How red are those tomatoes?

When it comes to fresh vegetables and fruits, colour is one of the best indicators of quality. Along with texture, size and flavour, colour plays an important role in the business of horticultural crop production and marketing.

In tomatoes, for example, colour and colour uniformity contribute directly to quality and marketability. The presence of yellow shoulder disorder, or YSD, a ripening disorder that results in blotchy discolouration under the skin of the tomato, is a major quality issue.

Colour disorders are also an economic problem. In the US, ‘grades’ are largely determined by the amount of off-colour tissue in products, and growers can receive premiums for fruit based on colour and uniformity. Discolouration due to YSD also reduces concentrations of nutrients such as lycopene and beta-carotene. Clearly, reducing YSD in tomatoes could benefit producers, processors and consumers alike.

In an issue of the Journal of the American Society of Horticultural Science (ASHS), David Francis and his colleagues at The Ohio State University's Agricultural Research and Development Center and the College of Wooster describe the use of a new tool they implemented in the Tomato Analyzer (TA) software called Color Test (CT). This tool allows scanning devices to be calibrated using colour standards. The objective of the research was to implement a new digital image analysis tool.

According to the study, Tomato Analyzer was originally designed to analyse the morphology of tomato fruit. The researchers in this study developed a module for colour measurement "to expand the array of objective phenotypic analyses implemented". TACT was applied to fruits and vegetables of various colour and colour uniformity.

"TACT was designed to be user friendly with minimum requirements for running it, yet accurate and precise for collecting objective measurements. It facilitates data collection and management, and requires equipment that is relatively more affordable," Francis explained.

Traditional tools used to measure colour of vegetables and fruits require extensive environmental control, especially for the quality and quantity of light, shadow and reflection. In contrast, the flatbed scanners used in this study required only a cardboard box as a cover to minimise the effect of shadow.

TACT was able to accurately capture and describe the characteristic colour for each crop when applied to other fruits and vegetables of varying colours and colour uniformity. Colour uniformity was also well characterised for fruit that tends to have non-uniform pigmentation, such as the strawberry. TACT proved to be a reliable, precise and affordable method for digital image analysis of colour.

The study authors envision that TACT could be used not only in colour analysis of fresh crops, but perhaps to evaluate discolouration of food after processing or cooking in food science applications.

The complete study and abstract are available on the ASHS J. Amer. Soc. Hort. Sci. electronic journal website.