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.     

Effect of Volatile Components of Carrot Seed Oil on Growth and Aflatoxin Production by Aspergillus parasiticus

The effect of the volatile fraction of carrot seed oil (VCSO) and its components on the growth and aflatoxin production by Aspergillus parasiticus was studied. Geraniol, citral and terpineol prevented growth and therefore aflatoxin production. VCSO inhibited growth and no aflatoxin was produced. Limonene and terpinene did not affect growth but inhibited aflatoxin production. The addition of VCSO, limonene and terpinene decreased the rate of primary metabolism as demonstrated by the higher final pH of the medium. VCSO, limonene and terpinene reduced the growth rate, measured by the incorporation of [³H] amino acids into trichloracetic acid (TCA) insoluble protein. The addition of VCSO at anytime up to 5 days reduced the aflatoxin accumulation at 7 days.     

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).     

Aspergillus Parasiticus Growth and Aflatoxin Production on Dehydrated Taro

A study was made of Aspergillus parasiticus growth and aflatoxin production on four taro media. The critical equilibrium relative humidity (ERH) for natural mold growth on unsterilized dehydrated taro was 88% at 20°C. However, nontoxigenic A. parasiticus NRRL 1957 did not grow at this ERH on dehydrated raw taro incubated at 20°, 30°, or 40°C. Instead, the growth of A. parasiticus NRRL 1957 on dehydrated taro was optimum at 30°C and an ERH of 96%. Aflatoxin production by toxigenic A. parasiticus NRRL 2999 was investigated on four taro media under optimal growth conditions. Only moderate quantities of aflatoxins were produced by A. parasiticus NRRL 2999 on uncooked dehydrated taro, but cooking or supplementation with peptone stimualted mycelial growth and aflatoxin production slightly. Nevertheless, growth and aflatoxin production on cooked or peptone-supplemented taro media was low.     

Aflatoxin and Cyclopiazonic Acid Production by Aspergillus flavus Isolated from Contaminated Maize

Seven truck-loads of maize were tested for mycotoxin contamination. Aflatoxin was identified in all 7 at concentrations from 3 ng/g-501 ng/g (aflatoxin B₁+ B₂). Cyclopiazonic acid was identified in 4 loads with concentrations from 25-250 ng/g. Deoxynivalenol was found in 4 of 5 loads tested, over a range of 46-676 ng/g. Ninteeen isolates of Aspergillus flavus from the samples were tested for ability to accumulate cyclopiazonic acid and aflatoxin in liquid culture. Fourteen produced cyclopiazonic acid (0.5-135 μg/mL), 12 produced aflatoxin (0.01-0.70 μg/mL, aflatoxin B₁+ B₂), and one aflatoxin-producing isolate did not produce cyclopiazonic acid.     

Influence of Temperature, pH, Water Activity and Antifungal Agents on Growth of Aspergillus flavus and A. parasiticus

Effect of temperature, pH, water activity, and nine antifungal agents on growth of Aspergillus flavus and A. parasiticus was determined on Sabouraud-Dextrose Agar and on corn. Maximal growth of the two molds occurred at 33°C, the highest temperature used, pH of 5.0 and a_w of 0.99. At 15°C, growth was observed at a_w of 0.95 but not 0.90. Slight growth was observed at an a_w, of 0.85 at 27°C and 33°C. Nine antifungal agents (Botran, Orthocide, Poly-ram 80, Topsin-M, Thiram, Imazalil, sodium propionate, sodium sulfite and DDVP) were tested for inhibition of growth. Activity of the antifungals increased as the a_w was decreased. All antifungals showed inhibitory activity, but Imazalil and DDVP were the most effective agents at the lowest concentrations.     

Influence of Some Spice Essential Oils on Aspergillus Parasiticus Growth and Production of Aflatoxins in a Synthetic Medium

Gas-liquid chromatography was used to determine the essential oil compositions of thyme, cumin, clove, caraway, rosemary, and sage. The basic components of these oils were thymol, cumin aldehyde, eugenol, carvonc, borneol and thujonc, respectively. The antifungal potential of the oils against Aspergillus parasiticus were investigated. The essential oils caused complete inhibition of both mycelial growth and aflatoxin production. The effectiveness followed the sequence: thyme > cumin > clove > caraway > rosemary > sage. The major components of the essential oils produced an inhibitory effect at minimum inhibitory concentrations equal to those obtained with the oils.     

Aflatoxin-producing potential of Aspergillus flavus and Aspergillus parasiticus isolated from samples of smoked-dried meat

Over a period of three years 420 samples of various smoke-dried meat products, collected from individual households in different region of Croatia were analysed for the presence of aflatoxigenic strains of the Aspergillus flavus group. Strains of A. flavus and A. parasiticus were present in 17,8% of the samples, and aflatoxin-producing ability was tested in 75 strains. In relation to sequential method of aflatoxin detection, 5 of 8 isolates were found in the first step (fluorescence in aflatoxin-producing ability medium - APA) and all of them in the second step (extraction method from syntheses on moist shredded wheat - SW). A. flavus strains produced mainly aflatoxin B₁, and had various levels of toxigenicity (1.4–3.12 mg/kg). Some strains of A. parasiticus produced all four aflatoxins B₁ B₂ G₁ G₂, while the other ones produced AF B₁ + G₁ only, with concentrations of aflatoxins from 0.1 to 450 mg/kg.     

Aqueous extracts of Tulbaghia violacea inhibit germination of Aspergillus flavus and Aspergillus parasiticus conidia

Aspergillus flavus and Aspergillus parasiticus are important plant pathogens and causal agents of pre- and postharvest rots of corn, peanuts, and tree nuts. These fungal pathogens cause significant crop losses and produce aflatoxins, which contaminate many food products and contribute to liver cancer worldwide. Aqueous preparations of Tulbaghia violacea (wild garlic) were antifungal and at 10 mg/ml resulted in sustained growth inhibition of greater than 50% for both A. flavus and A. parasiticus. Light microscopy revealed that the plant extract inhibited conidial germination in a dose-dependent manner. When exposed to T. violacea extract concentrations of 10 mg/ml and above, A. parasiticus conidia began germinating earlier and germination was completed before that of A. flavus, indicating that A. parasiticus conidia were more resistant to the antifungal effects of T. violacea than were A. flavus conidia. At a subinhibitory extract dose of 15 mg/ml, hyphae of both fungal species exhibited increased granulation and vesicle formation, possibly due to increased reactivity between hyphal cellular components and T. violacea extract. These hyphal changes were not seen when hyphae were formed in the absence of the extract. Transmission electron microscopy revealed thickening of conidial cell walls in both fungal species when grown in the presence of the plant extract. Cell walls of A. flavus also became considerably thicker than those of A. parasiticus, indicating differential response to the extract. Aqueous preparations of T. violacea can be used as antifungal treatments for the control of A. flavus and A. parasiticus. Because the extract exhibited a more pronounced effect on A. flavus than on A. parasiticus, higher doses may be needed for control of A. parasiticus infections.     

Inhibition of growth and mycotoxin production of Aspergillus flavus and Aspergillus parasiticus by extracts of Agave species

In this work, the effect of ethanolic, methanolic and aqueous extracts of Agave asperrima and Agave striata on growth and production of aflatoxin (in A&M medium) and cyclopiazonic acid (CPA; in Czpaek-Dox medium) and on growth in corn under storage conditions was determined. Aspergillus strains were inoculated (10(6) conidia per ml of medium or per 6 g of corn), then plant extracts were added and incubated without shaking at 28 degrees C for 8 days (for aflatoxin-producing analysis) or for 12 days (for CPA-producing analysis). Aflatoxin was assayed by HPLC and cyclopiazonic acid by absorbance at 580 nm using the Erlich reagent. The extracts that most effectively inhibited growth were those from the flowers of both plants. These exhibited an MIC from 0.5 to 2 mg/ml in culture media. Extracts from scape showed an MIC from 15 to 30 mg/ml in culture media. The MIC of the flower extracts was higher (>30 mg/g) when examined in corn. However, concentrations lower than the MIC drastically inhibited production of aflatoxins in culture medium or in corn. Half of the MIC inhibited 99% of the production of aflatoxins and 85% of cyclopiazonic acid.     

Property Characterization of Peanut Kernels Subjected to Gamma Irradiation and Its Effect on the Outgrowth and Aflatoxin Production by Aspergillus parasiticus

Peanut kernels inoculated with Aspergillus parasiticus conidia and uninoculated kernels were gamma irradiated with 0 to 15 kGy using ⁶⁰Co. Levels of 2.5 and 5.0 KGy were effective in retarding the outgrowth of A. parasiticus and reducing the population of natural mold contaminants. However, elimination of these molds was not achieved. When irradiated with doses higher than 10 KGy, seed germinations were inhibited, changes in proteins were observed and oil stabilities decreased. After 4 wk incubation of the inoculated kernels in a humidified condition, aflatoxins produced by surviving A. parasiticus ranged from 69.12 to 13.48 μg/g depending upon the original irradiation dose.     

Distribution of aflatoxin-producing Aspergillus flavus and Aspergillus parasiticus in sugarcane fields in the southernmost islands of Japan

The distribution of Aspergillus flavus and Aspergillus parasiticus in sugarcane field soils and on harvested sugarcane stems was studied on seven islands of Okinawa and Kagoshima Prefectures, the southernmost prefectures in Japan. With the use of a combination of dilution plate and plant debris plate techniques, the fungi were detected on all seven islands studied and in 74% of 53 soil samples. The fungi were also found on the cut surfaces of sugarcane stems from one of the islands. A. parasiticus was the predominant fungus, although many atypical A. parasiticus isolates that produced metulated conidial heads were also obtained. The proportions of isolates testing positive for aflatoxin production were ca. 89% (146 of 164) of all isolates and ca. 69% of A. flavus isolates. More than 40% of A. flavus isolates also produced G aflatoxins. Scanning electron microscopic observation of conidial wall texture was useful in distinguishing A. parasiticus from A. flavus. Cyclopiazonic acid, an indole mycotoxin, was never synthesized by any of the A. parasiticus or G aflatoxin-producing A. flavus isolates tested.     

Effects of Essential Oils from Plants on Growth of Food Spoilage Yeasts

Thirty-two essential oils from plants were screened for inhibitory effects on 13 food-spoilage and industrial yeasts. Of these, essential oils of allspice, cinnamon, clove, garlic, onion, oregano, savory, and thyme were most inhibitory. Oils were subsequently tested for their effects on biomass production and pseudomycelium formation of eight genera of yeasts. Garlic oil was a potent inhibitor of yeast growth at concentrations as low as 25 ppm. The oils of onion, oregano and thyme were also strongly inhibitory. Essential oils (100 ppm) had no effect on pseudomycelium production by Candida lipolytica. However, all eight essential oils delayed pseudomycelium formation by Hansenula anomala, whereas six oils stimulated pseudomycelium production by Lodderomyces elongisporus. Cinnamon and clove oils were clearly stimulatory to pseudomycelium production by Saccharomyces cerevisiae.     

PCR-restriction fragment length analysis of aflR gene for differentiation and detection of Aspergillus flavus and Aspergillus parasiticus in maize

Contamination of food and feedstuffs by Aspergillus species and their toxic metabolites is a serious problem as they have adverse effects on human and animal health. Hence, food contamination monitoring is an important activity, which gives information on the level and type of contamination. A PCR-based method of detection of Aspergillus species was developed in spiked samples of sterile maize flour. Gene-specific primers were designed to target aflR gene, and restriction fragment length polymorphism (RFLP) of the PCR product was done to differentiate Aspergillus flavus and Aspergillus parasiticus. Sterile maize flour was inoculated separately with A. flavus and A. parasiticus, each at several spore concentrations. Positive results were obtained only after 12-h incubation in enriched media, with extracts of maize inoculated with A. flavus (101 spores/g) and A. parasiticus (104 spores/g). PCR products were subjected to restriction endonuclease (HincII and PvuII) analysis to look for RFLPs. PCR-RFLP patterns obtained with these two enzymes showed enough differences to distinguish A. flavus and A. parasiticus. This approach of differentiating these two species would be simpler, less costly and quicker than conventional sequencing of PCR products.     

Effects of microwaves on the reduction of Aspergillus flavus and Aspergillus parasiticus on brown rice (Oryza sativa L.) and barley (Hordeum vulgare L.)

ABSTRACT

Aspergillus flavus and Aspergillus parasiticus are primary pathogen moulds on brown rice and barley. This study investigated the effects of microwave irradiation (MWI) (2450 MHz, 700 W, 10–50 s) on inactivation of A. flavus and A. parasiticus on brown rice and barley and the quality of these samples. The counts of both strains were significantly (p < 0.05) reduced by the stepwise increase in MWI treatment time. The log reductions of A. flavus on brown rice and barley were 0.05 and 0.04 after 10 s; 1.06 and 1.05 after 20 s; 1.59 and 1.52 after 30 s; and 3.04 and 2.78 after 40 s. The log reductions of A. parasiticus on brown rice and barley were 0.06 and 0.10 after 10 s; 1.20 and 1.00 after 20 s; 2.04 and 1.61 after 30 s; and 2.89 and 2.90 after 40 s. Moreover, neither strain survived after 50 s of MWI. The Hunter colour ‘L’ gradually increased with increasing MWI treatment time. However, there were no significant differences in the ‘L’ of brown rice after 10–40 s of MWI treatment and of barley after 10–30 s of MWI treatment. The Hunter colour ‘a’ and ‘b’ gradually increased with increasing microwave time. No significant change was observed in the moisture content of either cereal treated with 10–20 s of MWI. The differences in the sensory quality (colour, appearance, flavour, texture and overall acceptability) after 0–30 s of MWI were not significant. However, values for colour, appearance, texture and overall acceptability were significantly reduced when treated with 40–50 s of MWI. Therefore, with 20 s of MWI at 2450 MHz, 700 W could be effective for > 90% reduction of mould without causing deleterious changes to the colour, moisture content and sensory qualities of these cereals.     

柑橘类精油对食用油脂的抗氧化研究

以过氧化值为指标,以橄榄油和猪油为介质,分析了柠檬精油、葡萄柚精油及甜橙精油的抗氧化性能及增效剂的影响作用.结果表明:葡萄柚精油的抗氧化效果最好,0.2%的葡萄柚精油在橄榄油中无需增效剂,0.02%的Vc在橄榄油中对柠檬精油和甜橙精油有增效作用,在猪油中0.02%柠檬酸的增效作用最好.     

Effect of UV-C irradiation on inactivation of Aspergillus flavus and Aspergillus parasiticus and quality parameters of roasted coffee bean (Coffea arabica L.)

ABSTRACT

This study investigated the antifungal effect of ultraviolet-C (UV-C) against Aspergillus flavus and Aspergillus parasiticus on roasted coffee beans. Also, any changes in the quality of the roasted coffee beans were measured after UV-C irradiation. As UV-C irradiation time increased (0–2 h), the number of surviving A. flavus and A. parasiticus spores significantly (P < .05) decreased. The reduction values of A. flavus in round part, crack part, and whole roasted coffee beans were 2.16, 0.71, and 1.58 log₁₀ CFU g^?1, respectively, and the reduction values of A. parasiticus in round part, crack part, and whole roasted coffee beans were 1.03, 0.37, and 0.72 log₁₀ CFU g^?1, respectively, after 2 h of UV-C irradiation. Field emission scanning electron microscopy showed that the morphology of A. flavus and A. parasiticus spores included expanded wrinkles that were deformed by UV-C irradiation. The Hunter colours were significantly reduced (P < .05). There was no significant change (P > .05) in moisture content, but the pH was significantly decreased (P < .05). Most of the sensory parameters did not change, but there was a significant difference (P < .05) in flavour. Based on this study, 2 h of UV-C irradiation was effective in reducing 90% of A. flavus, but it was not effective against A. parasiticus present on roasted coffee beans. Also, Hunter colour, pH, and sensory parameters (flavour) were changed by UV-C irradiation.     

Growth and biosynthesis of aflatoxin by Aspergillus parasiticus in cultures containing nisin

Summary Nisin, 200 or 5000 Reading units/ml, was added toAspergillus parasiticus cultures. The cultures were incubated at 28 °C for 3, 7 or 10 days and analyzed for mycelial dry weight, pH and accumulation of aflatoxin B₁ and G₁. During the first 3 days of incubation, dry weight, pH decrease and aflatoxin accumulation were suppressed by nisin, when compared with similar values for the nisin-free control. After longer incubation, differences in dry weight and pH values decreased, whereas accumulation of aflatoxin in the nisin-containing cultures surpassed that of the control.

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Wachstum und Aflatoxin-Biosynthese von Aspergillus parasiticus in Nisin-enthaltenden Kulturen

Zusammenfassung Nisin (200 oder 5000 Reading-Einheiten/ml) wurdeAspergillus parasiticus Kulturen zugegeben. Die Kulturen wurden bei 28 °C für 3, 7 oder 10 Tage bebrütet und auf Mycel-Trockengewicht, pH und Aflatoxin-Inhalt geprüft. Während der ersten drei Tage wurden das Wachstum und die Aflatoxin-Biosynthese durch Nisin etwas gehemmt, nach längere Incubation jedoch gefördert.

     

Growth and biosynthesis of aflatoxin by Aspergillus parasiticus in cultures containing nisin

Nisin, 200 or 5000 Reading units/ml, was added to Aspergillus parasiticus cultures. The cultures were incubated at 28 degrees C for 3, 7 or 10 days and analyzed for mycelial dry weight, pH and accumulation of aflatoxin B1 and G1. During the first 3 days of incubation, dry weight, pH decrease and aflatoxin accumulation were suppressed by nisin, when compared with similar values for the nisin-free control. After longer incubation, differences in dry weight nd pH values decreased, whereas accumulation of aflatoxin in the nisin-containing cultures surpassed that of the control.