Freeze-drying of ‘Idor’ Longan ( Dimocarpus longan Lour.) Arils: Development of a stepwise shelf-temperature program based on DSC Thermograms

High-sugar fruit matrices such as longan arils are prone to structural collapse and prolonged drying during conventional freeze-drying. This study integrated differential scanning calorimetry (DSC) with experimental validation to develop a multi-stage freeze-drying protocol for ‘Idor’ longan (Dimocarpus longan Lour.) arils. DSC data analysis identified key thermal boundaries, including incipient melting at −25 °C, and a thawing peak at −2.2 °C. Although freezing below −25 °C was theoretically sufficient, experimental results showed that cooling to −45 °C was necessary to stabilize the material and enhance moisture removal. During primary drying, −2.2 °C was effective when maintained for 37 h, followed by secondary drying at 50 °C for 9 h, reaching a final moisture content of 2.72%. The baseline two-step profile required 46 h, but was further tailored into a four-step gradual heating program that reduced drying time to 41 h while maintaining product stability. Overall, this study provides a DSC-guided framework for developing efficient freeze-drying protocols for sugar-rich biomaterials.