Potential use of fruit waste containing in vivo de-esterified pectin as a thickener in canned products

Orange peel and tomato skins were treated with sodium carbonate to pH 8.5 to cause in vivo pectin de‐esterification principally by pectinesterase action. The resulting material was dried and powdered and then evaluated for thickening properties in canned systems. It was found that after autoclaving for 75 min at 121.1 °C in a rotating retort in the presence of guar gum, sodium tripolyphosphate and calcium sulphate dihydrate, high post process viscosities could be obtained when orange peel was included at a concentration of 0.5% provided the pectin degree of esterification was reduced below 20% and the intrinsic viscosity of the pectin measured after extraction was above 3 dl g−1. Thickening was also obtained with tomato skins providing these two conditions were fulfilled. The dependence of viscosity on the calcium level and the thixotropic nature of the solutions obtained after processing, demonstrate that a calcium pectate gel can be formed even after severe heat treatment at a neutral pH. It is suggested that fruit and vegetable material containing in vivo deesterified pectin may be of value as a thickener in canned foods.