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ARTICLE ORIGINAL ORIGINAL PAPER
Effect of processing and preservation on the iron and vitamin A (total carotenoid)
levels of some species of Vernonia
R. A. Ejoh
1*, A. N. Tanya, V. N. Djuikwo and C. M. Mbofung
RÉSUMÉ
Effet de la transformation et de la conservation sur les niveaux de fer et de vitamine A (caroténoïdes totaux) chez des espèces de Vernonia
Le Vernonia, généralement connu comme ndole ou Bitterleaf dans la plupart des pays l’Afrique de l’Ouest et Centrale, est un légume-feuille largement consommé au Came- roun. Bien qu’il soit consommé par une grande proportion de la population, sa culture est limitée à la partie Sud du pays, principalement pendant la saison des pluies. Afin d’assurer sa disponibilité en dehors des zones de culture et de la saison des pluies, ce légume-feuille est généralement transformé et conservé. La présente étude est menée pour déterminer les variations des teneurs en fer et vitamine A sous l’effet des modes de transformation et de conservation pour quatre espèces de Vernonia (V. amygdalina, V. calvoana var. amer, V. colorata et V. calvoana var. non amer). Les modes de transformation étudiés sont le lavage-pressage, la cuisson à ébullition et le lavage-pressage dans des solutions de natron (Na2CO3, 1N et 2N). Les modes de conservation pris en compte sont le séchage au soleil et dans des étuves à différen- tes températures (45, 60, et 75 °C) ainsi que la congélation pendant 0, 10, 30, 60, et 120 jours. La teneur en caroténoïdes totaux a été déterminée par chromatographie et la teneur en fer par spectrophotométrie d’absorption atomique.
Les résultats montrent que ces légumes-feuilles sont de bonnes sources de fer et de caroténoïdes totaux. Leurs teneurs varient de 6,4 ± 0,3 g/100gMS dans le V. calvoana à 15,2 ± 0,4 mg/100gMS dans V. colorata et sont significativement (P < 0,05) affectés par les méthodes de transformation avec des niveaux de pertes allant jusqu’à 42 % dans la variété V. calvoana non amer. D’autre part, l’utilisation de natron (W2) conduit à une augmentation de la teneur en fer pour V. amygdalina. Le séchage et la congélation après transformation n’ont pas modifié les teneurs en fer. Les teneurs en caroténoïdes totaux dans les échantillons frais vont de 30,0 ± 1,0 mg/100gMS dans V. amygdalina à to 41,5 ± 1,0 mg/100gMS dans le V. colorata et diminuent avec la transformation, spé- cialement dans les espèces amères (V. amygdalina et V. calvoana var. amer) qui néces- sitent un lavage-pressage et un rinçage intenses. La congélation des échantillons traités pendant 10 jours n’a pas eu d’influence significative sur la teneur en vitamine A.
Dans l’ensemble, le lavage-pressage et le rinçage se sont révélés les meilleurs traite- ments pour conserver les caroténoïdes totaux tandis que la meilleure température de séchage a été 45 °C.
Mots clés
espèces de Vernonia, séchage, congélation, transformation, fer, vitamine A.
1. Department of Food Science and Nutrition, ENSAI, University of Ngaoundere, P.O. Box 455 Ngaoundere, Cameroon.
* Correspondence : ejohrab@yahoo.com
SUMMARY
Vernonia, commonly known as Bitterleaf in most West and Central African countries, is a widely consumed leafy vegetable in Cameroon. Though consumed by a large pro- portion of the population, cultivation is limited to the southern parts of the country and mostly in the rainy season. In order to ensure availability in non growing areas or seasons, the vegetable is usually processed and preserved. The present study was carried out to determine the changes in iron and total carotenoid levels due to diffe- rent processing and preservation methods of four species of Vernonia (V. amygdalina, V. calvoana var. bitter, V. colorata and V. calvoana var. non bitter). The processing methods were squeeze-washing, boiling and squeeze-washing with different concen- trations of natron (Na2Co3, 1N and 2N). The methods of preservation were drying, using solar radiation and moisture ovens at different temperatures (45, 60 and 75°C) and freezing for 0, 10, 30 60 and 120 days. Total carotenoid was analysed using Chromatographic method while iron content was determined by atomic absorption spectrophotometry. Results showed that these leafy vegetables are good sources of iron and total carotenoids. Iron values varied from 6.4 ± 0.3 in V. calvoana to 15.2 ± 0.4mg/100gDW in V. colorata and are significantly (P < 0.05) affected by processing methods with losses amounting to as much as 42% in the non bitter vari- ety of V. calvoana. On the other hand the use of natron (W2) led to an increase in the iron content of V. amygdalina. Drying or freezing did not affect iron levels. Carotenoid levels ranged from 30.0 ± 1.0 in V. amygdalina to 41.5 ± 1.0mg/100gDW in V. colorata for the raw samples and tended to diminish with processing especially in the very bit- ter species (V. amygdalina and V. calvoana var. bitter) that required intense squeeze- washing and rinsing. Freezing processed samples for up to 10 days had no significant influence on the total carotenoid content.
On the whole, squeeze-washing and rinsing was the best treatment to preserve caro- tenoids, while the best temperature for drying was 45°C.
Keywords
Vernonia species, drying, freezing, processing, iron, vitamin A.
1 – INTRODUCTION
Iron and vitamin A deficiency are known to be one of the most common forms of mal- nutrition that affects the most vulnerable groups (1, 2). Worldwide, the highest prevalence of iron deficiency is found in infants, children, adolescents and women of childbearing age, especially pregnant women. In Africa vitamin A deficiency affects close to 18 million preschool children of which 1.3 million are affected by xerolphtalmia. In many developing countries, leafy vegetables provide the iron and vitamin A needs of the population (3).
These vegetables constitute a major component of most Cameroonian dishes (4) and provide the cheapest and most accessible sources of minerals and vitamins to the poor and most vulnerable populations that suffer from crude shortages of these micronutrients.
Vernonia is a leafy vegetable known in most West and Central African countries for both animal and human nutrition. In Asia it is also widely used in traditional medicine. Con- sumption in Cameroon is high and mostly in the form of “ndole” (5, 6). The bitterness and the foaming properties of the different species of Vernonia necessitate the use of different processing techniques such as squeeze-washing, crushing and rinsing, boiling and the use of natron (a local alkaline salt). LATUNDE-DADA (7) found that Vernonia amygdalina contains high levels of minerals. However, their bioavailability was low because of the presence of anti-nutritional factors. UDOSEN and UKPANAH, (8) observed that processing
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2 – MATERIALS AND METHOD
The leaves and young shoots of four species of Vernonia (two non bitter and two bit- ter) were collected from an experimental farm in Ngaoundere, Cameroon. They were then sorted and rinsed under running tap water to remove dust. These samples were fur- ther sliced before being subjected to different processing techniques such as squeeze washing, boiling and the use of natron. Squeeze-washing involved an elaborate crushing, washing, rinsing and squeezing to reduce bitterness and foam. The process is more elaborate for the bitter species. The boiling process involved boiling about 450g of the sliced vegetable in one litre of water containing 0, 10 or 20 grams of natron for 10 minutes. To determine the influence of drying, a 2×5×4 factorial design was used.
Two species (V. amygdalina and V. calvoana), subjected to the five treatments above were dried in 4 different drying conditions – sun drying and drying in a moisture oven at 45°C, 60°C, and 75°C. The effect of duration of freezing was determined on only one species (V. calvoana), stored at – 18°C in a freezer for 10, 30, 75, and 120 days (5×5 fac- torial design).
The samples thus treated were dried at 45°C, ground and stored in air tight contai- ners for laboratory analyses. The ash values were obtained after incineration of the sam- ples in a muffle furnace at 550°C for 24 hours and the iron levels determined by atomic absorption spectrophotometry (9). Total carotenoids were first extracted using a mixture of hexane – acetone 30/70 (v/v) then separated using neutral alumina column and quanti- fied using a spectrophotometer at 430nm (10). All analyses were done using triplicate samples.
3 – RESULTS
Results of the ash values of the raw samples of the four species of Vernonia are pre- sented in table 1. These values ranged from 7.69 ± 0.11 for V. amygdalina to 11.96 ± 0.1g/100g DW for V. calvoana non bitter. Significant variations (P < 0.05) were also observed within the different species analysed as well as due to the different processing techniques with losses of between 19.5 and 30%.
Table 1
The effect of processing on ash levels of the four species of Vernonia in mg/100g DW.
V. amygdalina V. calvoana var. bitter
V. colorata V. calvoana var.
non bitter
R 7.72 ± 0.11a 10.52 ± 0.30a 11.84 ± O.27a 11.96 ± 0.15a
W 5.65 ± 0.8b 9.08 ± O.18b 10.10 ± 0.21b 10.78 ± 0.19b
Wb 5.37 ± 0.59b 6.46 ± 0.27c 8.42 ± 0.08c 8.85 ± 0.14d
W1 6.19 ± 0.46b 6.15 ± 0.26c 8.86 ± 0.6c 9.491 ± 0.21c
W2 5.40 ± O.37b 6.61 ± 0.18c 10.09 ± 0.19b 10.85 ± 0.12b
Means ± SD, For each column, means with different superscripts are significantly different (P < 0.05).
R = Raw, W = Squeeze-washing, WB = Boiling and squeeze-washing. W1 = Boiling in1N natron and squeeze-washing;
W2 = Boiling in 2N natron and squeeze-washing.
Table 2 shows the effect of processing on the levels of iron of the different species of Vernonia studied. The non-bitter species (V. colorata and V. calvoana var. non bitter) had higher levels of iron (15.22 ± 0.35 and 12.08 ± 0.45mg DW/100g, respectively). Iron levels significantly varied (P < 0.05) with the different processing techniques. Boiled and squeeze-washed samples (Wb) had a maximum of 42% loss in Fe in V. calvoana var.
non bitter and the use of the natron (W2) caused a slight increase for V. amygdalina. No significant effect on the iron levels was observed when the different species were sub- jected to different drying and freezing conditions (tables 3, 4 and 5).
Table 2
The effect of processing on the Fe levels of four species of Vernonia in mg/100g DW.
Table 3
Effect of drying on the Fe levels of V. amygdalina subjected to different processing conditions in mg/100gDW.
Table 4
Effect of drying on the Fe levels of V. calvoana subjected to different processing conditions in mg/100gDW.
V. amygdalina V. calvoana var.
bitter
V. colorata V. calvoana var.
non bitter R 7.52 ± 1.57 a 6.39 ± 0.26 a 15.22 ± 0.35 a 12.08 ± 0.45 b W 5.30 ± 0.46 ab 3.46 ± 0.24 d 9.77 ± 0.32 b 6.91 ± 0.54 d Wb 4.79 ± 0.15 ab 3.92 ± 0.17 d 9.21 ± 0.74 b 8.70 ± 0.34 c W1 7.18 ± 0.38 a 5.81 ± 0.01 b 15.02 ± 0.96 a 16.02 ± 0.49 a W2 7.01 ± 0.73 a 4.68 ± 0.04 c 16.67 ± 1.10 a 16.09 ± 0.00 a Means ± SD, Means with different superscripts are significantly different (P < 0.05).
R = Raw, W = Squeeze-washing, WB = Boiling and squeeze-washing. W1 = Boiling in1N natron and squeeze-washing;
W2 = Boiling in 2N natron and squeeze-washing.
R W Wb W1 W2
Sun drying 5.84 ± 0.22 5.07 ± 0.63 5.11 ± 0.40 8.37 ± 0.58 8.21 ± 0.23 45°C 7.52 ± 0.00 5.30 ± 0.46 4.79 ± 0.15 7.18 ± 0.38 8.01 ± 0.73 60°C 6.59 ± 0.11 4.26 ± 0.89 5.92 ± 0.45 7.69 ± 0.66 7.64 ± 0.32 75°C 5.62 ± 0.33 4.98 ± 0.15 4.16 ± 0.20 8.86 ± 0.95 8.39 ± 0.51 Values are means ± SD, Means in a column are not significantly different at p < 0.05.
R = Raw, W = Squeeze-washing, WB = Boiling and squeeze-washing. W1 = Boiling in1N natron and squeeze-washing;
W2 = Boiling in 2N natron and squeeze-washing.
R W Wb W1 W2
0days 6.39 ± 0.96 3.46 ± 0.24 3.92 ± 0.17 5.81 ± 0.01 4.68 ± 0.04 10days 4.52 ± 0.27 4.14 ± 0.60 3.13 ± 0.08 6.30 ± 0.97 5.46 ± 0.03 30days 5.26 ± 0.64 4.64 ± 0.04 4.79 ± 0.46 6.13 ± 0.61 5.37 ± 0.11 75jdays 6.06 ± 0.85 5.40 ± 1.59 4.44 ± 0.19 6.61 ± 0.27 5.05 ± 0.97
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Table 5
Effect of freezing on the Fe levels of V. calvoana subjected to different processing methods in mg/100gDW.
The levels of carotenoids in the different species subjected to different processing techniques are shown in table 6. Carotenoid levels ranged from 30.0 ± 1.0 in V. amygda- lina to 41.5 ± 0.9mg/100gDW in V. colorata for the raw samples. These raw samples were considerably reduced when subjected to different processing methods (P < 0.05). More losses of carotenoids were observed for the bitter species (V. amygdalina had 50% and V. calvoana var. bitter had 67%). Meanwhile V. calvoana var. non bitter had 43% and V. colorata had 49% loss. The greatest losses, were noted when 2N natron was used in processing. Tables 7 and 8 show the variations of the different conditions of drying. Los- ses due to drying were significant for the raw samples with maximum loss of 43% when samples of V. amygdalina was dried at 75°C, while carotenoid levels dropped from 38.5
±0. 3 to 26.1 ± 0.2mg/100gDW, i.e. 32% when solar radiation was used in drying V. cal- voana var. bitter. Table 9 shows the effect of duration of freezing at – 18°C on the carote- noid levels of Vernonia calvoana. Significant losses at P< 0.05 were observed after 10 days of freezing. Freezing for periods from between 0 to 10 days showed no signifi- cant variation (P < 0.05) for both the raw and processed samples of V. calvoana var. bitter (P > 0.05).
Table 6
Effect of different treatments on carotenoid levels of the different species of Vernonia (mg/100g).
R W Wb W1 W2
0days 6.39 ± 0.96 3.46 ± 0.24 3.92 ± 0.17 5.81 ± 0.01 4.68 ± 0.04 10days 4.52 ± 0.27 4.14 ± 0.60 3.13 ± 0.08 6.30 ± 0.97 5.46 ± 0.03 30days 5.26 ± 0.64 4.64 ± 0.04 4.79 ± 0.46 6.13 ± 0.61 5.37 ± 0.11 75jdays 6.06 ± 0.85 5.40 ± 1.59 4.44 ± 0.19 6.61 ± 0.27 5.05 ± 0.97 120days 6.06 ± 0.48 4.62 ± 0.53 5.50 ± 0.56 6.51 ± 0.77 5.75 ± 0.80 Values are means ± SD Means in a column are not significantly different at p < 0.05.
R = Raw, W = Squeeze-washing, WB = Boiling and squeeze-washing. W1 = Boiling in1N natron and squeeze-washing;
W2 = Boiling in 2N natron and squeeze-washing.
V. amygdalina V. calvoana var. bitter
V. colorata V. calvoana var. non bitters
R 30.0 ± 1.0a 38.5 ± 0.3a 41.5 ± 0.9a 35.8 ± 0.2a
W 21.6 ± 0.4b 16.9 ± 1.0b 26.0 ± 0.5b 28.5 ± 0.2b
Wb 21.9 ± 0.4b 16.5 ± 1.4b 21.2 ± 3.3b 27.8 ± 1.8b
W1 16.4 ± 3.4c 14.9 ± 1.8b 22.5 ± 1.0b 21.8 ± 3.9c
W2 14.9 ± 0.4cd 12.8 ± 0.4c 21.2 ± 2.1b 20.2 ± 0.3c
Values are means ± SD, Means not sharing a common superscript letter in a column are significantly different at p < 0.05.
R = Raw, W = Squeeze-washing, WB = Boiling and squeeze-washing. W1 = Boiling in1N natron and squeeze-washing;
W2 = Boiling in 2N natron and squeeze-washing.
Table 7
Effect of drying on the carotenoid levels of V. calvoana subjected to different processing conditions (mg/100gDW).
Table 8
Effect of drying on the carotenoid levels of V. amygdalina subjected to different processing conditions (mg/100gDW).
Table 9
Effect of time of freezing on the carotenoid levels of V. calvoana subjected to different processing conditions (mg/100gDW).
R W Wb W1 W2
Sun drying 26.1 ± 0.2d 14.2 ± 3.3ab 12.8 ± 1.4a 12.7 ± 1.7b 17.5 ± 0.7a 45°C 38.5 ± 0.3a 16.9 ± 1.0a 16.4 ± 1.5a 14.9 ± 1.8a 12.8 ± 0.4b 60°C 34.2 ± 0.8b 17.0 ± 2.3a 14.6 ± 3.8a 15.4 ± 2.6a 17.0 ± 0.2a 75°C 36.2 ± 0.5c 13.4 ± 0.8ab 13.9 ± 4.6a 12.4 ± 0.8b 12.2 ± 2.2b Values are means ± SD, Means not sharing a common superscript letter in a column are significantly different at p < 0.05.
R = Raw, W = Squeeze-washing, WB = Boiling and squeeze-washing. W1 = Boiling in1N natron and squeeze-washing;
W2 = Boiling in 2N natron and squeeze-washing.
R W Wb W1 W2
Sun drying 17.7 ± 0.5b 13.4 ± 1.2b 14.3 ± 1.2b 7.0 ± 0.2c 8.7 ± 0.6c 45°C 30.0 ± 1.0a 21.6 ± 0.4a 21.9 ± 0.3a 16.4 ± 3.4a 14.9 ± 0.4a 60°C 19.5 ± 0.1b 12.3 ± 0.8b 12.1 ± 0.6b 12.1 ± 2.6a 11.6 ± 0.3b 75°C 17.1 ± 1.3b 13.1 ± 12.5b 11.2 ± 0.0c 8.4 ± 20b 9.8 ± 0.8c Values are means ± SD, Means not sharing a common superscript letter in a column are significantly different at p < 0.05.
R = Raw, W = Squeeze-washing, WB = Boiling and squeeze-washing. W1 = Boiling in1N natron and squeeze-washing;
W2 = Boiling in 2N natron and squeeze-washing.
R W Wb W1 W2
0day 38.5 ± 0.3a 16.9 ± 1.0a 16.5 ± 1.5a 14.9 ± 1.8a 12.8 ± 0.4a 10days 37.0 ± 0.2a 16.8 ± 0.4a 12.0 ± 0.1b 11.10 ± 1945a 11.0 ± 0.5b 30days 23.9 ± 0.5b 14.9 ± 0.6b 10.4 ± 0.2c 10.3 ± 0.1ab 6.7 ± 0.6c 75days 13.9 ± 0.4c 10.5 ± 1.8c 8.3 ± 1.4d 9.1 ± 0.8b 8.7 ± 1.8b 120days 14.1 ± 158c 10.5 ± 0.7c 11.0 ± 0.6c 6.1 ± 0.2c 6.7 ± O.6c Values are means ± SD.
Means not sharing a common superscript letter in a column are significantly different at p < 0.05.
R = Raw, W = Squeeze-washing, WB = Boiling and squeeze-washing. W1 = Boiling in1N natron and squeeze-washing;
W2 = Boiling in 2N natron and squeeze-washing.
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4 – DISCUSSION
Iron deficiency problems remain prominent in developing countries. It serves as a car- rier of oxygen to the tissues from the lungs by red blood cell haemoglobin, as a transport medium for electrons within cells, and as an integrated part of important enzyme systems in various tissues. The high values of iron observed in all four species of Vernonia is a good indicator that these food samples were good sources of this mineral when compa- red to values obtained for cereals and tubers (11). These values were also higher than values obtained for Amarathus paniculatus and A. teunifolious (12). High losses in ash and iron due to different processing methods could be explained by the fact that these mine- rals remain soluble in water in the course of squeeze-washing. However these loses were not so high in samples treated with natron and this could be explained by the fact that natron contains some minerals that could remain after processing.
Vitamin A deficiency remains a major problem in Cameroon, affecting mostly the peo- ple in the Northern provinces (13, 14). Its role in vision and growth regulation has made the public health officials to look for urgent and rapid methods of combating the problem.
Leafy vegetables remained one of the most important and cheapest sources of Vitamin A.
Processing generally leads to losses (15). High levels of carotenoids, found in the raw samples of the different species of Vernonia were decreased during processing. These losses were more important in the bitter species: V. amygdalina and V. calvoana var. bit- ter. This could be explained by the fact that processing was more intense in the bitter species. High losses, also found when 2N natron was used in processing proved that though carotenoid is not hydro soluble, it could be destroyed by the use of alkaline in cooking. The losses observed as a result of processing in the present study are higher than those in the literature (15, 16), and this can be attributed to variations in processing methods.
Conclusively, the Vernonia species studied provide substantial quantities of iron, and total carotenoids. The non-bitter species were found to be richer in these two nutrients.
Higher values of iron was found in samples boiled with natron. Squeeze-washing and rin- sing seems to be the best treatment to preserve total carotenoids. Losses were more prominent in the bitter species that require intense squeeze-washing and rinsing. Drying at 45°C is best recommended while freezing for less than 10 days is most appropriate for the conservation of total carotenoids. However because of the increased demand for these nutrients, and the lack of possibility to avoid processing and conservation, it is the- refore pertinent that the use of other sources of vitamin A and iron be considered impera- tive.
5 – ACKNOWLEDGEMENT
We thank the International Foundation for Science, Sweden and the Organisation of Islamic Conference, Pakistan for their financial support.
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