THE RICHNESS OF TIGER NUTS
Tiger nut (Cyperus esculentus) is a tuber that grows freely and is consumed widely in Nigeria and in various parts of West and East Africa. It has long been recognized as one of the best nutritional crops used to augment diets with its rich iron and calcium contents for body growth and development, since a substantial intake has reduced reported cases of various health related conditions such as cardiovascular disease, diabetes, cancer, and obesity, and also was found ideal for children, older persons and sportsmen.
The energy value of tiger nut tuber ranges within 400–413.8 kcal/100 g. The main components of tiger nut are carbohydrates, which represent 43.3 g/100g. Starch content, 29.9% in wet matter, is similar to that of cassava and about twice that of potato. Dietary fiber content, of 8.81 g/100g, is much higher than in other tubers, which contain 0.66–2.55 g/100g, and in similar ranges than nuts. It is constituted of insoluble dietary fiber at 99.8%. Sucrose content, 13.03 g/100g, is also much higher than in other tubers, ranging from 0.31 to 4.77 g/100g.
Tiger nut contains 22% to 45% of fat in dry matter, depending on the origin of the tubers. In wet matter, due to a higher moisture content of ca. 26%, lipid content is lower than in tree nuts. The examination of the fat structure in seed oils obtained from tiger nut showed that neutral lipids, dominated by triacylglycerols constitute the bulk of lipids and represent 65.9% of total lipids, while glycolipids and phospholipids represent 5.6–6.9% and 1.4–3.1%, respectively. The structural feature is consistent with most vegetable oils, with monounsaturated acids predominantly found in greater amounts at the sn-2 position, and a lower prevalence of saturated fatty acids, located in the sn-1 and sn-3 positions. The main fatty acids are oleic 56% to 85%, palmitic 10% to 20%, linoleic 8% to 12% and stearic 0.3% to 5.3% acids, while the minor acids were linolenic and palmitoleic. Tiger nuts composition in monounsaturated fatty acids is in agreement to that found for olive oil, being the fatty acid profile used as a possible geographical authenticity marker. Tiger nut naturally contains a number of sterol components that are of a different composition than the components found in olive oil. _-sitosterol was found as the main compound (49–60 mg/100g), followed by stigmasterol, campesterol, _ and _-tocopherol.
Protein content in tiger nut (5.04–6.67% wet matter) is higher than that found in other tubers, but lower than in nuts. For instance, the protein content of tubers ranges from 0.66% in sweet potato to 2.55% in yam, whereas pine nuts and peanuts contain 13.7% and 25.8% of proteins, respectively.
The predominant protein fraction (82–91%) corresponds to the water-soluble fraction of albumin and non-protein nitrogen. The analysis of these fractions by electrophoresis presented a high diversity in polypeptide molecular weights, highlighted at 20, 25, 37, 55, 75 and _106 kDa. The other solubilized fractions of globulins (1.11–3.96%), prolamins (0.91–3.45%) and glutelins (0.63–1.98%) presented a pattern with fewer different molecular weight polypeptides. The amino acid profile shows, in decreasing order, aspartic acid, glutamic acid, leucine, alanine and arginine. Tiger nut tubers exhibit high calcium, and phosphorus mineral contents. On the other hand, magnesium, manganese, iron, zinc and copper are also present, but at lower levels.
BY AKUBUO MARTIN
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