Changes in volatile compounds, flavour-related enzymes and lycopene in a refrigerated tomato juice during processing and storage

The industrial processing and cold storage of minimally processed tomato juice might produce changes in volatile compounds responsible for the fresh tomato flavour. Many of these changes are related to the activity of the enzymes lipoxygenase (LOX) and hydroperoxide lyase (HPL), which are involved in the production of volatile compounds. The aim of this research was to ascertain changes in these enzymes and the major volatile compounds contributors to the fresh and green aroma attributes (aldehydes, alcohols, and lycopene volatile derivatives) in a refrigerated tomato juice, following a standardized industrial short thermal processing (96 °C, 30 s) and during refrigerated shelf-life storage (4 °C, 22 and 40 days). Results showed that, after the heat treatment, residual LOX and HPL activities were reduced in a 97% and 60%, respectively, compared to homogenized fresh tomatoes. The content of the volatile aldehydes hexanal and (Z)-3-hexenal decreased substantially from homogenized tomatoes (fresh tomato juice) to short thermal processed juice, however, (E)-2-hexenal increased probably by the action of isomerases. The content of the related alcohols, 1-hexenol and (Z)-3-hexenol, was increased with processing. The slight increase of the lycopene derived compound 6-methyl-5-hepten-2-one during storage (from 0.68 to 0.73 mg L⁻¹) could be associated with residual enzymatic activities and lycopene oxidative degradation processes, contributing positively to aroma attributes in the tomato juice. The content of lycopene in this tomato juice (27.25 mg kg⁻¹ FW) only decreased 8% during storage. Minimizing the elapsed time from the initial tomatoes processing and the short thermal treatment is crucial to avoid volatile compounds degradation, mainly the aldehydes as the main contributors to the fresh aroma of tomato juice. The residual LOX and HPL enzymes activities should be studied in every particular case to avoid non-desirable changes in flavor-related compounds that could modify the final quality of the product.