In most cases, the wild-type strains contained a higher number of plasmids than the culture collection strains. The ability of the strains to ferment different carbohydrates was also investigated, but no obvious correlations between the fermentation patterns and the plasmid patterns could be observed. During the fermentation of the bakery sour dough, strains other than the inoculated starter culture gradually became dominant in the microflora. These new strains contained 1–3 plasmids, contrary to the plasmidless starter culture, and they also fermented more carbohydrates than the starter culture.     

Multiphasic approach to study the bacterial ecology of fermented sausages inoculated with a commercial starter culture

In this paper, the ability of a commercial starter culture to perform a sausage fermentation is evaluated. Molecular analysis revealed the presence of several strains of the same species contained in the starter culture with different behavior during the fermentation, and the contribution of Lactobacillus curvatus, which was only marginally isolated during the transformation.     

Utilization of KHR killer as genetic marker for purity test of starter yeast during fermentation of grape musts

An excellent wine yeast, Saccharomyces cerevisiae W3, which had KHR killer, was added as a starter yeast into grape must and behavior of the starter strain and wild yeasts was investigated during fermentation by using KHR killer as a genetic marker. The KHR killer was detected only in the strain W3 and not in other wine and wild yeast strains. Accordingly, the frequency of starter yeast W3 was monitored throughout the fermentation of grape musts by using KHR killer, W3 was discriminated efficiently from wild yeasts during fermentation by KHR killer activity and proved to lead the fermentation as a dominant yeast until their termination.     

Bioconversion of isoflavones during the fermentation of Samso-Eum with Lactobacillus strains

In this study, the possible application of Lactobacillus strains as a functional starter culture to ferment Samso-Eum (SE), an oriental herbal medicine formula, and the production of bioactive isoflavones (daidzein, genistein) were investigated. Four strains of Lactobacillus (Lactobacillus plantarum KFRI 144, L. amylophilus KFRI 161, L. curvatus KFRI 166, and L. bulgaricus KFRI 344) were used for SE fermentation. Declines in pH and in viable cell counts during fermentation were investigated and the quantification of isoflavones using HPLC were performed after fermentation at 37°C for 48 h. All the tested Lactobacillus strains lowered the pH level to approximately 3.6 after 48 h and showed the highest level of growth at 24 h during SE fermentation. During the SE fermentation of the four Lactobacillus strains, the conversion of isoflavone glycosides (daidzin, genistin) into bioactive aglycones (daidzein, genistein) was observed in all of the fermentations, but with different rates depending on the strains. L. plantarum KFRI 144 and L. amylophilus KFRI 161 exhibited the highest bioconversion rate of isoflavone glycosides into their bioactive aglycones. These results demonstrate that L. plantarum KFRI 144 and L. amylophilus KFRI 161 have potentials as functional starter cultures for manufacturing fermented SE with higher isoflavone bioavailability.     

Breeding Strategy To Generate Robust Yeast Starter Cultures for Cocoa Pulp Fermentations

Cocoa pulp fermentation is a spontaneous process during which the natural microbiota present at cocoa farms is allowed to ferment the pulp surrounding cocoa beans. Because such spontaneous fermentations are inconsistent and contribute to product variability, there is growing interest in a microbial starter culture that could be used to inoculate cocoa pulp fermentations. Previous studies have revealed that many different fungi are recovered from different batches of spontaneous cocoa pulp fermentations, whereas the variation in the prokaryotic microbiome is much more limited. In this study, therefore, we aimed to develop a suitable yeast starter culture that is able to outcompete wild contaminants and consistently produce high-quality chocolate. Starting from specifically selected Saccharomyces cerevisiae strains, we developed robust hybrids with characteristics that allow them to efficiently ferment cocoa pulp, including improved temperature tolerance and fermentation capacity. We conducted several laboratory and field trials to show that these new hybrids often outperform their parental strains and are able to dominate spontaneous pilot scale fermentations, which results in much more consistent microbial profiles. Moreover, analysis of the resulting chocolate showed that some of the cocoa batches that were fermented with specific starter cultures yielded superior chocolate. Taken together, these results describe the development of robust yeast starter cultures for cocoa pulp fermentations that can contribute to improving the consistency and quality of commercial chocolate production.     

Genotypic and phenotypic characterization of industrial autochthonous Saccharomyces cerevisiae for the selection of well-adapted bioethanol-producing strains

In northwestern Argentina, sugarcane-derived industrial fermentation is being extensively used for bioethanol production, where highly adaptive native strains compete with the baker's yeast Saccharomyces cerevisiae traditionally used as starter culture. Yeast populations of 10 distilleries from Tucumán (Argentina) were genotypic and phenotypic characterized to select well-adapted bioethanol-producing autochthonous strains to be used as starter cultures for the industrial production of bioethanol fuel. From the 192 isolates, 69.8% were identified as S. cerevisiae, 25.5% as non-Saccharomyces, and 4.7% as Saccharomyces sp. wild yeasts. The majority of S. cerevisiae isolates (68.5%) were non-flocculating yeasts, while the flocculating strains were all obtained from the only continuous fermentation process included in the study. Simple Sequence Repeat analysis revealed a high genetic diversity among S. cerevisiae genotypes, where all of them were very different from the original baker's strain used as starter. Among these, 38 strains multi-tolerant to stress by ethanol (8%), temperature (42.5 °C) and pH (2.0) were obtained. No major differences were found among these strains in terms of ethanol production and residual sugars in batch fermentation experiments with cell recycling. However, only 10 autochthonous strains maintained their viability (more than 80%) throughout five consecutive cycles of sugarcane-based fermentations. In summary, 10 autochthonous isolates were found to be superior to baker's yeast used as starter culture (S. cerevisiae Calsa) in terms of optimal technological, physiological and ecological properties. The knowledge generated on the indigenous yeast populations in industrial fermentation processes of bioethanol-producing distilleries allowed the selection of well-adapted bioethanol-producing strains.     

Starter Culture Selection for Making Chinese Sesame-Flavored Liquor Based on Microbial Metabolic Activity in Mixed-Culture Fermentation

Selection of a starter culture with excellent viability and metabolic activity is important for inoculated fermentation of traditional food. To obtain a suitable starter culture for making Chinese sesame-flavored liquor, the yeast and bacterium community structures were investigated during spontaneous and solid-state fermentations of this type of liquor. Five dominant species in spontaneous fermentation were identified: Saccharomyces cerevisiae, Pichia membranaefaciens, Issatchenkia orientalis, Bacillus licheniformis, and Bacillus amyloliquefaciens. The metabolic activity of each species in mixed and inoculated fermentations of liquor was investigated in 14 different cocultures that used different combinations of these species. The relationships between the microbial species and volatile metabolites were analyzed by partial least-squares (PLS) regression analysis. We found that S. cerevisiae was positively correlated to nonanal, and B. licheniformis was positively associated with 2,3-butanediol, isobutyric acid, guaiacol, and 4-vinyl guaiacol, while I. orientalis was positively correlated to butyric acid, isovaleric acid, hexanoic acid, and 2,3-butanediol. These three species are excellent flavor producers for Chinese liquor. Although P. membranaefaciens and B. amyloliquefaciens were not efficient flavor producers, the addition of them alleviated competition among the other three species and altered their growth rates and flavor production. As a result, the coculture of all five dominant species produced the largest amount of flavor compounds. The result indicates that flavor producers and microbial interaction regulators are important for inoculated fermentation of Chinese sesame-flavored liquor.     

Utilization of Lactose, Glucose, and Galactose by a Mixed Culture of Streptococcus thermophilus and Lactobacillus bulgaricus in Milk Treated with Lactase Enzyme

The mechanism responsible for an increased rate of acid production when yogurt starter cultures are grown in milk treated with lactase enzyme was investigated by studying carbohydrate utilization and acid development by a pure culture of Streptococcus thermophilus and a mixed yogurt starter culture consisting of S. thermophilus and Lactobacillus bulgaricus. In milk containing glucose, galactose, and lactose, glucose and lactose (but not free galactose) were fermented. Fermentation of lactose in control milk was accompanied by the release of free galactose, with the result that carbohydrate utilization was less efficient than in treated milk. This phenomenon also occurred when lactose was fermented by S. thermophilus in broth culture. Carbohydrate utilization by the mixed yogurt culture was more rapid when the lactose in milk was partially prehydrolyzed. Our results suggest that the more rapid acid development that took place when a mixed yogurt starter culture was grown in milk containing prehydrolyzed lactose was the result of a more rapid and efficient utilization of carbohydrate by S. thermophilus when free glucose in addition to lactose was available for fermentation. The evidence presented also suggests that uptake and utilization of glucose and lactose by S. thermophilus are different in broth and milk cultures.     

Monitoring of <Emphasis Type="Italic">Leuconostoc mesenteroides</Emphasis> DRC starter in fermented vegetable by random integration of chloramphenicol acetyltransferase gene

In 2004, Leuconostoc mesenteroides DRC was first used as a starter culture for achieving higher organoleptic effects in Korean kimchi manufacture. For a better understanding of starter growth in a mixed culture system, and for predicting starter predominance in kimchi, a monitoring system for the starter was established. The chloramphenicol resistance marker gene (cat) was randomly integrated into chromosomal DNA of L. mesenteroides DRC using a viral transposon and transposase. The DRC mutant, tDRC2, had a similar growth pattern to the host strain, with no major alteration in phenotypic characteristics. The mutant strain was inoculated into real kimchi, and monitoring of the starter population was successfully achieved. The overall predominance of Leuconostoc in kimchi inoculated with DRC followed the general growth pattern of this genus during kimchi fermentation. Our results also demonstrate the competitive ability of the DRC starter against Leuconostoc from natural flora, maintaining its predominance above 88% during the whole fermentation period. Based on this experiment, the random gene integration method using a transposon was shown to be of utility in transferring any commercial starter into a selectable and monitorable strain for simulation purposes.     

Experiences with the use of a starter culture in the fermentation of maize for ‘kenkey’ production in Ghana

Controlled fermentation of maize was carried out using six strains of Lactobacillus fermentum and one strain of yeast, Saccharomyces cerevisiae, isolated from traditionally fermented maize dough as starter cultures for inoculum enrichement. The fermentations were monitored by pH, acidity, microbiological analysis and taste panel evaluation of two products, kenkey and koko, prepared from the fermented doughs. The strains of L. fermentum used as starter culture dominated the microflora during fermentation and in most inoculated doughs the required pH was attained by 24 h instead of 48 h of dough fermentation. Higher contents of lactic acid bacteria and yeasts were observed in inoculated doughs at the initial stages of fermentation but the spontaneously fermented doughs attained similar lactic acid bacteria and yeasts counts by 24 h of dough fermentation. The organoleptic quality of kenkey and koko prepared from doughs fermented with starter culture for 48 h was not significantly different from the traditional products. Kenkey prepared from doughs fermented for 24 h with starter culture were found to be unacceptable by the taste panel although similarly produced koko was acceptable.The authors are with the Food Research Institute, Council for Scientific and Industrial Research, P.O Box M 20. Accra, Ghana.     

Halobacterium sp. SP1(1) as a starter culture for accelerating fish sauce fermentation

Aims: Application of Halobacterium sp. SP1(1) for the acceleration of fish sauce fermentation. Methods and Results: Traditional fish sauce fermentation was mimicked using Halobacterium sp. SP1(1) as starter culture. Protease activity, peptide release and α‐amino content (parameters used to monitor the progress of the fermentation) were high at day 10 in tests and day 20 in un‐inoculated controls. The total protein and nitrogen contents were also high in tests compared with controls. The amino acid profile observed at the end of fermentation in experimental samples, when compared with the commercial sauce preparation, was found to be better with respect to flavour and aroma contributing amino acids as well as essential amino acid lysine. Microflora analysis of the final fish sauce revealed the absence of any nonhalophilic or halotolerant micro‐organisms. The protease‐producing halophilic isolates obtained from the fish sauce of eviscerated and uneviscerated controls were identified as Halobacterium sp. F1 and F2, respectively, by 16S rDNA sequence analysis. Conclusions: Exogenous augmentation of Halobacterium sp. SP1(1) accelerated the fish sauce fermentation process with an additive effect on the existing natural microflora present in the fish during fermentation. Halobacterium sp SP1(1), therefore, can be used as an important starter culture for accelerating the fish fermentation process, which is attributed to its extracellular protease. Significance and Impact of the Study: The present study is the first report on use of Halobacterium species as a starter culture for accelerating fish sauce fermentation. Use of halobacterial starter cultures may revolutionize the process in fish sauce industries by reducing the fermentation time and making the process more economical with improved nutritive value of product.     

Redox Interactions between Saccharomyces cerevisiae and Saccharomyces uvarum in Mixed Culture under Enological Conditions

Wine yeast starters that contain a mixture of different industrial yeasts with various properties may soon be introduced to the market. The mechanisms underlying the interactions between the different strains in the starter during alcoholic fermentation have never been investigated. We identified and investigated some of these interactions in a mixed culture containing two yeast strains grown under enological conditions. The inoculum contained the same amount (each) of a strain of Saccharomyces cerevisiae and a natural hybrid strain of S. cerevisiae and Saccharomyces uvarum. We identified interactions that affected biomass, by-product formation, and fermentation kinetics, and compared the redox ratios of monocultures of each strain with that of the mixed culture. The redox status of the mixed culture differed from that of the two monocultures, showing that the interactions between the yeast strains involved the diffusion of metabolite(s) within the mixed culture. Since acetaldehyde is a potential effector of fermentation, we investigated the kinetics of acetaldehyde production by the different cultures. The S. cerevisiae-S. uvarum hybrid strain produced large amounts of acetaldehyde for which the S. cerevisiae strain acted as a receiving strain in the mixed culture. Since yeast response to acetaldehyde involves the same mechanisms that participate in the response to other forms of stress, the acetaldehyde exchange between the two strains could play an important role in inhibiting some yeast strains and allowing the growth of others. Such interactions could be of particular importance in understanding the ecology of the colonization of complex fermentation media by S. cerevisiae.     

Bacterial and fungal diversity in the starter production process of Fen liquor, a traditional Chinese liquor

Fermented foods and beverages are important parts of human diet. Fen liquor, a Chinese liquor is a fermented beverage that uses a traditional fermentation process. Starters are the main microbial source and also provide nutrients for microorganisms during fermentation. In this study, starters of Fen liquor were produced through a complex traditional fermentation process. To investigate the community structure and the composition of microorganisms in the starter production process, bacterial 16S rRNA and fungal internal transcribed spacer (ITS) regions were sequenced using clone libraries and pyrosequencing, respectively. There was much higher diversity among the bacteria than among the fungi in the starter production process. Bacteria on the surface of the starters belonged mostly to the Lactobacillaceae family, while members of the Bacillacae family were dominant in the interior of the samples that lacked access to air and water. In the fungi population, diversity was high only in the raw material. In all other samples, nearly all of the fungal sequences were from Pichia kudriavzevii, a member of the Saccharomycetaceae family. Nearly all samples showed similar fungal community structures, indicating that there was little change in the fungal community. To the best of our knowledge, this is the first report to reveal the whole process of the starter production of Chinese traditional liquor. The findings obtained in this study provide new insights into understanding the composition of the microbial community during the traditional Chinese liquor starter production process and information about the production process control and monitoring.     

Influence of stressful fermentation conditions on neutral lipids of a Saccharomyces cerevisiae brewing strain

The neutral lipid fraction of the aerobically grown starter yeast culture of a Saccharomyces cerevisiae brewing strain, and three-first recycled yeast generations exposed to multiple stress factors during beer fermentation was studied. No pronounced changes in the cellular neutral lipid content between the non-stressed starter and stressed recycled cells were found. However, it was found that recycled yeast generations modulate their neutral lipid composition during fermentation. The ergosterol content was increased at the expense of steryl esters (SEs) and squalene, which resulted in a higher ergosterol/SEs molar ratio and a slightly higher ergosterol/squalene molar ratio. In addition, the proportion of unsaturated fatty acids, mainly palmitoleic acid increased in the neutral lipid fraction of the stressed recycled yeast generations. These results suggest that some specific neutral lipid species and fatty acids stored in the neutral lipid fraction are involved in the adaptive response of the brewer’s yeast to stressful fermentation conditions. The striking finding was a high squalene content in the neutral lipid fraction of both the starter yeast culture and recycled yeast generations (22.4 vs. 19–20%, respectively), implying a possible biotechnological exploitation of this biologically active molecule from the yeast biomass.     

Inhibition of bacterial growth and malolactic fermentation in wine by bacteriophage

Bacteriophage present in wine can attack bacterial starter cultures and inhibit the malolactic fermentation. The possibility of starter culture failure due to phage attack was studied in a commercial dry red wine of pH 3·23, inoculated with a multiple strain starter culture. During two stages of malolactic fermentation, bacterial growth and malate degradation in the wine were inhibited. A phage capable of lysing isolates of Leuconostoc oenos was isolated from the wine. The isolated phage had an icosahedral head of 42–45 nm diameter and a flexible, regularly cross-striated tail 197–207 nm long with a small baseplate. The results confirm that phage can attack bacterial starter cultures in wine at low pH.     

Reduced nitrite and biogenic amine concentrations and improved flavor components of Chinese sauerkraut via co-culture of Lactobacillus plantarum and Zygosaccharomyces rouxii

The aim of this study was to investigate the effect of inoculated fermentation on the quality of Chinese sauerkraut. To this end we studied a co-culture system consisting of Lactobacillus plantarum Shanghai brewing 1.08 and Zygosaccharomyces rouxii CGMCC 3791 during inoculated sauerkraut fermentation. The nitrite concentrations in pickled cabbage and radish inoculated with starter cultures of L. plantarum and Z. rouxii were significantly lower than those in the spontaneous fermentation system during the whole fermentation process. In addition, co-culture of L. plantarum and Z. rouxii during the production of sauerkraut decreased the formation of biogenic amines in the pickled vegetables. Using gas chromatography–mass spectrometry we also compared the levels of volatile compounds in inoculated and naturally fermented Chinese sauerkraut. Sixty compounds were identified, with the sauerkraut inoculated with starter cultures containing overall higher contents of volatile compounds, including acids, alcohols, esters, and phenols. The structure of the microbial community during the production of sauerkraut was studied using phospholipid fatty-acid (PLFA) analysis. This analysis revealed that the brine of inoculated sauerkraut contained significantly higher contents of Gram-positive and fungal PLFAs and a lower content of Gram-negative PLFAs, suggesting that the improved quality of inoculated Chinese sauerkraut may be ascribed to the inhibition of the growth of Gram-positive during sauerkraut fermentation. These results may indicate a new strategy to enhance the quality of Chinese sauerkraut.     

Effect of starter culture inoculation on feed hygiene and microbial population development in fermented pig feed composed of a cereal grain mix with wet wheat distillers' grain

Aims:  Investigating the influence of an added starter culture on the properties of fermented liquid pig feed.
Methods and Results:  Diets of cereal grain blended with wet wheat distillers' grain that were either not inoculated (WWDG), inoculated with a silage starter culture at start (WWDGsc1) or at start and at each backslopping (replacement of 80% the content with fresh mixture, simulating feed outtake, WWDGsc5) were fermented for 5 days, followed by 5 days of daily backslopping. Numbers of undesirable micro-organisms (enterobacteria, moulds) were reduced in all fermentations; particularly enterobacteria in the starter culture inoculated diets. Lactobacillus plantarum present in the starter culture became dominant in diets WWDGsc1 and WWDGsc5. However, Lactobacillus panis that was dominating WWDG was also abundant in WWDGsc1 and WWDGsc5. Yeast populations were not influenced by the starter culture, with Pichia fermentans dominating all fermentations. All diets had similar chemical characteristics with the exception of a significant increase of all tested organic acids in WWDGsc5.
Conclusions:  The addition of a starter culture influences the bacterial population in fermented liquid feed, but there is also a strong impact of the flora already present in the feed ingredients. The yeast population is not influenced by adding a lactic acid bacteria (LAB) starter culture. A consortium of LAB and yeast strains adapted to the fermentation should be used as starter culture.
Significance and Impact of the Study:  The results suggest that it is possible to influence the current unpredictable and spontaneous process of feed fermentation when appropriate starter cultures are used. For this purpose, LAB and yeasts with desirable characteristics should be isolated.     

Lyophilized preparations of bacteriocinogenic Lactobacillus curvatus and Lactococcus lactis subsp. lactis as potential protective adjuncts to control Listeria monocytogenes in dry-fermented sausages

AIM: Study of the effectiveness of in situ bacteriocin production by lactic acid bacteria (LAB) to control Listeria monocytogenes in dry-fermented sausages. METHODS AND RESULTS: Two bacteriocin-producing strains: Lactococcus lactis subsp. lactis LMG21206 and Lactobacillus curvatus LBPE were grown in a pilot scale fermentor and lyophilized to be directly used in dry sausage fermentation. A commercial starter culture (Bel'meat SL-25) not inhibitory to L. monocytogenes (Bac- starter) was mixed (1 : 1) with each of the two lyophilized bacteriocin-producing strains to obtain starters active against the pathogen (Bac+ starter). Anti-Listeria effectiveness of the Bac+ starters was studied in dry-fermented sausages. The meat batter was experimentally contaminated with a mixture of four different strains of L. monocytogenes (10(2)-10(3) CFU g(-1)). The results showed that L. monocytogenes did not grow in any of the contaminated batches, but no significant decrease (P > 0.05) was observed either in the positive control (no added starter culture) or in samples fermented with the Bac- starter culture during the fermentation period and up to 15 days of drying. When the Bac+ starter contained Lb. curvatus LBPE, cell counts of L. monocytogenes decreased to below the detectable limit (<10 CFU g(-1)) after 4 h of fermentation and no survivors could be recovered by enrichment beyond day 8 of drying. When the Bac+ starter culture containing Lc. lactis LMG21206 was used, a decrease in Listeria counts to below the detectable limit was achieved after 15 days of drying. CONCLUSIONS: The bacteriocin-producing strains studied may be used as adjunct cultures for sausage fermentations to control the occurrence and survival of L. monocytogenes. SIGNIFICANCE AND IMPACT OF THE STUDY: Addition of the Bac+ strains, especially the Lb. curvatus strain would provide an additional hurdle to enhance the control of L. monocytogenes in fermented meat products.