The study was conducted in two towns of Burkina Faso (Figure 1), Ouagadougou (region du Centre) and Bobo Dioulasso (region des Hauts Bassins).

Tiger nut tubers and Tiger nut beverages were sampled aseptically at different retail sites in Ouagadougou and Bobo-Dioulasso. A total of 20 samples of tiger nut beverage and 12 samples of tiger nut tubers were collected.

Ten grams of each tiger nuts sample are collected aseptically in Stomacher bags and 90 ml of sterile saline solution (NaCl 9‰) are added and homogenized in a stomacher. For samples of tiger nut beverage, 10 ml of each sample are collected aseptically in a Stomacher bag and 90 ml of sterile saline solution (NaCl 9‰) are added and subjected to homogenization in a Stomacher. From these solutions, serial dilutions were made to obtain lower dilution solutions.

Culture and incubation conditions are given in Table 1.

For enumeration, the plates of two successive dilutions were considered and the number of microorganisms per ml of tiger nut milk or per gram of tiger nut tubers was calculated by applying the Equation (1).

N = ∑ ​ C V × ( n 1 + n 2 × 0.1 ) × d (1)

N: Total number of microorganisms (CFU/ml)

∑C: sum of colonies of Petri dishes of the two selected dilutions

V: volume of inoculum

d: dilution factor of the lowest dilution

n₁: Number of boxes of the lowest dilution

n₂: Number of boxes of the second dilution

The data were processed in Microsoft Excel. The Means and standard deviations were also calculated using Microsoft Excel.

The results of the microbiological analysis of tiger nuts samples are shown in Table 2. The total mesophilic load in dry tiger nuts is ranged between 1.5 × 10⁵ CFU/g and 6.0 × 10⁷ CFU/g with an average of 1.82 × 10⁷ CFU/g. Total coliforms were found in all the dry tuber samples analyzed up to 9.5 × 10² and 4.8 × 10⁵ with an average of 1.41 × 10⁵ CFU/g. Thermo-tolerant coliforms have also been found in samples of dry tubers in the load of 5.8 × 10² CFU/g and 2.5 × 10⁵ CFU/g with an average of 7.0 × 10⁴ CFU/g. The yeasts and mold load of dry tubers ranged from 1.2 × 10⁵ CFU/g to 1.2 × 10⁷ CFU/g with an average of 3.52 × 10⁶ CFU/g.

The rehydrated tiger nuts samples had a total mesophilic aerobic flora between 5.5 × 10⁵ CFU/g and 1.9 × 10⁷ CFU/g with an average of 4.86 × 10⁶ CFU/g. Rehydrated tubers have a load of total coliforms varying between 4.6 × 10³ CFU/g and 4.6 × 10⁵ CFU/g with a load of thermotolerant coliforms of 3.1 × 10³ CFU/g to 4.3 × 10⁵ CFU/g. yeasts and molds were counted up to 5.9 × 10¹ CFU/g and 2.6 × 10⁶ CFU/g with an average of 4.34 × 10⁵ CFU/g.

Table 3 presents the results of the microbiological analysis of the samples of tiger nut milk. The samples of Ouagadougou had a microbial load ranging between 5.5 × 10⁵ and 1.8 × 10⁸ CFU/ml with total coliforms ranging between 7.9 × 10² and 2.5 × 10⁶ CFU/ml, thermo-tolerant coliforms between 5.5 × 10² and 1.9 × 10⁶ CFU/ml and yeasts and mold between 9.8 × 10³ and 1.1 × 10⁶ CFU/ml.

The microbial load of the tiger nut milk samples collected in Bobo Dioulasso varied from 1.5 × 10⁵ to 8.9 × 10⁶ CFU/ml, total coliforms from 1.6 × 10³ to 3.4 × 10⁵ CFU/ml, thermo-tolerant coliforms from 5.7 × 10² to 2 × 10⁴ UFC/ml and yeasts and mold from 1.7 × 10³ to 2.3 × 10⁵ CFU/ml.

The average microbial loads of tiger nut milk samples from Ouagadougou were higher than those of samples from Bobo Dioulasso.

The results of microbiological analysis of tiger nuts samples are similar to those found by Ayeh-Kumi et al. [13] and Nyarko et al. [10] who have also reported an important mesophilic aerobic flora and coliforms in tiger nuts sold in Ghana. However, the aerobic mesophilic flora and the total coliforms in tiger nuts from the present study are very high compared to those of Ayeh-Kumi et al. [13] and Nyarko et al. [10] .

The presence of abundant microbial flora in the tubers and the tiger nut milk could be explained by the non-application of good manufacturing practices (GMP) by the processors. Poor post-harvest practices can be the source of microbial contamination of tiger nut tubers. During harvesting and drying the tubers are often in contact with the soil and can be contaminated by soil microorganisms. Thus, when good hygiene practices are not applied during the processing of tubers, these microorganisms can be found in the final product. The water used during processing can also be a source of microbial contamination.

The presence of a significant flora of coliforms may be due to fecal contamination or the sign of an uncontrolled sanitizing process. Certain coliforms are the cause of foodborne infections in the form of gastroenteritis and diarrhea. Yeasts and molds contaminate crops in the growing fields, during post-harvest treatments, or storage. They are usually the cause of food spoilage. However, certain molds (Aspergillus, Penicillium, Fusarium, etc.) produce toxins called mycotoxins (aflatoxins, ochratoxin, patulin, fumonisins, etc.) which can have various harmful effects on human health and farm animals (acute poisoning, deficiency immune system, cancer).