Characterization of antibacterial activity from protein hydrolysates of the macroalga Saccharina longicruris and identification of peptides implied in bioactivity

The macroalga Saccharina longicruris proteins were extracted and hydrolysed with the enzyme trypsin in order to recover antibacterial peptides, which could be used in reducing food spoilage. The >10 kDa protein hydrolysate fraction exhibited activity against the bacterium Staphylococcus aureus with a significant decrease of the maximum specific growth rate, µmax, from concentrations of 0.31 mg/mL to 2.5 mg/mL. Protein precursors were identified in a subfraction (Fr1) enriched in antibacterial peptides using liquid chromatography–tandem mass spectrometry (LC–MS/MS) with database searches. Identified peptides came from different precursors such as a protein similar to ubiquitin, histones, a hypothetical leucine rich repeat protein and a ribosomal protein. These proteins might be associated with the innate immune defences in S. longicruris. Peptidic sequences were chemically synthesized and their bioactivity confirmed, suggesting that activity probably results from synergies between peptides. This is the first time that antibacterial peptides originating from algal protein hydrolysates were isolated and characterized.