Comparative Microbial Analysis and Storage of Tigernut-Soy Milk Extract

Research Article

Austin J Nutri Food Sci. 2014;2(5): 1026.

Comparative Microbial Analysis and Storage of Tigernut-Soy Milk Extract

Udeozor LO1* and Awonorin SO2

1Department of Food Science and Technology, Federal University of Technology, Nigeria

2Department of Food Science and Technology, University of Agriculture Abeokute, Nigeria

*Corresponding author: :Udeozor LO, Department of Food Science and Technology, Federal University of Technology, P.M.B 1526, Owerri, Imo State, Nigeria

Received: March 18, 2014; Accepted: April 07, 2014; Published: April 08, 2014


Fresh tigernuts and soybean seeds were processed and blended at different proportions to formulate six new products of natural Tigernut–Soy Milk Extract (TSME) samples: (TME: SME)– 100:0, 90:10, 80:20, 70:30, 60:40 and 50:50 without addition of spices and chemical preservatives. The samples were evaluated for their microbiological status. Microbiological examination of the products was carried out for a period of 14 days under refrigeration storage (4°C) and ambient storage (28±2°C). A total of 7 different genera of microorganisms were isolated from the blends and a direct relationship existed between the microbial content of the samples and the rate of substitution. Varying proportions, length of storage and storage conditions significantly (p<0.05) affected the microbiological status of the samples. The refrigerated milk products were microbiologically stable during storage and had no coli form growth throughout the storage period. The bacterial and fungal growth at zero days of storage was not higher than 102cfu⁄ml; however, the samples stored under ambient condition had 104cfu⁄ml. The microbial status of the samples revealed that the different storage conditions (refrigeration and ambientstorage) affected the quality of beverages differently, thus the beverage should be consumed immediately after processing.

Keywords: Microbiological Status; Milk Extract; Storage; Soybean; Tigernuts


Tiger–nut (Cyperus esculentus L.) belongs to the Division– Magnoliophyta, Class–Liliopsida, Order–cyperales and Family– Cyperaceae and was found to be a cosmopolitan, perennial crop of the same genus as the papyrus plant. The tubers are about the size of peanuts and are abundantly produced in Nigeria. It has many other names like Zulu nut, yellow nut grass, ground almond, and chufa, edible rush and rush nut. Other names of the plant are earth almond as well as yellow nut grass [1]. In Nigeria, the Hausas call it “Aya”, Yorubas “imumu”, the Igbos “aki Hausa”, “ofio” in southern Nigeria [2]. Tiger–nut has been cultivated since early times (chiefly in south Europe and West Africa) for its small tuberous rhizomes which are eaten raw or roasted, used as hog feed or pressed for its juice to make a beverage. Non–drying oil (usually called chufa) is equally obtained from the rhizome. The nuts which are cultivated throughout the world are also found in the Northern part of Nigeria and other West Africa Countries like Guinea, Cote d'ivore, Cameroon, Senegal, America and other parts of the World (Irvine, 1969).

The nut was found to be rich in myristic acid, oleic acid, linoleic acid [3], with oleic acid being the most abundant [4]. Tiger–nut was reported as very healthy as it helps in preventing heart attacks, thrombosis and activates blood circulation. It is believed that they help to prevent cancer especially of the colon due to high content of soluble glucose. Tiger–nut was equally reported to have positive effect on cholesterol level due to high content of vitamin E. They are thought to be beneficial to diabetics and those seeking to reduce cholesterol or lose weight. The very high fibre content combined with a delicious taste; make them ideal for healthy eating [2]. The nut is rich in energy content (starch, fat, sugars & protein), mineral (phosphorus, potassium) and vitamins E and C. The nut was found to be ideal for children, older persons and sportsmen [5]. The inclusion of 33.33% of tiger–nut in the diet of cockerel starters was reported by [6]. Since the tubers contain 36% oil, C. esculentus has been suggested as potential oil crop for the production of biodiesel [4]. The oil remained uniformly liquid at refrigeration temperature; this makes the oil suitable for salad making [7]. Tiger nut was found to be a good substitute for some other (plant) milk sources. The nuts are valued for their highly nutritious starch content, dietary fibre, carbohydrate (mono, di and polysaccharides) [7]. The nut was reported to be rich in sucrose (17.4 to 20.0%), fat (25.50%), and protein (8%) [8]. The nut is also very rich in mineral content (Sodium, Calcium, Potassium, Magnesium, Zinc and traces of Copper [9]. Research studies have shown that 100g Tiger–nuts contain 386 kcal (1635 kJ), 7% proteins, 36% fats (oils), 31% starch, 21% glucose, and 26% fiber of which 14% is non–soluble and 12% soluble [4]. Tiger–nuts are regarded as a digestive tonic having a heating and drying effect in digestive system and alleviating flatulence. They also promote urine production. The nuts are said to be stimulant and tonic and also used in the treatment of indigestion, colic diarrhoea, dysentery and excessive thirst [10].

Soybean (Glycine max M) with 40% protein and 20% fat assumes the most predominant position in solving the nutritional imbalances prevailing. It not only provides quality macronutrients but also various other micronutrients, which are required to fight against malnutrition. Soybean is rich in protein content and can furnish protein supply to bridge up the protein deficiency gap at low–cost than any other crop [11]. Among the numerous soy food items, soymilk (extract of soybean) had been the first product ever prepared and consumed by human since long ago. Soymilk not only provides protein but also is a source of carbohydrate, lipid, vitamins and minerals [12]. Soymilk is an alternate of dairy animal milk due to its cheaper high–quality protein. Soymilk is a healthy drink and is important for people who are allergic to cow milk protein and lactose. In spite of its nutritional merits, it has not gained much popularity mainly due to its beany flavor and astringency [13].

In view of the scarce milk supply in various countries and the ever increasing gap between the requirement and population, efforts have been made over the years to develop alternative milk–like products from vegetable sources [14]. Soybeans, peanuts and cowpea have been accorded high attention in the investigations on milk substitutes. However, hardly any attention has been given to the use of locally available tiger–nut as such or in combination with milk to produce a palatable ready–to–serve bottled beverage, like ‘Horchata de chufas’ as done in South Europe especially in Spain [15]. Tigernut–Soy Milk (TSME) is a blended, processed commodity and is a source of high quality energy, protein, minerals, and vitamins. The implication of using the two different milk sources in the diet is the high contents of protein and fat. The total energy value of the milk is from the fat content hence, higher fat content is an indication of more total energies available [16].

The objectives of this work therefore were to evaluate the microbial status of tiger nut–Soy milk extract and to determine the effect of storage on the quality of tiger nut–soy milk extract.

Materials and methods

Fresh Tiger nuts and soybean seeds were purchased from the local traders in Eke–onunwa market in Owerri, Imo State, Nigeria. The equipment and chemicals used were obtained from Nigerian Institute of Science Laboratory Technology (NISLT), Samonda, Ibadan, Oyo State and Anthony Van–Leeuwenhoek Research Centre, Nekede, Owerri, Imo State.

Sample preparation: Fresh tubers of tigernuts and soybean seeds were sorted; foreign materials, bad⁄cracked nuts and seeds which may affect the taste and quality of the milk extract were removed, washed and rinsed with portable water and used to produce milk.

Tigernut milk extract: 1kg of the fresh tigernuts was blended several times into slurry with water (6L) in a Q–link auto–clean blender. The slurry was pressed using muslin cloth to extract the milk. The extract was pasteurized at 72°C for 15s. It was homogenized using improvised equipment; Q–link auto–clean blender, bottled when hot and rapidly cooled. The flow chart for tigernut milk extract (TME) production is shown in (Figure 1).