We have all found ourselves caught out by the wilted fresh herb. A beautiful, fresh addition to a dish that never lasts as long as we would like. Getting more life out of fresh produce like herbs is possible though with the help of eWater.

Fresh herbs are prized for their nutritional qualities and ability when cooked to elevate the taste of many foods. In Australia, Coriander, Parsley, Basil and Mint are the four most common herbs grown, accounting for 80% of the value of fresh herbs (Horticulture Innovation Australia, 2018). In an industry worth $155.5 million dollars, the opportunity to maximise the shelf life of fresh herbs from harvest to use is key to reducing food waste and extending value in the industry.

In a recent study by a team from the University of Tasmania, electrolysed oxidising water (eWater Sanitiser) and CO2 were evaluated as innovative post-harvest treatments to prolong shelf-life of fresh herb leaves.

Key Points from Study:

• Dipping and dry misting leaves with 5-20 ppm electrolysed oxidising water (EOW) increased shelf-life of all four herbs, as indicated by the retention of higher concentrations of total chlorophyll concentrations and carotenoids.

• Exposing leaves to 96% CO2 for 1 h benefitted total chlorophyll and carotenoid retention of coriander and parsley, but negatively affected shelf-life of basil.

• EOW has large potential as a sanitiser for fresh herbs.

The Supplier Chain Challenge

All four herbs are often sold as harvested, in non-airtight sleeves or punnets, and without washing or sanitation. Improving shelf-life is required to meet the growing year-round demand for fresh herbs in Australia. Research has shown that typical shelf life for each is as follows:

• BASIL - Depending on the storage temperature, basil normally can be stored for between one and two weeks (Patiñ o et al., 2018).

• MINT & PARSLEY - Mint is considered a high-risk herb for potential contamination (Hsu et al., 2010), and along with parsley have a shelf-life of 2-3 weeks at 0°C storage (Cantwell and Reid, 1993).

• CORIANDER - even under ideal cool storage conditions, the shelf-life of fresh coriander is between 5 and 7 days (Hassan and Mahfouz, 2012).

Electrolysed Water as a Sanitiser

Electrolysed oxidising water (EOW) is an organic certified sanitiser widely used in the fresh produce industry and is effective against many spoilage and pathogenic microbes. It is a safe and inexpensive antimicrobial agent that acts against a wide range of microorganisms (Huang et al., 2008). The antimicrobial properties of EOW have been attributed to its free chlorine contents, primarily hypochlorous acid (HOCl), and its high oxidation-reduction potential, as well as the presence of hydroxyl radicals and ozone (O3) (Gil et al., 2015).

Results and Discussion

• For basil, day 7 results showed no benefits of EOW treatment on chlorophyll and carotenoids retention, with significantly lower levels than the control, however 5, 10 and 20 ppm EOW significantly improved retention of both chlorophyll and carotenoids by day 14.

• For coriander, EOW at both 5 and 20 ppm significantly improved retention of both chlorophyll and carotenoids on day 10.

• In mint, EOW at both 5 and 20 ppm significantly improved retention of both chlorophyll and carotenoids on day 10

The effectiveness of EOW in retaining high levels of total chlorophyll and carotenoids in all four herbs could be attributed to its high redox potential, which has a strong effect in preventing fungal decay (Guentzel et al., 2008; Romanazzi et al., 2016).

Additionally, the available chlorine concentration of EOW would help minimise microbial growth. In an industrial setting, the presence of organic matter may limit the antimicrobial activity of electrolysed water (Huang et al., 2008), however, this issue was not encountered in the fresh, greenhouse grown herbs used in these trials.

Conclusions

EOW has large potential as a sanitiser for fresh herbs. Future trials could examine the effects of EOW in oxidising ethylene, and the role this plays in shelf-life extension.

CO2 shock could be a useful treatment for coriander, mint and parsley, however, the more delicate nature of basil renders shock treatments as unsuitable for use with this herb. Applying CO2 shock in an industrial setting could involve high initial capital costs to establish, potentially limiting its commercial uptake.

This article is an excerpt from:
Proceedings at the International Forum on Horticultural Product Quality
Link to Original Research Paper

Title: Shelf-life extension of fresh basil, coriander, mint and parsley

Authors: M.D. Wilson1, B. Wang2 and N.K. Huynh1

1Australian Research Council Training Centre for Innovative Horticultural Products, Tasmanian Institute of Agriculture, University of Tasmania, Locked Bag 1370, Launceston TAS 7250, Australia; 2Centre for Food Safety and Innovation, Tasmanian Institute of Agriculture, University of Tasmania, Private Bag 54, Hobart TAS 7001, Australia.