J . Sci. Food Agric. 1982, 33, 555-558

Effect of Moisture Content on the Development of Carboxylic Acids in Traditional Maize Dough Fermentation

W. A. Plahar and Henry K. Leung

Department of Food Science and Technology, Washington State University, Piillman, Washington 99164, USA

(Manuscript received 21 July 1981)

Maize dough samples containing 45, 52, 65 and 80% initial moisture were fermented over a 3 day period, and the rate of development of carboxylic acids was determined. The desired volatile: non-volatile acids ratio of 0.16, titratable acidity of 2.4 mg NaOH g-l sample, and pH of 3.7 could be achieved with only the 52% moisture samples. A slow rate of acid production and an early onset of mould growth was observed in samples with 45% moisture. The 65 and 80% moisture samples developed high concentrations of acids with resultant high degree of sourness. Acetic, propionic and butyric acids were the major volatile acids in samples with moisture contents over 52 %.

1. Introduction

Maize (Zea mays) is used for various food preparations in many African countries, mainly in the form of a sour dough or mea1.l For example, Nigerian Ogi is prepared with a thin slurry of sieved wet-milled maize grains.2 The traditional maize dough preparation involves the general steps of steeping maize grains for 24 h, milling, mixing into a dough with water, and fermenting spontaneously for 3 days to attain the desired degree of s o ~ r n e s s . ~ However, this method is not standardised and wide variations exist in the consistency of dough prepared for fermentation.

Plahar and Osei-Yaw4 reported that the moisture contents of samples of fermented maize dough from Ghanaian markets ranged between 46 and 64%, with a correspondingly wide range of acidity. In an earlier report, Banigo5 correlated dough acidity with acceptability. Other workers have sub- sequently established the major fermentation products and the relative percentages required for the typical flavour and taste of the dough. Lactic, acetic, and butyric acids were identified as the most important carboxylic acids produced during maize dough fermentation.6 Previous studies, however, have not examined the effect of moisture content on acid development of the dough.

The purpose of this study was to determine the effects of initial dough moisture content on the development of these carboxylic acids during a 3 day period of spontaneous fermentation. The percentages of the volatile acid components were compared with established values for accept- ability.

2. Materials and methods 2.1. Materials Shelled American yellow corn (normal dent) obtained from a local store was used throughout this study for preparing the maize dough samples. All milling operations were performed with a laboratory-size disc attrition mill with a split-phase motor (Model 4E, The Straut Co., Philadelphia, USA).

0022-5142/82/06O0-0555 1802.00 (0 1982 Society of Chemical Industry

555

556 W. A. Plahar and H. K. h u n g

2.2. Preparation of maize dough samples An adaptation of the traditional Ghanaian process for fermented maize dough preparation was used. Selected whole maize kernels were steeped in distilled water (200 g litre-1) for 24 h at 28°C and the steeped grains milled to 85 mesh particle size. Samples of dough containing 45, 52, 65 and 80 % moisture were prepared from the meal by kneading or mixing with the appropriate amount of water (,based on the initial meal moisture content) until a smooth dough or slurry was formed. Triplicate samples were placed in large beakers and left to ferment spontaneously at 30°C for 3 days. Samples were taken daily from each moisture group for analysis.

2.3. Analysis Titratable acidity and pH were determined according to AACC method^.^ The volatile: non- volatile acids ratio was determined by steam distillation and alkali titration of acidified water extracts as described by Akinrele.1 The non-volatile acid component was calculated as lactic acid.

To separate and determine the volatile carboxylic acids in the samples, steam distillates of acidi- fied water extracts (100 g litre-l) were made alkaline with 1~ NaOH and evaporated to about 10 ml on a steam-bath. The concentrated extracts were acidified with 0 . 5 ~ HzS04. The total volume was recorded and 2-pl aliquots were analysed on a gas chromatograph (Model HP 5840A, Hewlett Packard) equipped with a flame ionisation detector. The column was a 1.7 m x 2 mm diameter glass tube packed with 5% neopentyl glycol sebacate and 1 % phosphoric acid on 90-100 mesh Anakrom A (Analabs, Inc., North Haven, Connecticut, USA), operated at 95°C with helium as the carrier gas (206 kPa). Injection and detector temperatures were 200 and 300"C, respectively. The concentrations of acetic, propionic and butyric acids were determined using standard solutions of these volatile fatty acids.

3. Results and discussion

The pH and titratable acidity of the dough samples during fermentation are given in Table 1. The rates of acid production observed in the 45 % moisture samples suggest that maize dough with low initial moisture content as used in this study cannot attain the desired pH of 3.7 reported by Banigo and Mullera for Nigerian Ogi. Rapid mould growth was favoured at this low moisture content. This situation was responsible for the exclusion of the more favourable activity of bacteria and yeasts.

Table 1. Effect of moisture content (45-80%) on the pH and titratable acidity OF maize dough

Fermentation PH period (days) 45 % 52 y4 65 ;(, 80 76

0 6 . 0 6 . 0 6 . 0 6 . 0 I 4 . 2 4 . 2 4 .1 4 . 1 3 4 . 8 3 . 7 3 .8 3 . 6 3 3 . 9 3 . 7 3 . 8 3 . 6

Titratable acidity (mg NaOH g-' sample)"

0 . 7 0 . 7 0 . 7 0 . 7 2 . 4 2 . 2 2 .1 1 . 8 1 . 4 2 . 5 3 . 4 4 . 7 1 .7 2 . 2 2 . 8 4 . 5

" Expressed on a 50% moisture basis.

More satisfactory results were obtained with the 52% moisture samples. The drop in pH from the initial 6.0 to 3.7 after the second day of fermentation, and the corresponding increase in titratable acidity from 0.7 to 2.2 mg NaOH g-l sample (expressed on a 50% moisture basis) are consistent with acceptable values for the traditional Ghanaian corn dough4 and the Nigerian Ogi.s The relatively high acidity in the 65 and 80% moisture samples renders the product too sour to be acceptable.

In general, increasing the initial moisture content of the maize dough tends to increase the rate of acid development. The relatively poor relationship between pH and the corresponding increase

Fermented maize dough 551

Table 2. Effect of moisture content on the development of acetic, propionic, butyric and lactic acids in maize dough"

Moisture Fermentation content period

(%) (days) -

45 0 I 2 3

0 1 L 3

0 I

3 0 I 2 3

7

Lactic acid (YO

0.15 0.57 0.23 0.30 0. IS 0.48 0.80 0.42 0. I5 0.46 0.69 0 57 0.15 0.34 I .01 0.92

Acetic acid (?A)

0.010 0.052 0.032 0,062 0 010 0.058 0.103 0 064 0 010 0.060 0.041 0 052 0 010 0.101 0 087 0.141

Butyric acid

(mg kg-l)

0 18 0 0 0

40 30 44

0 93 50 33 0 0 0

164

Propionic acid

(mg kg-l)

0 31 41 I I 0

30 40 51

0 100 30 42 0 0

134 I23

Volatile: non-volatile ratio

0.10 0.14 0.38 0.26 0.10 0. I4 0.13 0.16 0.10 0.07 0.11 0.10

0.10 0.22 0.10 0.18

Expressed on a 50",1 moisture basis.

in titratable acidity in some of the samples may be due to the buffering effect of soluble proteins on pH change.

Development of individual carboxylic acids and the volatile : non-volatile acids ratios are given in Table 2. The reported values are means of triplicate samples with standard deviations of about 10-15 %. The main volatile acid components of fermented samples with moisture contents above 50% were acetic, propionic and butyric acids. No butyric acid was detected in the 45 % moisture samples. In the 80% moisture samples, propionic and butyric acids were not detected until the second and third days of fermentation, respectively. In contrast with the findings by Banigo and Muller,G propionic acid was produced in concentrations comparable with butyric acid in all of the samples. Differences in processing techniques may be responsible for this trend. The relatively low propionic acid content reported in Nigerian Ogi could be due to the steep water discarded after fermentation.6

The volatile: non-volatile acids ratios for the 52% moisture samples are similar to acceptable values.6 Higher ratios observed in the 45 and 80% moisture samples may be unacceptable. On the other hand, the relatively high lactic acid (non-volatile) component in the 65 % moisture samples caused low volatile: non-volatile acids ratios.

In conclusion, the desired rate of acid development to attain an acceptable degree of sourness and the correct ratio of volatile: non-volatile acids can be achieved with an initial dough moisture content of 52%. Different conditions may, however, be required when starter cultures are used to increase the rate of fermentation.

Acknowledgements The authors thank Dr Clark Brekke and Dr Cecilia Leung for their suggestions and technical assistance, respectively.

References I .

2.

Akinrele, 1. A. Fermentation studies on maize during the preparation of a traditional African starch-cake food. J. Sri. Food Agrir. 1970, 21, 619-625. Muller, H. G. Traditional cereal processing in Nigeria and Ghana. Ghana J. Agric. Sci. 1970, 3, 187-191.

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Muller, H. G.; Nyako-Mensah, B. Studies on Kenkey, a Ghanaian cereal food. J. Sci. Food Agric. 1972. 23, 544-545. Plahar, W. A,; Osei-Yaw, A. Chemical and Organoleptic Characteristics of Traditionul Market Samples of Corn Dough Food Research Memo, Food Research Institute, Accra, Ghana, 1978. Banigo, E. 0. I. An Incestigation into the Fernrentation and Enrichment of Ogi PhD Thesis, University of Leeds, 1969. Banigo, E. 0. 1.; Muller, H. G. Carboxylic acid patterns in Ogi fermentation. J. Sci. Food Agric. 1972, 23, 101-111. American Association of Cereal Chemists. AACC Approced Mcthods St Paul, Minnesota, USA, 1969 3rd edn. Banigo, E. 0. I . : Muller, H. G. Manufacture of Ogi: Comparative evaluation of corn, sorghum and millet. Can. Inst. Food Sci. Trihnol. J. 1972, 5, 217-221.