Thermal stability of skim milk with protein content standardized by the addition of ultrafiltration permeates

Nutritional, sensory and physico-chemical characterization of protein-standardized UHT milk

“…Immediately after direct or indirect UHT heating, there were no visible signs of destabilization. The result was expected; normal milk can be heated for up to 20 min at 140 "C without visible protein coagulation, and its heat stability is even greater upon the addition of skim milk permeate (Peter et al, 1996;Rattray and Jelen, 1996b). The improved heat stability of skim milk blended with skim milk permeate has been attributed to a lower concentration of minerais and possibly reduced collision frequency between casein micelles.…”

“…To avoid damage to the UHT machine, no further preliminary tests of milk products standardized with acid whey permeate at an unadjusted pH of 6.50-6.65 were carried out; destabilization would probably have been even greater due to the higher levels of acid whey penneate and the greater heat load applied during indirect UHT heating. Rattray and Jelen (1996b) observed that the addition of acid whey permeate to skim milk caused a general decline in heat stability over the pH range 6.4-7.1; this was especially evident at the unaltered pH of milk, where some samples heat-coagulated at 90 "C. Reduced heat stability was attributed to the high calcium content of the penneate, which shifted the heat stability-pH curve of type A milk to more alkaline pH values and led to a faster rate of heat-induced pH decline. An exception was an increased heat stability of milk with acid whey permeate at pH 6.8; extra calcium may have inhibited the formation of soluble complexes between~-Iactoglobulin and x-casein and hence heat-Iabile x-casein-depleted micelles.…”

“…In laboratory scale trials, Rattray and Jelen (1996b ) showed that standardization of type A skim milk with skim milk permeate or sweet whey UF permeate caused a general increase in heat stability at 140 "C, in the pH range 6.4-7.1, but the use of acid whey UF permeate caused a general decline in heat stability. Peter et al (1996) standardized 2% fat milk with skim milk permeate, and showed a similar heat stability trend in the presence of homogenized milkfat.…”

Rejection of dairy salts by a nanofiltration membrane

“…For instance, Gilron et al [13] observed an increase in permeation of a monovalent ion in the presence of a charged polyelectrolyte, while Balannec et al [14] showed that the rejection of divalent ions was higher during NF of whey permeate than during NF of whey when at low pH conditions. The authors speculated that Table 1 Typical composition and concentration ranges for UF whey permeates [4][5][6][7][8][9].…”

Isolation and characterisation of κ-casein/whey protein particles from heated milk protein concentrate and role of κ-casein in whey protein aggregation

“…The protein content in the supernatants may have been too low to be detected by the absorbance detector, while the aggregates larger than 450 nm may have been removed by centrifugation or filtration prior to separation by FPLC. High calcium activity has been identified as a major factor influencing the heat stability of concentrated milk (Jeurnink & De Kruif, 1995;Rattray & Jelen, 1996;Rose, 1961;Zittle & Dellamonica, 1956). Decreasing pH promotes a shift in the mineral equilibrium of milk, causing the release of ionic calcium into the serum.…”