嗜酸乳杆菌生长促进物质研究

为提高嗜酸乳杆菌活菌数,工业化生产嗜酸乳杆菌冻干菌粉,通过测定嗜酸乳杆菌发酵液的吸光度和活菌数,采用优选法研究了不同生长促进物质对嗜酸乳杆菌活菌数的影响。结果表明:在11%(m/m)的脱脂乳中加入麦芽汁、番茄汁、酵母膏、真菌浸汁、胡萝卜汁能显著促进嗜酸乳杆菌的生长,蛋白胨、葡萄糖次之,麦芽糖几乎无促进效果。因此,以脱脂乳为基础培养基,嗜酸乳杆菌的最佳生长促进物质的组合为0.5%(m/m)酵母膏、5%(V/V)番茄汁、5%(V/V)真菌浸汁、12%(V/V)胡萝卜汁和5%(V/V)麦芽汁,在此条件下其活菌数可达5.46×109cfu/mL。     

嗜酸乳杆菌应用高质量分数脱脂乳的发酵工艺优化

将筛选出的嗜酸乳杆菌接种于25%的高质量分数脱脂乳中发酵,在单因素pH值、温度以及接种量试验的基础上,采用响应面法优化发酵工艺,获得高浓度的嗜酸乳杆菌活菌。结果表明:高质量分数25%脱脂乳培养基对菌株的生长有一定促进作用,得到高活菌数嗜酸乳杆菌的最佳发酵工艺为发酵pH值为5.81、发酵温度37.30℃、接种量3.18%,活菌数可达2.78×109mL-1。     

西红柿益生菌酸乳的研制

利用鲜牛乳和番茄汁为原料,通过添加嗜酸乳杆菌发酵来制备西红柿益生菌酸乳;通过测定活菌数和感官评定确定了番茄汁最适的添加量,测定了嗜酸乳杆菌的发酵特性,发酵结束后在4℃下贮存,在此过程中测定了嗜酸乳杆菌的存活状态及贮存过程中酸度和pH的变化,分析了番茄汁对嗜酸乳杆菌发酵的影响.实验结果表明,蔗糖添加量为8%,嗜酸乳杆菌发酵剂的接种量为45,发酵温度为37℃,发酵时间为9h,可以得到呈浅红色,状态均匀,酸甜适口的西红柿益生菌酸乳,40C下贮存10d后嗜酸乳杆菌活菌数仍达107cfu/mL以上.     

嗜酸乳杆菌L101发酵增殖因子的研究

为促进嗜酸乳杆菌L101的生长,本研究以MRS为基础培养基,选取添加6种增殖因子(番茄汁、胡萝卜汁、平菇汁、黄豆芽汁、啤酒和低聚异麦芽糖),单因素试验比较了各因子增殖作用,正交试验研究选取促进活菌数提高的最佳增殖因子组合.试验结果表明:黄豆芽汁在各单因子中增殖效果最佳,当其在MRS培养基中添加浓度为10%(V/V),菌体在38℃下培养14 h时,活菌数可达4.034×109℃FU/ml;经正交试验所得最佳复合增殖因子组合为:黄豆芽汁5%(V/V)、平菇汁1O%(V/V)、番茄汁10%(V/V)和低聚异麦芽糖(10g/L).嗜酸乳杆菌L101在添加了该增殖因子组合的MRS培养基内培养14 h时,活菌数可达5.25×1O10CFU/ml.本研究为进一步提高嗜酸乳杆菌L101活菌数提供了必要的工艺参数.     

嗜酸乳杆菌的筛选及培养基的优化

通过模拟正常人体胃内状态,筛选出10株耐酸耐胆盐的嗜酸乳杆菌。针对嗜酸乳杆菌的营养需要,采用正交实验优化基础培养基及增殖因子的用量,得出最佳基础培养基配比:蛋白胨1%,葡萄糖0.5%,大豆低聚糖1.5%,酵母膏1.0%(均为质量分数);最佳增殖因子添加量为西红柿汁12%。最后使用优化出的增菌培养基测定生长曲线,同时测定pH值和OD值的变化确定增菌培养终止时间为16h,通过平板菌落计数,此时菌数可达2.2×1012mL-1。     

酸乳菌种分离纯化方法

本文研究了在脱脂乳中保藏的发酵酸乳菌种的分离纯化方法。确定了德氏乳杆菌保加利亚亚种的分离纯化培养基为改良MRS,以10-2稀释度划线分离法在烛缸中厌氧培养可以达到很好的分离效果,添加2%的玉米浆后有利于纯菌株的生长;采用涂布分离法和真空袋培养,在链球菌基础培养基上可很好地分离出唾液链球菌嗜热亚种的纯菌株。经鉴定所分离出菌株为纯种后,采用斜面保藏在不含乳基质的培养基上,在15d内可以保持其活力。     

豌豆蛋白酶解产物促进益生菌生长活性研究

研究豌豆蛋白酶解产物(PPH)对17株常见益生菌在普通液体培养基及脱脂乳培养基中生长的影响。比较这17株益生菌在含有PPH的MRS培养基和不含PPH的MRS培养基中的菌体密度、活菌数和发酵液pH值,结果发现添加4mg/mL的PPH,可显著改善干酪乳杆菌、保加利亚乳杆菌、嗜酸乳杆菌和双歧杆菌等益生菌在MRS培养基中的生长,其菌体密度提高10.78%～49.34%,活菌数提高1～3个数量级,发酵液的pH值显著降低;然而其对植物乳杆菌、鼠李糖乳杆菌和嗜热链球菌的生长无明显影响。比较这17株益生菌在含有PPH的10%脱脂乳培养基和不含PPH的10%脱脂乳培养基中的活菌数和pH值,结果发现这些菌在含有PPH的10%脱脂乳培养基中的生长均优于不含PPH的10%脱脂乳培养基中的生长, pH显著下降,经特定时间发酵后的活菌数显著提高。经24 h发酵,PPH对鼠李糖乳杆菌W119的促生长作用最强,能使其活菌数从4.23×108提高到7.47×1011,发酵液pH值从5.83降到4.90。综上所述,豌豆蛋白酶解产物可显著促进益生菌的生长,提高益生菌的存活率,缩短益生菌的生产时间。     

快速功能性嗜酸乳杆菌发酵乳的研制

对功能性嗜酸乳杆菌和嗜热链球菌混合菌种发酵乳的最佳生产工艺条件进行研究。结果表明:嗜酸乳杆菌和嗜热链球菌以1∶1配合、添加6%的蔗糖和适量的蛋白糖、9%的接种量、41℃5h培养生产出具有酸奶特有的质地和风味,嗜酸乳杆菌活菌数为2.9×107cfu/mL,保藏期为12d的功能性发酵乳。与单一嗜酸乳杆菌发酵乳的生产周期18h相比,缩短了13h,且风味更佳。     

嗜酸乳杆菌增菌培养基的确定

实验从嗜酸乳杆菌增菌培养基基质的确定以及碳氮源的筛选等方面研究,优化了的最佳增菌培养基,即脱脂乳10% 酶解乳清6%,葡萄糖1.6%,大豆蛋白胨0.5%,酵母粉0.7%,西红柿汁12%,平菇汁12%,啤酒16%。在此增菌培养基上进行发酵试验,结果菌数可达到8.3?09cfu/ml。     

嗜酸乳杆菌增菌培养研究

对培养嗜酸乳杆菌的基础培养基进行筛选,确定为11％NFM培养基。采用正交试验对增殖因子进行优化,得到最优增菌培养基:基础培养基+5％番茄汁+10％萝卜汁+0.1％肝浸汁+5％啤酒。以最优增菌培养基测定生长曲线、pH值和滴定酸度的变化,确定增菌培养终止时间为10hr,此时活菌数达7.49×10~9cfu/ml。     

酸乳储藏中双歧杆菌活性影响因素研究

以改良MRS液体培养基为保存基质,以双歧杆菌活菌数为考查指标,针对酸乳特性研究了基质起始pH、冷藏温度及混合菌种3因素对双歧杆菌活性的影响。结果表明:(1)不同的基质起始pH值对双歧杆菌存活的影响极显著,基质起始pH5.5时对双歧杆菌活性的影响最小,并且起始pH值提高到5.5可使双歧杆菌保持最小保健剂量(106cfu/mL)的时间延长至20d。(2)当基质起始pH为4.6时,双歧杆菌在4℃保存与在室温(25℃)保存活性情况基本一致。(3)双歧杆菌无论以单一菌种形式保存还是与嗜酸乳杆菌以1:1的比例混合保存,其活性情况无明显变化,即嗜酸乳杆菌对双歧杆菌无明显的促进或抑制作用。     

SURVIVAL AND GROWTH OF ACID ADAPTED ESCHERICHIA COLI STRAINS IN BROTH AT DIFFERENT PH LEVELS

Acid resistance of Escherichia coli O157:H7 strain UT 10 and Escherichia coli ATCC 25922 was determined in brain heart infusion broth at pH 7.4, 4.5 and 2.5. Variations due to acid stress in the counts of both strains were also determined. Acid adaptation enhanced the survival of both strains at pH 4.5, but neither strain could survive after 4 h at pH 2.5. At optimum growth conditions (pH 7.4), E. coli ATCC 25922 exhibited increased viability over E. coli UT 10. At pH 4.5, E. coli UT 10 was more tolerant to low pH than E. coli ATCC 25922. An increase in saturated fatty acids of both AA strains was observed, indicating the importance of lipid modification in enhancing survival at low pH. The results of this study indicated that the food industry should therefore adapt their processing/preservation procedures by taking the most acid tolerant pathogenic E. coli strains into consideration in order to ensure the safety of their products.

PRACTICAL APPLICATIONS

The study will enlighten the industry on the survival of acid adapted pathogens such as E. coli O157:H7 at low pH. It also indicates that current measures used in the preservation of low pH foods can trigger acid adaptation. For this reason, the effectiveness of current preservation measures in controlling foodborne pathogens should be reassessed. The importance of using cells adapted to different pH values in food challenge studies is also highlighted. Since fermented foods, which are generally regarded as safe, have been implicated in foodborne disease outbreaks, more attention should be given to the prevention of contamination of foods with pathogens such as E. coli O157:H7 since they may survive in low pH foods and cause disease.     

影响胡萝卜复合汁中双歧杆菌存活因素的研究

以胡萝卜复合汁为保存基质，分别试验了保存温度、基质的起始ｐＨ值、甜味剂、酸味剂和ＨＣｌ对两歧双歧杆菌存活的影响。结果表明，４℃下保存极显著优于９℃和２０℃；基质起始ｐＨ６．２、５．０、４．５和４．２时的活菌保存期（活菌数≥１０￣６ｃｆｕ／ｍｌ）分别为２６、１３、１２和８天；蔗糖和Ａｓｐａｒｔａｍｅ对菌体存活无不良影响；柠檬酸对菌体存活的影响程度最大，乙酸最小，乳酸和ＨＣｌ居中。     

Effect of stress induced by suboptimal growth factors on survival of Escherichia coli O157:H7.

This study investigated the growth and survival of E. coli O157:H7 exposed to a combination of suboptimal factors (22 degrees C, 7 degrees C, -18 degrees C/0.5% NaCl, 5.0% NaCl/pH 7.0, pH 5.4, pH 4.5/addition of lactic acid) in a simulation medium for red meat (beef gravy). Prolonged survival was noted as the imposed stress was more severe, and as multiple growth factors became suboptimal. At a defined temperature (7 degrees C or -18 degrees C), survival was prolonged at the more acid, more suboptimal pH (pH 4.5 > pH 5.4 > pH 7.0) while at a defined pH (pH 4.5), better survival was observed at 7 degrees C than at 22 degrees C. This suggests that application of the hurdle concept for preservation of food may inhibit outgrowth but induce prolonged survival of E. coli O157:H7 in minimal processed foods. At both 22 degrees C and 7 degrees C, the addition of lactic acid instead of HCl to reduce pH (to pH 4.5) resulted in a more rapid decrease of E. coli O157:H7. High survival was observed in beef gravy, pH 5.4 at -18 degrees C (simulation of frozen meat)-reduction of log 3.0 to log 1.9 after 43 days--and in beef gravy, pH 4.5 and 5% NaCl at 7 degrees C (simulation of a fermented dried meat product kept in refrigeration)--less than 1 log reduction in 43 days. In these circumstances, however, a high degree of sublethal damage of the bacterial cells was noted. The degree of sublethal damage can be estimated from the difference in recovery of the pathogen on the non-selective TSA medium and the selective SMAC medium.     

Orthophosphate sorption onto lanthanum-treated lignocellulosic sorbents

Inorganic/organic hybrid adsorbents for removing orthophosphate from water were prepared by lanthanum (La) treatment of bark fiber, a lignocellulosic material obtained from juniper (Juniperus monosperma). The La was anchored to the juniper bark (JB) fiber by ion exchange with Ca in the bark and was responsible for removing orthophosphate. Two La concentrations (0.01 and 0.1 M) were used that resulted in loadings of 0.198 (La/JB01) and 0.302 (La/JB02) mmol of La g(-1) of fiber, respectively. At circumneutral pH conditions, La exhibited a strong affinity for bark, but significant La desorption occurred under acidic conditions (pH < 4.5). For La/JB02, 86% of the initial La loading was released at pH 2.5, and only 0.1% at pH 7.3. Initial La loading in the bark fiber significantly influenced its orthophosphate sorption capacity, which was determined for La/JB01 and La/JB02, respectively, to be 0.188 and 0.233 mmol of P g(-1) (sorption envelopes) and 0.211 and 0.351 mmol of P g(-1) (sorption isotherms when surface site saturation occurred). The P-to-La molar ratio on the bark surface was extremely high (0.12-1.77for La/JB01 and 0.13-2.58 for La/JB02), implying that orthophosphate removal occurred by other mechanisms in addition to surface complexation. From the orthophosphate surface loading levels and the shape of the sorption isotherms, it appears that adsorption occurred at low sorbate-to-sorbent (P-to-La-treated JB) ratios and transitioned to surface precipitation at higher ratios. When surface precipitation occurred, orthophosphate uptake continued to increase with increasing initial P levels. Results from X-ray diffraction and infrared spectrometric analyses are also suggestive of the occurrence of surface precipitation during the interaction of orthophosphate with La-treated lignocellulosic materials.     

魔芋涂膜保鲜冷却肉研究

采用改性和不改性的魔芋精粉为涂膜材料,对经75%酒精消毒处理或5‰山梨酸钾溶液处理后的鲜猪肉进行涂膜处理,并与不同浓度的壳聚糖涂膜处理相比较,以冷却肉的pH值、过氧化物酶活性、挥发性盐基氮及细菌总数的变化为指标,评价不同处理的保鲜效果。结果表明:冷却肉采用碱法改性的魔芋精粉溶胶涂膜处理保鲜效果与2%的壳聚糖醋酸溶液保鲜效果接近,明显优于其它处理,一级鲜度货架期可达9d。     

芦荟对嗜酸乳杆菌酸乳发酵性能的影响

选择嗜酸乳杆菌、嗜热链球菌为发酵菌种 ,研究芦荟全叶汁对酸乳发酵过程中的滴定酸度、pH值、黏度及感官性状等的影响。试验发现 ,芦荟的添加对嗜酸乳杆菌和嗜热链球菌的生长影响不大 ,但影响酸乳的凝固性、pH值、黏度 ,进而影响品质等。试验结果表明 ,当芦荟添加量为 10 %左右时 ,成熟后的酸乳中La可达 10 9,产品的品质最佳。     

Enhancing inactivation of Staphylococcus aureus in skim milk by combining high-intensity pulsed electric fields and nisin

High-intensity pulsed electric fields (HIPEF) can be used as a nonthermal preservation method that is believed to enhance the effect of nisin on microorganisms such as Staphylococcus aureus. The survival of S. aureus inoculated into skim milk and treated with nisin, with HIPEF, or with a combination of nisin-HIPEF was evaluated. Nisin dose, milk pH, and HIPEF treatment time were the controlled variables that were set up at 20 to 150 ppm, pH 5.0 to 6.8, and 240 to 2,400 micros, respectively. HIPEF strength and pulse width were kept constant at 35 kV/cm and 4 micros, respectively. No reduction in S. aureus concentration was observed in skim milk at its natural pH after treatment with nisin, but 1.1 log units were recovered after 90 min of treatment at pH 5.0 with 150 ppm nisin. A reduction in viable S. aureus counts of 0.3 and 1.0 log unit in skim milk treated with HIPEF at its natural pH was observed at 240 and 2,400 micros, respectively. The nisin-HIPEF treatment design was based on a response surface methodology. The combined effect of nisin and HIPEF was clearly synergistic. However, synergism depended on pH. A maximum microbial inactivation of 6.0 log units was observed at pH 6.8, 20 ppm nisin, and 2,400 micros of HIPEF treatment time, whereas a reduction of over 4.5 log units was achieved when pH, nisin concentration, and HIPEF treatment times were set at 5.0, 150 ppm, and 240 micros, respectively.     

红叶甜菜红色素降解动力学研究

研究了光照、pH、温度对色素降解特性的影响。研究表明红叶甜菜红色素稳定性受pH、温度、光的影响,光照强度越大红叶甜菜红色素保存率越低,在pH2~6范围内色素较稳定,统计分析发现pH2、pH4和pH6色素保存率在实验温度下无显著差异;红叶甜菜红色素的热降解遵循Arrhenius定律,遵循一级降解动力学方程,随温度升高半衰期缩短,pH2、pH4和pH6的活化能分别为67.02kJ/mol、67.12kJ/mol和67.76kJ/mol,pH2、pH4和pH6的色素溶液在对应温度下的半衰期和活化能无显著差异。     

无水贮藏温度对克氏原螯虾保活期品质的影响

为探究无水贮藏温度对克氏原螯虾保活期间品质的影响,本文分析了不同无水贮藏温度下克氏原螯虾保活期间存活率、肌肉品质、生理指标的变化。结果显示,无水贮藏72 h时,4～16℃组的克氏原螯虾的存活率仍有80%～90%;24℃组降至40%;32℃组为0。虾尾肌肉的水分含量、持水率、硬度和弹性随着贮藏温度的升高与贮藏时间的延长显著下降(P<0.05),乳酸的生成降低了肌肉的pH。4、24与32℃组超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、总抗氧化能力(T-AOC)酶活力及丙二醛(MDA)含量随着贮藏时间的延长显著升高(P<0.05),8～16℃组的氧化应激响应较低于4、24和32℃组。酸性磷酸酶(ACP)和碱性磷酸酶(AKP)以及溶菌酶(LZM)活性在4、24与32℃贮藏条件下显著升高(P<0.05),8～16℃组的变化相对平稳。研究表明,无水贮藏中保持适当低温条件,在12～16℃范围内,可提高克氏原螯虾存活率和肌肉品质,这与机体保持较低的氧化应激水平及维持良好的免疫机制有关,本实验结果可为克氏原螯虾无水贮运提供理论依据。