两株乳酸菌浓缩培养过程中的细胞凋亡研究

采用优化培养基和二次培养对保加利亚乳杆菌(L.b)和嗜热链球菌(S.t)进行了超浓缩培养,研究了超浓缩培养过程中菌体的细胞凋亡、生长曲线和乳酸浓度变化曲线。结果表明,保加利亚乳杆菌和嗜热链球菌超浓缩培养过程中存在细胞凋亡现象,与产酸规律密切相关。本研究为揭示超浓缩培养过程中保加利亚乳杆菌和嗜热链球菌的细胞凋亡机制提供了实验依据。     

全脂乳中2种乳酸菌的HPLC研究

研究了可应用于高效液相离子交换色谱分析的嗜热链球菌及保加利亚乳杆菌的培养方法,同时探讨了全脂乳中培养的乳酸菌HPLC上样菌悬液的制备方法。对全脂乳中培养不同时间的嗜热链球菌及保加利亚乳杆菌进行色谱表征,并首次发现保加利亚乳杆菌在全脂乳培养过程中菌体形态变化与色谱表征的一致性。     

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。     

茶多酚对保加利亚乳杆菌生长的影响

本文通过测定脱脂乳培养基中保加利亚乳杆菌菌体数目变化及产酸能力变化,研究茶多酚对保加利亚乳杆菌生长的影响。结果表明,高含量茶多酚对保加利亚乳杆菌酸牛乳发酵具有明显的抑制作用,低含量茶多酚抑制作用较小。随着茶多酚浓度的增加,相同发酵时间的菌体数目先增大后减小,当茶多酚添加量为2.0g/L的时候,菌体数目最多;茶多酚浓度相同时,随发酵时间的进行,酸牛乳的酸度逐渐增大,到发酵后期酸度趋于稳定,当茶多酚添加量为2.0g/L时,最终酸度最大;发酵后期,菌体形态极不稳定,大量保加利亚乳杆菌衰亡。茶多酚添加量过多,保加利亚乳杆菌产酸能力下降。而且茶多酚的颜色影响酸牛乳的色泽。     

保加利亚乳杆菌微囊化活菌制剂的研究

制备保加利亚乳杆菌的微囊化制剂。液体发酵法制备保加利亚乳杆菌,以海藻酸钠为囊材制备保加利亚乳杆菌微囊。微囊化保加利亚乳杆菌的冻干存活率为45.07%,与传统方法(冻干存活率为44.35%)相比,差异无统计学意义。人体胃液和肠液耐受性试验结果显示,在人体胃液中微囊化的菌体3 h后菌体存活率达到71.16%,而对照的存活率仅为16.47%;在人体肠液中微囊化的菌体6 h后菌体存活率达到71.67%,而对照的存活率仅为30.46%。微囊起到了保护保加利亚乳杆菌免受人体胃液和肠液破坏的作用。     

碱性中和与补料分批高密度培养保加利亚乳杆菌的研究

本实验采用葡萄糖反馈抑制补料、调节发酵液pH 值、碱性中和与补料分批复合培养等方法对保加利亚乳杆菌高密度培养进行研究。研究表明,碱性中和与补料分批复合培养条件为：保加利亚乳杆菌培养18h 和26h 时,向培养液补加碳氮比为0.67 的补料液5ml,并且每隔1.5h 调节pH 值至6.5,培养36h,培养液中保加利亚乳杆菌菌体浓度最高达9.02 × 1011CFU/ml,菌体干重达14.266g/L。     

红曲酸奶中乳酸菌变化情况研究

利用超声波浸提法提取红曲中的有效成分,将红曲水提取液与全脂奶粉混合发酵制成新型红曲酸奶。通过荧光原位杂交（FISH）技术跟踪发酵过程中乳酸菌含量的变化,结果表明：红曲酸奶中保加利亚乳杆菌和嗜热链球菌数量显著高于普通酸奶。发酵2 h时,红曲酸奶中保加利亚乳杆菌与嗜热链球菌菌体数量分别为普通酸奶的2.63和2.24倍;发酵5 h时,发酵接近终点,红曲酸奶中保加利亚乳杆菌与嗜热链球菌菌体数量分别为普通酸奶的2.29和2.75倍。红曲酸奶的保藏期可达15 d,乳酸菌数符合国家标准的要求。     

冷适应对德氏乳杆菌保加利亚亚种FL6冻干存活率及其细胞膜脂肪酸的影响

保加利亚乳杆菌作为发酵剂在食品工业方面被广泛应用,但是在其生产和使用过程中,会面临各种环境胁迫的影响,菌体细胞为了应对这些不利条件,形成了自己的适应机制,表现出了适应性。对德氏乳杆菌保加利亚亚种FL6(Lactobacillus delbruecckll ssp.bulgaricus FL6)进行不同条件的冷适应,研究其在不同冷适应温度及冷适应时间下菌体冻干存活率及细胞膜脂肪酸的变化。结果表明:德氏乳杆菌保加利亚亚种FL6经过冷适应后,与对照组相比,冻干存活率有所增加,其中4℃、8 h冷适应后,菌体冻干存活率增加显著(p0.05),达62.1%,此时菌体细胞膜中不饱和脂肪酸含量较对照组有显著增加,U/S比值最高,菌种对冻干的抵抗力增强。     

蒺藜对L.acidophilus和L.bulgaricus生长的影响

研究了不同浓度的蒺藜药液及药液离心与否对嗜酸乳杆菌和保加利亚乳杆菌生长的影响。结果表明,蒺藜药液培养嗜酸乳杆菌和保加利亚乳杆菌的最佳浓度均为0．111g／mL;药液离心对嗜酸乳杆菌的生长和药液的pH几乎没有影响;药液离心对保加利亚乳杆菌的生长和药液的pH均有较大影响,与对照相比,其菌体减少,pH升高。     

5L立瓶发酵制备益生菌直投式发酵剂及应用试验

对长双歧杆菌、保加利亚乳杆菌、嗜热乳酸链球菌在5 L立瓶中分别进行培养,确定了各自的发酵最适收获期,菌体收集后经制备所获得冷冻浓缩直投式发酵剂活菌数大于1010mL-1,冷冻干燥直投式发酵剂活菌数大于1011g-1。以制备的冷冻浓缩、冷冻干燥直投式发酵剂,进行牛乳发酵应用试验,生产的益生菌酸奶风味纯正、品质良好。     

ε－聚赖氨酸抑菌机理研究

以大肠杆菌、枯草芽孢杆菌、青霉为研究对象,考察ε-聚赖氨酸的抑菌作用。首先通过抑菌实验确定ε-聚赖氨酸对大肠杆菌,枯草芽胞杆菌的最小抑菌浓度均为25mg/L,对青霉最小抑菌浓度为200mg/L。对于不同细菌,ε-聚赖氨酸表现出相似的抑菌动力学特征。通过细胞损伤实验,研究ε-聚赖氨酸不同浓度、不同时间后对菌体造成的伤害。通过细胞形态观察以及生化检测研究ε-聚赖氨酸对细菌的抑菌机理。初步结论：当ε-聚赖氨酸作用于菌体细胞后,逐渐破坏细胞结构,最终导致细胞死亡,从而起到抑菌作用。     

PHYSICAL, PHYSIOLOGICAL AND CHEMICAL CHANGES IN POTATO AS INFLUENCED BY ERWINIA CAROTOVORA INFECTION

Bacterial soft rot, caused by Erwinia carotovora ssp. carotovora (Ecc), is a major disease in stored potatoes. The pathogen causes different physical, physiological and chemical changes in potatoes, which may affect the acceptability of raw and processed products. This study was carried out to evaluate the effect of disease severity on different physico-chemical and physiological properties of raw and cooked potatoes and to select the parameters most responsive to disease severity. Potatoes were inoculated with bacteria and incubated at 20C for different lengths of time to produce different levels of disease. As incubation time increased the volume of disease (VDS) increased, which in turn influenced the respiration rate (RR). In both raw and cooked potatoes, the physical changes (texture and color) associated with the progress of disease were reduced hardness, firmness and L value, and increased a and b values and total color difference (ΔE). The chemical changes were reduced ascorbic acid and pH, and increased reducing sugars, total sugars and titrable acidity along with the activities of peroxidase and polyphenol oxidase. The changes in physical and chemical parameters of raw and cooked potatoes during storage were described by fractional conversion equation models. All parameters were quite sensitive to disease except reducing sugars, peroxidase and PPO activity. The correlation matrix indicated that several of the quality parameters were related and thus most of them could be successfully used to predict tuber quality from disease.     

Bacterial contamination of cucumber fruit through adhesion

In this study, the adhesion of bacteria to fresh cucumber surfaces in aqueous suspension was shown to be dependent on time of incubation, inoculum species and concentration, and temperature. The adhesion of bacteria to the fruit in wash water was less extensive at lower temperatures and shorter exposure times. Various species of bacteria were adsorbed to cucumber surfaces in the following relative order: Salmonella Typhimurium > Staphylococcus aureus > Lactobacillus plantarum > Listeria monocytogenes. Cells were adsorbed at all temperatures tested (5, 15, 25, and 35 degrees C) at levels that depended on incubation time, but the numbers of cells adsorbed were larger at higher incubation temperatures. Levels of adhesion of bacteria to dewaxed fruit were higher for L. monocytogenes and lower for Salmonella Typhimurium, L. plantarum, and S. aureus than were levels of adhesion to waxed fruit.     

高产酸性能乳酸菌的筛选及产酸机理研究

为选择产酸性能优良的乳酸菌用于酸奶生产,本实验对生产酸奶常用的保加利亚乳杆菌和嗜热链球菌的产酸能力进行了研究,测定了其发酵过程中滴定酸度和pH的变化,并对其产酸机理进行了初探。研究结果表明,乳酸菌各菌株的产酸能力各不相同,菌株TM111-S产酸速度较快,pH下降速度较快,发酵凝乳最终pH较低。乳酸菌产酸能力与菌体细胞内β-半乳糖苷酶的量相关。筛选性能优良乳酸菌菌株对生产高质量的酸奶,提高工业化生产效率具有一定的意义。     

乳酸菌发酵降解牛骨粉的研究

本实验利用两种乳酸菌发酵牛骨骨粉,在不同时间下,利用乳酸菌对不同浓度和不同粒度的骨粉进行发酵实验,发现发酵后骨粉液中离子钙含量明显提高,总结出在一定时间、一定骨粉浓度下乳酸菌发酵骨粉产生离子钙的最佳条件。研究结果显示,在本实验条件下,选用乳酸菌即保加利亚乳杆菌和嗜热链球菌以2∶1比例接种发酵骨粉液的最佳生产条件是蔗糖添加量5%,乳酸菌接种量3%,骨粉粒度120目,接种骨粉浓度20%。     

Growth of Listeria monocytogenes on iceberg lettuce and solid media

The growth of pathogenic bacterium Listeria monocytogenes on fresh-cut iceberg lettuce under constant temperatures was modelled in order to investigate microbial safety during distribution of this vegetable. We examined the effects of several incubation temperatures, ranging from 5 to 25 degrees C, on bacterial growth. These data were fitted to the Baranyi model and the curves showed a high correlation coefficient at all temperature (R2 > 0.95). In addition, the native bacterial flora of the lettuce did not affect the growth rate of L. monocytogenes regardless of incubation temperature. However, the lag time was reduced at a ratio of native bacteria to inoculated L. monocytogenes (100:1) at low incubation temperatures (5 and 10 degrees C). Furthermore, the maximum population density (MPD) was increased at a low ratio of native to inoculated L. monocytogenes (1:1) at all incubation temperatures. These results were compared with the previous work published by [Buchanan, R.L., Stahl, H.G., Whiting, R.C., 1989. Effects and interactions of temperature, pH, atmosphere, sodium chloride, and sodium nitrite on the growth of Listeria monocytogenes. J. Food Prot. 52, 844-851] that is being developed at the US Department of Agriculture (USDA) Agricultural Research Service's Pathogen Modelling Program (PMP). The broth-based Buchanan model for L. monocytogenes was found to markedly deviate from the observed data. In order to investigate this discrepancy, we examined the effects of medium environment and nutrient content on L. monocytogenes growth using tryptic soy agar plates (TSAP) and agar plates (AP) containing 1.7% sucrose. The inoculated bacteria on both TSAP and AP showed slower growth rates than that predicted by the PMP. The MPD of bacteria grown on TSAP was similar to the PMP model ( approximately 9 log10 CFU/ml or plate (circle of diameter of 90 mm)) regardless of the incubation temperature. By contrast, the MPD observed on AP was approximately 4 log10 CFU lower than that observed on TSAP or predicted by the PMP. Both the growth rate and the MPD of L. monocytogenes on AP were similar to those on lettuce. These results suggest that the solid medium and poor nutrient content inhibited the growth of L. monocytogenes on lettuce. The growth rates of the inoculated L. monocytogenes on all media were described using Ratkowsky's simple square root model.     

Preliminary investigation of the combined effect of heat treatment and incubation temperature on the viability of the probiotic micro-organisms in freshly made yogurt

The combined effects of heat treatment and incubation temperature were studied on the viability and fermentation time of probiotics in ABY 1 probiotic yogurt ( Lactobacillus acidophilus , Bifidobacterium spp. and yogurt bacteria). Three levels of heat treatment (85°C for 30 min, 95°C for 5 min and 95°C for 15 min) and three levels of incubation temperature (37, 40 and 44°C) were selected. At the end of fermentation, the maximum viability of probiotics (for both L. acidophilus and Bifidobacterium spp . ) was observed when the milk was heated at 95°C for 15 min and incubated at 37°C. Incubation time was only affected by the incubation temperature and, at 37°C, the longest incubation time of about 6 h was needed to achieve the highest viable counts of L. acidophilus and Bifidobacterium spp.     

D-异抗坏血酸钠对蓝莓果酱品质的影响

为提高蓝莓果酱的品质,以蓝莓鲜果为原料,测定花色苷、总酚含量和1,1-二苯基-2-三硝基苯肼（1,1-dipheny1-2-picryl-hydrazyl,DPPH）、2,2’-联氮基-双-（3-乙基苯并噻唑啉-6-磺酸）二铵盐（2,2’-amino-di(3-ethyl-benzothiazoline sulphonic acid-6)ammonium salt,ABTS）自由基清除能力在打浆、调配、灌装、杀菌等加工关键环节的变化。研究添加D-异抗坏血酸钠对蓝莓果酱功能性成分和抗氧化活性损失的抑制作用,测定蓝莓果酱贮藏期间花色苷、总酚含量和L*、a*、b*值的变化。结果显示：蓝莓果酱各加工关键环节,其总酚、花色苷含量逐渐下降,DPPH自由基、ABTS＋·清除能力也逐渐减弱;添加质量分数0.5%的D-异抗坏血酸钠可减缓这些指标的下降;保温实验表明,添加D-异抗坏血酸钠的果酱褪色程度比未添加的果酱约降低了21.07%。由此可见,适当添加D-异抗坏血酸钠可提高蓝莓果酱的营养和形态品质稳定性,延长产品货架期。     

耐受重金属铅乳酸菌的分离筛选及鉴定

通过对包头尾矿库区、白云鄂博采矿区重金属污染严重区域土壤样品中的乳酸菌进行分离、筛选,共得到62株乳酸菌,并对分离得到的乳酸菌进行耐受铅离子的测定,62株乳酸菌对铅离子均有一定的耐受能力,不同菌株对铅离子的耐受能力有所不同;铅离子浓度为1200⁹600 mg/L时,随着培养时间的增长,菌株对耐受铅离子的修复能力逐渐增强;30℃下分离得到的菌株对铅离子的修复能力明显优于37℃下分离得到的菌株;菌株BY-Fa4、BG-5b3、BG-8b2等13株菌可在铅离子浓度为7200 mg/L的环境下生长,菌株BY-Fa1、BY-Fc2、BG-6b1可在铅离子浓度为8400 mg/L的环境下生长。实验结果得出筛选得到的13株乳酸菌对铅离子不仅具有较强的耐受能力,而且还具有较强的修复能力。对筛选出13株高耐受铅离子的菌株进行16S rRNA序列分析,鉴定结果为戊糖片球菌2株、清酒乳杆菌1株、食窦魏斯氏菌5株、戊糖乳杆菌2株、植物乳杆菌3株。      

PCR-DGGE分析东北自然发酵酸菜中的微生物多样性

为了探明传统的自然发酵酸菜中微生物的多样性和优势菌群,通过聚合酶链式反应–变性梯度凝胶电泳(polymerase chain reaction-denaturing gradient gel electrophoresis,PCR-DGGE)技术分析酸菜发酵过程中微生物群落动态变化。结果表明:东北自然发酵酸菜中的细菌种类比较丰富,真菌在酸菜中存在相对较少。东北自然发酵酸菜在发酵早期的活跃菌为明串珠菌(Leuconostoc sp.),而后是发酵产酸的嗜酸乳杆菌(L.acidophilus)、发酵乳杆菌(L.fermentum)和植物乳杆菌(L.plantarum),最后是由植物乳杆菌完成发酵过程。其中明串菌株为酸菜发酵前期优势细菌,植物乳杆菌为发酵中后期优势细菌,东北自然发酵酸菜发酵过程中主要真菌为汉逊德巴利酵母(Debaryomyces hansenii)、热带假丝酵母(Candida tropicalis)、扩展青霉(Penicillium expansum),真菌数量随发酵时间的增加而减少,且种类也随时间的变化而不断变化。