Peeling mechanism of tomato under infrared heating: Peel loosening and cracking

Critical behaviors of peeling tomatoes using infrared radiation heating are thermally induced peel loosening and subsequent cracking. Fundamental understanding of the two critical behaviors, peel loosening and cracking, remains unclear. This study aimed at investigating the mechanisms of peel separation for tomatoes subjected to a newly developed infrared dry-peeling process. Microstructural changes in tomato epidermal tissues under infrared heating were compared with those of fresh, hot lye and steam treated samples. Theoretical stress analyses coupled with the experimentally measured failure stress of tomato skin were combined to interpret the occurrence of peel cracking within a framework of elastic thin shell theory. With the use of light microscopy and scanning electron microscopy, it was observed that peel loosening due to infrared heating appeared to result from reorganization of extracellular cuticles, thermal expansion of cell walls, and collapse of several cellular layers, differing from samples heated by hot lye and steam. Crack behaviors of tomato skin were attributed to the rapid rate of infrared surface heating which caused the pressure build-up under the skin and strength decrease of the skin. In order to achieve a sufficient skin separation for effective peeling using infrared, promoting rapid and uniform heating on the tomato surface is essential. The findings gained from this study provide new insights for developing the sustainable infrared dry-peeling technology. Published by Elsevier Ltd.