The incidence and distribution of ochratoxin A in Daqu, a Chinese traditional fermentation starter

Core microbes identification and synthetic microbiota construction for the production of Xiaoqu light-aroma Baijiu

Baijiu production has relied on natural inoculated Qu as a starter culture, causing the unstable microbiota of fermentation grains, which resulted in inconsistent product quality across batches. Therefore, revealing the core microbes and constructing a synthetic microbiota during the fermentation process was extremely important for stabilizing product quality. In this study, the succession of the microbial community was analyzed by high-throughput sequencing technology, and ten core microbes of Xiaoqu light-aroma Baijiu were obtained by mathematical statistics, including Acetobacter, Bacillus, Lactobacillus, Weissella, Pichia,Rhizopus, Wickerhamomyces, Issatchenkia, Saccharomyces, and Kazachstania. Model verification showed that the core microbiota significantly affected the composition of non-core microbiota (P < 0.01) and key flavor-producing enzymes (R > 0.8, P < 0.01), thus significantly affecting the flavor of base Baijiu. Simulated fermentation validated that the core microbiota can reproduce the fermentation process and quality of Xiaoqu light-aroma Baijiu. The succession of bacteria was mainly regulated by acidity and ethanol, while the fungi, especially non-Saccharomyces cerevisiae, were mainly regulated by the initial dominant bacteria (Acetobacter, Bacillus, and Weissella). This study will play an important role in the transformation of Xiaoqu light-aroma Baijiu fermentation from natural fermentation to controlled fermentation and the identification of core microbes in other fermented foods.

The Risk Monitoring of Aflatoxins and Ochratoxin A in Critical Control Point of Soy Sauce Aroma-Type Baijiu Production

Soy sauce aroma-type baijiu-producing regions are mostly in southwest China (Guizhou and Sichuan province) with a hot and humid subtropical monsoon climate, which is conducive to the propagation of toxigenic fungi. This suggests that there is a risk of potential contamination by mycotoxins in the soy sauce aroma-type baijiu production process, which poses significant food safety risks. Few studies on the safety of mycotoxins in soy sauce aroma-type baijiu production exist. Aiming to evaluate the safety of mycotoxins in soy sauce aroma-type baijiu during its production, this study screened and analyzed mycotoxic risk at critical points throughout the production process, investigated from raw materials, daqu, alcoholic fermentative grains, crude baijiu and microbial communities in different stages of the production process. The aflatoxins (AFs) and ochratoxin A (OTA) contents in wheat, daqu, alcoholic fermentative grains and crude baijiu samples were detected by ultra-performance liquid chromatography with tandem mass spectrometry. Mycotoxins were detected in wheat, daqu and alcoholic fermentative grains. The AFs and OTA detection rates, as well as their contents in the daqu samples, were relatively higher compared to those observed in the wheat and alcoholic fermentative grains. AFs were detected in 30% of the daqu samples, while OTA was detected in 20% of the daqu samples, though the contents of both AFs and OTA were under the maximum limit of the Chinese national standard. Furthermore, the fungi contained in daqu samples were isolated and identified, and the results showed that no fungi in the separated bacterial strains were producers of mycotoxins. According to the assessment results, the safety of soy sauce aroma-type baijiu production process in terms of AFs and OTA is confirmed.

Quantification of aflatoxin and ochratoxin contamination in animal milk using UHPLC-MS/SRM method: a small-scale study

Mycotoxin contamination in animal milk is an emerging concern around the globe. Here we developed and validated an ultrahigh-performance liquid chromatography and mass spectrometry-selected reaction monitoring (UHPLC/MS-SRM) method to quantify low concentrations of aflatoxins (AFs) and ochratoxins (OTs) in routinely consumed animal milk samples collected from southern India. Stable isotope dilution methodology was applied to quantify AFB1, AFB2, AFG1, AFG2, AFM1, AFM2 and OTA, OTB in n = 38 different milk samples, using 1 mL of milk. Bioanalytical parameters including method accuracy, precision, recovery, regression analysis and stability were assessed. Dynamic ranges for quantification were between 15.6-1000 pg/mL for AFB1, AFB2, AFG1, and OTA; 7.8-500 pg/mL for AFM1, AFM2 and OTB; 78.6-5000 pg/mL for AFG2. Method accuracy ranged between 80-120%, with ± 15% precision. Recoveries for spiked standards were > 88% in water and 75% in milk, with limits of quantification (LOQ) ranging between 31.3 pg/mL for AFB1, AFB2, AFG1 and OTA, 15.6 pg/mL for AFM1, AFM2 and OTB and 156 pg/mL for AFG2. R2 values for regression analyses ranged between 0.9991-0.9999. AFB2 [mean: 38 pg/mL (0.038 µg/kg)] was quantified in goat milk, AFM1 was quantified in cow, goat, pasteurized milk [mean: 331 pg/mL (0.331 µg/kg), 406 pg/mL (0.406 µg/kg), 164 pg/mL (0.164 µg/kg)]. Additionally, 90% of cow, goat and pasteurized milk samples were above European Union (EU) limits of 50 pg/mL (0.05 µg/kg) and 40% of cow and goat milk samples were above the Food Safety Standards Authority of India (FSSAI) limit of 500 pg/mL (0.5 µg/kg). AFM2 was also quantified in cow, goat, and pasteurized milk samples [mean: 249 pg/mL (0.249 µg/kg), 375 pg/mL (0.375 µg/kg), 81 pg/mL (0.081 µg/kg)]. Our dynamic ranges for quantification are lower than other published methods, with need for a smaller volume of milk. This validated method can be applied for routine quantification of mycotoxins in milk.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at (10.1007/s13197-021-04986-w).

Volatile Organic Compound-Mediated Antifungal Activity of Pichia spp. and Its Effect on the Metabolic Profiles of Fermentation Communities

Volatile organic compounds (VOCs) are chemicals responsible for antagonistic activity between microorganisms. The impact of VOCs on microbial community succession of fermentation is not well understood. In this study, Pichia spp. were evaluated for VOC production as a part of antifungal activity during baijiu fermentation. The results showed that the abundance of Pichia in the defect group (agglomerated fermented grains) was lower than that in control group, and a negative interaction between Pichia and Monascus was determined (P < 0.05). In addition, the disruption of fungi was significantly related to the differences of metabolic profiles in fermented grains. To determine production of VOCs from Pichia and its effect on Monascus purpureus, a double-dish system was assessed, and the incidence of M. purpureus reduction was 39.22% after 7 days. As to antifungal volatile compounds, 2-phenylethanol was identified to have an antifungal effect on M. purpureus through contact and noncontact. To further confirm the antifungal activity of 2-phenylethanol, scanning electron microscopy showed that 2-phenylethanol widely and significantly inhibited conidium germination and mycelial growth of filamentous fungi. Metatranscriptomic analysis revealed that the Ehrlich pathway is the metabolic path of 2-phenylethanol in Pichia and identified potential antifungal mechanisms, including protein synthesis and DNA damage. This study demonstrated the role of volatile compound-mediated microbial interaction in microbiome assembly and discovered a plausible scenario in which Pichia antagonized fungal blooms. The results may improve the niche establishment and growth of the functional yeast that enhances the flavor of baijiu.IMPORTANCE Fermentation of food occurs within communities of interacting species. The importance of microbial interactions in shaping microbial structure and metabolic performance to optimize the traditional fermentation process has long been emphasized, but the interaction mechanisms remain unclear. This study applied metabolome analysis and amplicon sequencing along with metatranscriptomic analysis to examine the volatile organic compound-mediated antifungal activity of Pichia and its effect on the metabolism of ethanol during baijiu fermentation, potentially enhancing the establishment of the fermentation niche and improving ethanol metabolism.