Ornamental crop as a source of food and fabric colourant

Abstract

The experiment was conducted in the Laboratory, Department of Horticulture during 2020-2022, Assam Agricultural University, Jorhat to harness the dyeing properties of four locally available flower crop sources viz., Melastoma malabathricum and Gomphrena globosa for food colouring and, Calendula officinalis and Hibiscus rosa-sinensis for fabric dyeing, using their semi-dried petals. The extraction condition for melastoma pigment had been standardized at 510 nm in 25:75 (v/v) ethanol: water solvent concentration with a solvent-to-solid ratio of 15:1 (ml/g) at 80°C for 75 minutes and that of gomphrena pigment at 533 nm in 0:100 (v/v) ethanol: water solvent concentration with solvent-to-solid ratio of 5:1 (ml/g) at 40°C for 105 minutes. The total anthocyanin content of melastoma pigment was found to be fairly high, about 313.88 mg/L with a reasonably low degradation index of 1.20 and tinctorial strength of 4.05. The betacyanin content of gomphrena pigment recorded 270.23mg/L with a tinctorial strength of 6.71. The degradation for both the pigments followed first order reaction kinetics and the extracted melastoma pigment recorded a rate constant of 0.001857 min-1 with half-life of 396.67 min while, the gomphrena pigment recorded a rate constant of 0.003133 min-1 with a half-life of 223.34 min, which is notably good for a natural colourant. The ten week storage study of both melastoma and gomphrena pigments was best recorded at 4°C in dark (or refrigerated condition) to obtain a half-life of 384.97 days and 92.41 days, respectively meaning greater pigment stability and longer shelf-life as compared to their storage at room temperature (30±2and#730;C) in dark conditions followed by light, which accelerated the pigment degradation rates and drastically reduced their half-lives. newlineFor fabric colourant both Calendula officinalis and Hibiscus rosa-sinensis pigments were standardized for extraction at 430 nm in alkaline medium (1% Na2CO3 solution) at 90 and 45 minutes, respectively. ...