ABSTRACT
Postharvest processing of maca (Lepidium meyenii Walp., Brassicaceae), a traditional high-altitude Andean root crop, involves slow field drying prior to milling into flour. The progressive tissue dehydration and release of hydrolytic enzymes and substrates from cellular compartments results in the slow accumulation of free monosaccharides, fatty acids and amino acids. A more complex, and faster, kinetic profile is that of glucosinolate breakdown. A number of reactive transient and stable accumulation products are generated during drying, some of which have noteworthy bioactive properties. Among these are macamides, inhibitors of endocannabinoid neurotransmitter degradation in mammalian nervous systems. They result from the condensation of benzyl amine, a glucosinolate hydrolysis product, with free fatty acids released from lipid hydrolysis. Recent research has focused on developing drying processes under controlled conditions that can modulate the biochemistry of glucosinolate hydrolysis to optimize the content of bioactive compounds in the root flour. Low temperature (35 °C) oven-drying of shredded maca roots under controlled air flow generates benzyl amine as primary accumulation product, accounting for up to 94% of hydrolyzed glucosinolate in the flour. Kinetic evidence suggests that both deaminated benzenoids and macamides are allocated from the benzylamine pool through amine oxidase activity or condensation with free fatty acids, accounting for the remaining hydrolyzed glucosinolate (<5%). These activities determine the allocation to either one of these pathways. Later stages of dehydration result in shifts in the molar ratios of deaminated benzenoids, the accumulation of benzoic acid esters and benzyl alcohol. We propose that these are the result of changes in the rates of the reductive and oxidative half-reactions of endogenous aldehyde dehydrogenases. It is the ratio of benzylamine deamination to amide formation that determines the eventual yields of macamides in relation to benzenoids and their esters in maca flour.
Subject(s)
Lepidium , Animals , Desiccation , Flour , Glucosinolates , Plant ExtractsABSTRACT
Ultraviolet (UV) radiation is a small fraction of the solar spectrum, which acts as a key environmental modulator of plant function affecting metabolic regulation and growth. Plant species endemic to the Andes are well adapted to the harsh features of high-altitude climate, including high UV radiation. Maca (Lepidium meyenii Walpers) is a member of Brassicaceae family native to the central Andes of Peru, which grows between 3500 and 4500 m of altitude, where only highland grasses and few hardy bushes can survive. Even though maca has been the focus of recent researches, mainly due to its nutraceutical properties, knowledge regarding its adaptation mechanisms to these particular natural environmental conditions is scarce. In this study, we manipulated solar UV radiation by using UV-transmitting (Control) or blocking (UV-block) filters under field conditions (4138 m above the sea level) in order to understand the impact of UV on morphological and physiological parameters of maca crops over a complete growing season. Compared to the UV-blocking filter, under control condition a significant increase of hypocotyl weight was observed during the vegetative phase together with a marked leaf turnover. Although parameters conferring photosynthetic performance were not altered by UV, carbohydrate allocation between above and underground organs was affected. Control condition did not influence the content of secondary metabolites such as glucosinolates and phenolic compounds in hypocotyls, while some differences were observed in the rosettes. These differences were mainly related to leaf turnover and the protection of new young leaves in control plants. Altogether, the data suggest that maca plants respond to strong UV radiation at high altitudes by a coordinated remobilization and relocation of metabolites between source and sink organs via a possible UV signaling pathway.
