Fatty Acid Profile of Cucumis melo var. acidulus (Culinary Melon) Seed Oil

Abstract

Sir, The melons (Cucumis melo, Cucurbitaceae) are a diverse group of fresh, dessert fruits including C. melo var. cantalupensis, with a rough and warty skin, not netted (cantaloupe), C. melo var. inodorus, with a green, yellow or orange skin (winter melons), C. melo var. reticulatus, with a netted skin (true muskmelon). However, some other melons are considered ‘culinary vegetables’ (C. melo var. acidulus) and they are used as vegetables rather than fruits. C. melo var. acidulus is widely cultivated in India and used as a vegetable throughout the year since it has a long shelf life. The seeds of melons are normally treated as waste products. Some reports available on the composition of melon seeds [1–3] and authors have reported lipid and protein contents of proximally 30 and 54 %, respectively. We were interested in the possibility of extending the range of products from melons and therefore examined the oil content and the fatty acid profile of oil extracted from culinary melon seeds. Prior to extraction of the oil, approximately 50 g of seeds were dried overnight at 80 C and ground in a coffee grinder. The oil was extracted by a heat reflux method using 100 ml of petroleum ether (b.p. 40–60 C). Three extractions were carried out from three different batches of seeds of the same melon accession/variety. The mass of oil was determined gravimetrically after removal of the solvent and results are expressed as a percentage of the seed dry weight. Oil from the seed was subjected to physical characterization. The color and state of the oil at room temperature were noted by visual inspection, while the specific gravity was determined by the AOCS method given in [4]. The refractive index of the oil at room temperature was measured using the Abbe refractometer as outlined in AOCS method. The acid value, free fatty acids, iodine value, saponification number, peroxide value and unsaponifiable matter were measured by AOCS methods [5]. The fatty acid composition of the oil sample was analyzed by GC after transesterification. Fatty acid methyl esters was analyzed on a Chemito GC 8610 gas chromatograph equipped with a flame ionization detector and a capillary column BP 9 70 (50 m 9 0.32 mm 9 0.25 lm films). The detector temperature was programmed for 260 C with flow rate of 0.3 ml/min. The injector temperature was set at 240 C. Nitrogen (purity 99.95 %) was used as the carrier gas. Identification of the peaks was performed by comparing retention times with those of genuine standards analyzed under the same conditions. The oil content obtained from the seeds was 34.68 % on a dry weight basis. Compared to results obtained in different varieties of melon (30.83–33.92 %) the oil content in C. melo var. acidulus was higher [1–3]. The oil was consistently liquid at room temperature (25 C); colorless, and the specific gravity and refractive index of the oil were 0.92 and 1.48, respectively. The total acidity (0.76 mg NaOH/ g), free fatty acid (0.88 %), peroxide values (8.21 mg/g) are within the allowable limits for edible oil. The saponification (186.21 mg KOH/g) and iodine values (109.2 mg/ 100 g) of the seed oil in our study were lower than the values reported by Ramakrishna et al. [6] and de Melo et al. [1]. Table 1 shows that there are nine kinds of fatty acids in C. melo var. acidulus seed oil with a high concentration of polyunsaturated fatty acids (80.54 %) and a low concentration of monounsaturated fatty acids (19.43 %). Linoleic S. H. Manohar H. N. Murthy (&) Department of Botany, Karnatak University, Dharwad 580003, India e-mail: hnmurthy60@gmail.com; nmurthy60@yahoo.co.in