Biochemistry

1) redox interaction of carbonyl groups and amino groups with the formation of colorless intermediate products; 2) aldehyde-amine polymerization of intermediate products and aldehyde condensation with the formation of dark-colored complex compounds called melanoidins. As a result of melanoidinogenesis reactions, both amino acid and sugar break down: the corresponding aldehyde, ammonia and carbon monoxide (IV) are formed from the amino acid, and furfural (from pentose) or hydroxymethylfurfural (from hexoses) are formed from sugar. For example, the reaction of leucine with xylose proceeds as follows: H OH H !-€ — |-CHO OH H H Pentose (xylose) H,C CH-CH.-CH-COOH + HOH 2 C H</ ...... I T . NH, Leucine J + CH 3 — (jZH-CH 2 -C\ СНз H Isovalerian aldehyde HC-CH n нс" jc -сГ +NH, + co, о H Furfural Aldehydes derived from amino acids have a pleasant odor. The combination of odors of different aldehydes determines the aroma of many foods. Furfural (oxymethylfurfural) easily enters further reactions, forming melanoidins. The appearance of the latter causes the darkening of a number of products during their manufacture and storage. Melanoidin-forming reactions are especially intense when the temperature rises: during drying of vegetables, fruits, baking bread, roasting nuts, coffee, canning milk, making confectionery, malt, sugar solutions, during heat treatment of wine, etc. Amino acid composition of proteins Proteins of different origin differ from each other in the number of amino acids included in them. Currently, the amino acid composition of many hundreds of proteins of microorganisms, plants and animals has been studied. Data on the quantitative content and qualitative composition of amino acids in some proteins are shown in Eable 2.4. 45