عنوان مقاله [English]
Fruit juices are an important part of modern diets in many countries and one of the best drinks. Fruit juices provide a significant portion of the body's needs for minerals and vitamins and are recommended by nutritionists. By definition, the liquid extracted from fruit that has not been fermented and contains major processes such as preprocessing, extraction of fruit extracts, and post-pressure treatments is called fruit juice. Consumption of fruit juices has increased significantly over the past years and is growing significantly because consumers are interested in healthy and ready-to-eat products. The fruit juice industry is one of the industries that play an important role in the food industry and providing a high-quality product is important to achieve effective competition. Watermelon (Citrullus lanatus) belongs to the family Cucurbitaceae. This plant grows in more than 96 countries. China leads in 2015 with 70.3% of total world watermelon production. Other leading countries are Turkey, Iran, Brazil, the United States and Egypt. Watermelon fruit produces 55.3% water, 31.5% shell and 10.4% pulp. Carotenoids such as lycopene and β-carotene indicate the red and orange colours of watermelon, respectively. Watermelon sweetness is mainly due to a combination of sucrose, glucose and fructose. Sucrose and glucose make up 20-40% and fructose 30-50% of the total sugars of ripe watermelon. Watermelon juice has amazing and dense amounts of nutrients. One cup of this drink has high amounts of vitamin C and vitamin A, which cover 30% and 25% of your daily requirement for these nutrients, respectively. This drink also has moderate amounts of potassium, dietary fibre, calcium, iron and 1.5 grams of protein. Most importantly, a cup of this water contains only 70 calories but is rich in antioxidants and active ingredients such as lycopene, beta-carotene, amino acids and flavonoids. Apart from their role in the human diet, fruits are prone to spoilage due to high humidity. Post-harvest spoilage losses can be caused by pests that occur on the farm during harvesting, storage or distribution. Post-harvest mortality has been reported at 20 to 50 per cent in developing countries. If these products are processed prematurely, these losses can be avoided. The high cost and lack of efficient tools for crop processing, poor marketing and transportation system, as well as fruit perishability, contribute to more post-harvest losses. The lack of local and simple mechanical tools for processing fruit into fruit juice often leads to limited use of the fruit and consequently more losses after harvest due to rot. In order to reduce fruit losses, fruit juice extraction is a suitable option. Traditionally prepared fresh fruit juices, although pleasant and palatable and containing the vitamins and minerals found in the original fruits, can in most cases act as potential sources of contamination due to non-compliance with health standards in their preparation. This contamination may occur before or after fruit juice extraction. So far, many researchers have worked on the design and optimization of fruit juicers for various fruits and agricultural products.
On the one hand, mechanization of the watermelon water production process is necessary to further improve the health of the production process. On the other hand, today, in addition to traditional methods, there are various devices for extracting different fruit juices. Most of these devices are versatile and are used for a variety of fruits. It is clear that these multipurpose devices, due to their different physical, mechanical and rheological properties, can not provide an effective fruit juicing process for several types of fruit. Therefore, to design an effective fruit juicer, accurate information about the watermelon juice extraction process is required. The aim of this study was to determine the effects of some factors affecting the kinetics of watermelon water extraction.
In order to perform the experiments, the product prepared from the local market of Karaj city was transferred to the laboratory. The experiments were performed in the laboratory of the Faculty of Agricultural Machinery, University of Tehran, located in Karaj. In order to perform the experiment, the skin of the watermelon crop was manually separated from its mantle. Using PVC cylindrical tubes with a diameter of 50 mm, the watermelon was divided into cylindrical parts and six-centimetre pieces were created. In order to reduce the error in the amount of extracted fruit juice and also to reduce the effect of the crop on the amount, parts of the product that had little core were used. The watermelon crop was divided into six-centimetre, two-centimetre and two-centimetre layers for testing. Then, the mass weight of the prepared product was measured before each experiment by a digital scale with an accuracy of 0.01. Necessary pressure for dehydration of the product was created by a multifunctional material strength test machine (-500-Hi SE, Farvardin Azma Tajhiz, Iran). The device was connected to a computer, and the test settings were applied through software. A cylinder with a height of 150 mm made of stainless steel with an inner diameter of 57 mm was used as a cylinder. A piston with a cross-sectional area of 57 mm in diameter was used to apply the pressure created by the multi-purpose test machine to the product mass. To record the force and displacement data simultaneously, a 500 kg load cell (type S, Zemic, China) was used to connect the piston to the jaw of the multifunction test device.
According to the analysis of variance tables, the effect of three variables of maximum load, the number of layers and loading speed as independent variables on the model of predicting fruit juice mass percentage, constant coefficients of force-displacement equations and moment juice-displacement mass equation was significant at 1% level. However, in all cases the P-value associated with each of the independent input variables or their interactions alone was not significant; but the significance of all forecasting models shows their high ability to evaluate data. Also, in most cases, the high explanation coefficient of the models indicates the high accuracy of the models and the proximity of the real value and prediction. The results show that the lowest percentage of extracted fruit juice is 5.95% with input variables (loading rate of 20 mm/min, maximum loading of 160 kg and single layer) and the highest percentage of extracted fruit juice with 95.36% with input variables (loading rate). 10 mm / min, maximum load of 400 kg and three layers); Therefore, in order to extract a high percentage of fruit juice, the loading rate must be reduced and the maximum loading and the number of layers must be increased.