Development of ready-to-eat, easy-chewing black peanut kernels for older adults through optimized pre-soaking and steamed softening.

This study investigated the effects of soaking time and temperature on the physical properties of black peanut kernels (BPK), a Taiwanese native peanut species. Results revealed that higher soaking temperatures and longer durations increased the water absorption rate and the moisture content of BPK. After soaking, the activation energy, enthalpy, and Gibbs free energy were positive, indicating that BPK was temperature-sensitive and capable of absorbing energy from its surroundings. Following steamed softening, the hardness of BPK decreased as soaking time and temperature increased. Specifically, BPK pre-soaked at 25 °C or 40 °C for 8 h and then steamed softening at 121 °C for 20 min (F₀ = 12) achieved a hardness of 4.68 and 4.87 × 10⁵ N/m², respectively, meeting the easy-chewing standard (< 5 × 10⁵ N/m²) based on Taiwan's Eatender guidelines. However, increasing the steamed softening temperature to 124 °C for 11, 16, and 20 min (with F₀ values of 5, 10, and 15, respectively) did not further soften BPK. In conclusion, pre-soaking BPK at 25 °C for 8 h and then steamed softening it at 121 °C for 20 min successfully developed a ready-to-eat and easy-to-chew product for older adults.