Dissertation for receiving a master's degree
Treatment: food industry
Abstract
Osmotic dehydration is the process of removing water based on the placement of foods in a hypertonic solution. In this research, the combination of osmotic dehydration process for thick kiwi slices 0.5 cm at a temperature of 60 degrees Celsius and time intervals of 120 minutes (6 time intervals of 20 minutes) and 180 minutes (6 time intervals of 30 minutes) and at different concentrations of sucrose and glucose mixture at 3 levels of 20, 30 and 40% in a static state at a temperature of 25 degrees Celsius, the ratio of osmotic solution to fruit was selected at 5:1.
The results showed that the amount of water removal and absorption of solids and weight reduction are directly related to the increase in concentration and time of exposure to ultrasound. Glucose osmotic solution has the highest amount of water removal and sugar absorption, and sucrose osmotic solution has the lowest amount of water removal. Osmotic solutions containing both sucrose and glucose have sugar absorption and water removal between glucose and sucrose solution. rtl;">Also, the results showed that the use of ultrasound increases the rate of water removal and sugar absorption and weight loss compared to samples without treatment (control) with ultrasound.
Key words:
Osmotic water extraction - ultrasound - water reduction - absorption of solids
Introduction
It is not clear since when drying was used to preserve food, but history speaks to the fact that our predecessors learned how to dry food by trial and error. Drying food is scientific. Based on the environment around this science, it enables the creation of a global industry that is able to prepare suitable and nutritious food.
Drying is the removal of maximum water from the product with the aim of increasing its shelf life, or in other words, it is a process in which water is removed from the food to stop or reduce the growth of spoilage microorganisms and the occurrence of chemical reactions. etc. are dried by various drying methods, which, while creating diversity in the product and increasing shelf life, significantly reduce storage costs.
The first report of food drying related to vegetables dates back to the 18th century AD (Van Ares Del and Copley 1963). Later, the expansion of the drying industry was closely related to the war in the world. The British soldiers in the Crimean War (1856-1854) received dried vegetables from their country during the war. Boer (1899-1902) Canadians sent dried vegetables to South Africa and about 4500 tons of dried vegetables were transported from the United States of America during the First World War. The drying process is suitable especially for military purposes due to the saving of space and weight. Iran has a historical record in the production and supply of dried fruit in the world. A significant part of Iran's dried fruit is produced by traditional methods, especially solar drying. The reason for the lack of control of drying parameters and contact of the product with environmental pollutants is of low quality, in addition to this lack of proper packaging has also caused the loss of export markets for the country's products, most of the fruits and vegetables have a specific harvest time and a limited shelf life, and they deteriorate quickly due to microbial and biochemical activities. However, various preservation methods are used to extend the shelf life of a few weeks, a year or more, these methods include: canning, freezing, drying, fermentation, chemical additives, packaging and irradiation and pasteurization. The most notable method used on an industrial scale is canning, freezing and drying. The choice of preservation method often depends on the raw material.
1-2.Background
The high consumption of vegetables and fruits all over the world has led to the invention of various methods for their processing and preservation. One of the most common of these methods is the drying process, which facilitates transportation (due to the smaller volume of the food), increases the storage capacity, and reduces chemical and microbial reactions (due to the reduction of the water activity of the product). In recent years, extensive efforts have been made to replace modern methods with conventional drying methods, which cause adverse effects in the final products (such as reducing the quality of color and texture, losing aroma and flavor, reducing density and not losing nutrients).
Also, today the market demand for processed vegetables and fruits that are similar to their fresh type and have undergone low or moderate heat during the process. are increasing, among the most important of these methods is the osmotic dehydration process.
Besides the preservation of other goals of the drying process:
reducing the cost or problem of packaging
facilitating storage and transportation
Weight reduction and sometimes volume reduction
Retention of desirable components
However, due to the negative effects of common drying methods such as: reducing the quality of color and texture, loss of aroma and flavor, and loss of nutrients, the demand for vegetables and fruits that are similar to their fresh type and have endured low or moderate heat has increased. Therefore, extensive efforts have been made to replace methods that do not have the above defects, one of these methods is osmotic water extraction. Dewatering by osmotic method is used as a pre-process step for various drying methods such as air drying, sun drying, freeze drying, and vacuum drying. 3. Statement of the problem 1. Hypertonic solutions are able to separate water from the fruit tissue within a certain period of time. 2. Factors Various, including concentration of osmotic solution, temperature, contact time. It can affect the speed and quality of product dewatering using the osmotic process method. 3-Using the osmotic dewatering process as a pre-drying process can improve the characteristics of the dried product in terms of quality indicators and its shelf life. 4-Combining osmotic dewatering with a gentle drying method such as ultrasonic drying is a new solution that can probably lead to an improvement in overall quality. dried products and reduce the drying time compared to other methods. 5-Ultrasonic can affect the time and quality of the final product. Fruits and vegetables are highly perishable due to their high moisture content and must be processed quickly after harvest.
Drying, a moisture removal process caused by the simultaneous transfer of heat and mass, is one of the processes used for preservation.
The drying process not only reduces the water content of food, but also physical, biochemical and chemical properties such as enzyme activity, microbial spoilage, crispness, It will change the viscosity, firmness, taste and aroma of the food.
The quality of the food product depends on the amount of physical and biochemical changes that occur in it during the drying process. Temperature, time and water activity [1] during the drying process affect the quality of the final product. Low temperatures have a positive effect on the quality of the product, but it also lengthens the process time.