Controlling the quality of maca (Lepidium meyenii) dietary supplements: Development of compendial procedures for the determination of intact glucosinolates in maca root powder products

Abstract

The demand and sales of dietary supplements derived from maca (Lepidium meyenii) have skyrocketed in the last decade and a variety of related nutritional and healthcare products have mushroomed into a business with market prominence. However, the lack of standard testing protocols for quality control could jeopardize the immediate benefits of these products for public health. We describe herein the development of analytical procedures for the determination of glucosinolates (GLs), the biologically active ingredients in maca. Because of the high polarity and instability caused by enzymatic hydrolysis, GLs in maca have been exclusively analyzed using desulfated GLs. This indirect analysis requires additional sample preparation steps, which is labor-intensive, and may lose the original GLs and introduce artificial compounds. Furthermore, the reported GL profiles of maca are inconsistent and incomplete, some GLs may be structurally misidentified. In this context, we focused on direct analysis of intact GLs in maca without the enzymatic desulfation. Four GLs (sinalbin, glucolepigramin, glucolimnanthin, and glucotropaeolin) were identified as the major GLs in maca root powder. An HPLC method based on ion pair chromatography was developed to determine individual and total GLs; chromatographic separations were achieved on a Luna column (C18, 4.6 × 100 mm,3 mm) using 0.1 % TFA in water and in methanol as mobile phase in a gradient elution mode. The developed procedures were validated within the calibration range of 10-500 μg/mL. Inter- and intra-day precision were shown to be lower than 3% at all concentrations levels with recovery between 100.2 % and 103.3 %. The procedures were applied to a total of 42 maca root powder products from 11 manufacturers. Sample analysis revealed a consistent correlation of glucotropaeolin: glucolimnanthin (1: 0.19) across all products with a correlation coefficient of 0.994. The correlation in combination with total GL contents for each product could be used for authentication and GL content determination. Incorporation of the developed procedures into USP monographs will strengthen the public standards for maca powder dietary supplements.

Keywords: Glucosinolates; Ion pair chromatography; Maca (Lepidium meyenii); Maca root gelatinized powder; Maca root glucosinolates dry powder; Maca root powder.