Dairy Chemistry And Biochemistry

408 DAIRY CHEMISTRY AND BIOCHEMISTRY

Table 10.5 Free fatty acids in a selection of cheese varieties (Woo and Lindsay, 1984; Woo,
Kollodge and Lindsay, 1984)
Variety FFA (mg kg-') Variety FFA (mg kg-')
Sapsago
Edam
Mozzarella
Colby
Camembert
Port Salut
Moneterey Jack
Cheddar
Gruyere

21 1

356

363

550

68 1

700

736

1028

1481

Gjetost

Provolone

Brick

Limburger

Goats' milk

Parmesan

Romano

Roquefort

Blue (US)

1658

2118

2150

4187

4558

4993

6743

32453

32230

Blue cheeses undergo very extensive lipolysis during ripening; up to 25%
of all fatty acids may be released. The principal lipase in Blue cheese is that
produced by Penicillium roqueforti, with minor contributions from indigen-
ous milk lipase and the lipases of starter and non-starter lactic acid bacteria.
The free fatty acids contribute directly to the flavour of Blue cheeses but,
more importantly, they undergo partial fl-oxidation to alkan-2-ones (methyl

ketones; (RX-CH,) through the catabolic activity of the mould (Figure
10.18). A homologous series of alkan-2-ones from C, to C,, is formed
(corresponding to the fatty acids from C, to CI8), but heptanone and
nonanone predominate; typical concentrations are shown in Table 10.6. The
characteristic peppery flavour of Blue cheeses is due to alkan-2-ones. Under
anaerobic conditions, some of the alkan-2-ones may be reduced to the
corresponding alkan-2-01s (secondary alcohols), which cause off-flavours.

, ,o

Proteolysis. Proteolysis is the most complex, and perhaps the most impor-
tant, of the three primary biochemical events in the ripening of most cheese
varieties. In internal, bacterially ripened cheeses, e.g. Cheddar, Dutch and
Swiss varieties, it is mainly responsible for the textural changes that occur
during ripening, i.e. conversion of the tough rubbery texture of fresh curd to
the smooth, pliable body of mature cheese. Small peptides and free amino
acids contribute directly to cheese flavour and amino acids serve as
substrates in several flavour-generating reactions, e.g. decarboxylation,
deamination and desulphuration. Amino acids may also react chemically
with carbonyls via the Maillard reaction and Strecker degradation, with the
production of a great diversity of sapid compounds (Chapter 2). Excessive
amounts of hydrophobic peptides may be produced under certain circum-
stances and may lead to bitterness which some consumers find very
objectional; however, at an appropriate concentration, and when properly
balanced by other compounds, bitter peptides probably contribute positive-
ly to cheese flavour.