Influence of pretreatments, drying and storage conditions on drying characteristics, nutritional and sensory properties of galega Kale (Brassica Oleracea L. var. Acephala)

Resumo

The industrial trial drying of vegetables can be a convenient transformation for the consumers and allows the increase of its added value. The objectives of this work were to evaluate the effects of six pretreatments, three different drying temperatures and vacuum packaging on quality and nutritional contents of Galega kale submitted to convective dehydration. The modelling of drying curves and the determination of desorption isotherm was carried out. Finally, the consumers acceptance was evaluated. Among all pretreatments, steam blanching was the most favourable, allowing improvements of the retentions of vitamin C, total antioxidant activity, and chlorophylls, in comparison with the absence of pretreatment. Total phenolic compounds losses were reduced by steam blanching application after immersion in a metabisulfite solution. Moreover, steam blanching improved the colour parameters and overall appearance, providing a final dried product more similar to the fresh sample. In relation to the nutritional content evaluation of dried Galega kale during 5 months of storage, losses were observed for all tested nutrients, being vitamin C the most affected. Packaging without vacuum resulted in higher vitamin C, total antioxidant activity and chlorophylls retentions in comparison with the vacuum package. Nevertheless, the latter resulted in better retention levels of total phenolic compounds. Concerning the study of the drying temperature, 40°C yielded improved nutritional features, but implied higher energetic cost inherent to longer drying periods required. So, drying at 55°C was selected for sensorial analysis, as a compromise between the overall quality and the cost of the final dehydrated product. Regarding the drying process modelling, it was found that the model that best describes the process is the modified Page model with R2 values between 0.9988 - 0.9996 and s values between 0.0288 - 0.0400. A one-step non-linear regression to all data was also performed to minimize the co-linearity between parameters and to accelerate the convergence. Values obtained for activation energy and drying rate were very similar with those found in the literature. The desorption isotherm was well described by the G.A.B. model. A Focus group was used to evaluate the consumers acceptance of the product after rehydration in a soup. The participants of the Focus group classified the product as a practical and convenient alternative to cook healthier dishes. The appearance of dried Galega kale was described as fragile, with a nice smell, a natural colour and flavour similar to the fresh product. The hardness of the dried sample after cooking was softer than the fresh kale. In conclusion, the herein presented product was addressed as an innovation in national and international market, with possible applications in several recipes.

Data de atribuição	3 dez. 2015
Idioma original	English
Instituição de premiação	Universidade Católica Portuguesa
Supervisor	Cristina L. M. Silva (Supervisor), Sara Melo Oliveira (Co-Orientador), Inês Nunes Ramos (Co-Orientador) & Teresa R.S. Brandão (Co-Orientador)