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ARS Home » Southeast Area » Raleigh, North Carolina » Market Quality and Handling Research » Research » Publications at this Location » Publication #277082

Title: Microstructures of oil roasted peanuts as affected by initial moisture content

item Dean, Lisa
item MINIAYAH, DEBRUCE - North Carolina State University
item Hendrix, Keith
item Davis, Jack
item Sanders, Timothy

Submitted to: International Journal of Food Sciences and Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2014
Publication Date: 9/15/2014
Citation: Dean, L.L., Miniayah, D.T., Hendrix, K., Davis, J.P., Sanders, T.H. 2014. Microstructures of oil roasted peanuts as affected by initial moisture content. International Journal of Food Sciences and Nutrition. 1(1):1-5.

Interpretive Summary: Oil roasted peanuts have been known to seep oil during storage or to become dry and lose their appealing shiny surface. It has been proposed that the moisture content of the peanuts before roasting is responsible for these results. Peanuts whose moisture was at the high (7%) and the low (4%) end of the range for oil roasting were roasted and their microstructures were examined using scanning electron microscopy. The micrographs showed distinct differences that were attributed to damage sustained by the peanuts due to the heat treatments. The surfaces of the high moisture content peanuts were more damaged after roasting, but the interiors of the lower moisture content peanuts appeared to be more damaged. This indicates that the moisture of the raw peanuts does affect the roasted end product.

Technical Abstract: Oil roasting of peanuts is a unit operation equal to that of deep frying of higher moisture foods. Retention of the oil taken up by the peanuts from oil roasting during the shelf life of the packaged product is necessary to prevent an unappealing greasy appearance. Properties of the end product were found to be influenced by the initial properties of the raw materials. Raw, inshell, Virginia-type peanuts were dried to moisture levels of 4 and 7%. Peanuts were shelled and extra large kernel (ELK) grade sizes were utilized in oil roasting. Each lot was oil roasted at 160 C in pure peanut oil to produce a surface color of Hunter L 49. The effects of the raw seed moisture on the morphology of the finished product were investigated. The roasted seed were examined by scanning electron microscopy (SEM). Escaping steam caused ruptures in the surface during the roasting process. The principal differences found were that the lower moisture samples had isolated pockmarks on the outer surfaces whereas the higher moisture samples had more complex elongated tears apparently as a result of a greater volume of steam escaping from the interior of the seed. The interior cell components were more distorted and compacted in the seed roasted at the lower moisture. Longer heating times were required for the higher moisture peanuts to reach the desired color, resulting in more cell destruction nearer to the surface, but the interior cell structure seemed to be protected by the presence of the moisture. These physical and cellular changes may have an effect on the retention of oil by the peanuts during storage.