Bioactive compounds in banana fruits and their health benefits

Banana is an edible fruit and is herbaceous flowering plant belonging to the genus Musa and the family Musaceae.Banana is also eaten as cooked vegetable(and is then called plantains).All the edible banana fruits are seedless(parthenocarpic)and belong to two main species,Musa acuminata Colla and Musa balbisiana Colla.The hybrid from these two species Musa x paradisiaca L.is also available nowadays.Although banana is native to Indomalaya and Australia,Papua New Guinea was the first to domesticate this fruit.Banana has now spread to almost 135 countries around the world.As per 2016 data,nearly 28 per cent of the total world’s banana production comes from India and China.Cavendish group banana,being the main export item from the banana-exporting countries,usually refers to soft,sweet,and dessert banana in the Western countries,but the plantain bananas have firm,starchy fruit which is suitable for cooking as a vegetable.Banana is known to be rich not only in carbohydrates,dietary fibres,certain vitamins and minerals,but is also rich in many health-promoting bioactive phytochemicals.General composition including various bioactives and their health contributions has been reviewed in this paper.

Effects of high CO_2 treatment on green-ripening and peel senescence in banana and plantain fruits

Banana fruit（Musa,AAA group,cv.Brazil） peel fails to fully degreen but the pulp ripens normally at temperatures above24°C.This abnormal ripening,known as green-ripening,does not occur in plantains（Musa,ABB group,cv.Dajiao）.Based on the fact that un-completely yellowing was also observed for bananas in poorly ventilated atmospheres,in the present study,the effect of high CO2 with regular O2（21%） on banana ripening was investigated along with that on plantains at20℃.The results showed that high CO2 conferred different effects on the color changing of bananas and plantains.After6 d ripening in 20%CO2,plantains fully yellowed,while bananas retained high chlorophyll content and stayed green.In contrast to the differentiated color changing patterns,the patterns of the softening,starch degradation and soluble sugar accumulation in the pulp of 20%CO2 treated bananas and plantains displayed similarly as the patterns in the fruits ripening in regular air,indicating that the pulp ripening was not inhibited by 20%CO2,and the abnormal ripening of bananas in 20%CO2 can be considered as green ripening.Similar expression levels of chlorophyll degradation related genes,SGR,NYC and PaO,were detected in the peel of the control and treated fruits,indicating that the repressed degreening in 20%CO2treated bananas was not due to the down-regulation of the chlorophyll degradation related genes.Compared to the effect on plantains,20%CO2 treatment delayed the decline in the chlorophyll florescence（F√F_m values and in the mRNA levels of a gene coding small subunit of Rubisco（SSU）,and postponed the disruption of the ultrastructure of chloroplast in the peel tissue of bananas,indicating that the senescence of the green cells in the exocarp layer was delayed by 20%CO2,to more extent in bananas than in plantains.High CO2 reduced the ethylene production and the expression of the related biosynthesis gene,ACS,but elevated the respiration rates in both cultivars.The up-regulation of the expression of anaerobic respiration pathway genes,ADH and PDC,might be responsible for the subtle effect of high CO2 on the pulp ripening.Taken together,the atmosphere of high CO2 and regular O2,delayed the senescence of the green cells in the exocarp layer of the banana peel,but conferred no obvious inhibition on the pulp ripening,leading to a distinct green-ripening that was different from the phenomenon induced by high temperatures.

Molecular Cloning and Characterization of Fruit Softening Related Gene β-Mannanase from Banana Fruit

A 1 250 bp cDNA fragment encoding β-mannanase, named MaMAN, was cloned from banana （Musa spp cv. Baxi） fruit using degenerate primers designed with reference to the conserved nucleic acid sequences of known β-mannanase genes by RT-PCR. Sequence analysis showed that MaMAN cDNA encompassed a 1 085 bp open-reading frame （ORF）, encoding a predicted polypeptide of 395 amino acids. Alignment of the deduced amino acid sequence of MaMAN and other putative β-mannanases showed that MaMAN has an identity of 86, 70, 69, 54, and 57%, respectively, to β-mannanases from tomato, lettuce, arabidopsis, carrot and oryza sativa. The catalytic residues： Asn203, Glu204, Glu318 and the active site residues： Arg86, His277, Tyr279, and Trp360, which were strictly conserved in the glycoside hydrolase family 5 to which all β-mannanases belonged, were found in MaMAN. Semi-quantitative RT-PCR revealed that the level of MaMAN transcript in the pulp increased during banana fruit ripening, suggesting that MaMAN was likely to be involved highly in banana fruit softening.

A Banana PHD-Type Transcription Factor MaPHD1 Represses a Cell Wall-Degradation Gene MaXTH6 during Fruit Ripening

Plant homeobox domain(PHD)-type transcription factors(TFs) are involved in a variety of biological processes. However, its involvement in commercially important fruit ripening process remains largely unclear. In the present work, the characterization of a PHD-type TF termed MaPHD1 from banana fruit is reported. Multiple alignments of the deduced amino acid sequence revealed that Ma PHD1 showed a high homology with Arabidopsis thaliana Alfin1-like proteins belonging to plant-specific sub-family of PHD finger proteins. MaPHD1 was found localized in the nucleus and exhibited trans-repression ability. It was down-regulated by ethylene and ripening. Electrophoretic Mobility Shift Assay(EMSA) and transient expression analysis demonstrated that Ma PHD1 directly bound to the G-rich motifs in the promoter of Ma XTH6, which is associated with cell wall degradation, and subsequently repressed its expression. These findings suggest that MaPHD1 may be negatively associated with banana fruit ripening, at least in part, by the direct suppression of Ma XTH6. Taken together, these findings provide new insights into the transcriptional regulatory networks of banana fruit ripening.

Pre-harvest and post-harvest application of benzothiadiazole for controlling anthracnose and extending shelf life of harvested banana

Anthracnose,caused by the fungus Colletotrichum musae,is a serious latent post-harvest disease of banana,which results in major economic losses during transportation and storage.Benzo-thiadiazole-7-carbothioic acid S-methyl ester(BTH),a functional analogue of the plant endogenous hormone-like compound salicylic acid(SA),has been known to possess resistant effects on some diseases caused by fungi.The aim of present study was to select an appropriate BTH concentration and an appropriate stage of banana ripening for its application in controlling anthracnose and extending shelf life of harvested banana fruit.Different concentrations of BTH(50,100,200 and 300μg/mL)were applied at different stages of banana fruit ripening,including one week,two weeks and one month before harvest.The results suggest that while the concentrations of BTH ranging from 50μg/mL to 200μg/mL in both pre-harvest and post-harvest application,this could control anthracnose of harvested banana fruit,the appropriate concentration of BTH in both pre-harvest and post-harvest treatment was 100μg/mL and the best time of BTH treatment was two weeks before harvest.Examination of quality parameters including peel color and firmness indicated that 100μg/mL BTH treatment delayed banana fruit ripening at room temperature.