Cucurbit seed

Research concerning the structure, composition, and usefulness of cucurbit seeds (gourds, melons, squash, etc.) is reviewed. Cytological features are typical of those for oilseeds. Composition-ally, decorticated seeds contain by weight 50% oil and 35% protein. The oil is unsaturated and edible however, certain species contain conju-ated trienoic fatty acids (drying oils). 

Cucurbit seeds are exalbuminous or lacking endosperm in the mature state. In such seeds the embryo is large in relation to the seed as a whole. It fills the seed almost completely and its body parts, particularly the cotyledons, store the food reserves for germination. Since the predominant tissue of the seed is cotyledonous, and since cotyledons are leaves, anatomy and histology of typical leaf tissue suffice to describe the preponderant part of the seed. Epidermal cells cover the cotyledonary surface followed by palisade and abundant parenchyma cells that contain the food reserves. Vascular tissues are also present. 

Other intracellular organelles, such as mitochondria, plastids, and endoplasmic reticula, all of which are rarely observed in the cytoplasm of quiescent seed cells, are not apparent in quiescent cucurbit seed cotyledons. Nuclei, however, are present. 

Unsaturated fatty acids are the preponderant fatty acids of cucurbit oils, and in some seeds conjugated triene comprises one-third of this unsaturation. Table I shows the fatty acid distribution in oils of cucurbit seeds (1 ). More recent determinations (7, 27, 3U 33) are in close agreement with these results. Occasionally a species... 

It is of interest that carotenoid pigments (xanthophylls), sterols (spinasterol and chondrillasterol) and a triterpene alcohol have been identified in cucurbit seed oil (31, 3 , 37L However, cucurbit oils such as that from Buffalo gourcT are amenable to refining, bleaching and deodorizing (38). 

Decorticated cucurbit seeds contain by weight about 35% protein. Traditionally, seed proteins are classified as globulins and albumins according to their solubility in certain aqueous solvents. Biochemically, oilseed globulins are generally considered storage proteins while albumins are believed to be metabolic (catalytic) proteins. 

From amino acid compositions, evaluations o7" the nutritional potentials of cucurbit meals and globulins can be calculated according to FA0/WH0 (54). The A E ratios, which are the amounts of each essential amino acid relative to the total amount of essential amino acids, are shown in Table II. These data indicate that, like most other oilseeds, cucurbit seeds are deficient in lysine and sulfur-containing amino acids. However, sulfur-containing amino acids are considerably high in CitrullI us colocynthis (egusi, ancestral watermelon) seed protein and exceed the suggested level in FA0/WH0 reference protein (55). 

Recent nutritional evaluations of cucurbit seeds have accentuated the currently popular Buffalo gourd ( . foetidissima) and are shown in Table III. PER (protein efficiency ratio) values of full-fat and natural and autoclaved fat-free meals fed to weanling... 

Ubiquitous in seeds is phytic acid, the hexaphosphate ester of inositol, which has been isolated from cucurbit seeds (57). Small amounts of free sugars and terpenoid glycosides (cucurbitacins) are also present (58-60), but starch is absent (1, 1). Cellulosic cell wall materials comprise the remaining carbohydrate content. 

The Cucurbitaceae are a diverse family of plants that grow in the temperate zone but also thrive in hot and arid regions of the world. The characteristics of cucurbit seed protein and oil were reviewed by Jacks et al. (1972) and by Jacks (1986). He noted a resurgence of interest in... 

Table 7.4 Fatty acid composition of Cucurbit seed oils...

Helmy, H.E. (1990) Studies on the pigments of some citrus, prune and cucurbit seed oils when processed with or without cottonseed oil. J. Am. Oil Chem. Soc. 67, 376-380. 

Jacks, T.J. (1986) Cucurbit seed protein and oil. Plant Proteins 312, 249-260. 

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