Control of restrictive supply chains: biomarkers as indicator for Erwinia infection on potato tuber

The Dutch Ministry of Agriculture, Nature and Food Quality has financially supported the research programme named “Total use of unrefined and unprocessed food(crops)”. The programme consisted of a number of projects and one of the projects was entitled “Control of Restrictive Supply Chains; biomarkers as indicator for shelf life” ( KB 33 002 011). The aim of the project is to build up knowledge needed to optimize and re-design restrictive supply chains of fruit, vegetables and flowers to avoid postharvest losses, maintain high resource use efficiency and connect consumer demands to production and supply chain restrictions. The objective of this project is to measure the production of volatiles in healthy and rotten (infected) potatoes and as such identify volatiles that may be used as a biomarker for rot development. A key aspect of the envisaged experimental design is to measure the development of these volatiles over time. This will give insight in the potential of this idea as an early detection method to avoid the further expansion of a rot infection during storage of potatoes. An experimental set up was built to allow the production of volatiles and respective sampling. The potatoes were placed in a glass jar and an air flow was applied. The volatiles were sampled and measured in the air flow. Three treatments were applied: potatoes wounded and infected with the bacteria Pectobacterium polaris, wounded potatoes (without infection) and healthy potatoes. Each treatment was applied in duplicate. The six glass jars with the potatoes were kept at room temperature for maximal 17 days and the production of volatiles was daily monitored. The volatiles in the out coming air were measured with a thermo-desorption GC, a PTR-ToF-MS and a GC-MS (via a SPME). In addition, the amount of oxygen consumed and carbon dioxide produced was also measured in the air flow with a CompactGC. The amount of infection was visually quantified (through the glass jar). The following has been concluded: - Clear differences in volatile production between infected and non- infected potatoes were found. - Those differences are measurable very early upon the infection. Even when the infection is not yet visible. This indicates that the production of volatiles is a suitable biomarker for bacterial infection in potatoes. - Next to the volatile production, the effect of bacterial infection on the production of CO2 and the consumption of O2 (respiration rate) was studied. The respiration rate of infected potatoes is much higher than that of healthy or wounded potatoes. The tubers react prompt to the infection by increasing the production of CO2 and consumption of O2. Also this change in metabolism may be used as biomarker. - Several methods have been explored for the measurement of the volatile production. The measurements were done with a Thermo-Desorption GC, a PTR-ToF-MS and a GC-MS. Despite the differences in the type of gas analysis the results of the different methods show a good agreement with each other and seem to be suitable for measurement of produced volatiles. - Another important result of the project is the development of a suitable inoculation protocol for the bacteria Pectobacterium polaris (an Erwinia infection has been chosen for this project because this is an aggressive type of microorganism and commonly found in potatoes). The developed protocol makes it possible to successfully infect the tubers in a controlled manner and create a suitable model system. The results are directly relevant for the industry as this kind of micro-organism is responsible for a large amount of infections during storage hence contributing for product waste. The volatiles measured with the Thermo-Desorption GC and the PTR-ToF- MS have not yet been identified. The GC-MS results do not allow to identify all the volatile compounds as the column and the sampling methods differ too much from the ones used with the GC with desorption unit. Only 10 of the 45 volatiles were identified with their chemical names via GC-MS analysis. At this time, not all compounds have been identified with certainty.