Impact of thermal blanching and thermosonication treatments on watercress (Nast...

• Author(s): Cruz, Rui M. S. ; Vieira, Margarida C. ; Fonseca, Susana C. ; Silva, Cristina L. M.
• Date: 2011
• Persistent ID: http://hdl.handle.net/10400.14/7633
• Origin: Veritati - Repositório Institucional da Universidade Católica Portuguesa
• Subject(s): Watercress; Thermosonication; Optimisation; Peroxidase; Colour; Vitamin C; Microstructure
• Document Type: Article
• Language: English

Description

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.