Marzieh Salami; Massoumeh Mehraban Sangatash; Ahmad Ehtiati
Abstract
Introduction: Yogurt is one of the most popular dairy products, which has numerous health effects on human body. Dietary fiber consumption is highly recommended. Fibers are highly hydrophilic and absorb water into the digestive track, increase the volume of food and thereby facilitating excretion. These ...
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Introduction: Yogurt is one of the most popular dairy products, which has numerous health effects on human body. Dietary fiber consumption is highly recommended. Fibers are highly hydrophilic and absorb water into the digestive track, increase the volume of food and thereby facilitating excretion. These are some health benefits of these compounds. Consumption of fiber-containing yogurt can be helpful for people who suffer from cardiovascular diseases, hypertension, diabetes and obesity. Zucchini, as a vegetable, is a source of fibers and due to its health-promoting effects, can be used in dairy products. The aim of this study is to evaluate the effects of different levels of dried zucchini on stirred yogurt during storage. Materials and Methods: The raw materials for the production of the functional yogurt were zucchini, milk, skim milk powder, whey powder, hydrocolloids stabilizer compound and starter culture. Fresh zucchini was hot-air dried at 70 °C for 7 hours. Two forms of the dried zucchini (powder and granule) were added to fresh yogurt at levels of 0.7, 1.4, and 2%. The samples were then tested on days 1, 5, 10 and 15 for acidity (titration method), pH, texture stiffness (back extrusion), syneresis, color (using image processing) and sensory properties, including color, taste, aroma, consistency, mouthfeel and overall acceptance. The experiments were triplicated and analysis of variance was performed using Minitab software at 95% confidence interval. For the significant variables, the means were compared using LSD method. Graphs were drawn using MS-Excel. Results and Discussion: The effects of zucchini form and level of addition, storage time and interaction of these variables were significant (P<0.05) on the titratable acidity, pH and firmness. Over time, pH decreased and acidity increased, which was related to the starter activity and acid production. Due to the use of stabilizer and whey protein, all samples showed no syneresis. The firmness of the samples containing zucchini powder was higher than that of the granule- (P<0.05). This might be related to the homogeneous structure of zucchini fiber, which increased water absorption regarding its lower particle size. Firmness increased from day one to day five, due to the high water absorption of hydrocolloids that bind to free water present in the yogurt structure. The presence of milk proteins and whey protein concentrate in the yogurt formula enhanced crosslinking in the particle gel network, which resulted in a stronger gel structure. During longer storage, firmness decreased from day 5 to day 10, probably was due to the increased pH, which affects the proteins and polysaccharides interaction. The effects of the form and level of zucchini and the interaction between these variables were significant (p <0.05) on the changes in L*, a*, and b*. The L* and a* values which were higher in the samples containing zucchini granules than in the zucchini powder, most probably due to the smaller particle sizes of the powder compared with the granules, causing the number of the powder particles per unit volume to be larger and the powder-containing samples to become darker. In terms of the level of addition, L* increased as the zucchini level rose to 1.4% and then declined to 2%. The sensory properties of all samples were significantly affected by the storage time (P<0.05). With increase in the storage time, all the sensory scores increased. The highest overall acceptance score belonged to the yogurt sample containing 1.4% granule on the 10th day of storage. Overall, zucchini is a good candidate for yogurt fortification. This incorporation results in a greenish yogurt with more health functionalities. The highest overall acceptance score was obtained for the yogurt containing 1.4% zucchini granule on the 10th day of storage (best consumption date) and the results showed acceptable firmness for this sample.
