Introduction

INTRODUCTION

  • Since muscle is the principal component of meat, a brief discussion of its composition is necessary.
  • Like the animal body, muscle contains water, protein, fat, carbohydrate and inorganic constituents.
  • Muscle contains approximately 75% water (range: 65- 80 %) by weight.
  • Water is the principal constituent of the extracellular fluid and numerous chemical constituents are dissolved or suspended in it.
  • Because of this it serves as the medium for the transport of substances between the vascular bed and muscle fibres.
  • Proteins constitute 16-22 % of the muscle mass and are the principal component of the solid matter.
  • Muscle proteins are generally categorized as sarcoplasmic, myofibrillar and stromal proteins based primarily upon their solubility.
  • The sarcoplasmic proteins are readily extractable in water or low ionic strength buffers (0.15 or less).
  • However, the more fibrous of the myofibrillar proteins require intermediate to high ionic strength buffers for their extraction.
  • The stromal proteins are comparatively insoluble.
  • The sarcoplasmic proteins include myoglobin, hemoglobin and the enzymes associated with glycolysis, the citric acid cycle and the electron transport chain.
  • Although the enzymes of the TCA cycle and the electron transport chain are contained within the mitochondria, they are readily extractable, along with those found directly in sarcoplasm.
  • The myofibrillar proteins constitute the proteins associated with the thick and thin filaments.
  • They include actin, myosin, tropomyosin, troponin, alpha - and beta - actinin, C protein and M proteins.
  • These salt soluble proteins are required for emulsion stabilization in the manufacture of emulsion type sausage products.
  • In addition to proteins, other nitrogenous compounds are present in muscle.
  • They are categorized as nonprotein nitrogen (NPN) and include a host of chemical compounds.
  • Notable among these are amino acids, simple peptides, creatine, creatine phosphate, creatinine, some vitamins, nucleosides and nucleotides including adenosine triphosphate (ATP).
  • The lipid content of muscle is extremely variable, ranging from approximately 1.5 to 13 %.
  • It consists primarily of the neutral lipids (triglycerides) and phospholipids.
  • While some lipid is found intracellularly in muscle fibres, the bulk of it is present in the adipose tissue depots associated with the loose connective tissue septa between the bundles, the latter type of fat deposit is called Marbling or intramuscular fat.
  • The carbohydrate content of the muscle tissue is generally quite small.
  • Glycogen, the most abundant carbohydrate in the muscle, has an abundance that varies from approximately 0.5-1.3 % of the muscle’s weight.
  • The bulk of the remainder of the carbohydrate is comprised of the mucopolysacharides associated with the connective tissues, glucose and other mono- or disaccharides and the intermediates of glycolytic metabolism.
  • Finally, muscle contains numerous inorganic constituents notable among which are cations and anions of physiological significance, calcium, magnesium, potassium, sodium, iron, phosphorous, sulphur and chlorine.
  • Many of other inorganic constituents found in the animal body are also present in muscle.
Last modified: Saturday, 3 December 2011, 7:32 AM