제품 ≫ 유가공 ≫ 치즈

유제품 - 가공치즈 processed cheese

출처 : CHEESE: CHEMISTRY , PHYSICS AND MICROBIOLOGY Volume 2

 

Processed cheese is produced by blending shredded natural cheeses of different types and degrees of maturity with emulsifying agents, and by heating the blend under a partial vacuum with constant agitation until a homogeneous mass is obtained.
In addition to natural cheeses, other dairy and non-dairy ingredients may be included in the blend.
Processed cheese was initially manufactured without an emulsifying agent; the first attempt was as early as 1895, but only after the introduction of citrates, and
especially phosphates, as emulsifying agents did the industrial production of
processed cheese become feasible. Production started in Europe on the basis of a
Swiss patent, using citrates, issued in 1912. The idea possibly originated from
the Swiss national dish, Fondue, for which cheese is heat-treated (melted) in the
presence of wine, which contains tartrate that has an emulsifying effect. Processed
cheese was developed independently in the USA a few years later (1917)
by Kraft, who processed Cheddar cheese with citrates and orthophosphates as
emulsifying agents. The newly developed product enabled utilization of natural
cheeses which otherwise would be difficult or impossible to utilize, e.g. cheeses
with mechanical deformations, localized moulds, trimmings produced during
cheese formation, pressing, packaging, etc. It also solved the problem of long-term
storage of hard cheeses which otherwise would undergo excessive proteolysis,
lipolysis and other detrimental changes, and are thus unsuitable for prolonged
storage in their natural form. The assortment was further expanded due to numerous
possible combinations of various types of cheese, not only hard varieties,
and the inclusion of other dairy and non-dairy components which make it possible
to produce processed cheese differing in consistency, flavour, size, and shape.

The principal advantages of processed cheese compared to natural cheeses are:
(i) reduced refrigeration cost during storage and transport, which are especially
important in hot climates;
(ii) better keeping quality, with less apparent changes during prolonged storage;
(iii) great diversity of type and intensity of flavour, e.g. from mild to sharp,
native cheese flavour or specific spices;
(iv) adjustable packaging for various usage, economical and imaginative;
(v) suitability for home use as well as for snack restaurants, e.g. in cheeseburgers,
hot sandwiches, spreads and dips for fast foods.
Processed cheeses are characterized essentially by composition, water content
and consistency; according to these criteria, three main groups may be distinguished:
processed cheese blocks, processed cheese foods and processed cheese
spreads (Table I). More recently established sub-types of processed cheeses are:
processed cheese slices and smoked processed cheese. The first sub-type belongs
to the category of processed cheese blocks, while the second could be either
block or spread. In addition, another group of processed cheese products should
be mentioned, i.e. processed cheese analogues which are usually based on vegetable
fat-casein blends. Finally, the most recent development in cheese processing
is processed cheese with a completely new look, i.e. natural cheese-like
appearance. Developed in France,4 this product has an open texture, similar to
traditional cheeses, with eyes of about O· 5 mm in diameter.


3 EMULSIFYING AGENTS: TYPES AND ROLE
Emulsifying agents (melting salts) are of major importance in processed cheese
production where they are used to provide a uniform structure during the
melting process, and also of the products. Phosphates, polyphosphates and
citrates2,34-37 are most common but sodium potassium tartrate2,36 or complex
sodium phosphates of the general formula
XNa20,Y AI203,8P20s,ZH20
where X = 6-15, Y = 1,5--4, 5 and Z = 4--40,2 are rarely used. Sodium potassium
tartrate, trihydroxyglutaric acid or diglycolic acid are sometimes used. Some
characteristics of the most commonly used emulsifying agents are presented in
These compounds are not emulsifiers in the strict chemical sense (i.e. they are not
surface-active compounds), and since emulsification is not their only purpose, melting
salts are conditionally termed 'emulsifying agents'. However, true emulsifiers
may be included in commercially produced emulsifying agents, which are usually
mixtures of compounds, their composition being protected by the producer.
The essential role of emulsifying agents in the manufacture of processed cheese
is to supplement the emulsifying capability of cheese proteins. This is accomplished
by: (i) removing calcium from the protein system; (ii) peptizing, solubilizing
and dispersing the proteins; (iii) hydrating and swelling the proteins; (iv)
emulsifying the fat and stabilizing the emulsion; (v) controlling pH and stabilizing
it; and (vi) forming an appropriate structure of the product after cooling.
The ability to sequester calcium is one of the most important functions of
emulsifying agents. The principal caseins in cheese (asl-' a s2-' f3-) have non-polar,
lipophilic C-terminal segments, while the N-terminal regions, which contain calcium
phosphate, are hydrophilic. This structure allows the casein molecules to
function as emulsifiers. 38-40 When calcium in the Ca-paracaseinate complex of
natural cheese is removed during processing by the ion-exchange properties of
melting salts, insoluble paracaseinate is solubilized, usually as Na-caseinate. The
equation shown earlier10 could be graphically presented as in Fig. 2. The affinity,
i.e. sequestering ability, of common emulsifiers for calcium increases in the following
order: citrate, NaH2P04, Na2HP04, Na2H2P20 7, Na3HP20 7, Na4P20 7,
NaSP30 IO' During processing (prolonged heat treatment with agitation), polyvalent
anions from the emulsifying agent become attached to the protein
molecules, which increases their hydrophilic properties. The binding of additional
quantities of water increases the viscosity of the blend, causing 'creaming'.
In order to avoid emulsion destabilization, it is necessary to ensure that there is
enough intact casein in the blend (a short, hydrolysed protein structure leads to
phase separation).
 
Polyvalent anions (phosphates, citrates) have a high water-adsorption ability
They become bound, via calcium, to protein molecules providing them with a negative
charge: basic salts also increase the pH of cheese. Both changes, i.e. increased
negative charge and pH, result in higher water adsorption by the proteins. The concentrations
of Ca and P are about twice as high in the insoluble phase of processed
cheese as in the natural cheese from which it was made. The reactivity between
the emulsifier and protein is defined by the ratio of insoluble to total proteins in
the natural cheese and in the processed cheese.34 The affinity of protein for the
cations and anions of melting salts is determined by the valency of the ions.41
Salts consisting of a monovalent cation and a polyvalent anion possess the
best emulsifying characteristics. Although some salts have better emulsifying
properties than others, they may have inferior calcium-sequestering abilities or
may not solubilize and hydrate the protein sufficiently. It is necessary to combine
two or more salts to achieve optimal emulsifying and melting characteristics
simultaneously and to produce a homogeneous and stable processed cheese. An
appropriate pH value is important for several reasons: it affects protein configuration,
solubility and the extent to which the emulsifying salts bind calcium.38
The pH of processed cheese varies within the range 5·0-6·5. At pH ~ 5·0, which
is near the isoelectric point of the cheese proteins, the texture of the cheese may
be crumbly, probably due to weakening of protein-protein interactions, but the
incidence of fat emulsion breakage is reduced. At pH ~ 6· 5, the cheese becomes
excessively soft and microbiological problems may be encountered also. The
effect of pH on the texture of processed cheese was clearly demonstrated by
Karahadian,42 using mono-, di- and trisodium phosphates, the respective pH of
1% solutions of which were 4·2,9·5 and no. Cheese made with NaH2P04 (low
pH) was dry and crumbly, whereas cheese made with Na3P04 (high pH) was
moist and elastic; the texture of cheese made with Na2HP04 was intermediate.
Similar pH-dependent effects apply to other emulsifiers also.38
Some emulsifying agents exhibit bacteriological effects. Monophosphates have
a specific bacteriostatic effect which is even more pronounced with higher phosphates
and polyphosphates.1,2 Citrates lack such effects and may even be subject
to bacterial spoilage. Since the usual heat treatment during processing is relatively
mild, processed cheeses are not sterile; although the final product contains
no viable bacteria, it may contain viable spores, including Clostridia, which may
originate from the natural cheese or from added spices.1.
2,43 Irradiation of spices
prior to usage is thus very important. Orthophosphates suppress the germination
of Cl. botulinum spores in processed cheese whereas citrates have no effect. 44
Differences in processing conditions, e.g. type of emulsifier, pH and moisture
level, also affect spore germination.
The characteristics of individually melting salts and their mixtures have been
studied extensively,l,43,44-55

3.1 Phosphates
Two types of phosphates are used: (i) Monophosphates (orthophosphates), e.g. NaH2P04, Na2HP04 and Na3P04 and (ii) condensed polyphosphates: (a) poly-phosphates, (b) metaphosphates - rings, e.g. Na3P30 9 and Na4P40 12 and (c) condensed phosphates - rings with chains and branches.
The ability to sequester calcium is closely related to the ability to solubilize protein. According to von der Heide,56 the solubilization of fat-free rennet casein was 30% with orthophosphate, 45% with pyrophosphate and 85% with polyphosphate. Similar findings were made by DaclinY The concentration of soluble nitrogen increased with the concentration of polyphosphates added in the range of 1_3%.58 Hydrolysis of polyphosphates to orthophosphates in processed cheese was evident after cooling. The calcium-sequestering ability of
sodium meta phosphate is markedly lower than that of sodium tetrametaphosphate; a smooth homogeneous processed cheese is obtained with the latter salt. 59,60 Differences in depolymerization of casein and changes in the flow properties of processed cheese are related to differences in calcium complexation between mono- and tetrapolyphosphates.
Melting rate, ultrafiltratable calcium concentration and textural properties (stress/relaxation, hardness, gumminess and elasticity) of processed cheese are affected more by varying the condensed phosphate than the polyphosphate concentrations,62
Sharpf 63 suggested that the emulsifying effect of chain phosphates
is associated with their interaction with paracasein in such a way that phosphate
anions form bridges between protein molecules.
Newly developed phosphate/polyphosphate emulsifying agents, KSS-4 (pH =
4) and KSS-11 (pH = 11), were examined in four processed cheese plants; all the
processed cheese blocks obtained, including smoked, were of excellent physicochemical,
microbial and organoleptic quality.55 Processed cheese of good quality
can be produced using 1 % of surface-active mono glyceride preparation in combination
with 50% of the usual amount of phosphate.64 A processed cheese with
improved rheological properties and storage stability can be produced using an
emulsifier consisting of tripolyphosphate and monoglycerides.65 Addition of
monoglycerides to the cheese blend increases the hydrophilic properties of the
cheese immediately after processing, as well as during storage.66
All condensed polyphosphates hydrolyse in aqueous solutions; hydrolysis also
occurs during melting and afterwards. The degradation of polyphosphates increases
with the duration of processing, irrespective of the rate of stirring and
the temperature usedY About 50% of the polyphosphates added are hydrolysed
during the melting procedure and the remainder is hydrolysed after 7 to 10
weeks of storage.68 The hydrolysis of phosphates and polyphosphates in 1 %
solution, as influenced by temperature, is shown graphically in a recently published
book.

3.2 Citrates
Of the many citrates available, only trisodium citrate, alone or in combination
with other salts, is used as an emulsifying agent in processed cheese production,
although citric acid may be used to correct the pH of the cheese. Potassium
citrate imparts a bitter taste to the finished product. Monosodium citrate is reported2
to cause emulsion breakdown during cheese melting because of its high
acidity, while disodium citrate leads to water separation during solidification of
the melt, also because of high acidity. Comparison of the effects of sodium
citrate, sodium citro-phosphate and sodium potassium tartrate on chemical
changes in processed cheese showed35 that the highest and the lowest acidity
were obtained with citro-phosphate and tartrate, respectively. Soluble nitrogen
was higher in all three processed cheeses than in the initial natural cheese and
was highest when Na citrate was used as emulsifier.
Trisodium citrate and NaH2P04 have similar effects on cheese consistency and
yield softer cheeses than several polyphosphates; the effect of the latter on cheese
firmness increases with the degree of phosphate condensation.69 The effect of
citrate, orthophosphate, pyrophosphate, tripolyphosphate and Graham's salt
[(NaP03)n.HP] on the physicochemical properties of processed cheese were examined
by Kairyukshtene et af.34 The pH values of 3% solutions of these salts
were 8·16, 8·89, 6·61, 9·31 and 5-49, respectively. Soluble protein contents in
processed cheese were increased and the water-binding capacity and plasticity of
the cheese blends during processing were markedly improved by the use of alkaline
salts. The finest fat dispersions were obtained with citrate, tripolyphosphate
or orthophosphate in the processing of fresh curds or green cheese and by using
citrate or Graham's salt with well-ripened cheese.
Addition of citrate, orthophosphate, pyrophosphate or sodium potassium tartrate,
all at 3%, to curds obtained from concentrated milk led to products with
poor sensory attributes, although citrate at 2% gave satisfactory results.36

3.3 Salt Combinations
As already mentioned, salt mixtures are used to combine the best effects of their
individual components.43,45-47,49-53,55 Some early results49.5' seem to favour citrate
in melting salt combinations, but more recent studies emphasize the desirable
effects of phosphates.
According to Shubin,49 a combination of sodium citrate, trihydroxyglutarate
and Na2HP04 gave the best results in the manufacture of processed cheese. Earlier
work5' showed that orthophosphates and pyrophosphates were generally unsatisfactory,
whether used alone or in a combination, but citrate was useful to a
limited extent; polyphosphates were satisfactory in every respect.
Thomas et al.52 produced processed cheeses with a 3% addition of disodium
phosphate, tetrasodium diphosphate, pentasodium triphosphate or trisodium citrate
or equal quantities of sodium polyphosphate and tetrasodium phosphate.
The general acceptability of all cheeses was about the same, but cheeses made
with disodium phosphate, tetrasodium diphosphate or pentasodium triphosphate
had elevated contents of water-soluble nitrogen compared to other
cheeses. When the melting salts were used at 2 or 4%, no differences were detected
in the levels of water-soluble nitrogen in any of the processed cheeses or
in their stickiness, crumbliness, sliceability or general acceptability.
In general, polyphosphates yield processed cheese with superior structure
and better keeping quality than other emulsifying agents,45 apparently due to
their ability to solubilize calcium paracaseinate because of their high calciumsequestering
capacity. Pyrophosphates and, in particular, orthophosphates contribute
undesirable sensory attributes to processed cheese and although citrates
are as efficient as emulsifiers as polyphosphates, they lack their bacteriostatic
effect.
Sood & Kosikowski53 investigated the possibility of replacing cheese solids
with untreated or enzyme-modified skim milk retentates in the manufacture of
processed Cheddar cheese. Casein in the retentates was largely insoluble and
therefore the retentates cannot be used alone for processing. However, cheese
containing up to 60% of retentate solids (treated with fungal protease and lipase
preparations) had better sensory attributes than the reference cheese; a combination
of sodium citrate (2·7%) and citric acid (0·3%) was the best emulsifier for
retentate-containing cheese. Increasing the retentate content to 80% resulted in
an unacceptable product with a hard, long-grained texture.

 


Effects of heating/shearing cheese (protein)

Heating (to temperatures applied to processed cheese manufacture) and shearing of natural
cheese usually results in the formation of a heterogeneous, gummy, pudding-like mass that
undergoes extensive oiling-off and moisture exudation during manufacture and on cooling.
These defects arise from the following.
• Further dehydration/aggregation and shrinkage of the para-casein/casein matrix as
affected by (a) increased hydrophobic interactions as induced by the relatively low pH
of cheese (for most cheeses, ∼4.6–5.6) and high temperature applied during processing,
(b) the precipitation of soluble (serum) calcium and phosphate, leading to further
calcium/phosphate-mediated interactions between the para-casein molecules (especially
in rennet-curd cheeses), and (c) the consequential decline in pH and negative charge.
• Destabilisation of the native milk fat emulsion, formation of non-globular fat, and lique
faction and coalescence of the latter, due to physical damage to, and removal of, the
NMFGM.
• The absence of an active emulsifying agent to re-emulsify the free fat.
The above effects may be considered as a more extreme form of the shearing/heating
applied to the curd during the manufacture of ‘pasta-filata’ cheeses where the heating
conditions (e.g. heating at 57–60◦C while kneading/stretching with screw type augers
or baffles) of the curd at the desired pH (5.3–5.8, depending on the calcium-to-casein
ratio) are applied to provide a controlled aggregation of the curd protein to form fibres
and limited coalescence of fat to impart the desired stringiness and free oil when the
finished cheese (e.g. Mozzarella, pizza cheese, string cheese) is subsequently cooked on
pizza (Guinee, 2003; Kindstedt et al., 2004). Indeed, the effect of heating as a means of
providing controlled protein destabilisation and moisture expulsion are exploited in several
areas of dairy product/ingredient manufacture (e.g. protein recovery from milk in the form
of casein powders, moisture regulation in cheese), while shearing of native fat globules is
the basis of fat recovery from cream as butter or anhydrous butteroil.