Effect of Calcium Propionate and Water Activity on Growth and Aflatoxins Production by Aspergillus flavus

ABSTRACT: The efficacy of calcium propionate at 2 different doses (0.5% and 1%) against growth and aflatoxins production by Aspergillus flavus (A-2092) was investigated in vitro on Czapek yeast extract agar at different levels of water activity (a_w) in the range of 0.94 to 0.996a_w. A. flavus spores germinated on all calcium propionate and a_w treatments; however, 1% calcium propionate at 0.94 a_w delayed the germination process for up to 10 d. The growing rate of mycelia was slower (0.28 mm/d) at 1% calcium propionate and 0.94 a_w. Aflatoxins (B1, B2, G1, and G2) were also produced minimally (36.1, 1, 1.86, and 1.01 ng/g of media, respectively) at the aforementioned dose rate of calcium propionate and water activity. It was concluded that addition of calcium propionate and a_w amelioration can prove effective tools for suppressing the germination, growth rate, and aflatoxins production by A. flavus in substrate.     

气体二氧化氯对谷物表面黄曲霉杀灭效果研究

采用气体二氧化氯作为杀菌防霉剂,以接种于甜荞、苦荞上的黄曲霉菌作为研究对象,探究气体二氧化氯浓度和作用时间对杀菌效果的影响,并确定不同载体的最优杀菌浓度和时间的组合。试验结果表明:气体二氧化氯对黄曲霉菌的杀灭效果显著。8.5 mg/L的气体二氧化氯作用于甜荞表面30 min,杀菌率达到98.4%;4.5 mg/L的气体二氧化氯作用于苦荞表面10 min,杀菌率达到99.9%。     

Use of PCR for Detecting Aspergillus flavus in Maize Treated by Gamma Radiation Process

The aim of this study was to verify the effects of gamma radiation process on the fungal DNA and the application of PCR in the detection of Aspergillus flavus in irradiated maize grains. The samples were inoculated with a toxigenic strain and incubated under controlled conditions of relative humidity, water activity, and temperature for 15 days. After incubation, the samples were treated with gamma radiation with doses of 5 and 10 kGy and individually analyzed. The use of PCR technique showed the presence of DNA bands of Aspergillus flavus in all irradiated samples that showed no fungal growth in agar medium.     

热休克对小麦未成熟种子萌发、生物发光和抗氧化酶活性的影响

以小麦（Triticum aestivum L.）品种石4185为材料,研究了45 ℃处理0～120 min对小麦未成熟籽粒谷甘胱肽转移酶（GST）、谷胱甘肽还原酶（GR）、过氧化氢酶（CAT）和过氧化物酶（POD）活性, 超微弱发光,种子萌发和愈伤组织诱导的影响.结果表明,热休克处理使未成熟籽粒萌发率、愈伤组织诱导率和GST活性明显增加,且其作用随处理时间的延长而增大;在处理过程中, CAT活性先减少后增加,热休克对GR活性无明显影响.GST的活性与蛋白质质量分数呈显著正相关.     

Spread of Aspergillus flavus and aflatoxin accumulation in postharvested maize treated with biocontrol products

Maize is a major staple crop and calorie source for many people living in Sub-Saharan Africa. In this region, Aspergillus flavus causes ear rot in maize, contributing to food insecurity due to aflatoxin contamination. The biological control principle of competitive exclusion has been applied in both the United States and Africa to reduce aflatoxin levels in maize grain at harvest by introducing atoxigenic strains that out-compete toxigenic strains. The goal of this study was to determine if the efficacy of preharvest biocontrol treatments carry over into the postharvest drying period, the time between harvest and the point when grain moisture is safe for storage. In Sub-Sahara Africa, this period often is extended by weather and the complexities of postharvest drying practices. Maize grain was collected from fields in Texas and North Carolina that were treated with commercial biocontrol products and untreated control fields. To simulate moisture conditions similar to those experienced by farmers during drying in Sub-Sahara Africa, we adjusted the grain to 20% moisture content and incubated it at 28 °C for 6 days. Although the initial number of kernels infected by fungal species was high in most samples, less than 24% of kernels were infected with Aspergillus flavus and aflatoxin levels were low (<4 ppb). Both toxigenic and atoxigenic strains grew and spread through the grain over the incubation period, and aflatoxin levels increased, even in samples from biocontrol-treated fields. Our molecular analysis suggests that applied biocontrol strains from treated fields may have migrated to untreated fields. These results also indicate that the population of toxigenic A. flavus in the harvested grain will increase and produce aflatoxin during the drying period when moisture is high. Therefore, we conclude that preharvest biocontrol applications will not replace the need for better postharvest practices that reduce the drying time between harvest and storage.     

不同基因型玉米籽粒发育过程中糖代谢相关酶活性的比较

对高淀粉玉米与低淀粉玉米籽粒发育过程中蔗糖代谢和淀粉合成相关酶活性的变化动态进行了比较研究。结果表明,费玉3号籽粒支链淀粉、直链淀粉及总淀粉积累速率高于豫玉22;费玉3号籽粒支链淀粉、直链淀粉及总淀粉含量大于豫玉22;豫玉22的高峰黏度、低谷黏度、最终黏度及胶凝值均显著高于费玉3号,其崩解值和糊化温度低于费玉3号;豫玉22的可溶性糖含量高于费玉3号;费玉3号的腺苷二磷酸葡萄糖焦磷酸化酶(ADPG-PPase)活性、尿苷二磷酸葡萄糖焦磷酸化酶(UDPG-Ppase)活性、可溶性淀粉合成酶(SSS)活性、束缚态淀粉合成酶(GBSS)活性高于豫玉22。     

高效液相色谱法同时检测粮谷中的黄曲霉毒素和赭曲霉毒素

建立粮谷类食品中黄曲霉毒素(B1、B2、G1 和G2)和赭曲霉毒素A 的同时检测方法。样品经过甲醇- 水(80:20,V/V)提取,液液萃取净化和富集后,三氟乙酸衍生,采用Agilent ZORBAX SB-C18 色谱柱(4.6mm ×250mm),以乙腈和体积分数2% 冰醋酸溶液为流动相梯度洗脱,在线变换波长荧光检测。根据3 倍信噪比的峰 响应值,确定黄曲霉毒素(B1、B2、G1 和G2)和赭曲霉毒素A 检出限分别为0.06、0.03、0.18、0.05μg/kg 和0.51μg/kg,上述5 种毒素分别在质量浓度0.05～100、0.125～25.00、0.05～100、0.125～25.00μg/L 和0.05～50.00μg/L 范围内呈线性相关,相关系数r 分别为0.9998、0.9998、0.9998、0.9996 和0.9998;在玉米、大米、小麦3 类样品中加标回收率平均为71.73%～115.37%,相对标准偏差为3.00%～9.88%,方法学验证结果表明,黄曲霉毒素和赭曲霉毒素A 5 种毒素同时检测结果与现行国标的单独检测方法检测结果无显著性差异(P ＞ 0.05)。     

Modeling Growth Rate and Assessing Aflatoxins Production by Aspergillus flavus as a Function of Water Activity and Temperature on Polished and Brown Rice

Abstract: The aim of this study was to model the radial growth rate and to assess aflatoxin production by Aspergillus flavus as a function of water activity (a_w 0.82 to 0.92) and temperature (12 to 42 °C) on polished and brown rice. The growth of the fungi, expressed as colony diameter (mm) was measured daily, and the aflatoxins were analyzed using HPLC with a fluorescence detector. The growth rates were estimated using the primary model of Baranyi, which describes the change in colony radius as a function of time. Total of 2 secondary models were used to describe the combined effects of a_w and temperature on the growth rates. The models were validated using independent experimental data. Linear Arrhenius–Davey model proved to be the best predictor of A. flavus growth rates on polished and brown rice followed by polynomial model. The estimated optimal growth temperature was around 30 °C. A. flavus growth and aflatoxins were not detected at 0.82 a_w on polished rice while growth and aflatoxins were detected at this a_w between 25 and 35 °C on brown rice. The highest amounts of toxins were formed at the highest a_w values (0.90 to 0.92) at a temperature of 20 °C after 21 d of incubation on both types of rice. Nevertheless, the consistencies of toxin production within a wider range of a_w values occurred between 25 to 30 °C. Brown rice seems to support A. flavus growth and aflatoxin production more than the polished rice. Practical Application: The developed models can be used to estimate to what extent the change in grain ecosystem conditions affect the storage stability and safety of grains without the need for running long‐standing storage study. By monitoring the intergranular relative humidity and temperature at different locations in the storage facility and inputting these data into the models, it is directly possible to assess either the conditions are conductive for the growth of A. flavus or aflatoxin production.     

Production of Grain Whisky and Ethanol from Wheat,Maize and Other Cereals

Wheat replaced maize as the main cereal raw material for Scotch grain whisky production 20 years ago. However, other cereals might also have potential for use in grain distilleries and ethanol production. Studies of the properties of wheat, maize, sorghum and millet, showed that they had good potential for grain distilling and ethanol production at comparable nitrogen levels, and had physiological processing characteristics within the range accepted for wheat or maize. Rapid‐Visco Analysis (RVA) studies of low and high nitrogen wheat confirmed that, as well as influencing the amount of alcohol produced, the total nitrogen content of the grain had a strong influence on its processing characteristics. In contrast, the alcohol yield potential of maize, sorghum and millet appeared to be largely unaffected by the grain nitrogen levels. The study shows that, while it is possible for wheat to produce similar alcohol levels to those previously associated with maize, cereals other than wheat can potentially be used without detriment to alcohol yield or processing performance. These could be possible long term alternatives, if the economic viability of wheat was to change. The extracted cereal starches also showed significant differences from the original cereals, which had important implications for successful processing, both in terms of cereal selection as well as cooking and fermentation performance.     

小麦粮堆中玉米象和黄曲霉发生与二氧化碳浓度变化关系研究

明确害虫和霉菌发生与粮堆CO2浓度变化的关系,可为通过粮堆CO2浓度变化来监测虫霉发生奠定基础,有利于粮食储藏安全。本文构建了四种不同模拟粮堆(模拟自然带菌粮堆、模拟害虫发生粮堆、模拟霉菌发生粮堆、模拟虫霉发生粮堆),具体研究了25℃下水分12.5%和15%小麦四种模拟粮堆CO2浓度变化情况。结果显示,水分12.5%小麦模拟自然带菌粮堆CO2浓度30天内未出现显著变化(P＞0.05),模拟玉米象发生(50头/kg)粮堆第2天CO2浓度即达0.5%以上,第15-17天后快速增长,并于第23天达到4.5%,粮堆处于虫霉共同发生状态;模拟黄曲霉发生粮堆在第15天前CO2浓度变化不显著,至第30天时CO2浓度也未超过0.04%;玉米象与黄曲霉共同发生粮堆第2天CO2浓度即达到0.6%以上,第13-17天出现快速增长期,并于第26天达到4.5%以上,粮堆虫霉共同发生状态明显。水分15%小麦四种不同模拟粮堆CO2浓度变化与水分12.5%小麦粮堆基本一致,霉菌开始生长繁殖,黄曲霉发生粮堆、玉米象和黄曲霉共同发生粮堆的CO2浓度增加更快、幅度更大。分别对四种模拟粮堆CO2浓度变化进行模型拟合,各拟合模型均具有较高的精度。研究结果初步明确了害虫和霉菌发生时粮堆CO2浓度变化的关系,为利用粮堆CO2浓度变化来监测粮堆粮情变化提供参考。     

Aflatoxins and ochratoxin A and their Aspergillus causal species in Tunisian cereals

ABSTRACT

Occurrence of aflatoxins (AFs) AFB1, AFB2, AFG1, AFG2 and ochra toxin A (OTA) was studied in 65 samples of stored and freshly harvested wheat, barley and maize collected in Tunisia. The mycotoxins were simultaneously extracted and quantified by high performance liquid chromatography. Determination of AF-producing (section Flavi) and OTA-producing Aspergillus species (sections Nigri and Circumdati) was conducted in these samples by species-specific polymerase chain reaction (PCR). Results showed that most of maize samples were contaminated with AFs, data after storage showing lower values than those collected at harvest. All contaminated maize samples contained AFG1 and AFG2, among which 27.78% also had AFB1 and AFB2. This AFs pattern was consistent with the A. parasiticus toxin profile. A. flavus however showed the highest frequency in maize but was also found in barley and wheat where no AFs were detected. In contrast, OTA was neither found in maize nor in barley and only one wheat sample contained OTA. A. niger was the only OTA-producing species detected.     

Effect of Soybean Volatile Compounds on Aspergillus flavus Growth and Aflatoxin Production

ABSTRACT:  Soybean homogenates produced volatile compounds upon exposure to lipase. These induced volatiles were identified by SPME. Seventeen volatile compounds identified by SPME were chosen for determination of their ability to inhibit Aspergillus flavus growth and aflatoxin B₁ (AFB1) production in a solid media assay. These volatiles included aldehydes, alcohols, ketones, and furans. Of the tested compounds, the aldehydes showed the greatest inhibition of fungal growth and AFB1 production. These compounds inhibited up to 100% of the observed growth and AFB1 production as compared to the controls. The greatest activity by the aldehydes to disrupt growth was ranked as follows: 2,4 hexadienal > benzaldehyde > 2-octenal > ( E )-2-heptenal > octanal > ( E )-2-hexenal > nonanal > hexanal. The greatest activity by the aldehydes to reduce AFB1 was ranked as follows: ( E )-2-hexenal > 2,4 hexadienal > ( E )-2-heptenal > hexanal > nonanal. ( E )-2-hexenal and ( E )-2-heptenal were tested further in an A. flavus -inoculated corn kernel assay. Both compounds prevented colonization by A. flavus and eliminated AFB1 production when exposed to compound volumes < 10 μL as also shown in the solid media assay. The results suggest that soybeans react to lipase by production of potent antifungal volatiles.     

Effect of Cycling Temperatures on Aflatoxin Production by Aspergillus parasiticus and Aspergillus flavus in Rice and Cheddar Cheese

Initiation of growth, sporulation and aflatoxin production at cycling temperatures took less time than at 15°C but more than at 18°C and 25°C. A. parasiticus produced more aflatoxins on rice under cycling temperatures than at 25°C, 18°C or 15°C, while A. flavus produced less aflatoxin under cycling temperatures. A. parasiticus produced more aflatoxins on cheese under cycling temperatures than at 18°C or 15°C, but much less than at 25°C. A. flavus produced less aflatoxins on cheese under cycling temperatures than at 18°C and 25°C. Both organisms produced trace amounts of toxins at 15°C on cheese. Preincubation at 25°C for 2 days before temperature cycling did not increase aflatoxin production on rice but increased production on cheese. The rate of aflatoxin production on cheese decreased as the temperature decreased. No growth, sporulation or aflatoxin production was observed at 5°C on either rice or cheese.     

花粉玉米乳的研制

以花粉和玉米为原料,研制一种营养全面、均衡、有玉米和花粉风味的混合饮料。     

黄曲霉生长预测模型的建立及其在玉米储藏中的应用

玉米储藏条件不当很容易导致黄曲霉污染而产生对人畜有害的黄曲霉毒素,找到适当的储藏条件可以保证玉米安全储藏.对黄曲霉在不同的温度和环境相对湿度条件下的生长状态进行了研究.分析了黄曲霉菌落生长速度,找出了抑制黄曲霉生长的温度和湿度条件,对玉米安全储藏具有现实意义.     

Efficacy of water-dispersible formulations of biological control strains of Aspergillus flavus for aflatoxin management in corn

Field experiments were conducted in 2011 and 2012 to evaluate the efficacy of water-dispersible granule (WDG) formulations of biocontrol strains of Aspergillus flavus in controlling aflatoxin contamination of corn. In 2011, when aflatoxin was present at very high levels, there was no WDG treatment that could provide significant protection against aflatoxin contamination. The following year a new WDG formulation was tested that resulted in 100% reduction in aflatoxin in one field experiment and ≥ 49% reduction in all five WDG treatments with biocontrol strain 21882. Large sampling error, however, limited the resolution of various treatment effects. Corn samples were also subjected to microbial analysis to understand better the mechanisms of successful biocontrol. In the samples examined here, the size of the A. flavus population on the grain was associated with the amount of aflatoxin, but the toxigenic status of that population was a poor predictor of aflatoxin concentration.     

基质组分对黑曲霉发酵啤酒糟产木聚糖酶的影响

采用固态发酵培养黑曲霉，研究以啤酒糟为主要原料生产饲用木聚糖酶的最佳基质组分及其配比。结果表明，黑曲霉An54-2-1在啤酒糟：玉米芯：麸皮=6：2：2，NH4NO3 2％，Tween 800．1％的基质上，以1：1加水，接入3．5％的孢子悬液，置30℃下培养65h，产酶量达6196．803IU／g。     

云南大叶种晒青毛茶提取物对产毒黄曲霉生长及产毒的影响

普洱茶在发酵过程中,微生物组成十分复杂,尤其是黑曲霉等霉菌起到主要作用,因此一些消费者担心普洱茶在发酵过程中受到黄曲霉毒素(AFS)的污染。本文通过测定菌落直径、孢子萌发及菌丝体干重等方法研究云南大叶种茶提取物对产毒黄曲霉AS3.4408生长的影响;采用紫外荧光法和HPLC法研究云南大叶种茶提取物对产毒黄曲霉AFS生物合成的影响;并将产毒黄曲霉AS3.4408接种到云南大叶种茶叶中,检测茶叶中的AFS含量,以求对普洱茶的安全性进行评估。研究表明,云南大叶种茶提取物对产毒黄曲霉AS3.4408菌落的生长及产毒均具有显著的抑制作用,且存在明显的剂量依赖关系;将产毒黄曲霉AS3.4408接种到云南大叶种茶叶中,菌株生长良好,但茶叶基质经HPLC检测,未检测到黄曲霉毒素B1、B2、G1和G2,表明云南大叶种茶中的某种(些)成分对黄曲霉毒素的生物合成具有抑制作用。