microstructure and tannin content of banana fruit and their likely influence on juice extraction

Extraction of banana juice using the traditional physical method is limited to Mbidde banana cultivars. Most other banana cultivars (including Matooke cultivars) do not produce juice by this method. A study of the microstructure and tannin content of banana fruit (Mbidde and Matooke cultivars) was carried out in order to understand the underlying factors in the juice extraction process and develop a working hypothesis to explain the mechanism of juice separation. Microscopic examination of pulp sections of Mbidde bananas revealed that their microstructure contained many more intensely stained and larger laticifer cells than pulp tissues of Matooke cultivars. On ripening, the intensity of staining of laticifer cells in Mbidde fruit appeared to increase, while there was limited or no staining in fruit of Matooke cultivars. There was also higher tannin content in Mbidde than in Matooke bananas at both unripe and ripe stages. The high tannin concentration corresponding to the unique presence of high numbers of laticifer cells in fruit of Mbidde cultivars suggests that the ability of the bananas to release juice is linked to tannins. During juice extraction the physical working of the banana pulp ruptures the laticifer cells, resulting in the release of tannins that interact with celluloses, hemicelluloses, proteins and, most importantly, pectins to form insoluble complexes, thus facilitating juice release.