The Effect of pH and Storage Temperature on the Stability of Emulsions Stabilized by Rapeseed Proteins

Rapeseed press cake (RPC), the by-product of rapeseed oil production, contains proteins with emulsifying properties, which can be used in food applications. Proteins from industrially produced RPC were extracted at pH 10.5 and precipitated at pH 3 (RPP3) and 6.5 (RPP6.5). Emulsions were formulated at three different pHs (pH 3, 4.5, and 6) with soy lecithin as control, and were stored for six months at either 4 °C or 30 °C. Zeta potential and droplet size distribution were analyzed prior to incubation, and emulsion stability was assessed over time by a Turbiscan instrument. Soy lecithin had significantly larger zeta potential (−49 mV to 66 mV) than rapeseed protein (−19 mV to 20 mV). Rapeseed protein stabilized emulsions with smaller droplets at pH close to neutral, whereas soy lecithin was more efficient at lower pHs. Emulsions stabilized by rapeseed protein had higher stability during storage compared to emulsions prepared by soy lecithin. Precipitation pH during the protein extraction process had a strong impact on the emulsion stability. RPP3 stabilized emulsions with higher stability in pHs close to neutral, whereas the opposite was found for RPP6.5, which stabilized more stable emulsions in acidic conditions. Rapeseed proteins recovered from cold-pressed RPC could be a suitable natural emulsifier and precipitation pH can be used to monitor the stability in emulsions with different pHs.

Reinventing the oilseeds processing to extract oil while preserving the protein

The move towards more sustainable production and consumption patterns is a goal shared by a large part of society. In the oil-mill sector, whether it be animal feed or human food, this development should make it possible to improve the protein autonomy of the territories and to use proteins more efficiently. Current methods make some of the rapeseed proteins indigestible and leave most of the undesirable compounds from the seeds in resulting meals. Residual oil, fibrous envelopes, glucosinolates, phytic acid, phenolic compounds and oligosaccharides, as well as overcooking, however, have negative effects on the value of proteins. An important part of the article is devoted to reviewing these effects. Their extraction, combined with milder heat treatments, would provide excellent quality proteins to the market and generate value for the entire value chain. Efficient dehulling and mechanical extraction would be the prerequisites for this development. An ethanolic extraction revisited to exploit the secondary metabolites would then complete this process with, however, a limited effect on phytic acid. All these technologies have the advantage of not posing major acceptability problems. This development requires new investments in applied research to make this new approach to processing oilseeds possible and efficient.

Protein Recovery from Rapeseed Press Cake: Varietal and Processing Condition Effects on Yield, Emulsifying Capacity and Antioxidant Activity of the Protein Rich Extract

Protein was recovered from five varieties and a mixed blend of cold-pressed rapeseed press cake by leaching and precipitation in a water-based process, and the protein recovery yield varied from 26–41% depending on variety. Exposure for heat during protein recovery severely reduced the rapeseed proteins’ ability to stabilize the oil–water interface of emulsion droplets. Protein extract from Lyside had the best emulsifying properties of the varieties investigated. Oxidation rate was assessed by the Thiobarbituric Acid Reactive Substances (TBARS) method and rapeseed protein extracts from Epure and Festivo had higher capacity to delay oxidation compared with soy lecithin. There are possibilities to broaden the use of rapeseed whereby recovered rapeseed protein can be used as a plant-based multifunctional ingredient with emulsifying capacity and which has a delaying effect on oxidation.