Presentation on “Post-mortem changes in meat and Grading” Prepared by:Pravin Adhikari Sajeeta Paudel Srijana Gole Ujjal Rayamajhi Contents • Introduction to PM changes in meat • Description about normal and abnormal changes • Grading • Summary • Conclusion • Acknowledgements • References Objectives of the presentation: 1. To disseminate the knowledge regarding post- mortem biochemical changes in meat. 2. To describe about normal and abnormal post- mortem changes in meat. 3. To know about the beef grading system and pork grading system in USA and Europe. INTRODUCTION • Post-mortem changes in meat refers to the bio-chemical changes that occur in meat animals after the completion of slaughtering process during the conversion of muscles to meat. Types:1. Normal Post-mortem changes & 2. Abnormal Post-mortem changes Normal post-mortem changes 1. Loss of homeostasis ( E.g. oxygen scarcity, temperature elevation etc.) 2. Post-mortem Glycolysis (PMG) 3. Rigor mortis 4. Degradation of carcass 5. Loss of structural integrity Post-mortem Glycolysis (PMG) • Depletion of glycogen level in muscle due to anaerobic respiration. • Initial: Glycogen % :- 1 pH range : 6.7 - 7.1 • Final : Glycogen % :- nil pH range : 5.6 - 5.8 • The lactic acid obtained during glycolysis is the cause of decreasing muscle pH to become ultimate pH, at that time the muscle becomes meat. • At normal condition (proper pre-slaughter handling), ultimate pH is in the range of 5.6 – 5.8 Contd.. Rigor mortis • It refers to stiffening of muscle after death of animal. • It starts when ATP level falls to 1 mol/gm tissue and the onset of rigor mortis begins when the concentration of ATP reaches the level of 0.1 mol/gm. • With the onset of rigor mortis elasticity of muscle disappears and the meat is inextensible and tough. Phases of rigor mortis Three phases:1. Delay phase: ATP level > 1 mole/gm tissue 2. Onset phase: ATP level 0.1 – 1 mole/gm tissue 3. Completion phase: ATP level < 0.1 mole/gm tissue When the ATP level is reduced to 1 mole or less, the texture of muscle becomes hard/stiff, the condition is known as rigor mortis. Degradation of carcass • Due to inherently present proteases. E.g. cathepsin, calpain etc. • Degradation due to invasion/contamination with external enzymes/micro-organisms. • Splitting of muscle fibers/filaments by different proteases in their respective sensitive region. Loss of structural integrity • Deamination : low muscle pH denatures protein and even collagenous connective tissues. • Destruction of Z-disc : microbial degradation as well as degradation by cathepsin and other proteases disintegrates Z-line(disc) structure which causes disruption of myofibrillar structure. Abnormal post-mortem changes 1. PSE meat (pale, soft and exudative meat) 2. DFD meat (dark, firm and dry meat) or, DCB meat ( Dark cutting beef) 3. Cold shortening 4. Thaw-rigor PSE meat • stands for pale, soft and exudative meat. • Stressful pre-slaughter handling of meat animals may result PSE meat. • Other causes are:i. Slaughtering without stunning ii. Lightning iii. Beating iv. Terrorizing v. High temperature etc. • Stressful pre-slaughter handling causes excitement to the meat animals. • It results in excess anaerobic glycolysis. • Accumulation of lactic acid in muscle. • Precipitation of sarcoplasmic protein resulting in loss of water holding capacity (WHC). • Open structure of meat tissue that causes scattering of light tissue • Muscle texture becomes soft/ weak linkage. DFD meat / DCB meat • DFD meat refers to dark, firm and dry meat. It is more related to cattle and sheep. • DCB meat refers to dark cutting beef meat. • The amount of glycogen in muscle becomes very low/less due to:i. Long distance walking ii. Starvation iii. Transportation through jerking roads etc. Result • High ultimate pH > 6.0 • Muscle structure remains closed • Dark color appearance • Dry i.e. there is no exudation of water from interior fibrillar spaces • Hard texture Cold shortening • If the temperature of meat is decreased below 14oC in early phase of postmortem glycolysis, Ca++ ions are not re-absorbed by sarcoplasmic reticulum and the meat has tendency to undergo excessive contraction. This phenomenon is known as cold shortening. • Cold shortened meat becomes tough after cooking. Prevention of cold shortening • For first 10 hrs, the meat should be chilled at temperature below 15oC at low RH to prevent slime formation, and to allow the completion of rigor mortis. This process is known as conditioning. • After conditioning, the temperature should be lowered below 5oC within 48 hrs otherwise bone taint occurs (i.e. putrefaction of inner tissues especially in tissues around femur) • Electric stimulation of carcass before chilling. Thaw-rigor • If the meat is frozen in pre-rigor state, rigor mortis sets in only after thawing. This phenomenon is called thaw rigor. • It is characterized by abnormal muscle contraction ad high drip loss (up to 30-40%). • Economical loss and loss of water holding capacity of meat are other results of thaw-rigor. • During thawing, ATPase is activated and the available ATP is consumed in very short time. Grading • means classification of meat according to quality. • It is the language of meat trade • serves as a basis of measuring quality • basis of pricing meat. • Types:1. Visual/manual grading 2. Instrumental grading Visual grading of beef • In USA, the criteria for subjective/visual grading system of beef are as follows:1. Conformation:- shape of carcass and body profile. E.g. plump in round, thickly fleshed 2. Finish:- distribution of fat 3. Quality:- Total of eating quality parameters i.e. tenderness, juiciness, marbling, flavor, color, texture etc. Federal beef grades • Based on the criteria of grading described, beef grades in USA are:1. Prime ( high degree of muscling, high marbling etc.) 2. Choice 3. Good 4. Standard 5. Commercial (lowest grade) Beef Grading in Europe • In Europe; conformation, muscling and finish make up the total criteria of beef grading. The five grades of beef in Europe are:1) E (Choice) 2) U (Very Good) 3) R (Good) 4) O (Middle) 5) P (Poor) Instrumental Grading 1. Based on electrical conductivity KSA ( Kod Spaek Automatic) 2. Based on reflectance of light HGP (Hennessy grading probe) FOM (Fat-O-Meter) 3. Based on photographic view SKG (Carcass Grading Equipment) KSA (Kod Spaek Automatic) • Probe type instrument • Works on the principle of electrical conductivity. • Higher the content of lean tissue, higher is the conductance. • High content of fat shows low conductivity. • Ham and back-fat are measured to grade the meat. • The conductance is recorded and computed which reflects the quantity of fatty or lean tissue. HGP & Fat-O-Meter • These are probe type instruments having light source on the tip of the probe. • When probe is inserted in flesh and lightened, the quantity of reflected light is detected and measured by photocell. • The signal given by the photocell is converted as % fatty tissue by the computer. • Fatty tissue reflects more light than lean tissue. SKG ( Carcass Grading Equipment) • Probe type equipment fitted with TV camera. • The photograph of inner part/layer of flesh and ham angle & ham contour are taken. • The quality of the meat is estimated by visuak inspection of the photograph. Instrumental Grading of Pork in Europe Grades Lean meat (%) E > 55 % U 50 - 55 % R 45 - 55 % O 40 – 45 % P < 40 % Summary • Post mortem changes in meat are of two types: normal post mortem changes and abnormal post mortem changes. These changes are undesirable and affect the cooking loss, economic value, sensory characteristics and overall eating quality of the meat. • Grading is done on the basis of quality of meat. It is done either visually/manually or with the help of an instrument working on one of the specific principle. Conclusion • Hence, this presentation is to be concluded by stating the following general facts: a) Postmortem changes in meat causes biochemical changes in meat both normal and abnormal leading to loss in the quality. b) Grading system is generally used to classify meat on the basis of their quality. Several factors such as age, sex, breed etc. has a great influence on that. References • Subba Dilip, “Post mortem changes in meat” in Textbook of Meat and Poultry Technology, NCFST, Ktm, pp: 44-50 • Subba Dilip, “Slaughtering of animal: Grading” in Textbook of Meat and Poultry Technology, NCFST, Ktm, pp: 22-25 Acknowledgements • Mr. Achyut Mishra, Subject teacher, Technology of Food Products :Meat, Poultry and Fish, CAFODAT • College Administration, CAFODAT, Ktm, Nepal. • Class mates, VI Semester, CAFODAT (7th Batch) … … ANY QUERRIES?
