Effect of storage time on physicochemical properties of extruded snacks containing pomegranate powder

In the past years, snack consuming in all age groups, special children have increased due to their low cost and eating readiness. Generally, these products have high starch content, but low nutrients such as vitamins, minerals, amino acids and fiber. In fact, most of the snacks are known as foods with high energy content and glycemic index, but low nutritional value. Adding fruits processing by-products to extruded snacks improves the nutritional value of snacks due to their high content of dietary fiber, bioactive compounds and minerals. Pomegranate (Punica granatum L.) is a perennial plant and is generally cultivated in tropical and subtropical regions the pomegranate seed is one of the pomegranate processing by-products including approximately 15-20% of total fruit. Pomegranate seed contains 36.5-42.4% fiber, 13.5-16.9% lipid, 8.5-11.3% protein and 24.09-33.41% carbohydrates. Therefore, pomegranate by-products rich in bioactive compounds and dietary fiber can be used as a functional ingredient. Since no research have been performed on using the pomegranate seed powder in making snacks yet, this research aimed to investigate the effect of pomegranate powders as a fiber supplement on the extruded physicochemical properties. The fruit of pomegranate were purchased from Khuzestan province in Iran. After peeling of pomegranate fruits, arils were pressed. The remaining pomaces were dried at 50 C for 48h. Dried pomace was powdered using a mixer grinder. The corn grits (Golden Corn Company, Iran) were prepared. The moisture and chemical component of raw materials were analyzed. The two screw extruders (model DS56, Jinan Saxin Company) was used to formulate and prepare snacks. First, response surface methodology (RSM) was used to optimize the amount of pomegranate powder to be added to the snacks. For this purpose, the influence of adding the pomegranate seed powder (0-20 %), extruder temperature (120-160 °C) and screw rotation speed (120-180 rpm) on the physicochemical properties of extruded samples were considered. For this reason, the moisture level of the input food was adjusted to 15 % and the feeding speed was 40 (kg/hr). The obtained results from optimization of the snacks formulation and process conditions shows that the optimum amount of factors are fallowing addition of fiber supplementary 11.8 %, the temperature of the extruder 160 °C, the screw speed of 147.1 rpm. After preparing optimal and control samples (without adding pomegranate powder), in order to evaluate the addition of pomegranate powder to the physicochemical properties of snacks, for this purpose, the effect of adding pomegranate powder on fat and protein content, total phenolic compounds, antioxidant activity, density, hardness, water and oil absorbance index, solubility index, soluble and in soluble fiber content, moisture content and microstructure of the produced snacks during 60 days of storage were investigated. By adding the pomegranate seed powder, the product moisture content decreased, which is probably due to high insoluble fiber content of pomegranate seed powder like apple residue. Moreover, by adding the pomegranate seed powder, the oil absorption index increased, which is probably due to presence of non-polar amino acids in the pomegranate seed powder. Existence of greater quantities of non-polar amino acids and presence of non-polar side chains in the extruded products may absorb oil hydrocarbon chains, leading to increase oil absorption index. Based on results, adding the pomegranate seed powder increases the hardness of the samples, which is probably due to the high amounts of oil and protein in the pomegranate seed powder. Researchers have reported that the use of food ingredients with high fat, protein, and fiber content increase the product tissue hardness. Also, the addition of pomegranate powder reduced water absorption of samples, which is probably due to the presence of insoluble water compounds such as fat and insoluble fibers in pomegranate powder and the reduction in the starch content of the samples due to the replacement of pomegranate powder. According to the results, addition of pomegranate powder increased the total phenol content and antioxidant properties of samples. While increasing the storage time, the total phenol content in the samples was reduced, which is probably due to the oxidation reactions that occur during storage. The results of this study showed that the addition of pomegranate powder increased the density, a * value, and nutritional value (such as iron, zinc, soluble and insoluble fiber, protein and fat content) in samples. While L* and b* values and water activity of the samples was reduced. Also, the addition of pomegranate powder decreased porosity and created heterogeneous and irregular cavities in the texture of snacks.