Antibacterial activity of a chitooligosaccharide mixture prepared by cellulase digestion of shrimp chitosan and its application to milk preservation

The antibacterial activity of a chitooligosaccharide mixture prepared by digestion of shrimp chitosan with cellulase at 50 degrees C for 14 h was evaluated. Sugars with 1 to 8 degrees of polymer (DP) were found in this chitooligosaccharide mixture, and the weight percentage of sugars with DP > or = 6 was 44.3%. Minimal lethal concentrations of this mixture against Aeromonas hydrophila, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, Shigella dysenteriae, Staphylococcus aureus, Vibrio cholerae, and Vibrio parahaemolyticus in nutrient broth were 5 to 29 ppm, which were much lower than those of the chitosan reactant (50 to 1,000 ppm). The antibacterial activity of this mixture in the sterilized milk against E. coli O157, L. monocytogenes, Salmonella Typhimurium, and S. aureus was much stronger at 4 degrees C than at 37 degrees C. When raw milk was supplemented with either 0.24% or 0.48% (wt/vol) of this oligosaccharide mixture and stored at 4 degrees C for 12 days, its mesophilic and psychrotrophic counts were reduced by at least 3 log cycles, and there was very little change in pH. In addition, this mixture retarded the growth of Salmonella species and caused quicker reduction of Staphylococcus species in raw milk. Accordingly, the shelf life of raw milk at 4 degrees C was extended by at least 4 days.     

Antimicrobial activity of native chitosan,degraded chitosan,and O-carboxymethylated chitosan

The antimicrobial activity of native chitosan was compared to that of lipase-degraded chitosan. The effects of O-carboxymethylated (O-CM) substitution on native (molecular weight, 120; degree of deacetylation, 84.71%) and lipase-degraded chitosans were also investigated. The antimicrobial activity of native chitosan was more extensive than that of lipase-degraded chitosan; however, lipase-degraded chitosan was still highly effective and more water-soluble. O-CM chitosan derived from degraded chitosan was more effective than O-CM chitosan derived from native chitosan. O-CM substitution enhanced lipase-degraded chitosan's antimicrobial activity without reducing its solubility.     

纤维素酶制备水溶性壳聚糖的研究

通过对溶液还原糖浓度以及黏度的测定研究了纤维素酶对壳聚糖的降解作用,探讨了酶解过程中温度、pH值以及反应时间对纤维素酶降解壳聚糖的影响,对降解前后壳聚糖的结构进行了表征并对其水溶性进行了测试.结果表明,纤维素酶降解壳聚糖的最佳pH值为4.5,温度为50℃,随着反应时间的延长,壳聚糖溶液的黏度逐渐降低:随着壳聚糖分子量的降低,水溶性增强,但是化学结构没有发生改变.     

纤维素酶水解壳聚糖条件的研究

利用绿色木霉产生的纤维素酶水解壳聚糖,并对其水解条件进行了研究.在50℃、pH5.0条件下,按照8 U/g底物的酶量,将纤维素酶添加到3%壳聚糖溶液中,水解20 h可得到平均聚合度为4的低聚壳聚糖.     

纤维素酶水解壳聚糖的特性研究

利用粘度法、还原端基法及TLC法,探讨了温度、pH、反应时间、底物的脱乙酰度和金属离子等对纤维素酶水解壳聚糖的影响。结果表明,纤维素酶能有效降解壳聚糖,其作用的最适温度为60℃,最适pH为5.2,酶水解反应米氏常数为Km=10mg/mL;Mn2+、Mg2+、Ca2+对该酶有较强的激活作用,Ag+、Cu2+、Hg+、葡萄糖等是该酶的抑制剂。该酶稳定性较强,在pH3～7的范围内均很稳定,60℃作用1h相对残余酶活为60.8%。其最适作用的底物为脱乙酰度（DD）90%的壳聚糖,根据水解产物分析判断其以内切酶为主,既能水解GlcN-GlcN键,又能水解GlcNAc-GlcN键。      

A natural clouding agent from orange peels obtained using polygalacturonase and cellulase

Clouding agents (CAs) provide high cloud stability when they are diluted and added to fruit beverages. Natural CA could also give the visual appearance and sensorial aspect of a natural cloudy fruit juice beverage. In addition, natural CAs are preferred over the synthetic ones by consumers. Therefore, the main objective of this study was to obtain a natural CA from orange peel that provided high cloud stability of fruit beverages. The treatment included the use of polygalacturonase (PG) and cellulase (C) to hydrolyze most of the peel components. Orange peels treated with 69 mg/kg of C and 90 μl/kg of PG during 80 min at 48 °C led to a CA that provided a cloudy stable solution on a fruit beverage. This CA presented a cloud stability of 94.7 days that represented a turbidity reduction of 9.1% after 9 days under fridge temperatures. Otherwise, the treatment conditions to get the highest cloud stability were not coincident to those necessary to preserve the color or to obtain the greatest extraction yield of the CA.     

Effects of chitosan and a low-molecular-weight chitosan on Bacillus cereus and application in the preservation of cooked rice

Shrimp chitosan with 95% deacetylation and low-molecular-weight chitosan (LMWC) isolated from chitosan hydrolysate were investigated for their effects on the growth of Bacillus cereus and for use in the preservation of cooked rice. Four strains of Bacillus cereus were used: standard strain BCRC 10603 and three isolates (nos. 1 through 3) from cooked rice. The antibacterial activity of chitosan against B. cereus was greatly decreased when the reaction pH was changed from 6.0 to 7.0, but LMWC activity was less affected by this pH change. The susceptibility of B. cereus cells to chitosan decreased with increasing of cell age, in accordance with the relative electronegativity of the cell surface. B. cereus spores were more sensitive to LMWC and chitosan than were vegetative cells. Addition of 80 ppm LMWC and chitosan in sterile saline (pH 7.0) greatly reduced the D-value for the tested four strains at 90 degrees C from 30.77 to 46.51 min to 7.47 to 10.17 min and 4.68 to 7.91 min, respectively, and at 100 degrees C from 1.95 to 2.56 min to 0.89 to 0.93 min and 0.72 to 0.80 min, respectively. Addition of 2,000 ppm LMWC to raw rice water before steam cooking effectively inhibited increases in total aerobic bacteria and B. cereus in cooked rice stored at 37 and 18 degrees C.     

Antimicrobial activity against foodborne pathogens of chitosan biopolymer films of different molecular weights

Antimicrobial activity against Listeria monocytogenes, Escherichia coli 0157:H7 and Samonella typhimurium of chitosan biopolymer films (CBFs) prepared with four different viscosities of chitosans (10, 40, 100 and 200 mPa s) were investigated by agar diffusion assay. The films were also characterized with measurements of color, tensile strength (TS), % elongation (EL), water vapor permeability and oxygen permeability. CBFs prepared with 100 mPa s chitosan showed an antimicrobial effect only on 10⁴ cfu/mL inoculation of L. monocytogenes while other viscosities showed an antilisterial effect on all concentrations (10⁴-10⁶ cfu/mL) of L. monocytogenes. CBFs prepared with 10 mPa s (CBF-10) and 40 mPa s (CBF-40) chitosans showed an inhibitory effect against E. coli 0157:H7 and S. typhimurium only at the 10⁴ cfu/mL concentration. CBFs prepared with the two higher viscosity chitosans did not show any effect regardless of bacterial level. TS and EL of the CBFs increased with increasing viscosity up to 100 mPa s. Molecular weight distribution was found to be positively correlated with viscosity. The oxygen permeability of the CBFs increased with increasing viscosity of chitosans, but water vapor transmission rate was not similarly affected. In conclusion, CBFs were more effective at inhibition of L. monocytogenes than S. typhimurium and E. Coli O157:H7. Molecular weight of chitosan must be chosen selectively to control the target foodborne pathogens.     

Antimicrobial activity of lactoferrin against foodborne pathogenic bacteria incorporated into edible chitosan film

The objectives of this research were to develop and characterize edible chitosan film containing lactoferrin as a natural antimicrobial agent, and to investigate the combination effects of lactoferrin with lysozyme in chitosan film against the growth of Escherichia coli O157:H7 and Listeria monocytogenes. Chitosan films containing lactoferrin, lysozyme, or nisin were fabricated, and the antimicrobial concentrations were 0.5, 1, or 2 mg in a circular disc of chitosan film. Three concentrations of lactoferrin or EDTA (0.28, 0.56, or 1.12 mg per disc) were also incorporated into the chitosan film containing lysozyme to investigate the combination effects of lactoferrin. The water barrier properties of the chitosan films containing lactoferrin were characterized. The antimicrobial activities against E. coli O157:H7 and L. monocytogenes were determined using the agar diffusion assay and cell count assay. The chitosan films containing lactoferrin less than 1 mg per disc did not alter the water vapor permeability of the chitosan film. Although the film containing lysozyme exhibited significant antimicrobial activity, the incorporation of lactoferrin alone into chitosan film did not exhibit significant antimicrobial activity against both E. coli O157:H7 and L. monocytogenes. However, the combination of lactoferrin with lysozyme-containing chitosan film significantly decreased the growth of E. coli O157:H7, exhibiting a comparable effect to that of the combination of EDTA with lysozyme (P < 0.05). Furthermore, the combination of lactoferrin with lysozyme in chitosan film exhibited greater reduction in the growth of L. monocytogenes than did the combination EDTA with lysozyme, resulting in an approximate 3-log reduction.     

Antimicrobial proteinaceous compounds obtained from bifidobacteria: from production to their application

Antimicrobial proteinaceous compounds such as bacteriocins or bacteriocin-like compounds produced by bifidobacteria are largely unknown but have been found to have potent antimicrobial activities toward closely related bacteria and undesirable harmful microorganisms. They are useful in the fields of food preservation or safety, health care, and pharmaceutical applications. The inhibition activity of these substances has been reported to be strain-dependent. Binding to the epithelial cell on the gastrointestinal surfaces is one of the important factors of resident microflora to colonize the intestine. Certain Bifidobacterium strains are able to produce substances that compete and prevent pathogenic bacteria from adhering to the receptors on epithelial cells of intestinal surfaces. The potential probiotic effects of bifidobacteria is well known in the human ecosystem and their production of antimicrobial peptides can contribute to elucidate the precise mechanisms by which bifidobacteria can dominate the intestinal microbiota and achieve their probiotic function. This paper presents a review of the antimicrobial proteinaceous compounds produced by various Bifidobacterium strains, the attempts made to purify them, their characterization, identification and useful applications.     

壳聚糖固定化纤维素酶的条件优化

采用Plackett-Burman试验设计和正交试验设计对影响固定化纤维素酶活的因素进行了筛选和优化.探讨了纤维素酶、壳聚糖、乙酸、乙醇、戊二醛、氢氧化钠等试剂对固定化效果的影响,筛选出制备固定化纤维素酶过程中的主要影响因素.结果表明:壳聚糖、乙酸、乙醇浓度、酶浓度分别为15g/L、2.0%、40%、100%时,以壳聚糖为载体制备固定化纤维素酶的活力最高,成型效果最好.     

中式灌肠生产中壳聚糖的抑菌效果研究

目的：研究壳聚糖在中式灌肠生产中的抑菌效果；方法：采用中性蛋白酶水解方法制备出不同黏均分子量的壳聚糖，添加到灌肠中，测定不同保存天数时的细菌总数和感观变化；结果：添加0．2％壳聚糖的灌肠在室温条件下的保质期提高2d以上，风味比其他添加量要好，且在同样添加量的条件下，黏均分子量低的壳聚糖比黏均分子量高的壳聚糖抑菌效果更好。     

Antioxidant potential and antimicrobial activity of chitosan–inulin conjugates obtained through the Maillard reaction

Food Science and Biotechnology - Chitosan (1%) was glycated with inulin (0.5, 1, and 2%) via the Maillard reaction at various initial pH values (5, 5.5, and 6). Higher pHs led to a greater pH drop...     

Antimicrobial activity and physical properties of chitosan–tapioca starch based edible films and coatings

Antimicrobial activity of edible coating solutions based on chitosan and blends of chitosan–tapioca starch with or without potassium sorbate (KS) addition was studied. The agar well diffusion assay showed an antagonist effect on the efficiency of chitosan against Lactobacillus spp. when KS and/or tapioca starch were present. A salmon slice coating assay showed that the chitosan solution was the best coating since aerobic mesophilic and psychrophilic cell counts were reduced, pH and weight loss remained acceptable throughout refrigerated storage, extending global quality to 6-days. Chitosan–tapioca starch based films reduced Zygosaccharomyces bailii external spoilage in a semisolid product but were not effective against Lactobacillus spp. The results suggest that antibacterial action depended on the application technique, due to the fact that chitosan is more available in a coating solution than in a film matrix. Interactions between chitosan–starch and/or KS could affect film physical properties and the antimicrobial activity of chitosan. The addition of chitosan reduced water vapor permeability and solubility of starch films.     

Antimicrobial activity of food-compatible plant extracts and chitosan against naturally occurring micro-organisms in tomato juice

BACKGROUND: Chitosan (AC) and five hydroalcoholic extracts from Lithospermum erythrorhizon (SE), Rheum palmatum (RE), Thymus vulgaris (AT), Lippia citriodora (PLX) and a mixture of Rosmarinus officinalis, Salvia lavandulifolia and Thymus mastichina (LA) were tested for antimicrobial activity against bacteria, yeasts and filamentous fungi using two broth dilution methods. The effects of adding single extracts on naturally occurring micro‐organisms and sensory qualities of raw tomato juice were also evaluated. RESULTS: SE extract exhibited the strongest activity, with minimum inhibitory concentrations (MICs) of 100–400 µg mL^?1 for Gram‐positive and 1600–3200 µg mL^?1 for Gram‐negative bacteria. Enterobacter aerogenes showed the greatest susceptibility to AC (MIC 1600 µg mL^?1). Lethal effects of extracts and AC were achieved at a minimum bactericidal concentration (MBC)/MIC ratio of 2 in 88% of assays. SE and RE extracts and AC also exhibited antifungal effect against yeasts, but they had no activity on filamentous fungi. Control and 100 mg L^?1 SE‐added tomato juices did not differ in acceptance, but this SE concentration was not effective in the control of microbial load throughout cold storage. CONCLUSION: Results confirm the antimicrobial potential of the plant extracts, but additional research is needed until the agents responsible for the activities have been determined in order to use them as natural constituents of multiple‐barrier food preservation systems. Copyright © 2012 Society of Chemical Industry     

壳聚糖协同竹醋液的抗菌性研究

研究了在壳聚糖和竹醋液(壳聚糖复配液)的协同下的抗菌抑菌性.测定了壳聚糖复配液对细菌、霉菌和酵母的最低抑微生物浓度,并研究了不同浓度壳聚糖复配液对抑菌活性的影响.以壳聚糖为主剂,竹醋液为助剂制成纯天然绿色型的复合保鲜剂水溶液涂膜处理蕨菜表面,室温存放进行保鲜实验.结果表明:保鲜过的蕨菜基本上保持了原有风味和营养成分;蕨菜仍为绿色,无霉变.     

山楂核精油的抗菌特性

为了提升山楂果实综合加工利用价值,对山楂核精油的抗菌作用进行了研究。结果表明,山楂核精油对大肠杆菌、金黄色葡萄球菌以及青霉菌均具有很强的抗菌性,且抗菌性的强弱与其作用浓度和作用时间有关。此实验结果为山楂核精油在食品工业或医药卫生等领域的应用提供了很好的理论基础与技术依据。      

益智提取物的抑菌性能研究

分别用水、甲醇、乙醇、乙酸乙酯、石油醚对益智进行提取,采用滤纸片法比较不同溶剂提取物对大肠杆菌、金黄色葡萄球菌及黑曲霉的抑制作用;通过二倍稀释法确定益智的80％vol乙醇提取物对大肠杆菌、金黄色葡萄球菌及黑曲霉菌的最小抑菌浓度分别为3.00mg/mL、1.50mg/mL和24.00mg/mL;并确定热处理、紫外线、介质pH值对益智的80％vol乙醇提取物抑菌活性无显著影响.     

化学助剂对纺织用纤维素酶活力的影响

选用C-1214、苯甲酸钠、山梨醇等化学助剂，分别加入纺织用纤维素酶处理液中，以CMC法测定各试剂不同加入量下的纤维素酶的酶活力，作出酶活力变化曲线，分析这些助剂对酶活力的影响，得出其最佳的工艺用量。