Effects of Shape and Size of Agar Gels on Heating Uniformity During Pulsed Microwave Treatment

• Published in: Journal of food science 2015-05, Vol.80 (5), p.E1021-E1025
• Main Authors: Soto-Reyes, Nohemí, Temis-Pérez, Ana L., López-Malo, Aurelio, Rojas-Laguna, Roberto, Sosa-Morales, María Elena
• Format: Article
• Language: English
• Subjects: Agar; Agar - chemistry; Agar model; Cold Temperature; Cooking; Cylinders; Food Handling - methods; Food science; Gels; Heating; Hot Temperature; Humans; Mathematical models; microwave heating; Microwaves; Models, Chemical; shape and size; Slabs; Temperature distribution; Thermal Conductivity; Water
• ISSN: 0022-1147; 1750-3841
• DOI: 10.1111/1750-3841.12854

Model gel systems with different shape (sphere, cylinder, and slab) and size (180 and 290 g) were prepared with agar (5%) and sucrose (5%). Dielectric constant (ε′), loss factor (ε″), thermophysical properties, and temperature distribution of the model system were measured. Each agar model system was immersed and suspended in water, and then, heated in a microwave oven with intermittent heating until the core temperature reached 50 °C. The ε′ and ε″ of agar gels decreased when frequency increased. The density and thermal conductivity values of the agar gels were 1033 kg/m3 and 0.55 W/m °C, respectively. The temperature distribution of sphere, cylinder, and slab was different when similar power doses were applied. The slab reached 50 °C in less time (10 min) and showed a more uniform heating than spheres and cylinders in both sizes. Agar model systems of 180 g heated faster than those of 290 g. The coldest point was the center of the model systems in all studied cases. Shape and size are critical food factors that affect the heating uniformity during microwave heating processes. Practical Application The analysis of microwave heating using model food systems is a valuable tool to study the influence of different factors on heating uniformity, such as size, shape, and composition. The results obtained in this work will be useful for further applications of hot water microwave treatments, such as mold and pest control or blanching, in real foods with characteristics similar to the studied models and heating conditions.