Investigation on effect of coating on the oil uptake during deep fat frying process of traditional sweet Pishmeh

Frying is a unit operation in which food is heated in oil to alter its eating quality. First reviews of frying performed on the principles of heat and mass transfer and oil uptake in foods, because during the frying process heat and mass transfer occurred between product and frying medium. In fact, the food loses moisture content and lost water will replace with oil. The moisture loss in the product causes rapid formation of the crust while the core remains soft and moist; therefore higher oil uptake occurred in the crust. There is an argument about the effect of frying on the sensory characteristics of foods, changes of nutritional value and health concerns in fried foods and methods applied to reduce oil content. Consumers prefer eating foods with lower oil content. One of the typical methods for reducing oil uptake in food commodities is using of coating before frying process. Edible coatings are known as a thin layer of edible polymers which is placed on the surface of the food. Application of edible coating decreases some destructive factors like the presence of various gases such as oxygen and carbon dioxide and humidity. Hydrocolloides are referred to a group of polysaccharides and proteins which create many features such as consistency in aqueous solutions, foams stability, emulsions, improve the sense of mouth and create a similar state of fatty and oily mode for products with lower content. In fact hydrocolloid coatings can reduce the excessive oil uptake due to their interesting thermogelling properties and at the same time they are invisible and have no negative influence on the sensory attributes of fried foodstuff. Even more, fried products have low fat content with improved nutritional values, higher crispiness and better palatability. Pishmeh is described as deep-fried dough pastry which is usually prepared by local producers of Turkmen (Iran). This product absorbed high oil content during frying process. This study was carried out to evaluate the effects of hydrocolloid coatings including Aloe Vera, Carboxymethyl cellulose (CMC) and Xanthan on the oil uptake of Pishmeh.
Hydrocholloid materials such as Aloe Vera, Carboxymethyl cellulose (CMC), Xanthan and complex of Xanthan-CMC were used. The gums were prepared at concentrations of 0.5 and 1% by dissolving in water at 70 ° C by stirring with a homogeneous mixer until a clear suspension was obtained. To extract the Aloe Vera gel, first, a thick epidermis (The shell) was separated from parenchyma using cutter. The parenchyma was immersed in a container of distilled water to lose bitter taste for 5 minand then parenchyma was taken out from water and transferred into a mixer (for 1 minute at 25 °C) and finally converted to a uniform colloidal solution. In the next step, the prepared dough samples were immersed in the colloidal suspensions for 1 min and the coated samples were placed on a mesh tray to remove the excess residuary coats. The samples were fried in sunflower oil at 170 °C for 6 min. The samples were then placed on a metal tray after frying to remove excess oil. After removing the oil and reaching the ambient temperature, physical and chemical tests were carried out on the sweet Pishmeh. The experiments included determination of moisture, fat content, measurement of coating parameters (such as coating ratio and frying efficiency) and color analysis.
The result showed that coating by hydrocholloid materials was led to decrease water loss in comparison to non-coated sample (control) during frying. Furthermore, oil uptake of coated samples was lower than control sample (p