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:: Volume 2, Issue 2 (9-2007) ::
2007, 2(2): 15-25 Back to browse issues page
Effect of Individual and Combined Addition of Salep, Tragacantin and Guar Gums on the Stabilisation of Iranian Doogh
S Foroughinaia, S Abbasi *, Z Hamidi Esfahani
Abstract:   (21686 Views)
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.
Keywords: Doogh, Serum separation, Hydrocolloids, Mechanical operations, Gums, Rheological properties.
Full-Text [PDF 346 kb]   (3852 Downloads)    
English: Research | Subject: Food Science
Received: 2008/07/1 | Published: 2007/09/15
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Foroughinaia S, Abbasi S, Hamidi Esfahani Z. Effect of Individual and Combined Addition of Salep, Tragacantin and Guar Gums on the Stabilisation of Iranian Doogh . Iranian Journal of Nutrition Sciences & Food Technology. 2007; 2 (2) :15-25
URL: http://nsft.sbmu.ac.ir/article-1-37-en.html

Volume 2, Issue 2 (9-2007) Back to browse issues page
Iranian Journal of  Nutrition Sciences & Food  Technology
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