Fermentation induced changes in volatile components of African oil bean (Pentaclethra macrophylla Benth) seeds

Abstract Fermented African oil bean (Pentaclethra macrophylla Benth) seed also referred to as “Ugba” is a known delicacy, mainly consumed by Africans. Human migration has also led to the introduction of this delicacy into most European and American countries. This study shows the changes in volatile components of African oil bean (P. macrophylla Benth) seed at different stages of fermentation. A quantity of 0.3 kg each of dehulled and sliced raw sample and cooked unfermented sample were separately ground, while 2 and 4 days fermented samples obtained by inoculating 0.6 kg of cooked, sliced and washed sample with 0.5 g of 4 days fermented seed was divided into two of 0.3 kg each and ground at the second and fourth day of fermentation. GC‐MS analyses of the volatile components showed 9,12‐Octadecadienoic acid (Z,Z)‐ and its esters as highest in raw seed, with total percentage concentration of 96.301, while 9‐Octadecenoic acid, methyl ester, (E)‐ was highest in cooked unfermented seed, with percentage concentration 55.204. Phenol, 2‐methoxy‐3‐(2‐propenyl)‐ and its esters were the highest observed in cooked 2 days fermented seed, with total percentage concentration of 50.596, while 9‐Octadecenoic acid (Z)‐, methyl ester was highest in cooked 4 days fermented seed with percentage concentration of 67.788. Aside from softening the delicacy, a 4 days chance fermentation of cooked P. macrophylla Benth seed also reduces the eight component lipids present in the cooked unfermented seed to a more nutriceutical three component lipids (Hexadecanoic acid methyl ester, 9‐Octadecenoic acid (Z)‐methyl ester and Methyl stearate).

its esters as highest in raw seed, with total percentage concentration of 96.301, while 9-Octadecenoic acid, methyl ester, (E)-was highest in cooked unfermented seed, with percentage concentration 55.204. Phenol, 2-methoxy-3-(2-propenyl)-and its esters were the highest observed in cooked 2 days fermented seed, with total percentage concentration of 50.596, while 9-Octadecenoic acid (Z)-, methyl ester was highest in cooked 4 days fermented seed with percentage concentration of 67.788. Aside from softening the delicacy, a 4 days chance fermentation of cooked P. macrophylla Benth seed also reduces the eight component lipids present in the cooked unfermented seed to a more nutriceutical three component lipids (Hexadecanoic acid methyl ester, 9-Octadecenoic acid (Z)-methyl ester and Methyl stearate).

K E Y W O R D S
fermentation, Inoculation, Nutritive properties, Therapeutic properties, Volatile components

| INTRODUCTION
Africans and other locals from developing countries usually practice a traditional fermentation method which involves a spontaneous development of different lactic acid producing bacteria. However, the unavailability of lactic acid bacteria starter cultures for small-scale processing of local African foods necessitate the adoption of the old traditional method of using a portion of a fermented food product to start a new fermentation batch. This traditional method of microbial seeding also referred to as chance inoculation, in principle resembles the modern starter culture method. In chance inoculation, the initial microbial consortia of the starter raw materials influence the microbial consortia of the fermented product. Fermented African oil bean (P. macrophylla Benth) seeds also referred to as "Ugba" is a known delicacy that is mainly consumed in the southern part of Nigeria especially by the Ibos and other ethnic groups. Human migration has also led to the introduction of this delicacy into most European and American countries. Though oil bean seed is mainly composed of proteins (42%), lipids (43%) and carbohydrates (15%) (Njoku & Okemadu, 1989;Ogueke & Aririatu, 2004), studies on the microbiology of its fermentation identified Bacillus spp (Bacillus subtilis) as the main fermenting organisms (Odunfa & Oyewole, 1986). Other species such Bacillus pumilus, Bacillus megaterium, Bacillus lichenformis have also been identified in the fermentation process (Diawara, Sawadogo, Amoa Awua, & Jaobsen, 1998;Odunfa & Oyewole, 1986). The improved taste and palatability of this delicacy after 3 to 4 days of fermentation indicates that the process is not only of lactic acid fermentation but also reduces the anti-nutrients, enhances the aroma and possibly alters the lipid composition of the product. The aim of this work is to determine the volatile components that are present in fermented African oil bean seed (Ugba) at different stages/days of fermentation.  of a 4 days fermented P. macrophylla Benth seed. At the second day of fermentation, a quantity of 0.3 kg of the fermenting sample was ground and the volatile oil was extracted and analyzed to give a 2 days fermented sample, while the remaining 0.3 kg was ground at the 4th day and the volatile oil was extracted and analyzed to give a 4 days fermented sample.

| GC-MS analysis of P. macrophylla Benth oil
A hundred gram each of the ground samples of P. macrophylla Benth seed paste was added to 3 dm 3 of distilled water. The oil obtained by hydro-distillation was collected into hexane and the solution was concentrated by evaporation at room temperature.
The oil was analyzed using a combined gas chromatograph model

| RESULTS
The chromatogram of the volatile components of raw, cooked unfer-

| DISCUSSION
The result of this study shows a progressive decrease in both the number and structural complicity of the volatile components of fermented P. macrophylla Benth seed. The high percentage concentration of 9,12-Octadecadienoic acid (Z,Z)-and its esters in the raw seed reveals the hidden nutritional potential of P. macrophylla Benth seed. As an essential polyunsaturated omega-6 fatty acid, 9,12-Octadecadienoic acid (Z,Z)-is required for a proper health as its deficiency has been reported to cause scaling of skin, hair loss (Cunnane & Anderson, 1997), and poor wound healing in rats (Ruthig & Meckling-Gill, 1999   hexadecanoic acid on human cancer (Pascual et al., 2016), the high concentration 9-Octadecenoic acid (Z)-, methyl ester in this fermented food may have a counter effect on the metastasis-inducing potential of hexadecanoic acid. The consumption of the salt of 9-Octadecenoic acid (Z)-, methyl ester (oleate) has been reported to decrease breast cancer in women (Teres et al., 2008). This anti-cancer effect of 9-Octadecenoic acid (Z)-, methyl ester (observed in higher concentration) may have a pronounced antagonistic effect on the metastasisinducing potential of hexadecanoic acid. As a monounsaturated omega-9 fatty acid, 9-Octadecenoic acid (Z)-, methyl ester (oleic acid) consumption has been associated with an increased concentration of high-density lipoprotein (HDL) and a concomitant decrease in lowdensity lipoprotein (Martin-Moreno et al., 1994). This indicates that fermented P. macrophylla Benth seed may be useful in the treatment and management of high blood pressure. A high percentage concentration of methyl seterate (methyl ester of octadecanoic acid) was also observed at the fourth day of fermentation. The bifunctional ability of the polar head group of this compound to attach metal cations and the solubility of its nonpolar chain in organic solvent makes it a notable surfactant and a softening agent. This may be responsible for the increase in softness and enhanced emulsification of fermented P. macrophylla Benth seed in palmitic oil as fermentation time increases.

| CONCLUSION
Aside from softening the delicacy, a 4 day chance fermentation of cooked P. macrophylla Benth seed also reduces the eight component lipids present in the cooked unfermented seed to a more nutriceutical three component lipids (Hexadecanoic acid methyl ester, 9-Octadecenoic acid (Z)-methyl ester and Methyl stearate).