The study, published in the Journal of Food Biochemistry, outlines how researchers from the Institut des Régions Arides Médenine, in Tunisia produced a fructose-rich syrup from ‘secondary varieties’ of local dates, which would otherwise be discarded. The researchers said that the low-cost syrup produced does not require the denaturation or elimination of processing enzymes, and presents no toxicity risk as all of the ingredients are extracts from edible fruit.
“This bioconversion may be applied on a large degree with a very low cost. It requires neither special chemical reagents, nor complicated installations,” said the researchers, led by Nizar Chaira from the Institut des Régions Arides Médenine.
They said that the date syrup product could be used to as an alternative to other fructose-rich syrups or sugars by the food industry.
The authors said that the date palm (Phoenix dactylifera) is considered to be the most important fruit tree in the Middle East. Other than the direct consumption of date flesh, they reported that dates are also traditionally used in the production of paste, juices and syrups.
Chaira and colleagues said that in 2007, the annual production of dates in Tunisia was around 124,000 tons, of which more than 40 per cent were ‘secondary varieties’ that are discarded or recycled as fertilizers for plants or animal feed.
They said the loss of these dates – considered to be of lower quality – “can be considered as a real economic loss”.
High-fructose syrup is mainly used as a sweetener in food and pharmaceutical industries, but can also be used as a source for attaining crystalline fructose. Typically, these syrups are produced from glucose syrup, derived from the hydrolysis of starch, said the researchers,
Invertase is an enzyme that catalyzes the breakdown of sucrose into a resulting mixture of fructose- rich syrup – known as inverted sugar syrup. Chaira and co said that the Tunisian ‘low-quality dates’ can be classified into two classes: dates from the coastal oasis (rich in reducing sugars and invertase) and the continental oasis variety Deglet Nour (rich in sucrose).
“Given that many studies have described the use of invertase based-processes to produce high-fructose syrups, the aim of this work is to evaluate the higher invertase activity of coastal date cultivars and the possible use of this enzyme to produce high-fructose syrup from Deglet Nour discarded dates,” said the researchers.
The authors reported that invertase activities were highest in extracts from the Korkobbi variety of dates from Gabes oasis region. Whilst the highest levels of sucrose were reported in Deglet Nour – from which an aqueous extract, rich in soluble sugars, was obtained.
The preparations – soluble sucrose from Deglet Nour and invertase extracted from Korkobbi variety – were then mixed at a 9:1 ratio and incubated at a previously reported optimum temperature of 40oC.
The researchers observed sucrose and trisaccharides present in the Deglet Nour extract were completely hydrolysed after 30 min of incubation, producing a high-fructose inverted sugar syrup.
Chaira and colleagues said the syrup was produced with a very low cost, from locally sourced by-products, and could be used as additive or ingredient in the food industry.
Source: Journal of Food Biochemistry
Published online ahead of print, doi: 10.1111/j.1745-4514.2010.00487.x
“Production of fructose rich syrups using invertase from date palm fruits”
Authors: N. Chaira, I. Smaali, S. Besbes, A. Mrabet, B. Lachiheb, A. Ferchichi