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Stimulation of Propionic Acid Bacteria by Lactic Acid Bacteria in Cheese.
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2001-06-01
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Condon, S., Cogan, T.M., Piveteau, P., O'Callaghan, J., Lyons, B., Stimulation of Propionic Acid Bacteria by Lactic Acid Bacteria in Cheese, End of Project Report, Teagasc, 2001.
Abstract
In the manufacture of Swiss-type cheese two successive fermentations
occur. During manufacture, lactic acid bacteria (LAB), particularly
Streptococcus thermophilus, Lactobacillus helveticus and
Lb. delbrueckii subsp. lactis, convert lactose to lactate while,
during ripening, propionic acid bacteria (PAB) convert lactate to
propionic acid, acetic acid and carbon dioxide (CO2). CO2 is
responsible for eye formation and propionic acid results in the typical
nutty flavour of Swiss-type cheese. There have been a few reports of
interactions between a small number of LAB and PAB but the
compounds involved have not been identified. A better
understanding of this phenomenon is necessary to select strains of
PAB for cheesemaking and improve the quality of hard cheeses.
Cheese cannot be used for such a study because of its complexity and
the length of time it is ripened. Hence, a simple whey-based model
developed by Piveteau et al (1995) was successfully used to study the
interactions between LAB and PAB. In this procedure, the LAB were
grown overnight in milk and the whey was collected by centrifugation.
After neutralisation and filter-sterilisation, the growth of strains of PAB
in this whey and in a control whey produced from the same milk by
acidification with lactic acid were compared.
The objectives of this study were to refine the model of Piveteau et al
(1995) to study the interactions between LAB and PAB and to
determine the nature of the stimulant(s) produced by the LAB. * Thirty-two combinations of different commercial strains of PAB and
LAB were evaluated in a modified whey model. None showed any
inhibition and all showed some degree of stimulation but the extent of the stimulation depended on the particular pair of PAB and LAB
used.
* An inhibitor of PAB was found in milk, which prevented the growth
of PAB from low (105 cfu/ml) but not from high inocula (107 cfu/ml).
The inhibitor was heat stable (to autoclaving for 15 min), of low
molecular mass and could be removed by pre-growth of some but not
all starter LAB in milk.
* Growth of P. freudenreichii DPC 3801 in control whey was
stimulated by peptone, tryptone, casein hydrolysed by the crude
proteinase of Lb. helveticus DPC 4571 and by pre-growth of the
lactobacillus in milk, but not by vitamins (riboflavin, thiamine, PABA,
Ca panthothenate, biotin and nicotinic acid) or minerals (MgSO4,
MnCl2, CoCl2 and CuSO4).
* Growth of Lb. helveticus DPC 4571 in milk resulted in significant
increases in peptide and amino acid production but the amino acids
produced did not stimulate the growth of the PAB. Based on these
results it was concluded that the stimulation was due to production of
peptides by the LAB from casein.
* The whey model developed by Piveteau et al (1995) to study the
interactions between PAB and LAB was shown to be reproducible.
Adjustment of the pH of the whey to 5.4 rather than 6.0, incubation
at 24ºC rather than 30ºC and addition of 1% NaCl, to simulate
cheese ripening conditions allowed growth of all the PAB tested.
* Several chromatographic procedures, including ion-exchange, gel
permeation and reverse-phase, high-pressure liquid chromatography
failed to categorically identify the peptide(s) responsible for the
stimulation of the PAB. In some of these chromatographic systems,the stimulatory activity was shown to be present in several peaks
implying that different peptides were involved.