Effect of Using Fructooligosaccharide and Isomaltooligosaccharides in Cocoa–Hazelnut Spread as Sugar Substitute and Prebiotic on Estimated Glycemic Index and Quality Parameters

Sucrose plays a critical role in fat-continuous confectionery systems such as cocoa-hazelnut spreads by contributing to sweetness, texture, flow behavior, particle interactions, and overall sensory quality. In this study, sucrose was replaced with fructooligosaccharide (FOS) and isomaltooligosaccharide (IMO) at replacement levels of 0, 25, 50, 75, and 100% in cocoa-hazelnut spread formulations. The effects of these substitutions on physicochemical, textural, and rheological properties, particle size distribution, color parameters, estimated glycemic index (eGI), and sensory characteristics were investigated. Sucrose replacement significantly altered the structural and rheological properties of the spread matrix depending on both the type of oligosaccharide and the level of substitution. Formulations containing FOS exhibited more pronounced reductions in firmness and sensory acceptability at higher replacement levels. In contrast, IMO-containing formulations better preserved particle dispersion, viscoelastic stability, and overall sensory quality, particularly at low to moderate substitution levels. However, complete replacement of sucrose showed an adverse effect on taste and spreadability in both oligosaccharide systems. Both oligosaccharides contributed to a reduction in the eGI values. The eGI decreased from 50.71 to 39.90 in FOS-containing formulations and from 51.39 to 41.94 in IMO-containing formulations. These findings suggest that FOS is more effective in lowering the eGI, whereas IMO demonstrates greater potential for maintaining the technological and sensory quality of cocoa-hazelnut spreads when used as a partial sucrose replacer.