Preparation and characterization of ginger starch based edible films incorporated with coconut shell liquid smoke by ultrasound treatment

In this study, the properties of ultrasound treated ginger starch nano-emulsion films incorporated with coconut shell liquid smoke (CSLS) were investigated. Inhibitory effects of films were determined against Escherichia coli O157:H7 on ground beef at 4 °C for 12 days. Oxidative stability and sensory properties of ground beef were also tested during storage. The film forming solutions containing CSLS exhibited small particle sizes ranging from 218.43 nm to 242.40 nm and film formulation had quite stable surface charge (-18,30 and -17,90 mV). Ultrasound treatment significantly affected the physical, mechanical, barrier, microstructural, and antibacterial properties of films, due to changing particle properties of films. Microstructure of films became more homogeneous after ultrasound treatment and caused to lower water vapor permeability (WVP). The WVP for the ginger starch film was 1,54±0,10 g.mm/m2h.kPa, which decreased significantly with the impregnation of CSLS. The WVP values of ginger starch-CSLS films gradually decreased with the increase of CSLS content (p <0.05). The incorporation of CSLS did not significantly change the absorbance band positions and structure of the films. This finding supported the improved water vapor barrier properties of ginger starch films. The addition of liquid smoke affected optical properties of films depending on the concentration. Analyzing color parameters, the incorporation of liquid smoke into films caused a decrease in L* and an increase in both a* and b*. Opacity increased when CSLS was incorporated into film formulation, and this effect was observed at all CSLS concentrations evaluated (p <0.05). Mechanical testing results showed that the addition of CSLS improved the mechanical properties of the films, since both tensile strength (TS) and elongation at break (EAB) significantly increased compared to control film (p<0.05). The results indicated that strong interactions between CSLS and films increased the thermostability of starch films and an increased amount of thermal energy is needed to dissociate interactions among components in composite films compared to starch films without CSLS. The antibacterial effect against test bacteria was enhanced significantly with US treatment (p<0.05). The antimicrobial activity of ginger starch films containing CSLS against E. coli O157:H7 on ground beef samples was concentration dependent and concentration was a significant factor in inhibiting E. coli O157:H7. CSLS inhibited effectively lipid oxidation for all treated ground beef samples throughout the storage period. The ginger starch film containing CSLS showed antibacterial activity against E. coli O157:H7, without the impact on the sensory properties of ground beef. These results indicate that CSLS have the potential as antimicrobial agents in ginger starch films for use as active packaging materials in the food application.