Optimizing the Production of Siahmazgi Cheese Containing Different Concentrations of Echinophora platyloba Essential Oil in Both Free and Nanocapsuated Forms and its Effect on its Physicochemical, Microbial and Sensory Characteristics

Siahmezgi cheese is a type of sheep cheese that is prepared in the villages of Shaft city in Gilan province, specifically in Siahmezgi village. Siahmezgi cheese, which is made from goat or sheep milk, is one of the traditional ripened cheeses of Iran, which is produced in Gilan province and in the rural areas of this province (Siahmezgi village, (Shaft city) and has its own fans in the northern region of the country. and neighboring provinces. This cheese has a higher nutritional value than white salt water cheese due to the retention of nutrients in the curd, and it is comparable to famous French cheeses in terms of sensory characteristics, especially aroma and taste. Siahmezgi cheese is one of the most expensive cheeses in the market due to its good taste. Therefore, its commercial and industrial production is justified. Khosharizeh is a native plant that grows naturally in northwest Iran and is used as a food seasoning in yogurt and cheese. Khoshareze species, which are rich in plant essential oils, are used as spices in traditional medicine in many countries, including Iran. Local cheeses are produced by heating the milk below 50 degrees Celsius and a significant percentage of the microbes in it show resistance at such a low temperature and are not destroyed.
The use of plants in dairy products, including cheese, has been common. therefore, manufacturers use industrial or natural antibacterial materials in order to destroy pathogenic microbes. Recently, the extract and essential oil of these plants have been used as a natural preservative in the dairy industry, which, of course, was inspired by the traditional and long-term use of this plant as a flavoring in yogurt and cheese.Microencapsulation techniques increase the dispersion of essential oils in aqueous formulations, increase chemical stability during storage, minimize sensory changes, and in some cases even improve their antimicrobial effect.Some plants have antimicrobial properties due to their volatile compounds, including phenolic compounds, and can fight against spoilage agents. Following the prohibition of chemical preservatives and the use of natural and organic materials, the use of plant antimicrobial compounds in food products has received much attention.Echinophora platyloba plant was collected from different regions of Mahalat city in the spring season at the flowering stage. First, it was rinsed to remove dust, and after initial washing, the aerial parts of this plant were separated and completely dried in the shade, and after drying, it was powdered by an electric mill. To prepare the essential oil, a Clevenger machine was used by the water distillation method (Hashmi et al. 2013). The essential oil prepared in 2 cc dark colored vials was stored in the refrigerator to prevent light from penetrating and changing its properties. Sheep's milk was obtained from Gachsar region of Karaj, and chemicals and microbial culture media, including skimmed milk plate Kant agar and YGC agar, were obtained from Merck, Germany.First, Echinophora platyloba essential oil as an oil phase was mixed well with Tween 80 as a surfactant using a magnetic stirrer; Then the aqueous phase (distilled water) was slightly acidified with citric acid (0.3%) and the mixture of the oily phase and surfactant was slowly added to the aqueous phase on a magnetic stirrer with a rotation speed of 700 rpm in order to prepare the emulsion premix. . Then, the prepared emulsion premix was exposed to ultrasonic waves for 20 minutes in an ultrasound bath (power 100 watts and frequency 40 kHz) to reduce the particles and produce nanoemulsion.
First, the sheep's milk was heated for 5 minutes at a temperature of 80 degrees Celsius to destroy the bacteria and possible contaminants in it. Next, the milk was divided into 7 parts with three repetitions based on the treatments. 10 kg of milk was allocated for each treatment. After boiling the milk and making it lukewarm, 50 grams of special cheese curd (Enzymax industrial curd) was added, the cheese curd process takes place for 1 to 2 minutes after adding the curd. As soon as the first signs of scabbing started, essential oil was added to the cheeses based on the determined amount (0.1, 0.3 and 0.5% free and encased). Stirring the milk several times in the curd process will spread the essential oil evenly in the cheese. After the passage of time and partial closure of the cheese, the cheese was pressed and the whey was removed and the product was made into 200 gram molds. Salt water was added to the cheeses and stored in disposable containers in zip-top bags for 3 months in the refrigerator.

Acidity and pH were measured based on the national standard number 2852. The fat test was done by Vangulic method according to the national standard 8785 and the amount of dry matter was measured according to the Iranian national standard number 1753 by oven method and the ash of the samples was measured according to the Iranian national standard number 1755. The color characteristics of the cheese samples were investigated by using the Huntlab system and by measuring the color indices L*, a* and b*.

In order to evaluate the effect of Echinophora platyloba essential oil on physicochemical, microbial and sensory properties of cheese, different percentages of Echinophora platyloba essential oil (0, 0.1, 0.3 and 0.5%) in both free and nanocapsuated forms were added to cheese. Cheese samples were analyzed at days 1, 30, 60 and 90 of storage time.
Texture tests of cheese samples after cutting with dimensions of 2 x 2 x 2 cm, with a Brookfield texture analysis machine made in the United States with a cylindrical probe with a diameter of 36 mm and a penetration speed of 60 mm per minute. It was done to a depth of 1 cm. This experiment investigated the hardness with three repetitions and at a temperature of 6 degrees Celsius
Total phenol content of cheese was measured according to Folin-Ciocalto method. First, extract was extracted from cheese and one milliliter of extract was added to 5 milliliters of Fulin-Ciocalto reagent (1:10) and mixed for 6 minutes. 4 ml of 20% sodium carbonate was added to the mixture and kept for 2 hours at room temperature and its absorbance at 760 nm wavelength was measured using a UV-vis spectrophotometer and was equivalent to mg of gallic acid per gram of cheese.
Mold and yeast counting was done based on the microbial standard of milk and dairy products number 10154. The total microbial count was also done according to the national standard number 5272-1 by the purple plate method in milk agar skim culture medium (manufactured by Merck, Germany).
10 trained panelists were used for sensory evaluation of cheese samples. Sensory characteristics including taste, color, texture and overall acceptance were evaluated using a 5-point hedonic scale (1: very bad to 5: very good).
In order to analyze the data obtained from the tests, a completely random design was used and the average obtained from repeating each test 3 times, through Duncan's multi-domain test, at a confidence level of 95% and using SPSS software. was analyzed. Graphs were also drawn with Excel software.
The results showed that, changes in the acidity of the samples during 90 days of storage were increasing and pH were decreasing. The addition of essential oil, especially in the nanocapsuated form, controlled the increase in acidity and the decrease in pH during the storage period in cheese. The use of Echinophora platyloba essential oil had no significant effect on texture and approximate composition of cheese, including fat, ash and dry matter, but during the storage period, dry matter, salt content and hardness increased. During the storage period, L* index decreased and a* and b* index increased. Also, the use of essential oil decreased the L* index and increased a* and b* index. According to the results, there was a significant difference between the treatments containing free essential oil and the samples containing nanocapsuated essential oil on the antioxidant activity of cheese (P<0.05) and the antioxidant activity decreased during the storage period and in The sample contained nanocapsuated essential oil was higher than other treatments. During the storage period, mold and yeast and total microbial count increased significantly. However, in the treatments containing essential oil, the intensity of microbial growth was lower than the control sample, and no Salmonella and Escherichia coli contamination was found in any of the treatments. Adding essential oil to cheese improved the aroma, taste and overall acceptance, but it did not have a significant effect on texture of the cheese. In general the treatment, containing 0.5% nanocapsuated essential oil had higher score in terms of sensory evaluation.