Waste tomato pulp could be cheap thickener for ketchup
could be used at low levels as a thickening agent in ketchup, in
place of other hydrocolloids, says a study from Iran.
Typical tomato processing involves crushing, heating and filtering the fruits to remove their skin, seeds and jelly.
The left over pulp, also known as pomace, is of little value to the processor, say the researchers of the new study published in the Journal of Texture Studies.
In Iran alone this waste is estimated to total around 150,000 tons per year - and sometimes processors have to pay to take have it taken away.
Finding uses for this waste could therefore both economical and environmentally friendly - as well as catering to greater demand for natural ingredients derived from foods, in place of synthetic additives.
The researchers from Shiraz University in Iran noted that the main component of pomace is polysaccharides, which may provide some valuable physical properties like water absorption and uptake.
"This property can make the powder an available, cheap, and natural replacer to be used instead of other expensive hydrocolloids in food products," they wrote.
Hydrocolloids with a precedent for use in ketchup include guar gum, xanthan gum and locust bean gum.
The key issue, however, would be to see whether this use resulted in acceptable flavour and colour of the finished product.
The primary aim of the study was to evaluate the potential for the dried pomace, milled to a powder, to increase consistency and aid texture in basic ketchup.
The secondary aim was to compare rheological properties of products made with and without the powder.
The team first analysed the chemical composition of the powder, and looked at its physoicochemical properties in ketchup samples.
They assessed it for its water absorption, solubility, colour of the resulting ketchup, and rheological properties.
Even at low levels - with just 1 or 2 per cent powder in the ketchup - the powder was seen to improve viscosity of the ketchup (by 50 and 100 per cent respectively.
The rheological data was positive, and the colour and flavour were said to be similar to ketchups made using other texturisers.
In their conclusion, the researchers drew attention to another, nutritional, point.
The removal of the seeds, skin and jelly from tomatoes takes away from processed tomatoes some of the nutritional and functional components, like cellulose, pectin and the carotenoid lycopene.
"The addition of the tomato pulp powder means returning these valuable materials to the product," they wrote.
Source Journal of Texture Studies 39 (2008) 169-182 "The use of tomato pulp powder as a thickening agent in the formulation of tomato ketchup" Authors: A Farahnaky, A Abbasi, J Jamalian, G Mesbahi
