Food Biochemistry and Food Processing (2 edition)

BLBS102-c25 BLBS102-Simpson March 21, 2012 13:23 Trim: 276mm X 219mm Printer Name: Yet to Come

474 Part 4: Milk

Table 25.4.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, e.g.:


Mould growth


Colour, due to growth ofBrevibacterium linens


Formation of eyes

Flavour Development, due to:


Formation of numerous sapid and aromatic compounds


Release of flavourful compounds from the cheese matrix due

to proteolysis

Changes in Functionality, e.g., Meltability, Stretchability,

Water-Binding Properties, Browning, due to:


Proteolysis


Catabolism of lactose

 Non-starter LAB (NSLAB): These are adventitious LAB

that contaminate the cheese milk at farm and/or factory.

Traditionally, cheesemakers relied on NSLAB for acid pro-

duction 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 cheesemaking operations.

Most NSLAB are killed by HTST pasteurisation and curd

made from good-quality pasteurised milk in modern en-

closed equipment has only a few hundred NSLAB, mainly

mesophilic lactobacilli, per gram at the start of ripening.

Indeed, only a limited number of species of mesophilic

lactobacilli grow in cheese curd. However, those NSLAB

that are present, grow at a rate depending 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 pasteurised milk; the difference is probably mainly

responsible for the more intense flavour of the former com-

pared to the latter. This situation applies to all cheese vari-

eties that have been investigated and the NSLAB dominate

the viable microflora of cheese ripened for>2 months.


 Secondary cultures: Most cheese varieties develop a sec-

ondary microflora, which was originally adventitious but

now develops mainly from added cultures. Examples are

Propionibacteria freudenrichiisubsp.shermanii(Swiss

cheeses),Penicillium roqueforti(Blue cheeses),Penicil-

lium camembertiandGeotrichium candidum(Camem-

bert and Brie),Brevibacterium linens, Arthrobacterspp.,

Corynebacteriumand yeasts (surface smear-ripened cheese)

and citrate-positiveLc. lactisandLeuconostocspp. (Dutch-

type cheeses). Most of the microorganisms used as sec-

ondary cultures are very active metabolically and many

secrete very active proteolytic and lipolytic enzymes. Con-

sequently, they dominate the ripening of varieties in which

they are used. Traditionally, a secondary culture was not

used for Cheddar-type cheese but it is becoming increas-

ingly common to add an adjunct culture, usually selected

mesophilic lactobacilli (equivalent to adding a NSLAB

population), to accelerate ripening, intensify flavour and

perhaps tailor-make flavour. Essentially, the objective is to

reproduce the microflora, and consequently the flavour, of

raw-milk cheese. It is also becoming more common to add

Str. thermophilusas an adjunct culture for Cheddar cheese.


 Exogenous enzymes: For some varieties of Italian cheese,

for example Provalone and Pecorino varieties, rennet paste

is used as coagulant. The rennet paste contains a lipase,

PGE, in addition to chymosin; PGE is responsible for ex-

tensive lipolysis and the characteristic piquant flavour of the

cheese. Rennet extract used for most varieties lacks PGE.

During ripening, a very complex series of reactions, which

fall into three groups, occur:

1. Glycolysis of lactose and modification and/or catabolism
   of the resulting lactate


2. Lipolysis and the modification and catabolism of the re-
   sulting fatty acids


3. Proteolysis and catabolism of the resulting amino acids

Glycloysis and Related Events Fresh cheese curd contains

approximately 1% lactose, which is converted to lactic acid

(mainly thel-isomer) by the starter LAB, usually within 24

hours. Depending on the variety, thel-lactic acid is racemised

todl-lactic acid by NSLAB, or catabolised to CO 2 and H 2 O

in mould-ripened and in smear-ripened cheese. In Swiss-type

cheese, lactic acid is converted to propionic and acetic acids,

CO 2 and H 2 ObyP. freudenrichiisubsp.shermanii;theCO 2 is

responsible for the characteristic eyes in such cheese.

Lipolysis Little lipolysis occurs in most cheese varieties, in

which it is catalysed by the weakly-lipolytic LAB or NSLAB,

and indigenous milk lipase if raw milk is used. Extensive lipoly-

sis occurs in some hard Italian-type cheeses, for example Proval-

one and Pecorino varieties, for which PGE is responsible, and in

Blue cheese, for whichP. roquefortiis responsible. Fatty acids

are major contributors to the flavour of Provalone and Pecorino

cheese and some may be converted to lactones or esters, which

have characteristic flavours. In blue-veined cheese, fatty acids

are converted to methyl ketones byP. roquefortiand these are

mainly responsible for the characteristic peppery taste of such

cheese. Some of the methyl ketones may be reduced to secondary

alcohols.

Proteolysis Proteolysis is the most complex and probably

the most important of the three primary ripening reactions for

the quality of cheese, especially internal bacterially ripened