Effect of Pretreatment on an Unconventional Tuber, Nzolo (Solenostemon rotundifolius), Cultivated in the Congo
Fanny Belgonde Ganongo-PO *
UNESCO CHAIR, Industrial Process Engineering Laboratory, Marien NGOUABI University. P.O. Box 69 Brazzaville, Republic of Congo and UNESCO CHAIR, Laboratory of Molecular and Sensory Food Engineering, Marien NGOUABI University. P.O. Box 69 Brazzaville, Republic of Congo.
Ernest Bitemo
National Institute for Research in Exact and Natural Sciences (INRSEN), Scientific City, Brazzaville, Republic of Congo.
Bertin Mikolo
UNESCO CHAIR, Industrial Process Engineering Laboratory, Marien NGOUABI University. P.O. Box 69 Brazzaville, Republic of Congo and UNESCO CHAIR, Laboratory of Molecular and Sensory Food Engineering, Marien NGOUABI University. P.O. Box 69 Brazzaville, Republic of Congo.
Jean Mathurin Nzikou
UNESCO CHAIR, Industrial Process Engineering Laboratory, Marien NGOUABI University. P.O. Box 69 Brazzaville, Republic of Congo and UNESCO CHAIR, Laboratory of Molecular and Sensory Food Engineering, Marien NGOUABI University. P.O. Box 69 Brazzaville, Republic of Congo.
*Author to whom correspondence should be addressed.
Abstract
The tuberous roots of Nzolo (Solenostemon rotundifolius) are cultivated in some West African countries and in the Republic of Congo for their edible, energy-rich tubers. However, this food remains relatively little known, and little research has examined its characterisation. This study therefore examines the influence of pretreatment on the physicochemical characteristics of Nzolo tubers. Three sample groups were examined: one control and two thermally pretreated by blanching at 90°C and cooking at 100°C for 10 minutes. The calibration results showed that the lengths of small, medium, and large tubers were 2.2 ± 0.3, 3.0 ± 0.2, and 4.0 ± 0.4, respectively. The diameters were 1.5 ± 0.3, 1.7 ± 0.4, and 2.2 ± 1.2. The weights were around 2.9 ± 1.3, 5.0 ± 2.0, and 9.4 ± 6.4. The moisture content was higher in the precooked sample (75.97 ± 1.62%) than in the blanched sample (69.99 ± 3.58%). Ash content was lower in the precooked sample (0.94 ± 0.09%) than in the blanched sample (1.23 ± 0.12%). A similar pattern was observed for crude fat and total carbohydrate contents, with values of (0.51 ± 0.01% and 16.49 ± 1.40%) for the precooked sample and (1.02 ± 0.01% and 21.98 ± 0.12%) for the blanched sample. For trace elements, the results showed a very significant increase in calcium values in the thermally pretreated samples: 23.6 mg/kg in the blanched sample and 12.3 mg/kg in the precooked sample compared to 7.1 mg/kg in the raw sample. Iron and zinc did not show any apparent difference. Moreover, pretreatment did not have a significant effect (P <0.05) on protein content, pH, and titratable acidity.
Keywords: Nzolo (Solenostemon rotundifolius), unconventional tuber, pretreatment, effect, Congo