Effect of blanching and drying on micronutrients and anti-nutritional factors in false sesame and common bean leaves

Abstract

The effects of blanching and drying on micro-nutrients: β-Carotene, Vitamin C, Folic acid, Iron (Fe), Zinc (Zn), Phosphorus (P) and anti-nutrients: Tannins and Oxalates composition of False Sesame Leaves (FSL) and Common Bean Leaves (CBL) were investigated. Vegetables consumption and preservation technologies used were assessed using questionnaire. Micronutrients content: β-Carotene, Vitamin C, and folic acid were analyzed using HPLC method while Fe, Zn were determined using Atomic Absorption Spectrophotometer (AAS) and Phosphorus was determined using UV-VIS Spectrophotometer. The oxalate and tannin were determined by titration and Folin Ciocalteu method. Several vegetables consumed were identified, FSL (16.9%) (Bahi) and CBL (21%) (Mbeya rural) were one of those. In vegetable processing, boiling (76.9%) and sun drying (15%) were reported in Bahi and Mbeya Rural Districts, respectively. Sun drying was the commonly used method in both Districts. Folic acid and β- Carotene were below detection limits in both vegetables. The vitamin C content in fresh FSL and CBL was 16.28 and 5.48 mg/ 100g, respectively, yet the content was significantly reduced (p<0.05) by blanching and sun drying. False sesame leaves contained P (700 mg/kg), Fe (115.75 ± 2.23

mg/kg) and Zn (14.13 mg/kg) whereas in CBL P was 600 mg/kg Fe (652.76 mg/kg) and Zn (41.04 ± 0.28 mg/kg). Levels of P, Fe and Zn were significantly (p<0.05) increased by sun drying. Tannin and oxalate content in blanched and sun dried leaves were lower than in fresh leaves. Sun drying of FSL and CBL while covering after blanching further reduced tannins and oxalates, thus it is recommended as an effective method in anti-nutrients elimination.