Research on the quality parameters of a functional low-fat peach yogurt produced by freeze-drying

In recent years, as manufacturers have expanded their range of functional fermented milk products, they have become increasingly interested in producing these products in dried form with good sensory characteristics. Among the many preservation methods, freeze-drying preserves nutritional value better than other drying methods, while retaining the actual color and shape of the raw materials. This paper presents the results of studies on the effect of freeze-drying on the quality parameters of low-fat peach yogurt intended for functional use. As a result of the freeze-drying process, freeze-dried yogurt enriched with peach juice was obtained. To prevent microbial growth and extend the product’s shelf life, optimal process parameters were selected (pressure p = 0.050 mbar, condenser temperature t = −80°C), enabling the production of a product of the required quality. The residual moisture content of the dry yogurt, which affects quality indicators, was 3.1%, 3.5%, and 3.8% for the three samples A, B, and C, depending on the thickness of the pre-frozen product before drying, which was 10 mm, 15 mm, and 20 mm, respectively. As the studies showed, the drying time depended on the thickness of the prepared frozen samples. A frozen sample thickness of 10 mm was found to be optimal and resource-efficient, with a drying time of 27 hours. For thicknesses of 15 mm and 20 mm, the drying time ranged from 32.2 to 36.5 hours, depending on the sample thickness, respectively. The addition of peach juice in an amount equal to 20% of the total mass of the finished yogurt, made from skim milk, increased the nutritional value of the final product by raising the content of carbohydrates, vitamins, and macro- and micronutrients.