Physico-chemical and nutritional properties of breadfruit pulp and peel flours: Insights into starch molecular characteristics and their impact on starch digestibility

Abstract

Breadfruit is an underutilized crop with significant nutritional potential as a gluten-free starch-rich food ingredient. This study evaluated the chemical, molecular, structural, and nutritional properties of breadfruit (BF) flours derived from both pulp and peel, along with banana flour as a reference. Starch digestibility, estimated in vitro, was linked to these properties. Both BF flours showed high starch and fiber contents, with low amylose levels. Flow Field-Flow Fractionation-MALS-dRI analysis revealed similar amylopectin molecular weights (MW = 1.04–1.15·108g/mol) and root mean square radius (rrms = 172–174 nm) in both BF flours, which were lower than those of banana flour (MW = 1.73·108 g/mol; rrms = 187 nm). Scanning electron micrographs revealed that BF starch granules were smaller (3–15 μm) and rougher compared to those found in the banana sample (15–50 μm). X-ray diffraction showed a B-type crystalline pattern in BF samples. Fourier-transform infrared spectroscopy showed a higher ordered crystallinity of starch and a significantly higher amount of disordered structures in the Amide I region in BF flours compared to banana. BF flours also exhibited higher gelatinization temperatures with a narrower range, indicating increased granular thermostability and amylopectin crystallite homogeneity. Peel flour contained high levels of polyphenols and minerals. The lower amylopectin molecular weight and size, smaller starch granules and lower amylose content of BF flours compared to banana flour could explain the higher starch-digestion-rate-index (SDRI) of their uncooked samples. Cooked BF flours, however, showed an SDRI 10 % lower than banana, suggesting a reduced glycemic index after gelatinization. This study provides valuable insights into BF flours composition, molecular and structural properties, and their relationship with digestibility. These findings are relevant for developing novel gluten-free foods. Further research is needed to assess the starch digestibility of real food products made with BF flours and to investigate their functional properties and technological performance.