Rapeseed and sunflower: from meal to meat analogue

Rapeseed and sunflower seeds are broadly used for oil production, while the co-products of rapeseed and sunflower meal after the oil extraction are mainly applied as animal feed. With high protein content and rich nutritional given the amino acid composition, rapeseed and sunflower cake/meal are considered as a potential plant protein source for foods as well. Therefore, the aim of this work was to enable the use of the co-product of rapeseed meal and de-oiled sunflower meal kernel for meat analogue application through creating new scientific insights in the fractionation process and the structuring potential of resulting ingredients. This thesis addressed a research question whether complete removal of phenolic compounds from de-oiled sunflower kernel is necessary

In chapter 2, rapeseed protein concentrate and isolate (RPC and RPI) were fractionated from rapeseed meals, and their functional properties were compared. The RPC was obtained by aqueous ethanol washing and consisted of 62% protein (DM) and 28% polysaccharides (DM). The washing process removed almost all the phenolic compounds and oil. The RPI was fractionated with alkaline extraction, ultrafiltration, and dialysis. It contained 94% protein (DM), but still contained a considerable amount of phenolic compounds (3.6% DM) after fractionation. The protein in RPC was completely denatured and had a low protein solubility, whereas the protein in RPI was still native and highly soluble. RPC particles were found to be sand-like when dispersed in water. Nevertheless, a concentrated RPC dispersion (40 wt% DM) leads to a much higher complex modulus (G*) by the temperature sweep using a closed cavity rheometer compared to the RPI dispersion.

The high complex modulus (G*) of the RPC dispersion suggested its potential for use as an ingredient in meat analogues (Chapter 3). The structuring properties of RPC were studied with two recipes: RPC-only and RPC-wheat gluten (WG) mixture of 40 wt% DM in the shear cell. It was found that RPC-only formed fibrous structure when the temperature was above 140 °C, while RPC-WG (1:1) mixture of 40 wt% formed fibrous structure at a lower temperature of 130 °C. Further, a more pronounced anisotropic structure with increased anisotropic index (AI) on tensile stress was found in all ratios of RPC-WG compared with RPC-only. Moreover, sheared RPC-WG product had a remarkably lighter color than the RPC-only product. It was concluded that RPC is a promising alternative protein source for meat analogue applications.

Chapter 4 presents research on the aqueous ethanol washing of the de-oiled sunflower kernel to remove the phenolic compounds (PCs). The parameters of PCs removal yield and protein loss were assessed under varied process conditions (temperature, pH, and solvent quality). Results showed that the PCs removal was accompanied by protein loss in most of the studied conditions, and the effect of process conditions was greater on protein loss than PC removal yield. More washing steps always led to a higher removal yield of PCs. A simulation of the multi-step washing process was performed using the equilibrium constant derived from the experimental data. It was concluded that intensive washing with multi-steps was necessary to remove 95% of PCs, which also recovered most of the protein after the process. However, these extensive process conditions raised a research question of whether complete removal of phenolic compounds is necessary from the de-oiled sunflower kernel for the meat analogue application.

Chapter 5 describes up to what extent the PCs should be removed from the de-oiled sunflower kernel to prevent a negative influence on the functional properties of the sunflower protein. To do so, a simple model blend was studied, in which chlorogenic acid (CGA) and sunflower protein was mixed at apparent CGA-protein molar ratios of 1:10, 1:5, 1:1, 5:1, and 10:1 (which corresponds to mass ratios of approximately 1:850, 1:450, 1:85, 1:15 and 1:10). The outcome of this simple model blend showed the possibility to keep the CGA in the sunflower protein even when non-covalent interaction occurred. However, partial removal of CGA was necessary in case the covalent interaction could not be avoided. Covalent interactions above an apparent CGA-protein ratio of 1:1 led to the green color formation and the gelling properties were negatively influenced. The effect of covalent modification on gelling properties was also validated in a model blend of CGA and dephenolized sunflower protein concentrate. Also in this blend, the CGA-protein molar ratio should not exceed 1:1.

In Chapter 6, the amount of CGA allowed in pressed sunflower kernel (PSK) and de-oiled sunflower kernel (DSK) for structuring properties was further investigated. The PSK and DSK were obtained by the different oil extraction methods. PSK was obtained after intensive pressing, without additional de-oiling steps, while DSK was obtained after mild pressing followed by ethanol washing. Upon shear cell processing, it was found that both DSK and DSK-washed concentrates (40 wt% DM) formed fibers. However, only crumble products were formed when processing PSK or the PSK-washed concentrates (40 wt% DM). Results suggested that the amount of CGA presented in the sunflower materials did not affect their structuring properties in the shear cell. The main reason for the different structuring properties was found to be the oil content which was suggested to be the determining factor to prevent fiber formation in the case of PSK.

In Chapter 7, the main findings and conclusion of this thesis were reviewed. The fractionation processes were discussed regarding their effects on the functional and structuring properties of the rapeseed and sunflower materials. The melting of the material treated by aqueous ethanol washing was found to be a prerequisite for fibrous structure formation. It was suggested to further study the different process conditions from aqueous ethanol washing and its impact on the particle melting behavior to lower the required temperature for the fibrous structure formation using shear cell. Although the phenolic compound’s removal was not considered to be necessary for the fiber formation, its impact on the sensory properties still requires further investigation for meat analogue application. Overall, it can be concluded that rapeseed protein concentrate and de-oiled sunflower kernel ingredients have good potential for meat analogue applications.