Bioactive amines, free amino acids and ammonia as quality indexes of fermented milk

Fermented milk is considered a healthy food because it carries probiotic microorganisms. The objective of this study was to investigate the profile and levels of free amino acids, amines and ammonia in five different brands of fermented milk before and after the expiration date. Within shelf life, the samples had pH of 4.044.06, titratable acidity of 0.82-0.99 g lactic acid/100 g, total solids of 7.33-12.0 g/100 g, and spermine levels of 0.28-0.80 mg/kg. Three to 11 amino acids were found depending on the brand, at total levels of 4.19 to 17.77 mg/kg. Arginine and asparagine were present in every brand, whereas aspartic acid, leucine and lysine were present each in only one brand. Phenylalanine was present in two brands. Arginine, asparagine, histidine, proline and threonine were the predominant amino acids. After the expiration date, there was no change in pH, acidity and total solids for all brands. The profile and levels of amino acids and amines changed for three brands. New amino acids (glycine and serine) and ammonia were detected. Overall, the levels of glycine, serine, proline, leucine, lysine and phenylalanine increased; whereas the levels of asparagine, histidine and threonine decreased. New amines were detected – serotonin and agmatine. Multivariate analysis (PCA and HCA) confirmed that the amino acids glycine and serine and the amines serotonin and agmatine are potential differentiators of the quality of three of the five brands of fermented milk.