Effect of activating lactoperoxidase system in cheese milk on the quality of Saint‐Paulin cheese

Saint‐Paulin cheese was made from cow’s milk refrigerated at 4 °C for 72 h and preserved by the lactoperoxidase (LP) system. The effect of the LP system on the microbiological, physicochemical and biochemical properties of cheese over a ripening period of 23 days was investigated, using a control (C0), refrigerated LP‐inactivated cow’s milk (C1) and refrigerated LP‐activated cow’s milk (LPA). The LPA treatment showed the least contamination in flora count, particularly salt‐tolerant bacteria at the end of the ripening period. LPA cheese had significantly lower coliform, yeasts and mould counts (P < 0.05) than the other cheeses; this demonstrated the bacteriostatic effect of the LP system. The proteolysis results showed the least value for LPA cheese as compared with the two other samples, as determined by using sodium dodecyl sulphate‐polyacrylamide gel electrophoresis of casein fractions extracted from the three samples. The findings indicated that the preservation of cow’s cheese milk by the LP system can be used to improve the microbiological quality, inhibit psychotropic germs, correct the losses of soluble nitrogen fractions in the whey and conserve the cheese yield affected by refrigeration.     

Microbial biodiversity of raw milk collected from Yangzhou and the heterogeneous biofilm-forming ability of Pseudomonas

This study aimed to reveal microbial populations in Chinese raw milk using both 16S rRNA sequencing and high-throughput sequence (HTS) methods. Psychrotrophic isolates were clustered into 23 genera and 57 species, and the abundant genera in raw milk were Pseudomonas, Acinetobacter and Lactococcus. Genetic diversity and biofilm-forming capacity of Pseudomonas isolates were analysed using random amplified polymorphic DNA (RAPD) and crystal violet staining assay, respectively. Heterogeneous biofilm-forming ability of Pseudomonas isolates with the same RAPD patterns was observed. HTS analysis revealed a 33-fold higher diversity at the genus level, and a different bacterial population was predominated by Flavobacterium, Pseudomonas and Acinetobacter. The results provide insight into the microbial contamination of raw milk.     

Characterisation of Macedonian white‐brined cheese: Effect of raw or heat‐treated caprine milk

This research analysed the use of raw and pasteurised milk in the production of Macedonian white caprine milk cheese. Pasteurisation resulted in a considerable decrease in the nitrogen fractions, urea‐polyacrylamide gel electrophoresis of caseins, peptide profiles and volatiles during the maturation period. Forty‐five volatile components were detected, including twelve acids, fourteen esters, six ketones, three alcohols, four terpenes and six other compounds. It was deduced that pasteurisation of milk for the manufacture of artisanal white‐brined cheese delayed the evolution of volatiles, which are related to the unique flavour of the cheese.     

室温下化学法激活乳过氧化物酶体系对原料乳品质的影响

本文对化学法激活乳过氧化物酶体系用于室温下原料乳保鲜进行了研究。研究结果表明,在25℃贮藏温度下,原料奶的货架期随着SCN-和H2O2的浓度增加而增加。对照组和实验组0.1mmol/L,0.25mmol/L,0.5mmol/L的保鲜期分别为19h,19.5h,21.5h和23.5h。在贮藏期间,所有的实验组的微生物数量均低于对照组。11.5h时,激活剂浓度为0.25mmol/L和0.5mmol/L的原料乳的菌落总数比对照组提高了3个卫生等级。在14h时,激活剂浓度为0.25mmol/L和0.5mmol/L的实验组比对照组的大肠菌群数分别低1.2和1.75个对数周期。     

Occurrence, virulence genes and antibiotic resistance of Escherichia coli O157 isolated from raw bovine, caprine and ovine milk in Greece

The examination of 2005 raw bovine (n = 950), caprine (n = 460) and ovine (n = 595) bulk milk samples collected throughout several regions in Greece for the presence of Escherichia coli serogroup O157 resulted in the isolation of 29 strains (1.4%) of which 21 were isolated from bovine (2.2%), 3 from caprine (0.7%) and 5 from ovine (0.8%) milk. Out of the 29 E. coli O157 isolates, only 12 (41.4%) could be classified as Shiga-toxigenic based on immunoassay and PCR results. All 12 Shiga-toxigenic E. coli serogroup O157 isolates belonged to the E. coli O157:H7 serotype. All except one of the 12 Shiga-toxin positive isolates were stx₂-positive, five of which were also stx₁-positive. The remaining isolate was positive only for the stx₁ gene. All stx-positive isolates (whether positive for stx₁, stx₂ or stx₁ and stx₂) were also PCR-positive for the eae and ehxA genes. The remaining 17 E. coli O157 isolates (58.6%) were negative for the presence of the H7 flagellar gene by PCR, tested negative for Shiga-toxin production both by immunoassay and PCR, and among these, only four and three strains were PCR-positive for the eae and ehxA genes, respectively. All 29 E. coli O157 isolates displayed resistance to a wide range of antimicrobials, with the stx-positive isolates being, on average, resistant to a higher number of antibiotics than those which were stx-negative.     

Texture and flavour development in Ras cheese made from raw and pasteurised milk

Texture, proteolysis and flavour development in Ras cheeses made from raw or pasteurised milk with two different thermophilic lactic cultures were monitored during ripening. Results showed that at day 1 of manufacture, the moisture content and pH were lower in raw milk cheese than in pasteurised milk cheeses. Levels of water-soluble nitrogen, casein breakdown, free amino groups and free fatty acids were higher in cheese made from raw milk than in that made from pasteurised milk. Textural characteristics, such as hardness, cohesiveness and chewines, increased in all treatments during the first 60 days of ripening due to the reduction in the moisture level during the second stage of salting (dry salting during the first 60 days of ripening). Cheese made from raw milk received the highest texture and flavour scores by panellists.     

Changes during ripening in chemical composition,proteolysis, volatile composition and texture in Kashar cheese made using raw bovine,ovine or caprine milk

Kashar cheeses were manufactured from pure ovine (OV), bovine (BV) and caprine (CP) milk, and the chemical composition, cheese yield, proteolysis, hardness, meltability and volatile composition were studied during 90 days. Gross chemical composition, cheese yield and level of proteolysis were higher in OV cheeses than those of BV or CP cheeses. Glu, Val, Leu, Phe and Lys were the most abundant free amino acids (FAA) in the samples, and the concentrations of individual FAA were at the highest levels in OV cheeses with following BV and CP cheeses. Urea‐PAGE patterns and RP‐HPLC peptide profiles of the BV cheeses were completely different from the small ruminants’ milk cheeses (OV or CP). Higher and lower hardness and meltability values were observed in CP cheeses, respectively. OV cheeses resulted in higher levels of the major volatile compounds. In conclusion, the Kashar cheese made using OV milk can be recommended due to high meltability, proteolysis and volatiles.     

A study of the growth of Lactobacillus acidophilus in bovine, ovine and caprine milk

The fermentation of reconstituted bovine, ovine and caprine milks with Lactobacillus acidophilus was investigated. Better growth of Lb. acidophilus was observed in ovine milk, but higher acidities developed in caprine milk. The high acidity produced after 12 h of fermentation (pH 3.9) created a hostile environment for the survival of the microorganism in caprine milk.     

Survey of raw milk cheeses for microbiological quality and prevalence of foodborne pathogens

Cheese may be manufactured in the United States using raw milk, provided the cheese is aged for at least 60 days at temperatures not less than 35 °F (1.7 °C). There is now increased concern among regulators regarding the safety of raw milk cheese due to the potential ability of foodborne pathogens to survive the manufacturing and aging processes. In this study, 41 raw milk cheeses were obtained from retail specialty shops, farmers’ markets, and on-line sources. The cheeses were then analyzed for the presence of Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, Staphylococcus aureus, and Campylobacter. Aerobic plate counts (APC), coliform and yeast/mold counts were also performed. The results revealed that none of the enteric pathogens were detected in any of the samples tested. Five samples contained coliforms; two of those contained E. coli at less than 10² cfu/g. Three other cheese samples contained S. aureus. The APC and yeast-mold counts were within expected ranges. Based on the results obtained from these 41 raw milk cheeses, the 60-day aging rule for unpasteurized milk cheeses appears adequate for producing microbiologically safe products.     

An automatic procedure for rapid online estimation of raw milk quality

A simple and inexpensive automatic procedure for rapid online assessment of raw milk microbiological quality was developed as an alternative to the presently available methods, which are either time consuming or require costly instrumentation. The technique was based on the monitoring of change in color of milk in methylene blue dye reduction test due to metabolic activity of the viable bacterial cells. The change in dye color was related to the output voltage signal of a specially designed light sensing probe (LSP) for about 40 min. The models developed for estimating SPC and MBRT from LSP output voltage showed R² of about 0.814 and 0.803, respectively. Subsequently, the output voltage of LSP was interfaced with a PC to predict and display the SPC (cfu/ml) and MBRT (h) of raw milk along with its quality grade in real time. The predictions of raw milk quality grades based on the calibration of LSP output voltage with SPC and MBRT were in good agreement with actual grades showing considerable promise for this novel assessment technique.     

Physicochemical, microbiological and coagulating properties of ewe's milk produced on the Calabrian Mount Poro plateau

Three hundred individual ewe's milks and six bulk milks were analysed over two seasons. The results show that in spring but not in winter the milks examined conform substantially to the standards laid down by Italian legislation. Nevertheless, the data acquired constitute a good starting point from which the quality of ewe's milk produced on the Calabrian Mount Poro plateau should be improved, by performing selection of sheep for mastitis resistance based on somatic cell count, improving the hygiene standards at the dairy, using selected autochthonous lactic starter cultures and, only if strictly necessary, thermal treatment of the milk.     

原料乳中腐败微生物对液态乳品质的影响及防控

乳因其营养丰富备受关注,被称为人体的“白色血液”,同时乳也是微生物良好的培养基,因此原料乳品质和液态乳加工过程都会受到严格把控,但目前液态乳在储藏期、流水线或货架期内发生腐败变质现象仍屡屡发生,引起行业对乳及乳制品安全的高度重视。原料乳作为液态乳生产的原料,是其品质保障的基础,原料乳中腐败微生物随着储藏时间的延长而大量繁殖,经过热处理后未被完全杀死的腐败菌及其产生的耐热酶仍会继续影响液态乳品质,此外生物膜的形成也为腐败菌在管道内残留提供了机会,加大了腐败微生物防控的难度。因此本文将从原料乳中腐败微生物多样性进行阐述并探究腐败微生物对于液态乳的不良影响,挖掘腐败微生物破坏液态乳可能存在的作用机制,总结现阶段国内外对腐败微生物的防控手段并探讨其商业应用价值,旨在为今后液态乳质量安全保障及延长货架期提供理论指导。     

Occurrence of moulds associated with ovine raw milk and cheeses of the Spanish region of Castilla La Mancha

The distribution of mould species was examined at several points of the processing chain in a Manchego cheese plant and associated dairy farms. Geotrichum and Fusarium were the genera most frequently isolated from milk samples as well as in cheeses ripened for one month, evidencing a direct transfer from raw milk. Conversely, the mycobiota of long‐ripened cheeses consisted mainly of Penicillium species, which gained entry to the cheese through the air of ripening rooms. This study contributes to the understanding of the dynamics of fungal populations in semihard and hard cheeses, highlighting that airborne transfer from the stables could have a direct impact on their quality.     

Effect of growth phase on the subsequent growth kinetics of psychrotrophic bacteria of raw milk origin

Psychrotrophs isolated at days 1, 3 and 5 from refrigerated raw milk were monitored for growth kinetics using conductance when they had been inoculated during their lag, log and stationary growth phases. The results indicated that there was a more rapid change in the microflora during the initial stages of storage when the lag phases of the 1, 3 and 5 day isolates were analysed. There was also evidence of the 'suicide response'. In addition, the fact that the stationary phase cells showed the greatest exponential growth rate may be a contributory factor to their selective advantage.     

原料乳与乳制品中碳水化合物质量控制研究进展

原料乳与乳制品中碳水化合物具有极高的营养价值,对人体健康具有重要作用,但其掺伪现象较普遍,严重影响了原料乳与乳制品的品质。文章综述了原料乳与乳制品中碳水化合物及其掺伪物质检测技术研究进展,旨在为做好原料乳与乳制品中碳水化合物质量控制提供科学依据。      

Effect of technological parameters on the characteristics of kasseri cheese made from raw or pasteurized ewes' milk

Two groups of kasseri cheese (pasta filata type) were manufactured from raw or pasteurized ewes' milk, without starter cultures. Cheeses of each group were divided into two subgroups: the first was ripened and stored at 4°C and packaged in plastic film; the second ripened and stored at 15°C and coated with paraffin wax. Milk pasteurization and technological parameters had a significant effect on the pH ( P  < 0.05), while only technological parameters had an effect on the total solids content. At day 120, the range of mean cfu/g counts for the mesophilic aerobic flora was 9.5 × 10⁷−1.4 × 10⁸; for the thermophilic streptococci, the range was 2.6 × 10⁷−7.6 × 10⁷; and for the thermophilic bacilli, 9.8 × 10⁶−1.7 × 10⁷. Changes in the N fractions became significant after 30 days of ripening. For mature 120-day-old cheeses, the percentage of total N soluble at pH 4.6 was 22.7%–22.9% in raw milk cheeses and 19.0%–21.7% in pasteurized milk cheeses. The percentage of total N soluble at 12% TCA was 10.1%–12.2% in raw milk cheeses and 7.3%–11.5% in pasteurized milk cheeses; the percentages of total N soluble at 5% PTA were 3.1%–4.0% and 2.6%–3.6%, respectively. The residual α_s-casein percentages at day 120 ranged between 63% and 78% of the respective area at day 1; the residual β-casein ranged between 67% and 75%. There were some characteristic differences in the reverse phase-HPLC peptide profiles of the four cheeses. In general, the effect of the different ripening conditions was more pronounced in cheeses made from pasteurized milk.     

Biochemical changes during the ripening of homemade 'San Simón da Costa' raw milk cheese

'San Simón da Costa' cheese is a traditional smoked variety produced in the northwest of Spain from cow's milk. Biochemical changes were determined during its ripening. Its high calcium and phosphorus content and its low NaCl and sodium content stand out. This cheese undergoes moderate proteolysis. The most abundant free amino acid at the end of the ripening was glutamic acid, followed by tryptophan, leucine, arginine and phenylalanine. The lipolysis throughout ripening is slight; the most abundant free fatty acid being oleic, followed by palmitic and butyric acid.     

Changes in the microbiological and chemical characteristics of an artisanal, low-fat cheese made from raw ovine milk during ripening

Changes in the microbial flora of batzos cheese made from raw ovine milk were studied during ripening. Lactic acid bacteria and Enterobacteriaceae were the predominant groups of micro-organisms. Cheeses manufactured in summer had higher microbial counts than those made in spring, with the exception of staphylococci. Nevertheless, Enterobacteriaceae and coliforms decreased more rapidly in cheese made in summer and counts at the end of storage were lower than those in spring cheese.
Enterococci predominated in the ripened curd of cheese made in spring, whereas lactobacilli were the most abundant lactic acid bacteria in cheese made in summer. Enterococcus faecium was the predominant species in spring, and Lactobacillus paracasei ssp. paracasei predominated in cheese made in summer. The pH of the cheeses was > 5.0 throughout ripening, and NaCl-in-moisture content (> 8.0%) permitted the growth and survival of salt-tolerant micro-organisms. α_s1-Casein degraded at a faster rate than β-casein; both caseins were hydrolysed more rapidly in spring than in summer. The free amino acid content became higher in summer cheese (566.24–3460.25 µg/g of glycine equivalent) than in spring cheese because of the progress of ripening. Moreover, the milk fat of the cheese was degraded more in the summer than in the spring. The results suggest that there could be advantages to using starter cultures and improving the level of hygiene during milk and cheese production in order to eliminate undesirable micro-organisms and standardize cheese quality.     

不同贮存条件对生牛奶品质影响的研究

从对生牛奶品质影响较大的贮存温度和时间着手，探讨了不同贮存条件对生牛奶中细菌总数以及组成的影响，旨在为优质生牛奶的贮运提供参考。     

Effect of carbon dioxide on improving the keeping quality of raw milk

Fresh cows' milk samples were treated with CO₂ to give a calculated CO₂ content of 77mM. The treated samples as well as the control were stored at 7° and 20 ± 5°C for three days and analysed periodically. The increase in the total count as well as the counts of psychrotrophic, lactic acid and coliform bacteria during storage at 7°C was found to be inhibited by the addition of CO₂. The treated samples had higher titratable acidity and lower pH values than the controls but satisfied the clot-on-boiling test. The keeping quality of cooled milk can therefore be improved by the addition of CO₂.