Nutritional Value and Quality of Processed Mango Fruits
Mango (Mangifera indica L.) is one of the most important tropical fruits commercialized and consumed worldwide, and an excellent source of fibre, bioactive compounds such as pro-vitamin A carotenoids, vitamin C (ascorbic acid) and phenolics. Mango was used in this thesis as a model fruit of fruits and vegetables that are rich sources of nutrients. They are highly perishable, prone to progressive undesired changes if stored untreated. As a result, large amounts of mango are lost annually in many areas of the world including Mozambique. To reduce postharvest losses of fruits, processing is recommended since it extends the shelf life and enable the availability off-season, and the promotion of consumption is a potential health enhancing strategy. However, processing of fruits and vegetables must be carefully designed to achieve a high sensory and nutritional quality of the final products. The aim of the present thesis was thus to evaluate the effect of conventional and novel processing techniques on the retention of vitamin C and β-carotene, two major bioactive compounds, in minimally processed or dried mango products.
The effect of osmotic dehydration (OD) with or without vitamin C or calcium prior to hot air-drying was evaluated in terms of the retention of vitamin C and β-carotene in dried mango. Fortification of OD solutions with either calcium or vitamin C was shown to be an efficient way to improve the retention of vitamin C and carotenoids in dried mango. OD pre-treatment reduced the hardness, drying time, and prevented colour changes.
The potential use of alternative blanching techniques to improve the retention of vitamin C and β-carotene in processed mango was explored using infrared (IR) and microwave (MW) dry blanching and blanching in a closed plastic bag immersed in water bath at (High-Temperature-Short-Time - HTST) or (Low-Temperature-Long-Time - LTLT), prior to hot air-drying. Complete inactivation of PPO was achieved, while a minor activity of AAO remained. An improved retention of vitamin C in dried mango was achieved using IR and MW dry blanching or water blanching in plastic bag in comparison to conventional water blanching. However, the retention of all-trans-β-carotene was higher in dried mango after water blanching than after dry blanching. In conclusion, a correct selection of suitable techniques and conditions for blanching can enhance the nutritional value of dried mango and inactivate enzymes that degrade vitamin C and β-carotene.
To address the problem of reduced sensory and nutritional quality during the processing of purées, the impact of acidification, addition of EDTA or water blanching at HTST, on the retention of vitamin C (L-AA and DHAA) and β-carotene was evaluated in mango purée. The results showed that the disruption of the cellular matrix during purée processing facilitates oxidative reactions of vitamin C and of all-trans-β-carotene unless protected by an initial blanching step, pH adjustments or addition of EDTA a chelating agent to inhibit AAO and PPO activities.
ascorbic acid oxidase