Impact of Osmotic Dehydration Techniques on Mass Transfer, Physicochemical and Antioxidant Properties of Osmotically Dehydrated Mango Slices

Abstract

Background and Objectives : Mango (Mangifera indica L.) is a tropical fruit with a unique color, aroma, and taste. It is rich in nutrients that benefit health, including carbohydrates, proteins, dietary fiber, vitamins, and minerals. Additionally, it contains important bioactive compounds such as phenolic acids, flavonoids, and carotenoids (Gupta et al., 2022). However, mangoes have a high moisture content, making them highly perishable after harvest. Excess mango production beyond market demand impacts production costs. Processing mangoes into dried fruit products is an alternative that adds value and extends shelf life. Nevertheless, hot-air drying methods have the drawback of being time-consuming, which negatively affects the product quality. The pretreatment method of mangoes before drying, such as osmotic dehydration, can reduce drying time. Osmotic dehydration is a method that involves soaking fruits or vegetables in a solution to remove water from them. This process reduces moisture content and water activity (a_w), which inhibits the growth of microorganisms responsible for food spoilage. It also Improve the physicochemical and sensory qualities, as well as extend the shelf life of fruits and vegetables. However, conventional osmotic dehydration methods take a long time. The application of non-thermal and environmentally friendly technologies, such as ultrasound and vacuum impregnation combined with osmotic dehydration, can enhance mass transfer efficiency, allowing water to be removed from the raw material more quickly while also improving the quality of the food material. The ultrasound technique induces cavitation, leading to microstructural changes in fruit tissue, which facilitates the movement of water and solutes (Trusinska et al., 2024). Meanwhile, vacuum conditions help eliminate gases in the intercellular spaces using a hydrodynamic mechanism, allowing solutions to impregnate the pores of the plant structure (Gautam et al., 2024). Thus, this study aims to investigate the effects of ultrasound and vacuum combined with osmotic dehydration on mass transfer, physicochemical properties, and antioxidant activity in mango slices.

Methodology : The preparation of Kaew Kamin mango for the osmotic dehydration study begins with slicing the mango lengthwise into pieces approximately 1 cm thick. The mango slices were soaked in a 0.5% calcium chloride solution to enhance firmness and then blanched in boiling water at 100°C for 30 seconds to help preserve color quality. Mango slices were pretreated using four osmotic dehydration techniques: traditional osmotic dehydration (OD), vacuum-assisted osmotic dehydration (VOD), ultrasound-assisted osmotic dehydration (USOD), and ultrasonic-assisted vacuum osmotic dehydration (USVOD). The mango slices were soaked in 60° Brix sorbitol solution at 1:3 mango to solution ratio for 8 hours. The study was conducted under vacuum conditions in a vacuum chamber with a pump (Gast model DOA-P504-BN Labmodel, Germany) at 150 mbar. For ultrasound pretreatment, a high-intensity ultrasonic processor (Sonics Vibra-Cell VCX-500, USA) with 500 watts and 20 kHz was used. Water loss (WL), solid gain (SG), weight reduction (WR), moisture content, and water activity were measured at various time intervals (2, 4, 6, and 8 hours). At the end of the osmotic dehydration process (after 8 hours), color (L*, a*, b*, and E), total soluble solids, pH, titratable acidity, total carotenoid content, total phenolic content, and antioxidant activity (using the DPPH method) were analyzed. The experiment was conducted using a completely randomized design (CRD). The experimental data were analyzed using analysis of variance (ANOVA), and significant differences between mean value of treatments were determined using Duncan’s Multiple Range Test (DMRT)at a 95% confidence level with SPSS for Windows. All experiments were repeated three times.

Main Results : The osmotic dehydration techniques, including OD, VOD, USOD, and USVOD significantly affected the mass transfer parameters, physicochemical and antioxidant properties of osmotically dehydrated mango slices.The experimental results showed that the USVOD technique effectively accelerated mass transfer in the osmosis process. At the end of the process, the mango slices exhibited the highest water loss and solid gain, reaching 68.09% and 19.56%, respectively. Meanwhile, the moisture content and water activity showed the greatest reduction, with values of 41.70% and 0.8773, respectively, when compared to other techniques. The study on the physicochemical properties of osmotically dehydrated mango after 8 hours revealed that the use of the USVOD technique resulted in the highest total soluble solids and pH values. Whereas the titratable acidity, lightness (L), greenness (-a), yellowness (b*), and color difference (E) were at their lowest. Additionally, the USVOD technique resulted in higher total carotenoid content, total phenolic content, and DPPH radical scavenging activity, compared to all other techniques used in the study.

Conclusions : Osmotic dehydration techniques affect the quality of osmotically dehydrated mango slices in terms of mass transfer, physicochemical and antioxidant properties. The application of the USVOD technique improves mass transfer efficiency by increasing water loss and solid gain, while reducing moisture content and water activity to the maximum. Additionally, mango slices pretreated with the USVOD technique resulted in the highest total soluble solid content, pH values, antioxidant activity, and bioactive compounds, including total carotenoid content and total phenolic compounds, while exhibiting the lowest E value. It can be concluded that the USVOD technique is a non-thermal and environmentally friendly technology that can be applied to raw material preparation to enhance efficiency in commercial drying processes. It reduces energy consumption, processing time, and production costs while preserving the nutritional value of the products.