Effects Of Supercooling-assisted Freezing On Physical And Structural Properties Of Agar Gel And Tofu
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2022
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University of Hawaii at Manoa
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Supercooling is the process of lowering the temperature of the product below its typical freezing point without forming ice crystals. Compared with well-known long-term preservation methods such as freezing, supercooling can slow down changes in food qualities and also shorten the processing time, reduce energy consumption, and potentially carbon emissions. During the supercooling process, the combined electric field and magnetic field treatments could enhance the mobility of water molecules while at freezing temperature ranges. Pulsed electric fields (PEF) have been reported to reorient and realign water molecules because of the electric dipole present in water molecules. Oscillating magnetic fields (OMF) vibrate water molecules due to water diamagnetism, preventing ice crystal nucleation. The purpose of this study was to evaluate the effect of the supercooling pretreatment before freezing on the physical and structural properties of solid model foods.In this experiment, agar gels (2% agar powder & 10% maltodextrin) and firm tofu were treated using four different methods: freezing at -18℃ for 24 hours, freezing at -18℃ for 24 hours with 6 hours of supercooling pre-treatment, freezing at -80℃ for 24 hours, and freezing at -80℃ for 24 hours after 6 hours of supercooling pre-treatment. The supercooling temperature of agar gel is about -6℃, and firm tofu was supercooled about -2℃. Before treatments, all samples were stored in a refrigerator at 4℃. Their syneresis and texture were measured after thawing for 24 hours. Microscopic observation and micro-CT scanning of the samples were committed at the same time. The results showed that compared with control samples, samples after supercooling treatment showed low syneresis, and the peak force was close to fresh samples. By analyzing the structure of the samples treated under different storage conditions, it was found that the ice crystal of the samples stored at -80°C were finer and denser than that of the samples stored at -18°C. This study proved that the supercooling pretreatment before freezing is beneficial in reducing the damage of ice crystals in the internal structure of the sample and can maintain post thawing physical properties as close to fresh samples. The experimental results of agar gels and firm tofu can serve as a foundation for the supercooling and freezing experiments of more complicated food materials in future studies.
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Food science
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