Effect of osmotic dehydration combined with citric acid on bioactive compounds in freeze-dried MD2 pineapple

The use of freeze drying process to prolong the shelf life of food products is considered mainstream in food industries due to its capability to retain the nutritional value. Citric acid and osmotic solution were used as a pre-treatment in this study to produce high-quality dried products. Four treatment groups were observed, including untreated (control), 1% citric acid (CA), 1% CA with 20% sugar solution (CAOD 20%), and 1% CA with 60% sugar solution (CAOD 60%). Physical properties such as moisture content; pH; total soluble solid; colour value; and bioactive compounds, such as vitamin C, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities were evaluated in freeze-dried pineapples. The result showed that CAOD 60% demonstrated a positive effect, with the least moisture content and the lowest value of colour changes (ΔE) at 5.69 ± 0.04% and 33.76 ± 2.17, respectively, as compared with that of other samples. In terms of phytochemical, the control and CA groups recorded higher retention of vitamin C, TPC, and TFC compared with other osmotic dehydration samples; however, there was no significant effect (p<0.05) on TPC and TFC. Interestingly, CAOD 60% possessed strong antioxidant activity, with the lowest IC50 value of 85.85 ± 5.93. From these findings, it was found that CAOD 60% resulted in positive effect on both the physical qualities and preservation of antioxidant activity, making it a recommended condition for pre-treatment in fruit preservation, which is essential in ensuring both the food security aspect and maintenance of its nutritional value.