Jatuphong Varith

Non-contact bruise detection in apples by thermal imaging

Abstract Thermal imaging is a non-destructive and non-contact infrared sensing technique. Such imaging creates a bit-map called a thermogram by detecting infrared radiation emitted from an object. Up to 100% of apple bruises were detected using thermal imaging during warming of the fruits by discriminating surface temperature between bruised and sound tissues. Apples were bruised by dropping them from 0.46 m onto a smooth concrete floor and then were held at 26 °C and 50% RH for 48 h. They were then thermally imaged using a ThermaCam™ PM390 (FLIR Systems, Inc., Portland, OR) during heating and cooling treatments. Thermal images of bruised tissue showed at least 1–2 °C difference from sound tissue within 30–180 s. The temperature differences between bruised and sound tissues were possibly due to the differences in thermal diffusivity. Under steady-state temperature, thermal imaging did not detect bruises, indicating that the temperature differences were not due to emissivity differences. The technique could provide a basis for automatic bruise sorting, and possibly a better understanding of bruised tissue.

Effects of Microwave Power, Treatment Time and Sample Orientation on Heat Distribution in Mango

Quarantine heat treatment to disinfest oriental fruit fly (Dacus dorsalis H.) in mangoes (Mangifera indica L.) is necessary for fruits exported to developed countries. Microwave provides rapid heating in food materials which may shorten the fruit quarantine process. The objectives of this work were to preliminarily assess the heat penetration of the microwave in mango and to determine the optimal condition to obtain a uniform heating in mango. A household 800 watt-microwave oven was used to provide heating on export-graded ‘Chokanan’ mango (weight of 320 g / fruit). The experiments were conducted to investigate factors including microwave power, heating time, and sample orientation affecting the heat penetration and heat distribution in mango. The internal temperature mapping of the mango was obtained to assess the heat distribution inside the fruit along with thermogram to illustrate its surface temperature. It was found that mango heated with microwave power of 50% for 40 sec yielded the internal temperature of 45 °C at 23 mm underneath the skin where the flesh was thickest and susceptible to the slowest heating. With the aforementioned condition, the mango treated with microwave in the transverse position retained better heating uniformity than did in the normal position. Microwave heat treatment on mangoes may offer advantages over the standard vapor heat treatment (VHT) during comeup time, in terms of less energy consumption, easier implementation for a continuous system, and possibly better product quality retention due to shorter come-up heating time.

Design of Multimode-Circular Microwave Cavity for Agri-Food Processing

This article presents a design for multimode-circular microwave cavity at 2.45 GHz as a section of vertical-typed microwave oven for agri-food processing. Microwave cavity with a diameter of 100 cm and a height of 25 cm was modeled using CST2006reg commercial software. Finite integral method was performed to solve the model for design criteria including waveguide arrangement to obtain low coupling and uniform distribution, and choke design to minimize microwave leakage. Simulation results show that perpendicular arrangement of two waveguides with 30deg angle apart from each other yielded the minimal mutual coupling. With this waveguide arrangement, microwave power density was linearly loss into the grape model in radial direction from wall toward the center of cavity. Simulated electric field (E-field) distribution agreed with experimental E-field distribution on fresh grape as it was converted into heat captured by thermal imaging camera. The cavity design with three square choke of 31x31 mm2 (lambda4) placing with space of 20 mm (lambda6) exponentially attenuated the E-field. Attenuation trend of simulation agreed with experimental that of measurement which was below safety limit of 5 mW/cm2. Findings from this work are useful for the scale-up of multi- section/multi-mode microwave oven suitable for agri-food drying process.

Wireless Sensor Network for Monitoring Maturity Stage of Fruit

In this letter, we present a wireless sensor network for monitoring the maturity stage of fruit. A dual-polari- zation coupled patch sensor, which is robust to environmental changes, was designed to operate at 2.45 GHz. It was attached to a Durian fruit for a period of days to measure the magnitude of mutual coupling corresponding mainly to the starch concentration of its pulp. Signal was transmitted from a sensor node, via tree nodes, to a master node that displays the variations occurring in the period. The maximum mutual coupling occurred at the maturity stage of 60% whereas the minimum occurred at 70%. These results demonstrate that this wireless sensor network can enable fruit growers to harvest their Durians at an appropriate time, providing a reliable quality control for export.

Thermal Image Bruise Detection

Thermal imaging is a non-destructive and non-contact infrared sensing technique, which creates a bit-map called a thermogram by detecting infrared radiation emitted from an object. Up to 100% of apple bruises were detected using thermal imaging during warming of the fruit, due to differences in thermal diffusivity and between bruised and sound tissue. Apples were bruised by dropping them from 0.46 m on a smooth concrete floor and then were held at 26°C and 50% RH for 48 hours. They were then thermally imaged using a ThermaCamaPM390 (FLIR Systems, Inc., Portland, OR) during heating and cooling treatements. Thermal images of bruised tissue showed at least 1-2°C difference from sound tissue within 30-180 s. Thermal imaging did not detect bruises under steady-state temperature conditions, indicating that detection was not due to differences in thermal emissivity. The technique could provide a basis for automatic bruise sorting, and possibly a better understanding of bruised tissue.

Quarantine Treatment on Mango using Microwave-Vapor Combined Process

The objective of this research was to develop a microwave-vapor heat treatment (MW-VHT) on mango (Mangifera indica L.) to quarantine oriental fruit fly, Bactrocera dorsalis (Hendel), which is a required process for exported fruits to developed countries. Thermal-Death-Time (TDT) and Thermal- Quality-Time (TQT) overlay plot was established and MW-VHT process was then developed based on the TDT and TQT information. Results showed that an effective quarantine temperature should be higher than 46°C with varied holding time up to 20 min at a selected temperature. Developed MW-VHT processes increased an internal temperature of mango fruit in a range of 48-55°C, which effectively disinfested oriental fruit fly egg by 100%. Physio-chemical properties of MW-VHT mango, such as, color, titratable acid (TA), total soluble solid (TSS), TSS/TA, and firmness, were not significantly different (p=0.05) than those of non-treated mango. Compared to the conventional VHT, MW-VHT offered less percent of heat damage on mango and shortened quarantine process time more than 90% during the come-up period.