Characterization of Heat-Set Gels from RuBisCO in Comparison to Those from Other Proteins

Abstract

To anticipate a future shortage in functional proteins, it is important to study the functionality of new alternative protein sources. Native RuBisCO was extracted from spinach, and its gelation behavior was compared to other native proteins from animal and plant origins. Protein gels were analyzed for their mechanical gel properties during small and large deformation and for their microstructure. Heat-induced aggregation and network formation of RuBisCO resulted in gels with unique characteristics compared to, for example, whey protein and egg white protein. Having a very low critical gelling concentration and low denaturation temperature, RuBisCO readily forms a network with a very high gel strength (G', fracture stress), but upon deformation it has a brittle character (low critical strain, low fracture strain). This breakdown behavior can be explained by the dominant role of hydrophobic and hydrogen bonds between RuBisCO molecules during network formation and by the coarse microstructure. RuBisCO was shown to exhibit high potential as a functional ingredient giving opportunities for the design of new textures at low protein concentration.

Comparison of the functional properties of RuBisCO protein isolate extracted from sugar beet leaves with commercial whey protein and soy protein isolates

“…Table summarizes the results on (true) fracture stress (hardness), (true) fracture strain (deformability) and Young's modulus (gel stiffness) for RPI and WPI gels at pH 4.0 and 7.0. At pH 7.0, WPI formed transparent (fine stranded) gels whereas RPI formed turbid (coarse) gels, in agreement with the literature . At similar G ′ values, 130 g kg −1 WPI formed stronger gels with higher deformability and stiffness than 50 g kg −1 RPI, which formed more brittle gels.…”

“…In the case of RPI, considerably high values for both moduli were observed already at 10–20 g kg −1 protein (pH 4.0 and 7.0), whereas for WPI and SPI, G′ only started to increase at protein concentration higher than 80 g kg −1 . Clearly, the critical gelation concentration ( C gel ) for RPI is much lower than that for WPI and SPI, as was also observed for RPI isolated from spinach and alfalfa in comparison with other proteins. It should be mentioned that the remaining fiber content of 57 g kg −1 in the RPI could contribute to the higher viscoelastic properties of its heat‐set gels as compared with those of WPI and SPI.…”

“…C gel (protein concentration where G′ starts to increase) for RPI was found to be ∼6 g kg −1 at pH 4.0 and ∼1 g kg −1 at pH 7.0, similar to values from other authors for RuBisCO from alfalfa . C gel values for WPI and native soy protein were much higher than those for RPI . At both pH values and especially at pH 7.0, RPI from beet leaves proved to be an excellent gelling agent in comparison with WPI and SPI.…”

“…This peak corresponds to the native association of the RuBisCO multimeric structure of 550 kDa. In addition, SDS‐PAGE in reducing conditions showed two main bands at 12.5 and 55.0 kDa, indicating the presence of the small and large subunits of RuBisCO respectively . Both analyses showed that a high‐purity RuBisCO isolate was obtained using the current extraction procedure.…”

“…Differences in gelation properties were found to be related to the type of interactions. In the case of RuBisCO, hydrophobic, electrostatic and hydrogen bonds play a more dominant role in gels, as opposed to disulfide bridges for WPI and SPI, as inferred from the gel solubility upon treatment with chaotropic agents (SDS, urea, mercaptoethanol) …”