Investigation of the characteristics of polycaprolactone-TiO2 nanofibers as nano- oxygen scavenger in the food active packaging exposed to UV-C radiation

It seems that by 2050 the world's population will increase up to 50%. Hence, human beings are looking for ways to increase productivity, reduce food waste and reduce energy consumption in order to cope with the sudden increase in population and the supply of foods. According to the FAO report, about one-third of annual agricultural production will be lost during production process to consumption. In this regard, oxygen is considered as one of the most important causes of food and agriculture spoilages. Oxygen by oxidation of oxygen-sensitive food can be directly (i.e. corrosion in metals, oxidation of fatty acids, formation of red color in meat and oxidation to metmyoglobin, oxidation of ascorbic acid, natural pigments and aromatic substances) and indirectly (with the growth of aerobic microorganisms) lead to food spoilage. In this way, the aroma, taste, color and nutritional properties of the food will change. Therefore, in order to remove oxygen and increase the shelf life of food in packaging, e.g. vacuum filling, hot filling, neutral gas injection and modified atmosphere packaging are used. Increasing production costs and reducing the nutritional value of these products, has been increased the attention of researchers to alternative methods. One of the best alternative methods to reduce the side effects of oxygen is the development of oxygen scavengers in food packaging. The general principles of the oxygen scavenger are based on one or more principles e.g. oxidation of antioxidant compounds, iron oxidation, oxidation of acid ascorbic, oxidation by glucose oxidase and alcohol oxidase, oxidation of unsaturated fatty acids, stabilized yeasts on the substrate, photosynthesis, ascorbate salt / metals, metal catalysts. The effectiveness of some of these adsorbents is affected by some reasons i.e. lack of iron-based adsorbents activity of at the absence of moisture, limited oxygen absorption capacity, low absorption rates, especially at low temperatures, color change in packaging and the possibility of food contamination. In this research, we were going to develop a nano-oxygen scavenger based on the photocatalytic activity of nano-TiO2 on the electrospun poly-caprolactone (PCL) as an oxygen scavenger in food packaging. The photo oxygen scavenger (e.g. electrospun poly-caprolactone-TiO2) can be used to reduce the photo-oxidation of foods by reducing the available oxygen and block the UV as initiator, simultaneously. In this study, a 15% solution of PCL and different TiO2 content (1%, 3% and 5%) were prepared in a chloroform:methanol (4:1) solvent. The solution were loaded in a plastic syringe and the syringe was placed on a syringe pump. The electric potential was applied to the metallic needle (23 gauge) by the high voltage power supply. The fibers were collected on an aluminium foil. The applied voltage was 22 kV, the solution flow rate was 0.6 ml/h, and the tip of the needle to collector distance was 15 cm. The microstructure of nano fibers was investigated by SEM microscopy. The volatile compound content (i.e. residual chloroform:methanol) of the nano fiber was measured by weight differences at 50 °C. The porosity of the electrospun nano fiber was measure by 50% ethanol solution using with pycnometer. The nanofibres were exposed to UV-C ray in an air tight chamber. Changes in oxygen content were measured for 72 hours. Oxygen absorption, porosity and mean diameter of nanofiber were increased with increasing TiO2 content of the nanofibers. On the other hand, the volatile compounds of the nanofibers was decreased, simultaneously. Regard to the result of current study the maximum oxygen absorption was achieved after 24 hours by PCL- TiO2 (5%). After that the oxygen content remained constant up to 72 hours. The visual properties of the electrospun nano fiber contain TiO2 showed the increasing of darkness of the specimens after the UV-C irradiation. Whereas, the irradiated PCL nano fiber by UV-C ray was white. It seems, it was due to the acceleration of photo-degradation of nano fibers under UV-C by TiO2. The color of aluminum was appeared in the background of the nano fibers, consequently. The electrospun PCL nanofibres contain nano-TiO2 where exposed to UV-C ray can be used as an oxygen scavenger in the oxygen-sensitive food packaging. However, the oxygen scavenging capacity of the nanofibers is not high. Furthermore, the nano oxygen scavenger is photoactive. So, it is not appropriate oxygen scavenger at no light condition. In the future study, development of photoactive oxygen scavengers under long wavelength (i.e. UV-A and visible) should be considered.