Impact of pH and Temperature on the Colour and Betalain Content of Colombian Yellow Pitaya Peel (Selenicereus Megalanthus)

Depósito de investigación de la Universidad de Sevilla https://idus.us.es/ “This version of the article has been accepted for publication, after peer review (when applicable) and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://doi.org/10.1007/s13197-016-2215-y” Impact of pH and temperature on the colour and betalain content of Colombian yellow pitaya peel (Selenicereus megalanthus) María Jesús Cejudo-Bastantea, Nelson Hurtadob, Angélica Delgadob, Francisco J. Herediaa* a Food Colour and Quality Laboratory, Dept. Nutrition and Food Science, Facultad de Farmacia, Universidad de Sevilla, 41012 Sevilla, Spain b Departamento de Química, Universidad de Nariño, A.A. 1175 Pasto, Colombia María Jesús Cejudo-Bastante: [email protected] Nelson Hurtado: [email protected] Angélica Delgado: [email protected] Francisco J. Heredia: [email protected]s * Corresponding author: Francisco J. Heredia Food Colour & Quality Lab., Dept. Nutrition & Food Science. Facultad de Farmacia. Universidad de Sevilla. 41012-Sevilla, Spain Tel.: +34 954556495 Fax: +34 954556110 e-mail: here[email protected] 1 57 58 59 60 61 62 63 64 65 5 10 22 27 32 ABSTRACT 1 2 The effects of different pHs (4, 5 and 6), temperatures (4, 20 and 80 ºC) and storage (up 3 4 to 12 days) on differential tristimulus colorimetry and betalain content related to the 6 7 colour of yellow pitaya (Selenicereus megalanthus) have been investigated. The peel of 8 9 the yellow pitaya was extracted with different solvents to see its colorant capacity. 11 12 Highly-acidic extracts (pH 4) showed the lowest betalain content, chroma (C*ab = 60 13 14 against 70) and the yellow component of the colour (b*). Storage temperature 15 16 17 manifested a great influence on CIELAB parameters when yellow pitaya peel was 18 19 added to highly-acidic foodstuffs, with a tendency towards red hues (hab, from 100º to 20 21 85º) and remarkable changes on lightness (L*, from 90 to 75) as temperature increased. 23 24 However, low-acidic extracts (pH 5 and 6) were superior from a colour stability 25 26 standpoint, not being influential the temperature of storage. All colour changes 28 29 according to pH and temperature were visua E*ab > 3). 30 31 New opportunities for diversification of colorant market could be possible by 33 34 employing yellow pitaya peel as natural resource. 35 36 KEYWORDS 37 38 39 Yellow pitaya (Selenicereus megalanthus); differential tristimulus colorimetry; 40 41 betalains; stability. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 5 10 22 27 32 44 49 INTRODUCTION 1 2 The interest about the displacement of synthetic substances in favour of coloured natural 3 4 products is continuously growing. In fact, the search for new coloured plant materials is 6 7 been recently stimulated, predicting an upward annual growth rates of 10-15 % in the 8 9 European markets (Stintzing and Carle 2004). 11 12 In that view, carotenoids, chlorophylls, anthocyanins and betalains, present in a high 13 14 number of fruits and vegetables, are responsible for a wide range of colours. Therefore, 15 16 17 natural resources containing them are being deeply considered as possible natural 18 19 colorants, above all carotenoids-, chlorophylles- and anthocyanins-rich products. There 20 21 is another group of pigments called betalains, which could represent a potential source 23 24 of natural colorant. However, up to the present, betalains have been scientifically 25 26 studied in a lesser extent. 28 29 Up to now, red beet (Beta vulgaris L.) (De Azeredo et al. 2009; Nemzer et al. 2011; 30 31 Pavokovi and Krsnik-Rasol 2011) and cactus pear (Opuntia sp.) (Castellanos-Santiago 33 34 and Yahia, 2008; Cejudo-Bastante et al. 2014) are the most investigated source of 35 36 betalains, but there are a large number of betalain-rich products potentially usable as 37 38 39 natural colorants. 40 41 On that concern, pitaya (Hylocereus sp.), also known as dragon fruit, is an orchard crop 42 43 and a member of the Cactaceae family. It is native to Central South America and is 45 46 distributed throughout Colombia, Ecuador, Peru, and Bolivia (Weiss, 1995). The fruit is 47 48 a medium-size oblong berry bearing tubercles and thorns that are shed during ripening. 50 51 It contains numerous small digestible black seeds and the pulp and skins adopt different 52 53 colourations pursuant to the specie (Nerd and Mizrahi 1997). Accordingly, among all 54 55 56 the existing species of Hylocereus, Hylocereus polyrhizus (red-purple pitaya), 59 60 61 62 63 64 65 5 10 22 27 32 44 49 Hylocereus undatus (white pitaya) and Hylocereus or Selenicereus megalanthus (yellow 1 2 pitaya) are the most widespread. 3 4 Some scientific studies of characterization of different species of Hylocereus have been 6 7 developed. In that way, some researches about the chemical characterization of red- 8 9 purple pitaya from different countries have been reported on the basis of several 11 12 perspectives. Thus, Stintzing et al. (2002, 2004) firstly characterized the betalain profile 13 14 of red-purple pitaya (Hylocereus polyrhizus (Weber) Britton & Rose) by HPLC-MS and 15 16 17 RMN, as well as Wybraniec et al. (2002) of several red and white species of Hylocereus 18 19 from Israel. Moreover, Esquivel et al. (2007b, 2007c) studied the pigment profiles, 20 21 colour, betalain contents and antioxidant activity of fruits of five different Hylocereus 23 24 sp. genotypes from Costa Rica during ripening (Esquivel et al. 2007a). In addition, 25 26 recently, Lee et al. (2014) defined the metabolite profiling of Korean red and white 28 29 pitayas (Hylocereus polyrhizus and Hylocereus undatus) by comparing betalain 30 31 biosynthesis and antioxidant activity. However, scarce studies of chemical 33 34 characterization of other species of Hylocereus (such as yellow pitaya, Selenicereus 35 36 megalanthus) has been previously conducted. That is the case of the researches about 37 38 39 phenolics (Jiang et al. 2011), amino acids (Kugler et al. 2006) and fatty acids of seeds 40 41 (Chemah et al. 2010), among others. Also, Nerd and Mizrahi (1998, 1999) observed the 42 43 effect of the ripening stage after storage on fruit quality (peel content, weight loss, water 45 46 content and titratable acidity) but only Kugler et al. (2007) deepened on the content of 47 48 total polyphenols, and their relationship with the antioxidant activity. 50 51 Despite of the potential use as natural colorant of the different species of Hylocereus, 52 53 scarce technological scientific studies about this fruit have been conducted; that is it, the 54 55 56 behaviour of pitaya as colorant under different commercial or industrial processes. In 57 58 that way, some advances have been published in red-purple pitaya, considering the 59 60 61 62 63 64 65 5 10 22 27 32 44 49 possible circumstances that colorant could suffer when it is added to foodstuffs 1 2 (Herbach et al. 2004; Woo et al. 2011) and also by developing and optimizing an 3 4 enzyme-assisted liquefaction treatment under low temperature to produce a colorant of 6 7 purple pitaya (Schweiggert et al. 2009). However, despite such possible broad agro- 8 9 alimentary implications as natural colorant, none research study about colorimetry and 11 12 betalain content of yellow pitaya has been found in bibliography yet. 13 14 Therefore, the present work was performed on yellow pitaya (Selenicereus 15 16 17 megalanthus) cultivated in Colombia, and the interest was focused on the colour 18 19 characterization and betalain content, not previously reported in that raw material. Only 20 21 the peel of the fruit was taken into account because of its yellow colour and location of 23 24 betalains, being the flesh purple of a white colour and devoid of betalains. Furthermore, 25 26 not only a colour characterization of yellow pitaya is needed, but also even to spotlight 28 29 the behaviour in terms of colour and betalains when it acts as colorant of other agro- 30 31 alimentary foodstuffs. As a result, stability assays at different pHs and temperatures 33 34 over time have been also carried out. It is highlighted that this research is the first 35 36 endeavour to tend to reproduce commercial conditions of processing and nature of the 37 38 39 food upon the yellow pitaya to be added as colorant. 40 41 MATERIALS AND METHODS 42 43 The effect of acidity and temperature over time on colour and betalain content was 45 46 scrutinized. Several temperatures (4, 20 and 80 ºC) and pHs (4, 5 and 6) were selected 47 48 as representative of several processing and storage conditions, and acidities of sources 50 51 where yellow pitaya was added as natural colorant. A follow-up over time (0 and 5 h, 52 53 and 1, 2, 6, 8 and 12 days) of CIELAB colour parameters, tristimulus differential 54 55 56 colorimetry and betalain content have been evaluated. In order to a better understanding, 57 58 59 60 61 62 63 64 65 5 10 22 27 32 44 49 the behaviour of temperature and acidities on yellow pitaya peel was separately 1 2 discussed. 3 4 Sample preparation 6 7 Yellow pitayas (Selenicereus megalanthus) (code 45988) were collected in San Juan de 8 9 Pasto (Nariño, Colombia). A random sampling of 60 shrubs distributing in an area of 11 12 approximatively 2000 m2 (1º35´15.2´´N latitude y 77º11´19.1´´O longitude, at 1920 13 14 meters above sea level) was carried out. Visual characteristics such as size or colour 15 16 17 were used at harvesting, and a total of 8 Kg of fruits were collected. According the NTC 18 19 3554 regulation, the samples were picked at a maturity stage of 5, based on the yellow 20 21 colour and the slight greenish tonality at the end of the fruit. 23 24 The quartering method was employed to reach a representative sample of the set. 25 26 Previous homogenization, the fruits were distributed into four quadrants. Two fruits of 28 29 opposite quadrants was randomly selected. The remainder fruits were mixed again and 30 31 the process was repeated twice more. As a result, six fruits were considered for the 33 34 analysis, with approximately 1126 g of total weight. They were washed and dried, and 35 36 prickles were manually removed. The white pulp and black seeds were also discarded. 37 38 39 Preparation of extracts 40 41 Yellow peels were only considered for the analysis, with around a 33 % of total yield. 42 43 They were cut into small pieces (1 cm2) and macerated with 1 L of methanol:water 45 46 (60:40) for 1 day at 10 ºC, according to the method described by Cejudo-Bastante et al. 47 48 (2014). Once filtration, the organic solvent was removed at 35 ºC using a rotary 50 51 evaporator (Heidolph, Schwabach, Germany) and re-dissolved with distilled water. The 52 53 extract was lyophilized (Labconco, MO, USA) and stored at 4 ºC until their analysis. 54 55 56 3 g of lyophilized peel were used for the extractions, with the addition of 9.5 mL of 57 58 methanol and water (50:50), containing 50 mM of sodium ascorbate. Samples were then 59 60 61 62 63 64 65 5 10 22 27 32 44 49 stirred at 225 rpm for 10 min in darkness, to avoid possible degradation by light. 1 2 Afterwards, a centrifugation at 12000 x g at 10 ºC and 5 min was carried out, according 3 4 to the method proposed by Cejudo-Bastante et al. (2014). Supernatants were separated 6 7 from the plant tissue and, in order to achieve the complete discolouration of the plant 8 9 material, the procedure was developed once more with the extraction solution and 11 12 finally with 100 % methanol. Later, the extract obtained was concentrated in vacuum 13 14 (30 ºC) and re-suspended in 15 mL with purified water. All experiences were carried 15 16 17 out in duplicate. 18 19 Technological treatments of the extracts 20 21 Extracts were adjusted to different acidities (pH 4, 5 and 6) using hydrochloride acid 0.1 23 24 and 1 M. Subsequently, each pH-sample were submitted to three different temperatures: 25 26 4 ºC, and 20º and 80 ºC, putting samples into a refrigerator and an oven JP Selecta, S.A. 28 29 (Barcelona, Spain), respectively. At each time-point, an aliquot of each sample were 30 31 picked and conserved for further analyses. 33 34 To try to reproduce as possible real situations of processing and storage, samples kept at 35 36 4 and 20 ºC were analysed at the beginning of the treatment (0 days), after 5 hours (0.21 37 38 39 days) and after 1, 2, 6, 8 and 12 days, whereas only the first three points were 40 41 considered for samples underwent 80 ºC. 42 43 Colorimetric measurements 45 46 A Hewlett-Packard UV-vis HP8452 spectrophotometer (Palo Alto, CA) was employed 47 48 to develop colour measurements. The whole visible spectrum (380-770 nm) was 50 51 52 53 distilled water as reference. The original software CromaLab© was used for 54 55 56 determining the CIELAB parameters (Heredia et al. 2004) following the Commission 57 58 recommendations: (CIE, 2004) the CIE 1964 10° 59 60 61 62 63 64 65 5 10 22 27 32 44 49 Standard Observer and the Standard Illuminant D65. Euclidean distance between two 1 2 points in the three-dimensional space define by L* (lightness), a* and b* (red and 3 4 yellow component of the colour, respectively) were used for calculating colour 6 7 E*ab E*ab L*)2 a*)2 b*)2]1/2. All experiences were carried 8 9 out in duplicate. 11 12 Spectrophotometric quantification of betalains 13 14 The UV-vis spectra were recorded from 360-800 nm in order to develop a photometric 15 16 17 quantification of betalains. Maximum absorbance of 484 nm was reported to quantify 18 19 betaxanthins (B), following the equation: 20 21 [B] (µg g-1 23 24 where Abs is the value of maximum absorbance at 484 nm, D is the dilution factor, V is 25 26 ular weight and the molar 28 29 extinction coefficient of indicaxanthin (308 g mol-1 and 48,000 L (mol cm)-1 in H2O), L 30 31 is the path-length (2 mm) and W the dried weight of the sample (g). All measurements 33 34 were carried out in duplicate. 35 36 Statistical analysis 37 38 39 Statistical analysis was carried out by using Statistica version 8.0 software (Statistica, 40 41 2007). Univariate analyses of variance (Tukey test and ANOVA) (p < 0.05) were 42 43 applied to discriminate among the means of chemical data. 45 46 RESULTS AND DISCUSSION 47 48 Colorimetric characteristics 50 51 The monitoring of the evolution of CIELAB colour parameters (L*, C*ab, hab) were 52 53 carried out along 12 days under different conditions of acidity and temperature of 54 55 56 processing or storage (Fig. 1). It is deserved to comment that the behaviour of the 57 58 59 60 61 62 63 64 65 5 10 22 27 32 44 49 As it could be appreciated in Fig. 4b, the content of betaxanthin greatly depended on the 1 2 temperature. Changes on betaxanthin concentration began to be noticeable (> 15%) 3 4 after six days of treatment (and only 5 hours when cooking). 6 7 It could be clearly observed how temperature made the content of betaxanthins 8 9 increased overmuch, appreciating significantly diverse among temperatures (ANOVA, p 11 12 < 0.05). However, low temperatures palliated this behaviour, observing a scarce or 13 14 lower evolution as time progressed when extracts were stored at 4 ºC. Similar results 15 16 17 were also reported by Cejudo-Bastante et al. (2014) when ulluco extracts were 18 19 submitted to different thermal storage conditions. 20 21 Upon heating (80 ºC), yellow pitaya extracts suffered a pronounced degree of 23 24 degradation, being a thermosensitive raw material at those conditions. The very high 25 26 content of betaxanthins at the end of the cooking (80 ºC) lead us to think that an 28 29 accelerated browning occurred, in light of the great maximum absorption at 484 nm. 30 31 The formed compounds could be characterized by decarboxylation of betacyanins at C- 33 34 17 and/or C-2, and dehydrogenation at C-14/C-15, which could modify appearance and 35 36 stability of the genuine pigments (Herbach et al. 2006). 37 38 39 Namely, low temperature avoided in a higher extent the possible variations of 40 41 betaxanthin amounts, regardless of pH. 42 43 CONCLUSIONS 45 46 Yellow pitaya peel is a potential and promising natural source with multiple 47 48 possibilities as colorant. This fruit is suitable for being added as natural colorant in a 50 51 range of 4-6 pHs (from vegetables- or fruit-based dishes to yoghurts, for example) 52 53 taking into account the behaviour of colorimetric parameters and betaxanthins, 54 55 56 assuming some restrictions of temperature to protect as possible the initial properties. 57 58 Extracts adjusted to acid pHs must be conserved under cold storage in order to avoid 57 58 59 60 61 62 63 64 65 5 10 22 27 32 44 49 remarkable changes on hue and lightness, not exerting the temperature of storage a 1 2 remarkable influence on possible colour changes of low-acidic foodstuffs. This study is 3 4 an important step towards diversification of colorants in the direction of the 6 7 displacement of synthetic colorants that provoke several inconveniences and value such 8 9 as a low-exploited natural resource. 11 12 ACKNOWLEDGMENTS 13 14 We are indebted to Consejería de Economía, Innovación y Ciencia, Junta de Andalucía, 15 16 17 Spain (Project P11-AGR-7843) for financial support. We thank technical staff of 18 19 Biology Service (SGI, Universidad de Sevilla) for technical assistance and University of 20 21 Nariño, San Juan de Pasto, Colombia. 23 24 REFERENCES 25 26 Castellanos-Santiago E, Yahia EM (2008) Identification and quantification of betalains 28 29 from the fruits of 10 Mexican prickly pear cultivars by high-performance liquid 30 31 chromatography and electrospray ionization mass spectrometry. J Agric Food 33 34 Chem 56:5758-5764 35 36 Castellar MR, Obón JM, Alacid M, Fernández-López JA (2003) Color properties and 37 38 39 stability of betacyanins form Opuntia fruits. J Agric Food Chem 51:2772-2776 40 41 Cejudo-Bastante MJ, Chaalal M, Louaileche H, Parrado J, Heredia FJ (2014) Betalain 42 43 profile, phenolic content, and color characterization of different parts and 45 46 varieties of Opuntia ficus-indica. J Agric Food Chem 62:8491-8499 47 48 Cejudo-Bastante MJ, Hurtado N, Mosquera N, Heredia FJ (2014) Potential use of new 50 51 Colombian sources of betalains. Color stability of ulluco (Ullucus tuberosus) 52 53 extracts under different pH and thermal conditions. Food Res Intern 64:465-471 54 55 56 57 58 59 60 61 62 63 64 65 5 10 22 27 32 44 49 Chemah TC, Aminah A, Noriham A, Wan Aida WM (2010) Determination of pitaya 1 2 seeds as a natural antioxidant and source of essential fatty acids. Intern Food Res 3 4 J 17:1003-1010 6 7 CIE. (2004). Technical Report Colorimetry; Commission Internationale de l'Eclairage 8 9 Central Bureau. Vienna, Austria. 11 12 De Azeredo HMC, Pereira AC, De Souza ACR, Gouveia ST, Mendes KCB (2009) 13 14 Study on efficiency of betacyanin extraction from red beetroots. Intern J Food 15 16 17 Sci Technol 44:2464-2469 18 19 Esquivel P, Stintzing FC, Carle R (2007a) Fruit characteristics during growth and 20 21 ripening of different hylocereus genotypes. Eur J Hortic Sci 7: 231-238 23 24 Esquivel P, Stintzing FC, Carle R (2007b) Phenolic compound profiles and their 25 26 corresponding antioxidant capacity of purple pitaya (Hylocereus sp.) genotypes. 28 29 Zeitschrift fur Naturforschung - Section C J Biosci 62:636-644 30 31 Esquivel P, Stintzing FC, Carle R (2007c) Pigment pattern and expression of colour in 33 34 fruits from different Hylocereus sp. genotypes. Innov Food Sci Emerg Technol 35 36 8:451-457 37 38 39 Fernández-López JA, Angosto JM, Giménez PJ, León G (2013) Thermal Stability of 40 41 Selected Natural Red Extracts Used as Food Colorants. Plant Foods Human Nutr 42 43 68:11-17 45 46 Fernández-Zurbano P, Ferreira V, Peña C, Escudero A, Serrano F, Cacho J (1995) 47 48 Prediction of oxidative browning in white wines as a function of their chemical 50 51 composition. J Agric Food Chem 43:2813-2817 52 53 Gordillo B, Rodríguez-Pulido FJ, Escudero-Gilete ML, González-Miret ML, Heredia FJ 54 55 56 (2012) Comprehensive colorimetric study of anthocyanic copigmentation in 57 58 59 60 61 62 63 64 65 5 10 22 27 32 44 49 model solutions. Effects of pH and molar ratio. J Agric Food Chem 60:2896- 1 2 2905 3 4 Havlíková L, Miková K, Kyzlink V (1983) Heat stability of betacyanins. Zeitschrift für 6 7 Lebensmittel-Untersuchung und -Forschung, 177:247-250 8 9 Herbach KM, Stintzing FC, Carle R (2004) Impact of thermal treatment on color and 11 12 pigment pattern of red beet (Beta vulgaris L.) preparations. J Food Sci 69:C491- 13 14 C498 15 16 17 Herbach KM, Stintzing FC, Carle R (2006). Betalain stability and degradation - 18 19 Structural and chromatic aspects. J Food Sci 71:R41-R50 20 21 Herbach MK, Stintzing FC, Carle R (2004) Thermal degradation of betacyanins in 23 24 juices from purple pitaya [Hylocereus polyrhizus (Weber) Brittonv & Rose] 25 26 monitored by high-performance liquid chromatography-tandem mass 28 29 spectometric analyses. Eur Food Res Technol 219:377-385 30 31 Heredia FJ, Álvarez C, González-Miret ML, Ramírez A (2004) CromaLab, análisis de 33 34 color. In, vol. Registro General de la Propiedad Intelectual: SE-1052-04. Seville, 35 36 Spain. 37 38 39 Jiang YL, Lin TS, Lee CL, Yen CR, Yang WJ (2011) Phenology, canopy composition, 40 41 and fruit quality of yellow pitaya in Tropical Taiwan. HortSci 46:1497-1502 42 43 Kugler F, Graneis S, Schreiter PPY, Stintzing FC, Carle R (2006) Determination of free 45 46 amino compounds in betalainic fruits and vegetables by gas chromatography 47 48 with flame ionization and mass spectrometric detection. J Agric Food Chem 50 51 54:4311-4318 52 53 Kugler F, Stintzing FC, Carle R (2007) Evaluation of the antioxidant capacity of 54 55 56 betalainic fruits and vegetables. J Appl. Botany Food Qual 81:69-76 57 58 59 60 61 62 63 64 65 5 10 22 27 32 44 49 Lee S, Suh DH, Heo DY, Kim YS, Cho SK, Lee CH (2014) Metabolite profiling of red 1 2 and white pitayas (Hylocereus polyrhizus and Hylocereus undatus) for 3 4 comparing betalain biosynthesis and antioxidant activity. J Agric Food Chem 6 7 62:8764-8771 8 9 Martínez JA, Melgosa M, Pérez MM, Hita E, Negueruela AI (2001) Note. Visual and 11 12 instrumental color evaluation in red wines. Food Sci TechnolIntern 7:439-444 13 14 Nemzer B, Pietrzkowski Z, Spórna A, Stalica , 15 16 17 Wybraniec S (2011) Betalainic and nutritional profiles of pigment-enriched red 18 19 beet root (Beta vulgaris L.) dried extracts. Food Chem 127:42-53 20 21 Nerd A, Mizrahi Y (1998) Fruit development and ripening in yellow pitaya. J Am Soc 23 24 Hortic Sci 123:560-562 25 26 Nerd A, Mizrahi Y (1999) The effect of ripening stage on fruit quality after storage of 28 29 yellow pitaya. Postharv Biol Technol 15:99-105 30 31 Nerd A, Mizrahi Y (1997) Reproductive biology of fruit cacti. Hortic Rev 18:322 346 33 34 Palazón MA, Pérez-Conesa D, Abellán P, Ros G, Romero F, Vidal ML (2009) 35 36 Determination of shelf-life of homogenized apple-based beikost storage at 37 38 39 different temperatures using Weibull hazard model. LWT - Food Sci Technol 40 41 42:319-326 42 43 Pavokovi D, Krsnik-Rasol M (2011) Complex biochemistry and biotechnological 45 46 production of betalains. Food Technol Biotechnol 49:145-155 47 48 Schweiggert RM, Villalobos-Gutierrez MG, Esquivel P, Carle R (2009) Development 50 51 and optimization of low temperature enzyme-assisted liquefaction for the 52 53 production of colouring foodstuff from purple pitaya (Hylocereus sp. [Weber] 54 55 56 Britton & Rose). Eur Food Res Technol 230:269-280 57 58 59 60 61 62 63 64 65 5 10 22 27 32 44 Statistica. (2007). StatSoft Inc. STATISTICA (data analysis software system). In 8 ed. 1 2 Tulsa, OK. 3 4 Stintzing FC, Carle R (2004) Functional properties of anthocyanins and betalains in 6 7 plants, food, and in human nutrition. Trends Food Sci Technol 15:19-38 8 9 Stintzing FC, Conrad J, Klaiber I, Beifuss U, Carle R (2004) Structural investigations 11 12 on betacyanin pigments by LC NMR and 2D NMR spectroscopy. Phytochem 13 14 65:415-422 15 16 17 Stintzing FC, SchieberA, Carle R (2002) Identification of betalains from yellow beet 18 19 (Beta vulgaris L.) and cactus pear [Opuntia ficus-indica (L.) Mill.] by high- 20 21 performance liquid chromatography-electrospray ionization mass spectrometry. 23 24 J Agric Food Chem 502302-2307 25 26 Vaillant F, Pérez A, Davila I, Dornier M, Reynes M (2005) Colourant and antioxidant 28 29 properties of red-purple pitaya (Hylocereus sp.). Fruits 60 1-10 30 31 Weiss J, Scheinvar L, Mizrahi Y (1995) Selenicereus megalanthus (the yellow pitaya) a 33 34 climbing cactus from Colombia and Peru. Cactus and Succulent J 67:280 283 35 36 Woo KK, Ngou FH, Ngo LS, Soong WK, Tang PY (2011). Stability of betalain pigment 37 38 39 from red dragon fruit (Hylocereus polyrhizus). Am J Food Technol 6:140-148 40 41 Wybraniec S, Mizrahi Y (2002) Fruit flesh betacyanin pigments in Hylocereus cacti. J 42 43 Agric Food Chem 50:6086-6089 45 46 47 48 49 50 51 52 53 54 55 56 5 10 22 27 32 FIGURE CAPTIONS 1 2 Fig. 1 Effect of pH on CIELAB parameters of yellow pitaya peel at different 3 4 temperatures over time. Significant differences (p < 0.05) according to the Tukey test 6 7 among pH 4 (*), and among 80 ºC (+), and the rest of temperatures. 8 9 Fig. 2 Effect of temperature on CIELAB parameters of yellow pitaya peel at different 11 12 pHs over time. Significant differences (p < 0.05) according to the Tukey test among pH 13 14 4 (*), and among 80 ºC (+) and the rest of pHs . 15 16 17 Fig. 3 Colou E*ab) of yellow pitaya peel between pH 5 and 6 at different 18 19 temperatures (a) and between 4 ºC and 20 ºC at different pHs (b). 20 21 Fig. 4 Betaxanthin content of yellow pitaya peel: effect of pH at different temperatures 23 24 over time (a) (significant differences (p < 0.05) according to the Tukey test among pH 4 25 26 and the rest of pHs (*), and among all pHs (+)), and effect of temperature at different 28 29 pHs over time (b) (significant differences (p < 0.05) according to the Tukey test among 30 31 4 ºC and 20 ºC (*), and among 80 ºC and the rest of temperatures (+)). 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 1 63 64 65