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Background and objectives: Annual production of Doogh (a yoghurt drink) in Iran exceeds 120000 metric tons. Iran is probably a leading producer and consumer of this type of dairy-based product in the world. Separation of Doogh into 2 phases (serum separation) during storage is a major problem which affects its market share. The present study was undertaken to investigate the stabilizing effects of salep and tragantin gums (as local gums) and guar gum (as a commercial gum), added individually or in combination, to Doogh (containing 40% yoghurt). Materials and methods: Various gums (salep, tragacantin and guar), individually (concentrations 0.1–0.5%) and in combination (at ratios 50:50, 20:80 and 80:20) over a range of 0.1 to 0.2%, were added to samples of Doogh (composed of 40% stirred yoghurt, 59.3% tap water, 0.7% NaCl), and their physical stability (serum separation percent) were monitored over a period of 30 days at various storage temperatures (5 and 25 C). In addition, some mechanical parameters, namely homogenization (up to 200 bars) and agitation speed (9000 and 11000 rpm for up to 2 min) of the samples, as well as their biphasic separation and rheological properties were determined. Sensory evaluation was also performed using semi-trained panelists and the 9-point hedonic scale procedure. Results: Our findings revealed that the individual gums could significantly reduce phase separation during storage (p <0.01). Gum tragacantin was the most effective, resulting in full stability of Doogh at a concentration of about 0.3%. Generally speaking, increasing the concentration of gums caused changes in the rheological behavior of the Doogh samples. Samples containing salep, tragacantin and guar gums showed a pseudo-plastic flow behavior, whereas in their absence, the Dooghs behaved as a Newtonian fluid. Mechanical operations, particularly agitation speed, led to a considerable reduction in the apparent viscosity of Doogh and, consequently, a significant increase in serum biphasic separation (p <0.01). In the organoleptic tests, the Doogh samples containing tragacantin and tragacantin-guar combinations received the highest scores. Conclusions: It is probable that the stabilizing effects of the gums, being non-absorbent hydrocolloids, were due to their viscosity-raising and water-holding properties. Moreover, mechanical operations (stirring and homogenization) could have disrupted the colloidal structure, leading to a decrease in viscosity and an increase in the biphasic separation.

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Background and objectives: Doogh is a kind of Iranian fermented dairy-based drink produced by adding water and salt to yoghurt. The major problem of this product is serum separation during storage, because of its low pH and aggregation of caseins. In the present study, the efficiency of some hydrocolloids in preventing serum separation as well as the stabilization mechanism of gum tragacanth–a local gum–were investigated. Materials and methods: The effects of high-methoxyl pectin, tragacanth, and locust bean gum at different concentrations, individually and in combined forms, tragacanthin, and soybean soluble polysaccharides type M, on the stability of sour Doogh were investigated. In addition, the influence of gum tragacanth and locust bean gum on the stability of prebiotic Doogh (containing inulin) was also studied. In each case the duration of the study was 30 days. In order to elucidate the stabilization mechanism of gum tragacanth, the rheological properties, zeta potential, and microstructural characteristics of the stabilized Doogh samples were measured. Results: According to our findings, tragacanthin, tragacanth and locust bean gum could inhibit serum separation for 30 days at a concentration of 0.1, 0.2 and 0.3%, respectively, while type M soybean soluble polysaccharides caused the stabilization at a concentration of 0.6% only for 6 days. Furthermore, combinations of gum tragacanth and locust bean gum were also effective in fully stabilizing Doogh (at a concentration of 0.15% and ratios of 80:20 and 50:50). Inulin was not effective in stabilizing the sour Doogh samples. However, tragacanth and locust bean gums inhibited serum separation in prebiotic Doogh. Based on our findings, the most suitable rheological model for the control samples and the samples containing hydrocolloids were the Newtonian and Power law, respectively. Conclusions: Based on the results of this study, tragacanthin (the water-soluble part of gum tragacanth) seems to have a major role in stabilizing Doogh, probably by being adsorbed onto caseins (via electrostatic and steric repulsion). On the other hand, bassorin (the water-insoluble part of gum tragacanth) may help stabilization by increasing viscosity. Therefore, gum tragacanth could be strongly recommended to be used as an adsorbing hydrocolloid in sour Doogh to inhibit serum separation.

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Background and Objectives: Probiotic dairy products with their valuable nutritional and therapeutic properties, whose positive effects on human health have been confirmed, present one of the most controversial issues globally in the current domains of industry, nutrition and medicine. In order to have an upward trend in the promotion of the production and consumption of such products, it is essential for them to have desirable sensory and textural characteristics and preserve the probiotic strain at the defined level during shelf life. Doogh, an Iranian milk drink, is a popular fermented drink in Iran, the probiotic content of which can promote community health. The objective of this study was to determine the effects of Lactobacillus acidophilus La-5, as the probiotic bacterium, on microbial characteristics, post-acidification rate, and overall sensory acceptability of Doogh. Materials and Methods: In this research, in addition to commercial yoghurt culture (YF-3331), Lactobacillus acidophilus La-5, a probiotic bacterium, was used to produce probiotic Doogh, and alteration of probiotic bacterium and yoghurt culture bacteria (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus), acidification, phase separation, and its sensory acceptability were evaluated during its twenty one-day storage at 4 °C and compared with the blank produced without probiotic strain. Results: The bacterial counts of the three bacteria reduced during cold storage. However, the probiotic bacteria, having the reduction of 0.93 log cycle/ml, could stand above the optimum level during the given time. Comparison between the probiotic Doogh and the blank showed that this bacterium could enhance the bacterial population reduction rate, reduce post- acidification, and improve the overall acceptability during storage. The addition of L. acidophilus did not have any significant effect on the textural stability of the probiotic sample, as compared to the blank. The percentage phase-separation of the 2 samples was high on days 1 to 7 of storage and then slowed down. Conclusion: The results demonstrated that Lactobacillus acidophilus La-5, as a probiotic bacterial strain, can be used in the production of Doogh with a pH=4.30, a salt content of 0.8 % (w/v) and a total solid content=7.4 % and it could enhance the yoghurt bacterial population reduction during storage. Thus, the probiotic Doogh produced was assessed as desirable with regard to the L. acidophilus viability, post-acidification reduction, overall sensory acceptability, and textural stability.

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Background and Objective: Doogh is an Iranian traditional beverage based on yoghurt. In this product, serum separation occurs during storage due to its low pH. In recent years, studies have been conducted on the stabilization of doogh using hydrocolloids. The objective of this study was to compare the effects of different species of gum tragacanth (Astragalus gossypinus, Astragalus rahensis, and Astragalus fluccosus) on the stabilization and rheological properties of this typical Iranian dairy drink during storage. Materials and Methods: Gum solutions were added to Doogh samples prepared from yoghurt made with skim milk. Phase separation was measured using graduated cylinders during storage (30 days), and particle size distribution at ambient temperature was determined by laser diffractometery. Furthermore, steady and unsteady rheological tests were carried out using a controlled shear rate rheometer (CSR) at 3°C. Finally, sensory analysis was performed with 30 panelists familiar with the product, using a 5-point hedonic scale. Results: In the samples containing 0.3% (w/w) A. gossypinus no phase separation occurred during the 30-day period. The data on particle size distribution indicated that addition of gum tragacanth resulted in a reduction in the size of aggregated particles, specially in the sample containing A. gossypinus. The apparent viscosity in this sample was higher than in the other samples. Also, its sensitivity to frequency (range = 0.01-10 Hz) was much less, which is very important from an industrial point of view. In addition, based on the sensory evaluation data, the sample containing A. gossypinus was the most acceptable product. Conclusion: The higher content of uronic acid and insoluble part of A. gossypinus can be the most probable reasons for the stabilized dispersion caused by A. gossypinus as compared to that caused by the other two species at the same concentration (0.3% w/w) in doogh. Keywords: Fat-free Doogh, Stabilization, Hydrocolloids, Rheology, Gum tragacanth

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Background and Objective: Milk and dairy products are generally recognized as healthful foodstuffs. Their negligible content of polyunsaturated fatty acids (PUFAs) has prompted investigators to consider fortifying them with long chain PUFAs, but the main challenge is the high susceptibility of PUFAs to oxidation and rancidity. Therefore, in the present study the possibility of using long chain PUFAs to fortify Doogh (a traditional Iranian yoghurt-based beverage), as a functional dairy product, as well as the effect of different factors on the physical stability and peroxide value of the fortified Doogh during storage, were determined. Materials and Methods: ω-3-Fatty acid-fortified Doogh was prepared using yogurt, water, salt, the soluble phase of gum tragacanth, and crude rapeseed, soy bean, and fish oil. The fortified Dooghs (a mixture of oil and yoghurt or of Doogh and oil) were homogenised using ultrasound at different amplitudes and durations in order to find the optimum processing conditions (amplitudes and duration). Moreover, effects of several factors (heat treatment, storage temperature, intensity and duration of sonication, and oil content) on the physical stability and peroxide value of the fortified Dooghs during storage (35 days) at 2 temperatures (5 and 22˚C) were determined. Results: The findings showed that the preparation method of fortified Doogh had significant effects on its homogenization extent and physical stability. Furthermore, during storage the peroxide value of the samples increased, particularly at the higher temperatures, while they were quite stable physically. Conclusion: It may be concluded that ultrasound treatment can homogenize and stabilize ω-3-fatty acid-fortified Doogh, with no undesirable effect on peroxide value during storage at refrigeration temperatures. Keywords: Fortification, ω-3 fatty acids, Ultrasound, Doogh, Stability

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Backgrounds and Objective:Viability of probioticmicroorganisms in the final product is the most important qualitative parameter. These organisms show poor viability incommercial products especially in fermented dairy products.The aim of this study was to assess the interactive effects of two Iranian native strains of Bifidobacterium (Bifidobacteriumanimlis spp. lactisPTCC 1631 and Bifidobacteriumbifidum PTCC 1644), sequential inoculation (inoculation of probiotics before or after fermentation) and final pH of fermentation (pH4.5or 4.2) on biochemical, microbiological, and sensory characteristics of Doogh. Materials and methods:The Bifidobacterium strains used in the study included Bifidobacteriumanimlis spp. lactisPTCC1631 (Persian Type Culture Collection-Iran) and Bifidobacteriumbifidum PTCC 1644obtained from microbial culture stock of ‘Department of Drug and Food Control’ (Tehran University Culture Collection Center, Tehran, Iran).Doogh was prepared with yogurt starter culture (YF-3331)andBifidobacterium strains.pH, titrable acidity, redox potential, fermentation time, and viability of probiotic organisms were analyzed during fermentation and over the refrigerated storage period (21 days at 5°C).Also, the sensory attributes of treatments were determined at the end of fermentation.Experiments were performed in triplicate and the comparison of the means was done using ANOVA test in significance level of 0.05 (p<0.05) from Minitab software. Results:The longest fermentation time was observed in treatmentsthat bifidobacteria was cultured with yogurt starter bacteria and incubated at 40°C until final pH4.2. The greatest survival of Bifidobacterium strains was determined in BlY-40-4.5 treatment (whenB.animlis spp.LactisPTCC 1631 strain was co-cultured with traditional yogurt starter bacteria at incubation temperature of 40°C and final pH4.5)in which B. animalis spp. lactis PTCC 1631 survived 8.69 log cfumL-1. The viability of B. animalis spp. lactis PTCC 1631 was significantly more than B. bifidum PTCC 1644. Alsofinal pH 4.5 rather than to pH 4.2 led toincrease the viability of bifidobacteria strainsin similar probiotic organisms. Conclusion:The variables including the type of bifidobacterium species, final pH, and sequence of probiotic inoculation significantly affected viability ofbifidobacterium species at the end of fermentation and during refrigerated storage.In general, the count of two species of Iranian native bifidobacteria in all treatments at the end of fermentation and throughout the storage time was more than 6.00 log cfu mL-1 per milliliter of Doogh. Therefore, the survival of this strain considerably was higher than the commercial probiotic starter cultures. Keywords:Bifidobacteriumanimalis, Bifidobacteriumbifidum, Probiotic, Doogh, Viability

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Background and Objective: Milk and dairy products are generally recognized as healthful foodstuffs. Their negligible content of polyunsaturated fatty acids (PUFAs) has prompted investigators to consider fortifying them with long chain PUFAs, but the main challenge is the high susceptibility of PUFAs to oxidation and rancidity. Therefore, in the present study the possibility of using long chain PUFAs to fortify Doogh (a traditional Iranian yoghurt-based beverage), as a functional dairy product, as well as the effect of different factors on the physical stability and peroxide value of the fortified Doogh during storage, were determined. Materials and Methods: ω-3-Fatty acid-fortified Doogh was prepared using yogurt, water, salt, the soluble phase of gum tragacanth, and crude rapeseed, soy bean, and fish oil. The fortified Dooghs (a mixture of oil and yoghurt or of Doogh and oil) were homogenised using ultrasound at different amplitudes and durations in order to find the optimum processing conditions (amplitudes and duration). Moreover, effects of several factors (heat treatment, storage temperature, intensity and duration of sonication, and oil content) on the physical stability and peroxide value of the fortified Dooghs during storage (35 days) at 2 temperatures (5 and 22˚C) were determined. Results: The findings showed that the preparation method of fortified Doogh had significant effects on its homogenization extent and physical stability. Furthermore, during storage the peroxide value of the samples increased, particularly at the higher temperatures, while they were quite stable physically. Conclusion: It may be concluded that ultrasound treatment can homogenize and stabilize ω-3-fatty acid-fortified Doogh, with no undesirable effect on peroxide value during storage at refrigeration temperatures. Keywords: Fortification, ω-3 fatty acids, Ultrasound, Doogh, Stability

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Background and Objectives: Recently, the demand for consumption of functional foods is growing rapidly due to the increased awareness of the consumers from the impact of these foods on health. Production of soy based probiotic Doogh will improve the functional potential of products. The aim of this study was to assess qualitative aspects of soy based probiotic Doogh. Materials and Methods: In this research, the effects of cow's milk to soy milk proportion (100:0, 75:25, 50:50, 25:75, 0:100) as well as the type of commercial culture composition (ABY-1, MY-720, YO-Mix-210) on biochemical, microbiological and sensory characteristics of probiotic soy-Doogh was investigated. pH, Titrable acidity and redox potential, lactic and acetic percentage as well as viability of probiotics and sensory properties of final product during fermentation and/or refrigerated storage were assessed. Results: results showed that the shortest fermentation time was observed in treatment with cow's milk to soy milk proportion of 50:50 and culture composition of ABY-1. The highest and lowest viable count of B. bifidum and L. acidophilus during 21 days of refrigerated storage were observed for the treatments with cow's milk to soy milk proportion of 25:75/ ABY-1 and 25:75/ MY-720, respectively. The influence of type of starter culture composition on sensory properties of final products was not significant, while the cow's milk to soy milk proportion 75:25 resulted in the most satisfactory sensory properties. Conclusion: Considering the results, the cow's milk to soy-milk proportion of 50:50 with any of the types of culture composition was selected as the best treatments from viability and sensory points of view. Keywords: Starter culture, Viability, probiotic soy-Doogh

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Background and Objective: Doogh is a fermented dairy product that is a national beverage in Iran. Considering the national importance of doogh and increased consumption in the population, the use of preservatives (sorbate and benzoate) to extend the shelf life of the product and reduce the microbial load should be controlled to guarantee the health of consumers. This study determined the amount of potassium sorbate and sodium benzoate in the doogh distributed in the city of Tehran. Materials and Methods: Factors affecting the potassium sorbate and sodium benzoate extraction from doogh (pH of the sample, the extraction solvent volume, amount of Carrez solution and speed of centrifuge) were optimized. Approximately 90 experiments were analyzed in the laboratory to optimize the effective parameters for extraction efficiency. Then 60 non-carbonated heated doogh samples were selected from the Tehran market during the summer season. The samples were analyzed using high performance liquid chromatography (HPLC) for 3 consecutive summer months after optimization. The data was analyzed with SPSS V.16.0. Results: The method proposed in this study was significantly less time-consuming than other techniques. It had the advantages such as acceptable accuracy, precision and elimination of interruptions in the samples. The results show there was no significant difference (p<0.05) between potassium sorbate and sodium benzoate in the samples supplied in Tehran during the summer. There were significant differences between samples (p>0.05) for potassium sorbate and the means of samples were not significantly different (p<0.05) for sodium benzoate. Samples 10 and 7 showed maximum potassium sorbate and sodium benzoate concentrations of 267.8 and 49.3 mg/kg, respectively. Samples 16 and 2 showed minimum concentration values of 8.2 and 4.6 mg/kg, respectively. Conclusion: Although there is a limited consumption rate for potassium sorbate and sodium benzoate in doogh, these preservatives are used in most doogh distributed in Tehran. The results of this study can be effective for standardization of a limited consumption rate for potassium sorbate and sodium benzoate in this product. Keywords: Potassium sorbate, Sodium benzoate, Doogh, High performance liquid chromatography

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study, the effects of probiotic strains (L. acidophilus, L. rhamnosus, L. casei and B. bifidum), inoculated probiotic population (7 and 9 log cfu/ml), physiology of probiotic bacteria and fermentation final pH (4.2 and 4.5) at four stages (respectively) on the reduction in 0.500 ppb of free aflatoxin M1 in Doogh during fermentation and refrigerated storage (5°C) were studied. Materials and Methods: Doogh milk with 4% of dry matter was made by reconstitution of skim milk powder. The mixture also contained 0.7% of sodium chloride and 0.500 ppb of aflatoxin M1. After heat treatment, treatments with different starter culture inoculations were prepared. The treatments were incubated until the determined final pH was reached. Immunoaffinity column and HPLC with fluorescence detector were used for extraction and measurement of free aflatoxin M1, respectively. Data were analyzed by SPSS software. Results: Treatment with L. acidophilus (AY-7-A-4.2) compared to other probiotic strains had highest reduction in free aflatoxin M1 during fermentation and refrigerated storage. L. acidophilus with inoculation of 9 log cfu/ml (AY-9-A-4.2) compared to 7 log cfu/ml (AY-7-A-4.2), had significantly more free aflatoxin M1 binding capacity.. However, AY-9-A-4.2 was not suitable treatment because of the strongly higher cost. Treatment containing 7 log cfu/ml dead (heat-killed) L. acidophilus (AY-7-D-4.2) significantly binded more free aflatoxin M1 than AY-7-A-4.2 treatment at the first day of storage. However, the live probiotics in AY-7-A-4.2 treatment were more effective in the reduction of free aflatoxin M1 at day 14 and 28 of storage. Treatment with higher fermentation final pH (AY-7-A-4.5) was more effective on free aflatoxin M1 binding than AY-7-A-4.2 at day 14 and 28 of storage. Conclusion: Live cells of L. acidophilus with inoculation of 7 log cfu/ml and final fermentation pH of 4.5 showed the highest free aflatoxin M1 binding capacity during refrigerated storage meanwhile, it was the best treatment from health and economic points of view. Keywords: Aflatoxin M1, Doogh, Physiology, Probiotic

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Background and Objectives: Sleep quality, which plays an important role in human physical and psychological well-being, can be affected by dietary intake. The present interventional study was conducted to investigate the effect of doogh (a traditional yogurt drink) consumption on improvement of sleep quality in university students with sleep disorders.
 Materials & Methods: This clinical trial was performed on 40 students residing at Ahvaz Jundishapur University of Medical Sciences in 2017. Participants with sleep disorders were identified through Pittsburgh Sleep Quality Index (PSQI). Then they were divided into two groups of intervention and control by random allocation. Participants in the intervention group received 300 mL of doogh one hour before bedtime for three weeks, and the control group was given 300 mL of mineral water instead. After intervention, all subjects filled in the PSQI questionnaire again.
Results: At the end of the intervention, subjective sleep quality, sleep duration and sleep efficiency improved in the intervention group significantly (p=0.013, p=0.039 and p=0.015, respectively). Sleep disturbances and sleep latency were also decreased significantly (p<0.001 and p=0.002, respectively).
Conclusion: It seems doogh consumption has a significant role in improving sleep quality and reducing sleep disorders in students. So it could be administrated for students with sleep disorders.