1-MCP as a tool to protect broccoli from ethylene exposure in the supply chain : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Horticultural Science at Massey University, Palmerston North, New Zealand

Abstract

In New Zealand, the annual broccoli (Brassica oleracea L. var. italic Plenck) harvest is approximately 30,000 tonnes, sourced from 2,080 hectares since 2014, with retail prices ranging from $3.57 to $13.95 per kilogram over that period (Figure NZ Trust, 2025). However, as a highly perishable vegetable, broccoli has a limited shelf life. Broccoli shelf life is primarily limited by yellowing, which is accelerated by higher than optimal temperatures (e.g., > 4 °C) and ethylene exposure. Ethylene contamination in the supply chain can hence promote broccoli senescence and induce yellowing. A potential solution to reduce the risk of yellowing as a result of exposure to ethylene is to provide a protective application of 1-MCP. Previously, postharvest treatment with 1-MCP has been shown to reduce weight loss and maintain chlorophyll content and h° values of broccoli at suboptimal storage temperatures. In this thesis, a preharvest spray of 1-MCP was evaluated for efficacy in preserving the postharvest quality of ‘Nobel’ and ‘Iron’ broccoli during storage at 1 °C and 4 °C under air and ethylene exposure conditions through two trials: In Trial 1, 1-MCP was sprayed four days prior to harvest with the control being untreated. During storage at 1 °C for 29 days, ‘Nobel’ broccoli heads from both 1-MCP treated and control blocks were exposed to either a continuous flow of 1 µL×L-1 ethylene or clean air (< 0.001 nL×L-1 ethylene) in a flow-through system. After storage, all broccoli heads, including those from untreated field blocks exposed to ethylene during storage, remained a marketable green colour. These results possibly suggest that the storage duration was too short or storage temperature was too low to observe any potential differences. Therefore, in a second trial, the benefits of a preharvest 1-MCP application were tested in the context of postharvest storage temperature not being optimal (e.g., 1 °C) and more typical for a mixed vegetables supply chain or home storage (4 °C). In Trial 2, 1-MCP was sprayed three days before harvest and two storage temperatures for ‘Iron’ broccoli were employed: storage at 1 °C for 28 days and 4 °C for 18 days. As in Trial 1, broccoli heads stored at 1 °C stayed a marketable green colour. For those heads exposed to ethylene during storage at 4 °C, 1-MCP treatment in field was observed to significantly lower weight loss, and result in greener appearance (measured as h° closer to 110°), demonstrating a benefit of 1-MCP treatment in maintaining the quality of broccoli under ethylene exposure conditions. These findings suggested that preharvest 1-MCP application could be a potential tool to protect broccoli from ethylene exposure in the supply chain.