Determination of ideal water activity and powder temperature after spray drying to reduce Lactococcus lactis cell viability loss

Abstract

Spray drying presents a promising technology for preserving bacteria despite a low survival rate of heatsensitive cultures when subjected to the drying process. The aim of this study was to determine the ideal powder parameters [water activity (Aw) and temperature (T°C powder )] needed to produce dehydrated Lactococcus lactis ssp. lactis with a high viability after drying. Cell concentrates injected into a spray dryer using varying cell concentrate flow rates (F concentrate = 0.3 to 1.0 kg/h), inlet air temperatures (T°C inlet air = 115 to 160°C), and outlet air temperatures (T°C outlet air = 70 to 115°C) resulted in powders with different values of Aw and T°C powder , and levels of cell viability loss. Lower cell viability reduction (~0.43 log cycles) was obtained in conditions of Aw = 0.198 and T°C powder = 52°C, which can be met by using T°C inlet air ~126°C and T°C outlet air = 88.9°C regardless of F concentrate values. After 60 d of storage at room temperature, cell population varied from 7.0 × 10 5 to 1.1 × 10 8 cfu/g. The initial powder Aw had no influence on cell death rate, but T°C powder influence was observed. The approach adopted in this study can be applied to other bacteria or spray dryer equipment to determine optimal drying conditions.

Functional probiotics of lactic acid bacteria from Hu sheep milk

“…In addition, spray drying is an economical storage technology being used for probiotics processing, which offers dry and stable powdered form of probiotics and thought to be convenient in transportation which is widely used in dairy industry [20,21]. However, heat-sensitive cultures have a low survival rate during spray drying procedures [21,22]. Therefore, it is significant to determine the thermal stability of probiotics and to optimize thermal threshold, which could be cost effective during industrial usage.…”

The influence of adaptive stresses on the survival of spray-dried Lactococcus lactis cells

“…Although the drying parameters have a strong influence on the ultimate viability of L. lactis , the sample powders' physical properties can also have a strong influence. In general, powders with values of Aw beyond to 0.20 are not ideal for the survival of spray-dried bacteria (Martins et al ., 2019 a ).…”

“…Microorganism and culture conditions L. lactis subsp. lactis was activated by adding 1% v/v of the culture to 10 ml of Man, Rogosa and Sharpe medium (MRS, Difco, France) with an incubation at 30°C for 18 h. This strain was chosen as a model for thermal-sensitive bacteria based on data reported in our previous studies (Martins et al, 2019a(Martins et al, , 2019b.…”

“…However, spray drying promotes osmotic, thermal and oxidative stresses which cause a loss of cell viability. To overcome these drawbacks, studies have pointed to controlling operational drying parameters and using encapsulating materials with protective thermal properties as ways to improve the cell survival (Martins et al, 2019a(Martins et al, , 2019b. Another way to prevent LAB cell death consists in adapting the microorganisms prior to spray drying by subjecting them to sublethal stresses.…”

Challenges associated with spray drying of lactic acid bacteria: Understanding cell viability loss

“…Although several studies have focused on ways to improve spray‐dried LAB viability (Gong et al., 2019; S. Huang, Cauty, et al., 2016; S. Huang, Méjean, et al., 2017; S. Huang, Rabah, et al., 2016; Jokicevic et al., 2020; Martins, Cnossen, Silva, Cezarino, et al., 2019; Martins, Cnossen, Silva, Vakarelova, et al., 2019), there has been no concise discussion of the spray‐drying process and how it may affect LAB cells to date. This review aims to demonstrate the operations and thermodynamic principles that govern spray drying, then correlate them to the damage suffered by LAB cells during the spray‐drying process.…”