UBC Theses and Dissertations
Some physical chemical and histological characteristics of ripening bananas Charles, Ronald John
A study of changes in bananas during ripening at 16 ± 1°C and 25 ± 1°C is described. Peel color was evaluated subjectively and by reflectance spectrophotometry; rheological properties by parallel plate compression and viscometry; selected chemical properties by appropriate tests and histochemical and histological properties by light microscopy. The rate of peel color change at the higher temperature was roughly twice that at the lower. Higher temperature-ripened fruits did not develop a full yellow color due to chlorophyll retention in the peel. Also pulp-to-peel ratio for such fruits tended to be lower than that of fruits ripened at the lower temperature. The pulp of high temperature-ripened fruits became progressively softer and was reflected by a linear increase of deformation under 1 kg force. For a given peel color index, maximum force and linear limit of the tissue as well as a power-law consistency coefficient of the puree were generally lower during ripening at the higher temperature. Reducing sugars increased linearly throughout ripening at the higher temperature while at the lower temperature the reducing sugar content was essentially constant beyond color index 6. On the basis of peel color index, total sugar and moisture content were higher while starch and AIS levels were lower in fruits ripened at the higher temperature. Ripening temperature therefore influences the relations of color index to mechanical and chemical properties. Ripening was characterized by a gradual loss of rigidity as well as an apparent thickening of the cell wall in over-ripe pulp tissue. Tannins decreased during ripening but did not disappear completely. Esterified pectins were not detected in hard green fruit; however, substantial amounts appeared at peel color index 3, then decreased steadily during ripening. Peel color was the best overall index of stage of ripeness for both ripening temperatures. Although rheological and chemical properties at a given color index differed for the two ripening temperatures, these intercorrelations remained higher (P ≤ 0.01). It is recommended, that ripening temperatures be taken into account when the color index chart is used to estimate the stage of ripeness of bananas.
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