Effect of gamma irradiation on microbiological and nutritional properties of the freeze-dried berries

Abstract

Lyophilization or freeze-drying is the technique of removing ice or other frozen solvents from a material through sublimation and the removal of bound water molecules through the process of desorption. Drying occurs in an absolute vacuum at temperatures from -40°C to -50°C. This technique is often used for the conservation of fruits, especially berries. During this process, the water changes from frozen to gaseous, with no thawing. Due to low temperatures and the high vacuum, most microorganisms are rendered inactive during the lyophilization process. However, if there is a necessity to destroy all microorganisms from treated food, subsequent irradiation with gamma rays is an appropriate method. This paper investigated the influence of different doses of gamma radiation on lyophilized berries' microbiological characteristics. It was shown that the radiation dose of 7 kGy is sufficient to eliminate the total number of microorganisms (excluding molds) to the extent that the number falls below the permitted limit according t o the law on the microbiological safety of foodstuffs of the Republic of Serbia, and 5 kGy is enough for molds to be rendered inactive. It was also concluded that gamma irradiation does not affect the nutritional value of lyophilized berries.