Influence of Storage Conditions on Physical Properties of Freeze-Dried Vegetable Snacks Packed in Pork Gelatin Films.

Abstract

The aim of this study was to investigate the changes in selected physical properties of freeze-dried vegetable snacks packed in edible films based on pork gelatin of different concentrations (8 and 12%), during storage at temperatures of 4 °C and 20 °C for periods of 3 and 6 months. The scope of this work includes the preparation of freeze-dried carrot snacks, obtaining edible films, packaging the snacks, and testing selected physical properties. The results show that storage time and temperature significantly affected the quality of the freeze-dried snacks. Water activity increased from an initial value of approximately 0.12 in the control samples to values ranging between 0.27 and 0.60 after storage, depending on gelatin concentration, temperature, and storage duration. The lowest water activity values (≈0.27-0.28) were observed for samples stored at 20 °C for 3 months, regardless of gelatin concentration, whereas storage for 6 months resulted in water activity values close to 0.5-0.6. Dry matter content decreased from about 97% in the control samples to values ranging from approximately 73.6% to 87.0% for samples coated with 8% gelatin and from 78.5% to 86.7% for samples coated with 12% gelatin, with greater reductions observed at longer storage times and lower storage temperature. Mechanical analysis indicated a strengthening of product structure after 3 months of storage, followed by a marked reduction in compression force-almost tenfold-after 6 months, indicating structural weakening. Color saturation (C) increased after 3 months of storage (values around 40-42), but significantly decreased after 6 months, reaching values as low as approximately 13-24, particularly at 20 °C. Porosity remained high throughout storage, generally in the range of 94-95%, although microscopic analysis revealed progressive pore collapse after 6 months of storage. Overall, a storage temperature of 20 °C and a storage time of 3 months were identified as