1. Introduction

Tiger nut (Cyperus esculentus L.) is a perennial crop that is cultivated extensively in Spain, almost exclusively in the Valencia region, Turkey, Southern India, Thailand, Ghana, Nigeria, Sierra Leone and Cameroon ^{[1, 2, 3, 4]}. Nutritionally, the tubers contain between 200-280 g kg-¹ of yellow non-drying pleasantly flavored oil, similar to olive or sweet almond oil [4, 5]^{[4, 5]}. The oil consists of 170-180 g kg-¹ saturated fatty acids, much of which (120-140 g kg-¹) is palmitic acid and the rest mainly stearic acid. Of the unsaturated fatty acids present, about 75 g kg-¹ is oleic acid and between 90-155 g kg-¹ linoleic ^[4]. The oil extract has been used in cooking and for the manufacture of body and hair creams ^[6]. Of the tuber weight, about 500.0 g kg-¹ is digestible carbohydrates, 40.0 g kg-¹ protein and 90.0 g kg-¹ crude fiber with a high fraction of it being indigestible carbohydrates mainly cellulose and lignin ^[7]. Tiger nuts also have a good profile of some essential minerals like zinc, 158 mg kg-¹; magnesium 430 mg kg-¹ and potassium, 265 mg kg-^1[4].

The tubers are used as food around the Mediterranean, especially in Egypt and Spain as well as countries in West Africa, particularly in Cameroon, Nigeria and Ghana. Dried nuts are ground into flour and incorporated into various foods. It is also baked and milled into powder for use as food additives, spices or made into a refreshing beverage called “Hochata De Chufas” or tiger nut milk ^{[8, 9, 10]}.

In Ghana two varieties, black and brown are mainly cultivated. Though it can be cropped through out the country, it has traditionally been cultivated at only a few places in the Eastern, Central and the Brong-Ahafo Regions ^[11]. Harvested tubers are first sorted, rubbed in baskets or washed in water and dried before distribution through intermediaries. The nuts are chewed raw, dried or roasted like sweets, or made into a highly cherished milk-like beverage referred to as “Atadwe” milk. Currently, nearly all nuts grown in Ghana are consumed locally. Due to increasing awareness of the nutritional potential, nutraceutical benefits of the tubers and the perception that it has aphrodisiac properties there is increased cultivation of tiger nuts and explorations of novel uses for its milk ^{[12, 13]}.

The plant variety, location and period of planting have been shown to have significant effects on physico-chemical properties of plant materials ^{[14, 15]}. However though considerable studies have been done on the proximate composition and mineral content of tiger nuts tubers ^{[4, 16, 17, 18, 19]} there is very little information on the effect of site and planting period on chemical composition of tubers and acceptability of milk. The objectives of this study therefore were to determine the chemical composition and acceptability of milk of two varieties of tubers from different sites and planting periods in Ghana.

2. Materials and methods

Sixteen samples of tiger nut tubers (Cyperus esculentus L.) grown in the two planting periods (major; April to July and minor; September to November) were studied. The tubers were sorted, washed and dried in a Sanyo oven (Model MOV-212, Japan) Between 55-60C till constant moisture content (≤10%).The oven-dried tiger nut tubers were milled in a blender (Waring) to pass through a sieve of pore size 0.5 mm and then stored in airtight containers in a freezer at -18C until used for laboratory analysis.

Moisture content was determined using the air oven drying method at 105C ^[20]. Total ash, crude lipid, crude fibre, protein (6.25 x N) were all determined in triplicate according to AOAC, methods ^[20]. Crude protein (N x 6.25) was determined by the Macro-Kjeldal method using 1.0 g samples. Ash was determined by the incineration of a 1.0 g sample placed in a muffle furnace maintained at 550C for 6 hours (until ash was obtained). Crude lipid (ether extract) was determined by exhaustively extracting 5.0 g of the sample with petroleum ether by use of a Soxhlet apparatus. The level of carbohydrate was obtained by the difference method, that is, by subtracting the sum of the protein, fat (lipid), fiber and ash from the total dry matter. The calorific value was calculated by multiplying the mean values of the crude protein, fat and carbohydrates by Atwater factors of 4, 9 and 4 respectively, ^[21]. Free fatty acids were determined by mixing 10.0 g of Soxhlet extracted oil with 25.0 ml diethyl ether, 25 ml ethanol and 1 ml phenolphthalein and titrating with 0.1M NaOH until a pink color persisted for 15 seconds. ^[22]. The FFA content was calculated as oleic acid (1.0 ml NaOH is equivalent to 0.0282 g oleic acid). Determinations were carried out in triplicate.

The wet digestion method using nitric acid was used ^[20]. All elements were analyzed in triplicate using the PerkinElmer Atomic Absorption Spectrophotometer model AA 220FS.

The procedure for extraction of milk from tubers is shown in Figure 1. One hundred grams (100g) of oven-dried nuts were soaked in covered vessels with 600 mL of water overnight. The water was discarded and the nuts milled in a Waring blender (Model 38BL41, USA) at high speed in twice its new weight of fresh water for 5 minutes. The milk was pressed through a cheese cloth, and the milk obtained was used for analysis.

Figure 1. Flow Diagram for extracting tiger nut milk and solids

Download as

PowerPoint Slide

Larger image(png format)

Figures index

Veiw figure

View current figure in a new window

The preference of milk extracted from the tubers was determined using simple ranking test in a randomized complete block design ^[23]. 2.0% w/w of sugar was used to sweeten the tiger nut milk to facilitate ranking by the panelists. Ranking of milk was done by a panel of 10 trained persons on a scale of 1-6. The most acceptable was ranked 1 and the least acceptable was ranked 6. Water was available for panelists to rinse their mouth.

The data obtained was subjected to ANOVA using MINITAB 14 statistical package (MINITAB Inc., U.S.A.). Tukey’s test was used to identify significant differences among means (p < 0.05) and the Friedman’s Rank Test was used to determine the rank sums of the treatments used for sensory analyses.

3. Results and Discussion

The Proximate composition, an indication of the nutritional potential of the tubers and the free fatty acid content, an indication of the effect of post harvest handling on the quality of tiger nuts obtained from different locations in Ghana are presented in Table 1. There were significant differences (p<0.05) in the indices measured between locations and varieties. Ampenyi black tubers planted in the major period recorded the highest energy value of 5016.2 kcal kg-¹ while Bawjiase brown tubers from the major planting period recorded the highest carbohydrate content of 734.7 g kg-¹. There were also significant differences (p<0.05) between planting periods. For example, Bawjiase and Danyameso which were the two sites that planted both varieties in major and minor periods recorded significant differences in their protein and fat content. The black tiger nut tubers obtained from Danyameso in the minor planting period recorded the highest fat content of 295.4 g kg-¹, while the major planting crop recorded 155.4 g kg-¹. Whereas Bawjiase brown tubers planted in the minor period recorded the highest protein content of 75.1 g kg-¹ the major period crop recorded 39.1 g kg-¹. These differences in indices of tubers from different planting periods, sites and varieties are similar to observations from other studies on plant materials ^{[24, 25, 26]} which has been attributed to differences in rainfall, climate, soil and crop variety ^[27]. Comparatively, the protein content of brown tubers planted in the minor period at Bawjiase (75.1 g kg-¹) was lower than the 80.7 g kg-¹ determined for raw tubers, but higher than the 68.0 g kg-¹ recorded for roasted tubers by the same researchers and also higher than the 50.0 g kg-¹ recorded in another study ^{[28, 29]}. The mean fat content recorded for all black and brown tubers for both seasons (219.2 g kg-¹, 192.7 g kg-¹) were also relatively lower than the 296.7 g kg-¹ recorded in an earlier study ^[30] and the 510.0 g kg-¹ recorded for cocoa beans which is a major economic crop in Ghana ^[31]. However, considering the fatty acids composition of tiger oil ^[32] it will make nutritional and commercial sense to exploit it.

Free fatty acid (FFA) was determined as an index for the effect of primary processing and handling on the tubers. The Free fatty acids (FFA) values obtained ranged from 0.37-1.18% for Tanoso black tubers of the major planting period and Danyameso black tubers of the major planting period respectively. The significant differences (p<0.05) is an indication of the impact of different post harvest handling practices on the quality of the nuts. Currently, harvested tubers in Kwahu are normally washed to remove residual soil, while in other sites like New Ebu and Twifo Praso the soil is rubbed off the tubers. There was no obvious trend in the free fatty acid content with respect to period of harvest; however it appeared that the black variety of tiger nuts showed higher free fatty acids in the major harvesting period than in the minor period (Table 1). The reverse was observed for the brown variety. If free fatty acids content is also taken as an index of stability of fatty food, then Black tiger nuts harvested in the minor period would keep longer (i.e. be more stable) than those harvested in the major period. The average free fatty acid of 0.66% for the tubers however is less than the industry limit of 1.75% for cocoa beans ^[33]. There was no significant differences in mean fiber values for black and brown tubers for both major and minor periods (94.0 g kg-¹, 92.6 g kg-¹; and 107.0 g kg-¹,111.2 g kg-¹) respectively. Comparatively, these figures were higher than the 8.8 g kg-¹ recorded for sweet potatoes and 11.8 g kg-¹ recorded for cassava ^{[34, 35]}. The casual relationship between consumption of high fiber diets and reduction of coronary heart diseases, diabetes mellitus and obesity suggests that the consumption of tiger nut tubers could reduce the risk of these diseases ^[36]. However, considering the traditional uses of tiger nut tubers in Ghana (tubers are mainly chewed for the juice and milk extraction) it can be said that till recipes are developed to make use of the whole tuber the many benefits of high tiger nut tuber diet cannot be realized.

Table 1. Chemical composition of two varieties of tubers from different sites and periods

Download as

PowerPoint Slide

Larger image(png format)

Tables index

Veiw figure

View current table in a new window

View next table

The mineral content of the two tiger nut varieties obtained from different locations of the two planting period are shown in Table 2. Sodium, potassium, magnesium and phosphorus which are very useful for very important reactions in the body and the proper development of bones and teeth ^[37] were the major macro elements in the tubers while iron, copper manganese were the least abundant. This was similar to studies conducted by other researchers on tubers from other countries ^{[38, 39]}. Sodium ranged from 484.51 mg kg-¹ to 1075.80 mg kg-¹ with Bawjiase brown of major planting period recording the highest. The minor period black variety in Bawjiase recorded the highest magnesium of 747.0 mg kg-¹, while the brown variety planted in the major period recorded the highest phosphorus of 478.37 mg kg-¹. Brown tubers planted in the minor period at Danyameso however recorded the highest potassium of 14241.0 mg kg-¹ with the black tubers planted in the major period at the same site recording the highest sodium 924.07 mg kg-¹ (Table 2). The trace amounts of calcium and iron which are essential in the development of strong bones and blood synthesis suggest that there is the need for the fortification of the vegetable milk produced from the tubers to prevent micro-nutrient deficiencies ^[37]. If used in cocoa products however there will be very little need for additional magnesium because of the high quantities in cocoa ^[40]. Zinc was the highest recorded minor element with the highest, 60.58 mg kg-¹ recorded for Tanoso black. This was however only 26% of the required daily intake for adults and children above 4 years ^[41]. Over all Black tubers harvested in the major period had minerals profile that was not significantly different from those of the brown variety.

Table 2. Elemental composition of two varieties of tiger nut tubers from different sites and periods

Download as

PowerPoint Slide

Larger image(png format)

Tables index

Veiw figure

View current table in a new window

View previous table

View next table

Table 3. Consumer preference of tiger nut milk extracted from tubers from different sites

Download as

PowerPoint Slide

Larger image(png format)

Tables index

Veiw figure

View current table in a new window

View previous table

The consumer preference for milk extracted from the tiger nut tubers was obtained through a simple ranking test. The rank sums are indicated in Table 3. Friedman’s ranking showed that there were significant differences (p < 0.05) in the acceptability of milk from the tubers of black variety with the milk from Tanoso falling below expectation due to unacceptable flavor. The unacceptable flavor could be due to the post harvest handling of the tubers, soil structure and the climatic conditions in the Tanoso area. These factors have been determined to affect the flavor of horchata de chufas ^{[42, 43]}.

4. Conclusion

The site and planting period of tiger nut tubers have significant effects on some of its chemical properties such as protein, fat and energy content, minerals as well acceptability of its milk. Tiger nut tubers have high fat, carbohydrate, fiber and energy value which could be exploited for industrial applications.

References

[1]	Rosengarten, Jnr. F. The book of edible nuts Walker Publication Inc East 2nd street, Niveda, NY 11501 pp 331-1984.
	In article
[2]	Fatoki, O.S., Omode, A.A. and Olaogu, K.A. Physicochemical Properties of some Underexploited and Non-conventional Oilseeds. Journal of Agriculture and Food Chemistry. 43; 2850-2853. 1995.
	In article		CrossRef
[3]	Er, F, Ozcan, M.M, Gumuscu, A, A. D, and Unver, A. The influence of planting time and planting Closeness of ground almond (Cyperus esculentus L.) populations of some agronomic and quality properties. World Applied Sciences Journal 6 (5): 616-623, 2009
	In article
[4]	CRDO: Consejo Regulador de la Denominación de Origen Chufa de Valencia. 2012. Available from: https://www.chufadevalencia.org Accessed June 20, 2014.
	In article
[5]	Kim, M., No, S. and Yoon, S.H. Stereospecific Analysis of Fatty Acid Composition of Chufa (Cyperus esculentus L.) Tuber Oil. Journal of American Oil Chemists Society. 84: 1079-1080. 2007.
	In article		CrossRef
[6]	Eyeson, K.K, and Ankrah, E.K. Composition of Foods commonly used in Ghana, CSIR, Ghana.
	In article
[7]	Linssen, J.P.H., Cozijnsen, J.L. and Pilnik W. Chufa (Cyperus esculentus): A new source of dietary fiber. Journal of the Science of Food and Agriculture 49, (3): 291-296. 1989.
	In article		CrossRef
[8]	Mosquera, L.A., Sims, C.A., Bates, R.P. and Okeefe, S.F. Flavor and Stability of Horchata De Chufas. Journal of Food Science. 61, (4) 856-861. 1996.
	In article		CrossRef
[9]	Umeri, S.C., Enebeli, J.N. Malt caramel from tubers of Cyperus esculentus. Bioresource Technology 57 (2): 215-216.1996.
	In article
[10]	Belewu, M.A and Abodunrin, O.A. Preparation of Kunnu from unexploited rich food source: Tiger nut (Cyperus esculentus). World Journal of Dairy and Food Sciences, 1: 19-21. (2006).
	In article
[11]	Tetteh, J.P. and Ofori, E. A baseline survey of tiger nuts (Cyperus esculentus) production in the Kwahu South District of Ghana. Ghana Journal of Agriculture Science 31, 211-216. 1998.
	In article
[12]	Ablordeppey, S.D., (2004). Tiger nut takes rightful place. Daily Graphic, 72: 13.
	In article
[13]	Sanful, R. E. Production and Sensory Evaluation of Tigernut Beverages Pakistan Journal of Nutrition 8 (5): 688-690, 2009.
	In article
[14]	Adjei-Nsiah, S. Yield and nitrogen accumulation in five cassava varieties and their subsequent affects on soil chemical properties in the forest/savanna transitional agro-ecological zone of Ghana. Journal of Soil Science and Environmental Management. 1: 015-020. 2010.
	In article
[15]	Makeri, M.U., Bala, S.M and Kasssum, A.S. The effect of roasting temperatures on the rate of extraction and quality of locally-processed oil from two Nigerian peanut (Arachis hypogea L.) cultivars. African Journal of Food Science 5: 194-199. 2011.
	In article
[16]	Pascual, B., Maroto, J.V., Lopez-Galarza, S., Sanbautista, A. and Alagarda J. Chufa (Cyperus esculentus L. var. sativus Boeck.): An unconventional crop. Studies related to applications and cultivation. Economic Botany 54: 439-448. 2000.
	In article		CrossRef
[17]	Coskumer Y., Ercan R., Karababa E., and Nalizcan A.N. Physical and chemical properties of chufa (Cyperus esculentus L.) tubers grown in the Cukurova region of Turkey. Journal of the Science of Food and Agriculture 82: 625-631. 2002.
	In article		CrossRef
[18]	Oladele, A.K. and Aina, J.O. Chemical composition and functional properties of flour produced from two varieties of tiger nut (Cyperus esculentus) African Journal of Biotechnology 6 (21), pp. 2473-2476, 2007.
	In article
[19]	Adejuyitan, J.A., Otunola, E.T., Akande, E.A., Bolarinwa, I.F., and Oladokun FM. Some physicochemical properties of flour obtained from fermentation of tigernut (Cyperus esculentus) sourced from a market in Ogbomoso, Nigeria. African Journal of Food Science 3: 51-55. 2009.
	In article
[20]	AOAC. Official Methods of Analysis of the Association Official Analytical Chemists., 14th edition. Arlington, VA. 1984.
	In article
[21]	F.A.O Corporate Document Repository (2006) Calculation of the Energy Content of Foods-Energy Conversion Factors. [http:/www.fao.org/ag]
	In article
[22]	(International Office of Cocoa Chocolate and Sugar Confectionery) Determination of the Free Fatty Acid Content of Cocoa Fat as a measure of Cocoa Nib Acidity. Analytical Method 42. 1998.
	In article
[23]	Montgomery, D.C. (2001). Design and Analysis of Experiments. New York: John Wiley and Sons.
	In article
[24]	Djomdi Ejoh. R. and Ndjouenkeu, R. Characteristics of tiger nut (Cyperus esculentus L.) tubers and their performance in the production of a milky drink. Journal of Food Processing and Preservation. 30 (2): 145-163. 2006.
	In article		CrossRef
[25]	Addo-Quaye, A. A. Darkwa, A. A and Ampiah M. K. P. Performance Of Three Cowpea (Vigna Unguiculata (L) Walp) Varieties In Two Agro-Ecological Zones Of The Central Region Of Ghana I: Dry Matter Production And Growth Analysis ARPN Journal of Agricultural and Biological Science 6, 2, 1990-6145, 2011.
	In article
[26]	Xiang, L., Xing, D., Lei, F., Wang, W., Xu, L., Nie, L., Du, L. Effects of Season, Variety, and Processing Method on Ellagic Acid Content in Pomegranate Leaves Tsinghua Science And Technology, 13, 4, 460-465 (2008).
	In article
[27]	Howeler RH Cassava mineral nutrition and Fertilization. In Cassava: Biology, Production and Utilization, Hilocks, R.J. Thresh J.M. and Bellotti A.C. (eds): 115-147. CAB International, Wallingford, UK. (2002).
	In article
[28]	Arafat, S.M., Gaafar, A.M., Basuny A.M., (Cyperus esculentus L.): As a New Source of Food World Applied Sciences Journal 7 (2): 151-156, 2009.
	In article
[29]	Ekeanyanwu R. C. and Ononogbu C. I. Nutritive value of Nigerian Tigernut (Cyperus esculentus L.) Agricultural Journal 5 (5): 297-30, 2010.
	In article		CrossRef
[30]	Umerie, S. C., Okafor, E. O. and Uka, A.S.. Evaluation of the tubers and oil of Cyperus esculentus. Bioresource Technology 61 (2): 171-173. (1997).
	In article		CrossRef
[31]	Takrama J.F Aculey, P.C., Owusu, E, Botchway, F, Frimpong,, K, Pawar, G. Bediako, S., and Asante, F. Physical And Biochemical Assessment of Ghana’s Cocoa for Quality Assurance. Proceedings of the 15 th International Cocoa Research Conference, San Jose, Costa Rica, 9-14 October, Cocoa Producers Alliance. 1179-1185, 2007.
	In article
[32]	Dubois V, Breton S, Linder M, Fanni J, Parmentier M. 2007. Fatty acid profiles of 80 vegetable oils with regard to their nutritional potential. European Journal Lipid Science and Technology 109: 720-32.
	In article		CrossRef
[33]	Chaiseri, S. and Dimick, P.S. Lipid and hardness characteristics of cocoa from different regions. Journal of Americal Oil Chemist Society. 66: 1771-1776. 1989.
	In article
[34]	Olayiwola, I.O., Abubakar, H.N., Adebayo, G.B. and Oladipo, F.O. Study of sweet potato (Ipomea batatas Lam) foods for indigenous consumption through chemical and anti-nutritive analysis in Kwara State, Nigeria. Pakistan Journal of Nutrition 8 (12): 1894-7. 2009.
	In article		CrossRef
[35]	Maieves, H.A., Cardoso de Oliveira, D., Bernardo, C., de Oliveira Müller, C.M. and Amante, E.R.. Microscopy and texture of raw and cooked cassava (Manihot esculenta Crantz) roots. Journal of Texture Studies 43 (2): 164-73. 2012
	In article		CrossRef
[36]	Anderson, J. W., Baird, P., Davis, R. H., Jr., Ferreri, S., Knudtson, M. and Koraym, A. Health benefits of dietary fiber. Nutrition Reviews, 67, 188-205. 2009.
	In article		CrossRef
[37]	Igoe, R.S., and Hui, Y.H. Dictionary of food ingredient 4th edn Aspen Publishers, Inc. Gaithersburg, Maryland, 2001.
	In article
[38]	Glew, R.H., Glew, R.S., Chuang, L.-T., Huang, Y.-S., Millon, M., Constans, D. and Vanderjagt, D.J., Amino acids, minerals and fatty acids content of pumpkin seeds (Cucurbita spp) and Cyperus esculentus nuts in the Republic of Niger. Plant Foods and Human Nutrition, 61, 51-55, Springer Science+ Business Media, Inc.
	In article
[39]	Oladele, A.K. and Aina, J.O. Chemical composition and functional properties of Flour produced from two varieties of tiger nut (Cyperus esculentus), African Journal of Biotechnology, 6 (21): 2473-2476, 2007.
	In article
[40]	Wester P.O. Magnesium. American Journal of Clinical Nutrition; 45: 1305-12 1987.
	In article
[41]	F.D.A. Guidance for industry, a food 2009.
	In article
[42]	Heath, H. and Reineccius, G. Flavor Chemistry and Technology. AVI Publishing Company, Inc., Westport, CT. 1986.
	In article		CrossRef
[43]	Pattee, H.E. and Singleton, J.A. Peanut quality: its relationship to volatile compounds. A review in quality of selected fruits and vegetable of north America R Teranishi and H Barrea-Benitez (Ed) p 147-161, American chemical society Washington, D.C. 1980.
	In article