PhD Vermeiren Lieve Compleet - Hogeschool Gent

Chapter 4
Co-culture experiments demonstrate the usefulness of
Lactobacillus sakei 10A to prolong the shelf-life of a
model cooked ham
Summary
In this chapter, the usefulness of two lactic acid bacteria, a Lactobacillus sakei subsp.
carnosus strain (10A) and the lactocin S producing Lactobacillus sakei 148 (LS5), to extend
the shelf-life of cooked meat products (CMP) was investigated. The interactions between
these potential protective cultures and the spoilage organisms, Leuconostoc mesenteroides
(LM4) and Brochothrix thermosphacta (BT1), were examined in co-culture studies on a
model cooked ham (MCH) product at 7°C under vacuum packaged conditions. The influence
of the glucose content of the model cooked ham on the interaction phenomena was
investigated by performing the co-culture studies on MCH with a low glucose content of
about 0.2% (w/w) glucose and MCH with a high glucose content of about 1.3% (w/w)
glucose. The difficulty in quantifying such an interaction was to individually follow the
growth of the homofermentative LAB-strain on the one hand and the growth of the
heterofermentative LAB-strain on the other hand when growing in co-culture on the MCH. To
resolve this issue a new medium, TC8-MRS-agar, consisting of MRS-agar supplemented with
tetracycline at 8 µg/ml, was developed. This agar medium allowed differentiation of LM4colonies
from 10A-colonies or LS5-colonies after incubation for three days at 30°C under
anaerobic conditions.
When artificially contaminating the model cooked ham with BT1 at 10 2 cfu/g in combination
with 10A at 10 5 cfu/g, the growth of BT1 was significantly slower compared to its
simultaneous growth in mono-culture. In a similar experiment with LM4, this strain reached a
level of 10 7 cfu/g approximately 14 days later if LM4 grew together with 10A compared to its
growth in mono-culture. The lactocin S producing LS5 did not demonstrate an antagonistic
action towards LM4 or BT1. On the MCH with low glucose content as well as on the MCH
with high glucose content, antagonistic interactions of 10A towards LM4 and BT1 occurred;
the antagonistic effect of 10A was not eliminated when glucose was abundant in the product.
The results of this chapter indicate that Lactobacillus sakei 10A has potential as protective
culture for the shelf-life prolongation of CMP, while Lactobacillus sakei LS5 has not.
Chapter 4 – Antagonism of protective cultures towards spoilage organisms 99