Water Activity as a Central Determinant of Tahini Quality, Safety, and Shelf Stability

Tahini, a low-moisture, high-fat emulsion produced by roasting and grinding sesame seeds, exhibits a complex interplay among chemical, physical, and microbiological stability factors. Despite its global relevance, the physicochemical basis of tahini stability has been poorly defined, and water activity (a_w) has rarely been treated as a central control variable. This review proposes a_w as the practical, primary lever governing the principal quality attributes of tahini from microbial lethality during roasting to Maillard flavor development, lipid oxidation, proteolysis, and textural stability during storage. Integrating kinetic theory with process data, three key a_w domains are identified: high (a_w = 0.6-0.7) for microbial lethality during humid-roasting, intermediate (a_w = 0.35-0.5) for Maillard flavor development, and low (a_w ≤ 0.35) for oxidative and microbiological stability in storage. Managing a_w trajectories, rather than temperature alone, offers the most effective route to ensure safety, texture, and flavor integrity. This a_w-centered framework bridges traditional processing knowledge with modern food physics, offering a roadmap for predictive control and shelf-life optimization in low-moisture foods. The proposed framework positions tahini as a reference model for understanding and optimizing other low-moisture, high-fat foods such as nut butters, seed pastes, halva, and chocolate.