15B-20 |
Aminopeptidase activity of Lactobacillus helveticus after high hydrostatic pressure treatment |
S. I. MANURUNG, J. R. Powers, L. O. Luedecke, S. Clark, and B. G. Swanson. Department of Food Science and Human Nutrition, Washington State University, Pullman, WA 99164-6376 Cheese flavor is developed by proteolysis largely due to starter and adjunct cultures. Lactobacillus helveticus is frequently selected as an adjunct culture in the production of Cheddar cheeses because cell lysis provides a substantial quantity of aminopeptidase that hydrolyzes peptides. Previous studies indicate that attenuation of Lb. helveticus with high hydrostatic pressure (HHP) increases cell lysis. The objective of our study was to enhance the lysis of Lb. helveticus without decreasing aminopeptidase activity. Lb. helveticus WSU 19 and Lb. helveticus W260R were incubated in MRS media for 16 h at 370C. Collected cells were transferred into sterilized 10% reconstituted nonfat milk prior to distribution into sterile polyethylene plastic bags. Cells in the sealed bags received HHP treatments at 275, 410, and 550 MPa for 20 min at room temperature. Untreated and HHP treated cells were assayed for the rates of lactic acid production, total plate counts, and cell free extract (CFE) aminopeptidase activities. HHP treatment as low as 410 MPa slowed lactic acid production of Lb. helveticus WSU19 and W260R for 6 h relative to controls. HHP treatment at 410 MPa reduced viable cell populations of Lb. helveticus WSU 19 and W260R by 2 and 0.5 logs, respectively. Lb. helveticus WSU 19 CFE retained about 60% specific aminopeptidase activity relative to CFE from untreated cells after 410 MPa treatments. HHP treatment of 410 MPa increased specific PepN and PepX activities of Lb. helveticus W260R CFE from 250 to 426 and 253 to 468 respectively. Selected Lb. helveticus strains exhibit variable sensitivity to high hydrostatic pressure. High pressure treatment increases aminopeptidase activity of Lb. helveticus that do not lyse readily. Increased aminopeptidase activity may accelerate flavor development in Cheddar cheese.
Session 15B, Dairy Foods: Chemistry, microbiology and sensory analysis of various cheeses
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