Effects of β-lactoglobulin and κ-casein genetic variants and concentrations on syneresis of gels from renneted heated milk

Abstract

Milk protein genetic polymorphism has a major influence on the composition of milk, and on its processing properties, including yield of cheese (see Schaar et al. 1985;McLean et al. 1984McLean et al. , 1987McLean, 1987). However, there appears to be little information on the effects of milk protein genetic variants on syneresis of cheese curd. The effect of casein composition on syneresis was studied by Pearse el al. (1986), who found that syneresis was affected only by the level of /?-casein. Syneresis is an essential requirement in cheese making from renneted or acidified milk, but is undesirable during the storage of products such as yogurt. Milk for yogurt manufacture is preheated to minimize syneresis and to give maximal firmness of the yogurt coagulum (Tamime & Deeth, 1980). Pearse et al. (1985) showed that the reduction of one-third in the extent of syneresis caused by heating artificial micelle milk (AMM) containing /Mactoglobulin (/?-lg) in natural concentrations was due to sulphydryl-mediated complex formation between /9-lg and micellar /c-casein which appeared to interfere with the micelle-micelle interactions responsible for syneresis. The results presented here were part of a study which investigated the effects of /ccasein and /ff-lg genetic variants and concentrations on syneresis of curd formed from renneted heated AMM. EXPERIMENTAL Preparation of protein fractionMilk used for the preparation of casein fractions was obtained from two cows which had been typed, using the method described by Schaar (1984), as <x sl -casein B, /^-casein A 2 , /c-casein A and a sl -casein BC, /?-casein A 2 B, /c-casein B. The milk was defatted (2500 g, 4 °C, 10 min) and the casein precipitated at pH 4-6 with 1 M-HC1 at 20 °C, washed three times, lyophilized and stored at -18 °C. Casein fractions (a s -, /?-and /c-casein) were separated on a 300 x 50 mm column of DEAE-Sephacel (Pharmacia). The eluting buffer (pH 7-0) contained 0-01 M-imidazole, 4 M-urea, 0-01 M-mercaptoethanol with a 0-06-0-33 M-NaCl gradient. Each fraction was dialysed against three changes of distilled water, lyophilized and stored at -18 °C. t Present address: Swedish Red Cross, Box 27316, S-102 54 Stockholm, Sweden.

Genotyping of β-Lactoglobulin gene by PCR-RFLP in Sahiwal and Tharparkar cattle breeds

“…Milk protein genetic polymorphism has received considerable research interest in recent years because of possible associations between milk protein genotypes and economically important traits in dairy cattle. Many research reports have indicated that certain milk protein variants may be associated with milk production [ 1 - 4 ], milk composition [ 5 - 15 ] and cheese production [ 5 , 6 , 12 - 14 , 16 - 20 ]. Therefore, milk protein genes could be useful as genetic markers for additional selection criteria in dairy cattle breeding.…”

Enhancing the gelation of .beta.-lactoglobulin

“…This latter reaction appears to inhibit the renneting process, perhaps by occluding the site of hydrolysis in x-casein (van Hooydonk et al, 1987). The naturally occurring BLG variants found in bovine milk can affect a number of properties including cheese yield and syneresis (Marziali and Ng-Kwai-Hang, 1986;Pearse et al, 1985; McLean and Schaar, 1989; Sweetsur and White, 1974). Preliminary * Address correspondence to this author at 413 Stocking Hall, Cornell University, Ithaca, NY 14853 [telephone (607) 255-2896; fax (607) 255-8741].…”

Reducing Whey Syneresis in Yogurt by the Addition of a Thermolabile Variant of β-Lactoglobulin

“…The reduction of whey separation by the addition of BLG however, reached a maximum when the concentration of BLG added was equivalent to that normally in milk. 18 ) In our studies, the addition of milk solids and small quantities of BLG decreased the whey separation of set-type yogurt produced with milk which was preheated at 85°C for 30 min. The reduction in whey confirmed the benefits of adding BLG to this type of product (Table).…”