Investigating cell wall degradation treatments, pH-shifting and extrusion as methods to increase the quality of Paecilomyces variotii as a protein source in fish feed

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Title: Investigating cell wall degradation treatments, pH-shifting and extrusion as methods to increase the quality of Paecilomyces variotii as a protein source in fish feed
Authors: Persson, Frida
Abstract: The increased demand for seafood, due to both population growth and an increased health awareness, has resulted in an increased demand for fish feed in aquaculture production. This since wild fish capturing cannot fulfill the demand in a sustainable way. Traditionally, fishmeal has been the major protein ingredient in fish feed, providing the fish with the essential amino acids needed for optimal growth. However, the production of fishmeal has decreased rapidly the past decades. Instead, plant based protein sources has partly replaced fishmeal. The issues with this replacement is the different amino acid composition and the presence of antinutritional substances, resulting in decreased growth rates. One alternative that is gaining interest is the use of single cell protein (SCP) as a potential protein ingredient in fish feed. SCP consists of microorganisms such as yeast, bacteria, algae and filamentous fungi. SCP has several advantages, such as similar amino acid composition to fishmeal, short generation time, no requirement to arable land and the ability to grow on various substrates. The filamentous fungus Paecilomyces variotii was selected in this project due to its high protein content and ability to grow on residual streams from the forest indutry. Since the proteins in SCP are intracellular, cell wall degradation can result in higher digestibility. Further, if the polysaccharides in the cell wall are decreased, the protein content of the SCP would increase, resulting in a fish feed ingredient of higher quality. To achieve this, the following cell wall degradation methods were investigated: High Pressure Homogenization (HPH), enzymatic lysis with b-glucanase and a combination of the two methods. After the different treatments, pH-shifting was performed in order to precipitate the proteins. The pellets obtained were analyzed for protein content. Further, the carbohydrate concentration was determined in the supernatant to investigate the effect of the enzyme, and samples from the pellets were studied in a light microscope to study the cell wall degradation. Further, extrusion was investigated as a possible treatment method, and both the physicochemical and structural properties of the extruded samples were investigated. Growth and survival of Artemia was evaluated in a feeding trial. The results showed that HPH resulted in the highest degree of cell wall degradation. The pH-shifting resulted in protein concentrate with a higher protein content (about 50 %) than the untreated biomass (35-40 %), with a yield of 53.81 %. When analyzing the physicochemical and structural properties of extruded samples, it was concluded that extrusion at 115 °C, with a screw speed of 120 rpm and with a moisture content of 40 % resulted in samples which held together well, both in the micro- and macrostructure, and had the lowest water solubility index (WSI) among the extruded samples. Finally, extrusion appeared to increase growth and survival in Artemia during the feeding trial, but no significant difference was found.
Keywords: single cell protein;cell wall degradation;fish feed;filamentous fungi
Issue Date: 2019
Publisher: Chalmers tekniska högskola / Institutionen för biologi och bioteknik
URI: https://hdl.handle.net/20.500.12380/300739
Collection:Examensarbeten för masterexamen // Master Theses



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