THE SHEAR FORCE OF VERY-RAPIDLY CHILLED LAMB 1: THE EFFECT OF CARCASS SPLITTING

The effect on tenderness of splitting lamb carcasses longitudinally under very-rapid chilling conditions was investigated. Whole (unsplit) and split carcasses were chilled in very-rapid chilling conditions (−20C for 3.5 h followed by chilling at 4C for 20.5 h) and conventional chilling conditions (4C for 24 h), giving a total of four treatments. Loin (M. longissimus thoracis et lumborum) shear force was measured at f and S days postmortem by Warner-Bratiler shear force measurement. By 5 days postmortem, split carcasses were not different (P>0.05) in shear force to unsplit carcasses when conventionally chilled but differences (P<0.05) were present between unsplit and split carcasses when very-rapidly chilled (57.7 N vs 41.5 N, respectively).     

EFFECT OF SIRE TYPE AND PLANE OF NUTRITION ON LAMB LOIN SHEAR FORCE, MYOFIBRILLAR FRAGMENTATION INDEX AND CALCIUM CONCENTRATION

The tenderness, myofibrillar fragmentation (MF) and calcium concentration of 140 female lambs sired by Poll Dorset sires of 3 sire types (3 selected for growth, 3 selected for muscling and 3 control) and fed either a low or high plane of nutrition from birth to slaughter was examined. Carcasses were electrically stimulated and portions of m. longissimus thoracis et lumborum (loin) aged for 1,3 or 5 days. Sire type had no effect on shear force values or MF values. Low plane animals produced tougher loins at each aging period with a greater reduction in shear force during aging in low plane animals. MF values increased with aging indicative of increased degradation, but were lower in low plane animals consistent with the increased toughness in this group. There was no effect of sire type on 'free' calcium concentration in loin muscle, but low plane lambs had a higher calcium concentration. The concentration of free calcium increased with aging. The findings suggest that plane of nutrition can influence loin tenderness and this is reflected in reduced myofibril degradation, but sire type effects are not important as tested in this work.     

THE SHEAR FORCE OF THE INDIVIDUAL MUSCLE FIBER AND ITS USEFULNESS IN PREDICTING MEAT TENDERNESSc1

This study was conducted in an effort to relate fiber shear force measurements obtained with a microsensitive shear instrument to objective and subjective measures of meat tenderness. Cooked and raw fibers from delay chilled and conventionally processed bovine tensor fascia latae muscles were measured for fiber diameter and fiber shear force. Each muscle was also evaluated for Warner-Bratzler shear force, Nip Tenderometer values, chew count and tenderness based on a structured tenderness scale. Partial correlation coefficients were determined between each of the fiber measurements and the objective and subjective measures of meat tenderness. The study demonstrated that fiber shear force as measured by the microsensitive shear instrument is not a reliable predictor of meat tenderness as it was assessed by the methods used in this study.     

EFFECT OF GAMMA IRRADIATION ON THE LIPID PEROXIDATION IN CHICKEN, LAMB AND BUFFALO MEAT DURING CHILLED STORAGE

Chicken, lamb and buffalo meat were subjected to low-dose gamma irradiation (2.5 kGy) and stored at 0–3C. Lipid peroxidation in terms of thiobarbituric acid (TBA) number and carbonyl content were monitored during storage. While irradiated meat showed slight increase in TBA number and carbonyl content on storage as compared to nonirradiated meat, this did not affect the sensory qualities of meat. Free fatty acid content decreased markedly on irradiation. Irradiated meats were microbiologically safe and sensorily acceptable up to 4 weeks in the nonfrozen state (0–3C) while nonirradiated meat had a shelf-life of less than 2 weeks .     

EFFECT OF HIGH HYDROSTATIC PRESSURE, GAMMA-IRRADIATION AND COMBINATION TREATMENTS ON THE MICROBIOLOGICAL QUALITY OF LAMB MEAT DURING CHILLED STORAGE

The effect of gamma irradiation (1.0 kGy) and high hydrostatic pressure (200 MPa for 30 min), either alone or in combination on the shelf-life of lamb mince meat at 0–3C was studied. Untreated control samples initially had total microbial counts of 10⁵ CFU/g, 10² CFU/g of coliforms and 10⁴ CFU/g of Staphylococcus spp. Coliforms were eliminated by all the treatments . Staphylococcus spp. however, were reduced only by 1 log cycle when treated with irradiation alone and high pressure alone. These species were a mixture of mannitol-fermenting and mannitol-nonfermenting strains. In samples subjected to the combination treatment , Staphylococcus spp. appeared only after 3 weeks of storage and all were mannitol-nonfermenting. On the basis of microbiological and sensory quality, the shelf-life of the control sample was less than 1 week. All treated meat samples had a shelf-life of 3 weeks, but only combination treated samples were free from potentially pathogenic Staphylococcus spp .     

Nisin对冷却猪肉冷藏保鲜效果的影响

研究Nisin对冷却猪肉保鲜效果的影响.研究中对比Nisin与山梨酸钾两种保鲜剂对冷却猪肉冷藏过程中6项鲜度指标(细菌总数、挥发性盐基氮、pH值、球蛋白、硫化氢以及感官指标)的变化情况.结果表明:Nisin在0.03 g/L～0.06 g/L浓度范围内可延长冷却猪肉货架期,其中以0.05 g/L Nisin保鲜液浸泡猪肉120 s保鲜效果最佳,货架期可延长6d,且与山梨酸钾保鲜剂(0.05 g/L)保鲜效果无明显差异.     

EFFECT OF RADURIZATION ON SHEAR RESISTANCE AND FRAGMENTATION OF CHICKEN MUSCLE

SUMMARY —Excised pectoralis muscles of chicken received radurizing doses of γ-radiation at varying times post-mortem to determine the effect on shear resistance, myofibrillar fragmentation (F-ratio) and pH. Irradiation doses between 0.1 and 0.3 Mrad produced decreases in F-ratio and increases in shear resistance. The magnitude of the changes was directly proportional to the duration of postmortem aging prior to irradiation. Muscle pH subsequent to irradiation between 2 and 12 hr post-mortem was not significantly affected by any of the dose-time treatment combinations. Shear resistance and F-ratio changes were strongly correlated on an average basis (r =+ .857; n = 6) but not on an individual sample basis.     

BEHAVIOR OF DIFFERENT FOODS IN THE STANDARD SHEAR COMPRESSION CELL OF THE SHEAR PRESS AND THE EFFECT OF SAMPLE WEIGHT ON PEAK AREA AND MAXIMUM FORCE

Abstract Twenty-four foods (encompassing fruits, vegetables, meat, bread, cheese and rice) were tested in the Allo Kramer Shear Press at various weight levels ranging from those needed to cover the bottom of the cell to those required for a complete fill. The relationship between maximum force values and sample weight was found to be different for different foods. Products could be grouped into three general categories: those exhibiting a constant force to weight ratio (e.g. white bread, sponge cake), those exhibiting a continuously decreasing force to weight ratio (e.g. raw apples, cooked white beans), and those exhibiting a constant force, independent of sample weight, beyond a certain cell fill level (e.g. canned beets, canned and frozen peas). Fitting the observed behavior into mathematical models allows to infer that extrusion, in addition to the previously recognized shear and compression, plays an important role in the behavior of foods in the standard cell of the Shear Press, and that most foods are subject to various combinations of these forces. The contribution of extrusion was confirmed by actual extrusion tests. Peak areas showed an exponential relationship to sample weight following the equation A = l0^aW^b. Some evidence was obtained that exponents a and b are related to the amount and the general type of resistance offered by the food.     

EFFECT OF TEMPERATURE ON THE QUALITY OF MUSCLE FOODS

Heating/cooking alters a food's flavor precursors yielding a product with a new pleasing taste. While heating to a high temperature destroys most pathogens thereby enhancing safety, it also alters the food's flavor by changing the precursors and final flavor components of the food. For example, heating meat to above 77C not only destroys many foodborne pathogens but also causes major changes in level of desirable flavor precursors. Many of these changes are due to alteration in activity of endogenous hydrolytic enzymes as well as heatinduced structural and functional changes. Heating induces differential production and distribution of flavor principles and flavor precursors. A secondary effect of temperature on food-flavor is its direct affect on analysis of flavor volatiles, i.e., high purge temperatures bias analysis of flavor components by production of new and destruction of existing components. This paper focuses on the structure/function relationship of meat proteins and their proteolytic products as they relate to meat flavor and end-point cooking temperature. The paper also will address the effect of analytical temperature on meat flavor analysis.     

EFFECT OF THE REDOX POTENTIAL ON THE MUSCLE ENZYME SYSTEM

ABSTRACT This work presents the effect of redox potential in the range +100 to ?250 mV on the muscle cathepsins B, H and L, lysosomal acid lipase and acid esterase and on neutral and basic lipases and neutral esterase from adipose tissue. Cathepsins B, H and L need reducing conditions (below ?50 mV) for maximal activity. Lysosomal acid lipase remains unaffected while activity of muscle acid esterase decreases sharply below ?175 mV. The activity of basic lipase from adipose tissue is also reduced below ?80 mV while neutral lipase remains unaffected. The activity of neutral esterase is drastically reduced to negligible values below ?100 mV.     

EFFECT OF SHEAR ON THE NEMATIC MESOPHASE OF THE WHEAT STORAGE PROTEIN A-GLIADIN

The nematic mesophase of A-gliadin exhibits rheopectic properties under oscillatory shear but not under unidirectional shear. The solutions change from a viscous sol to a stable gel after 28 cycles of oscillatory shear at 0.17 Hz, 22°C. The interaction energy between A-gliadin fibrils is estimated as 10.2 Kcal mole below 35°C and 6.25 Kcal/mole above 35°C with the change in interaction energy coinciding with a known change in the tertiary structure of the molecule. It is suggested that the different response of the solutions to oscillatory shear versus unidirectional shear results from the asymmetric tactoids present in the solutions and that any system which forms nematic tactoidal solutions would exhibit similar properties.     

THE EFFECT OF HEAT AND SHEAR ON THE VISCOELASTIC PROPERTIES OF SOY FLOUR DOUGH

This paper is concerned with the effect of heat and shear on the rheological properties of defatted soy dispersions and doughs of 30 to 60% flour by weight. Capillary and rotary rheometers (Rheometrics Mechanical Spectrometer) were used to heat doughs up to 75° C and shear them simultaneously. In one series of experiments using a modified Instron capillary rheometer the doughs were heated to several different temperatures and then sheared. The linear viscoelastic properties of the dough which were determined by means of a plate-plate rheometer were then compared to the fresh dough and those of a heated but nonsheared dough. In another experiment a cone-and-plate rheometer was used to heat and shear the dough. The linear viscoelastic response of the dough was used to monitor any changes as it was heated and sheared. It was observed that only in the higher moisture dispersions (i.e., moisture contents greater than 50%) were there any signs of an increase in rheological properties which might be associated with “cooking”. It was concluded that cooking of soy flour doughs most likely does not involve the formation of a permanent network formed by covalent chemical bonds. Hence, in extrusion cooking processes involving soy flour doughs, it may not be necessary to treat the rheological properties of the dough as a thermosetting system.