Effect of pre-roast moisture content and post roast cooling parameters on oil migration during oil roasting of peanuts

Authors: STRASSER, HANNAH - North Carolina State University; Dean, Lisa

Submitted to: American Peanut Research and Education Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/31/2017
Publication Date: 7/12/2017
Citation: Strasser, H.K., Dean, L.L. 2017. Effect of pre-roast moisture content and post roast cooling parameters on oil migration during oil roasting of peanuts. American Peanut Research and Education Society Abstracts. Vol. 49.

Interpretive Summary: Shelled, blanched peanuts are oil roasted and packed into cans and jars for retail sale as "cocktail" peanuts. They are often larger peanuts of the virginia market type and command a higher price than some other types of peanuts. Customers prefer that their appearance be slightly glossy with the salt added as seasoning be visible. Consumer complaints about these products are generated when the appearance is over oily, when the containers contain what seems to be excess oil pooled at the bottom, an overly dry appearance or the loss of salt to the container resulting from the salt not adhering to the peanuts. This study examined how the amount of moisture in the raw peanuts and how the peanut were cooled after roasting affected the final appearance after oil roasting. This was accomplished by controlling the moisture levels in 4 batches of raw peanuts between 3.3% (which would be considered very dry) and 8.4% (which would be considered more wet than normal). The peanuts were then roasted in an oil blend of peanut (90%) and coconut (10%) oils. The coconut oil contains a 12 carbon fatty acid that peanut does not. The low level of mixture prevent the cooking character of the peanut oil from being changed. By monitoring the unique fatty acid from the coconut oil, the movement of the roasting oil into the peanut could be determined. This was needed to show if the oil from the roasting was responsible for the oil on the peanuts or in the bottom of the storage container. Also, the oil inside of the peanuts after roasting was tested to determine if any of the oil from the roasted had migrated into the peanuts due to the vacuum formed when the water was cooked out of the peanuts during roasting. The study determined that the oil on the surface of the peanuts was entirely from the roaster, regardless of how the peanuts were cooled or what their raw moisture content was. Also, it showed that oil from the roaster is able to move into the peanuts during roasting and could be responsible for the loss of oil during storage.

Technical Abstract: Oil migration affects the quality and shelf-life of food products and consequently has an impact on overall consumer acceptance. Exchange of oil may occur during or after oil roasting of peanuts but little is known about the factors contributing to this exchange. This study examines the effect of pre-roast moisture content and post roast cooling parameters on oil migration during the oil roasting of peanuts. Peanuts with a range of moisture contents of 3.3%, 4.6%, 6.1%, and 8.4% were oil roasted in peanut oil containing 10% coconut oil. Lauric acid (C12:0) from the coconut oil served as a chemical marker to track oil movement on to the surface or into the peanut seeds. Upon removal from the roasting oil, peanuts were cooled using three different cooling parameters including immediate packing (no cooling), forced cooling (fast cooling), and ambient cooling (slow cooling). Fatty acid analysis indicated the presence of lauric acid (C12:0) in the oil collected from the surface of the peanuts as well as within the peanut seed. The average fatty acid profile of the surface oil from the peanuts of different moisture contents from the roasted seeds using no cooling, fast cooling and slow cooling revealed that the amount of C12:0 present was very close to that of the roasting oil being 3.3%, 3.5%, and 3.6% respectively. The internal seed C12:0 content was very similar for both the fast cooling and the slow cooling at 0.26% and .25% respectively however much less for the seeds with no cooling at 0.14%. The amount of C12:0 in the total seed oil (surface + internal oil) did not vary with different cooling parameters or moisture contents. However, the amount of C12:0 within the seed and the surface measured separately did vary with moisture content.