Studies on vegetables drying: development of new value-added products

Funder

Organizational Unit

Publications

Evaluation of drying and storage conditions on nutritional and sensory properties of dried galega kale (Brassica oleracea L. var. Acephala)

Publication . Araújo, Ana C.; Oliveira, Sara M.; Ramos, Inês N.; Brandão, Teresa R. S.; Monteiro, Maria J.; Silva, Cristina L. M.

This work evaluated the effect of the air-drying temperature and vacuum packaging on quality and nutritional compounds of dehydrated galega kale, previously steam blanched, during 5 months of storage. When compared with the vacuum packaged kale, the packaging without vacuum yielded improved nutritional features, in general. This approach combined with a drying temperature of 40°C resulted in retention percentages of 62, 38, 92, and 48% for vitamin C, total phenolic content, total antioxidant capacity, and chlorophylls, respectively. The acceptance of the dried product by the consumer was assessed through a focus group. The participants classified the product as a practical and convenient alternative to cook healthier dishes. The appearance of dried galega kale was described as being fragile and being with nice smell, natural colour, and flavour similar to the fresh product. In conclusion, the herein presented product was addressed as an innovation with multiple possible applications in several recipes.

2017Journal article

Open access

Influence of drying processes and pretreatments on nutritional and bioactive characteristics of dried vegetables: a review

Publication . Oliveira, Sara M.; Brandão, Teresa R. S.; Silva, Cristina L. M.

Drying has been applied to vegetables in order to preserve, store and transport these food products. However, drying implies not only physical changes, easily detectable by the consumer through visual assessment, but also chemical modifications. These are not always visible,but are responsible for alterations in colour, flavour and nutritional value, which compromise the overall quality of the final product. The main chemical changes associated with drying are related to the degradation of phytochemicals, such as vitamins, antioxidants, minerals, pigments and other bioactive compounds sensitive to heat, light and oxygen. Moreover, nutrient losses are inevitably associated with leaching as a result of the water removal from the vegetable during the drying process. In order to prevent or reduce nutrient losses and thus improve the quality of dried products, pretreatments are often applied. In this review, an overview of the procedures developed for dehydration of vegetables applying heat by convection, conduction or radiation is presented. The influence of pretreatments on nutritional and bioactive characteristics of dried vegetables is discussed. Blanching with steam, water or chemical solutions is the most commonly used, but power ultrasound, ohmic blanching, osmotic and edible coatings pretreatments have also been reported. The influence of the drying processes and conditions on nutritional contents and bioactive characteristics is also presented.

2016Journal article

Restricted access

Effect of air-drying temperature on the quality and bioactive characteristics of dried galega kale (brassica oleracea l. var. acephala)

Publication . Oliveira, Sara M.; Ramos, Inês N.; Brandão, Teresa R. S.; Silva, Cristina L.M.

The objective of this work was to evaluate the drying characteristics and the effect of drying temperature on the quality characteristics of Galega kale without any pretreatment. Drying times of 330, 162, 78 and 51 min provided minimal moisture contents, using temperatures of 35, 50, 70 and 85C, respectively. The L* and a* values diminished and b* increased, resulting in increasing values of chroma, total color difference and browning index, as well as decreasing values of the hue angle. A pronounced effect on the retention of total phenolic compounds and vitamin C losses ranging from 4.8 ± 9.7 to 55.5 ± 7.4% were observed. Regarding antioxidant capacity, losses from 51.7 ± 7.5 to 69.6 ± 3.7% were obtained. Chlorophyll a content decreased with increasing drying temperatures, with losses between 8.9 ± 6.7 and 35 ± 5.6%, while degradation of chlorophyll b was negligible. In conclusion, the air drying of Galega kale without any pretreatment resulted in considerable deterioration of its quality characteristics and nutritional value.

2015Journal article

Restricted access

Assessment of nutritional quality and color parameters of convective dried watercress (Nasturtium officinale)

Publication . Ek, Pichmony; Araújo, Ana C.; Oliveira, Sara M.; Ramos, Inês N.; Brandão, Teresa R. S.; Silva, Cristina L. M.

The purpose of this study was to evaluate the drying characteristics and the effects of convective drying temperature on quality attrib0utes of watercress, without any pretreatment. Drying temperatures of 40, 55, and 70 8C resulted in drying times of 230, 119, and 92 min, respectively. The nutritional parameters were negatively correlated with the drying temperature. Retentions of 12.563.8272.864.2%, 51.163.3280.464.8%, and 44.366.1292.1612.2% were obtained for vitamin C, total phenolic compounds, and total antioxidant capacity, respectively. Increased values of TCD (total color difference) and BI (browning index), and higher chlorophylls losses (26.163.9255.6614.9%) were also observed as the drying temperature increased. In conclusion, although longer drying periods are required for lower drying temperatures, these are more profitable in terms of watercress nutritional features and overall quality to the consumer.

2018Journal article

Restricted access