Changes in volatile organic compounds from wild rocket (Diplotaxis tenuifolia L.) during modified atmosphere storage

Abstract

Wild rocket (Diplotaxis tenuifolia L.) is packaged under modified atmosphere (MA) to maintain quality after harvest. Evaluation of the quality of packaged produce is complex because only visual quality can be accessed through the packaging film. A method for volatile analysis that allowed for multiple sampling without affecting the fresh produce was applied to wild rocket stored for 14 days at 5°C and 10°C in closed glass jars to resemble MA packaging of fresh produce. Changes in the volatile organic compounds (VOCs) were monitored during storage using solid-phase microextraction. The gas concentration was continuously monitored with non-invasive sensors, and from these data, the respiration rate, cumulative respiration, respiratory quotient (RQ), and the low O2 limit (LOL) was determined. The LOL of wild rocket was 2.1kPa O2. Below this level the RQ increased and above this level the RQ was unaffected. Most VOCs were released from wild rocket during storage under restricted conditions (O2 <2.1kPa); a total of 23 compounds were monitored representing eight sulfur compounds, five esters, four alkanes, two alcohols, two furans, one ketone, and one nitrogen-containing compound. The change in the RQ resembled those changes observed for carbonyl sulfide, methanol, methanethiol, ethanol, methyl acetate, methyl propionate, methyl isothiocyanate, methyl 3-methylbutanoate, ethyl 3-methylbutanoate, and dimethyl trisulfide. A different relationship was observed for acetone, carbon disulfide, dimethyl sulfide, nitromethane, pentane, 3-methylfuran, ethyl acetate, hexane, 2-ethylfuran, dimethyl disulfide, heptane, dimethyl sulfoxide, and octane. Acetone, carbon disulfide, dimethyl sulfide, nitromethane, pentane, 3-methylfuran, 2-ethylfuran, and dimethyl disulfide were released in high amounts (>0.1ngg−1 fresh weight) during prolonged storage under moderate O2 conditions (O2 ≥2.1kPa). Under these conditions, carbon disulfide, nitromethane, and 2-ethylfuran were linearly related to cumulative respiration. Large variations were observed between replicate samples for dimethyl sulfide, dimethyl disulfide, pentane, and acetone, although the leaves were sampled carefully at experimental start to reduce the biological variation. The results show that the VOC profile of wild rocket change in response to gas composition, temperature and storage time.