Influence of Pre-Roast Moisture Content and Post Roast Cooling Parameters on Salt and Oil Content of Oil Roasted Peanuts

STRASSER, HANNAH KATHLEEN. Influence of Pre-Roast Moisture Content and Post Roast Cooling Parameters on Salt and Oil Content of Oil Roasted Peanuts. (Under the direction of Dr. Lisa L. Dean). Oil migration affects the appearance and quality of oil roasted peanuts and consequently has an impact on overall consumer acceptance. Exchange of oil may occur during or after oil roasting (deep fat frying) of peanuts but little is known about the factors contributing to this exchange. Studies on deep fat frying have mainly focused on foods with higher moisture levels. For foods with lower moisture content such as peanuts, inconsistencies reported between different theories, urge further investigation on the roasting process. Current available research reports explaining the mechanisms that ensue during roasting suggest that pre-roast moisture content and post roast cooling parameters are probable factors that influence the movement of oil. The purpose of this study was to monitor and determine the effect of raw seed moisture content and post roast cooling practices on the migration of oil or salt to or from peanut seeds, during the frying and post roast cooling processes. To examine the effect of these factors raw high oleic peanuts were manipulated through forced air drying or the addition of moisture to achieve a range of moisture contents including: 3.3%, 4.6%, 6.1%, and 8.4% determined on a wet weight basis. Peanuts from each distinguished moisture level were then 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 from the fryer into or onto the peanut seeds. Upon removal from the roasting oil, peanuts were cooled using three different cooling parameters. Multiple analyses were utilized to trace and quantify oil migration and retention including the changes observed in seed moisture content and mean oil, fatty acid analysis, bulk density, true density, and porosity, as well as structural damage observed through the use of scanning electron microscopy. The results of these analyses revealed that pre-roast moisture content influences the transfer of matter during frying and post roast cooling influences oil migration after the seeds are removed from the fryer. As raw moisture levels increase the seeds experienced a greater and more violent expulsion of internal moisture upon entry into the hot frying oil. The turbulence and duration of the dehydration process was directly influenced by the amount of moisture present. High moisture seeds experienced more structural damage and loss of endogenous peanut oil and matter into the frying medium. SEM images confirmed these findings through the increased presence of cracks and voids in the peanuts’ surfaces. The determined presence of C12:0 found in the oil obtained from roasted seeds that had been rinsed of surface oil, confirmed that oil from the fryer migrated into the seed at some point in the process. Further differences reported between peanuts that were cooled in relation to those that were not cooled indicated that the majority of oil absorption occurs during the post roast cooling process. Peanuts that were not cooled showed a significant increase in amount of surface oil and decrease in oil the seed took up. Cooling at different rates did not show significant differences. Porosity data showed a slight increase as pre-roast moisture increased but was not determined to be statistically significant. © Copyright 2017 Hannah Strasser All Rights Reserved Influence of Pre-Roast Moisture Content and Post Roast Cooling Parameters on Salt and Oil Content of Oil Roasted Peanuts by Hannah Kathleen Strasser A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science