Adequacy of the extract aliquot for determining the activity of polyphenoloxidase in sweet potato varieties

The object of this study was to adjust dosages for measuring polyphenoloxidase activity in sweet potato under refrigerated conditions. The following cultivars were utilized: ESAM 1; ESAM 2; ESAM 3; Mãe de Família; Paraná; and Sr. Antônio. Plants were harvested after 120 of growth. The tubercles were refrigerated for four days at 10 °C and then washed, cut, packed, and stored at 5 °C for 12 days. At initial time (day zero) of conservation, 1 g of tissue sample was macerated in a mortar, under ice bath, containing 6 ml of sodium phosphate buffer [0.2 M; pH 6.0]. The extract was then centrifuged at 7690 x g for 23 minutes at 4 °C. For the PPO activity essay, it was used a mixture of 2.385 μL of phosphate buffer (0.2 M), pH 6.0, and 500 μL of 0.2M catechol as substrate, which remained at 30 °C until temperature stabilization. To this mixture, it was added 10 μL, 15 μL, 20 μL, and 25 μL of the enzyme extract at 425 nm. This was done every 10 seconds in an interval of 2 minutes. It was observed that increasing the volume of extract, increased the activity of polyphenoloxidase independent of the cultivar evaluated. However, the cultivars ESAM 2, ESAM 3, Mãe de família, and Sr. Antônio seemed to slightly lost linearity above 10 μL. Thus, we conclude that the volume of 10 μL is the most appropriate for determining enzymatic activity for all cultivars