Supervisar los aspectos relacionados con la bioseguridad

Unless noted otherwise, the focus of this section will be on breast muscle/meat because this economically significant part of the carcass has received the vast majority of the research attention. The breast has received this attention because of its postmortem bio- chemistry (see Chapter 4) and subsequent fiber characteristics that impact finished product quality. It should be noted that any of these methods can be used to evaluate leg/thigh meat and ground/comminuted products as well as intact meat products. One simply needs to determine the objective of the analysis and choose the appropriate method. Shearing may be most important for whole-muscle while compression may be best for frankfurters or cohesiveness for restructured products like nuggets and patties.

The majority of the instrumental data used to determine tenderness in cooked poultry meat have been generated on the Warner-Bratzler (W-B) or the Kramer Shear Press (KSP). These procedures are designed to shear or cut through fibers of muscle. Another technique,

instrumental Texture Profile Analysis (TPA) data, has been used to generate texture infor- mation for poultry meat products. An in-depth discussion of the concept and measurement of food texture was published by Bourne13and will only be briefly summarized here.

Shear test

Shear tests have been used for many years. Samples are positioned so that a single blade or multiple blades cut perpendicular to the fibers. The basic principle of the test is that the total force to cut through the sample is related to the tenderness/toughness of the cooked sample. The force has historically been recorded in weight measurements (i.e., lb, kg), but these can be converted to the force unit of Newtons, if appropriate.

Warner-Bratzler shear device. The W-B shear device has been used to shear or cut red

meat and poultry samples for the last 50 years.14The device is small and portable, con- sisting of a rectangular blade with a triangular hole cut from the center. This blade is attached to a circular fan scale. The sample of known dimensions, usually a circular core for red meat or a rectangular strip for poultry, is placed in the triangular notch of the sin- gle blade. Two bars are lowered by a hydraulic motor and the sample is pushed across the apex of the triangular notch. As the bars are lowered across the sample, the peak force to shear across the fibers is recorded in lb or kg on the circular fan scale. The benefits of this device are its reliability, ruggedness, ease of use, portability, and low cost (less than $1200). The device lends itself to on-site quality control work. The limiting factor is that only peak load or peak shear force is generated during the test, so the researcher or QC personnel must have sufficient background sensory panel data to add validity to the shear values (Figure 7.4).

Kramer Shear Press (KSP). The other shear test that has been extensively used for red

meat and poultry texture research is performed with a shear cell based on the KSP.15The shear test cell is composed of two main parts, a metal box with slots which holds the sam- ple and a top part with 5 or 10 blades spaced to fit into the slots. This device is attached to

a system designed to move the multiple blades down and through a rectangular sample placed in the cell. The multiple blades are lowered across the sample. They initially com- press and then shear across the fibers forcing the resulting strips out the bottom of the slot- ted cell. Results are recorded as kg/g of sample weight. The KSP is rugged, but it is much heavier, less portable, and more expensive. It has been modified from its original design to predict quality of lima beans and used to measure textural properties of a variety foods including fruits and other vegetables.

Both of the blade designs of the original W-B and KSP systems have been reproduced on other instruments such as the Instron Universal Testing Machine™ (UTM); (Instron Corp., Canton, MA) and the Texture Technologies Texture Analyzer™ (Texture Technologies Corp., Scarsdale, NY). The multiple blade cell is also referred to as the Allo- Kramer shear cell. The W-B blade and an Allo-Kramer shear cell are pictured in Figures 7.5, 7.6, respectively. The newer systems are accompanied by software to program the machines and to record more dimensions of the force/distance or force/time curves.

Texture profile analysis

The instrumental TPA was introduced as a way to generate multiple textural attributes for food.10–12The need for a multiple-point test was reinforced by Breene16who noted that texture is complex and multiple point procedures would be more useful than single point procedures. The TPA was recently updated by Meullenet et al.17

A typical two-curve TPA for chicken meat is shown in Figure 7.7. The significant attributes are noted and defined. Significant attributes such as hardness, springiness, cohe- siveness, and chewiness can be separated and analyzed. A TPA sample is usually a circular core taken from the cooked meat. A decision must be made by the researcher on percent of compression during the test. In the literature, ranges reported for percent compression range from 60 to 80% of the original height of the core. Compressing less than 60% usually does not compress the sample enough to result in measurable changes, while compressing more than 80% usually destroys the sample matrix so much during the first compression

Figure 7.6 Allo-Kramer shear cell for an Instron UTM.

Figure 7.7 A typical texture profile analysis (TPA) curve pattern for chicken meat. From Lyon et al.,

that the second compression curve yields little or no information. The core to be evaluated is placed on a flat metal plate, and the top metal plate attached to the load cell is positioned to contact the sample (initial point). The percent compression is converted to cross head travel from the initial point. After the first compression and return of the cross head to the initial point, the cross head is immediately engaged for the second compression. The TPA is more of a research tool than the shear tests. The TPA is more sensitive and versatile than the W-B or KSP shears. However, the purchase and maintenance costs for instruments such as the Instron UTM or the Texture Analyzer are much higher, and they are not as portable.