Antimicrobial activity of carvacrol toward Bacillus cereus on rice

The antimicrobial activity of carvacrol, a compound present in the essential oil fraction of oreganum and thyme, toward the foodborne pathogen Bacillus cereus on rice was studied. Carvacrol showed a dose-related inhibition of growth of the pathogen. Concentrations of 0.15 mg/g and higher inhibited the growth and the extent of inhibition depended on the initial inoculum size. To decrease the input of carvacrol on the taste and flavor of the product, a combined treatment with the structure analog cymene was tested. Due to the smell and taste of carvacrol at high concentrations, carvacrol was combined with cymene, a natural antimicrobial compound with a similar structure. A synergistic effect was observed when 0.30 mg/g carvacrol was combined with 0.27 mg/g cymene. Finally it was demonstrated that a common taste enhancer like soya sauce also increased the antimicrobial action of carvacrol toward B. cereus. The antimicrobial activity of carvacrol with cymene or soya sauce was influenced by the addition of NaCl.     

Prevalence and characterisation of Bacillus cereus in vacuum packed potato puree

Refrigerated processed foods of extended durability (REPFED) potato puree was analysed for Bacillus cereus contamination along the production line and during the product shelf‐life. Isolated B. cereus strains were tested for their psychrotrophic character and the ability to produce enterotoxins. Bacillus cereus contamination during four subsequent productions was in the range of 2.3–4.0 log cfu g^?1. Productions five and six were significantly less contaminated with B. cereus (≤1 log cfu g ^?1). All B. cereus isolates from the first four productions were able to grow at 7 ° and 10 °C, whereas the majority of the isolates from productions five and six did not. No B. cereus isolates grew at 4 °C. randomly amplified polymorphic DNA (RAPD) fingerprinting showed that the most of B. cereus contamination originated from one source. In total, 30.4% of isolates expressed enterotoxic character. The present study points out the necessity to prevent an ‘in house’ colonisation and contamination during food processing in order to accomplish the safety of REPFED throughout the shelf‐life. It also indicates the most critical steps in the production line of ready‐to‐eat potato puree and impact of failures regarding the food safety. The data provided can be used for risk assessment studies regarding B. cereus in REPFED.     

Combined effect of nisin and carvacrol at different pH and temperature levels on the viability of different strains of Bacillus cereus.

The influence of pH and temperature on the bactericidal action of nisin and carvacrol on vegetative cells of different Bacillus cereus strains was studied. The five strains tested showed significant differences in sensitivity towards nisin, at pH 7.0 and 30 degrees C. Carvacrol concentrations of 0.3 mmol l(-1) had no effect on viability of B. cereus cells. When the same carvacrol concentration was combined with nisin, however, it resulted in a greater loss of viability of cells than when nisin was applied alone. The concentration of carvacrol played an important role on the bactericidal effect of nisin and, therefore, on the synergistic action of both compounds combined. At lower pH values (6.30 and 5.75), nisin was more active against B. cereus cells than at pH 7.0 at 30 degrees C, with a different sensitivity of the strains tested. The combined effect of nisin and carvacrol was found to be significantly different at pH 7.0 and 5.75. When the temperature was 8 degrees C, nisin was significantly less active against B. cereus IFR-NL 94-25 than at 30 degrees C, both at pH 7.0 and 6.30. At 8 degrees C, there was a significant increased effect of nisin at lower pH values. Also at this low temperature, a synergistic effect between nisin and carvacrol on B. cereus cells was observed at the pHs tested. This study indicates the potential of nisin and carvacrol at lower pHs to be used for preservation of minimally processed foods.     

Influence of carvacrol on growth and toxin production by Bacillus cereus

The natural antimicrobial compound carvacrol was investigated for its effect on diarrheal toxin production by Bacillus cereus. Carvacrol (0-0.06 mg/ml) reduced the viable count and the maximal specific growth rate (mumax) of B. cereus in BHI broth. The total amount of protein was not affected by carvacrol. However, a sharp decrease (80%) in diarrheal toxin production was observed in the presence of 0.06 mg/ml carvacrol. Carvacrol also inhibited toxin production in soup, but approximately 50-fold higher concentrations were needed to achieve the same effect as in broth. From this study it can be concluded that carvacrol can be added to food products at doses below the MIC value, thereby reducing the risk of toxin production by B. cereus and increasing the safety of the products.     

Influence of food matrix on inactivation of Bacillus cereus by combinations of nisin, pulsed electric field treatment, and carvacrol.

Carvacrol was used as a third preservative factor to enhance further the synergy between nisin and pulsed electric field (PEF) treatment against vegetative cells of Bacillus cereus. When applied simultaneously with nisin (0.04 microg/ml), carvacrol (0.5 mM) enhanced the synergy found between nisin and PEF treatment (16.7 kV/cm, 30 pulses) in potassium-N-2-hydroxyethylpiperazine-N-ethanesulfonic acid (HEPES) buffer. The influence of food ingredients on bactericidal activity was tested using skimmed milk that was diluted to 20% with sterile demineralized water. The efficacy of PEF treatment was not affected by the presence of proteins, and results found in HEPES buffer correlated well with results in milk (20%). Nisin showed less activity against B. cereus in milk. Carvacrol was not able to enhance the synergy between nisin and PEF treatment in milk, unless used in high concentrations (1.2 mM). This concentration in itself did not influence the viable count. Carvacrol did act synergistically with PEF treatment in milk, however not in HEPES buffer. This synergy was not influenced by proteins in milk, as 5% milk still allows synergy between carvacrol and PEF treatment to the same extent as 20% milk.     

Synergistic bactericidal effect of carvacrol, cinnamaldehyde or thymol and refrigeration to inhibit Bacillus cereus in carrot broth

Possible use of three different essential oil components as natural food preservatives was studied by examining their influence in the kinetics of growth from activated spores of four Bacillus cereus strains in tyndallized carrot broth over the temperature range 5-16 degrees C. Selected low concentrations of carvacrol, cinnamaldehyde, or thymol showed a clear antibacterial activity against B. cereus in the vegetable substrate. The addition of 2 microl cinnamaldehyde or 20 mg thymol to 100 ml of broth in combination with refrigeration temperatures (相似文献   

The effect of nisin on growth kinetics from activated Bacillus cereus spores in cooked rice and in milk

The growth kinetics of germinated cells from activated spores of Bacillus cereus in cooked white rice and in milk were evaluated at different temperatures for control samples and for samples with 25 microg of nisin per ml added. Nisin was applied in the form of Nisaplin (10(6) IU/g), which contained 25,000 microg of nisin per g. The length of the lag phase for cooked white rice controls was 120 h at 10 degrees C, 8 h at 25 degrees C, and 2.5 h at 33 degrees C. The generation times for cooked rice were 327.7 min at 10 degrees C, 59.0 min at 25 degrees C, and 42.3 min at 33 degrees C; those for milk without nisin were 297.0 min at 20 degrees C, 31.2 min at 30 degrees C, 28.6 min at 35 degrees C, and 33.7 min at 40 degrees C; and those for milk with nisin added were 277.2 min at 20 degrees C, 66.9 min at 30 degrees C, and 66.4 min at 35 degrees C. No development of B. cereus was observed for milk with nisin added at 40 degrees C for 12 h, in which germinated cells decreased by a decimal reduction time (D) of 4.7 h. A temperature of 45 degrees C was shown to be harmful to B. cereus, decreasing the germinated cells in both formulations with D-values of 4.3 to 4.6 h. Similar inhibition of cell growth at 40 degrees C was not observed with lower nisin concentrations.     

The influence of nisin on the thermal resistance of Bacillus cereus

Decimal reduction times (D-values) at cooking and autoclaving temperatures (80 to 120 degrees C) of spores of Bacillus cereus ATCC 1479-8 in rice and milk (13% wt/vol) supplemented with nisin (25 microg/ml) were evaluated. The mean D-values at 97.8 degrees C in cooked white rice, phosphate buffer (pH 7.0), and rice water (pH 6.7) were 3.62, 1,99, and 1.34 min, respectively. From 80 to 100 degrees C, the mean reduction in D-values due to the addition of nisin to milk was 40%. The D-value at 110 degrees C was approximately 0.86 min for milk (control) and milk with nisin. The z-values ranged from 7.32 degrees C (phosphate buffer) to 10.37 degrees C (milk control).     

Presence and significance of Bacillus cereus in dehydrated potato products

Dehydrated potato contains Bacillus cereus at a prevalences of 10 to 40% and at numbers usually less than 10(3) CFU g(-1). B. cereus in dehydrated potato is likely to be present as spores that are able to survive drying of the raw vegetable and may represent a significant inoculum in the reconstituted (rehydrated) product where conditions favor germination of, and outgrowth from, spores. Holding rehydrated mashed potato alone, or as part of another product (e.g., potato-topped pie), at temperatures above 10 degrees C and below 60 degrees C may allow growth of vegetative B. cereus. Levels exceeding 10(4) CFU g(-1) are considered hazardous to human health and may be reached within a few hours if stored inappropriately between these temperatures. Foods incorporating mashed potato prepared from dehydrated potato flakes have been implicated in B. cereus foodborne illness. This review is a summary of the information available concerning the prevalence and numbers of B. cereus in dehydrated potato flakes and the rate at which growth might occur in the rehydrated product.     

Antimicrobial activities of tea catechins and theaflavins and tea extracts against Bacillus cereus

We evaluated the antimicrobial activities of seven green tea catechins and four black tea theaflavins, generally referred to as flavonoids, as well as the aqueous extracts (infusions) of 36 commercial black, green, oolong, white, and herbal teas against Bacillus cereus (strain RM3190) incubated at 21 degrees C for 3, 15, 30, and 60 min. The results obtained demonstrate that (i) (-)-gallocatechin-3-gallate, (-)-epigallocatechin-3-gallate, (-)-catechin-3-gallate, (-)-epicatechin-3-gallate, theaflavin-3, 3'-digallate, theaflavin-3'-gallate, and theaflavin-3-gallate showed antimicrobial activities at nanomolar levels; (ii) most compounds were more active than were medicinal antibiotics, such as tetracycline or vancomycin, at comparable concentrations; (iii) the bactericidal activities of the teas could be accounted for by the levels of catechins and theaflavins as determined by high-pressure liquid chromatography; (iv) freshly prepared tea infusions were more active than day-old teas; and (v) tea catechins without gallate side chains, gallic acid and the alkaloids caffeine and theobromine also present in teas, and herbal (chamomile and peppermint) teas that contain no flavonoids are all inactive. These studies extend our knowledge about the antimicrobial effects of food ingredients.     

Presence and growth of Bacillus cereus in dehydrated potato flakes and hot-held, ready-to-eat potato products purchased in New Zealand

Potato products prepared from dehydrated potato flakes have been implicated in foodborne illness incidents involving Bacillus cereus intoxications. B. cereus can survive as spores in potato flakes and can germinate and multiply in the rehydrated product. This study assessed the frequency and concentration of B. cereus in dehydrated potato flakes and hot-held, ready-to-eat mashed potato products. Of 50 packets of potato flakes tested, eight contained greater than 100 CFU/g B. cereus (maximum 370 CFU/g). The temperature of the potato portion of 44 hot-held food products was measured immediately after purchase, and 86% were below the safe hot-holding temperature of 60 degrees C. The potato portions were subsequently tested for B. cereus. Only two of the potato portions contained B. cereus at greater than 100 CFU/g, a potato-topped pastry (1000 CFU/g) and a container of potato and gravy (120 CFU/g). To assess multiplication of B. cereus in this food, we held rehydrated potato flakes with naturally occurring B. cereus at 37, 42, and 50 degrees C and tested them over 6 h. By 6 h, the number of B. cereus in potato stored at 37 degrees C had exceeded 10(3) CFU/g, was greater than 10(4) CFU/g at 50 degrees C, and was close to 10(6) CFU/g at 42 degrees C. Growth data were compared to predictions from the U.S. Department of Agriculture Pathogen Modeling Program (PMP 7.0). The PMP predictions were found to simulate the measured growth better at 42 degrees C than at 37 degrees C. Hot-held potato products should be safe for consumption if held at 60 degrees C or above or discarded within 2 h.     

Antimicrobial and antioxidant activities of carvacrol microencapsulated in hydroxypropyl-beta-cyclodextrin

Carvacrol is a hydrophobic compound that exhibits high antimicrobial and antioxidant activities. Cyclodextrins are used to increase solubility and dissolution through water-insoluble compounds inclusion into their hydrophobic cavities. Hence, this study aimed to characterize carvacrol inclusion complexes with hydroxypropyl-beta-cyclodextrin (HPBCD) by establishing the physico-chemical properties and evaluate their antimicrobial and antioxidant properties. Inclusion complexes were prepared by kneading (KN) and freeze-drying (FD) methods. Entrapment efficiency was 78.09 ± 1.24% for KN, and 83.74 ± 1.15% for FD. Polydispersity index was greater than 0.2 for both methods. Particle size for KN and FD were 0.360 ± 0.003 and 0.377 ± 0.007 μm, respectively. Carvacrol–HPBCD antimicrobial activity was higher (P < 0.05) than for free carvacrol for both bacteria, Escherichia coli K12 and Salmonella enterica serovar Typhimurium LT2, indicating that HPBCD increased water solubility and consequently increased contact between carvacrol and bacteria in medium. Antioxidant activity was lower (P < 0.05) for inclusion complexes indicating HPBCD makes carvacrol less available to react with free radical. The stability study indicated that light did not affect (P > 0.05) degradation, indicating that the microparticles were stable throughout storage. Therefore, carvacrol–HPBCD complexes may have important applications in the food industry as stable antimicrobial systems.     

Combined effect of lysozyme and nisin at different incubation temperature and mild heat treatment on the probability of time to growth of Bacillus cereus

Stochastic models can be useful to predict the risk of foodborne illness. The presence of Bacillus cereus in liquid egg can pose a serious hazard to the food industry, since a mild heat treatment cannot guarantee its complete inactivation. However, most of the information available in the scientific literature is deterministic, including growth of B. cereus. In this paper, a stochastic approach to evaluate growth of B. cereus cells influenced by different stresses (presence of nisin and lysozyme separately or in combination) was performed, using an individual-based approach of growth through OD measurements. Lag phase duration was derived from the growth curves obtained. From results obtained, histograms of the lag phase were generated and distributions were fitted. Normal and Weibull distributions were ranked as the bestfit distributions in experiments performed at 25 °C. At 16 °C, lag values (obtained in presence of combinations of both antimicrobials) were also fitted by a Gamma distribution. Predictions were compared with growth curves obtained in liquid egg exposed to mild heat, nisin and/or lysozyme to assess their validity.     

芽孢杆菌LWM1的分离鉴定及其对蜡样芽孢杆菌的抑制作用

从土壤样品中分离出10株芽孢杆菌（Bacillus spp.）,以蜡样芽孢杆菌（Bacillus cereus）为指示菌株,采用牛津杯扩散法筛选出一株具有较强抑菌活性的菌株LWM1。综合形态学、生理生化试验、基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）及16S rDNA基因序列同源性分析,菌株LWM1被初步鉴定为一株解淀粉芽孢杆菌（Bacillus amyloliquefaciens）,并研究了其在马铃薯葡萄糖水（PDW）和营养肉汤培养基（NB）中发酵上清液对蜡样芽孢杆菌的抑制效果。结果表明,PDW培养基更有利于菌株LWM1生长和抑菌物质产生。因此,可利用PDW培养基为主要底物大规模发酵制备菌株LWM1的抑菌物质。     

Effective use of nisin to control Bacillus and Clostridium spoilage of a pasteurized mashed potato product

Heat-resistant spore-forming bacteria such as Bacillus and Clostridium can survive and grow in cooked potato products. This situation represents both a public health problem and an economic problem. The natural food preservative nisin is used in heat-treated foods to prevent the growth of such bacteria. A cocktail of Clostridium sporogenes and Clostridium tyrobutyricum spores was inoculated into cooked mashed potatoes, which were vacuum packed, pasteurized, and incubated at 8 and 25 degrees C. The shelf life of the mashed potatoes at 25 degrees C was extended by at least 58 days with the addition 6.25 microg of nisin per g. At 8 degrees C, in control samples not containing nisin, the natural contaminant Bacillus grew, but the inoculated Clostridium strains did not until the temperature was raised to 20 degrees C after 39 days. No bacterial growth occurred in nisin-containing samples. The shelf life of the mashed potatoes was extended by at least 30 days with 6.25 microg of nisin per g. In trials involving a cocktail of Bacillus cereus and Bacillus subtilis strains, 6.25 microg of nisin per g extended the shelf life of mashed potato samples that were not vacuum packed by at least 27 days at 8 degrees C. At 25 degrees C, 25 microg of nisin per g extended shelf life by a similar period. Shelf life extension was also observed at lower nisin levels. Microbiological analysis of the mashed potato ingredients showed that a high spore level was associated with the onion powder. It is emphasized that the preservative and the ingredients must be well mixed to ensure good nisin efficacy. Nisin remained at effective levels after pasteurization, and good retention was observed throughout the shelf life of the mashed potatoes.     

Inactivation of spores of Bacillus cereus in cheese by high hydrostatic pressure with the addition of nisin or lysozyme

The objective of this work was to study high hydrostatic pressure (HHP) inactivation of spores of Bacillus cereus ATCC 9139 inoculated in model cheeses made of raw milk, together with the effects of the addition of nisin or lysozyme. The concentration of spores in model cheeses was approximately 6-log10 cfu/g of cheese. Cheeses were vacuum packed and stored at 8 degrees C. All samples except controls were submitted to a germination cycle of 60 MPa at 30 degrees C for 210 min, to a vegetative cells destruction cycle of 300 or 400 MPa at 30 degrees C for 15 min, or to both treatments. Bacillus cereus counts were measured 24 h and 15 d after HHP treatment. The combination of both cycles improved the efficiency of the whole treatment. When the second pressure-cycle was of 400 MPa, the highest inactivation (2.4 +/- 0.1 log10 cfu/g) was obtained with the presence of nisin (1.56 mg/L of milk), whereas lysozyme (22.4 mg/L of milk) did not increase sensitivity of the spores to HHP. For nisin (0.05 and 1.56 mg/L of milk), no significant differences were found between counts at 24 h and 15 d after treatment. Considering that mesophilic spore counts usually range from 2.6 to 3.0 log10 cfu/ml in raw milk, HHP at mild temperatures with the addition of nisin may be useful for improving safety and preservation of soft curd cheeses made from raw milk.     

Effective use of nisin to control lactic acid bacterial spoilage in vacuum-packed bologna-type sausage.

Lactic acid bacteria (LAB) commonly cause spoilage in minimal heat-treated vacuum-packed cured delicatessen meats. Predominant species are Lactobacillus sake and L. curvatus. LAB strains isolated from spoiled products of this type (liver sausage, ham and bologna sausage) were found to be sensitive to low nisin concentrations (maximum of 1.25 microg g(-1)). Addition of 25 microg g(-1) nisin (as Nisaplin) inhibited the growth of LAB spoilage organisms inoculated into vacuum-packed pasteurized bologna-type sausages stored at 8 degrees C. Control sausages became spoiled (>10(8) LAB CFU g(-1)) by day 7, whereas sausages containing nisin remained unspoiled for >50 days. The effect of three types of phosphates (used as emulsifiers) on nisin activity in the sausages was compared. LAB growth rate was fastest in samples containing orthophosphate, and slowest in sausages containing diphosphate. The shelf life was also greatly extended in the latter. Fat content also affected nisin activity. Nisin activity (as indicated by LAB inhibition) was greatest in samples containing 15% > 25% > 37% (wt/wt) fat. In a sausage formulation containing 37% fat and incorporating diphosphate as emulsifier, levels of nisin as low as 2.5 microg g(-1) showed antibacterial effects. A nisin level of 6.25 microg g(-1) totally inhibited LAB growth for over 4 weeks and 25 microg g(-1) for 5 weeks. Spoilage control was achieved in the same sausage formulation but with 25% (wt/wt) fat; 12.5 microg g(-1) nisin prevented LAB growth for 5 weeks.     

蜡样芽胞杆菌生长特性及大蒜精油对其抑菌活性的研究

主要研究了37℃条件下3种蜡样芽胞杆菌在营养肉汤中的生长状况,建立了37℃下蜡样芽胞杆菌在营养肉汤中的Boltzmann牛长模犁,3条牛长曲线相关系数鼯均大于0．97;检测了不同培养时间蜡样芽胞杆菌的产芽胞情况,结果表明1号菌株和14号菌株较早产芽胞,培养相同时间,产芽胞数：1号菌株,4号菌株〉标准菌株;采用牛沣杯法和平板计数法研究了大蒜精油对蜡样芽胞杆菌的抑制效果,结果表明浓度为lO。的人蒜精油对3种蜡样芽胞杆菌都有很好的抑制效果,3种菌株中l号菌株最难抑制。     

Deamidation of Soy Peptides and Proteins by Bacillus circulans Peptidoglutaminase

The ability of Bacillus circulans peptidoglutaminase to deamidate soy proteins was investigated. Peptidoglutaminase readily hydrolyzed the γ-amide of glutamine residues in soy peptides, but its activity toward soy proteins was low (0.4–1.3% deamidation). Molecular size and conformation of soy protein may be critical to enzymatic deamidation. Gel adsorption was used to partially purify the enzyme. Gel eluates exhibited higher acitivty than the cell extract toward soy peptides and all soy proteins but US globulin. The specific activity of the gel eluate toward 7S globulin and a water extract of soy flakes was doubled over the original cell extract.     

大蒜提取物对蜡样芽孢杆菌抑制效果的研究

该文采用抑菌圈法研究了大蒜的水提取物、乙醇提取物和酸性水溶液的提取物对蜡样芽孢杆菌的抑制作用.结果表明大蒜的乙醇提取物的抑菌效果好过水提取物,酸性的水溶液提取物效果最好,可以较好地控制蜡样芽孢杆菌的生长,有较好的应用前景.