The effects of different cooking times and temperatures on nutritive quality of mangoes, tomatoes and carrots

Abstract

The present study was conducted with the aim to determine the effect of cooking temperature and time on the nutritive value of mangoes, carrots and tomatoes. Fruits and vegetables are important components of a balanced human diet that provide essential vitamins, minerals and dietary fiber for our bodies. It is required to use a combination of mangoes, tomatoes and carrot to enrich ketchup, however the temperature and time required for cooking theses fruits with minimal loss of nutrients is not defined. Therefore, application of processing methods that will reduce the water content, as well as inhibit enzyme activities, are crucial to extending shelf life, avoiding wasting and increasing their availability off season. Thermal treatment or cooking is one of these processing methods used in this study. The mangoes, tomatoes and carrots were prepared individually into pulp using a blender. 25ml of the prepared samples was used as standard weight for the different heat treatments and each sample was labeled according to related time and temperature that is; 70, 80, and 90°C for 3, 5 and 10 minutes for carotenoids analysis and 7.0, 75, 80, and 90°C for 5, 10 and 15 minutes for determination of vitamin C. The water bath was preset to the required temperature and checked with a thermometer to match with the desired test temperature. The labeled beaker (50 ml) containing 25ml of sample was placed in the water bath set at the required temperature and time. The samples were then removed, cooked and analyzed for total carotenoids using the Harvest plus method and vitamin C using the 2,6- dichlorophenol-indophenol titration method. Statistical evaluation and graphical representation of the data were done using MS Excel. The results showed that interactions of both factors (temperature and time) had a significant effect on the vitamin C and total carotenoids, indicating the significance of their appropriate combination. From the results, cooking mangoes at 90°C for 5 minutes, tomatoes at 80-90°C for 5 minutes and carrots at 70°C for 10 minutes preserves both the total carotenoids and vitamin and hence can be used to produce ketchup of high quality. The results show that the interactions of both factors (temperature and time) were very important, indicating the significance of their appropriate combination. High temperature treatments for longer holding periods indicate an intensification of degradation of nutrients in the fruits and vegetables.