Variation B-carotene content and physicochemical properties of orange-fleshed sweet potato (Ipomoea batatas (L.) Lam) cultivars grown in Limpopo Province, South Africa

Abstract

In recent years, there has been a lot of interest in orange fleshed sweet potato (OFSP) [Ipomoea batatas (L.) Lam] cultivar, as a cheaper source of vitamin A. In Southern Africa, reports have shown that one in every three children has deficiency in vitamin A. This study investigated the variations in β-carotene (vitamin A precursor) content among selected OFSP cultivars grown in Limpopo Province, South Africa. In addition, the study investigated the effects of location on functional properties, total carotenoids and antioxidant profile of the sweet potato flour as well as their physicochemical, functional and nutritional properties. Four (4) sweet potato cultivars [Dagga, Bophelo, Impilo (orange fleshed) and Mvuvhelo (cream fleshed)] were obtained from two locations, namely, University of Venda (Univen) agricultural experimental farm and Tshiombo irrigation scheme (Tshiombo) and analysed for pasting, functional, physicochemical and nutritional properties. The sweet potato flours from these two locations were also analysed by computed tomographic (CT) scans for flour particle density. Mineral and microstructure of OFSP flours were analysed by scanning electron microscope (SEM). All measurements, except the tristimulus L* a* b* and other colour parameters from five replicates, were performed in triplicate. Statistical analysis was performed using a one-way analysis of variance and means were separated using Duncan’s multiple range test; P < 0.05 was considered to be statistically significant. Pearson’s correlation coefficients were used to determine the correlation among functional, physicochemical, nutritional and pasting properties of sweet potato flour. β-carotene content varied significantly between the two locations from 70.98 ± 0.8 μg/g (Tshiombo) to 86.09 ± 2.0 μg/g (Univen), among cultivars from 1.71 ± 0.0 μg/g (Mvuvhelo) to 201.50 ± 1.0 μg/g (Dagga) and among orange fleshed (Dagga, Bophelo and Impilo) flours from 28.38 ± 0.2 μg/g (Impilo) to 201.50 ± 1.0 μg/g (Dagga). There was a similar trend in the contents of α-carotene to that of β-carotene from the two locations, which ranged from 0.63 ± 0.0 mol/L (Tshiombo) to 1.01 ± 0.0 mol/L (Univen). Mvuvhelo had significantly the lowest α-carotene content (0.50 ± 0.0 mol/L) and Impilo the highest (1.28 ± 0.0 mol/L). The total carotenoids was highest for Impilo (7.56 μg/g) and lowest for Mvuvhelo (1.33 ± 0.1 μg/g) but did not vary significantly (P > 0.05) between ii the locations. The antioxidant activity, based on 2, 2-diphenyl-1picrylhydrazyl (DPPH) free radical scavenging activity, was significantly highest in Bophelo (63.37 ± 0.8 mMAAE ml-1) and lowest in Dagga (26.93 ± 1.4 mMAAE ml-1) flours. The ferric reducing antioxidant power (FRAP) varied significantly across the locations and among the cultivars and ranged from 14.45 ± 0.3 μMTE ml-1 (Tshiombo) to 17.40 ± 1.1 μMTE ml-1 (Univen). FRAP was significantly highest in Impilo (21.12 ± 2.1 μMTE ml-1) and lowest in Mvuvhelo (8.16 ± 2.0 μMTE ml-1). Total carotenoid content positively correlated with DPPH (0.486*), FRAP (0.830**), β-carotene (0.370*), and α-carotene (0.424*). The antioxidant content and the radical scavenging activity were significantly correlated (0.563**). Vitamin A content was significantly lowest (6.88 ± 0.38 μg/g retinol) in Dagga flour and highest (7.97 ± 0.25 μg/g) in Impilo flour. Protein content varied significantly across the two locations and ranged from 4.23% (Tshiombo) to 7.16% (Univen). Dagga had significantly the lowest (3.47%) protein content while Impilo had the highest (7.53%). The fat content of the flours varied significantly between the two locations ranging from 0.63% (Tshiombo) to 1.01% (Univen). The protein content was positively correlated 0.594** and 0.421* to vitamin A and fat contents respectively. The Bophelo colour luminosity was significantly lower (L* 76.2) than the other two OFSP, Dagga (L* 83.51) and Impilo (L* 82.07). Bophelo a* (14.09) also differed significantly across all sweet potato cultivars. All cultivars differed significantly in b* values. Colour intensity (ΔE*) ranged from 15.87 to 38.48 for Mvuvhelo and Bophelo, respectively. Chroma ranged from 87.52 to 84.95 for Dagga and Mvuvhelo respectively. Total starch content was significantly different in all sweet potato cultivars and ranged from 244.07 μg/100 g (Bophelo) to 325.04 mg/g (Dagga). Resistant starch differed significantly in all sweet potato cultivars ranging from 1.21 μg/100 g dwb (Bophelo) to 7.07 μg/100 g dwb (Impilo). Ash content was significantly different in all cultivars and ranged from 3.17% (Dagga) to 3.79% (Bophelo). Water holding capacity (WHC) varied significantly across the two locations and ranged from 1.44 g H2O/g DM (Tshiombo) to 1.72 g H2O/g DM (Univen). Bophelo had significantly the lowest (1.27 g H2O/g DM) WHC and Impilo the highest (1.99 g H2O/g DM). The ash content negatively correlated to total starch (-0.928**) but positively iii correlated to WHC (0.654**). Peak viscosity differed significantly across all cultivars under study and ranged from 126.54 RVU (Bophelo) to 302.36 RVU. (Dagga). There was significant difference in trough viscosity across all cultivars ranging from 55.97 RVU (Impilo) to 280.78 RVU (Dagga). There were significant differences in the final viscosity across all cultivars ranging from 78.99 RVU (Impilo) to 319.26 (Dagga). Peak time viscosity varied significantly across all cultivars ranging from 3.87 min (Impilo) to 8.47 min. (Bophelo). Dagga cultivar had significantly the highest pasting temperature (94.16oC) and Bophelo the lowest (77.75oC). The setback viscosity was significantly highest 51.10 RVU (Mvuvhelo) and lowest 23.01 RVU (Impilo). All cultivars from the two locations consistently showed high potassium content ranging from 0.46% (Impilo) to 1.38% (Dagga) as compared to other minerals such as magnesium, calcium and chlorine which ranged from 0.16% (Impilo) to 0.34%. (Dagga). The CT scans revealed that there was a possibility of evaluating the effect of location on the density of granules of sweet potato flour and also the inherent differences in granular distribution of various sweet potato cultivars. SEM revealed high amounts of potassium, magnesium and chlorine. A profile of physicochemical and functional properties of flour of some of the OFSP cultivars produced in Limpopo province, South Africa has been drawn. This study also highlights the nutritional quality of the flour from four sweet potato cultivars and provides a ranking of flour to help the producers in the selection process. Bophelo flour was ranked the highest in terms of β- and, α-carotenes, total carotenoids and antioxidant capacity while Impilo was ranked highest in terms of functional properties and ash content. This study has highlighted significant differences in a number of parameters measured among the sweet potato cultivars. Therefore, in order to derive the maximum benefit from aIn recent years, there has been a lot of interest in orange fleshed sweet potato (OFSP) [Ipomoea batatas (L.) Lam] cultivar, as a cheaper source of vitamin A. In Southern Africa, reports have shown that one in every three children has deficiency in vitamin A. This study investigated the variations in β-carotene (vitamin A precursor) content among selected OFSP cultivars grown in Limpopo Province, South Africa. In addition, the study investigated the effects of location on functional properties, total carotenoids and antioxidant profile of the sweet potato flour as well as their physicochemical, functional and nutritional properties. Four (4) sweet potato cultivars [Dagga, Bophelo, Impilo (orange fleshed) and Mvuvhelo (cream fleshed)] were obtained from two locations, namely, University of Venda (Univen) agricultural experimental farm and Tshiombo irrigation scheme (Tshiombo) and analysed for pasting, functional, physicochemical and nutritional properties. The sweet potato flours from these two locations were also analysed by computed tomographic (CT) scans for flour particle density. Mineral and microstructure of OFSP flours were analysed by scanning electron microscope (SEM). All measurements, except the tristimulus L* a* b* and other colour parameters from five replicates, were performed in triplicate. Statistical analysis was performed using a one-way analysis of variance and means were separated using Duncan’s multiple range test; P < 0.05 was considered to be statistically significant. Pearson’s correlation coefficients were used to determine the correlation among functional, physicochemical, nutritional and pasting properties of sweet potato flour. β-carotene content varied significantly between the two locations from 70.98 ± 0.8 μg/g (Tshiombo) to 86.09 ± 2.0 μg/g (Univen), among cultivars from 1.71 ± 0.0 μg/g (Mvuvhelo) to 201.50 ± 1.0 μg/g (Dagga) and among orange fleshed (Dagga, Bophelo and Impilo) flours from 28.38 ± 0.2 μg/g (Impilo) to 201.50 ± 1.0 μg/g (Dagga). There was a similar trend in the contents of α-carotene to that of β-carotene from the two locations, which ranged from 0.63 ± 0.0 mol/L (Tshiombo) to 1.01 ± 0.0 mol/L (Univen). Mvuvhelo had significantly the lowest α-carotene content (0.50 ± 0.0 mol/L) and Impilo the highest (1.28 ± 0.0 mol/L). The total carotenoids was highest for Impilo (7.56 μg/g) and lowest for Mvuvhelo (1.33 ± 0.1 μg/g) but did not vary significantly (P > 0.05) between ii the locations. The antioxidant activity, based on 2, 2-diphenyl-1picrylhydrazyl (DPPH) free radical scavenging activity, was significantly highest in Bophelo (63.37 ± 0.8 mMAAE ml-1) and lowest in Dagga (26.93 ± 1.4 mMAAE ml-1) flours. The ferric reducing antioxidant power (FRAP) varied significantly across the locations and among the cultivars and ranged from 14.45 ± 0.3 μMTE ml-1 (Tshiombo) to 17.40 ± 1.1 μMTE ml-1 (Univen). FRAP was significantly highest in Impilo (21.12 ± 2.1 μMTE ml-1) and lowest in Mvuvhelo (8.16 ± 2.0 μMTE ml-1). Total carotenoid content positively correlated with DPPH (0.486*), FRAP (0.830**), β-carotene (0.370*), and α-carotene (0.424*). The antioxidant content and the radical scavenging activity were significantly correlated (0.563**). Vitamin A content was significantly lowest (6.88 ± 0.38 μg/g retinol) in Dagga flour and highest (7.97 ± 0.25 μg/g) in Impilo flour. Protein content varied significantly across the two locations and ranged from 4.23% (Tshiombo) to 7.16% (Univen). Dagga had significantly the lowest (3.47%) protein content while Impilo had the highest (7.53%). The fat content of the flours varied significantly between the two locations ranging from 0.63% (Tshiombo) to 1.01% (Univen). The protein content was positively correlated 0.594** and 0.421* to vitamin A and fat contents respectively. The Bophelo colour luminosity was significantly lower (L* 76.2) than the other two OFSP, Dagga (L* 83.51) and Impilo (L* 82.07). Bophelo a* (14.09) also differed significantly across all sweet potato cultivars. All cultivars differed significantly in b* values. Colour intensity (ΔE*) ranged from 15.87 to 38.48 for Mvuvhelo and Bophelo, respectively. Chroma ranged from 87.52 to 84.95 for Dagga and Mvuvhelo respectively. Total starch content was significantly different in all sweet potato cultivars and ranged from 244.07 μg/100 g (Bophelo) to 325.04 mg/g (Dagga). Resistant starch differed significantly in all sweet potato cultivars ranging from 1.21 μg/100 g dwb (Bophelo) to 7.07 μg/100 g dwb (Impilo). Ash content was significantly different in all cultivars and ranged from 3.17% (Dagga) to 3.79% (Bophelo). Water holding capacity (WHC) varied significantly across the two locations and ranged from 1.44 g H2O/g DM (Tshiombo) to 1.72 g H2O/g DM (Univen). Bophelo had significantly the lowest (1.27 g H2O/g DM) WHC and Impilo the highest (1.99 g H2O/g DM). The ash content negatively correlated to total starch (-0.928**) but positively iii correlated to WHC (0.654**). Peak viscosity differed significantly across all cultivars under study and ranged from 126.54 RVU (Bophelo) to 302.36 RVU. (Dagga). There was significant difference in trough viscosity across all cultivars ranging from 55.97 RVU (Impilo) to 280.78 RVU (Dagga). There were significant differences in the final viscosity across all cultivars ranging from 78.99 RVU (Impilo) to 319.26 (Dagga). Peak time viscosity varied significantly across all cultivars ranging from 3.87 min (Impilo) to 8.47 min. (Bophelo). Dagga cultivar had significantly the highest pasting temperature (94.16oC) and Bophelo the lowest (77.75oC). The setback viscosity was significantly highest 51.10 RVU (Mvuvhelo) and lowest 23.01 RVU (Impilo). All cultivars from the two locations consistently showed high potassium content ranging from 0.46% (Impilo) to 1.38% (Dagga) as compared to other minerals such as magnesium, calcium and chlorine which ranged from 0.16% (Impilo) to 0.34%. (Dagga). The CT scans revealed that there was a possibility of evaluating the effect of location on the density of granules of sweet potato flour and also the inherent differences in granular distribution of various sweet potato cultivars. SEM revealed high amounts of potassium, magnesium and chlorine. A profile of physicochemical and functional properties of flour of some of the OFSP cultivars produced in Limpopo province, South Africa has been drawn. This study also highlights the nutritional quality of the flour from four sweet potato cultivars and provides a ranking of flour to help the producers in the selection process. Bophelo flour was ranked the highest in terms of β- and, α-carotenes, total carotenoids and antioxidant capacity while Impilo was ranked highest in terms of functional properties and ash content. This study has highlighted significant differences in a number of parameters measured among the sweet potato cultivars. Therefore, in order to derive the maximum benefit from a given cultivar careful selection of sweet potato cultivars would be necessary.