A new strategy to assess the quality of broccoli (Brassica oleracea L. italica) based on enzymatic changes and volatile mass ion profile using Proton Transfer Reaction Mass Spectrometry (PTR-MS)

The shelf life of high quality horticultural products such as broccoli is relatively short, thereby limiting their potential for export and long distance trade. To assess the quality and the shelf life of vegetables, a reliable, accurate and high-throughput technique is required. In this study, an approach that profiled enzyme activities and volatile mass ions was used. The possible relationship between volatile mass ions and changes in the activity of enzymes that influence quality of broccoli (i.e., peroxidase/POD and ascorbate oxidase/AAO) during post-harvest storage (25 °C for 6 days) was investigated. Proton Transfer Reaction Mass Spectometry (PTR-MS) was used to scan and quantify volatile mass ions in broccoli during storage, with m/z ratio of between 20 and 180. In this study, the effect of severe wounding on enzyme activities and the volatile profile was simulated by incubating crushed broccoli florets at different time intervals (2, 4 and 6 h). Based on one-way ANOVA, changes in enzyme activities were more influenced by incubation time after crushing rather than days of storage. POD activity gradually decreased over six days of storage, while AAO activity gradually decreased over 3 to 4 days, followed by an increase in activity until the sixth day of storage. Based on Partial Least Square Regression type 1 (PLSR 1) model, a good correlation between PTR-MS volatile mass ions fingerprints and enzymatic activity in broccoli florets that varied with days of storage and incubation time after crushing was found for POD and not for AAO.Industrial RelevanceThe shelf life of high quality horticultural products such as broccoli is relatively short, thereby limiting their potential for export and long distance trade. To assess the quality and the shelf life of vegetables, a reliable, accurate and high-throughput technique is required. In this study, an approach that profiled enzyme activities and volatiles was used. The possible relationship between volatile profile and changes in the activity of enzymes that influence quality of broccoli (i.e., peroxidase/POD and ascorbate oxidase/AAO) during post-harvest storage (25 °C for 6 days) was investigated.

Research Highlights
► Relation of enzyme activity and volatile profiles.
► Potential use of PTR-MS for volatile mass ion mapping.
► New analytical method to assess vegetable quality.