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.     

The influence of modified atmospheres and their interaction with water activity on the radial growth and fumonisin B(1) production of Fusarium verticillioides and F. proliferatum on corn. Part I: the effect of initial headspace carbon dioxide concentration

The effect of modified atmospheres on the growth and fumonisin B(1) production of Fusarium verticillioides and Fusarium proliferatum on corn is presented in a series of two papers. In this, the first part, the effect of initial headspace (IH) carbon dioxide concentration and its interaction with water activity (a(w)) on growth and fumonisin B(1) production was evaluated. It was observed that at all a(w) values studied, increase in the IH CO(2) concentration generally resulted in a decrease in the colony growth rate (g, mm day(-1)) and maximum colony diameter (D(max), mm) and an increase in the lag phase duration (lambda, day). Although both a(w) and IH CO(2) concentration had significant and synergistic effects on g, a(w) had the largest effect. As little as 10% IH CO(2) completely inhibited the production of fumonisin B(1) by F. verticillioides. F. proliferatum was more resistant and required 40, 30 and 10% IH CO(2) at a(w) 0.984, 0.951 and 0.930, respectively, to completely inhibit fumonisin B(1) production. These results demonstrate that modified atmospheres containing high CO(2) levels could potentially be employed for the protection of corn from fungal spoilage and mycotoxin contamination during the post-harvest period.     

The influence of modified atmospheres and their interaction with water activity on the radial growth and fumonisin B(1) production of Fusarium verticillioides and F. proliferatum on corn. Part II: The effect of initial headspace oxygen concentration

This paper is the second in a series of two that describe the effect of modified atmospheres on the growth and mycotoxin production of Fusarium verticillioides and Fusarium proliferatum on corn. In this part, the effect of initial headspace (IH) oxygen concentration and its interaction with water activity (a(w)) on growth and fumonisin B(1) production was investigated. In addition, the impact of vacuum packaging and in-cooperation of O(2) scrubbing sachets was also studied. It was observed that at all a(w) values studied, reduction of IH O(2) concentration from 20 to 2% had no significant effect on the colony growth rate (g, mm d(-1)) and lag phase duration (lambda, d). However, g and lambda were positively and negatively correlated to a(w). The IH O(2) concentration was determined to have a a(w) dependent effect on the oxygen consumption rate. Although the maximum colony diameter (D(max), mm) decreased with the reduction of the IH O(2) level, the greatest mycelial density occurred at 10% IH O(2) for both isolates. This observation was accompanied by a trend of a decrease in the value of the IH O(2) level at which the most fumonisin B(1) was produced from 15 to 5% when the a(w) was decreased from 0.976 to 0.930 for F. verticillioides. For F. proliferatum the optimum conditions for fumonisin B(1) production shifted from 20% at a(w) 0.976 to 10% at both 0.951 and 0.930. Vacuum packaging and the in-cooperation of O(2) absorbing sachets completely inhibited the growth of both isolates. These results together with those reported in Part I of the study indicate that O(2) should preferably be completely excluded from modified atmospheres that are employed to protect stored corn from fungal growth and mycotoxin production.     

主动自发气调对枝孢菌的抑制效果

为研究主动自发气调对霉菌的抑制效果,以枝孢菌为试材,研究O2/CO2主动自发气调对枝孢菌的抑菌效果.本试验设计初始O2/CO2体积比例分别为60％O2+40％CO2、70％O2+30％CO2、80％O2+20％CO2、90％O2+10％CO2和自然空气(ck)5个处理,在(28±0.5)℃处理条件下对枝孢菌的菌落直径、...     

不同含氧气调包装方式对调理鸭肉制品的保鲜效果

为延长调理鸭肉制品货架期,将调理后的鸭肉分别以托盘包装为对照,用不同含氧气调包装方式（MAP1（20% CO2＋80% N2）、MAP2（20% CO2＋40% O2＋40% N2）、MAP3（20% CO2＋80% O2））对调理鸭肉制品进行保鲜处理（0～4 ℃）,测定调理鸭肉贮藏期间微生物指标和生理生化指标。结果表明：与托盘包装组相比,3 种气调包装方式均能有效抑制调理鸭肉中微生物生长,减少挥发性盐基氮产生;含氧组（MAP2和MPA3）的保鲜效果显著优于MAP1组和对照组（P＜0.05）,含氧组的保质期均为12 d;在贮藏12 d时,MAP2组的TBARS值和肠杆菌数显著低于MAP3组（P＜0.05）,MAP3组的菌落总数显著低于MAP2组（P＜0.05）,且这两组的TVB-N含量和L*值均无显著差异（P＞0.05）。综合分析,MAP2包装对调理鸭肉制品保鲜效果最好。     

Simple and economical culture of Campylobacter jejuni and Campylobacter coli in CO2 in moist air.

Strains of Campylobacter jejuni and C. coli representing the 18 serogroups (Lior) most commonly isolated from humans in Canada were grown on solid media in an atmosphere of 10% CO2 in moist air, 99% relative humidity. When the growth of all 18 serogroups on Mueller Hinton agar in a microaerobic atmosphere (5% O2, 10% CO2 and 85% N2) was compared with the growth of all 18 serogroups on the same media in 10% CO2 in moist air, colony sizes were significantly larger (p less than 0.05) for strains grown in 10% CO2 in moist air. No significant difference in colony numbers was seen between the two atmospheres. The addition of blood to the media significantly enhanced the growth of the campylobacters in both types of atmospheres (p less than 0.05). This simple CO2 atmosphere permitted the use of a common CO2 incubator thereby reducing the cost and difficulty of culturing these organisms.     

The effect of vacuum and modified atmosphere packaging on the shelf-life of lamb primals, stored at different temperatures

Lamb primals (shoulders) were vacuum packaged or packaged in modified atmospheres containing 80% O(2)/20% CO(2), 50% CO(2)/50% N(2) or 100% CO(2), and stored at 5 or 0 °C. They were examined microbiologically at 7 day intervals for total counts obtained under (1) aerobic, (2) CO(2) enriched or (3) anaerobic conditions; B. thermosphacta; pseudomonad and Enterobacteriaceae counts. Off-odour assessments were also carried out at these times. In general, there were no significant differences between the total counts obtained from the different incubation conditions in any of the atmospheres. The only exception was noted in 80% O(2)/20% CO(2) at 5 °C. Significant differences between atmospheres for the total counts were observed at 0 °C only. In the case of B. thermosphacta, the pseudomonads and the Enterobacteriaceae, differences between atmospheres were noted at 5 and 0 °C. In general, vacuum packs and 80% O(2)/20% CO(2), and the two high CO(2) atmospheres fell into distinct groups. Storage temperature had a significant effect on all three counts. The relationship between bacterial counts and time was modelled using regression analysis. Data from total counts gave the equations of best fit. Significant differences between atmospheres in terms of off-odour production were observed at 5 °C only. The effect of temperature on off-odour production was significant in all atmospheres except 100% CO(2). A scheme was devised based on the growth of different groups of organisms which facilitated comparisons between studies on packaged meats. The results of the present work and that of others are discussed in relation to the different growth patterns which developed with packaging treatments and storage temperature.     

Fitting of colony diameter and ergosterol as indicators of food borne mould growth to known growth models in solid medium

Growth of a range of 14 common food spoilage fungal species was evaluated along time as a function of both colony diameter and ergosterol content on malt extract agar. Growth was assessed under different environmental conditions following a central composite design. The suitability of using either linear, Gompertz's or Baranyi's models for primary modelling of the results was tested. Regarding colony diameters, using either linear or asymptotic Baranyi's function gave better estimations of growth rate and lag phase when no asymptotic trend was observed. When a decrease in growth rate was observed with time, standard Baranyi's model was chosen, although the search for new mechanistic models specific for moulds would probably improve the estimations. The use of Gompertz equation led, in general, to overestimated parameters. Ergosterol showed good performance as a fungal growth indicator for the whole range of species. Finally, significant correlation coefficients were found between ergosterol and colony diameters, suggesting that both parameters may be useful for primary modelling and thus for subsequent secondary modelling.     

Effect of packaging atmosphere on the microbial attributes of pearlspot (Etroplus suratensis Bloch) stored at 0-2 degrees C

Effect of packaging atmosphere (air and under different modified atmospheres (MAs), 40% CO2/60% O2, 50%/50% O2, 60% CO2/40% O2, 70% CO2/30% O2 and 40% CO2/30% O2/30% N2) on the microbial and biochemical attributes of fresh pearlspot (Etroplus suratensis Bloch) stored at 0-2 degrees C was investigated. Trimethylamine nitrogen (TMA-N) and thiobarbituric acid (TBA) values remained lower than the proposed acceptability limits throughout the storage period. Results demonstrated that storage of pearlspot under air and MA 40% CO2/30% O(2)/30% N(2) resulted in growth of Enterobacteriaceae, Aeromonas and H(2)S-producing bacteria including Shewanella putrefaciens, while all other packaging atmospheres did not allow multiplication of Enterobacteriaceae and Aeromonas within 3 weeks. Aeromonas spp. identified were Aeromonas hydrophila, Aeromonas veronii biovar sobria and A. veronii biovar veronii. Significant reduction (p<0.01) was noticed in Aeromonas population of pearlspot stored under MA 60% CO2/40% O2 and 70% CO2/30% O2. A delay of growth of Pseudomonas below 5.0log(10)cfug(-1) was observed during the 15th day of storage at 0-2 degrees C under modified atmosphere packaging (MAP) conditions. Growth of faecal streptococci was significantly inhibited in all the packaging atmospheres at 0-2 degrees C during the entire storage period. Survival of coagulase positive Staphylococci (<50cfug(-1)) in low numbers was noticed during storage in all the packaging atmospheres. Clostridium botulinum toxin was not detected. All the packaging atmospheres did not allow multiplication of sulphite-reducing clostridia at 0-2 degrees C during the entire storage period. Packaging in MA 60% CO2/40% O2 resulted in the inhibition of growth of Aeromonas and Enterobacteriaceae, and the slowest growth of psychrotrophic bacteria, H(2)S-producing bacteria, including Shewanella putrefaciens and Pseudomonas and extended microbiological shelf life to 9-10 days. This study confirms the survival of potentially pathogenic A. hydrophila, A. veronii biovar sobria and A. veronii biovar veronii capable of growth at low temperature in pearlspot stored under MA.     

Mould contaminants on Jarlsberg and Norvegia cheese blocks from four factories.

Visible mould from 225 blocks of the Norwegian semi-hard cheeses Jarlsberg and Norvegia from four factories were subcultured and identified. Altogether 23 different fungal species were detected. The two most important contaminating species were Penicillium commune and P. palitans, constituting 21.4% and 17.9% of the total isolates, respectively. The other dominating contaminants were P. roqueforit spp. roqueforti, Geotrichum candidum, P. solitum and P. crustosum. These species, together with P. commune and P. palitans, represented 80.9% of the total isolates. P. commune, P. palitans, P. roqueforti spp. roqueforti and P. solitum were most common contaminants on cheese produced in all four factories, while G. candidum was found to be important on Jarlsberg cheese from only one factory. P. crustosum was one of the dominating species on Norvegia cheese.     

Production of zearalenone in vitro and in corn grains stored under modified atmospheres

The production of zearalenone by an isolate of Fusarium equiseti was studied in chemically defined medium and in corn grains stored under modified atmospheres. An increase in the concentrations of sucrose or xylose in Czapek's medium resulted in increased toxin production, while no toxin was produced when lactose was present in the medium. Methionine (10(-2) and 10(-3) M) and cystine (10(-3) M) added to Czapek's medium inhibited zearalenone production. When amino acids or nitrogen salts were added as the sole nitrogen source, only alanine, tryptophan and NH4Cl totally inhibited zearalenone production. Zearalenone production was inhibited almost completely in high-moisture corn grains (27%) kept under atmospheres enriched with high CO2 levels (60%, 40% or 20%) with either 20% or 5% O2. However, a lower amount of CO2 was needed to inhibit fungal development and toxin formation when a reduced O2 level was applied.     

Growth and metabolic activity of Shewanella putrefaciens maintained under different CO2 and O2 concentrations

Growth, trimethylamine (TMA), off-odour and biogenic amine production by a strain of Shewanella putrefaciens isolated from spoiled hake (Merlucius merluccius L.) and cultured in a model system, were tested under four different gas compositions (60% CO2/40% O2, 60% CO2/15% O2/25% N2, 40% CO2/60% O2, 40% CO2/40% O2/20% N2) and under air. After 3 weeks of incubation, the control (air) batch showed the highest microbial counts (> 9 log cfu/ml) and TMA concentrations (45 mg N-TMA/100 ml), and strong putrid off-odours were detected from day 15. High amounts of putrescine and cadaverine were produced in this batch, but histamine increased only slightly. Batches under controlled atmospheres showed reduced growth, TMA, off-odour and biogenic amine production. The 40% CO2/60% O2 mixture had the strongest inhibitory effect on bacterial growth, while the 60% CO2/15% O2/25% N2 mixture was less effective. Putrescine and histamine production was lowest in S. putrefaciens under the 40% CO2/60% O2 mixture. However, the level of histamine in S. putrefaciens was higher under 40% CO2/40% O2/20% N2 than when the bacteria was incubated in air. Under the gas mixtures, there was a similar decrease in the production of cadaverine and agmatine by S. putrefaciens, irrespective of the gas concentrations. The production of 2-phenylethylamine appeared to be inhibited under any atmospheric condition.     

Effect of different concentrations of carbon dioxide and low concentration of carbon monoxide on the shelf-life of fresh pork sausages packaged in modified atmosphere

This paper reports the effects of different concentrations of carbon dioxide and the presence of low levels of carbon monoxide on quality attributes throughout storage of fresh pork sausages. Four pork forelegs (initial pH 5.5-5.7) were used to prepare a total of 120 fresh sausages, which were packaged in different atmospheres containing (%O(2)/%CO(2)/%N(2)): 0/20/80; 0/60/40; 40/20/40; 40/60/0; 80/20/0; and 0.3% CO/30% CO(2)/rest argon. The packs were stored for 20 days at 2±1 °C in the dark. Three packs for each atmosphere were opened every 4 days for subsequent analysis of pH, colour CIE L*, a*, b*, TBARS formation, microbial psychotrophic aerobes and sensory discolouration and off-odour. Results showed that increasing concentrations of carbon dioxide promoted oxidation of both myoglobin and lipids, most probably due to its effect of lowering pH. Therefore, preservation of colour and odour of fresh pork sausages packaged in modified atmosphere was better achieved using atmospheres containing low CO(2) concentrations (20%) rather than high (60%). However, their shelf-life depended also on the concentration of O(2); 20% CO(2) with high O(2) (80%) enhanced the red colour, but shortened shelf-life, while 20% CO(2) in the absence of O(2) extended freshness to 16 days. The atmosphere containing 0.3% CO, together with 30% CO(2), maintained the red colour for 20 days, but failed to keep fresh odour longer than 16 days.     

Microbiological quality of shredded Cheddar cheese packaged in modified atmospheres

The microbiological quality of shredded Cheddar cheese packaged in different modified atmospheres with and without oxygen scavengers included in the packaging film was studied with the aim of determining how modified air packaging would affect the mould species present on shredded Cheddar cheese. The film with oxygen scavengers was more effective than the control film against mould growth, whereas the 73% CO₂/27% N₂ atmosphere resulted in the cheese with the best microbiological qualities. The three modified atmospheres and the packaging film influenced the mycoflora of shredded Cheddar cheese as the mould species isolated initially differed, from those isolated at 16 weeks in the six treatments. This study demonstrated that O₂ scavengers were effective in controlling the growth of moulds on shredded Cheddar cheese.     

O2/CO2气调对贮藏期间姜蛆生理代谢及死亡率的影响

生姜贮藏期间,异形眼蕈蚊（姜蛆）危害严重,对生姜贮藏造成极大的经济损失。研究O2/CO2气调对姜蛆生理代谢、生长发育的影响,并探讨O2/CO2气调对姜蛆的致死效应。实验设置了气体体积分数分别为100% O2、95% O2＋5% CO2、90% O2＋10% CO2、85% O2＋15% CO2和自然大气（CK）5 个处理,对20 ℃、相对湿度85%～95%条件下姜蛆生理活性指标进行定期测定。结果表明,O2/CO2气调,特别是95% O2＋5% CO2处理,能够显著抑制姜蛆生物酶活性,在处理60 h时,姜蛆的蛋白酶、多酚氧化酶、乙酰胆碱酯酶、羧酸酯酶、谷胱甘肽-S-转移酶活性分别降低了14.7%、53.59%、72.52%、80.3%、61.63%,死亡率比初始高出96.22%,达到97.83%。90% O2＋10% CO2处理对姜蛆控制效果稍差,但与95% O2＋5% CO2处理之间不存在显著差异。研究结果显示,O2/CO2气调可作为生姜贮藏保鲜过程中控制姜蛆危害的潜在措施。     

紫外线杀菌结合气调包装技术对带鱼品质的影响

为研究紫外线杀菌结合气调包装（modified atmosphere packaging,MAP）技术对带鱼品质的影响,以4 ℃真空冷藏鲜带鱼为空白对照,采用紫外线（253.7 nm）照射处理实验组带鱼,并对其进行不同气体比例的MAP,置于4 ℃条件冷藏。贮藏期间以带鱼的感官评分、硫代巴比妥酸值、挥发性盐基氮含量和菌落总数4 项指标作为带鱼品质的判定依据,对不同处理条件下带鱼品质的变化进行对比分析。结果表明：4 ℃真空包装贮藏条件下的带鱼可贮藏6 d,而在紫外线照射条件下,采用不同气体比例的MAP可将带鱼的保质期分别延长至12 d（50% CO2＋20% O2＋30% N2）、10 d（40% CO2＋20% O2＋40% N2）、13 d（60% CO2＋40% N2）和15 d（60% CO2＋7% O2＋33% N2）。这说明相比于4 ℃真空包装的贮藏条件,紫外线杀菌结合MAP技术能够有效延长带鱼贮藏期,在抑制带鱼脂肪氧化的同时阻碍带鱼体内细菌的生长。     

Physical characteristics of lamb primals packaged under vacuum or modified atmospheres

Lamb primals (shoulders) were packaged under vacuum, 80% O(2)/20% CO(2), 50% CO(2)/50% N(2) or 100% CO(2) and stored at 5 or 0 °C. Pack contents were examined at 7 day intervals to determine the composition of the pack atmosphere, drip loss, colour (muscle and fat) and pH (surface and internal). The composition of the gas atmospheres changed very little during storage. The only significant differences between developed head space compositions above primals stored at the two different temperatures (5 and 0 °C) were noted in packs stored for 28 days under 80% O(2)/20% CO(2). Low levels of drip loss (<0.5%) were noted in all packs stored under the modified gas atmospheres. In contrast, significantly higher levels of drip loss (0.5-1.1%) were noted in vacuum packaged lamb stored at 5 and 0 °C. Acceptable muscle colour was observed 2 hr after opening of all packs. The only significant differences between atmospheres for lean muscle colour were noted after 28 days storage. Fat colour did not generally change during storage in any of the atmospheres, apart from a slight bleaching effect at 7 days. There were no significant differences between the surface or internal pH values noted after storage under any of the atmosphere/temperature combinations. In general, higher pH values were observed at the surface of the meat than in the interior. This pattern was noted before and after storage.     

Comparison of methods for the assessment of growth of food spoilage moulds in solid substrates

The objective of the study was to evaluate the general suitability of ergosterol content, CFU, and colony diameters determinations for a range of fungi representing food spoilage moulds for the assessment of their growth on solid substrates, in particular intermediate moisture foods. Sixteen food-borne mould species were inoculated onto DG18 agar overlaid with cellophane, allowing determination of a direct measurement of biomass density weighing. The samples were also evaluated with regard to visible and microscopic colony diameters, total ergosterol content, Thoma counts, viable CFU counts, and so on. The same parameters were assayed in the spore suspensions obtained from those cultures. Data were evaluated by multivariate data analysis using projection methods such as principal component analysis (PCA), showing some groupings among the measured variables, mainly linked to the sporulating/nonsporulating nature of the different species tested. Ratios among the different variables were obtained, compared among the species, and evaluated along time (2-10 days). It was concluded that, as a general rule for all the species, ergosterol content and colony diameters were better correlated to fungal biomass dry weight than CFU counts were. Conversion factors were 0.3-3 microg ergosterol mg(-1) biomass dry weight and 76-227 mg biomass dry weight cm(-2), depending on the species.     

O_2/CO_2气调对西兰花保鲜的后续效应

为了研究O_2/CO_2气调对西兰花保鲜后续效应的影响,采用40%O_2+60%CO_2分别处理西兰花1~3 d,然后撤去气体进行自然大气贮藏,同时以自然空气为对照组(CK),对贮藏于(15.0±0.5)℃条件下的西兰花乙烯释放量、呼吸速率、叶绿素含量、VC含量、乙醇及乙醛含量进行定期测定。结果表明,40%O_2+60%CO_2处理1、2、3 d后的西兰花分别能保鲜6、7、9 d,CK中的西兰花保鲜期为4 d。同时,40%O_2+60%CO_2处理3 d的西兰花在后续的空气贮藏期间,能较好地控制乙烯释放量和呼吸速率,延缓其叶绿素和VC含量的下降,且乙醇、乙醛未表现出积累现象。研究表明,运输过程中对西兰花进行O_2/CO_2气调处理,销售货架期使之处于自然空气条件,利用O_2/CO_2气调的后续效应可有效延长西兰花保鲜期。     

Effects of controlled atmospheres on microbial spoilage, electrolyte leakage and sugar content of fresh 'ready-to-use' grated carrots

The effects of controlled atmospheres (CO2 concentrations ranging from 0.03 to 40% and O2 concentrations ranging from 21 to 1%, measured in pack) were studied on fresh 'ready-to-use' grated carrots, stored at 10°C. High CO2 or low O2 conditions favour the growth of lactic acid bacteria (LAB) on grated carrots, but not in a sterile carrot medium, and induce an increased potassium ion leakage. A 25% CO2 and 2% O2 atmosphere improves retention of sugars.
Grated carrots were inoculated by a strain of Leuconostoc mesenteroides , which caused increased potassium ion leakage and exudation only under an atmosphere containing 40% CO2 and 10% O2.
The origin of the spoilage of 'ready-to-use' grated carrots is discussed.