Exploring flavor enhancer metabolites of Chaya leaves cnidoscolus spp.

Umami, described as brothy and meat-like flavor, is one of the key factors in the successful savory food product development. It acts as a taste enhancer and improves overall acceptability. Monosodium glutamate (MSG) is the most common synthetic compound added to savory providing umami taste. Many consumers, however, have a negative attitude toward this substance. Thus, natural ingredients providing umami taste as a substitute for MSG could be beneficial for commercial purposes. Chaya (Cnidoscolus spp.) is a fast-growing and drought-resistant plant whose leaves have been widely used as a dried umami seasoning. However, the key umami substances in the leaves have not been reported. Therefore, this research aims to identify key umami compounds and to study the effects of drying methods on flavor-related substances of the chaya leaves.  To explore umami-related compounds in the leaves of two species (Cnidoscolus chayamansa and C. aconitifolius), we used a multiplatform untargeted metabolomics approach, electronic tongue, and in silico screening. The profile of nonvolatile metabolites varied between leaves of the two species and between leaf maturity stages. Young leaves exhibited the highest umami taste intensity, followed by mature and old leaves (p < 0.05). Partial least squares regression and computational molecular docking analyzes revealed five potent umami substances (quinic acid, trigonelline, alanyl-tyrosine, leucyl-glycyl-proline, and leucyl-aspartyl-glutamine) and three known umami compounds (L-glutamic acid, pyroglutamic acid, and 5'-adenosine monophosphate). The five substances were validated as novel umami compounds using an electronic tongue assay; leucyl-glycyl-proline showed synergistic effects with monosodium glutamate, enhancing the umami taste. Thus, substances contributing to the taste of chaya leaves were successfully identified, and the leaf maturation stages possessing higher umami intensity (young and mature leaves) were selected for the next study. Drying, in general, results in changes of flavor of food ingredients. Hence, the effects of different drying methods [freeze drying (FD), vacuum drying, oven drying at 50°C and 120°C (OD120), and pan roasting (PR)] on volatile and nonvolatile metabolites, umami intensity, and antioxidant properties of the young and mature chaya leaf mixture were investigated. The predominant volatile compound among all samples are aldehydes. 3-methylbutanal (malt-like odor) had the highest relative odor activity value (rOAV), while hexanal (green grass-like odor) and 2-methylbutanal (coffee-like odor) had the second highest rOAV in the FD and PR samples, respectively. The OD120 and PR samples possessed the highest concentration of umami-tasting amino acids and 5'-ribonucleotides as well as the most intense umami taste (p < 0.05), whereas FD samples exhibited the highest antioxidant capacity (p < 0.05). Ultimately, the findings contribute to fundamental knowledge and theoretical evidence for the production and use of dried chaya leaves as a natural umami flavoring. In addition, this study can be used as a model to identify key umami substances in other food ingredients.