Effect of Elevated Storage Temperatures on the Physicochemical and Sensory Properties of Apple Puree

Food products change their quality during storage not only under the external impact, but also because they are complex in composition. As a result, food scientists look for new methods to control these internal changes. The research objective was to describe the changes in the physicochemical properties of apple puree during storage at elevated temperatures (40–60°C) and link them with the changes in the sensory profile. The study featured homogenized apple puree packaged in composite material and heated up to 40, 50, and 60°C. The colorimetric studies were conducted at 45°/0°, light source D65. The proton relaxation time and the water diffusion coefficient (impulse gradient method) were studied at a frequency of 20 MHz. The analysis of molecular dynamics involved the method of electron paramagnetic resonance of spin probes. The samples were cooled down to –70°C to measure the content of non-crystallizing water by the method of differential scanning calorimetry. The color change rate was constant and followed the zero-order kinetic reaction equation with an activation energy of 92 kJ/mol. The changes in color, proton relaxation, and sensory properties correlated when the samples were stored at 50 and 60°C. The analysis of the magnetic relaxation time, the diffusion coefficient of water, and the content of non-crystallizing water indicated that the main changes in the physical structure of the puree during heat treatment occurred as a result of the aggregation of apple cell fragments. These findings were confirmed by the optical microscopy. A prolonged exposure to 40–60°C affected the color, the relaxation of water protons, and the size of aggregates of apple cell fragments. It also affected the amount of water that did not crystallize at –70°C. The correspondence between the values of the activation energies was determined by the methods of colorimetry and proton relaxation. Therefore, the coloration and the water changes depended on the same processes. These physical and chemical properties can be used for quantitative assessment of apple puree under thermal treatment.