Colour

Instrumental colour measurement reports a position in a defined colour space, most commonly CIE L*a*b*, where lightness, and the red-green and yellow-blue axes together locate a colour, or the derived hue angle and chroma, which describe the same information as an angle and a saturation. Both the illuminant used to light the sample and the geometry of the measuring instrument are part of the specification, because both change the reading obtained from an identical physical sample.

This is why a colour figure is only meaningful alongside the method that produced it. A reading taken under one standard illuminant is not the same measurement as one taken under a different illuminant, and figures from instruments with different measurement geometries should not be compared as though they were equivalent.

Colour is the attribute consumers actually use to judge fresh produce at the point of purchase, ahead of any internal quality attribute they cannot see or assess without buying the unit first. This makes colour disproportionately influential in purchase decisions relative to its actual predictive power over eating quality, and it is why colour is graded, monitored, and in some cases deliberately manipulated — through practices such as ethylene degreening of citrus — independent of what is happening to the commodity’s internal condition.

Chlorophyll loss

Breakdown of green chlorophyll pigment, unmasking underlying pigments as many fruit ripen.

Carotenoid accumulation

Synthesis of yellow, orange, and red carotenoid pigments during ripening in many fruit.

Anthocyanin accumulation

Synthesis of red, purple, and blue anthocyanin pigments, often concentrated in the skin and influenced by light exposure.

Enzymatic browning

Oxidation reactions at a cut, bruise, or other wound, catalysed by enzymes released when tissue is damaged.

Non-enzymatic (Maillard) browning

Chemical browning between sugars and amino compounds during drying and storage, distinct from enzymatic browning at a wound.

Because of this, colour should be read alongside — never in place of — attributes that more directly track ripening, and it says nothing about internal condition: a well-coloured unit can still carry internal browning or breakdown that only cutting the unit would reveal.

Colour is rarely uniform across a single unit. The sun-exposed side of a fruit typically differs in colour from its shaded side, and colour can vary between the stem end and the blossom end, or across a kernel surface. Because of this, where the instrument is pointed changes the reading obtained from the very same unit, and a single point measurement should not be presented as though it characterises the whole unit.

A colour figure reported for a lot, rather than a single unit, is only meaningful if it comes from a defined sampling pattern — a stated number of units, a stated number of readings per unit, and stated measurement locations — applied consistently. An undocumented sampling approach undermines the comparability of the resulting figure just as much as an undocumented illuminant or instrument geometry does.