Effects of Altitude on Phytochemistry and Genetics in Different Maca Phenotypes

Maca (Lepidium meyenii, Brassicaceae) tubers have been used by indigenous Peruvians as a medicinal food since antiquity. Age- and gender-specific physiological effects of maca have been seen in vivo and in human trials with male and pre- and postmenopausal female subjects. Effects vary by color phenotype and levels of bioactive compounds, including glucosinolates (GCs). In an earlier study, red maca (RM) was found to have the most GCs. RM is reported to have a selective therapeutic effect in men over 50 against prostate hyperplasia. Black maca (BM) and purple maca (PM) had the next-highest GC levels in the earlier study. BM was reported to improve sexual desire and function in healthy men. Yellow maca (YM), with the least GCs, in a mixed-phenotype, traditional blend, was reported to help hormone balance in pre- and postmenopausal women. The effect of altitude on plant composition has been well documented across various plants. The authors assessed the effect of altitude on phytochemical characteristics of maca. An extension study sought phenotype-specific DNA markers.

Hypocotyls of four main phenotypes grown in the Peruvian Andes at varying altitudes in organic mixed maca crops were examined for dietary characteristics and GC content in two trials. In the first, BM and RM hypocotyls were collected from three altitudes (3800, 4000, and 4200 meters above sea level [masl]) at geographically distant sites; one each in Chupaca, Junín, and Pasco provinces. Intact sun-dried hypocotyls went to three laboratories for GC analysis and one of those laboratories also determined nutritional content. In the second trial, sun-dried hypocotyls of four phenotypes from one plantation in Áncash, grown at three altitudes (4000, 4150, and 4300 masl), went to one laboratory for GC analysis. In the genetic study, DNA from the following five types of maca were compared: (1) freshly harvested at 4000 and 4300 masl, Áncash; (2) sun-dried at 4000 and 4200 masl, Junín, classed small; (3) same as (2) but large; (4) sun-dried RM from the same sites and heights as in the first trial above; and (5) dried hypocotyls, Áncash, 4300 masl, small. Earlier, samples of BM, RM, and YM (Junín site, 4200 masl, sun-dried) were tested as a cross-reference. Primers OPL-12 and OPL-13 were used. Results showed distinctive sequence patterns among phenotypes, with polymorphisms clearly visible.

In the first trial, RM grown at 4000 masl had more crude protein than BM at that altitude. At higher altitudes, mineral content significantly increased and fat significantly decreased (P<0.05 for both). Fatty acid (FA) composition differed among altitudes by phenotype. Myristic acid levels were much higher in RM than BM at all altitudes. At higher altitudes, palmitic, palmitoleic, and elaidic acids increased in both phenotypes; linoleic and α-linolenic acids decreased. In BM, α-linolenic acid content was much higher at higher altitudes; the reverse was true in RM. At every altitude and site, regardless of laboratory or analytical method, RM had significantly more GCs than BM (P<0.05). RM levels rose significantly at a higher altitude as well, while BM levels fell significantly (P<0.05 in both cases). There were visible differences in GCs and derivatives in 3D spectra of high-performance liquid chromatography (HPLC) resolution charts, especially in BM, with pronounced differences in GCs and derivatives for 4000 and 4200 masl samples, and with many unidentified peaks.

In the second trial, RM from 4000 masl had significantly less (P<0.05) GCs than BM, PM, or YM from the same altitude, with BM having the most. But at 4300 masl, both RM and PM had significantly more GCs (P<0.05 for both) than BM or YM, with the lowest levels in BM and the highest in PM. GCs in RM and PM phenotypes rose 3.3- and 2.3-fold, respectively, between 4000 and 4300 masl; those in BM fell 5.4-fold between the same altitudes. There were no significant differences among phenotypes at 4150 masl and no significant change in YM (about 61% of a traditional mixed maca crop) at any altitude.

In the DNA study, 31 samples were exposed to 20 primers. The four with the most distinctive bands were OPL-2, OPL-12, OPL-13, and OPL-14. Differences in DNA profiles within and between samples may indicate genetic polymorphisms, but fresh hypocotyls showed much clearer phenotypical differences than dried ones from the same sites and altitudes. DNA analysis has promise in distinguishing maca phenotypes but more research is needed. Once powdered and processed, it is impossible to identify maca color, raising the possibility of adulteration without a means of identification like DNA barcoding.

Imidazole alkaloids, tannins, saponins, sugars, anthocyanins, starches, and FAs had been linked to maca’s benefits as early as the 1960s. Its secondary metabolites, including GCs benzylglucosinolate and p-methoxybenzylglucosinolate, were unknown until the 1980s. Maca has more GCs than other Brassicaceae family members. Its catechins, amides, carbolines, and cyanogenic compounds also are bioactive. Evidence points to potential benefits in heart conditions, menopause, and women’s antidepressant-induced sexual dysfunction.

Altitude’s effect on plant compounds and secondary metabolites is thought to be linked to ultraviolet (UV)-B radiation and adaptation to high exposure. Lower GCs in BM, a sought-after medicinal, may indicate other metabolites with UV-B absorbance formed at higher altitudes. Sun-drying also could alter metabolite profiles. Maca grown this way is reported to prevent UV-A, UV-B, and UV-C damage in vivo. Open-air drying also brings repeated substantial temperature changes (day-night) that may alter the composition.

The study was funded by a research grant and travel fund from TTD International Pty Ltd (Elanora, Queensland, Australia). One of the authors (Meissner) is the director of research and development at TTD International Pty Ltd and has a financial interest in the company.

Resource:

Meissner HO, Mscisz A, Baraniak M, et al. Peruvian Maca (Lepidium peruvianum) – III: The effects of cultivation altitude on phytochemical and genetic differences in the four prime maca phenotypes. Int J Biomed Sci. June 2017;13(2):58-73.

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