Nanoencapsulation of thyme essential oil in chitosan-gelatin nanofibers by nozzle-less electrospinning and their application to reduce nitrite in sausages

Application of natural preservatives, such as essential oils, has attracted increasing attentions. Shirazi thyme essence with different phenolic compounds has antimicrobial and antioxidant properties. While it is sensitive to light, oxygen, humidity and high temperature. In this study, nanofibers were prepared by gelatin/chitosan in ratios of 1:6, 1:8 and 1:10 and thyme concentrations of 20 and 40% using nozzle-less electrospinning. Solution properties (i.e. viscosity and electrical conductivity) were measured. Results showed that encapsulation efficiency values were higher than 92% and loading capacity enhanced with increasing essence concentration. Diameter and morphology of fibers were analyzed by scanning electron microscopy (SEM). The nanofibers fabricated by gelatin/chitosan ratio of 1:6 containing 40% essences were the best samples with diameters in the range of 97–343 nm. Fourier transform infrared (FT-IR) indicated that not any chemical interaction was occurred between ingredients during electrospinning and differential scanning calorimetry (DSC) data demonstrated that thermal stability of the essential oil enhanced by encapsulation. Antioxidant activity and antimicrobial property of pure and encapsulated essential oils against Clostridium perfringens were examined and approved the efficiency of encapsulation for protection of antioxidant activity. The nanofibers containing thyme essential oil were then used for reducing nitrite in sausages and their microbial properties, moisture content, pH, color and sensory features were evaluated. The results indicated that the encapsulated thyme essence had bactericidal effect against C. perfringens, did not have significant adverse impact on color and sensory properties of sausages in comparison to sample containing 120 ppm nitrite. The data showed that nanofiber containing thyme essential oil could be a suitable nitrite substitute for meat products.