Issues with Industrial Probiotic Scale-up - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 355

feed processing conditions are harsher than those for farmed terrestrial animals. One of the
main challenges is high temperature, which is seen as a major drawback; this could explain
the limited development of in-feed application of probiotics for use in aquaculture and also
the disparity in label claims against content as discussed earlier in this chapter.
In order to overcome these issues, novel approaches include for example inducing heat
tolerance in the potential microorganism by optimizing the production conditions during the
manufacturing process. Altering different parameters such as pH and temperature during the
growing phase, application of pre-heat treatment, harvesting at a specific physiological state,
growth media characteristics and drying parameters could also assert particular influences that
might culminate in the ability of the microorganism to resist heat at a subsequent encounter. In
their study of autochthonous and allochthonous probiotics for consideration for use in shrimp
feed, Kosin and Rakshit (2010) showed that for several species (including Lactobacillus plan-
tarum , Leuconostocmesenteroides , Bacilluslicheniformis and Bacillussubtilis ), manipulating
the pH of the growth media, the physiological growth phase and the application of heat or
osmotic pre-treatment positively induced heat tolerance in these bacteria, when applied on
shrimp feed at higher temperatures. For instance, the authors reported that an Lb. plantarum
strain showed 48% survival after exposure to 60 ∘ C, after storage for 4 weeks at 4-5 ∘ C, when
the bacteria were prior heat-treated (50 ∘ C) and exposed to 0.3 M NaCl.
Lallemand SAS (France) and BioMar AS have successfully developed an industrial method
for the inclusion of Bactocell ® ( Pediococcus acidilactici CNCM 18/5MA) in commercial fish
feeds such as EFICO Vital ® and INICIO Plus ® (Castex and Aarestrup 2011). This break-
through followed some in-depth research and development centred on optimizing the produc-
tion parameters of the probiotic and of the commercial feed. The resulting conditions were
optimal for the probiotic's incorporation in extruded feeds with a recovery rate of 96.2% and
good stability during storage.
It is important to highlight that some bacteria naturally exhibit a better resistance to heat,
specifically spore forming bacteria. Spores are produced in nature by some microorganisms
as a means to survive extreme environmental conditions (i.e. UV radiation, extreme heat,
chemicals such as solvents, hydrogen peroxide, lysozyme etc.) and to enable longer term
survival in conditions that could otherwise kill the vegetative cell (Nicholson et al. 2000).
Spores can germinate under favourable conditions (appropriate nutrients and water) (Moir
2006) and thus could be ideal candidates for probiotic use in aquaculture. Therefore spore
forming bacteria, particularly Bacillus species, are often interesting potential probiotics for
feed applications: they can be heat stable, conferring fairly good viability after pelleting, and
have high resistance to gastric conditions (Casula and Cutting 2002; Hong et al. 2005; Cutting
2011). However their survivability during the higher temperature pelletization or extrusion
encountered in shrimp feeds is questionable. Suggestions to include spore forming bacteria
directly in aquaculture feeds before pelletization and/or extrusion may not be ideal. Temper-
atures could be as high as 85 to 90 ∘ C during aquafeed pelletization and could even exceed
100 ∘ C in the case of extrusion. Spore forming bacteria will not resist such harsh conditions.
Kosin and Rakshit (2010) evaluated two heat tolerant Bacillus sp. ( B.licheniformis and B.sub-
tilis ) for their viability after spraying onto shrimp feed pellets subjected to 80 ∘ C and 70 ∘ C,
respectively. They reported a survival rate (CFU) for B. licheniformis and B. subtilis of 40%
and 30%, respectively - less than that obtained with the heat adapted Lactobacillus . In con-
clusion therefore, where feed application of probiotics in aquaculture is concerned, attention
must be paid to the heat tolerance and stability of each potential probiotic as well as their