RESUMO
The cooking process is fundamental for bean consumption and to increase the bioavailability of its nutritional components. The study aimed to determine the effect of cooking on bean seed coat through morphological analyses with different microscopy techniques and image analyses. The chemical composition and physical properties of raw black bean (RBB) and cooked black bean (CBB) seeds were determined. The surface and cross-sectional samples were studied by Optical microscopy (OM), environmental scanning electron microscopy (ESEM), atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). The composition of samples showed significant differences after the cooking process. OM images and gray level co-occurrence matrix algorithm (GLCM) analysis indicated that cuticle-deposited minerals significantly influence texture parameters. Seed coat surface ESEM images showed cluster cracking. Texture fractal dimension and lacunarity parameters were effective in quantitatively assessing cracks on CBB. AFM results showed arithmetic average roughness (Ra) (121.67 nm) and quadratic average roughness (Rq) (149.94 nm). The cross-sectional ESEM images showed a decrease in seed coat thickness. The CLSM results showed an increased availability of lipids along the different multilayer tissues in CBB. The results generated from this research work offer a valuable potential to carry out a strict control of bean seed cooking at industrial level, since the structural changes and biochemical components (cell wall, lipids and protein bodies) that occur in the different tissues of the seed are able to migrate from the inside to the outside through the cracks generated in the multilayer structure that are evidenced by the microscopic techniques used.
RESUMO
The cuajilote (Parmentiera edulis D.C.) tree produces fibrous fruits with a high content of lignocellulosic compounds. However, this fruit and their fibers have been scarcely studied. For this reason, an integral study of their cellular architecture, physicochemical, micromechanical, and structural properties in two maturity stages were carried out. Physicochemical tests, light, confocal and electron microscopy, microindentation, and X-ray diffraction were used for the characterization of fruit and their fibers. Chemical analysis showed that the unripe fruits have the highest cellulose content (42.17%), but in ripe fruit the cellulose content decreases (32.76%) while lignin content increases from 35.26 to 40.79%, caused by the lignification of the sclerenchyma fibers. Microstructural and micromechanical studies in the different regions of the fruit provided relevant information about its cellular architecture, distribution of lignocellulosic compounds and its role in the micromechanical properties of their fibers. The thickening cell wall of sclerenchyma fibers was caused by the cellular lignification of the ripe fruits. According to the physicochemical and structural studies, cuajilote fibers are comparable to other fibers obtained from crops rich in lignocellulosic compounds. The current study provided new knowledge about the cellular architecture of fruit and criteria for selecting the ripening stage adequate for the extraction of cellulose or lignin. Furthermore, information regarding the micromechanical properties of their fibers and which structural arrangement could be more convenient for mechanical reinforcement of biodegradable materials was obtained.