Scientists develop new non-invasive method to determine fruit ripeness

Spanish researchers have developed a new non-invasive method to determine the optimal ripeness of fruit by analysing its leaves.

The technique, which has just undergone an eleven-week trial in a commercial nectarine orchard, employs infrared spectroscopy to determine the condition of the fruit from the leaves, using the direct physiological relationship between the two. As fruit ripens, its nutrient flows, biochemical compounds, and metabolism change, leaving a trace on the leaves.

The team behind the breakthrough at the Rovira i Virgili University said the method avoids production losses stemming from having to cut the fruit to determine its ripeness and paves the way for more precise harvesting decisions.

It could offer a more commercially viable alternative to scanning the fruit with a spectrometer, which can mark its skin resulting in a loss of commercial value.

The technology uses two spectrometers that analyse both the upper and lower surfaces of the leaves near the fruit. One operates in the near-infrared, the other in the mid-infrared. The way the leaf absorbs and reflects light at these wavelengths generates a specific spectral signature. This fingerprint, when interpreted correctly, reveals the fruit’s ripeness without needing to touch it.

According to the research team, the strongest correlations have been obtained for parameters such as weight and firmness, two key variables for determining the harvest time. Other common indicators – such as sugar content and acidity – still show less accuracy, although the system continues to be refined. The researchers stressed that this is very much an evolving technology.

They are now working on incorporating the technology in portable devices that can be used directly in the orchard.

In the medium term, the developers said the system could provide a useful tool for growers in an environment where climate change is making ripening windows increasingly difficult to predict.