Кемерово, Кемеровская область, Россия
Protein hydrolysates have a high biological and nutritional value and are widely used in various sectors of the food, medical, and pharmaceutical industries. This article deals with the chemical hydrolysis of the milk protein casein in the presence of hydrochloric or sulfuric acid and reports the hydrolysis parameters minimizing the loss of amino acids. In casein hydrolysis, peptide bonds of protein molecules break to form di- and tripeptides and free amino acids, enhancing protein absorption by the body. Inadequate intake of digestible forms of protein leads to disruption of growth processes and impairs the immune resilience of the human body. To avoid the decomposition of labile amino acids, hydrolysis was performed with triply distilled 6 M hydrochloric or sulfuric acid in a vacuum in sealed ampoules for 4, 8, or 24 (±0.05) h at a temperature of 110 ± 5°C and a substrate-to-acid ratio of 1 : 15, 1 : 20, or 1 : 25. The compositions of the casein hydrolysates obtained at various hydrolysis times are presented. For a more detailed evaluation of the properties of the casein hydrolysates, the hydrolysis time effect on the molecular weight distribution of proteins and peptides has been investigated. The problem of obtaining protein hydrolysates with the desired composition and properties remains topical.
acid hydrolysis, casein, protein, degree of hydrolysis, peptides, amino acids, hydrolysates
INTRODUCTION
Protein hydrolysates are the products of the hydrolytic decomposition of proteins. They consist mainly of separate amino acids, their sodium salts, and polypeptide residues. During hydrolysis, the peptide bonds in protein molecules break to yield di- and tripeptides and free amino acids, thus increasing protein assimilation in the living organism. Mixtures of various peptides are more rapidly and more completely absorbed in the digestive tract than proteins themselves. In addition, protein hydrolysates may contain various physiologically active peptides necessary for regulation of a number of essential functions of the living organism. Note that peptides contained in hydrolysates can possibly exert a favorable effect on the absorption of some essential micronutrients. Protein hydrolysis is used to produce preparations for the following applications: blood substitution and parenteral nutrition in medicine; protein deficiency compensation, resistance enhancement, and improvement of youngsters’ development in veterinary; sources of amino acids and peptides for bacterial and culture growth media in biotechnology. Casein hydrolysates contain peptides that are capable to form stable coordination compounds (chelates) with calcium ions and to considerably raise the absorbability of the latter [2–4]. Again there are data indicating that phosphopeptides of β-casein, like κ-casein glycomacropeptide and peptides of whey proteins, markedly increase the bioavailability of iron and can be considered as favorable factors in anemia prophylaxis.
In view of this, milk protein hydrolysates are widely used in the food, medical, pharmaceutical, and fragrance industries as rich sources of nonmacromolecular nitrogen compounds, amino acids, and proteins.
The chemical methods employed in the hydrolysis of milk proteins are facile and do not require use of uncommon or expensive enzymes, but they need severe processing conditions. The production of protein hydrolysates by acid hydrolysis is carried out above 100°C at pH 1–2 using inorganic (hydrochloric, sulfuric, orthophosphoric) acids. The rate of release and destruction of individual amino acids depends mainly on the nature of the protein.
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