The Journal of Food Technology in Africa Vol. 9 No. 1, 2004, pp. 3-12
The Effects of Technological Modifications on the Fermentation of Borde, an Ethiopian Traditional Fermented Cereal Beverage
*Kebede Abegaz1,2, Thor Langsrud1, Fekadu Beyene2 and Judith A. Narvhus1
1 Department of Food Science, Agricultural University of Norway,
P.O.Box 5036, N-1432 Ås, Norway.
Code Number: ft04001
Four independent experiments were carried out to study the effect of modifying some steps in the technology of the four-phase traditional borde fermentation using malt and a mixture of unmalted cereals. When maize flour was substituted for maize grits in Phase I fermentation, the titratable acidity was greater throughout this phase and decreased after 24 h. Substitution with flour resulted in a higher yield, improved acceptability and extended keeping quality of borde. In addition, the wet milling at the last stage of the process could be omitted. When Phase I was omitted from the process, the starting pH at Phase II was much higher than when fermented maize from Phase I was used. Although the pH by the end of Phase II was comparable in both treatments, the borde made using fermented maize from Phase I was superior in all sensory attributes. Unmalted ingredients were heat treated in various ways and all methods were found to produce acceptable borde. However, borde from uncooked ingredients was totally unacceptable. An investigation on the effect of merging some phases of the fermentation showed that it is possible to prepare an acceptable borde using a simplified method of production. There were no marked variations in microbial load of borde from all the above treatments. It was found possible to shorten the duration and simplify the technology of borde fermentation with some variations in acceptability.
Keywords: food processing; traditional fermentation; cereal beverage, borde; Ethiopia
Traditional fermentation processes are increasingly attracting the attention of scientists and policy makers as a vital part of food security strategies (van de Sande, 1997). Traditional methods and age-old techniques of food processing are still used in developing countries especially in communities with lowincome levels. These countries require food-processing technologies that are technologically appropriate, suitable for their regions and affordable in rural and urban economies. Household-level fermentation is one such indigenous technology that has been developed for a wide range of foods and beverages from an extensive range of raw materials. However, the transformation of home-based arts into modern industries necessitates acquisition of scientific knowledge of the raw materials and processes used (Novellie and De Schaepdrijver, 1986) so that the problems involved in scaling-up can be addressed. In many African countries, cereal-based traditional fermented products (Lorri, 1993; Steinkraus, 1996; Bvochora, 1999 et al; Mahgoub et al., 1999) are consumed both as beverages and foods. Ethiopian borde is one of those types of beverage among others. The recommended research priorities on traditional fermented foods are improving understanding of the fermentation process; refining the processes; increasing utilization of the process and developing local capabilities (BOSTID, 1992).
Borde is produced using traditional fermentation technology from a variety of locally available cereal ingredients. The unmalted cereals and the malt may be from one or a mixture of cereals. The amount, types and combinations of malt (maize, barley, wheat, finger millet) vary within and between households on the basis of availability and preferences of cereals regardless of localities (Abegaz et al., 2002).
There is only limited published information on the fermentation and microbiology of borde in southern and central Ethiopia (Ashenafi and Mehari, 1995; Bacha, 1997). Contrary to both of these reports, however, the traditional processing technology of borde in southern Ethiopia has been shown to have four major phases (Abegaz et al., 2002). This process is time-consuming and inefficient. Borde production involves grinding, fermentation, roasting, steam cooking, boiling, cooling, mashing, wetmilling and wet-sieving operations. To improve the fermentation of borde, it is necessary to undertake basic studies on its traditional processing technology and quality characteristics. To our knowledge, there is no published information on the effects of various process factors on fermentation and yield of borde.
The objective of this work was, therefore, to investigate the effect of modifying selected techniques used in the traditional production of borde in an attempt to simplify the technology and reduce loss of residues. The effects of substituting maize grits with flour, fermentation at Phase I, various methods of cooking, and merging some phases of the main fermentation at Phase II, III and IV on acceptability of the product were investigated.
MATERIALS AND METHODS
Four independent experiments were carried out in duplicate and repeated three times at room temperature (21- 25&$176;C) as described in sections 2.1-2.3 below. In all the experiments, borde was prepared (at the Awassa College of Agriculture) from malt and a mixture of unmalted cereal ingredients by an experienced brewer using a modified traditional (MT) recipe. The modifications were substitutions of: 1) earthenware pot with plastic jar; 2) maize fermented for 48-72 h at Phase I with 24-48 h; and 3) 13-18% malt with 3% (Abegaz et al., 2002; Unpublished results). In addition, substitutions of: 1) flour for maize grits; 2) non-fermented flour for 24-48 h fermentation at Phase I (omission of Phase I); 3) only one or two merged phases instead of three main fermentation phases (Phase II, III and IV); and 4) the combination of roasting, steaming and boiling with only one type of heating in the whole process were carried out in the present work. The main equipment used were plastic jars, metal plate and pan, grinding stone, bowls and sieve (1 mm pore size). Samples for analysis were collected at 6 h intervals and/or the beginning and end of each phase. The microbial load, pH, titratable acidity (TA) and acceptability of borde were evaluated.
Treatment and proportion of ingredients
Borde was prepared using unmalted maize (Zea mays), sorghum (Sorghum bicolor) and mixed flour from wheat (Triticum sativum), finger millet (Eleusine coracana), tef (Eragrostis tef) and malt flour. The proportions (w/w) of unmalted ingredients used in all the experiments were, 2 maize: 2 a mixture of wheat, finger millet and tef: 1 sorghum. The heat treatments of unmalted cereal ingredients used and the preparation of malt are described by Abegaz et al. (2002). The malt was prepared from barley (Hordeum vulgare) and maize. All the unmalted ingredients were cooked at 90-98°C and cooled to 23-25°C before blending with malt flour and/or the fermenting mash at the appropriate phases of borde fermentation. Whenever flour replaced grits, roasting of enkuro (granular mass) was substituted by baking of kita (flat bread) at Phase II except experiment 2.3A below. The malt required in all treatments was calculated against the weight of grits or flour used in Phase I. Then 80% of the total required malt was added at Phase II and the rest at Phase IV. Except where otherwise stated, 3% barley malt (w/w) was used.
Phases of borde fermentation
The four phases of borde fermentation (Abegaz et al., 2002) are briefly described as follow:
A. Effect of substituting flour for
The production of borde was carried out according to the traditional process except that it was unnecessary to wet mill the fermenting mash of F at Phase IV. The fermenting mash of G was wetsieved and repeatedly wet-milled, while F was wet-sieved only once. It was found that Phase IV took four instead of the normal six hours when F was used (result not shown). The production process was therefore timed so that both G and F borde were ready for consumption at the same time. The yield of borde and the residue of G and F were compared.
B. Effect of omitting Phase I in
NF and NFP fermentations were initiated together with that of Phase II for the MT. The malt flour and cooked ingredients were blended with water at this step of each treatment. All the treatments were sieved once and the filtrate was left for 4 h fermentation at Phase IV.
C. Effect of merging some phases
of borde fermentation
D. Effect of using different cooking
methods in borde production
After cooling, the ingredients were blended with malt and/or fermenting mash at the appropriate phases and finally, the filtrate was fermented for 4 h at Phase IV.
pH and titratable acidity (TA)
RESULTS AND DISCUSSION
A. Effect of substituting flour for
grits in borde production
When cooled enkuro was blended with malt flour in Phase II (Fig. 2), the starting pH (4.3±0.1) of F fermentation was thereby lower (p<0.05) than the G (4.6±0.2). During Phase II, the decrease in pH of F fermentation was not as rapid as when G were used. This lower initial pH and extensive utilization of carbohydrates in Phase I are probably the cause of the retarded pH reduction during F fermentation in Phase II. The lower pH would result in slow malt amylase activity, thus producing less fermentable carbohydrates for the microorganisms. Carbohydrate degrading enzymes in malted and unmalted finger millet have an optimal range of pH 4.6- 6 (Nirmala et al., 2000). However, slower hydrolysis of starch occurred at low pH and then production of reducing sugar decreased gradually (Syu and Chen, 1997). The fermentation of G progressed to a lower pH 3.8 compared to pH 4.0 in that of the F at the end of Phase II. Although the grits would be expected to have less soluble carbohydrates in Phase I, more substrate may become available after cooking in Phase II. The fermentation of F showed the highest pH from 18 h at Phase II to the end of Phase IV and the highest TA throughout borde fermentation. The reduction of TA after 24 h F fermentation in Phase I and the low TA in G contrary to its low pH after 18 h in Phase II onwards need further study. The high pH at the start of G in Phase II (Fig. 2) and M3/M4 in Phase III (Fig. 4), owing to less acid production in Phase I, resulted in a faster reduction of pH than that of F and M2 respectively. However, the carried-over effect of acid from preceding to the succeeding phases would be possible to optimise by monitoring the progress of pH and TA in each phase.
The temperature of fermenting mash increased from 23.2±0.2 to 29±1.2°C with no significant difference between F and G fermentation. Both reached maximum at about 12 h in Phase III.
Both F and G resulted in actively fermenting acceptable borde. However, borde made from the F was preferred and had a significantly better (p<0.05) aroma and taste (Table 1A). It was also observed that the keeping quality of borde from F was at least 4 h longer than borde from G, which soon developed a vinegary aroma (results not shown). The repeated wet milling and wet sieving of intact grits at Phase IV could create additional surface area of the substrate and also allow microbial contamination. This may cause secondary fermentation and result in production of acetic and butyric acids that are detrimental to flavour (van der Merwe et al., 1964/ 65). Acetic acid bacteria commonly occurred with the most visible characteristics of vinegary flavour and off-odour in deteriorating traditional fermented cereal beverages (Sanni et al., 1999). However, the mean counts (log CFU mL-1) of AMC and yeast in borde from F (10.6±0.3 and 8.5±0.5) were not significantly different (NSD) from that of in G borde (10.3±0.5 and 7.9±0.6). EB were not detected in both cases, which would be due to the acidic fermentation. The new ingredients added at different phases may reduce the acidic stress and also replenish substrates for microbial growth in the fermenting mash of borde.
The substitution of grits with flour considerably improved the efficiency of borde production since the problems of unhygienic and tedious wet-milling, large loss of residue and low profit were resolved. The spent residue from G was 3.7±0.0.16 kg compared to 0.3±0.05 kg in F fermentation. Thus, the net yield (recovery) of borde increased from 70% to 97%. Improvements in aroma, taste and keeping quality were observed in borde made from flour.
B. Effect of omitting Phase I in
No significant differences (p<0.05) were found in microbial load, pH and TA of borde regardless of the methods of cooking and whether fermented or nonfermented flour was used. The AMC was 10-10.5, while yeast increased to 8.2- 8.5 (log CFU mL-1) in all treatments. All sensory attributes achieved significantly lower scores when maize was not fermented in Phase I before cooking (Table 1B). When borde produced using the two methods of ingredient cooking were compared (NF and NFP), NFP borde achieved significantly lower scores (p<0.05) for foaming and consistency. This could be a compounded effect of using non-fermented flour and cooking into porridge. The results show that the fermentation at Phase I is important for the sensory quality of borde. In the traditional fermentation, Phase II and IV are initiated by the addition of malt, fermented and non-fermented ingredients to the pot. The results show the magnitude of the effect of adding fermented ingredients on the initial pH. This is particularly marked at the start of Phase II, where the initial pH differed by 1.6 units between treatments. It may be expected that this difference in pH would have a far-reaching effect on the development of the microbial flora at this stage. At the starting pH 4.4, as observed for the MT, only aciduric organisms such as lactic acid bacteria and yeasts would be able to grow. In Phase III and IV, the drop in pH is very small since the initial pH is already so low that few microorganisms would be able to produce additional acid. The effect of omitting Phase I was much greater than using different cooking methods on the fermentation and quality of borde. However, borde produced by all the three treatments was acceptable.
C. Effect of merging some phases
in borde fermentation
C.1 Merging of Phase III and IV
C.2 Merging of Phase II, III and IV
or II and III
The effect of high inoculum from Phase II on the main fermentation in the consecutive phases was pronounced. This may explain the leading progress of MT and M1 in comparison to that of M2, M3 and M4 fermentation. The malt and porridge added to MT and M4 at the final phase resulted in higher pH as compared to M1 and M3 respectively. After sieving and then fermenting the filtrate for 4 h, the pH in M3 (3.97±0.02) borde was NSD (p<0.05) from MT (3.94±0.08) in contrast to M1 (3.77±0.1) and M4 (4.09±0.04). The pH of M2 was 4.06±0.06. The TA of MT (0.44±0.1), M1 (0.44±0.14), M2 (0.6±0.16), M3 (0.59±0.29) and M4 (0.57±0.15) borde were NSD (p<0.05). In all the treatments, AMC and yeasts were in the ranges of 9.9-10.5 and 7.4-8.4 (log CFU mL-1), respectively. Despite the low pH (3.97-4.09) in "young" borde, the incidence of EB (<1-2.7 log CFU mL-1) in 66% of M3 and M4 samples may raise the issue of safety. It is possible that a slightly longer fermentation would improve the microbial safety and ripening of borde.
The results of the sensory assessment showed that the MT and M1 treatments resulted in borde that were NSD except from a reduced foaming in M1 (Table 1C). This indicates that the addition of a small amount of malt and more ingredients (porridge) at Phase IV is responsible for the short active fermentation that revitalized the basic sensory attributes of borde. The MT borde was also judged as sweet-sour compared to sourer taste of M1. The other treatments produced a significantly inferior borde, although all products were acceptable (score >3). The foaming, aroma and taste of M2, M3 and M4 borde were judged to be markedly inferior to MT and M1. However, these products were described by the judges to be having an acceptable taste but were "too young". After extra 3-4 h fermentation, it was observed that M3 and M4 achieved all the sensory attributes of borde in contrast to M2. The low pH of 48 h FM from Phase I negatively affected the quality of M2 borde. The M3 was significantly better (p<0.05) than M4 in foaming and texture. It may be possible to improve the quality M3 and M4 borde by slightly extending the final fermentation stage and/or increasing the amount of malt inoculum. M3 and M4 had a total fermentation time of 46 h compared to 70 h for other three treatments (Figs. 1a, b, c, d). Among all these options, M3 could be suggested as a simplified technology for production of acceptable borde that may help for modernization. Further work should be done to improve these methods. Optimisation of the pH in Phase I, amount of inoculum and duration of the main fermentation in subsequent phases appeared to be vital for production of quality borde using these methods.
These results show that it is possible to shorten and simplify the traditional production technology of borde by merging some of the phases, and produce an acceptable borde. The 96±2 h (4 phases) traditional fermentation (unpublished results) could be reduced to 46 and 70 h (2-4 phases) as shown in Figs. 1a, b, c, d. Scientific improvements of traditional product processing have often led to changes in quality characteristics especially organoleptic (Demuyakor and Ohta, 1993). However, a possible method to overcome changes in product quality is to understand the process and formulation required to improve the traditional product using participatory approach as was tried in this work.
D. Effect of using different cooking
methods in borde production
The NC ingredients resulted in totally unacceptable product (Table 1D). However, regardless of using only one form of cooking or their combination, the aroma and taste of borde were similar to MT. The aroma, taste and also foaming are the major quality attributes of borde. The borde made using only baking, steaming or boiling of ingredients was highly acceptable since all products attained a score >4, except for foaming, which was inferior to MT. The results illustrate that although it is important for the quality of borde that the ingredients are cooked, using only one form of heat treatment could be applied for a simplification of the process. Thus, boiling of the ingredients is the simplest technological process to be suggested for borde production. It has the advantage of: (1) less charring effect and smaller loss, (2) less tedious postcooking operations, (3) being easier to blend and sieve and (4) less or no addition of water and this also reduces postcooking microbial contamination.
When all the products were heated for 30 min at 80°C water bath, the NC was baked into stiff paste, while others were remained liquid (data not shown). This could indicate that cooking is a critical parameter in the production of acceptable borde due to the fact that gelatinisation of the starch improves its degradation by endogenous enzymes mainly from the malt. All the methods of cooking used in this work (90-98°C) would gelatinise cereal starch and inactivate enzymes and vegetative cells. However, the addition of malt at Phase II serves as sources of amylases and fermenting microbes for production of acceptable borde (unpublished results).
From this study and other basic works described by Abegaz et al. (2002; unpublished results), the traditional technology of borde production from gelatinised main ingredients and malt inoculum appeared to be developed consciously in an attempt to control the safety of borde using an acidic fermentation. The rationale of this technology reveals that: (1) the acid produced in Phase I creates acidic environment to the main fermentation that inactivates unwanted micro flora and selects for aciduric organisms. (2) The cooking of unmalted ingredients gelatinises the starch and eases its saccharification with malt amylases. (3) The use of only 16% of the total unmalted ingredients and 80% of the total amount of malt required indicates the attempt to select and attain high number of fermenting microorganisms mainly from the malt in Phase II. (4) Blending the "bulk starters" from Phase II (tinsis) and 56% of the total unmalted ingredients without malt at Phase III (difdif) indicates the major acidic fermentation of borde. (5) Addition of the remaining malt and 28% of the total unmalted ingredients in the form of porridge into the sourer difdif at the start of Phase IV eases the homogenisation and sieving processes. Thus, the malt liquefies the thick mash, reduces the bulk density and sweetens the end product (borde). It seems that the complexity of traditional technology of borde production is aimed at a step-by-step controlling of the bio-physico-chemical process parameters so as to get benefit from the merits of fermentation on safety and quality of the product.
In conclusion, the traditional method for production of borde is technologically complex, which does not readily lend itself to larger production volumes or to the introduction of production equipment. From the results of the experiments reported in this study, the opportunity for the simplification of the process has been observed: (1) Flour may be substituted for grits and whole grains. This modification resulted in a well-accepted borde, a less laborious process without wet milling and a reduction in residues from the final sieving that increased the net yield of borde. In addition, the fermentation proceeded faster than when grits were used and this may necessitate a slight adjustment of the times of the various phases. (2) Merging of the phases of borde process resulted in products that were acceptable, although organoleptically slightly inferior, which may require optimisation of the pH in Phase I, amount of inoculum and time of the main fermentation. A simplification of the process entailing a reduction of the number of fermentation phases would be advantageous. However, since products with a shortened total fermentation time showed the presence of EB, it may be possible to produce microbiologically safe borde by a shortened process only if all the ingredients are heat-treated and starter cultures are added. (3) Cooking of unmalted ingredients is a limiting step than omitting Phase I fermentation in the production of borde. Acceptable borde could be prepared by boiling the unmalted ingredients added after Phase I. This method could be readily adapted to small-scale production units.
The authors acknowledge the Norwegian Universities Committee for Development Research and Education (NUFU) for sponsoring this work. This work was carried out in the context of a North-South-South (NSS) program 26/96 "Research and development of indigenous fermented foods for small scale commercial processing in East and southern Africa" in collaboration with Agricultural University of Norway, Norway and Awassa College of Agriculture, Debub University, Ethiopia. We would like to thank Mrs. Warite Alambo for the traditional brewing of borde. The assistance of Wendosen Tadesse is highly appreciated.
Copyright 2004 - The Journal of Food Technology in Africa, Nairobi
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