R. N. Sinha

A simulation model of temperatures in stored grain

Abstract Temperature is one of the most crucial factors limiting the distribution and abundance of anthropods and fungi that contaminate stored grain. A mathematical model, based on the finite-difference method of calculating heat transfer, has been developed to simulate the temperatures in a cylindrical bin of grain. The main variables that can be studied using this computer model are: thermal properties of the grain, initial temperature of the grain, ambient air temperature, wind velocity, diameter of the bin, and type of bin-wall material. Simulation results indicated that grain stored on the Canadian Prairies would remain at lower temperatures and so would probably be in better condition than grain stored at the shipping points of Vancouver, Toronto and Montreal. In small bins, pests may not be able to overwinter while in large bins temperatures remain warmer and many pests may survive. Painting galvanized-steel bins white has a considerable effect on the temperatures of grain in the bin.

Odor volatiles associated with microflora in damp ventilated and non-ventilated bin-stored bulk wheat

Western hard red spring wheat, stored at 20 and 25% moisture contents for 10 months during 1985-86, was monitored for biotic and abiotic variables in 10 unheated bins in Winnipeg, Manitoba. The major odor volatiles identified were 3-methyl-1-butanol, 3-octanone and 1-octen-3-ol. The production of these volatiles was associated and correlated with microfloral infection. Ventilation, used for cooling and drying of grain, disrupted microfloral growth patterns and production of volatiles. The highest levels of 3-methyl-1-butanol occurred in 25% moisture content wheat infected with bacteria, Penicillium spp. and Fusarium spp. In non-ventilated (control) bins with 20% moisture content wheat, 3-methyl-1-butanol was correlated with infection by members of the Aspergillus glaucus group and bacteria. In control bins, 1-octen-3-ol production was correlated with infection of wheat of both moisture contents by Penicillium spp. The fungal species, isolated from damp bin-stored wheat and tested for production of odor volatiles on wheat substrate, included Alternaria alternata (Fr.) Keissler, Aspergillus repens (Corda) Saccardo, A. flavus Link ex Fries, A. versicolor (Vuill.) Tiraboschi, Penicillium chrysogenum Thom, P. cyclopium Westling, Fusarium moniliforme Sheldon, F. semitectum (Cooke) Sacc. In the laboratory, fungus-inoculated wheat produced 3-methyl-1-butanol; 3-octanone and 1-octen-3-ol were also produced, but less frequently. Two unidentified bacterial species isolated from damp wheat and inoculated on agar produced 3-methyl-1-butanol.

Carbon Dioxide as an Early Indicator of Stored Cereal and Oilseed Spoilage

ABSTRACT CONCENTRATIONS of carbon dioxide (C02) in interseed air were measured in 39 farm-stored bulks of wheat, rapeseed, barley and corn in Manitoba, Canada and Minnesota, U.S.A. Spoilage was confirmed by analyses of grain samples in 97% of the 34 bins having C02 concentrations greater than 0.03% of ambient air. Elevated C02 concentrations were detected in 87% of the 38 bins containing spoiled grain. Measurement of C02 concentration in interseed air is a practical method of detecting active spoilage in stored-grain.

Simulation Model of Two-Dimensional Heat Transfer in Controlled-Atmosphere Grain Bins

ABSTRACT A finite-difference model was developed to simulate conductive heat transfer in both the radial and vertical directions in free-standing, controlled-atmosphere cylindrical bins of stored grain. Temperatures throughout a grain bulk can be predicted during the storage period using input data of initial grain temperatures, mean daily temperatures, solar radiation, average monthly wind velocities and thermal properties of the grain, bin structure and soil. Heat generation in the grain bulk was assumed negligible but it could be readily incorporated into the model. To verify the model, predicted temperatures were compared with measured temperatures in 46 t of rapeseed stored for 41 months and 52 t of barley stored for 23 months. The standard errors of estimate for the temperatures at the centres of the bins were 1.3°C for rapeseed and 1.8°C for barley. Inclusion of a submodel of natural convection currents in the grain bulk did not result in more accurate predictions of temperature and computer time was increased by a factor of about 25 over that for two-dimensional conduction alone. Temperatures of grain in controlled-atmosphere bins predicted using both one-and two-dimensional heat transfer models were compared. The differences between the centre temperatures predicted by the two models were less than 0.2°C for diameter-to-height ratios of 0.5 or less while the differences increased to over 2.0°C for diameter-to-height ratios of greater than 1.2.

Mycotoxin formation in HY-320 wheat during granary storage at 15 and 19% moisture content

Eleven-kilogram parcels of HY-320 wheat, a cultivar of the new Canada Prairie Spring class, were kept at 15 and 19% initial moisture contents (IMC) in simulated storage in a Manitoba farm granary for 60 weeks to determine biotic and abiotic changes and mycotoxin production. Ochratoxin A reached a maximum of 0.24 ppm by week 20 in the 19% IMC wheat, but was absent in the 15% IMC wheat; no other mycotoxins were detected. Temperature, moisture content, O2 and CO2 levels, fat acidity values, seed germination, microfloral incidence and abundance, and the presence of other mycotoxins were monitored. Principal component analysis of all variables showed that the first principal components accounted for 32–41% of the system variability, and contained the ochratoxin A variable. Ochratoxin A was produced in moist grain that had decreased seed germination andAltermaria activity, and high fungal activity byPenicillium andAspergillus versicolor. Compared to other stored cereals previously studied, HY-320 wheat would be ranked in a low-risk category for mycotoxin formation, based on the ochratoxin A levels observed.

Evaluation of a model of drying and deterioration of stored wheat at near-ambient conditions

Abstract Drying and deterioration models of stored wheat at near-ambient conditions were tested using replicated storage environments in 0·61 and 1·22 m diameter bins, 3·66 m in height. The bins were located in Winnipeg, Manitoba, Canada. Fifteen storage environments were tested spanning three grain storage years, incorporating airflow rates from 0·8 to 23l s−1 per m3 of wheat and initial grain moisture contents of 15 to 25%. The grain drying model predicted slower than measured drying rates. The deterioratoon model predicted spoilage earlier than that observed in the experimental bins. Nevertheless, the drying and deterioration models are sufficiently accurate to be used as design tools to predict airflow rates required to cool and dry stored wheat.

Intergranular air temperatures of ventilated bulks of wheat

Abstract A low-temperature grain-drying facility consisting of 0·61 and 1·22 m diameter bins was erected in Winnipeg, Manitoba to monitor physical and biological changes in stored wheat (ranging in moisture content from 15 to 25% w.b.) during ventilation. The effects of outdoor-air conditions, ventilation rates and control strategies on intergranular air temperatures during three harvest years are presented. Speed of temperature fronts were approximately proportional to ventilation rates. Evaporative cooling in the drying front facilitated the use of temperature measurement to locate the drying front. Because of the larger radial heat transfer, 0·61 m diameter bins may not sufficiently model larger bins when using control strategies which incorporate no forced ventilation for periods of over 12 h.

Apparent coefficient of diffusion of carbon dioxide through samples of cereals and rapeseed

Abstract The apparent diffusion coefficients of carbon dioxide (CO2) through rapeseed, wheat, maize and oats were determined in the laboratory using a specially designed cylindrical diffusion apparatus. The diffusion coefficient was not affected significantly (P > 0.05) by the direction of CO2 flow in relation to force of gravity. The effect of compaction of wheat (38–42% porosity) on diffusion coefficient was not significant (P > 0.05). Coefficient of diffusion, however, decreased with increasing moisture content of wheat. At 10°C the mean diffusion coefficients of CO2 through stored seeds were: rapeseed at 8% moisture content, 2.8; wheat at 13% moisture content, 3.5; maize at 14% moisture content, 3.0; and oats at 14.5% moisture content, 3.9 mm2/s.

Odor volatiles associated with mite-infested bin-stored wheat

Tridecane, not previously reported in infested bin-stored grain, was associated with three mite species,Acarus siro (L.),Aeroglyphus robustus Banks, andLepidoglyphus destructor (Schrank), which were introduced into 15.2% moisture content wheat stored in two unheated experimental bins in Manitoba during 1986–1987. The mites and volatiles were sampled at weekly to bimonthly intervals throughout the year. The mites produced tridecane all year, although they overwintered at low numbers. Ventilation of one bin at an airflow rate of 1 liter/sec/m3 did not appear to affect mite survival and volatile production. Citral, an alarm pheromone for mites, was detected in mite-infested bin-stored grain. In laboratory studies all three mite species produced tridecane in wheat incubated at 20 °C and 70% relative humidity for two weeks.Acarus siro andAeroglyphus robustus reared at 25 °C and 90% relative humidity for four weeks on wheat and fungus-inoculated wheat also produced tridecane. Production of tridecane byA. robustus andL. destructor is being reported for the first time.

Mycotoxin formation in moist 2-row and 6-row barley during granary storage.

Eleven-kilogram parcels of 2-row and 6-row barley initially at 18% moisture content were implanted in dry bulk oats in a farm granary in Manitoba for 60 weeks between August 1983 and October 1984. Temperature, moisture content, O2 and CO2 levels, fat acidity values, seed germination, microfloral incidence and abundance and the presence of major mycotoxins (aflatoxins, sterigmatocystin, ochratoxin A, citrinin, penicillinic acid, patulin) were monitored. Ochratoxin A reached maximum levels of 0.97 ppm by week 24 in the 6-row barley, and 0.05 ppm by week 28 in the 2-row; no other mycotoxins were detected. The effect of cultivar type was significant (P<0.01) with greater effects in the 6-row barley for the following parameters: fat acidity value, germination, incidence of Alternaria alternata, Penicillium spp. and Helminthosporium sativum, total fungal propagule count and ochratoxin A levels. The effect of time was significant (P<0.05) for all variables except oxygen, carbon dioxide, Aspergillus versicolor, and total fungal propagule count. The interaction between cultivar and time was significant (P<0.01) for Alternaria and Helminthosporium only.