Effects of enzymatically-extracted purple rice bran fiber as a protectant of L. plantarum NRRL B-4496 during freezing, freeze drying, and storage

•Freezing methods influence the viability of Lactobacillus plantarum (probiotic).•Purple rice bran fiber (PRF) protects probiotic cells from damage during freeze drying and storage.•PRF protects the probiotic cells from bile.

This study investigated purple rice bran fiber (PRF) as a protectant for Lactobacillus plantarum NRRL B-4496 (LP) during freezing, freeze drying and storage. PRF was enzymatically extracted from purple rice bran. L. plantarum NRRL B-4496 was grown in MRS broth, centrifuged, and immobilized on PRF suspension. LP cells immobilized on PRF (LP-PRF) and free LP cell (control) samples were frozen in either air blast (AF) or cryogenic freezing (CF) before freeze drying. Freeze-dried (FLP) samples were stored either at room temperature or at refrigerated temperature. For either freezing method, PRF protected cells had less than one log reduction of viable cells while the control had reductions greater than six logs after freeze drying. The log reductions of viable LP cells protected with PRF after freeze drying and 12 weeks storage at 4° C for AF and CF treatments were 0.7 and 1.3 log cycle, respectively. The viable LP-PRF cell count for CF was significantly lower than for AF after 12 weeks at room temperature. PRF improved LP survival in both AF and CF samples in bile. This study demonstrated that freezing methods affected LP viability during storage and that PRF could protect at both refrigerated and room temperatures.