ARTICLE FEED & ADDITIVE MAGAZINE October 2023 73 SOURCES OF STARCH IN AQUAFEED Starch is a common carbohydrate source in aquafeed and can be derived from various ingredients. The commonly used starch ingredients are corn, wheat, rice, barley, and sorghum. In addition, starchy root crops including potatoes, sweet potatoes, and cassava are processed into starch-rich ingredients to use in aquafeed. Certain leguminous plants contain both protein and carbohydrates such as soybeans and peas are also used. Tubers, as well as rhizomes, are also can be incorporated in aquafeed. Starchy by-products from the food processing industry, such as brewers’ grains and distillers’ dried grains are commonly added in aquafeed. In specialized aquafeed, algae, and seaweed are used as alternative starch sources. STARCH GELATINIZATION Starch granules consist of water-soluble amylopectin and water-insoluble amylose structures. Gelatinization begins with heating starch at 60°C - 80°C in water leading to absorb water and swelling. This results in gel formation from leached amylose and melting of crystalline regions, losing birefringence. Swelled granules disintegrate into smaller ones. The extent of gelatinization varies according to starch’s amylose-to-amylopectin ratios, location, and strain. On the other hand, non-waxy starches form strong gels upon cooling due to high amylose networks with other ingredients, while waxy starches with low amylose require low temperatures but lack strong gel formation after cooling. BIOCHEMICAL MODIFICATION OF STARCH DURING PROCESSING Studies have reported the influence of starch gelatinization on their subsequent biochemical changes. On top of that, cooking reduces the amylose content in the rice whereas amylose content was unaffected between 83% gelatinized extruded maize flour and 20% gelatinized native maize flour. It was reported that crude protein and crude fiber content was increased with lower crude lipid content in extruded maize flour compared to native maize flour. The resulting decrease in lipid content is due to the process of oxidation during extrusion. In addition, the increase in crude fiber content might be due to elevated β-glucan with no change in arabinoxylan level. IMPLICATIONS OF STARCH GELATINIZATION ON PHYSICAL CHARACTERISTICS OF AQUAFEED Commercial aquafeeds are generally made by extrusion technology which is highly flexible over the type of pellet (floating or sinking) that can be produced. For floating pellets, high temperature and pressure are required for increased starch gelatinization. In addition, the starch type also has an influence on the type of pellet. For example, waxy starches create less dense and more expanded extrudates because their branched linkages are weaker.
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