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Lyophilized Lactic Acid Starter Culture Concentrates: Preparation and Use in Inoculation of Vat Milk for Cheddar and Cottage Cheese¹

Department of Microbiology, Oregon State University, Corvallis 97331

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.

¹ Technical Paper No. 3477. Oregon Agricultural Experiment Station.