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.

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 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).

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.

Yogurt, a widely consumed fermented milk product, is known for its health benefits attributed to the presence of probiotic bacteria.This study explores the impact of starter cultures on the texture and microbiological quality of yogurt. The production involved two types of starter cultures: a commercial culture and an heirloom culture. Various parameters, including chemical analysis of raw milk, yogurt production steps, texture parameter analysis, syneresis, water holding capacity, and microbial analysis, were examined. Statistical analysis was performed to indicate the effect of the type of culture on the production of yogurt.Results indicated that the physicochemical analysis of raw cow milk revealed parameters within recommended quality standards. Significant differences in hardness, gumminess, chewiness, resilience, and syneresis between commercial and heirloom yogurts were found. Microbiological analysis demonstrated higher Lactic acid bacteria counts in commercial yogurt compared to heirloom yogurt.  The study provides insights into the influence of starter cultures on textural and microbiological characteristics, emphasizing the importance of standardized production methods for consistent yogurt quality.

This study aimed to evaluate the sensorial, physicochemical, rheological, and microbiological properties of yoghurt fortified with Artemisia absinthium leaf powder during refrigerated storage. The valorization of this plant in food industry was realized by the incorporation of its dried leaf powder at various concentrations in order to produce a new functional yoghurt. It is interesting to note that the fortified yoghurt with the lowest Artemisia dose (2%) was the most preferred by the panel. Furthermore, this fortification did not affect the fermentation parameters nor the viability of lactic starter. During storage, the incorporation of Artemisia powder reduced syneresis and improved the microbiological properties of fortified yoghurts. Besides, at the end of storage, it was noted that yoghurt fortified with 2% of Artemisia powder presented the highest consistency (8.98±0.04 Pa sn) and antioxidant activity (60.08±3.61%) when compared to the control yoghurt. Finally, the accelerated shelf-life test showed the efficiency of Artemisia absinthium powder incorporation by increasing the shelf life of yoghurt by about 4 days.

Cheese whey is the most polluting by-product of the dairy industry, and whey use has been the subject of much research; however, the conversion of liquid whey into value-added yogurt products is insufficient. The aim of the current research is to study the effect of fermentation of a milk-liquid whey mixture into yogurt and strawberry supplementation on the syneresis index and textural and organoleptic characteristics during cold storage. For yogurt preparation, 25% liquid whey was substituted with the milk used for yogurt production, and after the fermentation process was complete, strawberry supplementation (12%). Results show that by using liquid whey in yogurt formulation, the syneresis index increased, whereas for texture properties, higher mean values of cohesiveness and springiness and lower values for hardness, adhesiveness, and gumminess were found. The time of storage also had a significant impact on the yogurt properties, and as the time of storage increased, the syneresis index increased and sensory scores reduced noticeably. The level of whey separation was significantly increased in yogurt samples containing liquid whey on the last day of storage, according to an evaluation of yogurt qualities (P<0.01). The results showed that although adding liquid whey into the yogurt production decreased the sensory characteristics (consistency and taste scores), yogurt with liquid whey and strawberry supplementation had an acceptable sensory score. Therefore, the use of liquid whey in the production of functional yogurt enables its reintroduction in the food supply chain and enhances sustainability.

Milk and dairy products such as yogurt and kashk have long been used as part of the human diet and are among the most important suppliers of a large part of the human need for calcium. This study aimed to investigate the microbial quality of Rasht traditional yogurt and kashk samples. 25 samples of traditional yogurt and 25 samples of traditional liquid kashk were randomly collected from the supply centers of Rasht from December to March 2021. The microbial quality of the samples was investigated in terms of contamination with coliform, Escherichia coli, coagulase-positive staphylococci, sulfite-reducing clostridia, mold, and yeast. The contamination with coliform in traditional yogurt and kashk was 0.35 ± 0.12 and 0.11 ± 0.08 log cfu/g, and the contamination with mold and yeast in traditional yogurt and kashk was 2.07 ± 0.52 and 0.60 ± 0.18 log cfu/g, respectively. No significant difference was found between the samples of traditional yogurt and kashk in terms of contamination with E.coli, but a significant difference was between traditional yogurt and kashk samples in terms of contamination with mold and yeast and their contamination level was much higher. According to the results, the microbial quality of traditional yogurt was low. Therefore, health control of production units and monitoring of traditional yogurt production in Rasht City should be done continuously until the contamination in traditional yogurt is reduced.

Colostrum is a secretion product produced by the mammary glands immediately after birth. This vital and unique composition is designed to meet all the animal's needs when it cannot eat. For various reasons, maternal accidents can occur during pregnancy and birth, making it impossible to produce appropriate colostrum for the newborn calf. Therefore, the main task of the farmer is to provide suitable replacement colostrum as quickly as possible so that he can maintain the results of his year-long efforts to continue the generation. Various methods are used to preserve colostrum. Methods of colostrum storage include fermentation and freezing. Fermentation of the colostrum results in physical and chemical changes in the colostrum that can aid in the transfer of nutrients to the calf. This research was carried out to study and compare the effect of different methods of colostrum preservation on the efficiency of newborn calves of the Simmental breed and to recommend the use of one of the more suitable methods so that if the farmer does not have access to suitable colostrum, he can use.
To carry out this study, 32 newborn Simmental calves with an average weight of 39.5 ± 3.2 kg were used. The calves were divided into four equal groups (eight replicates per treatment), including 1. group fed with fresh colostrum from the mother (control), 2. group fed with fermented colostrum without any additives (fermented without additives), 3. the group that was fed colostrum fermented with low-fat yogurt (fermented with yogurt), and 4. the group was fed with colostrum that was kept frozen (frozen) in the freezer and heated to a temperature of 37 °C before consumption. Initially, a colostrum bank was used with 110 liters of colostrum from the first and second lactation cows, which started colostrum production at the same time by synchronizing parturition. Colostrum samples were separated and prepared in polyethylene (PET) plastic containers with a volume of two liters. In the fermented colostrum group, after filling the containers of the group with yogurt, two percent yogurt was added, and the containers were completely sealed and stored at room temperature until the experiment. The dishes belonging to the frozen group were stored in the freezer at -20 °C. In the first two days, all calves received two liters of colostrum per meal twice daily in the morning and evening. Feed was consumed daily. Calves were weighed at the beginning of parturition, on the 30th and 60th days of the schedule in the morning and before feed distribution, and from the 27th day of the calves' birth, the apparent digestibility of nutrients (dry matter) was measured. Samples were taken from three-day experimental rations and feces. Blood was collected from the jugular vein on days 0, 1, and 30. After serum separation, blood factors such as glucose, cholesterol, triglyceride, and total blood protein were measured. At the beginning of the course and the end of the project, body parameters were measured to check the growth status of the calf: hip width, height from withers, chest circumference, body length, chest depth, wrist circumference, and eye relief.
The results of different treatments of colostrum consumption in newborn calves concerning blood biochemical parameters showed that the amount of glucose in all three sampling times was not significantly different in all treatments, and the amount of blood protein and triglycerides were also not affected by the treatments (P>0.05). Colostrum consumption with different storage methods had no significant influence on the amount of concentrate consumed, the digestibility of the dry matter consumed, the final weight of the calf, the daily weight gain, and the feed conversion ratio (P>0.05). Also, the results showed that there were no significant changes in physical indices among different groups (P>0.05). The use of colostrum with different storage methods had no difference in the amount of cells associated with the immune system, including types of white blood cells, and therefore the immune conditions were similar in all groups (P>0.05).
The results of this study showed that consumption of colostrum in simply fermented form or with the addition of fat-free yogurt, as well as colostrum stored in frozen form, had a positive influence on blood parameters in newborn calves compared to the control group that used fresh maternal colostrum. The use of colostrum stored in any of the mentioned methods, depending on the conditions of animal husbandry, can help provide the colostrum needed by the calf and solve the problem of the animal breeder.

Among the food products, yogurt is very popular due to its distinctive characteristics such as the presence of lactic acid bacteria and nutritional and therapeutic properties. In any case, consumption of high-fat yogurt can endanger health on the one hand, and on the other hand, reducing fat reduces the quality of the product. Therefore, this research was conducted with the aim of investigating the possibility of improving the characteristics of low-fat stirred yogurt using the treatment of microbial enzyme transglutaminase (MTG) and Persian gum (PG). Low-fat stirred yogurt samples were produced using levels of 0, 0.1 and 0.2% (w/v) of PG gum and levels of 0 and 0.015% (w/v) of MTG enzyme. The physicochemical characteristics and color values of the samples were evaluated during 14 days of storage in the refrigerator. Based on the results of this research, the addition of PG and MTG enzyme significantly reduced acidity and syneresis (p<0.05). Furthermore, the addition of gum increased lightness and redness and reduced yellowness. Although the enzyme treatment like PG increased the lightness and redness, it caused an increase in the yellowness of the yogurt. Storage time significantly decreased syneresis and lightness parameters and increased yogurt acidity and redness and yellowness indexes (p<0.001). In conclusion, the results of this research showed that by using transglutaminase enzyme treatment (0.015%) and adding Persian gum (especially 0.2%), low-fat stirred yogurt with acceptable physicochemical characteristics and color can be produced and the quality of low-fat stirred yogurt can be improved.

This research aimed to produce functional yogurt containing transglutaminase enzyme and Persian gum with acceptable physicochemical and microbial properties. Transglutaminase enzyme at three levels of 0, 0.01%, and 0.03% and Persian gum at three levels of 0, 0.5%, and 1% were used to produce functional yogurt and the physicochemical characteristics  (pH, syneresis, viscosity, color properties) and microbial properties (lactic acid bacteria viability) during 20 days of storage evaluated. The results showed that the addition of transglutaminase enzyme increased the pH of functional yogurt samples, while the addition of Persian gum decreased the pH of the samples. The lowest syneresis was observed in functional yogurt samples containing 0.03% transglutaminase enzyme and 1% Persian gum. The results showed that in all samples, the viscosity increased significantly with the increase of transglutaminase enzyme and Persian gum (p<0.05%). Although the transglutaminase enzyme and Persian gum increased the lactic acid content of the treated samples compared to the control sample, during the storage time, the lactic acid content decreased significantly (p<0.05). Based on the results, in the presence of transglutaminase enzyme and Persian gum, the color index L* of yogurt samples increased and the a* and b* indexes decreased significantly (p<0.05). According to the result, the use of transglutaminase enzyme and Persian gum in yogurt reduced syneresis, increased viscosity, and improved the viability of lactic acid bacteria and the color characteristics of functional yogurt samples.

The aim of the current research was microencapsulation of Streptococcus thermophilus and Lactobacillus bulgaricus bacteria by coacervation complex method and sodium caseinate and pectin coatings. Sodium caseinate and pectin have electrostatic attraction together at pH=4 and form a complex. Using a scanning electron microscope, the morphology of coacervates was investigated. The properties of pectin and sodium caseinate complexes were investigated by infrared spectrometry tests and measuring the size and distribution of particles. Physicochemical characteristics such as water absorption, pH and acidity and sensory characteristics were also investigated. The results showed that the efficiency of microencapsulation of bacteria by coacervation method was 66.6%. The particle size was 1.565 micrometers and the zeta potential was reported as -16 mV. Electron microscope images showed spherical coacervate without holes and wrinkles on the surface. The results of infrared spectroscopy also showed the creation of electrostatic interactions between pectin and sodium caseinate. Also, microencapsulation of bacteria caused a significant change (p>0.05) in pH (4.6 ± 0.091) and yogurt acidity (1.1 ± 0.03) compared to pH (4.6 ± 0.1). And the acidity of yogurt (0.8±0.01) produced with free bacteria did not. The water content of yogurts produced with microencapsulated bacteria (40±1.1) was reduced compared to yogurts produced with free bacteria (45±0.9) (p<0.05). Bacterial encapsulation has a negative effect on color sensory characteristics. It did not have the smell and taste of the produced yogurts (p>0/05), but a significant difference was observed in the texture of the yogurts produced with microencapsulated bacteria compared to the yogurts produced with free bacteria (p<0/05).

The presence of antibiotics in milk is one of the problems of dairy production units, especially yogurt and cheese, which leads to a decrease in lactic coagulation. Here, to assess the incubation conditions for fermentation of milk containing the antibiotic, concentrations of 50,75,100, and 200 parts-per-billion(ppb) of tetracycline were added to each liter of milk. The inoculation process with starter culture was performed at three temperatures (35,45,50°C). Afterward, pH, acidity, oxidation-reduction potential, and lactic coagulation of yogurt were evaluated. The results showed the existence of antibiotics in milk affects the quality and physicochemical properties of yogurt. However, antibiotic concentration and change in incubation temperature play a crucial role in the lactic coagulation of yogurt, such that the best lactic coagulation was observed at 50°C and a concentration of 50 ppb. Hence, in tetracycline concentrations less than 75ppb, a process temperature of 50°C and incubation time of ~10h is recommended for the fermentation of milk containing antibiotics.