Effects of heat on meat proteins – Implications on structure and quality of meat products

Dietary requirements and functions of α-linolenic acid in animals

To investigate the genetic factors that affect fatty acid composition of beef, we compared the full-length bovine stearoyl-CoA desaturase (SCD) cDNA from 20 Japanese Black steers. Two types of the SCD gene with single nucleotide polymorphisms (SNPs) were observed in the ORF of SCD cDNA, in which an amino acid replacement from valine (type V) to alanine (type A) was predicted. We developed a method for genotyping these two SCD genes based on PCR-RFLP. We have classified 1003 Japanese Black carcasses into three genotypes, VV, VA, and AA, and compared fatty acid composition among them. The SCD type A gene contributed to higher MUFA percentage and lower melting point in intramuscular fat. The SCD genotype was not the only genetic factor contributing to fatty acid composition of Japanese Black steers, but the SCD genotype was considered one of the causes of genetic variation in fatty acid composition of Japanese Black steers. Transcription factors such as sterol regulatory element binding protein-1c (SREBP-1c) may account for the remaining part of the genetic variation in fatty acid composition.

Genotype of stearoyl-CoA desaturase is associated with fatty acid composition in Japanese Black cattle

Forty-eight Angus x Hereford yearling steers were used to assess the effect of time on feed (TOF) on the nutrient composition of beef longissimus muscle (LM) Steers were fed a high-concentrate diet with the exception of the d-0 group, which served as a grass-fed control, and then were serially slaughtered at 28-d intervals during the 196-d feeding period Steaks were removed from the 10th rib and trimmed of exterior fat and epimysial connective tissue before nutrient analysis Intramuscular fat content doubled (P 05) from d 0 to 84 or from d 112 to 196 This increase in fat content resulted in decreased (P < 05) concentrations of moisture, protein, and ash in the LM Concentrations of Mg, K, and Fe in the LM increased (P < 10) with advanced TOF The increase in the total lipid (TL) content of the LM stemmed from a proportional increase (P < 05) in neutral lipid (NL) Polar lipid (PL) remained constant (P = 33) throughout TOF The NL and TL became more unsaturated as TOF increased, primarily due to a linear (P < 01) increase in oleic (C18:1) acid concentration In contrast, the polyunsaturated fatty acid (PUFA) concentration in the PL exhibited a linear (P < 01) decrease across TOF As a result, advanced TOF increased the monounsaturated fatty acid (MUFA) content by 22% and decreased the PUFA content by 72% in the LM The ratio of hypercholesterolemic (C14 + C16):hypocholesterolemic (MUFA+PUFA) fatty acids was unaffected by increasing TOF from d 28 to 196; however, this ratio was lower (P < 05) for grass-fed controls (d 0) than for d 28 to 84 and d 196 Cholesterol content (milligrams/100 grams) changed cubically (P = 06) across TOF Ultimately, by limiting TOF to 112 d, the beef industry could provide consumers a palatable beef product that easily fits into a healthy diet and at the same time diminishes the costs associated with external fat trim

Effects of time on feed on beef nutrient composition

Recent advances in muscle biology concerning the discoveries of a large variety of proteins have been described in this review. The existence of polymorphism in several muscle proteins is now well established. Various isoforms of myosin not only account for the difference in physiological functions and biochemical activity of different fiber types or muscles, but also seem to differ in functional properties in food systems. The functionality of various muscle proteins, especially myosin and actin in the gelation process in modal systems which simulate structured meat products, is discussed at length. Besides, the role of different subunits and subfragments of myosin molecule in the gelation mechanism, and the various factors affecting heat-induced gelation of actomyosin in modal systems are also highlighted. Finally, the areas which need further investigation in this discipline have been suggested.

Functionality of muscle proteins in gelation mechanisms of structured meat products.

SUMMARY: Relationships between the tenderness of very slowly cooked meat and its waterholding capacity, pH and the amount of water-soluble components were studied. Beef muscle portions from the longissimus, semitendinosus and rectus femoris muscles were heated under fixed temperature programs with samples from each analyzed at 1-hr intervals between the 3rd and the 10th hr of heating. Weight losses after holding at the final temperature to the 24th hr were determined. During the first 4 hr of heating there were only minor changes in tenderness. The major decrease in shear values occurred between the 4th and 6th hr, when the meat was warming from 50-60°C. The weight losses increased rather linearly to the 7th hr and remained constant for the longissimus and the semitendinosus muscle. The pH values gradually increased during heating. During the first 3 hr of heating, up to 45°C, there was only a slight decrease in the amount of the water-soluble fraction. During the following 3 hr. from 45 to 58°C, the water-soluble fraction decreased more rapidly and the decrease was only slight during a following 4-hr holding period. After 6 hr of heating to 60°C there were still uncoagulated water-soluble proteins. These studies indicate that the final temperature of meat has great influence on tenderness and weight loss. The significance of the shrinkage of collagen in long-time, low-temperature cooking is considered.

LOW-TEMPERATURE, LONG-TIME HEATING OF BOVINE MUSCLE 1. Changes in Tenderness, Water-Binding Capacity, pH and Amount of Water-Soluble Components

SUMMARY— Bovine intramuscular lipids extracted from the semitendinosus, triceps brachii and longissimus dorsi muscles were fractionated into phospholipids and neutral fats by silicic acid column chromatography. In spite of the wide range in total fat content at each location, phospholipids were present in all three muscles at a level of approximately 500 mg per 100 g of muscle tissue. This result, coupled with the lower total fat content of the semitendinosus as compared to the other two muscles, indicated a significantly higher percentage of phospholipid material in the total fat from the semitendinosus as compared to the triceps brachii or longissimus dorsi.



The fatty acids were identified in both lipid fractions using retention time data obtained on both a polar and a non-polar column. The identity of the unsaturated fatty acids was confirmed when their peaks did not appear on the chromatographs obtained from brominated samples. There was significantly more C14:0 in the longissimus dorsi neutral fat fractions than in the semitendinosus neutral fat fractions. In the phospholipids, there was significantly more C16:0 and significantly less C18:0 in the longissimus dorsi as compared to either the semitendinosus or triceps brachii. Although the two lipid fractions of the longissimus dorsi contained slightly higher percentages of total saturated fatty acids than the corresponding fractions in the other two muscles, the effects were not significant.

Composition of Bovine Muscle Lipids at Various Carcass Locations

SUMMARY: Naturally occurring collagenolytic activity was found in the water-soluble fraction of bovine muscle. General proteolytic activity determined with Azocoll indicated that this total activity was much greater than the collagenase activity specifically determined according to the method of Wunsch and Heidrich. The collagenase fraction was concentrated by polyacrylamide gel electrophoresis and the activity of the enzyme was studied under various pH and temperature conditions. This collagenase could remain active in the meat at cooking temperatures experienced in long-time, low-temperature cooking, 70-80°C, the collagenase observed in this study is inactivated.

LOW‐TEMPERATURE, LONG‐TIME HEATING OF BOVINE MUSCLE 3. Collagenolytic Activity

The extent of improvement in the oxidative stability of pork through dietary supplementation was determined by feeding pigs rations containing α-tocopherol acetate and ascorbic acid. Approximately 7.7, 5 and 4.3 μg of α-tocopherol per gram of tissue were deposited in the renal fat, the subcutaneous fat and the triceps muscle respectively by 200 ppm α-tocopherol acetate supplementation of the ration fed between beginning weights of 9–20 kg and a slaughter weight of 91 kg. The oxidative stability of the pork tissues was unaffected by ascorbic acid supplementation. However the stability of the adipose tissues was significantly increased (P < 0.01) by α-tocopherol acetate supplementation as indicated by the oxygen bomb stability test. There was a linear relationship between the stability of adipose tissues and their α-tocopherol content. Supplementation of 100 ppm of α-tocopherol acetate in the ration appeared to be the optimum level for improvement of the oxidative stability of the muscle.

Improvement in the oxidative stability of pork by dietary supplementation of swine rations

SUMMARY: Polyacrylamide gel electrophoresis was used to follow changes in the nature of the water-soluble proteins and juices of bovine muscle during low-temperature heating. The slowestmoving anodic proteins were coagulated first. The myoglobins and myoalbumins were altered significantly only by holding the meat at 60°C. The largest changes in tenderness and amount of water-soluble material in the meat occurred at the same temperatures under which the slow-moving proteins were denatured. The most heat-sensitive proteins detected were denatured before there were significant changes in tenderness or water-soluble substance content.

G. H. Wellington

Papers

LOW-TEMPERATURE, LONG-TIME HEATING OF BOVINE MUSCLE 1. Changes in Tenderness, Water-Binding Capacity, pH and Amount of Water-Soluble Components

Composition of Bovine Muscle Lipids at Various Carcass Locations

LOW‐TEMPERATURE, LONG‐TIME HEATING OF BOVINE MUSCLE 3. Collagenolytic Activity

Improvement in the oxidative stability of pork by dietary supplementation of swine rations

LOW‐TEMPERATURE, LONG‐TIME HEATING OF BOVINE MUSCLE 2. Changes in Electrophoretic Patterns