Investigation of β-Glucan-Producing lactic acid bacteria strains for the stabilization of fruit preparations

Introduction: Fruit preparations are used as intermediate products in many applications in the food industry. Hydrocolloids, predominantly polysaccharides, are usually added as thickeners and stabilizers to prevent sedimentation or floating of fruit pieces in a fruit puree matrix.

Goal:The reported study aimed at the development of a screening procedure enabling the selection of β-D-glucan-producing lactic acid bacteria (LAB) strains and their application in situ for the stabilization of fruit preparations as additive replacement.

Materials & Methods: Potential LAB strains were isolated from environmental sources and investigated together with over 200 strains from our strain collection. The screening procedure included the confirmation of phenotypic slime formation on solid media, PCR-based detection of the gene-encoding β-D-glucan-producing glycosyltransferase (gtf-PCR), detection of β-D-glucan polysaccharide capsule by specific antibodies, and an in situ qualitative assay for the thickening of fruit, vegetable or mixed fruit-vegetable purees. Two strains were selected for a controlled fermentation process involving peach, strawberry, carrot and beetroot purees. The fermentation products were freeze-dried and then incorporated into fruit preparations, with subsequent measurement of the viscosity.

Results & Summary: The screening resulted in 50 strains exhibiting slimy phenotype, 11 of which were carrying the gtf gene. Six strains exhibited slime production in strawberry and peach purees combined with beetroot or carrot puree, respectively. These strains were identified as belonging to the species Pediococcus parvulus, Lacticaseibacillus paracasei, Levilactobacillus brevis, Pediococcus claussenii, and Furfurilactobacillus rossiae. Pasteurized model strawberry fruit preparations containing fermentates of the two tested strains L. brevis TMW 1.2112 and P. parvulus LTH 1110 showed no significant increase in viscosity compared to the control products.The chemical composition of the occurring polysaccharides is being studied. Further approaches are included in the ongoing research into the applicability of β-D-glucan-producing LAB in fruit preparations.