T P Guinee

The functionality of cheese may be defined simply as a composite of properties of the unheated and/or heated cheese that affect its eating quality and/or its behaviour when used as an ingredient in assembled (e.g. pizza) or formulated foods (e.g. cheese sauce) [187]. The term functionality is usually retained for physical- and rheological-type properties that are dependent inter alia on cheese composition, microstructure, degrees of protein degradation and hydration. While cheese flavour and aroma of the unheated and heated cheeses are major quality determinants in most applications of cheese, they are not normally described as functional properties, and for this reason are also not included here. The various functional attributes of the unheated and heated cheese are listed in Table 1. Depending on the application in which the cheese is used, one or more are required.

Homogenisation of milk [31] reduces the fat-globule size and replaces the native phospolipid-protein membrane with a membrane consisting of mainly of

Table 1 Functional requirements of unheated cheeses

Functional Description requirements

Application Required rheological characteristics*

Shreddability Ability to cut cleanly into long thin strips with low susceptibility to fracture sticking/matting or clumping

Sliceability Ability to cut cleanly into thin slices, with low tendency to fracture and ability to bend before breaking

Grateability Ability to fracture easily into small hard particles that resist matting during shearing, crushing or vibrating

Spreadability Ability to spread easily when subjected to shear stress

Crumbliness Ability to fracture easily into small irregularly shaped pieces when rubbed

Shredded cheese for retail or catering, pizza

Slices for retail and food service ef - high omax - mediumhigh ef - high omax - mediumhigh

Dried cheese of - high for sprinkling ef - low

Cheese for spreading, e.g. on crackers and bread

Tossed salads, crêpes au fromage, soup garnishes

^max - high ef - high of - low Omax - low ef - low of - medium-low omax - medium-low

* Rheological terms relating to large strain deformation using uniaxial compression tests: ef, fracture strain; <rf, fracture stress; o"max, firmness.

Table 2 Functional properties of heated cheese

Types of properties

Description

Level of property required

Cheese types with property

Applications where property is required

Meltability

Ability to soften

High

Most cheeses, apart from low-fat and skim milk cheese

Application: most, if not all, applications

Flowability

Ability to flow or spread

High

Many mature full-fat cheeses such as Cheddar, Gouda, Raclette, Cheshire, Blue

Gratins, cordon bleu products

(plastic-type consistency)

Most young full-fat hard/semi-hard cheeses, Mozzarella, half-fat Cheddar

Many culinary dishes, such as toasted sandwiches and pizza

Flow resistance

Ability of cheese to resist flow and retain original dimensions on heating

Medium-high

Acid-heat coagulated cheese such as Paneer; rennet-curd cheeses made from high-heat treated milk or homogenised milk, some processed and imitation cheeses

Fried cheese, deep-fried cheese sticks, cheese for kebabs, cheese insets in burgers, cheese pieces in casseroles

Stretchability

Ability to form strings and/or sheets when extended

Medium-high Low

Mozzarella, Halloumi, Provolone, Kashkaval

Most cheeses apart from Mozzarella and related stretched curd cheeses

Pizza

Most applications, especially gratins, cordon bleu applications

Oiling-off

Ability to exude some free oil and create surface sheen on melted cheese

Low-moderate (with surface sheen)

Most rennet curd varieties

Most applications, ranging from moderate for gratins to low for omelettes and pizza

Low-very low

Some processed and imitation cheeses, low-fat cheeses, cheeses made from homogenised milks

Flow-resistant applications such as fried cheese

casein. It affects the functionality of both the heated and unheated cheeses. It generally reduces the stress required to fracture (o-f), firmness or hardness (cmax force required to compress the cheese to a percentage of the original thickness) and springiness (recovery in height of a cheese sample following compression) of the unheated cheese. These changes usually coincide with a higher moisture level and lower protein content of homogenised-milk cheeses. However, the magnitude of the changes depends on homogenisation pressure, milk composition (e.g. protein-to-fat ratio), cheese type and composition (moisture, pH, calcium level, fat content). Consequently, inter-study discrepancy vis-à-vis the effect of milk homogenisation on the functionality of unheated cheese is evident in the published literature.

The effects of homogenisation of cheesemilk on the functionality of the heated cheese include reductions in free oil, flowability and stretchability; the cheese becomes more flow-resistant, which may be advantageous in certain applications such as fried cheese (Table 2). These effects are due to the concomitant reductions in the degree of fat coalescence in the unheated and heated cheese and consequently the decrease in the level of free oil released on baking. The casein membrane of the newly formed fat globule in homogenised milk cheese is much more stable to shear and heat than the native fat globule membrane in cheeses made from non-homogenised milk, and thereby reduces the level of free oil formed on heating/baking the cheese. Normally, free oil released during heating of cheeses from non-homogenised milk lubricates casein surfaces and facilitates the movement of adjoining casein layers of the cheese matrix. Consequently, functional properties of heated cheese, such as flow and stretch, that rely on displacement of adjacent layers of the casein matrix are markedly impaired by homogenisation of the cheesemilk.

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