Drying of Grade-Out Cape Gooseberry (Physalis peruviana Linn.) with Mild Hydrostatic Osmotic Pretreatment Using Rotary Tray Dryer: A Case Study at Mae Hae Royal Project Development Center, Chiang Mai Province

This study develops a value-added processing technique for grade-out cape gooseberry (Physalis peruviana Linn.) by applying mild hydrostatic osmotic pretreatment combined with rotary tray drying. Fruits classified as grade-out, often discarded due to aesthetic flaws, were subjected to osmotic treatment at 0.5 bar for 12 h using a sucrose solution enhanced with citric acid and glycerin. Pretreatment significantly elevated water loss (52.61%) and solid gain (18.12%), reducing moisture content prior to drying. Rotary tray drying was conducted at temperatures of 50, 60, and 70 °C. Drying at 60 °C achieved the ideal balance between efficiency and product quality. Samples pretreated and dried at 60 °C exhibited a 35% reduction in drying time while preserving superior color (ΔE = 13.54 ± 1.81), vitamin C (71.76 ± 2.57 mg/100 g dry matter, DM), total phenolic content (202.9 ± 10.91 mg GAE/100 g DM), and antioxidant activity (ABTS = 95.87 ± 3.41 µmol TE/g DM; DPPH = 89.97 ± 1.27 µmol TE/g DM). A production trial was conducted using 1500 kg of raw material from the Mae Hae Royal Project Development Center in Chiang Mai, Thailand. This process yielded 220 kg of high-quality dried fruit at an overall cost of USD 6.93 per kg. Local farmers successfully applied this technique, demonstrating its potential to enhance livelihoods, avoid postharvest losses, and valorize low-quality produce in line with Sustainable Development Goal 12. This supports the Royal Project Foundation’s vision for sustainable agriculture.