Abstract
<p>Twin-screw extrusion cooking trials were performed to investigate the differential effects of conventional DDGS (DDGS) and HP-DDG inclusion, as fishmeal replacers, on physical properties (moisture content, water activity, thermal properties, expansion ratio, unit density, bulk density, water absorption, solubility and pellet durability indices, and color) of Rainbow trout (Oncorhynchus mykiss) feed. Four ingredient blends were formulated with 20 and 40% C- DDGS, and 20 and 40% HP-DDG, along with other required dietary ingredients. Each diet was extruded using two replications; a fishmeal based diet acted as the control diet. The highest and the lowest extrudate moisture content and water activity were observed for the diets containing 20% DDGS and 40% HP-DDG, respectively. Compared to the control diet, increasing HP-DDG content from 20 to 40% had no effect on the bulk density of the products, while increasing DDGS content from 20-40% led to a considerable rise in bulk density of the extrudates by 14.2 and 6%, respectively. Also, extrudates with the lowest brightness, greenness, and yellowness values were obtained from the diet containing 20% DDGS, whereas the most color intensity values were observed for the diets containing 40% DDGS and 20% HP-DDG. Increasing DDGS and HP-DDG from 0-40% caused a remarkable increase in water absorption index, by 72 and 30%, respectively. Likewise, the water solubility index increased, but in a considerably lesser order of magnitude. High pellet durability index of more than 99% was achieved with inclusion of either DDGS or HP-DDG. None of the diets impacted the thermal properties of the extrudates. Inclusion of 20 and 40% DDGS resulted in the extrudates with the largest and the smallest unit density values of nearly 887 and 750 kg/m<sup>3</sup>, respectively. As was expected, expansion ratio decreased with increasing unit density. Increasing inclusion levels of HP-DDG did not show any effect on unit density or expansion ratio of the products. Future research should concentrate on investigating the effects of both extrusion processing and graded levels of different types of DDGS on Rainbow trout feeds.</p>
Highlights
Expanding the aquaculture industry enhances the global food security and subsequently helps boost the living standards of the world’s growing population; the importance of the techno-economic feasibility of aquaculture production must be considered (Pritchard, 1976)
While addition of 20% HP-dried grains (DDGs) resulted in a 3.5 % increase in the R, further increasing of HP-DDG to 40% did not have any significant impact on the heat storage capacity of the extrudates.Regarding the α values of the extruded diets, our observations indicated that inclusion of 20% dried grains with solubles (DDGS) decreased the α by nearly 6.3%, while further addition of DDGS to 40% and inclusion of HP-DDG at both levels of 20% and 40% did not influence the α value, considerably compared to that of the control diet
The results from this twin-screw extrusion study revealed that, replacing fishmeal with HP-DDG at both levels of 20 and 40 % led to production of extrudates with higher Expansion Ratio (ER) and WSI values but lower Unit Density (UD), Bulk Density (BD), and WAI values compared to those of the diets produced with 20% or 40% DDGS incorporation
Summary
Expanding the aquaculture industry enhances the global food security and subsequently helps boost the living standards of the world’s growing population; the importance of the techno-economic feasibility of aquaculture production must be considered (Pritchard, 1976). Increasing consumer demands for aquaculture products coupled with a limited food supply (i.e. wild fish supply) for feeding the fish have resulted in a remarkable increase in aquafarm production expenses. The largest part of these costs comes for feed in which protein is the most expensive ingredient (Watanabe et al, 2002). Fish meal, which is the best source of protein and oil due to its high biological values in terms of essential amino acid, unsaturated fatty acids, minerals, and phospholipids for fish metabolism, comes largely from wild fish stocks (Cheng & Hardy, 2004). Anywhere from 2 to 6 pounds of ocean fish must be used to produce only one pound of farm-raised fish, resulting in a 25% average transfer efficiency (Marine Aquaculture Task Force, 2007)
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