1. AOAC (1975): Official methods of analysis, 12th edn, p. 529. Washington DC: Association of Official Agricultural Chemists.
2. AOVC (1966): Methods of vitamin assay, 3rd edn, p. 97. New York: Interscience Publishers. Alamo, K, Bosco, C., Credo, D., Melia, M. A., Schmidt-Hebbel, H., Vinagre, J. & Pennaechiotti.
3. Choudhury, B. (1967): Vegetables, p. 79. New Delhi: National Book Trust.
4. Schuphan, W. (1965): Nutritional values in crops and plants, p. 68. London: Faber