The role of some antioxidants in the HPMC film properties and lipid protection in coated toasted almonds

Hydroxypropylmethylcellulose based edible films with and without antioxidant additives were characterised as to their microstructure, water vapour and oxygen permeability, mechanical behaviour, optical properties and protective ability against lipid oxidation. The corresponding film-forming dispersions were also used to coat toasted almonds in order to test their effectiveness at protecting against rancidity development. The efficiency of three additives (ascorbic acid, citric acid or ginger essential oil) was tested and compared with antioxidant-free coatings. A cross-linking effect in the film matrices containing ascorbic or citric acid was detected through the analysis of the film microstructure, mechanical behaviour and barrier properties to oxygen and water vapour. These films were the most effective protectors against oxidation of almonds, due to both their antioxidant effect and the tighter structure which leads to lower oxygen permeability. In films with ginger oil, the hydrophobic effect markedly reduced water vapour permeability at low temperatures, but protection against lipid oxidation was less effective at long storage times.