Volume 116, August 2015, Pages 138–148
Bioactive maca (Lepidium meyenii) alkamides are a result of traditional Andean postharvest drying practices
- Under a Creative Commons license
Open Access
Highlights
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- The bioactive natural product profiles of fresh and dried maca are distinct.
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- Bioactive amides reported for maca are exclusively present in dried hypocotyls.
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- Glucosinolate and lipid hydrolysis during drying results in amine and free fatty acid buildup.
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- Benzylamine and free fatty acid accumulation correlates well with amide synthesis.
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- VOC monitoring during drying allows an indirect measurement of amide accumulation.
Abstract
Maca, Lepidium meyenii
Walpers (Brassicaceae), is an annual herbaceous plant native to the
high plateaus of the Peruvian central Andes. Its underground storage
hypocotyls have been a traditional medicinal agent and dietary staple
since pre-Columbian times. Reported properties include energizing and
fertility-enhancing effects. Published reports have focused on the
benzylalkamides (macamides) present in dry hypocotyls as one of the main
bioactive components. Macamides are secondary amides formed by
benzylamine and a fatty acid moiety, with varying hydrocarbon chain
lengths and degree of unsaturation. Although it has been assumed that
they are usually present in fresh undamaged tissues, analyses show them
to be essentially absent from them. However, hypocotyls dried by
traditional Andean postharvest practices or industrial oven drying
contain up to 800 μg g−1 dry wt (2.3 μmol g−1 dry
wt) of macamides. In this study, the generation of macamides and their
putative precursors were studied during nine-week traditional drying
trials at 4200 m altitude and in ovens under laboratory conditions.
Freeze–thaw cycles in the open field during drying result in tissue
maceration and release of free fatty acids from storage and membrane
lipids up to levels of 1200 μg g−1 dry wt (4.3 μmol g−1
dry wt). Endogenous metabolism of the isothiocyanates generated from
glucosinolate hydrolysis during drying results in maximal benzylamine
values of 4300 μg g−1 dry wt (40.2 μmol g−1 dry
wt). Pearson correlation coefficients of the accumulation profiles of
benzylamine and free fatty acid to that of macamides showed good values
of 0.898 and 0.934, respectively, suggesting that both provide
sufficient substrate for amide synthesis during the drying process.
Graphical abstract
Bioactive alkamides reported for maca (Lepidium meyenii)
hypocotyls are the product of tissue disruption during traditional
open-field or industrial drying and do not occur in intact tissues.
Keywords
- Maca;
- Lepidium meyenii;
- Brassicaceae;
- Post-harvest processing;
- Alkamides;
- Macamides;
- Glucosinolates;
- Benzylamine;
- Benzylisothiocyanate;
- Fatty acid amide hydrolase
1. Introduction
Maca (Lepidium meyenii Walpers or Lepidium peruvianum
Chacón), an annual herbaceous plant of the Brassicaceae family, is
native to the central Andes. It is the only reported species of the
genus Lepidium displaying a fused hypocotyl and taproot forming
an underground storage organ which is well adapted to the harsh climate
of the high-altitude central Andean plateau. The plant, also mentioned
as a “lost crop of the Incas” ( NRC, 1989),
has been cultivated and used for food and medicinal purposes since
pre-Columbian times. It has gained attention in the past two decades due
to reports on medicinal properties which make it a good candidate for
the nutraceutical market ( Canales et al., 2000 and Dini et al., 1994).
As a consequence, reported Peruvian exports of dried and processed maca
rose almost fourfold in the past decade, to over USD 10 million in 2013
( SCIICEX, 2013).
Maca presents three major phenotypes, red, yellow and black (Fig. 1),
based on their hypocotyl and stem coloration. As in most Brassicaceae,
glucosinolates accumulate in its tissues, of which benzylglucosinolate (1) (Fig. 2) is the main product. Depending on the chemotype, lesser amounts of the 3- or 4-, hydroxy or methoxylated benzyl derivatives (14–17) (Fig. S1) and of tryptophan-derived compounds (18–20) can be present (Fig. S1) (Li et al., 2001, Piacente et al., 2002, Clément et al., 2010 and Yábar et al., 2011).
Published reports suggest that differences in the chemical composition
of the phenotypes are associated with the reported biological effects or
medical target for which these different types can be used. For
example, black maca is useful in stimulating sperm count (Gonzales et al., 2006) while red maca is most useful for the treatment of benign prostate hyperplasia (Gonzales et al., 2005). Black maca has been also reported to increase memory and learning in mice (Rubio et al., 2006 and Rubio et al., 2007). Other reported properties which may not be related to phenotype include increases in female fertility and libido (Ruiz-Luna et al., 2005)
and a stimulatory effect on the central nervous system through
inhibition of mammalian fatty acid amide hydrolases (FAAH) and
potentiation of the endocannabinoid system (Pino-Figueroa et al., 2011). Wang and coworkers (2007) have published a comprehensive summary on the reported biological and pharmacological properties of maca.
- Fig. 1.Maca hypocotyls of three characteristic phenotypes, yellow, red and black. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
- Fig. 2.The main maca glucosinolate and metabolites analysed in this study. BGl (1): benzylglucosinolate, BITC (2): benzyl isothiocyanate, BIOC (3): benzyl isocyanate, BCN (4): benzyl nitrile, BOH (5): benzyl alcohol, BCHO (6): benzaldehyde, BNH2 (7): benzylamine, hexanal (8), FFA 18:2 (9): linoleic acid (9), FFA 18:3 (10): linolenic acid, MAC 16 (11): N-benzyl hexadecanamide, MAC 18:2 (12): N-benzyl-(9Z,12Z)-octadecadienamide, MAC 18:3 (13): N-benzyl-(9Z,12Z,15Z) octadecatrienamide.
