Introduction: Over the last few decades, development of the industrial life has remarkably increased the demand for consumption of ready-to-eat foods. Deep fat frying is a fast and conventional method for cooking and due to creating crispy surface, soft internal texture, desired color and taste has popularity among consumers. The main problem related to fried food products is the high oil absorption during deep fat frying that is harmful for human health and has negative effects on shelf life of the product. Therefore, the aim of this study was to investigate the role of breading particles size as well as the influence of addition of soy protein isolate in breading and batter layers on properties of chicken nugget.
Material and Methods: First, breading was divided to three particle sizes. Sieves with mesh size 40 (0.42 mm) and 60 (0.25 mm) were used for separation of small breading. Also, sieves with mesh size of 18 (1 mm) and 20 (0.84 mm) as well as 10 (2 mm) and 12 (1.68 mm) were used for preparation of breading with medium and large particle size, respectively. Three percent soy protein isolate was separately added to breading with particle size of small, medium and large and used for production of chicken nugget. Also, 3% soy protein isolate was added to batter mixture and then nuggets coated with three different breading particle size without soy protein isolate. Breading pick-up, moisture content, cooking loss, porosity, oil absorption and penetration, color and textural properties of the chicken nuggets were then evaluated.
Results and discussion: Based on the results, the coating of chicken nuggets with small breading size led to the product with the highest moisture content and lowest porosity, oil uptake, oil penetration and shear force. However, chicken nuggets coated with small breading size had the highest breading loss. After incorporation of soy protein isolate to breading, the highest hardness and lowest springiness, cohesiveness and gumminess were related to the nuggets coated with small breading size, however, chewiness was not affected by breading particle size. Breading with small particle size containing soy protein isolate caused the highest L*, a* and b* values in fried chicken nuggets. Addition of soy protein isolate to breading layer significantly caused a decrease in cooking loss, porosity, oil absorption and penetration (p < 0.05). These samples had higher moisture content than the control sample. After addition of soy protein isolate to batter layer, color of chicken nugget did not considerably change (p > 0.05). The effect of soy protein isolate on textural properties is dependent on breading particles size. Generally, the addition of this compound to batter layer decreased hardness, gumminess and chewiness; however, its effect on springiness and cohesiveness is dependent on breading particle size. The presence of soy protein isolate in batter layer increased moisture content which in turn could diminish porosity, cooking loss, oil absorption, and oil penetration (p < 0.05). Overall, the comparison between chicken nugget properties when soy protein isolate was added to breading or batter layer indicated that the presence of the protein in breading layer was more effective in retention of moisture, reducing of cooking loss, porosity, oil absorption and oil penetration. However, these samples had more hardness, gumminess and chewiness compared to those containing soy protein isolate in batter layer. Cohesiveness of chicken nugget containing soy protein isolate in breading was not significantly different with those produced with the compound in batter layer.
The production of chicken nugget with small breading size containing 3% soy protein isolate in batter layer was proposed for production of products with better nutritional and physicochemical properties.