An investigation of rapeseed protein as a new food product

Abstract: The combination of a growing global population and a limiting amount of farmland creates a need for new innovative food products to achieve a global sustainable development and a healthy population. Rapeseed press cake is a low-cost by-product of rapeseed oil production and is very high in protein and fiber. The rapeseed protein contains high concentrations of S-amino acids as methionine and cysteine, comparable with soy. Most of the rapeseed press cake is sold as animal feed. If the press cake instead could be used as human food directly, one step in the food chain could be eliminated and more of the plant nutrients could be utilized by humans. As there is a growing demand of meat-analogues due to the increase of the vegan scene in Sweden, there seem to be a market for at meat-analogue based on locally produced rapeseed protein. By up-cycling an existing agricultural by-stream and recover high quality protein for human consumption, the import of soy can be decreased in Sweden. In previous master’s thesis and studies a method to isolate proteins from cold-pressed rapeseed press cake has been developed. The current thesis has been focusing on improving the isolation method to achieve an edible food product as well as investigating different processing methods of the isolated rapeseed protein paste (RSPP). To optimize the protein yield two different approaches has been investigated, the incubation time and its performance in the leaching phase as well as recirculation of the first sediment at different pH. To decrease the content of anti-nutrients and discoloring compounds in the RSPP, ultrafiltration and diafiltration have been investigated. Drum drying, freeze drying and vacuum evaporation was investigated to decrease the water content. Finally, thermoplastic extrusion has been used to investigate the abilities of rapeseed proteins to be texturized. A single-screw extruder with a conventional screw (20 mm Ø x 25) was used. Two different dies were used, a heated round die (3 mm Ø) and a cooled flat die (2x20 mm) The results of the process optimization indicated that incubation in 60 min with stirring, instead of the previous incubation time of 180 min without stirring saved two hours of processing time without reducing the protein yield. By recirculation of the first sediment the total protein yield was increased by at least 7.2% (from 38% to 45.2%). Further it was showed that addition of Na2S2O5 in the diafiltration improved the color and taste of the rapeseed protein paste. The freeze- and drum-dried products achieved a water activity below 0.6, which is suitable for food applications. The result of the extrusion indicated that a single-screw extruder at an extrusion temperature of 100°C-120°C and water content of 50% did not seem to form the desired fiber structure. As the fat content was high and as a higher temperature could not be tested in the single-screw extruder, extrusion trials in a twin-screw extruder should be performed to further investigate the ability of rapeseed protein to form an elastic texture by thermoplastic extrusion.