Erin O'Donoghue from New Zealand Institute for Crop and Food Research Limited and co-workers report that, using different processes, high sugar pectins could be extracted and used a gelling agents in food.
The functionality of pectin is dictated by the chemical fine structure, and the majority of the pectin used currently comes from citrus peel and apple pomace. Other sources of the ingredient have remained largely unexploited because of certain undesirable structural properties.
"We have found that high sugar/low pH gelling pectins can be extracted from buttercup squash, although extraction conditions, particularly choice of acid, can markedly affect the biochemical characteristics and gelling profiles," wrote the authors in the journal Food Hydrocolloids.
Researchers from Denmark and England recently highlighted the possibilities of this ingredient and proposed that 'designer' pectin will become increasingly common in the future (Trends in Food Science & Technology, Vol. 17, pp. 97-104).
The ingredient, with worldwide production estimated at 35,000 tonnes a year, is currently widely used as gelling agents in jams, confectionary, and bakery fillings, and stabilisers in yoghurts and milk drinks.
The chemical and enzymatic modification of the pectin occurs after extraction from the plant, and the most industrially important pectinolytic enzymes coming from bacterial sources. This approach has enabled scientists to tailor the pectin according to the required functionality.
The researchers used hydrochloric acid, citric acid or nitric acid to extract pectin from buttercup squash (Cucurbita maxima X C. moshata). They report that the pectin content of the extracted material was always less than 40 per cent.
The use of citric acid produced longer chain-length pectin than hydrochloric acid or nitric acid extraction. Hydrochloric acid and citric acid extracted pectin was 40 to 50 per cent esterified, while nitric acid extraction reduced esterification to about 32 per cent, stated the researchers.
"Pectins extracted with nitric formed only weak gels. Gels containing the citric acid-extracted pectin were already forming solid structure at 90 degrees Celsius, similar to a commercial rapid-set pectin, while a sol-gel transition began for the hydrochloric acid-extracted samples at less than 70 degrees C, similar to a commercial slow-set pectin," wrote the researchers.
"A longer extraction time coupled with removal of starch by enzyme digestion during preparation affected isolated pectin chain length and esterification, resulting in altered subsequent gel rheology, dependent on the extraction acid," they added.
The researchers noted that the majority of squash produced in New Zealand was sold as the fresh, whole commodity with little or no added value. Therefore, if further research supports the ingredient potential of squash pectin this "could divert reliance on commodity trade and provide an alternative marketing choice for growers."
Source: Food Hydrocolloids (Elsevier)
Published on-line ahead of print, doi:10.1016/j.foodhyd.2007.07.002
"Biochemical and rheological properties of gelling pectic isolates from buttercup squash fruit"
Authors: E.M. O'Donoghue and S.D. Somerfield,