The effect of cooking method upon the titratable acidity of a popular vegetarian dish--scope for reducing its erosive potential?

The purpose of this in vitro study was to determine the effect of cooking method on the erosive potential of ratatouille. Two cooking methods, stewing and oven roasting, were applied to standardised ingredients taken from the same fruits and vegetables. The resultant dishes were liquidised and diluted with 100 mls of distilled water. Five 25 ml samples of each group were titrated to pH 7.0 against 0.1 Molar Sodium Hydroxide. In order to ascertain the relative contribution of each ingredient each was singly prepared and cooked by stewing or oven roasting following the same quantities and dilutions as for the dish as a whole. 25 ml samples of these were titrated to pH 7.0 against 0.1 Molar Sodium Hydroxide. For ratatouille as a dish significantly (P < 0.0001) more alkali had to be added to the oven roast group (Mean = 8.60 mls, S.D. = 0.31) than to the stewed group (Mean = 3.92 mls, S.D. = 0.50) in order to bring about neutrality. Oven roasting of ingredients significantly (P < 0.001) lowered the initial pH with the exceptions of tomatoes and red peppers. Stewing reduced the volume of alkali required to neutralise aubergine (P < 0.001), green peppers (P < 0.001) and courgettes (P < 0.05). Significantly (P < 0.001) more alkali however was required to neutralise stewed red pepper. It was concluded that the method of cooking identical ingredients affects the erosive potential of ratatouille. Although oven roasting results in a higher erosive potential of ratatouille compared to stewing the method of cooking, at an individual ingredient level, does not have a universal effect upon erosive potential as determined by titratable acidity. This should be borne in mind when advising patients.