Effects of Different Roasting Conditions on Peanut Quality

In the U.S., a major portion of the peanut crop is converted from whole seed into value-added products. For such purposes, the peanut seeds are processed using a thermal operation as the first step in the manufacture of the final products, to achieve specific flavors, colors, and textures. Peanuts are typically processed by dry roasting or oil roasting (deep frying and blister frying). Comparisons among different dry roasting conditions and different roasting methods were made in this work regarding their effects on the quality-related properties of roasted peanuts.;On an industrial scale, peanuts are typically roasted to a specific color for quality control. Recent lab scale experiments demonstrated that peanuts roasted to equivalent surface colors at different time/temperature combinations could vary substantially in chemical and physical properties related to product quality. This study expanded that approach to a pilot plant scale roaster. Jumbo-size runner-type peanuts were systematically roasted at 5 temperatures (149-204 °C) to three Hunter L-values of 53.0, 48.5, and 43.0 using the same peanut bed depth and air flow. The flavor of medium dry roasted peanuts was superior to light and dark roasts, with higher roasted peanutty and sweet aromatic flavor notes. Total tocopherols of oil extracted from the roasted peanuts was greatest in peanuts roasted to darker colors, with the medium and dark oil showing no significant differences from the raw oil. Yield stress of pastes prepared from the roasted peanuts increased as the final color increased, regardless of roast temperature. This was attributed to decreased moisture content, lower oil fluidity, as well as increased degree of polymerization. Kinetics of color development during peanut dry roasting were investigated. It was observed that the Hunter L values of the peanuts fitted well with either zero, first, or second order models (mean R2>0.95). The activation energies calculated from the Hunter L and b values were 1.0- 1.2x10 8 J/kg mol. High temperature roasting presented broader distributions of single seed color, indicating those roasts were less uniform in color development throughout the load, which indicated larger temperature differences among different locations within the roasting load.;Peanuts were also deep fried, blister fried, or dry roasted at 177 °C to Hunter L-values of 53.0 +/- 1, 48.5 +/- 1, and 43.0 +/- 1, respectively. Peanut microstructure was most extensively damaged by blister frying, followed by deep frying, and then dry roasting. The moisture content decreased with darker surface colors, due to increased moisture loss for darker roasts. For light roasting, blister fried peanuts had significantly higher moisture content than the deep fried and dry roasted, while for medium and dark roasting, blister fried had lower moisture than the other two. Descriptive sensory analysis distinguished among the texture profiles of peanuts prepared by different roasting methods. Flavor profiles were more related to roast color than roasting method. In the storage test of 16 weeks, using peroxide value measurements, the blister fried had the longest shelf life, followed by the dry roasted, and then the deep fried. Descriptive sensory analysis ranked the shelf life length as deep fry > blister fry > dry roast.;The conditions and methods of roasting could potentially affect the physical, chemical, sensory, stability properties of roasted peanuts. From this research, the ideal way to compare different roasting conditions and methods should be based on the concept of.