Supply of consistent quality fruit to consumers is one of the major challenges facing the Australian fresh fruit industry.
An important factor affecting fruit quality is maturity and it is essential to maintain optimum maturity at every step in the chain from harvest to consumption.
Despite being a major driver of fruit quality it is not easy to measure and maintain maturity at optimum levels from farm to consumer.
Fruit maturity is directly linked to most of the variables that comprise fruit quality such as total soluble solids, total acidity, flesh firmness, fruit colour and starch content.
These are normally determined destructively on a sample of fruit which is not always representative of the variability of fruit batches. There are currently only a few instruments that allow non-destructive measurements of specific fruit quality attributes such as soluble solids and flesh firmness.
Equipment that is commercially available commonly uses visible (vis) and near infrared (NIR) spectroscopy and acoustic technologies respectively. These devices can be used in the field or on packing lines, but can be expensive, relatively slow and generally require frequent, complex calibration on a large number of fruit to be useful.
Non-destructive fruit maturity meter
Recently, a new non-destructive fruit maturity meter was developed in Italy and is being tested by DPI Victoria.
The DA Meter (Figure 1) is an innovative instrument for non-destructively determining fruit maturity by measuring the decline in chlorophyll content immediately below the skin during ripening.
Developed and patented by Professor Costa and his team at the University of Bologna, Italy, the DA Meter is a portable spectrometer which can accurately monitor fruit maturity.
A maturity index is developed for each fruit variety by calculating the difference in absorbance (DA) between two wavelengths (670 and 720 nm) close to the absorbance peak of chlorophyll-a and comparing this with fruit ethylene production.
The DA value is strongly correlated with ethylene production of fruit, which is an indicator that ripening has started.
The DA decreases in value during ripening of the fruit, until it reaches a minimum value when fruit ripening is complete.
Potential use for DA values in stone and pome fruit
Each fruit species and cultivar has specific DA values according to the different phases of maturation.
Consequently a set of reference indices are required for each cultivar, but once established they can be used year after year as DA values are not affected by agronomic or postharvest practices.
This is a major advantage over other non-destructive technologies which require at least annual re-calibration.
Pioneering research by the University of Bologna team indicated that the DA Meter exhibited great potential in the peach production chain. In the field, it was used to establish the optimum time to harvest and in the pack house the DA value was used successfully to accurately sort fruit according to maturity.
It can also be used during the cold chain to establish maturity changes over time.
In another study, the potential of the DA Meter was assessed for segregating peaches and nectarines into consistent quality classes based on shelf life and consumer preference attributes.
The DA easily separated fully red peach varieties into consistent classes which had a high correlation with ethylene production rate, postharvest ripening behaviour and consumer acceptance.
Other research has shown that the DA Meter is a reliable tool for monitoring on-tree apple ripening to establish the optimum harvest time to maximise fruit storage life and quality.
Research needed to fully utilise potential
A great deal of additional research is necessary to fully utilise the enormous potential of this instrument.
Assigning DA values to each stage of the chain is one step required for adoption of the DA technology by the horticultural industry. Further research is required to identify the correct DA value ranges for each step.
To optimise maturity and quality during the entire fruit chain the DA Meter can be used as a tool to:
- optimise crop load and other agronomic practices to obtain a consistent, high quality crop
- reduce the number of picks and reduce fruit variability
- identify the optimal picking window
- monitor and quantify maturity of stored fruit and at any specific time the shelf-life potential of the fruit
- sort fruit according to maturity, thus guaranteeing optimal, predictable and consistent storage quality whether using normal air, CA or 1-MCP
- increase market flexibility by being able to measure and predict suitability of fruit for supplying local, national or export markets and minimising variability in shelf life and market performance
- enable retailers to rapidly and accurately measure fruit maturity to mange inventory thus presenting produce consistently at the required consumer preference.
Fruit maturity could become the quality parameter that allows full integration of information between practitioners at each step in the chain based on an exact reference value provided by the DA Meter.
Monitoring fruit maturity using DA values along the value chain will allow the identification of best management practices at each step which will reduce losses due to variable quality and will increase efficiency and profitability.
Knowing the ideal DA value that correlates with quality preferred by consumers will permit real time correlation at each step of the chain allowing fast decisions on the future of each fruit regarding the remaining shelf life and consequently the preferred market. This will increase consumer satisfaction and return sales.
Consistent, simple value chain protocols can be created and whole system models implemented to provide a high level of agility for the Australian industry and the ability to respond rapidly and strategically to market contingencies and outside pressures both locally and internationally.
Testing under Australian conditions
The Department of Primary Industries Victoria based at Knoxfield has recently acquired a DA Meter and is testing its efficacy on stone and pome fruit varieties under Australian conditions.
Close collaboration with the University of Bologna team has allowed data exchange and frequent discussion to further develop this revolutionary instrument.
Currently, DA value ranges at each step of the chain for key varieties are unknown and DPI is planning research projects which will help identify them. As a start, the DA Meter has been integrated as a standard measurement at harvest time in current and future DPI pome and stone fruit projects.
Future research projects cover all steps in the value chain including fruit production, harvest, handling, storage, fruit composition and quality and consumer preferences.
However, considerable industry investment and collaborative effort will be required to cover the broad range of possible fruit species and variety.
Preliminary results
Preliminary results in Australia indicate that the DA Meter is very effective for monitoring and quantifying the effects of irrigation on Royal Gala maturity at harvest (Figure 2) as well as measuring fruit maturity at harvest to predict storage life and susceptibility to chilling injury of mid season peach and nectarine varieties.
Full adoption of the DA-Meter will help project the current Australian horticulture supply chain into the 21st century, transforming it into a powerful value chain leading the world wide horticultural market in term of volume and quality.
For information and contact details, see the July 2012 Tree Fruit.
