Associations among Milk Microbiota, Milk Fatty Acids, Milk Glycans, and Inflammation from Lactating Holstein Cows.

Milk oligosaccharides (MOs) can be prebiotic and antiadhesive, while fatty acids (MFAs) can be antimicrobial. Both have been associated with milk microbes or mammary gland inflammation in humans. Relationships between these milk components and milk microbes or inflammation have not been determined for cows and could help elucidate a novel approach for the dairy industry to promote desired milk microbial composition for improvement of milk quality and reduction of milk waste. We aimed to determine relationships among milk microbiota, MFAs, MOs, lactose, and somatic cell counts (SCC) from Holstein cows, using our previously published data. Raw milk samples were collected at three time points, ranging from early to late lactation. Data were analyzed using linear mixed-effects modeling and repeated-measures correlation. Unsaturated MFA and short-chain MFA had mostly negative relationships with potentially pathogenic genera, including Corynebacterium, Pseudomonas, and an unknown Enterobacteriaceae genus but numerous positive relationships with symbionts Bifidobacterium and Bacteroides. Conversely, many MOs were positively correlated with potentially pathogenic genera (e.g., Corynebacterium, Enterococcus, and Pseudomonas), and numerous MOs were negatively correlated with the symbiont Bifidobacterium. The neutral, nonfucosylated MO composed of eight hexoses had a positive relationship with SCC, while lactose had a negative relationship with SCC. One interpretation of these trends might be that in milk, MFAs disrupt primarily pathogenic bacterial cells, causing a relative increase in abundance of beneficial microbial taxa, while MOs respond to and act on pathogenic taxa primarily through antiadhesive methods. Further research is needed to confirm the potential mechanisms driving these correlations. IMPORTANCE Bovine milk can harbor microbes that cause mastitis, milk spoilage, and foodborne illness. Fatty acids found in milk can be antimicrobial and milk oligosaccharides can have antiadhesive, prebiotic, and immune-modulatory effects. Relationships among milk microbes, fatty acids, oligosaccharides, and inflammation have been reported for humans. To our knowledge, associations among the milk microbial composition, fatty acids, oligosaccharides, and lactose have not been reported for healthy lactating cows. Identifying these potential relationships in bovine milk will inform future efforts to characterize direct and indirect interactions of the milk components with the milk microbiota. Since many milk components are associated with herd management practices, determining if these milk components impact milk microbes may provide valuable information for dairy cow management and breeding practices aimed at minimizing harmful and spoilage-causing microbes in raw milk.

Fatty Acid Profiles of In Vitro Digested Processed Milk.

Digestion of milkfat releases some long-chain (18-carbon) fatty acids (FAs) that can provide health benefits to the consumer, yet because they are found in small amounts and can be difficult to identify, there is limited information on the effects that common fluid milk processing may have on the digestibility of these FAs. This study provides FA profiles for raw and combinations of homogenized and/or heat-treated (high and ultra-high temperature pasteurization) milk, before and after in vitro digestion, in order to determine the effects of processing on the digestibility of these healthy fatty acids. Use of a highly sensitive separation column resulted in improved FA profiles that showed that, when milk was subjected to both pasteurization and homogenization, the release of the 18-carbon FAs, oleic acid, linoleic acid (an omega-6 FA), rumenic acid (a conjugated linoleic acid, CLA), and linolenic acid (an omega-3 FA) tended to be higher than with either pasteurization or homogenization, or with no treatment. Milk is noted for containing the omega-3 FAs and CLAs, which are associated with positive health benefits. Determining how processing factors may impact the components in milk will aid in understanding the release of healthy FAs when milk and dairy foods are consumed.

Effect of heat and homogenization on in vitro digestion of milk.

Central to commercial fluid milk processing is the use of high temperature, short time (HTST) pasteurization to ensure the safety and quality of milk, and homogenization to prevent creaming of fat-containing milk. Ultra-high-temperature sterilization is also applied to milk and is typically used to extend the shelf life of refrigerated, specialty milk products or to provide shelf-stable milk. The structures of the milk proteins and lipids are affected by processing but little information is available on the effects of the individual processes or sequences of processes on digestibility. In this study, raw whole milk was subjected to homogenization, HTST pasteurization, and homogenization followed by HTST or UHT processing. Raw skim milk was subjected to the same heating regimens. In vitro gastrointestinal digestion using a fasting model was then used to detect the processing-induced changes in the proteins and lipids. Using sodium dodecyl sulfate-PAGE, gastric pepsin digestion of the milk samples showed rapid elimination of the casein and α-lactalbumin bands, persistence of the ß-lactoglobulin bands, and appearance of casein and whey peptide bands. The bands for ß-lactoglobulin were eliminated within the first 15min of intestinal pancreatin digestion. The remaining proteins and peptides of raw, HTST, and UHT skim samples were digested rapidly within the first 15min of intestinal digestion, but intestinal digestion of raw and HTST pasteurized whole milk showed some persistence of the peptides throughout digestion. The availability of more lipid droplets upon homogenization, with greater surface area available for interaction with the peptides, led to persistence of the smaller peptide bands and thus slower intestinal digestion when followed by HTST pasteurization but not by UHT processing, in which the denatured proteins may be more accessible to the digestive enzymes. Homogenization and heat processing also affected the ζ-potential and free fatty acid release during intestinal digestion. Stearic and oleic acids were broken down faster than other fatty acids due to their positions on the outside of the triglyceride molecule. Five different casein phosphopeptide sequences were observed after gastric digestion, and 31 sequences were found after intestinal digestion, with activities yet to be explored. Processing affects milk structure and thus digestion and is an important factor to consider in design of foods that affect health and nutrition.

Physical and chemical changes in whey protein concentrate stored at elevated temperature and humidity.

In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (WPC) under adverse storage conditions to provide information on shelf life in hot, humid areas. Whey protein concentrates with 34.9 g of protein/100g (WPC34) and 76.8 g of protein/100g (WPC80) were stored for up to 18 mo under ambient conditions and at elevated temperature and relative humidity. The samples became yellower with storage; those stored at 35 °C were removed from the study by 12 mo because of their unsatisfactory appearance. Decreases in lysine and increases in water activity, volatile compound formation, and powder caking values were observed in many specimens. Levels of aerobic mesophilic bacteria, coliforms, yeast, and mold were <3.85 log10 cfu/g in all samples. Relative humidity was not a factor in most samples. When stored in sealed bags, these samples of WPC34 and WPC80 had a shelf life of 9 mo at 35 °C but at least 18 mo at lower temperatures, which should extend the market for these products.

Dairy Products and Health: Recent Insights.

Milk, cheese, yogurt, and other dairy products have long been known to provide good nutrition. Major healthful contributors to the diets of many people include the protein, minerals, vitamins, and fatty acids present in milk. Recent studies have shown that consumption of dairy products appears to be beneficial in muscle building, lowering blood pressure and low-density lipoprotein cholesterol, and preventing tooth decay, diabetes, cancer, and obesity. Additional benefits might be provided by organic milk and by probiotic microorganisms using milk products as a vehicle. New research on dairy products and nutrition will improve our understanding of the connections between these products, the bioactive compounds in them, and their effects on the human body.

Sensory and protein profiles of Mexican Chihuahua cheese.

Native microflora in raw milk cheeses, including the Mexican variety Queso Chihuahua, contribute to flavor development through degradation of milk proteins. The effects of proteolysis were studied in four different brands of Mexican Queso Chihuahua made from raw milk. All of the cheeses were analyzed for chemical and sensory characteristics. Sensory testing revealed that the fresh cheeses elicited flavors of young, basic cheeses, with slight bitter notes. Analysis by gel electrophoresis and reverse phase-high performance liquid chromatography (RP-HPLC) revealed that the Queseria Blumen (X) and Queseria Super Fino (Z) cheeses show little protein degradation over time while the Queseria America (W) and Queseria Lago Grande (Y) samples are degraded extensively when aged at 4 °C for 8 weeks. Analysis of the mixture of water-soluble cheese proteins by mass spectrometry revealed the presence of short, hydrophobic peptides in quantities correlating with bitterness. All cheese samples contained enterococcal strains known to produce enterocins. The W and Y cheese samples had the highest number of bacteria and exhibited greater protein degradation than that observed for the X and Z cheeses.

Comparison of SPME Methods for Determining Volatile Compounds in Milk, Cheese, and Whey Powder.

Solid phase microextraction and gas chromatography-mass spectrometry (SPME-GC-MS) are commonly used for qualitative and quantitative analysis of volatile compounds in various dairy products, but conditions have to be adjusted to maximize release while not generating new compounds that are absent in the original sample. Queso Fresco, a fresh non-melting cheese, may be heated at 60 °C for 30 min; in contrast, compounds are produced in milk when exposed to light and elevated temperatures, so milk samples are heated as little as possible. Products such as dehydrated whey protein are more stable and can be exposed to longer periods (60 min) of warming at lower temperature (40 °C) without decomposition, allowing for capture and analysis of many minor components. The techniques for determining the volatiles in dairy products by SPME and GC-MS have to be optimized to produce reliable results with minimal modifications and analysis times.

Characterization of antilisterial bacteriocins produced by Enterococcus faecium and Enterococcus durans isolates from Hispanic-style cheeses.

Enterococci are often identified as constituents of the indigenous microflora from raw milk artisanal cheeses and are believed to contribute to the unique organoleptic qualities of these products. Many strains of enterococci are also known to produce antimicrobial peptides, enterocins, which may prevent the growth of certain food-born pathogens. In this study 33 enterococcal isolates from Hispanic-style cheeses were screened for the production of bacteriocins. Of the 33 isolates, 5 Enterococcus faecium and 1 Enterococcus durans isolates inhibited the growth of Listeria spp. The antilisterial activity was lost after treatment with pepsin, trypsin, pronase, proteinase K and alpha-chymotrypsin suggesting the active component was a protein or peptide. The active compounds were heat stable and had molecular weights between 4 and 8 kDa, which is characteristic of Class II enterocins. A PCR screen showed that four E. faecium isolates contained nucleic acid sequences for multiple enterocins. Isolate H41K contained entA and entP; and isolates H51Ca, H51Cb and H41B contained entA, entP and entL50AB, with H41B also containing entB. All PCR tests performed were negative for E. faecium isolate H41D, suggesting the production of a novel enterocin. The isolates were also screened for susceptibility to antibiotics, with only two showing low-level resistance to vancomycin (8 microg ml(-l)). However, three isolates were highly resistant to both tetracycline and kanamycin, with two of the isolates also showing high resistance to erythromycin.

Rheological and proteolytic properties of Monterey Jack goat's milk cheese during aging.

To enhance the understanding of the quality traits of goat's milk cheeses, rheological and proteolytic properties of Monterey Jack goat's milk cheese were evaluated during 26 weeks of 4 degrees C storage. As expected with aging, beta-casein levels decreased with concomitant increases in peptide levels and were correlated with changes in rheological properties of the cheese. Hydrolysis of the protein matrix resulted in more flexible (increased viscoelastic properties) and softer (decreased hardness, shear stress, and shear rigidity) cheeses. During the first 4-8 weeks of storage, cheese texture changed significantly (P < 0.05) and then stabilized. Characterization of rheological and proteolytic properties of the goat's milk semihard cheese during aging provided insight into the changes occurring in the protein matrix, the relationship to structure, and a shift in cheese quality.

Transmission electron microscopy of mozzarella cheeses made from microfluidized milk.

The nanostructure of Mozzarella cheeses prepared from microfluidized milk was compared with that of control cheeses made from untreated milk. Milk heated to 10 or 54 degrees C and containing 1.0 or 3.2% fat was homogenized by microfluidization at 34 or 172 MPa prior to cheesemaking. The effects on the casein particles and fat globules in the cheese were determined by transmission electron microscopy after 1 day and 6 weeks of storage at 4 degrees C. The micrographs showed that electron-dense regions theorized to be casein submicelles rearranged from a homogeneous configuration to a pattern of clusters during the storage period. The nanostructure of the cheeses made from milk processed under the mildest conditions resembled the controls, but otherwise the fat droplets decreased in size and increased in number as the pressure and temperature were increased. The results indicate that both homogenization temperature and pressure affect the nanostructure of Mozzarella cheese.