Elsevier

Journal of Biotechnology

Volume 159, Issue 4, 30 June 2012, Pages 351-357
Journal of Biotechnology

Combined influence of fermentation and drying conditions on survival and metabolic activity of starter and probiotic cultures after low-temperature vacuum drying

https://doi.org/10.1016/j.jbiotec.2011.06.010Get rights and content

Abstract

The influence of low temperature vacuum drying process parameters on the survival, metabolic activity and residual water content of three different bacterial strains (Lactobacillus paracasei ssp. paracasei, Lactobacillus delbrueckii ssp. bulgaricus and Bifidobacterium lactis) was investigated. Shelf temperature and chamber pressure were varied and optimized by response surface methodology with regard to survival and residual water content. It is shown that the survival rate after low temperature vacuum drying is comparable to that of freeze drying. Based on the optimization experiments the combined influence of fermentation pH and drying process parameters was studied for the most detrimental and the best process condition, respectively. The results show that interactions between process and fermentation conditions have to be taken in account and that these influences are highly strain specific.

Introduction

In the manufacture of food, there is a demand of stable and well-conditioned starter, protective and probiotic cultures. The established process for the preparation of these cultures is freeze drying as it is known to be a very gentle drying method. However, freeze drying is a lengthy and energy intensive process (Knorr, 1998, Regier et al., 2004). Moreover, the survival of some bacterial strains is negatively affected by the freezing process (Meryman et al., 1977, Meryman, 2007).

An alternative drying method is vacuum drying, which works at reduced temperatures by applying vacuum. Using this drying method at conventional conditions (temperature range between 30 and 80 °C) may cause high losses of cells due to heat damage (Valdramidis et al., 2005). However, heat stresses can be reduced by further reducing the chamber pressure to values just above the triple point of water, which leads to low product temperatures close to 0 °C. This process is referred to as Controlled Low-Temperature Vacuum Dehydration (CLTV). King et al. (1989) developed this method for the drying of sensitive food ingredients and also showed that it is applicable to the drying of microorganisms such as Lactobacillus acidophilus (King and Su, 1993). However, the authors did not study the influence of drying process conditions on survival.

It is not known how the fermentation step prior to drying influences the drying behavior of cells during low-temperature vacuum drying. However, it is well known that the fermentation conditions have a large impact on the resistance against freezing and freeze drying. Lorca and De Valdez (2001) showed for Lactobacillus acidophilus that an uncontrolled fermentation (final pH 4.5) yields more stable cells against freezing, freeze drying and some substances (ethanol, H2O2) than a controlled fermentation (constant pH 6.0). However, it is unclear whether the protection can be explained by its effectiveness against the low temperatures during freeze drying or dehydration. Wang et al. (2005) investigated the cryotolerance of Lactobacillus acidophilus for different growth pH values and showed an increase in survival after freezing and frozen storage of pH stressed cells. This indicates that the fermentation pH mainly influences the protection mechanisms against low temperatures. However, Silva et al. (2005) showed that the survival of Lactobacillus delbrueckii ssp. bulgaricus after spray drying is higher for cells grown with free acidification compared with cells grown at a controlled optimum of pH 6.5. This refers to a protection effect against dehydration or high temperatures. Therefore, it is necessary to investigate the influence of the fermentation pH on the survival during dehydration at moderate temperatures.

It is also unknown whether a fermentation with free acidification leads to similar effects as a fermentation under acidic stress conditions with constant pH. This requires comparing both stress situations to the results of a controlled fermentation at optimum pH. Furthermore, the interrelation between fermentation and drying process conditions had not been studied before.

Additionally, there is no information available on the strain specific drying behavior, including survival rate and residual water content, within the same drying and fermentation setup. Publications so far only used one strain per study so that the question on comparability between studies arises.

Therefore, it is the aim of this work to investigate the influence of drying process parameters of low temperature vacuum dehydration on survival and metabolic activity of three different strains relevant for food applications. In addition, the interactions between different fermentation pH values and drying conditions will be studied. The purpose is further to assess strain specific differences in drying behavior within one experimental setup.

Section snippets

Cultures

Lactobacillus paracasei ssp. paracasei F19 from Medipharm AB (Kaageröd, Sweden) and Bifidobacterium lactis Bb12 from Chr. Hansen (Hoersholm, Denmark) were used as two of the three chosen model microorganisms. The cells were provided as a frozen concentrate with a titer of about 1011 CFU/g (CFU = colony-forming units). Concentrated cells were stored at −40 °C.

L. delbrueckii ssp. bulgaricus TMW 1.1377 from the Culture Collection of Microorganisms of the Chair for Technische Mikrobiologie of the TU

Influence of drying process conditions on survival

The influence of drying process conditions on survival was determined for the three different strains L. paracasei, B. lactis and L. delbrueckii. It is shown that the influence of process conditions on survival and metabolic activity is immense, as exemplarily shown for L. paracasei in Fig. 2.

Fig. 2 shows that the area A under the acidification curve as well as the lag-phase differs depending on the process conditions. It can be seen that a long lag-phase and a large area A correspond to a low

Conclusion

It was shown that within the low-temperature vacuum drying a decrease in product temperature and an increase in residual water content led to a higher survival rate of L. paracasei ssp. paracasei F19. However, this does not apply for B. lactis Bb12 and L. delbrueckii ssp. bulgaricus. B. lactis shows an increase of survival rate with higher residual water content. By employing a response surface methodology it is possible to optimize for both survival and residual water content. Comparing the

Acknowledgements

This research project was supported by the German Ministry of Economics and Technology (via AiF) and the FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn. Project AiF 15616N).

References (24)

  • K. Fischer

    Neues Verfahren zur maßanalytischen Bestimmung des Wassergehaltes von Flüssigkeiten und festen Körpern

    Angew. Chem.

    (1935)
  • G.E. Gardiner et al.

    Comparative survival rates of human-derived probiotic Lactobacillus paracasei and Lactobacillus salivarius strains during heat treatment and spray drying

    Appl. Environ. Microbiol.

    (2000)
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