Pasteurization of milk: the heat inactivation kinetics of milk-borne dairy pathogens under commercial-type conditions of turbulent flow

This is the first study to report kinetic data on the survival of a range of significant milk-borne pathogens under commercial-type pasteurization conditions. The most heat-resistant strain of each of the milk-borne pathogens Staphylococcus aureus, Yersinia enterocolitica, pathogenic Escherichia coli, Cronobacter sakazakii (formerly known as Enterobacter sakazakii), Listeria monocytogenes, and Salmonella was selected to obtain the worst-case scenario in heat inactivation trials using a pilot-plant-scale pasteurizer. Initially, approximately 30 of each species were screened using a submerged coil unit. Then, UHT milk was inoculated with the most heat-resistant pathogens at ~10(7)/mL and heat treated in a pilot-plant-scale pasteurizer under commercial-type conditions of turbulent flow for 15s over a temperature range from 56 to 66°C and at 72°C. Survivors were enumerated on nonselective media chosen for the highest efficiency of plating of heat-damaged bacteria of each of the chosen strains. The mean log(10) reductions and temperatures of inactivation of the 6 pathogens during a 15-s treatment were Staph. aureus >6.7 at 66.5°C, Y. enterocolitica >6.8 at 62.5°C, pathogenic E. coli >6.8 at 65°C, C. sakazakii >6.7 at 67.5°C, L. monocytogenes >6.9 at 65.5°C, and Salmonella ser. Typhimurium >6.9 at 61.5°C. The kinetic data from these experiments will be used by the New Zealand Ministry of Agriculture and Forestry to populate the quantitative risk assessment model being developed to investigate the risks to New Zealand consumers from pasteurized, compared with nonpasteurized, milk and milk products.     

Thermal treatment of aseptically processed tomato paste

The heat resistance characteristics of Bacillus coagulans (NRRL B-1103) spores suspended in buffer (pH 7.0, 4.5), tomato serum and tomato paste were studied. It was found that the heat resistance of spores was reduced significantly when buffer of pH 4.5, tomato serum or tomato paste was used as suspension medium instead of buffer pH 7.0. This effect was more apparent at higher temperatures. It was concluded that a thermal process of F_105°C = 3 min is capable of causing at least 3D destruction of spores of the most heat resistant strains of B. coagulans     

酸性条件下提取的大豆多糖的流变特性

研究了酸性条件下提取的大豆多糖的理化指标及其流变特性。结果表明,质量浓度为50g／L大豆多糖溶液表现出了牛顿型流体,100g／L的溶液表现出了轻微的剪切变稀;大豆多糖溶液黏度随着质量浓度的升高而增加,随着温度的升高而降低;质量浓度为50g／L大豆多糖溶液黏度几乎不受盐离子浓度的影响,在酸性范围内其黏度随着pH的上升而有所增加,但幅度不大。     

低聚异麦芽糖乳饮料体系流变特性研究及感官评定

研究脱脂奶粉溶液体系中κ-卡拉胶、蔗糖、低聚异麦芽糖对体系黏度的影响,并对不同低聚异麦芽糖浓度的乳饮料样本进行感官评定。结果表明,低聚糖乳饮料体系的流变特性与蔗糖乳饮料体系相近,但在高浓度糖的用量下低聚异麦芽糖对体系黏度的贡献更大。而根据感官评定结果,低聚异麦芽糖用量为0.06%(m/V)时,产品可接受程度最高。在乳饮料中以低聚糖全部或部分替代蔗糖,可降低产品总热量,但同时对乳饮料品质和感官特性也有一定影响。     

大豆水溶性蛋白质含量在设定条件下变化的研究

以豆奶制作中磨浆与前处理工艺为设定条件,在不同温度、时间、pH值以及盐浓度下对豆浆进行处理,以测定大豆水溶性蛋白质含量.初步对大豆水溶性蛋白含量在豆奶加工工艺条件下的变化进行了探索,进而根据试验总结出能提高大豆水溶性蛋白质含量和质量的豆奶加工新工艺.试验确定的豆浆前处理的最佳处理工艺为:温度40℃,时间30min,pH10.00,盐浓度0.01 mol/L.     

可溶性大豆多糖在酸性乳饮料中的应用工艺条件研究

目的研究不同工艺条件对含可溶性大豆多糖的酸性乳饮料的稳定性的影响。方法以产品离心沉淀率、粒径分布以及稳定性扫描结果为指标,测定可溶性大豆多糖浓度、调酸温度、调酸终点p H和调酸前后均质工艺对产品稳定性的影响。结果样品稳定性随着可溶性大豆多糖浓度增高而上升,当大豆多糖浓度大于0.3%时稳定性随大豆多糖浓度升高变化不大;样品稳定性随着调酸温度升高而降低;样品在调酸终点p H为3.75时最稳定;对于相同大豆多糖添加量的体系,仅在调酸后进行均质的样品稳定性较好。结论对于蛋白质含量约为0.7%的酸性乳饮料,大豆多糖最优添加量为0.3%,调酸温度应在20℃以下。如果需要在调酸前增加一道均质工艺可能需要调整大豆多糖用量。酸性乳饮料稳定性受调酸终点p H影响。     

Rheological characteristics of processed whole egg

Summary. Flow curves determined with a rotational Viscometer have shown that unfrozen raw and pasteurized liquid whole egg are Newtonian fluids and that thawed frozen whole egg is pseudo-plastic. For the latter a useful value for comparative purposes may be obtained by calculating the apparent viscosity at a selected low rate of shear. Some preliminary results illustrate the very large difference in viscosity between unfrozen egg and thawed frozen egg.     

益生菌混合发酵酸豆乳的工艺条件优化

对嗜热链球菌、保加利亚乳杆菌和植物乳杆菌3种菌分别进行驯化处理,使其能够较好地适应100%纯豆乳的发酵环境。再用驯化后的3种菌混种发酵制备酸豆乳,通过单因素和正交试验确定酸豆乳的适宜发酵条件。优化得到酸豆乳的适宜发酵条件为:3种菌配比1∶1∶1、接种量5%、发酵温度40℃、发酵时间5 h。在此条件下,制备得到的发酵酸豆乳的酸度可达98.7°T,黏度为3 875 mPa·s,菌数可达5.63×108CFU/g,且凝乳效果好,无乳清析出,无豆腥味,口感细腻润滑,呈乳白色。     

Rheological behaviour of processed avocado pulp emulsions

Shear rate vs. shear stress data were obtained on avocado pulp in water emulsions using a concentric cylinder rheometer and fitted to a power law model. Dilution, as volume fraction of water, had a pronounced effect on the apparent viscosity of the pulp emulsions and the Richardson equation, (η_R= exp.( a φ) for the emulsion viscosity fitted the data well. A mean slope coefficient, a , of 4.57 can be used as a first approximation. Enzymatic treatment (40°C, 1 h), is slightly more effective than thermal treatment (65°C, 1 h), in reducing the initial apparent viscosity of the pulp-water emulsions     

不同流通间隙排布条件下碳纤维束展纤行为研究

为探究不同流通间隙排布条件下气流展纤器内部流场的分布规律及流场内碳纤维束的受力情况,采用离散单元法,将碳纤维离散为纤维微元,对流场中数千纤维微元的扩散特性进行建模。通过将纤维微元所受各力与流体阻力进行量级比较,最终得到纤维微元运动方程。结合展纤工艺设置相应边界条件,利用COMSOL对流体-纤维微元间的相互作用进行数值模拟,研究流通间隙位置对碳纤维束的运动特性的影响。结果表明,随着流通间隙间距离的增大,流场中促使纤维展宽区域的长度增长,有利于纤维持续受力展开。随着最右流通间隙到纤维出口的距离逐渐减小,阻碍纤维展宽区域的长度减小,有利于纤维束的展宽。     

豆浆中豆浆伴侣的鉴别方法研究

目的 鉴别豆浆中是否有豆浆伴侣存在。方法 制备含有不同浓度豆浆伴侣的豆浆, 加入硫酸镁, 计算沉淀凝固物的含量。结果 硫酸镁溶液不能使豆浆伴侣沉淀, 但能使大豆蛋白凝固, 进而能快速鉴别豆浆中是否含有豆浆伴侣。结论 此方法简便、可行。     

A simple, rapid and sensitive method for monitoring contamination of aseptically processed tomato paste

A simple, rapid and sensitive method for the detection of microbial contamination of the system of aseptically processing tomato paste has been developed. The method involves the rapid growth of any lactobacilli present in the product and detection of metabolites produced by these micro-organisms. The metabolites used are acetoin, diacetyl, carbon dioxide and lactic acid. It was found that with this method it is possible to detect the presence of both homofermentative and heterofermentative lactobacilli within 10–25 hr, depending on the level of contamination.     

Improving fresh and processed garlic by irradiation under different storage conditions

Hungarian garlic bulbs were irradiated with gamma rays (0.15 kGy) and stored at 20, 4 and ?20 °C for 8 months. At the end of storage period, marketable value of bulbs increased especially with those kept under low temperatures, whereas the storage at room temperature (20 °C) produced high losses in bulbs due to infestation and/or infection in unirradiated but less in irradiated samples. Gas chromatographic analysis of volatile oils revealed the presence of 18 compounds. Diallyl disulphide and diallyl trisulphide compounds were cleary identified. Irradiation induced reduction in the percentages of these compounds especially for the first one. Cold or freezing treatment preserved the volatile sulphur contents on garlic cloves at their maximum value. Also, subsequently drying of irradiated cloves resulted in better quality than those unirradiated before drying process. It is concluded that irradiation as an alternative preservation method is useful in the improvement of storeability of fresh or dried garlic bulbs during long storage period.     

Effect of antioxidants on the sensory characteristics and storage stability of aseptically processed low-fat beef gels

Beef gels, formed by heating, targeted to contain 13% protein and 16% fat and subjected to one of four antioxidant treatments, including no antioxidant, rosemary oleoresin, sodium nitrite, or sodium nitrite and rosemary oleoresin combined, were produced, aseptically processed (AP), packaged in a sterile container and stored at 3°C. The day after aseptic processing, the four AP gels and a no-antioxidant, unprocessed gel were evaluated by a trained sensory panel for textural and flavor characteristics. On days 1, 14, 29 and 42 after processing, the AP gels were evaluated for shear stress and shear strain using torsion fracture analysis, and for oxidative stability using headspace gas chromatography. Sensory results indicated significant (P < 0·10) differences in hardness, juiciness and metallic flavor between the AP and unprocessed plain gels. Among the AP gels, the panel identified differences in oxidized flavor and beef flavor due to antioxidant treatment. Differences in shear stress were found due to aseptic processing and in shear strain due to storage time. Differences in the concentrations of total aldehydes, hydrocarbons and alcohols were found due to storage time (increased with time) and antioxidant treatment (decreased with antioxidant addition). Total ketones varied due to time only and total nonheterocyclic sulfur compounds varied due to antioxidant treatment only. The use of antioxidants appears to improve the sensory characteristics and oxidative stability of AP beef gels.     

乳蛋白体系流变学研究进展

乳蛋白体系的流变学特性与乳制品的质构和生产工艺关系密切。近年来,基于乳蛋白组分在食品中的重要性,食品科学家对乳蛋白体系的流变学性质进行了深入研究。文章就乳清蛋白和酪蛋白的凝胶特性以及乳清蛋白溶液的粘度流变特性作了介绍。     

EVOH的流变性能

为研制新型PET/EVOH复合吸湿纤维,确定合理的复合纺丝工艺参数,对芯层组分EVOH熔体的流动性能进行了系统研究.结果表明,EVOH属假塑性流体,非牛顿指数小于1,表观黏度随温度的升高或剪切速率的增加呈下降趋势.与加工温度为250、260℃时相比,当EVOH在加工温度为240℃进行挤出时,非牛顿指数为0.712,最接近牛顿流体.在240、250、260℃进行挤出时,EVOH的黏流活化能在400～500 J/mol之间,且黏流活化能随剪切速率增加而增加.     

Characterisation of soy extract processed under different drying methods and extraction conditions

Soybean extract (SE), enriched in soy soluble polysaccharide (SSPS), was evaluated in three different conditions varying in extraction temperature and drying process: SE‐A ?80 °C, freeze‐dried, SE‐B ?80 °C, spray‐dried, SE‐C ?95 °C, spray‐dried. Spray‐dried SE presented lower moisture content, smaller and more uniform particles. In addition, zeta potential showed the same negative surface charge for all extracts showing the prevailing behaviour of SSPS. Moreover, all biopolymers were composed of three main molecular weight (Mw) fractions, but the Mw distribution was different between the three ingredients, reflecting their rheological behaviour in aqueous solution. Higher mean Mw led to enhanced apparent viscosity observed in neutral and acid pH for SE‐A, followed by ‐B and ‐C, respectively. The inverse behaviour was observed for intrinsic viscosity at neutral pH. However, SE‐C showed lower intrinsic viscosity at acid pH, which was attributed to protein–polysaccharide interaction presents in the solution.     

Factors affecting application of milk allantoin as an estimator of microbial protein flow to the duodenum under commercial conditions

Three experiments were conducted to determine the effect of diet change, milk sampling technique, and bovine somatotropin (bST) on allantoin output in milk and the use of allantoin as a practical, noninvasive method for estimating microbial protein flow in dairy cattle. In experiment 1, four lactating Holstein cows were used in a 2 x 2 Latin square design with two treatments (ratio of forage to concentrate) and two periods. In experiment 2, six Holstein cows were used in a completely randomized design, and milk was collected by 1) a strip sample collected immediately before milking, 2) a strip sample collected 3 min from start of milking, and 3) a composite sample taken with an autosampler. In experiment three, 10 cows were used in a randomized block design to determine the effect of bST on milk allantoin. Milk samples were taken daily for 21 d, 7 d before, and 14 d after bST administration. In experiment 1, allantoin output (mmol/d) was significantly greater for cows fed the higher ratio of concentrate to forage, and there was a significant change in the amount of allantoin in milk 12 h (first subsequent milking) after a diet change. There was no difference in milk yield or dry matter intake between treatments. In experiment 2, no difference was detected in milk allantoin concentration among the three sampling methods. In experiment 3, milk yield, allantoin concentration, and total allantoin output was significantly increased after bST administration even though dry matter intake (DMI) remained unchanged. During the first 14 d following bST administration, estimates of microbial protein production derived from milk allantoin may be inaccurate due to increased milk production without an increase in DMI.     

花生乳、豆乳饮料的品质控制

从风味、状态、营养成分和卫生质量、综合控制及管理四大方面对花生乳、豆乳的品质控制进行了较为全面的论述，并试图从作用机理上对一些现象进行深层次的探讨，以求对生产实际起到一定的指导作用。     

水溶性聚酯的流变行为

由对苯二甲酸(PTA)、乙二醇(EG)、间苯二甲酸乙二酯-5-磺酸钠(SIPE)共缩聚合成水溶性聚酯(WSP)。采用Rosand RH7型毛细管流变仪对自制WSP的流变行为进行研究。结果显示,随着温度升高,WSP剪切黏度下降,非牛顿指数增大;相同温度和相同剪切速率下WSP的剪切黏度比PET大;WSP的剪切黏度随剪切速率的变化较PET更敏感,随着剪切速率的增大WSP的黏流活化能显著降低。同时分析了第3单体SIPE和温度对WSP流变行为的影响。