A. M. Pearson’s research while affiliated with Michigan State University and other places

Evidence suggests that both the myofibrillar proteins and collagen play important roles in meat flavor and tenderness. The probable contributions of the purified proteins to flavor are reviewed in terms of their amino acid composition, especially the sulfur containing and certain other amino acids that have been implicated in meat flavor development. Myofibrils solubilized in sodium dodecylsulfate (SDS) undergoproteolysis on warming to room temperature overnight or on storing for several days at 0–4°C as demonstrated by extra protein bands. The extra proteins appear to be due to the presence of indigenous muscle proteases. The implications of some indigenous muscle proteases are reviewed in terms of their probable role in tenderization of postmortem meat.

The effects of triglycerides and phospholipids on development of warmed-over flavor (WOF) in cooked meat was studied using model systems from beef and from chicken dark and light meat. Triglycerides, total lipids, total phospholipids, phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) were added back to the lipid extracted muscle fibers in each system and WOF development was followed by the TBA test and taste panel scores after heating to 70°C and holding at 4°C for 48 hr. Total phospholipids, especially PE, were shown to be the major contributors to development of WOF in cooked meat. The triglycerides enhanced development of WOF only when combined with the phospholipids (as total lipids). Phosphatidyl choline (PC) did not influence WOF in the model system. Changes in the PUFAs of the phospholipids were shown to be related to development of WOF in cooked meat. Addition of 156 ppm of nitrite significantly (P < 0.01) reduced TBA numbers and prevented development of WOF.

Intravenous antemortem injections of EDTA, EGTA and CDTA significantly inhibited muscle shortening during development of rigor mortis. Post-mortem micro-injections of CaCl2 increased shortening, but MGCl2 had no measurable effect. Even though average shear values for muscle from EDTA-treated rabbits were lower than those of untreated controls, the differences were not statistically significant. However, muscle from EDTA-treated pigs was significantly more tender than that from untreated controls. The interrelationships between ATP levels and pH values at 0 and 24 hr post-mortem were investigated and their effects upon muscle shortening and tenderness are considered and explained. A highly significant negative relationship was shown to exist between cooking losses and both initial pH and initial ATP values for both rabbit and pig muscle.

DTA (differential thermal analysis) thermograms of epimysial connective tissue from normal and low quality porcine muscle were compared at 0 and 24 hr post-mortem. In addition, the melting characteristics of intramuscular collagen were determined at 0 hr post-mortem. In all tissues studied, collagen from low quality muscle consistently gave slightly lower peak melting points than that from normal muscle. Epimysial collagen had a significantly (P < .05) lower peak melting point at 24 hr than at 0 hr post-mortem (64.24 vs. 65.77°C). Using epimysial collagen, a significantly (P <.01) greater proportion of the total melting range occurred at lower temperatures at 24 hr post-mortem as compared to 0 hr (4 1.1 vs. 30.9%). The thermal behavior of intramuscular collagen at 0 hr post-mortem was similar to that of epimysial collagen at 0 hr, but peak melting temperatures were slightly higher for intramuscular connective tissue.

Concentrations of inosine 5′-monophosphate (IMP) were not significantly different in the longissimus dorsi, biceps femoris, and semimembranosus muscles of six pork carcasses sampled 48 hr post-mortem. On aging beef for 28 days at 0.1–1.5°C (33–35°F) the peak concentration of IMP (5.4 μM/g) occurred at 12.hr post-mortem. Other values through the 4th day of post-mortem aging were approximately the same. Following the 4th day, a gradual but steady decline in IMP content was observed until a value of only 0.75 μM/g or less than 15% of the peak IMP concentration remained after 28 days storage. A wide range of IMP concentration was observed between muscles obtained from different species, with beef sampled at 0 hr containing the highest amounts (4.71 μM/g) and pork heart muscle sampled at 0 hr containing the least (0.13 μM/g).

Beef longissimus dorsi roasts weighing 200g, and cooked by microwaves or conventional methods for various times were evaluated for flavor and overall acceptability by an untrained panel. Analysis of the data by surface response methodology was utilized to ascertain optimum cooking times for flavor development. The optimum cooking time for conventionally roasted (electric oven at 177°C) meat was predicted to be 88 min as compared to 2.80 min for samples cooked by microwaves (2450 MHz). Samples cooked by conventional roasting generally received higher scores for acceptability and flavor than those cooked by microwaves. Flavor dilution profiles for aqueous extracts of the samples revealed that the conventionally cooked samples were rated slightly stronger in flavor, more pleasant and more meaty than samples cooked by microwaves.

Some tasters were more repeatable than others in making chew counts, and were thereby able to discriminate more between loins of differing tenderness. Mean chew counts by six tasters for 36 loins ranged from 25.3 to 47.0, with one exceptional value at 60.0. These showed a high correlation with mean shear values based on 10 shears per loin. On average, an increase of 1 lb in shear value corresponded to an increase of 4 in the chew count in this experiment. Mean chew counts and shear values both showed significant correlations with two measures of marbling fat made on the 36 loins (visual scores and intramuscular fat contents), the less marbled loins being somewhat tougher. On average, an increase of 1% in intramuscular fat corresponded to a decrease of about 1.5 in chew count or 0.4 lb in shear value.

This investigation was undertaken to determine the ultrastructural changes in porcine muscle due to autolysis and their relationship to muscle fiber type. The red and white portions of aseptic porcine semitendinosus muscle were sliced, placed in sterile petri dishes, and stored at 10°C. Samples were taken periodically for pH measurements, bacterial counts and electron microscopic examination. No bacterial growth or significant pH changes were observed in the experimental tissues. White fibers appeared to be slightly more labile to autolysis than red fibers. However, the ultrastructural changes occurred in the same sequence for both fiber types. Mitochondria underwent cristae aggregation with a subsequent loss of cristae material. Nuceli were found to progressively shrink in size during storage with a concomitant concentration of the chromatin material. The I-band was the area of the myofibril most susceptible to autolytic breakdown and vesicular structures were observed in all areas of myofibrillar degradation.

At least 3, and probably 4, distinct myoglobins were detected in bovine muscle by their different mobilities on starch-gel electrophoresis. The 3 major components, labeled Mb IA, Mb Ib, and Mb Ib and respectively comprising 10–15, 2–5, and 80–88% of the total myoglobin, were separated and isolated on DEAE cellulose columns employing a stepwise development technique. Various purification and separation procedures are discussed.

Studies are reported on the mechanism of browning occurring in model and meat systems. When model systems were heated, brownness appeared to be due largely to the amino-sugar reaction, although some brown color development apparently occurred from caramelization of the sugars. This was shown by blocking the amino group with acylation or the carbonyl group of sugars by addition of bisulfite or hydroxylamine. The same procedures were used for studying the development of brownness in meat systems, except that in some instances the free sugars naturally present in meat were removed by yeast fermentation or by the addition of glucose oxidase. Although the data with the meat systems were not clear-cut, evidence suggested that most of the browning occurred as a result of the amino-sugar reaction. However, a small but significant amount of browning seemed to be due to pyrolysis of the natural meat sugars.