Research to develop best practice recommendations for the use of ethylene on processing cultivars.

Control of sprouting is essential for efficient potato storage as without sprout control tubers rapidly become unsuitable for both processing and fresh marketing. Before 2020, the most common strategy for controlling sprouting in both fresh-marketed and processing potatoes was to treat tubers with the sprout inhibitor Chlorpropham (CIPC). At the time this research was commissioned there was a need to find alternatives to CIPC, especially for the processing sector.

Continuous application of ethylene (4-10 ppm) to potatoes during storage had been developed as an alternative to CIPC, as it inhibits the growth of sprouts once they have initiated.  However, an important constraint to its use is that varietal variability in ethylene sensitivity means that most varieties need to be held at low temperature for effective sprout control.  In addition to this, ethylene can induce increased respiration and sugar accumulation in some varieties.  This is not acceptable for processing varieties as sugar accumulation causes fried products to become unacceptably dark. 

A series of storage trials were carried out to understand the effect of ethylene on processing quality, over short and long term storage and to investigate the potential for reducing the use of CIPC by using it in combination with ethylene. The majority of the processing industry uses bulk storage. However, most research trials with ethylene had used small scale containers and commercial storage under ethylene at the time had been in boxes. As there are significant differences in the air circulation system between bulk and box storage the project also evaluated the use of ethylene for bulk storage.

The work was a companion to the Defra Sustainable Arable Programme Link project LK09127 “Reducing energy usage and wastage by improving ethylene control of potato sprouting". 

Results

2010-11 & 2011-12

A single application of 21 ppm CIPC was used at the beginning of storage. For the combined treatment,  ethylene was gradually introduced to and maintained at 10 ppm. The varieties assessed were Cabaret, Hermes, Maris Piper, Markies, Russet Burbank, Saturna and Verdi.

For both years, the CIPC and CIPC/ethylene treatments reduced sprout length compared with an untreated control in all varieties. CIPC alone controlled sprouting to less than 2 mm in all varieties for 2 months but was less effective thereafter in controlling sprouting in any variety other than Cabaret. However, combined treatment CIPC/ethylene controlled sprouting to commercially acceptable levels in all varieties except Hermes and Saturna. In all cases, sprout length was reduced in the combined treatment compared with either treatment alone. 

Generally, the highest French fry colour values in Cabaret, Maris Piper and Russet Burbank were found with CIPC/ethylene treatment, although they were all within commercially acceptable limits except for Cabaret after six months’ storage. Ethylene reduced Hunter L values of crisps even in the presence of CIPC. The severity of effect was varietal.

2013/14

Three different trials were carried out and  the treatments are described in the report (below). Ethylene provided good sprout control for the varieties Fontane, Markies, Ramos and Russet Burbank to 6 months all with acceptable processing colour quality. Ethylene gave satisfactory sprout control to 4 months storage for Desiree, Maris Piper and VR808 although fry colour was somewhat dark in Desiree.  Ethylene was ineffective for sprout control in Lady Claire, Innovator and Saturna other than for short term (2 months) storage and had no significant effect on fry colour on these varieties. 

In bulk storage trials, ethylene provided good sprout control to 6 months, with acceptable processing colour quality, for Ramos, Markies and Russet Burbank. Ethylene gave satisfactory sprout control to 4 months storage for VR808.  

Some effects of 1-MCP treatment on the sprouting of the varieties were observed, although the effects were both inconsistent and small.  1-MCP did not mitigate any effect on fry colour caused by ethylene in Markies or Saturna. Although there was a small decrease in the fry colour of Desiree at 4 months by 625 ppm 1-MCP treatment no effect was observed using 1-MCP concentrations either lower or higher than this.

2014/15

The treatments were 10 ppm ethylene, a single intake 9 g/tonne CIPC application and ethylene with 9 g/tonne CIPC. The varieties used were Arsenal, Chicago, Fontane, Lady Claire, Maris Piper, Markies, Ramos, Royal, Russet Burbank, VR808.

For all varieties at all sampling occasions, mean sprout length was smaller with the combination treatment than either treatment alone.  Sprout length was commercially acceptable for all varieties, including those varieties in which ethylene alone provided poor control, and at all sampling occasions (except for Lady Claire and Royal).

Ethylene had a statistically significant effect on French fry colour for Fontane, after 2 and 4 months in store, and Ramos on all three sampling occasions. Despite this, French fry colours were commercially acceptable for all varieties and sampling occasions except for Royal after 2 months only. There were no statistically significant differences in fry colour between the treatments for Maris Piper, Markies or Russet Burbank when stored in either box or bulk store types. Although ethylene treatment caused a slight decrease in crisp Hunter L score with Chicago, Lady Claire and VR808, the fry colours would have been commercially acceptable throughout the experiment.

2015/16

The treatments were single doses of chlorpropham (CIPC), at 9 and 16 grams per tonne respectively, both followed up with ethylene maintained at a target concentration of 10 ppm or CIPC only (12 g/tonne per treatment).

For all varieties and for every sampling occasion (except Ramos after 6 months’ storage),  the lowest mean sprout length was observed with CIPC 16g/t + ethylene with statistically significant differences from the other treatments in all varieties except for Maris Piper and Ramos. The lower dose CIPC 9g/t + ethylene treatment provided slightly less sprout control than the higher dose CIPC 16g/t + ethylene. Overall, treatment with ethylene resulted in slightly darker average fry colour scores, although only for Markies after 8 months’ storage were statistically significant differences found between treatments with and without ethylene.