Line Speed Implementation of Various Pork Quality Measures

John C. Forrest
Animal Sciences Department
Purdue University
West Lafayette, IN


Introduction

Competition with other protein sources in the domestic market and competition with other countries in the global market provides adequate incentive for improving the quality of pork produced in the United States. The challenge of that incentive has been taken up by the major seedstock companies in the US and worldwide. Over the last decade, pork processors have experienced increased pressure to provide quality pork in many specialized markets. Since there is a differential market based upon quality, the need for quality assessment is twofold. In the short term, there is increased need for better sorting techniques to satisfy the growing segment of the market that demands higher quality product. Long term, there is a need for more consistent feedback of quality information to all segments of the pork production chain to bring the overall level of quality up and increase market share for pork over other protein sources.

Pork Quality

Any factor that may influence a user's perception of the desirability of a product could be included as a quality factor; therefore, we must narrow our scope to those factors upon which we may want to place first priority. In the contemporary market, food safety is the major overriding factor for the entire food industry; however, that is not the focus of this presentation. The focus of this presentation is upon the factors that currently limit pork consumption because they affect utilization at the processor level or are a direct limiting factor on consumer demand for your product. Water holding capacity, which affects drip loss, limits the utilization of fresh pork in further processed products. Color of fresh meat in retail display cases influences the consumer's decision to purchase. In particular, consistency of color and texture may be of great importance. Tenderness, juiciness and flavor of the prepared product in turn influence repeat purchases of both fresh and processed pork products.

Technology for Assessment of Pork Quality at Line Speed

Current line speeds in plants that harvest and fabricate pork present a major challenge to technology that has the ability to detect the quality factors that are important to the industry. Typical line speed in modern plants exceeds 1,000 units per hour when operating at peak efficiency. The point in the process where the measurement is made also limits the technologies that can be used. For purposes of our discussion I would like to explore both Pre-rigor, early post-mortem assessment, and Post-rigor, assessment after carcass chilling. Pre-rigor measurements would be made during the first 3 hours after the harvest process begins. From a practical standpoint, these measurements would typically be made before the carcass enters the chillers which varies from 30 to 45 minutes after the exsanguination. Post-rigor measurements would be made in the range of 4 to 48 hours after exsanguination.

Pre-rigor assessment

Early postmortem prediction of meat quality would be desirable in situations where it is important to feedback quality information to producers and in situations where carcasses could be sorted into quality groups when going into the chill coolers.

Conductivity probes

Measurement of electrical conductivity on muscle membrane at a low frequency may offer opportunities for detection of early post-mortem changes. German scientists found that the dielectric loss factor measured at 15 kHz is ten times higher in PSE than normal muscle. However, results have been variable, and studies conducted in Canada found that neither dielectric loss factor nor electrical conductivity could reliably distinguish among the various Canadian quality standards used to identify PSE/DFD in pork. Further development appears to be required to improve its accuracy and commercial feasibility.

Early results from a tetra polar electrode system being developed at Purdue University indicate that it may be feasible to predict the water binding capacity of pork within 15 to 45 minutes post-mortem. Further testing of a new design of this instrument in a Danish pork processing plant confirms the potential usefulness of this technology either alone or in combination with other sensors. This would allow at least one quality assessment at the time carcasses are normally weighed and evaluated for leanness. If this system becomes a reality, this information could easily be included on kill sheets given to producers.

pH

Measurement of muscle pH at 45 minutes post-mortem has proven to be one of the more reliable methods currently available for early detection of PSE muscle. This involves either the insertion of a pH electrode into the muscle or the excision of a small muscle sample and preparation of a slurry. Although newer more robust pH measurement devices are now available, consistent, accurate, on-line measurement of pH is difficult in the early stages of the conversion of muscle to meat. In addition, the rate and complexity of the metabolic changes at this time suggest that a measurement of a single parameter at this time may be inadequate for prediction of meat quality.

Fiber optic probes

Recent studies in the laboratories of the Danish Meat Research Institute suggest that, early post-mortem prediction of water holding capacity in the longissimus muscle may be possible by measuring changes in the Near Infra-red (NIR) spectra over time. This may be superior to a single measure to predict color at 30-45 minutes postmortem. These investigations were conducted in an off-line area at an industrial plant, and confirm the potential for on-line adaptation of this technology.

Fiber optic probes (FOP) have also been developed to assess pork quality through measurement of muscle reflection or light scatter via fiber optics. Since color changes often do not occur within the first hour post-mortem, this technique seems to work better after carcasses have been chilled for a few hours. This time delay can cause problems in modern-day harvest facilities for two reasons. Carcass identity may be lost for feedback of information and, second, in most plants it would be difficult to sort carcasses for quality at that time. Further work over a wider range of wavelengths may improve the potential for this technology.

Elastography

A new application of ultrasound technology has been developed to test the hardness and softness of biological tissues. Elastography compares an initial traditional ultrasound scan with a second scan obtained after the tissues are slightly compressed. Scientists at Texas A&M University reported that quantitative elastography was not successful in detecting differences in pork quality groups; however, qualitative elastography was able to differentiate the elasticity differences among pork quality classes. They concluded that elastography has the potential to be a non-intrusive method for determining differences among pork quality groups.

Odor-flavor assessment

Skatole or androstenone content in fat of boars could be used to separate boars that may have odor and flavor problems when used as fresh meat (>.24 PPM skatole:>.5 mg/g androstenone). Some Danish pork processing plants utilize an automated chemical analysis system to measure the skatole level in boars slaughtered in order to reduce boar odor incidence in fresh pork.

Post-rigor assessment

Post rigor assessment is applicable when sorting of individual carcass parts is of primary importance. It is much easier to assess quality after all post-mortem changes have been completed. In general, this allows for measurement of a specific trait, rather than predicting what it will be after all of the changes that occur during the conversion of muscle to meat are completed.

Subjective visual

Traditional indicators of fresh meat quality include physiological maturity, marbling, color of lean, texture of lean, firmness of lean, wateriness of cut lean surfaces and firmness of fat. These indicators are typically evaluated subjectively, making them time consuming and subject to human error. Meat color, texture, wetness and marbling standards exist in photographic and/or color chip form for graders and evaluators to use in the subjective evaluation of quality. In 1991, the Japanese developed sets of standard color models for lean and fat based upon objective color coordinates measured on carcasses representing the full range of colors encountered in Japanese pork. Pigments were added to silicone resin until proper values were achieved to match desired grade standards. This approach still involves visual assessment; however, scientifically developed color standard models provide objective standards for direct comparison and matching to color scores. Purdue University and the University of Illinois are currently involved in a collaborative project sponsored by the National Pork Producers Council to develop a set of Color Reference Standards for U.S. Pork. These standards are designed to be used with both visual and objective technologies.

Pork processors that centrally package and brand fresh retail pork cuts for domestic or export markets usually sort these products for quality. Most utilize visual inspection for this sorting. Subjective evaluation is effective in eliminating major quality defects and narrowing the range of quality coming from any given processor. However, it is difficult to overcome the inconsistencies associated with any visual assessment, without an intensive training program. Visual assessment can only be applied after the carcasses have been chilled and are being fabricated. Once carcasses are on the fabrication line it becomes very difficult for most operations to maintain identity that would allow information to be passed back to producers.

Color meters

Several color meters are available for the objective evaluation of color. However, color alone does not fully describe the quality defects inherent in pork. Color meters are only effective in assessing color after the carcasses have had time to chill and develop their final color. They are effective in sorting meat by color, and in assessing quality in test lots where identity is maintained. Another limitation associated with most color meters is that the area of meat assessed is usually limited in size. Sometimes the result obtained is not fully representative of the cut or carcass.

Machine vision

Advancements in RGB (Red, Green, Blue) color video technology combined with newly developed computer neural network software offer great potential for objective visual assessment of meat quality. The application of color machine vision to meat quality assessment is being developed in several research laboratories around the world. Machine vision has the potential for assessment and classification of both color and marbling. There is also a possibility that textural properties and low water binding that results in wetness on a cut meat surface can be detected. If this technology is developed to its full potential it may be possible to sort centrally packaged retail pork cuts into uniform quality/color groups before shipping to retail.

Ultimate pH

On-line measurement of pH after most of the rigor associated chemical and physical changes are completed currently offers the best method of identifying carcasses that are PSE. Industrial experience shows that when pH is measured as carcasses are moved from the chill cooler to the fabrication line, Pale, Soft, Exudative pork can be detected with a high degree of accuracy. When ultimate pH (pHu) is 5.5 or lower, nearly 99% of the pork will be PSE. When pHu is 5.65 or higher there will be almost no Pale color, but the level of drip loss may be variable. Ultimate pH is less accurate in detecting Red, Soft, Exudative (RSE) pork.

Utilization of pHu offers the possibility of beginning to minimize the variability in pork by identifying the very dark and very light muscles.

Meat quality meter (MQM)

The Danish Meat Research Institute developed a single wavelength probe in the Near Infrared range. That detects color differences in pork carcasses after rigor changes are completed. Pale pork can be identified at line speeds using this instrument.

Optical fat/lean probes

Some optical fat-lean probes have been designed to detect color and marbling. These probes suffer from the same problems as the fiber optic probe when applied on the harvest line when fat depth and lean depth is typically measured to predict composition, in that major color changes may occur after the carcasses have been placed in the chill room. Scientists from the Netherlands reviewed various studies and stated that the relationship between harvest line measurements with either the optical fat-lean probes or fiber optic probe and ultimate meat quality attributes appeared to be of a low to moderate nature. The utilization of these probes after carcass chilling may offer more promise.

Tenderometers

Prediction or measurement of tenderness presents a major challenge because so many factors influence tenderness including the final preparation. Several devices have been designed for on-line measurement. One device measured the force required for a bank of needles to penetrate to a fixed depth in the cut surface of the meat. A more recent development is a portable device that measures the mechanical force required to shear meat fibers. Neither of these devices has proven effective enough for commercial application; however, further development of the concept may be worthy of merit.

Challenges to On-line Measurement

I paraphrase the way one industry researcher summed up the challenge "Post-rigor assessment is more accurate but provides fewer opportunities to adjust utilization - Pre-rigor assessment is less precise, but provides greater opportunity for sorting carcasses for specialized markets and feedback to production segment." The industry must continue to search for sensors that will detect the quality traits that most affect the utilization of pork products. These detectors must be precise, fast and robust enough to stand up to industrial conditions.

Summary and Conclusions

The entire pork chain is working together as never before to improve the quality of the products they place before their consumers. The biggest roadblock is the availability of accurate information upon which to base decisions on breeding and selection, as well as production and management. Technology is sorely needed to identify critical control points for the origin of meat quality problems in the industry. Once these are identified, the opportunity for rapid improvement in the quality and uniformity of pork is enhanced.

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