Comminution moisture

The performance of protein additives in food products is the ultimate test of functionality (7). Functional performance, particularly moisture absorption, has been used as a criterion for selection of protein additives for food systems. Yet this has for the most part been a trial-and-error situation. The majority of data on water and fat absorption of plant protein additives in food systems has involved the incorporation of such products into comminuted meat systems. In relation to water and fat absorption, meat systems are an excellent test system. 

Generally, the moisture content of coal is determined by measuring the weight loss of a sample (expressed as a percentage of the sample) that has been comminuted to pass through a 250-p.m (60-mesh) sieve (ASTM D-3173 ISO 331 ISO 687). The sample (about 1 g) is maintained under controlled conditions (107 3°C, 225 5°F) in an inert atmosphere for 1 hour. 

Mustafaev et al. (1989) found certain parameters useful in the determination of the quality of fatty oil in coriander fruits. Drying to -16% moisture, grinding in a pirouette mill for 60 s, ageing in a thin layer for 2h for evaporation of volatile oils, comminution in chloroform in a Foss—Lett apparatus, filtration and measurement of acid number and peroxide number are better techniques to be adopted. 

A)Flash Pulverization mills. This process for drying comminuting minerals w as introduced in 1945 by the Institute of Gas Technology. It was found that a wide variety of friable materials could be pulverized by introducing them into a stream of gas at mod pressure, and causing the stream to pass thru a nozde into a zone of lower pressure. When superheated steam was used as the motive fluid, the product was dried to less than 1% moisture content... 

Interestingly, the ball milling studies of microcrystalline cellulose by Nakai (Table 4) have shown that the Wqj values obtained from water sorption studies increase to a much greater extent than the increase in surface area because of comminution of the sample. In fact, as discussed earlier, moisture sorption was... 

Pulverization in this manner, by uniformly comminuting the particles, promotes tlieir equal expansion and the escape of contained moisture, and thus prevents the decrepitation of substances when heated. 

The most dilTicult powder mixtures to repeatedly restructure will have some submicron constituents, will have interlocking or plate-like shapes, will have some moisture present, and will have been subjected to compaction at some stage. To mix such a system the mixer is likely to need high shearing or impaction characteristics and could well be a particle comminuter rather than a conventional mixer . 

In the case of comminuted meat (e.g., burgers), the purpose of analysis is to characterize the main constituents (moisture, protein, fat, ash) and also to determine to what extent it differs from the intact meat. For example, typical analyses applied to comminuted meat samples might include meat species identification and determination of collagen and carbohydrate content. As the meat products move further away from the original entire meat, a range of analyses is used to characterize the food, particularly assays for nonmeat proteins, for additives such as salts, and for preservatives. In the case of cured meat and cured meat products, the important analyses are for salt, nitrite and nitrate, and other additives such as sugars and phosphorus (polyphosphates). 

Equipment used for sample preparation must be dry and clean and may be cooled or chilled. Speedy sample preparation is required to reduce heating and consequent evaporation of water, which would affect the determination of moisture content. Blades must be sharp to achieve consistent and fast comminution. Samples (preferably well chilled or slightly frozen) may be prepared by passing through a meat chopper or mincer multiple (3 x ) times, often using plates of decreasing size where the sample is very large. Often, quite small samples are received for analysis and a bottom-driven bowl cutter may be more appropriate. 

Centrifugal Disc Mill. A horizontal disc within a chamber is rotated at high speed by an electric motor. Clay is fed in near the axis, and comminuted by the centrifugal action of the mill, at constant moisture content. 

Polyolefins in fact lend themselves to this straightforward recycling procedure. Other thermoplastics like polyamides and polyesters need more careful handling because of their sensitivity to moisture absorption and molecular degradation. Thermosets are, by definition, not recyclable in the true sense however by comminuting and recompounding with fresh monomers, most thermoset polymers can in effect be recycled without significant loss of performance. 

The energy required for the comminution, or size reduction, of a material to a certain required fineness (characterized by the specific surface of the product obtained) will depend on the hardness of the material, its compressive strength, its brittleness (or its elasticity or its plasticity), the size and shape of its particles, its temperature and moisture content, and of course also on the nature of the comminuting action exerted by the grinding process employed These factors in combination determine the resistance that the material offers to size reduction and can be regarded as specific of the material. 

Another possibility is to add moisture to make the fine particles stick to the coarse ones, This is a simple measure, and it has been shown [17] that it can reduce segregation considerably. However, one should be aware that both raising (he moisture content, and reducing the particle size by comminution, will cause the cohesiveness of the powder to increase, which could enhance discharge problems. 

The position of organisms within a heated food also profoundly affects their apparent heat resistance. Notermans Kampelmacher, for example, demonstrated that 5. oranienberg became very resistant to temperatures close to 60 °C when attached to broiler chicken skin, whereas unattached cells were inactivated rapidly and exponentially. Hernandez found that S. senftenberg 775W was more resistant in the centre of beef cubes pre-equilibrated to 60 °C than it was in comminuted beef at the same temperature but Blankenship reported that S. typhimurium injected into the centre of dry-roasted beef at 58-64 °C survived better at the surfaces than at the core, possibly reflecting differences in available moisture. 

---