Top‐spray fluidization coating of paddy rice with zinc oxide nanoparticles to reduce infection fromAspergillussp

Abstract

Paddy rice varieties harvested in the rainy season are generally at risk of fungal contamination. This includes the local paddy rice variety, Sang Yod, that is harvested annually and requires a specific climate and agricultural geography for growth (Ministry of Commerce, 2006). After maturity, most farmers in Thailand, who not have a large godown and equipment for rice production, will sell the paddy rice to the nearest rice community enterprise, cooperative, or factory immediately after harvesting. The paddy rice is sun-dried on a concrete yard to equilibrium moisture content. A small quantity of paddy rice is processed to brown rice, packed, and transported. The remaining paddy rice is stored to serve customer demand over the coming year. Any fungi that infect paddy rice pre-, during-, or post-harvest will usually develop during long-term storage, especially in the South of Thailand where the weather is hot and humid with heavy rainfall year-round. Most of these fungi belong to the genus Aspergillus (Bertuzzi, Romani, Rastelli, & Giorni, 2019). The fungi of this genus can cause contamination of the final product with mycotoxins, for example, aflatoxins and ochratoxin, which are carcinogens, mutagens, and teratogens-the main causes of cancer (Reddy, Reddy, Abbas, Abel, & Muralidharan, 2008). Inhibition and prevention of paddy rice fungi is necessary to reduce the potential losses and consumer health impacts.

Optimization modeling of fluid bed drying and coating technique to control fungal growth and aflatoxin content in paddy

“…To concentrate only on the change of the crystalline form of the n‐ZnO that was coated on the surface of the treated sample under different conditions, we began by testing at a diffraction angle of 30°. Kongtragoul and Junka (2020) reported that diluting n‐ZnO powder to a solution using distilled water can decrease the intensity of all peaks and only peaks with a high intensity can be detected. The change in the intensity also depends on the quality and quantity of the coating material.…”

“…As suggested by the College of Nanotechnology at King Mongkut's Institute of Technology Ladkrabang, Bangkok, Thailand, n‐ZnO powder was mixed with distilled water at the lowest level of density of 400 ppm. The solution was injected at a flow rate of 0.6 ml/s and a pressure at 3.5 bar through a nozzle installed 35 cm above the distributor (Kongtragoul & Junka, 2020). Before the procedure started, air was let in through the air inlet tube and was warmed by the heater to enable the system to be in a steady state in accordance with the experimental hot air temperature, which was in the range of 70–130°C.…”

“…The crystalline form of n‐ZnO powder, reference paddy, and paddy treated at different hot air temperatures was analyzed. The reference and treated paddy were ground in a centrifugal mill (Retsch, ZM 100, Germany) before they were tested by an X‐ray diffractometer (Bruker AXS GmbH, D8 Discover, Germany) at a wavelength of ƛ = 1.54 A° (Cu‐anode source), 40 kV, 40 mA, and a scanning rate every 0.02° (Kongtragoul & Junka, 2020). The crystalline form is shown in a range between 30° and 80° of the diffraction angle.…”

“…The coating condition, nozzle height, atomized pressure, and mass flow rate of the n-ZnO solution used in this study were recommended by Kongtragoul and Junka (2020). This condition balanced the rate of moisture vaporization of the drying system and the coating rate of the coating system at the paddy surface, meaning that the installed coating system was not affected the drying system.…”

“…Zinc oxide nanoparticles have been selected as alternatives for further research. Zinc oxide is not harmful to human bodies and is also considered to be effective for controlling fungal growth (Kongtragoul & Junka, 2020; Siddiqi et al., 2018). An advantage of this method is that it can coat and dry harvest paddy at high moisture to suitable levels, by using a single procedure.…”