FucoPol and chitosan bilayer films for walnut kernels and oil preservation

Bilayer films composed of a bacterial exopolysaccharide (FucoPol) and chitosan were studied in terms of barrier material for walnuts (Juglans regia L.) preservation in opposition to a non-biodegradable commercial film used for that purpose (polyamide cast flexible-polyethylene - PA/PE 90). In experiments conducted under accelerated storage conditions (24 h of light, 33% RH, 38 °C for 14 days) using walnuts oil, the oxygen content in nitrogen flushed packages increased to 5-7% with both films. In addition, after one day, the oil stored in contact with 21% oxygen presented a peroxide value above the legal limit for olive oil in Portugal (15 meqO2 kg−1), while the oil stored with bilayer and commercial films only present values above that limit at the end of the experiment. The oil content in conjugated dienes and trienes over time was also quite similar for bilayer and commercial films. Furthermore, sensory analysis performed on walnut kernels, stored in the same conditions as the oil, revealed non-significant differences in rancidity. The results have shown that the preservation capacity of the biodegradable bilayer FucoPol/chitosan films was equivalent to that of the non-biodegradable commercial ones, which makes them a promising sustainable alternative as packaging materials for walnuts.