Abstract
Demands for seafood products are steadily increasing. Alternative protein sources are required to compensate for enormous amounts of fishmeal that is needed for global seafood production. Starch is a food polymer that can be added to fish feed formulations to enhance binding and expanding capabilities of extrudates. Floatability, a key factor for most aqua feeds, can be optimized by the addition of certain starch sources. Six ingredient blends with a similar protein content (~32.5%) containing two starch sources, Hylon VII (containing 70% amylose, 30% amylopectin) or Waxy I (containing 0% amylose, 100% amylopectin), 20% distillers dried grain with solubles (DDGS), and 15, 25, and 35% moisture content were used along with appropriate amounts of soybean meal, menhaden fishmeal, whey, vitamin and mineral mix to investigate nutritionally-balanced feeds for Nile tilapia (Oreochromis niloticus L.). The blends were processed using a laboratory single-screw extruder with varying temperature settings (90-90-90°C, 100-120-120°C, and 100-120-140°C), screw speeds (100, 120, and 140 rpm), and length/diameter ratio (3.4, 6.6, 9.2) of the die. Extensive analyses of expansion ratio (ER), unit density (UD), sinking velocity (SV), and pellet durability indices (PDI), water absorption (WAI) and water solubility indices (WSI) were conducted to evaluate the effects of the two starch sources on extrudate binding and floating capacity. By varying process conditions, significant differences (P>0.05) among the blends were detected for all extrudate physical properties. Significantly higher values for ER, UD, and PDI were achieved by using the Waxy I starch source, while values for SV and WAI decreased. For WSI no significant differences were detected. Increasing the moisture content from 15-35% resulted in a significant increase in ER, WAI, and PDI and a significant decrease in UD. WSI showed no clear pattern in changes. The impact of different amylopectin to amylose ratio, temperature and moisture content on extrudate stability, cohesion and physical properties was demonstrated in this study. All formulations yielded viable extrudates while the blends with the amylopectin as the sole source of starch resulted in higher quality extrudates.
Highlights
The world’s hunger for seafood products has tremendously exploited and damaged global wild fish resources
The moisture contents (15, 25, and 25%) significantly affected all tested parameters, except for water solubility indices (WSI), as well as increasing the screw speed from 100 to 130 and 160 rpm resulted in significant differences, except for unit density (UD) and pellet durability indices (PDI)
The incorporation of either of two starch sources with varying amylopectin portions in combination with distillers dried grains with solubles, soy, and other ingredients was investigated to determine their effects on resulting binding capacity
Summary
The world’s hunger for seafood products has tremendously exploited and damaged global wild fish resources. Limited supply of seafood can only be regenerated by changing the global attitude towards utilizing nature’s food resources and benefiting from aquaculture production. Aquaculture farming can take pressure of the dependency on wild fishery stocks by using alternative protein sources. Carnivorous species require high amounts of fishmeal and fish oil in their diets. Prices for fishmeal are so high that diets often represent 40-70% of aquaculture operating expenses (Thompson et al, 2008). Alternative protein sources are more cost effective and can support regional and local economies and can reduce environmental impact (Cheng and Hardy, 2004; Ayadi et al, 2009)
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