Milk protein characteristics

Because the symptoms of lactose intolerance are nonspecific, lactose intolerance needs to be differentiated from other common disorders causing diarrhea and abdominal pain or discomfort. These differential diagnoses include milk protein allergy, gastroenteritis, colitis, and irritable bowel syndrome. Allergy or sensitivity to one or more of cow s milk proteins characteristically occurs in formula-fed infants, and although no age is exempt, it is rare in the older... 

Casein. Milk contains proteins and essential amino acids lacking in many other foods. Casein is the principal protein in the skimmed milk (nonfat) portion of milk (3—4% of the weight). After it is removed from the Hquid portion of milk, whey remains. Whey can be denatured by heat treatment of 85°C for 15 minutes. Various protein fractions are identified as a-, P-, and y-casein, and 5-lactoglobulin and blood—semm albumin, each having specific characteristics for various uses. Table 21 gives the concentration and composition of milk proteins. 

Another product, defatted com germ flour was coextruded at 150 or 170 °C with 5% milk protein to produce a puffed nutrient snack (Peri et al., 1983). The addition of fhe milk profein af fhe lower temperature improved the organoleptic characteristics of fhe exfrudafes but adversely affected the product expansion and consistency of fhe samples at the higher temperature. 

Singh, R. K., Nielsen, S. S., Chambers, J. V., Martinez-Serna, M., and Villota, R. (1991). Selected characteristics of extruded blends of milk protein raffinate or nonfat dry milk with com flour. /. Food Process. Preserv. 15, 285-302. 

Traditionally, milk was paid for mainly on the basis of its fat content but milk payments are now usually based on the content of fat plus protein. Specifications for many dairy products include a value for protein content. Changes in protein characteristics, e.g. insolubility as a result of heat denaturation in milk powders or the increasing solubility of cheese proteins during ripening, are industrially important features of these products. 

In contrast to the caseins, the whey proteins do not precipitate from solution when the pH of milk is adjusted to 4.6. This characteristic is used as the usual operational definition of casein. This difference in the properties of the two milk protein groups is exploited in the preparation of industrial casein and certain varieties of cheese (e.g. cottage, quarg and cream cheese). Only the casein fraction of milk protein is normally incorporated into these products, the whey proteins being lost in the whey. 

In addition to simplifying and standardizing the nomenclature of the milk proteins, the characteristics of the various caseins and whey proteins are summarized in the above articles, which are very valuable references. 

About 20% of milk protein is soluble in the aqueous phase of milk. These serum proteins are primarily a mixture of /3-lactoglobulin, a-lactalbumin, bovine serum albumin, and immunoglobulins. Each of these globular proteins has a unique set of characteristics as a result of its amino acid sequence (Swaisgood 1982). As a group, they are more heat sensitive and less calcium sensitive than caseins (Kinsella 1984). Some of these characteristics (Table 11.1) cause large differences in susceptibility to denaturation (de Wit and Klarenbeek 1984). 

Table 11.2. Denaturation Characteristics of Some Milk Proteins (Heated at 21.4°K/mln In 0.7 M Phosphate Buffer at pH 6).

Determinative and confirmatory methods of analysis for PIR residue in bovine milk and liver have been developed, based on HPLC-TS-MS (209). Milk sample preparation consisted of precipitating the milk proteins with acidified MeCN followed by partitioning with a mixture of -butylchloride and hexane, LLE of PIR from aqueous phase into methylene chloride, and SPE cleanup. The dry residue after methylene chloride extraction was dissolved in ammonium hydroxide, and this basic solution was transferred to the top of Cl8 SPE column. The PIR elution was accomplished with TEA in MeOH. For liver, the samples were extracted with trifluoroacetic acid (TFA) in MeCN. The aqueous component was released from the organic solvent with n-butyl chloride. The aqueous solution was reduced in volume by evaporation, basified with ammonium hydroxide, and then extracted with methylene chloride. The organic solvent was evaporated to dryness, and the residue was dissolved in ammonium acetate. The overall recovery of PIR in milk was 94.5%, RSD of 8.7%, for liver 97.6%, RSD of 5.1 %. A chromatographically resolved stereoisomer of PIR with TS-MS response characteristics identical to PIR was used as an internal standard for the quantitative analysis of the ratio of peak areas of PIR and internal standard in the pro-tonated molecular-ion chromatogram at m/z 411.2. The mass spectrometer was set for an 8 min SIM-MS acquisition. Six samples can be processed and analyzed in approximately 3 hours. 

Carroccio, A., Cavataio, F., Montalto, G., and D Amicio, A.L. 2000. Intolerance to hydro-lysated cow s milk proteins in infant Characteristics and dietary treatment. Clin Exp Allergy 18 1597-1603. 

Vegarud, G.E., Langsrud, T., and Svenning, C. 2000. Mineral-binding milk proteins and peptides occurrence, biochemical and technological characteristics. Br. J. Nutr. 84, 91-98. 

Stern M, Gellermann B. Food proteins and maturation of small intestinal microvillus membranes (MVM). I. Binding characteristics of cows milk proteins and concanavalin A to MVM from newborn and adult rats. J Pediatr Gastroenterol Nutr 1988 7 115-121. 

Ratino, J.M.R. and Carrera, C. Structural, topographical, and shear characteristics of milk proteins and monoglyceride monolayers spread at the air-water interface, Langmuir, 20, 4530, 2004a. 

Food proteins are important in determining the characteristics of many food products. Frequently the protein used influences more than one characteristic of the food. The protein selected will vary as a function of the protein, the formulation of the food, and the processing of the product. The most common proteins used as food ingredients include egg proteins [83,84], soy proteins [85,86], milk proteins [87,88,89], wheat gluten [90], and fish proteins [91]. Other proteins have been used to a lesser degree and include rapeseed protein, sunflower protein, pea protein, cottonseed protein, peanut protein, and blood plasma. 

The coagulability of milk by acid or proteinases is due to certain characteristics of the milk proteins and is influenced by other milk constituents. 

Milk proteins have two important functions in ice cream. Firstly, they can stabilize water-continuous emulsions and foams because they are surface active. We will see in Chapter 4 that this has important consequences for the formation and stability of the air bubbles in ice cream. Secondly, they contribute to the characteristic dairy flavour. Milk proteins for ice cream manufacture are obtained from several different raw materials ... 

Domian E, Sulek A, Cenkier J, Kerschke A (2014) Influence of agglomeration on physical characteristics and oxidative stability of spray-dried oil powder with milk protein and trehalose wall material. Journal of Food Engineering 125 34-43. 

---