Determination of levels of some vitamins in amaranthus hypochondriacus and amaranthus cruenthus leaves and grains from selected areas of Kenya

Abstract

Vitamin deficiencies are health hazards in some parts of Kenya. These are attributed to inadequate access to vitamin-rich foods occasioned by decline in agricultural production due to unfavourable climatic conditions, low purchasing power due to poverty, over reliance on staple foods and dependence on highly refined foods, which are poor in vitamins. Higher intake of vitamin-rich vegetables and grains can alleviate this problem. Grain amaranth (GA), which is relatively a new crop in Kenya, is a dual crop whose seeds are used as grains and leaves as a vegetable. It has been found to have high nutritional and medicinal values, which could combat life-threatening diseases such as HIV/AIDS, diabetes, cancer, hypertension, liver diseases and haemorrhage. However, it is still an underutilized crop. As a leafy vegetable, it can be harvested at different maturity stages of growth, but data on the changes in leaf nutritional value with plant age are scanty. The objective of this study was to determine the levels of β-carotene, thiamin, riboflavin, pyridoxine, ascorbic acid (AA) and α-tocopherol in Amaranthus hypochondriacus (L-) and Amaranthus cruentus (L-) leaves at different ages of growth and their grains grown in different regions of Kenya in wet and dry seasons using high-performance liquid chromatography, spectrophotometric and titrimetric methods. The study areas were Kenyatta University, Bureti, Mt. Elgon, Kisii, Bondo, Meru and Embu districts. The mean vitamin levels (mg/100 g DW) in amaranth leaves were: β-carotene (35.985-49.797), α-tocopherol (29.494-34.779), thiamin (0.573-0.714), riboflavin (2.311-2.755), pyridoxine (2.581-2.921) and AA (440.077-619.210). The mean vitamin contents of leaves were significantly different between the species (P<0.05) except thiamin and riboflavin. Results showed that the amounts of β-carotene and α-tocopherol increased significantly (P<0.05) with the plants’ ages while those of thiamin, riboflavin, pyridoxine and AA decreased significantly (P<0.05). Between the study areas, no clear trend in the amounts of vitamins in the leaves was observed. Significant differences were noted in the leaf vitamin contents between the wet and dry seasons (P<0.05) except thiamin and riboflavin. The amounts of vitamins (mg/100 g DW) in amaranth grain ranged between 4.614-4.633 for β-carotene, 1.055-1.068 for α-tocopherol, 0.152-0.166 for thiamin, 0.273-0.285 for riboflavin, 0.223-0.229 for pyridoxine and 4.037-4.303 for AA. The levels of vitamins in amaranth grain were generally not different significantly between the species apart from AA (P<0.05) in some areas. The amounts of vitamins in grain between the seasons were not significantly different except thiamin in some areas (P<0.05). It can be concluded that the plant age, geographical location as well as the season influence the levels of vitamins in amaranth leaves. However, they do not have any pronounced effects on the levels of vitamins in amaranth grains. The results will be used to sensitise the public on the importance of amaranth leaves and grains as a reliable source of vitamins. The results will also be availed to relevant authorities, who may use it for policy formulation.