Analysis of microbial composition in acid whey for dairy fan making in Yunnan by conventional method and 16S rRNA sequencing

Dynamics of microbial communities associated with flavor formation during sour juice fermentation and the milk fan drying process

Milk fan is an acid-curd cheese with strong national characteristics (a traditional dairy product of the Bai nationality with a shape like a piece of paper) and a long history in Yunnan province, China. In our previous study, we characterized the microbial community diversity of milk fan, but the succession of microorganisms associated with flavor formation in milk fan is still unknown. Therefore, we examined the predominant microorganisms and their correlations with the formation of flavor in the fermentation of sour juice and drying of milk fan by gas chromatography mass spectrometry, high-throughput 16S rDNA sequencing, intergenic spacer sequencing and metatranscriptome analysis. We found that the relative abundances of Lactobacillus and Issatchenkia initially decreased and then increased with time during the fermentation of sour juice. However, the relative abundances of Acetobacter, Leuconostoc, Lactococcus, Geotrichum, and Dipodascus initially increased and then decreased. During the drying step, the relative abundances of Lactobacillus and Issatchenkia continuously increased and became the dominant microorganisms in the milk fan. The metatranscriptomes generated from the milk fan showed that "carbohydrate metabolism," "translation," and "signal transduction" were the main metabolic functions of the microbial communities. Rhodotorula and Yarrowia contained more differentially expressed genes than other genera, which indicated they may be associated with the production of the characteristic flavor. Furthermore, a Pearson correlation analysis showed that Lactococcus, Rhodotorula, Candida, Cutaneotrichosporon, and Yarrowia were significantly positively correlated with more aroma-active compounds, mainly ethyl acetate, 2-heptanone, isovaleraldehyde, butyric acid, nonanal, and hexanal. In conclusion, these findings contribute to a better understanding of the flavor production mechanism during the production of milk fan.

A newly developed strain of Enterococcus faecium isolated from fresh dairy products to be used as a probiotic in lactating Holstein cows

The objective of this study was to determine the ability of an isolated strain (EGY_NRC1) or commercial (NCIMB 11181) Enterococcus faecium as a probiotic for lactating cows. Two experiments were conducted: In Experiment 1, the effects of three levels (1, 2, and 3 g/kg diet, DM basis) of isolated and commercial E. faecium on in vitro ruminal fermentation kinetics, gas, methane (CH₄) and nutrient degradability were determined. In Experiment 2, thirty multiparous Holstein cows (633 ± 25.4 kg body weight) with 7 days in milk, were randomly assigned to 3 treatments in a completely randomized design in a 60-day experiment. Cows were fed without any additives (control treatment) or supplemented with 2 g/kg feed daily of E. faecium EGY_NRC1 (contain 1.1 × 10⁹ CFU/g) or commercial E. faecium NCIMB 11181 (contain 2 × 10¹² CFU/g). Diets were prepared to meet cow's nutrient requirements according to NRC recommendations. Probiotic doses were based on the in vitro Experiment 1. Feed intake, digestibility, blood parameters and lactation performance were evaluated. In Experiment 1, the isolated E. faecium linearly and quadratically increased (P < 0.001) in vitro total gas production (TGP), the degradability of dry matter (dDM) and organic matter (dOM) while decreased (P < 0.05) methane (CH₄) percent of TGP, NH₃CH₄ production, and pH. The commercial E. faecium increased TGP and decreased (P < 0.01) CH₄ production, pH and increased the dDM and dOM, short chain fatty acids and ruminal NH₃-N concentration. In Experiment 2, the isolated E. faecium increased (P < 0.01) total tract digestibility of DM, neutral and acid detergent fiber, daily milk production and feed efficiency compared to the control treatment without affecting feed intake and milk composition. Moreover, the isolated E. faecium increased (P < 0.05) the proportion of C18:1 trans-9, C18:2 cis-9-12 and C18:2 trans-10 cis-12. Both isolated and commercial E. faecium improved (P < 0.01) organic matter, crude protein and nonstructural carbohydrates digestibility, increased serum glucose (P = 0.002) and decreased serum cholesterol (P = 0.002). Additionally, both E. faecium strains decreased C23:0 (P = 0.005) in milk. In conclusion, the use of E. faecium (isolated and commercial) at 2 g/kg DM of feed improved feed efficiency and production performance, with superior effects on animal performance from isolated E. faecium compared to the commercial one.

Shifts in diversity and function of bacterial community during manufacture of Rushan

Rushan is a traditional dairy product consumed by the Bai people in the Yunnan Province of China, and its production still follows the traditional procedure of backslopping. However, how the microbial composition of raw materials and processing shape the microorganisms in Rushan have not been systemically reported. In this study, high-throughput sequencing technique was applied to analyze the microbial compositions of raw milk, fresh Rushan, curd whey, acid whey, and dry Rushan at the phylum, family, genus, and Lactobacillus species levels. The results indicated that Lactobacillus, Lactococcus, and Streptococcus were dominant genera in Rushan, whereas Lactobacillus kefiranofaciens and Lactobacillus helveticus were the 2 abundant species at the Lactobacillus species level. The network analysis indicated that raw milk mainly contributed to the microbial diversity of Rushan, whereas acid whey made a great contribution to shaping the relative abundance of microbes in Rushan and dramatically increased acid-producing genera, such as Lactobacillus and Acetobacter. The variation in microbial composition led to an increase in the relative abundance of pathways related to energy supply, acid production, fatty acid accumulation, cysteine, methionine, and lysine accumulation. The volatile profile of Rushan was rich in esters and acids, and the high relative abundance of Lactobacillus might be associated with reduction of amino acid metabolism, degradation of unpleasant flavored xylene, and accumulation of decanoic, dodecanoic, and tetradecanoic acids in the products. The accumulation of medium long-chain fatty acids might result from the relative abundance of FabF, FabZ, and FabI, particularly from Lactobacillus amylolyticus and Lacticaseibacillus paracasei.

First insights into molecular basis identification of 16 s ribosomal RNA gene of Staphylococcus aureus isolated from Sudan

Objective

In this study, we analyzed the molecular evolution of Staphylococcus aureus isolates using 16S rRNA gene and phylogenetic analysis to detect the prevalence of S. aureus infections in Sudan.

Results

Molecular detection of S. aureus has shown that 20 (43.47%) of patients were positive for S. aureus. The phylogenetic tree of 16S rRNA sequences was divided into three lineages of S. aureus isolates detected from wound infections in Sudan. Nucleotides base-pair substitution was appeared at position 249. This mutation do not linked with Macrolides, Lincosamides and Streptogramines b resistant phenotype. Further studies should investigate the effect of that mutation on resistance to other antibiotics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05569-w.

Simulated in vitro gastrointestinal digestion of traditional Chinese Rushan and Naizha cheese: Peptidome profiles and bioactivity elucidation

Chinese Rushan and Naizha, the traditional acid coagulated cheese types produced from cow and yak milk, respectively, have been consumed for more than thousands of years. In this study, we aimed to characterise peptides of Rushan and Naizha in simulated in vitro gastrointestinal digestion using label-free based peptidomic. The identified peptide sequences were subjected to BIOPEP database driven bioactivity search. In total, 309 and 225 peptides were identified from Rushan and Naizha cheese, respectively, corresponding to 20 protein annotations. Analysis of label-free quantification found different protein digestibility, where casein was the primary source of peptides in Rushan, among which 62% represented β-casein by peptide count. The release of peptides was concentrated in specific residues 145-155 of β-casein in Rushan. In contrast, κ-casein and 7 minor milk proteins were dominant in digestion of Naizha cheese (p < 0.05). In particular, there were 11 peptides from digestion that were exact matches in databases to sequences with immunomodulatory, antibacterial, ACE-inhibition, DPP IV inhibition and antioxidant activities. Four novel angiotensin I-converting enzyme inhibitory (ACEI) activities peptides (YPFPGPIH, LKNWGEGW, RELEEIR, and HPHPHLS) were explored using molecular docking, chemically synthesized, and in vitro ACEI activity. The peptides had lower estimated free energy values (-5.34 to -7.66 kcal/mol), and exhibited the lowest IC₅₀ value of 109.5, 77.7, 196.6, and 64.30 μM, respectively. Our study is the most comprehensive peptidomic analysis of Chinese Rushan and Naizha cheese to date.

The diversity of microbial communities in Chinese milk fan and their effects on volatile organic compound profiles

Milk fan is a cheese-like fermented milk product produced in Yunnan Province, China. In this study, we characterized the microbial communities of milk fan from 6 distinct geographical origins and investigated their generation of volatile organic compounds (VOC). The microbial communities found in all milk fan samples were dominated by Lactococcus, Lactobacillus, and Raoultella bacteria and Rhodotorula, Torulaspora, and Candida fungi. Samples from the Kunming and Weishan regions had greater bacterial richness, and samples from Xizhou had greater fungal community richness. Sixty prominent VOC (i.e., those having odor activity values ≥1), including esters, acids, alcohols, aldehydes, ketones, and aromatic compounds, were identified by gas chromatography-mass spectrometry analysis of milk fan samples. Pearson correlation analysis revealed that Lactobacillus, Rhodotorula, Lodderomyces, and Debaryomyces had significant correlations with various VOC, revealing a total of 13 compounds that are characteristic of the odor of milk fan. These bacteria and fungi are therefore identified as functional microorganisms that collectively create the complex VOC profile of milk fan. This study provides a comprehensive overview of the microbial community of milk fan and demonstrates its contribution to the unique aroma profile of this fermented milk product.

Characterization of the key aroma compounds in Yunnan goat milk cake using a sensory-directed flavor analysis

To identify the key aroma compounds in Yunnan goat milk cake, seven varieties of milk cake samples were subjected to sensory analysis and gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), aroma recombination, omission, and addition tests. The GC-MS results revealed 53 compounds with aroma characteristics in all the samples. A further comparison of odor activity values and aroma intensities (AI) revealed 25 of these compounds as the initial key aroma compounds. The contributions of these key aroma compounds to the sensory attributes were determined using a partial least squares regression. Of these compounds, 2-heptanone and 2-nonanone were closely related to the "milky" and "cheesy" attributes and were highly abundant in the samples from Kunming. Fatty acids, including butanoic acid, hexanoic acid, octanoic acid, and decanoic acid, were the most abundant compounds detected in the milk cakes. These fatty acids were closely related to the "rancid" and "animalic (goat)" attributes and were largely detected in the samples from Dali Dengchuan and Dali Xiaguan. Sensory-directed aroma recombination, omission, and addition tests further validated the important contributions of ethyl butyrate, benzaldehyde, 3-methyl-1-butanol, 2-heptanone, hexanoic acid, and octanoic acid to the overall sensory properties. Moreover, ethyl butyrate, benzaldehyde, and 2-heptanone, when added, had evident inhibitory or masking effects on the AI of "sour," "rancid," and "animalic (goat)" attributes. PRACTICAL APPLICATION: Goat milk cake is a popular acid-curd cheese in Yunnan, China, however, our limited knowledge to its key aroma compounds restricts its development and industrial production. In this study, a sensory-directed flavor analysis was used to characterized the key aroma compounds of Yunnan goat milk cake, which will help to enhance our understanding on the flavor profile of Yunnan goat milk cake and provide a reference for optimizing the flavor feature and organoleptic quality of this fresh goat cheese.

Contamination of Currency Notes with Kanamycin ResistantShigella flexneri.. [DOI: 10.1101/2020.03.07.982017]

Shigella flexneriis the main causative agent of shigellosis commonly distributed in developing countries with high morbidity and mortality rates. This study aimed to examine the presence ofShigellaspecies in Sudanese currency notes using both traditional and molecular techniques. One hundred thirty five currency notes were collected and their contaminants were isolated and identified conventionally and genetically using 16S rRNA gene amplification and sequencing. Eight isolates were identified asShigellaspecies in different notes, and 3 of them were resistant to penicillin, kanamycin and nitrofurantoin. OneS. flexneriisolate has insertion mutation of guanine nucleotide at position 730 of life’s essential gene 16S rRNA which known evolutionarily to be stable gene. Banknotes are highly circulating items and therefore, appropriate measures such as regular replacement of the dirty notes with new papers are necessary to protect peoples from being infected with drug resistant pathogens.

Construction of a shuttle expression vector for lactic acid bacteria

Background

Lactic acid bacteria (LAB) are a diverse group of Gram-positive bacteria, which are widely distributed in various diverse natural habitats. These are used in a variety of industrial food fermentations and carry numerous traits with utmost relevance to the food industry. Genetic engineering has emerged as an effective means to improve and enhance the potential of commercially important bacterial strains. However, the biosafety of recombinant systems is an important concern during the implementation of such technologies on an industrial scale. In order to overcome this issue, cloning and expression systems have been developed preferably from fully characterized and annotated LAB plasmids encoding genes with known functions.

Results

The developed shuttle vector pPBT-GFP contains two theta-type replicons with a copy number of 4.4 and 2.8 in Pediococcus acidilactici MTCC 5101 and Lactobacillus brevis MTCC 1750, respectively. Antimicrobial “pediocin” produced by P. acidilactici MTCC 5101 and green fluorescent protein (GFP) of Aequorea victoria were successfully expressed as selectable markers. Heterologous bile salt hydrolase (BSH) from Lactobacillus fermentum NCDO 394 has been efficiently expressed in the host strains showing high specific activity of 126.12 ± 10.62 in P. acidilactici MTCC 5101 and 95.43 ± 4.26 in the case of L. brevis MTCC 1750, towards glycine-conjugated bile salts preferably as compared to taurine-conjugated salts.

Conclusion

The present article details the development of a LAB/LAB shuttle expression vector pPBT-GFP, capable of replication in LAB hosts, P. acidilactici MTCC 5101, and L. brevis MTCC 1750. Pediocin and GFP have been used as selectable markers with the efficient production of heterologous extracellular bile salt hydrolase. Thus, the constructed vector pPBT-GFP, with its ability to replicate in multiple hosts, low copy number, and stability in host cells, may serve as an ideal tool for improving LAB strains of commercial value using genetic engineering.

Short communication: Enzymatic perspective of galactosidases reveals variations in lactose metabolism among Lactococcus lactis strains

To date, most studies of lactose utilization have focused on the genetic diversity of lactic acid bacteria or its influence on product quality, but phenotypic evaluation has rarely been based on metabolic characteristics. In the present study, we investigated the growth, acid production, β-galactosidase, and 6-phospho-β-galactosidase activities of 16 Lactococcus lactis strains obtained from various habitats with lactose as the sole carbon source. The 15 L. lactis strains obtained from various habitats exhibited significant differences in growth and acid production characteristics in the de Man, Rogosa, and Sharpe-lactose broth, and 4 strains consumed more lactose when cultured in skim milk than the type strain ATCC 19435. Among these strains, DQHXNQ38-12 mainly produced acetoin and diacetyl when cultured in skim milk, whereas the strains 15M2 and 5G2 produced high levels of acid and formed curd rapidly. We concluded that the use of lactose is necessary for strain adaptation to the dairy niche. Comprehensive studies of lactose use and the fermentation characteristics of L. lactis are of significant importance.

Isolation and Identification of Lactic Acid Bacteria from Traditional Dairy Products in Baotou and Bayannur of Midwestern Inner Mongolia and q-PCR Analysis of Predominant Species

In this study, traditional culture method and 16S rRNA gene analysis were applied to reveal the composition and diversity of lactic acid bacteria (LAB) of fermented cow milk, huruud and urum from Baotou and Bayannur of midwestern Inner Mongolia. Also, the quantitative results of dominant LAB species in three different types of dairy products from Baotou and Bayannur were gained by quantitative polymerase chain reaction (q-PCR) technology. Two hundred and two LAB strains isolated from sixty-six samples were identified and classified into four genera, namely Enterococcus, Lactococcus, Lactobacillus, Leuconostoc, and twenty-one species and subspecies. From these isolates, Lactococcus lactis subsp. lactis (32.18%), Lactobacillus plantarum (12.38%) and Leuconosto mesenteroides (11.39%) were considered as the dominated LAB species under the condition of cultivating in MRS and M17 medium. And the q-PCR results revealed that the number of dominant species varied from samples to samples and from region to region. This study clearly shows the composition and diversity of LAB existing in fermented cow milk, huruud and urum, which could be considered as valuable resources for LAB isolation and further probiotic selection.

Angiotensin-converting enzyme inhibitory activity of Lactobacillus helveticus strains from traditional fermented dairy foods and antihypertensive effect of fermented milk of strain H9

Hypertension is a major global health issue which elevates the risk of a large world population to chronic life-threatening diseases. The inhibition of angiotensin-converting enzyme (ACE) is an effective target to manage essential hypertension. In this study, the fermentation properties (titratable acidity, free amino nitrogen, and fermentation time) and ACE-inhibitory (ACEI) activity of fermented milks produced by 259 Lactobacillus helveticus strains previously isolated from traditional Chinese and Mongolian fermented foods were determined. Among them, 37 strains had an ACEI activity of over 50%. The concentrations of the antihypertensive peptides, Ile-Pro-Pro and Val-Pro-Pro, were further determined by ultra performance liquid chromatography with quadrupole-time-of-flight mass spectrometry. The change of ACEI activity of the fermented milks of 3 strains exhibiting the highest ACEI activity upon gastrointestinal protease treatment was assayed. Fermented milks produced by strain H9 (IMAU60208) had the highest in vitro ACEI activity (86.4 ± 1.5%), relatively short fermentation time (7.5 h), and detectable Val-Pro-Pro (2.409 ± 0.229 µM) and Ile-Pro-Pro (1.612 ± 0.114 µM) concentrations. Compared with the control, a single oral dose of H9-fermented milk significantly attenuated the systolic, diastolic, and mean blood pressure of spontaneously hypertensive rats (SHR) by 15 to 18 mmHg during the 6 to 12 h after treatment. The long-term daily H9-fermented milk intake over 7 wk exerted significant antihypertensive effect to SHR, but not normotensive rats, and the systolic and diastolic blood pressure were significantly lower, by 12 and 10 mmHg, respectively, compared with the control receiving saline. The feeding of H9-fermented milk to SHR resulted in a significantly higher weight gain at wk 7 compared with groups receiving saline, commercial yogurt, and captopril. Our study identified a novel probiotic L. helveticus strain originated from kurut sampled from Tibet (China), which is a valuable resource for future development of functional foods for hypertension management.

Isolation and identification of lactic acid bacteria from Tarag in Eastern Inner Mongolia of China by 16S rRNA sequences and DGGE analysis

Tarag is a characteristic fermented dairy product with rich microflora (especially lactic acid bacteria), developed by the people of Mongolian nationality in Inner Mongolia of China and Mongolia throughout history. One hundred and ninety-eight samples of Tarag were collected from scattered households in Eastern Inner Mongolia, and total of 790 isolates of lactic acid bacteria (LAB) were isolated by traditional pure culture method. To identify these isolates and analyze their biodiversity, 16S rRNA gene sequences analysis and PCR-DGGE were performed respectively. The results showed that 790 isolates could be classified as 31 species and subspecies. Among these isolates, Lactobacillus helveticus (153 strains, about 19.4%), Lactococcus lactis subsp. lactis (132 strains, about 16.7%) and Lactobacillus casei (106 strains, about 11.0%) were considered as the predominated species in the traditional fermented dairy products (Tarag) in Eastern Inner Mongolia. It was shown that the biodiversity of LAB in Tarag in Inner Mongolia was very abundant, and this traditional fermented dairy product could be considered as valuable resources for LAB isolation and probiotic selection.