R. L. HOSTETLER. s l i d e and a drop of s a l i n e s o l u t i o n added.

Transcription

1 221. A M E T H O D TO S T U D Y T H E E F F E C T O F H E A T ON MUSCLE f l B E R S R. L. HOSTETLER The changes t h a t take place i n meat a s it i s heated i n preparation f o r e a t i n g have been of i n t e r e s t t o many people. Cooking seems t o be necessary f o r making meat p a l a t a b l e, but t h e amount of cooking needed v a r i e s f o r d i f f e r e n t people. One man l i k e s h i s beef r a r e. A second p r e f e r s h i s w e l l done. Several p r o p e r t i e s of meat change markedly a s it i s heated. It i s with v i s u a l changes t h a t t h i s paper i s concerned. Instead of watching a s t e a k b r o i l, muscle f i b e r s w i l l be observed a s they cook. A technique f o r doing t h i s w i l l be described, and a s m a r y of r e s u l t s obtained using two techniques given. F i r s t, t h e e f f e c t of increasing temperature with time, and t h e second, t h e e f f e c t of holding temperature constant f o r a period of time a f t e r a desired temperature i s reached. Equipment used i n making t h e s e s t u d i e s has included t h e following items, b u t many v a r i a t i o n s on t h e technique could be made. Equipment War i n g blender Freezing microtome Saline s o l u t i o n P e t r i dish Glass s l i d e s Cover g l a s s e s Vacuum grease Medicine droppers Microscope with heating stage. ( L e i t z Labolux with heating stage HEDAD) Accessories f o r photomicrography Constant temperature water bath with pump Fragments of muscle f i b e r s f o r study were obtained by placing a small piece of meat i n a Waring blender with enough s a l i n e s o l u t i o n t o cover t h e blades of t h e blender. After running t h e blender f o r 15 t o 3 seconds, t h e separated f i b e r s were then poured i n t o a P e t r i dish. Fibers were picked up with a medicine dropper f o r placing on t h e s l i d e. A second means of obtaining f i b e r s was t o use a f r e e z i n g microtome and s e c t i o n about 1 u t h i c k. The s e c t i o n was t h e n placed on t h e s l i d e and a drop of s a l i n e s o l u t i o n added. A means of preventing t h e drying of t h e muscle f i b e r preparat i o n was necessary. To do t h i s, a square 18 x 18 m. was o u t l i n e d on a g l a s s s l i d e using vacuum grease. The muscle f i b e r preparation was then placed i n t h e c e n t e r of t h e square and a 22 x 22 mm. cover g l a s s placed over it and sealed t o t h e vacuum grease.

2 The prepared slide was then placed on the heating stage of the microscope. Objective lenses magnifying from 3.5 to 45 times were used, depending on what measurements it was desired to make. When many measurements of change of length were desired, the 3.5~ objective was used. For measuring width changes or sarcomere length, higher magnifications were more practical. After an area with suitable fibers was found, a photomicrograph was made at room temperature. The heating element in the stage was then turned on and photographs taken at intervals of 3 degrees from 29 to 5OoC, and 2 degrees from 5 to 8OoC. The heating element took about 45 minutes to go from room temperature to 8OoC. The temperature increased rapidly at first, and then leveled off as 8OoC was approached. The Leitz stage also had provisions for running either cold or hot liquids through it so that the stage temperature could be brought fairly quickly from room temperature to 8OoC or more. The constant temperature water bath with a pump was used for this purpose. A photograph was again taken at room temperature. The heated water was then pumped through the stage while the slide with the fibers remained in place as it heated. It took from 5 to 1 minutes to get the temperature of the stage up, depending on the water temperature. Photographs were taken every minute for the first 1 minutes, every two minutes fromten to twenty, and every five minutes from twenty to sixty. The temperature of the stage was recorded each time a photograph was taken. Measurements were made from prints of the fibers. It was usually possible to measure five fibers through the entire series of pictures. All values are given as percentages since we were not interested. in the actual length or width of the fiber fragments, but only in the change in length and width that took place. Two dimension changes were observed as muscle fibers were heated. The width and length of the fibers decreased. Decreases in width (Figure 1) occurred soon after heating was begun and were essentially completed by 62OC. This may be related to Ham's (1966) description of the coagulation of myofibrillar and globular proteins, the loss of waterholding capacity, and other changes occurring during the heating of muscle systems. Shortening of the muscle fibers proceeded slowly until about 54OC. At some temperature between 54 and 7OoC most muscle fibers shortened rather suddenly. Above this temperature, 7OoC, they continued to shorten, but gradually. This shortening may be occurring as stable cross linkages begin to form in the fibers. In the second study where temperatures were held constant after a desired temperature was reached, there was a two and a half percent decrease in width (Figure 2) as the fibers were heated to 37OC. Another two to three percent change took place in the next eight minutes, There was a ten percent decrease in width as the muscle fibers were heated to 45OC, and during the next 15 minutes another five percent decrease took place. Little change in width occurred later. At higher temperatures most of the decrease in width (2 to 24 percent) took place while the fibers were heating up, with little later change.

3 223. There was little change in length (Figure 3) as fibers were heated to 37 or 45OC. Some decrease in length took place as fibers were heated to 53OC, but practically none after they had reached that temperature. Ten percent shortening took place as fibers were heated to 61 C and Eontinued slowly for 2 to 25 minutes with very little change during the last 25 minutes they were held at the temperature. Twenty-five percent shortening took place in a little over 5 minutes as fibers were heated to 69 and 77OC. There was very little after this time. It was also observed that between 5 and 6OoC, a material (probably sarcoplasmic protein) coagulated around the muscle fibers. Tests have shown that these soluble proteins continue to come out of the muscle fibers at least until the temperature at which the proteins coagulate is reached. The shrinking of the fibers may have driven these soluble proteins from the fibers, or perhaps something associated with the loss of water-holding capacity causes the muscle fiber to shrink. We are also investigating the effect of enzyme systems on the response of muscle fibers to heat. An additional area of interest has been the use of polarized light and the related property of birefringence that muscle fibers possess. Reference Ham, R Heating of Nuscle Systems. In "Physiology and Biochemistry of Muscle as a Food". E. J. Briskey, R. G. Cassens and J. C. Trautman, eds. University of Wisconsin Press, Madison, Wis.

4 IG.1 v TEMPERATURE *C WIDTH LENGTH 7 CHANGE IN WIDTH AND LEIVGTH WITH INCREASING TEMPERATURE 8

5 STAGE TEMP. I 4 G2 IO OC 4S.C 53.C a6ioc V 5 TIME (MIN.) CHANGE IN WIDTH WITH TIME AT DIFFERENT TEMPERATURES 69.C 77.C

6 TEMP. I I G.3 IO a 61.C 3t.C a 53% v 45.C 69.C 77.c 5 TIME (MIN.) CHANGE IN LENGTH WITH TIME AT DIFFERENT TEMPERATURES

7 227. DR, WANDERSTOCK: Thank you, Dr. Hostetler. The final paper on this afternoon's program is on the chemical aspects of meat flavor. Dr. A. E. Wasserman of the U.S.D.A. has been working in this area for many years and will present the paper. ##if########