Basil seed gum improves the gelling properties of egg white albumin under various temperature conditions

Proteins and polysaccharides are well-known ingredients in food products which can interact with each other and alter the food properties. The interactions between proteins and polysaccharides depend on different parameters such as biopolymer type, pH, temperature, polysaccharide type, concentration of both protein and polysaccharide, and the concentration of cations present in the solution. Different conditions can have significant effects on the formation of such complexes or the associated thermodynamic incompatibilities (Rafe at el., 2012). Repulsive or attractive interactions can occur between proteins and polysaccharides and this interaction play an important role on various properties of the formed complexes (Razi et al., 2019a). The complex of protein and polysaccharide has various applications in different food systems such as emulsions, foams, and gels. When protein and polysaccharide mixtures are heated, the heat-induced gel can form, in which rheological and physical properties of gel samples are dependent on temperature, pH, ionic strength, biopolymer components, and polymer concentration (Rafe et al., 2012). Gel is a three-dimensional network with high humidity that resists to flow. Strong gels can be used in some of food products or delivery of active compounds in functional foods (Razi et al., 2018a). Egg white albumin (EWA) is one of the best ingredients for gel formation. A three-dimensional network can form during heat-induced gelation of EWA which can hold water at optimum conditions (Razi et al., 2018a). EWA has more than 40 different proteins, where ovalbumin contributes to about 54% w/w.The EWA gel properties can be improved with the addition of polysaccharides like basil seed gum (BSG) (Razi et al., 2018b). BSG is one of the newest polysaccharides that have recently been used in the food products for its different functionalities such as surface activity, emulsifying, stabilizing, foaming, thickening, and gelling properties (NajiTabasi and Razavi, 2017). Afsharnik et al. (2011) found that BSG chains was able to form a web network inside the protein matrix of milk proteins and reduce the amount of syneresis leading to an increase in the strength of a low-fat set yoghurt. This biopolymer can affect the functional properties of EWA by influencing upon the structure of food products (Razi et al., 2019a). Thus, the aim of the current study was to investigate the effect of different concentrations of BSG on the gelling properties of EWA. On the other hand, we wanted to introduce a gel system containing protein and polysaccharide which can be used in the food industry.

In the present study, the effect of different concentrations of basil seed gum (BSG; 0, 0.05, 0.1, and 0.3% w/v) on the gelling properties of egg white albumin (4% w/v) were studied. In order to form EWA gels, the samples were heated up to 85 °C in a water bath for 30 min, followed by storage at 4 °C for 24 h. Water holding capacity (WHC) was calculated after centrifuging the samples at 6000 rpm for 20 min. Textural properties of gel samples were analyzed using a texture analyzer equipped with cylindrical probe with the diameter of 12.1 mm, probe speed of 60 mm/min.  Gels color was reported using L*, a*, b* and Image g software. Rheological properties of the samples were analyzed by a rheomter (Physica, MCR 301, Anton Paar GmbH, Germany), with a parallel plate geometry. Amplitude sweep test was carried out at the strain range of 0.001 to 100 at 20 ˚C. During the temperature sweep test, the samples were heated from 5 to 95 ˚C in the rate of 1 ˚C/min. The physical and rheological properties of the manufactured EWA gels were examined under the influence of different concentrations of BSG. For this aim, all gel samples were prepared in triplicate in a completely randomized design and SPSS software was used to detect the significant differences.

The results showed that water holding capacity of the gels increased as BSG concentration increased (p<0.05) and the lowest WHC belonged to the gel made with 4% EWA-0% BSG. These results could be due to a higher water bonding capacity of the samples in the case of the higher concentration of BSG. Although, the sample containing 0.3% BSG had a higher hardness compared to the other samples, no significant difference was observed between samples. The same trend was observed in gels cohesiveness (p>0.05). L* decreased due to the increase in BSG concentration. B* showed the same trend with L* but no significant differences were observed in a* (p>0.05). The strain sweep test showed that linear viscoelastic (LVE) region was about the strain of 0.1%. As BSG concentration increased from 0 to 0.3%, both storage and loss moduli increased too; whereas, storage modulus was higher than loss modulus in the case of all concentrations. With increasing the temperature from 5 to 90 ˚C, storage modulus decreased slightly while during cooling step it was stable at the first stage but then increased with a high slope, in the case of all samples. After heating and cooling of specimens in temperature sweep test, storage and loss modulus of gel sample containing 4% EWA and 0.3% BSG was significantly higher than other samples (p<0.05). Considering these results, it seems that hydrogen bonds play the main role in EWA and BSG interactions.

In different food products, proteins and polysaccharides exist together, both of which (either individually or combined together) can affect the texture, structure, shelf life, and stability of the food, due to their gelling, thickening, and surface-active properties. The finding of the current study can be useful for the manufacture of the food products containing proteins and polysaccharides, in which the interactions between the two biopolymers play an important role in regard to their properties of the final products. Furthermore, these results can help with choosing the best concentration of BSG where the addition of this novel polysaccharide to the protein-rich foods is considered. Overall, the results of this experiment indicated that BSG can improve the gelling properties of egg albumin, with 0.3% being the best concentration in terms of the favorable effects on both physical and rheological properties of the manufactured gels.