Value of a tomato byproduct as a source of dietary fiber in rats

A residue consisting of tomato peel and seeds is a byproduct of the tomato paste industry. This product had, after drying and grinding, 101.4 g water, 175.6 g protein, 95.9 g lipids, 36.4 g ash and 590.7 g total carbohydrates per kilogram of residue. The carbohydrates in the residue were mainly dietary fiber (495.3 g) from which 405.4 g were insoluble fiber. Additionally, the residue had ascorbic acid 0.25 g, P 3 g, Ca 1.7 g, K 13.1 g, Mg 2.4 g, Cu 0.013 g, Fe 0.248 g, Mn 0.018 g and Zn 0.174 g per kilogram of residue. The residue fed to rats at increasing concentrations in the diet (0, 134, 263 and 387 g/kg diet) over 18 days had no effect on body weight gain; caused an increase in food intake and slightly reduced feed efficiency. Incorporation of the residue in the diet caused a substantial increase in fecal mass, which was proportional to the dietary fiber provided by the residue (r = 0.89); apparent absorption of protein, energy, Ca, Mg, Fe, Zn and Cu present in the diets was reduced. These reductions were proportional to the amount of dietary fiber provided by the residue and became substantial when the residue was included at 263 or 387 g/kg. However, when the residue was included at 134 g/kg, little effect on the apparent absorption of the dietary nutrients was noted. Because this concentration provided the rats with approximately 10 times more fiber than that recommended for humans, one can expect that if this tomato residue were consumed at concentrations recommended for humans, it should have no effect on nutrient availability. These results indicate that this tomato residue represents an attractive source of fiber, which in rats had a low apparent absorption (52-56%). In addition, it was very effective in increasing fecal mass with no negative effects on growth performance.