Physicochemical and antimicrobial properties of gelatin-carboxymethylcellulose-based edible film containing (Foeniculum vulgare) extract

Introduction: The use of edible films is rapidly expanding due to growing concerns about non-biodegradable packaging. Gelatin is a natural protein obtained from the hydrolysis of collagen and is widely used in the food, pharmaceutical, and cosmetic industries. In recent years, gelatin has been recognized as an effective material in the production of edible films. Unique properties such as degradability, stretchability, and biocompatibility lead to the use of gelatin in food coating and increase their shelf life (Khan et al. 2022). Using gelatin-based edible films not only helps maintain the freshness and quality of food but can also have antimicrobial and antioxidant properties. These properties make gelatin a suitable choice for packaging and preserving food products, especially in the field of creating protective coatings on fruits and vegetables (Gonzalez et al. 2023). Carboxymethyl cellulose (CMC) is a cellulose derivative that has been widely used in various industries due to its unique properties such as water solubility, mechanical stability, and transparency. In the food industry, CMC is used as a base material for the production of edible films. These films can be used as protective coatings to maintain the freshness and shelf life of food products (Maknon et al. 2023). The combination of carboxymethyl cellulose and gelatin has received widespread attention for the manufacture of edible films due to the complementary properties of these two materials. Such special properties make these films very effective for packaging and preserving food products, especially fruits and materials sensitive to moisture and oxidation (Lee et al. 2024). Fennel (Foeniculum vulgare) extract is known to be a rich source of bioactive compounds, including flavonoids, phenols, and essential oils. These compounds have significant antioxidant and antimicrobial properties that can be used in the food industry, especially in the production of edible films (Mansouri et al. 2023). The combination of gelatin-carboxymethyl cellulose and (Foeniculum vulgare) extract in the preparation of edible films is considered a new solution in the food industry. Due to the unique properties of each of these materials, this combination can produce edible films with useful and functional features.
Fennel is traditionally used for medicinal and culinary purposes. The entire plant is valuable in the medicinal industry; its enlarged base is used as a vegetable; its leaves are used for culinary purposes and its seeds as a spice and for essential oil extraction. The flowers and leaves are also used to make yellow and brown dyes. Fennel pollen is the most potent form of fennel, but it is extremely expensive. In early Sanskrit writings, fennel was known as madhurika and its cultivation in India is thought to date back at least to 2000 BC. To the ancient Greeks, fennel represented success and was called ‘marathon’, after which the battle of Marathon (490 BC) was named when it was fought in a field of fennel. Fennel was also a symbol of success to the Romans and fennel leaves were used to crown victors in games. The English name fennel comes from Old English fennel, or finol, and fennel is one of the nine plants invoked in the pagan Anglo-Saxon Nine Herbs Charm recorded in a tenth-century manuscript. During the thirteenth century in England, fennel was considered a royal spice and was served to kings with fruit, bread, and dishes such as pickled fish seasoned with fennel seeds.
The chemical composition of fennel varies with morphotype, source, climate, and harvesting stage. Every 100 g edible portion of fennel seeds contains on average: 8.8 g water; 15.8 g protein; 14.9 g fat; 36.6 g carbohydrate; 15.7 g fi bre; and 8.2 g ash (containing 1.2 g Ca, 19 mg Fe, 1.7 g K, 385 mg Mg, 88 mg Na, 487 mg P and 28 mg Zn). Every 100 g contains: vitamin A (135 IU); niacin (6 mg); thiamine (0.41 mg); and ribofl avin (0.35 mg); with an energy value of about 1440 kJ. The seeds contain mucilage, sugars, starch, tannin, essential oil, and fixed oil (the main components of the fixed oil are petroselenic, oleic, linoleic, and palmitic acids. The variety and quantity of vitamins contained are variable: folates, 270 mg/ kg; vitamin B3, 6.4 mg/kg; vitamin C, 8.7–340 mg/kg. Fennel contains potassium (4.24–5.85 g/kg), the most abundant mineral by far, with low amounts of phosphorus (500 mg/kg), calcium (5.6–363 mg/kg), magnesium (8.2–389 mg/k) and sodium (7.7– 512 mg/kg). The principal constituents of the essential oil extracted are anethole (50–60 %) and fenchone (15–20 %). The essential oil extracted is mainly composed of (E)-anethole, (Z)-anethole, and α-thujonecompounds in fennel essential oil of which 18 constituted 96.04 % of the total essential oil, the major components being anethole (68 %), limonene (11 %), fenchone (3.7 %) and a few others. Approximately 45 constituents have been determined from fennel seed oil, the main constituents being trans-anethole (60–65 %, but up to 90 %), fenchone (2–20 %), estragole (methyl chavicol), limonene, camphene, α-pinene and other monoterpenes, ethyl alcohol and anisaldehyde. Small quantities of α-pinene, camphene, δ-α-phellandrene, dipentene, methyl chavicol, and ρ-hydroxy phenyl acetone are also present. The main components of the fixed oil are petroselenic, oleic, linoleic and palmitic acids. Dried fennel seeds contain 0.6–6 % volatile oil.

The bulb, foliage, and seeds of the fennel plant are potential sources of different nutrients and thus all are widely used both raw and cooked in side dishes, salads, pastas, vegetable preparations, sausages, etc. Raw fennel bulb contains carbohydrates, dietary fibre, protein, vitamin B complex, vitamin C, and minerals. The fennel plant is aromatic and used as a pot herb. It is popularly used as a spice and as a vegetable, having many applications for flavoring and culinary purposes. The whole seed, powder, and oil are used as adjuncts for flavouring foods, as antioxidants and as a preservative in confectioneries and beverages. Fennel seeds are largely used to give flavour to a number of foods such as soups, sauces, pickles, breads and cakes. In industry, fennel is used for flavouring and aromatizing, and as an organoleptic flavour corrector, in non-alcoholic beverages, baked goods, condiments, ice creams and liqueurs such as Anisette, and as a seasoning for prepared meats such as hot pepperoni and sweet Italian sausages.

The genus Foeniculum (fennel) belongs to the family Apiaceae and the order Apiales. Three main varieties have been described: F. vulgare Mill. var. piperitum (Ucria) Cout. (bitter fennel), F. vulgare Mill. var. dulce DC Batt. et Trab. (sweet fennel) and F. vulgare Mill. var. azoricum Thell. (Florence fennel, or finocchio) . Bitter fennel is grown for its fruits and essential oil, whilst Florence fennel is cultivated for its fruits, essential oil, leaves (used for culinary purposes) and enlarged leaf base (eaten as a vegetable). Sweet fennel is cultivated for its enlarged leaf base, for its fruits and for the essential oil taken from its fruits.

In this study, the properties of a biodegradable active film based on gelatin and carboxymethyl cellulose with different concentrations of fennel extract (Foeniculum vulgar) (%0, %2, %4, and %6) were investigated.
The purpose of this study is to produce suitable films for use in food packaging.
Material and Methods: The tests performed in this research were physicochemical tests, mechanical tests, and measurement of antioxidant properties and antimicrobial activity of edible films. All experiments were performed in three replicates (n=3) with completely random sampling. One-way analysis of variance (ANOVA) and the comparison of average data based on Duncan's multiple range test were performed using Minitab18 software at a confidence level of 5%.
Results and discussion: The lowest solubility and thickness were observed in the 6% and 4% treatments, respectively. The highest permeability and turbidity were observed in the film treatments containing 4% and 2% (Foeniculum vulgare) extract, respectively. The highest tensile strength, elongation at break and Young's modulus were in the 4% treatment. In all edible film treatments, antioxidant properties using DPPH radicals were significant (p<0.05). The lowest and highest antioxidant activity was related to the control and 6% treatments, with antioxidant activities of 5% and 17%, respectively. The results of the evaluation of the antimicrobial activity of the film using the diffusion disk method showed that the largest diameter of the inhibition zone at a concentration of 6% was reported for Pseudomonas aeruginosa with an average diameter of 24.5 mm, followed by Staphylococcus aureus, Escherichia coli with 13.83 mm and 12.33 mm, respectively.
Conclusion: The results showed that adding fennel extract at a concentration of 6% produced films that, in addition to inhibiting the growth and proliferation of bacteria, had desirable mechanical properties, improved the antioxidant properties of the composite film, and could also be used as a suitable coating for protecting food