Ripening of Cheddar cheese made from blends of raw and pasteurised milk

Cheddar cheeses were made from pasteurised milk (P), raw milk (R) or pasteurised milk to which 10 (PR10), 5 (PR5) or 1 (PR1) % of raw milk had been added. Non-starter lactic acid bacteria (NSLAB) were not detectable in P cheese in the first month of ripening, at which stage PR1, PR5, PR10 and R cheeses had 10⁴, 10⁵, 10⁶ and 10⁷ cfu NSLAB g⁻¹, respectively. After ripening for 4 months, the number of NSLAB was 1–2 log cycles lower in P cheese than in all other cheeses. Urea–polyacrylamide gel electrophoretograms of water-soluble and insoluble fractions of cheeses and reverse-phase HPLC chromatograms of 70% (v/v) ethanol-soluble as well as -insoluble fractions of WSF were essentially similar in all cheeses. The concentration of amino acids were pro rata the number of NSLAB and were the highest in R cheese and the lowest in P cheese throughout ripening. Free fatty acids and most of the fatty acid esters in 4-month old cheeses were higher in PR1, PR5, PR10 and R cheeses than in P cheese. Commercial graders awarded the highest flavour scores to 4-month-old PR1 cheeses and the lowest to P or R cheese. An expert panel of sensory assessors awarded increasingly higher scores for fruity/sweet and pungent aroma as the level of raw milk increased. The trend for aroma intensity and perceived maturity was R>PR10>PP5>PR1>P. The NSLAB from raw milk appeared to influence the ripening and quality of Cheddar cheese.     

Microbiological and physicochemical stability of raw,pasteurised or pulsed electric field-treated milk

Pulsed electric field (PEF) processing was investigated as an alternative dairy preservation technology that would not compromise quality yet maintain safety. PEF processing of raw whole milk (4% fat) was conducted at two processing conditions (30 kV/cm, 22 μs, at either 53 or 63 °C outlet temperature) and compared with two thermal treatments (15 s, at either 63 or 72 °C) and a raw milk control and replicated twice. Milk bottles (2 L) from each treatment were incubated for two weeks, at 4 and 8 °C, and assessed for total plate count, pH, colour, rennetability, plasmin activity and lipid oxidation. The microbial quality of the thermal (72 °C/15 s) and PEF (63 °C) were similar. A drop in pH occurred after a change in counts was observed. Rennetability was not different between the treatments. Short chain acids dominated the volatile profile of the milk samples. Concentration of volatiles derived from microbial activity, namely 2,3-butanedione, acetic acid and other milk lipid derived short chain free fatty acids (e.g. butanoic and hexanoic acids), followed the trend of microbial activity in milk samples.Industrial relevanceResearch on the application of PEF to control spoilage and pathogenic microorganisms and enzyme systems in milk spans a wide array of processing equipment and reaction conditions. While industrial scale PEF processing of liquid milk for preservation and improved quality seems generally possible, substantiation of lower thermal damage under safe and scalable PEF conditions is required to enable economic feasibility.     

Effect of pasteurisation on the chemical composition of liquid whole egg. II.—Comparison of the protein fractionation patterns of raw and pasteurised liquid whole egg

Samples of commercial raw and pasteurised whole egg were re-examined after 41 weeks' storage under frozen conditions. As well as differences between the two samples, the protein fractionation patterns revealed marked differences from the original unstored material. A second comparison of commercial raw and pasteurised egg indicated that considerable differences could occur in the protein fractionation patterns of raw egg. This was confirmed in subsequent experiments. Two experiments on egg white showed that pasteurisation for 2 1/2 min at 135°F caused no change in the fractionation pattern of the proteins, and provided sound evidence for the reproducibility of the fractionation procedure. The separate influences of time and temperature of heating on liquid whole egg were studied in a series of laboratory-scale pasteurisation experiments. It appeared that time was a more important factor than temperature and that a heating time of 5 minutes, which is approximately the time that the bulk of the egg is held at the pasteurising temperature in commercial plants, caused significant changes in the fractionation patterns of both soluble and insoluble proteins. When pasteurisation was carried out for 2 1/2 min at 148–152°F, and also when time was varied at 150°F, the thiol and disulphide concentrations of the soluble proteins were not altered by any of the pasteurisation conditions studied. A short study was made of the distribution of α-amylase activity during the fractionation of the soluble proteins of raw whole egg. Preliminary experiments on gel filtration of the insoluble protein portions indicated that this technique is capable of revealing changes in molecular weight distribution resulting from pasteurisation and gave support to the view that heat treatment of whole egg results in aggregation or association of some of the proteins.     

Restrictions to the use of cleanrooms for packaging pasteurised milk

The study evaluated the effect of packaging pasteurised milk inside an ISO Class 8 cleanroom and an external Class 7 antechamber. Chemical, microbiological and sensory analyses of three trials did not show evidence of improvements in the product shelf life, although the total airborne particle and the viable airborne counts were considerable higher outside the cleanroom than inside it. Post‐pasteurisation contaminations inherent to the equipments should be considered in futures studies. Therefore, the use of cleanroom technology is an operational alternative to be taken into consideration, provided that the characteristics of the whole system is compatible with the high standards of the clean air.     

Differences in the peptide profile of raw and pasteurised ovine milk cheese and implications for its bioactive potential

Cheese produced using raw ovine milk (R) or pasteurised ovine milk (P) was subjected to peptide extraction, characterisation by mass spectrometry and bioinformatic analysis with the aim of assessing the impact of milk pasteurisation on the final peptide profile. In total, 187 peptides arising from β-casein, α_S1-casein, and α_S2-casein were identified. Upon label-free quantitation, 58 peptides were found to be significantly different in the two preparations; 38 were more abundant in R and 20 were more abundant in P. Of these, 27 were unique to R and 10 were unique to P. Bioinformatic analysis by EnzymePredictor provided insights into the influence of milk pasteurisation on susceptibility of cheese proteins to proteolytic enzymes during ripening. Finally, BIOPEP analysis predicted a biological activity for 37 of the 187 identified sequences (20%), with a significantly higher abundance of peptides with immunomodulating and ACE-inhibitor properties in R cheeses.     

Influence of ripening temperature on the volatiles profile and flavour of Cheddar cheese made from raw or pasteurised milk

Cheddar cheeses were made from raw (R1, R8) or pasteurised (P1, P8) milk and ripened at 1°C (P1, R1) or 8°C (P8, R8). Volatile compounds were extracted from 6 month-old cheeses and analysed, identified and quantified by gas chromatography-mass-spectrometry. A detailed sensory analysis of the cheeses was performed after 4 and 6 months of ripening. The R8 cheeses had the highest and P1 the lowest concentrations of most of the volatile compounds quantified (fatty acids, ketones, aldehydes, esters, alcohols, lactones and methional). The R8 and P8 cheeses contained higher levels of most of the volatiles than R1 and P1 cheeses. Ripening temperature and type of milk influenced most of the flavour and aroma attributes. Principal component analysis (PCA) of aroma and flavour attributes showed that P1 and R1 had similar aroma and flavour profiles, while R8 had the highest aroma and flavour intensities, highest acid aroma and sour flavour. The age of cheeses influenced the perception of creamy/milky and pungent aromas. PCA of the texture attributes separated cheeses on the basis of ripening temperature. The R8 and P8 cheeses received significantly higher scores for perceived maturity than P1 and R1 cheeses. The P1 and R1 cheeses had similar values for perceived maturity. In a related study, it was found that concentrations of amino acids and fatty acids were similar in R1 and P1 during most of the ripening period, and R1 and P1 cheeses had low numbers of non-starter lactic acid bacteria (NSLAB). The panel found that ripening temperature, type of milk and age of cheeses did not influence the acceptability of cheese. It is concluded that NSLAB contribute to the formation of volatile compounds and affect the aroma and flavour profiles and the perceived maturity of Cheddar cheese.     

Modelling the fate of Listeria monocytogenes during manufacture and ripening of smeared cheese made with pasteurised or raw milk

The dynamics of the physicochemical characteristics of foods help to determine the fate of pathogens throughout processing. The aim of this study was to assess the behaviour of Listeria monocytogenes during cheesesmaking and ripening and to model the growth observed under the dynamic conditions of the cheese. A laboratory scale cheese was made in 4 independent replicates from pasteurised or raw cow's milk, artificially contaminated with L. monocytogenes. No growth of L. monocytogenes occurred during raw milk cheese-making, whereas growth did occur in pasteurised milk. During ripening, growth occurred in raw milk cheese, but inactivation occurred in pasteurised milk cheese. The behaviour observed for L. monocytogenes was modelled using a logistic primary model coupled with a secondary cardinal model, taking into account the effect of physicochemical conditions (temperature, pH, water activity and lactate). A novel statistical approach was proposed to assess the optimal growth rate of a microorganism from experiments performed in dynamic conditions. This complex model had an acceptable quality of fit on the experimental data. The estimated optimum growth rates can be used to predict the fate of L. monocytogenes during cheese manufacture in raw or pasteurized milk in different physicochemical conditions. The data obtained contributes to a better understanding of the potential risk that L. monocytogenes presents to cheese producers (growth on the product, if it is contaminated) and consumers (the presence of high numbers) and constitutes a very useful set of data for the completion of chain-based modelling studies.     

Molecular approaches to analysing the microbial composition of raw milk and raw milk cheese

The availability and application of culture-independent tools that enable a detailed investigation of the microbiota and microbial biodiversity of food systems has had a major impact on food microbiology. This review focuses on the application of DNA-based technologies, such as denaturing gradient gel electrophoresis (DGGE), temporal temperature gradient gel electrophoresis (TTGE), single stranded conformation polymorphisms (SSCP), the polymerase chain reaction (PCR) and others, to investigate the diversity, dynamics and identity of microbes in dairy products from raw milk. Here, we will highlight the benefits associated with culture-independent methods which include enhanced sensitivity, rapidity and the detection of microorganisms not previously associated with such products.     

The antioxidant properties of skim milk supplemented with rosemary and green tea extracts in response to pasteurisation,homogenisation and the addition of salts

The aim of this study was to develop functional dairy products with high antioxidant activities to combat the risk of degenerative diseases. Rosemary and green tea extracts were added separately to reconstituted skim milk at the ratios of 2.0%, 4.0%, 6.0%, 8.0% and 10.0% respectively. The effect of pasteurisation, homogenisation, addition of calcium chloride and sodium chloride as well as the effect of added extracts on rennet coagulation time of milk were measured. The additions of green tea, rosemary extract, calcium chloride and pasteurisation significantly increased markedly the phenol content and the antioxidant activity of skim milk.     

Importance and significance of raw milk quality to the liquid milk processor

The importance and significance of raw milk quality to the liquid milk processor are considered in the light of changing commercial pressures. The attributes the processor seeks in his raw milk supplies are examined, how he handles and processes this milk to ensure customer satisfaction and, finally, what improvements still need to be made in the quality field.     

应用电子鼻区分不同气味的原奶

将电子鼻用于对原奶的检测,旨在寻求一种快速有效的方法以实现对原奶的质量控制.用电子鼻检测30个原奶样本的气味,结果表明,电子鼻可以准确地区分优质原奶、异味原奶,所建优质一异味原奶模型能够准确识别优质原奶,但不能准确识别所有异味原奶.     

Effect of ripening temperature on the growth and significance of non-starter lactic acid bacteria in Cheddar cheese made from raw or pasteurised milk

Two cheese-making trials were conducted, each involving four cheeses, two made from raw milk (R1, R8) and two from pasteurised milk (P1, P8), and ripened at 1°C (R1, P1) or 8°C (R8, P8). The 1-day-old R1 and R8 cheese in trials 1 and 2 contained ∼10⁴ non-starter lactic acid bacteria (NSLAB) g⁻¹. In trial 1, no NSLAB were detected in 1-day-old P1 and P8 cheeses while those in trial 2 contained 10² cfu g⁻¹. In both trials, the maximum differences between the number of NSLAB in the cheeses ripened at 1 or 8°C were observed at 4 months, when the number of NSLAB in cheeses ripened at 8°C were 3 log cycles higher than in those ripened at 1°C. At the end of ripening (6-months), the number of NSLAB in P8 and R8 were ∼2 log cycles higher than in P1 and R1 cheeses, respectively. Primary proteolysis in the cheeses was markedly affected by ripening temperature, but not by pasteurisation of the cheese milk. Urea-polyacyrlamide gel electrophoretograms and reverse-phase (RP)-HPLC of the water-soluble fraction showed differences between cheeses made from raw or pasteurised milk and between cheeses ripened at 1 or 8°C. The concentration of amino acids and fatty acids were in the order R8>P8>R1>P1. Commercial graders awarded highest flavour scores to the R1 cheeses during gradings at 4, 5 and 6 months. A sensory panel found that most flavour and aroma attributes and maturity were in the order of R8>P8>R1=P1. The results of this study suggest that NSLAB play an important role in the development of flavour in Cheddar cheese by contributing to the production of amino acids and fatty acids.     

Effect of pasteurisation on the chemical composition of liquid whole egg. III.—Effect of staling and freezing on the protein fractionation patterns of raw and pasteurised whole egg

Two particular fractions of the soluble proteins were consistently reduced by heating liquid egg for 5 min at 150°F. These fractions were quantitatively greater in the soluble proteins from frozen egg. The soluble proteins appeared to be more stable to heat in eggs that had been stored for 15 days at 70°F than in new-laid eggs. Unfrozen new-laid and stale egg and frozen new-laid egg all showed an increase in insoluble material after pasteurisation, and frozen egg contained more insoluble materials than unfrozen egg. Gel filtration showed that the proportion of compounds of high molecular weight in the insoluble proteins was markedly increased by pasteurisation and even more markedly increased by freezing.     

Comparison of DNA quality in raw and reconstituted milk during sterilization

Responses to milk sterilization are usually evaluated only in terms of physicochemical properties and microbial safety, thus undervaluing the importance of DNA quality in an authentication process by methods based on PCR. Because DNA is a heat-sensitive molecule, we hypothesized that the heating process may impair the detection or quantification of DNA in raw fresh milk (FM) or reconstituted milk (RM), and that differences in DNA quality might exist between FM and RM. We thus investigated the effects of sterilization on the quality of DNA extracted from FM or RM; differences in DNA quality between FM and RM were also evaluated. The quality of extracted DNA from FM or RM was assessed by the specific detection of FM or RM composition in goat milk mixtures using primers targeting the bovine 12S gene, as well as by monitoring DNA yield, purity, ratio of mitochondrial (mt) to nuclear (n) DNA, and the level of DNA degradation. Polymerase chain reaction readily detected both untreated and heat-treated FM or RM in cow-goat milk mixtures, and gave a good sensitivity threshold (0.1%) under all sterilization conditions. The DNA yield and mtDNA:nDNA ratio of FM and RM varied significantly during the sterilization process. These results demonstrated that the sterilization altered the quantification of DNA in FM or RM during sterilization, but DNA could still be readily detected in sterilized FM or RM by PCR. Furthermore, we noted significant differences in DNA integrity, yield, and mtDNA:nDNA ratio between FM and RM during sterilization, which may have potential as a means to distinguish FM and RM.     

Comparing techniques for detecting the number of somatic cells in raw milk

Evaluating the quality of milk and monitoring for cow mastitis requires an evaluation of the somatic cell count (SCC), an important parameter in the dairy industry. We studied the somatic cells of raw milk using a confocal laser scanning microscope (CLSM), flow cytometry (FCM), and a light microscope (LM). The CLSM method gave a good correlation (r=0.987) with the LM counts of somatic cells in raw milk. The FCM method also correlated well (r=0.904) with the LM method. The CLSM method gave a good correlation (r=0.908) with the FCM method. This study shows that the CLSM method and the FCM method both offer rapid and simple approaches to somatic cell detection.     

Psychrotrophic flora of raw milk: resistance to several common disinfectants

The psychrotrophic bacterial flora of milk was examined after aseptic hand milking. A total of 409 strains were tentatively characterized and classified into 17 groups by a reduced set of tests and cluster analysis. Lipolytic organisms (53.7% exceeded proteolytic organisms (29.6%), and a reported predominance of oxidase-positive organisms (54.5%) was not found. Gram-negatives were mainly Enterobacteriaceae, Flavobacterium, Acinetobacter and Pseudomonas. In the Gram-positive groups Micrococcaceae were the most abundant (44.4%) followed by coryneforms (16.3%). Only two of seven commonly used disinfectants acted differently with Gram-positive and Gram-negative organisms (P less than 0.01), although in general Gram-positives were more resistant than Gram-negatives.     

Application of novel technologies to reach net-zero greenhouse gas emissions in the fresh pasteurised milk supply chain: A review

This review assesses the potential of three novel technologies (3-nitrooxypropanol, ultraviolet C light cold pasteurisation and biochar) to reduce the carbon footprint produced by the fresh milk supply chain at global level. In addition to the adoption of these technologies: (i) new policies should enhance the development and implementation of international standards to optimise the quality and safety of such technologies whilst facilitating their traceability; (ii) dairy firms and technology start-ups should benefit from worldwide emissions trading systems to limit technology implementation costs; and (iii) consumers could participate in the net-zero challenge by adopting easy-to-apply sustainable practices, thus reducing their milk carbon footprint.     

Effects of pasteurisation and high-pressure processing on vitamin C,tocopherols and fatty acids in mature human milk

Holder pasteurisation has traditionally been used in human milk banks to inactivate the pathogenic microorganisms and part of the commensal flora that are potentially present in milk from donors. However, this process results in variable loss of nutrients. In the search for an alternative to pasteurisation, we assessed the ability of high-pressure processing (HPP) to maintain the fatty acid, vitamin C and vitamin E contents of human milk and compared this process with Holder pasteurisation. Fatty acid proportions in milk, as well as levels of delta-, gamma-, and alpha-tocopherols did not vary with any of the treatments. Total vitamin C and ascorbic acid levels were maintained after HPP. However, after pasteurisation, total vitamin C and ascorbic acid were about 20% and 16% lower, respectively, than in untreated samples. These results suggest that HPP merits further investigation as a potential alternative to Holder pasteurisation for treating donor human milk.     

Calibration of infrared milk analyzers: modified milk versus producer milk

Mid-infrared (MIR) milk analyzers are traditionally calibrated using sets of preserved raw individual producer milk samples. The goal of this study was to determine if the use of sets of preserved pasteurized modified milks improved calibration performance of MIR milk analyzers compared with calibration sets of producer milks. The preserved pasteurized modified milk sets exhibited more consistent day-to-day and set-to-set calibration slope and intercept values for all components compared with the preserved raw producer milk calibration sets. Pasteurized modified milk calibration samples achieved smaller confidence interval (CI) around the regression line (i.e., calibration uncertainty). Use of modified milk calibration sets with a larger component range, more even distribution of component concentrations within the ranges, and the lower correlation of fat and protein concentrations than producer milk calibration sets produced a smaller 95% CI for the regression line due to the elimination of moderate and high leverage samples. The CI for the producer calibration sets were about 2 to 12 times greater than the CI for the modified milk calibration sets, depending on the component. Modified milk calibration samples have the potential to produce MIR milk analyzer calibrations that will perform better in validation checks than producer milk-based calibrations by reducing the mean difference and standard deviation of the difference between instrument values and reference chemistry.     

Effect of pasteurisation on ascorbic acid,dehydroascorbic acid,tocopherols and fatty acids in pooled mature human milk

Ascorbic and dehydroascorbic acids (vitamin C), tocopherols (vitamin E) and unsaturated fatty acids are heat-sensitive and therefore, their concentrations in human milk could be affected by pasteurisation. Here we determined the concentrations of ascorbic acid plus dehydroascorbic acid, ascorbic acid alone, and α- and γ-tocopherols, and the percentages of fatty acids in samples of human milk after pasteurisation by a slow (62.5 °C, 30 min) or fast heating (100 °C, 5 min) procedure. Both methods led to a significant decrease in the concentrations of ascorbic acid plus dehydroascorbic acid (12% and 29%), ascorbic acid (26% and 41%), α-tocopherol (17% and 34%) and γ-tocopherol (13% and 32%), respectively. However, milk fatty acids, including the polyunsaturated long-chain fatty acids, were unaffected by the two methods. On the basis of these observations, we recommend that human milk be treated using a slow pasteurisation. In addition, we propose ascorbic acid as a marker of the degree of heat treatment.