BY-PRODUCTS TECHNOLOGY

Module 8. Nutritional characteristics of by-products

Lesson 48
NUTRITIONAL CHARACTERISTICS OF WHEY AND ITS BY-PRODUCTS

48.1 Introduction

The composition of whey and whey by-products varies considerably, depending on milk source and the manufacturing processes involved. Approximately 54% of the nutrients from milk are found in the fluid sweet whey of Cheddar cheese, while about 73% of the nutrients of the non-fat milk used for Cottage cheese show up in fluid acid whey. Being a rich source of lactose, whey is a good fermentation medium for a number of fermented products. In many applications, lactose in whole or deproteinised whey is hydrolysed to glucose and galactose. In the future, one of the most dynamic uses of whey by-products will continue to be as nutritional ingredients.

48.2 Nutritional Characteristics of Whey

In general, whey is rich in lactose, proteins, minerals and vitamins. Lactose acts as a major source of energy with high calorific value. Numerous studies have demonstrated that lactose increases calcium absorption and retention. It may also improve the absorption of magnesium and zinc. In animal studies, lactose extended life expectancy and reduced the accumulation of body fat. The proteins in whey are complete and of exceptional quality. They contain, in varying amounts and in the right proportion, all the amino acids required by humans, among which sulfur amino acids are particularly valuable owing to their anticancer activities. They are also readily digestible and completely bio-available. Clearly, whey proteins are among the most valuable component of whey. Whey proteins, though present in small quantities, have high protein efficiency ratio (3.6), biological value (104) and net protein utilisation (95), and are next only to egg protein in terms of nutritive value.

Whey is also rich source of Ca, P and water soluble vitamins. As the pH of milk decreases, more of the salts dissociate. This results in higher concentrations of soluble calcium, magnesium, zinc and phosphorous in acid whey. The concentration of calcium and other minerals may be altered during whey processing. The ratio of Ca:P is about 0.8 in whey (Modler, 2000); this is a high Ca:P ratio compared with other food products.Whey minerals are involved in the regulation of the water flow by osmosis between different regions of the body. Further, the composition of whey salts reveals a low ratio of sodium/potassium, which is important for preventing elevated blood pressures (hypertension). It also contains copper, zinc and iron as minor constituents. Zinc performs many functions, like the stimulation of the insulin activity for the absorption of glucose from blood. Iron is part of several metalloproteins such haemoglobin, lactoferrin, lactoperoxidase, catalase and supports several important functions as a carrier of oxygen.

Glycomacropeptide (GMP) derived from k-casein induces production of cholecystokinin, a hormone associated with satiety. GMP inhibits the adhesion of oral actinomycetes and streptococci to erythrocytes, and binding of cholera toxins to its receptor. GMP is free from aromatic amino acids, and therefore a suitable protein substitute for those suffering from hereditary disorder of aromatic amino acid metabolism, such as phenylketonuria.

48.3 Nutritional Characteristics of Whey By-products

48.3.1 Condensed whey

Condensed whey contains whey constituents in more concentrated form. Whey solids in the form of condensed whey is a cheap source of high-quality proteins and carbohydrate and the fat is generally removed by centrifugation. Sweetened condensed whey contains sugar equal to the weight of solids in whey which is a source of energy.

48.3.2 Whey powder

Whey powder is the dried form of whey that contains relatively high concentration of all whey constituents including lactose and protein. In the presence of moisture, lactose and protein readily participate in the maillard reaction. This interaction may result in a decrease in protein quality, which is accompanied or followed by undesirable colour changes. During drying, high heat denatures whey proteins, destroying some bioactive compounds, such as the amino acid cystine. Acid whey powder from Cottage cheese and related products contains approx. 65 percent lactose, 12 percent protein, 6 percent lactic acid, 2.5 percent moisture and large quantities of calcium; in fact, all of the calcium that originally existed in the milk. Furthermore, acid whey powder contains the vitamin B complex, vitamin C, and the natural milk fermentation flavour compounds, like diacetyl. Essential mineral content in acid and sweet whey powder is given in Table 48.1.

Because of low concentrations of sodium, potassium and chloride, but high lactose and high-quality whey proteins contents, demineralised whey powder at 90% demineralization level is eminently appropriate for the preparation of infant formulae for meeting the nutritional requirements of infants.

Table 48.1 Essential mineral content in acid and sweet whey powder

48.3.3 Whey based beverages

Whey based soups and fruit beverages possess low protein and high carbohydrate content. The high carbohydrate content is mainly due to the high lactose content of the whey, which contributes little to the product sweetness. Fruits are good source of ascorbic acid and fruits and vegetables contain flavonoids. These flavonoids influence the blood circulation, increasing the permeability and elasticity of capillary vessels and have a protective action against infections of the respiratory system. Soups are served as appetizers before meals as they stimulate the secretion of gastric enzymes that leads to feeling of hunger. Some lactic acid bacteria particularly L. acidophilus enhances nutritional properties and adds certain therapeutic attributes to beverages. Further, antibacterial substances produced during fermentation have curative properties in controlling several gastro-intestinal disorders. Fermented whey beverages can also be enriched with probiotic and prebiotic substances. Probiotics are the live microbes which when administered in adequate amounts confer a health benefit on the host. They reduce blood cholesterol, maintain intestinal health, alleviate intestinal bowel diseases, modulate immune system, reduce incidence of gastrointestinal (GI) infections, reduce incidence of urinary and vaginal infections, alleviate lactose intolerance, anti-cancerogenic and anti-tumorogenic, reduce incidence and severity of diarrheal diseases while prebiotics like fructooligosaccharide and galactooligosaccharide are the non-digestible food ingredients that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and then improve host health.

48.3.4 Fermented whey products

Whey being rich source of lactose, there is a good potential for production of fermented products like microbial biomass, alcohol, galactose, lactic acid, other organic acids, flavour concentrates, vitamins etc. Fermented whey products like food yeasts are highly nutritious nontoxic source of proteins and vitamins and under right circumstances, can find application in human and animal nutrition. Calcium lactate, being an easily re-absorbed calcium salt, offers an attractive way to improve the calcium intake potential in products for mineral deficient consumers.

48.3.5 Whey protein products

Whey protein concentrates (WPC), whey protein isolates (WPI) and whey protein hydrolysates are the whey protein products. Whey protein concentrates (WPC) contain 30-85% protein by weight and are indeed very rich in high quality whey proteins. Besides having functional properties, WPC improves the nutritional attributes of the product. The PER value of whey protein concentrates is similar to that of egg protein, i.e. it is higher than that of milk powder and of other milk protein products (caseinates, co-precipitates). The high protein and low fat content of whey protein concentrates makes them particularly suitable for incorporation into special diets which are thereby enriched with high quality protein. These products have been recommended for slimming diets, diets for patients suffering from hyperlipoproteinaemia and generally for feeding patients, particularly those suffering from liver and gall bladder diseases and from diabetes. They are especially suitable for addition to baby foods as well as to the diets of sportsmen, children and elderly people who also have benefits from a product rich in high quality protein.

Whey protein isolates in its purest form contains 90-98% protein, but no fat, lactose or cholesterol. It is packed with loads of essential and non-essential amino acids. Whey proteins are an excellent protein choice for individuals of all ages. They contain higher levels of bioactive compounds. Their content of essential amino acids is always greater than that of the FAO reference protein. This applies also to methionine and cystine. Whey proteins also have the highest levels of BCAAs (Branched Chain Amino Acids), which results in building and retaining muscle tissue of any natural food source and have been shown to boost immune system functioning and also helpful in blood sugar control. The quality of proteins in whey is incomparable. They provide a number of benefits in areas including sports nutrition, weight management, immune support, bone health, and general wellness. Whey proteins have recently been shown to have potential positive impact in other areas including appetite suppression, cholesterol reduction, and the inhibition of dental plaque and dental caries. It enhances the production of glutathione, one of the body's most powerful natural antioxidants. Therefore, whey proteins aid in improving the body's immune system, by acting as an antioxidant.

Whey protein hydrolysates find uses in high value specialist nutritional applications such as tube-feeding preparations or special dietary supplements. In a hydrolysate, we might seek to get all the protein into peptides of two to five amino acids, with few free amino acids and no larger peptides. Interestingly, some peptides released from milk proteins can be biologically active. Some can transport calcium from the gut into the blood during digestion, some can inhibit enzymes in the human body involved in excessive blood pressure and some can induce sleepy feelings. Hydrolyzed whey proteins can significantly increase glutathione level within the prostate epithelium. This represents a potential mechanism by which whey protein isolate can provide protection against the development of prostate cancer. Hydrolyzed Whey Proteins assist in reducing the blood pressure of hypertensive individuals by inhibiting ACE (Angiotensin Converting Enzyme). Without ACE, the changes in the body that result in hypertension cannot occur.

48.3.6 Lactose and its hydrolysed products

From the nutritional point of view, lactose is very important. Compared to other sugars such as sucrose, lactose produce minimal tooth decay. Several investigations have shown that lactose promotes the utilization of calcium, magnesium and phosphorus. The acidic condition created due to fermentation of lactose by intestinal bacteria may increase the solubilisation and absorption of calcium. Part of the effect may also be due to the ability of lactose to form soluble complex with calcium. Lactose promotes the diffusion of calcium across the intestinal wall, which is the only route of calcium transport in human infant, since the active transport system is not developed at the time of birth. The slow hydrolysis of lactose by the body during digestion generates a prolonged energy supply. Lactose stimulates the growth of acid forming lactobacilli in the intestinal tract. Recent nutritional studies suggest that lactobacilli helps to fight intestinal disorders and that lactose could be used in dietary therapy for ailing infants. In the gut, it is usually hydrolysed by β-galactosidase to glucose and galactose along with some oligosaccharides, commonly known as galactosyloligosaccharide (GOS). GOS are an interesting class of nutraceuticals having prebiotic properties. Lactose has relatively low glycemic index and low carcinogenicity, and is a precursor for other bioactives such as lactulose and lactobionic acid. Lactulose, a disaccharide, originally not present in milk, is produced from lactose during heating or long storage. It is not hydrolysed by intestinal lactase, and hence passes almost completely into large intestine where it is fermented by Bifidobacterium bifidus and L. acidophilus to produce lactic acid. Microbial flora in the intestine of infant fed on mother's milk consists almost entirely of anaerobic lactobacilli, e.g., B. bifidus. Glycoproteins and oligosaccharides, present in mother's milk in high concentration, promote the growth of bifidus bacteria and thus provide baby resistance against intestinal infection.

Hydrolysed lactose is nutritionally beneficial for lactose intolerant peoples. Galactose is important for the development of cerebrosides.

48.3.7 Milk mineral product

Milk mineral products rich in natural milk calcium and phosphate are valuable nutritional supplements in today osteoporosis-sensitive world. Milk minerals are used as a natural calcium supplement in health foods. Calcium and phosphate support the growth of bones and teeth, and also perform a variety of other functions in the body. Calcium from milk is readily absorbed in the intestinal tract, which is facilitated by the presence of lactose. The presence of phosphate reduces the excretion of calcium in urine.

Selected references

Fourie, P.C. 1996. Fruit and human nutrition. In: Fruit processing, first edition, ed. D. Arthey and P. R. Ashurst. Blackie Academic and Professional, New York: 20-39.
Modler, W. 2009. Pioneer paper: Value added components derived from whey. American Dairy Science Association: 1-33.
http://www.usdec.org/files/pdfs/US08_6.pdf
http://nzic.org.nz/ChemProcesses/dairy/3G.pdf