Additions of potassium iodate to milk at 0-05 and 0 -l DIM (10 and 20 ppm) before UHT treatment markedly reduced the rate at which pressure built up during processing. This permitted the use of longer processing times before unacceptable pressures were reached in the heat exchangers. Iodate reduced the amount of protein deposited, particularly in the higher temperature sections of the plant, but had no effect on the deposition of minerals. The more compact nature of the highly mineral deposits offered less resistance to the flow path. Reduction in the amount of protein deposited is likely to be caused by increased denaturation of /?-lactoglobulin and oxidation of heat activated sulphydryl groups by the iodate, thus reducing the formation of high molecular weight polymers of sulphur-containing proteins at the heated surfaces. Increasing the level of sulphydryl groups in the milk through the addition of L-cysteine-HCl caused an increase in the amount of deposit formed during UHT treatment. Whilst little detrimental effect on the quality of the milk resulted from additions of iodate at 005 DIM, milks with 01 mM-iodate became bitter during subsequent aseptic storage. Bitterness was a result of iodate-induced proteolysis of casein.The operating time of an indirect heat ultra-high-temperature (UHT) milk treatment plant is limited by the deposition of milk solids on the heated surfaces. Unacceptable pressures build up in the heat exchangers and the thermal efficiency of the plant is reduced (Burton, 1968). The deposits formed during the heating process have been examined by Ito, Sato & Suzuki (1962a, b) and by Lyster (1965). They found that most of the deposit formed in sections of the heat exchanger operating at temperatures of 100-105 °C and consisted largely of protein (50-60 %) and minerals (30-35%). In higher-temperature sections of the heat exchanger the deposit had an increased mineral content (70%) associated with less protein (15-20%). Small amounts of fat were present (4-8%) in deposits throughout the plant.Fore-warming of the milk at temperatures of 85-95 °C greatly reduced the rate at which deposit was formed, especially in the lower temperature sections of the UHT plant (Bell & Sanders, 1944;Lyster, 1965;Burton, 1966). This effect has been attributed to the denaturation of soluble proteins and the precipitation of Ca phosphate in the milk before it reaches a heated surface.

The use of a silica-based ion-exchange medium for the recovery of protein from wheys prepared by treatment with rennet or with acid has been investigated. The protein capacity of the medium whilst maintaining an adsorption greater than 75 % during the passage of rennet-and acid-whey was 0-079 and 0053 g/g respectively. Bovine serum albumin (BSA), a-lactalbumin (a-la) and/Mactoglobulin (/?-lg) adsorbed from acid-whey were mostly recovered in yields greater than 93 % in an undenatured form essentially free of lactose and milk salts by elution using 01 M-HC1. With rennet-whey, BSA and part of the a-la were not recovered in the native form, probably because of proteolysis during elution by enzymes originating in the rennet used in the manufacture of the whey. There was, however, no effect on the recovery of native yS-lg adsorbed by the medium. An unidentified proteinaceous fraction, thought to be of casein origin, was also adsorbed and recovered from rennet-whey. Fractions of the adsorbed proteins could not be obtained by eluting with a gradient increase in NaCl concentration. Nevertheless, purified /?-lg was obtained by passing a large quantity of whey through the medium. This protein had a high affinity for the functional groups of the medium, to the extent that other proteins initially adsorbed were subsequently displaced. Unidentified proteinaceous material in rennetwhey also had a high affinity for the functional groups of the ion exchanger but most of this fraction could be removed by a pretreatment procedure which involved passing the whey through the medium at pH 5-0; unidentified material was selectively adsorbed at this pH. The medium could also be used to produce a fraction containing a mixture of BSA and a-la but it was not possible to separate these proteins.The estimated world production of whey is 88*5 million tonnes of which about 28 -2 million tonnes is produced within the EEC (Allum, 1980). Of the latter, only one third is spray-dried, the remainder being used either as liquid stock-feed or for the production of lactose or disposed of as waste. Thus, considerable quantities of protein are at present being under utilized. Whey protein is particularly valuable as a human foodstuff for it contains even more of a surplus of essential amino acids than total milk protein, especially lysine (FAO/WHO Report, 1973). Skim milk is a further potential source of whey protein. Worldwide production of skim milk powder is nearly four million tonnes, 50% of which is produced in the EEC (Coton, 1980); at present 87 % of EEC production is used as animal feed. As these amounts also represent large

Whole milk was concentrated by a factor of two by ultrafiltration. It was used directly for making Cheddar and Cheshire cheese, an unripened soft cheese of the Coulommier type, and yoghurt. The yields of hard cheese from the concentrated milk were the same as those from normal whole milk. The cheeses were acceptable though the flavour was milder than that of good quality Cheddar and Cheshire cheese. Medium fat soft cheeses were made from the concentrated milk. The yield of cheese was 41 per cent greater than that made from normal whole milk and the making time was half that of the normal process. The cheeses were consumed fresh or stored in deep freeze. For making yoghurt, the usual reinforcement with skim milk powder was not necessary as the concentrated milk had a high total solids content, nor was it necessary to homogenize the mix. The yoghurt contained 21 per cent total solids and was a very acceptable product.

Investigation of the effect of pH on the formation of deposit from milk during ultra high temperature treatment using a plate-type plant showed that deposit formation was greatly increased when the pH of whole milk was reduced to 6-54, irrespective of whether the adjustment was made through the addition of HC1 or lactic acid. Most of the increase in deposition took place in the higher temperature sections of the plant. Conversely, an increase in milk pH to 6-8 using NaOH resulted in considerably less deposit being formed during heat treatment. Reducing the pH of whole milk increased the deposition of both protein and fat, but reduced the deposition of minerals. Despite very high concentration of fat in the deposits, it is unlikely that fat per se was responsible for increased deposit formation. Deposition also increased when the pH of skim milk was reduced to 6-51 before processing. Electron micrographs of the milks after heat treatment indicated that pH reductions caused the formation of large aggregates containing casein micelles during heating. Fat globules were also present in aggregates formed in whole milk with reduced pH. Slight reductions in the pH of milk before processing appear to enable the pH during heat treatment to fall below a critical value at which coagulation of milk takes place at the heated surfaces.The deposition of milk solids in heat treatment plant is a major problem in the dairy industry. Deposit formation during ultra high temperature (UHT) processing using tubular or plate-type plant results in the build-up of high pressures in the heat exchangers and thermal efficiency is reduced (Burton, 1968;Swartzel, 1983). Within a relatively short time a limiting pressure, as determined by the resistance of the plate gaskets to internal pressure, is reached. Processing must be stopped and the deposit removed by chemical cleaning before heat treatment of milk can be continued.The composition of deposits formed from milk during UHT processing is dependent on the temperature of the heated surface and on the heat treatment previously given to the milk (Ito et al., 1962a, b; Lyster, 1965;Burton, 1966;Skudder et al. 1981;Lalande et al. 1984). Most deposit normally forms in sections of the plant operating at 100-105 °C and consists of protein (50-60%), minerals (30-35%) and fat (15-20%). At higher temperatures the concentration of minerals

The addition of potassium iodate to milk at 0-1 mM before UHT treatment resulted in rapid breakdown of a s -and /?-casein during subsequent aseptic storage. Maximum rates of proteolysis were observed at storage temperatures of 37-45 °C, but the reaction was strongly inhibited by storage at 55 °C and by increased holding time at 140 °C during the UHT sterilization. Iodate-induced proteolysis of purified a sland /?-casein was detected only with solutions in the serum phase of raw milk; no proteolysis occurred with solutions in 0-1 M-phosphate buffer (pH 6-7) or in milk ultrafiltrate, irrespective of whether whey proteins and lactose were also added. Thus, it appears that iodate increased the activity of one or more proteolytic components which were present in milk and were unable to pass through an ultrafiltration membrane. However, it is unlikely that iodate acts by increasing the activity of proteinases produced by contaminant bacteria; the presence of iodate did not affect the activity of a proteolytic enzyme isolated from Pseudomonas fluorescens PM-1. Furthermore, iodate promoted protein breakdown during storage of milk drawn aseptically from the cow and subsequently UHT processed. It is suggested that iodate increased the activity of native milk proteinases, other than plasmin which was inactivated by UHT treatment, possibly by preventing thiol-disulphide exchange reactions during the heating process.