Demineralization of whey by electrodialysis

Whey is a green-yellow colored liquid obtained from cheese production. Whey can separated into sweet and acid whey, depending on the processing technique consequential in casein subtraction from fluid milk. Sweet (rennet) whey is obtained after chymosin treatment from the casein fraction of milk, which is the major fraction of milk proteins. After chymosin enzymatic reaction, colloidal solubility is lost. This leads to separation of coagulum from casein into the cheese curd and whey. Whey is made up of 93-94% of water and milk serum as lactose, soluble proteins, minerals, lactic acid and fats. In addition, whey can contains B group vitamins, citric acid and some non-protein nitrogen compounds (urea and uric acid), β-lactoglobulin, α-lactoglobulin, serum albumin, immunoglobulins and lactoferrin. The second type is acid whey, obtained from fermentation processes. For both of the sweet and acid wheys, lactose is the leading part, whey proteins and minerals follow subsequently. Acidity, whey protein composition and mineral content are the major differences between the two whey types. The chief difference between them is lactic acid content, acid whey can have more lactic acid than sweet whey, which can affect the processing of whey along with the nutritional properties. About whey production and processing techniques, there has been a significant development over the past three decays. Particularly separation and fractioning of whey constituents, has an increased commercial interest. Whey proteins have a high nutritional value and great functional properties. As a result of these properties, they are extensively used both in animal and human nutrition. Whey proteins have a great functionality and they can be used as emulsifiers, stabilizers, foaming and texturizing agents and also they can be part in infant formula, dairy and bakery products, meats and beverages as food additive. If whey proteins are purified and isolated from other constituents in whey, their functionality and nutritional value are increased. On the other hand, because of high salt content, application of whey constituents and whey are restricted. It is directly affect the functional and nutritional properties of whey, as well as its flavor and quality. Therefore, desalination process is precursor technique and should be applied effectively. For demineralization process; electrodialysis, ion exchange, nanofiltration, reverse osmosis and microfiltration are the main membrane techniques to be encounter, which differ, in their driving force and operation princibles. Electrodialysis with ion-exchange membranes is one of the most significant membrane separation processes where it separates ions from an aqueous solution with the help of electrically charged membranes influence of an electrical potential difference as a driving force. It can be used for many water treatments additionally; it is used in wine industry as stabilizer and in sugar industry for demineralization. There are ion exchange membranes in electrodialysis stack, which have two electrodes name as anode and cathode and consist of a chain of anion and cation exchange membranes settled in an alternating array. Under the influence of a direct current, an ionic solution is pumped through these membranes. Due to this driven force, positively charged cations pass easily through the negatively charged cation exchange membrane and move toward cathode and they retained by the anion exchange membrane. For anions situation take place contrarily. As a result of this process, one solution is concentrated conferring to ion content, named as brine or concentrate, whereas other solution is become depleted, name as diluate. For this purpose electrodialysis with anion-cation membranes is applied to rennet whey powder from Moravia Lacto a.s. company (Jihlava, Czech Republic) as four different percentage as 3.5, 7, 10 and 14 at negative and positive polarity. Before each experiment, electrodialysis stack was washed with distilled water. For the diluate part, whey solution was used with different concentration, for the concentrate part HNO3 solution was used with a pH 2, and the electrical solution was used a solution of NaNO3 at a concentration of 10 g.l-1. Before and after electrodialysis, in order to check the membranes working properly or not, a saline test for a model solution Na2SO4 was prepared and conducted. At the end of the test, Javg values are calculated by using macro excel document. During desalination process, changes in conductivity, pH, and temperature were recorded 5 minutes intervals. The experiment was conducted at a constant voltage of 16 V and terminated after reaching 95% desalination of the diluate. At the end of the each experiment 45 ml of diluate was collected in order to determine ash content and dry matter. In addition to electrodialysis, ultrafiltration is applied to 7% of whey solution unit from ARNO 700 with tubular ceramic TAMI-Industries membranes type Clover. Ultrafiltration was conducted at a constant pressure of 2 Bar with a 50 kDa membrane and it was terminated after obtaining 300 grams permeate. Concentration factor during experiment was 2, because of obtaining 3 liters of permeate and 3 liters of retentate from the 6 liters of feed.At the end of the each experiment 45 ml of feed, permeate and retentate were collected in order to determine ash content, dry matter and protein analysis. Correspondingly permeate and retentate samples collected ± 1000 ml for ED experiment. At the end of each experiment, datas are settled in to a macro excel document in order to assess the factors as Javg, CF, CD_DM, ΔmASH, α and W, which can influence efficiency and process of electrodialysis of whey. These factors are a novel parameters of electrodialysis process and can be used as a good source to optimize the desalination process especially for whey and whey products. It can assist to optimization of energy, quality, functional and nutritional properties of whey. It can be concluded, sweet rennet whey is treated by electrodialysis with ion exchange membranes and factors which influence efficiency and process of electrodialysis of whey are determined and calculated with a help of a macro excel document especial to this project. In addition, electrodialysis process of retentate and permeate solutions, which are obtained after ultrafiltration process are calculated. It is shown that retentate and permeate solution, successfully applied in electrodialysis. Without meeting any problem, retentate and permeate solutions can be desalinated. According to their W values, it can be said that ultrafiltration before electrodialysis can be effectively adapted to food industry and they are open to new research and development. Whey desalination is an essential and crucial process in food technology. On the other hand, it has been examined only for last few decays. Consequently, further research and examination is needed to apply. There are many features that have not been yet completely determined and some problems needed to be solved. Especially in dairy industry electrodialysis has an excessive potential because it is a safe, economic, fast and very effective method, that can be applied to remove salts even from highly salted wheys.