17Beta-estradiol and estrone concentrations in plasma and milk during bovine pregnancy

Estrone (E₁) and 17β-estradiol (E₂) are present in milk, but the mechanism(s) that regulate their appearance in milk are not known. The objectives of this study were to determine the impact of stage of pregnancy on the concentrations of E₁ and E₂ in plasma and milk and to determine the correlations between plasma and milk E₁ and E₂ and with milk components throughout pregnancy. Blood and milk samples were collected from 13 cows every 28 d throughout pregnancy. The E₁ and E₂ were quantified in plasma and milk using RIA after organic solvent extractions and Sephadex LH-20 column chromatography. Plasma E₁ concentrations averaged 0.8, 16.9, and 41.8 pg/mL in trimesters 1, 2, and 3, respectively. The respective E₁ concentrations in milk averaged 0.6, 7.9, and 27.1 pg/mL. The E₂ concentrations in plasma averaged 0.5, 0.9, and 2.0 pg/mL; milk E₂ averaged 0.3, 0.9, and 5.0 pg/mL. Plasma and milk E₂ concentrations were greater in trimester 3 compared with trimesters 1 and 2. The E₁ concentrations in milk were significantly correlated with plasma E₁ concentrations (r = 0.77), percentage of milk fat (r = 0.50), and milk yield (r = −0.43). The E₂ concentrations in milk were significantly correlated with plasma E₂ concentrations (r = 0.93), percentage of milk protein (r = 0.63), and milk yield (r = −0.57). The milk-to-plasma ratio of E₂ increased from 0.4 during trimester 1 to 2.2 in trimester 3, which suggested that the mechanism(s) regulating the appearance of E₂ in milk may change over the course of pregnancy.     

High-pressure-induced interactions between milk fat globule membrane proteins and skim milk proteins in whole milk

The association of beta-lactoglobulin (beta-LG) and alpha-lactalbumin (alpha-LA) with milk fat globule membrane (MFGM), when whole milk was treated by high pressure in the range 100 to 800 MPa, was investigated using sodium dodecyl sulfate (SDS)-PAGE under reducing and nonreducing conditions. In SDS-PAGE under reducing conditions, beta-LG was observed in the MFGM material isolated from milk treated at 100 to 800 MPa for 30 min, and small amounts of alpha-LA and kappa-casein were also observed at pressures >600 MPa for 30 min. However, these proteins were not observed in SDS-PAGE under nonreducing conditions. These results indicate that beta-LG and alpha-LA associated with MFGM proteins via disulfide bonds during the high-pressure treatment of whole milk. The amount of beta-LG associated with the MFGM increased with an increase in pressure up to 800 MPa and with increasing time of pressure treatment. The maximum value for beta-LG association with the MFGM was approximately 0.75 mg/g of fat. Of the major original MFGM proteins, no change in butyrophilin was observed during the high-pressure treatment of whole milk, whereas xanthine oxidase was reduced to some extent beyond 400 MPa. In contrast to the behavior during heat treatment, PAS 6 and PAS 7 were stable during high-pressure treatment, and they remained associated with the MFGM.     

全脂牛乳粉中糖基化酪蛋白分析

研究全脂牛乳粉中糖基化酪蛋白,探讨其酶解特性。重点考察了不同pH、酸及提取方法对酪蛋白提取质量百分数的影响,并通过SDS-PAGE电泳分析酪蛋白,高碘酸—希夫碱染色法及莫氏试验鉴定糖基化酪蛋白,木瓜蛋白酶水解酪蛋白,测定其氨基酸含量。结果表明,pH 4.6时提取酪蛋白的质量百分数显著高于其他组(P0.05);质量百分数为2%的乙酸(pH 3.58)提取酪蛋白的质量百分数为(40.45±0.66)%,显著高于其他组(P0.05);鞣酸提取酪蛋白的质量百分数为(46.13±0.46)%,显著高于其他方法(P0.05);酪蛋白SDS-PAGE电泳结果表明,不同酸、不同方法提取的酪蛋白均有3条带,其分子量均分别为34,24,60ku;高碘酸—希夫碱染色结果表明,分子量为34,24ku的酪蛋白是糖基化酪蛋白;莫氏试验结果表明,乳粉酪蛋白中存在糖基化酪蛋白;酶解结果表明,乳粉酪蛋白经木瓜蛋白酶水解后游离氨基酸含量显著高于鲜乳酪蛋白(P0.05)。说明全脂牛乳粉中有糖基化酪蛋白,其分子量分别为34,24ku,易于水解。     

Fluorometric determination of beta-hydroxybutyrate in milk and blood plasma

Determination of β-hydroxybutyrate (BHBA) in blood and milk samples is an important tool in the diagnosis of ketosis in dairy cattle. Apart from semiquantitative cow-side tests, well-established laboratory methods exist for measurements in blood serum or plasma. These spectrophotometric methods are, however, neither convenient nor reliable when transferred to analyses of milk. Due to its nontransparent nature, milk needs extensive pretreatment if traditional analyses are to be used. This paper describes a fluorometric determination of BHBA that is useful without pretreatment in opaque matrices such as milk and in blood plasma. The method is easy to automate, saves labor expenses, and is inexpensive. The analytical accuracy and precision are reliable for intensive as well as large-scale analysis; for example, in-line sampling from automatic milking systems. Analysis of 2500 random milk samples showed a BHBA content ranging from 10 to 631 μM (mean 49 μM). Furthermore, selected samples (n = 295) from diagnosed ketotic animals taken on d −35 to +35 from peak level ranged from 10 to 684 μM (median 79 μM, mean 141 μM). Using the same 1240 blood plasma samples, the fluorometric method was closely correlated with a traditional spectrophotometric method (r = 0.987). Hemolysis of samples does not appear to affect the fluorometric determination of BHBA.     

Plasmin activity in pressurized milk

The effects of pressure (up to 400 MPa), applied at room temperature, on native proteinase activity of milk were investigated by means of plasmin activity, plasmin-derived activity after plasminogen activation and their distribution in different milk fractions, micelle microstructure, beta-LG denaturation, and casein susceptibility to proteolytic attack. The pressure conditions assayed did not lead to plasmin inactivation and only decreased around 20 to 30% total plasmin activity after plasminogen activation. However, pressure caused severe disruption of the micellar structure, releasing high levels of caseins, plasmin, and plasminogen to the soluble fraction of milk. High levels of soluble denatured beta-LG were also found in the ultracentrifugation supernatants of pressurized milks, particularly in those treated at 400 MPa. Probably as a result of micellar disintegration, caseins became more susceptible to proteolysis by exogenous plasmin. However, no enhanced proteolytic degradation was observed when we compared the evolution of pressurized and unpressurized milks during refrigerated storage. Serum-liberated plasmin may become more vulnerable to the action of proteinase inhibitors leading to a reduced proteolysis on refrigerated storage, despite the increased susceptibility of caseins to proteinase action.     

Antioxidant nature of bovine milk beta-lactoglobulin

Heating is necessary for processing milk in the dairy industry, which evidently produces a conformational change in β-lactoglobulin (β-LG). β-Lactoglobulin, a major protein that accounts for approximately 10 to 15% of total milk proteins, is a globular protein consisting of 162 AA with a relative molecular mass of 18.4 kDa. The purpose of the present study was to determine the antioxidant role of β-LG in milk and the possible mechanism involved. We showed that β-LG is a mild antioxidant whose potency is less than that of vitamin E and probucol (the latter being an antioxidant used for clinical therapy). The conversion of the β-LG monomer to dimer was responsible, in part, for the mode of action in protecting low-density lipoproteins against copper-induced oxidation. Cross-linking the free thiol groups of β-LG by heating (100°C for 2 min), or chemically modifying the β-LG by carboxymethylation to block the thiol groups resulted in a substantial loss of antioxidant activity. The data suggest that Cys-121 plays an essential role in the antioxidant nature of β-LG. By using an anti-LG antibody affinity column to deplete the β-LG from milk, we observed from the lost antioxidant activity that β-LG contributes approximately 50% of the total activity. Because β-LG is extremely sensitive to thermal denaturation, to maintain its antioxidant nature, dairy products consumed daily should not be overheated in order to maintain its antioxidant nature.     

Short communication: Heat treatment and souring do not affect milk estrone and 17β-estradiol concentrations

The aim of our study was to establish whether heat treatment and souring of milk affect its estrone (E1) and 17β-estradiol (E2) concentrations. Milk samples were collected from 10 Holstein cows in late pregnancy. Concentrations of E1 and E2 were measured in milk samples that were previously heated to 70 and 95°C for 5 min. Additionally, E1 and E2 concentrations were determined in the same milk samples after 2 d of spontaneous souring at room temperature, and these samples were compared with E1 and E2 levels in raw, unprocessed milk. Concentrations of both hormones were determined by commercial ELISA kits. Concentrations of E1 in unprocessed and processed milk (milk heated to 70 and 95°C and soured milk) were (mean ± SE) 47.25 ± 4.16, 44.84 ± 3.47, 41.00 ± 4.55, and 44.92 ± 3.91 pg/mL, respectively. Concentrations of E2 in the same milk samples were 36.11 ± 10.01, 32.46 ± 9.88, 31.78 ± 9.56, and 31.43 ± 8.00 pg/mL, respectively. Concentrations of E1 and E2 in heat-treated milk did not differ significantly from those in unprocessed milk. Similarly, E1 and E2 concentrations in soured milk did not differ significantly from those in unprocessed milk samples. These results indicate that E1 and E2 are stable in milk and that milk processing (heating and souring) does not influence their degradation. Therefore, E1 and E2 concentrations are expected to be similar between commercial full-fat milk and the raw milk from which it was produced.     

Short communication: extraction of beta-casein from goat milk

Peptides derived from milk β-casein have potential biological activities, such as antihypertensive and immunostimulating properties. These biological properties increase the demand for the production of specific bioactive peptides. β-Casein can be isolated directly from renneted skim milk, based on the preferential solubilization of β-casein at low temperature. This study was conducted to compare the recovery and purity of β-casein extracted from goat and cow milks. Rennet casein was prepared from both milks, heat treated, and dispersed in demineralized water at various temperatures. β-Casein recovery in the soluble phase increased with decreasing incubation temperature. Concentration of β-casein was 43% higher in goat milk than in cow milk, which had a direct effect on β-casein recovery. Furthermore, β-casein was extracted more efficiently from goat rennet casein. As a result, the extraction yield of β-casein was 53% higher in goat milk than in cow milk. The purity of β-casein extracted from both milks reached approximately 90% after incubation at 0°C.     

Configuration of a bioreactor for milk lactose hydrolysis

Permeabilized microbial cells can be used as a crude enzyme preparation for industrial applications. Immobilization and process recycling can compensate for the low specific activity of this preparation. For biomass immobilization, the common support is alginate beads; however, its low surface area and the low biomass concentration limit the activity. We here describe a biocatalyst consisting of a paste of permeabilized Kluyveromyces lactis cells gelled with manganese alginate over a semicircular stainless steel screen. A ratio of wet permeabilized biomass to alginate of 50:4 (wt/wt) resulted in a paste with maximum immobilized beta-galactosidase activity and maximum gel biomass retention. The biocatalysts retained activity better when stored in milk at 4 degrees C than in 50% glycerol. The unused biocatalysts stored in milk did not lose activity after 50 d. However, repeated use of the same biocatalyst 40 times resulted in almost 50% loss of activity. A bioreactor design with two different conditions of operation were tested for milk lactose hydrolysis using this biocatalyst. The bioreactor was operated at 40 degrees C as packed bed or with recirculation, similar to a continuous stirred tank reactor. The continuous system with recirculation resulted in 82.9% lactose hydrolysis at a residence time of 285.5 min (flow of 2.0 ml/min), indicating the potential of this system for processing low lactose milk, or even in processing other substrates, using an appropriate biocatalyst.     

Distinction between dry and raw milk using monoclonal antibodies prepared against dry milk proteins

It is well established that the heating process during the preparation of dry milk (DMLK) causes structural changes in some milk proteins. However, because such changes are subtle, whether they can be detected by an immunochemical approach remains questionable. The present study attempted to develop a sensitive mAb that might distinguish the DMLK from freshly prepared raw milk. To test this possibility, we immunized mice with commercially prepared DMLK and produced a panel of mAb. From 900 hybridomas screened using an ELISA, 4 clones were found to be specific to DMLK; the other 68 clones recognized both DMLK and raw milk. In contrast to polyclonal antibodies, only the specific mAb could detect the DMLK spiked into the raw milk at as low as 5% in concentration (vol/vol). Western blot analysis shows that these specific mAb were all directed against beta-lactoglobulin (LG) and LG-milk protein conjugates. These mAb reacted with raw milk heated at 95 degrees for 15 min; the reaction with LG-conjugates, however, was abolished when treated with reducing reagent. Thus, results suggests that a new antigenic epitope was exposed in a heating process, and the thio group of LG cross linked with other protein moiety played a provocative role in mAb recognition. A hypothetical model with respect to the interaction between the mAb and DMLK is proposed and discussed.     

全脂乳粉和脱脂乳粉在1kHz～10MHz下的介电特征研究

分别研究了各4种不同品种的全脂乳粉和脱脂乳粉在1kHz～10MHz波段的介电特性。结果发现:随着频率的增加,全脂乳粉和脱脂乳粉的ξ’和ξ″值呈单调递减趋势;全脂乳粉的ξ’和ξ″值都高于脱脂乳粉,相同类型乳粉各品种间的ξ’和ξ″差异不大;全脂乳粉的ξ″值在103～105Hz频率段减小趋势明显,且ξ″值的对数与频率的对数成线性反比关系,而脱脂乳粉无此规律;全脂乳粉和脱脂乳粉的穿透深度Dp随频率的提高而减小,两类乳粉的介电特性差异可能与它们各自的脂肪和乳糖含量有关。     

Fluorescent labeling study of plasminogen concentration and location in simulated bovine milk systems

A fluorescent labeling method was developed to study plasminogen (PG) concentration and location in simulated bovine milk. Activity and stability of PG labeled with Alexa Fluor 594 (PG-594) were comparable to those of native PG. The fluorescent signal of PG-594 exhibited pH, temperature, and storage stability, and remained stable throughout typical sample treatments (stirring, heating, and ultracentrifugation). These characteristics indicate broad applicability of the fluorescent labeling technique for milk protease characterization. In an example application, PG-594 was added to simulated milk samples to study effects of heat and β-lactoglobulin (β-LG) on the distribution of PG. Before heating, about one-third of the PG-594 remained soluble in the whey fraction (supernatant) whereas the rest became associated with the casein micelle. Addition of β-LG to the system slightly shifted PG-594 distribution toward the whey fraction. Heat-induced PG-594 binding to micelles in whey-protein-free systems was evidenced by a decrease of PG-594 from 31 to 15% in the whey fraction accompanied by an increase of PG-594 from 69 to 85% in casein micelle fractions. When β-LG was present during heating, more than 95% of PG-594 became associated with the micelle. A comparison with the distribution pattern of PG-derived activities revealed that heat-induced PG binding to micelles accompanies heat-induced PG inactivation in the micelle fraction. Incubation of the casein micelles with the reducing agent β-mercaptoethanol revealed that disulfide bonds formed between PG and casein or between PG and casein-bound β-LG are the mechanisms for heat-induced PG binding to casein micelles. Western blotting and zymography results correlated well with fluorescent labeling studies and activity studies, respectively. Theoretically important findings are: 1) when heated, serum PG is capable of covalently binding to micellar casein or complexing with β-LG in whey and then coadhering to micelles, and 2) PG that associated with micellar casein through lysine binding sites before heating is capable of developing heat-induced disulfide bonds with casein. The overall results are PG covalently binding to micelles and inactivation thereafter. Our results suggest that, instead of thermal denaturation through irreversible unfolding, covalent bond formation between PG and other milk proteins is the mechanism of PG inhibition during thermal processing.     

Effects of milk fat composition, DGAT1, and SCD1 on fertility traits in Dutch Holstein cattle

Recently, selective breeding was proposed as a means of changing the fatty acid composition of milk to improve its nutritional quality. Before implementing such breeding objectives, effects on other economically important traits should be investigated. The objectives of this study were to examine 1) the effect of milk fat composition, and 2) the effect of polymorphisms of DGAT1 and SCD1 genes on female fertility in commercial Dutch Holstein-Friesian cattle. Data on 1,745 first-lactation cows were analyzed by fitting linear mixed models. We found that higher concentrations of trans fatty acids within total milk fat negatively affected reproductive performance. Furthermore, results suggested a potential effect of the DGAT1 polymorphism on nonreturn rates for insemination 28 and 56 d after the first service. Our results can be used to assess the correlated effects of breeding for improved milk fat composition on reproduction, thereby allowing for better evaluation of breeding programs before implementation.     

Effect of temperature on raw whole milk density and its potential impact on milk payment in the dairy industry

The objective of this study was to determine the effect of temperature on whole milk density measured at four different temperatures: 5, 10, 15, and 20 °C. A total of ninety-three individual milk samples were collected from morning milking of thirty-two Holstein Friesian dairy cows, of national average genetic merit, once every two weeks over a period of 4 weeks and were assessed by Fourier transform infrared spectroscopy for milk composition analysis. Density of the milk was evaluated using two different analytical methods: a portable density meter DMA35 and a standard desktop model DMA4500M (Anton Paar GmbH, UK). Milk density was analysed with a linear mixed model with the fixed effects of sampling period, temperature and analysis method; triple interaction of sampling period x analysis method x temperature; and the random effect of cow to account for repeated measures. The effect of temperature on milk density (ρ) was also evaluated including temperature (t) as covariate with linear and quadratic effects within each analytic method. The regression equation describing the curvature and density–temperature relationship for the DMA35 instrument was ρ = 1.0338−0.00017T−0.0000122T² (R² = 0.64), while it was ρ = 1.0334 + 0.000057T−0.00001T² (R² = 0.61) for DMA4500 instrument. The mean density determined with DMA4500 at 5 °C was 1.0334 g cm⁻³, with corresponding figures of 1.0330, 1.0320 and 1.0305 g cm⁻³ at 10, 15 and 20 °C, respectively. The milk density values obtained in this study at specific temperatures will help to address any bias in weight–volume calculations and thus may also improve the financial and operational control for the dairy processors in Ireland and internationally.     

Short communication: Attempts to identify Clostridium botulinum toxin in milk from three experimentally intoxicated Holstein cows

Three adult lactating Holstein cows were injected in the subcutaneous abdominal vein with 175 ng/kg of body weight of Clostridium botulinum type C toxin (451 cow median toxic doses) to determine if this botulinum toxin crosses the blood-milk barrier. Whole blood (in sodium heparin) and clotted blood serum samples were taken at 0 min, 10 min, and 3, 6, 9, and 12 h postinoculation. Milk samples were taken at 0 min and at 3, 6, 9 and 12 h postinoculation. All samples were tested for the presence of the toxin using the mouse bioassay and immunostick ELISA test. The immunostick ELISA identified the toxin in whole blood and the mouse bioassay identified the toxin in serum at all times examined in all 3 animals. Toxin was not identified by either detection method in milk samples collected from the 3 animals. From these results, it appears that Clostridium botulinum type C toxin does not cross from the blood to the milk in detectable concentrations.     

Long-term effects of ad libitum whole milk prior to weaning and prepubertal protein supplementation on skeletal growth rate and first-lactation milk production

Our objectives were to determine the effects of rapid growth rate during the preweaning period and prepubertal protein supplementation on long-term growth pattern and milk production during the first lactation. Forty-six Israeli Holstein heifer calves were fed either milk replacer (MR) or whole milk (WM) from 4 to 60 d age. Calves had free access to WM or MR for 30 min twice daily and free-choice water and starter mix for the entire day. From weaning until 150 d of age, all heifers were fed the same ration. At 150 d of age the heifers were divided into 2 subgroups, with one subgroup supplemented with an additional 2% protein until 320 d of age. Thereafter, all heifers were housed and fed together until calving. Another cluster of 20 heifers was raised on MR and WM treatments and 3 animals from each nursery treatment were slaughtered at 60 d and 10 mo age to determine effects of nursery treatment on organ and adipose tissue mass. Prior to weaning, the MR heifers consumed 0.12 kg/d more DM than the WM heifers, but metabolizable energy intake was not different. Body weight at weaning and average daily gain during the preweaning period were 3.1 kg and 0.074 kg/d higher, respectively, in the WM treatment than in the MR treatment, with no differences in other measurements. Nursery feeding treatment and added protein had no effect on growth rate in the prepubertal period, but the postweaning difference in BW between the WM and MR heifers remained throughout the entire rearing period. The age at first insemination was 23 d earlier and age at pregnancy and first calving was numerically lower for the WM heifers than for the MR heifers. Adipose tissue weights at weaning were doubled in the WM calves. First-lactation milk production and 4% fat-corrected milk were 10.3 and 7.1% higher, respectively, for WM heifers than for MR heifers, whereas prepubertal added protein tended to increase milk yield. In conclusion, preweaning WM at high feeding rates appears to have long-term effects that are beneficial to future milk production. The positive long-term effects of feeding WM on first-lactation milk production were independent of their effects on skeletal growth. Enhanced milk production observed with WM treatment may be related to the milk supply, paracrine or endocrine effects of fat tissues on mammary parenchyma, or a combination of both factors.     

Associations of a polymorphic AP-2 binding site in the 5'-flanking region of the bovine beta-lactoglobulin gene with milk proteins

Studies on a polymorphic position (R10) in an Activator-Protein-2 (AP-2) binding site of the bovine beta-Lactoglobulin (beta-Lg) gene promoter region and quantitative traits of individual milk proteins were based on material from 79 German Holstein Friesian (HF) and 61 Simmental (Sm) cows. At least four milk samples per cow were analyzed with alkaline Urea-PAGE in combination with densitometry for quantification of individual milk proteins. The two alleles of the R10 single nucleotide polymorphism (SNP) carry either G or C in position -435 bp of the beta-Lg promoter region. G- and C-alleles were found in Sm with nearly equal frequencies, while in HF the C-allele frequency was higher (0.73) than that of the G-allele. In both breeds, the R10 G-homozygotes had higher (P < 0.001) amounts of beta-Lg secreted per day and proportion of beta-Lg in milk protein compared with the C-homozygotes. A similar association was found for alpha-lactalbumin, whereas the relative proportions and daily secreted amounts of caseins (alphaS1, beta, kappa) showed lower values in beta-Lg R10 G-homozygotes. A positive association (P < 0.001) of R10 CC with milk yield has also been observed and indicates a close proximity of the beta-Lg locus to a candidate gene for this trait. The association between the SNP in the AP-2 binding site of the beta-Lg gene and its gene product can be explained as the result of differences in protein binding activity, and, therefore, allele specific differences in gene expression. Thus, our study clearly links a DNA polymorphism of molecular function very closely with in vivo expression parameters of the same locus.     

Use of β-cyclodextrin to decrease the level of cholesterol in milk fat

This study was carried out to determine optimum conditions (β-cyclodextrin concentration, mixing time, and holding time) for cholesterol removal from pasteurized nonhomogenized milk at 4°C on a commercial scale by adding β-cyclodextrin in a specially designed bulk mixer tank. The β-cyclodextrin (0.4, 0.6, 0.8, and 1.0%) removed from 65.42 to 95.31% of cholesterol at 4°C in 20 min. Treatment of milk with 0.8 and 1.0% (wt/vol) β-cyclodextrin was no better than treatment with 0.6% β-cyclodextrin. Maximum cholesterol removal was seen with 6 h of treatment. The β-cyclodextrin cholesterol complex was precipitated from milk during 20 min without stirring at 4°C and removed by centrifugation. After separating the milk, approximately 0.35% of residual β-cyclodextrin remained in the skim fraction and 0.1% in the cream from milk treated with 0.6% β-cyclodextrin. The rest of the β-cyclodextrin was complexed with the cholesterol and eliminated via the discharger of the separator. Individual fatty acid and triglyceride compositions did not differ between control milk and milk treated with 0.6% β-cyclodextrin.     

Rapid detection of bovine milk in yak milk using a polymerase chain reaction technique

Yak milk contains a greater percentage of protein and has better quality than bovine milk. There has been an increasing focus on yak milk and milk products during the last few years. In the present study, a PCR-based assay was developed for the specific identification of bovine milk in yak milk by designing 3 primers targeting the mitochondrial ND1 gene. The use of 3 primers in a single PCR reaction set yielded 2 amplification fragments of 293 and 190 bp from bovine milk DNA, whereas only 1 amplification fragment of 293 bp was obtained in yak milk DNA. The technique was applied to raw and heat-treated binary mixtures of yak and bovine milks and enabled the specific detection of bovine milk with a detection limit of 0.1%. The assay developed is sensitive, fast, and straightforward, and it might be useful in the quality control of yak milk and milk products.     

全脂乳中2种乳酸菌的HPLC研究

研究了可应用于高效液相离子交换色谱分析的嗜热链球菌及保加利亚乳杆菌的培养方法,同时探讨了全脂乳中培养的乳酸菌HPLC上样菌悬液的制备方法。对全脂乳中培养不同时间的嗜热链球菌及保加利亚乳杆菌进行色谱表征,并首次发现保加利亚乳杆菌在全脂乳培养过程中菌体形态变化与色谱表征的一致性。