HACCP在乳品生产中的应用探讨

在食品的生产管理中，对其质量的预防和控制传统的做法是把重点放在监督检查和对成品的监测上，而HACCP是把预防和控制重点前移，对全过程进行危害分析，找出关键控制点并采取有效措施加以控制。在实际应系统地分析整个生产过程，确定CCP点，并制定有效的控制措施。     

乳及乳制品中生物活性肽的种类及功能多样性

综述了乳制品即发酵乳和干酪中生物活性肽的种类及生物活性肽的功能多样性，以期为乳源生物活性肽的开发及其在保健食品中的潜在应用提供一定的参考。     

A Blend of Essential Plant Oils Used as an Additive to Alter Silage Fermentation or Used as a Feed Additive for Lactating Dairy Cows

A blend of essential plant oils was evaluated for its effects on silage fermentation and animal performance. In the first experiment, the blend of essential oils was mixed with freshly chopped whole-plant corn to achieve a concentration of 0, 40, or 80 mg of active product per kilogram of fresh forage weight. Whole-plant corn was also mixed with a buffered propionic acid-based product at 0.2% of fresh forage weight. The blend of essential oils did not affect the populations of yeasts, molds, lactic acid bacteria, or enterobacteria; the fermentation end products; or the aerobic stability of the corn silage. Addition of the buffered propionic acid additive moderately reduced the production of acids during fermentation and resulted in a small reduction in the numbers of yeasts after ensiling, but did not affect aerobic stability. In a second experiment, 30 Holstein cows (4 primiparous and 26 multiparous) averaging 118 ± 70 d in milk and producing 38 ± 16 kg of milk/d were fed a total mixed ration, once daily, that consisted of (on a DM basis) 25% corn silage, 15% alfalfa silage, 10% alfalfa hay, and 50% concentrate. One-half of the cows were fed a blend of essential oils that was mixed directly into their total mixed ration to provide 1.2 g/cow per d for 9 wk. Cows fed the essential oils ate 1.9 kg more dry matter/d and produced 2.7 kg more 3.5% fat-corrected milk/d than did cows fed the control diet. The percentages of milk fat and protein, the somatic cell count numbers, and the concentrations of milk urea nitrogen were unaffected by treatment. Feed efficiency, change in body weight, and change in body condition scoring were also similar between treatments. After 12 h of incubation, the addition of a moderate dose and a high dose of essential oils to in vitro ruminal fermentations had no effect on the concentration of total VFA compared with the control treatment. However, they decreased the molar proportions of acetic, butyric, and valeric acids and increased the proportion of propionic acid. The blend of essential oils evaluated in this study altered in vitro ruminal fermentation and improved animal performance when fed directly to cows, but it did not affect the fermentation or aerobic stability of corn silage.     

Evaluation of the response of ruminal fermentation and activities of nonstarch polysaccharide-degrading enzymes to particle length of corn silage in dairy cows

The main objective of this study was to evaluate effects of particle length (PL) of corn silage (CS) on distribution of dietary particle fractions, contents of physically effective neutral detergent fiber (peNDF), cows’ intake patterns and sorting activity, fermentation pro-file, and activities of nonstarch polysaccharide-degrading enzymes as well as degradation in the rumen and total tract in lactating dairy cows. Four ruminally cannulated Holstein cows, weighing 624 ± 50 kg and 60 ± 8 d in milk, were fed ad libitum 3 total mixed rations [about 16% crude protein, 34% neutral detergent fiber (NDF), and 7 MJ of net energy of lactation/kg of dry matter (DM)] containing on DM basis 50% concentrate, 10% grass hay, and 40% CS with 3 different theoretical PL at harvesting (14, 8.1, and 5.5 mm for long, medium, and short, respectively). Results showed that the amount of DM retained on sieves with 19- and 8-mm screens of Penn State Particle Separator decreased linearly with decreasing PL of CS. The latter was reflected in a significant decrease in the content of dietary peNDF including both the DM (peNDF_>8) and the NDF (peNDF_>8-NDF) retained on 19- and 8-mm screens. In contrast, the fraction of particles retained between the 1.18- and 8-mm screens was increased, such that no differences among the diets were observed regarding the content of peNDF that includes DM of particles >1.18 mm (peNDF_>1.18). The intake of particles retained between the 1.18- and 8-mm screens increased linearly, whereas the intake of peNDF_>1.18 increased quadratically with decreasing PL of CS. Sorting consumption was reduced by feeding the short CS, which was reflected in a reduced proportion of propionate and increased acetate-to-propionate ratio and butyrate pro-portion in the rumen. In contrast, no effects of PL of CS were observed on the concentration of total volatile fatty acids and pH in the rumen. In general, decreasing the PL of CS significantly increased the activities of nonstarch polysaccharide-degrading enzymes. However, greater ruminal and total tract degradation of fiber and nonfiber carbohydrates were observed only by medium CS. Results of the present study suggest that in addition to fractions of long particles (i.e., >8 mm), the particle fraction retained between 1.18- and 8-mm should also be considered to better predict rumen conditions and digestion. In conclusion, a moderate reduction of PL of CS has beneficial effects on nutrient digestion, and may maximize feed efficiency and energy supply in high-yielding dairy cows.     

Evaluation of factors associated with immunoglobulin G,fat, protein,and lactose concentrations in bovine colostrum and colostrum management practices in grassland-based dairy systems in Northern Ireland

The objectives of this study were to investigate colostrum feeding practices and colostrum quality on commercial grassland-based dairy farms, and to identify factors associated with colostrum quality that could help inform the development of colostrum management protocols. Over 1 yr, background information associated with dairy calvings and colostrum management practices were recorded on 21 commercial dairy farms. Colostrum samples (n = 1,239) were analyzed for fat, protein, lactose, and IgG concentration. A subset was analyzed for somatic cell count and total viable bacteria count. Factors associated with nutritional and IgG concentrations were determined using both univariate and multivariate models. This study found that 51% of calves were administered their first feed of colostrum via esophageal tube, and the majority of calves (80%) were fed >2 L of colostrum at their first feed (mean = 2.9 L, SD = 0.79), at a mean time of 3.2 h (SD 4.36) after birth, but this ranged across farms. The mean colostral fat, protein, and lactose percentages and IgG concentrations were 6.4%, 14%, 2.7%, and 55 mg/mL, respectively. The mean somatic cell count and total viable count were 6.3 log₁₀ and 6.1 log₁₀, respectively. Overall, 44% of colostrum samples contained <50 mg/mL IgG, and almost 81% were in excess of industry guidelines (<100,000 cfu/mL) for bacterial contamination. In the multivariate model, IgG concentration was associated with parity and time from parturition to colostrum collection. The nutritional properties of colostrum were associated with parity, prepartum vaccination, season of calving, and dry cow nutrition. The large variation in colostrum quality found in the current study highlights the importance of routine colostrum testing, and now that factors associated with lower-quality colostrum on grassland-based dairy farms have been identified, producers and advisers are better informed and able to develop risk-based colostrum management protocols.     

乳制品中邻苯二甲酸酯类化合物残留量检测方法

建立了测定乳制品中邻苯二甲酸之类物质残留量的气质联用方法。液体乳及含乳饮料采用正己烷萃取后直接测定;乳粉类样品先用正己烷萃取、再用凝胶萃取小柱净化后上机测定。色谱测定条件为采用DB-5MS(30 m×0.25 mm×0.25μm)石英毛细管柱梯度升温进行分离质谱条件为色谱与质谱接口温度280℃、电子轰击源、选择离子扫描模式、电力能量70 eV。通过各组分的定性与定量离子分别对邻苯二甲酸酯进行定性、定量测定。该方法样品加标回收率分别在86%~105%之间,液体乳及乳饮料检出限为0.05 mg/kg,乳粉为0.1 mg/kg。本法具有操作简单、测定快速、灵敏度高、专属性及准确性好等优点。     

Short communication: Identifying challenges and opportunities for improved nutrient management through the USDA's Dairy Agroecosystem Working Group

Nutrient management on US dairy farms must balance an array of priorities, some of which conflict. To illustrate nutrient management challenges and opportunities across the US dairy industry, the USDA Agricultural Research Service Dairy Agroecosystems Working Group (DAWG) modeled 8 confinement and 2 grazing operations in the 7 largest US dairy-producing states using the Integrated Farm System Model (IFSM). Opportunities existed across all of the dairies studied to increase on-farm feed production and lower purchased feed bills, most notably on large dairies (>1,000 cows) with the highest herd densities. Purchased feed accounted for 18 to 44% of large dairies' total operating costs compared with 7 to 14% on small dairies (<300 milk cows) due to lower stocking rates. For dairies with larger land bases, in addition to a reduction in environmental impact, financial incentives exist to promote prudent nutrient management practices by substituting manure nutrients or legume nutrients for purchased fertilizers. Environmental priorities varied regionally and were principally tied to facility management for dry-lot dairies of the semi-arid western United States (ammonia-N emissions), to manure handling and application for humid midwestern and eastern US dairies (nitrate-N leaching and P runoff), and pasture management for dairies with significant grazing components (nitrous oxide emissions). Many of the nutrient management challenges identified by DAWG are beyond slight modifications in management and require coordinated solutions to ensure an environmentally and economically sustainable US dairy industry.     

Methane production,rumen fermentation,and diet digestibility of Holstein and Jersey dairy cows being divergent in residual feed intake and fed at 2 forage-to-concentrate ratios

Improving feed efficiency of dairy cows through breeding is expected to reduce enteric methane production per unit of milk produced. This study examined the effect of 2 forage-to-concentrate ratios on methane production, rumen fermentation, and nutrient digestibility in Holstein and Jersey dairy cows divergent in residual feed intake (RFI). Before experimental onset, RFI was estimated using a random regression model on phenotypic herd data. Ten lactating Holstein and 10 lactating Jersey cows were extracted from the herd and allocated to a high or low pre-experimental RFI group of 5 animals each within breed. Cows were fed ad libitum with total mixed rations either low (LC) or high (HC) in concentrates during 3 periods in a crossover design with a back-cross and staggered approach. Forage-to-concentrate ratio was 68:32 for LC and 39:61 for HC. Cows adapted to the diets in 12 to 24 d and feces were subsequently collected on 2 d. Afterward, gas exchange was measured in respiration chambers and rumen liquid was collected once after cows exited the chambers. Pre-experimental RFI was included in the statistical analysis as a class (low and high RFI) or continuous variable. Methane per kilogram of dry matter intake (DMI) was lower for Holsteins than Jerseys and the response to increased concentrate level was more pronounced for Holsteins than Jerseys (27.2 vs.13.8%); a similar pattern was found for the acetate:propionate ratio. However, methane production per kilogram of energy-corrected milk (ECM) was unaffected by breed. Further, total-tract digestibility of neutral detergent fiber was higher for Jerseys than Holsteins. For RFI as a class variable, DMI, methane production regardless of the expression, and digestibility were unaffected by RFI. For RFI as a continuous variable, DMI was lower and methane per kilogram of DMI was higher for cows with negative (efficient) than positive (inefficient) RFI values, and neutral detergent fiber digestibility was higher for Holsteins with negative than positive RFI values, but not for Jerseys. Daily methane production and methane per kilogram of ECM were unaffected by RFI. In conclusion, methane per kilogram of DMI of Jerseys was lowered to a smaller extent in response to the HC diet than of Holsteins. When pre-experimental RFI was used as a continuous variable, higher methane per kilogram of DMI was found for cows with negative RFI than positive RFI values, but not for methane per kilogram of ECM. These findings call for validation in larger studies.     

Harnessing anaerobic digestion for combined cooling,heat, and power on dairy farms: An environmental life cycle and techno-economic assessment of added cooling pathways

Anaerobic digestion coupled with combined heat and power production on dairy farms is environmentally advantageous; however, high capital and operating costs have limited its adoption, especially in the United States, where renewable electricity and heat production are under-incentivized. Biogas is also at a disadvantage because it has to compete with very low natural gas prices. The objective of this study was to evaluate the feasibility of integrating absorption refrigeration technology for combined cooling, heat, and power (CCHP) on the farm to help bridge this economic hurdle. A combined environmental life cycle and techno-economic assessment was used to compare 2 cooling pathways with and without co-digestion. We considered using CCHP to (1) displace electricity-driven refrigeration processes (e.g., milk chilling/refrigeration, biogas inlet cooling) or (2) mitigate heat stress in dairy cattle via conductive cow cooling. All cooling scenarios reduced environmental emissions compared with combined heat and power only, with an appreciable reduction in land use impacts when employing conductive cow cooling. However, none of the cooling scenarios achieved economically viability. When using cooling power to displace electricity-driven refrigeration processes, economic viability was constrained by low electricity prices and a lack of incentives in the United States. When used for conductive cow cooling, economic viability was constrained by (1) low waste heat-to-cooling conversion efficiency; (2) limited conductive cow cooling effectiveness (i.e., heat-stress mitigation); and (3) low heat stress frequency and limited severity. However, we predict that with minor improvements in conductive cow cooling effectiveness and in hotter climates, CCHP for conductive cow cooling would be economically viable even in current US energy markets.     

新疆传统乳制品中产蛋白酶乳酸菌的筛选及产酶条件优化

以新疆传统发酵乳制品为分离源,分离筛选产蛋白酶的乳酸菌,并通过形态学观察及16S rDNA序列比对鉴定菌株。以碳源、氮源、金属盐、磷酸盐的种类和添加量为影响因素,以蛋白酶活作为评价指标,通过单因素试验和正交试验优化乳酸菌产蛋白酶的产酶条件。结果表明,从样品中分离筛选出乳酸菌16株,产蛋白酶的乳酸菌4株（编号为A1～A4）,分别被鉴定为戊糖片球菌（Peciococcus pentosaceus）、发酵乳杆菌（Lactobacillus fermentum）、短乳杆菌（Lactobacillxus brevis）、乳酸明串珠菌（Leuconostoc lactis）。在以4.0%葡萄糖为碳源、4.0%牛肉膏为氮源、0.02%的镁离子为金属盐、0.7%的K2HPO4为磷酸盐的条件下,菌株A2产蛋白酶活最高为65.92 U/mL。