**3. Postharvest pest management**

Pests pose a very big challenge during the postharvest storage of grain legumes, transportation as well as during distribution. The quality and quantity of grains are reduced by pests if not properly controlled. Pest infestation is a big source of worry for both farmers and food processors because of the losses in investment and profit depletion that come with it. Some of the grain pest control techniques conventionally adopted are fumigation and controlled atmosphere of CO2 and N2. Novel techniques have also been developed to take care of some of the shortcomings of conventional pest management practices like fumigation that make use of chemicals. Examples of some of the emerging technologies which have found use in pest management include irradiation, radio frequency, infrared, and microwaves [7]. Methyl bromide application and treatment with hot air on grain legumes storage facilities or systems is also a common practice for disinfection in the grain storage industry [4].

#### **3.1 Irradiation (IR)**

Food irradiation is a food preservation technique during which ionizing radiation (0.1–50 KGy) is used to destroy target microorganisms in order to extend the shelf life of foods. During irradiation, microbial inactivation is achieved through free radical development which disrupts DNA and cell membrane integrity [7]. It has shown to be effective in sprout inhibition, elimination of parasites and insects, destruction of spoilage, and pathogenic microorganisms [8].

Radiation treatment at low and moderate doses has been recommended for the disinfestation of legumes [8]. The treatment has also been found to be effective for the reduction of flatulence-causing oligosaccharides as well as trypsin and chymotrypsin inhibitors. With these effects of irradiation on anti-nutritional factors in legumes, the nutritive quality of irradiated beans is thereby improved. Stored produces, especially grains have been successfully decontaminated with ionizing radiation as it affects the internal structure [8, 9]. Irradiation technology has been very effective in controlling the *Aspergillus*, *Penicillium*, *Rhizopus,* and *Fusarium* fungi infection in many grains and prolonging the shelf life over 6 months [10]. The source of radiation that is usually utilized is Co-60 and selenium.

#### **3.2 Radio frequency (RF) heating**

Radio frequencies (RF) are electromagnetic waves that are able to penetrate dielectric materials. They usually are characterized by a wavelength of about 11 m and with a frequency range of 1 to 300 MHz [11]. With this ability to penetrate dielectric materials like food grains, they are able to produce heat volumetrically. They are able to do this through ionic polarization or dipole rotation. With the

higher moisture content in food grains, their ability to act as dielectric materials is increased, allowing them to act as electric capacitors and resistors and useful in the storage and conversion and electrical to thermal energy. This can be possible within an electromagnetic field [11].

In comparison, the higher moisture content in insects and the consequent higher electrical conductivity would make them require higher lethal temperatures and higher lethal time. At a lethal temperature and time of 50°C for 29 minutes or 54°C for 5 minutes, it would be possible to completely destroy a wide range of insects. This process of higher heating rates and its application finds use in the disinfection of grains on an industrial scale [9, 11].

When insects feed directly on grains, they produce webs and feces on stored pulses thereby reducing grain quality and this represents a huge challenge during the storage, transportation, and distribution of grains. To mitigate this huge challenge, RF heating has been used in the disinfection of dried cereals and legumes. This was demonstrated using a 27 MHz and 6 kW RF unit where the RF proved superior to forced hot air with respect to heating time required (5–7 minutes as against 275 minutes) to heat 3 kg of legumes to 60°C. Good quality product and uniformity in temperature distribution across the surface and interior of the legumes was achieved in the legume samples by a combination of RF heating followed by a movement of forced hot air as grains move through conveyors at 0.56metres per minute. The final interior temperatures of the containments used were above 55.8°C while 57.3°C was recorded for the surfaces of all legumes tested with resultant low index values for uniformity of 0.014–0.016 (ratio of standard deviation to the average temperature rise) for the distribution of interior temperature and 0.061–0.078 for the distribution of surface temperatures. Legumes treatment with RF in combination with forced hot air (60°C) to retain the needed treatment temperature for 10 min followed by the rapid cooling of the air through a 1 cm product layer yielded products with high quality. There were no significant differences in weight, moisture, color, and germination when samples used for control were compared to treated ones [12].

### **3.3 Infrared**

Infrared is a segment in the electromagnetic spectrum found in between the microwave region and the visible spectrum area characterized by a wavelength of about 0.5 to 100 μm [9]. The absorption of infrared rays produces vibrations in the molecules of water, with consequent heat generation. Infrared-based technologies have been found to be energy-efficient and eco-friendly when compared with other conventional methods. Infrared technology also has many other merits like short process duration, uniform effect on food material, low energy requirement, high rate of heat transfer, and enhanced quality of products [9]. As a result of some of the above-listed characteristics, infrared-based technologies have been used in very many food operations like boiling, heating, drying, peeling, recovery of polyphenols and antioxidants, freeze-drying, roasting, microbiological inactivation, grains sterilization, juice and bread production, and cooking. The idea of the usage of infrared rays to disinfect/sanitize grains was established in the early 1960s and 1970s. Based on its exceptionally effective microbial inactivation characteristics, grain industries usually adopt it as a preferred operation for grain disinfection against various chemical methods. Infrared operations involve three different mechanisms in destroying micro-organisms namely thermal inactivation, induction heating, and the distortion of DNA integrity. As documented by [9], the Infrared treatment of mung bean for 5 minutes at an intensity and temperature of 0.29 kWm and 70°C respectively resulted in the total inactivation of fungal growth. Since the

penetration rate of infrared is low, its effectiveness gets reduced with an increase in the depth of food. It is therefore recommended more for food surfaces sterilization than other processes. Catalytic-infrared emitters have also been developed and used for the control of weevils in rice, merchant grain beetle, and saw-toothed grain beetle. Generally, a little exposure of about 60 seconds is adequate to destroy insects that strive externally or internally in the grains kept in storage facilities [9].
