25.
BA'SIC CHEMICAL C O N S l D E R A T l O N S REGARDING
THE TENDERNESS OF MEA T
F. E.
DEATHERABE
O H I O STATE U N I V E R S I T Y
...................................................
Perhaps a place t o s t a r t i n a discussion of the basic chemical considerations on the subject of beef tenderness would be t o make a few generali z a t i o n s based on about 15 years' work i n t h i s f i e l d . F i r s t , there is l i t t l e
evidence t o indicate that c l a s s i c a l proximate analyses of chemical e n t i t i e s
can give us a d i r e c t measurement of tenderness. The reasons for t h i s a r e
t h a t meat is a biological system and gets much of i t s character through the
organization of the various constituents. Second, any approach t o t h e study
of tenderness requires t h a t a l l methods give reproducible and accurate res u l t s . Since a l l data comes from biological systems, it is necessary t o know
the magnitude of errors f o r a11 data and a t t h e same time it i s necessary t o
use s u f f i c i e n t numbers of samples o r animals i n order t o assure v a l i d conclusions. Perhaps t h i s i s a t r i t e statement, but the l i t e r a t u r e on foods and
p a r t i c u l a r l y on meats contains much opinion mixed i n f a c t s . Thirdly, any
attempt t o s i ~ ~ dbeef
y tenderness must take i n t o consideration not only t h e
animal itself', 4nd the post mortem changes which may take place i n t h e meat,
but a l s o must include changes which take place during processing and part i c u l a r l y during cooking. After a l l tenderness is a q u a l i t y of cooked meat
and not raw meat, and it i s t h i s q u a l i t y which d i c t a t e s consumer acceptability.
It is impossible i n t h i s short time t o give you i n any d e t a i l the
thinking which has gone i n t o our program. 1 w i l l , however, attempt t o give
you t h e core of our work as it has developed. Ferhaps it is w e l l t o start
w i t h a panorama of data showing the tenderness values of 500 d i f f e r e n t animals, some of which have been aged and some not. The f i r s t slide w i l l show
the r e l a t i o n between the tenderness value and the e r r o r of each determinat i o n . These data were obtained by a panel technique which we have demonstrated a t t h i s Conference before. Please note t h a t the e r r o r s show a minimal
e f f e c t i n t h e center of the tenderness scale. This may be interpreted t o
mean t h a t tenderness i s a function of more than one substance, o r r a t h e r tenderness may be considered a discontinuous o r non-linear function. The second
slide shows t h e tenderizing e f f e c t of approximately 85 carcasses which have
been aged, You w i l l note t h a t even i n aged meat there i s some tough meat and
a l s o i n the unaged group tbre i s also tender meat. This s l i d e shows t h e rel a t i o n s h i p of tenderness of aged meat of f o u r d i f f e r e n t carcasses. Observe
that two show a toughening e f f e c t with age. This i s well beyond t h e realm
of experimental e r r o r , so you see t h i s q u a l i t y i s a very coplplex system. The
next slide shows a composite group of c a t t l e and t h e changes i n tenderness
w i t h post mortem age. Notice t h e plateau e f f e c t a t t h e two-three week level.
The next s l i d e w i l l show a group of tenderness-time curves which we reported
some years ago. Y o u w i l l see the plateau e f f e c t has gradually moved over
towards zero t i m e as t h e temperature has increased. The three curves represent aging a t 33-35 degrees and so-called high temperature aging a t 68, which
has been preceded by a 24-hour c h i l l , and the t h i r d curve represents tenderi z a t i o n without the so-called hot c h i l l . I believe you can see f r o m these
curves that there i s so much one can do by aging and not much more.
26.
It has c l a s s i c a l l y been considered t h a t connective t i s s u e i s the
cause f o r tough meat. This i s perhaps t r u e f o r wide ranges i n market quality
and physiological age of the l i v e animal. We have evidence that this i s so,
but it i s extremely d i f f i c u l t t o get controlled experimentation on t h i s point,
f o r those doing research in production a r e not p a r t i c u l a r l y i n t e r e s t e d i n backtracking, even though such may be necessary t o do a complete job of meat research.
It has often been s a i d that marbling i s a mark of temkrness. I
can only s a y here t h a t i n any of our work o v e r t h e past 15 years we have not
found t h i s t o be so. Marbling i s largely a c h a r a c t e r i s t i c of sex and feeding
management. What, then, does marbling do? T h i s is a curve taken from the
work of D r , Hankins and h i s co-workers which shows that f a t is r e l a t e d t o the
q u a l i t y of juiciness up t o a point, and beyond which additional fat is of no
consequence. In f a c t I might say that consumers rebel against too much fat.
Connective t i s s u e accounts f o r a r e l a t i v e l y small part of meat.
Could it be that the muscle p l a s m proteins could be one of the major cont r i b u t i n g f a c t o r s t o q u a l i t y as w e l l as connective t i s s u e ? After a l l , when
meat is cooked muscle plasma proteins f o m a fibrous mass. Projecting now t o
t h e procese of post mortem tenderization, l e t us take a look a t the possib i l i t y of proteolysis. It would seem strange that i f such enzyme action were
the cause of n a t u r a l tenderization that t h i s plateau e f f e c t t h a t we have seen
previously should not occur. On several occasions we have done experiments
t o determine i f proteolysis d i d occur. The next s l i d e shows c l a s s i c a l protein
fractionations of meat on post mortem agSng. I believe we would have t o agree
t h a t there is very l i t t l e proteolysis taking place up t o 13 days. Let us give
some a t t e n t i o n t o t h e m s c l e plasma protein. Skeletal muscle is capable of
contracting and relaxing, and t h i s i s brought about by t h e reaction of a c t i n
and myosin t o form a high molecular weight protein, actomyosin. During n o m 1
contraction t h i s reaction goes back and f o r t h and i s brought about by c e r t a i n
ions going on and o f f the protein surface. Could it be t h a t actomyosin, which
i s formed during r i g o r mortis, was t h e key t o beef tenderness? This slide
shows t h a t there appears t o be some relation. The data on percent nitrogen
extracted by a s p e c i a l b u f f e r is an Inverse function of t h e actomyosin of
muscle. You w i l l note t h a t there is a f a i r l y good correlation between t h e
actolnyosin and tenderness. If t h i s i s so, then post mortem tenderization
might be related t o actomyosin i n two days. Could t h e resolution of rigor
mortis be a dissociation of actomyosin i n t o a c t i n and myosin, o r could it be
that there are some changes taking place i n actomyosin i t s e l f ? This slide
shows t h e formation of actin during r i g o r mortis. It a180 shows t h a t actomyosin does not dissociate during post mortem tenderization. W
e then have t o
look i n t o other directions. One of these might be t h e water-holding capacity
of the muscle proteins. We all appreciate that on cooking Juice is expressed.
We would a l s o expect that if proteolysis were extensive that the amount of
juice expressed would increase with post mortem age. This next slide shows
that the juice expressed on cooking a c t u a l l y decreased on post modem ctgiw
and tkt the amount of j u i c e expressed 1588 related t o tenderness. I n other
words, on cooking the proteins of aged beef a c t u a l l y hold more water than on
unaged beef. Hence t h e coagulum is less dense and more tender. The next s l i d e
shows t h e changes i n pH with post mortem age and t h e release of j u i c e on cooking. Although only two animals a r e shown here, t h i s same general trend has
been confinned i n more than 8 hundred cases. pH tends t o go up and j u i c e expressed on cooking goes &wn.
27.
What could cause these changes? It i s known that pX change alone
might cause it, but what causes t h e change i n pH? Could it be that t h e
randomization of ions during post mortem agiag does i n f a c t promote the waterholding capacity of meat proteins? This slide shows t h e total. amount of sodium,
potassium, calcium and magnesium in meat. This slide shows that the amount of
extractable calcium in the r a w meat and the amount of calcium in the Juice
expressed on cooking increase with post mortem age. The next slide shows
similar data f o r magnesium. Notice the rapid change with the onset of r i g o r
mortis. The next slide shows chawes with magnesium plus potassium and sodium.
The next slide shows changes in potassium. The next s l i d e shows the post
mortem changes i n magnesium expressed in terms of juice and i n terms of t o t a l
nitrogen. Notice t h a t the changes which are taking place reach a plateau
which coincides with the plateau of the tenderess curves. This slide shows
j u s t the composite values f o r t h e other ions. Let us now take a look at the
changes i n these ions with post mortem aging. This slide shows the amount of
each which may be extracted with water from t h e r a w mat with post mortem
aging. Notice that sodium i s goiw off the protein i n t o the water, potassium
i s going on t o the protein, calcium is going off the protein a d the net s h i f t
i s i n the negative charge i n the water e x t r a c t which means a positive charge
change on the protein. This, of course, means that t h e protein i s holding
more water. This shows the same kind of data f o r t h e j u i c e on t h e cooked meat.
Notice t h a t t h e changes are similar but even g r e a t e r i n order of magnitude.
Thus t h e more tender meat has a higher positive charge and thus holds more
water, making the coagulum s o f t e r and more tender. I should say t h a t even
t%ough these chamgee reflect primarily muscle plasma, they would a l s o profoundly affect the water-holding capacity of connective t i s s u e . Whether o r
not such c h q e s i n connective t i s s u e could cause tenderness has not been determined.
Let us now t u r n a l i t t l e b i t of a t t e n t i o n t o the chemistry of t h e
cooking process. W
e have =ported earlier that salt can produce profound
changes when infused i n t o meat i n such a way a6 t o improve tenderness, waterholding capacity, d r i p on freezing, e t c . The next slide shows the pH changes
with temperature on cooking. Notice t h e rapid changes which take place in the
very c r i t i c a l 40-70' range. Note a l s o t h a t salt decreases markedly t h e j u i c e
expressed on cooking. Note a l s o t h a t the water-holding c q a c i t y does not
markedly change beyond 700. This next slide we feel is very highly s i g n i f i cant and may open the door t o better understanding of meat problems. Notice
t h e i r r e g u l a r shape of the curves of Juice expressed with cookin@;temperature.
Note t h a t very dramatic changes are taking place i n the 50-6S0 range. There
i s considerable evidence which I cannot go i n t o a t t h i s time that t h i s Sshaped affair is a function of actomyosin content of meat and may be related
a l s o t o physiological age. Note a l s o that as t h e temperature approaches the
b o i l i n g point more and more juice i s expressed and I think you will a l l agree
that t h i s i s the range which makes meat tough. Note a l s o t h e effect of adding
water and salt. Salt increases the water-holding capacity of meat over t h e
e n t i r e range. The next slide w i l l show changes i n sodium and potassium with
heating. Note the i r r e g u l a r curves i n the 50-65' range. The next slide shows
similar data f o r j u i c e expressed. The next two s l i d e s show the changes of
heating aud added salt on calcium and magnesium i n both t h e meat proteins and
the Juice.
I w l l 1 conclude by simply showing t h e e f f e c t of c e r t a i n o t h e r salts
water-holding c a p m i t y of meat proteins. Notice the e f f e c t of increasi n g water-holding capacity by magnesium and even calcium.
oI1 t h e
26.
I have not had time t o explore with you the e f f e c t of water-holding capacity on other q u a l i t y a t t r i b u t e s of meat. I believe we must agree
that water-holding capacity has an effect on tenderness. It a l s o has an
e f f e c t on d r i p on freezing, shrink on cooking and perhaps o t h e r changes
found i n the processing of meat.
DR. HENRICKSON: Thank you, Fred, f o r t h i s very important
insight i n t o the chemical aspect of why some meat i s tender and some i s
less tender. I think that you have opened many avenues or many i n t e r e s t i n g facets of research f o r those who are i n t e r e s t e d i n a master o r
a Ph.D. problem.
Our next speaker is one whom you are a l l acquainted with.
However, I understand from him that he is soon going t o become a prof e s s o r a t Loyola University and will be working in t h e department of
anatomy
.
A t t h i s time it gives me a great d e a l of pleasure t o present
Harry Wang, who will speak on the h i s t o l o g i c a l and enzymatic aspects
of tenderization.