Effect of blanching time-temperature on potassium and vitamin retention/loss in kale and spinach

Hyperkalemia is common among patients with end stage kidney disease. Management involves diet modification. Hot water blanching is recommended to leach potassium in vegetables which results in losses of water-soluble and heat labile vitamins. Evidence on the effect of blanching in reducing potassium level of locally consumed vegetables in Kenya is limited. This study sought to establish effect of hot water blanching time-temperature on level of potassium, vitamin B1, B3 and C in kales (Brassica oleracea var. acephala) and spinach (Spinach oleracea) on potassium and vitamins B1, B3 and C retention/loss. The study adopted a full factorial experimental design. Vitamins were determined using high performance liquid chromatography. Potassium was quantified using atomic absorption spectrophotometry. To compare nutrient content between samples, independent t-test and Analysis of Variance were used at 95% confidence level. Nutrient content of fresh kales and spinach were potassium (102 mg/100 g and 615 mg/100 g), vitamin B1 (124 μg/100 g and 51 μg/100 g), vitamin B3 (1165 μg/100 g and 812 μg/100 g) and vitamin C (102 mg/100 g and 116 mg/100 g) respectively. In kales, blanching for 20 min at 1000°C resulted to retention of 86.9%, 55.6%, 27.6% and 12.9% of vitamin B1, B3, C and potassium respectively. In spinach, blanching for 20 min at 1000°C resulted in retention of 79.9%, 88.6%, 12.2% and 40.6% retention of vitamin B1, B3, C and potassium respectively. Vitamin C and Potassium were the most sensitive to heat and leaching. Time had a greater effect than temperature in this study. This study recommends blanching of kale at 15.2 min at 800°C, spinach at 17.7 min at 840°C. Further research on optimal blanching time-temperature for potassium and vitamin retention/loss is recommended.