As shown earlier in this chapter (Figure 5-4), water, in the form of whey, is released when milk is converted into cheese. In fact, the whey accounts for 90% of the original milk volume. The dilute nature of the whey (about 92% to 94% water) and low protein concentration (<1%) have historically contributed to the perception (at least in the United States) that whey has little economic value. However, in other parts of the world, whey is more widely used, especially in the manufacture of whey-derived cheese. For example, in Norway, the goat whey cheeses Gjetost and Mysost are among the most popular of all cheeses (accounting for about 20% of cheese consumption), and Ri-cotta, another whey-based cheese, is popular not only in Italy, but throughout Europe and the United States.Whey cheeses are also produced in Greece (Manouri,Anthotyros), Portugal (Re-quejno), and the Czech Republic (Urda).
Whey cheese manufacture is based on the principle that whey proteins will precipitate when slightly acidified (pH 6) and then heated to high temperatures (>70°C).Although whey alone is ordinarily used as the starting material, milk can also be added. Much of the Ricotta produced in the United States, for example, contains a portion of skim or whole milk.The finished cheese, in this case actually consists of a casein-whey co-precipitate.Whey cheeses are not fermented, and since the lactose content of whey may be as high as 75% (on a solids basis), these cheeses will also contain 3% to 4% lactose and are generally sweet.Although Ricotta is a very soft cheese with a white, creamy color, other whey cheeses, such as Gjestot, can be very hard and a light brown color.The tan-to-brown color results from lactose carameliza-tion and Maillard browning reactions that occur during high temperature heating.
In the United States, where the market for whey cheeses has been extremely small, most cheese manufacturers instead used whey as animal feed or fertilizer or, more likely, simply discarded it altogether. In the past thirty years this practice has changed for several reasons. First, whey is now considered to be environmental problem. It has a high biological oxygen demand (BOD), and, given that nearly 25 million kg are generated each year, discharging this much high BOD material down the drain or into the environment exceeds that which sewage treatment plants can handle.
Second, the dairy and food processing industries have developed products and applications in which economic value can be derived from whey and whey components. Many of these applications involve separation technologies (e.g.,ultrafiltration and reverse osmosis) in which the more valuable whey protein fractions are obtained. What remains from these processes is a lactose-rich material (whey permeate) that can be used directly, or further purified, as food- or chemical grade lactose.
Importantly, it is technologically possible to use whey, whey permeate, or whey-derived lactose as feedstocks for various industrial fermentations, including the production of organic acids, ethanol, and other small molecules. However, given their current market value and the capital and processing costs that would be necessary, it does not make economic sense at the present time to produce these commodity chemicals from whey fermentations.
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