Sunday, June 28, 2009

Extruded food and nutrition

Extrusion cooking is where a food is cooked (but not always) as it is extruded from a machine. The things that spring to mind are things like "chips" such as Pringles, or a breakfast cereal like WheetBix. However extrusion cooking, or extrusion made food is more common than these things. It covers most rectangle shaped foods e.g. Most muesli bars, fruit bars, square, rectangle, donut or any other shape breakfast cereals, pasta. It also it is used for less obvious food processing like baby foods, sweets, some cheeses. A good explanation of the process is:
extrusion cooking Food, commonly a cereal product, is heated under pressure, then extruded through fine pores, when the super‐heated water evaporates rapidly, leaving a textured product
Image borrowed from here.

This is a great video clip showing the machines in action

Reading through back issues of my journals, and have across an article in Journal of Food Engineering (vol 2 pg 281-3080. It is a rather old paper being published in 1983, but it serves as a good illustration, out of the 23 pages devoted to the topic of effects of extrusion cooking on nutritional value of food only 4.5 pages discuss the impact on vitamins. So this is only 20% of the article. It is a review article and any good review article should cover all the material on the subject. So there are only four and a half A5 pages about how our vitamins are effected by extrusion. To put this in perspective five times more information is known about the effect of extrusion on fat, protein and carbohydrates. This clearly shows the bias in food research towards the fats, proteins and carbohydrates. No wonder we are in the nutritional mess that we are in.

For those who are wondering what the effects of this process are on the vitamins, the results are as bad as you would expect. The highlights (or is that lowlights?) of the review are that there is a lot of variance in vitamin retention, this aside the following information can be gleaned

B Vitamins
  • "Average retention was 54% of Thiamine" for maize extrusion
  • Thiamine lost in potato flakes was 3 - 78%
  • "Under exclusion conditions producing a realistic breakfast cereal... the loss of thiamine and riboflavin was substantial - 90% of the thiamine and 50% of the riboflavin."
  • Substantial loss of thiamine 60-90% in wheat products
  • For maize and soy blends "significantly higher thiamine losses of 25-50% occurred"
And lastly
  • "Riboflavin degradation increased with increasing moisture content and screw speed..... thus for both vitamins an increase in screw speed had a detrimental effect."
Now if you had just purchased a quarter of a million dollar piece of equipment would you run it at a leisurely pace or as quickly as possible to maximize the return on the investment? I think we all know that answer to that.

Onto Vitamin C
  • "Boiling of 2 minutes caused 79% destruction of added vitamin C in a maize/soy/groundnut mixture" when using"Extrusion cooking... only 33% destroyed"
  • "When Vitamin C was added before extrusion, great looses occurred (57-66%)"
  • Vitamin C losses in potato flakes was 14 - 68%
  • Again higher screw speeds lead to higher losses of vitamin C
  • Finally this wonderful piece of news"It should be noted that the snack product that was most acceptable form a sensory point of view had the lowest content of vitamin C." Wonderful do you think produces want to maximize how consumers like their products. I think so.
The fat soluble vitamins
  • In maize 53% of carotene was destroyed
  • Only 26% of beta carotene added to the food was detected after extrusion
  • There were only two studies done on Vitamin E, one stated no loses the other were loses were only 15% in soy flour.
The summary was that "Due to difficulties in the analytical procedures, the stability of fat soluble vitamins needs further evaluation."

So remember this next time someone suggests that modern food processing does not impact on our nutrition!

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