R.A. Lawrie

Protein hydrolysates from meat industry by-products

Hydrolysates were prepared from bovine lung, bovine rumen and from partially defatted tissue by treatment at 50°C with either pepsin at pH 3·0, papain at pH 5·5, neutrase at pH 7·0 or alcalase at pH 8·5. For all substrates papain was the most effective hydrolysing agent of those studied whilst neutrase was the least effective. Yields of soluble hydrolysate were high with 45-85 % of the protein being solubilised. In addition, the tissue is, to some extent, defatted during hydrolysis. All enzymes, with the exception of alcalase, readily solubilised the collagen of heated by-products although undenatured (unheated) collagen was, to some extent, resistant to enzymic digestion. Amino acid analysis of the soluble hydrolysates indicated that there was no major loss of any amino acid following prolonged enzymic hydrolysis. In addition, no increase in tyramine concentration occurred during hydrolysis.

Post-mortem electrical stimulation and high temperature ageing of hot-deboned beef

The effects of electrical stimulation (80-100 V, 15 pps) of hot-deboned, bovine Longissimus dorsi muscles, followed by ageing at 30° or 40°Cfor 5, 7 or 10 h, on the solubility of sarcoplasmic and myofibrillar proteins, soluble non-protein nitrogen, and on the water-holding capacity, colour, tenderness and microbiological status of the meat, was assessed. Comparisons were made with the same traits measured on non-stimulated controls (average muscle temperature, 5°C), which were cold-deboned post rigor, and with hot-deboned, electrically stimulated muscles, subsequently held at 2°C. For each treatment and its corresponding control, six muscles each were studied. Such electrical stimulation produced a typical acceleration of pH fall post mortem and enhanced ageing changes at both 30°C and 40°C. It significantly increased tenderness over non-stimulated, cold-deboned controls. The higher temperature of ageing, however, was significantly associated with adverse colour development, loss of water-holding capacity and increased microbial growth. Electrical stimulation alone would not obviate the need for immediate refrigeration in hot-deboning operations with ambient temperatures of ∼ 40°C.

Effect of lipid-protein interactions on extrusion of offal protein isolates

Lung protein isolates after defatting with carbon tetrachloride, chloroform, dichloromethane, iso-propanol, ethanol and methanol, were extruded with and without admixed soya grits. Extrusion of these isolates showed a clear dependence of the process on the lipid content. Extruded products with better characteristics were obtained by defatting the samples. Progressive removal of lipid, as the polarity of the solvent used increased, however, did not promote a corresponding progressive improvement in the textural quality of the extrudates. Protein-protein interaction was assessed by the primary mechanical parameters, hardness, springiness and cohesiveness. It was maximal at intermediate lipid contents. These broadly corresponded to the range of lipid contents where maximum hydration and affinity towards water occurred. It was concluded that residual lipid is necessary in order to maximize protein-protein interactions during extrusion. The effects of lipid-protein interactions on the texturization of offal protein caused a wide variation in the degree of cross-linking between protein molecules during extrusion. The results showed that hydrophobic and electrostatic interactions can play an important rôle in texture formation during thermoplastic extrusion.

Efficiency of protein extraction and recovery from meat industry by-products

Data concerning the efficiency of protein extraction from meat waste tissues are presented. The tissues investigated were the lungs, stomach and small and large intestines of the ox, sheep and pig. Practically all of the protein, with the exception of connective tissue proteins, was solubilised under optimum extraction conditions both with alkali and anionic detergent. The disadvantages of isoelectric precipitation of alkaline extracted proteins have been investigated in detail using polyacrylamide gel electrophoresis incorporating sodium dodecyl sulphate (SDS). The compositions of the protein isolates from the various tissues studied differed from those of the soluble extracts and supernatants or wheys. However, a component of MW 75,000 daltons was characteristic of the wheys from each tissue. The compositions of both isolates and wheys are discussed in the light of structural and cytoplasmic proteins present in smooth muscle tissues. The usefulness of anionic polysaccharides as a means of whey protein recovery is discussed, together with similar benefits achieved using SDS.

Extrusion studies of mixtures containing certain meat offals: Part 1—Objective properties

A study was made of thermoplastically extruded products prepared from soy grits incorporating varying percentages of offal. Beyond 35% incorporation no satisfactory extrudate could be prepared. A comparison was therefore made of the expansion ratio, density and hydratability of extrudates prepared from mixes containing 20% and 35% of bovine or porcine offal with those containing soy grit alone. The offal sources consisted of untreated or alkali-extracted bovine and porcine lung and bovine tripe (rumen and reticulum) and bovine tripe extracted by sodium dodecyl sulphate (SDS). Under the determined optimum operating conditions, extrudates from all offal/soy mixtures had lower expansion ratios and rehydratability than those from soy grits alone. Nevertheless, mixtures containing 20% or 35% alkali-extracted offal protein expanded more (greatest expansion at 170°C), had lower density and greater hydratability than those containing these proportions of untreated offal or SDS-extracted offal protein. (The latter expanded most between 175-180°C.) Whereas the incorporation of SDS-extracted bovine or porcine lung protein failed to yield textured extrudates, the incorporation of SDS-extracted bovine tripe protein at the 20% level did so. Effects due to source were otherwise small.

Improved methodology for the electrophoretic determination of horse meat in heated foodstuffs

Using linear gradient polyacrylamide gel electrophoresis to separate constituent proteins, horse meat could be clearly distinguished from beef even after heating for 20 min at up to 120°C.

Reactivity of glycerol in intermediate moisture meats.

Non-enzymic browning (NEB) reactions between glycerol and some of the amino acids present in meat have been observed at 38 and 65°C; l-lysine is the most reactive of the amino acids studied and l-cysteine and l-arginine the least. These NEB reactions also occur between glycerol and proteins (gelatin and casein). The reactions are not unique to glycerol as other polyhydric alcohols also form brown pigments with lysine. On prolonged air storage at 65°C glycerol itself undergoes mild oxidation, ultimately yielding a brown solution.

Improved protein recovery from some meat industry by-products

The proportion of protein recoverable from bovine heart, kidney, liver, lung, rumen and spleen by alkaline extraction, followed by reacidification, was found to be related to the temperature of extraction, the recovery of both lung and rumen protein at 60°C being approximately twice that at 0°C. Extraction for more than 2 h gave increases in protein recovery. The increased protein solubility was partly due to increased solubilisation of collagen and to a reduction in the quantity of protein precipitated by acidification. Alkaline extraction of lung and rumen at 60°C resulted in the formation of the dipeptide lysinoalanine (0·39 and 0·49 g/16gN, respectively), with tracev amounts at 20°C and 40°C. The electrophoretic patterns of raw meat industry by-products are discussed in the light of previous findings.

Effect of oxygen and storage temperature on intermediate moisture meat products.

During storage of glycerol desorbed intermediate moisture meats at 38°C it was found that, for both protein crosslinking and loss of haemoprotein character to occur, oxygen must be present. However, collagen degradation, as monitored by the formation of water-soluble hydroxyproline containing fragments, still occurred in the absence of oxygen although the rate of degradation was slower than that observed in aerobically stored samples. The rates of the various deteriorative reactions also varied with storage temperature, there being the expected decrease in rate with temperature for both the crosslinking and haemoprotein breakdown reactions. However, the temperature dependence of the collagen breakdown reaction was apparently more complex as there was no measurable breakdown, even during several months of storage, at temperatures of 17°C and below.

Preparation and storage stability of dried salted mutton

Minced (8 or 18 mm plate) mutton with salt (25%) and sorbate (0·4%) was pressed into cakes about 11 cm in diameter and 3 cm high. The cakes were partially dried in an air oven at 40°C for 48 h to a water activity of about 0·75. The cakes were packed, either in vacuo or in air, and stored at 30 or 2°C for up to 60 days. Objective assessment of quality showed that these dried salted meats can be kept for up to 60 days at 30°C with little loss of textural or nutritional quality although some fading, due to haemoprotein breakdown, occurs. Packaging in vacuum, however, minimises this loss of colour and would be recommended for centralised manufacture prior to distribution in developing, tropical countries.