PROPOSAL OF AN INDEX FOR THE OBJECTIVE EVALUATION OF THE COLOR OF RED TABLE GRAPES

A colour index for the objective determination of the colour in red table grapes is described. This index is based on the CIELAB values. A statistical study revealed a high correlation between L* and b*, while a* was not a representative parameter. The usefulness of this index is investigated to classify the red grapes depending on their external colour. The proposed colour index for red grapes (CIRG) is based on the parameters L* (lightness), H (hue angle) and C (chroma) and its expression is ''(180-H)/(L* + C)''. All the colour indexes previously proposed were defined in fruits whose colour varied between yellow and red, and, therefore, were not suitable for red grapes which show a dark violet colour. This new index showed a good linearity with the visual colour of the berries and distinguished between sample groups of different external colour.