Metabolomic insights into quinoa perianth-derived inhibition of pre-harvest sprouting

Pre-harvest sprouting (PHS) in quinoa poses significant challenges to both its quality and yield, and presently, there is no effective method to prevent this phenomenon. Considering that allelopathic compounds derived from plants have demonstrated efficacy in inhibiting grain germination, this study seeks to identify prevalent inhibitors of PHS in quinoa through an analysis of its perianth. The inhibitory effects of aqueous extracts derived from both fresh and dried perianths of two quinoa varieties were evaluated through germination assays, utilizing both grains and whole spikes, with three biological replicates for each treatment. Furthermore, non-targeted metabolomics analyses were conducted in triplicate on the four types of water extracts to identify potential pre-harvest sprouting (PHS) inhibitors. The findings indicated that the four aqueous extracts derived from quinoa perianths demonstrated inhibitory effects on the germination of both quinoa seeds and whole spikes, with the dried perianth extracts showing the most pronounced inhibition. A comparative analysis of aqueous extracts derived from both fresh and dried perianths revealed that, in positive ion mode, metabolites with germination-inhibitory properties were identified in the extract from dried perianths, whereas these metabolites were not detected in negative ion mode. The inhibitory metabolites were predominantly enriched in the phenylalanine metabolism and phenylpropanoid biosynthesis pathways. Notably, coumarin was abundantly present in all four perianth extracts, serving as a synthetic precursor for multiple germination inhibitors and exhibiting significant correlations with various compounds. As a result, coumarin (classified as Level 1 ID) was confirmed to function as a sprouting inhibitor, with a 5 mM solution exhibiting inhibition rates of 85.56% for grains and 59.78% for whole spikes. In summary, the plant-derived allelopathic compound coumarin has been identified as a reliable and highly effective inhibitor of PHS. This finding addresses the current market deficiency in sprouting inhibitors and offers a biochemical foundation for the development of natural inhibitors aimed at mitigating pre-harvest sprouting (PHS) in quinoa.