Search

Background: Intramammary infections negatively affect milk quality, animal welfare and productivity in the dairy industry. Somatic cell count (SCC) is the most used screening tool to detect subclinical mastitis caused by intramammary infections. In dairy goats, SCC is greatly influenced by non-infectious factors, which complicates the interpretation. The aim of this research paper was to determine the association between SCC, intramammary infections and non-infectious factors including parity, season, lactation stage, and milk yield in dairy goats. In this longitudinal study, 451 goats from four Norwegian dairy goat herds were sampled for bacteriology and SCC up to nine times during two lactations. Factors like parity, milk yield, and stage of lactation were retrieved from the Norwegian goat recording system., Results: The most prevalent udder pathogen findings were Staphylococcus caprae (6.8%), Staphylococcus warneri (6.3%), and Staphylococcus epidermidis (3.8%), all of which had a mild but significant impact on SCC. Staphylococcus aureus was detected in 3.6% of the udder halves and had a major effect on SCC. Parity, stage of lactation, season, and milk yield significantly influenced SCC., Conclusions: This study highlights that intramammary infections caused by Staphylococcus aureus, along with factors such as increasing parity and the seasonal effects of pasturing, significantly influence the SCC. Understanding these key contributors is essential for improving udder health management and improving milk quality in goat milk production., (© 2024. The Author(s).)

Anaerobic spore-forming bacteria are a continuous threat to the dairy industry due to their ability to withstand processing conditions, such as those during heat treatment. These ubiquitous microorganisms have ample opportunity for multiple entry points into the milk chain, creating food quality and safety issues. Certain spore-formers, namely bacilli and clostridia, are more problematic due to their ability to spoil dairy products and pathogenicity. In this study, we investigated how milk treatment and milk powder production influenced the composition and survival of anaerobic spore-formers. Samples were obtained on three different days (replicate blocks) during the production of dairy powders and examined in a culture-dependent manner using the most probable number method coupled with 16S rRNA amplicon sequencing and metagenomic analysis of the enriched samples. Results revealed that the milk separation greatly affected the spore-former presence and composition which were detected along the entire production line from raw material to milk powders. Throughout the various points of the production line, the occurrence of species belonging to the Bacillus cereus sensu lato was higher than that of clostridia. Sequence variants (SVs) belonging to the anaerobic spore-forming genus Clostridium were taxonomically assigned to two SVs groups and were detected in all three replicate blocks. A total of 19 metagenome-assembled genomes were recovered from nine enrichments. Four near-complete and two medium-quality genomes were found in raw milk/milk powder samples and further assigned as Clostridium tyrobutyricum and Clostridium diolis, which may constitute a problem in the finished dairy product. In conclusion, our findings highlight spore-formers' importance on dairy quality and may aid in their intervention and control in the dairy production line., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

We examined the effects of substituting soybean meal with either yeast protein from Cyberlindnera jadinii or barley in concentrate feeds on feed intake, ruminal fermentation products, milk production, and milk composition in Norwegian Red (NRF) dairy cows. The concentrate feeds were prepared in pellet form as soy-based (SBM; where soybean meal is included as a protein ingredient), yeast-based (YEA; soybean meal replaced with yeast protein), or barley-based (BAR; soybean meal replaced with barley). The SBM contained 7.0% soybean meal on a dry matter (DM) basis. This was replaced with yeast protein and barley in the YEA and BAR concentrate feeds, respectively. A total of 48 early- to mid-lactation [days in milk ± standard deviation (SD): 103 ± 33.5 d] NRF cows in their first to fourth parity and with initial milk yield of 32.6 kg (SD = 7.7) were allocated into 3 groups, using a randomized block design, after feeding a common diet [SBM and good-quality grass silage: crude protein (CP) and neutral detergent fiber (NDF) content of 181 and 532 g/kg of DM, respectively] for 14 d (i.e., covariate period). The groups (n = 16) were then fed one of the dietary treatments (SBM, YEA, or BAR) for a period of 56 d (i.e., experimental period). The concentrate feeds were offered in split portions from 3 automatic feeders using electronic identification, with ad libitum access to the same grass silage. Dietary treatments had no effect on daily silage intake, total DM intake, or total NDF intake. Dietary CP intake was lower and starch intake was higher in the BAR group compared with the other groups. Ruminal fluid pH, short-chain volatile fatty acid (VFA) concentrations, acetate-to-propionate ratio, and non-glucogenic to glucogenic VFA ratio were not affected by dietary treatments. No effects of the dietary treatments were observed on body weight change, body condition score change, milk yield, energy-corrected milk yield, milk lactose and fat percentages, or their yields. In conclusion, yeast protein can substitute conventional soybean meal in dairy cow diets without adverse effect on milk production and milk composition, given free access to good-quality grass silage., (The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

This study addresses the biodiversity of Bacillus cereus group population present along the value chain of milk for consumption. The B. cereus population did not grow and remained mainly unaltered during storage of milk at 4 °C while storage at a suboptimal temperature at 8 °C (representative of a broken cold chain) caused a major shift in its composition. Mesophilic strains dominated the B. cereus population in raw milk and after storage at 4 °C, while psycrotrophic strains dominated after storage at 8 °C. All psycrotrophic and mesophilic isolates (n = 368) demonstrated high spoilage potentials of the milk components. Fifteen out of 20 mesophilic isolates but only two out of 40 psychrotrophic isolates, exhibited vero cell toxicity. No genes encoding the emetic toxin cereulide were detected in the genomes of 100 milk isolates while 14 of them harbored the enterotoxin genes cytK1/cytK2. Both psycrotrophic and mesophilic isolates carried the enterotoxin genes nheA and hblA. Together, the results provide insight into the composition and properties, of the B. cereus population present in milk along the value chain and during storage at optimal refrigerated temperature and at suboptimal temperature. This knowledge is useful in the dairy industry's work to assure high quality products and for risk assessment., (Copyright © 2020. Published by Elsevier Ltd.)

Members of the Bacillus cereus sensu lato (B. cereus group) are spore-forming organisms commonly associated with spoilage of milk and dairy products. Previous studies have shown, by using 16S marker gene sequencing, that the genus Bacillus is part of the core microbiota of raw bovine milk and that some members of this genus are able to grow during sub-optimal storage (8 °C) of pasteurized consumption milk. Here, the composition of this genus in pasteurized consumption milk samples, collected from two dairies, over a one-year period and stored at 4 or 8 °C up to the end of shelf life is uncovered. Our results show that the B. cereus group is the dominant Bacillus group in stored consumption milk. By applying a new marker gene sequencing approach, several dominating phylogenetic clusters were identified within the B. cereus group populations from the milk samples. There was a higher phylogenetic diversity among bacteria from milk stored at 8 °C compared to milk stored at 4 °C. Sampling period and the dairy the samples were collected from, also significantly influenced the diversity, which shows that the B. cereus group population in consumption milk is heterogeneous and subjected to temporal and spatial changes. The new approach applied in this study will facilitate the identification of isolates within the B. cereus group, of which some are potential spoilage bacteria and pathogenic contaminants of milk and dairy products., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Microbial contamination of bovine raw milk often occurs at the farm. To acquire a deeper knowledge of the microbiota of farm tank milk, we studied milk from 45 farms situated in 2 geographical areas in Norway. Each farm was visited on 3 different occasions, with at least 2 wk between visits. We combined both bacterial cell counts and a sequence variant inference method of amplicon-based high-throughput sequencing to achieve a high-resolution overview of the microbiota in each sample. Compositional variation of the farm milk microbiota was shown in relation to the 2 areas, between the farms and between the sampling times. Despite the near constant level of bacteria enumerated in milk from each individual farm, the dominant microbiota differed significantly between the samplings. The predominant microbiota was dominated by spoilage genera, such as Pseudomonas and Bacillus, as well as the dairy fermentation genus Lactococcus and mastitis-causing organisms (Streptococcus). Analysis of the identified sequence variants within these genera showed that the populations of Pseudomonas and Lactococcus in milk had similar composition between the farms, but that Bacillus and, in particular, Streptococcus populations changed between collection days from the same farm and between farms and geographical areas. Furthermore, the levels and composition of Bacillus and Paenibacillus were different between the 2 geographical areas. The results presented here provide new insight into the farm milk microbiota and show that this microbiota is a dynamic community highly subject to variation., (Copyright © 2019 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Bovine milk contains a complex microbial community that affects the quality and safety of the product. Detailed knowledge of this microbiota is, therefore, of importance for the dairy industry. In this study, the bacterial composition of consumption milk was assessed during different stages in the production line and throughout the storage in cartons by using culturing techniques and 16S rRNA marker gene sequencing. Monthly samples from two dairies were analyzed to capture the seasonal variations in the milk microbiota. Although there was a core microbiota present in milk samples from both dairies, the composition of the bacterial communities were significantly influenced by sampling month, processing stage and storage temperature. Overall, a higher abundance of operational taxonomic units (OTUs) within the order Bacillales was detected in samples of raw and pasteurized milk from the spring and summer months, while Pseudomonadales and Lactobacillales OTUs were predominant in the winter months. OTUs belonging to the order Lactobacillales, Pseudomonadales, Clostridiales and Bacillales were significantly more abundant in milk samples taken immediately after pasteurization compared to raw milk samples. During storage of milk in cartons at 4°C, the bacterial composition remained stable throughout the product shelf life, while storage at 8°C significantly increased the abundance of OTUs belonging to the genus Bacillus and the plate count levels of presumptive Bacillus cereus. The knowledge obtained in this work will be useful to the dairy industry during their quality assurance work and risk assessment practices., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Droplet digital PCR (ddPCR) is one of the newest and most promising methods for the detection and quantification of molecular targets by PCR. Here, we optimized and used a new ddPCR assay for the detection and quantification of the Bacillus cereus group in milk. We also compared the ddPCR to a standard qPCR assay. The new ddPCR assay showed a similar coefficient of determination and a better limit of detection compared to the qPCR assay during quantification of the target molecules in the samples. However, the ddPCR assay has a limitation during quantification of a high number of target molecules. This new assay was then tested for the quantification of the B. cereus group in 90 milk samples obtained over three months from two different dairies and the milk was stored at different temperatures before sampling. The ddPCR assay showed good agreement with the qPCR assay for the quantification of the B. cereus group in milk, and due to its lower detection limit more samples were detected as positive. The new ddPCR assay is a promising method for the quantification of target bacteria in low concentration in milk., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The objective of this study was to investigate how ceramic membrane pore size and filtration temperature influence the protein fractionation of skim milk by cross flow microfiltration (MF). Microfiltration was performed at a uniform transmembrane pressure with constant permeate flux to a volume concentration factor of 2.5. Three different membrane pore sizes, 0.05, 0.10, and 0.20µm, were used at a filtration temperature of 50°C. Furthermore, at pore size 0.10µm, 2 different filtration temperatures were investigated: 50 and 60°C. The transmission of proteins increased with increasing pore size, giving the permeate from MF with the 0.20-µm membrane a significantly higher concentration of native whey proteins compared with the permeates from the 0.05- and 0.10-µm membranes (0.50, 0.24, and 0.39%, respectively). Significant amounts of caseins permeated the 0.20-µm membrane (1.4%), giving a permeate with a whitish appearance and a casein distribution (αS2-CN: αS1-CN: κ-CN: β-CN) similar to that of skim milk. The 0.05- and 0.10-µm membranes were able to retain all caseins (only negligible amounts were detected). A permeate free from casein is beneficial in the production of native whey protein concentrates and in applications where transparency is an important functional characteristic. Microfiltration of skim milk at 50°C with the 0.10-µm membrane resulted in a permeate containing significantly more native whey proteins than the permeate from MF at 60°C. The more rapid increase in transmembrane pressure and the significantly lower concentration of caseins in the retentate at 60°C indicated that a higher concentration of caseins deposited on the membrane, and consequently reduced the native whey protein transmission. Optimal protein fractionation of skim milk into a casein-rich retentate and a permeate with native whey proteins were obtained by 0.10-µm MF at 50°C., (Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Staphylococcal food poisoning (SFP) is an important foodborne disease worldwide, and milk and milk products are commonly associated with SFP outbreaks. The objectives of this study were to investigate the distribution of staphylococcal enterotoxin (se) genes in Staphylococcus aureus from raw cow's milk and milk products and to assess their genetic background with the spa typing method. Of the 549 samples (297 bulk milk and 162 milk product samples) collected from Tigray region, Northern Ethiopia, 160 (29.1%) were positive for S. aureus, of which 82 (51%) were found to harbor se genes by a modified multiplex PCR. Nine se genes were identified: sea (n = 12), seb (n = 3), sec (n = 3), sed(n = 4), seg (n = 49), seh (n = 2), sei (n = 40), sej (n = 1), and tsst-1 (n = 24). The classical type of genes accounted for 27%. Of the 82 enterotoxigenic isolates, 41.5 and 12.4% harbored two or more se genes, respectively. The highest gene association was observed between sei and seg, whereas sea and seb were always found together with the new types of se genes. Altogether, 18 genotypes of toxin genes were identified, and 33% of the samples contained > 5 log CFU ml(-1) S. aureus. spa typing identified 22 spa types and three novel spa sequences, which showed the high genetic diversity of the isolates. No apparent relationship was observed between spa type and se genes. Of the 25 spa types, 13 (52%) were from raw milk, 3 (12%) from milk products, and 9 (36%) from both types of sample. Types t314 (20.7%,n = 17), t458 (18.3%, n = 15), and t6218 (9.8%, n= 8) were the most common spa types identified and were widely distributed in three of the eight studied localities. This is the first study from the Tigray region to report the high distribution of enterotoxigenic S. aureus with a diversified genetic background from dairy food. The study may provide valuable data for microbial food safety risk assessment, molecular epidemiology, and phylogenetic studies of S. aureus in Ethiopia.

The demand for whey protein is increasing in the food industry. Traditionally, whey protein concentrates (WPC) and isolates are produced from cheese whey. At present, microfiltration (MF) enables the utilization of whey from skim milk (SM) through milk protein fractionation. This study demonstrates that buttermilk (BM) can be a potential source for the production of a WPC with a comparable composition and functional properties to a WPC obtained by MF of SM. Through the production of WPC powder and a casein- and phospholipid (PL)-rich fraction by the MF of BM, sweet BM may be used in a more optimal and economical way. Sweet cream BM from industrial churning was skimmed before MF with 0.2-µm ceramic membranes at 55 to 58°C. The fractionations of BM and SM were performed under the same conditions using the same process, and the whey protein fractions from BM and SM were concentrated by ultrafiltration and diafiltration. The ultrafiltration and diafiltration was performed at 50°C using pasteurized tap water and a membrane with a 20-kDa cut-off to retain as little lactose as possible in the final WPC powders. The ultrafiltrates were subsequently spray dried, and their functional properties and chemical compositions were compared. The amounts of whey protein and PL in the WPC powder from BM (BMWPC) were comparable to the amounts found in the WPC from SM (SMWPC); however, the composition of the PL classes differed. The BMWPC contained less total protein, casein, and lactose compared with SMWPC, as well as higher contents of fat and citric acid. No difference in protein solubility was observed at pH values of 4.6 and 7.0, and the overrun was the same for BMWPC and SMWPC; however, the BMWPC made less stable foam than SMWPC., (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)