Rheological, sensorial, and chemopreventive properties of milk fermented with exopolysaccharide-producing lactic cultures

The objective of this research was to evaluate the rheological, sensorial, and chemopreventive properties of milk fermented with different exopolysaccharide (EPS)-producing lactic cultures. Reconstituted skim milk (11% wt/vol) was fermented with single strains of EPS-producing and non-EPS-producing cultures. Whey that collected on the surface of undisturbed fermented milks and after cutting was measured. All EPS-producing cultures reduced the amount of whey present on the surface of the undisturbed samples, whereas only 3 out of 5 strains reduced syneresis measured after cutting. All EPS-producing cultures except a strain of Lactobacillus delbrueckii ssp. bulgaricus reduced viscoelastic moduli in fermented milk. There was a linear correlation between ropiness and smoothness. In the chemoprevention study, 140 male Fisher rats were divided into 7 groups of 20 each. Rats in 6 groups were fed diets supplemented with fermented milks each made with a single strain of EPS-producing or non-producing cultures, whereas rats in group 7 (control) were fed a diet supplemented with milk acidified with glucono-δ-lactone (GDL). All rats were injected with azoxymethane (15 mg/kg, subcutaneous) at wk 7 and 8 of age to induce tumors and fed their respective diets ad libitum throughout the study. After 30 wk of initiation, all rats were anesthetized with ether, and their intestinal tissues were isolated and washed with cold normal saline. The number and size of tumors in the colon and small intestine were recorded. Rats fed diets supplemented with fermented milk made with 2 EPS-positive and 1 EPS-negative strains had significantly lowered incidence of colon tumor and colon tumor multiplicity. Cyclooxygenase-2 enzyme activity (the enzyme implicated in colon tumor development) was significantly lower in the colon tissue of rats fed diets containing milk fermented with 4 EPS-producing and 1 non-producing cultures than that in rats fed diets supplemented with GDL-acidified milk. Different EPS-positive cultures produced fermented milks with distinct rheological characteristics and levels of ropiness. No relationship was found between rheological properties or level of ropiness of fermented milk and its chemopreventive effect.     

Thermal conductivity as influenced by the temperature and apparent viscosity of dairy products

This study aimed to evaluate the rheological behavior and thermal conductivity of dairy products, composed of the same chemical components but with different formulations, as a function of temperature. Subsequently, thermal conductivity was related to the apparent viscosity of yogurt, fermented dairy beverage, and fermented milk. Thermal conductivity measures and rheological tests were performed at 5, 10, 15, 20, and 25°C using linear probe heating and an oscillatory rheometer with concentric cylinder geometry, respectively. The results were compared with those calculated using the parallel, series, and Maxwell-Eucken models as a function of temperature, and the discrepancies in the results are discussed. Linear equations were fitted to evaluate the influence of temperature on the thermal conductivity of the dairy products. The rheological behavior, specifically apparent viscosity versus shear rate, was influenced by temperature. Herschel-Bulkley, power law, and Newton's law models were used to fit the experimental data. The Herschel-Bulkley model best described the adjustments for yogurt, the power law model did so for fermented dairy beverages, and Newton's law model did so for fermented milk and was then used to determine the rheological parameters. Fermented milk showed a Newtonian trend, whereas yogurt and fermented dairy beverage were shear thinning. Apparent viscosity was correlated with temperature by the Arrhenius equation. The formulation influenced the effective thermal conductivity. The relationship between the 2 properties was established by fixing the temperature and expressing conductivity as a function of apparent viscosity. Thermal conductivity increased with viscosity and decreased with increasing temperature.     

加工工艺对脱脂发酵乳饮料酪蛋白颗粒粒径和稳定性的影响

介绍了脱脂发酵乳饮料生产工艺中发酵条件（温度）、菌种、发酵奶均质、稳定剂对产品酪蛋白颗粒粒径大小和稳定性的影响。结果表明，MA14菌种、低温35℃长时间发酵、发酵奶均质、选择高甲氧基果胶做稳定剂均能够降低发酵乳饮料的酪蛋白颗粒粒径和离心沉淀率．提高产品的稳定性。     

3 种发酵乳制品流变性质的比较与分析

用流变仪分析评价发酵乳制品的流变学特性。分别测定以牛乳和豆乳以及二者的混合乳为原料制备的3种发酵乳制品的流变学特性。结果表明：3种发酵乳制品均是正触变性流体,其滞后环面积之比为1:0.56:0.69。黏丝性指数之比为1:0.63:0.91;恒温恒速下表观黏度初始值之比分别为1:0.99:1.28,发酵豆乳表观黏度下降速率最慢;应变扫描中发现3种发酵乳制品的稳定性从高到低依次为：发酵豆乳、发酵混合乳和发酵牛乳;在温度扫描中发现发酵豆乳耐温度变化的能力最强,发酵混合乳的表观黏度值最高。通过比较三者的流变学特性说明发酵牛乳的稳定性较差,发酵豆乳的表观黏度值较低,但其稳定性较好。发酵混合乳不仅表观黏度值较高,而且其稳定性也高于发酵牛乳。     

Effect of Wheat Bran Particle Size on Dough Rheological Properties

Commercial hard red spring, hard red winter, soft white and durum wheat brans were used to investigate the effect of wheat bran particle size on the rheological properties of doughs. Wheat brans were first coarsely ground and passed through a bran finisher to remove additional endosperm and aleurone layers. These processes increased total dietary fibre content and decreased starch content of the wheat bran samples. Three particle size distributions, for each wheat bran class, were obtained by further grinding (not by sifting) of the bran samples by different experimental mills. Coarse bran can retain significantly more water than medium or fine bran as measured by a centrifuge method, but bran particle size had no significant effect on dough water absorption. Addition of wheat bran into bread dough systems increased dough water absorption rate, reduced mixing time and decreased dough mixing tolerance as measured by farinograph. Fine particle size wheat bran decreased dough mixing tolerance and reduced mixing time compared to coarse bran. Dough containing fine particle size bran exhibited more strength than dough containing coarse bran after a 180-min rest period as measured by the extensigraph. © 1997 SCI.     

缓解铅毒性植物乳杆菌CCFM8661的微生物学 性质及其应用的研究

植物乳杆菌CCFM8661是一株具有缓解铅暴露诱导氧化应激和毒性作用的益生菌。研究了植物乳杆菌CCFM8661的微生物学性质,分析了不同环境因素如温度、pH、食盐等对其的影响,并探究了植物乳杆菌CCFM8661用于发酵乳和发酵豆奶中的应用。结果表明,植物乳杆菌CCFM8661是一株嗜温性细菌,最适生长温度在32℃,最适起始生长pH在6.5。在液体MRS培养基中在32℃条件下,最大活菌浓度为4.8×109cfu/mL。CCFM8661能耐受的最高食盐浓度为8.5%(W/W)。CCFM8661可以作为补充发酵剂用于酸乳制作,对酸乳菌种的生长无抑制作用,同时对酸乳产品的理化指标、感官与质构指标无有害影响。植物乳杆菌CCFM8661在豆乳中生长和产酸良好,可作为发酵剂用于酸豆乳的制作。     

凝固型含醇发酵乳的研制

以米酒的制作工艺为基础,采用分步发酵和混合发酵两种工艺对含醇发酵乳制作进行探讨,筛选具有最佳风味产品的工艺参数。结果表明:采用分步发酵较好,其工艺参数为:酒酿用量为16%,乳酸菌为3%,加糖量为7%,发酵温度为42,时间为3h。产品中固形物含量为12%,乙醇量达0.33%,酸度高于750T,粘度达490cP.     

Effects of feeding intensity during the dry period. 1. Feed intake,body weight,and milk production

The objective of this experiment was to study dry matter intake (DMI), body condition, milk yield, and milk composition in cows with different body condition at the time of parturition. Twenty four multiparous cows with genetic merit for high or low milk fat content were assigned to one of three diets during the dry period. The treatments consisted of 6, 9, or 14.5 kg dry matter of a total mixed ration providing 71, 106, or 177 MJ/d of metabolizable energy and are referred to as low (L), medium (M), and high (H) dry period rations, respectively. These diets were introduced when the cows were dried off from the previous lactation, at least 8 wk before expected parturition. After parturition all cows were fed another total mixed ration ad libitum. The dietary treatments generated differences between the groups in body weight as well as in body condition score at parturition. There were no differences in DMI in early lactation, but during wk 6 to 12 DMI was lower among H cows, which was linked to a prolonged negative energy balance in this group. The milk yield was 38.5 +/- 0.8 kg of energy-corrected milk the first 4 wk postpartum and did not differ between treatments or selection lines. Body weight loss mainly occurred in lactation wk 1 to 4 and was greatest in H cows. The mobilization of body tissues was reflected in a higher milk fat content of C18:0 for the H cows during wk 1 to 4. There were no marked effects of treatments on milk fat content or milk protein content, which indicates that cows in early lactation have a potential to compensate for low nutrient intake during the dry period if they are offered a high-quality diet. The observed differences between treatments in DMI wk 6 to 12 could not be explained by differences in milk yield or mobilization of body tissues. Milk fat content was 4.7% in cows with genetic merit for high milk fat content and 4.2% in cows with genetic merit for low milk fat content. There was a tendency for higher body weight in cows with genetic merit for low milk fat content throughout the experiment.     

牛羊乳蛋白质粒度对其热处理沉淀率的影响

研究牛羊乳蛋白质粒度大小对其热处理沉淀率的影响。采用离心沉淀、原子力显微镜、激光粒度仪和SDS-PAGE分析热处理后(95℃,15 min)牛羊乳蛋白质沉淀率、表面形貌、牛羊鲜乳蛋白质粒度和酪蛋白组成。结果表明:羊乳热处理后沉淀率显著高于牛乳(p0.05);羊乳蛋白质粒子明显大于牛乳,其蛋白质热处理片状凝聚程度(35 858.15 nm~2)大于牛乳(18 215.18 nm~2);鲜牛乳蛋白质粒度大小主要集中在1 nm以下,鲜羊乳蛋白质粒度在1 nm以下相对较少,主要分布在1~1 000 nm之间;牛羊鲜乳酪蛋白主要有β-酪蛋白和αs1-酪蛋白两种,相对分子质量分别为34 000和26 000左右。牛乳的热稳定性高于羊乳;蛋白质粒度大小是影响其热稳定性的直接因素;原子力显微镜结合激光粒度仪是分析乳蛋白粒度的有效手段。     

粒度分析在牛奶均质化过程中的应用

目的为确保均质化效果,采用一种快速有效的方法对牛奶均质化前后的粒度进行监控。方法利用HORIBA LA-950激光粒度分析仪对牛奶的均质化过程进行监控。结果通过激光粒度法,可以快速得到均质化前后牛奶的粒度分布图,并可以看出均质化后的牛奶粒度分布明显小于均质化前。结论在牛奶的均质化的过程中,激光粒度法是一种快速有效的方法,它可以实现对均质化过程中牛奶粒度的实时监控。     

基于脂质组学技术探究热处理和发酵对乳脂质的影响

以羊乳和牛乳为研究对象,基于脂质组学技术,利用超高效液相色谱-串联四极杆静电场轨道阱质谱检测生乳、巴氏杀菌乳、发酵后酸乳3个阶段样品的脂质特性。结果表明,所有样品共检出27种脂质亚类包含1 607种脂质分子。巴氏杀菌对牛乳和羊乳的脂质特性基本无影响,而发酵使牛乳和羊乳的脂质特性产生显著变化,尤其是大幅下调了溶血型磷脂含量;分别筛选出27种和23种脂质分子可用作鉴定巴氏杀菌处理和发酵样品的潜在生物标志物。本研究提供了牛乳和羊乳及其酸乳的脂质特性和发酵过程中的动态变化,为酸乳加工过程中热处理和发酵阶段对乳脂的影响提供了分子基础,有助于对酸乳终产品质量和营养特性的理解。     

古老而新型的酒精性发酵乳饮料—开菲尔

对一种古老而新型的酒精性发酵乳饮料－开菲尔（Ｋｅｆｉｒ）作了一般性介绍。国际上对Ｋｅｆｉｒ引起极大兴趣,并进行了深入的科学研究,取得了很大成果,本文对此作了综述。关于Ｋｅｆｉｒ的语源和定义,Ｋｅｆｉｒ的规格标准,Ｋｅｆｉｒ粒,Ｋｅｆｉｒ含有的营养成分及对人体生理功能和Ｋｅｆｉｒ制法及其进步作了叙述。     

高效液相色谱法测定传统发酵乳中的有机酸组成

利用高效液相色谱(HPLC)法研究了传统发酵乳中的7种有机酸的分离测定条件,同时对青海省传统发酵乳酸牦牛奶、酸山羊奶和酸马奶等40个样品的乳酸、乙酸和柠檬酸含量进行了测定。结果表明,选择浓度为0.010 mol/L磷酸—磷酸二氢钠(pH=2.0)和甲醇(体积比为98︰2)做流动相,流速为0.5 mL/min,紫外检测波长为210 nm时可以较好地分离测定发酵乳中的乳酸、乙酸和柠檬酸。该方法不仅相对标准偏差小(0.35%～1.23%),回收率高(95.4%～103.8%),线性相关系数高(乳酸r>0.99994,醋酸r>0.99997,柠檬酸r>0.99999),而且具有较高的准确度和精确度;通过发酵乳样品的有机酸含量测定发现,发酵乳中除主要含有乳酸外还有微量的乙酸、柠檬酸和痕量的甲酸、苹果酸、琥珀酸及丙酸。3种家畜奶发酵乳中各种有机酸含量有较大差别。     

Soya-yoghurt starter culture development from fermented tropical vegetables

The development of soya-yoghurt starter culture from fermented tropical vegetables was initiated. Soya milk fortified with 10 g litre^?1 sucrose was sterilised (121°C for 15 min) and inoculated with the exudate of fermented tropical vegetables. Acid production in the soya milk medium during incubation at 42°C for 5 h was evaluated and compared with cows' milk based cultures. Aroma of the soya milk based and cows' milk based cultures was also compared. Cultures derived from fermented cassava and corn separately reduced soya milk pH from 6′8 to 43 and 45, and significantly greater culture activity was observed in soya milk than in cows' milk. The culture from corn produced the most acceptable yoghurt-like aroma in soya milk while that from African oil bean seed produced the least acceptable aroma. The consumer-acceptable mild buttermilk-like aroma of yoghurt was not produced in soya milk or cows' milk by the cultures evaluated.     

Influence of corn silage particle length on the performance of lactating dairy cows fed supplemental tallow

The objective of this study was to determine if the length of chop of processed corn silage influences the impact of supplemental fat on rumen fermentation and performance of dairy cows. We hypothesized that increasing forage particle length may alleviate the interference of fat on rumen fermentation. Sixteen Holstein cows averaging 120 d in milk were used in a replicated 4 x 4 Latin square design with 21-d periods. Treatments were arranged as a 2 x 2 factorial with 0 or 2% tallow (dry matter basis), and corn silage harvested at either 19 or 32 mm theoretical length of cut. The forage:concentrate ratio was 50:50, and diets were formulated to contain 18% crude protein and 32% neutral detergent fiber (dry matter basis). Cows were allowed ad libitum consumption of diets that were fed twice daily as a total mixed ration. Fat supplemented cows had lower dry matter intake and produced less milk fat relative to nonsupplemented cows. No effect of corn silage particle length was observed for dry matter intake and milk fat production. Proportion of trans-10 C18:1 and of trans-10, cis-12 conjugated linoleic acid was highest in milk fat of cows fed 2% supplemental tallow. Rumen pH was not affected by feeding tallow, and tended to be highest for cows eating the 32-mm theoretical length of chop corn silage diets. No effect of treatments was observed for rumen acetate-to-propionate ratio or rumen ammonia concentration. In this study, tallow supplementation had a negative impact on performance of dairy cows regardless of the corn silage particle length. Feeding tallow increased formation of trans-fatty acids in the rumen in the absence of significant changes in the rumen environment.     

均质法控制PET奶茶脂肪上浮的研究

采用物理方法——均质法控制奶茶中脂肪上浮,研究了不同的产品均质次数和奶粉均质方式对奶茶脂肪上浮的影响。研究结果显示,产品均质次数越多,所制备产品粒径越小,但随着均质次数的增加,粒径减小的幅度减小。奶粉的均质对奶茶产品脂肪上浮没有影响。粒度测量结果与奶茶脂肪上浮趋势一致。