Evaluation of the physicochemical and color characteristics of functional set yogurt containing yellow, red and orange bell pepper extract

Introduction: Yogurt is one of the most popular fermented milk products, which affords an excellent source of essential nutrients such as vitamins, calcium, and proteins. It also provides valuable lactic acid bacteria that are beneficial to the function of human gut microbiota. However, plain yogurt lacks a variety of health-beneficial antioxidant substances particularly phenolic compounds, flavonoids, anthocyanins, and vitamin C. Therefore, incorporation of natural functional ingredients such as fruits (Alirezalu et al., 2014; Raikos et al., 2019; Arslaner et al., 2021) and vegetables (Kim et al., 2010; Yang et al., 2012; Hong et al., 2020; Momenzadeh et al., 2021) can boost the chemical composition and health benefits of the yogurt. Most of these investigations revealed that adding natural edible ingredients to yogurt improved its chemical composition, biological activity, and quality characteristics. Fortification with these bioactive constituents is one of various methods to preclude the syndromes associated with dietary deficiencies. In addition to antioxidant activities, these compounds exert other beneficial health effects such as antimicrobial, antidiabetic, anticancer, anti-obesity, anti-inflammatory, and cardioprotective properties. The aim of this study was therefore to evaluate the the effect of addition of concentrated bell pepper extract (CBPE) with three different colors on the physicochemical and color properties of set yogurt.
Materials and methods: Bell peppers with yellow, orange, and red colors were washed and crushed by a blender. After straining for pulp extraction, the total soluble solids of juices were adjusted up to 30% by a rotary evaporator. The set-style yogurt samples were produced on a laboratory scale according to the method described by Yademellat et al. (2017) and Jooyandeh et al. (2023) with some modifications. For yogurt production, the milk was heated at 90 ◦C for 10 min and after the temperature reduction up to 65 ◦C, the CBPEs were added. After inoculation with 0.05% starter cultures (lyophilized powder) at 44-45 ◦C, the samples were incubated at 42 ◦C until the pH reached to 4.6. The yogurt samples were kept at refrigerator and analyzed for physicochemical characteristics (pH, total solids, syneresis and water holding capacity (WHC)) and color values (L*, a*, and b* indexes) during 21 (1, 11 and 21) days of storage. The yogurt sample without CBPE was prepared and considered as the control. For performing analysis, data were analyzed by a completely randomized factorial design using SPSS software, version 20. The mean of treatments was compared with Duncan test at 95% confidence level.
Results and discussion: Results showed that incorporation of CBPE in the yogurt samples and the storage perid had significant impact on the studied parameters. With incorporation of CBPE in the yogurt samples and with the passage of storage time, the amounts of pH, syneresis and lightness significantly decreased, while the amounts of total solids, WHC and a* and b* values increased. The amounts of pH of yellow CBPE was slightly higher than other fortified samples, but these differences were not significant (p>0.05). The red CBPE sample had higher total solids and syneresis than orange and yellow CBPE samples but these differences were also not significant (p>0.05). The control sample (yogurt without CBPE) had higher L* value (87.87) than yellow (85.36), orange (83.87) and red (80.32) CBPE samples. The red CBPE sample had higher a* value particularly at the end of 21 days of storage period as compare to other samples probably due to the higher anthocyanins content. The amount of a* value in red, yellow and orange CBPE samples were recorded as 8.94, -2.52 and -0.96, respectively. As the time of storage increased, the amount of redness particularly in the red CBPE yogurt increased probably due to the lower syneresis (Kim et al., 2010). Like a* values, results showed that fortified yogurt samples especially orange CBPE sample had higher b* value probably due to the higher carotenoids compounds. With agreement with our results, Kim et al. (2016) reported the higher amount of carotenoid substances in orange bell pepper (62.57 mg/100 g) as compare with yellow (35.32 mg/100 g) and red bell pepper (55.80 mg/100 g) on dry basis. Furthermore, in control sample with the passage of storage time, b* value increased slightly while in fortified samples decreased to some extent (p>0.05). The increase in b* value in control yogurt is probably due to destabilizing of casein micelles because of pH reduction during the storage (Garcia et al., 2005). The decrease in b* value in the fortified yogurts is undoubtedly due to disintegration of pigments mainly Xanthophylls during the storage period (Suwannasang et al., 2022).
Conclusion: Based on the results of the current study, incorporation of bell peppers in the form of concentrated extract had significant effect on physicochemical and color characteristics of set yogurts. One of the most common defects in set type yogurts is syneresis. The results revealed that by application of CBPE in yogurt formulation, the syneresis reduced and WHC increased significantly. Therefore, by incorporation of CBPE, a functional yogurt with a higher antioxidant substances and a lower syneresis could be produced. Based on sensory and antioxidant activities (results are not shown), the yogurt sample having orange CBPE was selected as the best functional product.