The effect of different pre-treatments on qualitative properties of freeze-dried Feijoa fruit

Abstract

Feijoa is an aromatic fruit with high vitamin C and anti-oxidant contents. Given its highly sensitive contents, it is necessary to select a suitable method for production of Feijoa chips. Despite its high energy consumption, freeze-drying can produce high-quality products. In this study, 7 pretreatments (ascorbic acid, microwave, blanching with hot water and steam, potassium carbonate, osmotic and ultrasound) were used at different levels to improve the quality of dried samples. The pretreated samples were freeze-dried, and their qualitative parameters (pH, rehydration, vitamin C, failure force, and total color differences) were analyzed. Results showed that the highest and lowest pH values were in samples pretreated with potassium carbonate and ascorbic acid, respectively. The highest and lowest rehydration ratios were observed in microwave-pretreated and control samples, respectively. Control and microwave-pretreatment led to the highest and lowest failure forces, respectively. The highest vitamin C content (0.33g/100g) belonged to the control treatment, whereas its lowest amount (0.08g/100g) was measured in hot-water blanching. The highest color difference (3.3) was obtained using the ascorbic acid pretreatment, and the microwave pretreatment led to the lowest color difference (0.8). In conclusion, the results from mean comparison of different treatments showed that the ultrasonic pretreatment can relatively preserve product parameters better than other pretreatments.