36E-8 Antioxidant activity of asparagus juice affected by a partially heat inactivated pectolytic enzyme preparation

T. SUN¹, J. R. Powers¹, and J. Tang². (1) Dept. of Food Science & Human Nutrition, Washington State Univ., PO Box 646376, Pullman, WA 99164-6376, (2) Dept. of Biological Systems Engineering, Washington State Univ., 213 L.J. Smith Hall, PO Box 646120, Pullman, WA 99164-6120

We have found that a commercial pectolytic enzyme preparation from Aspergillus niger (pectinase AN) contained peroxidase activity that could be responsible for the total loss of rutin and antioxidant activity of asparagus juice.

Our objective was to investigate if heated pectinase AN with decreased peroxidase activity could affect rutin content and antioxidant activity of asparagus juice.

Pectinase AN was heated at 70 degree C for various times to inactivate the peroxidase activity, then pectinase AN with 50% remaining peroxidase activity was added to asparagus juice at the same dose as that for unheated pectinase AN and incubated at 37 degree C for 8 hours. Rutin content and the antioxidant activity of asparagus juice at different sampling times were determined by HPLC and 2,2'-diphenyl-l-picrylhydrazyl (DPPH) method, respectively.

Due to the decreased peroxidase activity, the loss rate of rutin in asparagus juice treated with heated pectinase AN was 9% of that treated with unheated enzyme. A new compound was formed in asparagus juice treated with enzyme, the concentration of which increased with time. The antioxidant activity of asparagus juice was significantly increased from 1.5 mmol Trolox equivalent/L juice at time 0 to 2.1 mmol Trolox equivalent/L juice after 8 hours possibly due to the newly formed compound, which may based on spectra be related to rutin and also an antioxidant.

These results suggest that pectinase AN with partially inactivated peroxidase activity caused less loss of rutin and may increase the antioxidant activity of asparagus juice.