Upgrading winemaking by-products as innovative ingredients for tomato puree : from process and product design to the evaluation of consumers’ liking

The food industry is challenged in developing effective technologies for the utilization of by-products. The winemaking sector comprises a significant portion of the global food production and generates a substantial volume of valuable by-products. A promising application could be the recovery of phenolic- and fiber-rich fractions from grape pomace, which can be used as bioactive food ingredients. The aim of the present study (which is part of the AGER project, grant n. 2010-2222) was to assess the use of grape skins (GS) recovered from winemaking as a new food ingredient for a model tomato puree. GS from Chardonnay variety were subjected to drying, milling and sieving, to obtain three fractions having different particle sizes. These fractions were added to three different tomato purees. Twelve formulations (9 experimental and 3 control groups) were studied. The fortified formulations exhibited higher fiber (3%) and soluble phenolic (˃ 390 mg/kg) contents than those of the controls. Stabilization was performed by either an intensive autoclave treatment or an optimized microwave-treatment achieving 6D-reduction of the target microorganism (Alicylobacillus acidoterrestris). Upon autoclave treatment, flavonol components (analysed by HPLC-DAD) were partly deglycosylated. The content of soluble proanthocyanidins (measured with n-butanol/HCl assay) increased, probably due to depolymerization. The reducing capacity (FRAP assay) significantly increased in all the fortified purees. Microwave treatment did not affect the phenolic content of all the purees. The particle size of GS played a major role on the color (Hunter colorimeter) and rheological properties of the formulations. A sensory test based on consumers’ preference disclosed the formulation having the maximum appreciation. The overall results indicated that tomato puree could be a “vehicle” for delivering GS phytochemicals and fibers to the consumers, contributing to a sustainable innovation in the food industry.