Document Type

Article

Journal/Book Title/Conference

Journal of Dairy Science

Volume

98

Publication Date

2015

First Page

3645

Last Page

3654

DOI

doi.org/10.3168/jds.2014- 9293

Abstract

An obligatory heterofermentative lactic acid bacterium Lactobacillus wasatchii sp. nov. isolated from gassy Cheddar cheese was studied for growth, gas formation, salt tolerance and survival against pasteurization treatments at 63°C and 72°C. Initially, Lb. wasatchii was thought to only use ribose as a sugar source and we were interested in whether it could utilize galactose. Experiments to determine rate and extent of growth and gas production in carbohydrate restricted (CR) de Man, Rogosa, and Sharpe (MRS) medium under anaerobic conditions with various combinations of ribose and galactose at 12, 23, and 37°C were conducted with 23°C being the more optimum growth temperature of Lb. wasatchii. When grown on ribose (0.1%, 0.5%, and 1%), maximum specific growth rates (μmax) within each temperature were similar. When galactose was the only sugar, μmax was 2 to 4 times lower than with ribose. At all temperatures, highest final cell densities (OD640) of Lb. wasatchii were achieved in CR-MRS plus 1% ribose, 0.5% ribose and 0.5% galactose, or 1% ribose combined with 1% galactose. Similar μmaxvalues and final cell densities were achieved when 50% of ribose in CR-MRS was substituted with galactose. Such enhanced utilization of galactose in the presence of ribose to support bacterial growth has not previously been reported. It appears that Lb. wasatchii co-metabolizes ribose and galactose, utilizing ribose for energy and galactose for other functions such as cell wall biosynthesis. Co-utilization of both sugars could be an adaptation mechanism of Lb. wasatchii to the cheese environment to efficiently ferment available sugars for maximizing metabolism and growth. As expected, gas formation by the heterofermenter was observed only when galactose was present in the media. Growth experiments with MRS plus 1.5% ribose at pH 5.2 or 6.5, with 0, 1, 2, 3, 4, or 5% NaCl revealed that Lb. wasatchii is able to grow under salt and pH conditions typical of Cheddar cheese (4 to 5% salt-in-moisture, ~pH 5.2). Finally, we found Lb. wasatchii cannot survive LTLT pasteurization but survives HTST lab pasteurization with 4.5 log reduction occurred. The ability of Lb. wasatchii to survive HTST pasteurization and grow under cheese ripening conditions implies that the presence of this nonstarter lactic acid bacteria can be a serious contributor to gas formation and textural defects in Cheddar cheese.

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