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Effects of added connective tissues on the sensory and mechanical properties of restructured beef steaks
Meat Science 27 (1990) 61-74
Effects of Added Connective Tissues on the Sensory and Mechanical Properties of Restructured Beef Steaks E. D. Strange & R. C. W h i t i n g us Department of Agriculture, ARS, Eastern Regional Research Center, 600 East Mermaid Lane, Philadelphia, PA t9118, USA (Received 17 January 1989; accepted 13 June 1989) ABSTRACT To quantify objectionable levels of connective tissues, restructured beef products were made with 2"5 and5% added tendon; 5 and 10% added epimysium, gristle, or peri/endomysium; and a control Initial tenderness (IT), residual connective tissue ( CT ), and overall texture ( 0 T) were evaluated by a sensoo' panel. Panelists adversely scored IT, CT, and OT for 2"5 and 5% tendon and CT and OT for 10% epimysium and gristle. CT and OT scores correlated with hydroxyproline content and Lee-Kramer peak shear force for uncooked steaks with added tendon, gristle and epimysium but not peri/endomysium. Acceptable products can be made when raw materials are free of tendons and contain only limited amounts of epimysium.
INTRODUCTION Restructured beef(RSB) made from under utilized portions of carcasses, e.g. chucks, should have both greater appeal to consumers and a better return to producers than ground meats made from the same cuts (Briedenstein, 1982). Extensive trimming to remove connective tissue is perceived as necessary to make an acceptable restructured product from chuck (Briedenstein, 1982). Recio et al. (1987) showed that consumers preferred restructured beef (RSB) steaks made with thoroughly trimmed clods. Booren et al. (1981) found that acceptable RSB steaks could be made from choice chuck. Berry et al. (1986) found that an expert panel could detect the difference between restructured steaks made with and without added connective tissue, but no attempt was made to identify the types of connective tissue present in the RSB or to 61 ~ us Government
E. D. Strange, R. C. Whiting
62
correlate shear force measurements with quantity of connective tissue or panelists' responses. Berry et al. (1988) found that consumer panels could discriminate only between RSB steaks with 'extra high' levels and "high' or 'low' levels of connective tissue and concluded that trimming chucks of connective tissue may not be necessary for acceptable RSB products. The objectives of our studies were to determine the amount and type of connective tissues from beef forequarters that affect sensory quality of restructured beef and to relate sensory panel scores to hydroxyproline content (a measure of connective issue amount) and to Lee-Kramer multiblade peak shear force measurements. MATERIALS AND METHODS Restructured beef steaks Four square cut chucks (USDA Choice, Yield grade 2, NAMP No. 113~, were obtained from local sources. The chucks were dissected into component parts: muscle, fat, bone, tendon, epimysium (connective tissue surrounding individual muscles), and gristle (thick connective tissue contained within the muscle). The exact weight of each component was measured and its percentage of the chuck determined. The trimmed muscles from the chuck were frozen, tempered and diced into cubes 6-12 mm on a side. Isolated tendon, epimysium and gristle were diced 3-6ram on a side. The peri/endomysium (peri/endo) fraction (see below) was used without any further treatment. A series of restructured products was made from diced muscle mixed with different amounts of connective tissue. Gristle, epimysium, and peri/endo products were made to contain 5 and 10% (w/w) and tendon products to contain 2.5 and 5% (w/w) added connective tissue. A control product made with the extensively trimmed meat without any added connective tissue was also made. The cubed meat and the connective tissues with sodium tripolyphosphate (STPP) (0.125%) and NaCI (0.75%) were combined in a Hobart omni-mixer with a leaf-paddle attachment for 2 rain at the slowest speed. After mixing, the product was stuffed into 55 mm diameter casings and allowed to bind at 11°C for 4h before freezing at -20°C. The logs of RSB were tempered before being sliced into 2-5 cm thick steaks and vacuum packaged. There were nine different types of product.
Peri/endo fraction A fraction enriched in perimysium and endomysium was prepared from the supraspinatus and infraspinams muscles (Tucker et al., 1952). These muscles
Effects o f added connectire tissues on restructured beef steaks
63
Meat slice 2-5 kg Extract 2 x with 4 liters 50ram CaCI2 for 4h then 16h Discard liquid extract Extract 6 x with 4 liters I-0M NaCI once for 8 h then 5 × for 24 h each Discard liquid extract
Extract 1 × with 4 liters water for 6h Discard liquid extract Extract 1 x with 4 liter I'0M NaCI for 16h Discard liquid extract Wash with water until liquid tests free of Na Flame Discard washes
Peri/endo fraction 638G Fig. 1.
Extraction flow diagram for the preparation of perimysium and endomysium enriched meat fraction.
were dissected and trimmed of all visible fat and thick connective tissue (including the thick connective tissue within the muscle), partially frozen, and sliced 1-2 m m thick across the muscle fibers. The sarcoplasmic and myofibrillar proteins were selectively extracted using the procedure outlined in Fig. 1. The initial treatment with 50 mM CaC12 removes the sarcoplasmic proteins, the treatment with 1-0M NaCI removes the myofibrillar proteins and the water washes aid in the extraction of the myofibrillar proteins by osmotic shock. The washes were removed by straining the slice extracting mixture through a stainless steel metal screen (1.5 x 2mm). Protein, moisture and hydroxyproline content were measured on the starting material as well as the completed fraction. This procedure permits the isolation of a muscle fraction enriched in perimysium and endomysium with normal connective tissue architecture.
Chemical analyses Two tempered steaks from each product were ground twice through a meat grinder with 2 m m size holes. The ground restructured steaks were used for % protein (Kjeldahl N), % fat (Soxhlet extraction with petroleum ether), % moisture (16-18h at 100°C) (AOAC, 1965). Hydroxyproline assays (Woessner, 1961) were done on approximately 100mg (exact weight determined for each analysis) of 10 g samples of ground restructured meat
64
E. D. Strange, R. C. Whiting
which had been homogenized to a uniform paste in a Brinkman polytron tissue grinder.
Cooking Cooked restructured steaks were prepared for sensory panel evaluation and shear force measurements by grilling partly frozen steaks on a Farberware open hearth grill to an internal temperature of 70°C (measured with therrnocouples inserted into center of the restructured steaks) turning once during the cooking process.
Shear measurement A Lee-Kramer multi-blade shear cell attached to an Instron Universal Testing Machine was used to measure shear force on both raw and cooked restructured steaks. The raw steaks were defrosted at room temperature (20°C) and cut into two parts (semicircles of diameter 55 cm, 2.54 cm thick). The weight was determined and the peak shear force obtained using a cross head speed of 50mm/min. Four shears per product per carcass were obtained. Shear force measurements were also made on cooked restructured steaks. After the outer crusts were trimmed from the cooked steak, the remaining steak was cutinto two parts, weights recorded and the peak shear force measured on steak samples cooled to room temperature. Four shears per product per carcass were obtained (i.e. 16 shears per product). Shear force was calculated as Newtons per gram sample.
Sensory panel Sensory testing for texture was carried out by a fifteen member trained panel consisting of Eastern Regional Research Center employees. Panel members were trained by presenting them with cooked RSB steaks made with high levels of connective tissue and steaks made with thoroughly trimmed meat. The samples were identified and use of unstructured l0 cm scoring lines was explained. Panel members were asked to evaluate the steaks based on the following instructions: initial tenderness (IT) from very tender to very tough and to evaluate this property after 3-4 chews; connective tissue (CT) from minimal to excessive and to evaluate this property after completely chewing the product; and overall impression of the texture (OT) of the restructured steak from like extremely to dislike extremely. After the training sessions, prospective panelists were tested by presenting coded and unidentified RSB steaks made with high levels of connective tissue and made with thoroughly trimmed meat. Only those who could discriminate between the two steaks were chosen to be members of the texture panel. All texture evaluations were
Effects of added connectire tissues on restructured beefsteaks
65
carried out in individual testing booths with red lighting to prevent visual identification of high connective tissue samples. All sensory evaluations were completed in 4 days using both morning and afternoon sessions. The samples presented at any one session were determined by the experimental design. Each panelist at each session was presented with the coded (three random numbers) predetermined five samples in random order. Unknown to the panelists one of these samples was always a control (RSB made with trimmed meat). Meat samples were cooked as for the Lee-Kramer shear force measurements and were presented to the panelists hot. Each panelist received 16th part of 2.54 cm thick 55 cm diameter restructured steak. Sample size presented to the panelists was approximately 5 g. It was determined during the training sessions that this size sample was comfortable for the panelists to chew at one time and gave samples of sufficient size for evaluation. Each restructured steak from each carcass was tested by at least 14 panelists. After the panel evaluation, the sample scores were determined by measuring the distance the panelist had marked on the scoring sheet. For IT (Initial Tenderness) very tender would be a 10 and very tough would be a 0; for CT (Connective Tissue) minimal would be 10 and excessive would be 0; and for OT (Overall Texture) 10 would be like extremely and 0 would be dislike extremely. A hedonic scale was chosen for OT to detect any unusual texture changes not anticipated in the initial study.
Experimental design The experimental design for the sensory panel testing was a 2 x 4 factorial. Each main effect (gristle, epimysium, peri/endo, and tendon) was tested at two levels (5 and 10%; or 2.5 and 5% for tendon) in two sessions (morning and afternoon). There were four replicates (the chucks). The internal order of the samples tested, within the four replicates, was arranged so that all effects and interactions could be estimated from three replicates in which these effects and interactions were not confounded with the sessions. ANOVA and estimation of the partially confounded effects followed a method detailed by Yates (1958). Bonferroni least significant differences were determined for the sensory data. Linear correlation coefficients (SAS, 1985) were calculated for the sensory panel data, Lee-Kramer shear forces, hydroxyproline content and proximate analysis data. Least squares fits and slopes were determined on selected data sets. RESULTS AND DISCUSSION The peri/endomysium extraction procedure changed the composition of the original meat to a mixture that was higher in collagen, lower in protein and
E. D. Strange, R. C. Whiting
66
TABLE l Composition of the Peri/Endomysium Fraction
Protein (%)
Starting material Finished preparation
HzO (%)
Fat (%)
Protein basis"
Wet weight basis H)T b (%)
Col~ (%)
Hyp (%)
Col (%)
22-05
77.2
1.73
0" 131
0.94
0.594
4.24
12.15
83.2
3-82
0-294
2.10
2.42
17.28
a Calculated as % of protein. b Hydroxyproline. c Collagen (Hyp x 7-14 = Col) (Dransfield, 1977).
higher in fat. The data presented in Table 1 demonstrate that this extraction method removed myofibrillar and sacroplasmic proteins leaving connective tissue. By extracting thin slices rather than ground or macerated meat the architecture of the intramuscular connective tissue was maintained. Restructured beef (RSB) made with this fraction had slightly increased amounts of perimysium and endomysium. The composition of the square cut chucks used to make RSB is presented in Table 2. The most abundant connective tissue was epimysium and represented almost 3% of the weight of the lean tissue in the chuck. TABLE 2 Components of Square Cut Chucks Used to Make Restructured Beef Steaks
Chuck A (kg)
Chuck B (kg}
Chuck C (kg)
Chuck D (kg)
45.5 31-1 5-5 8"1 0.2
41.8 25.9 8.3 7-2 0.3
36-4 21'1 6.6 6.8 0.2
34'4 18"6 8'4 5-8 0-3
Original weight Muscle weight Fat weight Bone weight LN a weight
Mean original weight (%)
60'6 + 18'6 + 17"6 + 0-7 +
6"1 5-1 0"8 0"2
Connective tissues Tendon Epimysium Gristle
0" 115 0.813 0"369
0.190 0-880 0.370
0-136 0'610 0-233
0-104 0-556 0"234
0"35+0-09 1"80+0"22 0"75 + 0' ! 1
Total
1-3
1-4
1-0
0"9
2"89 ___0"32
* Ligamentum nuchae.
Effects of added connective tissues on restructured beef steaks
67
TABLE 3 M e a n Chemical C o m p o s i t i o n for Each Product
Connective tissue Control t Epimysium Gristle Peri/endo z Tendon
Level (%)
Hydroxyproline (ltg/mg wet wt)
Protein + SD ~ (%)
Fat + SD (%)
Water 4- SD (%)
5 10 5 10 5 10 2-5 5
1"12 + 0-07 2"58 + 0"87*** 3"484-0.88 b** 2-34 ___0-50 a** 4"04__ 0.58 b** 1.17 4- 0.07 ° 1.34 + 0.16" 2-00 + 0.21"** 3.004-0.56 h**
21"25 + 1-85 21.45 + 1"39" 21"94+ 1.59" 21"46 4- 2.00 ~ 21'544-1-78" 20'46 4- 1.49" 20-26 4- 1.66" 20.67 + 1.96" 21.404-2-09"
3"80 + 1-24 4.43 + 0-99* 4"89+0"30 ~ 3.82 4- 1.17" 4.63+0"56 a 3-58 + 1-24" 3-45 4- 1.58 a 3.99 + 1.44a 3.224- 1'28 °
73"12 + 0-57 72"05 + 0"55** 71"37+ 1-11"* 72.44 _ 0"81" 71-174-1.19"* 73-39 + 1.07" 73-90 + 0-98* 72.74 4- 0-64 ~ 7 2 . 7 4 + 1.18 °
' N o a d d e d connective tissue. " Product m a d e with p e r i / e n d o m y s i u m fraction. 3 SD, S t a n d a r d deviation; N = 4 ( n u m b e r of replicates). * M e a n significantly different from control mean, p < 0-05 (Student t). ** M e a n significantly different from control mean, p < 0.01 (Student t). Pairs o f values with different letter superscripts are different, p < 0"05 (Student t).
Isolatable connective tissue was 4-79% of the lean muscle tissue. The ligamentum nuchae was- excluded from all RSB steaks. Chemical composition data from each of the RSB products is shown in Table 3. Hydroxyproline contents (the marker amino acid of collagen, the major connective tissue protein) of the RSB products with added epimysium, gristle and tendon were significantly higher than the control RSB. There were no significant differences in % fat and % protein. Per cent water did show some significant changes. Samples containing 5 and 10% epimysium and 10% gristle had significantly less water though the actual differences were very small (1-2%). The composition of the products reflects the amount of added connective tissue. The hydroxyproline content of the samples containing the enriched peri/endo preparation is about what would be expected in such products given the composition of the starting materials. The difference in hydroxyproline content of products containing the enriched peri/endo preparation from the hydroxyproline content of the control product was not significant at p < 0.05 but the 10% peri/endo RSB had significantly more hydroxyproline than the control if tested at the p < 0"1 level, just outside of the usual standards of significance. ANOVA of the sensory data showed that the panel could discriminate between types and amounts of connective tissue. The ANOVA also showed that there was a significant effect on the sensory scores depending on when (morning or afternoon) the sample had been evaluated. The means and the
68
E. D. Strange, R. C. Whiting
TABLE
4
Mean Sensory Scores and Kramer Shear Forces for Each Product Connective tissue
Control 7 Epimysium Gristle Peri/endo s Tendon
Let, el added (%)
5 10 5 10 5 10 2"5 5
Mean sensory scores z
Kramer shear jorce'- {Newtons) q- S D 3
IT ~
CT ~
OT 6
6.42 6.59a 5.82b 6"06° 5-785 5.9l a 6-36" 5-53`'* 4"98"*
6.42 6.47a 4-96b* 5-765 4.94`'* 6.32~ 5.995 4"52`'* 3.48"*
6-22 6.36° 5.17b* 5.48a 4.995* 6-01`" 5.75° 4"415* 3.84`'*
Raw
62-0 + 80-3 + 91.2 + 81-8 + 98-1 + 61.9 + 60-2 + 71-4 + 83'6 +
5"5 8-50* 10.6a* 2'5`'* 7"7~* 6-4`" 9.8`" 6"1" 12'8"*
Cooked
78.8 + 78.8 + 74-8 + 76.6 + 72'5 + 79.5 + 79.1 + 83.9 _ 87-1 +
3.9 8'6" 2.5" 4'35 9"0~ 6"0~ 5-05 6-5a 2-9`'*
t Mean sensory score differences were evaluated using the Bonferroni least significant difference (LSD) method. LSD for IT = 0"76, for CT = 1-15, and for OT = 0-98. -" Lee-Kramer shear force differences were evaluated using Student t test. 3 SD, standard deviation; N = 4 (number of replicatesj. "~IT, initial tenderness. -~CT, connective tissue. 6 OT, overall texture. " No connective tissue isadded to the control. 8 Product made with peri/endomysium fraction. * Significantly different from control (p < 0"05). Pairs of values with different letter superscripts are different (p < 0-05). least significant differences for s e n s o r y scores are s h o w n in T a b l e 4. F o r I T (initial tenderness) the p a n e l c o u l d d i s c r i m i n a t e b e t w e e n 5 % a n d 1 0 % a d d e d e p i m y s i u m . T h e p a n e l also significantly d i s c r i m i n a t e d b e t w e e n s a m p l e s with a d d e d t e n d o n a n d c o n t r o l s a m p l e s . T h e panel, h o w e v e r , c o u l d n o t distinguish s a m p l e s c o n t a i n i n g 5 % a n d 1 0 % e p i m y s i u m , gristle a n d p e r i / e n d o f r o m c o n t r o l , a l t h o u g h 1 0 % e p i m y s i u m a n d gristle were scored lower, the d e c r e a s e w a s n o t significant. F o r C T ( c o n n e c t i v e tissue) a n d O T (overall texture) the p a n e l c o u l d d i s c r i m i n a t e b e t w e e n 5 a n d 10% a d d e d e p i m y s i u m a n d t h e y assigned significantly l o w e r scores to s a m p l e s c o n t a i n i n g e p i m y s i u m a n d gristle at the 10% level a n d all levels o f a d d e d t e n d o n c o m p a r e d to the c o n t r o l . B e r r y et al. (1986) f o u n d t h a t a n e x p e r t p a n e l c o u l d d i s t i n g u i s h b e t w e e n R S B s a m p l e s which c o n t a i n e d 1.25, 1.82 a n d 2.45 p g / m g h y d r o x y p r o l i n e , respectively. In c o n t r a s t , we f o u n d t h a t d i s c r i m i n a t i o n by o u r panelists was d e p e n d e n t o n the t y p e o f c o n n e c t i v e tissue present, as well as the q u a n t i t y . T h e results f r o m the L e e - K r a m e r p e a k s h e a r f o r c e m e a s u r e m e n t s are also s h o w n in T a b l e 4. T h e L e e - K r a m e r s h e a r forces on r a w R S B were
E[lbcts ~!1 a&led connectire tissues on restructured bee/steaks
69
TABLE 5 Correlations Between Hydroxyproline Content and Kramer Shear Forces for All Types of Restructured Products--Control Products Included (N = 40)
Hyp a K-S raw
K-S raw n
K-S cooked
0"837** 1.000
-0-301 -0.213
a Hydroxyproline. b Lee-Kramer shear force. ** Correlation coefficient significant p < 0-01.
significantly higher than control RSB for RSB containing both levels of added epimysium and gristle (5% and 10%) and 5% added tendon. These results reflect the sensory evaluation results better than the Lee-Kramer shear force of the cooked RSB. The Lee-Kramer peak shear forces of cooked RSB show only one significant change for RSB with added connective tissue. RSB with 5% tendon had a significantly higher shear force than that of RSB containing no added connective tissue. These results contrast with the panel scores for connective tissue (CT) and overall texture (OT) which show that the panel significantly downgraded RSB which contained 10% epimysium and gristle and both levels of added tendon (2.5% and 5%). Berry et al. (1986) used a single blade shear force device. They obtained increasing shear force measurements on cooked steaks as collagen content increased--we did not. Differences in technique, however, make it impossible to compare results in any detail (e.g. magnitude of changes observed). Correlation coefficients were calculated for Lee-Kramer shear forces on raw steaks and on cooked steaks and hydroxyproline content of the RSB steaks. The correlation coefficients are shown in Table 5. The significant positive correlation of hydroxyproline content with Lee-Kramer shear forces on raw RSB implies that as the amount of connective tissue increases the force necessary to shear the RSB sample also increases. Lee-Kramer shear forces on cooked RSB were not significantly correlated with hydroxyproline. Moiler (1981) showed that as cooking temperature increased the contribution of connective tissue to the shear force decreased. Strange and Whiting (1988) also showed that when RSB containing differing amounts of connective tissue was heated to temperatures above 60°C no significant differences in Lee-Kramer shear forces were found. The results of Booren et al. (1981) demonstrated that while Lee-Kramer shear force on cooked RSB was related to sensory tenderness it was not related to sensory residual connective tissue.
E. D. Strange, R. C. Whiting
70
TABLE 6 C o r r e l a t i o n s Between H y d r o x y p r o l i n e C o n t e n t , K r a m e r Shear Forces a n d Corrected Sensory Scores (Controls Set at Zero) for All Types o f Restructured Beef ( N --- 40)
Hyp a K-S b raw K-S cooked
Initial tenderness
Connective tissue
Overall texture
- 0"277 0"206 - 0"260
- 0-503"* -0.426** 0.042
- 0"397* -0.323* - 0" 116
" Hydroxyproline. b K r a m e r shear force. * C o r r e l a t i o n coefficient significant, p < 0-05. ** Correlation coefficient significant, p < 0.01.
When the sensory scores were evaluated for the effect of time of testing (i.e. was the tasting done in the morning or afternoon) the sensory scores for control samples were significantly higher for CT (Connective Tissue) (p < 0"01) and OT (Overall Texture) values (p < 0"05) in the morning than in the afternoon. The control samples' IT (Initial Tenderness) scores were also higher in the morning but not significantly (p < 0-1). Because the panel consistently judged samples more favorably in the morning a correction was applied to all sensory scores by subtracting the panelist's response to the control sample from the panelist's response to the test sample (epimysium, gristle, peri/endo, or tendon). It was assumed that panelists responded to control samples in the same manner that they responded to samples containing added connective tissue. These corrected sensory scores, with controls set at zero, gave a more accurate measure of how the samples varied in their sensory properties without the complication of morning or afternoon biases. The corrected values were used to calculate correlation coefficients which reflect the influence of composition on unbiased sensory responses. Corrected sensory scores for CT (Connective Tissue) and OT (Overall Texture) correlated significantly with hydroxyproline content (Table 6). As the hydroxyproline content increased, the scores for connective tissue decreased (0 = excessive; 10 = minimal) and the overall texture decreased (0 = dislike extremely; 10 = like extremely). Table 6 also shows how the Lee-Kramer shear force reflects the sensory evaluation. As the shear force on raw RSB increased, the connective tissue score and the overall texture score decreased. The Lee-Kramer shear force on cooked RSB, which is what the panelists tested, did not reflect the judgement of the panelists. The panelists were far more sensitive to the presence of cooked connective tissue in RSB than shear force on the cooked products. Table 7 presents the correlation coefficients calculated for individual types
Effects ~[ added connective tissues on restructured bee]" steaks
71
TABLE 7
Correlations Between Corrected Sensory Scores (Controls Set at Zero), Shear Forces and Hydroxyproline Content for Each Connective Tissue Additive Type of Restructured Beef. Control (No Added Connective Tissue) Sample Sensory Scores of Zero are Included in the Calculations. N = 12 Sensory scores Initial tenderness
Connective tissue
Overall texture
Hyp°
Epib Gri c Perid Ten"
- 0"635* -0"559* 0-231 -0-629*
- 0'762** -0-892** 0.042 -0"790**
-0'676" -0"837** 0' 115 -0"716"*
K-S: raw
Epi Gri Peri Ten
-0"631" -0"500 0'380 - 0"620*
-0"688** -0"701"* -0"027 - 0"825**
-0-603* -0"645* - 0"205 - 0-714"*
K-S cooked
Epi Gri Peri Ten
0"547 0.485 - 0"514 -0.620*
0"400 0-681" 0"392 -0.594*
0'350 0-796** - 0-594" -0-629*
K-S raw
K-S cooked
Hypa
Epi Gri Peri Ten
0"949"* 0'863** 0-320 0.648"
- 0"316 -0-524 - 0-056 0"469
" Hydroxyproline. b Samples containing added epimysium. ¢ Samples containing added gristle. J Samples containing added peri/endomysium preparation. e Samples containing added tendon. : Lee-Kramer shear force. *Correlation coefficient significant, p < 0-05. ** Correlation coefficient significant, p < 0"01. o f c o n n e c t i v e tissues. S e n s o r y scores for s a m p l e s c o n t a i n i n g e x t r a p e r i / e n d o m y s i u m did n o t correlate with h y d r o x y p r o l i n e or L e e - K r a m e r shear forces m e a s u r e d o n r a w m e a t ; o n l y O T c o r r e l a t e d with L e e K r a m e r s h e a r forces o n c o o k e d meat. T h e h y d r o x y p r o l i n e c o n t e n t o f the p e r i / e n d o m y s i u m samples was n o t significantly c o r r e l a t e d with either L e e K r a m e r shear force m e a s u r e d . T h e actual difference in h y d r o x y p r o l i n e c o n t e n t between c o n t r o l R S B ( 1 . 1 2 # g / r a g h y d r o x y p r o l i n e ) a n d 10% p e r i / e n d o R S B (1.34/~g/mg h y d r o x y p r o l i n e ) was small a n d the lack o f significant c o r r e l a t i o n is n o t surprising. H o w e v e r , M c K e i t h et al. (1985)
72
E. D. Strange, R. C. Whiting
showed significant differences in sensory connective tissue and WarnerBratzler shear forces, as part of a large study, when two round muscles, the gluteus medius (l'13l~g/mg hydroxyproline) and the biceps femoris (1"34 pg/mg hydroxyproline), were compared. These muscles have hydroxyproline content similar to control RSB and 10% peri/endo RSB. The hydroxyproline content was calculated from data presented by McKeith et al. (1985) using 1/7"14 as a conversion factor from collagen content to hydroxyproline content (Dransfield, 1977). Perimysium and endomysium (intramuscular connective tissue) is important to the texture of individual muscles (Dransfield, 1977) but RSB is a mixture of different muscles. The lack of correlation with hydroxyproline content and either type of Lee-Kramer shear force may indicate that the peri/endomysium contribution to texture would be better measured using other types of mechanical tests, such as compression tests (Dransfield, 1977). The hydroxyproline content of the other types of connective tissue samples correlated significantly with IT, CT and OT sensory scores. The three sensory scores also correlated significantly with the Lee-Kramer shear forces on raw RSB except for IT for gristle. Cooked RSB containing gristle had decreasing cooked shear forces as the CT and OT sensory scores decreased, opposite to what would be expected. This may be due to a lack of binding between the meat pieces and the added connective tissue which was detected by the Lee-Kramer shear force measurement but ignored by the panelists. Tendon RSB samples did correlate in the expected direction but examination of the data presented in Table 3 for tendon samples shows that the differences from control samples are much smaller for cooked shear forces than for raw shear forces. Correlation coefficients are higher for the individual types of connective tissues than when taken as a whole. Least squares fits of the sensory (CT) data with the hydroxyproline data are shown in Fig. 2. The slope of the line for the relationship between CT values and hydroxyproline content for RSB containing tendon is steeper than the lines for the relationships of the CT versus hydroxyproline for samples containing epimysium and gristle. The panelists perceive tendon connective tissue as more objectionable than epimysial and/or gristle connective tissue. Comparison of the panelist's scores for CT with the Lee-Kramer shear force measurements on raw tissue also shows that the panelists report lower scores for tendon than for samples containing epimysium or gristle which have similar shear forces. The least squares fit lines for gristle and epimysium for both hydro/~yproline and Kramer shear force versus corrected CT are not different from each other showing that the panelists perceived the epimysium and gristle in the same way. If the effect of tendon is ignored an increase of 1 mg hydroxyproline per gram of wet tissue results in a decrease ofone unit of our sensory score. Least squares fits of hydroxyproline content
Effects of added connectire tissues on restructured bee[ steaks Hydroxyprollne/~g / mg
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-5
Kramer Multiblade Shear Force Newtons / gram Raw Sample ÷1 40
r. Or)
"d
50
0
I
.1
60
70
80
•
90
100
110
120
I
I
I
I
............
"~-.......~
o ",
x
(b)
0
\
., O
-
- TENDON
-4-
x ............. EPIMYSIUM
-5 -
• GRISTLE A CONTROL
• "...
.............
\\
X
~ \~. \
Fig. 2. Least squares regressions for: (a) hydroxyproline versus corrected connective tissue sensory score (panelist's response to connective tissue sample minus panelist's response to
control sample).The larger the negativecorrected sensory score the more connective tissue (CT) was perceived by the panelist. (b) Kramer multiblade peak shear force in Newton's per gram raw sample versus corrected connective tissue sensory score (panelist's response to connective tissue sample minus panelist's response to control sample). The larger the negative corrected sensory score the more connective tissue (CT) was perceived by the panelist.
and raw Lee-Kramer peak shear force for the individual types of connective tissues (excluding peri/endo) show no significant differences in slope or intercept. One milligram of hydroxyproline per gram RSB increased the Lee-Kramer peak shear force by 10 N per gram of raw RSB. Production of RSB product from the chuck is possible with minimum trimming. RSB products containing up to 5% epimysium and/or gristle were not perceived as different from a RSB made with thoroughly trimmed meat. This finding confirms the results of Booren et al. (1981) and Berry et al. (1988). However, even small amounts of tendon caused severe downgrading by the panelists of RSB. The total amount of connective tissue in the chuck
74
E. D. Strange, R. C. Whiting
does not exceed 5% of the muscle weight, but certain individual muscles may contain more than 5% epimysium and gristle, particularly the supraspinatus which has gristle extending through the muscle and the infraspinatus which has tendon attached and gristle extending through the muscle. The most effective objective measurement of the panelists' responses was L e e - K r a m e r shear force measurement on raw samples. Hydroxyproline measurements were also effective but require extensive analytical techniques and are subject to sampling difficulties. Caution must be used if there is an appreciable a m o u n t of tendon in the product, because tendon has a stronger sensory effect than other types of connective tissue. ACKNOWLEDGEMENTS The authors would like to acknowledge J. Phillips (ARS-NAA, 600 E. Mermaid Lane, Philadelphia, PA 19118) for statistical assistance and D. Hoke for technical support. REFERENCES AOAC (I 965). In Official Methods of Analysis ( 10th edn), Assoc. Offic. Agr. Chem., Washington, DC. Berry, B. W., Smith, J. J. & Secrist, J. L. (1986). J. Food Prot., 49, 455. Berry, B. W., Smith, J. J., Secrist, J. L. & Douglass, L. A. (1988). J. Food Quality, il, 15. Booren, A. M., Mandigo, R. W., Olson, D. G. & Jones, K. W. (1981). J. FoodSci., 46, 1665. Briedenstein, B. C. (1982). Intermediate value beef products. National Live Stock and Meat Board, Chicago, IL., p. 1 and 13. Dransfield, E. (1977). J. Sci. Food Agric., 28, 833. McKeith, F. K., DeVol, D. L., Miles, R. S., Bechtel, P. T. & Carr, T. R. (1985). J. Food Sci., 50, 869. Moiler, A. J. (1981). Meat Sci., 5, 247. Recio, H. A., Savell, J. W., Branson, R. E., Cross, H. R. & Smith, G. C. (1987). J. Food ScL, 52, 146 I. SAS (1985). In S A S / S T A T Guide for Personal Computers Version (6 edn), SAS Institute Inc., Cary, North Carolina. Strange, E. D. & Whiting, R. C. (1988). J. Food Sci., 53, 1224. Tucker, H. Q., Voegeli, M. M. & Wellington, G. H. (1952). In ,4 Cross Sectional Muscle Nomenclature of the Beef Carcass, ed. L. J. Bratzler, Michigan State College Press, East Lansing, MI. Woessner, J. F., Jr (1961). Arch. Biochem. Biophvs., 93, 440. Yates, F. (1958). The Design and Analysis of Factorial Experiments. Technical Communication No. 35 of the Commonwealth Bureau of Soils, Harpenden, England, Commonwealth Agricultural Bureaux, Farnham Royal, England, pp. 21-22, 65.
Effects of Added Connective Tissues on the Sensory and Mechanical Properties of Restructured Beef Steaks E. D. Strange & R. C. W h i t i n g us Department of Agriculture, ARS, Eastern Regional Research Center, 600 East Mermaid Lane, Philadelphia, PA t9118, USA (Received 17 January 1989; accepted 13 June 1989) ABSTRACT To quantify objectionable levels of connective tissues, restructured beef products were made with 2"5 and5% added tendon; 5 and 10% added epimysium, gristle, or peri/endomysium; and a control Initial tenderness (IT), residual connective tissue ( CT ), and overall texture ( 0 T) were evaluated by a sensoo' panel. Panelists adversely scored IT, CT, and OT for 2"5 and 5% tendon and CT and OT for 10% epimysium and gristle. CT and OT scores correlated with hydroxyproline content and Lee-Kramer peak shear force for uncooked steaks with added tendon, gristle and epimysium but not peri/endomysium. Acceptable products can be made when raw materials are free of tendons and contain only limited amounts of epimysium.
INTRODUCTION Restructured beef(RSB) made from under utilized portions of carcasses, e.g. chucks, should have both greater appeal to consumers and a better return to producers than ground meats made from the same cuts (Briedenstein, 1982). Extensive trimming to remove connective tissue is perceived as necessary to make an acceptable restructured product from chuck (Briedenstein, 1982). Recio et al. (1987) showed that consumers preferred restructured beef (RSB) steaks made with thoroughly trimmed clods. Booren et al. (1981) found that acceptable RSB steaks could be made from choice chuck. Berry et al. (1986) found that an expert panel could detect the difference between restructured steaks made with and without added connective tissue, but no attempt was made to identify the types of connective tissue present in the RSB or to 61 ~ us Government
E. D. Strange, R. C. Whiting
62
correlate shear force measurements with quantity of connective tissue or panelists' responses. Berry et al. (1988) found that consumer panels could discriminate only between RSB steaks with 'extra high' levels and "high' or 'low' levels of connective tissue and concluded that trimming chucks of connective tissue may not be necessary for acceptable RSB products. The objectives of our studies were to determine the amount and type of connective tissues from beef forequarters that affect sensory quality of restructured beef and to relate sensory panel scores to hydroxyproline content (a measure of connective issue amount) and to Lee-Kramer multiblade peak shear force measurements. MATERIALS AND METHODS Restructured beef steaks Four square cut chucks (USDA Choice, Yield grade 2, NAMP No. 113~, were obtained from local sources. The chucks were dissected into component parts: muscle, fat, bone, tendon, epimysium (connective tissue surrounding individual muscles), and gristle (thick connective tissue contained within the muscle). The exact weight of each component was measured and its percentage of the chuck determined. The trimmed muscles from the chuck were frozen, tempered and diced into cubes 6-12 mm on a side. Isolated tendon, epimysium and gristle were diced 3-6ram on a side. The peri/endomysium (peri/endo) fraction (see below) was used without any further treatment. A series of restructured products was made from diced muscle mixed with different amounts of connective tissue. Gristle, epimysium, and peri/endo products were made to contain 5 and 10% (w/w) and tendon products to contain 2.5 and 5% (w/w) added connective tissue. A control product made with the extensively trimmed meat without any added connective tissue was also made. The cubed meat and the connective tissues with sodium tripolyphosphate (STPP) (0.125%) and NaCI (0.75%) were combined in a Hobart omni-mixer with a leaf-paddle attachment for 2 rain at the slowest speed. After mixing, the product was stuffed into 55 mm diameter casings and allowed to bind at 11°C for 4h before freezing at -20°C. The logs of RSB were tempered before being sliced into 2-5 cm thick steaks and vacuum packaged. There were nine different types of product.
Peri/endo fraction A fraction enriched in perimysium and endomysium was prepared from the supraspinatus and infraspinams muscles (Tucker et al., 1952). These muscles
Effects o f added connectire tissues on restructured beef steaks
63
Meat slice 2-5 kg Extract 2 x with 4 liters 50ram CaCI2 for 4h then 16h Discard liquid extract Extract 6 x with 4 liters I-0M NaCI once for 8 h then 5 × for 24 h each Discard liquid extract
Extract 1 × with 4 liters water for 6h Discard liquid extract Extract 1 x with 4 liter I'0M NaCI for 16h Discard liquid extract Wash with water until liquid tests free of Na Flame Discard washes
Peri/endo fraction 638G Fig. 1.
Extraction flow diagram for the preparation of perimysium and endomysium enriched meat fraction.
were dissected and trimmed of all visible fat and thick connective tissue (including the thick connective tissue within the muscle), partially frozen, and sliced 1-2 m m thick across the muscle fibers. The sarcoplasmic and myofibrillar proteins were selectively extracted using the procedure outlined in Fig. 1. The initial treatment with 50 mM CaC12 removes the sarcoplasmic proteins, the treatment with 1-0M NaCI removes the myofibrillar proteins and the water washes aid in the extraction of the myofibrillar proteins by osmotic shock. The washes were removed by straining the slice extracting mixture through a stainless steel metal screen (1.5 x 2mm). Protein, moisture and hydroxyproline content were measured on the starting material as well as the completed fraction. This procedure permits the isolation of a muscle fraction enriched in perimysium and endomysium with normal connective tissue architecture.
Chemical analyses Two tempered steaks from each product were ground twice through a meat grinder with 2 m m size holes. The ground restructured steaks were used for % protein (Kjeldahl N), % fat (Soxhlet extraction with petroleum ether), % moisture (16-18h at 100°C) (AOAC, 1965). Hydroxyproline assays (Woessner, 1961) were done on approximately 100mg (exact weight determined for each analysis) of 10 g samples of ground restructured meat
64
E. D. Strange, R. C. Whiting
which had been homogenized to a uniform paste in a Brinkman polytron tissue grinder.
Cooking Cooked restructured steaks were prepared for sensory panel evaluation and shear force measurements by grilling partly frozen steaks on a Farberware open hearth grill to an internal temperature of 70°C (measured with therrnocouples inserted into center of the restructured steaks) turning once during the cooking process.
Shear measurement A Lee-Kramer multi-blade shear cell attached to an Instron Universal Testing Machine was used to measure shear force on both raw and cooked restructured steaks. The raw steaks were defrosted at room temperature (20°C) and cut into two parts (semicircles of diameter 55 cm, 2.54 cm thick). The weight was determined and the peak shear force obtained using a cross head speed of 50mm/min. Four shears per product per carcass were obtained. Shear force measurements were also made on cooked restructured steaks. After the outer crusts were trimmed from the cooked steak, the remaining steak was cutinto two parts, weights recorded and the peak shear force measured on steak samples cooled to room temperature. Four shears per product per carcass were obtained (i.e. 16 shears per product). Shear force was calculated as Newtons per gram sample.
Sensory panel Sensory testing for texture was carried out by a fifteen member trained panel consisting of Eastern Regional Research Center employees. Panel members were trained by presenting them with cooked RSB steaks made with high levels of connective tissue and steaks made with thoroughly trimmed meat. The samples were identified and use of unstructured l0 cm scoring lines was explained. Panel members were asked to evaluate the steaks based on the following instructions: initial tenderness (IT) from very tender to very tough and to evaluate this property after 3-4 chews; connective tissue (CT) from minimal to excessive and to evaluate this property after completely chewing the product; and overall impression of the texture (OT) of the restructured steak from like extremely to dislike extremely. After the training sessions, prospective panelists were tested by presenting coded and unidentified RSB steaks made with high levels of connective tissue and made with thoroughly trimmed meat. Only those who could discriminate between the two steaks were chosen to be members of the texture panel. All texture evaluations were
Effects of added connectire tissues on restructured beefsteaks
65
carried out in individual testing booths with red lighting to prevent visual identification of high connective tissue samples. All sensory evaluations were completed in 4 days using both morning and afternoon sessions. The samples presented at any one session were determined by the experimental design. Each panelist at each session was presented with the coded (three random numbers) predetermined five samples in random order. Unknown to the panelists one of these samples was always a control (RSB made with trimmed meat). Meat samples were cooked as for the Lee-Kramer shear force measurements and were presented to the panelists hot. Each panelist received 16th part of 2.54 cm thick 55 cm diameter restructured steak. Sample size presented to the panelists was approximately 5 g. It was determined during the training sessions that this size sample was comfortable for the panelists to chew at one time and gave samples of sufficient size for evaluation. Each restructured steak from each carcass was tested by at least 14 panelists. After the panel evaluation, the sample scores were determined by measuring the distance the panelist had marked on the scoring sheet. For IT (Initial Tenderness) very tender would be a 10 and very tough would be a 0; for CT (Connective Tissue) minimal would be 10 and excessive would be 0; and for OT (Overall Texture) 10 would be like extremely and 0 would be dislike extremely. A hedonic scale was chosen for OT to detect any unusual texture changes not anticipated in the initial study.
Experimental design The experimental design for the sensory panel testing was a 2 x 4 factorial. Each main effect (gristle, epimysium, peri/endo, and tendon) was tested at two levels (5 and 10%; or 2.5 and 5% for tendon) in two sessions (morning and afternoon). There were four replicates (the chucks). The internal order of the samples tested, within the four replicates, was arranged so that all effects and interactions could be estimated from three replicates in which these effects and interactions were not confounded with the sessions. ANOVA and estimation of the partially confounded effects followed a method detailed by Yates (1958). Bonferroni least significant differences were determined for the sensory data. Linear correlation coefficients (SAS, 1985) were calculated for the sensory panel data, Lee-Kramer shear forces, hydroxyproline content and proximate analysis data. Least squares fits and slopes were determined on selected data sets. RESULTS AND DISCUSSION The peri/endomysium extraction procedure changed the composition of the original meat to a mixture that was higher in collagen, lower in protein and
E. D. Strange, R. C. Whiting
66
TABLE l Composition of the Peri/Endomysium Fraction
Protein (%)
Starting material Finished preparation
HzO (%)
Fat (%)
Protein basis"
Wet weight basis H)T b (%)
Col~ (%)
Hyp (%)
Col (%)
22-05
77.2
1.73
0" 131
0.94
0.594
4.24
12.15
83.2
3-82
0-294
2.10
2.42
17.28
a Calculated as % of protein. b Hydroxyproline. c Collagen (Hyp x 7-14 = Col) (Dransfield, 1977).
higher in fat. The data presented in Table 1 demonstrate that this extraction method removed myofibrillar and sacroplasmic proteins leaving connective tissue. By extracting thin slices rather than ground or macerated meat the architecture of the intramuscular connective tissue was maintained. Restructured beef (RSB) made with this fraction had slightly increased amounts of perimysium and endomysium. The composition of the square cut chucks used to make RSB is presented in Table 2. The most abundant connective tissue was epimysium and represented almost 3% of the weight of the lean tissue in the chuck. TABLE 2 Components of Square Cut Chucks Used to Make Restructured Beef Steaks
Chuck A (kg)
Chuck B (kg}
Chuck C (kg)
Chuck D (kg)
45.5 31-1 5-5 8"1 0.2
41.8 25.9 8.3 7-2 0.3
36-4 21'1 6.6 6.8 0.2
34'4 18"6 8'4 5-8 0-3
Original weight Muscle weight Fat weight Bone weight LN a weight
Mean original weight (%)
60'6 + 18'6 + 17"6 + 0-7 +
6"1 5-1 0"8 0"2
Connective tissues Tendon Epimysium Gristle
0" 115 0.813 0"369
0.190 0-880 0.370
0-136 0'610 0-233
0-104 0-556 0"234
0"35+0-09 1"80+0"22 0"75 + 0' ! 1
Total
1-3
1-4
1-0
0"9
2"89 ___0"32
* Ligamentum nuchae.
Effects of added connective tissues on restructured beef steaks
67
TABLE 3 M e a n Chemical C o m p o s i t i o n for Each Product
Connective tissue Control t Epimysium Gristle Peri/endo z Tendon
Level (%)
Hydroxyproline (ltg/mg wet wt)
Protein + SD ~ (%)
Fat + SD (%)
Water 4- SD (%)
5 10 5 10 5 10 2-5 5
1"12 + 0-07 2"58 + 0"87*** 3"484-0.88 b** 2-34 ___0-50 a** 4"04__ 0.58 b** 1.17 4- 0.07 ° 1.34 + 0.16" 2-00 + 0.21"** 3.004-0.56 h**
21"25 + 1-85 21.45 + 1"39" 21"94+ 1.59" 21"46 4- 2.00 ~ 21'544-1-78" 20'46 4- 1.49" 20-26 4- 1.66" 20.67 + 1.96" 21.404-2-09"
3"80 + 1-24 4.43 + 0-99* 4"89+0"30 ~ 3.82 4- 1.17" 4.63+0"56 a 3-58 + 1-24" 3-45 4- 1.58 a 3.99 + 1.44a 3.224- 1'28 °
73"12 + 0-57 72"05 + 0"55** 71"37+ 1-11"* 72.44 _ 0"81" 71-174-1.19"* 73-39 + 1.07" 73-90 + 0-98* 72.74 4- 0-64 ~ 7 2 . 7 4 + 1.18 °
' N o a d d e d connective tissue. " Product m a d e with p e r i / e n d o m y s i u m fraction. 3 SD, S t a n d a r d deviation; N = 4 ( n u m b e r of replicates). * M e a n significantly different from control mean, p < 0-05 (Student t). ** M e a n significantly different from control mean, p < 0.01 (Student t). Pairs o f values with different letter superscripts are different, p < 0"05 (Student t).
Isolatable connective tissue was 4-79% of the lean muscle tissue. The ligamentum nuchae was- excluded from all RSB steaks. Chemical composition data from each of the RSB products is shown in Table 3. Hydroxyproline contents (the marker amino acid of collagen, the major connective tissue protein) of the RSB products with added epimysium, gristle and tendon were significantly higher than the control RSB. There were no significant differences in % fat and % protein. Per cent water did show some significant changes. Samples containing 5 and 10% epimysium and 10% gristle had significantly less water though the actual differences were very small (1-2%). The composition of the products reflects the amount of added connective tissue. The hydroxyproline content of the samples containing the enriched peri/endo preparation is about what would be expected in such products given the composition of the starting materials. The difference in hydroxyproline content of products containing the enriched peri/endo preparation from the hydroxyproline content of the control product was not significant at p < 0.05 but the 10% peri/endo RSB had significantly more hydroxyproline than the control if tested at the p < 0"1 level, just outside of the usual standards of significance. ANOVA of the sensory data showed that the panel could discriminate between types and amounts of connective tissue. The ANOVA also showed that there was a significant effect on the sensory scores depending on when (morning or afternoon) the sample had been evaluated. The means and the
68
E. D. Strange, R. C. Whiting
TABLE
4
Mean Sensory Scores and Kramer Shear Forces for Each Product Connective tissue
Control 7 Epimysium Gristle Peri/endo s Tendon
Let, el added (%)
5 10 5 10 5 10 2"5 5
Mean sensory scores z
Kramer shear jorce'- {Newtons) q- S D 3
IT ~
CT ~
OT 6
6.42 6.59a 5.82b 6"06° 5-785 5.9l a 6-36" 5-53`'* 4"98"*
6.42 6.47a 4-96b* 5-765 4.94`'* 6.32~ 5.995 4"52`'* 3.48"*
6-22 6.36° 5.17b* 5.48a 4.995* 6-01`" 5.75° 4"415* 3.84`'*
Raw
62-0 + 80-3 + 91.2 + 81-8 + 98-1 + 61.9 + 60-2 + 71-4 + 83'6 +
5"5 8-50* 10.6a* 2'5`'* 7"7~* 6-4`" 9.8`" 6"1" 12'8"*
Cooked
78.8 + 78.8 + 74-8 + 76.6 + 72'5 + 79.5 + 79.1 + 83.9 _ 87-1 +
3.9 8'6" 2.5" 4'35 9"0~ 6"0~ 5-05 6-5a 2-9`'*
t Mean sensory score differences were evaluated using the Bonferroni least significant difference (LSD) method. LSD for IT = 0"76, for CT = 1-15, and for OT = 0-98. -" Lee-Kramer shear force differences were evaluated using Student t test. 3 SD, standard deviation; N = 4 (number of replicatesj. "~IT, initial tenderness. -~CT, connective tissue. 6 OT, overall texture. " No connective tissue isadded to the control. 8 Product made with peri/endomysium fraction. * Significantly different from control (p < 0"05). Pairs of values with different letter superscripts are different (p < 0-05). least significant differences for s e n s o r y scores are s h o w n in T a b l e 4. F o r I T (initial tenderness) the p a n e l c o u l d d i s c r i m i n a t e b e t w e e n 5 % a n d 1 0 % a d d e d e p i m y s i u m . T h e p a n e l also significantly d i s c r i m i n a t e d b e t w e e n s a m p l e s with a d d e d t e n d o n a n d c o n t r o l s a m p l e s . T h e panel, h o w e v e r , c o u l d n o t distinguish s a m p l e s c o n t a i n i n g 5 % a n d 1 0 % e p i m y s i u m , gristle a n d p e r i / e n d o f r o m c o n t r o l , a l t h o u g h 1 0 % e p i m y s i u m a n d gristle were scored lower, the d e c r e a s e w a s n o t significant. F o r C T ( c o n n e c t i v e tissue) a n d O T (overall texture) the p a n e l c o u l d d i s c r i m i n a t e b e t w e e n 5 a n d 10% a d d e d e p i m y s i u m a n d t h e y assigned significantly l o w e r scores to s a m p l e s c o n t a i n i n g e p i m y s i u m a n d gristle at the 10% level a n d all levels o f a d d e d t e n d o n c o m p a r e d to the c o n t r o l . B e r r y et al. (1986) f o u n d t h a t a n e x p e r t p a n e l c o u l d d i s t i n g u i s h b e t w e e n R S B s a m p l e s which c o n t a i n e d 1.25, 1.82 a n d 2.45 p g / m g h y d r o x y p r o l i n e , respectively. In c o n t r a s t , we f o u n d t h a t d i s c r i m i n a t i o n by o u r panelists was d e p e n d e n t o n the t y p e o f c o n n e c t i v e tissue present, as well as the q u a n t i t y . T h e results f r o m the L e e - K r a m e r p e a k s h e a r f o r c e m e a s u r e m e n t s are also s h o w n in T a b l e 4. T h e L e e - K r a m e r s h e a r forces on r a w R S B were
E[lbcts ~!1 a&led connectire tissues on restructured bee/steaks
69
TABLE 5 Correlations Between Hydroxyproline Content and Kramer Shear Forces for All Types of Restructured Products--Control Products Included (N = 40)
Hyp a K-S raw
K-S raw n
K-S cooked
0"837** 1.000
-0-301 -0.213
a Hydroxyproline. b Lee-Kramer shear force. ** Correlation coefficient significant p < 0-01.
significantly higher than control RSB for RSB containing both levels of added epimysium and gristle (5% and 10%) and 5% added tendon. These results reflect the sensory evaluation results better than the Lee-Kramer shear force of the cooked RSB. The Lee-Kramer peak shear forces of cooked RSB show only one significant change for RSB with added connective tissue. RSB with 5% tendon had a significantly higher shear force than that of RSB containing no added connective tissue. These results contrast with the panel scores for connective tissue (CT) and overall texture (OT) which show that the panel significantly downgraded RSB which contained 10% epimysium and gristle and both levels of added tendon (2.5% and 5%). Berry et al. (1986) used a single blade shear force device. They obtained increasing shear force measurements on cooked steaks as collagen content increased--we did not. Differences in technique, however, make it impossible to compare results in any detail (e.g. magnitude of changes observed). Correlation coefficients were calculated for Lee-Kramer shear forces on raw steaks and on cooked steaks and hydroxyproline content of the RSB steaks. The correlation coefficients are shown in Table 5. The significant positive correlation of hydroxyproline content with Lee-Kramer shear forces on raw RSB implies that as the amount of connective tissue increases the force necessary to shear the RSB sample also increases. Lee-Kramer shear forces on cooked RSB were not significantly correlated with hydroxyproline. Moiler (1981) showed that as cooking temperature increased the contribution of connective tissue to the shear force decreased. Strange and Whiting (1988) also showed that when RSB containing differing amounts of connective tissue was heated to temperatures above 60°C no significant differences in Lee-Kramer shear forces were found. The results of Booren et al. (1981) demonstrated that while Lee-Kramer shear force on cooked RSB was related to sensory tenderness it was not related to sensory residual connective tissue.
E. D. Strange, R. C. Whiting
70
TABLE 6 C o r r e l a t i o n s Between H y d r o x y p r o l i n e C o n t e n t , K r a m e r Shear Forces a n d Corrected Sensory Scores (Controls Set at Zero) for All Types o f Restructured Beef ( N --- 40)
Hyp a K-S b raw K-S cooked
Initial tenderness
Connective tissue
Overall texture
- 0"277 0"206 - 0"260
- 0-503"* -0.426** 0.042
- 0"397* -0.323* - 0" 116
" Hydroxyproline. b K r a m e r shear force. * C o r r e l a t i o n coefficient significant, p < 0-05. ** Correlation coefficient significant, p < 0.01.
When the sensory scores were evaluated for the effect of time of testing (i.e. was the tasting done in the morning or afternoon) the sensory scores for control samples were significantly higher for CT (Connective Tissue) (p < 0"01) and OT (Overall Texture) values (p < 0"05) in the morning than in the afternoon. The control samples' IT (Initial Tenderness) scores were also higher in the morning but not significantly (p < 0-1). Because the panel consistently judged samples more favorably in the morning a correction was applied to all sensory scores by subtracting the panelist's response to the control sample from the panelist's response to the test sample (epimysium, gristle, peri/endo, or tendon). It was assumed that panelists responded to control samples in the same manner that they responded to samples containing added connective tissue. These corrected sensory scores, with controls set at zero, gave a more accurate measure of how the samples varied in their sensory properties without the complication of morning or afternoon biases. The corrected values were used to calculate correlation coefficients which reflect the influence of composition on unbiased sensory responses. Corrected sensory scores for CT (Connective Tissue) and OT (Overall Texture) correlated significantly with hydroxyproline content (Table 6). As the hydroxyproline content increased, the scores for connective tissue decreased (0 = excessive; 10 = minimal) and the overall texture decreased (0 = dislike extremely; 10 = like extremely). Table 6 also shows how the Lee-Kramer shear force reflects the sensory evaluation. As the shear force on raw RSB increased, the connective tissue score and the overall texture score decreased. The Lee-Kramer shear force on cooked RSB, which is what the panelists tested, did not reflect the judgement of the panelists. The panelists were far more sensitive to the presence of cooked connective tissue in RSB than shear force on the cooked products. Table 7 presents the correlation coefficients calculated for individual types
Effects ~[ added connective tissues on restructured bee]" steaks
71
TABLE 7
Correlations Between Corrected Sensory Scores (Controls Set at Zero), Shear Forces and Hydroxyproline Content for Each Connective Tissue Additive Type of Restructured Beef. Control (No Added Connective Tissue) Sample Sensory Scores of Zero are Included in the Calculations. N = 12 Sensory scores Initial tenderness
Connective tissue
Overall texture
Hyp°
Epib Gri c Perid Ten"
- 0"635* -0"559* 0-231 -0-629*
- 0'762** -0-892** 0.042 -0"790**
-0'676" -0"837** 0' 115 -0"716"*
K-S: raw
Epi Gri Peri Ten
-0"631" -0"500 0'380 - 0"620*
-0"688** -0"701"* -0"027 - 0"825**
-0-603* -0"645* - 0"205 - 0-714"*
K-S cooked
Epi Gri Peri Ten
0"547 0.485 - 0"514 -0.620*
0"400 0-681" 0"392 -0.594*
0'350 0-796** - 0-594" -0-629*
K-S raw
K-S cooked
Hypa
Epi Gri Peri Ten
0"949"* 0'863** 0-320 0.648"
- 0"316 -0-524 - 0-056 0"469
" Hydroxyproline. b Samples containing added epimysium. ¢ Samples containing added gristle. J Samples containing added peri/endomysium preparation. e Samples containing added tendon. : Lee-Kramer shear force. *Correlation coefficient significant, p < 0-05. ** Correlation coefficient significant, p < 0"01. o f c o n n e c t i v e tissues. S e n s o r y scores for s a m p l e s c o n t a i n i n g e x t r a p e r i / e n d o m y s i u m did n o t correlate with h y d r o x y p r o l i n e or L e e - K r a m e r shear forces m e a s u r e d o n r a w m e a t ; o n l y O T c o r r e l a t e d with L e e K r a m e r s h e a r forces o n c o o k e d meat. T h e h y d r o x y p r o l i n e c o n t e n t o f the p e r i / e n d o m y s i u m samples was n o t significantly c o r r e l a t e d with either L e e K r a m e r shear force m e a s u r e d . T h e actual difference in h y d r o x y p r o l i n e c o n t e n t between c o n t r o l R S B ( 1 . 1 2 # g / r a g h y d r o x y p r o l i n e ) a n d 10% p e r i / e n d o R S B (1.34/~g/mg h y d r o x y p r o l i n e ) was small a n d the lack o f significant c o r r e l a t i o n is n o t surprising. H o w e v e r , M c K e i t h et al. (1985)
72
E. D. Strange, R. C. Whiting
showed significant differences in sensory connective tissue and WarnerBratzler shear forces, as part of a large study, when two round muscles, the gluteus medius (l'13l~g/mg hydroxyproline) and the biceps femoris (1"34 pg/mg hydroxyproline), were compared. These muscles have hydroxyproline content similar to control RSB and 10% peri/endo RSB. The hydroxyproline content was calculated from data presented by McKeith et al. (1985) using 1/7"14 as a conversion factor from collagen content to hydroxyproline content (Dransfield, 1977). Perimysium and endomysium (intramuscular connective tissue) is important to the texture of individual muscles (Dransfield, 1977) but RSB is a mixture of different muscles. The lack of correlation with hydroxyproline content and either type of Lee-Kramer shear force may indicate that the peri/endomysium contribution to texture would be better measured using other types of mechanical tests, such as compression tests (Dransfield, 1977). The hydroxyproline content of the other types of connective tissue samples correlated significantly with IT, CT and OT sensory scores. The three sensory scores also correlated significantly with the Lee-Kramer shear forces on raw RSB except for IT for gristle. Cooked RSB containing gristle had decreasing cooked shear forces as the CT and OT sensory scores decreased, opposite to what would be expected. This may be due to a lack of binding between the meat pieces and the added connective tissue which was detected by the Lee-Kramer shear force measurement but ignored by the panelists. Tendon RSB samples did correlate in the expected direction but examination of the data presented in Table 3 for tendon samples shows that the differences from control samples are much smaller for cooked shear forces than for raw shear forces. Correlation coefficients are higher for the individual types of connective tissues than when taken as a whole. Least squares fits of the sensory (CT) data with the hydroxyproline data are shown in Fig. 2. The slope of the line for the relationship between CT values and hydroxyproline content for RSB containing tendon is steeper than the lines for the relationships of the CT versus hydroxyproline for samples containing epimysium and gristle. The panelists perceive tendon connective tissue as more objectionable than epimysial and/or gristle connective tissue. Comparison of the panelist's scores for CT with the Lee-Kramer shear force measurements on raw tissue also shows that the panelists report lower scores for tendon than for samples containing epimysium or gristle which have similar shear forces. The least squares fit lines for gristle and epimysium for both hydro/~yproline and Kramer shear force versus corrected CT are not different from each other showing that the panelists perceived the epimysium and gristle in the same way. If the effect of tendon is ignored an increase of 1 mg hydroxyproline per gram of wet tissue results in a decrease ofone unit of our sensory score. Least squares fits of hydroxyproline content
Effects of added connectire tissues on restructured bee[ steaks Hydroxyprollne/~g / mg
÷1
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3
4
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Fig. 2. Least squares regressions for: (a) hydroxyproline versus corrected connective tissue sensory score (panelist's response to connective tissue sample minus panelist's response to
control sample).The larger the negativecorrected sensory score the more connective tissue (CT) was perceived by the panelist. (b) Kramer multiblade peak shear force in Newton's per gram raw sample versus corrected connective tissue sensory score (panelist's response to connective tissue sample minus panelist's response to control sample). The larger the negative corrected sensory score the more connective tissue (CT) was perceived by the panelist.
and raw Lee-Kramer peak shear force for the individual types of connective tissues (excluding peri/endo) show no significant differences in slope or intercept. One milligram of hydroxyproline per gram RSB increased the Lee-Kramer peak shear force by 10 N per gram of raw RSB. Production of RSB product from the chuck is possible with minimum trimming. RSB products containing up to 5% epimysium and/or gristle were not perceived as different from a RSB made with thoroughly trimmed meat. This finding confirms the results of Booren et al. (1981) and Berry et al. (1988). However, even small amounts of tendon caused severe downgrading by the panelists of RSB. The total amount of connective tissue in the chuck
74
E. D. Strange, R. C. Whiting
does not exceed 5% of the muscle weight, but certain individual muscles may contain more than 5% epimysium and gristle, particularly the supraspinatus which has gristle extending through the muscle and the infraspinatus which has tendon attached and gristle extending through the muscle. The most effective objective measurement of the panelists' responses was L e e - K r a m e r shear force measurement on raw samples. Hydroxyproline measurements were also effective but require extensive analytical techniques and are subject to sampling difficulties. Caution must be used if there is an appreciable a m o u n t of tendon in the product, because tendon has a stronger sensory effect than other types of connective tissue. ACKNOWLEDGEMENTS The authors would like to acknowledge J. Phillips (ARS-NAA, 600 E. Mermaid Lane, Philadelphia, PA 19118) for statistical assistance and D. Hoke for technical support. REFERENCES AOAC (I 965). In Official Methods of Analysis ( 10th edn), Assoc. Offic. Agr. Chem., Washington, DC. Berry, B. W., Smith, J. J. & Secrist, J. L. (1986). J. Food Prot., 49, 455. Berry, B. W., Smith, J. J., Secrist, J. L. & Douglass, L. A. (1988). J. Food Quality, il, 15. Booren, A. M., Mandigo, R. W., Olson, D. G. & Jones, K. W. (1981). J. FoodSci., 46, 1665. Briedenstein, B. C. (1982). Intermediate value beef products. National Live Stock and Meat Board, Chicago, IL., p. 1 and 13. Dransfield, E. (1977). J. Sci. Food Agric., 28, 833. McKeith, F. K., DeVol, D. L., Miles, R. S., Bechtel, P. T. & Carr, T. R. (1985). J. Food Sci., 50, 869. Moiler, A. J. (1981). Meat Sci., 5, 247. Recio, H. A., Savell, J. W., Branson, R. E., Cross, H. R. & Smith, G. C. (1987). J. Food ScL, 52, 146 I. SAS (1985). In S A S / S T A T Guide for Personal Computers Version (6 edn), SAS Institute Inc., Cary, North Carolina. Strange, E. D. & Whiting, R. C. (1988). J. Food Sci., 53, 1224. Tucker, H. Q., Voegeli, M. M. & Wellington, G. H. (1952). In ,4 Cross Sectional Muscle Nomenclature of the Beef Carcass, ed. L. J. Bratzler, Michigan State College Press, East Lansing, MI. Woessner, J. F., Jr (1961). Arch. Biochem. Biophvs., 93, 440. Yates, F. (1958). The Design and Analysis of Factorial Experiments. Technical Communication No. 35 of the Commonwealth Bureau of Soils, Harpenden, England, Commonwealth Agricultural Bureaux, Farnham Royal, England, pp. 21-22, 65.