Vol51. No I zyxwvutsrqponmlkji February 1998 zyxwvutsrqpon Original paper. zyxwvutsrq 0 1998 Society of Dairy Technology Whey crystalline lactose as a main constituent in growth and counting media for lactococci and Streptococcus thermoph ilus A TEMk and R YILMAZ Hacettepe University, Food Engineering Department, 06532 Beytepe. Ankara, Turkey In the present study, a dried whey crystalline lactose zyxwv f WCL) preparation IMS obtained from deproteinized whey by crystallization in an ethanol-water system. This was used as a major com- ponent in Streptococcus WCL ( S W C L ) broth and in Modijied MI7 (MMI7) agar media. S WCL broth and MMI 7 "gar were used as media for propagating and counting several strains of lactococci and Streptococcus thermophilus, respectively. The study zyxw as carried out to compare the alternative utilization ojS WCL broth to RSM (reconstituted skim milk) and MMI7 qar to original MI 7 agar. The streptococcal cultures tested in this study remained viable through sever- al transfers in S W C L broth medium. However, high acidity development was not observed in S W C L broth cultures. The presence of 4 g/l yeast extract in S W C L broth had more effect on growth than on acid production. Growth in S W C L broth or RSM was dependent upon the type of streptococcal culture used. MMI7 agar gave comparable results to MI7 agur in terms of counts of the lactococci and Strep thermophilus propagated in S WCL broth or in RSM. INTRODUCTION The major component of deproteinized whey (DW) and whey permeate zyxwvut (WP) is lactose, an efficient carbon source for microorganisms utilizing it. Thus there has been a growing interest in the utilization of DW or WP as a growth medium or a basic ingredient of growth media for propagating this kind of microorganism or microbial production of some products and byproducts such as food grade yeast, lactic acid, citric acid and ethanol.'-5 Lactic acid bacteria are typical lac- tose using organisms. There are several stud- ies on the utilization of whey or its products as a carbon source for lactic acid bacteria."" However, a limited number of studies have been reported on the use of DW or WP (ultrafiltered whey) as a medium for mesophilic lactococci to compare growth and acid produ~tion.l~-~~ Christopherson and ZottolaI2 indicated that whey permeate may be suitable as a growth medium for mesophilic lactococci. They pointed out the necessity of adding yeast extract to the whey based media as a growth factor for lactococci. In the second study propagation of several strains of mesophilic lactococci were carried out in WP or WP with 10 g/l yeast extract.I3 The authors reported that the cultures used in their study remained viable through several transfers in the permeate media. The researchers mentioned that the permeate media might be improved by adding buffering salts. On the other hand, researchers who have developed whey based media from reconstituted whey solids reported that the lactose level in the media should not exceed 30 g/1 for optimal culture activity.' At higher lactose levels, acid production by cells will continue after growth has halted.I5 MI7 agar has been recommended by the manufacturers for the growth and enumera- tion of lactococci and by the International Dairy Federation for the selective enumera- tion of Streptococcus thermophilus from yogurt.16 No reference to the use of whey or its products as a substrate for enumeration of lactic acid bacteria was found in the litera- ture surveyed. Moreover, we are not aware of any study related to the recovery of lactose from whey, DW or WP and the utilization of whey lactose as a growth medium for microorganisms. In this study, a dried whey crystalline lac- tose (WCL) was prepared from DW by crys- tallization in an ethanol-water system and this product was used as a basic ingredient in a growth medium named Streptococcus WCL broth (SWCL broth) and a plate count agar medium named Modified MI7 agar (MM17 agar). The objective of this study was to observe the growth and activities of several strains of lactococci and Strep thermophilus in these developed media. Reconstituted skim milk (RSM) as growth medium and original M17 agar as count medium were also included in the study as controls. MATERIALS AYD METHODS WCL In the first step concentrated whey containing approximately 380 gil total solids was 30