Some aspects of the microbiology of cheese ripening investigated using aseptic manufacturing techniques : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University
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Date
1988
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Massey University
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Abstract
The effect of non-starter lactic acid bacteria (NSLAB) on
the texture and flavour development in cheese was investigated
using Cheddar cheese matured in impermeable cheese barrier
bags. Cheeses made normally in open vats (and contaminated
with adventitious NSLAB) were compared with NSLAB - free
cheeses.
To produce NSLAB - free cheeses, two totally enclosed
cheese-making vats were designed and constructed. These vats
were sterilized by soaking overnight with Iodophor, then steam
flushed for 1 hour. This procedure was sufficient to exclude
NSLAB but did not produce complete sterility as evidenced by
the growth of bacillus - type organisms in UHT - treated milk
incubated in the sterilized vats.
The thermal death characteristics of representatives trains
of NSLAB showed that most species would not survive milk
pasteurization temperatures. However, two species,
Lactobacillus casei var casei and Leuconos toc lactis were
sufficiently resistant that, if present as the dominant flora
of a raw milk, they could survive into the curd. Therefore,
for aseptically manufactured cheeses, the milk was obtained by
careful milking of the cows, to avoid NSLAB contamination. In
the pasteurized vat - milks, the total bacterial count was
routinely less than 1c fujmL.
A panel of tasters was trained to determine the texture and
flavour of the cheeses using attribute scaling techniques.
Six textural and 5 flavour attributes were defined, and the
intensities of these were monitored in the cheeses at various
ages up to 9 months.
The aseptic cheese-making procedure effectively eliminated
NSLAB contamination from the cheeses. However, when cheeses
in bags were matured for long periods, a surface flora of
adventitious NSLAB developed, apparently by contamination
during sampling. Despite all sampling precautions, the only
method found to satisfactorily prevent this contamination was
waxing of the cheese surfaces prior to bagging. It was also
observed that in adventitiously contaminated cheeses, the
count of NSLAB in the surface 1-2mm was at least 10 times the
count in the remainder of the cheese.
The texture and flavour of Cheddar cheeses made without NSLAB and
matured at 10 C for 9 months could not be distinguished from
cheeses with adventitious NSLAB matured under the same conditions.
In equivalent cheeses matured at lSC, the textures were again
identical but the cheeses with NSLAB had greater intensities of
sharpness and sulphide than the cheeses without NSLAB. Thus,
starter alone appears to be the predominant contributor of those
compounds which produce Cheddar cheese flavour and NSLAB, although
present, do not normally contribute to flavour production.
In a final part, the growth and citrate utilizing capabilities of
three leuconos toc organisms were determined in a washed- curd
cheeses . Again , NSLAB - free cheeses were made since there are
currently no effective means of differentiating between leucono s toc
and NSLAB organisms , and NSLAB organisms can also utilize citrate.
While all three strains were capable of rapid growth to levels
around 107 cfu/mL in RSM , only one grew significantly in the
cheeses . This strain was capable of fermenting citrate in the
absence of a carbohydrate energy source and removed the citrate
present in brine - salted cheeses within 1 month at either 10 C or
15 c.
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Keywords
Cheese, Microbiology, Cheese industry, Process cheese, Processed cheese