Characterization of main primary and secondary metabolites and in vitro antioxidant and antihyperglycemic properties in the mesocarp of three biotypes of Pouteria lucuma
Introduction
The Andean region represents an interesting niche of biodiversity. Many crops endemic to this region such as maca (Lepidium meyenii Walp), mashua (Tropaeolum tuberosum Ruíz & Pavón), native potatoes (Solanum tuberosum), yacon (Smallanthus sonchifolius Poepp. & Endl), chicuru (Stangea rhizanta) and lucuma (Pouteria lucuma) have been cultivated for centuries by the native population being part of their traditional diet and medicine. These heritage crops have gained attention in recent years due to the wide spectra of phytochemicals they can bear (Hermann, 2009). Little known Andean crops are re-gaining ground thanks to the link of ancient folklore together with scientific investigation. The commercialization and use of these phytochemical-rich crops have positively changed and the re-valorization of these heritage crops and traditions is being considered as an effective tool for social change.
P. lucuma Ruiz and Pav. known as the ‘Gold of the Incas’ or ‘lucuma’, is a subtropical fruit from the Andean region of Peru, Chile and Ecuador that belongs to the Sapotaceae family and to the genus Pouteria. The chemistry and biological activities of this family were reviewed (Silva, Simeoni, & Silveira, 2009) and as main constituents, triterpenes and flavonoids were reported besides their antioxidant, anti-inflammatory, antibacterial and antifungal activities. However, studies specific on P. lucuma are very limited. P. lucuma is a food of ancient cultivation (Dini, 2011). Ceramic representations of lucuma date back to the Nazca and Moche pre Incas’ civilizations.
In Peru and Chile, ‘lucuma’ flavor ice-cream is very popular, beating the traditional vanilla and chocolate flavors. This is due to the sweet taste and wonderful flavor and aroma described as ‘caramel like, maple-like with a bit of pumpkin-like taste’ (Yahia & Gutiérrez-Orozco, 2011). Lucuma flesh pulp is rich in carbohydrates, protein, fiber mainly in the insoluble form, β-carotene, vitamins and minerals (Yahia & Gutiérrez-Orozco, 2011) and the hard inedible seed is rich in polyunsaturated fatty acids with attributes appreciated by the cosmetic industry in terms of skin regeneration (Rojo et al., 2010). This Andean fruit is mainly processed into frozen fruit or pulp and flour and then incorporated to be used in the baking and dairy industries.
P. lucuma belongs to the climacteric type of fruit (Yahia & Gutiérrez-Orozco, 2011). It has an ovoid to elliptical shape and size of 7.5–10 cm. The color of the skin varies from green to yellow or orange when the fruit is fully ripe. The pulp color varies from pale yellow to intense orange (Yahia & Gutiérrez-Orozco, 2011). Flowering period and fruit production extends the whole year depending on the biotype but the maximum production is concentrated in winter and spring. The fruit can take up to 15–16 months to reach harvest maturity. The harvest index used in practice is the natural abscission of the fruit from the tree even though the change of color of the calyx from green to yellow/orange has been suggested as a harvest index. The fruit can be stored up to 14 days after harvest at 13–18 °C. Temperatures below 7 °C are detrimental due to chilling injury (Yahia & Gutiérrez-Orozco, 2011).
Very little work has been reported so far on the primary and secondary metabolites present in lucuma and associated to its taste, flavor, color and potential functional attributes (Dini, 2011, Yahia and Gutiérrez-Orozco, 2011). To our knowledge, there are no studies up to date that has focused on a detailed characterization of the main primary and secondary metabolites and potential functional associated properties present in the fruit at harvest maturity and during different ripeness stages. Thus, the main aims of this research were: (i) to characterize and quantify the main primary metabolites present in three biotypes of lucuma at commercial ripeness; (ii) to characterize and quantify the main secondary metabolites present in three biotypes of lucuma at commercial ripeness, (iii) to analyze the in vitro antioxidant and antihyperglycemic potential of these 3 biotypes at commercial ripeness and (iv) to compare main primary and secondary metabolites and in vitro antioxidant and antihyperglycemic potential of a biotype at three different ripeness stages. Therefore, insights from this study would provide the basis for the potential standardization of lucuma harvest time and postharvest management focused on the enhancement of sensory and functional associated properties.
Section snippets
Fruit material, sampling and chemicals
Three biotypes of P. lucuma (Leiva 1, Montero and Rosalia) were harvested at the commercial ripeness stage (S2) from the Experimental Station La Palma of Pontificia Universidad Católica de Valparaíso (Quillota, Chile) from a collection of different trees. The S2 stage corresponds to the natural abscission of the fruit from the tree. Four biological replicates were used per biotype. Each biological replicate was composed of 4 independent pooled fruits. In addition, the biotype Leiva 1, was
Metabolites related to primary metabolism
The main sugars present in different concentrations in the mesocarp tissue of three biotypes of P. lucuma in descending order were: glucose (24.8–173.3 mg g−1 DW), fructose (18.8–127.1 mg g−1 DW), sucrose (41.2–77.5 mg g−1 DW) and myo-inositol (1.6–2.8 mg g−1 DW). In terms of total sugar content non-significant differences (p > 0.05) were encountered for the three biotypes. Yahia and Gutiérrez-Orozco (2011) reported values of glucose, fructose, sucrose and myo-inositol in the mesocarp tissue of P. lucuma of
Conclusions
P. lucuma biotypes displayed differences in the content of sugars, organic acids, total phenolics, total carotenoids and in vitro antioxidant and antihyperglycemic properties. The commercial practice of mixing different biotypes during harvest and postharvest management of the fruit for industrial purposes explains the lack of standardization of batches of processed product (frozen pulp or flour) in terms of color and sweetness.
The ripeness stage of the fruit significantly affected the content
Acknowledgments
We would like to acknowledge the Experimental Station La Palma of the School of Agronomy of Pontificia Universidad Católica de Valparaíso (PUCV) for providing us access to the collection of Pouteria lucuma biotypes. This research was financially supported with an internal PUCV DI grant # 37.340/2014.
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