Effects of Electromagnetic Heating on Quick Freezing

Abstract

Purpose: Quick freezing is widely used in commercial food storage. Well-known freezing techniques such as individual quick freezing require a low-temperature coolant and small cuts for the heat-transfer efficiency. However, the freezing method for bulk food resembles techniques used in the 1970s. In this study, electromagnetic (EM) heating was applied to improve the quick freezing of bulk food. Methods: During freezing, the surface of food can be rapidly cooled by an outside coolant, but the inner parts of the food cool slowly owing to the latent heat from the phase change. EM waves can directly heat the inner parts of food to prevent it from freezing until the outer parts finish their phase change and are cooled rapidly. The center temperature of garlic cloves was probed with optical thermo sensors while liquid nitrogen (LN) was sprayed. Results: When EM heating was applied, the center cooling time of the garlic cloves from freezing until -10°C was 48 s, which was approximately half the value of 85 s obtained without EM heating. For the white radish cubes, the center cooling time was also improved, from 288 to 132 s. The samples frozen by LN spray with EM heating had a closer hardness to the unfrozen samples than the samples frozen by LN only. Conclusions: The EM heating during quick freezing functions to maintain the hardness of fresh food by reducing the freezing time from 0 to -10°C.

Supercooling as a potentially improved storage option for commercial kimchi

“…The temperature immediately after this rise from the latent heat was considered as the freezing point, and the difference between nucleation temperature and the freezing point was considered as the supercooling degree (SD). To slowly lower the temperature of kimchi, a custom freezer (Sinhan freezing plant Co., Chungju, Republic of Korea) capable of stepwise control with 48 memories from 20 to −30 °C was used (Kim et al., 2015). The freezer temperature was decreased from 2 to −10 °C at 0.5 °C intervals.…”

Study of Radio Frequency Thawing for Cylindrical Pork Sirloin

“…To prevent the surface from defrosting to fast via heat transfer from air to the food, a custom-built chamber with temperature control from -40 to 10℃ was used ( Figure 6(a); Kim et al, 2014;Kim et al, 2015). An RF generator (TX-20, ADTEC Plasma Technology Co. Ltd., Hiroshima, Japan) and an auto-matcher (TST-2720, TST Co., Sungnam, Korea) were used for the RF power source.…”