Chemically Modified Starch Films with Menthol or Sulfobetaine as Antimicrobial Agents for Active Packaging Applications

This study aims to develop a modified starch with menthol (M) or sulfobetaine (S) using 1,6-hexamethyl diisocyanate (HMDI) as a linker to create biodegradable antibacterial materials for active packaging applications. The modification of potato starch is performed in a two-step reaction. First, the starch modifiers are synthesized through an equimolar reaction between HMDI and menthol or the sulfobetaine precursor. Next, the synthesized HMDI derivative is dissolved in a bio-based solvent (methyl-THF) with starch and K2CO3 (1:1 weight ratio) to chemically modify the starch. The chemical and thermal properties of the modified starch are analyzed. Starch films containing 25 wt.% glycerol and low amounts (0.5, 1, and 3% wt.) of M- or S-modified starch were successfully produced by extrusion. Although most film properties remain similar to the control, adding 3% of S-modified starch resulted in a 149% increase in Elastic Modulus and a 29% decrease in water vapor permeability. Additionally, just 0.5 wt.% of either M- or S-modified starch effectively inhibits S. aureus growth, indicating its potential as a bioactive compound for active packaging.