Effect of gamma radiation on ochratoxin production by the fungus Aspergillus ochraceus

Mycelial discs of the fungus Aspergillus ochraceus NRRL 3174 were exposed to gamma irradiation and then incubated on synthetic medium (SM). Growth rate, mycelial dry weight and ochratoxin production were measured. A delay in mycelial growth of 24 and 48h over the control occurred following irradiation of mycelial discs with 150 and 200 krad, respectively. No growth occurred from discs exposed to 300 krad. An increase in ochratoxin production occurred on the SM from cultures developing from discs of mycelium which had been irradiated with 50, 100, 150 and 200 krad. The amount of toxin produced was 3500, 4100, 3200 and 3000 ng per plate, respectively, as compared with 2800 ng per plate produced by the control. Exposure of mycelial discs to a temperature of 40°C for 15 and 30 min prior to treatment with 200 krad resulted in complete inhibition in mycelial growth. No growth inhibition or notable change in ochratoxin production was recorded when the mycelial discs were exposed to 25, 50 or 100 krad after the heat treatments. Pure ochratoxin was found to be stable even at 7.5 mrad, and no reduction in its fluorescence intensity under u. v. light was recorded following that dose.     

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).     

Effect of Irradiation on Discoloration, Phenols and Lipids of Potatoes

The effect of two irradiation doses, 10 and 100 krad, on discoloration, phenolic content and lipid content of Katahdin and Russet Burbank potatoes was studied. Potatoes were stored 1, 4 and 26 wk at 5°C and 20°C following irradiation. Irradiation increased discoloration and phenols and decreased crude lipids and the phospholipids. Potatoes receiving 100 krad dose discolored more, were higher in phenols, and lower in lipids than those given 10 krad dose. Potatoes stored at 5°C discolored more and were higher in phenols and in lipids than those stored at 20°C. Increased storage at both temperatures resulted in greater discoloration, increased phenolic content and decreased lipids content.     

Aspergillus flavus infection and aflatoxin production in mixtures of high-moisture and dry maize

High-moisture (26·6–27·9% m.c.) and dry (9·8% m.c.) fractions of white and yellow maize were examined for fungal development and aflatoxin production during an 8-week incubation at 25°C. Treatment procedures included blending of either high-moisture white with dry yellow or high-moisture yellow with dry white maize fractions (average moisture in blend, 14%) and inoculation of some test maizes with A. flavus spores. At sampling time white and yellow components of maize blends were manually separated and all of the maize samples were analyzed for levels of moisture, fungal infection and aflatoxin. Moisture levels in maize blends equilibrated rapidly during the initial 2–4 days of incubation; neither dry yellow nor dry white exceeded 13% moisture during the trial period. Only a limited incidence of A. flavus was observed on uninoculated maize. but in samples treated with A. flavus spores a high infection rate developed; from 58 to 98% of the kernels in dry fractions of inoculated blends were infected with A. flavus during the trial. Aflatoxin was detected in high-moisture maize and in both high-moisture and dry fractions of inoculated maize blends. Up to 500 μg aflatoxin B₁/kg of corn was found after the 8-week incubation in a dry fraction of inoculated maize blends.     

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.     

The production of ochratoxin A and citrinin in barley

The production of ochratoxin A by Aspergillus ochraceus and of ochratoxin A and citrinin by Penicillium viridicatum growing on previously sterilised barley for 200 days at 5, 10 and 20°C and a water activity of 0.85 is reported. A. ochraceus did not grow at 5°C, multiplied slowly at 10°C but did not produce toxin. At 20°C the organism multiplied more quickly and produced ochratoxin after 19 days, which slowly disappeared over the next 150 days. P. viridicatum grew slowly at 5°C but did not produce any toxin. It multiplied at 10°C and produced ochratoxin A which was only detectable during the period from 100 to 150 days. At 20°C both ochratoxin A and citrinin were produced. Ochratoxin A was detected after 10 days and was still present after 240 days, whereas citrinin was produced in large quantities between 118 and 129 days and then rapidly disappeared.     

The development,fecundity and longevity of Dermestes ater Degeer (Coleoptera: Dermestidae)

Larvae of Dermestes ater Deg. were bred on a diet of fishmeal, wheat germ, yeast and cholesterol at 15, 20, 25, 30 or 35°C with a constant 65% r.h. and at 25°C with 40, 50, 60, 70 or 80% r.h. Whenever possible emerging adults were paired and kept under the same conditions to determine longevity and fecundity. Eggs laid at 25°C and placed at 15°C failed to hatch. The egg period at 25, 30 and 35°C averaged 4–5 days and at 37.5°C it was about 3 days. Egg hatch was low approximating to about 40% except at 37.5°C where it was only just above 10%. No viable adults emerged at temperatures below 25°C. Development was completed in about 40 days at 30 and 35°C and at all humidities tested at 25°C (taking about 50 days at 80% r.h. and 65–70 days at 40% r.h.). Mortality was low at 25 and 30°C (less than 30%) but high at 35°C (90%). Fifty per cent of adults were dead after about 100 days at 25°C, after about 30 days at 30°C; the two adults at 35°C survived just over 20 days. A pre-oviposition period averaging about 33 days at 25°C and 4 days at 30°C was followed by an oviposition period of about 2 months. The number of eggs laid was very variable (0–135) as was the percentage hatch (0–69%). The results are compared with those obtained by other authors.     

DRYING AND STORAGE TREATMENTS FOR OVERCOMING DORMANCY IN MALTING BARLEY

A batch of deeply dormant Triumph barley was stored at ?18°C. The grain was so dormant that its viability, 97–98%, could not be determined using standard tests. Samples were dried to 12% moisture at various rates by varying the temperature and relative humidity of the drying air. Dried samples were stored at three temperatures (15°, 27° and 38°C). At intervals the germination characteristics of subsamples were determined. Germinability improved with storage time, improving faster at the higher temperatures. However some of the samples stored at 27°C and all the samples stored at 38°C suddenly showed a loss of viability, preceded by a loss in vigour. The rate of recovery from dormancy was independent of the drying regime used. Initially the germinability of the barley was 5–10% (1 ml agar test) and 0–4% (3 ml agar test). Recovery from dormancy was extremely slow at 15°C, so that after a year germination values were around 80% (1 ml agar test) and 45% (3 ml agar test). After 27 weeks the viability of grain stored at 27°C began to decline, germinability was 85–90% (1 ml agar test) and 50–60% (3 ml agar test). At 38°C the initial decline in dormancy was rapid, but germinability fell catastrophically at various times between 3 and 30 weeks storage. Other samples of the same lot of Triumph barley were dried to various moisture contents, 9.4%, 10.3%, 11.0%, 13.0% and 14.5%. These were stored at 38°C. The initial rate of recovery from dormancy was rapid, and was unrelated to the moisture content of the grain. The samples dried to 9.4% and 10.3% m.c. achieved germination values close to the viability value, around 95% (1 ml agar test) and 90% 3 ml (agar) tests in 15–18 weeks storage and showed no signs of deterioration in 30 weeks. Grain held at 11% moisture deteriorated after 12 weeks and that stored at 13% and 14.5% deteriorated after 3 weeks. The germinabilities of the samples dried to 9.4% and 10.3% and stored for 15–18 weeks at 38°C were so good, reaching maximal values at 2 days in the germination test, that it is concluded that they could probably not be matched by samples stored cool. The possibility of using higher storage temperature to overcome dormancy and water sensitivity more rapidly, is discussed. Experiments with other grain samples have confirmed that, in most respects, the original barley was typical of deeply dormant Triumph. Samples of Carmargue and Golden Promise matured much more rapidly than Triumph. However water sensitivity was extremely persistent in a sample of Doublet.     

INFLUENCE OF MOISTURE CONTENT AND STORAGE TEMPERATURE ON THE PRODUCTION OF AFLATOXIN BY ASPERGILLUS FLAVUS EA-81 IN MAIZE AFTER EXPOSURE TO GAMMA RADIATION

The effect of gamma radiation on aflatoxin production by Aspergillus flavus EA-81 in maize with different initial moisture levels was determined over a 15-day period. The viability of A. flavus on maize decreased over time with increasing moisture contents and storage at 8C. After 45 days at 28C, levels of viable conidiospores of A. flavus increased from 4.5 × 10⁷ to about 3.0 × 10⁸ per gram of maize. Levels of aflatoxin B₁ produced by A. flavus were 10 μg kg^-1 in the maize stored at 8C after 45 days. Production of aflatoxin was highest at 40% moisture and 28C. Irradiation of 1.0 or 2.0 kGy greatly reduced the level of mold growth relative to unirradiated controls. A dose of 4.0 kGy eliminated all viable fungi. Aflatoxin B₁ production decreased with increased levels of irradiation and was negligible at 4.0 kGy. When maize was inoculated after irradiation and stored, the spore counts and aflatoxin levels were higher than in unirradiated and inoculated controls after 30 days. Apparently, the natural competitive microflora prevented growth and thus limited higher concentrations of aflatoxin in maize.     

Influence of white light,near-UV irradiation and other environmental conditions on production of aflatoxin B1 by Aspergillus flavus and ochratoxin A by Aspergillus ochraceus

The effects of illumination, near-ultraviolet, incubation temperature pH and some minor elements on the growth rate and production of aflatoxin B₁ by A. flavus and ochratoxin A by A. ochraceus were investigated. Aflatoxin B₁ and ochratoxin A production was considerably higher in the light than in the dark. The greatest aflatoxin B₁ and ochratoxin A production was occurred after 11 days of fermentation with light- and dark-grown cultures at 25 °C. The mycelial dry weight was also greater in the light than in the dark for both A. flavus and A. ochraceus. Exposure of conidia to near-UV irradiation increased mycelial dry weight and mycotoxins by both fungi more than white light. The greatest aflatoxin B₁ and ochratoxin A was at 25 °C with UV-grown culture (24 h exposure) producing a mean of 400 and 260 μg/50 ml of medium, respectively. The maximum aflatoxin B₁ and ochratoxin A yield was obtained at pH 5.5 and with increasing the initial pH to near neutrality, both mycotoxins yield decreased. Iron, cupper and zinc were observed to stimulate aflatoxin B₁ and ochratoxin A production and enhanced the growth rate of both A. flavus and A. ochraceus.     

Effect of Low-Dose (100 krad) Gamma Radiation on the Microflora of Vacuum-Packaged Ground Pork With and Without Added Sodium Phosphates

Survival and growth of naturally occurring or inoculated bacteria were studied in refrigerated (5°C), vacuum-packaged ground pork irradiated at 100 krad (1kGy). Numbers of naturally occurring mesophiles, psycbrotrophs and anaerobes or facultative anaerobes were reduced (P<0.01) by irradiation, whereas lactic acid bacteria were least affected. Partial bacterial recovery during subsequent storage at 5°C suggested sublethal bacterial injury due to irradiation. Irradiation prolonged shelf-life 2.5–3.5 days (30–44%) in uninoculated and 1.0–1.5 days in inoculated (10⁵ CFU/g) meat. Added sodium acid pyrophosphate (SAPP) (0.4%) contributed two additional days to inoculated, irradiated pork shelf-life but had no effect on the naturally occurring micrbflora. Lipid oxidation did not increase (P>0.05) due to irradiation and was unaffected by phosphates.     

Decontamination of aflatoxin‐contaminated maize by dehulling

Dehulling of maize grains as an aflatoxin decontamination method was investigated. Sixty kilograms of maize (whose average moisture content was 110 g kg^?1) were thoroughly mixed and divided into two samples. The kernel moisture content of one sample was adjusted to 200 g kg^?1 while the other (control) was left at 110 g kg^?1. The two samples were kept at ambient temperature (25–30 °C) for 21 days. Twenty sub‐samples, ten from each, were further divided into two so that one lot was dehulled while the other was not dehulled. These sub‐samples were then milled to pass through a 1 mm screen and the meal was evaluated for aflatoxin contamination. It was found that there was a 92% decrease in aflatoxin levels in dehulled maize meal compared with undehulled maize meal. We therefore suggest that dehulling the grain can be used to reduce aflatoxin levels in maize. Copyright © 2005 Society of Chemical Industry     

Effects of Sorbate and Propionate on Growth and Aflatoxin Production of Sublethally injured Aspergillus parasiticus

Growth and aflatoxin production by injured spores (heat, 55°C for 15 min, γ-irradiation, 50 Krad) of Aspergillus parasiticus in the presence of sorbate (0.05 and 0.1%) and propionate (0.2 and 0.4%) were studied in YES broth at pH 4.5, 5.5 and 6.5, and 25°C for 21 days. Aflatoxin production was accelerated in the early stages of growth by γ-irradiation, but not heat. Growth and aflatoxin were delayed in cultures from low numbers of uninjured spores. Aflatoxin increased and was produced sooner by low numbers of uninjured spores in 0.05% sorbate. Both inhibitors slowed growth of injured spores more than non-injured. Inhibition of aflatoxin was dependent on the concentration of inhibitor, pH and injury.     

Farm‐Scale Experiments to Compare Infestation and Quality Changes in Malting Barley Stored at Three Moisture Contents

Comparison of changes in temperature, moisture content, infestation and germination were made in six aerated 20 t bins of malting barley. Two were at about 13.5% moisture content, three at about 15.5% moisture content, and one at about 16.5% moisture content. The grain started at between 20–25°C and, during aeration, fell at a rate dependent on the moisture content, damper grain being cooler, presumably due to evaporative cooling. The ‘high’ moisture content grain was often over 5°C cooler at 1m and 2m than the ‘low’ moisture content bins. Moisture uptake at the surface was related to bulk moisture content and trends in mite population changes were related to moisture content. Mite population achieved highest numbers at the grain surface but usually before the moisture content absorption was at its peak. They were commonest in the ‘high’ moisture content bin and least numerous in the ‘low’ moisture content bins. There were no apparent differences between bins in the numbers of insects trapped, for instance they were not less numerous in the coolest ‘high’ moisture content bin. However, the trends of numbers trapped followed a similar pattern in all bins; normally O. surinamensis and S. granarius only began to decline after nine weeks storage in December when temperatures fell below 10°C. Germination loss at the surface of the dampest bin was sufficient to cause rejection of the entire bulk for malting. Micromalting indicated that yield of extract and friability were particularly affected by the changes at the surface of the dampest barley.     

The Stability of Poly(lactic acid) Packaging Films as Influenced by Humidity and Temperature

The effect of moisture sorption on stability of poly(lactic acid) (PLA) films at food‐packaging conditions, obtained by different humidities (11% to 98% RH) and temperatures (5 °C and 25 °C), was investigated by decrease in number average molecular weight (M_n) and loss of tensile strength. Hydrolysis of the PLA ester linkages resulted in a 75% decrease over 130 d at 25 °C and 98% RH. At cooling conditions the decrease amounted to 35%. An equilibrium moisture sorption isotherm could not be determined as the irreversible hydrolysis of PLA induced an ongoing moisture uptake. The rate increased when the humidity and temperature increased from 5 °C to 25 °C. After 189 d at 98% RH, moisture sorption was 7 g/100 g and 86 g/100 g at 5 °C and 25 °C, respectively. Loss of tensile strength was minor and primarily due to reversible plastization by moisture. Only at 98% RH and 25 °C, loss of tensile strength became pronounced (45%). Consequently, the present PLA material is in general expected to be mechanically stable when packaging foods covering the region from dry to moist food and storage conditions from chill to ambient temperatures.     

Effect of insecticidal atmosphere and low dose X‐ray irradiation in combination with cold quarantine storage on bioactive compounds of clementine mandarins cv. ‘Clemenules’

Citrus fruits are a rich source of vitamins and polyphenolic compounds with antioxidant capacity that need to be maintained during postharvest storage. The aim of this study was to determine the effect of two innovative quarantine treatments, such as insecticidal atmospheres (IA) (95% CO₂ and balance air) applied at 20 or 25 °C for 20 h and low doses X‐ray irradiation (0, 30, 54 and 164 Gy), in combination with short periods of cold‐quarantine storage on the nutritional quality of ‘Clemenules’ mandarins. Mandarins were stored at 1.5 °C for 6, 9 or 12 days before the application of IA treatments or for 0, 6 or 12 days after the X‐ray radiation. Nutritional quality of mandarins was determined after the corresponding combination of quarantine treatment (IA or X‐ray) with cold quarantine followed by a shelf life period of 7 days at 20 °C to simulate shelf life conditions. Cold quarantine treatment combined with IA or with X‐ray radiation did not affect negatively total antioxidant capacity and total ascorbic acid content of ‘Clemenules’ mandarins. However, flavanone glycosides (FGs) and total phenolics content were slightly modified. Application of the IA at 20 °C induced a greater inhibition of the FGs than application at 25 °C. When X‐ray irradiation was applied without a previous quarantine period the synthesis of the FGs increased as irradiation dose increased.     

A New Method for Aflatoxin-Free Storage of Agricultural Commodities

Aflatoxin production was observed in the 2 kg lots of peanuts and corn that were stored for 90 days at ambient temperature (28–30°C) and a relative humidity of 100% after infecting with the spores of aflatoxin producing strain Aspergillus parasiticus NRRL 3145. Treatment of the samples with an aqueous solution of 2-chloroethylphosphonic acid prevented aflatoxin formation in both the commodities, whereas, the untreated lots supported aflatoxin formation.     

Effect of Hydrothermal Treatment on Formation and Structural Characteristics of Slowly Digestible Non‐pasted Granular Sweet Potato Starch

The formation and structural characteristics of slowly digestible non‐pasted granular starch in sweet potato starch were investigated under various hydrothermal treatment conditions. The moisture content of the sweet potato starch was adjusted to 20, 50 or 90%, and the starch was heated at 40, 55 or 100°C for 12 h in a dry oven. The relative crystallinity of the hydrothermally treated samples was decreased with increasing temperature, and the X‐ray diffraction patterns of the samples were altered from C_b‐type to A‐type. Microscopic observations did not reveal any changes in the starch granules of any samples except those with moisture contents of 50 and 90% that were heated at 100°C. When gelatinization parameters were examined, samples with moisture contents of 50 and 90% that were heated at 55°C and samples of all moisture contents that were heated at 100°C had peak temperatures higher than that of raw starch but gelatinization enthalpies lower than that of raw starch. The swelling factor of the samples heated at 40°C did not change significantly, whereas that of samples heated at 55 and 100°C was decreased at increased moisture levels. The sweet potato starch with 50% moisture content that was heated at 55°C had the highest content of granular slowly digestible starch, about 200% that of raw starch, although our study did not involve further hydrothermal treatment conditions. Further study is required to complete a process for more efficient production of heat stable and slowly digestible starch.     

Effect of superheated steam inactivation on naturally existent microorganisms and enzymes of highland barley

Superheated steam (SS) processing displayed noticeable effects on both microbial inactivation, including total bacterial count, Bacillus spp. and molds, and enzyme inactivation. Moisture content affected decontamination efficiency and recommendable moisture was 20%. Moisture adjusting method of spraying just before SS treatment was better than tempering. Molds were totally decontaminated by SS processing at 200 °C for 90 s and 120 °C for 180 s respectively. At 200 °C for 180 s, 99.98% of bacteria and 95.21% of Bacillus spp. were inactivated by spraying, while 99.95% of bacteria and 92.59% of Bacillus spp. were inactivated by tempering. The enzyme activity in highland barley processed with SS was decreased as processing time and temperature increased. Lipase showed better thermal resistance than peroxidase. Tempering was better in enzyme inactivation. SS treatment was effective in inactivating microorganisms and enzymes of highland barley, and could bring significant economic benefits to the highland barley industry.     

Methods for accelerating malting,a small scale investigation

It was confirmed that steeping fully after-ripened barley at 25° or 30°c, for various periods, induces different degrees of ‘water sensitivity’. Germination of such warm-steeped grain, set to grow at the steeping temperature, was maximal when the moisture content was about 35%. Sprays of hydrogen peroxide, applied immediately after draining the steeped grain, accelerated the subsequent germination of warm-steeped barley when grown at elevated temperatures. Exceptionally rapid steeping/germination schedules were elaborated, using micromalting techniques. For example, fully mature grain was steeped, (7 h 25°c) to a moisture content of about 36%. All subsequent processing was also at 25°c. After a drain (2 h) the grain was sprayed with a solution of gibberellic acid (0·25 mg/kg) in a dilute solution of hydrogen peroxide (2·5 vol.). Spraying with water was carried out twice more during the germination period to increase the moisture content of the barley to about 44%. The grain was set to kiln at 43°c, 48 h from steep out, that is 55 h from first wetting. Kilning conditions were chosen to allow maximal survival of enzymes. The malt had a hot water extract above 103 lb/Qr (fine grind, on dry matter) and was made at the expense of a 7·5% malting loss. It was acceptable by other analytical criteria. If the second water spray was replaced by a spray of a dilute solution of sulphur dioxide (400 mgjkg) a malt having an extract of 103·5 lb/Qr was obtained with a malting loss of 5·8%, but yielding more soluble nitrogen. The possibility of achieving even shorter processing times, by working at 30°c, was noted.