| Research Article |
Open Access |
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| Microbial and Biochemical Changes Occurring During Production of Traditional Rwandese Banana Beer “Urwagwa” |
| Parawira Wilson*, Tusiime David and Binomugisha Sam |
| Department of Applied Biology, Kigali Institute of Science and Technology (KIST), Avenue de I’ Armee, B.P. 3900 Kigali, Rwanda |
| *Corresponding author: |
Wilson Parawira
Department of Applied Biology
Kigali Institute of Science and Technology (KIST)
Avenue de I’ Armee, B.P.
3900 Kigali, Rwanda
E-mail: parawiradr@yahoo.co.uk |
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| Received November 25, 2011; Accepted April 24, 2012; Published April 26, 2012 |
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| Citation: Wilson P, David T, Sam B (2012) Microbial and Biochemical Changes
Occurring During Production of Traditional Rwandese Banana Beer “Urwagwa”,
Ferment Technol 1:104. doi:10.4172/2167-7972.1000104 |
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| Copyright: © 2012 Wilson P, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited. |
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| Abstract |
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| Banana beer, urwagwa, is one of the oldest and major alcoholic beverages traditionally processed in Rwanda
produced mainly at homes as a family business. The banana beer is manufactured from fermentation of bananas
which is an important crop economically and culturally in Rwanda. The processing methods of urwagwa have not yet
improved and traditional methods are still in use. Microbial and biochemical changes that occur during production of
traditional Rwandese banana beer were investigated in this study. Understanding the microbiological and physicochemical
changes is essential in attempts to upgrade the traditional processing commonly used to commercial
scale. Banana ripening, extraction of juice from banana and fermentation to produce beer was done using modified
traditional methods. During fermentation to produce banana beer, total aerobic mesophilic bacteria, lactic acid
bacteria, yeast and molds increased with fermentation time. The presence of high numbers of yeast and lactic acid
bacteria (3.12 x 109 and 4.12 x 1013 cfu/ml, respectively) shows that the natural fermentation was a mixed alcohol and
lactic acid fermentation. Titratable acidity increased from 0.18 % lactic acid to 0.9 % lactic acid, pH decreased from
4.78 to 4.0, while alcohol concentration increased to 7% v/v after 72h fermentation time. These results give an insight
into the microbial and biochemical changes during traditional fermentation processes which is important in attempts
to upgrade it to pilot and commercial scale. The study could serve as a starting point for a scientific understanding of
the microbiological and physico-chemical processes in urwagwa production with the aim of improving the efficiency
of the production. |
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| Keywords |
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| Banana beer; Microbial changes; Traditional
fermentation; Biochemical changes |
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| Introduction |
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| The use of fermentation techniques is one of the oldest and
most economical methods of producing and preserving foods [1-3].
Fermentation has many advantages such as inhibition of growth of
spoilage and pathogenic microorganisms by producing organic acids
and other compounds, improving organoleptic properties by producing
different flavor compounds and often improving the nutritional value
of the original foods [1,4-6]. |
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| Fermented beverages constitute a major part of the diet of
traditional African rural and peri-urban homes, including Rwanda.
Home-brewed banana beer or urwagwa is used to signify hospitality,
to affirm bonds of social cohesion, and consumed in various social
functions such as birth, weddings, and traditional festivals [7]. Brewing
banana beer and cereal based beers for sale has increased economic
importance for households [8,9]. Production and sale of banana beer
provides additional family income, and may contribute significantly
to the level of monetary transactions in rural and urban areas. The
banana’s year round harvest assures a continuous source of food and
income. |
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| Banana is the second largest produced fruit after citrus,
contributing about 16% of the world’s total fruit production [10,11].
Rwanda is one of the major producers of bananas in the East African
Great Lakes Region. Banana cultivation occupies 23% of the country’s
arable land and contributes more than 50% of annual crop production
in terms of fresh weight [12]. Banana is both a food and cash crop for
most producers and therefore it is a key component of Rwanda’s food
security. Most banana production is on small family plots. A large
number of clones are grown, including the local East African highland
cooking and beer cultivars (AAA-EAHB) and introduced beer (AB,
ABB) and desert (AAA, AB) types. For the last 15 years, beer cultivars have dominated banana production (increasing from 67% to 71% at
the expense of dessert types) (Food Security Research Project, 2000,
unpublished). The proportions of different banana types within each
region and at each site are influenced by market opportunities, dietary,
preference, food security and the relative performance of the cultivars
across a range of criteria [13]. The beer bananas are the predominant
cultivars because they are favored by local farmers due to their higher
market value, agriculturally better suitability and resistance to pests
and diseases compared to cooking bananas [14]. Cooking bananas
are widely viewed as poorly adapted to withstand stresses such as
untimely rainfall, drought, declining soil fertility, intensive cropping
systems (e.g., intercropping) brought on by land pressure and reduced
management levels. Beer bananas having high astringency are not
consumed by cooking but used for making beer. |
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| Traditional banana beer is one of the oldest and major alcoholic
beverage produced in most East African countries and is given
different names in the different countries, for example it is called
Urwagwa in Rwanda, Tonto in Uganda [15], Mbege in Tanzania [16],
Urwaga in Kenya [3] isongo in Burundi [17]. It is mostly consumed on
three quarters of Rwandan territory, where banana growing is a major
agricultural activity. Urwagwa is mostly consumed in Kigali, Cyangugu,
Kibuye, Kibungo and Gisenyi districts. Banana beer (commonly called urwagwa) is produced from banana juice extracted from a variety of
local bananas and blended with sorghum flour. The common local
banana varieties used in making urwagwa are the harsh tasting Igikashi
and the milder tasting Kamara [18]. Banana beer is made in different
districts in Rwanda but is given different names like Urwedensiya,
Rwabitoki, Urwarimu and Birenge. There are many variations in how
the beer is made. For instance, urwagwa banana beer in Rwanda is made
from bananas juice and sorghum or millet flour. In Rwanda, Burundi,
Uganda, and Democratic Republic of Congo, beer is made from the
blended juice of “beer” bananas and other banana varieties. Sometimes
the juice is diluted with water (1:3 ratio or higher) to make a weaker
beer which is preferred by other people while others prefer a strong
beer made from undiluted juice. The banana beer from undiluted juice
is regarded as very special and has a higher price than that from diluted
banana juice. Some people prefer to drink the strained beer soon after
one day fermentation while others prefer the product which has been
fermented for more days. |
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| To carry out any meaningful research on traditional beverages,
the fundamental procedures used traditionally should be understood
[19]. The preparation of banana beer is still basically a family art that
is passed on from generation to generation orally. It involves ripening
of bananas, juice extraction, and blending with ground sorghum and
spontaneous fermentation to an orange, alcoholic beverage. The beer
is consumed in an actively fermenting state and therefore has a quite
short shelf-life. Banana beer is sweet and slightly hazy with a shelf life
of several days under correct storage conditions. The beer is consumed
unrefined, including unfermented substrates and microorganisms. The
average alcoholic content of banana beer ranges from 6 to 11%v/v and
depends on the production procedure, species of banana used, and the
dilution ratio and, in many cases, the weather, since there is no proper
mechanism to control the fermentation temperature [15]. It is liable
to substantial changes in composition brought about by the actively
metabolizing yeasts and lactic acid bacteria and other microorganisms
which can be present. The microorganisms continue to grow even
after acceptable levels of alcohol and lactic acid have been achieved. At
this stage the presence of the microorganisms is no longer desirable.
The short shelf life of banana beer and year round domestic demand
is met by brewing at regular intervals. The short-life of most African
fermented beverages is one of the major deterrents to their large-scale
production and development as commercial products [20]. |
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| Urwagwa manufacturing is artisanal and characterized by absence
of instrumental and analytical control like in most traditional alcoholic
beverages. The fermentation of urwagwa is conducted using traditional
materials, umuvure (woodened tanks), Ikibindi (clay pot), Ikidomoro
(plastic tank). Urwina is a place where the bananas are kept for ripening. |
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| The knowledge on banana beer production in Rwanda has not been
scientifically documented and is in danger of being lost as technologies
evolve and families move away from traditional food preservation
practices. The manufacture of this beer is generally done under poor
hygienic conditions which result in product with short shelf-life and
variable quality and low alcohol content. The quality of the banana beer
varies from one manufacturer to another and one brew to another. As
a result, the urban consumers consider it a backward or poor people’s
drink. In Rwanda, no scientific studies of banana beer have been done
on the microbiological and biochemical changes which occur during
the production of the product. This study was, therefore, aimed at
determining the microbiological and biochemical changes which occur
during traditional banana beer production in Rwanda. |
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| Materials and Methods |
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| Preparation of banana beer |
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| The preparation of urwagwa was done using “beer” bananas
collected from rural areas in Rwanda. The ripening of the bananas,
juice extraction and fermentation was done traditionally as practiced
by the rural people of Rwanda. |
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| Banana ripening: Unripe banana was harvested and carried to the
home to be ripened. The different types of banana used were Kamara
and Igikashi. All these types of banana were covered with grass and
green banana leaves in order to ensure warm temperature condition
which contributes a great role in ripening. The bananas were checked
on the sixth day to assess their state of ripening where a yellow color
and ease of peeling indicated the degree of ripeness. The state of
ripening is tested by peeling the bananas by hand. On the seventh day
the extraction of juice and its fermentation was commenced. |
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| Juice extraction: The ripened bananas were peeled by hand and
placed in a large wooden mortar, umuvure, and mixed with a special
type of spear-grass (Imperata cylindirica) to assist in juice extraction.
The grass was initially cut to lengths of about 30 cm. The preferred
grasses may differ from one region to another. The bananas mixed with
the grass were worked or squeezed by hand to extract the juice until all
the pulp was exhausted of juice. The juice was then strained with a sieve
and the juice was collected into another wooden mortar or umuvure. |
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| Fermentation: The collected juice was transferred into a 100-liter
plastic tank (Ikidomoro) and diluted two times. Roasted red sorghum,
which was coarsely crushed and ground, was added to the filtered juice
to improve the color and flavor of the final product. The juice/sorghum
mixture was left to ferment spontaneously at room temperature for 72
hours in the plastic tank. The product became sweet-sour with time.
The brewing was done in duplicate plastic containers. The process
of ripening bananas, juice extraction and fermentation of the final
product took about 9 to 10 days. |
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| Sampling: During fermentation a 50ml sample from each plastic
container was collected after every 12 hours for 72 hours. The pH of
each sample was measured immediately using a Mettler Delta 320
pH meter. Subsamples were collected for immediate microbiological
analysis. The remaining part of the sample was centrifuged for 10
minutes at 6000 g and a sample of the supernatant was immediately
analysed for titratable acidity. During fermentation a 50ml sample from each plastic
container was collected after every 12 hours for 72 hours. The pH of
each sample was measured immediately using a Mettler Delta 320
pH meter. Subsamples were collected for immediate microbiological
analysis. The remaining part of the sample was centrifuged for 10
minutes at 6000 g and a sample of the supernatant was immediately
analysed for titratable acidity. |
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| Microbiological Analyses |
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| Subsamples collected for microbiological analysis were diluted
using peptone water and spread in triplicate on different media. Total
aerobic mesophilic bacteria counts were made on plate count agar
(DIFCO) after incubation at 37°C for 24 hours. Lactic acid bacterial
counts were made on Man, Rogosa and Sharpe (MRS) agar (Oxoid)
after incubation at 37°C for 48 hours. Yeast and molds counts were
made on Rose Bengal Chloramphenical agar (SIGMA) after incubation
at 30ºC for 48 hours. |
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| Biochemical Analyses |
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| All assays were done in triplicate. Titratable acidity was measured
immediately. The supernatant (5ml) collected during fermentation was
transferred into a conical flask and diluted twice with distilled water.
The solution was titrated against 0.1M NaOH using phenolphthalein
as the indicator [1]. The amount of acid produced was calculated as
percent lactic acid according to the formula: |
| |
 |
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| Sugar content was determined as °Brix using a refractometer, (Bs
eclipse, Bellingham Stanley 45-02 company UK). One degree Brix is
equivalent to 1 gram of sucrose in 100 grams of solution and represents
the strength of the solution as percentage by weight (%w/w) (strictly
speaking by mass). The banana juice contained dissolved solids other
than pure sucrose, therefore the ºBrix was only an approximate of the
dissolved solid content as an indicative of the sugar content [21,22].
Alcohol content was measured by density measurement using
hydrometer (Jeffy Welty, USA). |
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| Results and Discussion |
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| Results of the microbial analyses done during the fermentation of
banana juice to urwagwa are shown in Table 1. There was an increase
in numbers of total aerobic mesophilic bacteria, lactic acid bacteria and
yeast and molds during the fermentation process. |
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|
Table 1: Change in microbial populations during fermentation of banana beer. |
|
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| Lactic acid bacteria, yeast and molds and aerobic mesophilic
bacteria were found growing together during the 72 hours fermentation
period, contributing to the characteristics of the final product, banana
beer, probably by producing organic acids, ethanol, carbon dioxide and
other volatile flavor compounds. According to Holzapfel [23], African
beers are typical examples of lactic acid fermentation followed by
alcoholic fermentation in which initially lactic acid bacteria and later
yeasts play a predominant role. A symbiotic relationship could explain
the presence of both yeasts and lactic acid bacteria in the banana beer,
with lactic acid bacteria creating an acid environment favorable to
the proliferation of yeasts. The yeasts produce vitamin and increase
other nutritional factors such as amino acids for the growth of lactic
acid bacteria [24]. The coexistence and free proliferation of lactic
acid bacteria and yeasts, as was observed in this study, is a common
occurrence in food and beverage fermentations [25]. Lyumugabe
et al. [10] have recently reported the prevalence of total aerobic
mesophilic bacteria, yeast and lactic acid bacteria from their study on
microbiological and physicochemical analysis of Ikigage, a traditional
malted sorghum beverage in Rwanda. Banana beer is a naturally
fermented beverage from banana juice; no starter culture is added
and rudimentary utensils are used during its traditional preparation.
The fermentation process to produce banana beer is by the age-long
method of chance inoculation and uncontrolled fermentation process.
Some of these microorganisms were probably derived from banana
juice, water, handlers, containers and some from the roasted sorghum
flour. Therefore, the usual variations in the quality and stability of the
urwagwa are not unexpected. |
|
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| The changes in sugar level during the fermentation process are
shown in Figure 1. The initial sugar level in banana juice was 19°Brix,
but sugar levels decreased with increase in fermentation time to
7°Brix. Fermentable sugars in banana juice are about 20-23% [26].
The main sugars in ripened banana fruit are glucose (19-22% of total
sugars), fructose (12-17% of total sugars), and sucrose (62-68% of total
sugars) [27]. Sugar content of fully mature ripened banana is quite
high and that makes it an ideal substrate for beer making. The initial
sugar level plays a significant role in the final alcohol content of the
product of fermentation [11]. The initial sugar levels can be improved
by improving the degree of ripening the bananas and improving the
juice extraction methods. The sugar level decreased with fermentation
time probably due to mainly microbes that acted upon the sugars to produce lactic acid and alcohol while they are deriving energy from the
sugars in the banana juice and sorghum mixture. The completion of
fermentation was indicated by leveling of the Brix level. |
| |
|
Figure 1: Changes in sugar concentration and alcohol content during
fermentation of banana beer. |
|
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| The final alcohol content in banana beer (urwagwa) was 7% (v/v)
(Figure 1). From a previous report [15] the alcohol content in tonto
(a banana beverage in Uganda) ranged from 6 to 11%v/v. Similar
findings were obtained by Singh et al. [28] on alcoholic banana
beverage production. According to Davies [9], a strong alcoholic
beer with 11 to 15% alcohol (v/v) can be obtained from banana juice.
The alcohol content of the final product depends on the production
procedure, species of banana used, the yeasts present, and the dilution
ratio and, in many cases, the weather, since the fermentation process
is done at ambient or room temperature without means to control the
fermentation temperature. Generally, there are enough yeasts belonging
to the genus Sacharomyces in the environment of fermentable sugars to
allow the fermentation to proceed [6,25] Changes in pH and titratable
acidity during fermentation of banana juice to produce banana beer
were investigated and are shown in Figure 2. Total titratable acidity
increased from 0.18 to 0.9 % lactic acid after 72 hours of fermentation.
This resulted in a decrease in pH from 4.78 to 4. The progressive fall
in pH and rise in titratable acidity (Figure 2) that occurred during
fermentation is characteristic of fermenting cereal grains [28]. For
example, [29] reported changes in pH from 6.10 to 3.98 and titratable
acidity from 0.13 to 0.67 during fermentation of mangisi, a traditional
cereal beverage in Zimbabwe. The increase in acidity could possibly
be due to the activities of lactic acid bacteria breaking down sugars to
produce lactic acid among other secondary products, resulting in the
sweet-sour taste which makes banana beer popular among the Rwandan
people. The microbiological and biochemical changes reported in this
study are characteristic of traditional fermentation based on cereals and fruits [4,7,15,30,31]. The presence of unspecified microorganisms
complicates the control of fermentation process and gives products of
variable quality. There is need to isolate, identify and characterize the
microorganisms involved in the production of urwagwa in attempts to
upgrade the traditional beer. Currently, the manufacture of this beer
is declining because of poor hygienic quality, short-life, poor yield of
ethanol and variations in organoleptic and hygienic quality. |
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Figure 2: Changes in pH and titratable acidity during fermentation of banana
beer. |
|
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| Conclusion |
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| The microbiological and biochemical changes during a traditional
preparation of banana beer, urwagwa, in Rwanda were investigated in
this study. The presence of high numbers of yeast and lactic acid bacteria
shows that the natural fermentation process is a mixed alcohol and
lactic acid fermentation. The results reported could serve as a starting
point to understand the microbiological and biochemical processes
in urwagwa production with the aim of improving the efficiency of
the process. Traditional fermented banana beer is produced at the
household level in Rwanda and the microbial and biochemical changes
have not been investigated before. |
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| Acknowledgements |
| |
| The authors would like to acknowledge the financial assistance from Student
Financing Agency for Rwanda (SFAR). We also acknowledge the assistance of
Mrs. Mukankwaya Bernadette (Nyirabyenga Ukwe), from Kigali for her knowledge
on the art of urwagwa preparation and to allow us to use her facilities at her home
to make the urwagwa beer. |
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