Predicting broccoli head maturity


Predicting broccoli head maturity

The fresh produce industry is always looking for new types of technology to automate assessments of produce quality that don’t damage the produce itself. Non-destructive techniques that can predict storage quality are even more valuable.


Knowing the perfect time to harvest broccoli for optimal shelf-life and good storage behaviour has long been a tricky process for growers. Areas of a crop with seemingly identical heads, harvested at the same time, can display widely differing keeping qualities. This creates an obvious problem for scheduling a crop that, with variability in weather and consumer demand throughout the season, may need to be stored for up to three weeks to balance supply and demand.


In a three-season project funded by AHDB Horticulture, the Produce Quality Centre (a collaboration between University of Greenwich’s Natural Resources Institute and NIAB EMR)   has investigated the use of one particular technique, chlorophyll fluorescence, to predict the storage life of broccoli heads.


In green vegetables, a deterioration in quality is associated with the loss of the green colour associated with photosynthesis – because the chloroplasts that photosynthesise start to break down. As a technique that can measure both the concentration and the activity or health of chloroplasts within plant tissues, it was recognised that chlorophyll fluorescence has the potential to assess maturity and health for a wide range of crops.


Indeed, it had already been trialled in earlier levy funded work (FV 395). Changes in the health of broccoli heads had been mapped during storage and the subsequent retail supply chain – the research found that a decline in the number of active chloroplasts was directly related to a loss of head quality, leading to deterioration.


In FV 425 chlorophyll fluorescence has been tested on harvested broccoli heads over three seasons, harvested from locations in Kent and Lincolnshire. The chlorophyll fluorescence characteristics of the heads was measured immediately after harvest and then the heads were stored for two or three weeks under conditions that simulated commercial storage. Once out of storage the quality of the individual heads was followed over several days under ambient conditions to simulate retail environments.


This method allows the measurement of chlorophyll fluorescence characteristics of broccoli heads taken immediately after harvest to predict how well consignments will store. The measurement chosen is able to give a consistent predictions over three seasons and on crop produced from very different growing environments.




Having demonstrated a technology with potential to distinguish between broccoli consignments, work is underway to make this into a useful tool for the fresh produce industry. The Natural Resources Institute is working with Hansatech Instruments to develop a handheld tool which can assess broccoli heads quickly and easily. The prototype multi-sensor can take readings at different points on the head and the researchers will be looking for ways to improve its accuracy and speed up measurements.


“We have identified an efficient way of using chlorophyll fluorescence to predict storage quality of broccoli heads and will be working with broccoli growers this autumn to test the commercial potential of this technology” commented Dr Debbie Rees.


Samples are being taken this autumn during the storage season to compare predictions based on packhouse measurements against actual keeping quality. Next steps also include liaising with commercial growers to investigate exactly how this technology can be slotted into their normal practice for most benefit.