Acerola (Malpighia emarginata) and açaí (Euterpe oleracea) extracts as active compounds of starch/gelatin-based solutions: Rheological characterization

Abstract

This study aimed at an unprecedented rheological investigation of starch (S)/gelatin (G)-based solutions (SG) as possible candidates for food packaging films. Phenolic extracts from acerola (M. emarginata) fruit (AFE) and açaí (E.oleracea) seed flour (ASFE) were incorporated as active compounds in two different concentrations (2 and 4 mg extract g-1 solution). All the solutions were more elastic than viscous (G’ > G”) and the extracts incorporation decreased their elastic character, leading to higher tanδ (G”/G’) values (from 0.157 ± 0.006 in SG to 0.338 ± 0.036 in SASFE4G). The extracts improved the viscoelastic stability of the solutions, with critical strain values about 100% greater than SG. Moreover, G’ and G” moduli were more susceptible to cross (flow point) both as a function of frequency and temperature in the ASFE-containing solutions. The viscosity of the solutions was more influenced by the type of the extracts than by their concentration, ranging from 73.85 ± 9.22 Pa s (SASFE2G) to 116.50 ± 7.63 Pa s (SAFE4G). SASFE4G was the least sensitive solution to temperature changes, with the lowest activation energy (20.63 kJ mol-1). All the solutions presented non-thixotropic behavior, and the ASFE-containing solutions supported higher % of strain but recovered the least after deformation. Therefore, the results of the complete rheological assessment of starch/gelatin-based solutions containing phenolics from acerola fruit and açaí seed flour are a previous and unprecedent characterization of these materials and can be related to the application of the films formed by them in subsequent food packaging studies.