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Combine infrared and hot air to optimize almond production.

Almonds are California's largest tree nut crop. In 2010, California almond production totaled 1.65 billion pounds, with a value of $2.69 billion.

Almonds are traditionally processed using hot air at temperatures ranging from 129.5 C to 154.5 C. USDA-ARS scientists examined the shelf life of almonds heated and processed by infrared heating, sequential infrared and hot air (SIRHA) treatment, and hot air. The investigators found that the quality of roasted almonds produced using SIRHA and hot air was similar immediately after they were roasted and after three months of storage.

Essentially, the researchers believe that SIRHA processing is an effective way to produce pasteurized almonds that have a quality similar to those processed using hot air. SIRHA processing can lower production costs due to reduced roasting time compared with conventional hot-air processing.

To develop a more efficient roasting technique than traditional hot air roasting, the investigators evaluated the shelf life of almonds roasted using infrared, SIRHA and regular hot air techniques. They processed nine medium roasted almond samples at three different temperatures: 130 C, 140 C and 150 C. The samples were packed in paper bags and stored at 37 C for three, six or eight months. Shelf life was determined by measuring changes in color, peroxide value, moisture content, water activity, flavor components and the sensory quality of the samples.

There was no significant difference in the moisture content and water activity among the almond samples processed with the different roasting methods and stored under the same conditions.

Gas chromatography-mass spectrometry analysis showed that aldehydes, alcohols and pyrazines were the main flavor components of the almonds. Aliphatic aldehydes, such as hexanal, (E)-2-octenal and nonanal, were produced as off-flavors when the samples were in storage. Although the overall quality of the almonds produced with SIRHA and hot-air heating was similar during their first three months of storage, their peroxide value and the concentration of aliphatic aldehydes differed significantly and increased significantly during storage.

The researchers indicate that hexanal and nonanal--lipid oxidation marker compounds--might be better shelf life indicators than the current standard--peroxide value. Detection of peroxide gives the initial evidence of rancidity.

Further information. Zhongli Pan, USDA-ARS Western Regional Research Center, Room 1111, 800 Buchanan St., Albany, CA, 94710; phone: 510-559-5861; fax: 510-559-5851; email:
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Publication:Emerging Food R&D Report
Geographic Code:1U9CA
Date:Oct 1, 2013
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