kleurvorming en kleurstabiliteit van vers vlees
TRANSCRIPT
Ghent University
Laboratory for Animal Nutrition and Animal Product Quality
Member of the Food2Know network – www.food2know.be
Kleurvorming en kleurstabiliteit van
vers vlees
S. De Smet
Colour perception
of meat
• Quantity of pigment (myoglobin) and chemical
state
• Reflection characteristics of the surface
• Spectrum of the light used
PSE Normal
Myoglobin = heme
protein
Predominant meat pigment (80-95% of the meat pigment)
Stores O2 for aerobic metabolism
Water-soluble
Present in cytosol
Purplish in color
Protein portion: globin
Non-protein portion: heme
(porphyrin ring with iron)
Myoglobin chemistry
~ meat colour Heme group in protein
Protein can denature
and detach Hist 93
Hist 64
6th position on
iron for ligand
binding
Heme iron
Myoglobin chemistry
~ meat colour
• Quantity of myoglobin
– Differences between species and muscles (‘red’ vs. ‘white’
muscle fibers)
• Chemical state of myoglobin
– Ferrous Fe++ (red or purple) vs. ferric Fe+++ (red or brown)
• Ligand
– None, water, O2, NO, CO, Zn…
• Physical state of protein
– Native (red purple or brown) vs. denatured (pink or brown)
Myoglobin content in
meat ~ species
Myoglobin (mg/g wet tissue)
Tuna 0.5-1
Poultry 1-2
Pork 1-3
Veal 1-3
Lamb 4-8
Young beef 4-10
Mature beef 16-20
Fresh Meat Myoglobin
Redox Forms
Deoxy-
myoglobin
Fe++
Oxy-
myoglobin
Fe++
Met-
myoglobin
Fe+++
Melvin Hunt (USA) & Chris Raines (USA)
“Practical” Meat Colour
Triangle
Deoxymyoglobin
No oxygen - Fe++
Oxymyoglobin
Oxygen - Fe++
+ Oxygen
MRA: Reduction and
oxygen consumption
Metmyoglobin
Oxidized - Fe+++
Oxidation and
oxygen consumption
1. Cut
2. Bloom
3. Vacuum pkg.
Mancini & Hunt (2005)
Meat Science 71: 100-121
Myoglobin redox
interconversions on the
surface of meat
Mancini & Hunt (2005)
Meat Science 71: 100-121
Denatured metmyoglobin
(Cooked meats)
Cooking temperatures denature the various forms
of myoglobin to create denatured metmyoglobin
(purple) (red) (oxidized brown)
(cooked brown)
Heme iron detaches from
globin and oxidizes Insoluble and catalyzes
oxidation
Objective measurement
of colour and colour
stability
• Colour
– CIE L*, a*, b* values
– Hue, saturation
• Colour stability
– Decline in a* value and
saturation in time
– % pigment composition
based on reflectance
spectra
Factors affecting
meat colour
• Animal genetics and production
• Temperature and chilling
• Muscle differences
• Muscle chemistry: OC & MRA & NADH
• Meat pH, meat quality and lipid oxidation
• Postmortem age of the meat
• Ground versus whole muscle
• Oxygen partial pressure and exposure
• Packaging type and atmospheres
• Processing ingredients and heating
Myoglobin & O2
Partial Pressure
Oxymyoglobin
Deoxymyoglobin
0 5 10 15 20 %O2
0
% M
b F
orm
100
0 20 40 60 80 100 120 140 Oxygen Partial Pressure, mmHg
Metmyoglobin Air
Melvin Hunt (USA) & Chris Raines (USA)
Colour development at
meat surface
~ D
~ p
d oxymyoglobin
deoxymyoglobin
metmyoglobin
oxygen
bright red
brown
purple red
~ 1/A
d ~ p (partial O2 pressure)
D (O2 diffusion rate)
1/A (residual activity of mitochondria = respiration)
high O2 quick formation of oxymyoglobin
low O2 slow formation of metmyoglobin
Vac Pkg or
Fresh Cut DMb Exposure,
mins to O2 DMb
OMb
DMb
OMb Exposure, hrs to O2
OMb MMb Extended O2
Exposure DMb Partial Discolouration
OMb MMb DMb
Discoloured in O2
MMb DMb
Melvin Hunt (USA) & Chris Raines (USA)
Layering of Mb in meat with
and without exposure to 02
Vacuum packed
or Fresh Cut DMb
DMb
OMb Exposure, hrs to O2
Exposure, mins to O2
DMb OMb
Discoloured in O2
MMb DMb
OMb MMb Extended O2
Exposure DMb
DMb
OMb MMb Partial
Discolouration
Melvin Hunt (USA) & Chris Raines (USA)
Factors affecting
meat colour
• Muscle differences: huge variation in colour shelf life
– Myoglobin content
– Oxygen consumption (OC)
– Metmyoglobin reducing ability (MRA)
– Metabolites (e.g. NADH)
• Postmortem age of the meat
– OC, MRA and NADH decrease
– Colour shelf life decreases
– Ability to bloom increases
~ muscle fiber type
~ perimortem conditions
Oxygen
consumption (OC)
• Meat Enzymes & Mb compete for O2
• More OC = Less O2 penetration
• More OC = Slower bloom
• More OC at higher temperature
• More OC earlier postmortem
• More OC in more “red” type muscle
No OC, little or no MRA
Metmyoglobin reducing
activity (MRA)
• Enzymes (and non-enzymatic) iron
reduction delays MMb accumulation
• MRA differs between muscles
• MRA decreases postmortem
• More MRA at higher temperature
• Repeated use decreases MRA
MRA must conserve for colour shelf life
Metmyoglobin
reduction
• Transfer of one electron from a donating
source to the ferric heme of metmyoglobin
• NADH: an essential component but
declines early postmortem !
• The location of the NADH pool as well as
mechanisms that regenerate NADH in
postmortem muscle are unclear
Improve colour
stability
If we do not add substrates, we must rely on
natural muscle colour chemistry
Saturate muscle with antioxidants in feed
Effective rapid chilling and “normal” pH decline
Minimize post-mortem storage
Minimize processing to conserve MRA
Colour stability :
effect of vitamin E
Concentrate
supplementation
Richardson (2001)
Natural supply from
grass
Titration of vitamin E vs
colour stability and
TBARS in beef
100
80
60
40
20
0
0 2 4 6 8
-tocopherol ( g/g fresh muscle)
% m
etm
yoglo
bin
3-3.7 g/g
TB
AR
S (
g M
DA
/g m
eat)
Richardson (2002) after Arnold et al.
(1993) and Liu et al. (1995, 1996)
8
6
4
2
0