Organocatalytically salicylated starch-based food packaging obtained via reactive extrusion/thermo-molding

The goal of this research work was to explore the effect of the organocatalytic esterification of the salicylyl group on hermoplastic corn (Zea mays) starch by using salicylic acid (SalAc) as active substance to be esterified, and tartaric acid (TAc) as a food-grade green organocatalyst. TAc was used to facilitate said reaction during the one-step processing (mechanochemistry) of salicylated starch-based food packaging materials obtained via reactive extrusion (REx)/thermo-molding. These efforts aimed to improve the overall performance of thermoplastic starch (TPS)-based films. To this end, four corn starch-based film systems plasticized with glycerol and containing either SalAc and TAc, individually or mixed, were processed under REx conditions. To evaluate the effect of the organocatalytic reaction on starch and its potential impact on the development of active and sustainable food packaging materials, these materials were analyzed in structural, thermal, physicochemical, surface, mechanical, and functional terms. The results obtained here demonstrated that SalAc can be esterified (grafted) onto the starch structure. However, the product of this reaction (organocatalytically salicylated starch) was not decisive in the overall physicochemical and mechanical performance of the developed materials. Instead, this study revealed that low water contents, intrinsically related to the feedstocks (starch and glycerol), determined the starch hydrolysis in the presence of SalAc or TAc. In particular, TAc showed a superior starch hydrolyzing effect than SalAc. Apart from this, protruding antimicrobial properties against Listeria innocua (Gram-positive) and Pseudomonas aeruginosa (Gram-negative) were demonstrated. Finally, films containing SalAc and TAc, at the concentrations tested, negatively affected the growth of lettuce (Lactuca sativa) seedlings (ecotoxic effect).