Enhanced viability of freeze-dried Lactobacillus acidophilus using supercooling pretreatment

Abstract

Viability loss during the freezing process remains a big challenge for freeze-dried lactic acid bacteria. Oscillating magnetic field (OMF)-assisted supercooling pretreatment was studied and validated for the improving the viability of freeze-dried L. acidophilus. OMF-assisted supercooling decreased supercooling temperature to -7 °C without ice crystallization, while one of the reference groups without OMF assistance was frozen at -7 °C. Supercooling pretreatment increased surface layer protein (SLP) expression and improved cell viability. The SLP on supercooling pretreated cells was thicker than those without supercooling pretreated cells. Supercooling pretreatment significantly increased the viability of L. acidophilus after freeze-drying compared to those that did not undergo a pretreatment. The highest viability of 78% was observed after freeze-drying with supercooling pretreatment. SLP expression during pretreatment protected cells in the freezing process and helped maintain cell viability. These results suggested that OMF-assisted supercooling pretreatment enhanced the viability of freeze-dried L. acidophilus.