EFFECT OF BREAK TEMPERATURE AND HOLDING TIME ON PECTIN AND PECTIC ENZYMES IN TOMATO PULP

SUMMARY –The effect of break temperature and holding time on chemical and physical properties of canned tomato pulp and on the activity of polygalacturonase (PG) and pectin esterase (PE) was investigated. Samples preheated above 200°F were slightly higher in pH value and lower in titratable acidity than those preheated at 160°F and 140°F. The gross viscosity and serum viscosity of the canned tomato pulp increased as break temperature increased. A slight increase in serum viscosity was also observed when holding time was lengthened. The effect of break temperature on serum viscosity was much greater than that of holding time. The total pectin content of the tomato pulp as well as that of the serum increased as the break temperature increased. The same observation holds true for the effect of holding time on the total pectin content of the tomato pulp and tomato serum. This was explained by the inactivation of pectic enzymes at higher break temperature and longer holding periods. The level of PE and PG activity in the frozen tomato pulp decreased as break temperature and holding time increased. No PE activity was detected in samples preheated at 180°F for 15 sec. Samples preheated at 220°F for 15 sec showed no PG activity, while those preheated at 200°F for 15–87 sec still show some PG activity with a retention of about 3.54–5.68%. PG in tomatoes may be inactivated by giving the macerated fruits a hot break temperature higher than 200°F. The critical conditions for inactivation of PE (180°F for 15 sec) and of PG (220°F for 15 sec) found in the course of this investigation are supported by the data obtained on pectin analysis and serum viscosity.