CHAPTER ONE

INTRODUCTION

1.1              Background of the study

Palm wine is a fermented traditional beverage consumed in many parts of the world and well known as a white colored alcoholic drink. The drink is known by different names around the world (Santiago-Urbina and Ruíz-Terán, 2014) and is regarded as a heavy suspension of yeasts in fermenting palm sap (Okafor, 2007). Even though palm wine is consumed around the world and plays an important role in the economic and social life of the people, palm wine has not been comprehensively evaluated for quality improvement and possible exploitation of the biological and chemical constituents or byproducts (Ouoba, Kando, Parkouda, Sawadogo-Lingani, Diawara and Sutherland, 2012). The methods for tapping palms have been reported (Dalibard, 2016). According to the report, the techniques are numerous, varies drastically from one continent to another and sap yields may depend on the skills of the tapper. It was noted that in Ghana incision of stem apex of felled palm is preferred, whereas in Nigeria excision of male or female inflorescence is carried out to initiate sap flow, which is collected in a gourd or plastic container. The report pointed out that tapping the inflorescence is practiced throughout Southeast Asia and that the most advanced method of tapping is believed to be tapping applied to the inflorescence spadix, which guarantees a high yield of sap for long periods without affecting the well-being of the tree. Yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB) are the most reported microbial constituent in literature and the species Saccharomyces cerevisiae is normally the main organism of interest because it is mainly responsible for converting the sugary sap to alcohol. Palm wine drinkers know that the drink tastes differently at different stages of fermentation as a result of yeast fermentation and accumulation of organic acids especially acetic acid from fermentation by AAB as fermentation progresses each day (Amoa-Awua, Sampson and Tano-Debrah, 2007). It is common knowledge that palm wine fermentation consists of an initial lactic acid fermentation by lactic acid bacteria, a middle alcoholic fermentation by yeasts followed by a final acetic fermentation by acetic acid bacteria and the general consensus among other investigators is that the nature of fermentation depends on the composition of sap, type of palm tree and location of the tree (Ezeronye and Legras, 2009).

Most palm wine tappers in South East Nigeria get their palm wine from three types of palm trees namely, the palm oil tree Elaeis guineensis or Raphia palms, namely Raphia hookeri and Raphia vinifera (Okafor, 2007), and the flavor or aroma of palm wine obtained from Elaeis sp. is somewhat different from that of Raphia sp. To the best of the knowledge of the authors, the drink sourced from trees in Imo State area have not been subjected to current analytical methods (HPLC, APCI-MS and GC-MS) to generate more information. However, volatiles (Uzochukwu, Balogh, Tucknott, Lewis and Ngoddy, 2009) from the southwest region and odorants [8] of palm wine from E. guineensis sourced from other regions in Nigeria have been studied and it was found that no one compound is responsible for the characteristic palm wine odor. Odorants responsible for the intense aroma qualities perceived upon sample introduction into the mouth, while swallowing the drink and nasal aroma perception have been reported (Lasekan, Buettner and Christlbauer, 2007) but quantification of the intensity of the main compounds responsible for the intense odor of fermenting palm wine in the atmosphere is yet to be explored by many workers. To improve taste of palm wine during fermentation in southeastern region of Nigeria, the bark of a local plant Sacoglottis gabonensis known locally as Nche can be added as a supplement to preserve Raphia sp. palm wine (Elijah, Ojimelukwe, Ekong and Asamudo, 2010). Reports of toxicity to humans on consumption of palm wine containing the supplement are rare, but it has been reported that intraperitoneal administration of doses ranging from 400–3200 mg/kg aqueous extracts in rats produced varying degrees of toxicity that included depression, drowsiness, unsteady gait, paralysis of hind limbs, coma and death (Kuete, 2014). A holistic mechanism of palm wine preservation with the supplement showing the exact compounds in palm wine reduced or biochemical pathways involved has not been reported. Preservation may be aided by reduction in pH which has been reported to be due to the production of lactic acid and acetic acid by LAB and AAB. Reduction of pH for samples supplemented with S. gabonensis has been shown earlier by other investigators (Faparusi and Bassir, 2009). Current commercial production of bottled palm wine in Nigeria has failed to reproduce a drink with exactly the same flavor characteristics of the fresh local drink and in most labels on bottled palm wine, the nutritional composition showing quantities of other compounds apart from alcohol are not displayed. A better understanding of the palm wine fermentation products is needed to encourage the commercial exploitation of the numerous aroma found in the drink and enable quality and taste consistency across the various bottled commercial palm wines currently produced. Up to the time of this work the products of Nigerian palm wine have not been compared to the compounds listed by Jewison et al (2012) in the yeast metabolome database (YMDB). Therefore, the aims of this study were to evaluate the products of yeasts fermentation that contributes to the flavor of palm wine, establish if the equivalent compound produced is held in the yeast metabolome database and ascertain the effect of S. gabonensis supplement on the fermentation products of palm wine

1.2              Statement of the problem

Scholars have investigated the occurrence of yeast flora during tapping and fermentation of palm wine. The yeast diversity was investigated using both traditional culture-dependent and culture-independent methods. Moreover, to characterize the isolates of the predominant yeast species (Saccharomyces cerevisiae) at the strain level, primers specific for delta sequences and minisatellites of genes encoding the cell wall were used. The results confirm the broad quantitative presence of yeast, lactic acid bacteria and acetic acid bacteria during the palm wine tapping process, and highlight a reduced diversity of yeast species using both dependent and independent methods. Together with the predominant species S. cerevisiae, during the tapping of the palm wine the other species found were Saccharomycodes ludwigii and Zygosaccharomyces bailii. Because of the central role that the alcoholic beverage has played in the traditional society, it is important that the microbiology and biochemistry of the fermentation process are well understood. However, there is a limit to the number of studies carried out in this context. Hence, the need for this study.

1.3              Objective of this study

The general objective of this study is to investigate the chemical composition of palm wine samples at difference stages of fermentation.

Specific objectives of this study are:

1.      To examine the chemical composition of palm wine samples at difference stages of fermentation

2.      To assess yeasts present in palm wine samples at difference stages of fermentation

3.      To investigate the lactic acid bacteria present in palm wine samples at difference stages of fermentation

4.      To examine the acetic acid bacteria present in palm wine samples at difference stages of fermentation

1.4              Research questions

1.      What is the chemical composition of palm wine samples at difference stages of fermentation?

2.      Are there yeasts present in palm wine samples at difference stages of fermentation?

3.      Does lactic acid bacteria present in palm wine samples at difference stages of fermentation?

4.      Does acetic acid bacteria present in palm wine samples at difference stages of fermentation?

1.5              Significance of the study

Yeasts, lactic and acetic acid bacteria are all important in the fermentation of palm wine and influence the composition of the product.

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