Industrial partners sought to scale up process for low-fat donuts

TNO said its in-house trials demonstrated that it is possible to substantially reduce the fat content of doughnuts by using superheated steam (SHS) as a frying process, while maintaining the typical product characteristics of yeast raised doughnuts.

Steam frying of pre-fried French fries and defatting of French fries are already proven methods.

Joost Blankestijn, ​business development manager, food innovations at TNO, said the research group spent six months evaluating whether the process could be adapted for use in the manufacturer of doughnuts, which, in conventional production, are fried in frying oil for 2 to 4 minutes. It has since filed a patent on the method.

But he told BakeryandSnacks.com that the researchers have yet to determine an optimal fat content level for doughnuts, and TNO is seeking industry partners in this regard:

“We have to fine tune the product composition in combination with the process parameters in order to achieve the best quality doughnut prepared with SHS,”​ he said, adding that pilot scale facilities at TNO can be use by doughnut producers to assess the effect of steam on product quality.

Moreover, the Dutch group said it requires equipment manufacturers to get involved in the project in order accelerate scale up of the process from pilot to industrial level.

Superheated steam​

Finish-frying doughnuts in superheated steam, explained TNO, has a flow rate ranging from 1 to 20 m/s, at a temperature of 120 to 220°C for a period of 3 to 6 minutes.

The superheated steam transfers heat to the product allowing more than 75 per cent of the surface of the doughnuts to be in contact with the steam, said the researchers.

Energy consumption​

The evaporated water is released as pure steam during the process and its energy can be recovered by condensation, thus energy consumption, using SHS, is reduced by 50 to 75 per cent compared to processing with hot air, said TNO. “Without reuse, energy savings are still 20 to 40 per cent,”​ added the researchers.

TNO said the SHS method offers additional advantages including the elimination of oxidation reactions, no undesired enzymatic or Maillard reactions, as well as providing sterilisation through steam.

However, pre-treatment by either pre-frying or spraying with oil will still be necessary to maintain the typical product characteristics, said the Dutch group.