EFFECTIVENESS OF CELLULOSE NANOCRYSTALS APPLICATION AS BIO-BASED OXYGEN BARRIER FOR SHELLED WALNUTS SHELF-LIFE EXTENSION

The shelf-life of shelled walnuts is strongly affected by the oxidation of polyunsaturated acids content. Therefore, it is hugely important to use high oxygen-barrier packaging materials in order to maintain as long as possible their quality. Cellulose Nanocrystals (CNCs) isolated from cotton linter offer a very low oxygen permeability, thus can assure a significant shelf life extension. To obtain a fact-based confirmation, a comparative 30 days Accelerated Shelf-Life Test (ASLT) was carried out, using CNCs coated and uncoated packs of shelled walnuts. CNCs were obtained through the oxidative hydrolysis of the cotton linters, then a 7% water dispersion (pH=8) of freeze-dried CNCs was coated onto PET/LDPE film obtaining a 700-nm thick layer. Standard (uncoated) and barrier (CNCs coated) pouches were fabricated, packed with 40 g of shelled walnuts under 100% [N.sub.2], and stored at 40[degrees]C and 30% RH. The ASLT was carried out by assessing the sensorial changes of the shelled walnuts, the Peroxide Value (PV), Dienes content, TBA test and CIELAB color. As a preliminary and supporting information, the walnuts oxygen consumption rates, at different oxygen partial pressures, in the 0-0.19 bar range and at 40[degrees]C, were assessed by gas chromatographic analysis (TCD) performed on experimental samples. The oxygen consumption rate resulted linearly related to oxygen concentration in the headspace, with a [R.sup.2] = 0.923. The shelf life of shelled walnuts was significantly extended in CNCs coated pouches, as the sensory analysis carried out showed a significant difference between the products.Keywords: accelerated shelf life test, bio-based oxygen barrier, cellulose nanocrystals, shelf life extension, shelled walnuts