Conversion of nitrogen to protein and amino acids in wild fruits

Protein content of plant tissues is usually estimated by multiplying total nitrogen by a conversion factor of 6.25. This technique assumes that all ni trogen originates from protein. When applied to fruit pulp, it overestimate s protein content because pulp typically contains free amino acids and many nitrogenous secondary metabolites. At issue is the extent of error and, co nsequently, what the conversion factor between nitrogen and protein should be. We calculated a conversion factor based on pulp samples from 18 species collected in the southeastern United Slates. We also report a new and simp le method of estimating protein and free amino acids in fruit pulp. Because previous studies have found high variation in protein and secondary metabo lite content among fruit species, use of a single conversion factor for all species will generate error. In an attempt to reduce such error, we calcul ated protein contents and conversion factors separately for two common frui t types: lipid-rich/carbohydrate-poor and lipid-poor/carbohydrate-rich. We found no difference between these types of fruit and hence combined results in calculating an average conversion factor of 5.64, Use of an accurate co nversion Factor is important in estimating protein consumption by wild anim als and in formulating diets of captive animals. It can also reveal whether loss of body mass in captive animals on fruit diets is due to insufficient protein consumption, secondary metabolite toxicity, or an imbalance of ami no acids.