Cruz, R.M.

Silva, C. L. M.

Vieira, M.C.

English

Repositório Institucional da Universidade Católica Portuguesa

June 6-9, 2009Anaheim Convention Center Anaheim/OC, CAImpact of thermal blanching and thermosonication treatments on watercress (Nasturtium officinale) quality: process optimisation and microstructure evaluationRui M. S. CruzMargarida C. VieiraCristina L. M. SilvaCBQF         CIQAPortugal2- Family Cruciferae (mustard family), grows in andaround water- consumed in salads, soups and other recipes- prevention of cancer and related diseases- short shelf life of nearly seven daysWatercress (Nasturtium officinale)Freezing allows a longer period for distribution and storage3Pre-Treatment- stabilises foods- destroys microorganisms- inactivates enzymes- impairs sensory properties- reduces the contents orbioavailability of some nutrientsHot water immersion4ThermosonicationHeat + UltrasoundThermosonication treatments can be a good alternative to the traditional heat blanching processesPeroxidase Activity+Thermosonication is  more effective than thermal treatments in watercress peroxidase inactivationHeat (1.15 min) Thermosonication (4.4 s)PeroxidaseVitamin C retention90% 90%29.1% 94.4%90 ºC5Objective Study:٠ Watercress blanching optimisation6- Vitamin C retention maximisation - objective function- 90% inactivation in watercress peroxidase - constraint- Colour a-value- Microstructure analysisMaterials and Methods7Materials and MethodsHeat blanchingThermosonication (heat+ultrasound) blanchingTime range0-2 min+(20 kHz; 125 W)8Table 1- Studied watercress kinetic parameters for heat and thermosonication treatments    Quality parameter Treatment    Model    Kinetic parameter   Reference    Peroxidase  Heat      Biphasic first-order    C01 (µmol.min-1.mg protein-1) 0.49±0.08  Cruz et al. (2006) k1 84.6 ºC (min-1)  18.01±13.98 Ea1 (kJ.mol-1)  420.72±114.94          C02 (µmol.min-1.mg protein-1) 0.48±0.06          k2 84.6 ºC (min-1)  0.24±0.14 Ea2 (kJ.mol-1)  351.65±80.91 R2   0.94                Thermosonication*    First-order   C0 (µmol.min-1.mg protein-1) 1.01±0.05    k87.5 ºC (min-1)  9.64±2.21          Ea (kJ.mol-1)  496.45±65.52 R2    0.97       Colour (a parameter) Heat     Reversible first-order   C0   0.96±0.01  Cruz et al. (2007) Ce   1.01±0.02  Ea (kJ.mol-1)  422.37±126.63  k87.5 ºC (s-1)   0.028±0.024              R2    0.99     Thermosonication*     Reversible first-order   C0   1.01±0.01  Ce    1.09±0.01  Ea (kJ.mol-1)  187.70±160.07                                               k87.5 ºC (s-1)   0.28±0.18               R2   0.99   Vitamin C  Heat     First-order   C0   1  Cruz et al. (2008)             Ea (kJ.mol-1)  150.47±42.81             k87.5 ºC (min-1)  0.75±0.10                R2   0.98  Thermosonication*    First-order   C0   1             Ea (kJ.mol-1)  136.20±60.97             k87.5 ºC (min-1)  0.58±0.11                R2   0.97  *Ultrasound at 20 kHz and 125 W 9ResultsFigure 1- Graphical optimisation for heat and thermosonication watercress blanching in the temperature range of 82.5 to 92.5 ºC: (─) 90% of peroxidase inactivation with heat treatment; (--) 90% of peroxidase inactivation with thermosonication treatment. The grey lines correspond to 29, 50, 75, 94 and 95% of vitamin C retention for both treatments. 5% of greenness improvement with heat treatment is represented by the dashed dotted line; 5% and 8% of greenness improvement with thermosonication treatment are represented by the dashed double dotted lines. The continuous and dashed rectangular markers compare two time-temperature combinations at 90 ºC for heat and thermosonication, respectively. The elliptic markers indicate two time-temperature thermosonication combinations: 92 ºC, 2 s; 86 ºC, 30 s. 10ResultsThermosonicationPeroxidaseVitamin C retention 95% 75%90% 90%92 ºC  2 sa-value  improvement 5% 8%86 ºC  30 sWatercress initial values:Vitamin C (50.40±5.77 mg.100 g fw-1)     a-value (-9.66±1.08)Optimal condition Better condition11Figure 2- SEM micrographs of watercress cross section tissue at 400× magnification level: (a)-Fresh watercress; (b)-Thermosonicatedwatercress at 50 ºC, 60 s; (c)-Thermosonicated watercress at 92 ºC, 2 s; (d)-Heat blanched watercress at 92 ºC, 2 s (control); (e)- Thermosonicated watercress at 86 ºC, 30 s; (f)-Heat blanched watercress at 86 ºC, 30 s  (control). P= parenchyma cells, Vt= vascular tissue, white arrow indicates the chloroplasts.12The proposed optimal thermosonication blanching conditions will improve the blanched watercress quality and consequently, contribute to the development of a high quality new frozen product.A suitable scale-up study is mandatory for industrial production.Conclusion13AcknowledgmentsPh.D. grant SFRH/BD/9172/2002 to Fundação para a Ciência e a Tecnologia (FCT) from Ministério da Ciência e do Ensino SuperiorThe authors thank the Vitacress Company for supplying the raw watercress14Thank You!

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

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

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Repositório Institucional da Universidade Católica Portuguesa