Food Biochemistry and Food Processing

20 Biochemistry of Milk Processing 465

(e.g., junket or Burgos cheese), but most is ripened
(matured) for a period ranging from about 2 weeks
(mozzarella) to 2 years (Parmegianno-Reggiano,
extra-mature Cheddar), during which the character-
istic flavor, texture, and functionality of the cheese
develop. The principal changes in cheese during rip-
ening are listed in Table 20.4.
Ripening is a very complex biochemical process,
catalyzed by coagulants, indigenous milk enzymes,
starter LAB and their enzymes, nonstarter LAB, sec-
ondary cultures, and exogenous enzymes:

• Coagulant: Depending on the coagulant used, the
  pH of the curd at whey drainage, the temperature
  to which the curds are cooked and the moisture
  content of the curds, 0–30% of the rennet added
  to the milk is retained in the curd.


• Indigenous milk enzymes: These are particularly
  important in raw-milk cheese, but many
  indigenous enzymes are sufficiently heat stable
  to withstand HTST pasteurization. Important
  indigenous enzymes include plasmin, xanthine
  oxidase, acid phosphatase, and in raw-milk
  cheese, lipoprotein lipase. Information on the
  significance of other indigenous enzymes is
  lacking.


• Starter LAB and their enzymes: These reach
  maximum numbers (
  109 cfu/g) at the end of

curd manufacture (6–12 hours). They then die

and lyse at strain-dependent rates, releasing their

intracellular enzymes.

• Non-starter LAB (NSLAB): These are
  adventitious LAB that contaminate the cheese
  milk at farm and/or factory. Traditionally, cheese
  makers relied on NSLAB for acid production
  during curd manufacture; this is still the case
  with some minor artisanal varieties, but starter
  LAB are now used in all factory and most
  artisanal cheese-making operations. Most
  NSLAB are killed by HTST pasteurization, and
  curd made from good quality pasteurized milk in
  modern enclosed equipment has only a few
  hundred NSLAB, mainly mesophilic lactobacilli,
  per gram at the start of ripening. However, they
  grow at a rate dependent mainly on the
  temperature to 10^7 –10^8 cfu/g within about 3
  months. In cheese made from raw milk, the
  NSLAB microflora is more diverse and reaches a
  higher number than in cheese made from
  pasteurized milk; the difference is probably
  mainly responsible for the more intense flavor of
  the former compared with that of the latter. This
  situation applies to all cheese varieties that have
  been investigated, and the NSLAB dominate the
  viable microflora of cheese ripened for  2
  months.

Table 20.4.Changes in Cheese during Ripening

Softening of the texture. Due to

• Proteolysis of the protein matrix, the continuous solid phase in cheese


• Increase in pH due to the catabolism of lactic acid and/or production of NH 3 from amino acids


• Migration of Ca to the surface in some cheeses, e.g., Camembert
  Decrease in water activity. Due to


• Uptake of NaCl


• Loss of water through evaporation


• Production of low molecular weight compounds


• Binding of water to newly formed charged groups, e.g., NH 4
  or COO-
  Changes in appearance. Examples:


• Mold growth


• Color, due to growth of B. linens


• Formation of eyes
  Flavor development. Due to


• Formation of numerous sapid and aromatic compounds, as discussed above


• Release of flavorful compounds from the cheese matrix due to proteolysis
  Changes in functionality, e.g., meltability, stretchability, water-binding properties, Maillard browning, and
  browning. Due to


• Proteolysis


• Catabolism of lactose