Chemical profile, functional and antioxidant properties of tomato peel fiber

Tomato processing residue is defined as a secondary raw material that can increase its value, being considered a potential source of dietary fiber and bioactive compounds. Commercial tomato peel fiber has been analyzed to ascertain the proximate and nutritional composition (moisture, fat, protein, dietary fiber, ash, and minerals), the fractions (insoluble, IDF, and soluble, and SDF) and sugar composition of dietary fiber, functional properties (water retention capacity, WRC, swelling capacity, SWC, fat absorption capacity, FAC, glucose diffusion retardation index, GDRI, and osmotic pressure), total antioxidant activity (AA), and the content of antioxidant bioactive compounds (phenolic compounds and lycopene). To extract phenolic compounds and dietary fiber, three methods were assayed in this study: enzyme hydrolysis, maceration, and ultrasonic assistance. The content of TDF was 84.16%, and the major fraction was the IDF (71.82%), formed mainly by hemicelluloses. Tomato peel fiber retained 6.76 g of water/g as WRC, and it was significantly correlated with the IDF content. In addition, the content of IDF determined the low FAC and SWC and the GDRI at 60 min (39.22%). The main phenolic compound was rutin, followed by naringenin, rutin derivatives, and chlorogenic acid derivatives. These were better extracted using ultrasonic assistance, whereas lycopene showed mean values between 3 and 4 mg/100 g. The M of tomato peel fiber was low, since the phenolic compounds are mainly bound to the cell wall of plant, showing a low capacity for scavenging radicals. Due to its chemical profile and functional properties, tomato peel fiber can be used as a food supplement, improving the different physical, chemical, and nutritional properties of foods. However the color and flavor of this product must be considered in its applications to avoid a negative effect on the sensory characteristic of the foods to which it is added. (C) 2011 Elsevier Ltd. All rights reserved.