Hybridization of freeze drying and impacts on drying kinetics and dried product quality of kedondong fruits

Hybridization of freeze drying was carried out by incorporating hot air and infrared drying in a two-stage drying process with aims to investigate the drying kinetics and impacts on dried product quality of kedondong fruits (Spondias dulcis). The hybridization consisted of the first stage freeze drying (FD duration = 6 hours or 12 hours) and second stage hot air (HA temperature = 60 °C) or infrared (IR temperature = 60 °C) drying. Drying kinetics showed that drying rates improved drastically by 34-72% once it transitioned from the first stage freeze drying to the second stage hot air or infrared drying. Time saving of 16.7-37.5 hours were observed in all hybrid drying trials with reference to freeze drying alone due to the improved drying rates. Color measurement showed that FD12IR samples resulted in minimal total color change (ΔE) and no significant difference (p > 0.05) was observed with reference to freeze dried samples. In terms of total polyphenols content (TPC) and antioxidant capacities (DPPH and ABTS), hybrid drying was able to improve significantly (p < 0.05) retention of TPC as compared to hot air drying especially for FD12IR (5.45 mg GAE/g dry solid) and FD12HA (4.52 mg GAE/g dry solid) samples. The same set of samples (FD12IR and FD12HA) also showed significantly higher antioxidant capacities (p < 0.05) (DPPH = 119.62 − 121.42 mg AA/100g dry solid and ABTS = 8.75 − 9.55 μM Trolox equivalent/100g dry solid) as compared to those dried using a shorter duration of first stage freeze drying (FD6HA and FD6IR) (DPPH = 63.31-84.49 mg AA/100g dry solid and ABTS = 6.31-6.86 μM Trolox equivalent/100g dry solid). In overall, sensory evaluation concluded that FD12IR samples showed the best acceptance among all the dried samples in terms of Just About Right (JAR) scores for kedondong notes and aroma as well as comparable to freeze dried samples for browning and sourness attributes.