Yerba Mate and Water Kefir Grain Films for Food Preservation and Freshness Indicators

Abstract

Yerba mate infusion wastes (Ilex paraguariensis) were used to prepare an aqueous extract to develop active and intelligent films using water kefir grains as a polymeric matrix. The yerba mate extract (YM) demonstrated notable antioxidant activity attributed to its total phenolic content (245 ± 13 mg GAE/g) and exhibited colour variations at different pH values. The addition of 5% YM reinforced the matrix, increasing the mechanical strength (TS: 5.8 ± 0.7 to 7.4 ± 0.4 MPa) and increasing the initial degradation temperature (T0: 166 to 180 °C). The incorporation of 20% YM additionally produced a plasticising effect in the matrix that masked the reinforcement observed at low concentrations of YM. Films with YM had remarkable antioxidant activity, with a maximal radical scavenging activity (%RSA) of 98 ± 2 and 71 ± 2 measured by ABTS and DPPH assays, respectively. According to the migration test conducted in fatty food simulants, the quantity of migrated phenols depended on the original percentage of YM in the films. As a result of exposure to ammonia vapours, a pronounced colour change was observed on the films, indicating that the kefir films with YM could be used as a freshness indicator for food products.