Impact of thermal blanching and thermosonication treatments on watercress (Nasturtium officinale) quality: thermosonication process optimisation and microstructure evaluation

Cruz, R. M. S.; Vieira, M. M. C.; Fonseca, Susana C.; Silva, C. L. M.

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Abstract(s)

The objectives of the present work were to optimise watercress heat and thermosonication blanching conditions, in order to obtain a product with better quality for further freezing, and to evaluate the effects of thermosonication on the microstructure of watercress leaves. In a chart of optimal time–temperature conditions for a 90% peroxidase inactivation (imposed constraint), vitamin C (objective function) and a-value (improvement toward green) were mathematically predicted for both heat and thermosonication blanching treatments. Two optimal thermosonication combinations were selected: 92°C and 2 s, retaining 95% of vitamin C content and 5% a-value improvement, and a better condition in terms of practical feasibility, 86°C and 30 s, allowing a 75% vitamin C retention and 8% a-value improvement. The experimental values, for each thermosonication optimal time–temperature zone, were in good agreement with the models' predicted responses. In terms of microstructure, thermosonicated watercress at 86 and 92°C showed similar loss of turgor and release of chloroplasts. The proposed optimal thermosonication blanching conditions allow the improvement of the blanched watercress quality and consequently contribute for the development of a high-quality new frozen product. However, a suitable scale-up is mandatory for industrial implementation.

Keywords

Ultrasounds Frozen vegetables Watercress Emergent technologies

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http://hdl.handle.net/10400.1/2546

Citation

Cruz, Rui M. S.; Vieira, Margarida C.; Fonseca, Susana C.; Silva, Cristina L. M. Impact of Thermal Blanching and Thermosonication Treatments on Watercress (Nasturtium officinale) Quality: Thermosonication Process Optimisation and Microstructure Evaluation, Food and Bioprocess Technology, 4, 7, 1197-1204, 2009.