Probiotics in fish feeds have shown positive growth and survival results in several freshwater and marine fish species; however, maintaining probiotic viability in dry feed has been a challenge, especially regarding spray-dried microdiets, although it is assumed that the nature of the process has the potential to encapsulate and protect probiotics with minimal chemical modification. Scarce information exists about the influence of the process and microdiet handling conditions. This study evaluated the effect of the spray-drying process, storage time, and marine water exposure on the viability of L. acidophilus encapsulated in fish microdiets.
Two experimental micro-encapsulated diets were elaborated by spray drying. One was supplemented with Lactobacillus acidophilus La-14 (2.98 x109 CFU L-1), and the other was used as a control diet (Table 1). Probiotic viability was evaluated in the supplemented diet, in agar culture media with ultra-filtered marine water (35 g L-1) and distilled water, after 24 h of the spray drying and every 15 days during six months of storage at 4 °C. The same procedure was performed in the control microdiet to ensure no cross-contamination. Bacterial colonies (CFU g-1) were counted on a dark field colony counter.
The spray-drying process did not impact the viability of the probiotic in the supplemented microdiet. The viability of the encapsulated strain in the microdiet steadily decreased (p<0.05) at 30 and 45 days, irrespective of the culture media (Fig. 1). The results suggest that spray-dried microdiets, including L. acidophilus La-14, can be stored for up to 6 months at 4 ºC maintaining an adequate CFU count (>109) and can be used as a probiotic supplement in microdiets for marine and freshwater fish larvae.