Griffiths Atungulu 2015-06-23 01:02:56
Grains are normally harvested at a moisture content (MC) higher than the level required for safe storage. In order to reduce the MC to a safe storage level, some producers use low-temperature, natural air, in-bin drying systems. These in-bin drying systems generally maintain grain quality, but the associated slow air movement and occasional stagnation of the drying zone can result in differences in quality among the grain layers. Recently introduced drying technology based on the equilibrium moisture content (EMC), also known as “cabling and sensing technology,” for use in on-farm drying systems retains the advantages of low-temperature, in-bin drying of grain with potential to maintain consistent grain quality. This new technology uses sensors that measure ambient air conditions and monitor the MC and temperature of the grain throughout the bin. With the new cabling and sensing technology, operation of the drying fans depends on the EMC conditions of the drying air and the MC of the grain. The drying fans are operated only under certain conditions of drying air temperature and relative humidity to avoid over-drying or re-wetting of the grain. The MC trend of the grain during drying can be accessed at any time and from any location via the internet, which makes monitoring the grain much easier. While the new cabling and sensing technology appears very promising for managing grain drying, its ultimate success depends on (1) accurate EMC data to establish fan run time and air flowrate; (2) accurately assessing grain quality, especially in the upper layers where the grain remains at high MC for a longer time; and (3) providing efficient supplemental heating to speed up grain drying when the weather conditions do not allow complete and timely drying with ambient air. Our team recently conducted a field study to determine the vertical and spatial variations in the quality of rice that had been dried and stored using the new cabling and sensing technology. This study produced the following observations: • Rice samples from different layers within the bin exhibited variations in the standard quality indices, including milled rice yield (MRY), head rice yield (HRY), rice color, and pasting properties. • There were some variations in the quality indices for rice between the center and perimeter of the bin, but the differences were not significant. • In some drying scenarios, rice in the top layers and at the center of the bin had slightly elevated microbial populations compared with rice in the bottom layers and at the bin perimeter. The findings provided justification to develop better drying and storage strategies to maintain the uniformity and quality of the grain throughout the bin. Of greatest concern for most cereal grain consumers is potential contamination with mycotoxins, particularly aflatoxin, which is highly toxic even at doses as low as 20 ppb. Compared to grains such as corn, the problems of mycotoxin in rice have not been common. The capabilities of the new cabling and sensing technology to allow monitoring of grain MC and temperature, and the automated fan control accord on-farm, in-bin drying of grains a new paradigm to combat and protect in-bin dried grains from mycotoxin contamination after harvest. Various strategies are used to control this risk before harvest, including: • Selective breeding to advance the development of varieties resistant to mycotoxin-producing fungi. • Proper cultural practices, such as choice of planting and harvest dates, tillage practices, crop rotation, plant population, irrigation, and sanitation. • Applying crop protection chemicals or biological controls to mitigate mycotoxin contamination. However, the spores of some pathogenic fungi such as Aspergillus flavus are prevalent in the air, making the fungus a common contaminant of grain in the field. The spores of such fungi are very heat tolerant and may survive the convective heating used in conventional grain drying. When such spores encounter favorable conditions of equilibrium relative humidity, they may be activated, and their growth increases the risk of mycotoxin contamination. As a public health concern, survival of harmful fungi must be minimized. The best way to control mycotoxins is to prevent their formation. Our team is working on in-bin grain modeling and simulations to identify and optimize suitable on-farm, in-bin grain drying and storage strategies that retard mold growth on grain, thereby reducing chances of mycotoxin development, and the development of auxiliary drying systems that can be used on the farm to dry grain as well as decontaminate grain of harmful fungi. The accompanying photos show our recently built, pilot-scale system for continuous infrared (IR) heating of grain to achieve rapid drying and inactivation of microbes. The single- zone system uses catalytic IR emitters powered by either natural gas or propane and has a modular design to allow adjustment of process parameters, including belt speed, IR intensity, belt vibration intensity, air circulation within the drying zone, and gap size between the product and the emitters. This new IR heating system has been tested for corn drying and has shown promising results. Single-pass grain drying while simultaneously maintaining grain quality may also be possible with microwave heating. Microwave energy is typically associated with volumetric heating of agricultural products. In collaboration with microwave equipment manufactures, our team is developing treatment methods that use microwave technology for drying and decontamination of agricultural products. These methods may allow one-pass drying with reduced MC and temperature gradients within individual grain kernels, thereby preventing cracking, which is especially important for rice kernels, and may also inactivate harmful microbes during storage. When optimized, the new IR and microwave technologies will provide grain quality comparable to that of conventional drying systems. In addition, with the minimal cost of retrofitting at the front end of conventional dryers, the new technologies may find applications as auxiliary drying and/or pre-drying systems in both on farm and commercial grain drying facilities. ASABE member Griffiths Atungulu, Assistant Professor, Department of Food Science, University of Arkansas, Fayetteville, USA, firstname.lastname@example.org.
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