Tissue-Specific Accumulation of Sulfur Compounds and Saponins in Different Parts of Garlic Cloves from Purple and White Ecotypes.

Gianfranco Diretto,Purificación Castillo,Angela Rubio-Moraga,Oussama Ahrazem,Javier Argandoña,Lourdes Gómez-Gómez

doi:10.3390/molecules22081359

Gianfranco Diretto, Purificación Castillo + Show 4 more

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https://doi.org/10.3390/molecules22081359

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Abstract

This study set out to determine the distribution of sulfur compounds and saponin metabolites in different parts of garlic cloves. Three fractions from purple and white garlic ecotypes were obtained: the tunic (SS), internal (IS) and external (ES) parts of the clove. Liquid Chromatography coupled to High Resolution Mass spectrometry (LC-HRMS), together with bioinformatics including Principal Component Analysis (PCA), Hierarchical Clustering (HCL) and correlation network analyses were carried out. Results showed that the distribution of these metabolites in the different parts of garlic bulbs was different for the purple and the white ecotypes, with the main difference being a slightly higher number of sulfur compounds in purple garlic. The SS fraction in purple garlic had a higher content of sulfur metabolites, while the ES in white garlic was more enriched by these compounds. The correlation network indicated that diallyl disulfide was the most relevant metabolite with regards to sulfur compound metabolism in garlic. The total number of saponins was almost 40-fold higher in purple garlic than in the white variety, with ES having the highest content. Interestingly, five saponins including desgalactotigonin-rhamnose, proto-desgalactotigonin, proto-desgalactotigonin-rhamnose, voghieroside D1, sativoside B1-rhamnose and sativoside R1 were exclusive to the purple variety. Data obtained from saponin analyses revealed a very different network between white and purple garlic, thus suggesting a very robust and tight coregulation of saponin metabolism in garlic. Findings in this study point to the possibility of using tunics from purple garlic in the food and medical industries, since it contains many functional compounds which can be exploited as ingredients.

Highlights

Plants produce hundreds of thousands of different natural products known as secondary metabolites
In order to determine the distribution of sulfur and saponin metabolites throughout the different parts of garlic bulbs, two ecotypes were chosen: purple
To investigate the sulfur-containing compounds and saponins present in the two mentioned ecotypes, Liquid Chromatography coupled to High Resolution Mass (LC-HRMS) analyses were performed

Summary

Introduction

Plants produce hundreds of thousands of different natural products known as secondary metabolites These small organic molecules allow plants to withstand different types of environmental conditions and stresses [1]. Molecules 2017, 22, 1359 accumulating these compounds, which cover a vast range of ecophysiological functions. Often, these metabolites are produced through complex and highly regulated biosynthetic pathways [2]. The species Allium sativum L., commonly known as garlic, belongs to the genus Allium and represents one of the most numerous and important groups of the Alliaceae subfamily.

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