Butter and Margarine
Structurally, both butter and margarine consist of a continuous fat phase, in which droplets of water and liquid fat as well as small fat crystals are dispersed. The fat in butter is derived from milk, whereas it is usually plant-based in margarine (so margarine is not a true dairy product). However, their texture and usage are so similar, they are considered together.
The key texture characteristics of these products are firmness, spreadability and smoothness. Firmness and spreadability are influenced by the solid to liquid fat ratio, which is influenced by the product’s temperature. This ratio can be varied over a fairly wide range in margarine, but less so in butter. Consequently, margarines are generally more spreadable than butter. Some countries allow manufacturers to lower the solid-to-liquid-fat ratio in butter by the incorporation of vegetable oil.
The plastic character of butter and margarine is the result of a three-dimensional network of fat crystals. Mechanical treatment can be used to soften the product through the destruction of this structure.
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| Imitative test using the TTC Spreadability Rig |
The ability of butter or margarine to be spread by a customer has long been inferred by straightforward penetration tests using cone or cylinder probes, where firmness or hardness may be measured by the force required to obtain a given deformation or by the amount of deformation under a given force. However, spreadability is the ease with which a spread can be applied in a thin, even layer, and the use of a Spreadability Rig is ideal for measuring this property. Although spreadability is also a deformation under an external load, it is a more dynamic property. Measurements of firmness and spreadability are usually highly correlated, but the relationship is rarely perfect and this is partly a function of 'work softening'. Margarine, for instance, 'work softens' more easily than butter when spread onto bread. This makes it more spreadable even when hardness values are initially equal.
Cheese
Cheese is made from milk coagulated with rennin and acid, followed by cutting the curd and pressing out some of the water. Production of soft, unripened cheese such as cottage cheese stops at this point. Most cheeses, however, are ripened by the presence of bacteria (cheddar) or mould (blue cheese) to produce different textures and flavours. The growth of these microbes is controlled by storage temperature and humidity, salt concentration, moisture, and pH. Cheeses represent a wide range of textures, from soft, runny or spreadable to firm, sliceable, hard or grateable. Manufacturers should be aware of the optimum texture in each cheese type,
Unripe soft cheese has a very limited storage life and must be refrigerated. Any textural changes would be immaterial, since microbial spoilage soon makes the product unacceptable. The situation is different with ripened cheeses. Here, the early part of storage (up to several months) involves the ripening process and, thus, brings about desirable changes in texture as well as in flavour.
Structurally, cheese is a protein network containing fat globules and water. The exact nature of the structure is determined by milk composition and concentration, pH, salt level, and ripening conditions, as well as the structure of the curd and enzyme activity. The coarseness of the protein network causes crumbliness, granularity, and firmness in the cheese. It is affected by the structure of the coagulum and the presence of fat. Higher fat levels lead to a softer, more elastic, and smoother cheese. A softer texture is also produced by a higher degree of fat unsaturation. The size of the fat globules and the lipolysis do not appear to have significant effects on cheese texture.
The most noticeable texture changes on ripening involve firmness and fracturability. These parameters decrease with increasing proteolysis, higher fat, and moisture content. At the end of the ripening period, cheese texture is at its best. Depending upon the cheese type, subsequent storage may cause rapid texture deterioration (as with soft cheeses, such as Brie), a slow change (as with semisoft cheeses, such as Muenster), or essentially no change (as with hard cheeses, such as Parmesan). Soft cheeses may undergo additional softening, or may become firmer, chewier, and less spreadable due to further proteolytic changes and/or moisture loss. The texture of semisoft cheeses usually deteriorates because of desiccation in refrigerated storage. When poorly protected from moisture loss, these cheeses may become very firm, crumbly, and chewy.
Measuring the firmness, hardness and brittleness of a cheese is also essential in order to assess its crumbliness, springiness and elasticity, and to make sure that a product maintains a consistent texture and structure from batch to batch.
Fracture Wedges provide these measurements by measuring the force required to fracture a sample. One upper and one lower wedge, each with a cutting angle of 30°, is connected to the load cell and the base of a TA.XTplus Texture Analyser respectively. The wedges cut together and the force to fracture gives a measurable indication of the cheese’s composition and strength. For manufacturers, this is a tangible means of quality assurance and can highlight any variations in the finished product.
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| Various methods for testing cheese |
The Cheese Grating Rig accurately measures the force needed to grate cheese into shreds. This can be used by dairies to scientifically, objectively and repeatedly measure shreddability, enabling them to perfect their cheese recipes and production and packaging processes.
It is used in conjunction with the TA.XTplus Texture Analyser and comprises a grating platform consisting of interchangeable grating faces and a sample block holder that acts as a sample template and, during the test, holds the sample in place. The Texture Analyser is used in a horizontal position to ensure a constant application of force onto the sample. This configuration also means that samples can be tested repeatedly over several cycles without the need for reloading. Similarly, the location of a weight above the sample allows the cheese to maintain constant contact with the grating platform face for a consistent measurement. The rig is adaptable, with the provision of two types of grating face and a mandoline blade for the measurement of sliceability. This ensures realistic testing conditions and provides valuable information about the quality and performance of the cheese as well as how it is best processed.
Testing with cylinder or cone probes on samples larger than the probe itself is believed to give a good indication of cheese maturity. This is a method currently used in a major Camembert producer in France as an online quality control procedure. A small distance penetration test of uniform products using a Spherical Probe can measure the surface hardness, as well as the ripeness, of a cheese. In addition, by measuring the force required to puncture the surface of a cheese by penetrating to a greater distance, comparisons can be made between its inner and outer firmness. However, an increasing number of cheeses contain particulates, including fruit and other inclusions. Testing diverse elements within one product is not only tricky but often results in low reproducability and misleading data. It may show wide variances between maximum and minimum force resistance, depending on whether the probe reaches a piece of fruit or cheese first.
Ice cream
Ice cream is essentially a frozen foam, the cell walls of which are made up of milk proteins, soluble solids, fat globules, and ice crystals. It is made by simultaneously whipping and freezing a fat-in-water emulsion stabilised by milk proteins, nonionic emulsifiers, and stabilisers (usually vegetable hydrocolloids). It is then kept for at least 12 h at low temperature (about –25°C) to harden. The product contains about 50% air and about 10–20% fat depending on the type. Ice milk, which is similar to ice cream in structure, texture, and usage (but less creamy and “rich”), contains 1–6% fat.
The structure of ice cream is created during the freezing and aeration process, which causes partial destabilisation (flocculation) of fat globules. A small initial fat globule size is desirable. The membrane around the fat globule is formed by milk proteins, which influence fat coalescence. The texture of ice cream depends largely on the resistance of air cells to deformation, a property governed by the strength of the lamella, which in turn is affected by ice crystal size. The mechanical and mouthfeel characteristics play a paramount role in consumer acceptance of ice cream. It is particularly valued for its pleasing smoothness and meltdown.
Fluctuating and high storage temperatures, such as those encountered in household refrigerator freezer compartments, cause textural degradation in ice cream. The defects are accentuated in poorer ice cream grades and minimised in better quality mixes and stabilisers. Traditionally, better quality ice creams contain higher fat levels. Responding to consumer demands for low-fat products, the food industry has produced excellent quality low-fat ice creams by careful selection of stabilising hydrocolloids.
The following defects are recognised as storage-prompted in ice cream:
- Coarseness - presence of large/non-uniform ice crystals
- Butteriness - clumping of destabilised fat globules
- Sandiness - presence of large insoluble lactose crystals
- Crumbliness - poor protein hydration due to moisture loss and other factors
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| Testing Ice Cream using a Wire Cutter and Ice Cream Scoop |
A simple wire cutting test will demonstrate the firmness and consistency of block ice cream. Attached to the TA.XTplus Texture Analyser, the Stable Micro Systems Wire Cutter incorporates a standard 0.3mm diameter wire, and assesses the force required to cut through a 500g block of ice cream or similar self-supporting block-form sample. It can be used to measure the firmness of butter, ice cream or margarine and the consistency of cheese by measuring the force to drive the wire through the sample.
An alternative measurement is by the use of the Ice Cream Scoop. This is used to measure the scooping resistance of ice cream, and other similar samples which can be formed into a self-supporting block. The force is measured as a response to the scraping action of the scoop and used as an indicator of the ease with which a consumer might remove an ice cream portion from the sample mass.
Milk powder
Dried milk usually contains 3–4% moisture and 38% (whole milk) or 50% (skim milk) lactose, which exists in a glassy form. When its equilibrium relative humidity is exceeded on storage by the relative humidity of the surrounding atmosphere, milk powder will absorb moisture and become sticky. Adherence of the particles to one another will lead to caking. Solid lumps will form when the moisture content reaches about 9%, causing crystallisation of lactose.
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| The Powder Flow Analyser on the TA.XTplusC Texture Analyser |
It helps manufacturers to avoid typical problems such as batch and source variation of ingredients, caking during storage, bridging in hoppers and sticking during production. The Powder Flow Analyser is supplied with library tests so operators can start testing quickly and conveniently after straightforward installation and calibration. Users can, however, fully program the instrument to carry out slicing, shearing, compressing, compacting and aerating cycles in any combination.
The Powder Caking and Consolidation Rig, designed for location on a Powder Flow Analyser, allows the assessment of the sample’s caking behaviour after consolidation. The tendency of a powder to cake can give important data about the properties of the powder after storage and transportation. The formation of strong cakes may lead to issues with discharge of powders from storage hoppers or silos and may also impact on customer perception of products – as it could appear that the product is less voluminous than stated.
The sample is prepared by filling a static consolidation tube to a chosen volume or weight. A 2kg compactor is introduced into the tube and allowed to rest on the powder column under controlled environmental conditions for a given period of time after which the sample is tested using a special PFA blade. The area under the curve in the mid-section of the graph is taken as the work to break the cake. The greater this value, the stronger the cake.
Texture Analysis is an advantageous step in the quality control process of any dairy manufacturer, enabling quick and easy measurements of the most important quality parameters in any given product, and reducing the capacity for human error.
Reference: Food Storage Stability, Chapter 8 “Effect of storage on texture” – Alina S. Szczesniak
There is a Texture Analysis test for virtually any physical property. Contact Stable Micro Systems today to learn more about our full range of solutions.
For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.
The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.No-one understands texture analysis like we do!
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