LITMIR.BIZ

Figure 2.4 P. ruscifolia Griseb. seeds, endosperm after alkaline treatment, and the obtained vinal gum are shown.

      When dispersed in water, ECG and VG shows a pseudo-plastic behavior [57] in the concentration ranges 0.25–1.50% w/w and above 0.04% (w/v). At intermediate concentrations, in high frequency range there is a cross point where the solid behavior (represented by the elastic modulus G′) becomes higher than the viscous behavior (represented by the loss modulus, G”). Meanwhile, in the low frequency range, G” prevails over G’ [57].

      Zeta potential is an important property in coacervation processes and other applications, including molecular interactions with other components. VG, as GG and other galactomannan gums, is nearly neutral with weak acid behavior in solution and high stability to pH changes [58].

      Galactomannans (such as ECG, GG and VG) are able to produce stable emulsions and reduce oil in water interfacial tensions. The emulsifying activity of galactomannans is not completely explained. The possible reasons are their non-polar regions, their protein content, or the protein moieties bounded to the gum, besides to their ability to thicken the aqueous phase [59, 60].

       2.2.4.2 Gums From Fabaceae Family Exudates

      The international market of exudate gums comprises only few varieties: arabic gum (Acacia Senegal Willd.), karaya (Sterculia urens Roxb.), tragacanth (Astragalus gummifer (Labill.) Podl.) and gatti (Anogeissus latifolia Roxb.) Wall., which producer trees are confined to specific Asian regions [61]. Certain trade difficulties related to sustained supply, variable quality and high importation costs has focused the researchers’ attention on the search and exploitation of non-conventional exudate gums to find local alternatives to commercially available gums [36]. The environment particularities and botanical identity of gum producer trees, impart distinctive functional properties resulting in gums with different applications.

      Exudate gums are generated in response to stress conditions, such as mechanical injuries, dehydration, microorganisms and insects attack [62]. Their main components are different carbohydrates, and also proteins, minerals and also polyphenols, among other antioxidant compounds [63].

Their appropriate physical properties and biocompatibility favored their use from ancient times [63]. Particularly, the exudate gum obtained from P. alba Griseb. trees or “algarrobo blanco”, PAEG (Figure 2.5) is comparable to arabic gum [37]. It grows in South America arid and semi-arid regions [38], and its seeds and pods are often employed as ingredient for a variety of food products [64]. The exudate gum is hand collected in several locations in Chaco, Argentine, and purified by dissolution in water, heat treatment, filtration to remove impurities and finally dried [37]. Obtained gum powder exhibits a bright brown color and transparent shiny appearance (Figure 2.5).

      Protein fraction in PAEG is markedly higher than in arabic gum, with better interfacial and emulsifying properties. PAEG is able to lower the interfacial tension and to stabilize emulsions based on high charge distribution (negative ζ-potential) and good interfacial rheological properties [37]. When PAEG was included in beads obtained by ionic gelation, fish oil oxidation was inhibited [65–67]. Additionally, PAEG affected water–solid interactions of the beads, favoring the formation of glassy matrices and improving the protection against lipid oxidation [68].