Amidated pectins to boost fish gel properties

By Stephen Daniells

- Last updated on GMT

Related tags Nutrition

Ammonia-treated pectins could boost the mechanical and functional
properties of fish gels, with no perceptible colour changes, and
enhance the nutritional profile of underutilised fish species.

"[Since] pectin has been reported as beneficial for people at risk of cardiovascular disease, amidated low methoxyl pectin can be used to offer to consumers a healthier fish food, rich in proteins, polyunsaturated fatty acids and pectin and low in cholesterol,"​ wrote lead author J. Ramirez in the journal Food Hydrocolloids​.

The functionality of the pectin is dictated by the chemical fine structure, and the majority of the pectins used currently come from citrus peel and apple pomace. Other sources of the ingredient have remained largely unexploited because of certain undesirable structural properties.

Researchers from Denmark and England recently highlighted the possibilities of this ingredient and proposed that 'designer' pectins 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 pectins 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.

By treating pectins with ammonia, the hydrophobic methoxy groups in the pectin structure are replaced with hydrophilic amide groups, thus changing functional properties of the resulting gel.

Previous studies have reported some improvements of functional properties of fish gels made from carp and sole, but no such results are reported for striped mullet, an abundant and under-utilized fish found in the Gulf of Mexico.

The researchers, from the Universidad Autonoma de Tamaulipas in Mexico and the Universidad de Santiago de Compostela in Spain, looked at the effects of different pectin concentrations (0 as control, 10, 20, 30 or 50 g/kg) and differing degrees of amidation (5, 10 and 25 per cent) on the mechanical and functional properties of fish gels.

The amidated pectins were all provided by Tic Gums and added directly into the paste in dry form.

"Results obtained suggest that amidated low methoxyl pectins (ALMP) with higher level of amidation increased mechanical properties and the water holding capacity of fish gels. Gels containing up to 50 g/kg of 25 per cent ALMP showed adequate mechanical and functional properties with almost no changes perceptible in colour attributes,"​ said the researchers.

"Results obtained from this and previous studies suggest that amidation seems to modify the hydrophilic nature of the pectin molecule obtaining a more compatible hydrocolloid to be employed for processing of fish foods,"​ they said.

The research may also be important considering the fears about dwindling fish stocks, suggest the scientists.

"Unutilised or underutilised species (so-called trash-fish) with a nutritional value comparable to that of valued fish species can be an excellent source of raw materials to obtain restructured fish products by gelling,"​ said Ramirez.

Source: Food Hydrocolloids​ Published on-line ahead of print. doi:10.1016/j.foodhyd.2006.06.002 "Fiber-rich functional fish food from striped mullet (Mugil cephalus) using amidated low methoxyl pectin"​ Authors: J.A. Ramirez, N.R. Rodriguez, R.M. Uresti, G. Velazquez and M. Vazquez

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