Abstract: Peanuts in North America and Europe are primarily consumed after dry roasting. Standard industry practice is to roast peanuts to a specific surface color (Hunter L-value) for a given application; however, equivalent surface colors can be attained using different roast temperature/time combinations, which could affect product quality. To investigate this potential, runner peanuts from a single lot were systematically roasted using 5 roast temperatures (147, 157, 167, 177, and 187 °C) and to Hunter L-values of 53 ± 1, 48.5 ± 1, and 43 ± 1, corresponding to light, medium, and dark roasts, respectively. Moisture contents (MC) ranged from 0.41% to 1.70% after roasting. At equivalent roast temperatures, MC decreased as peanuts became darker; however, for a given color, MC decreased with decreasing roast temperature due to longer roast times required for specified color formation. Initial total tocopherol contents of expressed oils ranged from 164 to 559 μg/g oil. Peanuts roasted at lower temperatures and darker colors had higher tocopherol contents. Glucose content was roast color and temperature dependent, while fructose was only temperature dependent. Soluble protein was lower at darker roast colors, and when averaged across temperatures, was highest when samples were roasted at 187 °C. Lysine content decreased with increasing roast color but was not dependent on temperature. MC strongly correlated with several components including tocopherols (R2 = 0.67), soluble protein (R2 = 0.80), and peak force upon compression (R2 = 0.64). The variation in characteristics related to roast conditions is sufficient to suggest influences on final product shelf life and consumer acceptability.
Practical Application: Peanuts are typically dry roasted to a specified surface color for a given food application; however, it is possible to obtain equivalent colors using different temperatures. This simple observation led to the overall goal of this research which was to determine if peanuts roasted to equivalent surface colors using different temperatures are equivalent from a quality perspective. Several compositional and textural measurements important to product quality differed based on the temperature used to achieve a given roast color. Overall, this study suggests there is good potential to optimize peanut quality by simply adjusting the time/temperature profiles during roasting.