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Byline: Monica Flores (1), M. Concepcion Aristoy (1), F. Toldra (1) Keywords: Key wordsaAminopeptidase; Muscle exopeptidases; Curing agents Abstract: aThe effect of curing agents (salt, nitrite, nitrate, ascorbic acid, glucose and polyphosphates) on the main pure aminopeptidases involved in the release of amino acids during the processing of cured meat products has been studied. Salt strongly inhibited alanyl aminopeptidase and pyroglutamyl aminopeptidase: about 40--50% of their original activities were recovered in the presence of 4--5% salt, the typical concentration in dry-cured meat products, while leucyl aminopeptidase was not affected. However, arginyl aminopeptidase was activated to 2--3 times its control level. Nitrate and nitrite did not affect aminopeptidase activity. Ascorbic acid (500 mg/l) slightly inhibited arginyl, alanyl and pyroglutamyl aminopeptidases whereas glucose (20 g/l) activated (to almost 5 times its control level) leucyl aminopeptidase activity. Polyphosphates inhibited (25%) alanyl and arginyl aminopeptidases. Author Affiliation: (1) Instituto de Agroquimica y Tecnologia de Alimentos (CSIC), Apt. 73, E-46100 Burjassot, Valencia, Spain, ES Article note: Received: 11 February 1997 / Revised version: 25 April 1997

The addition of alkali and alkali-earth halides to cooked comminuted lean pork inhibits lipid oxidation in meat model systems. The fluorides and iodides of alkali metals are antioxidative as they retard the activity of catalytic enzymes and form pairs with non-heme iron ions. The fluorides of alkali-earth metals lack such antioxidant activity due to ion-pairing interactions of fluoride anions with divalent cations. Bromide, chloride and sulfate salts of alkali and alkali-earth metals have a prooxidative effect on lipid oxidation in lean pork.

Electron beam and gamma irradiation of vacuum or air packaged, frozen or chilled boneless pork chops produces a redder and stabler product in terms of rancidity and color. Chops irradiated in vacuum packages have lower oxidative rancidity and higher stability of display color as compared to chops irradiated in aerobic packages. The removal of oxygen by vacuum packaging or freezing at a temperature of -17 degree celsius decreases autoxidation and increases shelf life of the pork chops.

Ground pork treated with carnosine were examined to determine the mechanisms by which carnosine inhibits spoilage and deterioration of texture and color in pork. Electron paramagnetic resonance spectroscopy and lipid oxidation assay revealed that carnosine accelerates the oxidation of myoglobin into its redox states to inhibit lipid oxidation reactions, which are the primary cause of spoilage in foods. However, the basis of this oxidation still needs to be studied.

The scattered light from the myofibrils of the pork has a direct effect on the pH of the pork. The effect is partially reversible after the removal of myoglobin from the pork and affects the overall reflectance of the normal pork. The paleness of the pork is created by this effect. This effect of pH produces a minor contribution to the very high reflectance of severely pale, soft and exudative pork. A computer control technique has been used for the measurement of pH.

The analysis of precooked pork patties at the time of refrigerated storage shows that the preformed Maillard reaction products are effective at reducing lipid oxidation. The result of the TBA test shows that the reaction products have an antioxidant effect of various rates. The lipid oxidation occurs mostly during the first five days of refrigerated storage. The reaction products can be made from natural precursors used in precooked ground meats.

Experimental auction markets were designed and used to investigate consumer preferences for sandwiches produced with meat from pigs treated with porcine somatotropin. A second-price, sealed-bid auction procedure was used to determine willingness to pay to exchange a pork loin sandwich with leaner meat from pigs treated with somatotropin for a similar sandwich with meat from untreated pigs. The research was conducted using a sample of 114 undergraduate students in Iowa, Arkansas, Massachusetts, and California. At the end of the experiment 33 of 58 subjects would not bid to change their leaner pork for typical pork, whereas 15 of 56 subjects would not bid to change their typical pork for leaner pork. The results suggest a preference for leaner meat from the treated pigs, but also the potential for niche markets for meat and meat products from untreated pigs. Key Words: Somatotropin, Pork, Consumer Preferences

Addition of sodium or potassium salts along with kappa or lambda carrageenan to low-fat regular bologna does not reduce cooking losses. However, two carrageenan-salt combinations lowered working losses when added to a bologna-like low-fat beaker sausage, and the lambda-potassium combination had the most effect. Lambda carrageenan also made the cooked product softer.

Variations in the pH of the marinade influences flavor and microbial and chemical characteristics of fresh and precooked pork longissimus chops and fresh semi-membranosus/adductor roasted pork. The increase in pH due to addition of sodium tripolyphosphate improved the flavor, yields and water-holding capability. Sodium acid pyrophosphate and citric acid lowered pH-caused reduction in microbial population. Marinade with low pH checked microbial growth, while marinade with high pH improved sensory qualities, processing yield and water-holding capacity.

Preslaughter oral base or acid load affects flavor, juiciness and textural properties of pork roasts from halothane positive animals. This implies that feeding animals before slaughter can change the quality of meat. Ammonium chloride content in animal fodder affects the acid-base equilibrium and the palatability of meat.

A cation exchange ion exclusion HPLC technique was evolved to isolate and measure uronic acids of alginate or pectin added at different concentrations to lean ground pork. An Aminex HPX-87-H+ column, an isocratic 0.009N H2SO4 eluent and ultraviolet detection were used in this technique. The technique facilitated preferential measurement of uronic acids and ion exclusion column packing did not undergo rapid degeneration or contamination.

Assay and storage condition effects on yields of salt soluble protein were analyzed using pork and beef muscles. Extraction volume of 15 X sample weight, centrifugation at 4000 g, homogenization time of 90 to 120 sec for pork or beef and pH value of 6.0 were the assay conditions minimizing procedural effects.

Low-fat (8% fat) control patties, typical pork sausage patties (40%) and low-fat (8%) with 0.4% carrageenan and 20% added water were compared with identically treated preparations having 20% potassium lactate. The percent discoloration or lean color during refrigerated aerobic storage was unaffected by the lactate. The lactate salt failed to influence the sensory characteristics of pork sausage preparations. The typical patties with 2% potassium lactate had less microbial members during refrigerated storage than typical fresh pork sausage, but the bacterial populations of low-fat pork sausage patties did not vary.

The advantages of a surimi-like process for mechanically separated pork (MSP) are investigated. Results show that washing with either water or 1.5% salt removes most of the fat, and 1.5% salt removes much of the heme pigment. Moreover, the washed MSP shows a suppression of lipid oxidation during storage, which is a boon to flavor stability and shelf life. Aside from this, washed MSP shows little improvement over unwashed MSP for texture and water binding.

The effectiveness of surimi binders from boar and sow muscle and from Alaskan pollack fish for restructured sow muscle roasts was evaluated. Proximate analysis, sensory panel assessments thiobarbituric analysis texture measurements, mesophilic and psychrotropic counts and statistical analyses were used to characterize the functional properties of surimi-like products in restructured, precooked pork roasts. Product appearanceimprovement and microbe and lipid oxidation reduction were achieved by washing boar muscle.

The physical, chemical and sensory changes induced by modified atmospheric packaging and irradiation in fresh pork were investigated through factorial design experiments. The sensory shelf life of pork was extended from nine to 29 days upon irradiation without oxygen at 5 degrees celsius. An adverse effect was observed on the physical, chemical and sensory properties of the end product with the presence of oxygen in the package headspace.

The effects of low-temperature moist heat cooking on the chemical and sensory properties of fresh pork leg roasts at four different oven temperatures were analyzed. Sensory analysis measured the warmed-over-flavor (WOF) of roasts cooked at different temperatures. Results indicated that roasts cooked at 82 and 93 degrees celsius were of higher quality and exhibited less WOF after refrigeration and reheating.

The concentration of dietary linoleic acid (C18:2) influenced the fatty acid composition of subcutaneous fat and lean tissue in pigs. Increasing linoleic acid concentrations increased the levels of C18:2, C20:2 and C20:3 fatty acids in fat and C18:2 in lean meat while decreasing C18:3 and C24:0 fatty acids in lean meat. The high level of C18:2 raised the concentrations of several volatile compounds including pentanal, hexanal, trans-2-heptanal, 2-pentyl furan and 2-ethyl-1-hexanol in pork. However, no effects on sensory evaluation were detected.

The effects of cryogenic, plate, or blast freezing techniques and frozen storage on subcellular membrane integrity of Atlantic cod muscle tissue was evaluated after 12 weeks of storage at -12 degrees and -35 degrees centigrade. Extensive membrane condensation was noted on all frozen samples but a lesser degree of membrane damage was noted on samples kept at -35 degrees. Microscopic studies revealed that there were no significant difference in membane disruption found among the muscle tissue samples frozen by the 3 methods.

The consumer demand for lean meat products prompted a study to discover the effects of porcine somatotropin (PST) on the fatty acid composition of pigs' adipose tissue and its effects on pork products. Results showed that PST administration enhanced moisture and protein content as well as reduced crude fat content in all samples of adipose tissue. However, there were differences in textural properties of different pork products obtained from PST-treated pigs. Pepperoni had better drying characteristics, bacon had softer texture and lesser fat content although there was no significant difference in boneless ham.