Enzyme activity and firmness in tomatoes

The effect of storage at 3 ‘safe’ temperatures and one chilling temperature on the firmness, water loss and activity of selected enzyme systems (PG) of tomatoes (cv. Tradiro), harvested at two stages of maturity, was experimentally determined. Models built on assumed but plausible reaction mechanisms explain very well the behavior of these product properties as a function of storage temperature and duration simultaneously. Firmness was determined experimentally as the slope and as the compression distance in a flat plate compression test up to a maximum force of 3 N. By using the same fundamental model description both variables, describing tomato texture could be analysed in a combined analysis. It was found that firmness is built up from at least two different type of chemical structures, one decaying mainly at ‘chilling’ temperatures, while the second one decays both at ‘chilling’ and at ‘safe’ temperatures. The percentage variance accounted for was almost 90%. For the activity of polygalacturonase (PG) it was found, that a self initiated autocatalytic production exist. The effect of harvest maturity could be restricted to a different level of initially present activity. The percentage variance accounted for in the statistical analysis, based on the entire dataset simultaneously, was almost 89%.