Recent citrus research on red grapefruit from Spain and South Africa

Collated from the literature by John Golding, Horticulture Market Access Group, NSW Department of Primary Industries

New research appears to show that increased lycopene helps to prevent chilling injury during storage in red grapefruit.

The distinctive colour of red grapefruit is due to lycopene, which is an unusual carotene (chemical) in citrus. It has been observed that red Star Ruby grapefruit grown inside the tree canopy develop a more intense red coloration than those exposed to higher light intensities.

To investigate the effect of light on Star Ruby peel pigmentation, researchers in Spain and South Africa placed paper bags on growing fruit and compared those with fruit exposed to normal growing conditions. Bagging the fruit on the tree accelerated chlorophyll breakdown and induced carotenoid accumulation, rendering fruit with an intense coloration. Remarkably, lycopene levels in the peel of shaded fruits were 49-fold higher than in light-exposed fruit.

Lycopene has been shown to have significant human health benefits and is also responsible for the red colour in tomatoes.

This research group further showed that high lycopene concentration appears to be responsible for the induction of tolerance to chilling in the red-coloured areas of the flavedo of grapefruit during postharvest storage at low temperatures.

Grapefruit are among the most susceptible citrus species to develop chilling injury when stored at temperatures below 8–10 °C. Chilling injury symptoms in grapefruit start as small brown pits on the fruit surface that get bigger, forming shrunken brown spots and depressed areas that can affect large surface areas of the rind after cold storage.

Dr Joanna Lado and her research team showed that the chilling injury symptoms in red Star Ruby grapefruit were restricted to the yellow areas of the rind; the red-coloured zones showed almost no cold damage. This tolerance to chilling injury in the red flavedo was associated with high carotenoid (×2) and lycopene (×14) contents compared with yellow-coloured flavedo.

References

Lado J., Cronje P., Alquézar B., Page A., Manzi M., Gómez-Cadenas A., Stead A.D., Zacarías L. & Rodrigo M.J. (2015). Fruit shading enhances peel color, carotenes accumulation and chromoplast differentiation in red grapefruit. Physiologia Plantarum, 154: 469–484. doi: 10.1111/ppl.12332.

Lado J., Rodrigo M.J., Cronje P. &  Zacarías L. (2015b). Involvement of lycopene in the induction of tolerance to chilling injury in grapefruit. Postharvest Biology and Technology, 100:176–186.