HPLC Determination of Carotenoid, Organic Acid, and Sugar Content in Pepino (Solanum muricatum) Fruit During the Ripening Period

Abstract

Pepino, Solanum muricatum, is a herbaceous plant of South American origin [1, 2]. Currently, several commercial varieties are being developed in New Zealand and Australia through selection and breeding (e.g., Suma, Miski, Lincoln Long, Golden Litestripe, etc.), while other cultivars (e.g., El Camino and Schmidt) are direct introductions of material grown in Chile [3]. The pepino (Solanum muricatum Aiton, Solanaceae) is a little-known crop from the tropical and subtropical Andes esteemed for its edible fruits, which are aromatic, juicy, scented, mildly sweet, and greatly varying in size, shape, and color depending on the cultivar [1, 2]. The fruit matures 30 to 80 days after pollination. Its color starts with green and during ripening changes to golden yellow covered with purple stripes [4]. El-Zeftawi et al. [5] reported that the fruit often fails to ripen normally and thus fails to develop its characteristic flavor after harvest. Hence, appropriate harvesting of pepino fruit is essential for high pepino quality [6–8]. The pepino is said to have medicinal properties. It is a good antiscorbutic since it contains vitamin C (25–70 mg/100 mL) at higher levels than normally found in most fruits [9–11]. This work is a first step to identify and quantify organic acids and sugars and some properties in pepino fruits and fruit juices (cv. Miski) from Turkey using HPLC methods. The overall objective of the study was to determine the quality characteristics of pepino fruits during the maturation period and to identify objective indices of the properties of both the fruit and the juice. Pepino fruits (cv. Miski) were harvested at three stages (green, strapped green, mature) from December 2009 to February 2010 at Akyazi and Antalya, Turkey. Pepino fruits were harvested and kept at a temperature of 5 C until analysis. All chemicals and solvents were obtained from Sigma Chemical Co. (St Louis, MO, USA) and Merck (Darmstadt, Germany). Pepino fruits (cv. Miski) were 168.2–258.2 g/fruit weight, 6.50–8.78 cm in diameter, and 8.17–9.32 cm long. The juice yield (%) of pepino samples varied from 43.0 to 51.0% (Table 1). During the maturation period a small increase in fruit weight, fruit width, and fruit length was detected. Antalya pepinos were approximately 10% more massive than Akyazi pepinos at the mature stage. The chemical properties of pepino juice samples are given in Table 1. In this study, the total acidity (%) in pepino fruits was determined as ranging from 0.06 to 0.08, the Brix (total soluble solids, SSC) from 4.00 to 7.10, and pH values from 4.89 to 5.84. The total soluble solids content of the two different pepinos increased during the maturation period. Gonzalez et al. [7] found pH values ranging from 4.74–5.40 and 4.89–5.14 in the sweet round and sweet long kinds. In their study on the quality and physiological behavior of pepinos, Lizana and Levano [12] reported that typical Chilean pepinos had 8.5% soluble solids when ripe. De Arriola et al. [9] also reported a total acidity of 0.06%, a Brix (total soluble solids) of 9.5%, total sugars of 4.06 g/100 g, and ascorbic acid of 34.25 mg/100 g in ripe pepino fruits of a local selection.