Coating and defatting improve oxidation resistance in roasted peanuts.

Peanuts are a very good source of monounsaturated fats, the type of fat that is emphasized in heart-healthy diets. Not only do peanuts contain oleic acid, but research shows these legumes are also as rich in antioxidants as many fruits. Unfortunately, lipid oxidation is one of the leading causes of flavor deterioration in roasted peanuts. The product's fat content and oxygen uptake play an important role in the oxidation process.

Scientists at Tuskegee University believe that inhibiting oxygen uptake in peanuts by applying an edible coating and reducing the product's fat content may decrease the rate of lipid oxidation. This, in turn should improve the storage stability of roasted peanut products. The results of their research indicate that a coating and ultrasonic defatting inhibit roasted peanut oxidation and improve the storage stability of this product.

Investigators wanted to determine whether a coating and an ultrasonic defatting treatment could inhibit the extent of flavor deterioration in roasted peanuts at different storage times. The peanuts--Georgia green runner variety--were roasted at about 178 C for 20 minutes. For the defatting process, researchers packed peanuts into glass jars with 100 ml of hexane. The jars were subjected to sonication.

Then the samples were treated in a variety of ways. Some were roasted and coated with carboxymethylcellulose, whey protein isolate and zein. Others were roasted, sonicated and coated with carboxymethylcellulose, whey protein isolate and zein. The samples were stored at 35 C to 37 C at a relative humidity of about 60% to 70%.

Flavor compounds were analyzed using static headspace gas chromatography-mass spectrometry at the start of the testing period, as well as at one month and three months of storage. The scientists found that the coated samples were more resistant to oxidation than the uncoated control. The relative hexanal content was significantly lower in the coated samples. The whey protein isolate-coated samples showed the lowest oxidation rate. The defatted samples were also more resistant to oxidation than the non-defatted product.

Further information. Zhiliang Huang, George Washington Carver Agricultural Experiment Station, 211 Campbell Hall, Tuskegee University, Tuskegee, AL 36088; phone: [phone]; [e-mail].