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Characterization of cell wall polysaccharides of purple pitaya (Hylocereus sp.

) pericarp Alexander Montoya-Arroyo a,1 , Ralf M. Schweiggert b , María-Lourdes Pineda-Castro a , Martin Sramek c , Reinhard Kohlus c , Reinhold Carle b , Patricia Esquivel a,* a Escuela de Tecnología de Alimentos, Universidad de Costa Rica,

2060 San Pedro, Costa Rica b Institute of Food Science and Biotechnology, Plant Foodstuff Technology, Hohenheim University, Garbenstrasse 25, D-70599 Stuttgart, Germany c Institute of Food Science and Biotechnology, Food Process Engineering, Hohenheim University, Garbenstrasse 25, D-70599 Stuttgart, Germany a r t i c l e i n f o Article history: Received

28 May

2012 Accepted

16 July

2013 Keywords: Hylocereus Pectin fractions Pitaya pericarp Neutral sugars Anhydrouronic acid Pectin esteri?cation a b s t r a c t While the fruit pulp of purple pitaya (Hylocereus sp.) is highly valued, its pericarp is unsuitable for consumption. Cell wall polysaccharides of fruit pericarp were analyzed to identify potential valorization of this by-product. The alcohol insoluble residue (AIR) was extracted yielding 6.16 ? 0.09% on FW of AIR, which was subsequently fractionated into water-, oxalate-, acid- and alkali-soluble pectins, hemicellu- lose and cellulose. Water and oxalate-soluble pectin were the major pectin fractions. Anhydrouronic acid (AUA) contents of the AIR and of the fractions were measured using the m-hydroxydiphenyl (MHDP) assay, resulting in 24.1% of the AIR. AUA contents were higher in the water (WSP) and oxalate (OXP) soluble pectin fractions, reaching 46.62 and 56.16% of their total, respectively. Moreover, the degree of esteri?cation (DE) of the AIR and its fractions was determined spectrophotometrically, where the highest DE values were found in the WSP and acid (HSP) soluble fractions. Fractions were analyzed for their neutral sugar composition by gas chromatography after derivatization. Pectin fractions were mainly composed of arabinose, galactose and rhamnose, while the hemicellulose fraction mainly consisted of glucose and xylose. The thickening properties of the AIR were evaluated after determining relative viscosities of AIR solutions and comparing the data with various mathematical models. With increasing shear rates a power law decay of shear viscosity was observed for AIR solutions indicating structure viscous shear-thinning behavior. Flow curves of 1% solutions of commercial thickeners showed high similarity to a 5% solution of pitaya AIR, thus indicating the requirement of further puri?cation of the pitaya AIR. ?

2013 Elsevier Ltd. All rights reserved. 1. Introduction The genus Hylocereus (Britton &

Rose) belongs to the vine cacti from the subfamily Cactoideae within the Cactaceae (Raveh, Weiss, Nerd, &

Mizrahi, 1993). Hylocereus undatus [(Haworth) Britton &

Rose], the white-?eshed red pitaya possessing a red-colored peri- carp, is the most widely cultivated vine cactus. Further commer- cialized species are Hylocereus polyrhizus [(F.A.C. Weber) Britton &

Rose] and Hylocereus costaricensis [(F.A.C. Weber) Britton &

Rose], both purple-?eshed pitayas exhibiting red pulp and pericarp (Esquivel, 2004;

Mizrahi &

Nerd, 1999). Similar to cactus pears (Opuntia ?cus-indica L.), one of the most studied Cactaceae species, red ?eshed pitayas were reported to be valuable sources of beta- lains (Esquivel, Stintzing, &

Carle, 2007b;

Stintzing, Schieber, &

Carle, 2002;

Wybraniec et al., 2001). The production of mucilaginous substances is characteristic of members of the Cactaceae (Nobel, Cavelier, &