Influence of pH on the growth of some toxigenic species of Aspergillus, Penicillium and Fusarium

The effect of pH on the growth rates of 61 isolates belonging to 13 important toxigenic fungi are reported here: four species each of Aspergillus and Fusarium, and five of Penicillium, over the pH range 2 to 11 at 25, 30 and 37 degrees C. Nearly all species studied were able to grow over the entire range examined on a laboratory agar medium. However, in general, Aspergillus species were more tolerant of alkaline pH while Penicillium species appeared to be more tolerant of acidic pH.     

Impact of processing treatments and packaging material on some properties of stored dehydrated cauliflower

Investigations were carried out to see the impact of blanching time, pretreatment and storage and packaging on the physico‐chemical properties of solar dehydrated cauliflower. The processing treatments selected for the study were blanching time of 3, 5, 7 and 9 min, potassium metabisulphite (KMS) pretreatment having 0.5%, 1.0% and 1.5% concentration level and storage in high‐density polyethylene, laminated aluminium foil and polypropylene. The cauliflowers were further processed and dehydrated in solar dryer before packing it into different packaging materials. Packed dehydrated cauliflower was stored for 6 months at room temperature. The stored cauliflower samples were tested periodically for their moisture content, rehydration ratio, rehydration coefficient, ascorbic acid and browning. Ranking of blanching time, chemical concentration level and packaging materials were statistically analysed by using SAS package. The samples with 9 min blanching time, followed by dipping in 1.0% KMS solution, and packed in laminated aluminium foil showed better results in comparison with other treatments.     

Studies on the selection of a suitable packaging material for pre- and post-irradiation storage of cereal grains in Ghana

Twenty different species of fungi belonging to the genera Aspergillus, Cephalosporium, Dreschlera, Fusarium, Mucor, Neurospora, Rhizoctonia, Rhizopus, Penicillium and Trichoderma were isolated from jute and woven polypropylene sacks using the blotter test, solid medium test and the decimal serial dilution technique. There was a highly significant difference (Students' t-test, P < 0.05) between the larger number of fungal colonies associated with jute sacks than with woven polypropylene sacks. Correspondingly, more fungal species (16) were isolated from jute sacks than from woven polypropylene sacks (9). The blotter test showed that in the absence of an exogenous supply of nutrients, 88% of the sections of jute sacks supported in vivo growth of fungal spores whilst woven polypropylene sacks could not support the growth of contaminating spores. Evidence is presented that mould and yeast counts on sections of new-woven polypropylene sacks incubated at 80 and 90% relative humidity (R.H.) for four months increased by less than 1 log cycle, whilst in similar sections hung on a line under ambient conditions (75 ± 10% R.H. and 28 ± 3°C) viable counts of spores decreased. Sections of fresh jute sacks similarly treated supported 1 log cycle increase in mould and yeast counts at 80% R.H. and 2 log cycles increase at 90% R.H. after four months of storage. Gamma-ray irradiation (4.0 kGy) reduced the mould and yeast counts on new jute and new woven polypropylene sacks by 1 and 2 log cycles, respectively, but post-irradiation storage at 80% R.H. allowed moulds like Aspergillus flavus, A. niger, Fusarium nivale and Penicillium verrucosum var. cyclopium to commence growth on jute sacks. This presumably, may act as a springboard for infecting grain contents of jute sacks. Inert woven polypropylene sacks failed to support fungal growth.     

Mycological and physical parameters for selecting suitable packaging material for pre- and post-irradiation storage of cereal grains in Ghana

Owing to the rough warehouse handling of storage sacks in tropical areas in Africa, a suitable storage sack should not support de novo growth of fungal spores because this would reduce the tensile strength of the packaging material and act as a springboard for infecting grain contents. This paper reports the effect of activity of saprophytic fungi on the tensile strength of jute and woven polypropylene sacks. New woven polypropylene sacks carried lower levels of fungal spores (1.3×10¹ cfu/72 cm²) than jute sacks (3.0×10³ cfu/72 cm²). The natural mould penetration and growth was examined on sections (4×5 cm) of both jute and woven polypropylene after previous incubation at relative humidities of 55, 60, 65, 70, 75, 80, 90 and 95% for 10 weeks by placing them on Sabouraud's Agar. There was a significant difference (P = 0.05 level of significance) between the higher penetration of mould growth on jute sacks and that obtained on woven polypropylene sacks. Saprophytic fungi (Aspergillus candidus, A. flavus, A. fumigatus, A. niger, A. japonicus, A. parasiticus, A. ustus, Fusarium oxysporium, F. moniliforme, Penicillium verucosum var. cyclopium, Rhizopus oryzae and Trichoderma viride) isolated from jute sacks reduced tensile strength, measured by an Instron Model 1026, by 50–75% after 10 weeks at 90% R.H. Same fungal species on woven polypropylene sacks did not alter the tensile strength. Woven polypropylene sacks did not absorb moisture whilst the moisture content of jute sacks increased by 5.3–6.0% in 10 weeks at 90% R.H. with concomitant increase in mould and yeast counts by 1–2 log cycles. Evidence is presented to show that there was a positive correlation between the final mycoflora on jute sacks and loss in tensile strength. No correlation, however, was found between the total aerobic bacteria on jute sacks and the concomitant reduction in tensile strength. Fungi therefore play a major role in the reduction of tensile strength of jute sacks. Sterilization by gamma irradiation (8.0 kGy) of jute and woven polypropylene sacks did not affect their intrinsic tensile strength. Woven polypropylene sacks therefore have many microbiological and physical advantages over the traditional jute sacks to merit their use for grain storage in tropical areas like Ghana.     

Evaluation of the effect of moisture content on cereal grains by digital image analysis

Physical appearance and kernel morphology significantly affect the grade of a harvested crop in addition to other factors such as test weight, percentage of foreign matter and constituent components. Moisture content of grain can potentially affect the physical appearance and kernel morphology. The objective of this study was to evaluate the effect of moisture content on the classification capability of colour, morphology and textural features of imaged grains. Colour images of individual kernels and bulk samples of three grain types, namely Canada Western Amber Durum (CWAD) wheat, Canada Western Red Spring (CWRS) wheat and barley were acquired using a machine vision system. The grain kernels were conditioned to 12%, 14%, 16%, 18% and 20% moisture contents before imaging. Previously developed algorithms were used to extract 123 colour, 56 textural features from bulk sample images and 123 colour, 56 textural, 51 morphological features from individual kernel images. The extracted features were analysed for the effect of moisture content. Statistical classifiers and a back propagation neural network model were used for classifying the grain bulk at different moisture contents. The colour and textural features of bulk grain images were affected by the moisture content more than that of the single kernel images.     

Presence of the toxigenic fungi Aspergillus spp. and Fusarium spp. in Musca domestica L. (Diptera: Muscidae) collected from dairy farms

The objective of the study was to identify the presence of toxigenic fungi Aspergillus spp. and Fusarium spp. in domestic flies collected from dairy farms. We selected 10 dairy farms distributed in the central valley of the state of Aguascalientes, México. The flies were trapped using entomological traps with an olfactory attractant in 7 sites of the farm (silo-cutting surface, feed store, milking parlor, 3 feeders, and the rearing room). The fungi were cultivated in Sabouraud agar through direct sowing by serial dilutions to obtain the isolates, and a taxonomical identification was carried out under the microscope. The aflatoxins and zearalenone production capacity of the pure isolates were quantified using the ELISA test. The flies were present in all of the capture sites (45.3 flies, 567 mg, trap per day). We obtained 50 isolates of Aspergillus spp. genus, 12 of which produced aflatoxins (327 ± 143 µg/kg), whereas from 56 of the Fusarium spp. isolates, 10 produced large quantities of zearalenone (3,132 ± 665 µg/kg). These results suggest that the presence of domestic flies on dairy farms can constitute a source of dissemination for toxigenic fungi that can eventually contaminate grains and forage that are part of the daily cattle diet.     

Identification and toxigenic potential of the industrially important fungi, Aspergillus oryzae and Aspergillus sojae

Mold strains belonging to the species Aspergillus oryzae and Aspergillus sojae are highly valued as koji molds in the traditional preparation of fermented foods, such as miso, sake, and shoyu, and as protein production hosts in modern industrial processes. A. oryzae and A. sojae are relatives of the wild molds Aspergillus flavus and Aspergillus parasiticus. All four species are classified to the A. flavus group. Strains of the A. flavus group are characterized by a high degree of morphological similarity. Koji mold species are generally perceived of as being nontoxigenic, whereas wild molds are associated with the carcinogenic aflatoxins. Thus, reliable identification of individual strains is very important for application purposes. This review considers the pheno- and genotypic markers used in the classification of A. flavus group strains and specifically in the identification of A. oryzae and A. sojae strains. Separation of A. oryzae and A. sojae from A. flavus and A. parasiticus, respectively, is inconsistent, and both morphologic and molecular evidence support conspecificity. The high degree of identity is reflected by the divergent identification of reference cultures maintained in culture collections. As close relatives of aflatoxin-producing wild molds, koji molds possess an aflatoxin gene homolog cluster. Some strains identified as A. oryzae and A. sojae have been implicated in aflatoxin production. Identification of a strain as A. oryzae or A. sojae is no guarantee of its inability to produce aflatoxins or other toxic metabolites. Toxigenic potential must be determined specifically for individual strains. The species taxa, A. oryzae and A. sojae, are currently conserved by societal issues.     

Freeze-drying of raw beef. 3. Influence of some packaging and some storage variables

Minimisation of oxygen exposure of freeze-dried raw beef before packaging and during storage was studied in multifactorial experiments for its effect on the quality of the product, as was the effect of storage time and temperature, intramuscular fat content, and different head-space gas compositions. Exposure of the freeze-dried meat to the air before packaging under nitrogen, which is commercial practice today, clearly shortened storage life, particularly of meat with a high fat content. The effect could be counteracted by the application of an oxygen scavenging system, which proved effective at initial head-space oxygen levels as high as 4%. The use of carbon dioxide in the head-space reduced product quality compared with nitrogen or the hydrogen-nitrogen mixture employed in the oxygen scavenging system. The red meat colour as well as quality as a whole was much better preserved by cold storage and particularly frozen storage, by packaging without pre-exposure to the atmosphere or by using an oxygen scavenging system based on the reaction of oxygen with hydrogen over a palladium catalyst enclosed in the package. Of these methods, refrigerated storage is probably not a realistic solution under present commercial conditions.     

Influence of packaging material on pomegranate juice colour and bioactive compounds,during storage

Pomegranate juices were assessed after pasteurisation and storage in different packaging materials: transparent and green glass, and paperboard carton with polyethylene layers (Minibrik‐200). The main objective was to establish the influence of the container on the stability of colour and bioactive compounds (anthocyanins, ellagic acid and other non‐coloured phenols). Results showed that non‐coloured phenols and ellagic acid were quite stable during the storage period. In contrast, anthocyanins degraded, to an extent directly proportional to colour loss, less for those juices stored in glass bottles than for those stored in Minibrik. These results indicated that these paperboard carton containers are oxygen permeable, and that oxygen has a greater influence on anthocyanin, and consequently on colour degradation, than light on pomegranate juice during storage. Nevertheless, the antioxidant activity was not influenced by the packaging material employed. Copyright © 2004 Society of Chemical Industry     

Oxidative stability of cream cheese stored in thermoformed trays as affected by packaging material,drawing depth and light

The oxidative stability of cream cheese stored in thermoformed trays made of amorphous polyethylene terephtalate (A-PET)/polyethylene (PE), polystyrene (PS)/Ethylene-vinylalcohol copolymer (EVOH)/PE and Polypropylene (PP)/PE with different depth (25, 50 and 70 mm) and colour (black, white and transparent) was studied by sensory evaluation and gas chromatographic analysis of volatile compounds. The polymer combination had an important effect on sensory scores of both sunlight and acidulous flavour in cream cheese stored in the dark for 2, 4 and 6 months. Cream cheese stored in trays made of A-PET/PE had higher acidulous flavour and lower content of hexanal and 2-nonanone. Only small differences were observed between PS/EVOH/PE and PP/PE despite the great diversity of oxygen transmission rates. The drawing depth of the packages had no significant effect on oxidative stability of cream cheese, irrespective of storage in the dark or under illumination. The colour of the examined packaging material had a pronounced effect on photoxidative changes in cream cheese.     

稻谷储存水分和温度对真菌生长和稻谷主要品质的影响

研究水分、温度对稻谷储存过程中真菌生长和主要储存品质的影响。将稻谷设为含水量分别为12.1%、13.1%、14.0%、15.1%、16.0%的样品,分别置于10、15、20、25、30、35℃温度条件下模拟储存180 d后,检测稻谷样品中真菌生长、发芽率和脂肪酸值的变化。结果表明,水分是真菌生长的决定因素,13.1%水分处于真菌生长临界水分以下,即使温度适宜真菌也不生长;14.0%处于真菌生长临界水分以上,水分越高越利于真菌孢子萌发生长,温度越高真菌生长速度越快;脂肪酸值受真菌生长的影响程度要大于水分和温度,13.1%以下水分稻谷,没有真菌生长,脂肪酸值上升缓慢。14.0%以上水分稻谷,一旦真菌生长,就会加速脂肪酸值的升高;发芽率受温度影响程度最大,高温储存半年,无论是否有真菌生长,发芽率基本降为0,低温储存不仅能抑制真菌生长还利于保持种子发芽率。     

储存水分、温度和真菌生长对大豆品质的影响

研究大豆储存过程中水分、温度和真菌生长对其品质的影响。采用11.2%、11.8%、12.7%、13.9%和14.7%水分的大豆,分别置于10、15、20、25、30、35℃下模拟储存,周期180 d,检测储存真菌、发芽率和脂肪酸值的变化情况。结果表明,大豆储存中,真菌生长受储存水分和温度的影响,水分是决定真菌生长的主要因素,而温度影响真菌生长速度。真菌生长临界水分(11.8%左右)以下储存,种子发芽率和脂肪酸值主要受温度的影响,20℃以下低温储存能维持较高的发芽率,30℃以上储存会加剧脂肪酸值升高。真菌生长临界水分以上储存,种子发芽率和脂肪酸值受真菌生长和温度协同作用的影响,大豆储存水分越高,真菌生长越快,即使低温也会在一定程度上导致大豆品质劣变。     

多孔绵材料层对防水透湿复合织物性能的影响

为开发新型防水透湿保暖型层压复合织物,选用多孔绵、热塑性聚氨酯（TPU）薄膜,以机织物为面层,摇粒绒为基材,利用湿固化聚氨酯热熔胶（PUR）黏合剂,通过2 或3 次层压复合试制系列复合织物样品。观察并分析了含多孔绵材料层复合织物横截面形貌结构,研究了多孔绵材料对层压复合织物防水、透湿、保暖等主要功效的影响,同时分析了多孔绵膜层压复合织物的剥离强度。结果表明,所制备的多孔绵膜层压复合织物在防水、透湿、剥离强度等基本不变的情况下,保暖率提高了0%左右,基本解决在极地寒域服装面料保暖性能不足的问题。     

Studies on the gluten-specific peptidase activity of germinated grains from different cereal species and cultivars

Grains of common wheat, spelt, emmer, einkorn, rye, barley, oats, and maize (two cultivars each) were germinated for 7?days at 15 and 25?°C, respectively, lyophilized, and milled into flour and bran. The rate of storage protein (prolamins, glutelins) degradation in the bran was determined by an extraction/HPLC method and was used as an indication for gluten-specific peptidase activity. Species and cultivars with high storage protein degradation during germination were selected for further studies. The peptidase activity of the germinated grains was determined by using two gluten substrates namely gliadin (wheat prolamin fraction) and the celiac-toxic peptide PQPQLPYPQPQLPY. The activity assay implied extraction of bran with a sodium acetate buffer (0.2?mol/L, pH 4.0), incubation of the extract with both substrates, and quantitation of gliadin or peptide degradation by RP-HPLC. The assays were simple and generated reproducible values for the peptidase activity. In general, the activity was strongly affected by cereal species, cultivar, germination temperature, and pH value of the application. Some of the bran extracts were capable of degrading both gliadin and the celiac-toxic peptide extensively. Maximum degradation rates of gliadin and the celiac-toxic peptide were 67 and 100?%, respectively. Alternatively, germinated cereal grains were kiln-dried at 45?°C for 24?h instead of being lyophilized and were separated into kernels and roots/sprouts. When compared to the lyophilized bran, the combined kiln-dried material showed a more balanced peptidase activity toward both the gliadin and the peptide substrate.     

Influence of nitrogen and carbon sources on the production of ochratoxin A by ochratoxigenic strains of Aspergillus spp. isolated from grapes

This work studies the influence of nitrogen and carbon source on ochratoxin A production by three Aspergillus isolates A. ochraceus (Aso2), A. carbonarius (Ac25) and A. tubingensis (Bo66), all isolated from grapes. A basal medium (0.01 g/l FeSO4.7H2O, 0.5 g/l MgSO4.7H2O, 0.5 g/l Na2HPO4.2H2O, 1.0 g/l KCl) was prepared. This medium was supplemented with different nitrogen sources, both inorganic [(NH4)3PO(4), 0.3 g/l plus NH4NO3, 0.2 g/l] and organic (histidine, proline, arginine, phenylalanine, tryptophan or tyrosine) at two concentrations (0.05 g/l or 0.3 g/l), and different carbon sources (sucrose, glucose, maltose, arabinose or fructose) at three concentrations (10 g/l, 50 g/l or 150 g/l). A medium with sucrose (18 g/l) and glucose (1 g/l) was also tested. After a 10-day incubation period at 25 degrees C the highest levels of OTA (44.0 ng/ml, 13.5 ng/ml and 0.49 ng/ml for A. ochraceus, A. carbonarius and A. tubingensis, respectively) were obtained in the cultures containing 150 g/l of arabinose and 0.05 g/l of phenylalanine. Analysis of variance of the data showed that there were significant differences (p-value 0.05) among the OTA levels in the cultures with regard to carbon source and isolate. No significant differences were detected in OTA production regarding nitrogen source, although 0.05 g/l of phenylalanine generally favoured OTA production in the cultures of the three isolates. The dynamics of toxin production in the cultures of each isolate using the optimized basal medium supplemented with 0.05 g/l of phenylalanine and 150 g/l of arabinose for a period of 42 days at 25 degrees C was also studied. The maximum level of OTA was detected on the 3rd day of incubation in A. tubingensis cultures and on the 35th and 43(rd) days of incubation in A. ochraceus and A. carbonarius, respectively. This is the first study in which defined media have been used to assess the influence of carbon and nitrogen sources on OTA production by isolates of OTA-producing species isolated from grapes and to analyse the dynamics of toxin production in these species in a defined culture medium. This optimized medium for OTA production is being used in current studies aimed at elucidating its biosynthetic pathway.     

Effects of anticaking agents and storage conditions on the moisture sorption,caking, and flowability of deliquescent ingredients

Deliquescent highly soluble crystalline ingredients are prone to caking and dissolution when they are stored above a certain relative humidity (RH) but exhibit minimal moisture adsorption below this RH. Anticaking agents are added to improve the flowability of powders and to prevent or reduce caking. The objective of this study was to determine the effects of anticaking agents on the moisture sorption behavior, flowability, and caking characteristics of deliquescent ingredients and blends thereof. Single deliquescent food ingredients (sodium chloride, sucrose, fructose, and citric acid) and binary systems (sodium chloride blended with sucrose, fructose, or citric acid) were used as the host powders, and silicon dioxide, calcium silicate, and calcium stearate were the three anticaking agents studied. Moisture sorption isotherms were generated to investigate the water–solid interactions of the anticaking and host powders. Following controlled RH storage treatments, caking was assessed by the sieve test and flowability by avalanche power and avalanche angle measurements. Formulation had variable effects on deliquescence behavior and moisture sorption, while formulation, storage RH, length of storage, and RH cycling all significantly affected the physical stability of the powder blends. Calcium stearate was the most effective anticaking agent at reducing moisture sorption and delaying the onset of deliquescence, as well as maintaining the flowability properties of all powders tested. In particular, calcium stearate was able to substantially alter the moisture sorption behavior of blends of deliquescent ingredients, which are inherently more susceptible to the deleterious effects of moisture due to deliquescence lowering. The results are of great significance because they show that the effectiveness of an anticaking agent in preventing moisture-induced caking depends on the complexity of the host powders as well as on the interaction with environmental moisture. Thus, the type of anticaking agent added to a deliquescent ingredient must be tailored to the host powder to enhance product quality and stability.