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Calcium alginate hydrogel beads have been widely studied as a carrier matrix for the delivery of food and pharmaceutical compounds. Typically, calcium alginate beads have a short dissolution time of between 1 to 2 h in simulated intestinal fluid, thus limiting some applications that require prolonged release of compounds. This study was aimed at fabricating calcium alginate beads with a prolonged dissolution profile by increasing the alginate concentration beyond the critical viscosity limit (approximately 5000 mPa s) that can be processed using the existing extrusion-dripping system. A temperature-controlled extrusion method was developed and the feasibility of producing alginate beads at ultra-high concentration (UHC) with an initial viscosity ranging from 33000 mPa s to 353000 mPa s was studied for the first time. The operating temperatures studied ranged from 40 °C to 80 °C. Spherical UHC alginate beads were successfully produced using an alginate solution with an initial viscosity of 33000 mPa s. Fourier-transform infrared (FTIR) analysis indicated that the chemical properties of the alginate gels were not affected by the operating temperature. The dissolution time of the UHC alginate beads was three times longer than that of the beads produced using the normal alginate concentration. In addition, the UHC alginate beads have a unique internal structure that differs from the normal beads. In conclusion, a facile method to produce the UHC alginate beads, without the need for chemical modification of the beads or/and additional processing steps, is demonstrated. The long dissolution time of the UHC alginate beads opens up windows of opportunity for applications in the sustained delivery of drugs and food ingredients.

The aim of this work was to determine the effect of formulation of alginate beads on their mechanical behavior and stiffness when compressed at high speed. The alginate beads were formulated using different types and concentrations of alginate and gelling cations and were produced using an extrusion-dripping method. Single wet beads were compressed at a speed of 40 mm/min, and their elastic limits were investigated, and the corresponding force versus displacement data were obtained. The Young's moduli of the beads were determined from the force versus displacement data using the Hertz's contact mechanics theory. The alginate beads were found to exhibit plastic behavior when they were compressed beyond 50% with the exception of copper–alginate beads for which yield occured at lower deformation. Alginate beads made of higher guluronic acid contents and gelling cations of higher chemical affinity were found to have greater stiffness. Increasing the concentration of alginate and gelling ions also generated a similar effect. At such a compression speed, the values of Young's modulus of the beads were found to be in the range between 250 and 900 kPa depending on the bead formulation.

A comparative study on the stability and potential of alginate and pectin based beads for production of poultry probiotic cells using MRS medium in repeated batch fermentation was conducted. The bead cores, made of three types of materials, i.e., ca-alginate, ca-pectinate and ca-alginate/pectinate, were compared. The effect of single and double layer coatings using chitosan and core material, respectively, on the bead stability and cell production were also studied. The pectin based beads were found to be more stable than that of the alginate beads and their stability was further improved by coating with chitosan. The cell concentration in pectin based beads was comparable to that in the alginate beads. On the other hand, pectin based beads gave significantly lower cell concentration in the growth medium for the initial fermentation cycles when compared to the alginate beads. In conclusion, pectin was found to be potential encapsulation material for probiotic cell production owing to its stability and favourable microenvironment for cell growth.

The aim of this work was to develop a standard quantitative method to measure the acid tolerance of probiotic cells when exposed to a simulated gastric fluid. Three model strains of different cell concentrations were exposed to a standard simulated gastric fluid of fixed volume. The fluid pH ranged from pH 1.5 to 2.5. In general, the death kinetics followed an exponential trend. The overall death constant, k d, for all strains was found to be in a power relationship with the pH value and the initial cell concentration, and it can be expressed as $$ {k_{\text{d}}}{\text{ = }}{k_{\text{AII}}}\left( {{\text{p}}{{\text{H}}^{ - {\text{9}}.0}}{N_0}^{ - 0.{\text{19}}}} \right) $$ where k AII is defined as the acid intolerance indicator and N 0 is the initial cell concentration (CFU/ml). This equation was validated with the experimental data with an average R 2 of 0.98. The acid intolerance of cells can be quantitatively expressed by the k AII values, where higher value indicates higher intolerance. In conclusion, a standard quantitative method has been developed to measure the acid tolerance of probiotic cells. This could facilitate the selection of probiotic strains and processing technologies.