Starch–Apple Pomace Mixtures: Pasting Properties and Microstructure

Apple pomace (AP) is a by-product of the juice industry that could be used as an accessible fiber source for foods. The objective of the present work was to evaluate the effect of different levels of AP on the pasting properties of composite starch systems using a rapid visco analyzer (RVA) and to relate rheological behavior to microstructural characteristics. AP was dried, ground, sieved, and sterilized before being applied. In assays at constant solid content (3 g/25 ml water), rice flour (RF) and cassava starch (CS) were mixed in equal proportions and increasing replacements with AP (0–50 %) were performed. The level of AP in starch–water dispersions had a significant influence on pasting properties such as peak viscosity (PV) and final viscosity (FV), which decreased when AP level increased, particularly when it was above 25 % (w/w). When the effect of AP addition at a constant starch concentration was analyzed, viscosity increased with the increase in total solid content. By microstructural studies (light microscopy, SEM), it was observed that fiber particles were not totally solubilized, remaining embedded in the starch paste. Water imbibing capacity (WIC) measurements indicated that AP particles were able to absorb water to a higher extent than starch. This could lead not only to less water availability in starch suspensions during gelatinization but also to a certain compensation for viscosity loss due to AP particle swelling.