Food packaging is very important for food, which can protect food from physical, chemical and microbial hazards and extend the shelf life of packaged food during storage and sale [1]. With the improvement of living standards, consumers are increasingly concerned about the quality and safety of food, which makes the active packaging that can maintain the quality, freshness and safety of food become a research hotspot [2,3]. Konjac glucomannan (KGM) is a neutral non-ionic polysaccharide, which is extracted from the tuber of Amorophophallus Konjac and has a certain effect on diabetes, constipation, hypertension, obesity and colon cancer [4]. In addition, KGM is widely used in food packaging materials due to its excellent biocompatibility, biodegradability and film-forming properties [5]. However, it has some disadvantages, including poor antibacterial activity, poor barrier property, and poor mechanical property [6]. It has been demonstrated that the incorporation of essential oil extracted from plants is an effective way to improve the properties of KGM-based films [1].

Thyme essential oil (TEO) containing phenolic compounds (thymol and carvacrol), are widely used in food packaging due to its good antioxidant activity, broad spectrum antibacterial activity and barrier property [4]. However, the hydrophobic TEO is not able to be well dispersed in the hydrophilic polysaccharide film-forming matrix. Furthermore, the thymol in TEO is easy to volatile during the film preparation, thus greatly limiting its application [1]. It has been demonstrated that the loading approaches of TEO in the hydrophilic polysaccharide film-forming matrix could overcome the shortcomings of TEO in food packaging [4]. Especially, the loading of TEO via Pickering emulsions approach has strong evaporation resistance to volatile oil and has a sustained-release property due to the super stability property of Pickering emulsions stabilized by solid particles [7,8]. While a few of solid particles can be used as Pickering emulsion stabilizers in food science. In our previous work, we found that the synthesized bacterial cellulose nanofibers/Ag nanoparticles (BCNs/Ag nanoparticles) were able to stabilize Pickering emulsions [9]. Furthermore, it had been demonstrated that the greenly synthesized BCNs/Ag nanoparticles had no cytotoxicity [10]. In addition, BCNs/Ag nanoparticles used as Pickering emulsion stabilizers, not only have excellent antioxidant and antibacterial activities, but also have high mechanical properties due to their nano-scaled size [11]. Taken together, it would be an effective way to improve the properties of KGM-based films through the incorporation of TEO via BCNs/Ag nanoparticles stabilized Pickering emulsions. However, to our knowledge, there is little information about the properties of KGM-based films loaded with TEO via BCNs/Ag nanoparticles stabilized Pickering emulsions.

Since then, the aim of this study was to compare the properties of the KGM-based highly antibacterial active films loaded with BCNs/Ag nanoparticles and TEO through different loading approaches. The properties of the prepared KGM-based active films, including the microstructure, thermal stability, physical, mechanical, antioxidant, sustained-release and antibacterial properties were investigated in the present work. Finally, the film-forming solutions with best properties were used as coatings of tangerines to investigate their fresh-keeping effect. The parameters of the coated tangerines, including the total number of colonies, weight loss, skin hardness, total soluble solids (TSS) content and titratable acidity (TA), were determined in the present work.