Preparation and evaluation of the characteristics of active electrospun nanofibers based on polycaprolactone containing cinnamon essential oil/β-cyclodextrin inclusion complex

Oxidation is one of the main factors affecting the shelf-life of food susceptible to lipid deterioration (Almasi et al., 2014). To reduce oxidation in sensitive food products, the direct addition of antioxidants to food formulation, dipping food in antioxidant solution and the design of a suitable vacuum or modified atmosphere packaging technology are the three most common alternatives. However, there are many foodstuffs that cannot be protected in these ways, as they are fresh or raw foodstuffs in which the addition of other substances is not permitted. One of the most promising systems to protect the foods against oxidation is to use an antioxidant active packaging. Active nanofibrous mats synthesized by electrospinning technique is a novel type of food active packaging materials. The electrospinning process is an electro-hydrodynamic phenomenon forming micro and nanoscale fibers by applying electrical force on a polymeric solution (Forghani et al., 2021). Poly(caprolactone) (PCL) is an aliphatic polyester film-forming candidate widely used in pharmaceutical and biomedical applications owing to its biodegradability, biocompatibility, and high mechanical properties, but recent studies have increasingly focused on the potential of PCL for electrospun nanofibers preparation with food packaging application purposes. Cinnamon has been widely used in the food industry. The dried inner bark of the tree and the milled bark are the commercial forms of cinnamon. Cinnamon essential oil (CEO) obtained from bark of the plant has been found to have an effective antimicrobial activity and listed as GRAS by the Food and Drug Administration (Zhang et al., 2017). Cinnamaldehyde, the major active component of CEO, has been shown to have broad-spectrum antimicrobial activity and a good antioxidant activity (Ojagh et al., 2010). In the development of an active packaging, it is a challenge to design of a controlled release system. Many approaches have been utilized for release controlling of active agents from packaging materials. Complexation with cyclodextrins (CDs) in aqueous solutions is an effective method for release controlling especially for herbal extracts and EOs. Amongst the CDs, Beta-cyclodextrin (βCD) is widely used for release controlling of bioactive compounds from active packaging (Sun et al., 2014). The aim of this work was to fabricate the antioxidant active nanofibers based on PCL containing CEO in the free form and βCD-complex form. The physical and morphological properties of nanofibers were investigated and also their antioxidant activity was studied.

The CEO was extracted by hydrodistillation method and the CEO-βCD inclusion complex was fabricated by ultrasonication method. The PCL in the concentration of 10% w/v was dissolved in ethanol/dichloromethane mixture solvent and after that, the free CEO and CEO-βCD inclusion complex were added in the concentrations of 0.5% and 1% w/w of PCL. The prepared solutions were loaded into a 5 mL plastic syringe equipped with a blunt-tipped 21-gauge stainless steel needle. Then, the electrospinning was carried out by applying a high voltage power of 15 kV and a flow rate of 1.0 mL/h at 25 ± 2 °C and 30 ± 1 % relative humidity. Nanofibers were collected on an aluminum foil collector with a horizontal distance of 10 cm from the needle tip (Amjadi et al., 2020). The structural parameters of films were analyzed by FT-IR, XRD and FE-SEM tests. Water contact angle and mechanical properties were also studied. Antioxidant activity of films was examined by DPPH scavenging method. The one-way ANOVA method by using SPSS software was used for statistical analysis of obtained data.

FT-IR analysis confirmed the formation of new hydrogen bonds between CEO and PCL in the free form and encapsulated in βCD. XRD test revealed that free CEO had no effect on semi-crystalline structure of PCL nanofibers. But the CEO- βCD inclusion complex caused to increase the intensity of peaks related to crystallinity of PCL increased. According to FE-SEM images, the free CEO addition disrupted the uniformity and ordered design of PCL nanofibers but the CEO-βCD inclusion complex addition produced uniform nanofibers without beads. The water contact angle and Young’s modulus of mats increased but strain to break decreased by addition of CEO-βCD inclusion complex. The nanofibers containing 1 % free CEO and CEO-βCD inclusion complex had the highest DPPH scavenging activity.

The results of this research demonstrated the successfulness of active PCL nanofibers preparation by electrospinning process. The CEO-βCD inclusion complex was incorporated into PCL nanofibers. The addition of CEO in the free form had adverse effect on the physical, thermal and structural properties of nanofibers. But when CEO-βCD inclusion complex was used, the improved properties of nanofibers were observed. The PCL active nanofibers had strong antioxidant potential and was proposed as potential antioxidant active packaging. This research approved the good antioxidant effect of CEO loaded PCL nanofibers. Therefore, it would be suitable for those foods such as edible oils, butter and other fatty foods, suffering from oxidative deterioration as their main problems. Further studies are required to investigate the effects of fabricated active nanofibrous mats on the shelf-life extension of real food systems.