Harvest Watch™ — A Type of Dynamic Controlled Atmosphere

Dynamic controlled atmosphere (DCA) storage uses technology that involves monitoring the responses of fruit to low oxygen. Fruit responses can be detected by measuring metabolic processes, such as ethanol production, fruit respiration, or chlorophyll fluorescence.

HarvestWatch™ is a fluorescence-based DCA technology, which has been marketed by Satlantic Inc. (Nova Scotia) for several years. Recently, however, the South African company Gas At Site Inc. became the license holder for this technology in North America. With this, there seems to be a resurgence of interest and questions about the HarvestWatch technology.

Chlorophyll fluorescence can be used to measure stress in apple fruit, such as that from low oxygen or high CO₂ atmospheres (DeEll et al.,1995). HarvestWatch monitors these fluorescence changes and indicates when the fruit is under low oxygen stress during storage (DeLong et al., 2004). The monitors (fluorescence interactive response monitor, FIRM^TM) used by the HarvestWatch system are connected to a computer control system and the operator adjusts oxygen levels in response to any fluctuations in the fluorescence signals. As such, more operator training is required than that for a traditional CA, in order to interpret the fluorescence information. It is recommended that a buffer of ~0.2% oxygen be added to the level of at which fluorescence changes in order to provide a safety margin against injury (Watkins, 2008).

There is limited literature investigating the fruit quality benefits from using HarvestWatch and most involves comparison to standard CA regimes (not less than 1.5% O₂). DeLong et al. (2004) evaluated several apple cultivars, comparing the use of HarvestWatch (<1% oxygen) and static CA at 1.5% oxygen. For the longest storage durations, there was no significant difference in the firmness of ‘Delicious’ (9 months) or ‘Honeycrisp’ (6 months) apples, while ‘McIntosh’ (8 months) and ‘Golden Delicious’ (9 months) were ~1 lb firmer using HarvestWatch. Other studies have shown a reduction in superficial scald incidence with HarvestWatch, such as 8 vs 17% (in standard CA) in ‘Delicious’ and 31 vs 79% in ‘Cortland’ (DeLong et al. (2007) as cited by Watkins, 2008), and no significant effects on senescent-related disorders (Prange et al., 2003).

British Columbia has had extensive commercial experience using 0.5-0.7% or 1-1.2% oxygen on various apple cultivars since 1989 without any CA-induced fruit injury. After substantial testing of HarvestWatch, it was concluded there that inclusion of the system to commercial CA rooms was not justified due to the equipment cost and no additional low-oxygen benefit. Most importantly, any fruit loss under a commercial setting was to be the sole responsibility of the end-user and not the distributor of HarvestWatch, and thus the packinghouse management / CA operators were not willing to risk their fruit pushing the low limit of oxygen for little added benefit (Lau, personal communication).

The use of HarvestWatch is limited to storage operations that have high quality CA rooms with adequate air-tightness, as well as accurate gas control systems to maintain oxygen levels below 1%. These are also the same commercial factors that limit the use of known safe low oxygen regimes (0.7-1.5%) for certain apple cultivars.

Each HarvestWatch sensor monitors only six apples, so the variability in fruit behaviour within that storage room must be considered. It is well known that there are major differences in the minimal acceptable oxygen level among apple cultivars, growing seasons, and orchard blocks. Watkins (2008) concluded that there has been insufficient work in New York to show whether the variability among orchard blocks typical of our growing region will permit the safe adoption of HarvestWatch technology.

HarvestWatch is one type of DCA technology that is being marketed commercially. However, it is not the only way to utilize lower oxygen levels or programmable CA storage. The use of low oxygen by measuring the alcohol content of apples and adjusting the oxygen level accordingly is being promoted by an Italian company (Schaefer, personal communication). Others are simply using combinations of ultra-low oxygen (<1%) storage and initial low oxygen stress (~0.5%) to eliminate the use of postharvest chemicals. Research in Ontario and Québec has shown that programmed CA regimes with sequential reductions in oxygen and/or temperature can increase firmness retention (+3.6 lb) and reduce incidence of storage disorders (0 vs. 25-32%) in apples (Lévésque et al., 2006).

Whatever you choose, always be sure to evaluate the risk to your fruit in addition to the economics and potential benefits of the technology. A thorough risk-benefit analysis of any new technology is more likely to result in a better investment decision.

Literature Cited

DeLong, J.M., R.K. Prange, J.C. Leyte, and P.A. Harrison. 2004. A new technology that determines low-oxygen thresholds in controlled-atmosphere-stored apples. HortTechnology 14:262-266.

DeLong, J.M., R.K. Prange, and P.A. Harrison.2007.Chlorophyll-fluorescence based low-O₂ CA storage of organic ‘Cortland’ and ‘Delicious’ apples. Acta Hort. 737:31-37.

Lévésque, G., J.R. DeEll, and D.P. Murr. 2006.Sequential controlled atmosphere storage for ‘McIntosh’ apples. HortScience 41:1322-1324.

Prange, R.K., J.M. DeLong, P.A. Harrison, J.C. Leyte, and S.D. McLean. 2003. Oxygen concentration affects chlorophyll fluorescence in chlorophyll-containing fruits and vegetables. J. Amer. Soc. Hort. Sci. 128:603-607.

Watkins, C. B. 2008. Dynamic Controlled Atmosphere Storage – A New Technology for the New York Storage Industry. New York Fruit Quarterly 16(1):23-26.

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