The DEMETER project studies new pathways to increase resource efficiency in the agri-food value chain for the valorisation of vegetable residues that are currently not valorised and are seen as a nett loss for the vegetable growers and first transformation industries. These pathways are the production of high quality juices, cold and hot soup production and cracking of pomace and processing residues into functional ingredients for human consumption.
The main vegetables for by-product valorisation are carrot (broken, small pieces, tops and bottoms), broccoli (stems and florets), leek and cabbage. After sampling, the quality was evaluated by analysis of texture, colour, dry matter, soluble solids, titratable acidity, sugars, organic acids, cell wall (fibre), polyphenols and carotenoids. Results show that the by-products of carrot and broccoli are particularly interesting as rich source of fibre, polyphenols and carotenoids.
The composition, properties and enzymatic degradability of pomaces were studied and ingredients based on pomaces were prepared to study their use as fibre enrichment and texture modifier in food. Following pomaces were selected: carrot, broccoli florets, broccoli stems, orange and apple. The dietary fibre content for carrot was 26% cell-wall dw, 40% for broccoli florets and 57% for broccoli stems, indicating a good source of dietary fibre. To improve pectin solubility in food, to modify texture and increase the availability of soluble dietary fibres, ingredients based on carrot and broccoli florets pomaces were produced by pre-treatment with natural deep eutectic solvents (NADES). Results show that phenolics were removed from the pomace by the NADES pre-treatment, but were not recovered in the NADES extract, indicating modification during the process or removal by water washes.
Enzymatic treatment of orange and apple pomace was applied as an aid to improve juice recovery. Four commercial enzymes were tested and all enzymes improved juice recovery from the pomaces. The most efficient enzymes improved 23% juice recovery for apple and 14-16% for orange.
Juices and soups were produced from the by-products of carrot, broccoli, cabbage and leek. They were analysed on rheology, colour, dry matter, soluble solids, titratable acidity, sugars, organic acids, fibre content, polyphenols and carotenoids to evaluate the effect of processing on their organoleptic and nutritional properties. These properties of the juices and soups were similar to those of their corresponding raw materials. The effect of dilution was observed on soups due to the water addition during the processing. For the juices, there was a large reduction of quality due to retention of most micro- and macroconstituents in the pomaces, indicating the importance of the valorisation of the pomaces.
Furthermore, different types of drying and freezing as pre-treatment of vegetable by-products were qualitatively compared from an environmental point of view. Drying, especially the drying oven, is the better pre-treatment technology. However, in the specific case of the production of juices and soups, the freezing technology could be more adapted because it avoids removing water that will have to be added in the juicing process. A detailed environmental assessment will be performed to compare soup from vegetable by-products with soup from fresh vegetables in order to highlight the potential environmental benefits of a soup based on by-products.