Analysis of Phenolic Compounds and Antioxidant Enzyme Activity during the Growth and Metabolism of Red Raspberry Leaves

In order to explore the changes in the content of phenolic compounds and the activity of antioxidant enzymes during the growth and metabolism of red raspberry leaves, the leaves of ‘Heritage’ and ‘Autumn Bliss’ red raspberry were analyzed and compared for the contents of total flavonoids and seven phenolic substances and the activities of three antioxidant enzymes. The results showed that from May to December, the content of ellagic acid and peroxidase (POD) activity in the upper, middle and lower leaves of the two varieties showed a double peak curve during the process of growth and metabolism, the content of salicylic acid showed a downward trend, the contents of ferulic acid, catechin, epicatechin, rutin and total flavones showed a single peak curve, the superoxide dismutase (SOD) activity remained at a high level, and the catalase (CAT) activity decreased, then increased and finally decreased again. The content of caffeic acid in the upper leaves of the two varieties showed a downward trend, while those in the middle and lower leaves showed a single peak curve. The highest contents of salicylic acid, ferulic acid, ellagic acid and epicatechin were determined in the upper leaves of ‘Autumn Bliss’ in May, upper leaves in June, middle leaves in July and upper leaves in July, which were 59.33 mg/100 g, 158.18 mg/100 g, 250.84 mg/g and 350.04 mg/100 g, respectively. The highest contents of rutin, caffeic acid, catechin and total flavonoids were determined in the lower leaves of ‘Heritage’ in June, middle leaves in July, middle leaves in July and upper leaves in July, which were 8.00 mg/100 g, 100.48 mg/100 g, 18.71 mg/g and 34.18 mg/g, respectively. The highest activities of POD, SOD and CAT were determined in the upper leaves of ‘Autumn Bliss’ in July, the lower leaves of ‘Heritage’ in July and the lower leaves of ‘Heritage’ in July, which were 13.05 U/(g·min), 37.00 U/g and 41.12 U/(g·min), respectively. In conclusion, the contents of phenolic substances and antioxidant enzyme activities in the leaves of ‘Heritage’ and ‘Autumn Bliss’ red raspberry are highest from May to July. This study provides an important theoretical basis for the timely harvest and better development and utilization of red raspberry leaves.