IMPACT OF OSCILLATING MAGNETIC FIELD ASSISTED FREEZING ON Lactobacillus plantarum VIABILITY: EFFECTS OF FROZEN STORAGE TIME AND FREEZE-THAW REPETITIONS

Abstract

BACKGROUND: Oscillating magnetic field (OMF) assisted freezing has been proposed for improving the frozen preservation of biological materials. However, contradictory results have been reported on foods, tissues and cells, and so doubts exist in its actual benefit. OBJECTIVE: To study the effect of OMF-assisted freezing on the viability of fermentation starter Lactobacillus plantarum. MATERIALS AND METHODS: L. plantarum bacteria were frozen in a batch air blast freezer (-20 degrees C, 5 m s(-1)) by OMF-assisted freezing (0.57 mT). Bacterial viability was examined after 60 days of frozen storage and five freeze-thaw cycles. RESULTS: OMF showed no statistically significant effects (P > 0.05) in key freezing curve characteristics, refuting Cell Alive System (CAS) technology claims. OMF-assisted freezing did not improve bacterial preservation. CONCLUSION: There was no effect ofthe application of the maximum OMF (0.57 mT) on cell viability independently of the frozen storage time (up to 60 days) and freeze thaw repetitions (up to five cycles).