Reducing the atypical odour of dawadawa: effect of modification of fermentation conditions and post-fermentation treatment on the development of the atypical odour of dawadawa.

摘要

Dawadawa, an indigenous African alkaline fermented condiment has a distinct atypical odour which is often described as strong, pungent, and ammoniacal, but sometimes also as unpleasant, undesirable, objectionable, offensive. To improve the marketability of dawadawa, procedures capable of reducing the atypical odour were assessed. These were addition of humectants, NaCl (1.5 mol/kg) and glycerol (1.7 mol/kg), or irradiation by gamma radiation (2.5 kGy) partway through fermentation, and also steaming of the fermented product. The sensory profiles of the products were determined by Quantitative Descriptive Analysis (QDA). Changes in microbiological and chemical characteristics were monitored on Nutrient Agar, and by measurement of pH, titratable acidity, proximate composition, and elemental analysis by atomic absorption spectrophotometry. All treatments applied significantly reduced the population of Bacillus species and also pH during fermentation. The pH at end of fermentation for the control was 8.9, NaCl-treated sample 7.6, glycerol-treated sample 7.5, and irradiated-sample 7.3 indicating suppression of ammonia formation which is responsible for the rise in pH and pungent odour in dawadawa. Steaming for 25 min also resulted in loss of ammonia as indicated by slight reduction in pH from 8.8 to 8.3. Apart from the ash content, significant differences were observed in the concentration of protein, fat, carbohydrate, Fe, Mn, Zn, Na, K and Cu in most of the treated samples in comparison to the control. Odour descriptors generated by the semi-trained panel for dawadawa were ammoniacal, stink fish, faecal, urine, old smoked fish, marmite, shea butter, rancid palm kernel oil, corned beef, beany, and damp cocoa beans. In two sets of QDA, the control scored higher intensities for the undesirable descriptors, ammoniacal, faecal, stink fish and urine than the treated samples. In a difference from-control-test based on intensity of undesirable descriptors a semi-trained panel scored 5.61 for steamed-sample, 6.11 for irradiated-sample, 7.17 for NaCI-treated sample, and 7.5 for glycerol-treated sample on a scale of zero (no difference) to ten (extreme difference)