Survival, fermentation activity and storage stability of spray dried Lactococcus lactis produced via different atomization regimes

Dried powders containing Lactococcus lactis ssp. cremoris were produced using laboratory and pilot scale spray dryers with lactose:whey protein isolate (3:1) as a protective medium. The effects of storage temperature (25, 4 and −18 °C) and time (30, 60 and 90 days) were studied. The survival and fermentation activity of the dried bacterial cells were significantly lower when the powders were stored at 25 °C compared to those stored at 4 and −18 °C; powders stored at 4 and −18 °C were statistically similar. The survival and fermentation activity of bacterial cells obtained from a laboratory scale two-fluid nozzle spray dryer were found to be higher than those of cells obtained from a pilot scale two-fluid spray dryer. A rotary wheel atomizer gave significantly higher survival and activity in the same dryer. These observations are consistent with cell damage due to high characteristic shear rates in the atomization process in nozzle type atomizers. The presence of ascorbic acid (oxygen scavenger) in the powder composition was found to improve both the survival and the maintenance of fermentation activity of the dried bacterial cells significantly during storage. The survival and fermentation activity of dried bacterial cells in stored powders indicated that these parameters are system-specific and can be strongly affected by the storage temperature and presence or absence of antioxidant, and also by upstream processing conditions such as the mode of atomization and presence or absence of antioxidants in the dryer feed.

► Survival/bioactivity of Lactococcus lactis in stored powders obtained through two-fluid atomizer is lower.
► Survival/bioactivity of L. lactis in stored powdered obtained through rotary atomizer is higher.
► Survival/bioactivity of L. lactis in stored powders atomized/dried in the presence of antioxidant is higher.
► Survival/bioactivity of L. lactis in stored powders is affected by shear rate and level of oxygen during atomization.
► Survival/bioactivity of L. lactis stored at 25 °C was the lowest while those stored at 4 °C and −18 °C were the same.