Fruit colour progression in grapefruit with relation to carotenoid and Brix-acid ratio

In citrus, fruit colouration is considered one of the criteria to assess the optimum harvest maturity. The present study the fruit colour variations, β-carotene and its relation to soluble Brix/acid ratio (B/A ratio) during development in four grapefruit varieties viz. Marsh Seedless, Flame, Rio Red and Redblush were investigated. Among different grapefruit varieties, the highest peel colour coordinate a* value and β-carotene content were recorded in cv. Flame at 270 days after full bloom (DAFS). The peel β-carotene concentration varied from 3.61 to 61.42 μg.g-1 during fruit development. L*coordinate showed a declining pattern in the pulp, while it increased in peel till 270 DAFS. Likewise, b* values also increased in both peel and pulp. Chroma (C*) and B/A ratio values of fruit increased with maturity, while the hue angle (h°) decreased. L*a*b*colour coordinates showed a strong correlation with B/A ratio compared to β-carotene content. At the final fruit harvest, the higher value for L* coordinate in peel and pulp was noted in ‘Redblush’ and ‘Marsh Seedless’. In contrast, the highest b* coordinate was observed in the peel and pulp of the Marsh Seedless variety. Overall, a* coordinate was observed to be the most reliable colour parameter to determine the maturity index in the studied varieties of grapefruit.