Zinc Levels in Raw and Blanched Slenderleaf sp. ( Crotalaria ochroleuca & Crotalaria brevidens ) Indigenous Vegetables

An estimated 20% of the world’s population is at risk for zinc (Zn) deficiency. Micronutrient deficiencies are most prevalent in Africa and remain a major problem facing poor populations, whose impact is worsened by HIV/AIDS pandemic. Adequate zinc nutrition is essential for adequate growth, immu-nocompetence and neurobehavioral development. In Sub-Saharan Africa, Zn deficiency risk stands at 34.6% with 25.6% of its population having inadequate zinc intake. It is widespread in areas where diets lack diversity and it has been implicated as a contributing factor to stunting in approximately a third of children in low-income countries. In Kenya, it is a public health problem that about 50% of children under 6 years and 50% of women are af-fected. Zn deficiency rates are severe and pose severe consequences whose impact would translate into poor economic development and would set a vi-cious cycle effect that will take many generations to correct if left unchecked. It is important to examine zinc in the diet but its concentration in food varies depending partly on processing besides other factors. The objective of this study was to assess blanching as a food preparation method’s implication to Zn levels in vegetables. Blanching is a method where vegetables are dipped in boiling water for around two minutes and removed to avoid over cooking. levels in slenderleaf sp. Indigenous vegetable commonly found in the Lake Victoria Basin region is not known. An experimental study was carried out to analyze zinc levels in raw and blanched slenderleaf sp. vegetables. indicated that blanching reduces Zinc levels in slenderleaf vegetables, however, the reductions are not significant; the levels after blanching are still vital. It is, there-fore, recommended to minimize blanching time in order to reduce loss of vital nutrient in slenderleaf vegetables.


Introduction
Zinc deficiency is widespread and affects the health and well-being of populations worldwide. The supply of nutritionally adequate foods to the global population is still challenging (Gudrun, Katja and Irmgard, 2013) [1]. While protein-energy malnutrition (PEM) is the most lethal form of malnutrition, micronutrient deficiency (MND) is the most serious threat to health and development of populations worldwide (WHO, 2004a) [2]. Trace mineral deficiencies affect populations in both developed and developing countries (IOM, 2001) [3]. "Hidden hunger", a deficiency of micronutrients, vitamins and minerals, affects as many as 3 billion people globally while 38% of children under five in Sub-Saharan Africa are stunted due to chronic malnutrition (Anonymous, 2013) [4]; (Mason and Garcia, 1993) [5]; (R.M. Welch, Combs-Jr. and Duxbury, 1997) [6]; (WHO, 1999) [7]. Studies indicate that the prevalence of stunting is positively correlated with the estimated prevalence of inadequate zinc intake. The mean prevalence of stunting in countries identified as being at low, moderate and high risk of inadequate zinc intake are 19.6%, 28.8% and 43.2%, respectively.
Africa has plenty of neglected and underutilized crops rich in micronutrients im- Consumption of a broad range of plant species, in particular, those currently identified as "underutilized", can contribute to improved health and nutrition, livelihoods and household food security (Jaenicke, H. and Höschle-Zeledon, I., 2006) [24]. Among many micronutrients of public health concern is zinc, has

Ethical Clearance
Approval for the study was obtained from the Ministry of Higher Education, and Maseno University School of Graduate Studies, Kenya.

Materials and Methods
All the reagents, chemicals and standards used in this work were from Aldrich supplied by Kobia Limited Nairobi. The methods used in this work for the various determinations of the samples are standard methods and all chemicals used for the study were of analytical grade.

Source of the Slenderleaf sp. Vegetables
Slenderleaf vegetables were procured at Luanda market located at 34˚36' East and 0˚ North at an altitude of about 1530 meters above sea level. The same amount (500 g) of each species (Crotalaria ochroleuca & Crotalaria brevidens) was procured from three different sellers at different locations of the market and mixed. were then dried and ground into powder using mortar and pestle and sieved by a 0.5 mm size sieve.
The following procedure was followed in blanching the vegetables 1) A large pan half-full of double glass-distilled water was brought to rapid boiling.
2) Clean raw vegetables were put in a wire basket and gently lowered in the boiling water.
3) Once the water began to boil again, vegetables were left in for two minutes. 4) The wire basket containing vegetables was removed from the boiling water and plunged into ice-cold water for two minutes to stop the cooking process.
5) The blanched vegetables were drained and dried under shade until completely dry then powdered in readiness for elemental analysis.

Sample Preparation for Elemental (Zn) Analysis
The procured vegetables were cleaned and made free from dirt, foreign matter and other stubbles; this was followed by washing using distilled and deionized water after which processing was carried out in readiness for analysis. Processing of the vegetables involved the following activities; fresh vegetable leaves were separated from roots, washed under running double glass-distilled and deionized water. Vegetables were then blanched, drained completely and dried under shade. All samples were then labeled as raw sample and processed sample. The dried samples (raw & processed) were ground into powder and then stored in clean and dried 100 ml polypropylene bottles for further processing. Digestion of food samples was carried out as follows: Food samples of 0.1 g were put in a beaker and 10 ml of tri-acid mixture (concentrated HNO 3 , HClO 4 and H 2 SO 4 ) in the ratio 3:1:1 was added. The mixture was heated on a hot plate at 105˚C until white fumes were observed (Lindsay, W.L. and Norvell, A.W., 1978) [28]. The digested samples were then filtered using a Watmann filter paper No. 42 into a 50 mL volumetric flask and topped up to the mark with distilled water and two drops of HNO 3 added for preservation. The digested sample was transferred into plastic bottles ready for analysis using the Atomic Absorption Spectrophotome-

Statistical Analysis
Data analysis was performed using ANOVA with critical significance levels set at P ≤ 0.05. Paired samples T-test was used to compare zinc levels between raw and processed vegetables.

Zinc Levels in Raw and Processed Selected Underutilized Crops
The two species of slenderleaf contained essential micronutrient (Zn). Data present the mean Zn concentration of the raw and processed vegetables. Processing reduced zinc concentration (Table 1). All data were based on dry weight.
Results indicate that, among the selected indigenous food crops, raw bitter slenderleaf (C. brevidens) recorded the highest mean zinc content of followed by raw mild slenderleaf (C. ochroleuca) ( Table 1). Similar to raw crops, processed bitter slenderleaf (C. brevidens) recorded higher mean zinc content compared to mild slenderleaf (C. ochroleuca) ( Table 1).

Limitation of the Study
The elemental experimental method used can only be used of dry samples, therefore, it was not possible to determine whether the water used for blanching the vegetables contained zinc which could have leached from the vegetables during blanching.

Conclusion
The study has shown that the two species of Slenderleaf indigenous vegetables are good sources of Zn; however, processing has effect on the levels. Blanching leads to leaching of Zn into the water used for blanching thus resulting in reductions in mean Zn levels in slenderleaf vegetables.

Recommendations
Slenderleaf sp. indigenous vegetables are good sources of zinc and should, therefore, be promoted and included in our diets.
It is important to minimize blanching time and water temperature in order to minimize zinc loss in vegetables.

Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this paper.