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

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 a & ccedil;a & iacute; (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 tan delta (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 re-sults of the complete rheological assessment of starch/gelatin-based solutions containing phenolics from acerola fruit and acai 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.