Proteins are one of the primary components of the food, both in terms of nutrition and function. They are main source of amino acids, essential for synthesis of proteins, and also source of energy. Additionally, many proteins exhibit specifi c biological activities, which may have effect on functional or pro-health properties of food products. These proteins and their hydrolysis products, peptides, may infl uence the properties of food and human organism. The number of commercially available food products containing bioactive peptides is very low, apart from that milk proteins are their rich source. It could be supposed that number of available products with declared activity will rise in near future because of observed strong uptrend on interest in such products. Molecular and biological properties of milk proteins, as precursors of bioactive peptides was characterised in the work. Therefore, the strategy of research and obtaining of such peptides both in laboratory and industrial scale, as well as the range of their commercial application, was presented. Several examples of research efforts presenting high potential to develop new products containing bioactive peptides from milk proteins and predetermined as nutraceuticals was described.
New peptides with potential antimicrobial activity, encrypted in milk protein sequences, were searched for with the use of bioinformatic tools. The major milk proteins were hydrolyzed in silico by 28 enzymes. The obtained peptides were characterized by the following parameters: molecular weight, isoelectric point, composition and number of amino acid residues, net charge at pH 7.0, aliphatic index, instability index, Boman index, and GRAVY index, and compared with those calculated for known 416 antimicrobial peptides including 59 antimicrobial peptides (AMPs) from milk proteins listed in the BIOPEP database. A simple analysis of physico-chemical properties and the values of biological activity indicators were insufficient to select potentially antimicrobial peptides released in silico from milk proteins by proteolytic enzymes. The final selection was made based on the results of multidimensional statistical analysis such as support vector machines (SVM), random forest (RF), artificial neural networks (ANN) and discriminant analysis (DA) available in the Collection of Anti-Microbial Peptides (CAMP database). Eleven new peptides with potential antimicrobial activity were selected from all peptides released during in silico proteolysis of milk proteins.
Lactic acid bacteria were subjected to screening for the ability of the analyzed strains to synthesize surface-active compounds. The most favorable synthesis of biosurfactants was observed in the culture of Lactobacillus casei 8/4, thus this strain was applied in the subsequent stages of the study. The research enabled determining the optimal conditions of biosurfactants synthesis, which was shown to be mainly determined by the composition of the culture medium and growth phase of L. casei 8/4. Aqueous solutions of biosurfactant preparations displayed antimicrobial activity against the test pathogenic species: Staphylococcus aureus 11, Bacillus subtilis T91, and Micrococcus roseus R2. Analyses conducted with the FTIR demonstrated that biosurfactants were constituted by protein fractions and polysaccharide fractions, i.e. possessed the structure typical of glycoproteins, which is affected by medium composition and the phase of growth of the biosurfactants-synthesizing strain. The same factors determine the structure of proteins in glycoproteins, which was confirmed after electrophoretic separation with the NuPAGE method.
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