Commercial Fermented Products Research Articles

Assessment of dietary yeast-based additives for cultured catfish and tilapia health.

Channel catfish (Ictalurus punctatus) and Nile tilapia (Oreochromis niloticus) are two aquaculture species of great importance. Intensive production is often hindered by poor growth performance and disease mortality. The aim of this study was to evaluate the potential of a commercial fermented yeast product, DVAQUA, on channel catfish and Nile tilapia growth performance metrics and disease resistance. Channel catfish and Nile tilapia were fed practical diets supplemented with 0%, 0.1% or 0.4% of DVAQUA over approximately 2-month feeding periods in recirculation aquaculture systems. To assess the potential of the postbiotic against common aquaculture pathogens, juvenile catfish were subsequently challenged by immersion with Edwardsiella ictaluri S97-773 or virulent Aeromonas hydrophila ML09-119. Nile tilapia juveniles were challenged by injection with Streptococcus iniae ARS-98-60. Serum lysozyme activity, blood chemistry and growth metrics were measured at the end of the feeding period, but no differences were observed across the different metrics, except for survival. For the pathogen challenges, there were no differences in endpoint mortality for channel catfish with either pathogen (p > .05). In contrast, Nile tilapia survivability to S. iniae infection increased proportionally to the inclusion of DVAQUA (p = .005). Changes to sera lysozyme activity were also noted in the tilapia trial, with a reduction of activity in the fish fed the 0.4% DVAQUA diet compared to the control diet (p = .031). Expression profiles of proinflammatory genes and antibodies were also found to be modulated in channel catfish fed the postbiotic, indicating some degree of protective response. These results suggest that this postbiotic may be beneficial in protecting Nile tilapia against S. iniae infection by influencing immune parameters and additional research is needed to evaluate the potential of this DVAQUA for improving catfish health and disease control.

Connection of spectral pattern of carbohydrate molecular structure to alteration of nutritional properties of coffee by-products after fermentation.

The objective of this study was to determine internal structure spectral profile of by-products from coffee processing that were affected by added-microorganism fermentation duration in relation to truly absorbed feed nutrient supply in ruminant system. The by-products from coffee processing were fermented using commercial fermentation product, consisting of various microorganisms: for 0 (control), 7, 14, 21, and 28 days. In this study, carbohydrate-related spectral profiles of coffee by-products were correlated with their chemical and nutritional properties (chemical composition, total digestible nutrient, bioenergy values, carbohydrate sub-fractions and predicted degradation and digestion parameters as well as milk value of feed). The vibrational spectra of coffee by-products samples after fermentation for 0 (control), 7, 14, 21, and 28 days were determined using a JASCO FT/IR-4200 spectroscopy coupled with accessory of attenuated total reflectance (ATR). The molecular spectral analyses with univariate approach were conducted with the OMNIC 7.3 software. Molecular spectral analysis parameters in fermented and non-fermented byproducts from coffee processing included structural carbohydrate, cellulosic compounds, non-structural carbohydrates, lignin compound, CH-bending, structural carbohydrate peak1, structural carbohydrate peak2, structural carbohydrate peak3, hemicellulosic compound, non-structural carbohydrate peak1, non-structural carbohydrate peak2, nonstructural carbohydrate peak3. The study results show that added-microorganism fermentation induced chemical and nutritional changes of coffee by-products including carbohydrate chemical composition profiles, bioenergy value, feed milk value, carbohydrate subfractions, estimated degradable and undegradable fractions in the rumen, and intestinal digested nutrient supply in ruminant system. In conclusion, carbohydrate nutrition value changes by added-microorganism fermentation duration were in an agreement with the change of their spectral profile in the coffee by-products. The studies show that the vibrational ATR-FT/IR spectroscopic technique could be applied as a rapid analytical tool to evaluate fermented by-products and connect with truly digestible carbohydrate supply in ruminant system.

Isoflavone aglycone contents of commercial fermented soybean products in Korea and the isoflavone aglycone-producing ability of <i>Bacillus subtilis</i> isolated from the products

Isoflavone aglycone contents of commercial fermented soybean products in Korea and the isoflavone aglycone-producing ability of <i>Bacillus subtilis</i> isolated from the products

Pilot market surveillance of GMM contaminations in alpha-amylase food enzyme products: A detection strategy strengthened by a newly developed qPCR method targeting a GM Bacillus licheniformis producing alpha-amylase

Using high-throughput metagenomics on commercial microbial fermentation products, DNA from a new unauthorized genetically modified microorganism (GMM), namely the GM B. licheniformis strain producing alpha-amylase (GMM alpha-amylase2), was recently discovered and characterized. On this basis, a new qPCR method targeting an unnatural association of sequences specific to the GMM alpha-amylase2 strain was designed and developed in this study, allowing to strengthen the current GMM detection strategy. The performance of the newly developed qPCR method was assessed for its specificity and sensitivity to comply with the minimum performance requirements established by the European Network of GMO Laboratories for GMO analysis. Moreover, the transferability of the in house validated qPCR method was demonstrated. Finally, its applicability was confirmed by a pilot market surveillance of GMM contaminations conducted for the first time on 40 alpha-amylase food enzyme products labelled as containing alpha-amylase. This pilot market surveillance allowed also to highlight numerous contaminations with GMM alpha-amylase2, including frequent cross-contaminations with other GMM strains previously characterized. In addition, the presence of full-length AMR genes, raising health concerns, was also reported.

Development of a Taxon-Specific Real-Time Polymerase Chain Reaction Method to Detect Trichoderma reesei Contaminations in Fermentation Products

Recently, a genetically modified microorganism (GMM) detection strategy using real-time PCR technology was developed to control fermentation products commercialized in the food and feed chain, allowing several unexpected GMM contaminations to be highlighted. Currently, only bacterial strains are targeted by this strategy. Given that fungal strains, like Trichoderma reesei, are also frequently used by the food industry to produce fermentation products, a novel real-time PCR method specific to this fungal species was developed and validated in this study to reinforce the GMM detection strategy. Designed to cover a sequence of 130 bp from the translation elongation factor alpha 1 (Tef1) gene of T. reesei, this real-time PCR method, namely TR, allows for the screening of commercial fermentation products contaminated with T. reesei, genetically modified or not, which is one of the major fungal species used as an industrial platform for the manufacturing of fermentation products. The developed real-time PCR TR method was assessed as specific and sensitive (LOD95% = eight copies). In addition, the developed real-time PCR TR method performance was confirmed to be in line with the “Minimum Performance Requirements for Analytical Methods of GMO Testing” of the European Network of GMO Laboratories. The validated real-time PCR TR method was also demonstrated to be applicable to commercial microbial fermentation products. Based on all these results, the novel real-time PCR TR method was assessed as valuable for strengthening the current GMM detection strategy regarding major fungal species used by the food industry to produce microbial fermentation products.

Detection of the Microbial Composition of Some Commercial Fermented Liquid Products via Metagenomic Analysis.

The fermented liquid sector is developing all over the world due to its contribution to health. Our study has contributed to the debate about whether industrially manufactured fermented liquids live up to their claims by analyzing pathogens and beneficial bacteria using a 16S rRNA sequencing technique called metagenomic analysis. Paenibacillus, Lentibacillus, Bacillus, Enterococcus, Levilactobacillus, and Oenococcus were the most abundant bacterial genera observed as potential probiotics. Pseudomonas stutzeri, Acinetobacter, and Collimonas, which have plant-growth-promoting traits, were also detected. The fact that we encounter biocontroller bacteria that promote plant growth demonstrates that these organisms are widely used in foods and emphasizes the necessity of evaluating them in terms of public health. Their potential applications in agriculture may pose a danger to food hygiene and human health in the long term, so our data suggest that this should be evaluated.

Determination of γ-aminobutyric acid in fermented soybean products by HPLC coupled with pre-column derivatization

This study reports a pre-column derivatization HPLC stragety to determine the content of GABA in fermented soybean products. 9-Fluorenylmethyloxycarbonyl chloride (Fmoc-Cl) is employed as the derivative reagent with chromophore linked to GABA, which lacks of chromophore for UV/DAD analysis in its pristine structure. After the detection wavelength was confirmed, the derivatization and analysis conditions were also optimized, including pH and amount of boric acid buffer, amount of derivative reagent, the mobile phases and their gradient. Methodological investigation showed that the derivatized GABA (Fmoc-GABA) has good linearity in the range of 1–100 µg/mL, low limit of quantification (LOQ, at 1 µg/mL) and limit of detection (LOD, at 0.3 µg/mL), and good recoveries of three spiked levels (between 83.8% and 100.8% with RSDs less than 5%). Furthermore, thirty-two commercial fermented soy products in four matrices (soy sauce, soy paste, bean curd, lobster sauce) were analyzed by the proposed method for validation. As a consequence, the concentrations of GABA in these soy products were in the range of 48.4–381 mg/kg.

Effects of fermentation on protein profile of coffee by-products and its relationship with internal protein structure measured by vibrational spectroscopy.

To our knowledge, there is few studies on the correlation between internal structure of fermented products and nutrient delivery from by-products from coffee processing in ruminant system. The objective of this project was to use advanced mid-infrared vibrational spectroscopic technique (ATR-FT/IR) to reveal interactive correlation between protein internal structure and ruminant-relevant protein and energy metabolic profiles of by-products from coffee processing affected by added-microorganism fermentation duration. The by-products from coffee processing were fermented using commercial fermentation product, called Saus Burger Pakan (SBP), consisting of various microorganisms: cellulolytic, lactic acid, amylolytic, proteolytic, and xylanolytic microbes, for 0, 7, 14, 21 and 28 days. Protein chemical profiles, Cornell Net Carbohydrate and Protein System (CNCPS) CP and CHO subfractions, and ruminal degradation and intestinal digestion of protein were evaluated. The attenuated total reflectance-Ft/IR (ATR-FTIR) spectroscopy was used to study protein structural features of spectra that were affected by added-microorganism fermentation duration. The molecular spectral analyses were carried using OMNIC software. Molecular spectral analysis parameters in fermented and non-fermented by-products from coffee processing included: Amide I area (AIA), Amide II (AIIA) area, Amide I heigh (AIH), Amide II height (AIIH), α-helix height (αH), β-sheet height (βH), AIA to AIIA ratio, AIH to AIIH ratio, and αH to βH ratio. The relationship between protein structure spectral profiles of by-products from coffee processing and protein related metabolic features in ruminant were also investigated. Fermentation decreased rumen degradable protein and increased rumen undegradable protein of by-products from coffee processing (P<0.05), indicating more protein entering from rumen the small intestine for animal use. The fermentation duration significantly impacted (P<0.05) protein structure spectral features. Fermentation tended to increase (P<0.10) AIA and AIH as well as β-sheet height which all are significantly related to the protein level. Protein structure spectral profiles of by-product form coffee processing could be utilized as potential evaluators to estimate protein related chemical profile and protein metabolic characteristics in ruminant system.

Application of kombucha combined with fructo-oligosaccharides in soy milk: Colony composition, antioxidant capacity, and flavor relationship

Plant-based milk is considered a healthy and environmentally sustainable option. In order to solve the physical and chemical instability problem of most plant milk and increase the chance of consumer acceptance of the flavor, this experiment used soybean as raw material, fructo-oligosaccharides (FOS) as prebiotics, and added kombucha for fermentation. The microbial composition, functional components, antioxidant capacity, physicochemical properties and flavor relationship of fermented soy milk at different fermentation times (up to 96 h) were studied by high-throughput sequencing, laser confocal scanning imaging, and gas chromatography−mass spectrometry. According to the results, the synbiotic interaction of FOS and kombucha consortium promoted the growth of yeast and lactic acid bacteria in soy milk. The ideal fermentation time was 84 h. At this time, fermented soy milk added with FOS displayed increased β-glucosidase activity (by 68.10 mU/mL), isoflavones mainly represented by genistein content (by 612.41%), and DPPH radical scavenging activity (by 25.02%). Furthermore, the addition of FOS intensified the sour taste of the 84 h-fermented soy milk. The content of hexanal was reduced, while favorable flavor substances, such as citric acid and linalool, were also produced. Soymilk fermented with kombucha and FOS provides an opportunity to explore the physical and chemical characteristics and the mechanism of flavor formation in multi-strain co-fermentation systems and to develop commercial plant-based fermentation products.

Microbial Diversity and Flavor Regularity of Soy Milk Fermented Using Kombucha.

Plant-based milk is considered a healthy and environmentally sustainable option. However, due to the low protein content of most plant-based milk and the difficulty of gaining flavor acceptance by consumers, its production scale is usually limited. Soy milk is a kind of food with comprehensive nutrition and high protein content. In addition, kombucha is naturally fermented by acetic acid bacteria (AAB), yeast, lactic acid bacteria (LAB), and other microorganisms, and the microorganisms in its system can improve the flavor characteristics of food. In the present study, LAB (commercially purchased) and kombucha were used as fermenting agents for soybean, which was used as a raw material to produce soy milk. A variety of characterization methods were used to study the relationship between the microbial composition and flavor regularity of soy milk produced with different proportions of fermenting agents and different fermentation times. In soy milk produced at 32 °C with a mass ratio of LAB to kombucha of 1:1 and a fermentation time of 42 h, the concentrations of LAB, yeast, and acetic acid bacteria in the milk were optimal at 7.48, 6.68, and 6.83 log CFU/mL, respectively. In fermented soy milk produced with kombucha and LAB, the dominant bacterial genera were Lactobacillus (41.58%) and Acetobacter (42.39%), while the dominant fungal genera were Zygosaccharomyces (38.89%) and Saccharomyces (35.86%). After 42 h, the content of hexanol in the fermentation system of kombucha and LAB decreased from 30.16% to 8.74%, while flavor substances such as 2,5-dimethylbenzaldehyde and linalool were produced. Soy milk fermented with kombucha offers the opportunity to explore the mechanisms associated with flavor formation in multi-strain co-fermentation systems and to develop commercial plant-based fermentation products.

Identification of Lactic Bacteria in Commercial Fermented Products in Ho Chi Minh City by Using PCR Approach

Identification of Lactic Bacteria in Commercial Fermented Products in Ho Chi Minh City by Using PCR Approach

Metagenomic Characterization of Multiple Genetically Modified Bacillus Contaminations in Commercial Microbial Fermentation Products.

Genetically modified microorganisms (GMM) are frequently employed for manufacturing microbial fermentation products such as food enzymes or vitamins. Although the fermentation product is required to be pure, GMM contaminations have repeatedly been reported in numerous commercial microbial fermentation produce types, leading to several rapid alerts at the European level. The aim of this study was to investigate the added value of shotgun metagenomic high-throughput sequencing to confirm and extend the results of classical analysis methods for the genomic characterization of unauthorized GMM. By combining short- and long-read metagenomic sequencing, two transgenic constructs were characterized, with insertions of alpha-amylase genes originating from B. amyloliquefaciens and B. licheniformis, respectively, and a transgenic construct with a protease gene insertion originating from B. velezensis, which were all present in all four investigated samples. Additionally, the samples were contaminated with up to three unculturable Bacillus strains, carrying genetic modifications that may hamper their ability to sporulate. Moreover, several samples contained viable Bacillus strains. Altogether these contaminations constitute a considerable load of antimicrobial resistance genes, that may represent a potential public health risk. In conclusion, our study showcases the added value of metagenomics to investigate the quality and safety of complex commercial microbial fermentation products.

Probiotics dairy drink for patients with Galactosemia

Objective: The objective of this study was to develop probiotic dairy products with lactose free and low-galactose contents were produced for patients with galactosemia from four different raw materials including conventional cow’s milk, lactose free cow’s milk and mixtures containing lactose free cow’s milk and three different lactose and galactose free infant formulas. Material and Methods: Probiotic fermented dairy drinks, specifically acidophilus milk and kefir, with lactose free and low galactose content for patients with galactose intolerance were produced by using a 1:1 mixture of lactose free milk and two different types of infant formula, fortified with strawberry flavor. Storage period was set for 30 days. Said types of products were also produced with lactose free milk and conventional milk as raw material in order to use as control groups. With priority, lactose and galactose contents, and some other chemical, physical, microbiological and sensory properties were examined. Results: Chemical, physical, microbiological and sensory properties of these products were found to match the common quality characteristics of a commercial fermented dairy product. Also, such properties of fermented dairy drinks produced from lactose free milk have the same quality characteristics of a fermented dairy product. Conclusion: The galactose contents of fermented dairy beverages produced from lactose free raw materials were reduced to a level suitable for the diets of galactosemic patients.

Development of a Taxon-Specific Real-Time PCR Method Targeting the Bacillus subtilis Group to Strengthen the Control of Genetically Modified Bacteria in Fermentation Products

Most of the bacteria that are used to produce fermentation products, such as enzymes, additives and flavorings, belong to the Bacillus subtilis group. Recently, unexpected contaminations with unauthorized genetically modified (GM) bacteria (viable cells and associated DNA) that were carrying antimicrobial resistance (AMR) genes was noticed in several microbial fermentation products that have been commercialized on the food and feed market. These contaminations consisted of GM Bacillus species belonging to the B. subtilis group. In order to screen for the potential presence of such contaminations, in this study we have developed a new real-time PCR method targeting the B. subtilis group, including B. subtilis, B. licheniformis, B. amyloliquefaciens and B. velezensis. The method’s performance was successfully assessed as specific and sensitive, complying with the Minimum Performance Requirements for Analytical Methods of GMO Testing that is used as a standard by the GMO enforcement laboratories. The method’s applicability was also tested on 25 commercial microbial fermentation products. In addition, this method was developed to be compatible with the PCR-based strategy that was recently developed for the detection of unauthorized GM bacteria. This taxon-specific method allows the strengthening of the set of screening markers that are targeting key sequences that are frequently found in GM bacteria (AMR genes and shuttle vector), reinforcing control over the food and feed chain in order to guarantee its safety and traceability.

Nitrite, biogenic amines and volatile N-nitrosamines in commercial Chinese traditional fermented fish products

ABSTRACT To examine the safety of Chinese traditional fermented fish products (CTFPs) available on the Chinese market, nitrite, nitrate, biogenic amines (BAs) and volatile N-nitrosamines (VNAs) content in 33 commercial CTFPs from different provinces was investigated. The mean content of nitrite and nitrate wase 0.63 and 749.5 mg/kg, respectively. Concerning the occurrence of BAs, the accumulation in all CTFPs samples remained at low levels, whereas only in one sample from Guangxi the histamine content exceeded the critical level (50 mg/kg). In addition, six types of VNAs, including N-nitrosodimethylamine (NDMA), N-nitrosoethylmethylamine, N-nitrosopiperidine, N-nitrosopyrrolidine, N-nitrosomorpholine and N-nitrosodiphenylamine, were detected in a high number of samples. The NDMA content in 36.4% of the samples and the total VNAs content in about 63.6% of the samples were unacceptable. Principal component analysis indicated that the accumulation of NDMA and total VNAs was closely related with the content of histamine, tyramine and nitrate.

A Solid-State Fermentation (SSF) supplement improved performance, digestive function and gut ultrastructure of rainbow trout (Oncorhynchus mykiss) fed plant protein diets containing yellow lupin meal

A nutritional investigation was conducted to determine whether growth performance, feed efficiency and midgut morphology of rainbow trout (Oncorhynchus mykiss) is affected by United Kingdom cultivars of Yellow Lupin (Control, Y) (LC) compared to the addition of a commercial solid-state fermentation product (SSF) in separate dietary treatments 0.1 and 0.5% (LS0.1 and LS0.5, respectively). At the end of feeding trial, LC- and LS0.1-fed fish did not differ from one another, whilst significant improvement was observed in LS0.5 fed fish (P < 0.05). Apparent digestibility of crude protein and crude fibre were significantly higher in fish fed LS0.1 and LS0.5 than LC. No significant differences (P < 0.05) in Haemoglobin (Hb) concentrations were observed among dietary treatments. Fish fed the 0.1% SSF inclusion exhibited significantly (P < 0.001) higher haematocrit (Hct) concentration than all other treatments. Significantly (P < 0.005) higher serum glucose levels were observed in FMC fed fish compared to fish fed LC and LS0.1, whilst elevation was also observed in LS0.5 over LC and LS0.1. Activity of serum lysozyme was significantly (P < 0.05) higher in the LS0.5 treatment compared to LC, S0.1 and FMC groups. Fish fed 0.5% SSF were observed to have a significant (P < 0.05) reduction in goblet cell counts (GC) compared to those fed LC and LS0.1.). Median enterocyte height (EH) of LS0.1 and LS0.5 fed fish did not differ from one another but were both significantly greater than LC fed fish. Mean microvilli length (MVL), diameter (MVD) and enterocyte apical area (EAA) did not differ significantly between dietary treatments (P > 0.05). Fish fed 0.5% SSF displayed a higher microvillar percentage coverage (MVCV) compared to fish fed LC and LS0.1. Total alkaline protease (TAP), trypsin and chymotrypsin activities in the digesta of fish were unaffected by dietary treatment (P > 0.05). Activity of alkaline phosphatase (ALP) in digesta was significantly (P < 0.05) higher in SSF treatments than LC. Activity of L-leucine aminopeptidase (LAP) in digesta was marginally significantly (P = 0.045) higher in LS0.1 SSF fed fish than LC fed fish. Activity of LAP was also significantly higher in LS0.5 fed fish than LC fed fish.

Capacidad metabólica de cultivos mixtos probióticos formados por cepas de Lactobacillus y Bifidobacterium para uso en alimentos lácteos fermentados funcionales

The metabolic capacity of probiotic mixed cultures formed by Lactobacillus and Bifidobacterium strains was assessed through the determination of the acidification profile and the production of amino acids and volatile compounds, during the fermentation of ultra-pasteurized skim milk. Two mixed cultures formed by [L. acidophilus + B. bifidum] and [L. acidophilus + B. animalis] stood out in the production of essential amino acids: His, Ile, Leu, Met, Thr, Trp and Val. As well as increased production of volatile compounds such as: acetoin, 2-heptanone, 2-nonanone, acetic acid, acid butanoic and hexanoic acid, in contrast to commercial fermented dairy products. Additionally, these bacterial mixed cultures were characterized by the production of distinctive volatile compounds: 1-heptanol, diisobutylcarninol, hemellitol, 1-dodecanol, acetone, 2-pentanone, 2-undecanone, ethyl acetate, benzaldehyde as well as valeric, acetyl valeric and isopropylpyruvic acids. Finally, the culture formed by [L. acidophilus + B. bifidum] presented a good acidification profile with a lactic acid production of 26.1 ± 0.1 g / L and pH 3.6 at the end of fermentation. This data suggests a great potential of these mixed cultures to improve the nutritional value and organoleptic characteristics of fermented dairy products, when added as starter or adjunct cultures in the fermentation process.

Development of a highly sensitive HPLC method for the simultaneous determination of eight biogenic amines in aquatic products

AbstractA highly sensitive high-performance liquid chromatography (HPLC) method was developed for the simultaneous determination of eight biogenic amines in aquatic products. The biogenic amines in the sample were extracted with 5% trichloroacetic acid, derived with dansyl chloride (Dns-Cl) and quantified by a UV detector. The results showed that tryptamine (TRY), 2-phenethylamine (PHE), putrescine (PUT), cadaverine (CAD), histamine (HIS), tyramine (TPY), spermidine (SPD), and spermine (SPM) were effectively separated in 18 min in the range of 0.1–50 mg/kg with a good linear coefficient (r2 &gt; 0.999). The detection limits (LODs) of the eight biogenic amines were 0.007–0.021 mg/kg while the limits of quantification (LOQs) were 0.024–0.069 mg/kg with the recoveries basically between 68 and 123%. The determination of eight biogenic amines in five commercial fermented aquatic products indicating that the developed method could be applied for the simultaneous detection of biogenic amines in multiple aquatic products.

Modified PMA-qPCR Method for Rapid Quantification of Viable Lactobacillus spp. in Fermented Dairy Products

Quantification of viable lactic acid bacteria is an important quality index of fermented dairy products, but the current detection method, which is plate counting, is time-consuming. This study describes a modified PMA-qPCR assay that allows the detection and enumeration of total viable Lactobacillus spp. in commercial fermented milk products. Here, a new pair of genus-specific primers and minor groove binder probes was designed based on the 16S rRNA gene sequences of 24 reference strains, 13 of which were from different Lactobacillus species commonly used in commercial fermented dairy products. Subsequently, compared with the heat killing method, the 20-cycle homogenization method was chosen for initial PMA-qPCR optimization. Standard curves were prepared, and the efficiency obtained was 97% (R2 = 0.992), demonstrating that this PMA-qPCR method was feasible and effective. Additionally, the viable Lactobacillus spp. detection range was 103–109 CFU/mL, which meets the detection requirements in fermented dairy products. Furthermore, total number of viable Lactobacillus spp. in six different commercial fermented dairy products was estimated by three individual methods (plate count in MRS agar, qPCR, and PMA-qPCR). Comparison of results obtained by PMA-qPCR and plate counts was similar, and both decreased accordingly, showing a good correlation with the decline of strain vitality, 30 days after the expiration date. The PMA-qPCR procedure established in this paper allows the quantification of viable Lactobacillus spp. in approximately 3 h, greatly improving detection efficiency, and has broad application prospects in the testing of fermented dairy products.

Viability of acid-adapted and non-adapted Bacillus cereus during the lactic fermentation of skim milk and product storage at 5°C

In this study, Bacillus cereus was subjected to acid adaptation at pH 6.3 for 40 min. It was found that acid-adapted B. cereus exhibited a higher survival percentage than non-adapted cells after exposure to an acidic condition of pH 4.6. The viable population of both acid-adapted and non-adapted B. cereus increased during the first 12-18 hr of lactic fermentation of skim milk by Streptococcus thermophilus or Lactobacillus bulgaricus, and then declined as the fermentation extended. However, the acid-adapted cells exhibited a lower population reduction rate than the non-adapted B. cereus. A higher viable population of acid-adapted B. cereus than the non-adapted cells was also noted in Str. thermophilus-fermented skim milk and the two commercial lactic fermented products kept at 5°C. Additionally, the acid adaptation could reduce the susceptibility of B. cereus to acidity, refrigerated temperature and other detrimental principles present in lactic fermented milk products.