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    Analysis of microwave distribution for ready-to-cook fresh-cut asparagus packaging
    (2009-12-01)
    Noochuay, Chanisara
    ;
    Varith, J.
    ;
    Chinsirikul, W.
    ;
    Krairiksh, M.
    This article presents an analysis of 2.45 GHz microwave (MW) distribution for ready-tocook fresh-cut asparagus in polypropylene (PP) packaging. Pre-packed asparagus was simulated for cooking process inside a domestic microwave oven with size of 30×30×20 cm (w × l × h). The MW process simulation applied finite integral method and Maxwell equations to solve an E-field inside microwave cavity. The E-field was further converted into temperature mapping based on heat transfer equations. Validation was performed by comparing the simulated and actual temperatures of MW asparagus captured on thermal imaging camera. Then heat distribution by modified microwavable packaging for asparagus was studied. The result indicates that the simulated temperature mapping of asparagus on a regular PP packaging agreed with the thermal images. The temperature distribution of asparagus was not uniform within a range between 76.8 and 28.2°C. From simulation, the modified microwavable package with dielectric loss, ε, of 16 (similar to ε of asparagus) improved heating uniformity and reduced mean temperature difference between hot and cold spots by 9.5°C compared to ε of 0.41 (regular PP packaging). This work provided guidelines to modify the MW cooking conditions and the microwavable packaging with minimal experimental cost for ready-to-cook foods.
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    Microwave sensor response in relation to durian maturity
    (2009-12-01)
    Suttapa, S.
    ;
    Varith, J.
    ;
    Krairiksh, M.
    ;
    Noochuay, C.
    ;
    Phimpimol, J.
    This research studied the microwave response in relation to maturity development of durian fruit (Durio zibethinus Murry cv. Monthong) using a microwave sensor at frequency of 2.45 GHz. The microwave sensor applied two patch antennas to couple the microwave signal from durian. The experiment was conducted on 30 intact durian fruits at 91-123 days after full-bloom. One intact fruit on the tree was attached with the microwave sensor onto durian peel. The microwave sensor response was recorded everyday. Meanwhile, three durian fruits with the same size and age were picked from the tree for every third day to determine their maturity indices e.g., reducing sugar, starch, moisture content, dry matter and dielectric properties of durian pulp. Result showed that the microwave sensor response linearly decreased during the first period day 91-103, then linearly increased during day 104-118. As the wave from microwave sensor penetrated through the peel, it may interact to one of the maturity indices in the pulp, possibly moisture content during maturity of 50- 70% maturity and starch content during maturity of 70-90%. Dielectric constant of durian pulp at 2.45 GHz was found as a confound factor affecting microwave sensor response relating to durian maturity. The transition of microwave response was approximately at day 103, implying that durian maturity was about 70%, corresponding to an onset of reducing sugar. The microwave responses may be beneficial for durian farmers to predict the suitable harvesting period because of its nondestructive characteristic for durian maturity prediction.
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    Design of multimode-circular microwave cavity for agri-food processing
    (2007-12-01)
    Varith, J.
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    Noochuay, C.
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    Netsawang, P.
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    Hirunstitporn, B.
    ;
    Janin, S.
    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 CST2006® 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 30° 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 31×31 mm2 (λ/4) placing with space of 20 mm (λ/6) exponentially attenuated the E-field. Attenuation trend of simulation agreed with experimental that of measurement which was below safely limit of 5 mW/cm<sup>2</sup>. Findings from this work are useful for the scale-up of multisection/multi-mode microwave oven suitable for agri-food drying process.