Peroxidase and polyphenoloxidase activity in tomato in natura and tomato puree

Oxidative enzymes are responsible for changes in flavor, texture, color and also in some nutritive properties of several fruits and vegetables processed in industries. The present investigation aimed to study the activity of Peroxidase (E.C. 1.11.1.7) and Polyphenoloxidase (E.C. 1.10.3.1) in tomato fresh pulp in natura and in three different trademarks of tomato puree sold in supermarkets. Crude extracts of peroxidase (POD) and polyphenoloxidase (PPO) enzymes, from both fresh tomato pulp in natura and processed tomato puree, purchased in supermarkets, were prepared, by using sodium phosphate buffer at different pHs. The best pH values for extraction of peroxidase and polyphenoloxidase were 6.2 and 7.5, respectively. Protein precipitations were carried out using acetone at the ratio of 1: 2 enzymatic extract/acetone. The enzymatic extract from Santa Clara tomato cultivar was concentrated 10 times, before being applied to the chromatographic column packed with Sephacryl 100-HS. From the samples eluted, one isoenzyme was isolated (A(1)) and the molecular weight and isoelectric point (pI) was determined (MW 45 kDa and pI 4.5). The fraction with A(1) was stored at -18 degrees C, and later used for thermostability studies. A decrease in the enzymatic activity was observed at 85 and 90 degrees C, in the enzymatic extracts obtained from fresh tomato pulp; nevertheless, in the processed tomato purees the loss of activity was more significant.