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- Impact of thermal blanching and thermosonication treatments on watercress (Nasturtium officinale) quality: thermosonication process optimisation and microstructure evaluationPublication . Cruz, R. M. S.; Vieira, M. M. C.; Fonseca, Susana C.; Silva, C. L. M.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.
- The response of watercress (Nasturtium officinale) to vacuum impregnation: Effect of an antifreeze protein type IPublication . Vieira, M. M. C.; Silva, C. L. M.; Cruz, R. M. S.The setting up of methodologies that reduce the size of ice crystals and reduce or inhibit the recrystalli-sation phenomena could have an extraordinary significance in the final quality of frozen products and consequently bring out new market opportunities. In this work, the effect of an antifreeze protein type I (AFP-I), by vacuum impregnation (VI), on frozen watercress was studied. The VI pressure, samples’weight, Hunter Lab. colour, scanning electron microscopy (SEM), and a wilting test were analysed in thiswork. The water intake of watercress samples augmented with vacuum pressure increase. The results also showed that, independently from the vacuum pressure used, the Lab. colour parameters between raw and impregnated samples were maintained, showing no significant differences (P > 0.05). A VI of 58 kPa, during 5 min, allowed impregnating the AFP-I solution (0.01 mg ml 1) into the water-cressb samples. The scanning electron microscopy (SEM) analysis showed the AFP-I impregnated frozen samples with better cell wall definition and rounded cell shape with smaller ice crystals compared with the control samples. The wilting test results corroborated that AFP-I is a valuable additive, since the leaves impregnated with AFP-I showed higher turgidity compared to the control samples. The present findings will help to better understand the effect of AFP-I, particularly, on frozen water-cress microstructure and its importance as valuable food additive in frozen foods and mainly in leafy vegetables.