Changes in Pectinases, Dietary Fibers, and Physicochemical Indices Related to the Flavor of Cubiu Fruits During Ripening

Acta Scientiarum http://www.uem.br/acta ISSN printed: 1679-9275 ISSN on-line: 1807-8621 Doi: 10.4025/actasciagron.v37i2.19683 Changes in pectinases, dietary fibers, and physicochemical indices related to the flavor of cubiu fruits during ripening Moacir Couto de Andrade Júnior1* and Jerusa Souza Andrade1,2 1Universidade Nilton Lins, Av. Professor Nilton Lins, 3259, Parque das Laranjeiras, 69058-040, Manaus, Amazonas, Brazil. 2Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, Brazil. *Author for correspondence. E-mail: [email protected] ABSTRACT. The objective of this study was to evaluate the changes in the activity of pectinases (pectinesterase and polygalacturonase), dietary fiber content (alcohol-insoluble solids, pectin, and total fiber), and physicochemical indices related to the flavor (pH, titratable acidity, soluble solids, Brix/acid ratio, and reducing and nonreducing sugars) of cubiu fruits (Solanum sessiliflorum Dunal) at different stages of ripening (green, turning, ripe, and fully ripe). Alcohol-insoluble solids and pectin were very similar, with the highest levels detected at the green and turning stages, and the lowest levels occurring at the fully ripe stage. The amount of total fiber was consistent at the green, turning, and ripe stages, but declined at the fully ripe stage. These changes correlated with the pectinase activities, the profiles of which resembled those of other species of the Solanaceae family during fruit ripening. However, cubiu fruits were significant sources of dietary fiber at all stages. The reducing sugar content reached the highest level at the turning stage, with glucose as the major sugar. The content of nonreducing sugars, such as sucrose, remained low at all stages. The other physicochemical indices displayed increases during ripening, characterizing cubiu as a very acidic fruit with a small degree of sweetness. Keywords: Solanum sessiliflorum Dunal, fruit peel color, pectin concentration, medicinal plants. Mudanças nas pectinases, fibras dietéticas e índices físico-químicos relacionados ao sabor de frutos de cubiu durante a maturação RESUMO. O objetivo deste estudo foi avaliar as mudanças na atividade de pectinases (pectinesterase e poligalacturonase), teor de fibras dietéticas (sólidos insolúveis em álcool, pectina e fibra total) e índices físico- químicos relacionados ao sabor (pH, acidez titulável, sólidos solúveis, relação Brix/acidez, açúcares redutores e não-redutores) de frutos de cubiu (Solanum sessiliflorum Dunal) em diferentes estádios de maturação (verde, de vez, maduro e muito maduro). Os sólidos insolúveis em álcool e pectina apresentaram perfis muito similares, com teores maiores nos estádios verde e de vez, e menores no estádio muito maduro. Teores de fibra total mostraram-se uniformes nos estádios verde, de vez e maduro, diminuindo no estádio muito maduro. Essas mudanças correlacionaram-se com a atividade das pectinases, cujos perfis assemelharam-se àqueles de outras espécies da família Solanaceae durante a maturação dos frutos. No entanto, os frutos de cubiu apresentaram teores significativos de fibras dietéticas em todos os estádios. O conteúdo de açúcares redutores atingiu teores maiores no estádio de vez, sendo a glicose o açúcar principal. O conteúdo de açúcares não-redutores, como a sacarose, permaneceu baixo em todos os estádios. Os demais índices físico-químicos apresentaram aumento durante a maturação, caracterizando o cubiu como um fruto muito ácido com pequeno grau de doçura. Palavras-chave: Solanum sessiliflorum Dunal, coloração da casca de frutos, concentração de pectina, plantas medicinais. Introduction Guaharibos Falls and the juncture of the Casiquiare and Orinoco rivers (VOLPATO et al., 2004). The population of the Amazonian region has long used fruits from a species of the Solanaceae Mature and ripe fruit can be distinguished by the family commonly referred to as cubiu (Solanum following description: mature fruit is ready for sessiliflorum Dunal) in Brazil, cocona in Colombia consumption, whereas ripe fruit is ready for picking and Peru, and tupiru in Venezuela (WHALEN et al., (POTTER; HOTCHKISS, 1998). Fruit ripening is 1981). Cubiu is native to western Amazonia and was a complex, genetically programmed process domesticated by the pre-Columbian Amerindians resulting in remarkable changes in the color, texture, (LOPES; PEREIRA, 2005). Other historical records flavor, and aroma of the fruit (ALEXANDER; indicate that in 1760, a Spanish surveyor, Apolinar GRIERSON, 2002). In addition to aiding in the Diaz de la Fuente, found cubiu growing with maize judgment of fruit maturation time, the fruit peel and beans in an Indian garden located between color is an important quality parameter and Acta Scientiarum. Agronomy Maringá, v. 37, n. 2, p. 171-179, Apr.-June, 2015 172 Andrade Júnior and Andrade marketing attribute that influences consumer galacturonic acid linked by 1,4-α bonds and acceptance (LARRIGAUDIERE et al., 1996; methoxylated to a varying extent at the carboxyl YONG-ZHONG et al., 2006). This and the other moieties (JOLIE et al., 2010). Among the pectinases, sensory attributes mentioned above are at prime pectinesterase (EC 3.1.1.11) catalyzes the quality in the fully ripe fruit. In contrast, overripe demethoxylation of esterified pectins (JOLIE et al., fruit is likely to become soft and mealy soon after 2010). This enzymatic activity releases protons when harvest (WU et al., 2011). Soluble solids mainly the pectin methoxyl groups are converted to consist of sugars (e.g., sucrose and fructose) and carboxyl groups, reducing the pH of the milieu and organic acids, which are good indicators of the being thereby easily detectable in the laboratory ripening stage of fruits (PEDRO; FERREIRA, 2005; (HENSEL et al., 2002). Polygalacturonase (EC PRETEL et al., 2008; PURKAYASTHA; 3.2.1.15), another pectinase, is considered a key MAHANTA, 2011). enzyme involved in pectin depolymerization and However, in the Amazonian region, the fleshy solubilization (OBENLAND et al., 2003). Notably, berries of the cubiu shrubs are picked regardless of not only is pectin disassembly important for the the ripening stage. This timing of the fruit harvest is food industry, but its derived oligosaccharides have used in part because the ingredients necessary to also been found to exert various positive effects on prepare the traditional fish stew are not easily human health (BURANA-OSOT et al., 2010). available throughout the Amazonian territory; thus, Thus, the first objective of this study was to the native population uses whatever foods are evaluate the changes in the pectinase activities at available to add substance to the daily meal. When different ripening stages, providing a basis for the used as condiments, these fruits have a pleasing food industry to preserve the textural quality and acidulous flavor reminiscent of citrus, which is extend the shelf life of cubiu fruits. The second objective of this study was to evaluate the changes in suitable for direct consumption or use in salads, fish, dietary fibers, thereby providing pertinent data for and meat dishes as well as juices and other beverages researchers and consumers. The third objective of (WHALEN et al., 1981). As food supplements, ripe this study was to evaluate the changes in the basic and fully ripe cubiu fruits are relatively poor in physicochemical indices related to the flavor of these macronutrients such as proteins and lipids, but fruits at different ripening stages, e.g., pH, titratable rather rich in secondary metabolites such as total acidity, soluble solids, Brix/acid ratio, reducing carotenoids (ANDRADE JÚNIOR; ANDRADE, sugars (glucose and fructose), and nonreducing 2012). These fruits are also rich in iron, niacin, and sugars (sucrose, a disaccharide of glucose and dietary fibers (ANDRADE et al., 2010; fructose). These data were previously unknown; SCHUELTER et al., 2009). Dietary fibers are hence, this study was designed to address these usually classified into two types according to their knowledge gaps. solubility in water. These fibers are designated as insoluble fibers (e.g., cellulose and lignin) or soluble Material and methods fibers (e.g., pectin). The gelling properties of the pectin present in cubiu fruits are well known to both Sample preparation researchers in the Amazonian region and home jam Cubiu fruits were randomly, manually harvested makers (ANDRADE et al., 2010; WILLATS et al., from shrubs grown in low-humic gley soil in the 2006; YUYAMA et al., 2008). As a medicinal plant, municipality of Iranduba, in the Amazonas State of cubiu has tested positively for hypoglycemic effects Brazil (03°14'22" south and 60°13'50" west). The in rats and humans in short-term studies (PARDO, determination of the ripening stages for the fruits 2004; SILVA FILHO et al., 2003; YUYAMA et al., was based on the four color patterns described by 2008). Mid-term and long-term studies should still the native population: green (over the entire fruit be conducted for a more detailed assessment of surface), turning (first appearance of yellow color at cubiu efficacy in diabetes mellitus. the blossom end), ripe (yellow color over the entire Other appearance factors (e.g., the consistency) fruit surface), and fully ripe (deep red-wine color of cubiu fruits are also important for the fresh over the entire fruit surface). In addition to these market. Breakdown of the cell wall polysaccharides standard colors, an additional criterion for the by pectinase activities during fruit ripening causes

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