Ornamental crop as a source of food and fabric colourant
Loading...
Date
2023
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
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±2˚C) in dark conditions followed by light, which accelerated the pigment degradation rates and drastically reduced their half-lives.
For 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. The dye absorption percentage was recorded highest for dye: material concentration of 3g/100ml in both the pigment classes. The carotenoid content in calendula pigment was estimated to 270.23 mg/L and the total anthocyanin content in hibiscus pigment resulted in 209.10 mg/L. The dyeing time for calendula pigment was standardized at 30 minutes for cotton fabric and in silk at 60 minutes while that for Hibiscus pigment it was standardized at 90 and 30 minutes for cotton and silk fabrics, respectively. With alum as mordant the standardized mordant concentration for both calendula and hibiscus pigment-dyed cotton and silk fabrics recorded optimum results at 2% while with fresh tea leaves the optimum concentration
was recorded at 1%. During standardization of mordanting time, both alum based calendula and hibiscus pigment-dyed cotton fabrics resulted best at 60 minutes and were further standardized for mordanting method i.e., pre-mordanting and simultaneous mordanting methods, respectively. Similarly, for their results upon silk fabric the optimum mordanting time was recorded at 45 minutes and, further standardized with simultaneous mordanting method in silk fabrics and pre-mordanting method in cotton. With fresh tea leaves as mordant, irrespective of the dye or fabric source used, the mordanting time was standardized at 15 minutes and the optimum mordanting method was evaluated as pre-mordanting method. Among the various treatment combinations calendula pigment-dyed and alum-mordanted silk fabrics resulted best for all the physical properties tested and fastness to washing, crocking and sunlight, followed by hibiscus pigment-dyed and fresh tea leaves-mordanted silk fabrics with excellent fabric thickness property and fastness to washing, pressing and perspiration.
Thus, all the four locally available ornamental crop sources viz., Melastoma malabathricum, Gomphrena globosa, Calendula officinalis and Hibiscus rosa-sinensis, studied in the present investigation could be put forward as potential natural colourant sources for food and fabric dyeing.