Commercial Raw Milk Research Articles

Fabric Phase Sorptive Extraction of Selected Steroid Hormone Residues in Commercial Raw Milk Followed by Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry.

Hormones in edible matrices, such as milk, are a subject of concern because of their adverse effects on the endocrine system and cell signaling and the consequent disruption of homeostasis in human consumers. Therefore, the assessment of the presence of hormones in milk as potential endocrine-disrupting compounds is warranted. However, the complexity of milk as a sample matrix and the ultra-low concentration of hormones pose significant analytical challenges. Fabric phase sorptive extraction (FPSE) has emerged as a powerful analytical technique for the extraction of emerging pollutants from complex aqueous matrices. FPSE allows for substantially simplified sample handling and short extraction and desorption times, as well as the decreased use of organic solvents. It is considered a green alternative to traditional extraction methodologies. In this work, the FPSE technique was evaluated to perform the simultaneous extraction of 15 steroid hormones from raw milk without employing any sample pretreatment steps. Clean and preconcentrated hormone solutions obtained from FPSE of raw milk were analyzed using ultra-high-performance liquid chromatography–tandem mass spectrometry to achieve low detection limits, which ranged from 0.047 to 1.242 ng·mL−1. Because of the presence of many interferents in milk, such as proteins, lipids, and sugar, the effect of fat content on the extraction procedure was also thoroughly studied. Additionally, for the first time, the effect of lactose on the extraction of steroid hormones was evaluated, and the results showed that the extraction efficiencies were enhanced in lactose-free samples. Finally, the optimized methodology was applied to commercial samples of cow and goat milk, and no measurable concentrations of the studied hormones were detected in these samples.

Volatile and sensory evaluation of Mexican Fresco cheese as affected by specific wild Lactococcus lactis strains

Lactococcus lactis is the lactic acid bacteria most frequently used for the production of cheese starter cultures, mainly because of their efficient production of aroma compounds. However, commercial cultures do not always produce the typical aroma notes of artisanal raw-milk cheeses. Thus, the objective of this study was to characterize the volatile compounds generated by wild L. lactis strains in Mexican Fresco cheese made with pasteurized milk. Four strains of wild L. lactis were evaluated for their aroma production in Mexican Fresco cheese using sensory and instrumental analysis. The aroma profiles were evaluated by descriptive sensory analysis. Volatiles were determined by solid-phase microextraction and gas chromatography-mass spectrometry. Principal component analysis was applied to interpret analytical and sensory data. Mexican Fresco cheese aroma was described as milkfat, yogurt, yeasty, barny, dirty socks, and Fresco cheese. Cheese with L. lactis strains R7 or B7 were most similar to commercial raw milk Fresco cheese in all aroma descriptors. Volatiles identified in all cheeses were esters, acids, alcohols, ketones, and aldehydes, but the main differences were found for total volatile relative abundance. Also, volatile concentrations (µg/g) in commercial raw milk Fresco cheese and cheeses made with L. lactis R7 or B7 were 4 methyl esters [C4 (4.15 vs. 5.47-13.74), C6 (0.12 vs. 1.53-15.34), C8 (1.06 vs. 0.32-6.65), and C10 (0.62 vs. 0.41-3.74)], 7 acids [C4 (1.92 vs. 0.30-9.29), C6-C10 (0.05-4.48 vs. 0.11-30.45), and C12 (0.13 vs. 0.28-0.30)], 2 alcohols [(3-methyl-1-butanol (3.48 vs. 3.4-13.13) and phenylethyl alcohol (0.10 vs. 0.63-2.04)], and 1 ketone (acetoin; 1.22 vs. 0.28-0.99). The first 3 principal components explained 78.2% of the total variation and clearly distinguished 3 main groups. Cheese made with L. lactis R7 was classified in the same group as key compounds associated with Fresco cheese aroma and show potential as a starter in Mexican Fresco cheese manufacture.

Comparison of volatile compounds produced by wild Lactococcus lactis in miniature Chihuahua-type cheeses

Strains of Lactococcus lactis used for a long time as starter cultures in the production of cheese have not only acquired special features like fast utilization of lactose, but it is also believed that they have lost certain metabolic capabilities. Certain wild strains of L. lactis isolated from vegetables or raw milk products are able to generate flavors different from those produced by industrial strains. The aim of this work was to assess the production of volatile compounds in miniature Chihuahua-type cheeses manufactured with different strains of L. lactis isolated from vegetables, raw milk products, and industrial cultures. There was variation among volatile profiles in the miniature cheeses manufactured with different strains of L. lactis. However, some compounds were seen in most of the cheeses such as acetic, lactic, butyric, and caproic acids, acetoin, 3-methyl-1-butanol, and 2,3-butanediol. The source of isolation of the strains (plants, raw milk products, and industrial cultures) did not have a clear influence on the production of volatile compounds in miniature cheeses. According to principal component analysis, 19 out of 21 strains of L. lactis produced volatile profiles similar to the three pasteurized Chihuahua cheeses analyzed, but only 2 strains generated profiles similar to the commercial raw milk cheese. However, further research is required to understand the metabolic and genetic differences of these strains.

Using Major Outer Membrane Protein Typing as an Epidemiological Tool To Investigate Outbreaks Caused by Milk-Borne Campylobacter jejuni Isolates in California

We describe using major outer membrane protein (MOMP) typing as a screen to compare the Campylobacter jejuni porA gene sequences of clinical outbreak strains from human stool with the porA sequences of dairy farm strains isolated during two milk-borne campylobacteriosis outbreak investigations in California. The genetic relatedness of clinical and environmental strains with identical or closely related porA sequences was confirmed by multilocus sequence typing and pulsed-field gel electrophoresis analysis. The first outbreak involved 1,644 C. jejuni infections at 11 state correctional facilities and was associated with consumption of pasteurized milk supplied by an on-site dairy (dairy A) at a prison in the central valley. The second outbreak involved eight confirmed and three suspect C. jejuni cases linked to consumption of commercial raw milk and raw chocolate colostrum at another central valley dairy (dairy B). Both dairies bottled fluid milk on the farm and distributed the finished product to off-site locations. Altogether, C. jejuni was isolated from 7 of 15 (46.7%) bovine fecal, 12 of 20 (60%) flush alley water, and 1 of 20 (5%) lagoon samples collected on dairy A. At dairy B, C. jejuni was cultured from 9 of 26 (34.6%) bovine fecal samples. Environmental strains indistinguishable from the clinical outbreak strains were found in five flush alley water samples (dairy A) and four bovine fecal samples (dairy B). The findings demonstrate that MOMP typing is a useful tool to triage environmental isolates prior to conducting more labor-intensive molecular typing methods.

Interpretation of the irregularly fluctuating microbial counts in commercial dairy products

Abstract Microbial records of commercial raw milk (total counts) and two ice creams (standard plate counts, coliforms and yeasts) were de-rounded. Their autocorrelation function showed that the counts were independent and had no discernible trend or periodicity. The first half of each record was used to estimate the frequencies of high counts in the second half, assuming that the counts have a lognormal, log-Laplace or non-parametric distribution. The estimated frequencies were all on the same order of magnitude of those actually observed and in some cases in close agreement. None of the three distributions was found to be consistently superior to the others, most probably because the available records for the analysis were too short. In general, the lognormal and log-Laplace distributions yielded closer estimates than the non-parametric distribution because they allow for high counts at levels not previously recorded. The results strengthen the view that at least, in principle, the irregular fluctuating pattern of the microbial records of dairy products can be translated into a set of probabilities of future high counts, and that these can serve as a risk or quality measure.

Analysis of the Fluctuating Microbial Counts in Commercial Raw Milk—A Case Study

Microbial counts of raw milk from eight commercial dairy farms recorded over a period of about 2 years were obtained from a processing plant. All the counts formed irregular fluctuating series whose statistical properties were examined. In all eight cases the autocorrelation function indicated that the counts were random and had no underlying periodicity. This suggested that the fluctuations, at least to some extent, reflected the combined effect of numerous factors, some unknown, and that these factors operate randomly and independently. In five out of the eight cases the fluctuating pattern of the record could be described by a probabilistic model based on the assumption that the counts have a lognormal distribution. The validity of the model was confirmed by comparing the calculated frequencies of counts exceeding preselected levels with those actually observed in fresh data. The model enabled ranking the five sources on the basis of anticipated frequencies of excessive counts rather than on the basis of mean performance. Two sequences had clearly identified regions with different statistical characteristics. They were interpreted as a reflection of changes in the sanitary conditions at the corresponding farms. In one case, both the overall magnitudes and the fluctuation amplitude of the counts progressively decreased, a situation for which the described model as formulated was inapplicable.

Proteolysis detection in milk: III. Relationships between bacterial populations, tyrosine value and organoleptic quality during extended cold storage of milk and cream

SummaryRaw bulk milk samples were stored at 5°C in the laboratory mostly for 7 or 8d and examined at intervals for bacterial content, proteolysis as indicated by tyrosine value, and organoleptic quality. Data are presented for these samples illustrating relationships between bacterial population counts, tyrosine values and organoleptic quality ratings. Bacterial counts (total bacteria, psychrotrophs and proteolytic psychrotrophs) generally exceeded 106/ml before a definite increase in tyrosine value or any deterioration in organoleptic quality could be detected. Tyrosine value was indicated to be useful as a general index of bacteriological and organoleptic quality of commercial raw milk subjected to prolonged cold storage. The tyrosine value procedure was also shown to have application for monitoring the development of proteolysis in cold-stored pasteurized milk and cream.

The Effect of Holder and Flash Pasteurization on some Flavors of Milk. I. The Effect on Miscellaneous Flavors Common to Commercial Raw Milk

Summary Samples of milk from each of ten producers were secured weekly over a six-month period, divided into lots, were holder pasteurized with and without aeration at 143° F. for 30 minutes and flash pasteurized at 160° F. for 15 seconds. The samples were scored and rescored “blind” at the first and third days of storage by two judges working independently. The predominating off flavor in the day-old, raw control samples was feed, the percentage frequency of which was materially decreased by pasteurization. The predominating off flavor of unaerated and aerated holder pasteurized day-old milk was heated. Less heated flavors were noted in the flash pasteurized samples than in the holder pasteurized samples. Flash pasteurized milk showed not only a higher percentage of observations of excellent flavor milk, score of 23, than were noted in the raw control or in the holder pasteurized samples but greater stability of excellent flavor upon storage as well. No significant difference was found between the mean scores of milk holder pasteurized with aeration or similar pasteurization without aeration and that of the raw samples at the first day of storage. However, the increase in score of the pasteurized samples over the raw samples at three days of storage was significant. Storing the milk for three days at 40° F. resulted in a significant decrease in the score over that noted at one day of storage. Raw milk scores decreased a mean of 0.91 points as a result of storage, whereas, the decrease in score of the pasteurized milk ranged from 0.43 to 0.55 points. The pasteurization processes increased the frequency of heated, oxidized, cooked, and old flavors and decreased the frequency of feed, high acid, flat, salty, cowy, rancid, unclean, and off but unidentified flavors. Storage of the milk at 40° F. for three days increased the frequency of high acid, old, oxidized, unclean, and rancid flavors in the raw samples and the oxidized and old flavors in the pasteurized samples, whereas, similar storage decreased the percentage incidence of feed, cowy, flat, heated, cooked, and off but unidentified flavors. The mean score of the raw milk of all patrons decreased steadily from January through June. A gradual increase in the incidence of feed flavors was found in the raw samples from January to June. During the same period of time there was noted a rather constant frequency of oxidized flavors in the samples of the pasteurized milk, until May when the per cent frequency decreased markedly. As the frequency of feed flavors increased a very similar decrease in the occurrence of the oxidized flavors was noted. The two judges varied slightly in rescoring ability, the one judge rescoring 42.0 per cent of the samples identically with the first score, whereas, the other judge rescored 54.3 per cent of the samples identically with the first score. Both judges, working independently, scored 39 per cent of all the samples with the same score.