Issues with Industrial Probiotic Scale-up - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 354

probiotic activity might be related to halting fermentation when the bacteria are at their most
active, which does not necessarily equate to maximum yield. Producers who use stationary
phase bacteria might maximize production yield but this could be at the expense of quality
and viability.
The microorganisms are then usually separated from the culture medium through centrifu-
gation and concentration; around 80-90% of the water is removed, resulting in a concentration
of ×5to×10. The next step(s) is a further concentration and stabilization process, usually dry-
ing. With regards to aquaculture practices, Panigrahi et al. (2005) concluded that the freeze
drying method merited consideration as an efficient method of probiotic preservation rather
than spray drying.
Freeze drying was first used as a method of food preservation some 600 years ago by
the Incas. The process was first applied to live bacteria in the 1940s by Institut Rosell in
Canada (today part of Lallemand SAS), thus revolutionizing bacterial preservation and indus-
trial applications. Freeze drying involves quickly reaching a very low temperature, with water
eliminated by sublimation under low pressure. Given the quick reduction of cell temperature
involved, freeze drying is a very delicate process with regards to microorganisms as they are
very sensitive to extreme temperatures. The current practice in preserving the viability of bac-
teria for example is to mix it with a suitable cryo-protectant. As they are live organisms, each
strain will behave differently under freeze drying; thus careful consideration should be given
to optimizing the cryo-protectant used and the freeze drying parameters (temperature cycle,
pressure etc.).
The subsequent treatment of the freeze-dried organism such as grinding, blending and even
the final formulation and packing are also crucial steps to monitor. For example the packag-
ing material will affect the subsequent viability and performance of the microorganism; as
examples, the live bacteria could be highly sensitive to moisture or oxygen. Packaging mate-
rials have varying levels of oxygen and moisture permeability (transmission rates) and this
should be considered to meet the needs of the microorganism concerned. There is also a need
for stringent control of environmental temperature and humidity during packaging. Storage
conditions are also critical with regards to the subsequent probiotic survival, viability and use.
13.3 MODE OF ADMINISTRATION
Another aspect which is vital for consideration in using probiotics in aquaculture is their means
of administration (and particularly with regards to the host's digestive tract). Many studies
have provided proof of concepts but probiotic administration methods have been shown to
vary extensively and are not always practical for fish and shrimp farming. The review under-
taken by Merrifield et al . (2010a) summarized the most important practical aspects that must
be considered and emphasized the need for further research with regards to form of supple-
mentation, vector of administration, dose levels and duration of application; therefore, this
chapter will only focus on the vector of administration.
One of the most common routes of administration for probiotics is via incorporation in the
feed. For industrial scale application, therefore, the technology associated with incorporation
in extruded and pelleted feeds is paramount. In order to exert their effects, probiotics must be
viable at their site of action, meaning that the selected microorganism must survive the stressful
conditions of feed processing and storage. This is of particular concern in aquaculture since