Anthocyanins in Sweet Potato Leaves-Varietal Screening, Growth Phase Studies and Stability in a Model System

Abstract

The sweet potato genotypes in the CTCRI germplasm collection were screened for anthocyanin content in the young top leaves and the values varied from 20-200 mg/100g fresh weight of the leaf samples, the highest being recorded for the genotype S-406. Total anthocyanin content (TAcy) showed significant difference among genotypes, growth phases, and growing seasons. The TAcy in the leaves reached a peak at 20 days after planting, declined after 35 days, returned to 20 day levels or higher by 50-65 days and remained stable or exhibited a slight decrease by 105 days after planting, for most of the genotypes selected for growth phase studies. Approximately 50-60 % decrease was observed in the TAcy of the frozen/thawed leaf samples. The stability of anthocyanin pigments in a model sugar-citrate solution at ambient (30 ± 2 °C) and refrigerated (8 ± 2 °C) conditions was studied. The solutions stored at low temperature and in dark showed higher retention of pigments. Compared to anthocyanins extracted from grape pomace, the sweet potato anthocyanins were more stable as indicated by the higher values of half-life and pigment retention. The anthocyanins were more stable at the pH range of 3.2-3.4 and the colour shifted from red to pale yellow at higher levels.