β-lactoglobulin and α-lactalbumin Hydrolysates as Sources of Antibacterial Peptides

The presence of antibacterial activity in bovine β-lactoglobulin and in α-lactalbumin hydrolysates was investigated. The Plasmin-Digest of β-lactoglobulin (PDβ) and of α-lactalbumin (PDα) were fractionated, using reversed phase high performance liquid chromatography. The antibacterial activity of β-lactoglobulin, α-lactalbumin, nisin, plasmin, PDβ and PDα were in vitro tested against pathogenic (Escherichia coli and Staphylococcus aureus) and probiotic (Lactobacillus casei and Lactobacillus acidophilus) bacteria. Although α-lactalbumin, β-lactoglobulin and plasmin exhibited no antibacterial activity, PDβ, PDα and nisin revealed antibacterial activity against the bacteria tested. The Minimum Inhibitory Concentration (MIC) of these compounds was determined for the bacteria cultures. Similar to nisin, the MIC of PDβ and of PDα against Gram-positive bacteria was recorded as considerably lower than the MICs against Gram-negative bacteria. The study also evaluated the effect of PDβ, PDα and nisin on the growth curves and on the plate count confirmations of the target bacteria. The results revealed that nisin, PDβ and PDα have inhibitory effects on the lag phase, maximum OD۶۲۰ and on plate count confirmation of the bacteria tested. The maximum inhibitory effect of these compounds was created during the log phase. Their inhibitory effects depended upon their concentrations, higher concentration causing stronger antibacterial activity. The PDβ and PDα proved more active against Gram-negative bacteria than did nisin, but nisin revealed substantial inhibitory activity against Gram-positive bacteria.