Sonication aids oxidative stability of roasted peanuts.

Power ultrasound has been used for many years in industrial applications. Over the last decade or so, interest has increased in its potential for use over a much wider range of chemistry and processing applications.

Scientists at Alabama A&M University used power ultrasound to remove the surface lipids from roasted peanuts in order to reduce the potential for lipid oxidation to occur before an edible coating is applied. They wanted to see what effect edible coatings and sonication would have on the oxidative stability of roasted peanuts. It turns out that the coatings along with power ultrasound can inhibit rancidity and extend the shelf life of the nuts.

Runner-type peanuts were roasted in an oven at 178 C for 20 minutes. Roasted samples, 50 grams each, were subjected to sonication in 100 ml of hexane at room temperature at various intervals for up to 30 minutes using combined frequencies of 25 kHz, 40 kHz and 80 kHz. The investigators then used solutions of whey protein isolate (WPI) at 11%, zein at 15% and carboxylmethlycellulose (CMC) at 0.5% to coat the nuts. They did this by immersing 200 gram kernels in the coating formulations for about 30 seconds.

Both the uncoated (control) and the coated samples were stored in an accelerated shelflife testing chamber set at about 35 C. Oxidative stability values were determined at 110 C and a fixed air flow rate of 120 ml per minute. After 16 weeks of storage, there was a steady improvement in oxidative stability for both the coated and sonicated-coated samples, compared to the control. The sonicated-coated samples had a more pronounced improvement than did the coated.

As compared to the control, the oxidative stability of the samples, to which ultrasound was not applied, improved by 66%, 35% and 4% when coatings of CMC, WPI and zein were used, respectively. But the oxidative stability of the sonicated-coated samples improved by 76%, 48% and 22% when coatings of CMC, WPI and zein were used, respectively. Sonication created an additional 10%, 13%, and 18% improvement beyond the use of the coatings alone.

Further information. Wade Yang, Department of Food and Animal Sciences, Alabama Agricultural and Mechanical University, P.O. Box 1628, 4900 Meridian Street N., Normal, AL 35762; phone: 256-372-4158; fax: 256-372-5432; email: weihua.yang@email.aamu.edu.