Aminoasitlerin Farklı Fermantasyon Koşullarında Ortaya Çıkan Değişimlerinin İncelenmesi
Özet
Fermentation is one of the food processing techniques, which can change the chemical composition of foods. Changes in chemical composition during fermentation stem from metabolism of microorganisms found in fermented foods, which leads to formation of microbial metabolites. Their formation in fermented foods is of critical importance due to the fact that microbial metabolites can affect human health positively or negatively. The main focus of this thesis was to understand changes of amino acids and thereby, formation of bioactive amines and tryptophan derivatives during fermentation.
At the beginning of this study, the effect of S. cerevisiae on the formation of gamma-aminobutyric acid (GABA) and the other bioactive amines during wort fermentation was investigated. For this purpose, spoiled and unspoiled worts were evaluated in terms of content of bioactive amines. Unspoiled wort was prepared by adding antibiotic to the wort. During fermentation, concentration of GABA increased in both unspoiled and spoiled worts. In spite of that, tyramine and histamine were found only in spoiled wort. Decreased concentrations of tyrosine and histidine were associated with increased concentrations of tyramine and histamine, respectively, in spoiled wort. The results indicated that occurrence of GABA in beers should not be considered as one of the indicators of microbial contamination differently from tyramine and histamine.
In the second part, the formation of tyramine during yoghurt fermentation with the focus on interaction between Streptococcus thermophilus RSKK 04082, Lactobacillus delbrueckii subsp. bulgaricus DSM 20081 and Lactobacillus plantarum RSKK 02030 was investigated. These microorganisms were used in the yoghurt fermentation as single strains or mixed cultures containing double or triple strains. The interactions between microorganisms have been also revealed by determining total free amino acids and the pH of the medium together with the microbial count of the strains. It was observed that L. delbrueckii subsp. bulgaricus DSM 20081 did not produce tyramine while S. thermophilus RSKK 04082 and L. plantarum RSKK 02030 could produce tyramine depending on the fermentation conditions. Synergistic interactions between S. thermophilus RSKK 04082 and L. delbrueckii subsp. bulgaricus DSM 20081 and, between L. delbrueckii subsp. bulgaricus DSM 20081 and L. plantarum RSKK 02030 were found in terms of tyramine production. It was observed in this study that L. delbrueckii subsp. bulgaricus DSM 20081 had indirect impact for accumulation of tyramine in the yoghurts.
In the third part, a method for the detection of tryptophan derivatives in kynurenine pathway using tandem mass spectrometry in various fermented food products (bread, beer, red wine, white cheese, yoghurt, kefir and cocoa powder) was developed. The method entails an aqueous extraction and reversed phase chromatographic separation using pentafluorophenyl (PFP) column. It allowed quantitation of low ppb levels of tryptophan and its derivatives in different fermented food matrices. Dairy products (yoghurt, white cheese and kefir) were found to contain kynurenine. Although bread samples analyzed did not contain kynurenic acid, beer and red wine samples as yeast-fermented foods were found to contain kynurenic acid. Among foods analyzed, cacao powder had the highest amounts of kynurenic acid, which is a neuroprotective compound.
In the fourth part, the formation of tryptophan derivatives in kynurenine pathway by S. cerevisiae NCYC 88 and S. pastorianus NCYC 203 during wort fermentation by using Gompertz model was investigated. As a result of this study, more tryptophan was utilized by S. cerevisiae NCYC 88 during fermentation as compared to S. pastorianus NCYC 203. The kynurenic acid concentration of wort fermented with S. cerevisiae NCYC 88 and S. pastorianus NCYC 203 increased during fermentation. When tryptophan was added into the wort fermented with S. cerevisiae NCYC 88 and S. pastorianus NCYC 203, the concentrations of the kynurenic acid increased. Moreover, the kynurenine content of worts fermented with S. cerevisiae NCYC 88 increased when tryptophan was added into the wort. It was also observed in this study that S. pastorianus NCYC 203 used more niacin than S. cerevisiae NCYC 88 during beer fermentation.
