Starch isolation from turmeric dye extraction residue and its application in active film production

In this study, we have isolated starch from turmeric dye extraction residue by steeping in acid medium (AS), steeping in water (WS), or steeping in alkaline medium (KS) and assessed the filmogenic capacity of the resulting starches. We have also characterized the chemical composition, morphology, swelling power, solubility, crystallinity, and active properties of the AS, WS, and KS starches and investigated the mechanical, functional, antioxidant, and antimicrobial properties of the corresponding films. The AS and KS starches showed lower apparent amylose content and higher purity, relative crystallinity, swelling power, and solubility than the WS starch. All the starches retained phenolic compounds and curcuminoids; their phenolic and curcuminoid contents were higher than the contents in the residue, especially in the case of the AS starch, which yielded films with the best antioxidant and antimicrobial activities. The AS and KS starches yielded films that were more resistant at break, less soluble in water, and less hydrophilic than the film obtained from the WS starch. Thus, submitting turmeric dye extraction residue to AS in ascorbic acid yielded a starch that resulted in films with good mechanical properties and better antioxidant and antimicrobial properties, to ensure safe and prolonged food shelf life.