Changes in bioactive compounds, antioxidant and antimicrobial activities of raspberry (Rubus idaeus L.) pulp during different heating temperatures

In this study, effect of heating at different temperatures on bioactive compounds (total anthocyanins, total phenolics, L-ascorbic acid) and visual colour of raspberry pulp was studied. The change in antimicrobial and antioxidant activities were also evaluated over the temperature range 60?90°C during 7 hours. Total monomeric anthocyanins, total phenolics and L-ascorbic acid degraded with increasing heating temperature and time. First-order reaction models were determined for the degradation of total monomeric anthocyanins and L-ascorbic acid. Zero-order reaction model was determined for the degradation of total phenolics. The activation energies for the degradation of total monomeric anthocyanins, total phenolics and L-ascorbic acid were found as 49.3 kj mol-1, 32.2 kj mol-1 and 15.7 kj mol-1, respectively. The change in visual colour (+a, +b and chroma) of raspberry pulp was determined using Hunter colour parameters. The loss of colour parameters also followed first-order reaction kinetics. Activation energy for colour loss was found in the range of 49.0-75.5 kj mol-1.Antioxidant activities of heat treated raspberry pulp were determined as 13.8-15.9 µmoL TE g-1 at the beginning of heating in the temperature range 60-90°C. These values were found as 13.3-17.2 µmoL TE g-1 after 7 hours heating at the same temperature range. The antimicrobial activity of raspberry pulp extracts which posses against Staphylococcus aureus, Escherichia coli, Leuconostoc mesenteroides and Salmonella enteriditis tended to increase after heating.