## 4 Discussion  
We evaluated the production of short chain peptides in CP test foods and reported the changes in 19 types of di- and tripeptides including cyclic peptides, following the ingestion of the three CP test foods. Our results revealed that \"yogurt-fermented CP\" increased the concentration of 12 linear and two cyclic short chain Hyp-containing peptides in CP. However, we did not observe significant differences in the concentration of Hyp-containing cyclic peptides in any test food. Lactic acid bacteria are known to degrade peptides using their proteolytic systems, including cell envelope proteases and intracellular peptidases [18]. [PERSON] et al. reported the proteolytic effects of four strains of lactic acid bacteria, _Lactobacillus delbrueckii_, on soybean proteins \(\beta\)-conglycinin and glycinin, and they demonstrated that the lactic acid bacteria could degrade proteins that were not milk-derived [24]. Figure 3: The average concentration (nmol/mL) of Hyp and Hyp-containing peptides in the plasma of four subjects before and after the ingestion of three CP test foods. Measurement was conducted by LC-MS. Plasma samples were collected before and 1, 2, and 4 h after ingestion of “yogurt-fermented CP” (\(\blacktriangle\)), “CP in yogurt” (\(\blacksquare\)), and “CP in water” (\(\blacktriangle\)), respectively. For the preparation of our CP test foods, yogurt--containing _Lactobacillus delbrueckii subsp. Bulgarius 2038_ and _Streptococcus thermophiles 1131_--and CP with an average molecular weight of 3000 Da were used in this study. The lactic acid bacteria used in our yogurt sample contained X-prolyl dipeptidyl peptidase (PepX) that might degrade CP into dipeptides [25; 26]. Based on the results of previous studies and the present results, it can be concluded that yogurt fermentation by lactic acid bacteria could result in the degradation of CP into Hyp-containing di- and tripeptides. These short chain peptides are small enough to enter the bloodstream following absorption in the small intestine. Moreover, mixing CP and yogurt could increase the levels of some CP-derived peptides, especially Glu-Hyp-Gly, shortly following CP test food preparation and prior to ingestion. Although the mechanism underlying the increase in the levels of CP-derived short chained peptides just by mixing CP with yogurt is unclear, lactic acid bacteria proteases in yogurt possibly contributed to this process. Both the \"yogurt-fermented CP\" and \"CP in yogurt\" test foods contained 50 g of yogurt. However, they (and the yogurt) were not exactly the same. This difference in the yogurt content of each test food may have affected the amounts of milk-derived peptides and peptidases and, consequently, altered the absorption of Hyp-containing peptides into the bloodstream after the ingestion of \"yogurt-fermented CP\" or \"CP in yogurt.\" Short chain peptides may be absorbed into the bloodstream more efficiently than the long-chain peptides; this might be due to the characteristic features of the peptide absorption system that transports di- or tripeptides from the intestinal lumen [15; 16]. Based on the results of CP degradation by yogurt fermentation in vitro, \"yogurt-fermented CP\" was expected to be the best enhancer of Hyp-containing peptide absorption into human blood among the three CP test foods. However, while the ingestion of \"yogurt-fermented CP\" significantly increased Hyp-containing peptide absorption represented by C\({}_{\text{max}}\) and AUC compared to the ingestion of \"CP in water,\" the values were not significantly higher than those with \"CP in yogurt\" (Table 2). In fact, the C\({}_{\text{max}}\) and AUC values for Pro-Hyp-Gly were significantly enhanced upon ingestion of \"CP in yogurt,\" compared to those observed upon ingestion of \"yogurt-fermented CP.\" Thus, the increase in the levels of short chain Hyp-containing peptides in the CP test foods due to yogurt fermentation could not be the only the reason for the enhancement of Hyp-containing peptide absorption in human blood.