Standardisation of natural dye powders via spray drying: initial physicochemical characterisation

Liquid natural dyes exhibit some drawbacks in terms of storage, distribution, dosage control, and quality consistency. This study aimed to evaluate the initial standardisation of natural dye powders from the bark of Tingi (Ceriops tagal), wood of Tegeran (Cudrania javanensis), and leaves of Indigofera (Indigofera tinctoria) through a spray drying process with the addition of 15% (w/w) maltodextrin as a physical matrix. The resulting powders were characterised in terms of yield, colour strength (UV-vis spectroscopy), molecular composition (FTIR spectroscopy), solid-state structure (XRD), moisture content, water activity, particle size distribution, and morphology (SEM). The study achieved a yield of 72.33-85.67%, with the highest yield obtained by Tingi. The UV-vis comparison of fresh extract and reconstituted powder indicated that despite the intensity changes and peak shifts experienced by some samples, the main absorption characteristics after spray drying were still observable. The FTIR spectrum showed the existence of main functional groups related to the dye components and maltodextrin, while the XRD patterns showed dominant amorphous or semi-amorphous characteristics. These findings indicate the possibility of a physical association between the pigment and the maltodextrin matrix, albeit not used as definitive evidence of hydrogen bond formation. The moisture contents were in the range of 9.87-11.27%, with water activity of 0.60-0.64, demonstrating the initial moisture-related risks. The PSD and SEM analyses implied the differences in the size characteristics and particle morphology among the dyes. Overall, this study provides initial information regarding the physicochemical characteristics of maltodextrin-aided spray-dried powder. Further evaluation of storage stability and dyeing performance is necessary.