C O N T E N T S JOURNAL OF HORTICULTURAL SCIENCES Volume 16 Issue 1 June 2021 In this Issue i-ii Review Moringa (Moringa oleifera L.): An underutilized and traditionally valued 1-13 tree holding remarkable potential Jattan M., Kumari N., Raj Kumar, Kumar A., Rani B., Phogat D.S., Kumar, S. and Kumar, P. Original Research in Papers Characterization and evaluation of mountain sweet thorn 14-25 (Flacourtia montana J. Grah) collections Tripathi P.C., Ganeshan S., Radhika V. and Shetti D.L. Optimization of methodology for the extraction of polyphenolic compounds 26-35 with antioxidant potential and á-glucosidase inhibitory activity from jamun (Syzygium cumini L.) seeds Arivalagan M., Priyanka D.R. and Rekha A. Genetic variability studies in amaranthus (Amaranthus spp.) 36-44 Agadi A.H., Kolakar S., Lakshmana D., Nadukeri S. and Hanumanthappa M. Morpho-physiological parameters associated with chlorosis resistance to 45-52 iron deficiency and their effect on yield and related attributes in potato (Solanum tuberosum L.) Challam C., Dutt S., Sharma J., Raveendran M. and Sudhakar D. Responses of different Okra (Abelmoschus esculentus) cultivars to water 53-63 deficit conditions Ayub Q., Khan S.M., Hussain I., Naveed K., Ali S., Mehmood A., Khan M.J., Haq N.U., Shehzad Q. Induced variability for yield and its attributing traits in cluster bean 64-68 [Cyamopsis tetragonoloba (L. ) Taub] through gamma irradiation Lavanya H.N., Mishra S., Sood M., Aghora T.S., Anjanappa M., Rao V.K. and Reddy A.B. In vitro multiplication protocol for Curcuma mangga : Studies on carbon, 69-76 cytokinin source and explant size Waman A.A., Bohra P., Karthika Devi R. and Pixy J. Effect of fungicide and essential oils amended wax coating on quality and shelf life 77-90 of sweet orange (Citrus sinensis Osbeck) Bhandari M., Bhandari N. and Dhital M. Post-harvest quality and quantification of betalains, phenolic compounds and 91-102 antioxidant activity in fruits of three cultivars of prickly pear (Opuntia ficus-indica L. Mill) Gonzalez F.P.H., Saucedo V.C., Guerra R.D., Suarez E.J., Soto H.R.M. Lopez J.A., Garcia C.E. and Hernandez R.G. Soil microbial community dynamics as influenced by integrated nutrient 103-113 management practices in sweet basil (Ocimum basilicum L.) cultivation Baraa AL-Mansour and D. Kalaivanan Effect of spectral manipulation and seasonal variations on cut foliage production 114-120 and quality of Philodendron (Philodendron ‘Xanadu’) Sujatha A. Nair, Laxman R.H. and Sangama Short Communications Studies on mutagenic sensitivity of seeds of pummelo (Citrus maxima Merr.) 121-124 Sankaran M., Kalaivanan D. and Sunil Gowda D.C. Isolation and characterization of microsatellite markers from 125-129 Garcinia indica and cross species amplification Ravishankar K.V., Vasudeva R., Hemanth B., Nischita P., Sthapit B.R., Parthasarathy V.A. and Rao V.R. 91 J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 Original Research Paper Post-harvest quality and quantification of betalains, phenolic compounds and antioxidant activity in fruits of three cultivars of prickly pear (Opuntia ficus-indica L. Mill) Gonzalez F.P.H.*1, Saucedo V.C.1, Guerra R.D.2, Suarez E.J.1, Soto H.R.M.1, Lopez J.A.1, Garcia C.E.1 and Hernández R.G.1 1 Colegio de Postgraduados. Carretera México-Texcoco Km. 36.5, Montecillo, Texcoco 56230, Estado de México. 2 Universidad Autónoma Chapingo. Km. 38.5 Carretera México – Texcoco Chapingo, Texcoco 56230, Estado de México. *Corresponding author e-mail : gonzalez.paulina@colpos.mx ABSTRACT Postharvest quality, quantification of betalains, phenolic compounds and antioxidant activity of peel, pulp and juice of fruits of three prickly pears (Opuntia ficus-indica L. Mill.) cultivars of Colegio de Postgraduados in México, were measured. The red and orange cultivars showed outstanding features of postharvest quality (size, texture, TSS and pulp and juice content), highest content of betalains and phenolic compounds. Therefore, highest antioxidant activity. In general, highest content of bioactive compounds was detected in peel, besides the content in pulp and juice did not show statistically significant differences. Phenolic content is very high in comparison with other fruits. Antioxidant activity was measured by three assays: FRAP, ABTS and DPPH. Three cultivars showed high correlation between antioxidant activity and phenolic compounds. The methodologies used in this work are a very useful tool for the quantification of bioactive compounds in O. ficus-indica fruit tissues. Keywords : Betalains, Flavonoids, Opuntia ficus-indica, Phenolic compounds and Prickly pear INTRODUCTION Prickly pear (Opuntia ficus-indica L. Mill.) is the species of ca cti with the gr ea test economic importance in the world (Bravo, 1978); (Kiesling, 1999); (Griffith, 2004); (Feugang et al., 2006). It is cultivated in several continents, but is native to America, where, there are more than 93 species of Opuntia (Hunt, 1999). In the southern highlands of Mexico, there are more than 243 varieties, used as fodder, vegetables and fruit. Most of the prickly pear cactus is collected from the wild, since there are only approximately 20,000 commercial plantations of prickly pear cactus. The semiarid regions of central Mexico hosted the greatest genetic diversity, as well as the largest cultivated area of prickly pear cactus in the world. Variability is found in both cultivated and wild populations. Prickly pear has become an important fruit crop in the semi-arid lands of Mexico, wher e it pla ys a str a tegic r ole in subsistence agriculture (Pimienta, 1994). The prickly pear has been recognized for its numerous nutritional virtues, nutritional and functional properties. Recent data have r evea led the high content of some chemica l components, which can give added value to this fruit. High levels of betalains, taurine, calcium, magnesium and antioxidants stand out. In addition, some of the components show promising characteristics in terms of functionality (Piga, 2004). The diversity of betalains found in these prickly pear cultivars, indicate the potential value of Opuntia cactus pear fruit, as a good source of pigments, and their potential industrial exploitation for drinks and food products. Therefore, consumption of cactus pear fruit may provide nutritional and health benefits (Castellanos & Yahia, 2008). Flavonoids have been reported by several authors (Feugang et al., 2006); (García et al., 2019). Also, Kuti (2000) reported about the presence of phenolic compounds in fresh prickly pear fruits. (Lee et al., 2002) also reported the antioxidant effects of Opuntia extracts. There is few information on the quantification of betalains and This is an open access article d istributed under the terms of Creative Commons Attribution-NonCommer cial-ShareAl ike 4.0 International License, which permits unrestricted non-commercial use, d istribution, and reproduction in any med ium, provide d the original author and source are credited. 92 Gonzalez et al J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 phenolic compounds in different fruit tissues, and juice of Opuntia ficus-indica cultivars. The purpose of the following work was to evaluate the postharvest quality, quantification of betalains, phenolic compounds and antioxidant activity of fruit tissues of three prickly pears (Opuntia ficus-indica L. Mill.) cultivars grown at Colegio de Postgraduados. MATERIALS AND METHODS Plant material Three O. ficus-indica cultivars colors red, white and orange developed in the fruticulture experimental field of Colegio de Postgr a dua dos, loca ted in Montecillo, State of Mexico (coordinates 19°272 513 N 98°542 153 O, altitude 2250 msnm), high altitude, temperate climate, the driest of the sub-humid, with rainfall in summer, precipitation 572. 25 mm and mean annual temperature of 15.3 ºC (García, 1988) were selected for the study according to flesh color, identified as CP1 (red), CP3 (white) a nd CP4 (orange). For fruit harvesting, the criteria established were the fla ttening of the floral ca vity and the moment when the glochids or thorns fell (Cantwell, 1995). Color characteristics The fruit color was measured by CIELAB system. The epicarp color was measured on two opposite sides of the equatorial zone of the fruit, with a Hunter-Lab model D-25 reflection color imeter (Reston, Virginia, USA); CIELAB parameters L*, a*, b* were recorded and the hue angle (°h=tan-1(b*/a*) and saturation index (Chroma (C) (a2+b2) 1/2 ) were calculated (McGuire, 1992). Postharvest quality A total of 50 fruits per cultivar were harvested and measured for size, structural components (peel, pulp and seeds), epicarp (peel) color, texture, juice content, total soluble solids, juice pH, betalains, flavonoids, phenols contents and antioxidant capacity. Size was determined based on longitudinal and equatorial diameter, measured with a trupper-14388 digital vernier on a total of 15 fruits; data were reported in millimeter s (mm). T he str uctur a l components evaluated were the proportion of peel, pulp and seeds, determined on a weight basis with an Ohaus Scout- Pro electronic balance with a sensitivity of 0.1 mg and the percentage of peel, pulp and seeds was calculated; in addition, the number and area (mm2) of seeds was determined using an Epson Scan scanner with WinSeedle TM 2013 software. Firmness was measured based on the deformation of the fruit when a force of 1 kg was applied with a Cha ntillon texturometer (Wagner Force Five model FDV-30) with a flat strut; the results were expressed in Newtons/cm2 (N/cm2). Juice extraction To deter mine the juice content, the juice wa s extracted from a total of 15 fruits separately with an Oster ® FPSTJE317 centrifugal extractor; for the calculations, the equation % juice= (juice weight/pulp weight) x100 was applied. Total soluble solids (%) and pH were measured according to the methods of the (AOAC, 1990) using a portable refractometer Palette Atago, PR-320 (0-.32%) and a Corning Model 12 potentiometer, NY, USA, respectively. Obtaining prickly pear tissues Samples of the epicarp (30g), mesocarp and endocarp (30 g), as well as juice from the pulp (15 mL) were obtained separa tely by ha nd using a n Oster ® FPSTJE317 centrifugal extractor. All samples were kept in Ultrafreeze at -65°C and subsequently freeze- dried for 3 days at -45°C and 1.3 × 10-3 MPa in a Labconco Freezone 2.5 L equipment. The freeze- dried samples were homogenized using a Nutribullet Nb-101b to obtain a fine particle. Finally, they were preserved in airtight aluminum bags for storage at - 18°C until analysis. Extraction procedure of freeze-dried prickly pear tissues Extraction was performed by placing 1 g of freeze- dried prickly pear sample in 50 mL of methanol: water (80/20, v/v) and mixed by vortex for 3 min, subsequently pH was adjusted to 3 with hydrochloric acid, and put in an ultrasonic bath (Bransonic™ CPXH series) for 15 min. After that, the samples were rotated for 30 min at 150 rpm and 27°C. Finally, they were centrifuged for 15 min (3500 rpm) and the supernatant was separated. The extracts were stored at -18°C in dark for further analysis. Spectrophotometric quantification of total betalains and phenolic compounds For the determination of total betalains and phenolic compounds, the prickly pear extracts mentioned above were used. Betalain content was measured 93 Post-harvest quality and anti-oxidant activity in prickly pear according to the method of (Castellanos & Yahia, 2008) using a Sinergy 2 microplate multidetector equipped with Gen 5 Data Analysis Software (Biotek Instr uments Inc. , Winoosky, VT USA). T he absorption spectrum was obtained from 200 to 700 nm to obtain the absorption maximum and an OD <1. Readings were obtained for each extract in triplicate. The betalain content was expressed as: µg betanin equivalents for betacyanin content (BC) and µg indicaxanthin equivalents for betaxanthin content (BX). The calculation was made using the following formula: BC or BX (mg/g) = [A(Df)(Mw)(Vd)/ ε(L)(Wd)] where A is the absorption value at the a bsor ption ma ximum of 535 a nd 483 nm for betacyanins and betaxanthins, respectively, DF is the dilution factor, Vd is the dried pulp solution volume (mL), Wd is the dried pulp weight (g), and L is the path-length (0.38 cm) of the cuvette. The molecular weight (Mw) and molar extinction coefficient (ε) of betanin [Mw) 550 g/mol; ε) 60,000 L/(mol cm) in H2O] wer e a pplied in or der to qua ntify the betacyanins. Quantitative equivalents of the major betaxanthins (Bx) were determined by applying the mean molar extinction coefficient [ε) 48,000 L/(mol cm) in H2O]. In all cases, water extracted the highest level of pigments. The total flavonoid determination was conducted according to the colorimetric method defined by Chang et al. (2002) with modifications. The prickly pear extract was mixed with 100 µL of potassium acetate, 100 µL of 10% aluminum chloride and 4.7 mL of distilled water. After incubation at room temperature for 30 min in darkness, the absorbance of the reaction mixture was measured at 415 nm in a microplate multidetector mentioned in section 2.7 placing 200 µL of sample and reagent blank in respective microwells. The amount of 10% aluminum chloride was substituted by the same amount of methanol: water (80/20, v/v) in blank. Quercetin (0.4 – 1.6 µg/mL) was used to make the calibration curve and the results were expressed as mg quercetin equivalents per g dry weight (mg EQ/ g dry weight). The total phenolic determination was expressed as µg gallic acid equivalents per g of dry weight (mg GAE g dry weight), according to the Folin-Ciocalteau assay which detects electron transfer by measuring the reducing capacity of the sample and can therefore also be considered as antioxidant activity assay (Cano et al. 2017). Antioxidant activity The antioxidant activity of each cultivar of prickly pear was determined using three assays: FRAP, ABTS and DPPH which have been widely applied in the analysis of food samples (Re et al., 1999). The FRAP assay was performed according to the methodology (Benzie & Strain, 1996) with some modifications. The FRAP solution includes 10 mL of 300 mM acetate buffer at pH 3.6, 1 mL of 10 mM TPTZ and 1 mL of 20 mM FeCl36H 2O. The prickly pear extracts (20 µL) were allowed to react with 180 µL of FRAP solution and 60 µL of distilled water for 10 minutes in dark conditions. Readings were taken at 595 nm. The calibration curve was linear between 50 and 600 µM Trolox. Results were expr essed in µM Trolox equivalents (µM TE)/g dry weight. For ABTS assay, the procedure of (Re, 1999) was followed with some modifications. The ABTS-+ radical solution included 7.4 mM ABTS-+ and 2.6 mM sodium persulfate solution. The working solution was prepared by mixing the two stock solutions in equal quantities and allowing them to react in the dark for 16 hours. The solution was then diluted by mixing 600 µL of ABTS-+ solution in 9.4 mL of methanol. The prickly pear extracts (20 µL) were allowed to react with 180 µL of ABTS solution for 10 minutes in dark conditions. Readings were taken at 734 nm. The calibration curve was linear from 50 to 500 µM Tr olox. Results are expressed in µM Trolox equivalents (µM TE/g dry weight). DPPH assay was done according to the method of Williams et al. (1995) with some modifications. The DPPH stock solution was prepared by dissolving 19.7 mg of DPPH in 100 mL of 80% methanol. Prickly pear extracts (200 µL) were allowed to react with 50 µL of DPPH solution for 30 min in dark conditions. Readings were taken at 515 nm. The calibration curve was linear from 50 to 500 µL of Trolox. The results were expressed in µM Trolox equivalents (µM TE/g dry weight). Additional dilutions were made when the values obtained from the samples were outside the linear range of the calibration curve. Statistical analysis The compositional data were expressed as mean ± standa rd devia tion of at least five independent determinations. Significant differences between results were calculated by one-way analysis of variance J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 94 (ANOVA), followed by a post hoc Tukey’s test. A level of p < 0. 05 was considered a significant difference. To investigate the relationship between main phytochemicals, a bilateral Pearson correlation analysis was performed with a significance of p < 0.01 and p < 0.05. All statistical analyses were executed with SAS Institute, Inc 9.4. RESULTS AND DISCUSSION Morphological characterization The morphological and physical characteristics of three prickly pear cultivars are directly influenced by selection (Table 1). Fruit length averages (mm) were significantly different among them, with CP4 and CP3 obtaining the highest and lowest values (97. 15 a nd 73.2 mm, respectively). Regar ding diameter, no significant differences were found between selections with averages of 52 and 55 mm respectively. The values of both lower and upper limits are very similar to those reported by Parish and Felker (1997) with average ranges of 73 to 88 mm for length and 56 to 57 mm for diameter. Cerezal & Duarte (2005) evaluated prickly pears har vested in the Andea n highla nds of the 2nd Region of Chile, reporting average length values of 62 t o 78 mm a nd 4 6 to 5 2 mm in dia meter. Karababa et al. (2004) reported fruit length values ranging from 66 to 71 mm and diameter values from 45 to 52 mm for a variety harvested in five loca tions in Tur key. On the other ha nd, Singh (2003) reported length and diameter values lower than those found in this study for prickly pear clones from the USA and introduced to India with average ranges of 55 to 76 mm in length and 33 to 46 mm in diameter. CP1 and CP4 had values of epicarp firmness of 32 and 36.5 N/cm2 respectively, higher than CP3 ( 2 6 . 6 N / c m2) . We ight of f r u it of C P 3 wa s significantly lower (124 g) compared to CP1 and CP4 (160 and 164 g respectively). There are other published works about the size of fruit, weight, TSS, pH and number of seeds (Cerezal & Duarte, 2005); (Karababa et al., 2004); (Parish & Felker, 1997); (Singh, 2003). CP1 (red) CP3 (white) CP4 (orange) Size of fruit (mm) 87.18±6.64b 73.19±8.72c 97.15±6.62a Diameter (mm) 55.39±2.95a 54.02±6.7a 52.22±4.24a Firmness (N/cm2) 31.99±9.54a 26.63±6.94b 36.51±6.98a Total weight of whole fruit (g) 159.91±23.81a 123.95±33.55b 154.26±17.67a Peel content (%) 37.19±4.15b 40.9±3.33a 39.67±3.51ab Pulp content (%) 62.3±4.18a 57.57±5.2b 60.54±2.93ab TSS of pulp (%) 15.53±1.22a 12.59±1.73b 11.4±0.78ab Juice content (%) 74.99±5.36a 66.57±7.11b 67.72±5.64b pH 7.31±0.16a 6.55±0.15c 7.03±0.13b TSS of juice (%) 13.52±0.86a 12.86±2.33a 11.91±0.54a Seed content (%) 2.74±0.17ab 2.08±0.61b 3.09±0.60a Weight of seeds (g) 4.18±0.86a 3.11±0.39b 4.12±0.69a Number of seeds 329.67±61.8a 188.11±32.65bc 231.56±50.7c Average area of seeds (mm2) 15.75±0.7c 18.41±0.68b 19.592±1a *Values are the mean of 15 independent determinations ± standard deviation. *Different letters indicate statistically significant differences (pd” 0.05) between columns. Table 1: Morphological, physical and physico-chemical characteristics of fresh fruits of three prickly pear cultivars (Opuntia ûcus-indica L. Mill.) Gonzalez et al J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 95 In contrast with studies of Barbera et al. (1994) the biggest fruit (CP4) don´t have the high quantity of seeds, in this case the fruit of CP1 had high quantity of seeds. The cultivar with less number of seeds was CP3 (white), it has been cultivated to produce prickly pear for many years. So, it has had a selection process. El Behi et al. (2015); Barbera et al. (1994); Mejía & Cantwell (2003) mention in their studies that the relationship between fruit size and seed content is highly variable and influenced by factors such as genotype, crop load and fruit position within the canopy. Firmness is a mechanical property gives post-harvest quality in fresh fruits. A loss of firmness is caused by loss of cell turgor due to aging or dehydration. Both thinning and softening of the peel contribute to increased susceptibility to physical damage and deter ior ation of prickly pea rs during ha ndling (Cantwell, 1995). However, this characteristic is also due to genetic and nutritional issues of the crop. Guerrero (2018) reports firmness values for white prickly pear Opuntia amyclaea green mature (36.28 N/cm2) and mature (26.48 N/cm2). In this study we obtained values between 23.63 N/cm2 for CP3 and 36.51 N/cm2 for CP4. Red cultiva r (CP1) wa s cha r a cter ized by the significantly higher content of pulp (62.3%), TSS of pulp (15.53 Brix) and juice (13.52%), juice content (74.99%), and lower content of peel (37.19%). Significant differences in the pH of the three cultivars were observed with values between 6.55 (CP3) and 7.31 (CP1). This values were higher than reported by Andreu et al. (2018) in six cultivars of prickly pears grown in Spain, who showed values of pH between 5.2 and 6.06. Regarding seed content, cultivars CP1 (red) and CP4 (orange) showed higher seed weight (4.18 and 4.12 g respectively), and higher seed quantity (329 and 231 seeds respectively) tha n CP3 (white). However, CP1 (red) has significantly smaller seeds (15.75 mm) than CP3 and CP4. Color Table 2 shows that the three cultivars had L* values less than 50, the CP3 (white) was the closest with (L= 47.5), so it is the one with the least dark color. Between CP1 (red) and CP4 (orange) cultivars, no significant differences were observed for lightness. Hue values suggest that there are three types of shades; white with high hue values (112.27), red with intermediate value (25.72) and orange with low hue values (7.49). The highest chroma values were also presented by CP3 (white) (21.88), CP1 (red) and CP4 (orange) obtained very close values (16.17 and 15.32) respectively. Table 2: Color of fruit or three prickly pear cultivars (Opuntia ficus-indica L. Mill.) CP1 (red) CP3 (white) CP4 (orange) L* 35.19±2.76b 47.5±3.96a 34.33±1.86b a 6.2±2.5 b -8.3±2.3 c 9.6±2.1 a b 9.3±3.0 b 19.8±1.5 a 11.4±1.2 b Hue 25.72±9.59b 112.27±5.52a 7.49±7.49c Chroma 16.17±3.97b 21.88±2.4286a 15.32±1.7b * Values are the mean of 15 independent determinations ± standard deviation. * Different letters indicate statistically significant differences ( 0.05) between columns. Quantification of betalains Betalains are water soluble compounds present in a restricted number of families of plants from the Caryophyllale family. They are classified in two chemical families: betacyanins and betaxanthins with 540 and 480 nm absorption maxima. Betalains are powerful radical eliminators in chemical system and act as an efficient antioxidant in biological models (Cano et al., 2017). Betalain content was measured in CP1 (red) and CP4 (orange) cultivars, in the peel, pulp and juice of prickly pear. The CP1 cultivar showed higher betacyanins (BC) and betaxanthins (BX) content than CP4 (orange) with values of 1181 and 1137 µg/g d.w in peel, respectively for CP1 (red) and values of 161 a nd 408 µ g/g d. w in peel for CP4 (or a nge), respectively. These compounds are responsible for the red and orange shades respectively. Betacyanins appear to be in higher concentration in the peels of both prickly pear cultivars (red and orange), however, betaxanthins are observed evenly distributed in both peel, pulp and juice in the CP4 (orange) cultivar. This is consistent with the findings of (Cano et al., 2017). On the other hand, no significant differences are shown between BC and BX content in pulp and juice J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 Post-harvest quality and anti-oxidant activity in prickly pear 96 for both selections (Table 3). In this sense, we could assume that no significant betalain content is lost during the juice extraction process. Table 3: Betalain content in two prickly pear cultivars (Opuntia ficus-indica L. Mill.) CP1 (red) CP4 (orange) BC1 Peel 1181.67±151.3aA 161±6.08bA Pulp 496±30.51aB 69.67±0.58bB Juice 472.33±12.74aB 65.67±5.69bB BX2 Peel 1137.67±169.82aA 408±2.65bA Pulp 552.67±26.65aB 435.33±58.77aA Juice 398±19aB 457±21.07aA * Values are the mean of 3 independent determinations ± standard deviation. * Lowercase letters indicate statistically significant differences ( 0.05) between cultivars of the same tissue for each given compound. * Uppercase letters indicate statistically significant differences ( 0.05) between cultivars of the same tissue for each given compound. BC1: Betacyanins expressed as µg of betanin equivalents per gram of dry weight. BX : Betaxanthins expressed as µg of indicaxanthin equivalents per gram of dry weight. Castella nos & Yahia (2008) reported values of betacyanins of 5290 µg/g dw in Camuesa cultivar, followed by 2060 µg/g in Roja Pelota, 2040 µg/g dw in Cardona and much lower contents in the Reyna variety (50 µg/g dw). Betaxanthins were f ou nd in t h e yellow p r ic kly p ea r va r iet ies Naranjona, 2651 and 21441 with values of 160, 140 and 120 µg/g dry weigt, respectively. These values differ greatly from those found in this work. García et al. (2019) reported betacyanin values of 1670 µg/g d.w and 450 µg/g and betaxanthin values of 730 a nd 370 µg/g in the pulp of Mexica n va r iet ies o f p u r p le a nd r ed p r i c kly p ea r, respectively. The values reported for red tuna are more consistent with what was found in this study. Quantification of total phenols (TP) and total flavonoids (TF) Some of the published wor ks on the chemica l composition of prickly pear showed information about the main compounds with antioxidant activity (Fernández et al., 2010). Phenolic compounds are known as bioactive or functional compounds that s er ve a s pr ot ec tor s a ga ins t c er t a in dis ea s es ( Bu t er a e t a l . , 2 0 0 2 ) , whi c h a r e ma inly characterized by their antioxidant activity (Andreu et al., 2018). Table 4 shows the content of total phenols in the peel, pulp and juice of the three cultivars evaluated. CP1 (red) and CP3 (white) presented the highest Total phenols content (TP) in peel (7225.67 and 7486.67 µg GAE. g-1 dw, respectively), which was significantly differ ent for CP4 (or ange), which obtained 59.39% with respect to the CP3 (white) cultivar. No significant differences were found in the total flavonoid content in the peel of the three selections studied (2505, 2114 and 2239 µg QE g- 1 d.w.) respectively. The Total Flavonoids content (TF) in pulp and juice of the three cultiva rs did not show significa nt differences with average values of 2121, 1422.5 and 1911 µg GAE. g-1 dw for CP1, CP3 and CP4, respectively). García et al. (2019) found values of 2067 µg GAE. g-1 dw for red prickly pear fruit pulp and 3501 µg GAE. g-1 dw in peel. This value is close to that we found in this study for the orange selection (4446 µg GAE. g-1 p.s.). TP a nd T F were found in 70 a nd 83% higher concentrations in peel than in pulp and juice in CP1 (red). In 82 and 83% in CP3 (white) and 62 and 93% in CP4 (orange). This corresponds with the findings of several authors, giving clear evidence that the highest antioxidant contents are present in the peel of the fruit (Andreu et al., 2018); (García et al., 2019); (Morales, 2009). CP1 presented the highest content of TP and TF in pulp (2149 µg GAE. g-1 dw and 558 µg QE g-1 dw respectively). In addition, cultivars CP1 and CP4 had the highest TP in juice (2092 and 2138 µg GAE. g-1 dw and CP3 had the highest TF in juice (555.33 µg QE g-1 dw). The content of total phenols in prickly pear is very high compared to other fruits. The TP ranges (µg GAE. g-1 dw) are 140 to 1020 in nectarines, 210 to 110 in peaches and 420 to 1090 in plums (Gil et al., 2002). On the other hand, the results are close to other fruits with high antioxidant capacity such as guava, which obtained values of 1700 to 3000 µg GAE. g-1 dw in a study carried out on pink- fleshed clones (Thaipong et al., 2006). Gonzalez et al J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 97 On the other hand, other species such as xoconostle (Opuntia matudae) have shown higher values of these compounds (TP) with values of up to 8590 and 9180 µg GAE. g-1 dw in pulp and peel (Morales, 2009). Similarly, values from 4950 to 9800 µg GAE. g-1 dw have been reported in blueberry (Wada, 2002) and from 526 to 6819 µg GAE. g-1 dw at different maturity stages in garambullo (Felix, 2018). Antioxidant activity (AOA) Antioxidant activity, is one of the main mechanisms in which vegetables and fruits provide health benefits to humans (Andreu et al., 2018). Several studies have established inverse correlations in the consumption of fr uits a nd vegeta bles a nd ca r diova scula r, inflammatory, cancer and age-dependent diseases (Willet, 2001). The use of a single technique to determine antioxidant activity may prove to be unrealistic and not as useful, however there are a large number of published techniques that pur port to measure antioxidant a ctivity in vivo (Wua ng et al. , 2005). T he measurement of antioxidant activity in prickly pear fr uits wa s eva lua ted ba sed on thr ee spectrophotometric assays; DPPH, ABTS and FRAP. The results are shown in Table 4. As with total phenols and flavonoids, the highest antioxidant activity was clearly observed for the three assays and three cultivars (CP1, CP3 and CP4) in the fruit peel, except in the peel and pulp of CP1 (red) by ABTS. For the FRAP assay, CP1 (red) and CP4 (orange) show higher antioxidant activity (17.6 and 19.13 µmol ET g-1 dw) than CP3 (white) in peel. CP3 Table 4: Content of total phenols, total flavonoids and antioxidant activity (FRAP, ABTS y DPPH) in three prickly pear cultivars (Opuntia ficus-indica L. Mill.) CP1 (red) CP3 (white) CP4 (orange) Total Phenols1 Peel 7225.67±198.07aA 7486.67±461.24aA 4446.67±295.5bA Pulp 2149.33±211.05aB 1529.67±163.09bB 1683.33±54.37bB Juice 2092.67±132.08aB 1315.33±155.58bB 2138.33±127.45aB Total Flavonoids2 Peel 2505.33±194.54aA 2114.67±78.56aA 2239.67±176.52aA Pulp 558±55.51aB 249±21.52bC 168±5.57bB Juice 425.67±68.38bB 555.33±25.66aB 148.67±2.08cB FRAP3 Peel 17.68±0.74aA 14.94±0.48bA 19.13±0.35aA Pulp 8.63±0.75aB 6.83±0.84aB 7.71±0.32aB Juice 7.48±0.49aB 5.23±0.16bB 8.14±0.17aB ABTS4 Peel 20.61±0.74aA 20.49±0.32aA 19.08±0.35aA Pulp 18.34±1.34aA 7.39±0.45bB 7.65±0.32bB Juice 14.38±1.21aB 6.09±0.19cC 8.09±0.17bB DPPH5 Peel 16.03±4.23bA 32.38±1.61aA 19.82±5.65aA Pulp 8.96±0.74aAB 6.56±0.89bB 2.41±0.24cB Juice 5.05±0.37aB 2.89±0.15bC 2.38±0.22bB * Values are the mean of 3 independent determinations ± standard deviation. * Lowercase letters indicate statistically significant differences (p 0.05) between cultivars of the same tissue for each given compound. * Uppercase letters indicate statistically significant differences (p 0.05) between cultivars of the same tissue for each given compound. 1 expressed as µg of gallic acid equivalents per gram of dry weight. 2 expresado as µg of quercetin equivalents per gram of dry weight. 3,4,5 expressed as µmol de trolox equivalents per gram of dry weight. *DPPH (2,2-difenil-1-picrilhidrazilo), ABTS (ácido -3 etilbenzotiazolino-6-sulfónico) y FRAP (Ferric Reducing Antioxidant Power). J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 Post-harvest quality and anti-oxidant activity in prickly pear 98 shows the lowest antioxidant activity in this assay in the three tissues (14.9, 6.8 and 5.2 µmol ET g-1 dw) in peel, pulp and juice, respectively. In the ABTS assay, CP1 (red) showed higher antioxidant activity in pulp and juice with values of 18.34 and 14.38 µmol ET g-1dw, respectively. There are no significant differences in the antioxidant activity of the three cultivars in peel. In DPPH, CP3 (white) a nd CP4 (or a nge) s howed higher a nt ioxida nt activity in peel 32.3 a nd 19.8 µmol ET g-1dw, respectively. On the contrary, CP1 (red) showed higher antioxidant activity in juice and pulp than the other cultivars with values of (8.96 and 5.05 µmol ET g-1dw), respectively. FRAP technique estimates the reducing activity of Fe(III), which is not necessa r ily r eleva nt for calculating its antioxidant capacity (Ou, et al., 2002). Taking into account that not all antioxidants reduce Fe(III) as fast as required (Pulido et al., 2 0 0 0 ) , t hei r a nt iox ida nt c a p a c i t y c ou ld b e underestimated. The ABTS technique is considered to be highly sensitive (Kuskoski et al., 2005), however, the working solution for this technique needs to be kept in the da r k for 12 hour s to generate free radicals. As the reacting solution is not a lwa ys of the sa me a ge, this ca n lea d to dif f er enc e s in va lu es dep end ing on t he determination times (Thaipong et al., 2006). The DPPH assay has been a widely used method to detect the ability of compounds to scavenge free radicals or the antioxidant activity of extracts (Hou, e t a l . , 2 00 3 ) . S a nchez s u ggest ed t ha t 2 , 2 - diphenyl-1-picrylhydrazyl (DPPH) is an easy and a cc u r a t e method t o mea su r e t he a nt iox ida nt capacity in fruit and vegetable extracts (Sánchez, 2002). As concluded by Frankel and Meyer, these assays differ fr om ea ch other in ter ms of substr ates, probes, r ea ction conditions a nd qua ntifica tion methods, making it very difficult to compare the results obtained between them (Frankel & Meyer, 2000). A single method is not sufficient to determine the antioxidant capacity of plant extracts; more than one type of AOA deter mination is r equired to r ep r es ent t he dif f er ent modes o f a c t ion of a ntioxida nts. T he methods used a re ba sica lly classified into two types: assays based on hydrogen atom transfer (HAT) and assays based on electron transfer (ET) (Dudonné et al., 2009). In this study, AOA was determined by two HAT-type assays: ABTS and DPPH, as well as Fe reduction capacity, using the FRAP assay. T he presence of phenolic compounds in plant extracts contributes significantly to their antioxidant potential (Dudonné et al., 2009). Part of this AOA comes fr om fla vonoids, low molecula r weight polyphenolic compounds distributed in fruits and vegetables (Hertog et al., 1992). For their part, betalains are powerful free radical scavengers that act as efficient antioxidants in biological models (Cano et al., 2017). Antioxidant capacity varies considerably from one type of fruit to another. (Wuang et al., 2005) and c owor ker s c ondu c t ed a s t u dy in whic h t he antioxidant capacity of 12 fruits and 5 commercial juices was measured by ORAC assay, resulting in st r a wb er r y ha ving the highes t AO A (1 5. 36 ), followed by plum (9.49), or ange (7. 50), gra pe (7.39), kiwi (6.02) and melon (0.97 µmol ET g-1 fresh fruit). (Andreu et al., 2018) and coworkers reported high levels of antioxidant capacity in prickly pear fruits of different cultivars for peel and pulp showing higher values than those found in this study in the thr ee met hods. By the ABT S technique, t hey reported the lowest AOA value in peel for cultivar NA (14.7) and the highest value for cultivar NA (14.7 µmol ET g-1 dw). In pulp, the lowest value was obtained by cultivar NJ (6.4) and the highest value by NT (30 µmol ET g-1 dw). By the DPPH technique, the lowest AOA va lue in peel wa s obtained by cultivar NE (54.8) and the highest value in cultivar FR (60 µmol ET g-1 dw). In pulp, the lowest value was obtained by cultivar NO (57.4) and the highest value by NT (60 µmol ET g-1 dw). Finally, measured by FRAP, the lowest value of AOA in peel was obtained by cultivar NE (40.2) and the highest value by cultivar NA (116 µmol ET g-1 dw). In pulp, the lowest value was obtained by cultivar NA (15) and the highest value by FR (32 µmol ET g-1 dw). This exceeds the r esults found for a ntioxida nt capacity in this study for the three selections, with Gonzalez et al J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 99 the highest values found by the DPPH technique for CP3 peel (32.3) and for CP1 pulp by the ABTS technique (18.3 µmol ET g-1 dw). Some authors have reported results consistent with this study, finding a higher antioxidant capacity in fruit peel than in the pulp of pomegranate (Calín et al., 2013), guava (Marquina et al., 2008) and berries (Oszmiański  et al., 2016). Correlation between tests To determine the linear relationship between the antioxidant capacity methods performed and the phenolic compounds a nd beta la ins, Pea r son’s correlation coefficient was ca lculated. Ta ble 5 shows high correlations between the three methods and phenolic compounds (Phenols and Flavonoids). The correlation coefficient between total phenols a nd fla vonoids a nd the AOA mea sur ed by the FRAP assay was 0.85 and 0.93, respectively. The correlation between total phenols and flavonoids and AOA measured by ABTS was 0.79 and 0.81 and by DPPH was 0.85 and 0.77, respectively. T he c or r ela t ion c oef f ic ient s of b et a la ins (betacyanins and betaxanthins) and AOA by FRAP wer e lower, wit h va lu es of 0 . 4 1 a nd 0 . 4 8 , respectively, 0.67 and 0.51 by ABTS and 0.50 and 0.466 by DPPH. All t echniqu es used for t he deter mina tion of a nt iox ida n t c a p a c it y ( AO A) s ho wed a high correlation with TP and TF for three evaluated cultiva r s (CP1, CP3 a nd CP 4). T his ma y be because phenolic compounds, known as hydrophilic antioxida nt compounds, ar e the most abundant secondary metabolites in plants (Gil et al., 2002). This corresponds with what has been found by other authors such as (Thaipong et al., 2006) in guava extracts (r=0.97) using the FRAP technique a nd by (Dudonné et al. , 2009) in Pinus ba r k (r=0.96) using the ABTS technique. In addition, high correlations have been reported between total phenols and antioxidant activity by FRAP in fruit juices (Gardner et al., 2000). Kuti also reports similar correlations to those found in this work between t ota l fla vonoids a nd the a ntioxida nt ca pacity of four varieties of prickly pea r with values ranging from 0.76 to 0.88 using the ORAC technique (Kuti, 2000). Table 5: Pearson correlation matrix FRAP ABTS DPPH BC 0.415* 0.670** 0.504* BX 0.489* 0.516* 0.466* FT 0.854** 0.798** 0.853** FL 0.938** 0.811** 0.775** *,**= significant ( 0.05 y 0.01 respectively). BC: Betacyanins, BX: Betaxanthins. TP: Total phenols, TF: Total Flavonoids. FRAP= total antioxidant capacity determined using Cu (III) complex as oxidant. ABTS= total antioxidant capacity determined with the 2, 2'-azino-bis-3-ethylbenzothiazoline6-sulfonic radical (ABTS•+); DPPH= total antioxidant capacity determined with the radical 2,2-diphenyl-1-picrylhydracil (DPPH •). The high correlation shown by both TP and TF, as determined by the three techniques, indicates that both compounds are important contributors to the antioxidant activity of prickly pear fruit. In the case of betalains, low correlations were found with the three techniques, ranging from 0.41 to 0.67: the lowest correlation was by the FRAP technique and the highest by ABTS. This may be attributed to the assays used, considering the fact that individual antioxidants may, in some cases, act by multiple mecha nisms depending on the reaction system (Fernández et al., 2010). Cano and collaborators reported a negative correlation of total betalain content and antioxidant capacity determined by the DPPH technique (-0.08) (Cano et al., 2017). The body’s defense system is composed of several antioxidant components. Supplementation with one or few antioxidants may not be as effective. Fruits contain a group of natural antioxidants that could have not only high antioxidant activity, but also a good combination or mixture of antioxidants (Wuang et al., 2005). CONCLUSIONS T he p r es ent s t u dy p r ovides inf o r ma t ion on physicochemical characterization and antioxidant pr oper ties of thr ee selections of pr ickly pea r (Opuntia ficus-indica Mill) grown at the Colegio de Postgraduados, Mexico. The results show that prickly pear has considerable levels of phenolic compounds that play an important role against oxidation. The highest content of these compounds is found in the peel of the fruit and there are no significant differences between the content in pulp J. Hortl. Sci. Vol. 16(1) : 91-102, 2021 Post-harvest quality and anti-oxidant activity in prickly pear 100 and juice. Therefore, prickly pear peel has a great potentia l for ob ta ining bioa ctive compou nds, antioxidants. These natural antioxidants can be formulated to give nutraceuticals, which can help prevent oxidative damage from occurring in the body. I n r ela t ion t o qu a lit y a nd p hys ic oc hemic a l characteristics, CP1 (red) and CP4 (orange) were outstanding in aspects of size, weight, gr eater resistance to deformation, higher total soluble solids content, greater quantity of pulp and juice, and smaller seed. All these a spects ma ke the CP1(r ed) a nd CP4(orange) selections interesting materials for both fresh and processed products. Further research is needed to find alternatives to take full advantage of the compounds found in all parts of the fruit, as well as to understand the role played by betalains in the antioxidant activity of the fruit. ACNOWLEDGMENT Author Paulina Haydeé Gonzalez Fierro wishes to a cknowledge the fina ncia l suppor t r eceived from Consejo Nacional de Ciencia y Tecnología of Mexico (CONACyT). REFERENCES Andreu, L., Nuncio, J. N., Carbonell, B. 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