Surplus whey

It was shown how industrial waste like surplus whey, crude glycerol phase, lignocellu-loses, molasses and residues from the slaughtering and biodiesel industry can be upgraded to substrates for biopolymer production. Applying such waste streams as carbon source can be regarded as the most promising route to make the entire PHA biopolymer production process economically competitive this is valid for bulk plastics made of petrochemical competitors as well as for special polymers currently used for niche products. 

In addition to their main components, complex waste streams can contain additional substances that make them advantageous in direct comparison with pure and expensive substrates. For example, the permeate of surplus whey from the dairy industry provides the production strain in bioprocesses not only with a rich source of the carbohydrate lactose, but also with minor components such as minerals and protein residues that have positive impacts on the microbial cultivation. Additionally, beneficial growth components such as vitamins and biotin are reported to be available from complex, unrefined resources such as molasses (reviewed by Purushothaman et al. 2(X)1). 

The major component of whey is lactose, and while there various uses for the protein in making protein concentrates these leave a surplus of lactose. Impure grades of lactose have been available to the food industry for some time. They are relatively successful in biscuits as a raw material for the Maillard reaction to produce pleasant colours and flavours. 

With the increase in the production of cheese, not only in the United States but throughout the world (USDA 1981C), and more stringent controls on disposal of waste materials, the use of surplus cheese whey is one of the most critical problems facing the dairy industry. Whey, the liquid that remains after casein and fat are separated as curds in... 

Whey proteins are slightly superior to casein because of the limiting quantity of the total sulfur-containing amino acids (methionine plus cystine) in casein. However, because whey proteins have a relative surplus of these amino acids, casein and whey proteins, as found in milk,... 

About 10 million gallons of the fermentation alcohol is derived from wastes such as sulfite liquor or whey, but the balance presently depends on damaged grain or sugar, crop surpluses and molasses. Relative costs of ethylene and carbohydrates will change this in a few years, but no reversal to ethanol-based ethylene is likely in this country for much longer, perhaps through 1990. ... 

It has been accounted that, on a production scale of PHB of 100,000 tons per year, the production costs will decrease from US 4.91 to US 3.72 kg , if hydrolysed com starch (US 0.22 kg ) is chosen as the carbon source instead of glucose (US 0.5 kg ) [33]. But this is still far beyond the cost for conventional polymers, which in 1995 was less than US 1 [32]. Lee et al. estimated that PHB and mcI-PHA can be produced at a cost of approximately US 2 kg [36]. The precondition therefore would be attaining high productivity and the use of inexpensive carbon sources. Among such substrates, molasses [37], starch [38], whey from the dairy industry [37-42], surplus glycerol from biodiesel production [39, 43], xylose [44, 45], and plant oils [46] are available. 

On the other hand, whey retains much of the milk nutrients, including fimctional proteins and peptides, lipids, lactose, minerals and vitamins and therefore has a vast potential as a source of added value compotmds, challenging the industry to face whey surplus as a resource (OECD-FAO Agricrrltural Outlook, 2008 Smithers, 2008). In Iran, about 1.8 million tons of whey which is the by-product of cheese producing factories is produced each year. The changing of whey into alcohol, due to the low price of whey (compare to the price of other raw materials), has become the focus of considerable attention in the world. Use of whey in the preparation of ethanol was... 

Whey protein—A by-product of cheese and casein manufacture, whey is the liquid that remains after the removal of casein and fat from milk. Like casein, whey protein is a complex mixture of a large number of protein fractions, with beta-lactoglobulin and alpha-lactalbumin being the principal ones of commercial interest. The whey proteins have a relative surplus of the sulfur-containing amino acids. 

If a fermentation process is used for PHA synthesis this problem can partially be overcome by using cheap surplus and waste materials as renewable carbon sources (e.g. molasses, whey, cellulose hydrolysate) or other cheap carbon sources from fossil resources like methanol derived from natural gas, because roughly 50% of the total production costs derive from the carbon source costs. Unfortunately many of the well known production strains can not be used for PHA production from such substrates, because these microbial strains show either low yields or low production rates, when they grow on these substrates, or they simply cannot utilize these carbon sources at all. These drawbacks can be overcome either by isolating new microbial strains or by applying genetically modified strains for the production process. 

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