提高ε-聚赖氨酸产量的研究进展

ε-聚赖氨酸是自然界中所熟知的由微生物产生的氨基酸同型聚合物,由于从自然界中筛选聚赖氨酸产生菌所产生的产量极低,提高产量成为亟待突破的生产难题.本文介绍了国内外已报道的通过诱变、筛选获得ε-聚赖氨酸高产菌株的方法,以及通过优化培养条件提高ε-聚赖氨酸产量的方法,通过分析各种方法的优缺点,对提高ε-聚赖氨酸产量的途径提出建议.特别对初步大量筛选ε-聚赖氨酸产生菌的方法进行综述、分析,以期得出快速高效的筛选方案.     

ε- 聚赖氨酸在冷鲜猪肉保鲜中的应用

研究ε- 聚赖氨酸(ε-PL)保鲜冷鲜猪肉的处理条件,考察在优化条件下ε-PL 对冷鲜猪肉感官、微生物、理化等指标的影响。结果表明：400mg/L ε-PL 单独使用时就能显著抑制冷鲜猪肉感官品质的下降、微生物的生长繁殖、pH 值的上升和TVB-N 的积累,而当ε-PL 和乙酸复配使用后抑制作用更佳,特别是对微生物的生长繁殖有明显的抑制作用,浸泡时间对ε-PL- 乙酸助剂的抑菌效果影响很大,随着浸泡时间的增加,ε-PL- 乙酸助剂抑菌效果逐渐加强。综合抑菌效果、处理成本以及处理效率考虑,优化组合为：ε-PL 质量浓度400mg/L,助剂为0.2% 乙酸,浸泡时间为5min。优化处理后冷鲜猪肉保质期从对照组2d 延长至8d。结果揭示：ε-PL 作为冷鲜肉生物保鲜剂,具有广阔的应用前景。     

微生物发酵液中ε-聚赖氨酸的分离提纯

筛选适用于分离提纯微生物发酵液中ε- 聚赖氨酸的树脂并确定其工艺条件。以ε- 聚赖氨酸吸附量和回收率为考察指标,采用静态吸附法选择适合的树脂,采用动态吸附法确定提取工艺。结果表明,弱酸型阳离子交换树脂HD-2 对ε- 聚赖氨酸具有良好的吸附分离性能。其动态分离提纯工艺条件为：层析柱为22mm × 300mm 时,上样流速为3mL/min;以0.1mol/L 的HCl 为洗脱液,洗脱流速为3mL/min。此工艺条件下,ε- 聚赖氨酸的回收率为92.0%。     

新型琼脂扩散法检测食品中天然防腐剂ε-聚赖氨酸含量

为分析食品中ε-聚赖氨酸(ε-poly-L-lysine,ε-PL)含量,建立一种新型琼脂扩散法,并对分析条件进行优化,验证在检测食品中ε-PL含量时的有效性。结果表明,质量分数0.002%亚甲基蓝、0.75%琼脂、ε-PL溶液pH值为2.0、牛津杯加液量750μL时检测结果最佳。本方法允许检测橙汁中ε-PL最低含量为2 mg/kg、糕点和猪肉火腿中最低为10 mg/kg。这种新型琼脂扩散法具有操作简便、使用成本低、专一性高等优点,可以广泛应用于ε-PL生产企业和食品工业。     

ε-聚赖氨酸与羧甲基纤维素钠的相互作用

以ε-聚赖氨酸（ε-polylysine,ε-PL）与羧甲基纤维素钠（sodium carboxymethylcellulose,CMC-Na）相互作用体系的混浊度、Zeta电位和粒度为指标,研究了CMC-Na的取代度（degree of substitution,DS）和相对分子质量对ε-PL/CMC-Na相互作用体系的影响。结果表明,在pH 4.0时,ε-PL与CMC-Na之间的静电相互作用主要依赖于ε-PL氨基与CMC-Na羧基的物质的量比;同时,CMC-Na的取代度和相对分子质量均对ε-PL/CMC-Na相互作用具有显著影响,且CMC-Na取代度对体系稳定性的影响更大。     

ε-聚赖氨酸-壳聚糖/PE复合膜对鲜切茄子保鲜作用

利用ε-聚赖氨酸-壳聚糖/聚乙烯（PE）复合膜对鲜切茄子进行真空包装,并考察ε-聚赖氨酸含量（1%、3%、5%、7%）对鲜切茄子的保鲜效果影响。结果发现,随着贮藏天数的增加,鲜切茄子的感官品质、可溶性固形物均呈下降趋势,失质量率、褐变度均在增加。其中5% ε-聚赖氨酸含量的ε-聚赖氨酸-壳聚糖/PE复合膜对鲜切茄子的保鲜效果最佳。     

ε-聚赖氨酸作为天然防腐剂在食品中的应用研究进展

ε-聚赖氨酸是由25～35个赖氨酸残基通过分子间羧基与氨基缩合形成酰胺键连接而成的L-赖氨酸同型聚合物,作为一种高效、安全、环保的天然生物防腐剂受到了欢迎.ε-聚赖氨酸可以通过影响细胞膜、遗传物质、酶及蛋白质完成抑菌作用,在食品中添加ε-聚赖氨酸不仅可以抑制腐败微生物的生长繁殖,还能延缓食品品质变化,提高食品质量,延长...     

新型生物食品防腐剂ε-聚赖氨酸的提取

为建立从发酵液中高效分离提取ε-聚赖氨酸(ε-PL)的方法,比较了离子交换和膜分离以及二者组合对ε-PL分离提取的影响。实验结果显示,在离子交换之前增加一个30 k超滤操作能够很好地去除杂蛋白,并提高离子交换树脂对ε-PL吸附容量;最终样品纯度达到95.3%,收率65.4%;获得的样品聚合度分布范围为9²9,平均分子质量为2 602.3Da;且样品对细菌具有强烈的抑制作用。这表明,离子交换和膜分离组合策略是从发酵液中高效分离与提取ε-PL的核心单元操作工序。     

ε-聚赖氨酸在食品中应用的进展

ε-聚赖氨酸是一种阳离子聚合多肽,作为一种天然的营养型生物防腐剂,ε-聚赖氨酸不仅具有抑菌效果好、抑菌谱广,对酵母菌、霉菌、革兰氏阳性革兰氏阴性菌、噬菌体都有良好的抑制作用,而且还具有耐高温、对人体无毒副作用等特点。ε-聚赖氨酸的抑菌性质及特点,使其在食品的保鲜防腐中有良好的应用前景。主要介绍ε-聚赖氨酸的理化性质、安全性,对微生物的抑菌效果、作用机理以及在一些常见食品中的应用,对ε-聚赖氨酸在食品中的应用研究有非常重要的意义。     

ε-聚赖氨酸作为食品防腐剂的应用

ε-聚赖氨酸具有抑菌谱广、水溶性好、安全性高、热稳定性好、抑菌pH范围广等特点,是目前天然防腐剂中具有优良防腐性能和巨大商业潜力的微生物类食品防腐剂.介绍了ε-聚赖氨酸的结构特性、测定、抑菌作用机抑菌机理,重点介绍了ε-聚赖氨酸在食品行业中特别是作为食品防腐剂的应用,并对其今后在我国的发展应用进行展望.     

奶酪及乳清中β-内酰胺酶的检测

为探讨原奶中β- 内酰胺酶在制作奶酪过程中的去向,向无抗无酶的原奶中添加β- 内酰胺酶,使其终水平为50U/mL,按照工艺制作原生奶酪,用E50 法和杯碟法检测奶酪和乳清中的β- 内酰胺酶。结果显示,奶酪中β- 内酰胺酶检测结果为阴性,乳清中β- 内酰胺酶检测结果为阳性,β- 内酰胺酶在奶酪制作中主要残留在乳清中。     

基于酶联适配体快速检测食品中葡萄球菌肠毒素A

该研究基于双适配体夹心原理,建立了一种酶联适配体检测葡萄球菌肠毒素A(Staphylococcal enterotoxin A,SEA)的新方法,并对适配体浓度、链霉亲和素-辣根过氧化物酶浓度、反应体系、封闭条件、反应时间等条件进行了优化.结果显示,在适配体浓度40 nmol/L、牛血清白蛋白(Bovine serum...     

速冻食品中沙门氏菌和金黄色葡萄球菌多重PCR检测方法的建立与应用

为实现速冻食品中沙门氏菌(Salmonella spp.)和金黄色葡萄球菌(Staphylococcus aureus)的多重聚合酶链式反应(PCR)检测,首先优化多重PCR扩增的反应条件,比较基因组DNA提取方法,结果表明：退火温度采用60℃、各引物浓度200nmol/L及扩增循环35次,本多重PCR检测技术可以有效地将沙门氏菌和金黄色葡萄球菌同时检出,检测特异性为100%。3种DNA提取方法中试剂盒法纯度最高,检出限分别是31、26DNA copies/reaction。经过在人工污染致病菌的速冻水饺中应用试验后,该多重PCR方法经过4h的增菌培养即可从速冻水饺中同时检测出起始菌落数低至100CFU/g的沙门氏菌和金黄色葡萄球菌。     

Development of a Solid-Phase Extraction–Enzyme-Linked Immunosorbent Assay for the Determination of 17β-19-Nortestosterone Levels in Antifatigue Functional Foods

ABSTRACT:  17β-19-nortestosterone (17β-NT) has been illegally used in antifatigue functional foods to promote muscle growth and improve endurance. A rapid and sensitive solid-phase extraction–enzyme-linked immunosorbent assay (SPE-ELISA) method was developed and successfully applied to analyze the levels of 17β-NT in antifatigue functional foods. A polyclonal antibody against 17β-NT was produced from rabbits immunized with the 17β-NT-BSA conjugate, and a competitive direct enzyme-linked immunosorbent assay was developed for the rapid detection of 17β-NT. The concentration causing 50% inhibition ( IC ₅₀) and the limit of detection (LOD) were found to be 0.08 and 0.0055 ng/mL, respectively; this was better than methods previously reported that had a LOD of 2.4 ng/mL. C₁₈ cartridges were investigated for use in removing the effects of matrix in foods, and the sample purification protocol was optimized. Using the developed SPE-ELISA method, recoveries of functional food samples were obtained in the range of 71% to 91.5%. Moreover, 2 kinds of antifatigue functional foods were analyzed using the established ELISA and HPLC methods. The correlation coefficient of the results obtained using the 2 methods was greater than 0.98. Thus, the preliminary evaluation of the SPE-ELISA method proved that it is a specific, sensitive, and precise tool that can be used for the practical detection of 17β-NT in various antifatigue functional food samples.     

Rapid Cell‐Based Assay for Detection and Quantification of Active Staphylococcal Enterotoxin Type D

Food poisoning by Staphylococcus aureus is a result of ingestion of Staphylococcal enterotoxins (SEs) produced by this bacterium and is a major source of foodborne illness. Staphylococcal enterotoxin D (SED) is one of the predominant enterotoxins recovered in Staphylococcal food poisoning incidences, including a recent outbreak in Guam affecting 300 children. Current immunology methods for SED detection cannot distinguish between the biologically active form of the toxin, which poses a threat, from the inactive form, which poses no threat. In vivo bioassays that measure emetic activity in kitten and monkeys have been used, but these methods rely upon expensive procedures using live animals and raising ethical concerns. A rapid (5 h) quantitative bioluminescence assay, using a genetically engineered T‐cell Jurkat cell line expressing luciferase under regulation of nuclear factor of activated T cells response elements, in combination with the lymphoblastoid B‐cell line Raji for antigen presentation, was developed. In this assay, the detection limit of biologically active SED is 100 ng/mL, which is 10 times more sensitive than the splenocyte proliferation assay, and 10⁵ times more sensitive than monkey or kitten bioassay. Pasteurization or repeated freeze–thaw cycles had no effect on SED activity, but reduction in SED activity was shown with heat treatment at 100°C for 5 min. It was also shown that milk exhibits a protective effect on SED. This bioluminescence assay may also be used to rapidly evaluate antibodies to SED for potential therapeutic application as a measurement of neutralizing biological effects of SED.