Development of freeze-dried miyeokguk, Korean seaweed soup, as space food sterilized by irradiation

Abstract

The purpose of this study was to evaluate microbial populations, Hunter's color values (L⁎, a⁎, b⁎) and the sensory quality of freeze-dried miyeokguk, Korean seaweed soup, in order to use it as space food. Microorganisms were not detected in non-irradiated freeze-dried miyeokguk within the detection limit of 1.00logCFU/g. However, the microbial population in rehydrated miyeokguk was 7.01logCFU/g after incubation at 35°C for 48h, indicating that freeze-dried miyeokguk was not sterilized by heat treatment during the preparation process. Bacteria in the freeze-dried miyeokguk were tentatively identified as Bacillus cereus, B. subtilis, Enterobacter hormaechei, and Ancinetobacter genomosp. using the 16S rDNA sequencing. In samples that were gamma-irradiated above 10kGy, it was confirmed that all microorganisms were inactivated. Hunter's color values of the samples irradiated at doses less than 10kGy were not significantly altered from their baseline appearance (p>0.05). Sensory evaluation showed that preference scores in all sensory properties decreased when freeze-dried miyeokguk was irradiated at doses greater than 10kGy. Therefore, the results of this study suggest that gamma irradiation at 10kGy is sufficient to sterilize freeze-dried miyeokguk without significant deterioration in the sensory quality, and thus, the freeze-dried and irradiated miyeokguk at 10kGy fulfills the microbiological requirements as space food.