Analysis of protein and animo acids in Usak tarhana

Tarhana is one of the most important fermented foods for our country. Researchers have extensively employed the Kjeldahl method for determination of protein composition of this foodstuff which has been the subject of numerous scientific publications. The method utilizes the titratable nitrogen amount which when multiplied with a general conversion factor yields the crude protein content. There have been reports of increase in crude protein content of tarhana throughout prolonged fermentation. The extent to which the crude protein composition can reflect the true protein composition is not clear. The aim of this study was the utilization of the Kjeldahl method as well as the determination of total and free amino acids throughout fermentation in order to determine crude and true protein contents and to compare the methods. Uşak type tarhana samples were prepared based on the the recipe provided within the designation of geographical origin, with yeast (Saccharomyces cerevisiae) addition and without, corresponding to the spontaneous fermentation which is also commonly applied in household production. Samples taken from these dough samples throughout fermentation (lasting 21 days) were analyzed in order to determine the effect of fermentation on the protein composition. Dry matter content, pH and titratable acidity were also determined for characterization of the dough material. The results of the amino acid analyses showed that the levels of amino acids in spontaneous fermented dough were higher than that of yeast leavened dough. The crude protein contents of the doughs determined according to the Kjeldahl method were found to be 11.56% and 13.78% for spontaneous and yeast leavened doughs, respectively on dry basis. The mean protein content of samples calculated from the amino acid analysis results was 5.79% for spontaneous tarhana and 5.10% for yeast added tarhana. The findings revealed that the amount of crude protein in tarhana expressed with values above the actual protein amount and that the fermentation process should be considered for the selection of protein analysis methods. In the last part of the study, protein conversion factors specific to tarhana were calculated.