| Maca (Lepidium meyenii) is a herbaceous plant of Brassicaceae family that grows in high plateaus. Maca root has been used as both food and folk medicine for its high nutritional and medical value for a long time. In 2011, maca powder was authorized by China's national ministry of health to be a new resource food, which legalized the maca products. With the rapid development of maca industry, technologies for identification, residual resource utilization, bioactive constituent analysis and quality and safety evaluation of maca are needed. Therefore, in this work, methods were established for identification of maca, utilization of maca residue, synthesis and detection of maker compounds, macamides. Furthermore, macamide composition and content were studied in different maca samples. Finally, sensorial, physicochemical and microbial properties of maca samples were analyzed comprehensively. This work laid the basis for the resource utilization and quality and safety evaluation of maca. The major findings are as follows:(1) A method for maca identification was established based on the ITS (Internal Transcribed Spacer) sequence.Total DNA of 43 different maca samples were extracted respectively using SDS method. Then the ITS sequences were amplified, sequenced and aligned. The result showed that the ITS sequence of maca was 621 bp long and without any variation site, which indicated the intraspecies consistent of maca ITS. Furthermore, nineteen ITS sequences of maca adulterants were collected in NCBI and aligned. The result showed that there were 5 to 332 bp variation sites betweem ITS seqences of maca and its adulterants, which indicated the interspecies specific of maca ITS. Therefore, a method for maca identification was established using the ITS sequence as the DNA barcoding and verified by maca powder adulterated with 10% of turnip.(2) High-activity dietary fiber was prepared from maca liquor residue.Using maca liquor residue (residue after soaking with white spirit) as material, dietary fibers were prepared by enzymic and chemical methods, respectively. Surface morphology, infrared spectra, proximate composition and monosaccharide composition of these fibers were analyzed. And the swelling capacity, water holding capacity, oil holding capacity, glucose adsorption capacity and glucose retardation index were further studied. The results showed that the dietary fiber prepared by enzymic method had more loose morphology, higher content of total fiber (81.10%), more abundant monosaccharide composition (rhamnose:arabinose:xylose mannose:glucose:galactose of 1.84:1.53:0.29:0.26:1.63:1) and higher swelling capacity (26.17 mL/g), water holding capacity (16.29 g/g), oil holding capacity (5.79 g/g), glucose adsorption capacity (905.91?mol/g) and glucose retardation index (24.59%).(3) Methods for macamide synthesis and HPLC (High Performance Liquid Chromatography) detection were developed and the extraction conditions were optimized.Nine macamides were synthesized by the EDC/HOAt method. The structures and purities of these synthetic macamides were verified by HPLC-UV, HPLC-MS2 and NMR. The results showed that high yields (?90%) and purities (>95%) of macamides were obtained by this synthetic method. Furthermore, a method for ultrasonic-assisted extraction of macamides with petroleum ether was optimized based on orthogonal design. The optimal extraction conditions were as follows: ultrasonic power,200 W; temperature,50?; time,15 min; solvent to sample ratio, 40:1. Besides, an isocratic HPLC method was developed and validated for the detection of macamides. The HPLC conditions were C18 column eluted with acetonitrile:water (containing 0.2% formic acid) of 90:10 at 0.6 mL/min. Calibration curves of all analytes showed good linearity (r2?0.9990). The intra-day and inter-day relative standard deviations (RSDs) of the nine macamides were?2.12% and? 3.21%, respectively, which indicated that the method had good repeatability and precision.(4) Macamide composition and content in different maca samples were investigated.Macamide composition and content in maca with different colors, parts, sizes, sources, product types and drying methods were analyzed. The results showed that the compositions were similar, but the contents showed significant variance among all tested maca samples. For the total content of macamides, black root (871.72?g/g)> yellow root (704.58?g/g)> purple root (676.83?g/g), fibrous root (1942.90?g/g)> main root (704.58?g/g)>leaf (40.54?g/g)> seed (0), small root (928.92?g/g)> big root (435.79?g/g), domestic (578.42-2773.92?g/g)> imported (41.24-502.97?g/g), essential tablet (1235.67?g/g)> dry slice(1036.94?g/g)> fresh root (264.15?g/g), air-dried root (280.78?g/g)> freeze-dried root (58.70?g/g). The total contents of macamides increased obviously with the storage time in different dried maca samples.(5) The local food safety standard of Yunnan Province of dried maca products was established.According to Food Safety Law of China, sensorial, physicochemical and microbial properties of 79 maca samples from Yunnan were analyzed. The content of macamides was used as the quality indicator for dried maca products (root, slice and powder). "Local food safety standard of Yunnan province of dried maca products" was established and enacted on Sept.27,2015. |
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