Quantification of porosity in sliced bread using two-dimensional digital image analysis and its relationship with drying kinetics

Abstract

This study quantifies the porosity of sandwich-bread crumbs using two-dimensional (2D) digital image analysis and links the microstructure to drying kinetics during baking. Breads were produced with four yeast levels (0.5%, 1.0%, 1.5%, and 2.0%), keeping the base formulation constant. Moisture loss kinetics were modeled using the Page equation based on the moisture ratio (MR); parameters k (overall drying constant) and n (curve shape related to internal resistances) were estimated by nonlinear regression. Microstructure was characterized on scanned slices (400 dpi, TIFF), calibrated in ImageJ/FIJI; RGB images were converted to 8-bit grayscale and segmented with a fixed threshold (100–155). Using Analyze ? Particles, we extracted area, circularity, and frequency by size classes (0.2–5.0 mm²). A completely randomized design was evaluated with analysis of variance (ANOVA) and the Least Significant Difference (LSD) test (p < 0.05). Histograms revealed high frequencies of small pores (<1 mm²) across treatments, with significant differences at approximately 0.38 mm². Yeast level directly modulated the cell structure: 1.0% yielded fine, homogeneous pores and the best kinetic fit (k = 1.864; n = 0.1579; R² = 0.8707); 0.5% produced a denser crumb and faster initial drying (k = 1.929; n = 0.132); 1.5% exhibited a stronger diffusive contribution with internal moisture retention (k = 1.827; n = 0.1807; R² = 0.7978); 2.0% produced larger pores and preferential vapor channels (k = 1.916; n = 0.1523). Intermediate yeast levels (1.0–1.5%) optimized texture and dehydration. The proposed 2D workflow is non-destructive, reproducible, and valuable for quality control and formulation, as it correlates morphometric metrics with kinetic parameters.