乳酸菌冷冻保护剂配方设计

乳酸菌浓缩发酵剂的制备过程中,冷冻对菌体的损伤比较明显。通过在保加利亚乳杆菌和嗜热链球菌混菌菌悬液中添加不同的保护剂并测定冷冻前后乳酸菌菌数,筛选出适用的保加利亚乳杆菌和嗜热链球菌混菌的保护剂。最终确定的保加利亚乳杆菌和嗜热链球菌混菌保护剂配方为:蔗糖浓度为10%,脱脂乳浓度为10%,谷氨酸钠浓度为5%。菌体经冷冻处理后,冷冻存活率可达到95.0%,比不添加保护剂的菌体存活率大大提高。此配方也简单易得,完全可以满足生产需要。     

青花椒精油对致龋菌的体外抑菌活性

为研究青花椒精油（Zanthoxylum schinifolium Siebold & Zucc. essential oils,ZSEOs）对变形链球菌、血链球菌和远缘链球菌的体外抑菌活性,采用水蒸气蒸馏法从重庆、贵州、四川、云南4 个产地的青花椒果皮中提取ZSEOs,分别记为ZS1EO、ZS2EO、ZS3EO、ZS4EO。通过全二维气相色谱-飞行时间质谱分析不同ZSEOs的化学组成,同时测定抑菌圈直径、最小抑菌质量浓度（minimum inhibitory concentration,MIC）、最小杀菌质量浓度（minimum bactericidal concentration,MBC）、致龋菌生长曲线评估ZSEOs的抑菌活性,并通过扫描电子显微镜观察ZSEOs处理后细菌的形态变化。结果表明,芳樟醇（18.86%～22.00%）、柠檬烯（9.56%～14.84%）、β-月桂烯（5.79%～12.70%）、桧烯（5.49%～8.93%）和β-蒎烯（3.33%～6.41%）在4 个产地ZSEOs中的含量均普遍较高。ZSEOs对3 种致龋菌均有一定的抑制效果,其中ZS1EO抑菌活性最强,对3 种致龋菌的MIC和MBC范围分别为0.5～1.0 mg/mL和1～2 mg/mL。在致龋菌生长的延迟期和对数生长期加入MIC ZS1EO会导致细菌停止增殖。ZS1EO的抑菌活性与细菌链状结构的破坏和细菌细胞膜的损伤有关。综上,ZSEOs可作为植物来源的潜在龋病抗菌剂。     

西藏灵菇中产胞外多糖嗜热链球菌的分离筛选及其发酵性能测定

从西藏灵菇中分离筛选、鉴定高产胞外多糖的乳酸菌菌株,并对其发酵性能和流变学参数进行测试。筛选的9株菌,菌种鉴定结果均为嗜热链球菌,其中菌株KC1、KC2、KC6、KC17产胞外多糖,菌株KC5、KC7、KC15、KC16、KC22不产胞外多糖。产胞外多糖菌株发酵乳发酵性能、黏度和黏附性指标均明显高于不产胞外多糖的嗜热链球菌,进一步证实了嗜热链球菌产生的胞外多糖可以赋予发酵乳良好的质地。     

低聚木糖对酸奶菌株生长及产酸的影响

研究了益生元——低聚木糖及酸奶菌株比例对酸奶发酵过程中总菌数、pH值及酸度的影响。低聚木糖质量分数为0,0.5%,0.6%,0.7%,0.8%,0.9%,1.0%,保加利亚乳杆菌和嗜热乳链球菌的比例(Lb∶St)分别为2∶1,1∶1和1∶2。结果表明:Lb∶St的最佳比例为1∶1,低聚木糖的最适添加量为0.8%,42℃发酵3.5h,总菌数达到最大值为7.14×108CFU/mL(对照为5.92×108CFU/mL),pH值为4.51(对照为5.09),酸度达到72°T(对照为64°T),乳酸量为6.45mg/mL(对照为5.77mg/mL)。低聚木糖的添加可促进酸奶发酵菌株的生长,促进产酸和缩短发酵时间。     

Subclinical and clinical mastitis in heifers following the use of a teat sealant precalving

This study investigated the effect in heifers of infusion of a bismuth subnitrate teat-canal sealant and bacterial intramammary infection (IMI) precalving on prevalence of postcalving IMI and incidence of clinical mastitis in the first 2 wk postcalving. Glands (n = 1,020) from heifers (n = 255) in 5 seasonally calving, pasture-fed dairy herds were randomly assigned within heifer to 1 of 4 treatment groups (no treatment; mammary gland secretion collection; infusion of a teat sealant; or sample collection with infusion of teat sealant). Heifers within a herd were enrolled on one calendar day, 31 d on average before the planned start of the seasonal calving period. Duplicate milk samples were collected from each gland within 4 d after calving for bacterial culture. Herd owners collected duplicate milk samples, before treatment, for bacterial culture from glands they defined as having clinical mastitis. The gland prevalence of IMI precalving was 15.5% and did not differ between herds. Bacteria isolated precalving included coagulase-negative staphylococci (76.9% of all bacteriologically positive samples), Streptococcus uberis (14.1%), Staphylococcus aureus (5.1%), Corynebacterium spp. (3.8%), and others (0.1%). The presence of an IMI precalving increased the risk of an IMI postcalving 3.6-fold and the risk of clinical mastitis 4-fold, relative to no IMI precalving. Infusion of the teat sealant reduced the risk of postcalving IMI due to Strep. uberis by 84%, and of clinical mastitis by 68%. Sampling the glands precalving had no effect on postcalving IMI or on clinical mastitis incidence. Use of an internal teat canal sealant in heifers precalving may be a useful tool for reducing the risk of subclinical and clinical mastitis in heifers.     

嗜酸乳杆菌和乳酸链球菌混合培养及产物分析

嗜酸乳杆乳菌(LA)和酸链球菌(SL)在33℃培养48 h的发酵液中抑菌(金黄色葡萄球菌ATCC25923)效果最好;2菌混培20h后生物量和体系总产酸量远大于各自纯培养,乳酸含量一直上升,到24 h达23.175 mg/L,乙酸含量一直稳定在12 mg/L左右,变化不大,乳酸与抑菌关系密切。LA和SL两菌混培接种比例的抑菌优先顺序为(1:1)、(2:1)、(1:2)。     

Biochemical and thermal properties of β-galactosidase enzymes produced by artisanal yoghurt cultures

β-Galactosidases, produced by pure and mixed cultures of Streptococcus thermophilus 95/2 (St 95/2) and Lactobacillus delbrueckii ssp bulgaricus 77 (Lb 77) isolated from the Toros mountain region of Turkey, were characterised with respect to their biochemical and thermal properties. Optimum pH and temperature for maximum activity were determined and these enzymes were stable in the pH range 7–9 and in the temperature range 20–37 °C, retaining 80–90% of their initial activities. The inactivation energies of β-galactosidase from Lb 77, St 95/2 and mixed culture (Lb 77 and St 95/2) were 51.3, 44.0 and 48.3 kcal mol⁻¹, respectively. Moreover, thermodynamic (ΔG, ΔS, ΔH) and kinetic constants (K_m and V_max) were determined and effects of metal ions were investigated. As a result, these enzymes could be considered as potential candidates for lactose hydrolysis of milk and milk products.     

Monitoring biofilm development in a microfluidic device using modified confocal reflection microscopy

The feasibility of a method to monitor biofilm development non-destructively in a microfluidic device was addressed. Here, we report that biofilm growth could be non-destructively monitored by an image analysis technique based on modification of confocal reflection microscopy.     

微生物法在原料奶验收中的应用

对微生物法的应用进行了研究。采用对抗生素最敏感的嗜热链球菌,从产酸能力和凝乳时间两个因素来检测牛乳中抗生素的残留,并定量得出该嗜热链球菌的最低检出量为0．04单位。结果表明,该方法操作简便。     

无乳链球菌产CMP-唾液酸合成酶发酵培养基优化

为获得低成本高酶活的产CMP-唾液酸合成酶(Cytidine 5'-monophosphate N-acetylneuraminic acid synthetase,NmCSS)培养基,对无乳链球菌(Streptococcus agalactiae)产CMP-唾液酸合成酶发酵生产培养基进行优化。通过单因素试验筛选发酵温度、碳源、氮源、pH,确定对NmCSS酶活具有明显影响的因子及水平值;采用响应面法(Box-Behnken)确定以氮源浓度、碳源浓度、pH为三个主要影响因子的最适条件。结果表明,当培养温度为34℃时,蔗糖浓度为0.10%,氮源浓度为2.50%,pH为7.5、Na₂HPO₄ 2.5 g/L、NaCl 5.0 g/L时,NmCSS酶活为(5.895±0.005)×10⁷ U/mol,较基础发酵培养基的酶活(0.507±0.002)×10⁷ U/mol提高了10.627倍,显示出了良好的优化效果。响应面方法优化得到的低成本高酶活培养基为无乳链球菌产NmCSS及其应用奠定了基础。