INTRODUCTION Peanut (Arachis hypogaea L.) is a cheap, nutrient-dense, and frequently grown crop that produces one of the most significant edible oils in the world. As a significant source of edible oil, peanuts or groundnuts are revered in India as the "King of Oil Seeds" (Kanabur, 2019). Mixed glycerides make up groundnut oil, which has a high content of unsaturated fatty acids including oleic (50–65%) and linoleic acid (18 to 30 percent) (Dudekula et al., 2021). Peanuts are eaten in raw and processed forms, as well as peanut butter, confectionery, and peanut oil. Indian cuisine showcase an inclusive spectrum of culinary variety arising from India’s pluralism (Dhanshetty et al., 2021). Peanuts have received a lot of attention as a functional food (Francisco & Resurreccion 2008). One of the major concerns of the peanut industry is the contamination of peanuts with insects, insect fragments (Torres et al., 2014), fungi, and mycotoxin (Fu et al., 2018). Groundnut postharvest losses due to insects, mould, and rodents range from 10 to 25 percent. Tamarind/groundnut bruchid, Caryedon serratus (Olivier) is the main pest of peanuts found in storage godowns. Many additional minor pests like Tribolium castaneum, and Coecyra cephalonica also attack peanuts, making them unfit for consumption (Nataraja et al., 2014). Pesticides were traditionally used to control stored product pests. However, as insects develop resistance and possibility of residues in product, consumers are concerned about pesticide toxicity (Ahmed et al., 2021). Hence, non-chemical methods need to be developed for managing the insects in storage and to avoid residues in food products. The application of Radio Frequency (RF) at an optimum condition is an alternative for the management of insects in food products. In recent years, RF is gaining a lot of importance for applications such as drying, baking, and disinfestation. The molecules inside a product positioned in an RF environment continuously reorient themselves (27 M times/s at 27 MHz) in reaction to the applied field. This is how radio frequency heating works. Because of the frictional interaction amongst the molecules, the reaction starts volumetric heating inside the entire product, which selectively heats only the product and not the air or surrounding equipment (Mahendran & Jojo 2013). RF is used to control stored-product insects through direct treatment of the food materials, resulting in a residue-free procedure of pest control through complete insect mortality. The disinfestation with RF technology is based on a lethal time of 100 percent mortality, allowing the population of insects invading stored commodities to be controlled. The RF disinfestation process involves exposing the product and the insect to alternating currents, which causes the insects to die. It is critical to experiment with the insect’s mortality when considering RF's potential use in the food processing line. Hence, the investigation was planned to study the effect of RF treatment on the life stage of C. serratus (eggs and adults). MATERIALS AND METHODS A. Procurement of peanuts The dried peanut samples with an initial moisture percent of 7.5 were obtained from the local market of Pudukkottai, Tamil Nadu. All the dirt and unwanted materials were removed. The malformed, contaminated peanuts were screened off and a collection of uniform-shaped peanuts was done. The sorted peanuts were stored in airtight containers for further analysis. B. Insect culturing The parent adults of C. Serratus were obtained from the NIFTEM Thanjavur Storage Entomology department. About 50unsexed adults were introduced to each 500 ml glass jar containing about 100 g of susceptible peanut seeds. The containers were covered with muslin cloth to avoid suffocation and passage of insects. It was observed for 28 ± 3 days at a temperature of 28 ± 0.5 °C for the arrival of new adults. The insects used in the study were of the same age (Sewsaran et al., 2019). C. RF sterilizer The infested peanuts were disinfested with a 10 kW RF sterilizer (40.68 MHz; Make: Lakshmi Insta 10/4) was utilized. The system consists of an applicator linked with a generator and two parallel flat plate rectangular electrodes (Fig. 3). A high voltage (5kV) alternating electric field was applied to the sample placed between the electrodes. A current of 0.5 A was required for the disinfestation. D. RF treatment for mortality assessment Peanut samples (250 g) were placed in Petri plates (200X30 mm), and eggs (20 in no’s) and adults (10 in n’s) were introduced into the Petri plate. These were then subjected to RF treatment with various combinations of electrode height and conveyor speed. The selected electrode heights were 230, and 250 mm with conveyor speeds of 2.5, 5, 7.5, 10, and 12.5 m/h for each electrode height. The time required for exposure was noted for each conveyor speed. Then the samples were cooled and stored (eggs) in plastic containers covered with muslin cloth for 60 days to investigate any emergence of adults. And to check the mortality of adults after treatment, it was kept for 24 hours for observation. E. Imaging of insect morphology before and after RF treatment The life stages of insects were imaged using a stereomicroscope (Leica S8 APO; Make: Leica microsystems from Wetzlar, Germany) that was linked with a computing system (Fig. 4) in order to determine the changes in insect eggs and adults. The object was then observed on the computer screen by changing the focus and zoom to make it clear for observation. Later, then images were captured and saved using the software, Leica Application Suite 2.0. F. Statistical analysis The experiential response was analysed using the Poloplus 2.0 software (LeOra Software, Petaluma, CA, USA) to calculate the Lethal Time for 50 and 99.99 percent of mortality due to dielectric treatments for both life stages. The results were interpreted by comparing the time required for mortality (Loganathan et al., 2011) of the egg and adult stages of the insect. RESULTS AND DISCUSSION A. Radiofrequency-assisted disinfestations of eggs The infestation of C. serratus must be controlled from the egg stage itself because it reduces the quality of peanuts and results in losses of up to 73 percent (Nataraja et al., 2014). The egg stage of C. serratus was attempted to be eradicated by the RF disinfestation at various electrode heights and conveyor speed combinations with an aim to minimize the loss. The results of disinfestations of egg stage showed that eggs subjected at 230mm electrode height took minimum time to kill, with LT50 and LT99 of 5.51 and 14.22 minutes, respectively. The electrode height of 250 mm required more time with 8.40 and 49.05 minutes for the LT50 and LT99 respectively to control the insect. The temperature was recorded as 70 ± 2 ºC, fluctuating with treatment time. The electric field intensity increases as the electrode gap/ height are lowered (Jiao et al., 2014; Li et al., 2017). B. Radiofrequency-assisted disinfestations of adults The results of disinfestations peanut with adult bruchid showed that insects subjected at 230mm electrode height took minimum time to kill, with LT50 and LT99 of 3.01 and 11.60 minutes respectively. The electrode height of 250mm required more time, taking 5.69 and 35.72 minutes for the LT50 and LT99 respectively. The temperature was recorded as 70 ± 2 ºC, fluctuating with treatment time. Because RF waves penetrate deeper than microwaves, they can heat low moisture goods more quickly (Boreddy et al., 2014; Chen et al., 2019). A similar study was performed by Tiwari et al., (2021) using various electrode height and conveyor speed combinations to investigate the mortality of Callosobruchus maculatus in blackgram (Vigna mungo) where it was reported that LT for 99.99 percent mortality (LT99.99) was ranged from 3.62 to 8.23 for the egg stage,4.70 to 7.27 min. for larvae 7.10 to 8.96 min. for pupae, and 5.40 to 7.73 min. for the adults. Earlier, Indumathi et al., (2021) reported that there was 100 percent mortality at each stage of T. castaneum lifecycle at 0.9 A of radiofrequency current and 0.5 kV for 15 minutes. T. castaneum was susceptible to RF heating in the following order: adults

How to cite this article

Karuna Ashok Appugol, Irengbam Barun Mangang, Vidhya Lakshmi A. and Loganathan Manickam* (2022). Radiofrequency Assisted Disinfestation of Caryedon serratus in Peanuts. Biological Forum – An International Journal, 14(3): 295-301.