原料奶安全质量控制体系应用研究

结合生产实际从对原料奶安全性影响较大的存贮条件和时间入手，研究分析不同的存贮条件对原料奶品质影响变化，并制定HACCP计划，为保证优质原料奶应用于生产提供科学依据。     

Associations among milk quality indicators in raw bulk milk

The objective of this study was to determine characteristics and associations among bulk milk quality indicators from a cohort of dairies that used modern milk harvest, storage, and shipment systems and participated in an intensive program of milk quality monitoring. Bulk milk somatic cell count (SCC), total bacteria count (TBC), coliform count (CC), and laboratory pasteurization count (LPC) were monitored between July 2006 and July 2007. Bulk milk samples were collected 3 times daily (n = 3 farms), twice daily (n = 6 farms), once daily (n = 4 farms), or once every other day (n = 3 farms). Most farms (n = 11) had direct loading of milk into tankers on trucks, but 5 farms had stationary bulk tanks. The average herd size was 924 cows (range = 200 to 2,700), and daily milk produced per herd was 35,220 kg (range = 7,500 to 105,000 kg). Thresholds for increased bacterial counts were defined according to the 75th percentile and were >8,000 cfu/mL for TBC, >160 cfu/mL for CC, and ≥310 cfu/mL for LPC. Means values were 12,500 (n = 7,241 measurements), 242 (n = 7,275 measurements), and 226 cfu/mL (n = 7,220 measurements) for TBC, CC, and LPC, respectively. Increased TBC was 6.3 times more likely for bulk milk loads with increased CC compared with loads containing fewer coliforms. Increased TBC was 1.3 times more likely for bulk milk with increased LPC. The odds of increased TBC increased by 2.4% for every 10,000-cells/mL increase in SCC in the same milk load. The odds of increased CC increased by 4.3% for every 10,000-cells/mL increase in SCC. The odds of increased CC increased by 1% for every 0.1°C increase in the milk temperature upon arrival at the dairy plant (or at pickup for farms with bulk tank). Laboratory pasteurization count was poorly associated with other milk quality indicators. Seasonal effects on bacterial counts and milk temperature varied substantially among farms. Results of this study can be used to aid the interpretation and analysis of indicators of milk quality intensively produced by dairy processors’ laboratories.     

Microbial quality of raw horse milk

Consumption of horse milk has become popular in developed countries, especially among people suffering from bowel problems and skin diseases. Since the positive effect is supposedly not observed after pasteurisation, the product is mostly consumed as raw milk. Since the microbiological quality of this milk has not been systematically surveyed, in this study we examined the presence of spoilage- and pathogenic microorganisms in 123 samples of horse milk collected in The Netherlands and Belgium. Hygiene and faecal indicators were found in a wide range of numbers. Although Salmonella, Campylobacter and Listeria were not found, these pathogens showed no reduction in challenge tests with artificially contaminated horse milk stored for 1 week at 7 °C. Since faecal indicators were present and able to grow at 7 °C, combined with the fact that pathogens may easily end up and survive in the milk, it is not advised to consume raw horse milk.     

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。      

绿色原料奶的生产及质量控制

从奶牛的饲料构成，饲料基地的大气、水和土壤的环境监测控制，农药和化肥的使用，对饲料种植农户的一体化管理．奶牛饲料的采购、饲料加工工艺、生产和贮存过程中的质量控制，奶牛场的卫生与消毒，兽药的管理，奶牛常见疾病的防治，牛群的检疫与防疫以及原料奶的贮存和运输等方面，讨论了生产绿色原料奶所应具备的必要条件和实行“从土地到餐桌”的全程质量控制。     

Effect of high pressure processing on the safety,shelf life and quality of raw milk

High pressure processing (HPP) was investigated as an alternative to standard raw milk processing. Different pressure levels (400–600 MPa) and exposure times (1–5 min) were tested against artificially inoculated pathogenic E. coli, Salmonella and L. monocytogenes. HPP effectively inactivated bacterial concentration by 5 log CFU/ml. The most effective HPP conditions in terms of pathogen reduction were subsequently utilised to determine the effect of pressure on microbiological shelf life, particle size and colour of milk during refrigerated storage. Results were compared to pasteurised and raw milk. HPP (600 MPa for 3 min) also significantly reduced the total viable counts, Enterobacteriaceae, lactic acid bacteria and Pseudomonas spp. in milk thus prolonging the microbiological shelf life of milk by 1 week compared to pasteurised milk. Particle size distribution curves of raw, pasteurised and HPP milk, showed that raw and HPP milk had more similar casein and fat particle sizes compared to pasteurised milk. The results of this study show the possibility of using HPP to eliminate pathogens present in milk while maintaining key quality characteristics similar to those of raw milk.     

Influence of raw milk quality on fluid milk shelf life

Pasteurized fluid milk shelf life is influenced by raw milk quality. The microbial count and somatic cell count (SCC) determine the load of heat-resistant enzymes in milk. Generally, high levels of psychrotrophic bacteria in raw milk are required to contribute sufficient quantities of heat-stable proteases and lipases to cause breakdown of protein and fat after pasteurization. Sanitation, refrigeration, and the addition of CO2 to milk are used to control both total and psychrotrophic bacteria count. It is not uncommon for total bacterial counts of raw milk to be < 10,000 cfu/mL. In the past, fluid milk processors have not focused much attention on milk SCC. Increased SCC is correlated with increased amounts of heat-stable protease (plasmin) and lipase (lipoprotein lipase) in milk. When starting with raw milk that has a low bacterial count, and in the absence of microbial growth in pasteurized milk, enzymes associated with high SCC will cause protein and fat degradation during refrigerated storage, and produce off-flavors. As the ability to kill, remove, or control microbial growth in pasteurized refrigerated milk continues to improve, the original milk SCC will be the factor limiting the time of refrigerated storage before development of an off-flavor in milk. Most healthy cows in a dairy herd have a milk SCC < 50,000 cell/mL. Bulk tank SCC > 200,000 cell/mL are usually due to the contribution of high SCC milk from a small number of cows in the herd. Technology to identify these cows and keep their milk out of the bulk tank could substantially increase the value of the remaining milk for use in fluid milk processing. To achieve a 60- to 90-d shelf life of refrigerated fluid milk, fluid processors and dairy farmers need to work together to structure economic incentives that allow farmers to produce milk with the SCC needed for extended refrigerated shelf life.     

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.     

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.     

Microbiological quality of raw goat's and ewe's bulk-tank milk in Switzerland

A total of 407 samples of bulk-tank milk (344 of goat's milk and 63 of ewe's milk) collected from 403 different farms throughout Switzerland, was examined. The number of farms investigated in this study represents 8% of the country's dairy-goat and 15% of its dairy-sheep farms. Standard plate counts and Enterobacteriaceae counts were performed on each sample. Furthermore, the prevalence of Staphylococcus aureus, Campylobacter spp., Shiga toxin-producing Escherichia coli, Salmonella spp., and Mycobacterium avium ssp. paratuberculosis was studied. The median standard plate count for bulk-tank milk from small ruminants was 4.70 log cfu/ml (4.69 log cfu/ml for goat's milk and 4.78 log cfu/ml for ewe's milk), with a minimum of 2.00 log cfu/ml and a maximum of 8.64 log cfu/ml. Enterobacteriaceae were detected in 212 (61.6%) goat's milk and 45 (71.4%) ewe's milk samples, whereas S. aureus was detected in 109 (31.7%) samples of goat's milk and 21 (33.3%) samples of ewe's milk. Campylobacter spp. and Salmonella spp. were not isolated from any of the samples. However, 16.3% of the goat's milk and 12.7% of the ewe's milk samples were polymerase chain reaction (PCR)-positive for Shiga toxin-producing E. coli. Seventy-nine (23.0%) goat's tank-milk and 15 (23.8%) ewe's tank-milk samples were PCR-positive for insertion sequence 900, providing presumptive evidence for the presence of M. avium ssp. paratuberculosis. These results form the basis for determining the microbiological quality standards for goat's and ewe's milk. Moreover, the data presented form part of the risk assessment program for raw milk from small ruminants in Switzerland.     

谈原料奶按质论价

通过阐述欧洲原料奶付款系统，介绍了欧洲一些国家决定原料奶价格的参数，包括乳脂、乳蛋白、细菌总数、体细胞数、抗生素、冰点、季节等，以及这些参数的奖罚措施，并从中分析了国内按质论价体系与国外的差别。     

Profile of gelatinolytic capacity of raw goat milk and the implications for milk quality

Both endogenous and exogenous proteinases occur in milk, and they can have beneficial or detrimental effects on dairy production. Because the lactation length of dairy goats is shorter and the somatic cell count (SCC) of goat milk is generally greater compared with dairy cows, the objectives of the present study were to investigate the prevalence of major proteinases in raw goat milk, their association with SCC and production stage, and their effects on milk quality. Milk samples were collected from individual goats in consecutive weeks for different durations, covering regular lactation, late lactation, and post-milk stasis. Long-term (monthly) or short-term (weekly) fluctuations of milk fibrinolytic and gelatinolytic capacities of individual goats were revealed chronologically on fibrin and gelatin zymograms, respectively. In a separate trial involving milk samples from 23 goats at random production stages, the percentage of ultracentrifuge force-precipitable casein of total milk protein was calculated to represent milk quality and was assessed to evaluate its correlation with the corresponding proteolytic capacities. The results for regular milk indicate that gelatinase B was more abundant than gelatinase A when they first appeared at SCC of ∼1 × 10⁶/mL. During the last month before milk stasis, both gelatinases A and B were found to be prevalent and prominent in milk regardless of the broad SCC range recorded there. Fibrinolytic activity and the active form of gelatinase A were only regularly detected in post-stasis secretions and were scarce before stasis. The results of the milk quality trial indicate that milk of relatively high proteinase capacity tended to have a low casein ratio. Correlation analysis confirmed a significant relationship between gelatinase capacity of goat milk and production stage, SCC, or casein ratio. It is suggested that an elevation of gelatinolytic capacity of goat milk coincides with an increase in somatic cell number accompanying the extension of lactation length, which is unfavorable for the production of a more desirable quality of goat milk.     

Microbial quality and safety of milk and milk products in the 21st century

Milk and milk products have been utilized by humans for many thousands of years. With the advent of metagenomic studies, our knowledge on the microbiota of milk and milk products, especially as affected by the environment, production, and storage parameters, has increased. Milk quality depends on chemical parameters (fat and protein content and absence of inhibitory substances), as well as microbial and somatic cells counts, and affects the price of milk. The effects of hygiene and effective cooling on the spoilage microbiota have shown that proteolytic and lipolytic bacteria such as Pseudomonas or Acinetobacter spp. predominate the spoilage bacterial populations. These bacteria can produce heat‐stable proteases and lipases, which remain active after pasteurization and thus can spoil the milk during prolonged storage. Additionally, milk can become contaminated after pasteurization and therefore there is still a high demand on developing better cleaning and sanitation regimes and equipment, as well as test systems to (quantitatively) detect relevant pathogenic or spoilage microorganisms. Raw milk and raw milk cheese consumption is also increasing worldwide with the growing demand of minimally processed, sustainable, healthy, and local foods. In this context, emerging and re‐emerging pathogens once again represent a major food safety challenge. As a result of global warming, it is conceivable that not only microbiological risks but also chemical risks relating to presence of mycotoxins or plant toxins in milk will increase. Herein, we provide an overview of the major microbial hazards occurring in the 21st century.     

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。     

控制体细胞数在优质生鲜奶生产中的应用

本文主要介绍了生鲜奶中体细胞数的作用、检测方法以及国内外的应用现状，讨论了体细胞数的影响因素及其控制措施．建议在我国开展牛群的体细胞数控制，从而提高生鲜奶的产量和质量。     

The effect of extended low-temperature storage of raw milk on the quality of pasteurized and UHT milk

The effect of storage of raw milk at 2 and 6°C on the quality of pasteurized and UHT milks produced from them has been investigated. There was no difference in shelf-lives of pasteurized milks produced from raw milks which had no obvious physical defects, odours and taints after storage at 2 and 6°C. This was true for pasteurized milks in the presence and absence of post-heat-treatment contamination. However, pasteurized milks of good quality could be produced from more than 80% of raw milk samples which had been stored for up to 5 days at 2°C, but this was only possible with raw milks which had been stored at 6°C for 2 days.Failure rates of experimentally-produced UHT milks were much higher in products manufactured from raw milks stored at 6°C for 4 days than those produced from raw milks stored at 2°C for 4 days. The main cause of failure was due to thermostable bacterial protease associated with high levels of bacterial growth in the raw milks. Other causes of failure included spore-forming bacteria, which may have survived UHT processing, and other organisms probably introduced as contaminants on filling.