Use of non-lactic acid bacterial proteolytic enzymes to reduce bitter peptides in dairy products

Principal Investigator:	Bart Weimer, Utah State University
Co-Investigators:

Project Summary:

Proteolysis is an important process in Cheddar cheese manufacture and plays a role in flavor and texture development of the cheese. Initial hydrolysis of intact caseins is catalyzed by chymosin and endogenous milk enzymes. Subsequently, the concerted action of the proteolytic systems of the starter and non-starter bacteria hydrolyzes peptides during aging. The interaction between these enzymes is directly linked to bitter peptide production in Cheddar cheese. Bitter peptides are hydrophobic and usually originate from ?s1 - and ??- casein. Two peptides commonly associated with bitterness are ?s1- casein f(1-9) and ??- casein f(193-209). Hydrolysis of these peptides is associated with decreased bitterness in Cheddar cheese. The aim of this study was to investigate the ability of flavor adjunct bacteria and non-starter lactobacilli to degrade bitter peptides.

Cheddar cheese was made with Lactococcus lactis ssp. cremoris S1 with and without Brevibacterium linens BL2 and Lactobacillus helveticus CNRZ32 as adjuncts. In addition, Cheddar cheese was made with Lactococcus lactis ssp. lactis S2 with and without B. linens BL2 and L. helveticus CNRZ32 combined as adjuncts. Each bacterial population was followed during ripening. RP-HPLC analysis was used to determine ?s1- casein f(1-9) and ??- casein f(193-209) content and sensory attributes were evaluated by a trained taste panel.

The s1- casein f(1-9) and - casein f(193-209) content in each cheese, with and without adjuncts, increased during ripening. However, the concentration of these peptides was lower in cheeses made with adjuncts. When the adjuncts were added in combination they did not produce an appreciable reduction in s1- casein f(1-9) and - casein f(193-209) content in comparison to the individual adjunct addition. Addition of the adjuncts did not affect the overall flavor acceptability. But the Cheddar cheese did receive lower bitter scores. Cheddar cheese made with B. linens BL2 was rated the best by the panel, in addition to having lower s1- casein f(1-9) and - casein f(193-209) content. These studies suggest that adjunct bacteria reduce bitterness during ripening.

The NSLAB counts remained low for the initial aging period compared to a consistently high count for the starter population. Further analysis of the peptides is underway.

Publications:

Koka, R., and B. C. Weimer. 2000. Isolation and characterization of a protease from Pseudomonas fluorescens RO98. J. Applied Microbiol. 89:280-288.

Koka, R., and B. C. Weimer. 2000. Investigation of the ability of a purified protease from Pseudomonas fluorescens RO98 to de-bitter cheese. Int. Dairy J. 10:75-79.

Weimer, B. C., Xie Yi, and Rod Brown. 2000. Autocatalytic processing of the protease from Brevibacterium linens BL2: a kinetic analysis for the degradation of casein. International Dairy Federation Biennial Cheese Flavor Conference, Banff, Alberta.

Theses:

P. Joseph - Ph.D. in progress

Published Abstract:

Weimer, B. C., P. Joseph, J. Petersen, and J. Steele. 2000. The proteinases of lactobacilli. International Dairy Federation Biennial Cheese Flavor Conference, Banff, Alberta.

B. Weimer, P. Joseph, R. Koka, and Y. Xie. 2002. Use of non-lactic acid bacterial enzymes to degrade casein. Institute of Food Technology, Anaheim, CA

Presentations:

Joseph, P., B. C. Weimer, J. Petersen, and J. Steele. 2000. The proteinases of lactobacilli. Intermountain Graduate Forum, Logan, UT.