Sustained release of an essential oil by a hybrid cellulose nanofiber foam system

Abstract

As natural antimicrobials, essential oils (EOs) are used for food preservation because they are both antibacterial and antioxidant. However, the preservative effect can be lost and the food destroyed before the expected date if the EOs release too quickly, resulting in excessive concentration of EOs in the package, followed by exhaustion in a short time span. Here, using cellulose nanofibers (CNFs) and thyme essential oil (EO), we demonstrate a simple and environmentally-friendly approach to fabricate a foam hybrid system (CNF-EO) for sustained release of EO. CNFs can be prepared by enzymatic hydrolysis pre-treatment and TEMPO (2, 2, 6, 6-tetramethylpiperidine-1-oxide)-mediated oxidation pre-treatment. Enzymatically hydrolyzed cellulose nanofibers (EHCN) and TEMPO-oxidized cellulose nanofibers (TOCN) are immersed in EO nanoemulsion before the freeze-drying process, which forms CNF-EO foam hybrid systems, enzymatically hydrolyzed cellulose nanofibers-EO foam (EHCN-EO) and TEMPO-oxidized cellulose nanofibers-EO foam (TOCN-EO), with porous structure and sustained EO release property. The morphology and structure of the CNF-EO foam hybrid systems were measured by scanning electron microscopy, Brunaner–Emmett–Teller and Fourier transform infrared spectrophotometer (FTIR), and the sustained-release property was measured by gas chromatography-mass spectrometer (GC–MS). Meanwhile, the antibacterial property of EHCN-EO and TOCN-EO was investigated through fresh beef antibacterial experiment. EHCN-EO displays larger pore size and smaller specific surface area than that of TOCN-EO. According to the FTIR signal, EO has been successfully incorporated into cellulose nanofiber (CNF) foams. The results of GC–MS illustrate that EHCN-EO and TOCN-EO exhibit good absorption capacity and sustained release property, of which TOCN-EO illustrates superior performance. The beef in the CNF-EO foam groups shows higher acceptability in the senses such as flavor and color at the same time, compared with the Control without essential oil at the same time and TOCN-EO is shown to be able to prolong the shelf life of fresh beef by 5 days. This CNF-EO foam hybrid system fabrication strategy would be of great importance for the preservation of fresh food.