Amino acids based total protein versus crude protein in mixed fermented food: Case study of tarhana

Protein in fermented food originates from raw materials or microbial synthesis. Tarhana, a complex food matrix, is obtained through fermentation of dough containing plant and dairy ingredients. Dough fermentation, either spontaneous or yeast leavened, may last several weeks. Studies on tarhana have relied on nitrogen-based methods for determining protein content. This method offers limited insight in evaluating protein degradation and synthesis dynamics throughout fermentation. The present study aims to provide an assessment of crude and total protein levels throughout tarhana fermentation over a period of 3 weeks. Crude protein, free and total amino acid profiles of dough fermented with autochthonous culture or yeast leavening were determined at weekly intervals throughout fermentation. Fermentation type and duration were important factors affecting protein composition. The range for crude protein levels was 10.7–13.9 % and for total protein levels was 4.8–6.1 % on a dry basis at various stages of fermentation. Findings indicate that using the universal nitrogen-to-protein conversion factor (NPCF, K=6.25) results in a significant overestimation of protein content. Remediated factor values (K’) were calculated to more accurately estimate total protein equivalents in tarhana when using nitrogen-based assay methods.