Antioxidant activity of enzymatically modified soybean protein film with two different forms of added lignin (alkali lignin and lignosulfonate) was investigated using two stimulated food systems involving direct and indirect contact with soybean oil and fish fatty acid ethyl ester (FAEE). For the direct system, control and lignin-doped films were added to oil vials which were stored at dark under 40 °C whereas for indirect, films were used to cover oil-containing glass vials stored under standard commercial lighting conditions. Autoxidation of oil samples in the direct contact system was determined by peroxide value (PV), color, headspace oxygen, and volatile compounds, while for the indirect contact system photoxidation was determined by using PV and color. For the direct contact system with soybean oil, the PV was significantly lower during storage for both lignins used compared to the control (packaging system without lignin film). There was not a significant effect of lignin on the color of the oils (P > 0.05). Modified films tested in this study did not have a significant effect on headspace oxygen contents of oil samples; however, it resulted in reduced volatile compounds for both soybean oil and fish oil samples. Based on our observation, soybean protein films with lignin showed a greater impact on soybean oil than fish oil, possibly because of high initial oxidation levels in the fish oil. Enzymatic modified soy protein films with lignin are alternative active packaging materials for highly sensitive to oxidation by radical and UV light. PRACTICAL APPLICATION: Plastic packaging materials require the use of petroleum oil and are not biodegradable. Packaging materials made from renewable, biodegradable biopolymers are of great interest but often suffer from performance problems, such as weak mechanical properties compared to petroleum-based plastics. Applying modified biopolymeric film with lignin in the inner layer of food packaging system improved some aspects of their performance during storage, not only by preventing the migration of chemical compounds from the package to the food but also by radical scavenging activity and UV-blocking ability of the packaging system.
Keywords: fish oil; lignin; oxidation; soybean oil; soybean protein film.
© 2019 Institute of Food Technologists®.