Comparison of newly isolated strains of Lactobacillus delbrueckii subsp. lactis for hydrogen peroxide production at 5 degrees C

Isolates of Lactobacillus delbrueckii subsp. lactis obtained from raw milk samples were compared for the ability to produce hydrogen peroxide (H2O2) at 5 degrees C. Nineteen out of 101 lactobacilli isolated were identified as L. delbrueckii subsp. lactis. The isolates of L. delbrueckii subsp. lactis from most raw milk samples produced more H2O2 than did isolates of other species of lactobacilli from the same samples. Seven isolates of L. delbrueckii subsp. lactis, which produced the highest levels of H2O2 at 5 degrees C were selected for comparison with a laboratory strain, L. delbrueckii subsp. lactis I. In 24 h, isolate RM2-5 produced 7.0 microg/10(9) cfu in buffer containing 5 mM sodium lactate and 4.4 microg/10(9) cfu in buffer containing 5 mM glucose. Three other isolates also produced more H2O2 on sodium lactate than on glucose. However, three remaining new isolates produced more H2O2 on glucose than on sodium lactate. All seven of the most active new isolates of L. delbrueckii subsp. lactis produced significantly higher concentrations of H2O2 than did L. delbrueckii subsp. lactis I in both solutions. Strain RM2-5 produced more H2O2 than did the other six most active newly isolated strains of L. delbrueckii subsp. lactis in this comparison.     

Biomass and Patulin Production by Byssochlamys nivea in Apple Juice as Affected by Sorbate, Benzoate, SO2 and Temperature

The effects of potassium sorbate, sodium benzoate, SO₂ and incubation temperature on biomass and patulin production by Byssochlamys nivea in apple juice were determined. Growth at 21, 30 and 37°C over a 25-day incubation period was significantly retarded by 75 ppm SO₂, 150 ppm potassium sorbate and 500 ppm sodium benzoate. Biomass accumulated to approximately 500 mg/100 ml in control samples of apple juice. Patulin was produced in the highest concentrations at 21°C after 20 days incubation. After reaching a maximum concentration at 30 and 37°C, a rapid decline in patulin content was observed. Patulin production was also observed at 12°C. On the basis of concentration, SO₂ had the most significant effect on the rate of biomass and patulin production by B. nivea followed by potassium sorbate and sodium benzoate, respectively.     

Inactivation ofEscherichia coliO157:H7 by combinations of GRAS chemicals and temperature

Reported outbreaks of foodborne illness involvingEscherichia coliO157:H7 have increased in the United States during the last decade, with a variety of food products being implicated as vehicles of infection. Studies were carried out to determine the efficacy of combinations of various GRAS chemicals and moderate temperatures to killE. coliO157:H7. A five-strain mixture ofE. coliO157:H7 of approximately 10⁸cfu ml⁻¹was inoculated into 0·1% peptone solutions containing 1·0 or 1·5% lactic acid plus 0·1% hydrogen peroxide, 0·1% sodium benzoate or 0·005% glycerol monolaurate. The solutions were incubated at 8°C for 0, 15 and 30 min; at 22°C for 0, 10 and 20 min; or at 40°C for 0, 10 and 15 min; populations ofE. coliO157:H7 were determined at each sampling time. At 40°C, the pathogen was inactivated to undetectable levels within 10 min of incubation in the presence of 1·0 or 1·5% lactic acid plus hydrogen peroxide, and within 15 min of incubation in the presence of 1·5% lactic acid plus sodium benzoate or glycerol monolaurate. At 22°C, complete inactivation ofE. coliO157:H7 was observed after 20 min of exposure to 1·5% lactic acid plus 0·1% hydrogen peroxide, whereas a reduction of 5 log₁₀cfu ml⁻¹was observed with a treatment of 1·5% lactic acid plus glycerol monolaurate. None of the treatments resulted in total inactivation of the pathogen at 8°C. The aforementioned treatments could potentially be used to inactivate or reduceE. coliO157:H7 populations on raw produce.     

Optimization of Aspergillus niger Fermentation for the Production of Glucose Oxidase

A number of nutritional factors influencing glucose oxidase (EC 1.1.3.4) production by Aspergillus niger NCIM 545 were studied. The synthesis of glucose oxidase by A. niger was investigated in two steps using submerged fermentation at 30 ± 2 °C and 180 rpm for 96 h. Primarily, nutritional components were selected by one-factor-at-a-time method, and the significance of each component with respect to glucose oxidase production was identified by Plackett–Burman design (seven variables including six nutritional viz. sucrose, sodium nitrate, peptone, calcium carbonate, magnesium sulfate, and potassium dihydrogen phosphate, and one dummy or unassigned variable were studied with eight experiments). In the second step, concentration of most significant factors and their interaction were studied with response surface methodology (central composite design). Each variable in the design was studied at five different levels, with all variables taken at a central coded value of zero. Considerable amount of glucose oxidase was produced from A. niger species with sucrose as the carbon source, sodium nitrate as the inorganic nitrogen source, and peptone as the organic nitrogen source. Glucose oxidase activity increased remarkably by 28.93 fold (from 0.00993 to 0.29 U ml⁻¹) with CaCO₃-supplemented media. The outcome of Plackett–Burman design showed CaCO₃, peptone, and MgSO₄ as significant parameters. Further optimization using a three-factor central composite design with 20 experiments increased yield of glucose oxidase from 0.29 to 2.05 U ml⁻¹ (sevenfold) with a decrease in cultivation time from 96 to 72 h.     

Versuche zur Glucoseoxidation in Glucose-Fructose-Gemischen mittels fixierter Glucoseoxidase und Katalase

Trials to Oxidize Glucose in Mixtures of Glucose and Fructose by Means of Fixed Glucose Oxidase and Catalase The glucose oxidase catalase system from Aspergillus niger was fixed via glutardialdehyde binding onto particles of gelatin previously hardened by formaldehyde. Working and stability characteristics of the resulting enzyme preparation are given as a function of pH-value, temperature and substrate concentration. The data are discussed with regard to the possible industrial use. Basic trials for the application of the enzyme combination were carried out in four different reactor types. Highest glucose conversion rates were obtained when hydrogen peroxide was used for oxygen supply instead conventional aeration, but the peroxide caused a rapid decrease of the enzymes stability, so that the economical use of the enzyme system is not given. Application trials in a special type of stirred tank with reaction temperatures less than 10 °C brought encouraging results with regard to the possible industrial application.     

INFLUENCE OF SODIUM NITRITE ON THE AEROBIC CATABOLISM OF GLUCOSE BY STAPHYLOCOCCUS AUREUS1

The inhibitory effect of sodium nitrite upon glucose catabolism by Staphylococcus aureus was investigated using [U–^{1 4}C] glucose, liquid chromatography, and gas-liquid chromatography. Acetate and acetoin are the end-products of glucose metabolism by S. aureus at 37°C and pH 6.3. In the presence of inhibitory levels of sodium nitrite, acetate and lactate with traces of pyruvate and acetoin are the end products. Acetate production per unit of growth is significantly lower in the sodium nitrite inhibited cultures. The decreased acetoin accumulation was not due to inhibition of diacetyl reduction. The production of acetoin was induced by the addition of acetate to the sodium nitrite containing medium.     

Increased Aflatoxin Production by Aspergillus parasiticus Under Conditions of Cycling Temperatures

The effects of cycling temperatures (5°C for 12 hr and 25°C for 12 hr) on aflatoxin production by Aspergillus parasiticus NRRL 2999 in yeast extract sucrose (YES) medium were studied. Cycling temperatures, after preincubation at 25°C for various times, resulted in more aflatoxin B₁, G₁, and total aflatoxin production than did constant incubation at either 25°C, which is generally considered to be the optimum for aflatoxin production, or 15°C, which is the same total thermal input as the 5-25°C temperature cycling. With increased preincubation time at 25°C, toxin production increased and the lag phase of growth was shortened or not evident. Cultures that were preincubated at 25°C for 1, 2, and 3 days prior to onset of temperature cycling showed the greatest increase in maximum aflatoxin production over the 25°C and 15°C constant temperatures. Cultures that were not preincubated at 25°C but subjected to constantly fluctuating temperatures produced maximum amounts of aflatoxin equivalent to cultures incubated at a constant 25°C. The maximum aflatoxin production at all temperatures studied occurred during the late log phase of growth and at pH minimums. Aflatoxins were found in higher concentrations in the broth than the mycelia under temperature cycling conditions, at 15°C, and at 25°C during the first 21 days of incubation, whereas greater amounts of toxin were retained in mycelium at 25°C in the later incubation period (28-42 days).     

Microbiological Safety of Cooked Beef Roasts Treated with Lactate, Monolaurin or Gluconate

Beef roasts were pumped with sodium lactate, glycerol monolaurin or sodium gluconate and inoculated with Clostridium sporogenes and Listeria monocytogenes either internally or on external (surface) locations. Microbiological evaluations were conducted during simulated wholesale (2°C), retail (7°C) and consumer storage (10°C) and after simulated mishandling (25°C). Sodium lactate resulted in effective inhibition of pathogens at concentrations up to 3.5%. Glycerol monolaurin was less effective than sodium lactate. Sodium gluconate did not provide significant control of these pathogens. No chemical or quality effects of these compounds occurred on the beef roasts except a lower pH and increased purge caused by monolaurin.     

Water Activity and Temperature Effects on Fungal Growth and Ochratoxin A Production by Ochratoxigenic Aspergillus carbonarius Isolated from Tunisian Grapes

ABSTRACT: This study investigated the effects of temperature (15 to 37 °C) and water activity (0.90 to 0.99) on the growth and production of ochratoxin A (OTA) by Aspergillus carbonarius cultured on synthetic nutrient medium (SNM) after 5 and 10 d of incubation. Total of 8 ochratoxigenic A. carbonarius, isolated from vineyards located in different regions of Tunisia, were used. Growth data were modeled by the flexible model of Baranyi and growth rates at each set of conditions were obtained. For both growth and OTA production, optimal water activity was 0.99; however, optimal temperature varied. The optimal temperature for growth was 30 °C. At 37 °C, the growth rate decreased significantly (P < 0.05). Maximum toxin production occurred at temperatures in the range of 15 to 25 °C with the optimum one depending on the isolate tested. Significant amounts of OTA were produced after only 5 d of incubation. Our results showed that A. carbonarius isolated from Tunisian grapes behave as those from European and Australian grapes, as reported in the literature, although some differences in trends for growth and OTA production were observed.     

Resistance of phages lytic to pathogenic Escherichia coli to sanitisers used by the food industry and in home settings

Phages are potentially useful as antimicrobial agents in food‐processing environments, provided they can remain active upon extended storage and in the presence of sanitisers. Survival of six phages lytic against enteropathogenic (EPEC) and shiga‐toxigenic (STEC) Escherichia coli strains was assessed upon storage at 4 °C, ?20 °C and ?70 °C in phosphate‐buffered‐saline (PBS) and Tris‐magnesium‐gelatine buffer (TMG) for up to 1 year. The phages were also exposed to ethanol, sodium hypochlorite, peracetic acid, quaternary ammonium chloride (biocide A), hydrogen peroxide/peracetic acid/peroctanoic acid (biocide B), p‐toluensulfonchloroamide (biocide D) and alkaline chloride foam (biocide C). Plaque‐forming units remained unchanged when the phages were stored at 4 °C in both buffers tested, but decreased by 3.5 and 5.7 log₁₀ PFU when stored in PBS at ?20 and ?70 °C, respectively. Moreover, TMG seems to be the most protective suspension medium with decreasing temperature because a 1?log₁₀ PFU reduction was observed at ?20 and ?70 °C. Incubation in 100% ethanol for 24 h reduced plaque counts only by 2.5 log₁₀ PFU. In 10 ppm of sodium hypochlorite and in biocide B (0.13%), the counts decreased by ~5 and ~6 log₁₀ PFU after 15 min. Finally, biocide A and D reduced counts by 4 and 2–4 log₁₀ PFU after 30 min and 8 h of incubation, respectively. Phages were completely inactivated only by peracetic acid and biocides C and E. Therefore, the phages evaluated might be potentially applied together with classical sanitisers such as ethanol and industrial biocides A, B and D, in disinfection programs against pathogenic STEC and EPEC strains.     

Bacterial Histamine Production as a Function of Temperature and Time of Incubation

Optimal temperature, lower temperature limit, extent, and rate of histamine production in a tuna fish infusion broth (TFIB) varied for the strains of Proteus morganii, Klebsiella pneumoniae, Hafnia alvei, Citrobacter freundii, and Escherichia coli studied. P. morganii and K. pneumoniae produced large quantities of histamine in a relatively short incubation period (<24 hr) at 15°C, 30°C, and 37°C; production was fastest at 37°C. H. alvei, C. freundii, and E. coli produced toxicologically significant levels of histamine (>2500 nmoles/ml) only at 30°C and 37°C on prolonged incubation (≥48 hr). At 72 hr of incubation, optimal temperature for histamine production was 37°C for E. coli and C freundii; 30°C for P. morganii strain 110SC2, K. pneumoniae, and H. alvei; and 15°C for P. morganii strain JM. The lower temperature limits for production of toxicologically significant levels of histamine in TFIB were 7°C for K. pneumoniae; 15°C for both P. morganii strains; and 30°C for H. alvei, C. freundii, and E. coli.     

Maillard Reaction Products as Encapsulants for Fish Oil Powders

The use of Maillard reaction products for encapsulation of fish oil was investigated. Fish oil was emulsified with heated aqueous mixtures comprising a protein source (Na caseinate, whey protein isolate, soy protein isolate, or skim milk powder) and carbohydrates (glucose, dried glucose syrup, oligosaccharide) and spray‐dried for the production of 50% oil powders. The extent of the Maillard reaction was monitored using L*, a*, b* values and absorbance at 465 nm. Encapsulation efficiency was gauged by measurement of solvent‐extractable fat and the oxidative stability of the fish oil powder, which was determined by assessment of headspace propanal after storage of powders at 35 °C for 4 wk. Increasing the heat treatment (60 °C to 100 °C for 30 to 90 min) of sodium caseinate‐glucose‐glucose syrup mixtures increased Maillard browning but did not change their encapsulation efficiency. The encapsulation efficiency of all heated sodium caseinate‐glucose‐glucose syrup mixtures was high, as indicated by the low solvent‐extractable fat in powder (<2% powder, w/w). However, increasing the severity of the heat treatment of the sodium caseinate‐glucose‐glucose syrup mixtures reduced the susceptibility of the fish oil powder to oxidation. The increased protection afforded to fish oil in powders by increasing the temperature‐time treatment of protein‐carbohydrate mixtures before emulsification and drying was observed irrespective of the protein (sodium caseinate, whey protein isolate, soy protein isolate, or skim milk powder) and carbohydrate (glucose, glucose/dried glucose syrup, or oligosaccharide/dried glucose syrup) sources used in the formulation. Maillard reaction products produced by heat treatment of aqueous protein‐carbohydrate mixtures were effective for protecting microencapsulated fish oil and other oils (evening primrose oil, milk fat) from oxidation.     

Depletion of glucose in Egyptian egg white before dehydration

Glucose was completely removed from egg white in h by using Streptococcus lactis and 0.2% yeast extract at pH 6.0 and 30 °C. A distinct objectionable odour was developed accompanied by a change in the appearance of egg white. Using Aerobacter aerogenes at pH 7.0 and 37 °C, glucose depletion was completed after 3 to 4 h depending on the initial number of bacteria used. The undesirable changes in odour and appearance of egg white were not observed. Saccharomyces cerevisiae succeeded, in presence of 0.2% yeast extract, in depleting sugar in egg white in 9 h. The optimum pH for the reaction was in the range of 6.0 to 7.5 at 32 °C. Glucose oxidase powder of fungal origin was also used for glucose depletion. Glucose was completely removed after 8 h by adding 3.8 glucose oxidase units/100 ml egg white at pH 7.3 and 14.5 °C. 1.9 and 0.95 glucose oxidase units per ioo ml egg white were not enough for complete glucose removal. No objectionable odour or undesirable changes in egg white were observed.     

Clostridium sporogenes and Listeria monocytogenes: Survival and Inhibition in Microwave-ready Beef Roasts Containing Selected Antimicrobials

Beef roasts were pumped with brines containing phosphates and acetic acid, sodium lactate, potassium sorbate, or glycerol monolaurin, and cooked in-the-bag once or twice to 62.8°C. Samples were examined during storage at 2, 5, and 10°C and after mishandling at 25°C for survival of inoculated Clostridium sporogenes spores and Listeria monocytogenes. Clostridia and listeriae survived one cooking when surface inoculated and two cookings in roasts inoculated internally. Lactate in brine afforded protection against clostridial survival and growth in temperature-abused roasts. Clostridia grew after 24 hr at 25°C in untreated roasts cooked once, and after 48 hr of abuse in most others except those with lactate or monolaurin. Listeria survival was reduced by lactate and monolaurin in recooked surface-inoculated roasts.     

Effects of sodium metabisulphite,hydrogen peroxide and heat on aflatoxin B1 in lafun and gari - two cassava products

Sodium metabisulphite and hydrogen peroxide alone or in combination with heat (50–70°C) were found to be effective in degrading aflatoxin B1 (AFB1) in lafun and gari. Hydrogen peroxide (H₂O₂) at a concentration of 3 % in the aqueous phase gave a 12.5 % degradation of aflatoxin B1 in lafun and at 50°C, degradation levels of 25 % and 50 % were obtained with 6.0 and 9.0 % H₂O₂, respectively. When sodium metabisulphite was applied during the production of gari (a fermented cassava product heated to 50-70°C during production) AFB1 degradation levels were found to be 65.8 %, 60.9 %, 41.5 % and 36.6 %, respectively, for sodium metabisulphite levels of 1.0 %, 0.8 %, 0.5 % and 0.3 %.     

Multi-enzyme biosensors with amperometric detection for determination of lactose in milk and dairy products

 In home-made sensors coimmobilizing enzymes in thin-layer plexi-cells on natural protein membranes, three enzyme cells: β-galactosidase and galactose oxidase (A), β-galactosidase and glucose oxidase (B) and β-galactosidase, galactose oxidase and glucose oxidase (C) were built into a flow-injection-analyzer system. The lactose was decomposed and oxidized by the immobilized enzymes and the hydrogen peroxide generated during the enzymatic reactions was determined by amperometric detection. The parameters for biochemical and electrochemical reactions (concentration of buffer, temperature, flow rate) were optimized in each enzyme cell. The pH optima of the lactose measurement was determined in the three enzyme cells mentioned above. The pH optimum of the cells A, B and C were 6.4, 4.5 and 4.8, respectively. The measuring ranges were 1–5 mM, 2–10 mM and 1–5 mM, while the detection limits were 0.5, 1.0 and 0.5 mM, respectively. More than 600, 1000 and 800 samples could be measured with these cells, respectively. Commercial milk and instant dessert powder products were analysed also. Our results showed that the cells B and C were more suitable for the determination of the lactose content of milk. For samples of dairy products containing added glucose, starch and other carbohydrates, enzyme cell A could be used for the efficient determination of lactose in one step. Received: 24 August 1998 / Revised version: 9 November 1998     

Ames Test for Mutagenicity on Pacific Whiting Treated with Hydrogen Peroxide

Raw Pacific whiting (Merluccius productus) treated with hydrogen peroxide or potassium bromate was tested for mutagenicity by the Ames Salmonella/microsome assay with strains TA 98 and TA 100 without and with S-9 activation. To examine the effects of long-term exposure, cooked whiting treated with hydrogen peroxide and stored up to 6 months at -26°C was also tested. In contrast to the raw-treated fish, the cooked sample contained 78% catalasereactive peroxide up to 6 months later. For testing, acidic, neutral and basic fractions were obtained by modifying the procedure of Felton et al. (Mutat. Res., 1981) to reduce emulsion formation. No extract from either potassium bromate or hydrogen peroxide treatment produced mutagens.     

SAKE BREWING FROM LIQUEFIED-RICE WITH IMMOBILISED FUNGAL MYCELIA AND IMMOBILISED YEAST CELLS

Sake brewing from liquefied-rice solution with immobilised fungal mycelia and immobilised yeast cells was investigated. Rice was liquefied by α-amylase in order to improve fluidity. Aspergillus oryzae was used for the production of saccharifying enzymes, and Saccharomyces cerevisiae for fermentation. The saccharifying enzyme productivity of immobilised fungal mycelia grown in highly aerobic conditions was much higher than that of fungal mycelia grown in liquid culture. Furthermore, saccharifying enzyme production was stimulated by the use of liquefied-rice treated with protease. The enzyme activity of immobilised mycelia was 4.5 times higher than that of rice-koji. The saccharifying enzyme was produced 10 times over a period of about 30 d at 41°C using protease treated liquefied-rice. Ethanol production was carried out with immobilised yeast using liquefied-rice containing saccharifying enzyme extracted from immobilised fungal mycelia. 19.0% (v/v) ethanol was obtained after incubation at 15°C for 5 d.     

蜂蜜中抗菌活性物质及其抑菌作用机理研究进展

蜂蜜是由工蜂采集的花蜜及其自身分泌物混合而成的一种天然甜味物质,具有良好的抗菌活性,含有多种天然抗菌活性物质。近年来,已有大量研究报道了蜂蜜中抗菌活性物质的研究进展,包括甲基乙二醛、过氧化氢、多酚、抗菌肽和王浆主蛋白等。大量研究表明,过氧化氢是蜂蜜中最重要的抗菌活性物质之一。本文着重综述了各抗菌有效活性物质在蜂蜜抑菌过程中所发挥的重要作用,进一步以蜂蜜中的过氧化氢为例,总结了葡萄糖氧化酶催化葡萄糖生成过氧化氢的过程,并对产生和降解过氧化氢的其他途径以及影响过氧化氢产生的理化因素进行了综述。合理调控蜂蜜中过氧化氢的产生,对蜂蜜抑菌乃至其他生物活性发挥起着重要的作用。本综述也为蜂蜜的临床安全用药及相关功能食品研发提供参考依据。     

Microbiological Characteristics of Enhancement Solutions

The objective of this study was to assess the survival of Escherichia coli K‐12 in solutions of ingredients used for enhancing meat products and to evaluate the effect of potentially lethal temperatures. Enhancement solutions were prepared to contain water only (W); water + salt + phosphate (control, C); water + salt + phosphate + sodium lactate (SL); water + salt + phosphate + sodium acetate (SA); or water + salt + phosphate + lactate + diacetate (SLDA). The SLDA solution resulted in the highest log reduction of E. coli K‐12 followed by SL. Heating solutions to 70 °C resulted in about a 4 log reduction, whereas heating to 60 °C produced about a 2 log reduction. For samples with an initial microbial load of 10⁶ colony‐forming units (CFU)/mL, addition of SL and heating to 50 °C resulted in about a 2 log reduction, addition of SA gave <0.5 log reduction, whereas addition of the SLDA combination produced a > 4.0 log reduction. The SLDA combination could allow for lower heating temperatures to achieve similar microbial reductions.