Radio Frequency Pasteurization of Peanut Butter: Quality Evaluation

Introduction: The low thermal conductivity of peanut butter creates a significant challenge in developing a pasteurization process that sufficiently inactivates Salmonella. In addition, Salmonella is heat-resistant in low water activity foods such as peanut butter. Alternative methods such as radiofrequency (RF) heating have the potential to overcome the limitations of conventional thermal processing. However, any form of thermal processing could degrade the quality of food.

Purpose: This study aims to investigate the effects of an RF heating pasteurization process on the quality of peanut butter.

Methods: Thermal treatments for the peanut butter (83°C for 110 min and 90°C for 49 min) were chosen based on Salmonella thermal inactivation studies in the literature. The quality parameters measured include fatty acid composition, peroxide value, volatile compounds, oil separation, color, spreadability, and water activity. Quality evaluations were done immediately after RF heating, after a month of storage at 23°C, and after a month of accelerated storage (40°C) in triplicates.

Results: The spreadability (hardness and adhesiveness) of RF heated peanut butter was not significantly (P-value < 0.05) different from the control for all storage conditions. The largest color difference, ΔE (versus control) was 1.6, which would be hardly discernible by consumers. Oil separation was unaffected (P-value < 0.05) by RF heating, although accelerated storage induced oil separation in all samples. Four phytosterols (campesterol, stigmasterol, β-sitosterol and Δ⁵-avenasterol) were identified in the samples and two of them (campesterol and stigmasterol) were significantly (P-value < 0.05) higher in peanut butter treated at 83°C for 110 min, regardless of storage time. The remaining quality analyses are being performed, but results thus far suggest that RF heating can pasteurize peanut butter without significant quality degradation.

Significance: These results can serve as guidance for determining the appropriate thermal intensity of pasteurization processes for inactivating Salmonella in peanut butter.