food group meat panel annual discussion meeting, 1985

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J. Sci. Food Agric. 1985,36,1334-1340 Food Group Meat Panel Annual Discussion Meeting, 1985 The following are summaries of papers presented at the Annual Discussion Meeting of the Meat Panel of the SCI Food Group. It was held at the Society of Chemical Industry, 1415 Belgrave Square, London SWlX 8PS on 6 March 1985. The papers published here are entirely the responsibility of the authors and do not reflect the views of the Editorial Board of the Journal of the Science of Food and Agriculture. The Interactions of Proteins in Meat Products Malcolm K. Knight Food Research Association, Leatherhead, Surrey KT22 7RY Many characteristics of meat products are controlled by the gelling and emulsifying properties of meat proteins. For example, the meat binding properties of exudates, produced during massaging or tumblin meat with brine, are thought to be directly associated with the heat-induced gelation of myosin.E2 One objective of this investigation is to determine the effects of protein interactions on the properties of meat gels. Initially the information available concerning the measurement of meat protein gel properties has been reviewed. Frequent mention is made in the literature of the functional properties of myosin in meat products,334 but little information is available about the gelation of myosin and its interactions with other meat protein^.^,^.^^^ Various methods may be employed to measure the rigidity or firmness of meat protein gels’ and these will be listed and their relative merits discussed. The structures of gels containing mixtures of myosin and sarcoplasmic (or water soluble) proteins, sodium chloride and sodium pyrophosphate have been examined under the electron microscope. There appears to be a close association between the two protein fractions, where the sarcoplasmic proteins seem to form a coating over the surface of myosin. This observation supports the suggestion of MacFarlane et al. that salt-denatured sarcoplasmic proteins are absorbed onto myosin molecules. It also possibly explains the negative effect on the binding of meat pieces exerted by sarcoplasmic proteins. References 1. 2. 3. 4. 5. 6. 7. 8. 9. Yasui, T.; Ishioroshi, M.; Nakano, H.; Samejima, K. Changes in shear modulus, ultrastructure and spin-spin relaxation times of water associated with heat-induced gelatin of myosin. J. Food Sci. 1979, 44, 1021-11024 & 1211. Ziegler, G. R.; Acton, J. C. Mechanisms of gel formation by proteins of muscle tissue. Fd. Technol. 1984, May, 77-80 & 82. MacFarlane, J. J.; Schmidt, G. R.; Turner, R. H. Binding of meat pieces: a comparison of myosin, actomyosin and sarcoplasmic proteins as binding agents. J. Food Sci. 1977, 42 (Z), 160>1605. Siegel, D. G.; Theno, D. M.; Schmidt, G. R.; Norton, H. W. Meat massaging: the effects of salt, phosphate and massaging on cooking losses, binding strength and exudate composition in sectioned and formed ham. J. FooiSci. 1978, 43 ( l ) , 331-333. Deng, J.; Toledo, R. T.; Lillard, D. A. Effect of temperature and pH on protein-protein interaction in actomyosin solutions. J. Food Sci. 1976,41 (2), 273-277. Ishioroshi, M.; Samejima, K.; Yasui, T. Heat induced gelatin of myosin filaments at a low salt concentration. Agric. Bid. Chem. 47 (12), 2809-2816. Ishioroshi, M.; Samejima, K.; Yasui, T. Heat induced gelatin of myosin: Factors of pH and salt concentrations. J. Food Sci. 44, 1280-1284. Suzuki, T.; MacFarlane, J. J. Modification of the heat-setting characteristics of myosin by pressure treatment. Meat Sci. 11 (4), 263-274. Kerese, I. Methods of Protein Analysis. Ellis Honvood Ltd, Chichester, 1984. 1334

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J . Sci. Food Agric. 1985,36,1334-1340

Food Group Meat Panel Annual Discussion Meeting, 1985

The following are summaries of papers presented at the Annual Discussion Meeting of the Meat Panel of the SCI Food Group. It was held at the Society of Chemical Industry, 1 4 1 5 Belgrave Square, London SWlX 8PS on 6 March 1985. The papers published here are entirely the responsibility of the authors and d o not reflect the views of the Editorial Board of the Journal of the Science of Food and Agriculture.

The Interactions of Proteins in Meat Products

Malcolm K. Knight

Food Research Association, Leatherhead, Surrey KT22 7RY

Many characteristics of meat products are controlled by the gelling and emulsifying properties of meat proteins. For example, the meat binding properties of exudates, produced during massaging or tumblin meat with brine, are thought to be directly associated with the heat-induced gelation of myosin.E2 One objective of this investigation is to determine the effects of protein interactions on the properties of meat gels. Initially the information available concerning the measurement of meat protein gel properties has been reviewed.

Frequent mention is made in the literature of the functional properties of myosin in meat products,334 but little information is available about the gelation of myosin and its interactions with other meat protein^.^,^.^^^ Various methods may be employed to measure the rigidity or firmness of meat protein gels’ and these will be listed and their relative merits discussed.

The structures of gels containing mixtures of myosin and sarcoplasmic (or water soluble) proteins, sodium chloride and sodium pyrophosphate have been examined under the electron microscope. There appears to be a close association between the two protein fractions, where the sarcoplasmic proteins seem to form a coating over the surface of myosin. This observation supports the suggestion of MacFarlane et al. that salt-denatured sarcoplasmic proteins are absorbed onto myosin molecules. It also possibly explains the negative effect on the binding of meat pieces exerted by sarcoplasmic proteins.

References 1.

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Yasui, T.; Ishioroshi, M.; Nakano, H.; Samejima, K. Changes in shear modulus, ultrastructure and spin-spin relaxation times of water associated with heat-induced gelatin of myosin. J. Food Sci. 1979, 44, 1021-11024 & 1211. Ziegler, G. R.; Acton, J. C. Mechanisms of gel formation by proteins of muscle tissue. Fd. Technol. 1984, May, 77-80 & 82. MacFarlane, J. J.; Schmidt, G. R.; Turner, R. H. Binding of meat pieces: a comparison of myosin, actomyosin and sarcoplasmic proteins as binding agents. J . Food Sci. 1977, 42 (Z), 160>1605. Siegel, D. G.; Theno, D. M.; Schmidt, G. R.; Norton, H. W. Meat massaging: the effects of salt, phosphate and massaging on cooking losses, binding strength and exudate composition in sectioned and formed ham. J . FooiSci. 1978, 43 (l), 331-333. Deng, J.; Toledo, R. T.; Lillard, D. A. Effect of temperature and pH on protein-protein interaction in actomyosin solutions. J . Food Sci. 1976,41 (2), 273-277. Ishioroshi, M.; Samejima, K.; Yasui, T. Heat induced gelatin of myosin filaments at a low salt concentration. Agric. Bid . Chem. 47 (12), 2809-2816. Ishioroshi, M.; Samejima, K.; Yasui, T. Heat induced gelatin of myosin: Factors of pH and salt concentrations. J . Food Sci. 44, 1280-1284. Suzuki, T.; MacFarlane, J. J. Modification of the heat-setting characteristics of myosin by pressure treatment. Meat Sci. 11 (4), 263-274. Kerese, I. Methods of Protein Analysis. Ellis Honvood Ltd, Chichester, 1984.

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Annual Discussion Meeting 1335

The Future of the Stubbs and More Procedure

N. M. Griffiths

Meat and Livestock Commission

With the increasing complexity of meat and meat products there appears to be increasing problems associated with the analysis of meat products for compliance with the legislation with which they are governed. This is particularly true with reference to the main method that has been used since 1919, the Stubbs and More procedure.

The Stubbs and More method, with minor modifications, has been used to estimate the apparent meat content of meat products for over 50 years. The method is based on the estimation of lean meat from total nitrogen content, corrections being applied for the contributions from any cereal filler or other nitrogeneous material present.

The Analytical Methods Committee of the Society of Analytical Chemistry in the early 1960s recommended factors for conversion of nitrogen content of various species into the equivalent raw fat free meat contents. There are no agreed factors for conversion of nitrogen into cooked, cured or processed meat. The meat content of such products may be expressed in terms of ‘raw meat equivalent’. The typical calculation using the Stubbs and More procedure depends on the determination of water, protein, fat and ash content of the sample. Carbohydrate may be determined directly or by difference.

As anyone can see by studying modern chemical data for the major and minor constituents of different meat cuts, it is clear that considerable variation can occur as meat is a naturally variable product. The factors recommended by the Analytical Methods Committee were the averages to be used for comminuted meat products and were never intended to be used for individual cuts of meat. It is, therefore, clear that this can cause considerable problems when these factors are applied to individual cuts of meat, for example, brine cured joints.

Further problems occur when other nitrogen containing ingredients are present, such as soya, skimmed milk protein, cereal, excess blood, excess connective tissues, etc. All this will contribute to the apparent meat content and, therefore, to arrive at a true meat figure correction must be made to the total nitrogen content for any other nitrogen containing ingredients other than meat. Obviously each of these determinations has errors associated with it which produces errors in the true meat content results.

It seems obvious that a far better approach is to try to determine meat protein directly rather than this indirect approach, but attempts using Enzyme-Linked Immunosorbent Assay’ procedure and 3-methylhystidine methodology although appearing promising have problems associated with them which require further research before a replacement for the Stubbs and More procedure can be found.

In conclusion, it is important that industry and enforcement authorities alike take due account of the variation and applicability of this technique when applied to modern day meat products and that research must be encouraged to find a replacement for what is fast becoming an outdated technique.

Reference 1. Griffiths, N. M.; Billington, M. J. Evaluation of an enzyme-linked immunosorbent assay for beef blood serum to

determine indirectly the apparent beef content of beef joints and model mixtures. J. Sci. Food Agric. 1984, 35, 909-914.

Resolution of Rigor

Eric Dransfield

AFRC, Food Research Institute-Bristol, Langford, Bristol BS18 7DY

Conditioning, originally called ‘resolution of rigor’, is an important means of enhancing tenderness and reducing variability in beef quality. Storage of raw meat above its freezing point

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causes an increase in tenderness in proportion to the logarithm of the length of storage. Variations in the rate of tenderisation between species has led to recommended storage times and temperatures for the production of tender meat.

Several proteolytic enzymes have been isolated from raw meat but their relative importance to structural weakening in post rigor meat has not been determined. This paper characterises the weakening processes in raw meat which initiate tenderising in cooked meat.

The mechanical technique chosen was, in principle, that of a creep test, i.e. the increase in length in the direction of muscle fibres is measured whilst the stress is maintained at a predetermined level. In practice, a cyclic application and removal of stress was used since this would also allow rigor development to be monitored and controlled so that its importance to conditioning could be investigated. Suspended in liquid paraffin at 15"C, pre-rigor beef M . pectoralis profundus extended 25% when the stress was increased from 0.1 to 1.1 N cm-': this reversible extensibility was maintained for about 15 h from stunning but then declined to about 1.6% at 25 h when the muscle was in rigor.

After rigor, the muscle lengthened irreversibly with little change in extensibility. Lengthening reached a maximum rate of about 4.3mmh-' at about 20h post rigor and the length eventually reached about 140% of the rigor length. With increasing temperature, over the range 1 to 25"C, the time taken to reach the maximum rate of lengthening in raw meat decreased in proportion to the increase in rate of tenderising in cooked meat. Lengthening occurred earlier when greater upper stresses were employed. At 0.3N cm-' lengthening occurred 120h after rigor but a stress of 2.1 N cm-' caused lengthening in only 22 h. Extrapolation of the relationship of lengthening to stress, predicted that no lengthening would occur at a stress of 0.07N cm-' or less which is indicative of the strength of the components remaining intact after conditioning. Those structures modified during conditioning are therefore weaker than previously supposed, with strengths much lower than the breaking strength of post-rigor meat as a whole (ca20N cm-').

Longitudinal histological sections, taken after lengthening had occurred, showed regular transverse cracks between the A-bands. The cracks were about 6 sarcomeres (17pm) apart and were occasionally stretched out up to 200 pm wide. The periodic cracking can be modelled using man-made fibre-reinforced composites in which periodic cracking of the fibres is produced by stress-transfer through the fibre matrix interfaces and through the matrix. In meat, therefore, conditioning causes a weakening in the region of the Z-line and stress is transferred through the cytoskeleton and structures surrounding the myofibril to effect tenderisation.

Sintermatic Tenderskin Process

Timothy J . M. Treharne

T. Treharne Ltd, Clays, West Lane, East Grinstead, West Sussex RH19 4HH

The Sintermatic Casing System is a cold process for the manufacture of comminuted proteinaceous products without utilising a supporting membrane or casinglskin to determine and control end product configuration.

The nucleus of the process, as the name denotes, is the utilisation of sintered stainless steel, in the form of moulds.

Sintering-the technique used to produce the moulds-is a solid state reaction joining metallic particles to each other at a temperature below their melting point. Bridges are formed between the particles by defusion resulting in a porous metal through which liquids can pass. The flow rate of the liquids through the sintered metal is totally controllable and is determined by: 1. The particle size of the powdered metal; 2. The process of sintering; 3. The pressure applied to the liquids to be passed through the wall of the sintered moulds.

In the manufacture of meat products, for example sausages, it is acid precipitants which are passed through the sintered moulds.

The precipitant which is a blend of food grade acids, has the ability to react with the soluble protein fraction of meat to form a skin. This reaction which is virtually instantaneous produces a stable skin over the whole surface in less than two seconds.

Annual Discussion Meeting 1337

The total machine process cycle, which is about seven seconds;may’be broken down into six stages having first produced the sausage paste, using conventional methods, and transferred it to the system.

1. The paste is low pressure pumped into portioners. Meat pastes/emulsions are very prone to mechanical damage as well as damage in the form of separation caused by filling/moving meat at high pressure. The Sintermatic process is built around the technique of moving meat at low pressures therefore minimising any damage to the meat paste.

2. The meat is transferred from the portioners into the sintered moulds. During the transfer the soluble protein is drawn to the surface of the paste, orientated and deposited against the wall of the moulds.

3. Precipitants (food grade acids) are passed through the sintered moulds which react with the soluble meat protein and form a skin. Skin strength and thickness may be controlled and altered dependant on the percentage of the acid in the precipitant, contact time of the precipitant and the amount of available protein for coagulation. 4. Ejection from the moulds of the formed product. 5. Neutralisation of the surface by washing with potable water. Acid coagulation is always

progressive, therefore by washing and raising the surface pH the skin depth is controlled. Normally skin thickness is approximately 0.3 mm.

6. Removing free surface water by means of an air knife. The finished product is then ready for freezing or packaging. The skin formed in this manner from the meat itself is very stable. It provides resistance to bite without having the fibrosity and chewyness associated with conventional skins. It has the added advantage of not splitting or shrinking on frying.

The cost of producing a skin in this manner is about 7% of the cost of using a conventional skin. Furthermore the process provides savings on giveaway, labour, inventory etc., as well as lending itself to total automation of packaging and further processing.

Electrical Stimulation and Beef Colour

David A. Ledward, Robert Dickenson, Victor H. Powell and Robin Shorthose

CSIRO Division Food Research, Brisbane, Australia

Electrical stimulation (ES) accelerates post-mortem glycolysis in meat animals so that the muscle pH falls to 6.0 or less within 1 or 2 h of slaughter. Even with efficient chilling the temperature of the subsurface muscles of the carcase will remain high (340°C) during this period. These conditions of high temperature and low pH may modify the initial colour of the meat by modifying the structural characteristics and interactions of the myofibrillar and sarcoplasmic proteins and may also affect the colour stability of the meat by inactivating one or more of the enzyme systems thought to be involved in catalysing the formation of metmyoglobin, or in reducing the metmyoglobin formed during aerobic storage.

On each of 4 weeks half the daily kill of a large retailer (-100 beef animals) were subjected to low voltage ES at a commercial abattoir. Twenty-four hours post-slaughter carcases were chosen, within selected pH ranges, of similar age and fat cover and the muscles sliced and displayed, in retail cabinets working within specification, either 6 days post-slaughter or after ageing for 35 days at 1°C. Colour measurements were made at regular intervals during display.

No significant differences were found in longisimus dorsi muscles from low voltage ES and non-ES carcases but in the slower cooling semimembranosus muscles (topsides) significant differences were observed. In muscles in the pH range 5.5 to 5.7 and displayed 6 days after slaughter the ES samples were significantly paler and more uniform in colour than the non-ES ones (higher Hunter ‘A’ values). During retail display, in air at temperatures in the range 1 to 8”C, all the samples discoloured in such a way that the Hunter ‘a’ values, hues and chromas decreased although the ‘A’ values were not affected. However the changes were far more marked in the ES samples. Results for the muscles displayed 35 days after slaughter indicated that ageing had no effect on the initial colour characteristics. However the changes observed during retail display occurred more rapidly than in the fresher samples with the ES samples again being less stable. Thus the aged non-ES samples had similar colour stabilities to the non-aged ES ones.

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Analysis indicated that the changes in colour observed during retail display were due almost exclusively to the formation of metmyoglobin at the surface of the muscles. Subsidiary experiments suggested that the loss of stability observed on stimulation and ageing was due to a decrease in activity of the metmyoglobin reducing system present in meat.

Experiments carried out on muscles of pH 5.8 to 6.0 suggested that ES caused similar differences to those found in the muscles of lower pH but these differences were not significant. In this higher pH range metmyoglobin accumulation at the surface of the slices was significantly less than in the lower pH muscles for all treatments.

Microbiological and Chemical Changes in Some Comminuted Meat Products

Jeffrey G. Banks

School of Biological Sciences, University of Bath, Bath BA2 7AY, UK

Sulphur IV oxospecies, referred to here as SO2 for convenience, are the most widely used preservatives of uncured, comminuted meat products. Traditionally used in British fresh sausage,' these chemicals now find favour in a variety of novel refrigerated meat products (e.g. 'burgers, meat loaf, etc.) most of which contain additional carbohydrate as an ingredient. Although it is evident that a more effective chill chain has developed between production and consumption of such products and that judicious use of SOz may extend their shelf life, there is a lack of knowledge (cf. the literature concerned with primal cuts of meat) about the microbiological and chemical changes which occur during storage. The present work is set against this limited background of information and had three main objectives. To determine the changes in (a) the amounts of free (active/antimicrobial) and bound (inactive) SO2 (b) the size and composition of the principal microbial contaminants and (c) the concentrations of carbohydrate during chilled storage. Most samples of sulphited meat products were obtained at either the point of manufacture or retail sale.2 Minced beef containin relatively low levels of glucose, on the other hand, was treated with SO2 in the laboratory.' Full experimental details are described e l~ewhere .~ It is evident that the shelf life is dependent largely on the maintenance above a critical threshold of the active SO2 as this retards or prevents growth and activity of the microbial spoilage association. In the majority of products which contained relatively large amounts of carbohydrate, there was a negligible loss of total, but an appreciable diminution in active preservative. At storage temperatures below 10°C binding of free SO2 was negated. Recent studies5 have shown that many of the yeasts present in carbohydrate-rich products produce SO2-binding compounds of which acetaldehyde is of major importance. An agar plate method has been developed (V. Dillon pers comm.) which allows for a differential count between those microorganisms which have the capacity to remove active SO2 from the stored product and those which do not. It is notable that the dominant yeasts and moulds (e.g. Candida lipolytica, C. zeylanoides, Debaryomyces and Geotrichum spp.) isolated from products (e.g. beef and turkey burger and fresh sausage) where appreciable binding was noted all gave a strongly positive reaction with the agar plate method. In contrast, the major yeast contaminants (Cryptococcus albidus and Crypt. laurentii) of lamb burger, a product in which levels of free SOz, were maintained during chilled storage, were negative (i.e. non-binders of free SO2) in the same test. In carbohydrate-rich products SO2 has an elective action and a spoilage association of Gram positive bacteria e.g. Brochothrix thermosphacta, Lactobacillus and Enterococcus spp. and yeasts develops at the expense of Pseudomonas spp. and Enterobacteriaceae. As substrate levels of glucose, maltose and maltotriose are available to the microbial contaminants throughout storage, inadequate chilling and/or a substantial reduction in the level of active SO2 results in an acid drift in the product which leads to souring and spoilage. A different pattern of spoilage occurs in sulphited products which contain relatively low levels of total carbohydrate. Thus due to the high levels of active preservative in the production stage, there is an initial selection of a microbial association similar to that in sausage and 'burgers. With storage, however, there is a rapid loss of both active and total SO2 with the result that Pseudomonas fragi dominates exclusively (>99% of microflora) the spoilage association. With depletion of glucose, gluconate and lactate, ammonia

Annual Discussion Meeting 1339

is produced causing a rise in the pH (mirrored by a fall in the extract release volume) leading to putrid spoilage. Subtle differences in the concentration of low molecular weight materials in sulphited and unsulphited beef mince suggest that in the absence of the preservative, unrestricted growth of Pseudomonas spp. results in a conversion of glucose to gluconate thus denying would-be competitors the preferred carbon and energy source.

References 1. Banks, J. G.; Board, R. G. Sulphite-the elective agent for the microbial association in British fresh sausages. In Food

Microbiology-Advances and Prospects (Roberts, T. A , ; Skinner, F. A,. Eds), Society for Applied Bacteriology Symposium Series No. 11 1983, 369. Banks, J. G. Spoilage Potential of Yeasts and Moulds in Chilled Meat and Dairy Products. MAFF Report 1984, Project No. 178, Spoilage and Shelf life. Nychas, G. J. Microbial growth in minced meat. PhD thesis 1984, University of Bath, UK. Banks, J . G.; Board, R. G.; Nychas, G. J. Sulphite preservation of meat products. In Preservafives in the Food, Pharmaceutical and Environmental Industries. (Allwood, M. C.; Banks, J. G.; Board, R. G., Eds), Society for Applied Bacteriology Technical Series No. 22 1985. In Press. Dalton, H. K. The yeasts and their chemical changes in British fresh sausage. PhD thesis 1984, University of Bath, UK.

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The Development of Opacity in Bacon as a Function of Temperature During Curing

Douglas B. MacDougall, Katharine M. Jenkins and Susan E. Pritchard

AFRC Meat Research Institute, Langford, Bristol BS18 7DY, UK

In the Wiltshire method of manufacturing bacon, most operations are performed at <4”C; the product is bright pink, moderately translucent and somewhat sticky to touch. The ‘sweet cure’

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I I I I I 0.01 0.1 I 10 100 1000

Time ( h 1 Figure 1. Increase in opacity as measured with the MRI Fibre Optic Probe (FOP) for bacon cured with only NaCl and

NaNOz and stored at temperatures between 0 and 60°C.

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method has a heating step during which the product reaches 40 to 60°C giving the bacon a pale, almost cooked, appearance. This study was designed to relate opacity development to temperature and time over the range that might be used in bacon manufacture, to observe what effect polyphosphate has on opacity development, and to investigate the correlation between opacity and protein denaturation.

Pork M. longissirnus dorsi, chilled for 24 h, were cut into 3 mm thick slices and cured by a slice curing technique using a 20% NaCl brine containing 1000 mg kg-' NaN02 either with or without 1.5% pentasodium tripolyphosphate (TTP) and 15OOmg kg-' sodium ascorbate to give a target concentration of 3 4 % NaCl in the bacon. The cured slices were vacuum packed and held in water baths at 0, 10, 20, 30, 40, 45, 50, 55, 60°C for times ranging from 1 h for the 60°C samples to 10 days for those at 0°C.

Colour was measured on a Hunterlab D25-A Tristimulus Colorimeter and opacity by the MRI Fibre Optic Probe (FOP). Protein denaturation was monitored using a Perkin-Elmer DSC-2 C Differential Scanning Calorimeter.

Increase in opacity with time is shown in Figure 1. There was little increase up to 30°C; 0, 10, 20°C samples became slightly more translucent during the first day. At 60°C almost complete development in opacity occurred within the first 10 min, whereas at 50°C it took >10 h. Between 40 and 60°C the reaction rates were found to fit an Arrhenius type plot. From 0°C to between 50 and 60°C there was a 7 fold increase in light scatter. Visual lightness (L) ranged from 35 to a final value of 64 after 1 h at 60"C, that is a 2-fold increase which is of the order expected from the increase in scatter. Inclusion of TPP increased the moisture content of the bacon from 71 to 79%, increased initial translucency and depressed final FOP and L values at all temperatures. Although starting and finishing opacity values were depressed, the reaction rates were similar to bacon made without TPP.

At low temperatures (0 to 30°C) the residual enthalpy of denaturation (AH) showed no indication of decreasing with storage; in fact some increase with time was apparent. By 45"C, AH decreases slowly with time, mirroring the slow increase in opacity; as the temperature of storage was increased so the fall in AH became more rapid until <2 days at 60°C or <1 h at 70°C AH was zero and protein denaturation was complete.

Extent of opacity development was therefore negatively correlated with AH and, by inference, pale appearance is positively correlated with severity of protein denaturation.