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Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

First Advisor

Kurt A. Rosentrater

Abstract

Rising demands for seafood products have made aquaculture to one of the fastest growing sectors in the food industry, but have increasingly depleted wild fish stocks through capture fisheries. Commonly, fish meal has been used as the primary source to supply fish with essential proteins, but it is expensive. Feed represents over half of the operating costs for aquaculture operations. This study investigated using distillers dried grains with solubles (DDGS) as a sustainable, less expensive alternative protein source for fish feeds. Two extrusion studies using a single-screw extruder and two studies using a twin-screw extruder were conducted to prepare nutritionally-balanced diets for yellow perch (Perca flavescens), rainbow trout (Oncorhynchus mykiss), and Nile Tilapia (Oreochromis niloticus L.). The ingredient blends included combinations of DDGS, soybean meal, fish meal, fish oil, corn starch, whole wheat flour, corn gluten meal, whey, vitamins and minerals, respectively. DDGS levels were adjusted between 10 and 50% and the net protein content varied between 30 and 53% db. Various extruder settings were used, including screw speed (100-298 rpm) and processing temperatures (15°C to 140°C). For the twin-screw extruder, varying amounts of steam (6.9-9.7 kg/h) were injected into the conditioner and water (4.3-13.1 kg/h) into the extruder to modulate the cooking and resulting cohesiveness of the final extrudates.
The effects of varying formulations and extruder settings on extruder processing parameters and on the resulting physical properties of the extrudates were examined. During processing, mass flow rate (g/min), moisture content at the die and at the conditioner exit (% db), respectively, and barrel temperatures (°C) were measured. The analyses of the extrudates included moisture content (% db), water activity (-), unit density (kg/m3), bulk density (kg/ m3), expansion ratio (-), compressive strength (MPa), compressive modulus (MPa), pellet durability index (%), water stability (min), angle of repose (°), color (-), sinking velocity (SV), water absorption (WAI) and water solubility indices (WSI), respectively.
The first study was performed using a laboratory-scale single-screw extruder for the production of nutritionally-balanced diets for juvenile yellow perch. The effects of increasing DDGS levels (0-50%) on the extruder processing parameters and physical properties of the resulting extrudates were investigated. The mass flow rate generally increased with higher amounts of DDGS. Expansion ratio and compressive strength of the extrudates were low. On the other hand, all blends showed very high pellet durability and water stability. Each of the ingredient blends resulted in viable, high quality extrudates.
In the second study, a twin-screw extruder was used to investigate the production of balanced diets for juvenile yellow perch. Compared to the first study, the ingredient composition of the blends for yellow perch varied. The effects of DDGS levels (0-40%) on the extruder processing parameters and on the resulting physical properties of the extrudates were analyzed. With increasing DDGS levels; significant differences (P For the third study, twin-screw extrusion trials were performed to investigate the inclusion of DDGS (0-50%) on the production of rainbow trout feeds. The experimental conditions were the same as for the second study. The compressive strength was low for all extrudates and increased significantly with higher DDGS amounts. The expansion ratio was low for all extrudates, while the water stability was very high. Pellet durability index of the final product was high for all formulations. Ail ingredient blends containing DDGS up to 50% yielded viable extrudates.
The fourth study examined the effects of two starch sources Hylon VII (containing 70% amylose and 30% amyiopectin) and Waxy I (containing 0% amylose and 100% amylopectin), respectively, on DDGS-based Nile tilapia feeds. The effect of different amylose to amylopectin ratio of the starch sources, varying feed moisture (15, 25, and 35% db); temperature setting (90- 90-90°C, 100-120-120°C, and 100-120-140°C), screw speed (100,120, and 140 rpm) and length/diameter ratio of the die (3.4, 6.6, 9.2) on extrudate binding and floating capacities were investigated. All formulations yielded viable extrudates while the blends with Waxy I resulted in higher quality extrudates. Significant differences with varying processing conditions were detected for ail extrudate physical properties among the different blends. Expansion ratio, water absorption and pellet durability index increased significantly with higher feed moisture, whereas unit density decreased. Expansion ratio, unit density, and pellet durability index significantly increased when using Waxy I as a starch source. 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. Blends containing Waxy I as the starch source yielded the best results for the majority of all tested physical properties.
These studies demonstrated that DDGS could be included up to 40% and 50%, respectively, to produce viable fish feed extrudates that were highly water stable and durable using a single-screw and twin-screw extruder. Adding a starch source with a 100% amylopectin can enhance extrudate stability and cohesiveness. Additionally, the effects of the temperature setting and feed moisture on extrudate physical properties were examined.

Library of Congress Subject Headings

fishes
feeding and feeds
distillers feeds
extrusion process
distilling industries
by-products

Description

Includes bibliographical references (pages 159-188)

Format

application/pdf

Number of Pages

206

Publisher

South Dakota State University

Rights

Copyright © 2011 Ferouz Y. Ayadi. All rights reserved

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