Production of edible film based on chitosan - gelatin, containing Ferulago angulate essential oil and evaluation of optical, sensory features and shelf life of packaged Turkey meat in it

From the mid-twentieth century, petroleum-based polymers including polyethylene and polypropylene have very good stretching properties, high strength, and low weight and plasticity and are widely used in the food packaging. The non-polar and hydrophobic nature of carbon compounds and low surface of these polymers, compared with their high molecular weight, reduce the activity of degrading enzymes and the resistance of synthetic polymers to microorganism attack. As a result, these polymers are not degradable and their aggregation is destructive of the ecosystem of the earth, causing serious environmental problems, which are referred to as white contamination. The use of essential oils (EO) directly in food can cause poisoning, severe aroma, flavor changes, and a change in the appearance of food, while the use of EO in combination with edible films (active packaging), in addition to eliminating that deficiencies, reduce dosage of EO is consumed. Seven species of Ferulago are grown in Iran. Ferulago angulate species has been grown in Kermanshah province and the natural source of mono-terpenes and sis coi-terpenes that have antimicrobial features. Several studies have confirmed the antioxidant and antibacterial effects of Ferulago angulate essential oil (FAEO). However, no valid studies have yet been made about the effects of FAEO in combination with edible films on the physicochemical and thermal properties of the combined gelatin-chitosan film. On the other hand, due to changes in lifestyle, decreased mobility and its problems, including cardiovascular disease, the consumption of white meat, like turkey meat instead of red meat, increased. Turkey meat has been understood and marketed as a healthy substitute to red meat due to its leanness, low cholesterol and desirable fatty acid profile. Turkey breast meat (filet) is believed by consumers worldwide, but is ready to rapid spoilage. Therefore, food industries are seeking technologies to increase its stability. Novel packaging (e.g. active) and processing technologies, in some cases, compounded with “natural” antimicrobials such as EO, have been suggested. So, the combined gelatin-chitosan films contain FAEO produced and its effect on the quality of turkey meat were studied to appointment the suitability of the gelatin-chitosan edible film containing FAEO for keeping and increasing turkey meat shelf life.

The gelatin–chitosan blend edible films were provided according to the casting technique. For interactions of polysaccharides and gelatin, a ratio of 40 to 60 has been reported by the previous works as the optimal ratio for interactions of polysaccharides and gelatin. Therefore, a solution containing 60% gelatin and 40% chitosan (v/v) was prepared to obtain a solution with film forming ability. FAEO was mixed with Tween-80 at 25% (w/w) was added into film forming solution at a concentration of 0, 0.25 and 0.50 % (v/v). The sensory evaluation of the 9-point Hedonic technique was performed (1 was very bad, 9 very good) and 10 panelists were done. The panels were asked to compare the film samples with the control sample in terms of odor, color, and acceptance or overall acceptance. The image processing method was used to examine the color of the films. L*, a* and b* parameters were measured with hunter lab colorimeter and microbial properties assessed as well.

The chitosan-gelatin films were affected by the addition of essential oil in all three parameters, L*, a* and b*. By adding the essential oil, the b * index and opacity increased significantly but the L * index decreased and reduced the transparency of the film. This phenomenon can be attributed to phenolic compounds in the essential oils, which can absorb light at low wavelengths. The control sample-free coatings due to lipid oxidation and microbial growth have shown signs of corruption as inappropriate for smelling and causing stubbornness. Therefore, they were considered as weak samples and eliminated. For samples that were packaged in the film, they had different sensory scores according to the percentage of EO. Therefore, it can be concluded that using chitosan-gelatin containing FAEO significantly increased the sensory properties of turkey meat (P <0.05). The results of the study indicate that FAEO, improves the sensory properties of turkey meat during the storage period. The initial TVC (log10 CFU/ g) in the control turkey fillet was 3.784 log10 CFU/g, it was 1.897 and 0.401 log10 CFU/g for Staphylococcus aureus and Coliform count respectively. Turkey samples reached or exceeded the value of 7.0 log CFU/g for TVC, which was considered as the upper acceptability limit for poultry fresh meat. The TVC increased slowly during the storage with a long lag phase for packaged samples, while the increase was significantly quick for the control (p < 0.05). The counts of all assessed microbiological indicators were significantly affected (P ≤ 0.05) by the addition of antimicrobials and especially gelatin chitosan edible film containing 0.5 % FAEO. In this study, and of the treatments examined, a film containing 0.5% FAEO was the most effective in inhibiting the growth of TVC, Staphylococcus aureus and Coliform everywhere the storage period. It is well known that, the antimicrobial activity of EO is related to mostly the phenolic ingredients. This result could be attributed to the inhibitory effect of the combined antimicrobials non-polar components such as phenolic di-terpenes (e.g. α-Pinene) are responsible for the antimicrobial properties of FAEO.

The use of edible film containing EO is a suitable way to respond to the needs and demands of today's societies to achieve minimal processed foods without using preservatives or chemical additives. In this study, the addition of FAEO to gelatin-chitosan film, in addition to inhibiting the growth and replication of bacteria and increasing the shelf-life of turkey meat in the refrigerator, caused and improved the sensory properties of the samples. In summary, based on the results of this study and according to the previous study, the addition of FAEO oil at a concentration of 0.5%, significantly altered the color and transparency of the films.