Caractéristiques microbiologiques et organoleptiques du nététu du commerce

Résumé

Netetu is a fermented product from African locust beans (Parkia biglobosa) . It is the most important food condiment in many African countries. Traditional netetu manufacturing procedures vary between regions. In this study, beans were boiled for 15-24 h until soft; cooked beans were pounded and then washed to remove tough fibrous testa from the seeds. The cotyledons obtained were then cooked for 30 min, and drained and cooled 1 h later. Cotyledons were left to ferment for 72 h in a warm room in order to obtain netetu. After fermentation, they were salted and sun-dried for 1 day (in Senegal) or sun-dried for 1 day prior to pounding, moulded into balls, cooked and then sundried (Mali). Three batches of netetu, produced in Guinea, Mali and Senegal, were purchased from a local market in Dakar to compare their microbiological and organoleptic characteristics. Differences were noted in their biochemical, microbiological and organoleptic characteristics. In Casamance (Senegal), the netetu drying process (38.3-49.1% moisture content) includes the addition of salt (22.6-23.2% NaCl), and the final product differs from netetus produced in Guinea and Mali, which are less moist (11.8-17.2% and 10.8-20.1% moisture content, respectively). There are also differences with respect to other parameters, e.g. protein, ash, lipid, crude fiber and calcium contents (Table 1) . The microflora of all types of netetu mainly contains Bacillus species (involved in the fermentation process), in addition to microflora that cause spoilage: Staphylococcus and Micrococcus (> 10 3 CFU/g), Clostridia sulfide reducers at 46° C (> 10 3 CFU/g) for 7 samples out of 9, Streptococci D (> 10 3 CFU/g) in 6 samples out of 9, and hydrogen sulfide-forming flora at 45° C (> 10 3 CFU/g) in all samples. Counts in 1 g of wet product were 1.3.10 7 -3.5.10 7 Bacillus spores at 30° C for netetu from Casamance, whereas the results in Guinean and Malian products were 1.0.10 5 -1.6.10 8 and 6.0.10 5-1.6.10 6 (Tables 2 and 3) . In organoleptic terms, the most serious microbiological spoilage is due to hydrogen sulfide (H2 S) production by H2 S +germs, which has a negative impact on netetu aroma (i.e. products from Guinea). After evaluation, all three types of netetu showed higher than mean (40) sensorial grades, i.e. around 42, 51 and 49 for products from Guinea, Mali and Senegal, respectively (range 8-42; Table 4 ). Commercial netetu purchased in a local market of Dakar was found to mainly contain sporulated Bacillus and other microflora that spoil the hygienic and organoleptic qualities of the product. This mixture of different flora is responsible for the complex metabolic chemistry of netetu, and for the sensorial qualities of this product as perceived by consumers. It is essential to define the optimal microbiological quality, critical points, and organoleptic criteria concerning netetu in order to improve this product. Further biotechnology studies are required to find a suitable starter so that the quality of the final produc and its marketing can be fully controlled.