Effect of pretreatments on quality characteristics and water activity of air-dried litchis (Litchi chinensis Sonn.) cv. Rose Scented

The effect of pretreatments on the quality of dried litchis was studied. Dried whole litchis were brown, blanching in boiling water reduced browning but colour was still disliked. Peeling and destoning fruits before drying gave superior product (extent of browning or EB: 0.27, mean sensory score or MSS: 6.74) and they dried faster. Pre-drying dip of peeled and destoned litchis for 10 min in 2% Na₂SO₃ + 1% sodium metabisulphite at room temperature improved colour (EB 0.03) but reduced MSS (5.80). Litchis syruped in 40% syrup containing 0.5% citric acid and 3000 ppm SO₂ for 30 days gave best dried product (EB: 0.08, MSS: 8.08). They dried faster for first 4h after which untreated peeled and destoned (control) litchis dried faster. Dried syruped litchis were hygroscopic, water activity for product of 11.1% moisture (moisture free basis) was 0.27 and critical moisture content was 20g H₂O per 100g solids.