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Microwave Heating Modelling of a Green Smoothie. Effects on Glucoraphanin, Sulforaphane

Background: The heating of a green smoothie during an innovative semi−continuous microwave treatment (MW; 9 kW for 15 s) was modelled. Thermal and dielectric properties of the samples were previously determined. Furthermore, the heating effect on the main chemopreventive compounds of the smoothie and during its subsequent storage up to 30 days at 5 or 15 °C were studied. Such results were compared to conventional pasteurization (CP; 90 °C for 45 s) while unheated fresh blended samples were used as control (CTRL).  

Results: A procedure was developed to predict the temperature distribution in samples inside the MW oven with the help of numerical tools. MW−treated samples showed the highest sulforaphane formation after 20 days, regardless of the storage temperature, while its content was 2−fold reduced in CP samples. Storage of the smoothie at 5 °C is crucial for maximizing the levels of the bioactive compound S−methyl cysteine sulphoxide.

Conclusion: The proposed MW treatment can be used by the food industry to obtain an excellent homogeneous heating of a green smoothie product retaining high levels of bioactive compounds during subsequent retail/domestic storage up to one month at 5 °C.

This paper highlights application of the C-Therm TCi Thermal Conductivity Analyzer.

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