PREGELATINIZED STARCHES IMPROVED PELLET CHARACTERISTICS AND THE GROWTH AND PHYSIOLOGY OF TILAPIA

Starches are less well utilized in fish than terrestrial animals, but are included in aquafeeds as an inexpensive source of energy but also to act as a binder.  Starch utilization as well as their binding properties may be improved through pregelatinization.  This is when starches are heated in the presence of water and the crystalline regions break down and gels, which can allow more sites for digestive enzymes as well as binding of nutrients.  The aim of the current study was to assess the potential differences of native or pregelatinzed (PG) starches on the growth and various physiological parameters of tilapia after 9 weeks as well effects to various pellet characteristics.  

Four isonitrogenous, isolipdic and isoenergetic diets were formulated to contain tapioca starch, PG tapioca starch, corn starch or PG corn starch, at 250 g kg^-1.  The PG starches were made by mixing with water (1:1 ratio), autoclaved for 15 min., oven dried and then hammer milled.  Pellets were extruded and after oven drying, the bulk density, expansion ratio, pellet durability index, water absorption index, water solubility index, water stability and protein solubility were measured and then the microstructure of surface and cross sections were examined.  Pellets were then fed to triplicate groups of tilapia and the growth, muscle/plasma biochemistry, intestinal short chain fatty acids, and liver glycogen after 9 weeks.

The PG diets had significantly higher water stability, water solubility, bulk density, and protein solubility along with a smoother surface. Tilapia fed the TS diet had lower growth than all other treatments, but was significantly improved when pre-gelatinized.  In the PG treatments, intestinal SCFA significantly decreased while plasma glucose, cholesterol and triglycerides as well as liver glycogen significantly increased.  Fish fed the CS diet had significantly more long chain polyunsaturated fatty acids compared to the other treatments. Pre-gelatinization may improve fish productivity and offer greater flexibility during aquafeed production.