电子舌技术在橄榄油检测中应用研究进展

电子舌技术在橄榄油定性、定量检测应用中有了很大进展。综述了电子舌传感器类型以及电子舌在橄榄油检测中的主要应用,包括橄榄油理化性质与感官评价、橄榄品种、源产地鉴别与掺假识别、生物活性成分预测等,并对上述技术、方法、应用进行了归纳,最后对电子舌技术在橄榄油检测中存在的问题进行分析,并对电子舌技术在橄榄油检测中的研究方向进行了展望。     

西藏乳及发酵乳制品中乳酸菌与酵母菌分布

西藏当地牦牛乳及发酵乳制品中的微生物分布备受科研人员的关注,而且重点多集中在其中的乳酸菌和酵母菌。本文对西藏当地乳及乳制品中乳酸菌与酵母菌的分布做了详细的介绍,包括原料乳、曲拉和藏灵菇乳中的乳酸菌和酵母菌的研究现状,并对今后的发展趋势做了分析。      

Heat stability of reconstituted, protein-standardized skim milk powders

We determined the effects of standardization material, protein content, and pH on the heat stability of reconstituted milk made from low-heat (LH) and medium-heat (MH) nonfat dry milk (NDM). Low-heat and MH NDM were standardized downward from 35.5% to 34, 32, and 30% protein by adding either edible lactose powder (ELP) or permeate powder (PP) from skim milk ultrafiltration. These powders were called standardized skim milk powders (SSMP). The LH and MH NDM and SSMP were reconstituted to 9% total solids. Furthermore, subsamples of reconstituted NDM and SSMP samples were set aside to measure heat stability at native (unadjusted) pH, and the rest were adjusted to pH 6.3 to 7.0. Heat stability is defined as heat coagulation time at 140°C of the reconstituted LH or MH NDM and SSMP samples. The entire experiment was replicated 3 times at unadjusted pH values and 2 times at adjusted pH values. At an unadjusted pH, powder type, standardization material, and protein content influenced the heat stability of the samples. Heat stability for reconstituted LH NDM and SSMP was higher than reconstituted MH NDM and SSMP. Generally, decreased heat stability was observed in reconstituted LH or MH SSMP as protein content was decreased by standardization. However, adding ELP to MH SSMP did not significantly change its heat stability. When pH was adjusted to values between 6.3 and 7.0, powder type, standardization material, and pH had a significant effect on heat stability, whereas protein content did not. Maximum heat stability was noted at pH 6.7 for both reconstituted LH NDM and SSMP samples, and at pH 6.6 for both reconstituted MH NDM and SSMP samples. Furthermore, for samples with adjusted pH, higher heat stability was observed for reconstituted LH SSMP containing PP compared with reconstituted milk from LH SSMP containing ELP. However, no statistical difference was observed in the heat stability of reconstituted milk from MH NDM and MH SSMP samples. We conclude that powder type (LH or MH) and effect of standardization material (ELP or PP) can help explain differences in heat stability. The difference in the heat stability of powder type may be associated with the difference in the pH of maximum heat stability and compositional differences in the standardization material (ELP or PP).     

高效液相色谱法测定婴儿奶粉中维生素B12

建立了奶粉中维生素B12的反相高效液相色谱的测定方法,奶粉经去蛋白质-糖分-超声提取-富集浓缩超滤后进高效液相色谱仪,采用C18色谱柱,水-乙腈流动相体系,梯度洗脱能够快速有效地分离奶粉中的维生素B12.线性范围为0.010μg/mL～10μg/mL,相关系数为0.9998,检出限为0.1 μg/100g,加标回收率为78.8％～84.0％.该方法适用于实际样品的测定,速度快、成本低,结果令人满意.     

初乳、常乳及其制品中的雌性激素

简要介绍了人和牛初乳、常乳及其制品中天然雌性激素的种类、结构、含量、存在状态,并讨论了常规乳品加工对不同雌性激素的影响.     

Commercially important characteristics of Turkish origin domestic strains of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus

Thirty native (Turkish origin) strains of Streptococcus thermophilus and 24 strains of Lactobacillus delbrueckii ssp. bulgaricus were isolated and identified. These strains were examined for their technologically important properties such as acidification, proteolysis, acetaldehyde production and antimicrobial activity. By taking into consideration their phage resistant properties, two strains of S. thermophilus (St.7.7, and St.26.2) and one of L. bulgaricus, numbered as 2004, were found to have the potential to be starters for yogurt production.     

Prolonged,low-grade inflammation in the first week of lactation: Associations with mineral,protein, and energy balance markers,and milk yield,in a clinically healthy Jersey cow cohort

Our objectives were to perform a proof-of-concept study to assess the association of a prolonged inflammatory state (based on a continually elevated haptoglobin concentration at the end of the first week after parturition) with mineral, protein, and energy balance markers in the first 2 wk after parturition, and milk production in the first 60 d of lactation in clinically healthy cows. We conducted a cohort study in 1 herd in west Texas that was milking Jersey and Jersey–Holstein crosses. Only multiparous Jersey cows were eligible for enrollment. Cows were classified as having or not having elevated haptoglobin concentrations based on plasma concentrations evaluated on d 4 and 7 postpartum. We used median concentrations of haptoglobin in the reference population (i.e., before the exclusion of cows diagnosed with clinical diseases) as the limits for categorizing cows into 2 groups: cows with plasma haptoglobin concentrations greater than the median values on both d 4 (0.49 g/L) and 7 (0.35 g/L) had continually elevated haptoglobin (with eHp); and cows with plasma haptoglobin concentrations lower than or equal to the median values of the reference population on d 4 or 7 did not have continually elevated haptoglobin (without eHp). Next, cows with clinical diseases in the first 2 wk of the postpartum period were excluded, so that 233 cows remained for the final analyses. Evaluated outcomes were average daily milk production across the first 60 d of lactation, plasma Ca, Mg, and glucose concentrations on d 1, 2, 3, 4, 5, 7, 10, and 14 postpartum, and β-hydroxybutyrate (BHB), nonesterified fatty acids (NEFA), fructosamine, albumin, urea, and creatinine concentrations on d 3, 5, 7, 10, and 14 postpartum. Rectal temperatures measured on d 4, 7, and 10 postpartum were also analyzed. We performed statistical analyses using linear mixed models while accounting for the repeated effect of sampling time (plasma analytes and rectal temperature models) and weekly milk test (milk production model). Cows with eHp had lower plasma Ca concentrations in the first 2 wk after calving, but no differences in Mg, BHB, NEFA, glucose, or rectal temperatures compared to cows without eHp. Cows with eHp had lower plasma fructosamine, albumin, and urea concentrations in a time-dependent manner. They also had lower milk production (2.3 kg/d less than cows without eHp in the first 60 DIM). Our study demonstrated that 25% of cows without clinical disorders in the first 2 wk after parturition had continually elevated haptoglobin concentrations at d 7 after parturition relative to d 4, suggestive of a prolonged, low-grade systemic inflammatory state. More observational studies are needed to more fully characterize the duration of prolonged postpartum subclinical inflammation in cows without clinical diseases, as well as its long-term effects, and to evaluate the use of other potential markers of systemic inflammation to describe this disorder.     

Hypertonic milk replacers increase gastrointestinal permeability in healthy dairy calves

Hypertonic milk replacers are commonly used in animal production systems and their effect on the gastrointestinal system of young animals is insufficiently studied. Total lactose inclusion or its partial replacement with dextrose increases intestinal osmotic pressure, which may compromise gastrointestinal barrier function. In this experiment, we investigated the effect of increased osmolality of calf milk replacer (CMR) on gastrointestinal permeability in 30 Holstein Friesian (n = 17) or crossbred (n = 13) bull calves. The osmolality of CMR increased as result of a gradual replacement of lactose by monosaccharides (dextrose and galactose). Calves were acquired from dairy farms that followed a standardized protocol for colostrum management, including 3 feedings of colostrum in the first 24 h. Calves were then transported to the research facility between 0 and 3 d of age, fed a milk replacer with 0% dextrose twice daily for the first 2 wk of age, and subsequently exposed to their respective treatments from 3 until 7 wk of age. Meal size was 3.2 L at 3 wk of age and increased to 3.5 L at 7 wk of age. No solids were provided throughout the study and calves had ad libitum access to water. Treatments included 4 levels of dextrose inclusion (replacing lactose): 0% (L1, n = 5), 13.3% (L2, n = 5), 26.7% (L3, n = 5), and 40% (L4, n = 5) and an additional treatment (G+D, n = 10) that included 20% galactose and 20% dextrose and matched the galactose supply of L1 and the osmolality of L4. Carbohydrates were exchanged based on hexose equivalents. Across treatments, the estimated osmolality ranged from 439 (L1) to 611 mOsm/kg (L4 and G+D). Gastrointestinal permeability was assessed by fractional urinary recovery of indigestible markers (lactulose, d-mannitol, and Cr-EDTA) delivered as a single dose at 3 and 7 wk of age. Marker recoveries were expressed as percentage of oral dose and assessed in 6-h and 24-h quantitative urinary collections. Increasing the osmolality of the CMR linearly increased urinary Cr-EDTA and lactulose recoveries at 3 and 7 wk of age. Lactulose and Cr-EDTA recoveries did not differ between G+D and L4, suggesting that the source of monosaccharide (dextrose and galactose) in CMR had no effect on gastrointestinal permeability. The observed increase in gastrointestinal permeability to large molecules (Cr-EDTA and lactulose) with increased osmolality suggests that hypertonic CMR may compromise gastrointestinal barrier function.     

Effects of curd heating with or without previous milk pasteurisation on the microbiological quality and safety of craft‐made ‘Pasta Filata’ Kashkaval cheese curds

An empirical ‘Pasta Filata’ process used for traditional Kashkaval cheese manufacture from raw ewes’ milk improved the hygiene of fresh curd. Coagulase‐positive (RPF+) staphylococci and coliforms declined by 2.4 and 4.5 log units, respectively, and Listeria contamination was minimised. Before Pasta Filata, RPF+ staphylococci exceeded the 5‐log threshold level specified in EC Regulation 1441/2007 in raw milk curds despite the prevalence of indigenous mesophilic lactic acid bacteria. Pasta Filata favoured enterococci in raw milk curds. Pasteurisation enhanced prevalence of Streptococcus thermophilus and Lactococcus lactis starters and microbial quality and safety of pasteurised milk curds before and particularly after Pasta Filata.     

高效液相色谱法检测牛奶及其制品中的溶菌酶

目的建立一种测定牛奶及奶酪制品中低含量溶菌酶的高效液相色谱-荧光检测新方法。方法样品经p H 6.0的氯化钠溶液活化,再在低p H值条件下除蛋白后,采用反相色谱柱(PLRP-S 250 mm×4.6 mm,300?,5μm)用A水(0.1%的三氟乙酸(trifluoroacetic acid,TFA)),B乙腈(0.1%TFA)体系作为流动相进行梯度洗脱,使用荧光检测器在激发波长(λ_(ex))276 nm,发射波长(λ_(em))345 nm处检测。结果最优实验条件下,溶菌酶在2.0~30.0 mg/L浓度范围内线性良好,加标实验结果显示回收率和相对标准偏差(relative standard deviation,RSD)分别在92.3%~104.3%和0.81%~3.26%之间,对牛奶和奶酪制品的检出限分别为20和40 mg/kg。结论该方法操作简便,结果准确、可靠,可用于乳制品中溶菌酶含量测定。