Relationship between electrical conductivity, softening and color of Fuerte avocado fruits during ripening

Abstract

To identify the most important ripening parameters of Fuerte avocado fruits, and to quantify the relationship between color changes, electrical conductivity and softening of avocado fruits, the ripening process was investigated to fulfill the consumer and market demands. Mature and high quality avocado fruits (Persea Americana Mill.) were held to ripe at 20C in controlled temperature rooms with 90-95% relative humidity for two weeks. Fruit quality characteristics (respiration rate, soluble solids content (SSC), total acidity (TA), ascorbic acid and oil content) during ripening period at 20C were evaluated. Moreover, ripening parameters as color changes, chlorophyll contents, fruit firmness and electrical conductivity and ripening enzymes (CX and PME) were also investigated throughout ripening process. During ripening period for 2 weeks at 20C, fruit quality criteria showed that respiration rate and oil content had a noticeable significant increase with the ripening increase. While, acidity (TA), soluble solids (SSC) and ascorbic acid content cleared a slight and significant decrease. Throughout color development, the three parameters lightness (L*), hue (h◦) and chroma (C*) changed significantly, hue decreased little, lightness moderately, while chroma changed more quickly. Moreover, an significant decline in chlorophyll a and b concentration occurred and reflected to color changes during ripening process. For ripening enzyme activities, Fuerte avocado fruits showed a great increase in cellulase activity compared with gradual decrease in Pectinmethylesterase activity after ripening. Avocado fruit firmness markedly reduced gradually after harvest till ripening at 20C, and this decline was positively correlated with an increase of electrical conductivity of the fruit tissue suggesting a gradual loss of cell membrane integrity. This increase in conductivity was promoted by ripening process. These results have allowed us to set that ripening process had some parameters were simple and rapid to measure as ripening indices. We conclude that in Fuerte avocado fruits, electrical conductivity (EC) can serve as a good indicator of membrane permeability and that it is highly correlated with ethylene production, softening and also demonstrates a relationship between firmness and EC.