Research Article
Effects of Fermentation on Nutrient Enrichment of Locust Beans (Parkia biglobosa, Robert bam)
Department of Microbiology, School of Sciences, Federal University of Technology, P.M.B. 704, Akure, Nigeria
The genus Parkia to which the locust beans belong is large in the family leguminoseceae. The pods are flat, large, irregular clusters from which the locust bean seeds are obtained (Omafuvbe et al., 2004) The species of the genus include Parkia filicoidea, Parkia biglobosa, Parkia bicolor and Parkia clappertoniana. The seeds of P. biglobosa and P. filicoidea had been successfully fermented for the production of food condiments in seasoning foods in Nigeria and other West African countries. The locust bean tree is planted mainly because the fruit is rich and provides valuable protein in the dry season (Odunfa, 1986). It is also used for medicinal purposes and as a source of mouth wash to relieve toothache. The bean husk (seed coat) are used with indigo dye to improve the luster of fabrics while the tree bark yield a red tannin for dying leather. Mugo Park, a Scottish surgeon, first described this tree in his Travels in the interior district of Africa and was named after him by Robert Bran in 1826.A lot of foods products have been prepare by fermentation process with the action of microorganisms (Tweyongyere and Katongole, 2002). This had led to development of characteristics flavours, textures and changes in nutritive properties of the food usually from different carbohydrate rich food substances such as tubers cereals and legumes (Amoa-Awua et al., 2005).
Since fermentation of locust beans have been found to produce food condiments (Omafuvbe et al., 2004), then it is necessary to know the effect of fermentation on the nutritional qualities of the seeds since this process have been reported to diversify the use of foods and their organoleptic quality (Amoa-Awua et al., 2005). It is also necessary to ascertain the microbial safety with respect to shelf stability. There have not been any information or that such data are largely unknown with locust beans. The unprocessed and raw seeds is nutritionally deficient and unpalatable.
Thus the objective of this research is to examine the possibility of enhancing the organoleptic quality and diversify the uses of the seeds. The research is designed to determine the proximate composition of naturally fermented, inoculated fermented using Saccharomyces cerevisae as starter culture and unfermented locust beans to evaluate the effect of fermentation on the improvement of the nutritional qualities of the seeds. Qualitative and quantitative microbial analysis will also be investigated in order to correlate the effect of pH change on the microbial load and types on the naturally fermented, inoculated fermented and unfermented locust seeds sample.
Locust Beans
The locust beans seeds were purchased from Oja-Oba Market, Ondo State, Nigeria. They were those harvested from the previous season. The seeds were sun dried to reduce the moisture content. The microbial analysis was carried out in the Department of Microbiology while the Chemical characteristic was determined in the Biochemistry Department, both in Federal University of Technology, Akure, Nigeria in 2004.
Fermentation
The dried locust bean were fermented by soaking in water for 15 min and boiled for 6 h. The seed were then dehulled and washed thoroughly. The washed beans cotyledons were boiled for 1 1/2 h with potassium bicarbonate. Fermentation proceeds for 36 h in a fermentor under carefully controlled environment conditions of temperature, pH, pressure and humidity. The controlled fermentation was carried out by inoculating part of the dehulled beans wit pure strain of Saccharomyces cerevisiae as a starter culture.
Chemical Characteristics
The chemical characteristic that was determined for the naturally fermented, inoculated fermented and unfermented locust beans include moisture content, crude content, crude protein, ash content and crude fibre using AOAC (1990). The mineral content was evaluated for using Atomic absorption Spectrophotometer. The minerals are Iron, Calcium, Magnesium, Potassium and Ascorbic acid (Cordenunsi et al., 2004).
The soluble salts of the metals determined were used for the preparation of the standards. Ascorbic acid was determined by titrating the sample with 1% ascorbic acid solution using dichlorophenol-indolphenol solution as standard dye indicator. Phosphorus was determine as hydrolysable phosphate using HACH DR/2000 direct reading spectrophotometer at 490nm using phosover 3 phosphate powder pillow containing ammonium molybdate and as ascorbic acid. (Preet and Punia, 2000).
Potassium, calcium, magnesium and Iron content were measured with Atomic Absorption spectrophotometer (Unicam 929 model) using the potassium, calcium, magnesium and Iron lamps with prepared standard solution of each model (Adeniran, 2003).
Microbial Analysis
Quantitative and qualitative microbial analysis of the locust beans were carried out using the standard methods of Madigan et al. (2002). Bacteria were isolated and characterized using the gram reaction, colonial morphology and biochemical characteristics. Fungi were identified using the colors on potato dextrose agar, staining and reproductive structures using lactophenol cotton blue (Prescott et al., 2005).
The results of the proximate composition of raw, naturally fermented and inoculated fermented are shown on Table 1. The moisture content was found to be higher in the two fermented samples than the unfermented. Increase in moisture content may be due to addition of water and soaking during fermentation. This was in agreement with the report of Omafuvbe et al. (2004) while carrying out similar research on African locust bean and melon reported an increase in moisture content.
Naturally and inoculated fermentation with Saccharomyces cerevisae give an increase in the crude protein value over the unfermented This might be due to reduction in crude fiber and carbohydrate in the unfermented. Another reason for the increase in protein content may be due to the structural proteins that are integral part of the microbial cells (Tortora et al., 2002). The apparent increase in growth and microbial proliferation of microorganisms in the form of single cell protein of the starter culture and the normal floral may account for the observed trend in crude protein (Oboh, 2006).
There was significant reduction in the crude fibre, fat and carbohydrate. The reduction may be attributed to the ability of the fermenting micro floral to hydrolyze and metabolize them as carbon source (substrate) in order to synthesize cell biomass (Madigan et al., 2002). There was no significant difference in the ash content between the fermented and unfermented locust bean sample. This was at variance with the report of Omafuvbe et al. (2004) that showed a reduction in the ash content. The disparity might be due to the processing of the seeds during fermentation; which involve boiling and dehulling in their own investigation whereas this stage was excluded in this study.
The mineral compositions of fermented, naturally fermented and inoculated fermented locust bean are presented on Table 2. Ascorbic acid value was shown to be reduced in the inoculated fermented sample than the unfermented. This may result from the ability of the starter culture to metabolize the ascorbic acid thereby leading to its reduction. The growth of the Saccharomyces may be an exothermic reaction which ultimately leads to increase in temperature. Ascorbic acid has been shown to be heat labile.
Phosphorus and magnesium were also found to be significantly reduced in both types of fermentation and the same reason for the ascorbic acid reduction may be advanced for the observed patterns. Also during the processing some of the minerals may be leached into the growth medium. Calcium and iron was found to increase in natural fermentation and that with inoculated culture. This may result from the insolubility of these mineral in water and hence could not be easily leached into the growth medium. It may also be that they are relatively heat stable.
The microbial count and pH of the three samples are shown on Table 3. The count was highest for the naturally fermented probably due to proliferation of microbial cells as a result of availability of essential nutrients and minerals in the seeds during processing. The inoculated fermented bean was also lower due to the boiling in order to eliminate the other microbial floral during the control fermentation. The unfermented has the least value because of unavailability of essential minerals that form the component of the seeds for metabolism and subsequent conversion to biomass.
The pH value revealed that the inoculated fermented beans are acidic whereas the unfermented was near neutral or slightly alkaline, respectively (Table 3). The acidity in the controlled fermentation may be due to the nature of Saccharomyces with respect to pH requirement for optimum growth which has been shown to be acidic (Madigan et al., 2002). The naturally fermented and the unfermented samples may be populated by organisms that may be predominatly bacteria which has been shown to thrive better at near neutral or alkaline pH.
The identities of the bacteria involved in the fermentation process were found to be Bacillu cereus, Bacillus subtilis Staphylococcus aureus and Lactobacillus plantanum. Fungi isolated and identified include Penicillium species, Aspergillus niger, Fusarium species and yeast. These isolates can be normal floral of the seeds or contaminants from the processor and environment during fermentation (Motarjemi, 2002). Similar organisms had been reported in earlier and similar work by Odunfa (1986) and Amoa-Awua et al. (2005).
Table 1: | Proximate composition of unfermented, naturally fermented and inoculated fermented locust beans |
Table 2: | Mineral composition of unfermented, naturally fermented and inoculated fermented locust beans (mg/100 g) |
Table 3: | Microbial count and pH of unfermented, naturally fermented and inoculated fermented locust beans |
From the study, the use of starter culture was shown to play important role in nutrient enhancement of African locust beans. There was significant increase in the amount of minerals from the naturally fermented and inoculated fermented over the unfermented locust beans. The research therefore demonstrated a strategy for optimal utilization of Africa locust beans for food and nutrition.
The author is grateful to Mr. A. Okafor of Biochemistry Department, Federal University of Technology, Akure, Nigeria for his technical assistance with the chemical characteristics.