Physicochemical, rheological and functional properties of Dorema Ammoniacum gum and its application in Lactobacillus acidophilus encapsulation

Abstract

Because of increasing request for hydrocolloids, with specific practicality in current societies, introducing new hydrocolloid origins with appropriate effects is an important area of study in food chemistry. The gum was extracted from the mucilage of Dorema Ammoniacum (AMG) using solvent followed by alcohol precipitation and finally purification was performed using excess amounts of alcohol and acetone. Physicochemical, rheological, emulsyfing and edible film forming properties, moreover, encapsulating of L. Acidophilus were determined. The gum included high carbohydrate and low protein contents. Calcium and potassium are the major minerals of this gum. The main sugars existed in this gum were galactose and arabinose Therefore, AMG can be considered as arabinogalactan. The average molecular weight of this gum was 35 kDa. Presence of glycoside bonds and carboxyl, hydroxyl and methyl groups in the FT-IR spectra of this gum indicated that AMG behaved like a typical polyelectrolyte. The elemental analysis indicated the absence of sulfur in AMG. 1H and 13C NMR analysis demonstrated that AMG structure included β-D-Glucopyranose A-(1-6)-D-Galactopyranoronic–(1-. Intrinsic viscosity of AMG was in the range of 0.310 – 0.318 dl/g. The results of steady shear flow experiments of AMG solutions showed that the shear stress–shear rate, apparent viscosity–shear rate, shear stress–time data were well fitted with Herschel–Bulkley, Carraeu and cross models, respectively (higher R2 and lower RMSE). The strain and frequency sweep experiment results demonstrated that the samples with 3 and 6% w/v gum indicated viscous-like and samples with 10 and 20% w/v gum showed gel-like behavior. The results of droplet size analysis of emulsions containing AMG demonstrated that by increasing gum from 5 to 15% w/v, Zeta potential decreased but Z-average and PdI values increased which is related to depletion fluctuation therefore, the emulsifying capacity and emulsion stability were decreased. The foaming stability, capacity and dencity increased by increasing gum concentration. The results of steady shear flow experiments of emulsions containing AMG showed that apparent viscosity–shear rate was well fitted with sisko model and showed the highest R2 and lower RMSE. The strain and frequency sweep data indicated that except for emulsions containing 5% AMG, all emulsions showed weak gel-like behavior. The optimize point was achieved from RSM and CCD design for AMG-CMC based edible films included 4.5% AMG, 1.5% CMC and 14.19% clove essential oil. Probiotic microencapsulation L. Acidophilus by AMG increased its viability under acidic and alkaline conditions, which may be because of the protective effect of AMG with appropriate concentration. Chemically, AMG is similar to gum arabic which makes it a competent substitute of gum arabic for various applications. The main functional properties of AMG are its water solubility, thermal stability, surface activity, emulsifying ability, foaming and encapsulating capacity.