EFFECT OF OPERATIONAL PARAMETERS OF MICROWAVE VACUUM DRYING COMBINED WITH HOT-AIR PRE-DRYING TO PHYSICAL, SENSORY, AND NUTRITIONAL PROPERTIES OF DRIED APPLE SNACK

Microwave vacuum drying is a novel and mild food preserving technology. Beside its basic preserving function, it can be combined with other technologies, like hot-air drying. As a result of this combination, special snack can be produced from apple. The product is characterized by its unique consistency, high nutritional value, and consumer preference. In this work physical (dry mass content, hardness, bulk density, and colour), sensory (appearance, colour, odour, taste, texture) and nutritional (antioxidant activity and total phenolics) properties of dried apple snack were investigated as a function of pre-drying, microwave energy input, and batch weight. For evaluation of data, central composite experimental design was applied. According to the results, the physical properties of products produced by microwave vacuum drying combined with hot-air pre-drying (CMVD) mainly depend on the specific energy input. Higher specific energy input results higher dry mass content, which is associated with harder consistency, lower bulk density, and positive consumer perception as well. Bulk density had an optimum point of batch weight at 336 g. Higher value of pre-dried dry mass content resulted lighter colour but less antioxidant activity and less total phenolics, therefore shorter hot-air drying and prolonged microwave vacuum drying is recommended.