Levels of Phytotoxins and Nutrients in Hibiscus sabdariffa as Influenced by Freezing Storage

Aims: The biochemical changes affecting the quality and chemical contents (which include nutrients and phytotoxins) in leafy vegetables during storage depend on the storage conditions. It is in line with this that the work was designed to investigate the effect of freezing time on some nutrients, namely, vitamins (β-carotene and vitamin C) and mineral elements (Fe, Cu, Mg, Na and K) and plant toxins (cyanide, nitrate, soluble and total oxalates) in Hibiscus sabdariffa.
Methodology: The leaves of the vegetable were stored in a deep freezer at - 4ºC for the period of four weeks and chemical analyses were conducted at weekly intervals.
Results: The concentrations of cyanide, nitrate, oxalates (soluble and total), vitamin C and Mg in Hibiscus sabdariffa decreased significantly (p < 0.05) during one week of freezing and remained significantly the same throughout the storage duration, except that the soluble oxalate concentration further decreased significantly in the fourth week of freezing. β-carotene content decreased significantly (p < 0.05) in the first and second weeks of freezing, however, in the third and fourth weeks, the provitamin A concentration remained significantly unchanged. Freezing had no significant effect on Cu content in Hibiscus sabdariffa. While freezing beyond two weeks significantly (p < 0.05) decreased the Fe and K contents, the concentration of Na in Hibiscus sabdariffa was reduced significantly (p < 0.05) only in the fourth week of freezing.
Conclusion: The results thus suggest that one week of freezing at - 4ºC significantly reduced the concentrations of the phytotoxins in Hibiscus sabdariffa and preserved most of the micronutrients in amount required for the normal metabolic activity of a healthy individual.