Growth studies on the lactic streptococci: IV. Some observations on redox potential
Summary Redox potential changes at 30°C in anaerobic reconstituted skim-milk cultures of Streptococcus cremoris AM1 and AM2 and Streptococcus lactis ML8 have been investigated in batch cultures and continuous cultures maintained at constant pH by the addition of fresh medium. Str. lactis ML8 was more strongly reducing than either Str. cremoris AM1 or AM2. The positive Eh values which can arise in dense continuous cultures of lactic streptococci are not likely to affect either the lactic acid formation or proteolytic activity of the resultant bacterial concentrate. An electrolytic reduction cell is described which allows variations in redox potential in cultures to be controlled simply and effectively.
Lyophilized Lactic Acid Starter Culture Concentrates: Preparation and Use in Inoculation of Vat Milk for Cheddar and Cottage Cheese
Abstract A method to concentrate and lyophilize milk-grown cultures of lactic streptococci which produced cells active in fermentation is described. Inoculated nonfat milk was maintained at pH 6.3 by continuous addition of 30% aqueous sodium carbonate. After growth for 15 to 18 h at 30 C, the pH was adjusted to 6.9, and 4.5% sodium citrate was added to allow recovery of the cells by centrifugation. The cells were resus-pended in a medium of 10% sucrose, 5% sodium citrate, 5% gelatin, and 2% monosodium glutamate to l/20th the original culture volume, and were frozen and lyophilized. Vials containing the dry concentrate were sealed under vacuum, stored at −22 C and +22 C, and examined for cell viability and activity. Activity was assayed by simulating cottage and Cheddar cheese making procedures and measuring the final pH. Several lyophilized cultures maintained activity similar to conventional culture for storage of up to 3 mo. Cheddar and cottage cheese were made in 363-kg capacity vats with lyophilized and conventional cultures, and the dry concentrates performed as well as conventional cultures.
On the fractionation of β-lactoglobulin and α-lactalbumin
Abstract Existing methods for the preparation of α-lactalbumin and β-lactoglobulin are examined critically. It is proposed that the most satisfactory method for the preparation of the whey protein fraction from bovine milk is (NH 4 ) 2 SO 4 fractionation. A number of new gentle procedures for the fractionation of the whey proteins are compared with some existing methods. The distribution of total protein at various stages is determined by total Kjeldahl nitrogen and the kind of protein by starch-gel electrophoresis. The effect of variables, such as pH, salt concentration and temperature on the separation of α-lactalbumin and serum albumin from β-lactoglobulin is studied. Differences in the behavior ( e.g. solubility) of genetic variants of β-lactoglobulin are noted. The solubility of each of the major whey proteins, under similar conditions to those used in the fractionation, is compared with its solubility in the whey protein mixture. The understanding gained of factors important in the fractionation is used in recommending new procedures for α-lactalbumin and β-lactoglobulin isolation.