Investigation of different time points of anthesis for intrinsically isotopic deuterium labelling on the enrichment of deuterium-labelled indispensable amino acids in mung bean (Vigna radiata L. Wilczek)

Abstract

Dietary protein quality has great importance for human health throughout the life cycle. Indispensable amino acid (IAA) digestibility of dietary protein is an integral component of protein quality evaluation, which can be properly measured by dual-stable isotope approach. This advanced technique requires intrinsically labelled protein sources (animals or plants). Nevertheless, the study of producing intrinsically labelled plant protein at different time points of anthesis is still scarce. Therefore, the present study examined the appropriate time points of anthesis to produce deuterium-labelled plant proteins. Mung bean (Vigna radiata (L.) Wilczek) was selected and watered with 20% deuterium oxide (2H2O) at different time points of anthesis (25, 50, 75 and 100%). The amount of 2H2O was technically calculated based on the amount of water lost by transpiration from the previous day, measured by the gravimetric method. Seed yield, the amount of 2H2O used, and deuterium-enriched IAA (2H-IAA) analysis was investigated at the selected time points. Results revealed that the average amount of 2H-IAA at the time of 25, 50, 75 and 100% anthesis were 0.20, 0.19, 0.23 and 0.25 atom percent excess, respectively. Remarkably, the treatment at anthesis time 75 and 100% produced the highest amount of 2H-leucine, 2H-phenylalanine, and 2H-lysine; whereas the treatment at the anthesis stage of 50%, provided the lowest 2H-valine and 2H-isoleucine. Notably, positive relationship between the amount of 2H2O used and the average amount of 2H-IAA was observed (R2=0.828, p=0.09). The 2H2O watering based on the transpiration loss at the anthesis time of 75 and 100% appears to be a major factor for the efficient production of enriched 2H-IAAs. This study provides a simple and efficient method for the production of highly enriched 2H-IAAs in plant protein, which can be used to explore the protein digestibility in human-beings.