Title : Optimizing extrusion cooking parameters for a multi-grain blend
Abstract:
Introduction: This study investigated the optimization of extrusion cooking parameters for a multi-grain blend containing rice, mung bean, cowpea, sesame, and isolated soy protein. The focus was on understanding how temperature and screw rotation speed affect the quality of the extruded product, particularly focusing on starch gelatinization, protein denaturation, and various functional and nutritional properties.
Materials and Methods: A multi-factorial design was applied, varying both temperature (135-175°C) and screw rotation speed (175-300 rpm) to create 36 extruded samples. The raw material mixture contained 25% each of rice and mung bean, 20% isolated soy protein, 25% cowpea, and 5% sesame. The effects of the processing parameters on the following quality attributes were evaluated:
- Trypsin inhibitor activity (TIA): Reduced TIA levels are crucial for digestive health, as high levels can inhibit protein digestion.
- Nitrogen solubility index (NSI): This index indicates protein functionality and digestibility. Higher NSI values are generally desirable.
- Water activity level (aw): Low aw levels enhance product shelf life and stability by inhibiting microbial growth.
- Water solubility index (WSI) & Water absorption index (WAI): These influence the texture and functionality of the extruded product. WSI reflects the water-soluble components, while WAI indicates the product's water holding capacity.
- Expansion ratio (ER): Higher ER indicates better starch gelatinization, impacting product texture and density.
Results and Discussion: The analysis revealed that a temperature range of 155-175°C and a screw speed of 250 rpm yielded optimal processing conditions. This combination achieved the following:
- Reduced TIA content: Processing at these parameters effectively reduced TIA content to a safe level, ensuring digestive health.
- Increased NSI: NSI values increased within the optimal temperature and speed range, indicating improved protein functionality and digestibility.
- Acceptable levels of WSI, WAI, aw, and ER: The chosen processing conditions maintained WSI, WAI, aw, and ER within acceptable ranges. This ensures a desirable product texture, functionality, and shelf life.
These findings suggest that processing at 155-175°C and 250 rpm promotes optimal starch gelatinization, a crucial step for improved digestibility and product quality. Additionally, protein denaturation likely occurs at these parameters, enhancing protein functionality. The combination of these factors contributes to a multi-grain extruded product with superior nutritional and functional properties.
Further research could investigate the effect of these processing parameters on other quality attributes, such as color, sensory properties, and nutritional profile (e.g., vitamin content). Additionally, exploring the optimal screw
configuration and residence time could provide further insights for optimizing the extrusion process for this multi-grain blend.
