Investigation of the potentially detrimental effect of CIPC application on the processing quality of stored potatoes
The provision of crops of a light fry colour, from store, is of the utmost importance to processors. Poor fry colour leads to rejection of crops on a quality basis. The application of Chlorpropham (CIPC) sprout suppressant, as a thermal fog is associated with a deterioration in fry colour. The BPC funded project at the University of Glasgow and its collaborator Sutton Bridge Experimental Unit investigates the effects of CIPC use on the processing quality of stored potatoes. CIPC is the only sprout suppressant available for medium and long-term storage for processing in Britain. In the UK the majority of CIPC treatments are conducted as thermal fog applications. This is considered to be the most practical means of achieving successful sprout control. The introduction of a hot fog into potato stores has a disruptive influence. It can physiologically alter the potatoes by creating a stressful environment. Tuber respiration rate increases and so the crop will age. Experimental trials conducted as part of this project have shown that it is the fogging process itself that is responsible for the decrease in crop quality following application, not the CIPC formulation applied. Studies revealed that both carbon dioxide and ethylene were produced naturally by crop and from the combustion of petrol used to generate thermal fogs. Initially the fry colour problems were linked with carbon dioxide in combustion gases and from increased respiration. However, carbon dioxide output from thermal fogger machines was less significant than expected. The levels were consistently lower than concentrations shown to have a deleterious effect in previous BPC funded work. Ethylene is present in thermal fogs as a by-product of burning the hydrocarbon fuel used to generate fog. The concentration of ethylene produced is associated with the running conditions of the fogger machine I.e. burner temperature, type and volume of fuel used etc. The ethylene created in a standard CIPC thermal-fog application is sufficient to induce a physiological response in tubers. Exposure of crop to ethylene effects respiration, dormancy period, sprout morphology, reducing sugar concentration and hence fry colour. The extent of the outcome depends on exposure time and concentration. Following assessment of the fogging situation, various means of reducing the impact of CIPC application on fry colour were evaluated. Different approaches were undertaken and included both attempting to control and remove the contaminants present in thermal fogs. By ventilating stores earlier than the recommended twenty-four hour period after treatment a vast improvement in fry colour was observed. In doing this the exposure time of crop to contaminants was greatly reduced. In the experimental work the stores were ventilated eight hours after treatment. This allowed adequate time for the effective fraction of the thermal god to settle.