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Chr. Hansen
Breakthrough in understanding how food cultures
with bioprotective effect work
FreshQ food cultures from Chr.
Hansen are natural lactic acid
bacteria (LAB) specifically selected
for their ability to help
protect dairy products from
spoilage caused by yeasts and molds.
Scientific activities related to understanding
the underlying mechanisms
used by LAB to delay the growth of
yeasts and molds have so far focused
very much on trying to identify specific
antimicrobial compounds produced by
LAB1,2. However, no scientific studies
have been able to identify compounds
that could explain a substantial part of
the inhibitory effect seen against yeast
and mold spoilage. Therefore, it became
apparent that other mechanisms
played a major role, but until now the
specific mechanism was not elucidated.
Competition for
a specific nutrient
Certain lactic acid bacteria are able to
delay the growth of spoilage organisms
by effectively using the nutrients
that the spoilage organisms need to
grow. Chr. Hansen scientists Siedler
et al (2020)3 made a breakthrough
discovery showing that in fermented
dairy products, competitive exclusion,
i.e. competition for a limited nutrient
by different organisms, is a major
mechanism of fungal growth inhibition
by lactobacilli. It was discovered that
the depletion of the essential trace element
manganese by two Lactobacillus
species; Lb. paracasei and Lb. rhamnosus
from FreshQ food cultures was the
main mechanism for inhibition of yeast
and mold spoilage in fermented dairy
products. A manganese transporter
(MntH1), identified by the research
team at Chr. Hansen, represents one
of the highest expressed gene products
for FreshQ food cultures in a fermented
dairy product, and facilitates the uptake
of manganese from the food matrix,
preventing the availability of this
essential growth factor for the unwanted
contaminants.
In collaboration with North Carolina
State University in USA, the scientists at
Chr. Hansen proved the mechanism at
the genetic level: Deletion of the mntH1
gene in the tested Lactobacillus species
resulted in loss of bioactivity, proving this
gene and the depletion of manganese as
the most important mechanism which
can explain the delay in growth of yeasts
and molds. The importance of mntH1
gene activity in Lactobacillus was proven
in fermented milk, where yeast growth
was found only to be inhibited by Lb.
paracasei having an active manganese
transporter. However, addition of excess
manganese to the fermented dairy product
in the concentration of 0.6 mg/L resulted
in restored yeast growth whether
or not the manganese transporter was
inactivated in Lb. paracasei (Fig.1).
The effect of competitive exclusion
by manganese depletion on the growth
of three different spoilage molds from
the family Penicillium were additionally
shown by the Chr. Hansen scientists
Siedler et al 20203. The sample with
the FreshQ food culture showed clear
inhibition of the mold growth compared
to the reference (Fig.2). Addition
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November/December 2020
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of manganese in increasing concentrations,
however, restored mold growth.
Evaluating the bioprotective ability
in fermented milk of selected lactobacilli
from ten major phylogenetic groups
identified a correlation between the presence
of the mntH gene and bioprotective
activity. Thus, manganese scavenging
emerges as a common trait within the
Figure 1: Effect of Mn transporter deletion
on yeast growth inhibition (absorbance,
600 nm). Yeast growth in
milk fermented by Lb. paracasei (A),
Lb. paracasei with deleted Mn transporter
gene (B), Lb. paracasei added
manganese 0.6 mg/L (C) and Lb. paracasei
with deleted Mn transporter
gene added manganese 0.6 mg/L (D).
Growth of D. hansenii was measured
after 5 days of incubation at 17 oC. Values
are presented as means ± standard
deviations (n = 2 biological replicates).
And bars bearing * are statistically different
(p < 0.0001). Adapted from Siedler
et al 2020.
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