Evaluating the roughness dynamics of kefir biofilms grown on Amazon cupuaçu juice: a monofractal and multifractal approach.

We conducted a comprehensive analysis of the surface microtexture of kefir biofilms grown on Theobroma grandiflorum Shum (cupuaçu) juice using atomic force microscopy. Our goal was to investigate the unique monofractal and multifractal spatial patterns of these biofilms to complement the existing limited literature. The biofilms were prepared dispersing four different concentrations of kefir grains in cupuaçu juice. Our morphological analysis showed that the surface of the obtained biofilms is essentially formed by the presence of cupuaçu fibers and microorganisms like lactobacilli and yeast. The topographic height-based parameter analysis reveals that there is a dependence between surface roughness and the concentration of kefir grains used. The strongly anisotropic well-centralized topographical height distribution of the biofilms also exhibited a quasi-symmetrical and platykurtic pattern. The biofilms exhibit comparable levels of spatial complexity, surface percolation and surface homogeneity, which can be attributed to their similar topographic uniformity. This aspect was further supported by the presence of similar multifractality in the biofilms, suggesting that despite their varying topographic roughness, their vertical growth dynamics follow a similar pattern. Our findings demonstrate that the surface roughness of kefir biofilms cultivated on cupuaçu juice is influenced by the concentration of kefir grains in the precursor solution. However, this dependence follows a consistent pattern across different concentrations. Graphical Abstract.

Stereometric analysis of Amazon rainforest Anacardium occidentale L. leaves.

MAIN CONCLUSION: AFM, profilometry and SEM measurements on both sides of the Anacardium occidentale L. leaf reveal that ultrastructure presented some singularities due to their different morphologies and roughness. The advanced stereometry and power spectrum density of both sides of the Anacardium occidentale L. leaf were carefully studied. We use three different microscopy techniques such as scanning electron microscopy, profilometry, and atomic force microscopy for a complete description of the leaf surface morphology. The morphology of the adaxial and abaxial sides revealed a surface composed of striated cuticles and stomata cells, respectively. The height parameters obtained by profilometry revealed that the abaxial side was rougher. However, both sides presented similar Gaussian height distribution and asymmetry. The advanced stereometric parameters obtained by the topographic maps of AFM revealed that the two sides have some singularities due to their different morphologies and roughness, but with similar microtextures. However, average PSD spectra showed that adaxial and abaxial sides are dominated by relatively low and high spatial frequencies, showing that the microtextures, unlike what was shown in stereometric parameters, are different. These results revealed that leaves surface morphology under different aspects and scales and the quantitative parameters confirmed the different spatial patterns displayed, which can be of great interest for the study of the biological behavior of plants from their leaves.

3D micromorphology evaluation of kefir microbial films loaded with extract of Amazon rainforest fruit Cupuaçu.

We performed qualitative and quantitative analysis of surfaces of kefir biofilms loaded with Amazon rainforest fruit extract. Scanning electron microscopy and atomic force microscopy were used to evaluate the micromorphology of the biofilms. The films surface displayed a lower density of microorganisms (∼ 0.061 microorganisms/µm2) for the lowest concentration of fruit extract, however, a greater density (∼0.220 microorganisms/µm2) was observed for the higher concentration. Height stereometric parameters revealed that the biofilms with the highest concentration presented the highest roughness. However, almost all the stereometric parameters related to texture showed no significant difference. Furthermore, the Hurst coefficients of the average power spectrum density were similar for all biofilms. Fractal parameters confirmed that higher concentrations of fruit extract induced a superior topographic irregularity. However, fractal lacunarity does not show any significant difference confirming the similarity of the microtextures. Moreover, fractal succolarity and surface entropy exhibited values that suggested ideal percolation and strong topographic uniformity, respectively, indicating that these films can uniformly adhere to other surfaces. Our results confirm that the stereometric and fractal parameters can be relevant for the surface characterization of microbial films, which can be of great importance to the biomedical field.