Demineralisation of whey

Guilt Free Deserts

Guilt Free Desserts

Get Instant Access

Whey is supersaturated with calcium phosphate and contains high levels of potassium and sodium. Calcium phosphate precipitation can cause problems such as fouling of the membrane or evaporator. High levels of minerals can inhibit lactose crystallisation which can adversely affect non-hygroscopic whey production and reduce yields and purity for lactose manufacture. The presence of high mineral levels limits the use of whey powder in infant formula and adversely affects the flavour and range of applications for whey products. A range of demineralisation techniques have been developed including precipitation, ion exchange, electrodialysis and nano-filtration. Some techniques preferentially remove divalents (e.g. calcium

Table 14.17 Properties and uses of whey and permeate co-products. Based on Durham et al. (1997b)

Product

Properties

Usage

Whey powder

Low-cost milk solids

Skim milk replacer

Demineralised

High-quality protein

Infant formula

whey powder

Whey protein

High-quality protein,

Infant formula, sports

concentrate

gelation, adhesion,

diets, non-fat milk

(35-85% protein)

emulsification, foaming

replacement, processed meats, desserts

Whey protein

High-quality protein

Infant formula, sports

isolate (90%+)

diets

a-Lactalbumin

High-quality protein

Infant formula

(a-fraction)

ß-Lactoglobulin

Gelling solubility and

Restructured meat or fish

(ß-fraction)

nutrition

Sports and dietetic beverages

Aeration

Meringues, desserts

Lactoferrin

Antibacterial

Infant formula

Lactoperoxidase

Anticaries

Toothpaste

Glycomacropeptide

Bifidobacteria, enhanced immunity

Infant formula

Immunoglobulins

Anticancer

Cancer prevention, treatment

Enhanced immunity

Diets for AIDS patients

Peptides

Bioactive

Convalescent diets,

(hydrolysates)

athletes

Edible lactose

Carrier, filler

Colour, flavour carrier

Free-flow agent

Instantised powdered foods

Maillard browning, crumb

Bakery, coffee whitener

texture

Protein stabiliser

Milk standardisation

Pharmaceutical

Bulking agent, binder,

Tabletting excipient

lactose

flavour

Lactulose

Bifidobacteria enhancement

Infant formula

Laxative

Laxatives

O2 uptake, NH3 reduction

Diet for athletes

Lactitol

Bifidobacteria enhancement

Infant formula

Non-caloric sweetener

Chewing gum

Lactobionic acid

Bifidobacteria enhancement

Infant formula, baby foods

Oligosaccharides

Bifidobacteria enhancement

Infant formula, baby foods

Hydrolysed lactose

Sweetener

Yoghurt, ice cream

Milk salts

Calcium, potassium

Diet supplement

Flavour

Table salt substitute, health drinks

phosphate) or monovalents. These processes can be combined to remove a greater proportion of minerals.

Precipitation/whey pretreatments

Calcium and phosphate are present in milk, whey and permeate at concentrations where precipitation is inevitable (Schmidt & Both 1987). Calcium phosphate precipitation is enhanced by raised pH, heat (Brule et al. 1978) and concentration. This leads to evaporators fouling, shortened process runs and additional cleaning losses. Removal of protein further destabilises calcium phosphate, causing more fouling to occur during the evaporation of ultrafiltration permeate (Schmidt & Both 1987). Calcium phosphate precipitation is also responsible for fouling of ultrafiltration membranes (Ramachandra Rao et al. 1994).

Calcium phosphate precipitation is not rapid and involves a number of stages. Initially the solution becomes opalescent with the formation of hydrated amorphous calcium phosphate. This is followed by one of the precursor phases - dicalcium phosphate dihydrate (DCPD), dicalcium phosphate (DCP), tricalcium phosphate (TCP) or octacalcium phosphate (OCP) - the structure and composition depending on the pH, temperature and concentration. Then finally recrystallisation to hydroxyapatite (HAP) occurs (Feenstra & de Bruyn 1979).

The fact that this process is slow and continues through stages is central to the problem of calcium phosphate removal. Rapid removal of calcium and phosphate prior to heat and concentration is the preferred option, but this is not always possible when the whey protein needs to be protected. Researchers have described heat treatments and pH adjustments (Hayes et al. 1974; Hickey et al. 1980; Hobman 1984), and additives such as calcium (Hayes 1982; Karleskind et al. 1995), phosphate (Hiddink et al. 1981) and ethylene diamine tetraacetic acid (EDTA) (Ramachandra Rao et al. 1994) to force the equilibrium one way or the other.

Many dairy manufacturers are now recovering calcium phosphate from whey to produce dairy calcium supplements, marketed to combat osteoporosis. The precipitated calcium phosphate can be recovered using centrifugal separators, followed by washing, drying and milling.

Nanofiltration

Nanofiltration is a membrane process used to separate small molecules such as mineral ions and water salts but retain larger molecules (including lactose and proteins), coupling demineralisation with concentration. By allowing relatively free passage of monovalent ions, nanofiltration membranes are able to reduce the build-up of the osmotic pressure gradient. High fluxes are possible at lower pressures, with energy and equipment costs lower than those for reverse osmosis (Hoppe & Higgins 1992).

Nanofiltration using 300 Da membranes preferentially removes up to 65% of the monovalent ions (Na+, K+, Cl-), with further reductions achieved by diafiltration. Removal of monovalents improves lactose crystallisation from whey permeate. Guu and Zall (1992) reported that lactose recovery was improved by 8-10% after nanofiltration of permeate or sweet whey.

Nanofiltration is also advantageous for the production of demineralised whey powder for infant formula, as calcium phosphate is retained, yet monovalents are removed. The limited removal of divalent ions is due to their hydrated size, with up to 94% calcium and magnesium retained (van der Horst et al. 1996).

The nanofiltration permeate contains about 0.3-0.5% solids including potassium, sodium, non-protein nitrogen (NPN) and lactose. The permeate can be cleaned by reverse osmosis to produce clean water with the remaining solution being a 'dairy salt' concentrate. This monovalent salt mixture could be a useful by-product as a natural low-sodium table salt substitute or it could be used in sports and health beverages. This salt has also been reported to be recovered and used to regenerate ion exchange resins, as described in the following section (Durham et al. 2004).

Ion exchange demineralisation

Ion exchange has been used for the industrial demineralisation of whey and permeate since the 1970s. Ion exchange is capable of removing up to 95% of the minerals that are present in whey, with the demineralised whey mostly used in infant formula. Ion exchange can be conducted on either mixed-bed or sequential cation and anion resin-filled columns. The process involves passing the clarified whey or ultrafiltration permeate through a cation exchange resin whereby the cations in whey - such as sodium, potassium and calcium - are adsorbed on to the resin, displacing the hydrogen counter-ions on the cation resin. Subsequently, the decationised whey is passed through an anion exchange resin which absorbs the anions - such as chloride, sulphate and phosphate - displacing the hydroxyl counter-ions on the anion resin (Houldsworth 1980). When all of the fixed ionic sites on the resins are saturated with whey cations and anions, the whey is rinsed from the column and the resin is regenerated with strong acid and alkali solutions to remove the adsorbed ions and replace them with H+ and OH-(Jonsson & Arph 1987).

There are many difficulties with the ion exchange process, such as short running times between regeneration, high consumption of regenerant chemicals and associated waste problems, high water requirements to remove excess regenerant, losses of whey protein due to irreversible adsorption and loss of protein functionality due to pH fluctuations during processing (Jonsson & Arph 1987).

Ion exchange resins can also be used just to decalcify whey and permeates, by employing cationic resins in the sodium or potassium form; thereafter the decalcified whey or permeate is nanofiltered to remove the excess sodium and potassium. The ion exchange resin can be regenerated using the concentrated permeate from the nanofilter, thereby recycling the salt from within the process, and avoiding the cost and pollution associated with purchasing salt to regenerate the resin (Durham et al. 2004; Groupe Novasep 2005).

Decalcification improves downstream processing, eliminating problems associated with calcium phosphate precipitation fouling evaporators and membranes. Decalcified whey can be further deionised by ion exchange with reduced regeneration costs; decalcified whey permeate can be further treated by ion exclusion chromatography to produce purified lactose.

Electrodialysis

Electrodialysis is an electrically driven membrane demineralisation process and has been employed in the dairy industry since the early 1970s. Electrodialysis is used to partially demineralise whey, mostly for infant formula. Monovalents are preferentially removed, enhancing the Ca : Na ratio in electrodialysed whey and minimising chloride levels, thus providing a nutritional advantage for use in infant formula.

Anion and cation membranes (ion exchange resins cast into thin films) are stacked alternatively with plastic spacers, with an anode or cathode at each end. When a direct current voltage is applied, the anions move towards the anode and the cations move towards the cathode. The membranes form alternating compartments of ion diluting and ion concentrating channels. The whey is pumped through the ion diluting channels, while the whey ions collect in the ion concentrating channels and are removed (Batchelder 1987). At the mineral levels normally found in whey, electrodialysis is more suited to partial (50%) demineralisation as higher levels of demoralisation require a disproportionate increase in recirculating time and electrical power, with membrane fouling also a problem at high levels of demineralisation.

Was this article helpful?

0 0
Making Chocolate 101

Making Chocolate 101

If you love chocolate then you can’t miss this opportunity to... Discover How to Make Homemade Chocolate! Do you love gourmet chocolate? Most people do! Fine chocolates are one of life’s greatest pleasures. Kings and princes have for centuries coveted chocolate. Did you know that chocolate used to be one of the expensive items in the world, almost as precious as gold? It’s true!

Get My Free Ebook


Post a comment