PROPOSAL OF AN INDEX FOR THE OBJECTIVE EVALUATION OF THE COLOR OF REDTABLE GRAPES

A colour index for the objective determination of the colour in red ta ble grapes is described. This index is based on the CIELAB values. A s tatistical 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 c olour. The proposed colour index for red grapes (CIRG) is based on the parameters L (lightness), H (hue angle) and C (chroma) and its expre ssion is ''(180-H)/(L + C)''. All the colour indexes previously propo sed were defined in fruits whose colour varied between yellow and red, and, therefore, were not suitable for red grapes which show a dark vi olet colour. This new index showed a good linearity with the visual co lour of the berries and distinguished between sample groups of differe nt external colour.