Quantification of betacyanin content variation of amaranth varieties by an Android App, colorimeter, and infrared spectroscopy

Abstract

• The Color Grab Android App measured a * value was correlated to betacyanin content. • Leaf extract absorbance at 540 nm related to 15 color traits of intact leaves. • Infrared bands at 656 cm −1 , 665 cm −1 , 687 cm −1 , 689 cm −1 , 735 cm −1 , 737 cm −1 , 741 cm −1 related to betacyanin. Betacyanin of amaranth leaves serves as an important food colorant. The study involves three methods (spectrophotometer, Smartphone-based Color Grab App, and mid-Infrared Spectra) to measure foliar betacyanin content variation in leaves, leaf extracts of seven amaranth genotypes, betanin standards. Absorbance values of samples at 540 nm were measured using conventional spectrophotometry. It showed a significant linear regression with 15 leaf color attributes ( p = <0.001 with R 2 = 0.77). The color grab app showed linearity (0.94), sensitivity (4.76 μg μL −1 ), in betanin standards (0.025 to 7.5 μg μL −1 ). It also had a limit of detection (0.18 μg μL −1 ) and a limit of quantification (0.56 μg μL −1 ). Absorbance was measured at 270 nm and 475 nm to understand protein and betaxanthin contents, respectively. Fourier transformed infrared spectra (399–4000 cm −1 ) indicated correlation with betacyanin at 656 cm −1 , 665 cm −1 , 687 cm −1 , 689 cm −1 , 735 cm −1 , 737 cm −1 and 741 cm −1 wavenumbers. Android App-based non-invasive betacyanin estimation is significant to food processors, consumers, farmers, and a frugal science laboratory for educational & research institutions.