Abstract
Lignin is a byproduct of agricultural industries and only has limited applications. In this study, lignin was investigated for use in sustainable biopolymeric packaging film. Alkali lignin (AL) and lignosulfonate (LSS) were added to enzymatically modified soy protein isolate (SPI) biopolymeric film with different concentrations with the goal of improvement of film physical and functional properties. A radical scavenging activity test revealed that films containing LSS had values 28 and 6% higher than control and AL-based films, respectively; AL itself (not in films) had significantly higher radical scavenging activity than LSS. This indicates the activity of lignin is affected by interaction with SPI. The higher compatibility between LSS and enzymatically modified SPI resulted in a positive effect on surface smoothness, water absorption, and mechanical properties of LSS-based films. Films containing AL showed a high light absorption range in the UV region, and this UV-blocking ability increased with increasing level of lignin. Deconvoluted Fourier transform infrared spectra confirmed that the addition of lignin resulted in some changes in the secondary structure of the protein matrix, which were aligned with X-ray diffraction results. The addition of lignin improved tensile strength (TS) and thermal stability of films compared to the lignin-free control. This improvement in TS and thermal stability was probably a result of new intermolecular interactions between lignin and SPI. Water vapor permeability of the films containing lignin decreased to 50% of the control because lignin played a role as a filler in the matrix. On the basis of our observations, the incorporation of lignin into biopolymeric film is capable of providing additional benefits and solutions to various industries, such as food, packaging, agriculture, and pharmaceuticals.
Highlights
Active packaging is one of many types of smart packaging that offers extra functionality for food preservation other than providing an inert barrier.[1]
The ultimate objective of this study is to investigate the effect of the enzyme treatment on both physicochemical properties and cross-linking possibility of biopolymeric films fabricated with soy protein isolate (SPI) and lignin types and concentrations, as well as processing conditions
It was expected that the enzyme may catalyze cross-linking between soy protein isolate (SPI) and lignin due to many functional groups, such as abundant free amino groups, in both materials and it may bring in increased viscosity of the solution (Figure 1)
Summary
Active packaging is one of many types of smart packaging that offers extra functionality for food preservation other than providing an inert barrier.[1] Because of the customer demand and market trends, the area of active packaging is becoming increasingly important. Incorporating antioxidants to food packaging, especially for products sensitive to oxidation, is designed to provide additional safety and security by inhibiting the initiation or propagation of oxidizing chain reactions.[2] Lipid oxidation is associated with coronary heart disease, atherosclerosis, cancer, and the aging process.[3] Antioxidants prevent oxidation by three main mechanisms: UV-light blocking, radical scavenging, and chelation.[4−6] In general, there are two categories of antioxidants: natural and synthetic. Common synthetic antioxidants, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), have some restrictions in application to food products due to their carcinogenicity.[7]
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