Gelation Process of a Sweet Product with Apple Pomace

Fruit processing to obtain juices generates a large amount of secondary flows (pomace), which are an important upcycling opportunity, adding value to the value chain and, at the same time, reducing food waste, contributing to the sustainability of the ecosystem. The main goal of this work is to create a jam, incorporating apple pomace and no added sugar or sweeteners, to be used as toppings or complement, packaged in tube format, in order to facilitate its use and storage. Firstly, various formulations with a gelling agent (pectin - Pc) and a thickener (xanthan gum - XG) were tested at concentrations of 0.25%, 0.5% and 0.75% (w/w) of the mixed systems, in order to obtain a final formulation with characteristics close to a commercial jam (target). To optimize the gelation process, response surface methodology (RSM) was applied, considering as independent variables heating time (from 10 to 40 min) and the temperature (from 50 to 90 ºC). The formulation with results closest to the target formulation was: 0.5% Pc + 0.25% XG prepared at 84.2 ºC during 35.6 min. Firmness (N), elastic modulus (G \(^{\prime}\) ) at 1 Hz (Pa) and zero shear rate limiting viscosity – η0 (Pa.s), obtained by adjusting the Williamson model, were considered as dependent variables. When increasing the time and temperature, the firmness also increased (varied between 0.058 ± 0.001 N and 0.062 ± 0.001 N). The same trend was confirmed in limiting viscosity values and elastic modulus values. For the formulation t = 35.6 min/T = 84.2 ºC the viscosity was 3.66 ± 0.04 × 104 Pa.s and G \(^{\prime}\) was 2596 ± 104 Pa. In short, it was possible to upcycle apple pomace as a sustainable food ingredient, optimizing the thermal treatment and hydrocolloid systems, in order to obtain final physical properties, close to the commercial target.