Effects of Processing Treatments on the Chemical Composition of Tiger 2 Nut ( Cyperus esculentus ) Milk Products

Department of Biochemistry, Faculty of Basic Medical Sciences Bayero University Kano, PMB 3011 Kano State, 5 Nigeria 6 * Correspondence: aminasaid02@yahoo.com; Tel.: +2348065270866 7 8 Abstract: Tiger nut (Cyperus esculentus) is an edible perennial grass-like plant that has long been 9 recognized for its health benefits as it is rich in fiber, protein, vitamins, minerals and 10 natural sugars. It can be eaten raw, roasted or made into a refreshing milk which is very nutritive 11 and healthy for consumption. There were several efforts to mass-produce the locally prepared tiger 12 nut milk in our locality, but the fact that it has a shorter shelf-life, brings about a hindrance. The main 13 objective of the present study is to unveil the cause for the easily spoilage of tiger nut milk and 14 device ways to promote its production using different treatments. Tiger nut milk products were 15 prepared using different methods; water soaked tiger nut milk (WSTM), toasted tiger nut milk 16 (TTM), methanol soaked tiger nut milk (MSTM), and the pasteurised tiger nut milk (PTM). Each of 17 these milk proucts prepared was divided into two portions; the first portion is treated with an 18 antibiotic preservative, Nisin and the second portion was left untreated. The two portions were 19 further divided into two; one stored at refrigerating temperature and the other at room temperature, 20 making four different treatments per mixture and a total of 16 samples. These samples were 21 subjected to proximate analysis; protein, fat, moisture, ash and carbohydrate. The chemical 22 composition of the samples was significantly (P < 0.05) affected by processing treatment. All the 23 samples had high moisture content, and a considerable amount of fat. The preservative treated 24 samples that received pasteurized treatment were found to stay more than a week with fair quality. 25 Findings from the study shows that the chemical characteristics of the various milk products were 26 significantly affected by the different processing treatments. 27


Introduction
Milk is an important source of nutrients and serve as a source of food for infants, growing children and adults [1].It is the primary source of nutrients for infant mammals before they are able to digest other types of food.The high cost of milk in developing countries has led to the development of alternative source of milk from plant materials [2].A protein-rich drink can be produced from locally available plant foods at an affordable price in place of animal protein which is scarce and expensive, and could play an important role to reduce protein malnutrition.
Plant milk has been consumed for centuries in various cultures, both as a regular drink (such as the Spanish horchata) and as a substitute for dairy milk.The most popular varieties are soy milk, almond milk, rice milk and coconut milk.Their protein content varies.It contains no lactose or cholesterol, and is usually sold with added calcium and vitamins, especially B12.Only soybean has been extensively investigated while other oil seeds and tubers such as tigernut, have not been studied comprehensively.Little research attention has been given to bambaranut [3], baobab [1], peanut [4], melon seed [5] and tiger nut milk [6] as sources of vegetable milk.Tiger nut, an under-utilized crop, was reported to be high in dietary fibre content, which could be effective in the treatment and prevention of many diseases including colon cancer, coronary heart diseases, obesity, diabetes and gastrointestinal diseases [7].It has 5.8% moisture, rich in protein (7%) [8] and carbohydrates such as reducing sugar (7.4%), soluble polysaccharide (7.4%) and starch (86.4%) [9].Tiger nut is also rich in mineral elements such as sodium, calcium, potassium, magnesium, zinc and traces of copper [10].According to Ojobe and Tempo [11], the protein in tiger nut is of high biological value considering the many essential amino acids it contains.These amino acids are higher than those proposed in the standard by the FAO/WHO [12,13] and satisfy amino acid need of adults [14].
Tiger nuts are a rich source of nourishment, and remain a significant source of food for both the poor and the wealthy throughout Northwest Africa.They are a good sources of oleic acid (a monounsaturated fat also found in olive oil and avocado), and which is associated with increased HDL (good) cholesterol levels.Tiger nuts can be processed into varieties of milk products like water soaked tiger nut milk, toasted tiger nut milk, methanol soaked tiger nut milk and the pasteurised tiger nut milk.Tiger nut milk can be used by special people having milk allergies such as galactosemia and lactose intolerance.
The tiger nut milk is a stimulating vegetable drink prepared mainly with tiger nut, water and sugar.It's milk can serve as a good alternative to cow milk with a natural sweetened taste [15].The milk is said to be rich in minerals, like phosphorus, calcium and magnesium, iron and in vitamin C and E which are vital for body growth and development.It does not contain lactose or gluten; this makes it a suitable choice for people who are not able to tolerate gluten (celiac patients) and also for the lactose-intolerant who stay away from cow milk and other dairy products [16].
Due to its content of some digestive enzymes like catalase, lipase, and amylase, tiger nut milk could be recommended for people with problems of digestion, flatulence and diarrhea [17].
The ability to keep the milk for a long period of time has been a major drawback as it easily got spoiled.The aim of the research is therefore, to determine the effect of various processing treatments on the chemical composition of the tigernut milk.

Materials and Methods
Fresh tigernuts (Cyperus esculentus) and spices were obtained from Rimi market in Kano State, Nigeria.The tigernut was authenticated in the Department of Plant Biology, Bayero University Kano with the accession number BUKHAN 0367 by Baha'uddeen Sa'id Adam.The spices used include ginger (Zingiber officinate) and cloves (Eugenia coryphée).The chemical preservative used was Nisin, then vanilla flavor and sugar.

Preparation of Tigernut Milk
Fresh tubers of tigernut were sorted, washed and rinsed with distilled water then used to produce different milk products as follows: Water Soaked Tigernut Milk (WSTM): In this portion, the fresh tigernut was directly soaked in water for 2hours, blended, filtered, sugar and flavor were added.The filtrate was then divided into two portions; one treated with Nisin preservative (2g to 2L of the filtrate) and the other portion was not treated with any preservative.Each of these two portions was again divided into two; one stored at refrigerating temperature and the other one at room temperature, making four different treatments: • Water soaked tigernut milk + Preservative (2g to 2L of the filtrate) at refrigeration temperature (WSTM+PRef.T).

Toasted Tigernut Milk (TTM):
The fresh tigernut was toasted at 110±5°C for 30minutes in an open pan.It was then blended and mixed; and divided into four portions as done for the first portion.

Methanol Soaked Tigernut Milk (MSTM)
In this portion, the tigernut was partly ground and soaked in methanol solution for an hour.It was then removed, dried (so as to allow the methanol to evaporate) and soaked in water (water was changed three times).It was also divided into four portions as above: • Methanol soaked tigernut milk + Preservative (2g to 2L of the filtrate) at refrigeration tempe rature (MSTM + PRef.T).

Pasteurized Tigernut Milk (PTM):
Tigernut (2kg) was blended into slurry with water (400 ml).The slurry was pressed using cheese cloth to extract the milk.The extract was pasteurized at 75ºC for 15 min.It was homogenized, bottled when hot and rapidly cooled.
The proximate composition and pH of each sample were analysed at an interval of 4 days.

Chemical Analysis:
Moisture, ash, fat, protein, carbohydrate by difference and pH were determined according to standard methods [18].

Statistical Analysis:
The analyses were performed in triplicates.The mean values and standard deviation were calculated (mean ± SD) using SPSS package16.

Effect of Processing on the Chemical Characteristics of Tigernut Milk Products:
The effects of processing on the chemical characteristics of tigernut milk products are presented on Tables 1-5.
All the samples in table 1 had high moisture content, with TTM+PRT having the highest percentage.Also, TTM+PRefT and PTM+PRefT were significantly different from other samples in terms of their carbohydrate contents.While WSTMRefT and MSTMRT had the highest percentage of protein.
No significant difference existed in almost all the samples in the various parameters after eight (8) days of production.Only PTM+PRT had high percentage of protein (10.7%).
Twelve (12) days after production, all samples had high percentages for moisture content ranging from 71-82%.WSTMRefT and PTM+PRT showed significant difference in their protein contents (10.9%).
In table 4, the percentage fat content of PTMRefT was statistically significant; and WSTMRT and MSTMRT showed significant difference in their percentage moisture content.
Significant difference existed between WSTM+PRT and PTM+PRT and other samples in terms of percentage fat content.While WSTM+PRT and WSTMRT samples had highest moisture content after twenty (20) days of production.Values in same columns bearing the superscript ( * ) are significant at P<0.05

Discussion
It was observed that all samples had high moisture content, with the samples stored at room temperature having the highest percentage of moisture.This could affect the stability and safety of the various beverage samples with respect to microbial growth and proliferation; as high moisture content allows microbial growth [19].Total ash content in the various treatments was lower than the ash content of 1.5% as reported by Ukwuru et al. [6].The crude fat content of the various milk samples were within the range of 2.3 -6.5% and were below the minimum of 8% standard for dairy milk [12,13].According to Belewu and Abodurin [16], tigernut itself is rich in fat (25.5%).This shows that there is a wide difference between fat in tigernut tubers and its milk.
The current study is in accordance with the result of a previous study by Adgidzi in 2010 [20] , where production of acceptable beverages were made from tiger nuts.The beverage products were found to contain a proximate composition of 1.89% protein, 0.92% fat, 0.16% ash, 0.24% crude fiber, 76.86% moisture and 15.96% carbohydrates.
In general, it was established that processing treatment of the various tigernut milk samples has effect on the chemical characteristics of the milk products.Processing treatments affected the characteristics of the various samples in different ways; soaking increased the protein and fat, but sometimes reduced the moisture and carbohydrate content.It also reduced soluble antinutrients (eg tannins and polyphenols) which can be eliminated with the discarded soaking water.Toasting on the other hand, aids flavour development, removes heat labile antinutrients and increased the protein and fat contents.The increase in protein and fat could be attributed to the concentration of the constituents during toasting brought about by loss of moisture and reduction/destruction of certain protease inhibitors and other anti-nutrients like phytic acid and tannins which form complexes with protein and make protein unavailable during hydrolysis.A similar increase in protein content has been reported for Terminalia catappa seeds toasted at a high temperature [21].
Soaking in methanol reduced the fat content in the tigernut milk samples, as the raw tigernut was defatted with methanol.Pasteurization of the tigernut milk mixture also aided in destroying pathogens likely to be present as well as most spoilage organisms in the mixture as it normally controls both health and spoilage hazards.
Addition of preservative during processing had a significant effect on the chemical characteristics of the tigernut milk samples.During storage, the samples which had no preservative and were stored at room temperature dropped significantly in quality after 2 days, whereas the preserved samples without pasteurization deteriorated significantly (P<0.05) in quality on the first week, while the preserved samples that received pasteurization were found to stay more than a week with fair quality.All samples fell below acceptable range at third week.
There is increased utilization of tiger nut (Cyperus esculentus) nowadays, which might be as a result of awareness on the composition of tiger nut especially the protein content which helps in body development and tissue repair [15].

Conclusions
Tigernut tubers can be processed into various tigernut milk products using different treatments.The chemical characteristics of the various beverage products were significantly affected by the different processing treatments.The preservative treated samples that received pasteurized treatment were found to stay more than a week with fair quality.

Table 1 . Proximate composition of tigernut milk products obtained from various processing treatments after four (4) days of production.
T = Water soaked tigernut milk (at refrigerating temperature), WSTMRT = Water soaked tigernut milk (at room temperature);