Diversity of natural pigments and phytochemical compounds from exocarp and mesocarp of 27 Cucurbita pepo accessions
Graphical abstract
Introduction
In recent decades, agricultural globalization and modernization in many developing countries has encouraged a simplification in the nutritional intake by consumers resulting in nutritional deficiencies promoting diets low in diversification but high in energy. Cucurbitaceae is a large family including diverse groups which originate from the tropics of the American continent, being introduced in Europe (about 500 years ago) (Whitaker, 1947). The Cucurbita genus comprises several species, five domesticated (Cucurbita argyrosperma, Cucurbita ficifolia, Cucurbita maxima, Cucurbita mostacha and Cucurbita pepo) and ten wild species (Robinson and Decker-Walters, 1997), with the Cucurbita pepo subspecies pepo the highest variability (Nesom, 2011). Additionally, four morphotypes widely grown around the world (pumpkin, vegetable marrow, cocozelle and zucchini) are included in the subspecies pepo (Ferriol et al., 2003, Paris et al., 2003).
C. pepo is mainly commercialized in countries around the Mediterranean Sea, such as Spain, Italy, France, Turkey and Greece. In particular, Almería (Southern Spain) is the main area of vegetable production in Europe, summer squash being one of the most important vegetables in terms of production volume.
On the other hand, C. pepo is one of the seasonal vegetables that plays an important part in healthy nutrition due to being low in calories, high in nutritional content and its beneficial medicinal value (Shokrzadeh et al., 2010) attributing these beneficial properties to its antioxidant/anti-radical, anticarcinogenic, anti-inflammatory, antiviral, and antimicrobial activities (Oloyede et al., 2012). In this respect, C. pepo is an excellent source of both natural pigments and antioxidant constituents such as chlorophyll a (Chl-A), chlorophyll b (Chl-B), total phenolic compounds (TPC) and ascorbic acid (AA) that play an important role in its visual appearance and the nutritional value within the human diet (Tadmor et al., 2005, Blanco-Díaz et al., 2014, Martínez-Valdivieso et al., 2015). Furthermore, several epidemiological studies have indicated that a high intake of these phytochemicals could be associated with a reduced risk of a number of chronic diseases, such as atherosclerosis and cancer (Gundgaard et al., 2003, Gosslau and Chen, 2004).
In recent years, the evaluation of nutritional compounds in fruits belonging to the Cucurbitaceae family has motivated works such as those about dry matter, soluble sugars, and vitamin C on cucumber (Huang et al., 2009); carotenoid content on melon (Condurso et al., 2012); ascorbic acid and antioxidant activity on gourd (Karmakar et al., 2013). In this context, different nutritional properties have been recently attributed to edible parts of C. pepo, such as fatty acids, carotenoids and vitamins on seeds (Procida et al., 2013); ash, crude protein, fiber, fat and protein free extract on flowers (Sotelo et al., 2007), or mineral composition on fruits (Víllora et al., 2000, Martínez-Valdivieso et al., 2014).
However, as far as we know limited scientific literature referring to natural pigments and antioxidant compounds in C. pepo fruit is available, in spite of the development of new varieties with high nutritional compounds being one of the main goals for both consumers and plant breeding programmes. For this purpose, in the present study we have characterized and investigated the ascorbic acid, chlorophylls and total phenolic compounds as well as dry matter of a wide C. pepo fruits collection, distinguishing between exocarp and mesocarp tissues, corresponding to twenty seven traditional and marketed cultivars presenting different external coloration. Therefore, this study would provide a way of allowing breeders to select those superior accessions for showing a high natural pigments and phytochemical compounds.
The objectives of the present work were to (i) identify the variation in natural pigments and phytochemical composition of exocarp and mesocarp summer squash tissues, (ii) detect similarities among C. pepo accessions and point out morphotype selection advantages, and (iii) study the potential contribution of the different C. pepo morphotypes to the required daily intake.
Section snippets
Plant material
A total of 27 accessions of a C. pepo spp. pepo germplasm world collection (from the European Central Cucurbits germplasm database collection developed at COMAV and other countries) currently kept at the ‘IFAPA Centro La Mojonera’ were evaluated in this work (Table 1). Summer squash samples used in this work were representative of traditional and commercial cultivars and were classified as follow: 14 traditional accessions from different regions of Spain (4 belonging to ‘Zucchini’ morphotype, 9
Dry matter
The descriptive analysis (mean, range, standard deviation and coefficient of variation) as well as statistical ANOVA of DM are summarized for exocarp (Table 2) and mesocarp (Table 3) of C. pepo fruits. Mean and range of DM in exocarp tissues (7.23%, 4.2–11.76%, respectively) were higher than in mesocarp (Table 2), showing accessions from commercial hybrids the highest variation, due to this group including the ‘zucchini’ morphotype represented by accessions with the highest (Ac-18 and Ac-19)
Conclusions
The results obtained in this work confirmed that exocarp and mesocarp tissues of C. pepo have a great potential to be exploited due to a large variability in dry matter as well as natural pigments and nutritional compound profile, accessions selection being a key factor for increasing the desirable attributes. In relation to the whole fruit, modern or improved varieties (commercial hybrids) showed the highest levels in dry matter, ascorbic acid (Ac-23) and chlorophylls (Ac-2 and Ac-27), while a
Acknowledgements
This work was supported by the projects RTA2009-00036-00-00, RTA2009-00039-00-00 (INIA) and Fondo Europeo de Desarrollo Regional (FEDER) funds. Authors thank to the germplasm seed sources for providing the material used in this study, to Nicholas Davies and Beatriz Gutierrez-Casanovas editing service for their help in the grammatical revision of the manuscript. M.T. Blanco-Díaz acknowledges the financial support from the Spanish Ministry of Economy and Competitiveness as a contracted researcher
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