Resistant starch-enriched bread. Fibre content, analytical method comparison, and in-vitro digestibility effects

Modern diets are often deficient in dietary fibre, increasing chronic disease risk. Reformulating staple foods like bread with resistant starch (RS) offers a practical solution. This study evaluated the partial replacement of flour with high concentration of RS-II, RS-III, RS-IV, and RS2-IV in bread, analysing their structural, nutritional, and digestibility impacts. Generally, breads enriched with RS showed in a decrease of specific volume ranged between 32% and 42%, and an increase in hardness of up to 475%. Additionally, two fibre quantification methods were compared: AOAC 991.43 and AOAC 2017.16, as established by the AOAC (Association of Official Analytical Collaboration). All RS-enriched formulations met the “high in fibre” claim under AOAC 991.43, providing 17–31.5% of the daily fibre intake per 50 g portion versus 4.6% in the white control formulation. However, AOAC 2017.16 classified only RS-II and RS-III as “high in fibre,” while the two types of RS IV qualified as a “source of fibre”. Despite this, RS type IV showed the greatest reduction in reducing sugar release during in-vitro digestion (32% lower maltose release compared to the control), highlighting its potential to modulate postprandial glycaemic response. The study clarifies method-dependent fibre classification discrepancies and demonstrates RS-IV unique functional benefits compared to the other RS ingredients. These findings align with global reformulation policies, offering actionable strategies to enhance fibre intake through staple foods. Future research should focus on in-vivo studies and prioritise consumer acceptance and long-term health outcomes of RS-fortified products.