Journal of the Science of Food and Agriculture J Sci Food Agric 87:437446 (2007)

Effect of genotype, maturity stageand post-harvest storage on phenoliccompounds, carotenoid content andantioxidant capacity, of Andean mashua tubers(Tropaeolum tuberosum Ruiz & Pavon)Rosana Chirinos,1,4 David Campos,1 Carlos Arbizu,2 Herve Rogez,3Jean-Francois Rees,4 Yvan Larondelle,4 Giuliana Noratto5 andLuis Cisneros-Zevallos51Instituto de Biotecnologa (IBT), Universidad Nacional Agraria-La Molina, Lima 12, Peru2Centro Internacional de la Papa (CIP), La Molina, Lima 12, Peru3Departamento de Engenharia Qumica e de Alimentos, Universidade Federal do Para, Belem-PA, Brazil4Unite de Biologie Animale & 4Unite de Biochimie de la Nutrition, Institut des Sciences de la Vie, Universite Catholique de Louvain, B-1348Louvain-La-Neuve, Belgium5Department of Horticultural Sciences, Texas A&M University, College Station, Texas 77843-2133, USA

Abstract: The total phenolics, anthocyanins, flavan 3-ols, carotenoids and antioxidant capacity of mashua(Tropaeolum tuberosum Ruiz & Pavon) tubers from 10 yellow and purple cultivars were determined at differentmaturity stages (57.5 months after planting) and sunning post-harvest storage periods (735 days). Both theantioxidant capacity (ORAC and ABTS assays) and the content of the bioactive compounds tested variedmarkedly between cultivars. Purple varieties reached the highest antioxidant capacity during tuber development(271446 mol Trolox equiv g1 DM, ORAC assay). The kinetics of accumulation or disappearance of the bioactivecompounds tested during maturation was dependent both on the cultivar and on the compound considered. Foranthocyanins, there was a marked increase during maturation in all the purple cultivars. During the sunning post-harvest storage, the changes in antioxidant capacity (ABTS assay) and content of the bioactive compounds testedalso varied between cultivars. A marked decrease in anthocyanins was observed for the anthocyanin-containingcultivars. In general, the correlation between antioxidant capacity and the content of bioactive compounds variedmarkedly between cultivars. Antioxidant capacity in purple varieties correlated with total phenolics or flavan 3-olswhile only in some yellow varieties antioxidant capacity correlated with total phenolics. 2007 Society of Chemical Industry

Keywords: mashua; Tropaeolum tuberosum; antioxidants; phenolic compounds; carotenoid; maturity stage; post-harvest

INTRODUCTIONThere is growing interest in the search for edible plantsas novel sources of health-promoting phytochemicals.Mashua (Tropaeolum tuberosum Ruiz & Pavon) isa tuber crop indigenous to the Andean highlandsand is of economic value as a food and medicinalcrop. It is cultivated in the Andes of Bolivia, Peru,Ecuador, Colombia and Venezuela1 and is currentlybeing grown experimentally in New Zealand andthe Pacific northwest to evaluate its potential forworldwide cultivation.2 Mashua is adapted to highAndean altitudes, low minimum temperatures, largeranges of diurnal temperatures and is highly productive

under low levels of input.3,4 Mashua is also a valuablecrop because it is resistant to many insects, nematodes,fungi and other pathogens that attack potatoes andother tuber crops.5 The nutritional value of mashuais high. For example, 100 g dry tubers may contain1416 g protein, almost 80 g carbohydrate and about77.5 mg vitamin C.6,7 It has been traditionally andextensively used in the folk medicine of the Andeanregion, and its domestication may have been relatedto its importance as a medicinal agent.8 Recentstudies indicate that mashua has a high contentof phenolic compounds (0.923.37 mg chlorogenicacid equivalent g1 fresh weight), anthocyanins

Correspondence to: Luis Cisneros-Zevallos, Department of Horticultural Sciences, Texas A&M University, College Station, Texas 77843-2133, USAE-mail: lcisnero@tamu.eduDavid Campos, Instituto de Biotecnologia (IBT), Universidad Nacional Agraria-La Molina, Lama 12, PeruE-mail: dcampos@lamolina.edu.peContract/grant sponsor: USAID, through the Association Liaison Office for University Cooperation in Development (ALO).; contract/grant number: HNE-A-00-97-00059-00Contract/grant sponsor: Consejo Nacional de Ciencia y Tecnologa del Peru (Concytec)Contract/grant sponsor: Belgian Cooperation Universitaire au Developpement(Received 13 April 2005; revised version received 18 January 2006; accepted 5 September 2006)Published online 10 January 2007; DOI: 10.1002/jsfa.2719

2007 Society of Chemical Industry. J Sci Food Agric 00225142/2007/$30.00

R Chirinos et al.

(0.52.05 mg cyanindin 3-glucoside equivalent g1fresh weight), as well as an important hydrophilicantioxidant capacity (9559800 g Trolox equivalentsg1 fresh weight, ABTS assay).9 It was also found thatextracts of mashua induced concentration-dependentsuppression of the proliferation of human DU145prostate carcinoma cells, human Caco-2 colonadenocarcinoma cells and murine B16F10 melanomacells.10 This Andean crop is ready for harvest in68 months and farmers often harvest it progressivelyaccording to their needs, sometimes leaving tubers inthe ground for several weeks after the normal harvesttime. It is folklore knowledge that after sunning storagethe tubers become more suitable for eating,3 mainlybecause of a lowering of their glucosinolate content.11

Interest in the role of antioxidants from fruit andvegetables in human health has prompted researchwithin horticulture and food science to determine howtheir content and activity can be maintained or evenimproved through cultivar development, productionpractices and food processing.12,13 The effects ofharvest time (age of plant) and post-harvest storageon the retention of these dietary antioxidants is alsoof major importance, together with differences inthe stability of these compounds between differentcultivars. Although there is a large germplasm ofmashua available at the International Potato Center(Lima, Peru), very little research has been carried outon the phytochemicals and antioxidant capacity ofdifferent mashua cultivars. Virtually no informationis available on the changes of these constituentsduring tuber development and post-harvest storage.The purpose of this investigation was to compare 10morphologically well identified cultivars of mashuain terms of tuber antioxidant capacity and contentsin bioactive compounds such as phenolics andcarotenoids and to determine the effects of harvesttime (age of plant) and sunning post-harvest storageon these parameters.

MATERIALS AND METHODSChemicals and reagentsAll solvents (methanol, ethanol, acetone and hex-ane) and other chemicals of analytical grade wereobtained from Merck (Darmstadt, Germany) andRiedel de Haen (Seelze, Germany). 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), fluo-rescein, 2,2-azobis (2-amidinopropane) dihydrochlo-ride (AAPH), 4-(dymethylamino)-cinnamaldehydesolution (DMCA), Folin-Ciocalteu reagent (Catalog# F9252), chlorogenic acid, (+)-catechin hydrate,Trolox (6-hydroxy-2,5,7,8-tetramethyl chromane-2-carboxylic acid) and -carotene were purchased fromSigma Chemicals Co. (St Louis, MO).

Mashua samplingTubers of 10 cultivars of mashua (Tropaeolumtuberosum Ruiz & Pavon) were supplied by theInternational Potato Center (CIP, Lima, Peru). The

tubers were grown in the rural community of LaLibertad, Huancayo (Junin, Peru) at approximately3700 m above sea level, at approx. 70% relativehumidity and 10 C (average temperature). They wereplanted at the end of September 2002 and harvestedat 5 (beginning of tuberization process), 5.5, 6, 6.5,7 and 7.5 months (usual harvest time) after beingplanted. Sets of tubers harvested at 7.5 months werestored on a rooftop at CIPs experimental stationSanta Ana (Huancayo, Peru) at 3280 m above sealevel and exposed 10 h a day to bright sunlight (averagetemperature 15 C) during 7, 14, 21, 28 and 35 days.During the night period (12 h) the tubers were coveredwith Ichu (Andean grass) to protect them from thelow temperatures (2 to 15 C). Harvested tuberswere immediately packed in paper bags and sent tothe Universidad Agraria La Molina (Lima, Peru)where they were lyophilized and stored at 20 C.Three samples made of 10 tubers of each cultivarwere randomly collected for analysis. The lyophilizedsamples were rehydrated prior to the analyses toimprove the recoveries of the extraction procedures.All analyses were conducted in triplicate.

DETERMINATION OF ANTIOXIDANT CAPACITYABTS assayAntioxidant capacity was determined by the ABTSmethod adapted from Arnao et al.14 For hydrophilicantioxidant capacity, a sample of 0.3 g was homog-enized with 20 mL of methanol for 2 min using anUltra-Turrax homogenizer (IKA works, Inc., Wilm-ington, NC) and left at 4 C for 24 h. The extract wascentrifuged at 20 000 g for 15 min and the super-natant was collected. A 150 L of supernatant wasmixed with 2.85 mL of ABTS solution prepared asdescribed by Awika et al.15 with an absorbance ofapprox. 1.1 measured at 734 nm. This mixture wasallowed to react at 20 C until a steady absorbancewas reached. For measurements of lipophilic antioxi-dant capacity (LAC), the pellet was mixed with 20 mLof dichloromethane and shaken for 15 min before fil-tration. An aliquot of the yelloworange supernatantwas taken and treated as described above. Simultane-ously, a 150 L aliquot of either solvent was treatedin the same way as the sample and used as a con-trol. The Genesys-5 UVvisible spectrophotometer(Milton Roy, New York, NY) was blanked with therespective solvent, and the decrease in absorbance dueto antioxidants was recorded at 734 nm. Both antiox-idant capacities were calculated as mol of Troloxequivalents (TE) g1 dry matter (DM) from a standardcurve developed with Trolox.

Oxygen radical absorbance capacityThe oxygen radical absorbance capacity (ORAC)assay was carried out on d