The effect of preheating skim milk and artificial micelle milk on curd syneresis was studied. The inhibition of syneresis caused by heat was dependent on the presence of β-lactoglobulin (β-lg) and to a lesser extent α-lactalbumin. The degree of inhibition increased with increasing amounts of added β-lg and preheating temperature. This agrees with the hypothesis that the detrimental effect of preheating on syneresis is due to complex formation between β-lg and κ-casein. This complex appeared to be mediated via thiol–disulphide exchange and its formation appeared to interfere with the micelle–micelle interactions responsible for syneresis.

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 0·053 g/g respectively. Bovine serum albumin (BSA), α-lactalbumin (α-la) and β-lactoglobulin (β-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 0·1 M-HC1. With rennet-whey, BSA and part of the α-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 β-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 β-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 rennet-whey 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 α-la but it was not possible to separate these proteins.

A commercial neutral proteinase was encapsulated in liposomes (multilamellar) and incorporated into cheese curd via the cheese milk. The milk proteins were protected from proteinase attack during curd manufacture. A significant proportion of the liposome-entrapped enzyme was retained in the curd and its subsequent release into the cheese matrix was inferred from an increased rate of β-casein breakdown.

The effects of sorbic and propionic acids on shelf life and organoleptic characteristics of West African soft cheese stored at 7–9 °C were investigated. In cheeses treated with 0·1% sorbic acid spoilage was delayed and microbial growth, especially mesophilic bacteria, yeasts and moulds, was suppressed compared with untreated controls. Treatment with 0·05% sorbic acid or up to 10% propionic acid was less effective. An objectionable bitter flavour was reported for sorbate-treated cheese but other qualities were not adversely affected.

Yogurt, made from fortified skim milk by conventional methods using Streptococcus thermophilus and Lactobacillus bulgaricus, was used in studies of the effect of fermentation on nutritional value of milk. In all experiments, the product was compared with the uninoculated base milk. The concentration of most vitamins was less in yogurt than in milk and was most noticeably so for biotin which was 60% less. The effect on folic acid content was inconsistent. In nutritional experiments with rats, high values for true digestibility, biological value and net protein utilization were obtained for both yogurt and its base milk, only minor differences being apparent between the two materials. In growth tests with rats, yogurt was not found to be consistently superior to the base milk when the milk was subjected to a double heat treatment to reduce bacterial contamination. Yogurt did not confer a nutritional advantage on fresh milk in this respect.