Influence of water activity and temperature on growth and mycotoxin production by Alternaria alternata on irradiated soya beans

The aim of this study was to determine the effects of water activity (a_w) (0.99-0.90), temperature (15, 25 and 30 °C) and their interactions on growth and alternariol (AOH) and alternariol monomethyl ether (AME) production by Alternaria alternata on irradiated soya beans. Maximum growth rates were obtained at 0.980 a_w and 25 °C. Minimum a_w level for growth was dependent on temperature. Both strains were able to grow at the lowest a_w assayed (0.90). Maximum amount of AOH was produced at 0.98 a_w but at different temperatures, 15 and 25 °C, for the strains RC 21 and RC 39 respectively. Maximum AME production was obtained at 0.98 a_w and 30 °C for both strains. The concentration range of both toxins varied considerably depending on a_w and temperature interactions. The two metabolites were produced over the temperature range 15 to 30 °C and a_w range 0.99 to 0.96. The limiting a_w for detectable mycotoxin production is slightly greater than that for growth. Two-dimensional profiles of a_w × temperature were developed from these data to identify areas where conditions indicate a significant risk from AOH and AME accumulation on soya bean. Knowledge of AOH and AME production under marginal or sub-optimal temperature and a_w conditions for growth can be important since improper storage conditions accompanied by elevated temperature and moisture content in the grain can favour further mycotoxin production and lead to reduction in grain quality. This could present a hazard if the grain is used for human consumption or animal feedstuff.     

Effects of food preservatives on Alternaria alternata growth and tenuazonic acid production

The effects of different organic acids on Alternaria alternata growth and tenuazonic acid production (TeA) were evaluated. Both TeA pure toxin solution and TeA production in solid medium were considered. Sodium benzoate, potassium sorbate and sodium propionate, all preservatives commonly used by food industry in Argentina, were tested. TeA was stable as pure toxin solution when was treated with the salts of organic acids used. A differential effect was observed when the preservatives were evaluated in relation to A. alternata growth and TeA production in solid medium. L evels above 10mg/kg of sodium benzoate and potassium sorbate produced a total inhibition of fungal development and toxin biosynthesis. Sodium propionate produced a 59% decrease in A. alternata growth and total inhibition of TeA production only at the highest concentration of preservatives used.     

继代培养对链格孢菌生长及产毒的影响

目的 探究连续继代培养对链格孢菌(Alternaria alternata)菌株的生长以及产毒的影响。方法 将10株链格孢菌在马铃薯葡萄糖琼脂培养基(potato dextrose agar, PDA)上连续继代培养,分析菌株的生长、产孢情况;利用超高效液相色谱-串联质谱法(ultra performance liquid chromatography-tandem mass spectrometry,UPLC-MS/MS)检测并分析主要链格孢霉毒素[包括交链孢酚(alternariol,AOH)、交链孢酚单甲醚(alternariol monomethyl ether, AME)、交链孢烯(altenuene, ALT)、细交链格孢菌酮酸(tenuazonic acid, TeA)]的含量变化。结果 在PDA培养基中,连续继代培养链格孢菌极易出现角变、菌丝变白、菌丝生长速率加快等菌株退化现象。随着继代培养次数的增加,菌株生长速度加快,菌落直径变大,角变率增大;10株链格孢菌中有7株(MY-4、MY-12、MY-15、MY-73、MY-80、MY-103、MY-117)产孢量随着继代次...     

Effects of gamma radiation on the growth of Alternaria alternata and on the production of alternariol and alternariol monomethyl ether in sunflower seeds

The objective of the present study was to evaluate the effects of different gamma radiation doses on the growth of Alternaria alternata and on the production of toxins alternariol (AOH), and alternariol monomethyl ether (AME) in sunflower seed samples. After irradiation with 2, 5 and 7 kGy, the spore mass was resuspended in sterile distilled water and the suspension was inoculated into sunflower seeds. The number of colony-forming units per gram (CFU/g) was determined after culture on Dichloran Rose Bengal Chloramphenicol and Dichloran Chloramphenicol Malt Extract Agar. The presence of AOH and AME was investigated by liquid chromatography coupled to mass spectrometry. The radiation doses used resulted in a reduction of the number of A. alternata CFU/g and of AOH and AME levels when compared to the nonirradiated control group. Maximum reduction of the fungus (98.5%) and toxins (99.9%) was observed at a dose of 7 and 5 kGy, respectively. Under the present conditions, gamma radiation was found to be an alternative for the control of A. alternata and, consequently, of AOH and AME production in sunflower seeds.     

Worldwide stable carbon and nitrogen isotopes of Big Mac® patties: An example of a truly “glocal” food

The Big Mac®, McDonald’s® signature burger, is a global food served in over 100 countries. We measured carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios of Big Macs® from twenty-six countries. The δ¹³C values varied from −25.4‰ to −11.1‰, representing cattle-rearing systems based exclusively on C₃ plants, exclusively on C₄ plants, or both C₃ and C₄ plants. Median δ¹⁵N value was 6.6‰; the 25th and 75th percentile were 5.9‰ and 7.3‰, respectively. Calculated percentages of imported beef were consistent with the δ¹³C values of purchased Big Macs®. Japanese patties had higher δ¹³C values than expected based on that country’s C₃ agriculture, however Japan imports beef from Australia, where C₄ plants are prevalent. Lower latitude countries generally had higher δ¹³C values than higher latitude countries, reflecting the larger distribution of C₄ plants in warm regions. Although Big Macs® are a global food, we conclude they also contain local components.     

Effect of heat shock on the fatty acid and protein profiles of Cronobacter sakazakii BCRC 13988 as well as its growth and survival in the presence of various carbon,nitrogen sources and disinfectants

In the present study, Cronobacter sakazakii, a foodborne pathogen, was first subjected to heat shock at 47 °C for 15 min. Effect of heat shock on the fatty acid and protein profiles, carbon and nitrogen source requirements as well as the susceptibilities of C. sakazakii to Clidox-S, a chlorine-containing disinfectant and Quatricide, a quaternary ammonium compound were investigated. Results revealed that heat shock increased the proportion of myristic acid (14:0), palmitic acid (16:0) and the ratio of saturated fatty acid to unsaturated fatty acid, while reducing the proportion of palmitoleic acid (16:1) and cis-vacceric acid (18:1). In addition, eleven proteins showed enhanced expression, while one protein showed decreased expression in the heat-shocked compared to the non-heat-shocked cells. Non-heat-shocked cells in the medium supplemented with beef extract exhibited the highest maximum population. On the contrary, the highest maximum population of heat-shocked C. sakazakii was noted in the medium having either tryptone or yeast extract as the nitrogen source. Among the various carbon sources examined, the growth of the test organism, regardless of heat shock, was greatest in the medium having glucose as the carbon source. Furthermore, heat shock enhanced the resistance of C. sakazakii to Clidox-S or Quatricide.     

Water activity and temperature effects on mycotoxin production by Alternaria alternata on a synthetic tomato medium

Alternaria spp. have been reported to be the most frequent fungal species invading tomatoes. Certain species, in particular the most common one, A. alternata, are capable of producing several mycotoxins in infected plants and in agricultural commodities. Alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TA) are some of the main Alternaria mycotoxins that can be found as contaminants of food. The objective of this study was to determine the effect of water activity (a_w, 0.904, 0.922, 0.954, and 0.982) and temperature (6, 15, 21 and 35 °C) on mycotoxin production on a synthetic tomato medium of a cocktail inoculum of five strains of A. alternata isolated from tomato fruits affected by Blackmould. The optimum AOH production occurred at 0.954 a_w after 28 days of incubation at 21 °C. A temperature of 21 °C was the most favourable for AOH synthesis at all a_w levels. The maximum concentration of AME was determined at 0.954 a_w and 35 °C. The optimum conditions for TA accumulation were 0.982 a_w and 21 °C. At the 0.904 a_w no growth or germination was registered at 6 °C and 15 °C over the whole incubation period. At 21 °C and 35 °C growth occurred slowly but none of the toxins were detected at this a_w level. In general, high a_w levels were favourable for mycotoxin production. None of the other toxins was detected at quantifiable levels at 6 °C after the whole incubation period. A storage temperature of 6 °C or below could be considered as safe for tomato fruits and high moisture tomato products (a_w > 0.95), in relation with Alternaria toxins. The results obtained here could be extrapolated to evaluate the risk of spoilage in tomato fruits and tomato products caused by this pathogen.     

Growth and mycotoxin production by fungi in atmospheres containing 80% carbon dioxide and 20% oxygen

The effect of atmosphere containing 80% CO₂ and 20% O₂ on growth of Mucor plumbeus, Fusarium oxysporum, Byssochlamys fulva, Byssochlamys nivea, Penicillium commune, Penicillium roqueforti, Aspergillus flavus, Eurotium chevalieri and Xeromyces bisporus was investigated. Production of aflatoxin by A. flavus, patulin by B. nivea, roquefortine C by P. roqueforti, and cyclopiazonic acid by P. commune was also studied. Fungal growth was evaluated by three methods: colony diameter, hyphal length or mycelium dry weight and ergosterol content. Among the nine fungal species examined, two E. chevalieri and X. bisporus, did not grow under these conditions. In this study, fungi differed in their response to modified atmospheres in biomass, ergosterol content, mycotoxin production and morphology. Reductions of 57.8-96.9%, 73.7-99.6% and 91.5-99.9% were obtained in colony diameter, hyphal length and ergosterol content, respectively, under this atmosphere compared to air. Ergosterol content was more affected in most species than other measurements. Patulin, cyclopiazonic acid and roquefortine C were produced in this atmosphere, although levels were very low and aflatoxin was not produced at all. Growth was quite extensive as measured by colony diameters, but hyphal lengths were low and ergosterol production was also affected in all species of this study.     

Effect of water activity and temperature on growth of Alternaria alternata on a synthetic tomato medium

Alternaria alternata is a toxigenic fungus, predominantly responsible for Blackmould of ripe tomato fruits, a disease frequently causing substantial losses of tomatoes, especially those used for canning. The objective of this study was to determine the effect of water activity (a_w, 0.904, 0.922, 0.954, 0.982) and temperature (6, 15, 21 and 35 °C) on germination and radial growth rate on a synthetic tomato medium of a cocktail inoculum of five strains of A. alternata isolated from tomato fruits affected by Blackmould. The shortest germination time (1.5 days) was observed at 0.982 a_w, both at 21 °C and 35 °C. The germination time increased with a reduction on a_w. The fastest growth rate was registered at 0.982 a_w and 21 °C (8.31 mm/day). Growth rates were higher when a_w increased. No growth or germination was observed at the lowest a_w level evaluated (0.904) after 100 days of incubation at 6 °C and 15 °C. A temperature of 6 °C caused a significant reduction in growth rates, even at the optimum a_w level. The knowledge on the ecophysiology of the fungus in this substrate is necessary to elaborate future strategies to prevent its development and evaluate the consumer health risk.     

糖碳源和氨基酸氮源对苍白杆菌属发酵产生物表面活性剂的影响

该实验为优化苍白杆菌（Ochrobactrum sp.）产生物表面活性剂的发酵条件,比较了不同糖碳源（蔗糖、乳糖、甘油、木糖、果糖）、氨基酸氮源（谷氨酸、天冬氨酸、赖氨酸、精氨酸和缬氨酸）、碳氮比（C/N）（1、10、20、30、40）对生物表面活性剂发酵的影响。结果表明,最优碳源为蔗糖,发酵5 d达最大乳化活性56.30%;最优氮源为天冬氨酸,发酵4 d达最大乳化活性54.00%;最优C/N为10,发酵4 d达最大乳化活性55.75%。     

Lipase production by Rhizopus oryzae growing on different carbon and nitrogen sources

Nitrogen and carbon sources influencing the growth and production of lipase by Rhizopus oryzae were studied. High yields of enzyme activity were obtained when proteose peptone was the nitrogen source in media with olive oil (MWO) and without olive oil (MWHO). Carbon sources increased lipase activity in MWHO but decreased it slightly in the presence of oil. Lipase activity was significantly (P < 0.5) higher in MWO than in MWHO. Biomass concentration was also higher in the presence of oil. Industrial by-products bran and whey have been used as efficient media for the production of lipase by R oryzae. © 1999 Society of Chemical Industry     

不同氮源对脱胚玉米挤出物发酵生产柠檬酸的影响

为了选择合适的氮源,提高使用脱胚玉米进行柠檬酸发酵的产率,该文将脱胚玉米经低温加酶挤压处理得到脱胚玉米挤出物,作为发酵原料用于柠檬酸生产。使用该挤出物制备发酵液,采用黑曲霉Co827作为发酵菌种,添加无机氮源((NH_4)_2SO_4、NH_4NO_3、NH_4Cl)或有机氮源(尿素、玉米渣)进行柠檬酸发酵。结果表明,无机氮源中添加质量浓度3 g/L的(NH_4)_2SO_4促进产酸的效果较好,有机氮源中添加质量浓度1 g/L糖化后玉米渣效果较好。由发酵产酸的效果可知,脱胚玉米经低温加酶挤压处理后制备柠檬酸发酵液,在同等条件下添加糖化后玉米渣有机氮源(柠檬酸产率9.82 g/100 g)优于添加(NH_4)_2SO_4的无机氮源(柠檬酸产率7.86 g/100 g)的发酵效果。上述研究为提高脱胚玉米生产柠檬酸的产率、降低生产成本、提高玉米综合利用率的研究提供参考。     

Intraspecific variability of growth and patulin production of 79 Penicillium expansum isolates at two temperatures

Penicillium expansum is the main species responsible for patulin production in apples and pears. Generally, fruit is stored at suboptimal conditions for mould growth and this situation could influence on the intra-species variability in both capability for growth and mycotoxin production. The aim of this research was to assess the impact of suboptimal environmental conditions on the intra-specific variability of P. expansum growth and patulin production using seventy nine isolates of this mould. Petri dishes with Apple Concentrate Agar Medium (ACAM) were inoculated centrally and incubated at two temperatures, one near optimal (20 °C) and the other representative of suboptimal cold storage (1 °C). For each condition, 10 Petri dishes were inoculated, and colony growth and patulin production was measured over time. The Kruskal-Wallis test revealed significant differences among growth rate (μ) and lag phase (λ) within the seventy nine assayed isolates. Coefficients of variation revealed a wider dispersion of μ (mm/day) and λ (days) at 1 °C compared with 20 °C. There were significant differences (p < 0.05) among patulin levels (ng/mm²) for the different conditions, values being lower at the lower temperature. Coefficients of variation revealed a wider dispersion of mycotoxin production at 1 °C. In order to address the strain variability in growth initiation and prove the well-established notion of reducing patulin production in foods by preventing fungal growth, a greater number of strains should be included.     

Protective effect of Pracparatum mungo extract on carbon tetrachloride-induced hepatotoxicity in rats

Pracparatum mungo is a traditional and functional food in Traditional Chinese Medicine, especially for treating a variety of liver disorders. In this study, we first report the in vivo hepatoprotective effect of P. mungo extract (PME) on carbon tetrachloride (CCl₄)-induced acute hepatotoxicity in rats. Pre-treatment with PME for 56 days significantly reduced the impact of CCl₄ toxicity on the serum markers of liver damage, aspartate aminotransferase (AST) and alanine aminotransferase (ALT). The results were confirmed histopathologically. In addition, an increased lipid hydroperoxide (LPO), a decreased glutathione (GSH) concentration and a decreased superoxide dismutase (SOD) were observed in the hepatic tissues. On the contrary, treatment of PME prior to the administration of CCl₄ resulted in markedly decreased lipid peroxidation, increased the levels of GSH and SOD in rats. The results indicated that PME has a protective effect against acute hepatotoxicity induced by the administration of CCl₄ in rats, and that the hepatoprotective effects of PME may be due to both the inhibition of lipid peroxidation and the increase of antioxidant activity.     

How three adventitious lactic acid bacteria affect proteolysis and organic acid production in model Portuguese cheeses manufactured from several milk sources and two alternative coagulants

Model cheeses were manufactured according to a full factorial experimental design to help shed light on the individual and combined roles played by 3 native lactic acid bacteria (Lactococcus lactis ssp. lactis, Lactobacillus brevis, and Lactobacillus plantarum) upon proteolysis and organic acid evolution in cheese. The model cheeses were manufactured according to a generally representative Portuguese artisanal protocol, but the (ubiquitous) adventitious microflora in the cheesemaking milk were removed via sterilization before manufacture; therefore, the specific effects of only those lactic acid bacteria selected were monitored. In addition, 2 types of coagulant (animal and plant) and 3 types of cheesemaking milk (cow, sheep, and goat) were assessed to determine their influence on the final characteristics of the model cheeses. The nature of the coagulant appeared to be essential during the first stage of proteolysis as expected, whereas the contribution of those bacteria to the pools of total free AA and organic acids was crucial afterward. This was especially so in terms of the differences observed in the metabolisms of lactic acid (in the case of Lactococcus spp.) as well as acetic and citric acids (in the case of Lactobacillus spp.).     

温度和叶面湿润时数对烟草赤星病菌侵染的影响

在控制条件下接种烟草赤星病菌的试验结果表明 ,在品种和菌株组成一定的情况下 ,接种温度 (DT)和叶面湿润时数 (WD)是影响病菌侵染的 2个主要因素。接种温度在 12～ 37℃范围内 ,病菌可以侵染寄主 ,成功侵染的最适温度为 2 7～ 30℃。在适宜温度条件下 ,接种后保湿 2h病菌即可侵入 ,保湿时间延长 ,侵染概率增大。侵染概率与接种温度、叶面湿润时数及其互作之间具有线性关系。     

Isolation of Alicyclobacillus and the influence of different growth parameters

Alicyclobacillus species are thermo-acidophilic, endospore-forming bacteria that are able to survive pasteurisation and have been implicated in a number of spoilage incidents involving acidic foods and beverages. The aim of this study was to compare three isolation methods used for the detection of Alicyclobacillus acidoterrestris and to investigate the influence of incubation temperature on the growth of A. acidoterrestris and A. acidocaldarius. Peach juice samples inoculated with A. acidoterrestris K47 were analysed using either the International Federation of Fruit Juice Producers (IFU) Method No. 12 (Method A), which involved spread plating onto Bacillus acidoterrestris (BAT) agar at pH 4.0; Method B, which involved pour plating using potato dextrose agar (PDA) at pH 3.7; or Method C, which made use of membrane filtration followed by incubation on K agar at pH 3.7. The performance of the three methods differed significantly, with the IFU Method No. 12 recovering the highest percentage of cells at 75.97%, followed by Method B at 66.79% and Method C at 3.43%. These findings strengthen the proposal of the IFU for the use of the IFU Method No. 12 as a standard international method for the detection of Alicyclobacillus. To investigate the effect on growth of different incubation temperatures A. acidoterrestris (three strains) and A. acidocaldarius (two strains) were incubated at either 45 °C or 25 °C. Growth at 25 °C was slower and maximum cell concentrations were lower (1 × 10⁵-10⁶ cfu/mL compared to 1 × 10⁷-10⁸ cfu/mL) than at 45 °C for A. acidoterrestris. A. acidocaldarius was unable to grow at 25 °C and cell concentrations decreased by 1-2 logs. Since a growth temperature of 25 °C could not inhibit growth of A. acidoterrestris, cooling to room temperature (20°-25 °C) is not an effective control measure for A. acidoterrestris inhibition.