乳清浓缩蛋白在酸奶生产中的应用

以鲜奶，奶粉，乳清蛋白等乳成分为主要原料，研究了乳清浓缩蛋白在酸奶生产中的制做方法，对乳清浓缩蛋白代替部分高档脱脂奶粉生产酸奶产品的保水率，粘度，口感及组织状态进行了比较分析。结果表明，在酸奶生产中，添加一定的浓缩乳清蛋白代替高档脱脂奶粉是可行的，产品较为理想。     

固相萃取-高效液相色谱-柱后衍生荧光法测定奶粉中维生素B11含量

建立了固相萃取-高效液相色谱-柱后衍生荧光法用于测定奶粉中维生素B11含量。奶粉酶解样液经固相萃取小柱纯化后,在ZORBAX SB-C18色谱柱上,以pH=3.5、浓度为0.05mol/L磷酸二氢钾-乙腈体系为流动相,流速为1.0mL/min,进样量20μL,以0.5%过硫酸钾溶液为衍生试剂,反应器温度为60℃,流速0.5mL/min,经荧光检测器(Ex=365nm,Em=440nm,增幅值100,衰减值16)检测定量。结果表明:在0.02～1.76μg/mL范围内该方法线性良好,R2=0.9999,检测限为4ng/mL,定量限为12ng/mL,灵敏度足以满足奶粉检测的需要,方法回收率在92.5%～95.7%之间,变异系数为1.32%。     

Metabolic effects in mice of cream formulation: Addition of both thickener and emulsifier does not alter lipid metabolism but modulates mucus cells and intestinal endoplasmic reticulum stress

Additives stabilize or improve the organoleptic or functional properties (or both) of many dairy products including whipping cream. Their influence on the metabolic effect of dairy cream is scarcely known. We tested the hypothesis that added emulsifier (lactic acid esters of mono- and diglycerides; MAG/DAG), thickener (carrageenan, CGN), or both, could modify the metabolic effect, notably in the intestine and liver. Nine-week-old male C57Bl/6J mice were fed UHT cream (indirect treatment) mixed with nonlipidic powder (final: 13% milkfat) for 1 or 4 wk. We compared creams (1) without additive (Ctl), (2) with thickener (Th), 0.02% of κ-CGN, and (3) with both thickener and emulsifier, 0.1% of MAG/DAG esters (Th/Em). We analyzed plasma parameters, intestine, and liver. Fasting glycemia, insulinemia, triglyceridemia, nonesterified fatty acids, body weight gain, and liver weight did not differ among groups. After 1 wk, Th/Em had higher expression in the duodenum of some of the genes involved in (1) intestinal lipid absorption and (2) tight junction proteins versus Ctl and Th. After 4 wk, mucus cell number in the small intestine was higher in Th/Em versus Ctl and Th. Genes involved in endoplasmic reticulum (ER) stress in the duodenum were more expressed in Th/Em after 1 wk. After 4 wk, in the colon, a higher expression of ER stress genes was observed for Th versus Th/Em and Ctl. Liver damage score was not altered by additives. Adding both CGN (0.02%) and MAG/DAG esters (0.1%) in dairy cream did not result in deleterious outcomes in mice after 4 wk regarding lipid metabolism, intestinal permeability, and liver disorders. The longer term effect of intestinal ER stress modulation deserves further investigation.     

Inactivation of Enterobacter sakazakii by pulsed electric field in buffered peptone water and infant formula milk

The effect of high-intensity pulsed electric field (PEF) treatment on the survival of Enterobacter sakazakii suspended in buffered peptone water (BPW) and powdered infant formula milk (IFM) was evaluated. Reference medium and IFM samples were treated with PEF. Electric field intensity and treatment time were varied from 10 to 40 kV cm⁻¹ and from 60 to 3895 μs, respectively. Samples of buffered peptone water (3 g L⁻¹) and IFM were inoculated with E. sakazakii (CECT 858) (10⁹ cfu mL⁻¹) and then treated with PEF. The inactivation data were adjusted to the Weibull frequency distribution function and Bigelow model, and constants were calculated for both substrates. A maximum 2.7 log (cfu mL⁻¹) reduction was achieved in BPW after exposure of E. sakazakii to PEF for 360 μs (2.5 μs pulse width) at 40 kV cm⁻¹. In IFM, exposure of E. sakazakii to PEF, with the same conditions, led to a 1.2 log (cfu mL⁻¹) reduction. The greater the field strength and treatment time, the greater the inactivation achieved in both substrates. Even though further research will be necessary, according to the results, there are good prospects for the use of PEF in hospitals to achieve safe reconstituted infant formula before storage at refrigerated temperatures.     

Determination of chlorine ions in raw milk by pulsed amperometric detection in a flow injection system

Chloride ion concentration in milk was determined by pulsed amperometric detection in a flow injection system. Results showed that the Au electrode lost 3 electrons at 1.10 V and formed chloroaurate ions (AuCl₄^?) by combining with chloride ions, after which AuCl₄^? was partly reduced to Au at 0.6 V. Based on the electrochemical process, a triple waveform with detection potential of 1.15 V, detection time of 150 ms, oxidation potential of 1.4 V, oxidation time of 550 ms, reduction potential of 0 V, and reduction time of 400 ms was applied to the Au electrode for detecting chloride ion concentration in milk. The approach is rapid and automatic and features a detection limit of 0.005 g/L. The relative standard deviation obtained by 60 repetitive injections reached 1.48% at 2 g/L of NaCl. The method developed using the Au electrode without modification was used to analyze the chloride ion concentration in raw milk without preprocessing. The method showed good agreement with potentiometric titration.     

Influence of a supplement containing conjugated linoleic acid on dairy performance,milk fatty acid composition,and adipose tissue reactivity to lipolytic challenge in mid-lactation goats

The objective of this work was to evaluate the effect of the supplementation of conjugated linoleic acid (CLA; 4.5 g of cis-9,trans-11 C18:2 and 4.5 g of trans-10,cis-12 C18:2) on milk performance, milk fatty acid (FA) composition, and adipose tissue reactivity in dairy goats fed a high-concentrate diet based on corn silage. Twenty-four multiparous dairy goats in early to mid lactation were used in a 10-wk trial, with a 3-wk adaptation to the experimental total mixed ration that contained corn silage (35%, dry matter basis), beet pulp (20%), barley (15%), and a commercial concentrate (30%). Goats were randomly allocated to 2 experimental groups and they were fed 45 g/d of a lipid supplement (either CLA or Ca salts of palm oil added on top of the total mixed ration). Individual milk production and composition were recorded weekly, and milk FA composition was analyzed in wk 2, 5, and 6. In the last week of the trial, an isoproterenol challenge was performed for 12 goats before morning feeding. The CLA supplementation had no effect on dry matter intake (DMI), body weight (BW), milk yield, milk protein content, and lactose yield and content, but it significantly decreased milk fat yield and content by 18 and 15%, respectively. The decrease in milk fat yield was related to a lower secretion of FA synthesized de novo, of the medium-chain FA, and to a lesser extent of the long-chain FA that are taken up from the peripheral circulation. The CLA supplementation decreased the proportion of the sum of C16:0 and C16:1 and the sum of total cis C18:1, and it increased the proportions of the sum of long-chain (C >16) and the sum of iso FA without modification of the total trans C18:1 and the sum of FA synthesized de novo (C <16). During the first 25 min relative to isoproterenol injection, the maximal concentrations, the increases above basal concentration, the changes in area under the curve, and the total area under the curve for glucose and nonesterified FA were not affected by CLA treatment. In conclusion, CLA supplementation associated with a high-concentrate diet based on corn silage resulted in decreased milk fat yield, increased net energy balance, and it did not affect the sensitivity of the adipose tissue to lipolytic challenge in lactating goats.     

牛乳蒸汽热力杀菌技术的发展历程和技术特点

通过对牛乳蒸汽热力杀菌技术的发展历程和各种加热方式进行对比和阐述,使广大读者了解蒸汽热力杀菌方式的特点,以便在无菌牛乳生产过程中进行杀菌方式的工艺设计与相关的运用。     

气相色谱-质谱法测定奶粉中香兰素的不确定度评估

目的采用气相色谱-质谱法对奶粉中香兰素含量的不确定度评估。方法建立不确定度评估的数学模型,通过对不确定度的各主要分量进行分析计算,得出合成不确定度以及扩展不确定度。结果当香兰素的测定结果为57.1 mg/kg时,其扩展不确定度为4.4 mg/kg,k=2。结论采用气相色谱-质谱法测定奶粉中香兰素含量,其不确定度的主要来源为样品的回收率和最小二乘法拟合的标准曲线,该评估模型为检测奶粉中香兰素的不确定度评估提供了参考依据。     

大豆多糖在调配型酸性乳饮料中的应用

通过改变调配型酸性乳饮料的调酸工艺之及调酸以后的处理,确定了大豆多糖SSPS(soluble soybean polysaccharide)作为稳定剂的最佳工艺参数。结果表明,蛋白质含量为1.5%的脱脂酸性乳饮料在SSPS添加量为0.6%,5℃调酸,搅拌速度为1000r/min,均质压力为30MPa下,SSPS对酸性乳饮料的稳定性最好,沉淀率最低。     

乳脂中天然生物活性物质的存在和生化特性

在充分考虑到季节变化的影响后，总结了牛乳脂肪中各种生物活性成分的含量。研究表明，牛乳脂肪中生物活性物质总的质量分数大约为75%，但要对这些生物活性物质对人体的健康的利弊进行全面的评价是较困难的。