Effect of cultivar and ripening on the polyphenol contents of East African highland bananas (Musa spp.)

East African highland bananas (EAHBs) contain high amount of phenolics especially tannins, and are used to produce low-viscosity banana juice by a purely mechanical process. Occasional juice failure and cloudy appearance are the major problems facing juice production. The present work thus examined the variations in phenolic content of EAHB cultivars and their changes during ripening. The aim was to obtain a better knowledge of the various forms and amounts of phenolic compounds in different EAHBs, and how these properties may affect the ability of cultivars to produce low viscosity banana juice. Eleven banana cultivars including juice-producing and cooking bananas were harvested at the green maturity stage and analysed for total phenolic content (TPC), tannin content (TC), and tannin monomers at different ripening stages for five days. Analyses of TPC and TC were performed using the Folin-Ciocalteu method, whereas tannin monomers were identified by High-Performance Liquid Chromatography (HPLC) with UV detection. Multivariate analysis of variance was used to evaluate the relationship between cultivar, ripeness stage, and TPC/TC. A substantial difference in TPC was observed between juice-producing and cooking cultivars. The highest TPC was found in the juice-producing cultivar Kibungara (360.68 ± 17.12 mg GAE/100 g) at day 5 (the ripe stage), while the lowest TPC (8.67 ± 0.22 mg GAE/100 g) was observed in the cooking cultivar Malindi at ripening day 5. The results revealed that TPC and TC of banana pulp seemed to be more related to cultivar (p ≤ 0.05) than physiological changes during ripening (p ≥ 0.05). Further, HPLC analysis showed that among the individual catechins, gallocatechin was the predominant monomer in juice-producing cultivars, whereas in cooking cultivars, gallic acid was dominant. The present work indicated that high amount of total phenolic such as tannins especially gallocatechin in juice-producing banana cultivars favour the release of banana juice, and that analysis of phenolic compounds will provide a basis in the selection of banana cultivars with high potential for juice production.