جستجوی مقالات مرتبط با کلیدواژه « Yogurt » در نشریات گروه « صنایع غذایی »

Dairy products such as yogurt are considered as one of the most popular foods in the world. Beside the probiotics, functional ingredients such as prebiotics are also used in various products. One of the functional ingredients is propolis which has antioxidant, anti-inflammatory, anti-bacterial, anti-fungal, anti-viral and anti-tumor properties, and in addition to this properties it can be a prebiotic which can have beneficial effects on the human digestive system. This study was conducted to investigate the effect of propolis extract on the physicochemical, sensory and microbial characteristics of synbiotic yogurt inoculated with Lactobacillus casei. This study was conducted in five treatments (control (A), 1% (B), 2% (C), 3% (D), 4% (E)) and three replications. Physical and chemical properties such as antioxidant activity and total polyphenol, acidity and pH, syneresis, texture (hardness, stickiness, springiness and chewiness), probiotics survival as well as sensory properties (taste, odor, texture, color and general acceptance) of yogurt samples in days 1, 7, 14 and 21 were measured. According to the results of the sensory evaluation team, the highest level of favorability was related to the control treatment. The lowest pH value in the control sample was 1% and showed a significant difference with the 2%, 3% and 4% treatments. The highest level of acidity was related to the 4% treatment and also on the 21st day compared to the seventh day, the highest level of acidity was observed in the 4% treatment. The results of the survival of L. casei on different days showed that the effect of time and propolis percentage on the survival of probiotic bacterium was significant. The highest number of L. casei was observed in 4% treatment. It can be concluded that propolis can be used as a prebiotic in yogurt, which can improve the functional and textural properties of yogurt.

Yogurt, a widely consumed dairy producton a global scale, is highly regarded for its outstanding nutritional composition, gastrointestinal advantages, prolonged storage capability, rapid digestibility and assimilation rates, economic importance, and therapeutic properties.  And It is shown in this research illustrates that yogurt with an increased quantity of alfalfa extract elevates the levels of phenolic compounds and antioxidant capabilities. In this study, alfalfa extract was incorporated into yogurt formulation at varying concentrations of 2, 4, 6, and 8 percent by weight. Following a storage period of 20 days, the assessment of antioxidant activity was conducted by measuring DPPH radical inhibition. Moreover, an analysis of phenolic compounds and an evaluation of yogurt quality attributes including pH, acidity, water content, and viscosity were carried out. Subsequently, a factorial experiment design was employed, utilizing a completely randomized design with three replications for statistical purposes. Statistical analysis involved the comparison of means at a significance level of 1% using SAS software version 9. The results showed that the presence of alfalfa extract led to an augmentation in the levels of water-soluble phenolic compounds as well as the antioxidant capacity of yogurt. So that, at the conclusion of a 10-day period, the highest antioxidant activity was associated with yogurt formulations incorporating 6% and 8% alfalfa extract. Furthermore, the yogurt sample containing 8% extract exhibited the lowest water content, a statistically significant variance compared to the remaining samples (p≤0.05). It should be noted that Considering the impact of dairy products on health and the need to increase per capita consumption of dairy products, more attention should be paid to the production of products that have more health benefits and high rheological properties. Hence, within this study, it was demonstrated that the inclusion of alfalfa extract resulted in an augmentation of the samples' antioxidant characteristics.

This study aimed to investigate the effect of green tea and green coffee powders at 0, 1, and 2% levels, each separately on the viability of Lactobacillus paracasei in probiotic yogurt. The viability of Lactobacillus paracasei was evaluated in terms of microbial count, pH, and sensory evaluation of yogurt samples in three replicates on days 1, 7, 14, and 21. The results showed that the addition of green tea and green coffee powders to probiotic yogurt significantly increased the viability of Lactobacillus paracasei in all samples compared to the control yogurt (p<0.05). The highest number of bacteria in yogurt samples containing 1% green tea and 2% green coffee contained 13.78 ± 0.17 and 11.54 ± 0.2 log CFU/g, respectively. The lowest and the highest pH values belonged to the yogurt sample containing 2% green tea and 2% green coffee, respectively. The best taste was related to the yogurt sample containing 1% green coffee and the most favorable texture and color was related to the control yogurt sample. The highest scores in terms of overall acceptance were in the control yogurt sample, yogurt containing 1% green tea and yogurt containing 1% green coffee, respectively. In conclusion, the results showed that the addition of 1% green tea, had a good effect on the viability of Lactobacillus paracasei and can be used for commercial production.

One of the common adulterations in milk and dairy products, is the addition of low-priced vegetable oils such as palm oil in order to increase the profitability of products. Therefore, there is an urgent need to develop accurate, fast and reliable identification techniques to protect consumers against this type of adulteration. The aim of the present study was DNA barcoding with real-time PCR as a reliable method for detecting palm oil fraud with levels of 2, 3, 4, 5, 10, 30, 50 and 100 % and positive and negative control samples in yogurt. According to the results, the highest and lowest concentrations of DNA extracted belonged to the palm oil sample of 100 % and 3% , respectively, while among all samples, the concentration of DNA extracted in sesame oil and then in the control oil sample was lower. It was determined from other samples. The lowest and highest adsorption rates (10mm) between the samples were control oil (excluding palm) and 100 % palm oil, respectively. There was no significant difference in absorption rate between 4%, 5% and sesame oil samples. The range for detecting palm oil adulteration was from 0.05% to 100% palm oil. LOQ and LOD were 0.1 % and 0.05 % of palm oil, respectively.

In this study, the effect of Tragopogon collinus extract on the viability of probiotic bacteria, physicochemical and sensory properties of probiotic yogurt was investigated. For this purpose, Tragopogon collinus plant extract was extracted using ultrasound method and the amounts of phenolic compounds and chemical compounds of the extract were measured. The results showed that the amount of total phenolic compounds in Tragopogon collinus plant extract was equal to 890.04±2.18 mg gallic acid per gram and most of the extract compounds included n-Hexadecanoic acid (24.25), 4-vinyl guaiacol (19.78). ), Β -Caryophyllene (15.55) and Heneicosane (9.45). In order to investigate the effect of Tragopogon collinus extract on the properties of probiotic yogurt during the 15-day storage period, 3 treatments including control, extract with a concentration of 750 ppm, extract with a concentration of 1000 ppm and physicochemical properties including pH, acidity, synergy, viscosity, viability probiotic bacteria and sensory properties (color, odor, taste and general acceptance) were examined. The results showed that the addition of Tragopogon collinus extract to yogurt affects the physicochemical properties. Samples with extract had lower pH and synergy and higher acidity and viscosity compared to the control sample (P <0.05). Also, in these samples, the process of reducing the survival of probiotic bacteria during the storage period was slower than the control treatment, and despite the effect of the extract on the physicochemical properties of yogurt, yogurt containing the extract was acceptable in terms of sensory properties. In general, Tragopogon collinus extract can be used to enhance the quality and organoleptic properties of beneficial dairy products.

Phytosterols are among the most important plant sterol compounds. This study was conducted to identify and determine the amount of phytosterols in distributed yogurts in Tehran by gas chromatography method without derivatization. A total of 60 yogurt samples, including 20 pasteurized high-fat yogurt samples, 20 pasteurized cream yogurt samples, and 20 traditional high-fat yogurt samples, were collected randomly from dairy product supply centers in Tehran from January to March 2022. Then, the amount of cholesterol and four phytosterol compounds including brassicasterol, campesterol, stigmasterol, and beta-sitosterol in yogurt samples were determined using gas chromatography assay without derivatization. The results showed that the total sterols in high-fat, creamy, and traditional yogurt samples were 504.08±55.79, 816.21±51.87, and 332.8±41.22  mg/100mL, respectively. The highest and lowest percentage of cholesterol belongs to cream (%54.75±065) and traditional yogurt (%46.57±0.65), respectively(p<0.05). Also, the highest percentage of phytosterol belongs to traditional yogurt(%54.75±065) and there was a significant difference with other yogurts(p<0.05). The results also showed that the total phytosterols were more than the permissible limit of the national standard (3%) in all samples. According to the results, phytosterols are used in various yogurts distributed in Tehran, which is against the national standard of Iran. Therefore, periodic and regular evaluation of phytosterols in distributed yogurts should be done throughout the year by regulatory bodies and prevent the violation of consumers' rights.

Enrichment is one of the ways to increase the nutritional value of foods. In this research, enrichment of yogurt with Saccharomyces cerevisiae yeast was done as a cheap source of fiber, protein, vitamins and minerals to produce a functional food. Physico-chemical and sensory characteristics of enriched treatments were evaluated. Cow's milk was mixed at 3 levels of fat (1.2, 1.8 and 3%) with yeast at 4 levels (0, 0.3, 0.6 and 0.9%) and used in preparing yogurt samples. The results showed that, in general, fat percentage, yeast percentage and duration of storage on pH and acidity changes were significant at the 95% confidence level. With increasing fat percentage, pH increased and acidity decreased. Increasing the percentage of yeast caused a decrease in pH and an increase. Synergy decreased with increasing the percentage of fat or yeast and also with increasing the duration of storage. The stifness of the tissue increased due to the increase of fat and decreased due with the increase of yeast. The highest level of tissue stifness was 0% in the yeast level and the lowest level was 0.9% in the yeast level. The percentage of fat, percentage of yeast and also the interaction of these two variables were significant and effective on the color index a*, b* with 95% confidence. However, only the variable of yeast percentage had a significant effect on the color index L*. Sensory evaluation results showed that only the variable of fat percentage had a significant effect on aroma, mouthfeel, internal texture, spoon acceptability and overall acceptance.

One of the most important applications of biotechnology in the food industry is the production of various additives. Among the additives produced by biotechnology method is the production of exopolysaccharides produced by bacteria in dairy products.Diversity in the structure and chemical composition of microbial exopolysaccharides has made them superior to animal and plant polymers. Due to these cases, these compounds can be used as food additives with health effects. In the present study, Bacillus bacteria producing exopolysaccharides were isolated from the soils of desert areas and then, the structural and functional groups of exopolysaccharides were identified using FT-IR method. The presence of peaks in the frequency range 400-4000 (cm-1)indicates the polysaccharide and purity of the extracted material. Then, their effects on the quality of yogurt were investigated. Based on the results, the quality of yogurt samples containing exopolysaccharide of bacteria K, C, B, A and E significantly increased compared to the control group that did not contain exopolysaccharide.Exopolysaccharide from E bacterium significantly reduced hydration compared to other samples and control samples and also significantly increased the viscosity and water holding capacity and consistency of yogurt. Finally, based on the 16S rDNA sequence, the bacterium whose exopolysaccharide had the greatest effect on improving the quality of yogurt, Bacillus wiedmannii strain HBUM207173 was identified.

According to the increasing demand of advanced societies for the consumption of functional foods, especially in dairy products, the use of natural-based materials such as plant essences in the field of enriching food products with their antimicrobial and antioxidant compounds, as well as the use of wheat germ powder as a rich source of dietary fibers and vitamins and minerals and their effects on the viability of starter bacteria (due to their prominent role in improving human health) are seem to be necessary. Investigating the effects of using processed essential oils and wheat germ powder simultaneously in yogurt is considered in this research. Sensory, physicochemical characteristics and bacterial conting of set yogurt including Streptococcus thermophilus and Lactobacillus bulgaricus, were tested during the storage period to study the simultaneous effect of plant essential oils and sprouted wheat powder. The essential oils used included tarragon and thyme with different proportions and at three levels (400, 1200, 2000 microliters per liter of yogurt). Yogurt physicochemical tests such as acidity and water holding capacity, hedonic sensory test, rheology test (apparent viscosity) and microbial count tests were conducted to check the viability of starter bacteria in yogurt during the 14-day storage period. Based on the results obtained from the analysis of variance of the tested samples, the concentration of essential oil significantly (p<0.05) reduced the acidity and viability of starter bacteria of the product, but it had not a significant effect on the viscosity the sensory characteristics. In this regard, thyme and wheat germ powder showed a negative and unfavorable effect, especially in high concentrations.

The aim of the present study was to optimization of enriched yogurt with chia seed oil and mucilage. This purpose was done with the aim of maximizing omega-3 level and minimizing changes in physical and chemical properties (pH, titrate acidity, syneresis, dry matter, peroxide values and color changes) compared to the control sample. First, in order to increase the oxidative stability, chia seed oil was encapsulated with sodium alginate and chia seed mucilage using emulsification/ internal gelation method. The physical characteristics results showed that the enrichment caused a decrease in the syneresis, an increase in the water holding capacity and viscosity. Then, yogurt was enriched and optimized with free and encapsulated chia seed oil (0 to 4%) and chia seed mucilage (0 to 0.25%). The sample without chia seed mucilage and oil used as a control sample. The results of scanning electron microscopy images showed that the successful alginate-sodium-mucilage microfiber coating of chia seeds has been made with a uniform structure. Yogurt contained 3.41% encapsulated chia seed oil and 0.213% chia seed mucilage was selected as an optimum treatment. The results showed that the number of starter bacteria of optimum sample were not significantly different from the control (p˃0.05). The texture of the yogurts was found to be viscoelastic. The flow behavior index in all samples was less than one, which indicates the non-Newtonian (pseudoplastic) behavior of the samples. Herschel Balky model had R2 and lowest RMSE in both samples, which indicates the suitability of this model to investigate the shear flow behavior in terms of shear velocity of samples.

The aim of the present study was to investigate the physicochemical and sensory properties of yogurt fortified with chia seed mucilage and oil, as a rich source of omega-3 fatty acids. For this purpose, mucilage (0.213%), free and encapsulated oil (3.41%) were added to the yogurt formulation. The prepared sampleswere compared in terms of some physicochemical (pH, titratable acidity, syneresis, dry matter, peroxide values and color attributes) and sensory properties with control (without oil and mucilage) during storage for 30 days at refrigerator temperature (4 °C).The results showed that the addition of mucilage and chia seed oil in a free and encapsulated forms caused a significant increase in water holding capacity (decrease in syneresis), acidity (decrease in pH) and dry matter during storage (p <0.05). In addition, the sample containing mucilage and encapsulated oil showed the lowest color difference (∆E) with the control. Furthermore, this sample showed an increase in whiteness index (WI) and a decrease in yellowness index (YI) compared to the sample containing free oil. The amount of peroxide value in the samples containing free and encapsulated oil after 30 days of storage was 3.19 and 1.16 meq / kg of oil, respectively, which indicates the protective effect of encapsulation process against oxidation of samples. Evaluation of sensory attributes showed that the addition of mucilage and encapsulated chia seed oil did not have significantly effects on the sensory properties of fortified yogurt samples (p˃0.05).

Yogurt production by milk fermentation is one of the oldest methods used by humans to convert milk into a product with longer shelf life and better sensory evaluation. This study aimed to investigate the characteristics of lactic acid bacteria isolated from yogurt in Zanjan rural areas and these strains ability in the diacetyl production. This study collected and transferred seven yogurt samples to the laboratory under standard conditions. Then the isolated strains were examined for morphology, several test such as catalase, hemolysis, antibiotic susceptibility, growth rate at different temperatures and yogurt sensory evaluation. The selected yogurt samples were examined for diacetyl production using SPME-GC after bwing stored at 5°C for 14 days. According to the results, the strains were divided into two groups based on morphology: bacilli and cocci. All strains were gram-positive and catalase negative. Most of the studied strains were antibiotic sensitive and shown negetive hemolysis. In the selected yogurt samples L1and N7, the diacetyl production was 5/6,10ppm respectively. The studied strains had high diacetyl production ability and also caused the butter aroma and the traditional Iranian yogurt memory, which leads to the production of yogurts that is more compatible with the Iranian people’s taste.

Prosopis farcta is a kind of subaltern silk flowers that due to its healthful effects and its use in the prevention of chronic diseases, this plant can be used as a natural and safe food additive. Main component and major constituent of this plant root is luteolin which is a flavonoid. The objective of this research was to determine the antioxidant and quality characteristics of set-yogurt samples containing aquatic extract of prosopis farcta root (T1: 0.01, T2: 0.03 and T3: 0.05%v/v) and luteolin (T4: 0.005 and T5: 0.01%v/v) stored at 4°С for 15 days. After storage, the starter bacteria count in yogur samples containing aquatic extract of prosopis farcta root was more than that in yogur samples containing luteolin and control (p< 0.01). DPPH radical scavenging activity increased upon increasing the content of the aquatic extract of prosopis farcta root and lutelin. In sensory evaluations, T1 gave the highest overall acceptability score (after control) among the experimental groups. The results of this study thereby demonstrate that aquatic extract of prosopis farcta root can be used to improve the antioxidant capacity of set-yogurt.

Due to the problems associated with fat intake in diets and on the other hand, the positive role of fat in dairy products such as yogurt, the use of fat substitutes such as starch will help maintain the ultimate quality. Chevil is one of the most important aromatic and medicinal plants in Iran, traditionally used in dairy products and ghee. The aim of this study was to evaluate the effect of corn starch (1, 1.5, 2 %) and F.angulata extract (0.1, 0.2, 0.3%) on some physicochemical characteristics including pH value, acidity, syneresis, viscosity and sensory parametrs color, flavor, consistency and overall acceptance of low-fat probiotic yogurt. The results showed that with increasing the corn starch content and F. angulata extract, pH value increased and decreased, respectively. Yogurt sample containing the highest corn starch (2%) and F.angulata extract (0.3%) had the highest pH value and lowest acidity, respectively. With increasing corn starch, syneresis decreased. The sample containing 1.5% corn starch had the highest viscosity. In contrast, samples containing more F.angulata extract had more syneresis and the lowest viscosity was related to yoghurt containing 0.2% F.angulata extract. Over time, the sensory scores of samples were declined. The yogurt sample containing 0.1% F.angulata extract showed the highest color score. The highest average flavor, consistency and overall acceptance scores during cold storage belonged to the sample containing 2% corn starch. As a conclusion, we can introduce sample containing 2% corn starch as a sample with superior quality properties.

Today, consumers increasingly believe in the effects of food on their health, and food should provide the necessary nutrients to prevent nutrition-related diseases as well as improve their physical and mental condition. Therefore, functional foods have been considered with the aim of improving the nutritional status, most of which is related to low calorie foods. Like many popular dairy products, yogurt consumption shows significant growth; The popularity of this product is primarily due to its high content of calcium, vitamins, minerals and low levels of fat, and secondly due to its health-promoting effect and inhibition of harmful bacteria. In the fresh mass of the pumpkin (Cucurbita moschata), total carotenoid content, a major contributory factor in the high nutritional value of pumpkins, ranges from 2 to 10 mg/100 g, the content of vitamins C and E accounting for 9–10 mg/100 g and 1.03–1.06 mg/100 g, respectively (Hosseini Ghaboos et al., 2016; Nawirska et al., 2009). Pumpkin fruit is also a valuable source of other vitamins, e.g., vitamin A, B6, K, thiamine, and riboflavin, as well as minerals, e.g., potassium, phosphorus, magnesium, iron and selenium (Mirhosseini et al., 2015; Obradović et al., 2015). Since pumpkin is a valuable micronutrients source, dried pumpkin could be processed into powder for foods to increase fibers, vitamin A and mineral contents. In addition, pumpkin powder can be used in bakery products because of its highly-desirable flavor, sweetness and deep yellow-orange color (Salehi, 2020).

At first, the pumpkin and spinach were dried and powdered in controlled conditions. Fresh pumpkins (Cucurbita moschata) were purchased from local market. The pumpkin slices with 5 mm thickness were dried in an oven (45°C). The dried pumpkins were milled, powdered and passed through a 125 mesh screen (Hosseini Ghaboos et al., 2016). To prepare yogurts containing pumpkin, skimmed milk was used form yogurt production factory with 1.5% fat. In fact, milk that was homogenized with a homogenizer (at a temperature of 70-60 ° C and a pressure of 150-160 bar) and by a pasteurizer (temperature at 92 ° C for 5 minutes) was pasteurized in the required amount in 5 liter containers. The starter culture (2% at 42°C) and squash powders (0, 2.5, 5 and 7.5%) were added to the milk. Then they were filled and closed. Approximately 100 samples were prepared at each time. Then, incubation was performed until the sample acidity reached 65°Dornic. For this purpose, the acidity of the sample was measured every 5 minutes at the end of the predicted fermentation time (experimentally). The used cold-room was an industrial cell greenhouse. The samples were placed in such a way that all the samples were on the same level and position in the greenhouse, which is very important for the uniform heating of the samples. After incubation, the samples were refrigerated at 4°C. Viscosity was measured using a viscometer with an LV64 spindle at a constant shear rate of 40 rpm and a temperature of 8°C. For this purpose, 250 ml of the sample was poured into a 250 ml glass beaker and stirred with a plastic spoon for 20 seconds. After turning on the device, and 30 seconds, the viscosity in centipoises was reported. Acidity was measured every 30 minutes to measure the fermentation time since the samples were incubated. When the acidity reached 70 degrees Dornic, the acidity was measured once until the acidity reached 80 degrees of Dornic. For yogurt, 10 g of the sample was titrated in the presence of phenolphthalein using 0.1 normal NaOH and the result was expressed based on °Dornic degree.

In this study, pumpkin powder in the amount of 0, 2.5, 5 and 7.5% in the formulation of 1.5% fat yoghurt was used and its chemical and rheological properties were studied for 20 days of storage. The results showed that the highest rate of syneresis (41.68%) was related to the interactions of the control sample with a shelf life of 20 days. The highest viscosity (3194 cp) was related to 7.5% pumpkin powder sample. The highest pH (4.39) was related to pumpkin powder 5%. The results also showed that the highest amount of acidity (74 °Dornic) was related to the control sample. The highest amount of total phenol (10 mg/g) and antioxidant activity (75%) was related to pumpkin powder 7.5%. The results showed that by adding 2.5% pumpkin powder to the yoghurt, the gel strength of sample was decreased and with increasing concentration up to 7.5%, its gel strength was increased but it is still less than the control sample. The results of comparing the means, the interaction effects of shelf life and pumpkin powder show that the highest rate of syneresis (41.68%) was related to the interaction effects of the control sample with a shelf life of 20 days. The results also showed that the lowest amount (39.98%) was related to the interaction effects of 5% pumpkin powder at a shelf life of 1 day, which was statistically 7.5% with a pumpkin powder at a shelf life of 1 day and pumpkin powder 5 and 5. 7.7% had no significant difference in shelf life of 12 and 20 days. According to the results of comparing the means, the highest viscosity (3173 cp) was related to the shelf life of 20 days and the lowest (3170 cp) was related to the first day of shelf life, which is statistically different from days 7 and 12. Based on the results of analysis of variance, the data showed that the effect of different levels of pumpkin powder and shelf life in terms of total phenol in yogurt showed a significant difference (P<0.05). As the results of comparing the means shows the highest amount of total phenol (10 mg/g) was related to pumpkin powder 7.5% and the lowest amount (8 mg/g) was related to pumpkin powder was at 0%.

In general, adding pumpkin powder to yogurt formulation can reduce the syneresis of the product and also increase its nutritional value.

The tasty yogurt is dairy formulation for which fruits and vegetables and various extracts are used in preparation process. In the present study, Ginger extract (Zingiber Officinale) was used in yogurt formulation in different quantities (2, 4, 6 and 8%) and inhibitory function of free radicals, phenol compounds as well as qualitative tests of product (pH, acidity, watering amount and viscosity) were evaluated after storing yogurt for 1, 10 and 20 days. The results illustrated that ginger extract caused water-soluble phenol compounds and their antioxidant function to become more than in simple yogurt during 10 days storage so that after 10 days the highest antioxidant activity belonged to yogurt including 6 and 8% of ginger extract. The lowest watering amount (water formation) was observed in yogurt including 8% ginger extract and it significantly differed from other samples (P>0.05). The pH loss increased further in yogurt with rising percentage of extract and also increasing storage period. Moreover, adding ginger extract to yogurt reduced viscosity, but there was no significant impact on acidity level of product during storage time (P<0.05).

Gamma aminobutyric acid (GABA) is a bioactive molecule with various physiological functions in the body that by inhibiting neuronal stimulation and the Prevent of delivery messages containing stressful compounds cause relaxation and has an effective role in the treatment of various diseases. Therefore, the aim of this study was to investigate the effect of two independent variables including pH (4-4.6), glutamic acid (300-600 ppm) on survival and GABA production by Lactobacillus brevis and general acceptance of yogurt. According to the results, with increasing pH and glutamic acid, the survival of probiotic bacteria, the amount of produced GABA and general acceptance significantly (p≤0.05) increased. Simultaneous optimization results (viability of Lactobacillus brevis, GABA content and general acceptance) showed the maximum survival rate (7.7278 log cfu/g), GABA content (342.9444 ppm) and general acceptability score (4.8367) after 28 days of storage, with 98.406% desirability in probiotic yogurt inoculated with Lactobacillus brevis containing 600 ppm glutamic acid and pH 4.60 was observed. The results showed that by using GABA producing probiotic bacteria in yogurt formulation, probiotic yogurt can be produced with desirable nutritional properties and take a positive step towards producing functional products and promoting consumer health.

Yogurt is one of the widespread dairy products, which is especially important in people's diets due to its high nutritional value and health-promoting effect. In this study, the physicochemical, quality, sensory, and microbial characteristics of yogurt containing sesame oil (1, 2, and 3%) after homogenization at two pressures of 100 and 200 bar, for 21 days storage was investigated. The samples with sesame oil had higher pH and this value increased with increasing homogenization pressure. During storage, acidity of all yogurt samples increased. Moreover, peroxide value of yogurt increased and this value was higher in sesame oil samples. Syneresis was higher in yogurts with sesame oil, but this value decreased with increasing oil especially in yogurt containing milk fat. Power law was fitted appropriately by experimental data of rheological properties. Sesame oil addition resulted in no significant effect in hardness value of samples in comparison with milk fat. The lightness of yogurts showed that only the sample contained 3% sesame oil and treated at 100 bar pressures had significant difference with other samples (P<0.05). Microbial characteristics of samples were in accordance with institute of standards of Iran. Although, sensory evaluation of samples showed that yogurt containing sesame oil had better texture than yogurt containing milk fat; however, taste and mouthfeel of them showed lower scores. Sesame oil addition caused reducing overall acceptability of yogurts that may be related to the applying of oil without deodorization.

One of the most important factors in producing yogurt is choosing the right starter. Native isolates of any country are among the genetic resources of that country, which play a major role in the production and development of the organoleptic properties of fermented products. Therefore, it seems necessary to study the industrial applications of native isolates. In this study, the production of yogurt was investigated by using native starter isolates from traditional Khorasan yogurts and its comparison with yogurts produced with two types of commercial starters.  

Six strains of Streptococcus thermophilus and three strains of Lactobacillus delbrueckii subsp. Bulgaricus isolated from traditional Khorasan yogurts were selected. The proteolytic activity of Streptococcus thermophilus strains was determined according to the method of Erkus et al(2012) and the proteolytic activity of Lactobacillus delbrueckii subsp. Bulgaricus was determined according to the method of Nespolo et al.(2010). Milk acidification activity byall examined strains was evaluated according to the method of Erkus et al.(2012). The production property of gamma-aminobutyric acid of native isolates was also evaluated using the method of Lacroix et al. (2013). Yogurt was produced using commercial starters and native isolates. Acidity and pH were measured according to Iranian National Standard No. 2852. Synersis of yogurt samples was measured using centrifugation according to Çelik (2007) method. In order to measure textural properties, a combination of backward extrusion techniques and Texture Profile Analysis (TPA) was used (Yang et al, 2010). Sensory characteristics of yogurt samples were evaluated by 20 panelists using five-point hedonic scale. This study was conducted based on factorial experiment using a completely randomized design. Statistical analysis of data was performed using Minitab Statistical Software (version 17) and ANOVA. Comparison of means was performed using Tukey’s test at the significant level (p < 0.05).  

The results of proteolytic activity of Lactobacillus delbrueckii subsp. Bulgaricus showed that the L3 code was weaker than the other two strains. All Streptococcus thermophilus strains were positive protease. All Streptococcus thermophilus strains of the study decreased the pH of the milk to 4.6 in less than five hours, and Streptococcus thermophilus strain S6 code, as the fastest acid producer, decreased the pH of the milk to 4.6within 3 and half hours (Figure 2). The results of GABA production showed that among the streptococcus thermophilus strains, S1, S5 and S6 codes had distinct blue discoloration. Among the Lactobacillus strains, except the L3 strain, two other strains produced green color. Of the 18 samples of the yoghurt, S5L2 and S2L2 samples showed the highest decrease in pH and increased in acidity compared to other samples after being stored refrigerated overnight (P <0.05). The other samples had the same pH and acidity changes as the control samples after overnight refrigeration. The results show the ability of yogurt producion by native starters to compete with those produced by commercial starters in terms of technological characteristics. Thus, samples with codes S2L2, S3L1, S3L2, and S1L1 showed less Synersis of   yogurt than commercial starters. This decrease in the Synersis of yogurt might due to the possibility of exopolysaccharide production by these strains. Textural characteristics of yogurt samples were the hardness of the samples in the range of 3 to 4 N, which was significantly different (P <0.05). The lowest hardness was observed for the S3L3, which can be attributed to the poor proteolytic activity of the strain. L3, S6L2, S3L2 and S2L2 had the highest   hardness compared to other compounds and control samples (P <0.05). This differences in the hardness of the samples can be attributed to the possible production of some metabolites by the strains. There was no statistically significant difference in the adhesion properties of the samples (p <0.05). Considering the sensory evaluation scores, it was found that in all respects, S3L3 had the lowest score among the other samples (P <0.05). This was in good correlation with the results of the textural properties of the test. Therefore, this compound was eliminated compared to the control samples. Finally, considering the proteolytic behavior of the strains and the ability to produce acid and GABA, as well as the sensory, rheological and physicochemical properties of 18 samples in comparison to the two control samples, Streptococcus thermophilus strains with codes S4, S2, S5, S1, S6, and Lactobacillus delbrueckii subsp. Bulgaricus strains with codes L1 and L2 have the potential to be used as commercial starters in the form of compounds S1L1, S2L2, S5L1, S6L2, S4L2.