Evaluation of physicochemical, antimicrobial, and antioxidant properties of the set yogurt containing anthocyanin extract of pomegranate peel during storage

Introduction: set yogurt is considered one of the most widely consumed fermented dairy products, which is rich in nutrients. Recently, synthetic colors have been used to diversify yogurt, which harms the body. Therefore, it is necessary to use edible color compounds that have antimicrobial and antioxidant properties and can also cause variety in the product's taste. Extracts obtained from waste plants such as pomegranate peel are rich in compounds with antioxidant properties, which in addition to increasing the shelf life of the product, have a positive effect on the health of the consumer. On the other hand, pomegranate fruit is one of the native products of Iran, and its waste, such as peel, can be used as a valuable compound containing antioxidants and antimicrobials in the formulation of food products, especially fermented dairy products such as yogurt. Material and methods: First, anthocyanin extract was extracted from pomegranate peel with the help of ethanol solvent, and then the amount of phenolic and anthocyanin compounds was measured. Also, its antioxidant properties were measured in different concentrations through the Bleaching of beta-carotene: linoleic acid. The minimum inhibitory concentration (MIC) and the minimum microbicidal concentration (MBC) of anthocyanin extract were evaluated. Then the best concentration to add to the yogurt formulation was determined. After the preparation of yogurt containing anthocyanin extract, the characteristics of yogurt such as pH, acidity, antioxidant properties, and antimicrobial properties were investigated during the storage period (8 days). Results and discussion: The extraction efficiency of pomegranate peel anthocyanin extract was 23.80±0.30%. The amount of anthocyanin and total phenol measured was equal to 59.57 mg of cyanidin-3-glucoside per hundred grams of pomegranate peel powder extract and 1973.02 mg of gallic acid per 100 grams of extract. The highest antioxidant activity in beta-carotene: linoleic acid Bleaching test, minimum bacterial inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) were related to the concentration of 600 ppm, 300 ppm, and 400 ppm of pomegranate peel extract, respectively. Therefore, a concentration of 600 ppm of pomegranate peel extract was used in yogurt formulation. By increasing the concentration of anthocyanin extract in pomegranate peel, the antioxidant and antimicrobial properties also increased. During storage (8 days) of yogurt containing pomegranate peel extract, parameters such as acidity, and antioxidant activity (Bleaching of beta-carotene: linoleic acid) increased. But the pH value decreased. The antimicrobial activity of yogurt extract containing anthocyanin extract of pomegranate peel was suitable so that Staphylococcus aureus bacteria was not observed during the storage period (8 days). The effect of antimicrobial activity of yogurt extract containing pomegranate peel anthocyanin extract was different against Pseudomonas aeruginosa bacteria. So that this bacteria was not observed on the first day, but it was observed on the 8th day of storage. The effect of yogurt containing anthocyanin extract had a greater effect on inhibiting the activity of Staphylococcus aureus bacteria. Because this bacterium is gram-positive and its wall does not have a peptidoglycan layer it was more sensitive to the extract. Conclusion: In general, the results showed that yogurt containing pomegranate peel anthocyanin extract, in addition to increasing its shelf life and improving its physicochemical properties, has antioxidant properties, which, in addition to its valuable nutritional properties, play a significant role in the health of consumption.
The results (Table 4) showed that the water content increased with the storage time of the yogurt sample containing the extract. The lowest and highest water content was on the first day (41.12%) and on the 8th day (47.18%), respectively. In a study by Alirezaloo et al. (2015) on functional colored yogurt (storage period of 21 days), the water content of the control yogurt sample, yogurt containing blackberry extract, and yogurt containing carrot extract increased (Alirezaloo et al., 2015). Golmakani et al. (2020) also stated in a study on the effect of different concentrations of pomegranate fruit in molded and stirred yogurts that the yogurts underwent acidification, which led to a decrease in pH, which ultimately increased the water content of the yogurt (Golmakani et al., 2015).et al., 2020) which is consistent with the results of this study. Beta-carotene: Linoleic Acid Decolorization Test Yogurt sample containing anthocyanin extract showed high antioxidant properties in this test, indicating the antioxidant properties of yogurt containing pomegranate peel extract. The results also showed that the antioxidant properties increased during storage until the 8th day (Figure 1). In a study conducted by Sehangil et al. (2022) on the enrichment of fortified yogurt (5-20%) with rose, the addition of rose to yogurt caused a proportional increase in the amount of total phenols. They also observed that it helps and increases the antioxidant activity of yogurt (Sehangil et al., 2022). A study by Sandia et al. (2018) was conducted to prepare pomegranate peel extract powder and evaluate its effect on the functional properties and stability of curd. The antioxidant activity increased with increasing the concentration of pomegranate peel extract. The shelf life of whey containing pomegranate peel extract was increased by 6 days compared to the control sample (at 5°C) (Sandia et al., 2018).
In this study, the antimicrobial activity of pomegranate peel anthocyanin extract on pathogenic and food spoilage bacteria was investigated and the results were shown in the form of MIC and MBC in Table 3. Pomegranate peel anthocyanin extract at different concentrations (50, 100, 300, 200, 400 and 800 ppm) had inhibitory and killing effects on two bacteria (Pseudomonas aeruginosa, Staphylococcus aureus) under study, which had the same response for both bacteria. Antimicrobial agents with low activity against an organism have high MIC and MBC, while a highly active antimicrobial agent gives low MIC and MBC (Bansu, 2009), which indicates the high antimicrobial property of pomegranate peel extract.
Selection of the optimal concentration of pomegranate peel powder anthocyanin extract
Based on the results obtained from antioxidant and antimicrobial tests, the optimal concentration was used for use in yogurt formulation. The highest antioxidant activity for the beta-carotene-linoleic acid discoloration test was 600 ppm and 800 ppm, which were not significantly different from each other. On the other hand, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) test for pomegranate peel extract for two bacteria, Staphylococcus aureus and Pseudomonas aeruginosa, were 300 ppm and 400 ppm. InThe result was that the concentration of 600 ppm of the extract was selected as the optimal concentration for addition to the molded yogurt formulation.
pH measurement
The pH of the yogurt containing anthocyanin extract was measured with a pH meter. The yogurt containing anthocyanin extract was stored at refrigerator temperature for 8 days. The results in Table 4 showed that the pH of the yogurt sample containing pomegranate peel anthocyanin extract decreased during higher storage. The highest and lowest pH values were for the yogurt sample containing the extract on the first and eighth day, respectively. In a study by Alirezaloo et al. (2015) on functional colored yogurt enriched with blackberry and carrot extracts, they stated that during a storage period of 21 days, the pH decreased for both the control sample and the samples containing blackberry and carrot extracts (Alirezaloo et al., 2015). Golmakani et al. (2021) in a study on the effect of different concentrations of pomegranate juice in molded and stirred yogurts stated that when pomegranate juice was added to yogurt, it had a significant effect on the pH of yogurt. On the other hand, adding pomegranate juice to yogurt had negative effects on the number of starter cultures due to damage caused by acids (Golmakani et al., 2021), which is consistent with the results of this study. Because yogurt containing the extract was incubated for a longer period of time to reach the standard pH.
The yogurt sample containing anthocyanin extract showed high antioxidant properties in this test, indicating the antioxidant properties of yogurt containing pomegranate peel extract. The results also showed that the antioxidant properties increased during storage until the 8th day (Figure 1). In a study conducted by Sehangil et al. (2022) on the enrichment of fortified yogurt (5-20%) with rose, the addition of rose to yogurt caused a proportional increase in the amount of total phenols. They also observed that it helps and increases the antioxidant activity of yogurt (Sehangil et al., 2022). A study by Sandia et al. (2018) was conducted to prepare pomegranate peel extract powder and evaluate its effect on the functional properties and stability of curd. The antioxidant activity increased with increasing the concentration of pomegranate peel extract. The shelf life of curd containing pomegranate peel extract increased by 6 days compared to the control sample (at 5 ° C) (Sandia et al., 2018).
It has makers. Also, as a fermented dairy product that has natural and healthy ingredients, it is suggested to be widely produced industrially and to replace yogurt with synthetic pigments