Science Q & A

Which nut is healthier: raw or roasted?

New York TimesMay 5, 2013 

Q: Nuts are good for you, but is there a difference between raw nuts and roasted nuts?

No research has specifically addressed how roasting nuts may change their nutritional value, said Rui Hai Liu, a professor of food science at Cornell University, but he said that in his opinion, “I predict you will get health benefits from consuming either raw or roasted nuts.”

“I don’t think processing will decrease the benefits, and it may actually improve the bioavailability of some bioactive compounds,” such as flavonoids, said Liu, who has studied the benefits of eating nuts.

The positive effect of processing has been shown in his laboratories for such compounds in tomatoes and sweet corn.

Phenolic compounds in nuts “have high antioxidant activity and are able to quench free radicals that lead to cell damage and oxidative stress,” Liu said. “Nuts also have a very nice fatty-acid balance and are a good source of vegetable proteins.”

And they are linked to a lower risk of cardiovascular disease.

Walnuts have the most phenolic compounds and antioxidant activity, followed by pecans. Then come peanuts (actually a legume). Pistachios, cashews, hazelnuts and almonds also have high levels.

“Do you think roasted nuts taste better?” Liu asked. “Then roasting will encourage you to include them in your diet.”

Q: Why does my microwave’s turntable switch directions when I stop it and start it again? Does it affect how the food heats?

“The direction of rotation should have no effect on the rate of heating or uniformity of heating for any conceivable food-heating situation,” said Ashim K. Datta, professor of biological engineering at Cornell University.

The reversal has to do with the relatively inexpensive turntable motors designed for use in most microwaves, said Robert J. Thomas, professor of electrical and computer engineering at Cornell. By design, they reverse their direction of rotation if a load greater than their output torque, or twisting force, is present, he said.

“All motors require a starting torque in order to start themselves from zero rotation speed to design speed, with or without a load attached,” Thomas said.

It takes very little torque to rotate the turntable once it is turning, he said, but it can take several times the running torque to start it.

After a full stop, the drive mechanism is usually pressed against the load in the direction of the last rotation. When the motor encounters the load, it reverses itself and gets a small running start to pick up speed before engaging the load again.

The mechanical linkage needed to perform this is much cheaper than the additional windings of copper wire that a stronger motor would require, Thomas said.

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