Thermal properties of fresh and dried cranberry (Vaccinium macrocarpon) fruits determined by differential scanning calorimetry and thermogravimetric analysis

Abstract

The aim of this study was to determine selected thermal properties of cranberries based on DSC and TGA curves, and to compare the properties of fresh cranberries, the dry matter of cranberries, cranberries processed by hot‐air convective drying (HACD) at 80°C, and cranberries processed by microwave‐vacuum drying (MWVD) at 150 W. Thermal analysis techniques can be used to determine the thermal stability of fruits and indicate the best temperature of processing, which can minimize the thermal‐oxidative damage, as well as extend the shelf life of fruits. Dry matter of cranberries was analyzed at −30°C to 500°C. The first endothermic peak was determined at −14.7°C, the last endothermic peak at 362.3°C. The area under the DSC curve was 874.8 J/g, and mass loss was 64.70%. The temperature of the first and last endothermic peak was determined at 4.8 and 84.6°C (fresh fruits), −10.6°C and 86.0°C (HACD), 2.0°C, and 84.5°C (MWVD), respectively. The area under the DSC curve was determined at 4970.0 J/g (fresh fruits), 525.1 J/g (HACD), and 518.5 J/g (MWVD), and mass loss reached 65.54% (fresh fruits), 1.84% (HACD), and 4.27% (MWVD). Practical applications The results of this study expand our knowledge about the thermal properties of the dry matter of cranberries, fresh cranberries, cranberries processed by hot‐air convective drying (HACD) at 80°C and by microwave‐vacuum drying (MWVD) at 150 W. Differential scanning calorimetry (DSC) proved to be a useful technique for determining the temperature of endothermic phase transition peaks and the area under the DSC curve of cranberries. Thermogravimetric analysis (TGA) supported the determination of mass loss during the measurements. Processing of food products, including drying can change their thermophysical and chemical properties. These changes can affect the thermal stability of dried products, which can be seen in the course of DSC and TGA curves. In this study, the temperature, at which the phase transitions of cranberries occur, was indicated. On this basis, the optimal processing temperature can be selected to preserve the berries content. The best temperature of fruit processing can minimize the thermal‐oxidative damage and extend shelf life of cranberries. Similar thermal stability of cranberries dried by hot‐air convection (HACD) at 80°C, and fruits dried by microwave‐vacuum (MWVD) at 150 W was found. The obtained findings can be further expanded by calculating the specific heat of cranberries.

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“…In addition, the DSC thermograms also showed temperature of endothermic phase transition for the NLC. The changes in physical, chemical, and biological properties due to the influence of temperature and moisture loss caused phase transition (Ropelewska, ). There was an onset of endothermic phase transition around 40 °C for all the samples during heating which was due to abrupt change of the heat transfer between the pan and DSC sensor (Brittain and Bruce, ).…”

“…However, the largest area under the DSC thermogram for S7 could suggest more intense phase transitions (Ropelewska, ). This is probably due to higher moisture content in S7 compared to F1 and F2 as well as the transfer of water from the liquid state to the gaseous state (Ropelewska, ). Whereas, the peak area for F1 is smaller than F2.…”