How pH causes paleness or darkness in chicken breast meat.

Chicken breasts (Pectoralis) at a low-pH (5.91±0.12,n=10) were compared with breasts at a high-pH (6.36±0.25,n=10,P<0.001). Low-pH breasts had the highest reflectance (P<0.001 from 400 to 700 nm). High-pH breasts had the greatest transmittance into their depth and across individual muscle fibres (P<0.001). The differences in refractive index between ordinary and extraordinary rays across individual muscle fibres were greater in low-pH than in high-pH breasts (P<0.001). Light at low wavelengths had greater reflectance and lower transmittance than light at long wavelengths (P<0.001). Myofibrillar refraction contributed to differences in light scattering between PSE (pale, soft, exudative) and DFD (dark, firm, dry) chicken meat, as it does in pork and beef.

Stratification of toughness in beef roasts.

Most meat scientists adopt a reductionist approach to the study of meat toughness, taking a few intramuscular cores from one or more muscles to simplify the enormous complexity of toughness in all the retail cuts derived from a whole carcass. This is a valid approach to a complex problem, but we should also start to consider how consumers respond to bulk meat such as steaks and roasts. Probing whole roasts reveals a complex internal structure, detectable by both connective tissue fluorescence and resistance to penetration. The dorsal aponeurosis of the Longissimus thoracis is a major connective tissue stratum in beef rib roasts and its properties are correlated with those of adjacent intramuscular connective tissues. When the aponeurosis is cooked, its reflectance first increases with protein denaturation, then decreases with gelatinisation. Heat-induced contraction is concurrent with the increase in reflectance. Gelatinisation is reduced if the aponeurosis is mechanically restrained to resist contraction. Thus, mechanical restraint interacts with heat penetration in explaining stratification of toughness in bulk meat.

A method for simultaneous fluorometry and rheology of connective tissue in bulk meat.

A probe tipped with optical fibres was mounted on the load cell of a compression tester and pushed into well-aged beef rib roasts (Canada Grade AAA, n=6, 33±3.6days post-mortem). Fluorescence (F; excitation 365nm, emission >420nm) and reflectance (R; 365nm) were measured through single optical fibres. Diffuse R was measured using different fibres for illumination and detection, thus responding to tissue between the two fibres. Replication was by a matrix pattern of penetrations on single roasts. For example, in a typical roast, F was correlated with the force of penetration (mean r=0.86±0.06, n=20, all P<0.001). R was less (P<0.001) strongly correlated with penetration force (mean r=0.46±0.10, n=20, all P<0.001). F signals from connective tissue contained less peaks than R signals from both connective and adipose tissue (respectively, 2.75±0.43 versus 5.57±0.67peakscm(-1), P<0.001, n=20 pairs) and F peaks were wider than R peaks (respectively, 3.54±0.88 versus 1.38±0.19mm, P<0.001, n=20 pairs). For the spinales dorsi aponeurosis, the depth at which peak force was reached was strongly correlated with the depths at which both peak F and peak R were reached (r=0.98, P<0.001, n=20 for both). Diffuse R was only weakly correlated with penetration force (mean r=0.29±0.12 with only 5/10 correlations significant P<0.001). This new method showed the primary resistance to dorso-ventral penetrometry of well-aged beef rib roasts originated from connective tissue.

The histochemistry of very small muscle fibres in growing skeletal muscles.

Serial sections of biceps femoris muscles from 10 rapidly growing pigs were reacted for succinate dehydrogenase (SDH) and myofibrillar adenosine triphosphatase (ATPase) and were stained with silver to delineate the endomysial boundaries of their muscle fibres. The histochemistry of very small fibres (less than 0.001 mm2) was similar to that of surrounding fibres with a normal diameter. Of the small fibres, 71.5% had strong ATPase, 27.5% had weak ATPase, 22% had strong SDH, 23.8% had intermediate SDH and 54.1% had weak SDH reactions. Corresponding values for surrounding fibres with a normal diameter were 87.9% with strong ATPase, 11.8% with weak ATPase, 35.1% with strong SDH, 14.5% with intermediate SDH, and 50.5% with weak SDH reactions. An appreciable number of small fibres were histochemically unrelated to any of their surrounding fibres: 11.0% for ATPase, 12.8% for SDH, and 5.5% for both ATPase and SDH. The cross-sectional shapes of small fibres were similar to those of their surrounding fibres. It was concluded that these small fibres were probably the tapered ends of intrafascicularly terminating muscle fibres rather than new muscle fibres formed by splitting.

Histochemical development of myofibres in neonatal piglets.

The periodic acid-Schiff (PAS) reaction and tests for glycogen phosphorylase, oxidative enzymes and acid-stable and alkali-stable adenosine triphophatase (ATPase) were used to determine the degree of histochemical differentiation between myofibres of sartorius muscles from neonatal piglets. Within 24 h of birth, the ratio of myofibres with acid-stable ATPase to those with acid-labile ATPase was 1:21-0. By 10 days the ratio had changed to 1:5-2. Mean minimum myofibre diameters (all histochemical types combined) increased steadily after birth although diameters of myofibres with acid-stable ATPase showed no increase until 6 days. By 10 days, consistent differentiation was observed with the alkali-stable ATPase and glycogen phosphorylase reactions but not with the PAS reaction. During the 10 day neonatal period, all types of myofibres contained large or moderate numbers of mitochondria.

Autofluorescence of bovine ligamentum nuchae, cartilage, heart valve and lung measured by microscopy and fibre optics.

The fluorescence of bovine tissues was measured post mortem by microscopy of frozen sections and by using optical fibres to excite fluorescence and to measure fluorescence emission spectra. Mechanical disruption of the tissue (by comminution or sectioning) did not appreciably change tissue fluorescence spectra. Ligamentum nuchae had the strongest fluorescence and lung tissue had the weakest. In samples measured with a minimum prior exposure to ultraviolet light, the peak fluorescence emission was at 410 or 420 nm (with excitation at 365 nm). Exposure to ultraviolet light for about 1 minute shifted the fluorescence peak to 450 to 470 nm. Further exposure (about 30 minutes) caused a loss of the 450 to 470 nm fluorescence peak, while emissions above 530 nm were maintained or strengthened. Microscopy showed that the fluorescence that was measured by fibre optics from intact connective tissues originated mostly from collagen and elastin fibres.

Growth of motor end plates and histochemistry of intrafusal myofibres in neonatal piglets.

Between birth and 10 days the mean growth rate of peroneus longus motor end plates was 0-298 mum/day. A similar rate was found in seven other muscles from different anatomical regions. At birth, sartorius spindles contained three types of intrafusal myofibres; (i) large diameter with conspicuously strong acid-stable, and moderate or strong alkali-stable adenosine triphosphatase (ATPase) reactions; (ii) large diameter with weak or negligible acid-stable and alkali-stable ATPase; (iii) small diameter with weak or negligible acid-stable, and strong alkali-stable ATPase. All had a high mitochondrial enzyme content and positive PAS reaction. With the exception of some large diameter fibres, all reacted positively for phosphorylase. The frequency distribution of diameters was unimodal at birth but by 9 or 10 days was bimodal.

Measurement of the gristle content in beef by macroscopic ultraviolet fluorimetry.

Ultraviolet light (365 nm) was directed at an angle of 45 degrees onto meat samples in a circular aperture (3 cm diameter). Fluorescence emissions were measured with a monochromator and a photomultiplier tube. Intact tendons and elastic ligaments had a strong fluorescence emission peak around 440 to 450 nm and only weak fluorescence around 510 nm. Tissues such as lean meat and adipose tissue that contain a matrix of reticular fibers (Type III collagen) had very low fluorescence around 440 to 450 nm so that their peak emittance was the weak fluorescence peak at 510 nm. The 510/440 nm ratio of fluorescence emissions was measured in comminuted meat samples containing varying mixtures of lean meat and gristle and varying mixtures of muscles with a high and low gristle content. The 510/440 nm ratio was correlated with the ratio of lean meat/gristle (r = .96, P less than .005). The 510/440 nm ratio was correlated with the ratio of longissimus/shank meat (two trials; r = .93, P less than .01; and r = .94, P less than .005). Results were only slightly changed when samples had dry surfaces or when samples were mixed with adipose particles. The relationship between the area of gristle in the samples and the 510/440 nm ratio was curvilinear with the greatest sensitivity to the fewest gristle fragments.

Evaluation of probe designs to measure connective tissue fluorescence in carcasses.

Three probes were evaluated for their effectiveness in measuring connective tissue fluorescence within carcasses or primal cuts: 1) a quartz-glass rod, 2) a light guide formed from bundles of optical fibers, and 3) a single optical fiber. The shape of the fluorescence emission spectrum of tendon was altered by the method of measurement, probably because of differences in the intensity of excitation. The single optical fiber design provided the best solution to the problem caused by the irregular distribution of connective tissue in meat, and a modified fat-depth probe was tested as a prototype. Beef shank had more fluorescence peaks per millimeter (P less than .01), a greater area above minimum fluorescence (P less than .01), and a greater mean peak intensity (P less than .005) than did psoas major.

Observations on rheological, electrical, and optical changes during rigor development in pork and beef.

Electrical and optical changes were measured in bovine sternomandibularis and porcine sternocephalicus strips tested sinusoidally in a rigorometer up to 3 h postmortem. Rigor development was detected by decreased muscle elongation, decreased stress-strain hysteresis area, and increased elastic modulus. Elastic modulus was affected by loading rate (r = .98, P < .005) from loading rates of 3.6 to 13.3 kPa/s. Capacitance decreased and resistance increased at 120 Hz, 1 kHz, and 10 kHz as rigor developed. Sometimes changes were irregular at one frequency but steady at another. The most consistent electrical predictors of rigor development were capacitance at 120 Hz and resistance at 10 kHz. Electrical impedance changed as muscle strips were stretched in the rigorometer, so that dimensional effects could be a source of error if testing causes muscle contraction. The dominant fiber-optic reflectance changes during rigor development were increases toward 400 nm and decreases toward 700 nm, although transient increases were sometimes detected toward 700 nm. Optical changes generally were later than electrical changes. All these complex changes are an obstacle to the early prediction of pH-dependent aspects of meat quality from electrical and optical measurements.

Aerobic activity in the axis of growing myofibers in the porcine biceps femoris.

Twenty-four pigs between 9 and 29 wk of age were slaughtered at intervals of 4 wk. A microscope photometer was used to measure the staining intensity of histochemical types of myofibers. Biceps femoris myofibers were categorized as either strong-ATPase or weak-ATPase. The growth in cross sectional area of strong-ATPase myofibers was greater than that of weak-ATPase myofibers (allometric growth ratio, k = 1.36, P less than .005). Among strong-ATPase myofibers of animals at each different age, myofibers with a large diameter tended to have weaker succinate dehydrogenase (SDH) activity in their central axis than myofibers with a small diameter. Hence, correlations of cross sectional area with axial SDH staining (transmittance) ranged from r = .27 at 9 wk to r = .43 at 29 wk (all correlations significant, P less than .005). When the means for strong-ATPase myofibers of pigs at different ages were compared, SDH staining in the central axis of strong-ATPase myofibers tended to decrease as myofibers grew larger in cross sectional area. On this basis, myofiber cross sectional area was correlated with SDH transmittance, r = .85 (P less than .025). Among weak-ATPase myofibers of animals at each different age, large diameter myofibers sometimes tended to have weaker axial SDH activity than small myofibers, but no significant decrease in axial SDH activity was detected as myofibers grew larger.

Developing a fiber-optic probe to combine subcutaneous fat depth and meat quality measurements.

This feasibility study demonstrates that the boundary between porcine subcutaneous fat and longissimus muscle can be detected with a probe using optical fibers to illuminate and detect anatomical boundaries. A relatively large optical window (approximately 3 mm2) seemed to give the best resolution of fat to muscle boundaries, whereas a smaller window gave a better resolution of marbling. Scattered, obliquely sectioned optical fibers gave reflectance spectra of fat and muscle that were relatively flat and parallel (fat > muscle). Thus, white light may be used with optical fibers to detect fat to muscle boundaries, although the greatest monochromatic separation was at 820 nm. In comparing measurements made as the probe penetrated the meat with those made as the probe was withdrawn, structures appeared to be deeper on the way in than on the way out, because of compression of the meat. Multichannel operation allowed tissue transmittance to be measured as well as reflectance and channels to be averaged to improve performance. These observations will be useful in developing new apparatus to measure fat depth and meat quality in one operation using optical fibers.

Effect of wavelength on spatial measurements of light scattering for the measurement of pork quality.

White light from a xenon arc was focused onto the upper surface of 25-mm-thick transverse sections of pork longissimus muscle. A servo motor moved an optical fiber across the lower surface of the muscle to collect transmitted light, which then was passed through a grating monochromator and onto a photomultiplier for spatial measurements of scattering (SMS) and transmittance spectra. The SMS were calculated as the slope of the logarithm of transmittance relative to path length through the sample (which was calculated trigonometrically). Pale, soft, exudative (PSE) pork was measured with an index that included a subjective evaluation of meat color and objective measurements of reflectance, drip loss, and centrifugation fluid loss. The strongest correlation of SMS with PSE was at 610 nm (r = .86, P less than .005) and the strongest correlation of transmittance with PSE was at 650 nm (r = -.95, P less than .005). This supports the use of a red laser at 633 nm for the detection of PSE pork.

X-ray diffraction measurements of postmortem changes in the myofilament lattice of pork.

Postmortem changes in the lateral spacing between filaments of the longissimus muscle in pork were examined by small-angle x-ray diffraction. Samples that were fixed in glutaraldehyde as soon as they were collected showed a rapid decrease in filament spacing from 1 h to 3 h and then a further, slower decrease to 24 h. Samples that were examined immediately or were kept prior to examination in buffered Ringer's solutions at pH values similar to those expected in the carcass showed a rapid decrease in filament spacing from 1 h to 3 h and then little further change to 24 h. In contrast, samples taken at various times postmortem and stored in Ringer's solutions at pH 7.2 for several hours before examination showed little postmortem change in lattice spacing. Fixed samples showed similar changes to those of unfixed samples, but the lattice spacing always was less in fixed than in unfixed samples. These results support the classic theory that much of the water that may be lost by drip and evaporation from meat originates from the spaces between the filaments. The major factor that caused shrinkage of the filament lattice and loss of water from the fibrils was pH.

Fluid distribution in pork, measured by x-ray diffraction, interference microscopy and centrifugation compared to paleness measured by fiber optics.

Moderately PSE (pale, soft, exudative) and moderately DFD (dark, firm, dry) pork was examined by x-ray diffraction for interfilament separation, by differential interference contrast microscopy for interfiber area, and was centrifuged to measure water holding capacity (WHC). Internal reflectance spectra were measured by fiber optics. For PSE to DFD pork, filament separation ranged from 39 to 48 nm, interfiber area from 42 to 3%, and WHC from 49 to 64%, respectively. The correlation of reflectance with interfilament separation varied considerably with wavelength (reaching r = -.83 at 680 nm, P less than .005). The correlation of reflectance with interfiber area was more uniform across the spectrum (reaching r = .90 at 450 nm, P less than .005), as was the correlation of reflectance with WHC (reaching r = -.80 at 400 nm, P less than .005). At 24 h postmortem, fiber-optic spectrophotometry may be used as a rapid, nondestructive method to predict WHC and potential fluid losses from commercial pork with a moderate range from PSE to DFD. Interfiber area was correlated negatively with filament lattice area and WHC, but no significant correlation was found between filament lattice area and WHC. Filament separation was decreased only slightly by centrifugation. These results indicate that at 24 h postmortem the extra fluid released from PSE pork already has been lost from the myofilament lattice and is awaiting release from compartments downstream such as interfiber and interfascicular spaces.

A review of probes and robots: implementing new technologies in meat evaluation.

Changes in function from fat-depth measurement to meat quality measurement, and vice versa, have occurred in the history of electrical and optical meat probes. In the future, robotic systems might use ultrasonics to measure subcutaneous fat depth while at the same time positioning a fiber-optic probe relative to the skeleton to measure meat quality. There is a major distinction between probes that make a measurement at a single site within the carcass and those that produce a vector of measurements as they move through the carcass. Vector measurements were introduced to find subcutaneous fat thickness, but they may be used for meat quality measurements to deal with intra- and intermuscular variation. Replacement of hand-held probes by robots is in progress and could change meat distribution and marketing, perhaps replacing conventional meat grading by lowering the unit cost of grading and improving reliability for consumers. The feasibility of using ultrasonics to find probe measuring sites in the thoraco-lumbar region of pork carcasses has been proven. This requires new types of carcass morphometry data, such as rib angles and curvatures, and intercostal dimensions.

Meat quality variation in the robotic sorting of pork loins.

A robot was used to make fiber-optic reflectance measurements from 400 to 700 nm in 10-nm increments at six sites, 10 cm apart, along the length of 48 pork loins. Meat quality was assessed in the longissimus dorsi near the thoracolumbar junction using 1) a bag-drip method for fluid loss, 2) a subjective evaluation of wetness, 3) a colorimeter measurement of paleness (CIE L), and 4) a subjective evaluation for Japanese pork color scores (JPCS). Sorting of the loins in the commercial plant from which they originated was correlated (P < .01) with fluid loss (r=.57), with wetness scores (r=-.57), with CIE L* (r=.71), and with JPCS (r=-.64). Laboratory measurements of pH at the site of meat quality assessment were correlated (P < .01) with fluid loss (r=-.61), with wetness scores (r=.65), with CIE L* (r=-.74), and with JPCS (r=.77). Average spectra obtained robotically were correlated (P < .01) with fluid loss (r=.56 at 670 nm, and R=.76 adding 560 and 540 nm), with wetness score (r=-.65 at 480 nm, and R=.75 adding 530 and 570 nm), with CIE L* (r=.76 at 480 nm, and R=.82 adding 690 and 520 nm), and with JPCS (r=-.70). In sorting loins that were all categorized as normal at the plant, mean reflectance data collected robotically were correlated with fluid loss, r=.42 (P > .05) at 700 nm and R=.58 (P > .05) adding 430 nm; with wetness score, r=.25 (P > .05); with CIE L*, r=.58 (P < .025) at 700 nm; and with JPCS, r=-.71 (P < .01) at 700 nm. Thus, as well as detecting obvious PSE loins, the robotic probe also had a limited capability to sort loins all categorized as normal at the plant.

Refractometry of pork muscle and beef connective and adipose tissue.

Bulk refractive index (RI) was measured with an Abbe refractometer using a red laser for transmittance (T) and a green laser for reflectance. The critical angle, although obscured by scattering, was detected subjectively at the red-green boundary. The refractometer also was operated under computer control, detecting RI photometrically. Pork longissimus thoracis (n=20) had higher RI than biceps femoris (1.357±0.004 versus 1.352±0.005, respectively, P<0.001). Longissimus thoracis also had lower Japanese pork colour scores (JPCS) than biceps femoris (2.92±0.37 versus 3.87±0.48, respectively, P<0.001). In pooled samples (n=40), RI was correlated with JPCS, r=-0.55, P<0.001. RI of bovine tendon (n=10) was higher than for adipose tissue (1.415±0.009 versus 1.343±0.001, P<0.001). Refraction may contribute to the inverse relationship between meat pH and paleness, and may affect signals from fibre-optic meat probes.

Effect of connective tissue on the shape of reflectance spectra obtained with a fibre-optic fat-depth probe in beef.

A fat-depth probe was fitted with optical fibres to combine depth detection with spectrophotometry and fluorometry. Measurements were made through forelimb flexor, triceps brachii and longissimus thoracis muscles on 22 beef carcasses in a meat cooler. All strong fluorescence peaks had matching strong reflectance peaks (presumably connective tissue), but some strong reflectance peaks did not have equivalent fluorescence peaks (presumably adipose tissue). When the probe stopped at full depth and a complete reflectance spectrum was obtained, no effect from adipose tissue at the optical window of the probe was detected, whereas connective tissue increased reflectance across the visible spectrum (P < 0.005). The strongest effect was at 600 nm. Thus, spuriously high reflectance readings obtained with a fibre-optic meat probe are more likely to originate from connective tissue than from intramuscular adipose tissue.

Physical measurements of meat quality: optical measurements, pros and cons.

This review describes recent progress in understanding the optical properties of meat and considers how optical properties of meat might be used for quality control in the meat industry. The birefringence of myofibrils changes with pH so that, as the pH decreases towards the isoelectric point, the optical path difference increases. Thus, transmittance through muscle fibres is decreased and scattering of light in meat is increased. New ways have been found to monitor pH-related paleness by measuring the light scattered at different wavelengths and angles through the meat. A prove for the optical detection of subcutaneous fat depth in carcasses has been modified so that now it detects the distribution of collagen. UV light is reflected from a dichroic mirror into an optical fibre in the probe, andnd the fluorescence of connective tissue passing by the optical fibre is detected. Although these and other methods for the optical measurement of various aspects of meat quality are technically very promising, there are formidable problems to be overcome in developing a commercial application. A major industrial commitment to measuring meat quality in individual carcasses is required, together with a willingness to invest in the development of new technology.