A comparative study of the nutritional and microbial profiles of the raw and processed seeds of the African Locust Bean (Parkia biglobosa)

M Boateng, D B Okai, Y O Frimpong and C O Asabere

Department of Animal Science, Faculty of Agriculture, College of Agriculture and Natural Resources, KNUST, Kumasi-Ghana
mickyboat@gmail.com

Abstract

This study sought to determine the effects of the traditional system of processing on proximate components, minerals and microbial composition of African Locust Bean seeds (Parkia biglobosa). Six batches of African locust bean seeds (ALBS) were purchased from the open market in Kumasi and each batch was halved. One part was kept in its raw state and the other part processed into a fermented condiment called “Dawadawa”. Proximate, mineral and microbial analyses were done on the samples and results obtained were analysed using the one way analysis of varience described by Genstat statistical software.

Results obtained indicated that processing ALBS into Dawadawa increases the level of moisture, crude protein and ether extract but decreases carbohydrate, fibre and ash content. Processing of ALBS into Dawadawa also increased the sodium and phosphorus and resulted in a reduction in calcium, magnesium and potassium content. Processing of ALBS into Dawadawa further reduced its microbial count. Microbes isolated from both raw and processed ALBS were Bacillus spp, Aspergillus niger, A. flavus, A. tamari and Penicillium sp. whilst Mucor was isolated from the raw (unprocessed) ALBS. It was concluded that processing influences the nutrient and microbial composition of ALBS.

Keywords: Dawadawa, fermentation, minerals, protein-enrichment

Introduction

Though no scientific evidence exists to prove why certain foods are processed by certain traditional methods, there may be some actual reasons as to why some of these forms of processing are done. Processing according to Odunfa (1985) is important since it may help boost the nutritional composition, enhance the digestibility as well as reducing the levels of certain anti-nutrients within most plant products. Dawadawa, a strong smelling and sharp tasting condiment produced from the African locust bean seeds (ALBS), is a typical example of such forms of traditional processing.

African locust bean (Parkia biglobosa) trees are widely spread across West Africa and provide valuable food. Leakey (1999) intimated that Parkia biglobosa, a perennial deciduous tree produces pods which contain up to 30 seeds which are embedded in a yellow pulp. It has been stated (Odunfa, 1985; Omafuvbe et al 2004) that the processing of ALBS into Dawadawa gives the product not only its peculiar aroma which enhances the taste and smell of several traditional dishes but also results in reducing the level anti-nutrients and improving its digestibility and nutritional value (Odunfa, 1985).

Furthermore, there is a dearth of information on the effects of processing of ALBS into Dawadawa on its nutrient as well as microbial composition but it has been indicated (Akinyele and Akinlosotu 1991; Egounlety and Aworh 2003; Mugendi et al 2010; Osman 2011) that dehulling, soaking and fermentation may significantly influence the nutrient whilst improving the balance between salutary and morbific microflora. Thus, this study was carried out to investigate the effects of processing ALBS into Dawadawa on its proximate, mineral and microbial composition.

Materials and methods

Study location and source of ALBS

The study was conducted at the Department of Animal Science of the Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi. The ALBS used for the study were purchased from the open market in Kumasi.  

Treatments and design of experiment

Six batches of ALBS were acquired for this study. Each batch was divided into two parts; one part was processed into Dawadawa whilst the other part was not processed. Thus there were 2 treatments, which were unprocessed ALBS and processed ALBS or Dawadawa, in this study. The individual batches served as replicates.

Processing of ALBS into Dawadawa

One portion of the ALBS seeds obtained was washed and cooked in water at a temperature of 100^oC for 12hours. Water was topped-up occasionally to compensate for water lost through evaporation. After cooking, the water was strained away with the aid of a basket lined with a mesh. Seeds were then dehulled by pounding them in a mortar after which they were washed thoroughly with water and sieved in a colander to remove the hulls. The resultant dehulled seeds were then boiled for 5 hours at a temperature of 100^oC. The seeds were then fermented in a basket which was covered with jute sacks to enhance anaerobic conditions for 4 days. The fermented seed were pounded and sun-dried to obtain the final product called Dawadawa. Figure 1 is a summary of the processes involved in making Dawadawa.

Figure 1: Processing of ALBS into Dawadawa

Chemical analyses

Proximate composition of the 2 products was determined. Moisture, fat, ash, crude fibre and crude protein content of the unprocessed ALBS and Dawadawa were determined using methods recommended by the Association of Official Analytical Chemists (AOAC 1990), carbohydrate content of the samples was however determined by difference [% CHO = 100 –(% moisture + % fat + % ash + % crude fibre + % crude protein)] as described by Ijarotimi and Keshinro (2012). Potassium and sodium content were analyzed using a flame photometer (Sherwood model 360, Cambridge, England), whilst calcium and magnesium were analyzed with an atomic absorption spectrophotometer (UNICAM 939 model, Vassel, Germany). Phosphorus was analyzed using Technicon Auto-analyzer.

Microbial analyses

Quantitative data on the microbes and qualitative data on bacteria and fungi composition of both the raw and processed ALBS were determined. A four-fold serial dilution was done and 1 ml of the diluent was inoculated into a plate count agar (PCA) and allowed to incubate at a temperature of 37°C for 24 hrs. Colonies formed were counted using a colony counter. Fungal and bacteria cultures formed were identified using methods described by Atlas (1995).

Statistical analysis

The data obtained were analysed using the one way analysis of variance described by Genstat statistical package (2008). Confidence intervals were set at P < 0.05 using the Studentized Maximum Modulus (Stoline and Ury 1979).

Results and Discussion

Proximate composition

Processing resulted in differences in the proximate composition of ALBS. The processing of raw ALBS into Dawadawa significantly (P < 0.001) increased moisture, crude protein (CP) and ether extract (EE) (P=0.004) content but decreased (P < 0.001) the percentage composition of carbohydrates, crude fibre (CF) and ash (Table 1). The increase in the content of moisture can be attributed to the addition of water during the processing of the seeds. Furthermore, it has been indicated that moisture content may increase with metabolic activity of microbe since fermentation yields moisture (Omafuvbe et al 2004). Pelig-Ba (2009) also recorded increases in the moisture content of Parkia biglobosa seeds when they were fermented along with millet.

The increases in the percentage of CP and EE after soaking, dehulling and fermentation of ALBS agree with earlier works reported by Esenwah and Ikenebomeh (2008) and Pelig-Ba (2009) who explained that this may be due mainly to the decrease in the concentration of carbohydrates. Furthermore, Alabi et al (2005) reported that cellulose and fibre accounts for approximately 70% of testa and thus dehulling of seeds results in the reduction of carbohydrates as well as crude fibre. Adebowale and Maliki (2011) also observed increases in the CP and fat and reduction in the percentages of fibre and carbohydrates when Cajanus cajan seeds were fermented. Achi (2005), Alnahdi (2012), Kiers et al (2000), Nitschke and Pastore (2006) and Rolfe (2000) explained that Bacillus sp., one of the predominant microorganisms aiding in the fermentation of ALBS into Dawadawa produce several enzymes including amylase, fructofuranosidase, glucosidase and galactanase which degrade carbohydrates into simple sugars which may be leached-out or may be used as an energy source by the microorganisms. Water soluble sugars and minerals (ash) are said to be leached out during the soaking and boiling of the ALBS whilst fermentation further results in the utilization of some sugars by the microbes (Esenwah and Ikenebomeh 2008). Ijarotimi and Keshinro (2012) also indicated that the activities of some of these fermentative microbes can result in the increase in the CP content of fermented foods. Moreover, Odunfa (1981) intimated that some microbes are known to hydrolyse proteins into amino acids and peptides releasing ammonia as a by-product in the process. This process is said to increase the protein content of fermented food products. Morris et al (2004) further explicated that processes such as boiling soaking and fermentation may not only increase protein content but may improve the digestibility of proteins in food. It is withal noteworthy that the fact that fermentation resulted in about 36% (Table 1) loss in weight of dehulled seeds indicates that, the increase in the CP content cannot only be attributed to the enrichment of the seeds through microbial fermentation but also an increase in its concentration as a result of the loss of some carbohydrates. The reduction in CF content of ALBS after processing can partly be attributed to the activities of some enzymes released by the fermentative microbes which are noted to breakdown the fibre in food and feed substances (Rolfe 2000) into simple sugars which can be leached out or may be absorbed by microbes.

Mineral composition

The processing of ALBS into Dawadawa resulted in a reduction (P < 0.001) in the levels of calcium, magnesium and potassium but increased the levels of phosphorus (P < 0.001) and sodium (P = 0.005) (Table 2). Ajeibe et al (2012) reported decreases in the levels of phosphorus, potassium, calcium and magnesium but indicated that soaking and fermentation did not influence the concentration of sodium in Canavalia ensiformis seeds. The author (Ajeibe et al 2012) further explained that the diminution in the levels of most of the minerals may be due to leaching resulting from the soaking and boiling of the seeds during processing, the therefore justifies the reduction in ash stated earlier.

Severi et al (1997) citing several sources explained that potassium is the most sensitive mineral to this form of loss as it may be extracted into the water used for cooking. From this study, it was observed that more than 60% potassium was lost through processing. A similar work on taro (Colocasia esculenta, L.), reported significant reduction in minerals and attributed these losses to the fact that the supernatant from such forms of processing are normally discarded (Adane et al 2013).

Microbial composition

Processing resulted in a reduction (P = 0.001) in the microbial composition of ALBS (Table 3). Species of the bacteria; Bacillus and fungal species; Aspergillus niger, A. flavus, A. tamari and Penicillium sp. were isolated from both processed and unprocessed ALBS whilst Mucor was isolated from only the unprocessed seeds. Achi (2005), in a review on traditional fermented protein condiments indicated that bacteria predominantly found in Dawadawa include Bacillus sp., Staphylococcus saprophyticus and Leuconostoc sp. Bacteria isolated from fermented Lima beans (Phaseolus lunatus) by Tope (2013) included Bacillus sp., Staphylococcus aureus, Leuconostoc sp, Lactobacillus sp. and Proteus vulgaris while fungi species including Aspergillus, Geotrichum, Penicillium, Rhizopus and Saccharomyces were isolated.

It has been explained that though the boiling of the legumes meant to be fermented into these condiments may drastically reduce the quantity of microorganisms present in them, the microbes may be reintroduced into them through the hands of handlers, utensils, other materials being used for the processing and even from the air (Nwagu et al 2011; Tope, 2013). Achi (2005) on the other hand attributed the composition of microbes in traditional fermented condiments to the composition of the substrate and the hygiene of the environment during the preparation of the product. The decrease in the quantity of microbes present in the final product (Dawadawa), however, can be attributed to the fact that fermentation results in a change in pH which does not favour most non-fermenting and pathogenic microorganisms (Achi 2005).

Attention should be paid to the presence of the these microbes in the finished product (Dawadawa) since it has been reported that microbes like Bacillus, Aspergillus and Penicillium can contaminate food and lead to food poisoning (Ramanathan 2010). Furthermore, Aspergillus sp., for example, can be pathogenic and can cause Aspergillosis in birds and man (Pattron 2006). Again, some of these microbes may produce mycotoxins which are carcinogenic (Pattron 2006; Schuster et al 2012). Ramanathan (2010) therefore recommended that, proper cooking of food should be done when such condiments are being used. 

Conclusion

• It can be concluded from this study that, unprocessed ALBS and Dawadawa are all rich sources of nutrients but processing ALBS into Dawadawa increased crude protein, fat, moisture, sodium and phosphorus and decreased carbohydrate, fibre, calcium, magnesium and  potassium content. Soaking, boiling and fermenting ALBS reduced its microbial level. It will however be advisable if more work is done to establish the effects of processing on the anti-nutrient composition of ALBS.

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Received 2 August 2014; Accepted 8 September 2014; Published 3 October 2014

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