Structural polysaccharides in xoconostle (Opuntia matudae) fruits with different ripening stages Rosario Álvarez Armenta and Cecilia Beatriz Peña-Valdivia* Botánica, Colegio de Postgraduados, Campus Montecillo. Km 35.5 carretera México-Texcoco. Montecillo, Texcoco, 56230, México. *Author for correspondence, E-mail: [email protected] Received 26 August, 2008; accepted 24 January, 2009 Abstract The objective of this research was to isolate, purify and quantify the content of mucilage, pectins, hemicelluloses and cellulose of the acidic cactus fruits of Opuntia matudae with commercial maturity. Fruits were collected in an orchard for commercial production of cactus pear fruit and pads in San Martin de Las Pirámides, Mexico. Fruits were grouped according to the receptacle depth, fruit dimensions and proportion of structures. The structural polysaccharides of the dehydrated and finely crushed skin (edible portion) fruits, were sequentially extracted with water and aqueous solutions of ammonium oxalate and potassium hydroxide, precipitated with ethanol, purified by dialyzing or watery washing and gravimetrically quantified after being lyophilized. Although, fruits were harvested with significantly homogenous size, and identified by the farmer like adequate for commercialization (with equatorial and polar diameters homogenous between the fruits, 51.7 mm, 45.2 mm respectively), they were grouped in three depending on receptacle depth (between 3.8 and 6.9 mm) and other parameters, like total wet biomass (between 64 and 81 g/fruit) and dry biomass (between 1.9 and 33.3 g/fruit), skin thickness (between 11.3 and 12.7 mm) and total number of seeds (120 to 205 abortive plus normal seeds/fruit). In addition, also it was confirmed that fruit ripeness of O. matudae is inversely related to the depth of receptacle. Mucilage, pectin and cellulose represented a significantly higher amount in the ripe fruits (7.5, 8.0 and 15.4%, respectively) than in the unripe (1.8, 2.5 and 10.0%, respectively); whereas the hemicelluloses content in all three classified ripe states was significantly similar (in average 3.2 and 1.5 % of loosely and tightly bound hemicelluloses). The results indicate that xoconostle fruits are rich in soluble (7.8 to 18.6%) and insoluble (11.6 to 16.5%) dietary fiber, and the type of polysaccharides varies in dependence of fruit ripening. Key words: dietary fiber, soluble fiber, insoluble fiber, mucilage, pectin, hemicelluloses, cellulose. Resumen El objetivo de esta investigación fue aislar, purificar y cuantificar el contenido de mucílago, pectinas, hemicelulosas y celulosa de los frutos de Opuntia matudae con madurez comercial. Los frutos fueron recolectados en un huerto para producción comercial de tuna y nopal de San Martín de las Pirámides, México. Los frutos fueron clasificados con la profundidad del receptáculo, se determinaron las dimensiones de los frutos y proporción de sus estructuras. Los polisacáridos estructurales de la cáscara (tejido comestible) de los frutos, deshidratada y triturada finamente, fueron extraídos en secuencia con agua y soluciones acuosas de oxalato de amonio e hidróxido de 26 J. PACD (2009) 11: 26−44 potasio, precipitados con etanol, purificados mediante diálisis o lavado acuoso y cuantificados gravimétricamente después de ser liofilizados. Aunque los frutos fueron cosechados con tamaño medio significativamente homogéneo, e identificado por la productora como el adecuado para la comercialización (con diámetros ecuatorial, 51.7 mm, y polar, 45.2 mm, estadísticamente iguales entre los frutos), se formaron tres grupos con madurez diferente en dependencia de la profundidad del receptáculo (entre 0.6 y 6.9 mm) y otros parámetros, como la biomasa total húmeda (entre 64 y 81 g/fruto) y seca (entre 1.9 y 3.3 g/fruto), grosor de la cáscara (11.3 a 12.7 mm) y número total de semillas (120 a 205 abortivas y normales/por fruto) fueron significativamente diferentes entre los grupos. Además, esto también confirmó que la madurez de los frutos de O. matudae está relacionada inversamente con la profundidad del receptáculo. El contenido de mucílago, pectinas y celulosa representó una cantidad significativamente superior en los frutos con mayor madurez (7.5, 8.0 y 15.4%, respectivamente) respecto a los menos maduros (1.8, 2.5 y 10.0%, respectivamente); mientras que el contenido de hemicelulosas fue significativamente similar en los tres estados de madurez identificados (en promedio 3.2 y 1.5% de hemicelulosa débilmente y fuertemente unida a la celulosa). Los resultados indican que los frutos de xoconostle son un alimento rico en fibra alimentaria soluble (7.8 a 18.6%) e insoluble (11.6 a 16.5%), y el tipo de polisacáridos que los conforman varían en dependencia de la madurez del fruto. Palabras clave: fibra alimentaria, fibra soluble, fibra insoluble, mucílago, pectinas, hemicelulosa, celulosa. Introduction Medicinal plants have been used with therapeutic aims in the Mexican herbalism (a traditional Medicine or folk medical practice based on the use of plants and plant extracts; also known as botanical medicine, medical herbal, herbal medicine, herbology, and phytotherapy) since pre- Columbian times, and these plants have continuously been used until now, and seems that every day they acquires greater scientific importance, because the formal investigation of their effects on human health care. On the matter, almost 500 vegetal species has been documented in Mexico, for the treatment of diabetes mellitus. According to Andrade-Cetto and Heinrich (2005) the best represented families in medicinal plant research, by number of genus, are the Asteraceae (47), Fabaceae (27), Cactaceae (16), Solanaceae and Euphorbiaceae (10) and Laminaceae (9). Cactaceae includes the genera Opuntia and Lophocereus which have been widely studied and the results that endorse these genera because popular uses like antidiabetic agents have been published (Bravo and Sanchez, 1991; Yeh et al., 2003). Alarcon-Aguilar et al. (2003) assured that the Ethnobotanic information which documents the use of Opuntia for diabetes treatment in Mexico dates from the decade of the 1970s. The potential use for Opuntia plants in Mexico is ample, since 83 Mexican species have been registered (Guzmán et al., 2003). Alarcon-Aguilar et al. (2003) indicated that among the anti-diabetics plants most frequently used are O. ficus-indica and O. streptacantha plants; and it seems that the fruits known like “xoconostle” (name of the prickly acid or sour cactus pear fruit), corresponding to O. joconostle, O. duranguensis, O. leucotricha y O. matudae are significantly more important (Cassiana, 2007). Xoconostle has low pulp content, and heavy, acid edible skin (Reyes-Agüero et al., 2005; Scheinvar, 1999). Xoconostle fruits are consumed as much for therapeutic aims as in the preparation of foods, treats, drinks and other products (García-Pedraza et al., 2005a). The biological effects on human health of Opuntia spp. pads (mature stems), “nopalitos” (young cladodes), fruits (“tunas”) and flowers have been documented. These plant tissue could be J. PACD (2009) 11: 26–44 27 consumed crude, roasted or cooked, as well as its juice for cardiovascular and oxidation protection, as antiulcerant, and hepatoprotector; and positive effects on acidosis, hyperglycemy, gastritis, hyperlipidemia, fatigue and dyspnoe, have also been described; besides the Opuntia spp. tissues are used to improve digestion and enhance the general detoxification processes, also they are applied to treat rheumatic disorders, erythemas and chronic skin infections and many others illness (Alarcon- Aguilar et al., 2003; Bwititi et al., 2000; Cassiana, 2007; Fernandez-Harp et al., 1984; Fernández et al., 1992 and 1994; Frati et al., 1990; Ibanez-Camacho et al., 1983; Livrea and Tesoriere, 2006; Perfumi and Tacconi, 1996; Wolfram et al., 2002). The chemical compounds of the Opuntia spp. tissue that cause such beneficial effects are only partially known; some of them are dietary complex carbohydrates (polysaccharides), like mucilage, pectins, and some other compounds like vitamins and polyphenols (Galati et al., 2002; Wolfram et al.; 2002). In relation to the physiological effects of complex molecules mainly in humans, it has been documented that dietary fiber of a given composition, or some fiber components, are useful to controlling body weight, diabetes and arteriosclerosis, and also prevent or reduce the incidence of cancer, constipation, hemorrhoids, cardiovascular diseases, accelerate the healing processes, and many others (Cummings et al., 2004; Wolfram et al., 2002). The insoluble polysaccharides (conformed by tightly bound hemicelluloses and cellulose) increase the volume of the alimentary bolus and the passage of the food throughout the digestive tract (Hsu et al., 2004); while, the soluble fiber (mucilage, pectins and loosely bound hemicelluloses) increases the viscosity of the intestinal content and regulates the concentration of glucose and cholesterol in blood (Binns, 2003; Cummings et al., 2004; Englyst and Englyst, 2005; Figuerola et al., 2005; Sáenz, 2004 and 2006).It has been demonstrated that nopalitos (Opuntia spp.) are a natural source of a variety of polysaccharides (mucilage, pectins, hemicelluloses and cellulose), and that the content of each class of polysaccharide is also variable but, remarkably abundant depending on the specie, variant (cultivar or wild), and growth conditions (temperature, humidity, soil type, etc); besides, the process of blanche and cook of nopalitos modified the