A comparative study of DNA extraction methods to be used in real-time PCR based quantification of ochratoxin A-producing molds in food products

Evaluating the Potential of Korean Mudflat-Derived Penicillium nalgiovense SJ02 as a Fungal Starter for Manufacturing Fermented Sausage

The objective of this study was to isolate, identify, and evaluate novel Korean starter cultures for use in fermented sausages. A total of 72 strains were isolated from various indigenous sources, including Nuruk, Jeotgal, and mudflats on the west coast of South Korea. Two strains were identified as Penicillium nalgiovense (SD01 and SJ02), a traditional starter used in the production of fermented sausages. A comparative analysis was performed between SD01 and SJ02 using the commercial starter culture (M600). Strain SJ02 exhibited superior lipolytic and proteolytic activities, as well as an enhanced growth rate at the optimal salinity level of 2% NaCl compared to M600. No significant differences were observed in thiobarbituric acid reactive substances values, sausage colors, and texture properties between SJ02 and M600 fermented sausages, except for adhesiveness. Profiles of mycotoxin-related genes were similar for both strains. Electronic nose analysis revealed distinct aroma profiles between SJ02 and M600 fermented sausages, with a relatively higher levels of propan-2-one and butyl butanoate in SJ02, and a higher level of ethanol and propanal in M600. In electronic tongue analysis, there was no significant differences in taste characteristics between SJ02 and M600. These results indicate that P. nalgiovense SJ02 is a potential starter culture to produce dry fermented sausages, enhancing Korean style cured meat processing industry.

Composition and activity of antifungal lipopeptides produced by Bacillus spp. in daqu fermentation

Daqu is a solid-state fermentation and saccharification starter for the Chinese liquor baijou. During the daqu stage, amylolytic and proteolytic enzymes are produced by Bacillus and fungi. Bacillus spp. also produce lipopeptides with a broad spectrum of antimicrobial activities but direct evidence for their impact on community assembly in daqu is lacking. This study aimed to study the interaction between Bacillus spp. and fungi in daqu models. The antifungal activity of surfactin, fengycin, and iturin A was initially assessed in vitro. Iturin A displayed the strongest antifungal activity (MIC = 10-50 mg/L). In situ antifungal activity of B. amyloliquefaciens and B. velezensis against molds was observed in a simple daqu model inoculated with single strains of Bacillus species. Formation of lipopeptides in situ was supported by quantification of mRNA encoding for enzymes for surfactin, fengycin, and iturin A biosynthesis. In situ antifungal activity of Bacillus species was also observed in a complex daqu model that was inoculated with 8 bacterial or fungal strains plus one of the three strains of Bacillus. A relationship of lipopeptides to in situ antifungal activity was further supported by detection of the lipopeptides by liquid chromatography coupled to mass spectrometry. Both results indicated that B velezensis FUA2155 had higher antifungal activity in the daqu model, and was the only strain that produced multiple iturin A congeners in situ. Taken together, this study provides evidence that production of lipopeptides by Bacillus species in daqu may impact community assembly and hence product quality.

Relationship between cyclopiazonic acid production and gene expression in Penicillium griseofulvum under dry-cured ham processing environmental conditions

Cyclopiazonic acid (CPA)-producing Penicillium griseofulvum is usually found on the dry-cured ham surface during its ripening. The objective of this work was to evaluate the effect of temperature and water activity (a_w) of dry-cured ham processing on growth, CPA production, and temporal relative expression of genes involved in CPA biosynthesis on dry-cured meat-based media. P. griseofulvum CECT 2919 grew faster than P. griseofulvum IBT 14319 in all conditions tested, although no growth occurred at 0.85 a_w. Besides, the dry-cured ham-based medium favoured CPA synthesis for both strains compared to the meat-based medium. For the strain CECT 2919, the expression of the mfs-1 and pks-nrps genes were stimulated at 0.90 and 0.95 a_w, respectively, while the dmaT gene expression was inhibited during the incubation time. By contrast, the strain IBT 14319 showed that the dmaT gene expression was stimulated at 0.90 a_w, while the pks-nrps and mfs-1 genes were repressed throughout incubation time. In conclusion, it is necessary to reduce a_w on the surface of the hams below 0.85 during ripening before to increase temperature to reduce growth of P. griseofulvum and CPA production. This information may be useful to design preventive and corrective actions to minimise risks associated with the presence of CPA in dry-cured ham.

Specific Volumetric Weight-Driven Shift in Microbiota Compositions With Saccharifying Activity Change in Starter for Chinese Baijiu Fermentation

Chinese starter Jiuqu, traditionally produced by spontaneous fermentation and always squeezed into bricks, serves as a vital saccharifying agent for simultaneous saccharification and fermentation of Chinese Baijiu. It is important to reveal the key saccharifying microbiota and the driving force to improve the quality of Jiuqu. Here we studied the compositions of the microbiota by high-throughput amplicons sequencing analysis in Jiuqu, and revealed eight bacterial and seven fungal genera as the dominant community members. Among them, Lactobacillus, Aspergillus, Pichia, Saccharomyces, Rhizopus were the main contributors of proteins by metaproteomics analysis. Whereas, only Lactobacillus, Pichia, Rhizopus appeared as key actors for saccharification by secreting three glycosidases and two glycosyltransferases, and it indicated they were the key saccharifying microbiota in Jiuqu. Especially, Rhizopus secreted the most abundant glucoamylase. Interestingly, these three active genera significantly decreased and the key saccharifying enzymes were down-expressed, when Jiuqu was produced in diffused shape with a low volumetric weight. Rhizopus microsporus, the main producer of glucoamylase, was positively correlated with volumetric weight of Jiuqu. It indicated volumetric weight was the major driving force of the key saccharifying microbiota in Jiuqu. This work provides deep insights of key saccharifying microbiota, and indicates the main driving force for the key microbe. Furthermore, this finding can contribute to the improvement of saccharifying agent for food fermentation.

Mould spoilage of foods and beverages: Using the right methodology

Fungal spoilage of products manufactured by the food and beverage industry imposes significant annual global revenue losses. Mould spoilage can also be a food safety issue due to the production of mycotoxins by these moulds. To prevent mould spoilage, it is essential that the associated mycobiota be adequately isolated and accurately identified. The main fungal groups associated with spoilage are the xerophilic, heat-resistant, preservative-resistant, anaerobic and psychrophilic fungi. To assess mould spoilage, the appropriate methodology and media must be used. While classic mycological detection methods can detect a broad range of fungi using well validated protocols, they are time consuming and results can take days or even weeks. New molecular detection methods are faster but require good DNA isolation techniques, expensive equipment and may detect viable and non-viable fungi that probably will not spoil a specific product. Although there is no complete and easy method for the detection of fungi in food it is important to be aware of the limitation of the methodology. More research is needed on the development of methods of detection and identification that are both faster and highly sensitive.

Synergistic Effect in Core Microbiota Associated with Sulfur Metabolism in Spontaneous Chinese Liquor Fermentation

Microbial sulfur metabolism plays crucial roles in various food and alcoholic beverage fermentations. 3-(Methylthio)-1-propanol and dimethyl disulfide are important sulfur compounds in fermented foods and alcoholic beverages. Here, we studied the dynamics of these two compounds during spontaneous Chinese liquor fermentation. The two compounds reached the maximum concentration at day 10 and the maximum production rate at day 3. Metatranscriptomic analysis at days 3 and 10 revealed a total of 354 metabolically active microorganisms. Saccharomyces and Lactobacillus were identified as core microbiota critical for sulfur compound production based on both the transcript abundances of the principal genes and the distribution frequencies of 31 enzymes involved in sulfur metabolism. Saccharomyces transcribed genes encoding 23 enzymes related to the generation of 3-(methylthio)-1-propanol and dimethyl disulfide, and Lactobacillus was active in the methyl cycle, which recycles methionine, the precursor of the two sulfur compounds. Furthermore, the sulfur metabolism-related characteristics of two representative species were studied in coculture during a simulated fermentation. Saccharomyces cerevisiae JZ109 produced 158.4 μg/liter 3-(methylthio)-1-propanol and 58.5 μg/liter dimethyl disulfide in monoculture, whereas Lactobacillus buchneri JZ-JN-2017 could not produce these two compounds in monoculture. Their coculture significantly enhanced the generation of 3-(methylthio)-1-propanol (350.0 μg/liter) and dimethyl disulfide (123.8 μg/liter). In addition, coculture significantly enhanced the gene transcriptions (fold change, 1.5 to ∼55.0) that convert methionine to these two compounds in S. cerevisiae and in the methyl cycle of L. buchneri This study reveals a novel synergistic effect between members of the core microbiota in the production of sulfur compounds via methionine recycling in spontaneous Chinese liquor fermentation.IMPORTANCE Sulfur compounds play a crucial role in the aroma quality of various fermented foods and alcoholic beverages. However, it is unclear how these compounds are produced by microbes during their spontaneous fermentations. Here, we identified the core microbiota (Saccharomyces and Lactobacillus) associated with sulfur metabolism by determining both transcript abundance and distribution frequency of each genus in spontaneous Chinese liquor fermentation. This study provides a system-level analysis of sulfur metabolism by the metatranscriptomic analysis and culture-dependent methods. It sheds new light on how the metabolic behavior of the microbiota contributes to the liquor aroma quality. Furthermore, this work reveals a novel synergistic effect between Saccharomyces and Lactobacillus in the production of sulfur compounds, in which Lactobacillus regenerates the precursor methionine for sulfur compound production by Saccharomyces Our findings can contribute to the enhancement of aroma characteristics in Chinese liquor and open new avenues for improving various food and alcoholic beverage fermentation processes.

Targeting Other Mycotoxin Biosynthetic Genes

Real-time PCR (qPCR) methods are adequate tools for sensitive and rapid detection and quantification of toxigenic molds contaminating food commodities. Methods of qPCR for quantifying zearalenone (ZEA)-, sterigmatocystin (ST)-, cyclopiazonic acid (CPA)-, and patulin (PAT)-producing molds have been designed on the basis of specific target genes involved in the biosynthesis of these mycotoxins. In this chapter reliable qPCR protocols to detect and quantify such toxigenic molds are described. All of these methods are suitable when working with mold pure cultures and mold contaminated foods. For ZEA-producing molds, two qPCR using the SYBR Green fluorochrome and based on two polyketide synthase (PKS) genes are detailed. qPCR protocols relied on the fluG and the idh genes able to quantify ST- and PAT-producing molds, respectively, which can be performed by both SYBR Green and TaqMan methodologies are described. Regarding CPA-producing molds a TaqManq PCR method including a competitive internal amplification control is detailed. Since DNA extraction is a critical step in the detection and quantification of toxigenic molds by qPCR, a protocol for extracting DNA from mold pure cultures and food is also described.

Impact of bacterial biocontrol agents on aflatoxin biosynthetic genes, aflD and aflR expression, and phenotypic aflatoxin B₁ production by Aspergillus flavus under different environmental and nutritional regimes

The objectives of this study were to examine the efficacy of four bacterial antagonists against Aspergillus flavus using 50:50 ratio of bacterial cells/conidia for the control of aflatoxin B1 (AFB1) production on two different nutritional matrices, nutrient and maize-based media at different water availabilities (0.98, 0.94 water activity (aw) on nutrient medium; 0.995, 0.98 aw on maize meal agar medium) at 35°C. The indicators of efficacy used were the relative expression of one structural and regulatory gene in the biosynthetic pathway (aflD and aflR respectively) and the production of AFB1. These studies showed that some of the bacterial species could significantly inhibit the relative expression of the aflD and aflR genes at both 0.98 and 0.94 aw on nutrient agar. On maize-based media some of the bacterial antagonists reduced the activity of both genes at 0.94 aw and some at 0.995 aw. However, the results for AFB1 production were not consistent with the effects on gene expression. Some bacterial species stimulated AFB1 production on both nutrient and maize-based media regardless of aw. However, some bacterial treatments did inhibit AFB1 production significantly when compared to the control. Overall, this study suggests that temporal studies are required on the biosynthetic genes under different environmental and nutritional conditions to evaluate the potential of antagonists to control AFB1.

The use of real-time PCR to study Penicillium chrysogenum growth kinetics on solid food at different water activities

Fungal growth on solid foods can make them unfit for human consumption, but certain specialty foods require fungi to produce their characteristic properties. In either case, a reliable way of measuring biomass is needed to study how various factors (e.g. water activity) affect fungal growth rates on these substrates. Biochemical markers such as chitin, glucosamine or ergosterol have been used to estimate fungal growth, but they cannot distinguish between individual species in mixed culture. In this study, a real-time polymerase chain reaction (rt-PCR) protocol specific for a target fungal species was used to quantify its DNA while growing on solid food. The measured amount of DNA was then related to the biomass present using an experimentally determined DNA-to-biomass ratio. The highly sensitive rt-PCR biomass assay was found to have a wide range, able to quantify the target DNA within a six orders-of-magnitude difference. The method was used to monitor germination and growth of Penicillium chrysogenum spores on a model porous food (cooked wheat flour) at 25°C and different water activities of 0.973, 0.936, and 0.843. No growth was observed at 0.843, but lag, exponential and stationary phases were identified in the growth curves for the higher water activities. The calculated specific growth rates (μ) during the exponential phase were almost identical, at 0.075/h and 0.076/h for aw=0.973 and 0.936, respectively. The specificity of the method was demonstrated by measuring the biomass of P. chrysogenum while growing together with Aspergillus niger on solid media at aw=0.973.

Mycotoxigenic fungi and mycotoxins associated with stored maize from different regions of Lesotho

Samples of stored maize from villages located in five different agroecological zones (southern lowlands, northern lowlands, Senqu river valley, foothills and mountains) of Lesotho were collected in 2009/10 and 2010/11 and assessed for contamination with toxigenic fungi. The water activity of all samples collected during the two seasons was <0.70. The total fungal populations of the maize from different regions in the two seasons was not significantly different (p > 0.05). Fusarium verticillioides, F. proliferatum and F. subglutinans predominated in different regions in both seasons based on molecular analyses. In the 2009/10 season, the isolates of these species all produced FB1, while in the 2010/11 season, very few produced FB1. A. flavus isolates (2009/10) were recovered from mountains and Senqu river valley samples while the 2010/11 isolates were predominantly from the foothills and northern lowlands. The mountain isolates of Aspergillus section Flavi produced the highest levels of AFB1 (20 mg kg(-1)). Aspergillus parasiticus was only isolated from the foothills, Senqu river valley and southern lowlands samples, and the AFB1 levels produced ranged from 'none detected' to 3.5 mg kg(-1). The Aspergillus ochraceous isolates were least frequently encountered in both seasons. In the 2009/10 season, the isolates from the northern lowlands produced ochratoxin A (OTA) in culture. No isolates of A. niger from different regions in both seasons produced any OTA. Multi-mycotoxin analyses of the maize samples were done for a range of mycotoxins. At least one sample from each region in both seasons was FB1-positive. FB1 levels for 2010/11 samples (7-936 μg kg(-1)) were higher than in the 2009/10 season (2-3 μg kg(-1)). In both seasons, the mountains registered the highest levels of FB1. Deoxynivalenol (DON) was recovered from all the samples analysed, with the highest mean contamination of 1,469 μg kg(-1) in samples from the northern lowlands. Moniliformin (MON) was detected from all agroecological zones in the two seasons (5-320 μg kg(-1) in 2009/10; 15-1,205 μg kg(-1) in 2010/11). Emerging toxins such as fusaproliferin (FUS) and beauvericin (BEA) were also detected. OTA was not detected in any of the samples analysed. Only one 2009/10 sample in the Senqu river valley was positive for AFB1. This is the first report on toxigenic fungi and multi-mycotoxin contamination of maize samples from subsistence farmers' stores in different agroecological zones of Lesotho.

Naked Eye DNA detection: synthesis, characterization and DNA binding studies of a novel azo-guanidine

A novel class of azo-guanidine compounds is introduced in this article. The novel compound 2-(2-hydroxyphenyl)-1-(phenylamino)-3-(phenylimino)guanidine (AG) was synthesized and well characterized by using different analytical instrumental techniques like elemental analysis, FTIR, (1)H and (13)C NMR, UV-Visible spectroscopy and cyclic voltammetry. The new compound was found interacting with DNA and shows clear color change in the solution. The AG-DNA complex was qualitatively and quantitatively characterized with UV-Visible spectroscopy and cyclic voltammetry. Electrostatic mode of interaction, clear color change and moderate binding constant (K(b)=10(4)) indicate its potential use as DNA staining agent.