Ogueri Nwaiwu

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http://dx.doi.org/10.5772/intechopen.79958

#### **Abstract**

Sequences from three palm wine yeast genera namely *Saccharomyces cerevisiae*, *Pichia kudriavzevii*, and *Candida ethanolica* were analyzed to establish their phylogenetic relationships, geographical origin, and food matrix source of their close relatives. Up to 600 sequences present in yeasts representing close relatives of palm wine yeasts were examined. Pyhlogenetic trees constructed showed polyphyletic relationships in *C. ethanolica* whereas close relatives of *S. cerevisiae* and *P. kudriavzevii* showed little- divergence. Sequence data for both *Elaeis* sp. and *Raphia* sp. palm trees showed that highest number of palm wine yeasts relatives sequence submissions to the Genbank were from China and beverages were mainly the sources of close relatives of *S. cerevisiae*  and *P. kudriavzevii* whereas *C. ethanolica* closest relatives were from various non-food sources. Overall relatives of palm wine yeasts were not specific to any particular food or- fermentation mix. The guanine-cytosine (G+C) content in *P. kudriavzevii* (57–58%) and *C. ethanolica* (56–57%) was higher than that of *S. cerevisiae* (47.3–51%). This suggests that the *P. kudriavzevii* and *C. ethanolica* have a higher recombination rate than *S. cerevisiae*  strains analyzed. The data may help to understand palm wine yeast conservation and the diverse food matrixes and geographical origins where their close relatives exist.

**Keywords:** yeasts, phylogeny, *Saccharomyces cerevisiae*, *Pichia kudriavzevii*, *Candida ethanolica* 

## **1. Introduction**

Palm wine is a traditional drink consumed mainly in sub-Saharan Africa, parts of Asia, and South America. It is obtained from fermentation of saps of different palm trees. Palm wine is- sourced from palm trees and they grow throughout tropical and subtropical regions with just a few species found in temperate regions possibly due to freeze intolerance of seedlings [1]. The method of obtaining the drink by tapping has been described in many reports [2] and the

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palm sap varies according to palm trees found in different geographical location. Yeasts are- the main organisms implicated in the fermentation of the drink and they exist as natural flora- on palm trees. Irrespective of the palm tree source, a common feature of the drink is that it goes sour within 24 h unless it is subjected to cold storage. The two trees from which palm wine is mostly tapped in Nigeria are *Raphia hookeri* and *Elaeis guineensis*. There is a debate on the possible origin or source of these palm trees. The tree *Raphia hookeri* is known as the wine palm and is the most widespread familiar Raphia palm in fresh water swamps of west and central Africa [3]. Many local varieties exist in the tropical rain forest of Nigeria and it is also grown in India, Malaysia, and Singapore [4]. The *E. guineensis* oil palm variety is more widely found around the world. A report pointed out that *E. guineensis* palm tree originated in the tropical rain forest region of West Africa and can be found in Cameroon, Côte d'Ivoire, Ghana, Liberia, Nigeria, Sierra Leone, Togo Angola, and the Congo [5]. It is believed in the report that during the fourteenth to seventeenth centuries, some palm fruits were taken to the Americas and from there to the Far East where it thrived. Yeast are known to reflect human history [6] hence it is possible the yeast strains found in palm wine were introduced to new regions via the plant materials introduced in those locations.

Although it is known that yeasts have been used for food and beverage fermentations [7] hundreds of years ago and domestication is believed to have been initiated before the discovery of microbes [8], the extent of genetic diversity is still under study around the world. Recent reports have shown that non-*Saccharomyces* yeasts have different oenological properties to those of *S. cerevisiae* [9]. Other reports emphasize that even though biochemical and genomic studies of *S. cerevisiae* have helped our understanding of yeasts, the other lesser known yeast species have not been fully exploited [10]. More understanding of *S. cerevisiae* and non-*S. cerevisiae* yeasts in palm wine is needed [11] in order to get more information on the capabilities of yeasts present in the drink or to probe for novel species [12]. To generate more information, molecular characterization has been used by many investigators and this has led to proper identification- of new yeast strains in the drink. The diversity of yeasts from palm wine has not had much in-depth investigation and reports that show evolutionary trees which are the basic structures necessary to establish the relationships among organisms [13] are few in literature. This chapter examines evolutionary relationships of palm wine yeasts and their close relatives based on 26S rRNA sequence data and aims to shed more light on the diversity of yeasts found in the drink.
