From Milk to Dairy Products 57
natural inhibitors (immunoglobulins, lactoperoxidase, lysozyme, lactoferrin,
nisin, free fatty acids, leukocytes, etc.) and stimulants such as growth factors
(group
B vitamins, amino acids, nitrogenous bases, small peptides, proteose
peptones). Subjecting milk to heat treatment may
destroy natural inhibitors
and growth factors, but it can also generate growth factors such as peptides,
amino acids, formic acid and so on. Other exogenous factors such as
bacteriophages, antibiotics or chemical residues can inhibit the growth of
lactic acid bacteria.
Finally, coagulation defects (longer rennet clotting time, slower firming
rate, formation of a soft gel with reduced cheese yield) may occur in milk due
to its physicochemical and bacteriological composition (mastitis milk, milk
from the beginning or end of lactation) or the
type of treatment it has
undergone (refrigeration, heat treatment, etc.).
Ripening defects
Ripening defects can be classified into three categories:
–
texture and swelling defects:
these defaults can be caused by processing
(dry, oily or runny
rind, split in the body of the cheese, untypical number, size
and uniformity distribution of eye in certain semi-hard cheese
,
etc.) or
microbiological reasons (early or late blowing, off-odor);
–
appearance defects (crust texture, undesirable mould growth)
: these can
be caused by fungus on the cheese surface (“blue”, “cat hair” or “toad skin”
defects), or fungus and bacteria on the surface and inside the cheese (cheese
rind rot, mottled appearance with flecks of orange, cream, pink, brown, white,
red, etc.);
–
flavor and aroma defects
. These include:
-
bitter flavor
, frequently encountered in pressed, blue and soft cheeses.
Caseins (mainly hydrophobic
β
-casein) are responsible for the formation of
bitter peptides by the action of residual rennet, plasmin, penicillii,
psychrotrophic bacteria and some starter cultures
that acidify the curd rapidly,
-
rancid flavor
, which occurs with excessive lipolysis during ripening
causing a large amount of short and medium chain-free fatty acids to form.
The agents responsible are certain penicillii
,
psychrotrophic bacteria, natural
or microbial lipases (contamination,
heat-resistant enzymes, starter cultures,
etc.),
58 Handbook of Food Science and Technology 3
-
other flavor defects
including cruciferous vegetable, mushroom, potato,
or malt odors among others. The origins and mechanisms of their formation
are diverse and difficult to establish.
In conclusion, the preparation of milk is an important step because it plays
a key role in the production of cheese. With the increase in scientific
knowledge over the past 30 years, the various stages of processing milk into
cheese have become better controlled: the biological, biochemical, chemical,
and physical properties of products are constantly changing, demonstrating a
vast variety and complexity of reactions, in particular during ripening.
However, greater understanding of the physicochemical
and microbiological
mechanisms involved in the various stages of cheese production is needed.
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