Effect of Butternut Squash (Cucurbita moschata) Seed Powder on the Chemical and Rheological Properties of Stirred Cultured Camel Milk and Yoghurt

Research shows that producing fermented camel milk is hard because of the milk’s inability to form a firm coagulum, attributed to low levels of κ-casein and ꞵ-lactoglobulin and the large casein micelle size, leading to a weak network of casein formation. In an effort to address this issue, researchers turned to corn starch as a thickening agent, discovering that a concentration of 2.0% effectively improved the viscosity and significantly reduced syneresis in stirred camel milk yoghurt and cultured camel milk. This study explores alternatives to corn starch, focusing on butternut squash seeds as a promising substitute due to their hydrocolloid composition. By incorporating butternut squash (Cucurbita moschata) seed powder (BSSP) as a thickening agent, this study aimed at enhancing the chemical and rheological properties of stirred camel milk yoghurt and cultured camel milk. Fermented camel milk was prepared using 4 litres of camel milk, 2% starter cultures (thermophilic culture for yoghurt and mesophilic aromatic culture for stirred cultured camel milk) and BSSP 0.0% (negative control), 0.4%, 0.8%, 1.2%, 1.6%, 2.0% mixed with 0.4% gelatin. 2.0% corn starch mixed with 0.4% gelatin was used as a standard for comparison. Results showed that increasing the BSSP level significantly (p < 0.05) decreased the moisture content while increasing the total solid content of stirred fermented camel milk products. There was an increase in ash content with an increase in BSSP levels. There was a significant (p < 0.05) reduction in the pH, with an increase in BSSP levels in stirred fermented camel milk samples. Increasing the concentration of BSSP from 0.4% to 2.0% resulted in a significant (p < 0.05) increase in viscosity and a reduction in syneresis of stirred camel milk yoghurt and stirred cultured camel milk samples. This study demonstrated that BSSP effectively enhances the viscosity, reduces syneresis and increases acidity in stirred fermented camel milk products during storage.

Antioxidant, Some Flavor Components, Microbiological and Microstructure Characteristics of Corn Milk Yoghurt

Corn milk is considered as a new innovation especially in the making of yoghurt based products. The present study was conducted to study antioxidants components such as (phenols compounds and DPPH scavenging activity), total volatile free fatty acids, microbiological and microstructure characteristics in yoghurt samples produced from two different ratios of buffalos and corn milk (70:30 coded A and 60:40 coded B) respectively. Results indicated that the increasing ratio of corn milk led to increase the content of phenolic components and DPPH scavenging activity. Total viable content decreased in samples (70:30 and 60:40). Streptococci and lactobacilli count decreased by the increase of corn milk in produced samples. Results also show that the trend of yeasts content was the opposite ones. Election microscopy examination revealed that adding corn milk to yoghurt had more smoothly and systematically distributed casein with a bit coarse structure less porosity in the network of casein. From these results could be concluded that adding 40% corn milk during processing of yoghurt is increasing the antioxidant activity and improves the microstructure as well.

Physicochemical and Organoleptic Characteristics of Manufactured Buffalo Milk Yoghurt Incorporated Soy and Corn Milks

Soy-corn-yoghurt is a fermented product that obtained from inoculation of yoghurt starter to soy corn milk. The present study was conducted to study the use of different ratios of soy corn milk and corn milk only with buffalo milk in the manufacture of yoghurt. Two experiments were carried out , the first experiment was 100 ml buffalo milk :soy corn milk ratios 90:10, 80:20, 70:30, 60:40 and 50:50 (w/w), the second was buffalo milk with Corn milk 90:10, 80:20, 70:30, 60:40, 50:50 and 40:60 respectively and 100% buffalo milk as control. Treatments were coded B1, C1, D1, E1 and F1 in the first experiment, while B2, C2, D2, E2, F2 and G2 for the second respectively. All treatments subjected to chemical and organoleptic assessment. It was found those pH, total protein, fat content were decreased with increasing the ratio of soy corn milk in the product. Also, increasing the ratio of corn milk led to decrease all the previously mentioned characteristics. Curd firmness values for yoghurt made from (70:30) coded D2 and (60:40) coded E1 were higher than that of other treatments. Results indicated that mixes of (50:50) coded F1, (60:40) coded E1 and mixes (90:10) coded B2, (80:20) coded C2 and (70:30) coded D2 had the highest sensory scores and chemical quality.

Application of Renneted Skim Milk as a Fat Mimetics in Nonfat Yoghurt

For a long time, fermented dairy products have been consumed for human’s nutrition and health. Recently, consumption of whole dairy products, such as full fat yoghurt, has declined due to the awareness of probable harmful effects of fat on consumers’ health, resulting change of market interest in favor of low or non fat dairy products. It is a challenge for food scientists to produce a suitable fat substitute providing the functionality of the missing fat. The present investigation was carried out to examine the effect of 0 to 50% renneted skim milk (RSM) as a fat mimetic upon the physico-chemical, physical, rheological and sensory characteristics of nonfat yoghurt in comparison to control samples (full fat and skim yoghurt). By increasing RSM content, the chemical characteristics (titratable acidity, pH as well as the content of fat and total protein) of yoghurts did not alter except decrease of total solid in sample with 50% RSM. The yoghurts with more content of RSM exhibited higher b*and a* values, while the highest L* value, viscosity, water holding capacity (WHC), firmness and lowest syneresis were found in sample containing 30% RSM. It seems that new interaction in gel network of yoghurts containing RSM, exhibited greater ability to bind water than control skim yoghurt. In addition, probably new bridges between milk proteins (interacting partially hydrolyzed casein with casein) can increase the number of bounds between protein particles leading to lower syneresis. However, excessive RSM content (higher than 30%) did not increase the L* value, viscosity and WHC of samples probably because of too much aggregation of casein. Sensory results revealed that sample containing 30% RSM was exactly alike to full fat yoghurt in terms of overall sensory attributes. New formulation of palatable skim yoghurt was developed using 3% RSM successfully.

Antioxidant Activities of Exopolysaccharides Produced by Lactic Acid Bacteria Isolated from Commercial Yoghurt Samples

An antioxidant is a substance that inhibits the oxidation of other molecules caused by free radicals. The inbuilt antioxidant systems possessed by living organisms are generally not enough to prevent them from oxidative damages and the uses of synthetic antioxidants also have some harmful effects. This study was aimed at evaluating the antioxidant activities of exopolysaccharides produced by lactic acid bacteria isolated from yoghurt. Lactic acid bacteria (LAB) were isolated from six different brands of commercially available yoghurt using deMan Rogosa Sharpe (MRS) agar. The LAB isolates were identified based on morphological and biochemical analyses and were screened for exopolysaccharide (EPS) production. The LAB isolates screened positive were used for EPS production in a liquid medium and the EPS produced were purified and quantified using standard methods. Antioxidant activities of the EPS were evaluated by determining the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity, ferric ion reducing power, and total phenolic contents. Data obtained were analysed using Analysis of Variance. Total lactic acid bacterial count obtained from the yoghurt samples ranged from 0 - 3.9 × 104 CFU/mL with sample A (Fan Yoghurt) having the highest LAB count (3.9 × 104 CFU/mL). The isolated LAB and their incidence rate were Lactobacillus plantarum (25.49%), L. delbrueckii (19.61%), L. fermentum (15.69%), L. acidophilus (13.73%), Leuconostoc mesenteroides (11.76%), Lactococcus lactis (7.84%), and Lactobacillus casei (5.88%). Fifty-one out of the 64 LAB isolates were screened positive for EPS production and only six were able to produce substantial quantity of EPS ranging from 127.4 - 208.5 mg/L. The exopolysaccharides produced by L. fermentum had the highest DPPH radical scavenging activity (62.90%) while that of L. plantarum had the lowest (23.10%) at a concentration of 1000 μg/mL. Also, the EPS produced by L. fermentum recorded the highest ferric ion reducing power (12.89 mg AAE/mL) at 1000 μg/mL while that of L. plantarum had the lowest (5.62 mg AAE/mL). At 1000 μg/mL, the total phenolic contents of the EPS samples ranged from 1.41 - 1.58 mg GAE/mL, and the EPS produced by L. fermentum had the highest (1.58 mg GAE/mL) while those produced by L. paracasei had the lowest (1.41 mg GAE/mL). This study revealed that the exopolysaccharides produced by the LAB isolates showed high antioxidant activities with respect to their DPPH free radical scavenging activity, ferric ion reducing power and total phenolic contents.

Perfluorinated compounds in milk, milk powder and yoghurt purchased from markets in China

The exposure to perfluorinated compounds (PFCs) through the diet for humans is of great concern. Among the diet, dairy products are in great demand. This paper reports the study on the levels of 9 perfluorinated acids and 2 fluorotelomer acids in milk, milk powder and yoghurt purchased from Chinese markets from 2008 to 2009. The analytes were quantitated by high performance liquid chromatography/electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). In milk samples, perfluoroheptanoic acid (PFHpA) and perfluorononanoic acid (PFNA) were detected frequently, both in 68% of samples. In milk powder samples, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and PFNA were the only detected PFCs and none of them was observed in more than 35% of samples. In yoghurt, PFOA was the most frequently detected compound, found in 69% of samples. None of fluorotelomer acids was observed in any samples. The mean concentrations of total PFCs were 178 pg/g (wet weight) in milk, 98 pg/g (dry weight) in milk powder and 42 pg/g in yoghurt (wet weight). It is notable that the data of this study indicate significant differences (P<0.001) among three kinds of packaging of milk in the concentration of total PFCs. A preliminary human health risk assessment of milk and dairy products consumption was conducted in this study. For adults, the mean daily intake of PFOS and total PFCs was equal to or lower than 23 and 167 pg kg-1 d-1 (body weight), respectively.

Effects of the substitution of cow’s milk with soymilk on the micronutrients,microbial,and sensory qualities of yoghurt

The consumption of imported dairy products is high especially in developing countries including Nigeria where little or no milk is produced locally which makes the products expensive,out of reach to common consumers and also inconvenient for lactose intolerance and vegans.Soymilk,as plant-based milk was substituted for cow’s milk in parts and in whole for the production of yoghurt and the effect of substitution was evaluated on the minerals,vitamins,microbial,and sensory properties of the products using the established methods.Significant differences(p<0.05)exits among the yoghurt samples in the micronutrient contents.The soymilk substitution produced yoghurts with trace/macro mineral contents’range of 0.14–28.50 mg/100 g and vitamin contents(ranged 0.02–0.43 mg/100 g)that were of comparable range of values with the yoghurt made with 100%cow’s milk(0.21–29.60 mg/100 g minerals and 0.05–0.58 mg/100 g vitamins).Generally,no significant difference(p<0.05)was observed in most of the sensory attributes evaluated(range 8.00–8.01)in the entire samples(except in the 100%soymilk yoghurt).The microbial analysis proved the safety of the entire products for consumption.These showed the positive effect of substituting soymilk for cow’s milk at all the levels used,thus,the lactose intolerance and vegans can find alternative to dairy yoghurt in the 100%soymilk substitution and enjoy the functional health benefits of yoghurt.Also,the total dependence on importation of dairy milk and cost of production of composited milk yoghurt could be reduced to improve the nation’s economy and make the product economically accessible to common man.

活性酵母对冷季泌乳牦牛产奶量、乳成分及血液指标的影响

为探讨活性酵母对冷季泌乳牦牛产奶量、乳成分及血液指标的影响,试验将16头泌乳牦牛随机分为两组,分别为对照组和活性酵母组(80 g/头·d),试验期为6周。结果显示:(1)与对照组相比,活性酵母组第18天产奶量提高了0.45 kg(P <0.05);35天乳蛋白率、乳脂肪率及乳糖率分别提高了0.68、0.49、0.11个百分点(P <0.05)。(2)与对照组相比,活性酵母组第18天血液葡萄糖(GLU)含量提高了0.26 mmol/L(P <0.01);第35天白蛋白(ALB)和甘油三酯(TG)含量分别提高了4.34 g/L(P <0.01)和0.08 mmol/L(P <0.05),尿素氮(UN)含量降低了0.55 mmol/L(P <0.01)。(3)与对照组相比,活性酵母组第18天免疫球蛋白G(Ig G)、第35天免疫球蛋白A(Ig A)和试验全程免疫球蛋白M(IgM)含量分别提高了1.26 pg/mL(P <0.05)、0.04 g/L(P <0.05)和0.23 g/L(P <0.01)。结果表明,活性酵母可通过调控瘤胃内环境和微生物区系结构,提高饲粮能量、蛋白质等营养物质消化率及利用率,进而提高机体免疫力并改善泌乳性能及乳成分。

益生菌对发酵乳品质影响的研究进展

发酵乳营养丰富、风味独特,市场发展迅速,是益生菌在食品领域的重要产品应用形式。与嗜热链球菌、德氏乳杆菌保加利亚亚种等发酵菌株相比,益生菌在主发酵过程中参与度较低,但通过协同发酵对发酵乳的质构、风味、后酸化程度等产生一定作用,影响发酵乳品质。本文综述了益生菌对发酵乳质构、风味品质、后酸化进程的影响;分析了益生菌利用代谢及产EPS维持发酵乳的质构,通过产生风味化合物改善发酵乳的风味品质,以及通过影响商业发酵剂的生长而影响发酵乳后酸化进程的相关机理;总结提出了提高益生菌在发酵乳中稳定性的相关技术,以期为功能性发酵乳的研发和品质提升提供参考。

大豆油体替代牛乳脂肪对牛乳稳定性及其酸乳品质的影响

本研究首先从大豆种籽中提取大豆油体,然后将大豆油体替代牛乳中的脂肪,探讨大豆油体替代牛乳脂肪乳在不同环境下的稳定性,最后将大豆油体替代牛乳脂肪乳进行酸乳加工,以无水奶油替代牛乳脂肪乳及牛乳进行对照,考察大豆油体替代牛乳脂肪乳对牛乳稳定性及酸乳品质的影响。结果表明,大豆油体替代牛乳脂肪乳、无水奶油替代牛乳脂肪乳及牛乳在pH 2.0和4.0时,粒径较大。在pH 2.0~10.0,大豆油体替代牛乳脂肪乳的粒径显著高于无水奶油替代牛乳脂肪乳及牛乳的粒径(P<0.05)。除200 mmol/L外,在NaCl浓度0~500 mmol/L条件下,大豆油体替代牛乳脂肪乳的平均粒径显著高于无水奶油替代牛乳脂肪乳及牛乳的粒径(P<0.05),但是3种乳液油滴均没有明显的聚集,表现较稳定。在不同热处理温度条件下,大豆油体替代牛乳脂肪乳、无水奶油替代牛乳脂肪乳及牛乳都具有较高的热稳定性。大豆油体替代牛乳脂肪乳经过6 h发酵后其pH值能达到酸乳的理想pH值4.5左右,而且用时较无水奶油替代牛乳脂肪乳及牛乳短。大豆油体替代牛奶脂肪乳发酵形成的酸乳黏度显著高于无水奶油替代牛乳脂肪乳及牛乳发酵的酸乳的黏度(P<0.05),而且酸乳的感官和质地均较好。本研究可为大豆油体替代牛乳脂肪进行乳制品加工提供参考。

五种特色乳中活性蛋白及活性肽的生物活性功能研究进展

乳制品作为人类重要的食品之一,其中所含的活性蛋白及活性肽引起了广泛关注。本综述对五种特色乳(山羊、绵羊、驴、骆驼和牦牛)中的活性蛋白及活性肽在调节免疫功能、抗氧化、抗菌以及抗肿瘤等方面的生物活性功能进行了总结。在此基础上,结合相关研究,对其在疾病预防和保健促进方面的潜在应用进行了前瞻性展望。本综述将有助于更全面地理解特色乳中活性蛋白及活性肽的功能机制,为未来相关研究提供有益参考。

乳源活性肽在功能性食品中的应用

乳源蛋白营养丰富,能够调节特定生理功能。乳源蛋白富含多种生物活性肽,生物活性肽在乳源蛋白经过特定消化过程后产生,具有独特生物活性,不同种类乳蛋白会产生具有不同性质的生物活性肽。乳源活性肽在宿主系统中具有多种有益功能,被广泛用于功能性食品和营养补充剂中。本文综述乳源生物活性肽在功能性食品抗血栓、抗高血压、抗微生物、免疫调节、延缓骨质疏松等方面应用进展,探究其功能作用及安全性,为未来乳源生物活性肽应用及开发提供参考。

乳源生物活性肽在炎症调节方面的研究进展

目的:综述乳源生物活性肽在炎症调节方面的研究进展并对其前景进行展望。方法:总结与乳源生物活性肽相关的综述及研究性论文等。结果:乳源生物活性肽可以通过调节炎症介质释放,调控炎症相关信号通路,减少氧化应激反应等来发挥炎症调节作用。结论:乳源生物活性肽具有一定的抗炎活性,其在炎症调节方面具有广阔的应用前景。

基于文献计量学可视化分析发酵乳风味研究现状

通过文献计量学方法,该研究对Web of Science核心合集及中国知网数据库中2003—2023年间发表的发酵乳风味研究文献进行了可视化分析。分析结果表明,中国(247次)、巴西(131次)、土耳其和美国(各120次)为该研究领域的主要国家。国际上埃及知识库(Egyptian Knowledge Bank,EKB)和内蒙古农业大学是目前该领域中最为重要和关键的机构,各机构合作较为紧密。国内内蒙古农业大学乳品生物技术与工程教育部重点实验室、江南大学食品学院、石家庄君乐宝乳业有限公司和云南农业大学食品科学技术学院是研究发酵乳风味领域研究的核心力量,但合作相对较少。研究热点主要聚焦于“乳酸菌”“风味物质”“发酵乳加工工艺”“风味评价”“品质与应用”等方面,未来还需加强跨机构及跨学科的合作,运用创新技术,以期开发出风味更佳且安全的发酵乳优质产品。

A2β-酪蛋白牛奶和普通牛奶的体外消化特性和抗氧化能力评价

[目的]研究体外模拟胃肠消化对A2β-酪蛋白牛奶和普通牛奶的分子量分布及抗氧化能力的影响。[方法]以巴氏杀菌A2β-酪蛋白牛奶、超高温灭菌A2β-酪蛋白牛奶、巴氏杀菌普通牛奶、超高温灭菌牛奶为原料,通过INFOGEST 2.0对牛奶进行体外模拟胃肠消化,采用SDS-PAGE、高效液相色谱仪对体外模拟胃肠消化前后的牛奶样品进行分子量分析,并对体外模拟胃肠消化后各样品的抗氧化能力进行测定。[结果]在体外模拟胃肠消化后,4种牛奶的分子量主要分布于<1000 Da组分,A2β-酪蛋白牛奶小于500 Da组分的比例显著低于普通牛奶。超高温灭菌普通牛奶、超高温灭菌A2β-酪蛋白牛奶表现出较强的铁离子还原能力和1,1-二苯基-2-三硝基苯肼(DPPH)自由基清除能力。[结论]本研究为各类牛奶产品的加工和功能特性提供基础数据。

冷链贮运条件对液态乳品质变化的影响研究

贮藏时间、温度波动一直是影响低温液态乳品质的重要原因,本试验通过模拟低温液态乳冷链贮运,研究贮藏时间、温度波动下生鲜乳和巴氏乳主要乳成分、活性蛋白、嗜冷菌及菌落总数等表征指标的变化,阐明冷链贮藏对生鲜乳、巴氏乳主要乳品质变化的影响。结果显示,生鲜乳在贮运第24h期间,8℃组嗜冷菌及菌落总数显著高于0℃组、4℃组(P<0.05),乳成分、活性蛋白含量显著低于0℃组、4℃组(P<0.05)。巴氏乳在贮藏第48~72h,15℃、20℃组乳成分、活性蛋白含量显著低于对照组、4℃组(P<0.05),嗜冷菌数及菌落总数显著高于对照组、4℃组(P<0.05),且15℃组活性蛋白含量显著高于20℃组(P<0.05)。生鲜乳及巴氏乳的对照组(CK组)不做处理,其测定值为所有指标原始量。因此,生鲜乳脱冷达8℃后,建议送达加工厂的时间控制在12h内。巴氏乳在脱冷温度达15℃、20℃时,48h内能最大限度保存低温液态乳的营养成分。

Buffalo stirred yoghurt fortified with grape seed extract:New insights into its functional properties

Grape seed extract(GSE)is considered one of the major byproducts,which are rich in phenolic content and possess several health-promoting activities including antibacterial,anticancer,and antioxidant.The current research was devoted to improve the bioactive properties of stirred yoghurt through supplementation with GSE at three concentrations(0.1,0.25,and 0.5 g/100 g yoghurt).The obtained stirred yoghurts were analyzed for determining their composition,pH,syneresis,viscosity,and sensory evaluation.Furthermore,some functional properties including antioxidant,antibacterial,anticancer activities were estimated.Significant increments(p≤0.05)were observed in total solids,ash contents,pH,water holding capacity,and viscosity values,especially when 0.5%GSE was added.Moreover,adding 0.5%GSE showed higher(p≤0.05)in vitro antioxidant,antibacterial,and anticancer activities.Interestingly,the improved bioactive properties resulting from adding GSE,even at the higher concentration,were not accompanied by any change in sensory properties.In particular,the color descriptor was mostly preferred by panelists when 0.5%GSE was added.The assessors did not observe any off-flavors in any of the tested stirred yoghurt samples.Therefore,the functional properties of stirred yoghurt could be improved by adding GSE preparation without affecting its organoleptic properties.

树莓籽粉末油脂豆奶粉制备工艺及其抗氧化活性研究

以黄豆粉、脱脂奶粉、木糖醇和树莓籽粉末油脂(RSOP)为主要原料制备RSOP豆奶粉。以感官评分为指标,通过单因素试验和响应面试验优化RSOP豆奶粉配方,并对其营养成分和抗氧化活性进行分析。结果表明:最优配方为以黄豆粉质量为基准,RSOP添加量20%、木糖醇添加量14%、脱脂奶粉添加量65%。在此条件下制得的RSOP豆奶粉均匀无结块,呈淡黄色,无豆腥和油脂气味,蛋白质含量为29.41%±2.04%,对DPPH自由基和羟基自由基具有较高的清除能力,表明RSOP豆奶粉具有较好的抗氧化活性。

新疆维吾尔自治区呼图壁县驼乳源乳酸菌分离鉴定及其对金黄色葡萄球菌的抑制作用

[目的]分离、鉴定新疆维吾尔自治区呼图壁县驼乳源乳酸菌,评价其对金黄色葡萄球菌的抑制作用。[方法]从呼图壁县某驼场采集健康驼乳样本45份,使用MRS培养基分离乳酸菌,采用细菌16S rDNA序列PCR扩增及测序方法进行分子生物学鉴定。利用点种法、琼脂斑点法和牛津杯双层琼脂扩散法筛选对金黄色葡萄球菌ATCC 29213具有抑制作用的乳酸菌。将MRS培养基的pH值调节至1~10,测定乳酸菌的耐酸能力;在MRS培养基中添加0~0.30%的牛胆盐,测定乳酸菌的耐胆盐能力。应用微量肉汤倍比稀释法测定乳酸菌无细胞上清液(cell-free culture supernatant,CFCS)对金黄色葡萄球菌ATCC 29213的最低抑菌浓度(minimum inhibitory concentration,MIC)和亚抑菌浓度(subinhibitory concentration,SIC);考查CFCS在不同pH值条件下及经酶处理后对金黄色葡萄球菌ATCC 29213的抑制作用变化,初步分析CFCS的抑菌活性物质;利用牛津杯双层琼脂扩散法测定CFCS对驼乳源和奶牛乳房炎源金黄色葡萄球菌野生株的抑制作用。[结果]从45份驼乳中分离得到5种20株乳酸菌,分别为粪肠球菌(Enterococcus faecalis,n=13)、鼠李糖乳杆菌(Lacticaseibcillus rhamnsus,n=1)、发酵黏液乳杆菌(Limosilactobacillus fermentum,n=3)、副干酪乳杆菌(Lactobacillus paracasei,n=1)和融合魏斯氏菌(Weissella confusa,n=2)。经3种方法筛选,鼠李糖乳杆菌KC4株对金黄色葡萄球菌ATCC 29213的抑菌作用最强,且具有良好的耐酸和耐胆盐特性,在pH值为4~7和牛胆盐浓度为0~0.20%的条件下均可正常生长。KC4株的CFCS对金黄色葡萄球菌ATCC 29213的MIC和SIC分别为62.5 mg/mL和7.8125 mg/mL;在pH值为2~5时仍具有抑菌效果,经过胃蛋白酶、过氧化物酶、胰蛋白酶、肽酶、蛋白酶K、过氧化氢酶和木瓜蛋白酶处理后抑菌效果极显著(P<0.01)降低;对驼源和牛源金黄色葡萄球菌野生株均具有良好的抑菌效果。[结论]在呼图壁县驼乳中筛选出1株对金黄色葡萄球菌标准菌株以及驼源和牛源金黄色葡萄球菌野生菌株均具有较强抑制作用的鼠李糖乳杆菌,具有较强的耐酸和耐胆盐能力,其抑菌活性物质可能包括酸、过氧化物和蛋白类物质等。研究结果为驼乳源乳酸菌的开发利用提供了潜在菌种资源。

氮肥调控对紫云英-水稻轮作系统结瘤固氮特征及生产力的影响

[目的]研究不同水平氮肥管理对绿肥季共生固氮、固氮酶活性及后茬单季稻养分吸收和产量的综合影响。[方法]本试验以长期紫云英-水稻轮作系统为研究对象,设置4个处理:水稻-冬闲-NO (RF-N0)、水稻-紫云英-NO (RM-N0)、水稻-紫云英-N1 (RM-N1)、水稻-紫云英-N2 (RM-N2),NO、N1、N2分别代表绿肥季施用NO、50、100 kg/hm^(2),水稻季则统一施入N200 kg/hm^(2)。进行两个轮作周期的田间试验,测定紫云英季植株氮吸收量、根瘤量、根瘤固氮酶活性及水稻季植株氮吸收、籽粒产量和品质。[结果]在绿肥季,RM-N0处理紫云英两年平均共生固氮量达N 78.3 kg/hm^(2),共生固氮率高达91.1%。与RM-N0处理相比,RM-N1和RMN2处理两年平均固氮量分别减少6.5%和50.8%,共生固氮率分别降低22.1%和72.1%。配施氮肥改善了根瘤固氮酶活性,但配施高量氮肥显著降低了紫云英根瘤重量。RM-N0处理紫云英氮吸收量为N 86.0 kg/hm^(2),与之相比,RM-N1和RM-N2处理紫云英两年平均氮吸收量分别提高25.5%和62.7%。与RF-N0处理相比,RM的3个处理水稻产量2021年提高了6.1%~10.8%,2022年提高了6.7%~10.9%。与RF-N0相比,RM-N1和RMN2处理水稻籽粒蛋白质含量分别显著提高了11.5%和21.5%,籽粒直链淀粉含量和食味值则无显著变化。与RF相比,RM的3个处理均显著抑制杂草生长,改善土壤全氮含量。紫云英根际土壤RM-N0处理AOA基因拷贝数最大,RM-N2处理AOB基因拷贝数最大,RM-N1处理nifH基因拷贝数最大。[结论]种植并翻压紫云英可显著抑制杂草生长,增加水稻产量,改善水稻品质。紫云英施用氮肥可提高其氮吸收量,改善固氮酶活性;低氮肥用量还可显著提高根瘤生物量,显著增加土壤中nifH基因拷贝数。因此,在水稻-紫云英轮作系统,紫云英季施用N 50 kg/hm^(2)可显著提升绿肥对水稻的增产提质效果,提高土壤生产力。