Potato, protein content

Potatoes are an excellent source of carbohydrates and contain significant amounts ofphosphorus, potassium, calcium, and vitamins, especially vitamin C. Potato protein content, at over 10%, is relatively close to that of wheat flour (11%) also, thanks to their lysine, methionine, cystine and cysteine contents, potatoes are a valuable supplement to cereal proteins. For instance, potatoes provide a significant source of proteins (10-15% of total requirements), a major source of vitamin C, an important source of energy, and also minerals like iron and other vitamins such as thiamin, nicotinic acid, riboflavin, and pro-vitamin A (p carotene) (Salunkhe and Kadam, 1991). 

Data are not available for protein production worldwide. However, an estimate of the protein contribution provided by sweet potatoes can be made if we assume a mean dry matter content of 28% and a mean protein content of 5%. Based on these assumptions, the sweet potato provides 1.92 million metric tons of protein worldwide. The yield of protein would be 134 kg/ha using worldwide yield values or 184 kg/ha using US production values. 

Table I. Crude Protein Content (% Fresh Sweet Potato) of Ten Cultivars From Upper Mendi Grown in Different oo...

Walter et al. (38) measured the protein efficiency ratio (PER) of flour prepared from sweet potatoes which were cooked in a drying oven. Because the PER is determined on the basis of a diet containing 10% protein, the Jewel and Centennial sweet potatoes used in this study were stored until sufficient starch had metabolized to increase crude protein content to 11.25% (dry basis). When the flour was fed to Sprague-Dawley strain rats, the corrected PER values were 2.22 and 2.00 for Centennial and Jewel cultivars, respectively, compared to 2.50 for casein. Centennial had the highest PER value of the two cultivars because its NPN content was lower. The net effect of increased NPN content is to lower the amount of essential amino acids as a percentage of the total nitrogen and thus decrease the PER value. 

In tomato and potato plants, two families of Pis have been identified that show wound-inducible expression. Within 48 h after wounding of leaves of these plants, up to 2% of leaf protein content is made up of protease inhibitors. Potato type I (Potl) inhibitors are not only expressed in wounded leaves but also in tissue of leaves away from the site of attack. ° This finding prompted the search for a hormone or inducing factor that carries the signal for enhanced inhibitor expression through the plant system. Systemin, an 18-residue peptide hormone, has since been reported to induce more than 15 genes of defense nature in tomatoes. ... 

Refstie, S, Tiekstra, H. A. J. (2003). Potato protein concentrate with low content of solanidine glycoalkaloids in diets for Atlantic salmon. Aquaculture, 216,283-298. 

Why might a sweet potato plant genetically engineered for a higher protein content have a greater intolerance for nitrogen-poor soils ... 

Wash, hand-peel, chop and lyophilize each plant tissue material for 3-4 h at 25°C (e.g., soybean (Table 17.1), potato, banana, eggplant, sweet potato and artichoke (Table 17.2). Grind the dry tissue to obtain a fine powder and select the particle size using sieves of lower than 200 pm mesh. Store the dry powder in a desiccator at 25°C and use it as the enzymatic source of PPO or peroxidase in the preparation of biosensor. Determine enzymatic activity and total protein content as described in Procedure 22 (in CD accompanying this book). Prepare the carbon paste electrode with dry tissue as described in the same procedure. 

Gelder, W.M.J. and van Vonk, C.R. (1980) Amino acid composition of coagulable protein from tubers of 34 potato varieties and its relationship with protein content. Potato Research 23,427-434. 

Potato protein dry matter content should be —90% in order to produce a balance between microbiological deterioration, energy consumption and fine powder content. The protein content of the dry matter is —85% and the bulk density is —550kg/m3. Potato protein contains a high amount of protein, as compared to fishmeal, milk powder and soy protein. Also, the amount of important amino acids, such as lysine, methionine and cystine, is relatively high. Potato protein is mainly sold as cattle feed. 

Starch for use in papermaking has to meet specific purity requirements in residual oil, protein, bran and ash content. Industrial starches have a protein content (N X 6.25), ranging from about 0.05% for potato starch to 0.3-0.6% for com starch, depending on separation efficiency during production. Excess protein content will induce foaming in dispersions of starch and affect the quality and strength of the coated surface. Starch for use in the paper industry should not contain more than 0.4% protein. Oxidized starches tend to have the lowest protein content. Residual oil will cause retrogradation due to complex formation with amylose. 

---