Use of hydrolysates from yellowfin tuna Thunnus albacares fisheries by-product as a nitrogen source for bacteria growth media

Hydrolysates of tuna head, using commercial enzymes Alcalase® (Alc) and Protamex™ (Prot), were tested as growth media for the bacterial strains of Pseudomonas putida, Pseudomonas aeruginosa, Streptococcus faecium, Listeria monocytogenes, Bacillus subtilis, Bacillus licheniformis and Micrococcus lysodeikticus, as an alternative to commonly used complex sources (peptones and/or extracts). Peptones from the enzymatic hydrolysis by Alcalase and Protamex were used instead of standard peptones used in commercial media. All bacteria were cultured on traditional standard media as controls, and their growth was compared to ones grown on experimental media containing Alc- and Prot-peptone instead of the standard peptone. Peptones produced by Alcalase and Protamex had obtained 34 and 19% degree of hydrolysis, respectively. The results showed that both the Alcalase and Protamex peptones were more effective at promoting bacterial growth than the standards used in traditional media, while the peptone from Alcalase, with a higher percent of hydrolysis, was more effective than the peptone from Protamex, also in terms of biomass production, Thus the choice of the proteolytic enzymes used to produce the fish hydrolysates had a considerable impact on the performance of the resulting hydrolysate.