A new study from Spain has found that portions of asparagus spears that are unused by vegetable processors could be tapped as a source of fibre, to bring both nutritional and technological benefits to food.
Asparagus is a popular vegetable in Europe and the US. The main growing countries are China, Peru, the US, Germany and Spain. The latter country produced some 50,00 tons of asparagus in 2005 – both the green and the white variants.
According to the authors of the new paper accepted by the journal Food Chemistry, around 15cm of each harvested asparagus spear is used by vegetable canners. Half of each spear, measuring 15 to 18cm, is considered a by-product.
On one hand this creates “significant waste for producers”; but on the other, if the waste portions are seen to have a similar composition to the edible portions, they “represent a promising source of new value-added compounds (phytochemicals and fibre)”.
The commercial potential in tapping into the nutritional potential of the waste parts is all the greater since there fruit and vegetables are increasingly being considered as sources of fibre for packaged foods like juices, dairy products and baked goods. In the past, cereals have been the fibre-source of choice.
The team’s mission was to prepare various fibre-rich powders from asparagus by-products using different methods, and look at their chemical composition and functional properties using in vitro tests.
Waste parts of spears were obtained from a Spanish processor and arrived at the laboratory within 24 hours, where they were stored at 4ºC before processing.
They were then subjected to either intense extraction for 90 minutes at 60ºC, or gentle extraction for one minute at room temperature. Two different solvents were used – water or 96 per cent ethanol.
The extracts were then either freeze dried or oven dried at 60ºC for 16 hours.
In fact, little difference was seen in the chemical composition of the asparagus powders obtained by the different extraction methods; the only difference was in components with high solubility – that is, soluble sugars, uronic acids and proteins.
However the researchers did note that the degree of treatment severity seems to have an impact on the physiological quality of the fibre. The gentler the treatment, especially when ethanol was used, the lower the rations between insoluble and soluble fibre.
“The average composition of asparagus fibre, obtained under different conditions, was similar to those of other good sources of fibre,” concluded the team.
But when it came to functional properties, the drying systems used were seen to have an impact. In particular, the freeze-dried powders had more solubility and oil-holding capacity than the oven dried.
On the other hand, the oven dried fibres had more capacity for water-holding. This functionality could make the fibres suitable for modifying texture and viscosity, and could allow formulators to reduce calorie content in products.
Positive though they are, the Spanish findings are by no means the end game in investigations into the usefulness of asparagus waste.
The same team has already identified bioactive compounds in the fibres and their antioxidant activity, so as to see their potential for health benefits. They are preparing to publish their findings in a separate paper.
The need for studies on the hypoglycaemic effect of the fibres and other physiological effects in animal models were also highlighted so that the asparagus fibres could be assessed for possible use as food ingredients – both for nutritional and technological purposes.
“All these studies are thus of economic interest to producers,” said the researchers.
Food Chemistry (early online)
“Effects of extraction method on chemical composition and functional characteristics of high dietary fibre powders obtained from asparagus by-products”
Authors: JM Fuentes-Alventosa, G Rodríguez-Gutiérrez, S Jaramillo-Carmona, JA
Espejo-Calvo, R Rodríguez-Arcos, J Fernández-Bolaños, R Guillén-Bejarano,