تولید بامیه با استفاده از پوشش پروتئین آب‌پنیر و بررسی ویژگی‌های کیفی آن طی نگهداری

Introduction: Bamieh is one of the traditional confectionaries that are produced by deep frying, and it has high oil content. Coating of foods with edible coatings and films has been suggested to reduce oil absorption during the frying process. Films and edible coatings are natural polymers made from agricultural materials. Edible films are either formed as coatings or embedded in food components, limiting the migration of moisture, lipids, and color between food components to improve the quality of non-homogenous foods (Khawaldia et al., 2004). Edible coating is a surface polymer coating that reduces surface porosity and impedes the entry of oil into the food (Ziaeifar et al., 2008). Whey protein based films and coatings have been noticed in recent years because, in addition to being biodegradable, they utilize whey as a major by-product of cheese industry.   Moreover, they have excellent oxygen and water vapor barrier properties, and consequently can be used in food packaging. The aim of this study was to investigate the effect of whey protein based coating on qualitative characteristics of Bamieh during storage. In this research, coating of Bamieh coating using whey protein solution (0.25, 0.5 and 0.75% w/w) was studied in order to reduce the oil uptake of the product.
Material and methods: For preparing of Bamieh dogh, the raw materials, including flour and water, were mixed well with a small amount of vanilla, then the dough was spread on the table and cooled to ambient temperature. Then, it was poured into the mixer and the eggs and saffron were added and stirred well in the mixer to obtain a smooth and uniform dough. To prepare colloidal suspensions, the required concentrations of whey protein (80% purity produced by Agri Mark, USA) and sorbitol (70% purity Cargill, USA) were mixed with water and heated to 90℃. It was completely homogenized to give a transparent solution. The solution was cooled to ambient temperature and the Bamieh samples were coated by immersing in the solution (Garcia et al., 2007). Three types of coating frmulations with different percentages of whey protein were prepared (0.25, 0.5 and 0.75%) with a constant ratio of sorbitol (0.5%). Qualitative characteristics of Bamieh samples including oil uptake (by Soxhlet method, moisture (according to Iranian National Standard Procedure No. 2705), acidity (by titration method with 0.1N sodium hydroxide), peroxide value (According to AOAC method No. 965/33) and sensory evaluation of samples were investigated. All of analysis were performed with 3 replications and the results were reported as mean of 3 replicates.
 Results and discussion: Analysis of oil uptake showed that, control samples had the highest oil uptake. By increasing the percentage of whey protein in the coating formulation, the oil uptake of Bamieh significantly decreased (P <0.05). Bamieh coated with 0.25%, 0.5% and 0.75% whey protein showed 10%, 20% and 31% lower oil uptake, respectively. This decrease in oil uptake in coated samples is due to the use of edible coating. Hydrocolloid coatings are able to physically prevent the penetration of oil into the nutrient due to the film-forming properties during heating. In the frying process due to the evaporation of moisture in the food, the oil replaces with water molecules. Thereby reducing the moisture content and increasing the oil content (Kester et al., 1986). Albert and Mittal (2002) showed that the use of hydrocolloids such as gelatin, gellan gum, capacaragine, methylcellulose, pectin, and whey protein isolate reduced the oil uptake in fried cereal products. The use of a plasticizer in the coating formulation contributes to the uniformity and enhances the coating's inhibitory property, reducing oil absorption and moisture outflow (Garcia et al. 2002). The results of moisture content analysis showed that Bamieh samples coated with different percentages of whey protein (0.25, 0.5 and 0.75%), had decreasing trend of moisture content during storage time on different days (1, 10, 20 and 30). During storage time, the acidity of all samples increased, which was higher in the coated samples compared to the control. However, the acidity of all samples was lower than the standard limit (0.2% maximum). The increased acidity is due to the hydrolysis of glycerol and the release of fatty acids that occur during the storage of edible oils and fats and oil-containing foods. The amount of hydrolysis depends on various factors such as the amount of food product moisture, the amount of oil, the storage temperature and the type of oil (Azadmard Damirchi, 1391). Analysis of peroxide values shoed that, the peroxide value of control and treated samples increased with different percentages of whey protein probably due to the oxidation of the oil in the samples during storage. All samples showed the highest peroxide value on day 30. Coating did not have significant effect on delaying oxidation. By coating the Bamieh with different percentages of coatings, the peroxide content in all samples were acceptable.
Comparing of the scores obtained for different characteristics of appearance, color, taste, texture and overall acceptance between different treatments showed that samples coated with different percentages of whey protein had better appearance, color, taste and texture compared to control. As the percentage of whey protein in the coating increased, the appearance, color, texture and overall acceptability increased. The samples coated with 0.5% and 0.75% whey protein showed higher overall acceptability score compared to other treatments. Applying the coating before frying creates a uniform layer around the food and causes the fried products to reduce their crispness by preventing moisture transferred into the shell or absorbing moisture from the food (Jorjani and Hamrahi, 2015).
Conclusion: Coating of Bamieh with whey protein concentrate edible reduced the absorption of oil uptake but had no effect on the reduction of the final product acidity and peroxide value. Coating of Bamieh with whey protein based coating at a concentration of 0.5 and 0.75% produces a low oil content and desirable sensory properties in terms of appearance, color, taste and texture. SoWhey protein coatings can be used as an edible coating to reduce oil absorption in Bamieh.