Evaluation of the nutritional composition in effect of processing cassava leaves (Manihot esculenta) using multivariate analysis techniques

Abstract Cassava leaves (Manihot esculenta) are used to prepare “manicoba”. Of indigenous origin, this dish is considered of high nutritional value for Brazilian cuisine. However, the leaves should be processed in order to eliminate the hydrocyanic acid that they contain. In this work, the centesimal composition, physical-chemical characteristics, micro (Cu, Mn, and Zn) and macronutrients (Ca, K, and Mg) were evaluated in cassava leaves cultivates in the State of Bahia, Brazil, according to different types of processing the leaves. The centesimal composition and physical-chemical characteristics were determined employing methodologies described by Adolfo Lutz Institute. The determination of the mineral composition was performed employing ICP OES, after microwave-assisted acid decomposition procedure of leaves samples. The accuracy of the method was confirmed by the analysis of spinach and apple leaves certified reference materials (NIST 1570a and NIST 1515) from the National Institute of Standards and Technology (NIST). Residual carbon content was evaluated by ICP OES. The samples were evaluated raw and after the cooking and fermentation processes. Losses of nutrients occurred after the cooking and fermentation processes. Average mineral concentrations in raw, cooked and fermented samples (in mg 100 g−1) were: 502.0, 487.6 and 458.4 for Ca; 40.1, 37.6 and 29.1 for Cu; 781.2, 180.9 and 57.8 for K; 150.3, 133.2 and 111.4 for Mg; 20.3, 18.8 and 15.7 for Mn; and 5.01, 4.64 and 4.02 for Zn. Average centesimal composition concentrations in raw, cooked and fermented samples (in % m m−1) were: 29.9, 12.2 and 11.1 for moisture content; 2.03, 0.66 and 0.54 for ashes; 10.2, 4.66 and 4.64 for proteins; 1.64, 1.88 and 1.07 for lipids; 56.3, 80.6 and 82.6 for carbohydrates; and 281, 358 and 359 for calorific value. Average physical-chemical characteristics values in raw sample were: 0.16–1.17% (titratable acidity); 5.91–6.41 (pH); 2.75–3.27 °Brix (soluble solids); 2.75–3.27 (ratio) and 4.53–38.7 mg 100 g−1 (vitamin C). The results were evaluated using multivariate analysis (PCA and HCA), in which there is a tendency of separation of the samples in groups, according to the treatment type that the samples were submitted.