Effect of Encapsulated Probiotic Starter Culture on Rheological and Structural Properties of Natural Hydrogel Carriers Affected by Fermentation and Gastrointestinal Conditions

The suitability of natural hydrogel carriers with probiotic starter culture as whey beverages supplements was examined by assessing their rheological and structural changes during the fermentation and gastrointestinal conditions. Effect of encapsulated cells on the carrier structure is of great importance for the selection of proper material for the preparation of functional supplements. The structural changes of the chitosan-coated alginate/whey carriers were considered based on (1) cell viability and the carrier average volume vs. time (2) the storage and loss modulus vs. time obtained under low oscillator strain conditions, (3) FTIR analysis and (4) SEM cross-sectional observation of the hydrogel carriers. The presence of chitosan coating and fermentation conditions increased cell viability up to 9.01 ± 0.18 (log CFU/g). According to our results, the encapsulated cells induce weakening of carriers under the gastric conditions but improve their mechanical stability under the intestinal condition. The mechanical behaviour of carriers was also considered in order to formulate the rheological constitutive model equation for describing the irreversible structural changes under the gastric and intestinal conditions. The cell leakage under the gastric condition after the 2 h was less than 5%. Carriers are rapidly degraded under the intestinal condition which ensures the release of cells and provides their beneficial effects on the host health. Our results indicate that this type of coated carrier is suitable to be used for encapsulation of probiotic starter culture in the production of fermented whey-based products.

     

Immobilization of Lactobacillus rhamnosus in polyvinyl alcohol/calcium alginate matrix for production of lactic acid

Immobilization of Lactobacillus rhamnosus ATCC7469 in poly(vinyl alcohol)/calcium alginate (PVA/Ca-alginate) matrix using “freezing–thawing” technique for application in lactic acid (LA) fermentation was studied in this paper. PVA/Ca-alginate beads were made from sterile and non-sterile PVA and sodium alginate solutions. According to mechanical properties, the PVA/Ca-alginate beads expressed a strong elastic character. Obtained PVA/Ca-alginate beads were further applied in batch and repeated batch LA fermentations. Regarding cell viability, L. rhamnosus cells survived well rather sharp immobilization procedure and significant cell proliferation was observed in further fermentation studies achieving high cell viability (up to 10.7 log CFU g⁻¹) in sterile beads. In batch LA fermentation, the immobilized biocatalyst was superior to free cell fermentation system (by 37.1%), while the highest LA yield and volumetric productivity of 97.6% and 0.8 g L⁻¹ h⁻¹, respectively, were attained in repeated batch fermentation. During seven consecutive batch fermentations, the biocatalyst showed high mechanical and operational stability reaching an overall productivity of 0.78 g L⁻¹ h⁻¹. This study suggested that the “freezing–thawing” technique can be successfully used for immobilization of L. rhamnosus in PVA/Ca-alginate matrix without loss of either viability or LA fermentation capability.