Characterizing apple microstructure via directional statistical correlation functions

Our understanding of food is tightly related to the complex food microstructure. We introduce the use of statistical correlation functions to quantitatively describe the spatial distribution of cell and void phases of ‘Braeburn’ and ‘Kanzi’ apples. The lineal-path distribution function, L(r), and the two-point correlation function, S2(r), were measured from bi-dimensional (2D) microtomographic images. While the void fraction of both apples cultivars was similar, 0.840% and 0.853%, the pores of ‘Braeburn’ apples were bigger in size. Pores with an extension of 25 μm were found in percentage of 12.6% and 4.3% for ‘Braeburn’ and ‘Kanzi’ respectively. The cell phase of ‘Braeburn’ apples was described by larger clusters as a result of a greater degree of connectivity among the individual cells. ‘Kanzi’ apple tissue was structured by more separated cell clusters due to the presence of small pores with a greater spatial distribution. The clusters showed a good homogeneity in shape for both varieties while the voids of ‘Kanzi’ apples appeared more inhomogeneous and elongated in one of the dimensions. The obtained structural information were employed to model tissue structures of apples. We found that the cell phase could be modeled by overlapping disks having a mean radius of 58 and 53 mm for ‘Braeburn’ and ‘Kanzi’ apples, respectively. In this way macroscopic properties of apple tissue could be estimated precisely.