The effect of refrigeration and room temperature storage conditions on the physico-chemical characteristics of hybrid and freeze-dried blueberries

In order to preserve the nutritional properties of fruits after dehydration, it is necessary to use appropriate storage methods. The traditional freeze-dried and combination -dried i. e. vacuum pre- and freeze post -dried, freeze pre- and vacuum post -dried, mid -infrared -freeze-dried, and freeze -mid -infrared dried blueberry samples were stored in vacuum packs for 6 months. The reference drying method, i.e. freeze drying at a pressure of 80-90 Pa and a temperature range between -25 and 20 degrees C, with a drying time of 22 h, was used. The blueberries were mid -infrared dried at 60 degrees C for 5 min before and after freeze-drying, and the experimental materials were also vacuum dried at 60 degrees C for 4 h at 7 kPa vacuum pressure before and after freeze-drying. Drying operation times were ranked from the shortest to the longest as follows: freeze -mid -infrared drying, mid -infrared freezedrying, freeze pre- and vacuum post -drying, and vacuum pre- and freeze post -drying and conventional lyophilization. The aim of this study was to investigate the effects of different storage conditions, namely refrigeration (5 degrees C in a refrigerator) and room temperature (23 degrees C on a shelf in a dark place) on the moisture content, water activity, firmness, rehydration ratio, polyphenol- and flavonoid content, as well as antioxidant capacity of dried blueberries. The dried and vacuum -packaged blueberries stored in the refrigerator and at room temperature can be characterized by the stability of their physical and chemical properties throughout the storage period. It was found that a traditional freeze-drying (FD), freeze-drying and vacuum -drying combination of 4 h at 60 degrees C (FDVD4h60 degrees C) together with vacuum packaging at ambient temperature, is sufficient to ensure a shelf -stable whole blueberry product.