The food potentials of tigernut tubers (Cyperus esculentus) locally know as “aki awusa” in Igbo, ”aya” in Hausa and “ofio” in Yoruba were evaluated. The proximate composition of 100g of raw and processed tigernuts showed that moisture content of tigernuts ranged from 4.19 – 51.93 %, crude protein 2.61 – 10.12 %, ash 0.70 – 1.77 %, crude fibre 7.48 – 13.97 %, crude fat 10.79 – 32.06 %, and carbohydrate 22.73 – 56.85 %. Energy values ranged from 232.31- 487.15 Kcal. Tigernuts contain significant amounts of Mg (95.32 -140.96 mg), K (106.44 – 427.92 mg), P (121.78 – 195.95 mg), Fe (1.60 – 4.03 mg), Cu (0.08 – 0.99 mg), Zn (0.32 – 2.46mg), vitamin C (30.90 – 84.66 mg), vitamin E (2.22 – 5.26 mg), moderate Ca (24.42 – 62.29 mg) and low Na (15.77 – 18.27 mg) content. Processing of tigernuts generally increased carbohydrate but decreased magnesium and sodium values. Malting significantly increased calcium content (85 %) and drying and roasting increased Zn and Cu by 100 %. Physico-chemical and functional properties  showed that tigernuts and its products are acidic while viscosity of the products per 100 ml was between 88 – 90 cP, specific gravity 1.01 – 1.07, reducing sugar 0.30 – 0.44 g , foaming capacity 18 %. Foaming stability 5.35 %, emulsion capacity 21.88 %, and emulsion stability 49.38 %. Alcohol content of tigernut wine was between 3.17 – 7.13 %. Fresh tigernuts were utilized in the development of tigernut products (milk, coffee and wine) using household methods such as soaking, drying, roasting, malting, fermentation and freezing.  Organoleptic and acceptability assessment of the developed tigernut products showed that there was no significant difference (P > 0.05) between tiegrnut products and their controls in most of the parameters tested. All then products were highly acceptable. Tigernuts products (milk extract and wine) evaluation per 100 ml showed high ascorbic acid (6.18 – 7.8 mg), thiamin (0.80 – 1.25 mg), riboflavin (0.35 – 0.59 mg), vitamin E (0.22 – 0.75 mg) and cyanocobalamin (0.03 – 0.05 ug) content. The result of the microbial count of tigernut products (milk and wine) showed values between 3.0 x 102 – 8.0 x 102 cfu / ml and keeping quality ranged from 6 hours to 10 months.

1. Introduction

1.1 Background study

Tigernut (Cyperus esculentum) is a perennial grass-like plant with spheroid tubers, pale yellow cream kernel surrounded by a fibrous sheath. It is also known as yellow nut sedge, earth or ground almonds, “souchet” in French, “ermandeln” in German and “chufa” in Spanish (TTSL, 2005). Grossman and Thomas (1998) reported that chufa came to Spain from Africa. Tigernut is found wild and cultivated in Africa, South America, Europe and Asia. Tigernuts grow in the wild, along rivers and are cultivated on a small scale by rural farmers mostly in the northern states of Nigeria. It is locally called “aya” in Hausa; “aki awusa” in Igbo; “ofio” in Yoruba and “isipaccara” in Effik. Tigernuts are edible, sweet, nutty, flavoured tubers which contain protein, carbohydrate, sugars, and lots of oil and fiber (FAO, 1988). Grossman and Thomas (1998) showed that tigernuts have been cultivated for food and drink for men and planted for hogs for many years in Spain and that the lovely milky elixir is served in health Spas, Pubs, and Restaurants as a refreshing beverage (competing successfully with other soft drinks). Unfortunately, despite these potentials in tigernuts it has been a neglected crop in Nigeria. This probably may be due to inadequate knowledge on its production, utilization and nutritional value.

 Tigernut could provide a basis for rural industries in Africa. It is an important food crop for certain tribes in Africa, often collected and eaten raw, baked as a vegetable, roasted or dried and ground to flour. The ground flour is mixed with sorghum to make porridge, ice-cream, sherbet or milky drink. It is mostly consumed raw as snack without knowledge of the food and nutritional quality (FAO, 1988). It has also been found to possess good therapeutic quality (Moore, 2004; Zimmerman, 1987; Farre, 2003; Bixquert, 2003; Valls, 2003). Moore stated that “the expansion of tigernut milky drinks will significantly help the research linking tigernut milk to healthier cholesterol levels and other non-dairy manufacturers. This could also gain a boost from an increased consumer interest in health foods”.

Variety of food products can be derived from tiger nut tubers though there is little documentation at large. Various food processing techniques can be applied to tiger nut processing to modify its appearance, develop its natural flavour, stimulate the digestive juices, add variety to the menu, make it easily digestible and bio-available, destroy harmful microorganisms, improve its nutritional quality and prevent decomposition. This project work intends to basically evaluate, promote production and utilization of tiger nuts using various processing techniques.

1.2 Statement of problems

Food insecurity continues to threaten large proportions of households in low income countries. In view of the operational definition of household food security stated by ACC / SCN (1991), a household is food secure when it has access to the  food needed for a healthy life for all its members (adequate in terms of quality, quantity, safety and culturally acceptable), and when it is not at undue risk of losing such access. Adequate nutrition is essential for individual development, activity, good health, fulfillment function and success in societies and nations (ACC / SCN, 1991). Some of the factors that may affect food security as well as nutrition are as follows:

  • Inadequate production and knowledge of the food use
  • Poor processing, preservation and storage techniques
  • Poor infrastructure, especially poor housing,sanitation and storage facilities, education,communications, and transporting systems.
  • Poverty
  • Extreme imbalances in food or population ratio
  • War / political or civil unrest
  • Rapid depletion of natural resources
  • Cultural attitudes toward certain foods
  • High external debt
  • Seasonal factors or climatic variations
  • Food prices     

Tigernut has been for many years one of the underutilized food crops in Nigeria. It is mostly eaten raw as snack and un-identified as a very important food crop that has great potential in managing, preventing and eliminating malnutrition (macronutrient and micronutrient deficiencies) or food insecurity problems. It has been demonstrated by nutritionist that the major nutritional problems could be solved through exploitation of the nutrition and economic potentials of the local food resources. Tigernut is one of the under utilized tubers with great potentials for domestic and commercial purposes. There is no documentation of a successful product made from tigernuts in the Nigerian market. A successful product offers a benefit that is perceptible and valued by the consumer (NUTRA, 2005).

There is little documentation on the nutritional quality and versatility of tigernuts in food preparation despite its availability. However, tigernut is still one of the least popular tubers in Nigeria and hence the need for this research which intends to evaluate, promote production and utilization of tiger nuts using various processing techniques.

  1.3 Objectives of study

The broad objective of this study is to evaluate the food potentials of tigernut tubers (tigernuts) and its products.

            Specific objectives are as follows: to

1) determine the proximate, mineral, vitamin, physico-chemical and functional properties of tigernuts.

2) develop products from tiger nuts using traditional processing techniques such as natural fermentation, malting, drying and roasting.

3) assess the organoleptic properties and general acceptability of the developed tigernut products (milk, coffee and wine beverages).

4) determine some nutritional properties and microbial load of developed tigernut products (milk, coffee and wine beverages).

1.4 Significance of study

In recent years, the need to increase the production and utilization of locally available food resources has been highlighted at different national and international fora. Tigernuts, one of the under utilized food crops locally available in Nigeria could be demonstrated to aid in solving major nutritional problems through exploitation of its nutritional and economic potentials.

The results of this study will provide a baseline data on tigernut utilization. This will go a long way to diversify its use and in turn lead to its increased production both at household and national levels ultimately to ensure food security. Furthermore, it is expected that through the knowledge of its composition, tiger nut may be exploited for use in the prevention and treatment of some non communicable diseases for example cancers, diabetes, heamorrhoids and cardiovascular diseases.

Chapter Two

2. Literature review

2.1 History of tigernuts

Tigernuts are not actually nuts but tubers found on the root of a sedge plant. It was first discovered 4000 years ago and comes in several varieties.  The tubers were originally cultivated by ancient Egypt’s populations at the Nile valley. Their cultivation was subsequently extended throughout other areas with temperate climate and fertile soil. Reports have shown that tigernuts came to Spain from Africa (IHS, 2005; HBR, 2005; CVNews, 2006; Deatra, 1999).  Tigernuts are edible tubers with a sweet nutty flavour. Other common names for these tubers are “earth almond” and “yellow nut sedge”. They are quite hard and are generally soaked in water before consumption.

In Egypt and the Mediterranean nut sedges were used as sources of food, medicine and perfumes. Tigernut tubers were routinely roasted and consumed by nursing mothers.  The dried ground tubers were used in coffee and chocolate drinks. Oil extracted from the tubers was an ingredient in soap maikng as well as a lubricant for fine machinery. The leafy plant parts of the nut sedge were fed to livestock. Egyptians made very efficient use of the nut sedge. They used them in cultivation as early as 2400 BC. One such example of tigernuts is depicted in a wall painting of an Egyptain tomb in 15th century BC (Deatra, 1999). In the painting, workers are shown to be weighing the nuts while a scribe records their work. In another part of the same tomb, instructions were written for eating the tubers as sweets after grinding and adding honey. Tigernut tubers have been found in the tombs and are considered to be locally domesticated in Egypt. This gives the impression that the tubers were greatly valued by the Egyptian people as a food source (Deatra, 1999)

2.2 Botany of tigernuts

Cyperus esculentus (tigernut sedge / chufa sedge / yellow nut sedge / earth almond) is a species of sedge, native to warm temperate to subtropical regions of the Northern Hemisphere. Tigernut is a highly adaptable crop and grows well under a wide range of climatic and soil conditions. It is found throughout the tropics, subtropics and warm temperature regions. It is cultivated in Western Africa, but is a serious weed of cotton, cereals, potatoes and sisal in Eastern Africa. It is also grown in south America, Europe and Asia. The tiuber grows 50- 250 tubers per plant and weigh 2 – 26 g per tuber (FAO, 1988).

Tigernut is an annual or perennial plant, growing to 90 cm tall, with solitary stems growing from a tuber. The stems are triangular in section, and bear slender leaves 3-10 mm wide. The flowers of the plant are distinctive, with a cluster of flat oval seeds surrounded by four hanging leaves positioned 90 degrees from each other. The plant foliage is very tough and fibrous, and is often mistaken for a grass (Deatra, 1999). Tigernut plant produces edible yellow to yellow brown spike-lets flowers, mostly only 1 cm to 1.5 cm long. The root system is by yellowish rhizome, ending in single tubers of 5-20mm in length, with a thin brown outer skin which darkens with maturity. In its non-flowering state it resembles Cyperus rotundus which is dark brown, slightly fragrant, unpleasant tasting tubers produced in a chain and blunt tipped leaves with no shoulders. The leaves of tigernut (Cyperus esculentus leptostachyus) are long, narrow, shiny, light green, arranged in 3 rows around the triangular stem often with characteristic pointed tip separated from the rest of the leaf by a distinct shoulder (FAO, 1988). 

Tigernut is classified in the division: Magnoliophyta; class: Liliopsida; order: Cyperales; family: Cyperaceae. Cyperus esculentus is in the order Commelinales and the family Cyperaceae. Cyperus esculentus can be distinguished from other species of New World nut sedge by its persistent linear brown spikelets that have closely overlapping scales. The stem of yellow nut sedge is triangular and has a light green-yellow color. Rhizomes that terminate in tubers are the main means of reproduction, although it does produce viable seed (Deatra, 1999; HBR, 2005).

In West Africa the plant often grows in great concentration and is gathered from the wild.  It is interesting to note that esculentus, means edible in latin (Negbi, 1992). Tigernut tubers are of different varieties, the notable ones are black yellow and brown with various sizes (Barminas et al., 2001).The most common varieties are long and round.The varieties are:

  • Cyperus esculentus var. esculentus.
  • Cyperus esculentus var. hermannii.
  • Cyperus esculentus var. leptostachyus.
  • Cyperus esculentus var. macrostachyus.
  • Cyperus esculentus var. sativus
  • Cyperus esculentus var. rotundus

The two varieties of interest to us are Cyperus esculentus var. esculentus (weedy) and Cyperus esculentus var. sativus (cultivated). Most literature uses the name Cyperus esculentus for both the weedy and the useful sedge. The weedy variety esculentus produces many seeds although the cultivated variety sativus produces few (Lapham and Drennan, 1990). Cyperus esculentus var. esculentus and Cyperus esculentus var. sativus are closely related (ONRG, 2005; Negbi, 1992). The color of the tubers appears to be one unusual character. Variety sativus has a grey-orange color and variety esculentus has a grayed brown color according to the Royal Horticultural Society Colour Chart as reported by De Vries and Femke(1991).

The cultivated variety does not have capability of the perennial yellow nut sedge grown as annual plants. They also lack the abundant seed production typical of the perennial nut sedge. Cultivated tubers are also known to be larger than perennial yellow nut sedges. These characteristics seem to indicate a possible pattern of human selection that may have separated the edible tigernut from the weedy nut sedge. The taste of the weedy tigernuts compared to the cultivated has been found to be very similar. Also, the weedy nut sedge is more fibrous to chew it is less desirable (De Vries, 1991).

The perennial yellow nut sedge is sometimes a troublesome invasive weed in planted fields (FAO, 1988). It is often regarded as a useless pest to home gardeners as well as commercial growers. Along with being a useless weed it is difficult to control. However, several commercial herbicides have been labeled for use exclusively on yellow nut sedge and are available at local retailers (Deatra, 1999).

2.3 Ecology of tigernuts

Tigernut is common in seasonally wet grassland, irrigated crops, damp grassland, and along banks, but at the same time is considered fairly drought resistant. It does not tolerate shade. Best yield are obtained with moderately high temperature throughout the growing season, and well distributed rainfall. High temperature of 27 – 30 ºC, with low nitrogen levels favors tuber formation. Light sandy loamy soils of PH 5.5 – 6.5 are preferred, but can grow in any soil provided it is well drained. Alluvial soils containing relatively high quantities of Manganese (Mn), sulfur (S), calcium (Ca), Magnesium (Mg), and boron (Bo) are particularly suitable. It is tolerant of salty soils.  Short photo periods of 8-12 hours favor tuber formation and long photo periods of more than 16hrs favor vegetative growth (FAO, 1988).

Tigernut cultivation requires sandy soil and a mild climate. Tubers are soaked in water for 24 – 36 hours before being planted out, either by hand or using a drill. In United States of America, tubers which had been chilled were found to germinate better and to produce more sprouts per tuber. Tubers may be planted at 10-15cm intervals along rows 60-90cm apart, about 2.5-4cm deep. At closing spacing, 1 tuber per hole is used, with 2 per hole at wider spacing seed rates (FAO, 1988). Tigernuts are planted during March, April and May and must be irrigated every week until they are harvested in November and December. Harvest time may take 90-120 days only and at the end of dry season. Immediately after harvest, tigernuts are washed with water in order to remove any sand and small stones. Once the Tigernuts have been cleaned, they are dried out in order to preserve them. This is a natural process that requires 1-3 months. Temperature and humidity levels are carefully monitored during this period. The Tigernuts are turned over every day to ensure uniform drying.  Small and damaged tigernuts are removed before packaging and utilization (TTSL, 2005; FAO, 1988).

2.4 Nutritional composition of tigernuts and its products

FAO (1988) and TTSL (2005) showed that tigernut tubers are rich in starch (20-30% of DW) and fat (20-28% DW) with small quantities of protein which is about twice of that of cassava. Table 2.1 showed the energy and nutrient content of tiegrnuts as reported by other researchers (Umerie et al.,1997); TTSL, 2005; Addy and Eteshola, 1984; Temple et al., 1990). Tigernuts have relatively higher fat content and gross energy, and in this regard compared better with nuts than that of cereals which also belong to the same other Cyperales. Research has been done on the oil extracted from the seeds of yellow nut sedge (Cyperus esculentus var. esculentus) as a non-conventional oilseed. This study was used to determine oil substitutes for more conventionally used oil types such as soybean, palm and olive oils. Non-conventional oils would be less expensive and therefore more available to poorer (developing) countries.

Tigernut oil is 80% unsaturated fatty acid, mainly oleic (64.2 – 68.8 %) and this shows that tigernut oil has a good potential as a substitute for imported olive oil (Deatra, 1999; Mc Namara, 2004; TTSL, 2005). Fat in diets provide twice much energy as carbohydrate or protein, thus low fat diets are recommended to aid weight control. Different types of fat (fatty acids) have different effects on health and the risk of diseases states such as coronary heart disease (CHD). Saturated fatty acids (SFA) increase levels of blood cholesterol and should be avoided whenever possible. There is evidence that the replacement of SFA with monounsaturated fatty acid (MUFA) may have a favorable effect on the risk of CHD. Venho et al. (2000) investigated types of fat intake in relation to CHD risk in women and reported that for every increase of 5% in energy from MUFA there is a decrease in CHD relative risk of 0.81%.

Tigernut is a good source of phosphorous, potassium and iron. It also contains magnesium, calcium, zinc, copper, sodium and manganese (TTSL, 2005). Phosphorus found in plant is usually bound to a compound called phytate meaning that it is poorly absorbed from the gut into the body. Phosphorous (P), together with calcium, constitutes the bulk of the mineral substance of the bones and teeth. It plays a part in the formation of ATP (an energy compound indispensable for “activating” glucose, fatty acids, etc) and in improvement of intellectual performance. Phosphate is important in the body. It helps regulate acidity/ alkalinity by acting as a buffer (Moore, 2004).

Potassium (K) is important in maintaining electrolyte and chemical balance between the tissue cells and the blood. K is the most important neural element in intracellular behaviour. It plays a part in numerous enzymatic reactions and in important physiological processes, such as cardiac rhythm, nervous conduction, and muscular contraction. Iron (Fe) in food is often in a complex form. Vitamin C aids in the absorption of iron. Vitamin C is a reducing agent and changes Fe into a more easily absorbed form. An acid medium also helps Fe absorption. Consequently, Fe helps prevent anaemia. Zinc has a wide variety of functions in the body and is found in all body tissues.  It is involved in many enzyme reactions including those involved in energy generation from carbohydrate, fat and protein. It also has a role in cell division, the transport of carbon dioxide and oxygen in the blood and also in immunity.  Since it has a wide range of role in the body, symptoms of zinc deficiency are also wide-ranging and include a delay in wound healing, poor appetite, a suppressed immune system and poor growth (Moore, 2004; Wardlaw and Kessel, 2002).

Magnesium is also involved in many enzyme systems and in particular those involving the currency of energy in the body, ATP. Magnesium is also required for the synthesis of proteins, the production of energy and muscle contraction (Moore, 2004). Research studies have suggested that a low intake of magnesium may increase the risk of coronary heart disease (Al-Delaimy et al., 2004) and type 2 diabetes (Lopez-Ridaura et al., 2004).

Table 2.2 showed the amino acid composition of tigernuts. Bosch et al. (2005) observed that the essential amino acid contentsof tigernuts were greater than those proposedin the protein standard for adults by the FAO/WHO,with the exception of histidine. The arginine content (1414.0 ± 4.75 mg) is found to be very high compared to the other essential amino acids while the Tyrosine (50.0 ± 0.13 mg / g N ) and methionine content as total sulphur (58.1 ± 0.62 mg) is found to be low. Lysine content of tigernuts (307.5 ± 0.30) may supplement foods deficient in lysine such as maize. This can be useful in the development of multi-mixes in infant nutrition.

A 200 ml glass of “horchata” contains about 1.12% starch, 1.30% fat, 12.60%, protein; 0.35% carbohydrate, 0.38% fibre and 132 Cal energy value (TTSL, 2005). Tigerwhite, a brand of vegetable milk by Bottlegreen as reported by Moore (2004) contains vitamins E, thiamin, niacin, vitamin B6 and folate. Results on the nutrient content of tigerwhite and the results of a comparative study on the nutrient content of tigerwhite with other milk beverages (cow milk and soya milk) has been shown in table 2.3 and 2.4.