Characterization and modelling of pumpkin chips production with microwave assisted drying method

Drying method for foods is, removing the water existing in the food product; decreasing the amount of water of the food with the combination of transferring mass and heat under monitored circumstances. By means of the drying process of foods, the dried food products are transported and stored much more efficiently and spoilage of products are prevented because microbial evolvements and other reactions are limited. As a result of these, the desired food product can be consumed easily, outisde of the growing season of the product. By drying foods, it is made easier to obtain different tastes from the product by means of processing. Similarly, by dehydrating the product, qualities such taste, smell and nutrition values are preserved. Also, using heat treatment during the process of drying foods, increase the amounf of some antioxidative compounds in the food products. Therefore, persons who cannot consume fresh food products due to health reasons can easily consume dried food products. Food drying is a very old process that has been used for centuries, it has been developed throught time according to the evolving and changing technology, life standards and the desired end product quality. In literature, the traditional drying methods are drying in sun and conventional methods; and modern methods are freeze drying, ultraviolet drying and microwave drying. Conducting traditional methods to dry foods cause long drying times and low quality end products. The freeze drying method, prevents; chemical and enzymathic reactions as well as vitamin and phenolic matters therefore preserving the end product quality. However, as opposed to the stated advantages, this method has a costly setup and operation. Ultraviolet drying method prevents nutritient and quiality loss and it has a short amount of time to dry products. However, due to the facts that this method is more suitable for low amounts of food and dependent on the product geometry. In dealing with edged products the drying is not homogeneous therefore the method does not have a high utility. The microwave method preserves the food color and volatile organic compounds in the product; and it is preventing the hardening and cracking of the product surface. Due to the microwave working principle, the heating starts from the center of the product and causes heat and mass transfer faster therefore decreases the drying time. Microwave method can be used with wide range of products; with its low-cost setup and easy operation, and engery saving traits makes it more advantageous compared to the other methods. Heat treating methods used to remove the hydration from the product harms the physicial and physico-chemical structure of the food product. Additionally, it can also harm the end product's phenolic matter and antioxsidative compounds while having a negative impact on vitamin, color and texture quality. Because of that it is very important to conduct pre-treatments depending on the product type such as osmotic or ultrasonic; to decrease the harmful effects of various types of drying procedures as well as decreasing the drying time and increasing the end product quality. Ultrasonic method accelerates the removal of water from the product by causing cavitation effect on the products and increasing the mass and heat transfer. Additionally, the cavitation effect causes protein denaturation thus inactivating polyphenoloxydase (PPO), peroxidase (POD), and lipoxygenase (LOX) enzymes. Therefore the dried products have a lesser change of color while preserving antioxidative matters. Osmotic pre-treatment method prevents the product from oxidative spoilage while decreasing the volatile compound and increasing the drying speed. In addition, osmotic pretreatement can help to product to protect the their color and texture quality of products. Therefore it is suggested that the osmotic method to be used with other accompanying drying methods instead of using it on its own. This study focuses on dried fruits and vegetables as healthy snacks and healthy life practices. Microwave supported conventional method is used to make pumpkin chips samples and osmotic and ultrasonic pre-treatments are used to monitor quality, drying time and sensory like changes. Osmotic pre-treatment experiment set is designed with DOE (Designing of Experiment); and sugar density is used as 25 and 50 °Brix; dipping period parameters were 60 and 90 minutes. In ultrasonic pre-treatment experiement set under 50 Khz frequency, 10, 20, and 30 minute pre-treatment parameters were used. During the pre-treatment methods in each drying set 200 W microwave force, 60°C air temperature and 1.5 m/s air speed was used. Drying try-outs were checked with online weight measurement apparatus and stopped when it reached 92% weight-loss. The optimum pre-treatment was decided according to the results of drying time after pre-treatment, total amount of phenolic matter and sensory like. It was concluded to continiue the pumpkin chips samples' parameters optimization analysis with 30 minutes of ultrasonic pre-treatment. Response Surface Methodology (RSM), Central composite experiemental design method was used to design the pumpkin chips drying experiement set with; 200-300W microwave force, 60-70°C air tempreture and 1,5-2,5 m/s air speed parameters and 20 experiments (double-repeated 40 experiments) were designed. After each experiment, drying time, rehydration capacity, color (L, ΔE), and texture values were measured. Afterwards, according to the most important parameters to determine the quality of the cips: drying time, color and texture values were used to optimize and model and a solutions were determined for each individual parameter using Minitab 'Response optimizer' function. For optimum drying time, 275 W microwave force, 73,5°C air temperature and 1,16m/s air speed; for optimum color quality; 230 W microwave force, 73,41°C air temperature and 1,16 m/s air speed solutions were reached. To verify the above stated models, the three optimum solutions were tried again and experiment prints, model prints were compared and seen that the results were very similar. After verification of model, antioxidant capacity, total phenolic matter and beta carotene were used to characterize the optimum solutions.