Expenditures – HarvestWatch has a one-time capital expenditure for chlorophyll fluorescence sensors and software. Since DCA costs are one-time capital expenditures, there are no recurring annual charges compared with other chemical-based alternatives, e.g. ethanol, and the HarvestWatch technology adds to the asset value of the storage facility.
The technical features of DCA that are appealing to users are:
• Non-destructive measurements on large surface areas can be taken of any chlorophyll-containing fruit or vegetable.
• The measurement is rapid, ca. 1 minute, and the frequency can be easily altered. The default setting is every hour.
• The method is non-chemical. It does not rely on adding any chemicals or analysing any chemicals.
• Real-time monitoring of produce allows for on-site or remote monitoring and archiving of data for future reference.
• There is no calibration needed, either before or while in operation. The sensors are very stable. Some of them are over 10 years old.
• It detects changes in the product due to senescence, decay or incorrect storage conditions, i.e. temperature, unwanted toxic gases such as ammonia refrigerant.
Its non-chemical feature makes it appealing to industrial users who wish to reduce post-harvest chemical use or store ‘organic’ product. Others have adopted it because it is a one-time capital expense that can have a pay-back period of 2-3 years, compared with repeated annual expense with competing chemical-based methods.
The sample fruit in the kennel should reflect the average of the fruit in terms of maturity, size and colour. The fruit should be placed so that the side facing the sensor is at the transition between the sun and shade side. In some fruit, e.g. apples, the ‘sun’ side, compared with the ‘shade’ side, has not only more chlorophyll but may also differ slightly in maturity and LOL.
Once the Fα ‘spike’ is observed, indicating the lower oxygen limit (LOL), the O2 should be increased at least 0.2% (or 0.3% in ‘Delicious’ apple) to account for the small LOL variation that may occur in the fruit.
In the raw Fα setting, the values should be at least 1,500 to 2,000 initially. One can have initial values that are lower, but this is not recommended since it will result in the normalised Fα setting having more signal noise due to calculation of the normalised value.
The recommended procedure to achieve raw Fα values of 1,500 or more is to fill the kennel with sample fruit so that each fruit is ‘seen’ by the small fluorescence detector located in the middle of the FIRM sensor. DO NOT stack fruit because only the top fruit in the stack will be measured.
Take some raw Fα measurements and if the values are too low, replace fruit with ones that are larger or greener so long as they are still representative of the fruit.
If the signal remains lower than 1500 even after this is done that is not a problem so long as one recognises that the normalised Fα values may have more noise. An alternative is to use the raw Fα measurements.
Based on our >18 years of experience with commercial users of the HarvestWatch system, new users tend to start with 1 FIRM sensor per 250 bins of each orchard/cultivar lot in a CA room.
We have observed that some users, after several storage seasons with the same orchard/cultivar lot, reduce the number of sensors per CA room.
However, one should always have at least 2 sensors in each CA room. If the fruit in one FIRM kennel is giving unusual readings, it is good to have a second FIRM sensor for comparison.
Fruit of a single cultivar from different orchard lots can have different Low Oxygen Limits (LOLs) and it can vary with the season.
The HarvestWatch system is the only system that permits a commercial user to monitor these different orchard lots in a single CA room.
If you suspect orchard differences, put a representative sample from each orchard lot under a separate FIRM sensor and, if there are different LOLs, control the oxygen level in response to the sample that has the highest LOL value.