food group (meat panel) water in meat and meat products
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J . Sci. Food Agric. 1983,34,1018-1022
Food Group (Meat Panel) Symposium Water in Meat and Meat Products The following are summaries ofpaperspresented at a symposium organised by the Meat Panel of the Food Group. It was held at the Society of Chemical Industry, 14 Belgrave Square, London, S WI X 8PS on 20 October, 1982. The papers published here are entirely the responsibility of the authors and do not reject the views of the Editorial Board of the Journal of the Science of Food and Agriculture.
The Water Content of Meat Products and Legislative Aspects of its Control
Roland S. Hannan and Kenneth C. Crook
Meat and Livestock Commission, Bletchley, Beds, and Unigate Meat Holdings Ltd, Trowbridge, Wilts.
With meat products made from small pieces of meat there are relatively few problems in establish- ing how much water is present in excess of that contributed by the meat component. With products, such as bacon and ham, made from large pieces there are difficulties due to non uniformity of meat composition and variability of manufacture.
The content of added water in the latter products can be assessed by following changes in weight during manufacture or by retrospective chemical analysis. The British analyst assumes that the nitrogen content of average fat-free meat is known and can be used as a basis for estimating meat content and hence, by difference, the content of added curing brine. Data in the literature, however, show that nitrogen content can vary from carcass to carcass and from one part of a carcass to another and with pork legs, for example, there is a potential variation of k 10 %. A review of recent studies shows that the general position is unchanged. Lean meat has also been shown to contain relatively more nitrogen on a fat-free basis than adipose tissue and modern lean products will show lower apparent meat content by analysis, quite apart from their greater uptake of curing brine.
Collaborative production tests with bacon and ham have been carried out in attempts to assess what degree of variation can be expected in practice. Apparent Meat Content by analysis for in- dividual production batches showed marked variation with a difference of at least 10% between extreme values, The mean level also varied widely between one type of ham and another and be- tween different parts of Wiltshire Bacon sides.
Any legislation designed to define standards for the added water content of whole meat products must take these factors into account, particularly if every sample must comply.
A Unifying Hypothesis for the Mechanism of Changes in the Water-holding Capacity of Meat
Gerald Offer and John Trinick
Muscle Biology Division, ARC Meat Research Institute, Langford, Bristol BS18 70 Y
Despite considerable research (reviewed by Hamm1r2 and Ranken3 water-holding in meat has been rather poorly understood and it has not been explained at all in structural terms. We present a unifying hypothesis for this phenomenon: gains or losses of water in meat are due simply to swelling or shrinking of the myofibrils caused by expansion or shrinking of the filament lattice.
Myofibrils have been observed by phase contrast microscopy and are seen to swell quickly to about twice their original volume in salt solutions resembling those used in meat processing.
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Such swelling is highly co-operative. Pyrophosphate reduces very substantially the sodium chloride concentration required for maximum swelling. In the absence of pyrophosphate, swelling is accom- panied by extraction of the middle of the A-band; in its presence the A-band is completely ex- tracted beginning from its ends.
We suppose that the swelling force is electrostatic repulsion (Rome4, Elliott5) but that expansion of the filament lattice does not occur until, at a critical salt concentration, one or more of the transverse structural constraints within the lattice are ruptured. Such constraints could be cross- bridges, the M-line or the Z-line.
When muscle fibres are heated to - 60C they shrink very substantially in diameter. This could be due to shrinkage of the connective tissue surrounding the fibres (Sims and Baileye). Alternatively the fibres themselves may be actively shrinking. In experiments on isolated myofibrils, which contain no connective tissue, we observed substantial shrinkage on heating. It therefore appears that active shrinking of myofibrils contributes in a major way to cooking losses.
It is known that the filament lattice shrinks when relaxed fibres enter the rigor state; the losses occurring as drip can therefore also be explained in terms of myofibrillar shrinkage. It seems likely that the enhanced drip occurring in the PSE condition is due to further shrinkage of the lattice as a result of myosin denaturation.
Changes in the myofibrillar volume would be expected to cause changes in light scattering. This leads to a simple hypothesis explaining the relationship between water holding and light scattering (Hamml): in normal meat the myofibrils are more refractile than the sarcoplasm, in PSE meat they are much more refractile because they have shrunk more, in DFD meat the re- fractive index of the sarcoplasm and myofibrils are more nearly matched because the myofibrils have shrunk less.
References 1. 2.
Hamm, R. Biochemistry of meat hydration Adv. Food Res. 1960 10, 355463. Hamm, R. Water-holding capacity of meat. In Meat (Cole, D. J. A.; Lawrie, R. A., Eds) Butterworths, London, 1975, pp. 321-327. Ranken, M. D. The water-holding capacity of meat and its control. Chem. Znd. 1976, 1052-1057. Rome, E. Light and X-ray diffraction studies of the filament lattice of glycerol-extracted rabbit psoas muscle. J. Mol. Biol. 1967, 27, 591-602. Elliott, G. Force-balances and stability in hexagonally-packea polyelectrolyte systems. J. Theoref. Biol. 21,
Sims, T. J.; Bailey, A. J. Connective tissue. In Developments in Meat Science Vol. 2 (Lawrie, R. A., Ed.), Applied Science Publishers, Barking, 1981, pp, 29-59.
Stability of Intermediate Moisture Foods
Ian E. Burrows
Pedigree Petfoods, Melton Mowbray, Leicestershire
A wide range of intermediate moisture foods is commercially available and includes dried fruit, jam, cheese, some sausages and certain types of pet food. Their resistance to spoilage can be attri- buted to the water activity (Aw) of the food, and its pH which typically lie within the ranges Aw 0.75-0.85 and pH 4.0-7.0. The major advantage of such foods over dried foods is that they retain many of the organoleptic properties of the original raw materials especially succulence.
Intermediate moisture foods generally rely on the use of humectants to lower the water activity to give protection from bacterial spoilage. Many fungi however can grow at these reduced water activity levels, and must be controlled by the addition of a mycostat.
This is especially true of the modern IMF technology exploited by many pet food manufacturers. The use of humectant combinations, typically salt, sugar and propylene glycol, with potassium sorbate as mycostat, has enabled manufacturers to produce a range of preserved meat products. Typically these products are intended to have an indefinite shelf life, and are usually packaged in gas tight pouches, thus preventing changes in water activity.
1020 Food Group Symposium
In practical manufacturing terms it is important to ensure that the products are not only formu- lated with the correct quantities of humectants, but actually possess them. A technique has been derived which has resulted in a simple linear relationship between the preservative parameters, viz. humectant and mycostat concentrations, Aw and pH. This relationship can then be used both in a predictive or a control situation, in order either to predict, or to ensure, the microbiological stability of a given product.
The Effect of Freezing Rate on the Drip Loss from Frozen Beef
Chandra Nair and Stephen J. James
Agricultural Research Council, Meat Research Institute, Langford, Bristol BSI8 70 Y
The influence of freezing rate on drip loss has long been a source of controversy. Anon and Calvelo have devised a simple experimental method that can be reproduced, and have thus overcome the problems of varying techniques which made it difficult to compare andlor intepret previous work.
A cylindrical sample of muscle, with its axis parallel to the fibres, was placed in an insulated container with only one end exposed. The sample was frozen from the exposed end and the rate of freezing measured at intervals along the longitudinal axis. After freezing, the cylinder was divided into discs, centred on the measurement points, each having a particular freezing rate. A standard centrifuge technique was used to measure the drip potential of each thawed disc.
Freezing rate was defined as the time taken for the sample to freeze from - 1 to - 7"C, and drip as the difference between the loss from frozen and unfrozen discs of the same muscle. Their results showed that drip loss increased with freezing time and reached a maximum between 17 and 19 min reducing to a constant value at times over 24 min.
Inherent in the method is the assumption that drip potential along the axis of the unfrozen sample is constant. However, our initial experiments revealed wide variations in drip loss along unfrozen samples, while the final results showed no obvious relationship between drip and freezing time, and no peak value. There was considerable scatter in the drip losses obtained at any one freezing time, which was not reduced by subtracting the drip loss from unfrozen samples.
Our results indicate that any effect of