- Email: [email protected]
The effect of injection level on the quality of a rapid vacuum cooled cooked beef product
Journal of Food Engineering 47 (2001) 139±147
www.elsevier.com/locate/jfoodeng
The eect of injection level on the quality of a rapid vacuum cooled cooked beef product Karl McDonald a, Da-Wen Sun a,*, Tony Kenny b a
FRCFT Group, Department of Agricultural and Food Engineering, University College Dublin, National University of Ireland, Earlsfort Terrace, Dublin 2, Ireland b Teagasc, The National Food Centre, Dunsinea, Castleknock, Dublin 15, Ireland Received 24 May 2000; accepted 28 June 2000
Abstract The in¯uence of vacuum cooling (VC) on the quality of a cooked beef product injected with brine over a range of levels was studied as compared with a control water immersion (WI) cooling system. Samples were cooked in an oven at 82°C until core temperatures reached 72°C and then cooled to core temperatures of 4°C. Mean results showed that VC was very rapid (64 min) compared to 300 min for WI. Chill loss for VC products was on average 10.55% and not aected by injection level compared to only 1.88% for WI samples. Total yield in VC samples was improved as injection level increased and was comparable to WI samples at injection levels of greater than 130% of green weight. Sensory analysis indicated that overall WI samples were more tender and juicy than VC samples up to 130% injection, while VC samples had a better overall colour acceptability and ¯avour. However, high injection levels in VC samples resulted in increased saltiness and unfavorable sensory scores. Instrumental texture results indicated that increasing injection level decreased Warner±Bratzler shear force required for the vacuum cooled beef product. Ó 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction Commercial cooling systems such as air blast (AB) and water immersion (WI) for cooked meat products are designed to reduce the temperature of products as rapidly as possible to a predetermined point where microbial growth is signi®cantly retarded. In Europe, the most severe cooling guidelines for a cook-chill product recommend that 80 mm trays of product should be chilled to below 10°C in 2.5 h (Evans, Russel, & James, 1996). For cooked meats such as beef, both the British and Irish Government guidelines (Anon, 1989, 1991) recommend that cooked meat joints should not exceed 2.5 kg in weight and 100 mm in thickness, and should be cooled from a core temperature of 74°C to below 10°C in 2.5 h. These guidelines apply only to catering operations but many cooked meat manufacturers and caterers still produce products in excess of 2.5 kg (up to 10 kg) for economic reasons. The American Meat Institute recommends that cooling should begin within 90 min of *
Corresponding author. Tel.: +353-1-706-7493; fax: +353-1-4752119. E-mail address: [email protected] (D.-W. Sun).
cooking and that cooling times from 48°C to 12.7°C should not exceed 6 h with cooling continuing to 4.4°C (Anon, 1984, 1998a). Few data have been reported to indicate whether the above guidelines can be realistically achieved within the cooked meats industry. It has been reported that in some commercial operations cooling systems and cooling times are variable, in some cases up to 21 h with high ®nal temperatures of 15±20°C (James, 1990). Conventional cooling systems such as WI cannot cool these products eciently to meet the guidelines (Burfoot, Self, Hudson, Wilkins, & James, 1990; Mc Donald, Sun, & Kenny, 2000). This is because these systems rely on heat conduction to cool the inside of a cooked product and as meat has a low thermal conductivity, cooling is slow (Sun & Wang, 2000). Previous research has indicated that vacuum cooling (VC) can meet all European guidelines and American regulations as related to product cooling and safety (Burfoot et al., 1990; Mc Donald, 1999; Mc Donald et al., 2000). VC has been used in horticulture industry for over 50 years for rapid precooling of lettuce, mushrooms and more recently ¯owers (Anon, 1981; Frost, Burton & Atkey, 1989; Noble, 1985; Sun, 1999a,b; Sun &
0260-8774/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 0 - 8 7 7 4 ( 0 0 ) 0 0 1 1 0 - 2
140
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
Brosnan, 1999; Mc Donald & Sun, 2000a). In recent years, applications of VC have been extended to cooked meats (Burfoot et al., 1990; Mc Donald, 1999; Mc Donald et al., 2000). Manufacturers of cooked meat products in addition to product safety are increasingly concerned with product quality. Rapid cooling of cooked meat products can improve quality by reducing over cooking and destruction of heat labile micronutrients such as folic acid, cyanocobalamin, retinol and tocopherols (Anon, 1986). Furthermore, rapid cooling such as VC oers advantages to manufacturers through increased product throughput and reduced energy usage (Mc Donald & Sun, 2000a; Chen, 1986). However, as the eectiveness of VC is dependent on surface area to volume ratio its application to meat products such as beef and ham joints still appears limited (Mc Donald, 1999). Research has been performed to investigate the use of VC with meat products and has shown its possible application (Burfoot et al., 1990; James, 1990; Everington, 1993; Hofmans & Veerkamp, 1976; Mc Donald et al., 2000; Self, Nute, Burfoot, & Moncrie, 1990). However, despite rapid cooling, mass losses due to water evaporation in VC meats are often greater than 10%, which is of major economic signi®cance to producers. Loss of water during VC also has signi®cant eects on meat quality attributes such as texture (Mc Donald et al., 2000; Self et al., 1990). In spite of the above research, research examining the eects of VC on the quality aspects of large beef products is minimal. Previous work on cooked beef products (Mc Donald et al., 2000) has indicated signi®cant detrimental eects of VC on meat quality. In the current study, the eect of injection level, salt and phosphate concentration on the cooling times, mass losses and organoleptic properties of similar cooked beef products are investigated. 2. Materials and methods 2.1. Sample preparation Triceps brachii muscles of weight (1.495±1.995 kg) were seamed from top rib joints of beef chucks, vacuum packaged and stored at 4 1°C for no longer than 3 days. All muscles were obtained from a local meat processing plant on the same production date, 3±5 days post-mortem and pH (5.66±5.84). They were trimmed of extraneous fat and connective tissue sheets. Muscles for VC were pumped to levels ranging from 120% to 145% of their green weight with a brine solution (water 84.5%, salt 11.7%, sodium tripolyphosphate 2.3% and sucrose 1.5%) using a Dorit Model No PSM-21-4.5 multi-needle brine injector to give samples of increasing salt and phosphate concentrations from 120% to 145%. Muscles for WI cooling were used as quality controls
and pumped to 120% of their green weight only. Following injection all muscles were placed into a Dorit Vario-Vac VV-T-50 vacuum tumbler and tumbled under vacuum at a speed of 6 rpm and a temperature of 2 1°C for 12 h, with intermittent tumbling every 30 min for 30 min. After tumbling, the muscles were removed and beef samples formed by hand using a ham stuer into elastic netting and vacuum packed in heat shrinkable cooking bags (Cryovac BC300 300 ´ 55 mm2 ). The samples were cooked at 82°C until a core temperature of 72°C using a Zanussi Model FCV6 electric steam convection oven. 2.2. Cooling Samples were immediately taken from the cooker and their cooking bags removed. The samples for WI cooling were placed in sterile plastic bags before been cooled to prevent contact with cooling water. All samples were cooled to a core temperature of 4°C. The vacuum cooler was set at the evacuation speed of 500 m3 /h and the WI cooler at a cooling temperature of 1 1°C. Dimensions and weights of all samples were taken both before and after cooling using sliding vernier callipers and calibrated Sartorious Model LP12000P balance. Temperature readings were monitored using T-type thermocouples inserted into core positions around the geometric centre of the samples (Fig. 1). Thermocouples were linked through a data logger to a personal computer, which recorded temperatures at 1 min intervals both during cooking (Fig. 2) and cooling (Fig. 3). 2.3. Mass loss Mass loss during the dierent stages of processing was carefully monitored including cooking loss, cooling loss and total weight loss. All losses were calculated as a percentage of weight taken prior to each processing stage (Table 1). 2.4. Chemical analysis For each sample moisture was determined by oven drying to constant weight (AOAC, 1990) and fat by solvent extraction (AOAC, 1960). Protein content was determined by the Kjeldahl method using the Foss Tecator Kjeltec system (AOAC, 1990). Salt content was determined using the Volhard method (AOAC, 1990) and ash content by oxidation at 500°C (Anon, 1998a, 1998b). Water activity (aw ) was measured using a water activity centre (Novasina AWC200). All samples were prepared by blending 100 g of trimmed tissue using a Robot Coupe Blender. Two replicates of each treatment were analysed.
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
141
Fig. 1. Cooked beef product in VC chamber.
Fig. 2. Cooking curves for beef product at dierent sample positions.
2.5. Sensory analysis An eight-member panel was employed to evaluate the sensory characteristics of the cooked beef products, 48 h post cooking/cooling using the methodology of the American Meat Science Association (AMSA, 1995). The panel was chosen from a group of 12 panellists selected for their experience in sensory analysis of meat products. Prior to formal sensory sessions panellists were familiarised with the characteristics to be evaluated with two additional sessions. Beef products were sliced into 1.5 mm thick slices rolled and allowed to equilibrate to room temperature for 30 min. Four samples (two for each cooling treatment) were presented in random order in each session. The samples were rated on descriptive hedonic scales for tenderness, juiciness, binding,
Fig. 3. Cooling curves for vacuum cooled cooked beef product injected at dierent levels.
saltiness, overall ¯avour, overall colour and overall acceptability. Each treatment replicate was presented twice over a total of 12 sessions. 2.6. Warner±Bratzler measurement For each treatment samples were cut into 20 mm thick slices parallel to the muscle ®bres and tempered at 4°C overnight for ease of coring. Core samples 70 mm length ´ 12.5 mm diameter was cut parallel to the longitudinal orientation of the muscle ®bres. Cores were sheared with a Warner±Bratzler shear device attached to a universal testing machine (Model 4301, Instron Universal Testing Machine, Instron, USA), 48 h post cooking/cooling. A 1 kN load cell detected the force required to shear through the sample core at a crosshead speed of 50 mm/min and fail criterion was 75% (Shackelford
142
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
Table 1 Mass losses at dierent processing stagesA Cooling method
% Cooking loss
VC 120% VC 125% VC 130% VC 135% VC 140% VC 145% WI 120%
10.40 10.28 10.06 10.08 10.06 10.53 10.33
(0.18)a (0.20)a (0.15)a (0.21)a (0.05)a (0.44)a (0.14)a
% Cooling loss
% Total lossB
10.43 (0.11)a 10.38 (0.12)a 10.43 (0.08)a 10.31 (0.10)a 10.48 (0.03)a 10.28 (0.11)a 1.88 (0.04)b
20.83 20.66 20.49 20.39 20.54 20.81 12.21
(0.28)a (0.14)a (0.13)a (0.12)a (0.14)a (0.24)a (0.24)b
% Total yieldC 85.80 (0.70)a 90.85 (0.61)b 100.33 (0.13)c 106.09 (0.22)d 112.17 (0.62)e 115.97 (0.91)f 109.17 (0.65)d
A a±f means in the same column with dierent superscripts are dierent (P < 0.05). Standard error of the means in brackets. VC/WI vacuum cooled and water immersion cooling followed by % injection level. B Cooking loss plus cooling loss. C Calculated from green weight divided by ®nished cooled product weight.
et al., 1991). The peak force (N) was recorded with a personal computer using software provided by Instron Corporation and analysed as an objective measurement of tenderness. 2.7. Measurement of instrumental colour The internal colour of the cooled beef joints was measured by the CIE LAB system using a pulsed xenon arc lamp (Minolta Chroma Meter CR-300), 48 h post cooking/cooling. Lightness (L ), redness (a ) and yellowness (b ) values were recorded (CIE 1976 system). 2.8. Density and porosity Cylindrical samples were cut from the geometric centre of each sample (perpendicular to muscle ®bre orientation in whole muscle samples) after cooling using a cork borer to give samples of 30 mm length, 12.7 mm diameter and 4±5 g in weight. True density (qT ) was determined using helium displacement equipment with accuracy of 0.03% (Micromeritics, AccuPyc 1330). The system was internally calibrated using a standard steel bar (22.9382 g and q 7:733 g=cm3 ). Envelope density (qE ) was determined using quasi-¯uid displacement with consolidation force of 10 N (Micromeritics GeoPyc, 1360). All sample replicates were analysed in triplicate at 20°C. Internal percentage porosity was calculated using the relationship between envelope and true density of the beef samples (Murphy & Marks, 1999). 2.9. Statistical analysis To allow for determination of signi®cant statistical eects due to injection level (treatments) while allowing for variation in raw material between animals (blocks), in a setup where there are six treatments and one sample per animal, a balanced incomplete block design was used. Each treatment was replicated six times in 36 blocks and every treatment occurred in a block with all other treatments, which gave balance to the design.
Data for each treatment was combined and analysed using one-way analysis of variance with the injection level as the factor (Minitab, PA, USA Version 10.2, 1994). When F values were signi®cant (P < 0.05) the Tukey±Kramer multiple comparison procedure was used to compare treatment means.
3. Results and discussion 3.1. Processing times, porosity and mass loss Analysis of cooling times for VC samples indicated no signi®cant dierences as aected by injection level to 50°C and 4°C at the core (P > 0.05). However, cooling times to 4°C at the core were quickest in 120% injection samples. Signi®cance was seen in cooling times to 10°C at the core (P < 0.05). It was anticipated that increasing the injection level would decrease cooling times due to increased availability of water. However, the results indicated that cooling times to 4°C decreased from 73.5 to 48 min (P < 0.05) as injection level decreased from 145% to 120% (Table 2). Percentage porosity was signi®cantly highest in 120% injection VC samples and decreased as injection level increased, which agreed with the increasing cooling times recorded (P < 0.05). Decreasing porosity (Table 3), as injection level increased may have been the result of the excess brine solution ®lling a greater proportion of the beef samples internal matrix, thus reducing void space (Mc Donald & Sun, 2000b). All WI cooled samples had signi®cantly longer cooling times than VC samples which cooled quicker due to the high latent heat removed when water evaporates during the VC procedure as opposed to slower heat transfer by conduction in WI cooled samples (P < 0.05). Cooling times to 4°C at the core for WI samples ranged from 240 to 300 min depending on sample size and were comparable to WI cooling times for cooked ham (5.9 h) recorded by Burfoot et al., (1990) and James (1996). Mass losses (Table 1) after VC was not signi®cantly in¯uenced by injection level (P > 0.05). It was expected
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
143
Table 2 Eect of injection level on VC timesA
A B
% Injection level
Time (min) to 50°CB
120 125 130 135 140 145
3.17 1.83 2.50 5.67 2.67 5.00
Time (min) to 10°CB
(0.48)ab (0.17)c (0.43)ab (1.33)ab (0.49)ab (0.68)ab
31.33 23.17 60.33 45.50 40.33 58.17
Time (min) to 4°CB
(1.89)ab (1.49)a (0.76)cd (4.64)b (3.41)b (2.98)bd
48.00 57.00 65.67 68.83 69.67 73.50
(4.23)a (1.75)ac (0.99)bc (3.73)ac (3.47)ac (1.41)ac
a±d means in the same column with dierent superscripts are dierent (P < 0.05). Standard error of the means in brackets. Mean temperature at sample core.
Table 3 Eects of injection level on instrumental analysisA Cooling method
Warner±Bratzler (N)
VC 120% VC 125% VC 130% VC 135% VC 140% VC 145% WI 120%
20.59 20.39 14.88 13.80 13.88 11.90 17.38
(1.08)a (1.42)a (0.99)b (0.91)c (0.37)c (0.64)d (0.99)e
Colour (L) 45.99 50.58 51.37 51.30 52.14 52.52 52.65
(0.55)a (0.22)b (0.44)b (0.64)b (0.35)b (0.45)b (0.74)b
Colour (a)
Colour (b)
% Internal porosity
10.57 (0.06)a 9.58 (0.06)b 9.35 (0.07)c 8.50 (0.13)d 8.47 (0.04)c 8.24 (0.03)d 10.49 (0.23)e
10.62 (0.20)a 10.86 (0.28)a 9.13 (0.13)b 8.35 (0.22)b 8.08 (0.25)b 8.85 (0.11)b 10.08 (0.35)a
6.64 5.21 5.25 3.66 2.81 2.80 2.96
(0.25)a (0.08)b (0.17)b (0.10)c (0.28)c (0.31)c (0.18)c
A
a±e means in the same column with dierent superscripts are dierent (P < 0.05). Standard error of the means in brackets. VC/WI vacuum cooled and water immersion cooling followed by % injection level.
that increasing salt and phosphate concentrations would have reduced cooking loss as injection level increased (Trout & Schmidt, 1984; Siegel, Theno, Schmidt, & Norton, 1978). Polyphosphates were incorporated into the beef products to enhance their water holding capacity (Boles & Swan, 1997; Lee, Hendricks, & Cornforth, 1998). However, at all injection levels cooking losses were similar, which suggests that not all the phosphate and salt was incorporated by the samples. Inadequate blending of the phosphate into the brine solution may have contributed towards the observed cooking losses (Eilert, 1996; Pepper & Schmidt, 1975). The beef muscles structure particularly the fat distribution and brine injection distribution may have partly accounted for the observed cooking losses (Kinsman et al., 1994). At all injection levels, percent cooling losses were similar for all VC samples. This was expected as VC losses among other variables is related to ®nal product temperature. As all samples were cooled from, 72°C to less than 4°C so cooling losses should be similar (Mc Donald et al., 2000). Thus, the combination of cooking and cooling losses resulted in an unexpected similarity of percent total losses from 120% to 145% injection levels. WI cooled samples were signi®cantly dierent to VC samples (P < 0.05) with up to 9% lower cooling and total losses. This was as expected as moisture loss is an inherent requirement of VC for adequate cooling and leads to high cooling losses (Mc Donald and Sun, 2000a). As a consequence of high cooling losses VC samples had a signi®cantly lower percent total yield than
WI samples up to a 130% injection level (P < 0.05). At 135% injection VC samples were similar to WI cooled samples, while injection levels above 135% resulted in VC samples having higher yields than WI samples (Table 1). It is apparent from the results that to compensate for increased cooling loss during VC up to 115% injection of original green weight is required to make samples comparable to WI. Furthermore, it should be noted that although the 120% injection samples cooled the quickest (Table 2) and had the highest porosity (Table 3), they also resulted in the lowest yields (85.69%) compared to (112.30%) for 145% injection samples (Table 1). 3.2. Sensory analysis The dierent injection levels signi®cantly aected (P < 0.05) all the sensory attributes in VC samples except for cohesion as shown in Table 4. However, cohesion was improved slightly as injection level increased (Table 4) and was comparable to previous research which indicated that VC signi®cantly (P < 0.05) damaged the cohesion of a cooked beef product in comparison to more conventional cooling systems (Mc Donald et al., 2000). Tenderness and juiciness in VC samples were improved with increasing injection level and was better than WI cooled samples at injection level greater than 125% and 135%, respectively, with 145% injection samples being the most tender and juicy. These results were consistent with instrumental results, which
144
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
Table 4 Eect of injection level on the sensory quality of the cooked beef productA Cooling method
Sensory attributes
VC 120% VC 125% VC 130% VC 135% VC 140% VC 145% WI 120%
4.75 5.09 5.09 5.17 5.33 5.59 5.07
Tenderness (0.03)a (0.04)b (0.04)b (0.00)b (0.00)c (0.03)c (0.02)b
Juiciness 4.17 4.25 4.34 5.33 5.59 5.84 4.58
(0.00)a (0.03)a (0.07)a (0.00)b (0.03)b (0.07)c (0.00)a
Binding 3.84 4.17 4.25 4.25 4.34 4.42 4.89
(0.07)a (0.00)b (0.03)b (0.03)b (0.07)b (0.03)b (0.03)c
Overall ¯avour 4.42 4.92 5.17 3.83 3.84 3.17 3.93
(0.10)a (0.03)b (0.07)c (0.00)d (0.07)d (0.07)e (0.02)d
Overall colour 4.75 4.84 4.92 5.00 4.34 4.25 4.36
(0.03)a (0.07)a (0.03)a (0.00)b (0.07)c (0.03)c (0.01)a
Saltiness 4.25 4.17 4.17 3.67 3.33 2.92 4.00
(0.03)a (0.00)a (0.07)a (0.07)b (0.00)c (0.03)d (0.01)a
Overall acceptability 4.17 4.92 5.00 4.75 4.17 4.09 4.18
(0.00)a (0.03)b (0.07)b (0.03)b (0.00)a (0.03)a (0.02)a
A
Sensory attributes were evaluated by means of six-point scale (6: very tender/juicy/extremely good/extremely acceptable/extremely good/extremely acceptable; 1: very tough/dry/poor/poor/not acceptable/ver salty/not acceptable. a±e means in the same column with dierent superscripts are different (P < 0.05). Standard error of the means in brackets. VC/WI vacuum cooled and water immersion cooling followed by % injection level.
indicated a lower shear value for VC samples as injection level increased. Furthermore, as injection level increased so mean moisture content increased (P > 0.05) which will have contributed towards panellists indicating better juiciness in higher injection VC samples. Signi®cant dierences in juiciness between dierent cooling methods have been made in other research where there are signi®cant dierences in weight loss (Self et al., 1990). In the present research, panellists appear to have made this association between dierent injection levels within a single VC treatment. However, it is interesting to note that although the control WI cooled samples had a signi®cantly higher moisture content than the VC samples, panellists still rated VC samples with levels of injection greater than 135% injection more juicy. Flavour of VC samples was signi®cantly in¯uenced (P < 0.05) by level of injection (Table 4). The ¯avour was signi®cantly in¯uenced by the level of salt that was present in the samples due to injection level. The ¯avour as shown in previous research (Mc Donald et al., 2000) was better in VC samples than WI cooled samples and was best at injection levels of 130%. Some panellists indicated that VC samples at this level have a more natural or intense beef ¯avour. This observation may have been due to concentration of ¯avour compounds in the VC samples as a result of water loss and alteration of the muscle structure (increased porosity) caused by the VC procedure (Ima®don & Spanier, 1994). Injection levels greater than 130% resulted in panellists ®nding saltiness objectionable and subsequently marking down sample ¯avour. Injection level signi®cantly in¯uenced (P < 0.05) colour scores (Table 4). Colour acceptability improved in VC samples, as injection levels increased from 120% to 135%. It was apparent that panellists overall preferred the colour of VC samples in comparison to the WI controls with scores only slightly lower (P > 0.05) at 140 and 145% injection levels. Instrumental colour analysis (Table 3) agreed with these results as a -values decreased as injection level increased, leading to a less pronounced
red colour to the beef product. In general, people prefer cooked meat products to have the appearance of being well done with little or no pink or red colouration. Overall acceptability of VC samples was improved by increasing injection level in primary processing (P < 0.05). Best overall acceptability was at an injection level of 130% and this was signi®cantly better than the WI control samples (P < 0.05). It should be noted that as in previous research (Mc Donald et al., 2000) VC samples were comparable to WI samples at initial injection levels of 120%. The greatest in¯uence on the overall acceptability of the VC samples was the high percent salt in samples as injection level increased which signi®cantly decreased acceptability (P < 0.05). 3.3. Chemical analysis Compositional analysis (Table 5) indicated that injection level did not have a signi®cant eect on the mean moisture content of the VC samples (P > 0.05) although moisture loss due to VC was up to 3.35% higher than WI cooling which compares favourably with earlier research (Mc Donald et al., 2000). It was expected that increased injection levels would increase overall moisture contents in the VC samples and this would signi®cantly aect the protein and fat contents. It was observed that the lowest mean moisture content (70.09%) was in the 120% injection samples and increased up to a maximum of 71.04% in 145% injection samples. This subsequently impacted on percentage protein values in the samples which decreased in relative terms as percentage moisture increased, although not signi®cantly (P > 0.05). Increased protein and decreased moisture contents relative to VC samples will have an impact on sample texture. WI cooled samples had a signi®cantly higher (P < 0.05) mean moisture content than all VC samples (Table 5). These results aggress with previous research, which indicated that in comparison to more conventional cooling systems VC cooked beef
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
145
Table 5 Chemical analysis of the cooked beef productA Cooling method
% MoistureB
VC 120% VC 125% VC 130% VC 135% VC 140% VC 145% WI 120%
70.34 70.63 70.64 70.86 71.41 72.06 73.44
(0.11)a (0.17)a (0.09)a (0.09)a (0.15)b (0.21)c (0.22)d
% Protein 22.34 22.05 21.05 20.75 20.53 19.42 21.38
(0.11)a (0.10)a (0.05)a (0.05)a (0.11)a (0.36)b (0.13)c
% Fat 3.77 3.84 3.56 3.81 3.26 3.42 3.68
% Ash
(0.10)ac (0.06)a (0.06)ac (0.14)ac (0.18)bc (0.16)ac (0.14)ac
3.35 3.43 4.47 4.63 4.73 4.94 3.39
(0.03)a (0.02)a (0.04)b (0.03)b (0.02)b (0.02)c (0.02)a
% Salt 2.33 2.94 3.40 3.78 4.10 4.48 2.22
(0.08)a (0.05)b (0.05)c (0.04)d (0.05)e (0.04)f (0.07)a
Water activity 0.96 0.96 0.96 0.96 0.95 0.95 0.98
(0.00)a (0.00)a (0.00)a (0.00)a (0.00)a (0.00)a (0.00)b
A a±f means in the same column with dierent superscripts are dierent (P < 0.05). Standard error of means in brackets. VC/WI vacuum cooled and water immersion cooling followed by % injection level. B Mean moisture content.
products have lower moisture contents (Mc Donald et al., 2000). Analysis of moisture contents at dierent positions in the VC samples revealed the presence of a moisture gradient with signi®cant dierences between moisture contents at the surface, intermediate (half way point) and core (P < 0.05). As expected the surface had the lowest moisture content in all VC samples with moisture contents increasing towards the core region. Within the meat structure, the process of VC is dierent to that at the surface. Water vapour will both evaporate due to depressed pressure and condense on cooler parts of the beef simultaneously. Furthermore, conductive cooling from the cooler surface to the internal regions will also facilitate evaporative cooling. Therefore, moisture content as demonstrated by analysis will be greater within the meat matrix. Percentage dierences between moisture contents for the core, surface and intermediate regions were 10.35% and 3.95%, respectively (P < 0.05). In comparison the WI samples had no signi®cant dierences (P > 0.05) in moisture content between dierent regions. However, it was observed that moisture content was slightly higher at the surface perhaps due to the samples been cooled in a plastic bag. Diusion of water and water vapour through the meat during VC is the result of dierences in concentration and pressure and will only occur if the meat is porous (Crank, 1975; Labuza & Hyman, 1998). Monitoring of diusion rates from dierent regions during VC could be examined by perhaps using magnetic resonance imaging (Chen, Long, Ruan, & Labuza, 1997). Moisture loss from the core and other regions of the samples will continuously occur in order to reach thermodynamic equilibrium with the surrounding beef components and the vacuum chamber environment (Labuza & Hyman, 1998). If VC were continued beyond ®nal cooling temperature a point would be reached where the whole structure of the meat would equilibrate to mean moisture content. Changes in the moisture content of a multi-domain cooked beef product can aect not only yield (Table 1), but also its physical and chemical composition (Table 5)
along with its safety and shelf-life (Labuza & Hyman, 1998). The excessive loss of moisture at the surface of the samples is unacceptable. To improve the acceptability of VC beef products a means must be found to equilibrate moisture loss from dierent regions during VC. Pre-spraying of the product surface with water prior to VC has been shown to reduce water losses in vegetables and in some cases increase yield (Sun, 1999a,b). Perhaps this could be used with cooked beef products, however there are concerns about product safety due to contamination of the meat from the water used in spraying (Mc Donald, 1999). The eect of increasing injection level in VC samples was the signi®cant increase of percentage salt (P < 0.05). This in turn had objectionable eects with some taste panellists in terms of sample ¯avour. Increasing salt concentrations lead to an increase in percentage ash content and a decrease in water activity (P < 0.05) as was expected with increasing salt concentrations (Table 5). Thus, to implement the use of increased injection levels care will be needed in considering the eects of salt on the sensory attributes of the product if the use of injection level to improve quality in VC samples is to be of any real commercial bene®t. 3.4. Instrumental texture and colour The injection level had a signi®cant eect (P < 0.05) on both the texture and colour of the VC samples in comparison to each other and the WI control samples (P < 0.05). At injection levels of 120% Warner±Bratzler results for VC and WI samples were 20.59 and 17.38 N, respectively and comparable to previous research which indicated that WI had the lowest shear force results and best texture in comparison to VC samples (Mc Donald et al., 2000). As injection level increased shear values decreased in VC samples indicating a more tender beef product (Table 3). These results were substantiated by sensory analysis (Table 4) which indicated that panellists found VC samples with greater than a 125% injection level superior to WI samples in terms of tenderness (P < 0.05). Overall results indicate that both VC and
146
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
injection level aect cooked beef tenderness. Increasing injection level in VC samples will help oset the eects of water loss on texture in the samples thus resulting in more tender products. Furthermore, a higher level of salt and sodium tripolyphosphate in higher injection samples may have contributed towards a higher water binding and better texture in VC samples (Lamkey, Mandigo, & Calkins, 1986). Self et al. (1990) indicated that VC did not aect cooked chicken breast tenderness, although no instrumental analysis was carried out in this research. The overall dark nature of the cooked beef product makes dierences in colour dicult to distinguish visually. However, instrumental measurement of colour (Table 3) indicated that injection level aected the internal colour of the cooked beef product (P < 0.05). Increasing injection level resulted in samples appearing lighter in colour as indicated by a higher L -value. The lighter colour as injection level increases is likely due to increased water which results in lower concentrations of meat pigments and decreases light penetration (Lawrie, 1998). Lower a -values in VC samples as injection level increased were preferred by panellists which indicated a less pronounced red/pink or undercooked colour in comparison to WI samples (P < 0.05). 4. Conclusions The results indicate that injection level can signi®cantly improve the quality of a VC beef product. An optimum injection level of 130±135% of sample green weight allows for a VC cooked beef product, which is comparable in quality to a high quality cooked beef product cooled using WI. However, the ingredients in the injection solution, particularly the salt and sodium polyphosphate will have to be carefully monitored to prevent adverse eects on sensory attributes such as ¯avour. This research has provided information, which may be used to improve the acceptance and implementation of VC as a practical cooling operation in the production of cooked meat products such as beef. Further research will investigate the eects of injection level on the quality of a rapid vacuum cooled cooked beef product using a brine solution with a constant salt and phosphate concentration. Acknowledgements This research has been part-funded by grand aid under the European Regional Development Fund, which is administered by the Department of Agriculture, Food and Forestry, Ireland. Thanks are given to Mr. Patrick Ward (Teagasc, National Food Centre, Ireland) for his help and guidance in the preparation of the
samples for this research. Special thanks are also given to Mr. Michael Cooney (Department of Food Science, University College Dublin) for his assistance in the analysis of the samples.
References AMSA (1995). Research guidelines for cookery, sensory evaluation and instrumental tenderness measurements of fresh meat. Chicago: National Livestock and Meat Board. Anon (1981). Rapid vacuum cooling. Food Processing Industry, 9, 49. Anon (1984). American meat institute. Good manufacturing practices. Guidelines for the production of fresh and cured cooked beef. Washington DC: AMI. Anon (1986). Losses of food and nutrients in food processing. In R. Passmore, & M.A. Eastwood, Human nutrition and dietetics (pp. 231±235). New York: Churchill Livingston. Anon (1989). Chilled and frozen. Guidelines on cook-chill and cookfreeze catering systems. London: HMSO Publications Centre. Anon (1991). Guidelines on cook-chill systems in hospitals and catering premises. Irish food safety advisory committee. Dublin: Government Publication Sale Oce. Anon (1998a). United States Department of Agriculture Code of Federal Regulations-Animals and Animal Products. In Requirements for the production of cooked beef, roast beef and cooked corn beef (pp. 270±271). 9 CFR Ch. III (318.17). Anon (1998b). Determination of ash in meat and meat products (reference method) ISO 936 (BS 4401). AOAC (1960). Ocial methods of analysis (9th ed., Sec. 960.39). Arlington, Virginia: Association of Ocial Analytical Chemists. AOAC International. (1990). Ocial methods of analysis (15th ed., Sec. 950.46A, 935.47, 935.48, 992.15). Arlington, Virginia: Association of Ocial Analytical Chemists. Boles, J. A., & Swan, J. E. (1997). Eects of brine ingredients and temperature on cook yields and tenderness of pre-rigor processed roast beef. Meat Science, 45, 87±97. Burfoot, D., Self, K. P., Hudson, W. R., Wilkins, T. J., & James, S. J. (1990). Eect of cooking and cooling method on the processing times, mass losses and bacterial condition of large meat joints. International Journal of Food Science and Technology, 25, 657±667. Chen, Y. L. (1986). Vacuum cooling and its energy use analysis. Journal of Chinese Agricultural Engineering, 32, 43±50. Chen, P. L., Long, Z., Ruan, R. R., & Labuza, T. P. (1997). Nuclear magnetic resonance studies of water mobility in bread during storage. Lebensmittel ± Wissenschaft und ± Technologie, 30, 178± 183. Crank, J. (1975). The mathematics of diusion (2nd ed.). Oxford: Clarendon. Eilert, S. J. (1996). Phosphate type, concentration and preblend duration to improve water holding capacity of beef connective tissue. Journal of Muscle Foods, 7, 255±269. Evans, J., Russell, S., & James, S. (1996). Chilling of recipe dish meals to meet cook-chill guidelines. International Journal of Food Refrigeration, 19, 79±86. Everington, D.W. (1993). Vacuum technology for food processing. Food Technology International Europe, 71±74. Frost, C. E., Burton, K. S., & Atkey, P. T. (1989). A fresh look at cooling mushrooms. Mushroom Journal, 193, 23±29. Hofmans, G. J. P., & Veerkamp, C. H. (1976). Vacuum cooling of broiler carcasses. In B. Erdtsieck, Proceedings of the Second European Symposium on Poultry Meat Quality, European Federation Branch of the World Poultry Science Association. Ima®don, G. I., & Spanier, A. M. (1994). Unravelling the secret of meat ¯avour. Trends in Food Science and Technology, 5, 315±321.
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147 James, S. J. (1990). Process engineering in the food industry ± 2: convenience foods and quality assurance (pp. 88±97). London: Elsevier Applied Sciences. James, S. J. (1996). The chill chain from carcass to consumer. Meat Science, 43, S203±S216. Labuza, T. P., & Hyman, C. R. (1998). Moisture migration and control in multi-domain foods. Trends in Food Science and Technology, 9, 47±55. Lamkey, J. W., Mandigo, R. W., & Calkins, C. R. (1986). Eect of salt and phosphate on the texture and colour stability of restructured beef steaks. Journal of Food Science, 51, 873±875, 911. Lawrie, R.A. (1998). Lawrie's meat science (pp. 130±137, 212±257). Cambridge, England: Woodhead Publishing. Lee, B. J., Hendricks, D. G., & Cornforth, D. P. (1998). Eect of sodium phytate, sodium pyrophosphate and sodium tripolyphosphate on physico chemical characteristics of restructured beef. Meat Science, 50, 273±283. Mc Donald, K. (1999). Safety in the cooling of large cooked meats. The Food Science. Times, 2, 3±12. Mc Donald, K., & Sun, D. W. (2000a). Vacuum cooling technology for the food processing industry. Journal of Food Engineering, 45, 55± 65. Mc Donald, K., & Sun, D. W. (2000b). The formation of pores and their eects in a cooked beef product on the eciency of vacuum cooling. Journal of Food Engineering (in press). Mc Donald, K., Sun, D. W., & Kenny, T. (2000). Comparison of the quality of cooked beef products cooled by vacuum cooling and by conventional cooling. Lebensmittel ± Wissenschaft und ± Technologie., 31, 21±29. Murphy, R. Y., & Marks, B. P. (1999). Apparent thermal conductivity, water content, density, and porosity of thermally processed ground chicken patties. Journal of Food Processing and Engineering, 22, 129±140.
147
Noble, R. (1985). A review of vacuum cooling of mushrooms. Mushroom Journal, 149, 168±170. Pepper, F. H., & Schmidt, G. R. (1975). Eect of blending time, salt, phosphate and hot-boned beef on binding strength and cook yield of beef rolls. Journal of Food Science, 40, 227±230. Self, K. P., Nute, G. R., Burfoot, D., & Moncrie, C. B. (1990). Eect of pressure cooking and pressure rate change during cooling in vacuum on chicken breast quality and yield. Journal of Food Science, 55, 1531±1535, 1551. Shackelford, S. D., Koohmaraie, M., Whipple, G., Wheeler, T. L., Miller, M. F., Crouse, J. D., & Reagan, J. O. (1991). Predictors of beef tenderness: development and veri®cation. Journal of Food Science, 56, 1130±1135, 1140. Siegel, D. G., Theno, D. M., Schmidt, G. R., & Norton, H. W. (1978). Meat massaging: the eects of salt, phosphate and massaging on cooking loss, binding strength and exudate composition in sectioned and formed ham. Journal of Food Science, 43, 331±333. Sun, D. W. (1999a). Comparison of rapid vacuum cooling of leafy and non-leafy vegetables. ASAE Paper No. 996117, ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. Sun, D.W. (1999b). Eect of pre-wetting on weight loss and cooling times of vegetables during vacuum cooling. ASAE Paper No. 996119, ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. Sun, D. W., & Brosnan, T. (1999). Extension of the vase life of cut daodil ¯owers by rapid vacuum cooling. International Journal of Refrigeration, 22, 472±478. Sun, D. W., & Wang, L. (2000). Heat transfer characteristics of cooked meats using dierent cooling methods. International Journal of Refrigeration, 23, 508±516. Trout, G. R., & Schmidt, G. R. (1984). Eect of phosphate type and concentration, salt level and method of preparation on binding in restructured beef rolls. Journal of Food Science, 49, 687±694.
www.elsevier.com/locate/jfoodeng
The eect of injection level on the quality of a rapid vacuum cooled cooked beef product Karl McDonald a, Da-Wen Sun a,*, Tony Kenny b a
FRCFT Group, Department of Agricultural and Food Engineering, University College Dublin, National University of Ireland, Earlsfort Terrace, Dublin 2, Ireland b Teagasc, The National Food Centre, Dunsinea, Castleknock, Dublin 15, Ireland Received 24 May 2000; accepted 28 June 2000
Abstract The in¯uence of vacuum cooling (VC) on the quality of a cooked beef product injected with brine over a range of levels was studied as compared with a control water immersion (WI) cooling system. Samples were cooked in an oven at 82°C until core temperatures reached 72°C and then cooled to core temperatures of 4°C. Mean results showed that VC was very rapid (64 min) compared to 300 min for WI. Chill loss for VC products was on average 10.55% and not aected by injection level compared to only 1.88% for WI samples. Total yield in VC samples was improved as injection level increased and was comparable to WI samples at injection levels of greater than 130% of green weight. Sensory analysis indicated that overall WI samples were more tender and juicy than VC samples up to 130% injection, while VC samples had a better overall colour acceptability and ¯avour. However, high injection levels in VC samples resulted in increased saltiness and unfavorable sensory scores. Instrumental texture results indicated that increasing injection level decreased Warner±Bratzler shear force required for the vacuum cooled beef product. Ó 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction Commercial cooling systems such as air blast (AB) and water immersion (WI) for cooked meat products are designed to reduce the temperature of products as rapidly as possible to a predetermined point where microbial growth is signi®cantly retarded. In Europe, the most severe cooling guidelines for a cook-chill product recommend that 80 mm trays of product should be chilled to below 10°C in 2.5 h (Evans, Russel, & James, 1996). For cooked meats such as beef, both the British and Irish Government guidelines (Anon, 1989, 1991) recommend that cooked meat joints should not exceed 2.5 kg in weight and 100 mm in thickness, and should be cooled from a core temperature of 74°C to below 10°C in 2.5 h. These guidelines apply only to catering operations but many cooked meat manufacturers and caterers still produce products in excess of 2.5 kg (up to 10 kg) for economic reasons. The American Meat Institute recommends that cooling should begin within 90 min of *
Corresponding author. Tel.: +353-1-706-7493; fax: +353-1-4752119. E-mail address: [email protected] (D.-W. Sun).
cooking and that cooling times from 48°C to 12.7°C should not exceed 6 h with cooling continuing to 4.4°C (Anon, 1984, 1998a). Few data have been reported to indicate whether the above guidelines can be realistically achieved within the cooked meats industry. It has been reported that in some commercial operations cooling systems and cooling times are variable, in some cases up to 21 h with high ®nal temperatures of 15±20°C (James, 1990). Conventional cooling systems such as WI cannot cool these products eciently to meet the guidelines (Burfoot, Self, Hudson, Wilkins, & James, 1990; Mc Donald, Sun, & Kenny, 2000). This is because these systems rely on heat conduction to cool the inside of a cooked product and as meat has a low thermal conductivity, cooling is slow (Sun & Wang, 2000). Previous research has indicated that vacuum cooling (VC) can meet all European guidelines and American regulations as related to product cooling and safety (Burfoot et al., 1990; Mc Donald, 1999; Mc Donald et al., 2000). VC has been used in horticulture industry for over 50 years for rapid precooling of lettuce, mushrooms and more recently ¯owers (Anon, 1981; Frost, Burton & Atkey, 1989; Noble, 1985; Sun, 1999a,b; Sun &
0260-8774/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 0 - 8 7 7 4 ( 0 0 ) 0 0 1 1 0 - 2
140
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
Brosnan, 1999; Mc Donald & Sun, 2000a). In recent years, applications of VC have been extended to cooked meats (Burfoot et al., 1990; Mc Donald, 1999; Mc Donald et al., 2000). Manufacturers of cooked meat products in addition to product safety are increasingly concerned with product quality. Rapid cooling of cooked meat products can improve quality by reducing over cooking and destruction of heat labile micronutrients such as folic acid, cyanocobalamin, retinol and tocopherols (Anon, 1986). Furthermore, rapid cooling such as VC oers advantages to manufacturers through increased product throughput and reduced energy usage (Mc Donald & Sun, 2000a; Chen, 1986). However, as the eectiveness of VC is dependent on surface area to volume ratio its application to meat products such as beef and ham joints still appears limited (Mc Donald, 1999). Research has been performed to investigate the use of VC with meat products and has shown its possible application (Burfoot et al., 1990; James, 1990; Everington, 1993; Hofmans & Veerkamp, 1976; Mc Donald et al., 2000; Self, Nute, Burfoot, & Moncrie, 1990). However, despite rapid cooling, mass losses due to water evaporation in VC meats are often greater than 10%, which is of major economic signi®cance to producers. Loss of water during VC also has signi®cant eects on meat quality attributes such as texture (Mc Donald et al., 2000; Self et al., 1990). In spite of the above research, research examining the eects of VC on the quality aspects of large beef products is minimal. Previous work on cooked beef products (Mc Donald et al., 2000) has indicated signi®cant detrimental eects of VC on meat quality. In the current study, the eect of injection level, salt and phosphate concentration on the cooling times, mass losses and organoleptic properties of similar cooked beef products are investigated. 2. Materials and methods 2.1. Sample preparation Triceps brachii muscles of weight (1.495±1.995 kg) were seamed from top rib joints of beef chucks, vacuum packaged and stored at 4 1°C for no longer than 3 days. All muscles were obtained from a local meat processing plant on the same production date, 3±5 days post-mortem and pH (5.66±5.84). They were trimmed of extraneous fat and connective tissue sheets. Muscles for VC were pumped to levels ranging from 120% to 145% of their green weight with a brine solution (water 84.5%, salt 11.7%, sodium tripolyphosphate 2.3% and sucrose 1.5%) using a Dorit Model No PSM-21-4.5 multi-needle brine injector to give samples of increasing salt and phosphate concentrations from 120% to 145%. Muscles for WI cooling were used as quality controls
and pumped to 120% of their green weight only. Following injection all muscles were placed into a Dorit Vario-Vac VV-T-50 vacuum tumbler and tumbled under vacuum at a speed of 6 rpm and a temperature of 2 1°C for 12 h, with intermittent tumbling every 30 min for 30 min. After tumbling, the muscles were removed and beef samples formed by hand using a ham stuer into elastic netting and vacuum packed in heat shrinkable cooking bags (Cryovac BC300 300 ´ 55 mm2 ). The samples were cooked at 82°C until a core temperature of 72°C using a Zanussi Model FCV6 electric steam convection oven. 2.2. Cooling Samples were immediately taken from the cooker and their cooking bags removed. The samples for WI cooling were placed in sterile plastic bags before been cooled to prevent contact with cooling water. All samples were cooled to a core temperature of 4°C. The vacuum cooler was set at the evacuation speed of 500 m3 /h and the WI cooler at a cooling temperature of 1 1°C. Dimensions and weights of all samples were taken both before and after cooling using sliding vernier callipers and calibrated Sartorious Model LP12000P balance. Temperature readings were monitored using T-type thermocouples inserted into core positions around the geometric centre of the samples (Fig. 1). Thermocouples were linked through a data logger to a personal computer, which recorded temperatures at 1 min intervals both during cooking (Fig. 2) and cooling (Fig. 3). 2.3. Mass loss Mass loss during the dierent stages of processing was carefully monitored including cooking loss, cooling loss and total weight loss. All losses were calculated as a percentage of weight taken prior to each processing stage (Table 1). 2.4. Chemical analysis For each sample moisture was determined by oven drying to constant weight (AOAC, 1990) and fat by solvent extraction (AOAC, 1960). Protein content was determined by the Kjeldahl method using the Foss Tecator Kjeltec system (AOAC, 1990). Salt content was determined using the Volhard method (AOAC, 1990) and ash content by oxidation at 500°C (Anon, 1998a, 1998b). Water activity (aw ) was measured using a water activity centre (Novasina AWC200). All samples were prepared by blending 100 g of trimmed tissue using a Robot Coupe Blender. Two replicates of each treatment were analysed.
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
141
Fig. 1. Cooked beef product in VC chamber.
Fig. 2. Cooking curves for beef product at dierent sample positions.
2.5. Sensory analysis An eight-member panel was employed to evaluate the sensory characteristics of the cooked beef products, 48 h post cooking/cooling using the methodology of the American Meat Science Association (AMSA, 1995). The panel was chosen from a group of 12 panellists selected for their experience in sensory analysis of meat products. Prior to formal sensory sessions panellists were familiarised with the characteristics to be evaluated with two additional sessions. Beef products were sliced into 1.5 mm thick slices rolled and allowed to equilibrate to room temperature for 30 min. Four samples (two for each cooling treatment) were presented in random order in each session. The samples were rated on descriptive hedonic scales for tenderness, juiciness, binding,
Fig. 3. Cooling curves for vacuum cooled cooked beef product injected at dierent levels.
saltiness, overall ¯avour, overall colour and overall acceptability. Each treatment replicate was presented twice over a total of 12 sessions. 2.6. Warner±Bratzler measurement For each treatment samples were cut into 20 mm thick slices parallel to the muscle ®bres and tempered at 4°C overnight for ease of coring. Core samples 70 mm length ´ 12.5 mm diameter was cut parallel to the longitudinal orientation of the muscle ®bres. Cores were sheared with a Warner±Bratzler shear device attached to a universal testing machine (Model 4301, Instron Universal Testing Machine, Instron, USA), 48 h post cooking/cooling. A 1 kN load cell detected the force required to shear through the sample core at a crosshead speed of 50 mm/min and fail criterion was 75% (Shackelford
142
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
Table 1 Mass losses at dierent processing stagesA Cooling method
% Cooking loss
VC 120% VC 125% VC 130% VC 135% VC 140% VC 145% WI 120%
10.40 10.28 10.06 10.08 10.06 10.53 10.33
(0.18)a (0.20)a (0.15)a (0.21)a (0.05)a (0.44)a (0.14)a
% Cooling loss
% Total lossB
10.43 (0.11)a 10.38 (0.12)a 10.43 (0.08)a 10.31 (0.10)a 10.48 (0.03)a 10.28 (0.11)a 1.88 (0.04)b
20.83 20.66 20.49 20.39 20.54 20.81 12.21
(0.28)a (0.14)a (0.13)a (0.12)a (0.14)a (0.24)a (0.24)b
% Total yieldC 85.80 (0.70)a 90.85 (0.61)b 100.33 (0.13)c 106.09 (0.22)d 112.17 (0.62)e 115.97 (0.91)f 109.17 (0.65)d
A a±f means in the same column with dierent superscripts are dierent (P < 0.05). Standard error of the means in brackets. VC/WI vacuum cooled and water immersion cooling followed by % injection level. B Cooking loss plus cooling loss. C Calculated from green weight divided by ®nished cooled product weight.
et al., 1991). The peak force (N) was recorded with a personal computer using software provided by Instron Corporation and analysed as an objective measurement of tenderness. 2.7. Measurement of instrumental colour The internal colour of the cooled beef joints was measured by the CIE LAB system using a pulsed xenon arc lamp (Minolta Chroma Meter CR-300), 48 h post cooking/cooling. Lightness (L ), redness (a ) and yellowness (b ) values were recorded (CIE 1976 system). 2.8. Density and porosity Cylindrical samples were cut from the geometric centre of each sample (perpendicular to muscle ®bre orientation in whole muscle samples) after cooling using a cork borer to give samples of 30 mm length, 12.7 mm diameter and 4±5 g in weight. True density (qT ) was determined using helium displacement equipment with accuracy of 0.03% (Micromeritics, AccuPyc 1330). The system was internally calibrated using a standard steel bar (22.9382 g and q 7:733 g=cm3 ). Envelope density (qE ) was determined using quasi-¯uid displacement with consolidation force of 10 N (Micromeritics GeoPyc, 1360). All sample replicates were analysed in triplicate at 20°C. Internal percentage porosity was calculated using the relationship between envelope and true density of the beef samples (Murphy & Marks, 1999). 2.9. Statistical analysis To allow for determination of signi®cant statistical eects due to injection level (treatments) while allowing for variation in raw material between animals (blocks), in a setup where there are six treatments and one sample per animal, a balanced incomplete block design was used. Each treatment was replicated six times in 36 blocks and every treatment occurred in a block with all other treatments, which gave balance to the design.
Data for each treatment was combined and analysed using one-way analysis of variance with the injection level as the factor (Minitab, PA, USA Version 10.2, 1994). When F values were signi®cant (P < 0.05) the Tukey±Kramer multiple comparison procedure was used to compare treatment means.
3. Results and discussion 3.1. Processing times, porosity and mass loss Analysis of cooling times for VC samples indicated no signi®cant dierences as aected by injection level to 50°C and 4°C at the core (P > 0.05). However, cooling times to 4°C at the core were quickest in 120% injection samples. Signi®cance was seen in cooling times to 10°C at the core (P < 0.05). It was anticipated that increasing the injection level would decrease cooling times due to increased availability of water. However, the results indicated that cooling times to 4°C decreased from 73.5 to 48 min (P < 0.05) as injection level decreased from 145% to 120% (Table 2). Percentage porosity was signi®cantly highest in 120% injection VC samples and decreased as injection level increased, which agreed with the increasing cooling times recorded (P < 0.05). Decreasing porosity (Table 3), as injection level increased may have been the result of the excess brine solution ®lling a greater proportion of the beef samples internal matrix, thus reducing void space (Mc Donald & Sun, 2000b). All WI cooled samples had signi®cantly longer cooling times than VC samples which cooled quicker due to the high latent heat removed when water evaporates during the VC procedure as opposed to slower heat transfer by conduction in WI cooled samples (P < 0.05). Cooling times to 4°C at the core for WI samples ranged from 240 to 300 min depending on sample size and were comparable to WI cooling times for cooked ham (5.9 h) recorded by Burfoot et al., (1990) and James (1996). Mass losses (Table 1) after VC was not signi®cantly in¯uenced by injection level (P > 0.05). It was expected
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
143
Table 2 Eect of injection level on VC timesA
A B
% Injection level
Time (min) to 50°CB
120 125 130 135 140 145
3.17 1.83 2.50 5.67 2.67 5.00
Time (min) to 10°CB
(0.48)ab (0.17)c (0.43)ab (1.33)ab (0.49)ab (0.68)ab
31.33 23.17 60.33 45.50 40.33 58.17
Time (min) to 4°CB
(1.89)ab (1.49)a (0.76)cd (4.64)b (3.41)b (2.98)bd
48.00 57.00 65.67 68.83 69.67 73.50
(4.23)a (1.75)ac (0.99)bc (3.73)ac (3.47)ac (1.41)ac
a±d means in the same column with dierent superscripts are dierent (P < 0.05). Standard error of the means in brackets. Mean temperature at sample core.
Table 3 Eects of injection level on instrumental analysisA Cooling method
Warner±Bratzler (N)
VC 120% VC 125% VC 130% VC 135% VC 140% VC 145% WI 120%
20.59 20.39 14.88 13.80 13.88 11.90 17.38
(1.08)a (1.42)a (0.99)b (0.91)c (0.37)c (0.64)d (0.99)e
Colour (L) 45.99 50.58 51.37 51.30 52.14 52.52 52.65
(0.55)a (0.22)b (0.44)b (0.64)b (0.35)b (0.45)b (0.74)b
Colour (a)
Colour (b)
% Internal porosity
10.57 (0.06)a 9.58 (0.06)b 9.35 (0.07)c 8.50 (0.13)d 8.47 (0.04)c 8.24 (0.03)d 10.49 (0.23)e
10.62 (0.20)a 10.86 (0.28)a 9.13 (0.13)b 8.35 (0.22)b 8.08 (0.25)b 8.85 (0.11)b 10.08 (0.35)a
6.64 5.21 5.25 3.66 2.81 2.80 2.96
(0.25)a (0.08)b (0.17)b (0.10)c (0.28)c (0.31)c (0.18)c
A
a±e means in the same column with dierent superscripts are dierent (P < 0.05). Standard error of the means in brackets. VC/WI vacuum cooled and water immersion cooling followed by % injection level.
that increasing salt and phosphate concentrations would have reduced cooking loss as injection level increased (Trout & Schmidt, 1984; Siegel, Theno, Schmidt, & Norton, 1978). Polyphosphates were incorporated into the beef products to enhance their water holding capacity (Boles & Swan, 1997; Lee, Hendricks, & Cornforth, 1998). However, at all injection levels cooking losses were similar, which suggests that not all the phosphate and salt was incorporated by the samples. Inadequate blending of the phosphate into the brine solution may have contributed towards the observed cooking losses (Eilert, 1996; Pepper & Schmidt, 1975). The beef muscles structure particularly the fat distribution and brine injection distribution may have partly accounted for the observed cooking losses (Kinsman et al., 1994). At all injection levels, percent cooling losses were similar for all VC samples. This was expected as VC losses among other variables is related to ®nal product temperature. As all samples were cooled from, 72°C to less than 4°C so cooling losses should be similar (Mc Donald et al., 2000). Thus, the combination of cooking and cooling losses resulted in an unexpected similarity of percent total losses from 120% to 145% injection levels. WI cooled samples were signi®cantly dierent to VC samples (P < 0.05) with up to 9% lower cooling and total losses. This was as expected as moisture loss is an inherent requirement of VC for adequate cooling and leads to high cooling losses (Mc Donald and Sun, 2000a). As a consequence of high cooling losses VC samples had a signi®cantly lower percent total yield than
WI samples up to a 130% injection level (P < 0.05). At 135% injection VC samples were similar to WI cooled samples, while injection levels above 135% resulted in VC samples having higher yields than WI samples (Table 1). It is apparent from the results that to compensate for increased cooling loss during VC up to 115% injection of original green weight is required to make samples comparable to WI. Furthermore, it should be noted that although the 120% injection samples cooled the quickest (Table 2) and had the highest porosity (Table 3), they also resulted in the lowest yields (85.69%) compared to (112.30%) for 145% injection samples (Table 1). 3.2. Sensory analysis The dierent injection levels signi®cantly aected (P < 0.05) all the sensory attributes in VC samples except for cohesion as shown in Table 4. However, cohesion was improved slightly as injection level increased (Table 4) and was comparable to previous research which indicated that VC signi®cantly (P < 0.05) damaged the cohesion of a cooked beef product in comparison to more conventional cooling systems (Mc Donald et al., 2000). Tenderness and juiciness in VC samples were improved with increasing injection level and was better than WI cooled samples at injection level greater than 125% and 135%, respectively, with 145% injection samples being the most tender and juicy. These results were consistent with instrumental results, which
144
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
Table 4 Eect of injection level on the sensory quality of the cooked beef productA Cooling method
Sensory attributes
VC 120% VC 125% VC 130% VC 135% VC 140% VC 145% WI 120%
4.75 5.09 5.09 5.17 5.33 5.59 5.07
Tenderness (0.03)a (0.04)b (0.04)b (0.00)b (0.00)c (0.03)c (0.02)b
Juiciness 4.17 4.25 4.34 5.33 5.59 5.84 4.58
(0.00)a (0.03)a (0.07)a (0.00)b (0.03)b (0.07)c (0.00)a
Binding 3.84 4.17 4.25 4.25 4.34 4.42 4.89
(0.07)a (0.00)b (0.03)b (0.03)b (0.07)b (0.03)b (0.03)c
Overall ¯avour 4.42 4.92 5.17 3.83 3.84 3.17 3.93
(0.10)a (0.03)b (0.07)c (0.00)d (0.07)d (0.07)e (0.02)d
Overall colour 4.75 4.84 4.92 5.00 4.34 4.25 4.36
(0.03)a (0.07)a (0.03)a (0.00)b (0.07)c (0.03)c (0.01)a
Saltiness 4.25 4.17 4.17 3.67 3.33 2.92 4.00
(0.03)a (0.00)a (0.07)a (0.07)b (0.00)c (0.03)d (0.01)a
Overall acceptability 4.17 4.92 5.00 4.75 4.17 4.09 4.18
(0.00)a (0.03)b (0.07)b (0.03)b (0.00)a (0.03)a (0.02)a
A
Sensory attributes were evaluated by means of six-point scale (6: very tender/juicy/extremely good/extremely acceptable/extremely good/extremely acceptable; 1: very tough/dry/poor/poor/not acceptable/ver salty/not acceptable. a±e means in the same column with dierent superscripts are different (P < 0.05). Standard error of the means in brackets. VC/WI vacuum cooled and water immersion cooling followed by % injection level.
indicated a lower shear value for VC samples as injection level increased. Furthermore, as injection level increased so mean moisture content increased (P > 0.05) which will have contributed towards panellists indicating better juiciness in higher injection VC samples. Signi®cant dierences in juiciness between dierent cooling methods have been made in other research where there are signi®cant dierences in weight loss (Self et al., 1990). In the present research, panellists appear to have made this association between dierent injection levels within a single VC treatment. However, it is interesting to note that although the control WI cooled samples had a signi®cantly higher moisture content than the VC samples, panellists still rated VC samples with levels of injection greater than 135% injection more juicy. Flavour of VC samples was signi®cantly in¯uenced (P < 0.05) by level of injection (Table 4). The ¯avour was signi®cantly in¯uenced by the level of salt that was present in the samples due to injection level. The ¯avour as shown in previous research (Mc Donald et al., 2000) was better in VC samples than WI cooled samples and was best at injection levels of 130%. Some panellists indicated that VC samples at this level have a more natural or intense beef ¯avour. This observation may have been due to concentration of ¯avour compounds in the VC samples as a result of water loss and alteration of the muscle structure (increased porosity) caused by the VC procedure (Ima®don & Spanier, 1994). Injection levels greater than 130% resulted in panellists ®nding saltiness objectionable and subsequently marking down sample ¯avour. Injection level signi®cantly in¯uenced (P < 0.05) colour scores (Table 4). Colour acceptability improved in VC samples, as injection levels increased from 120% to 135%. It was apparent that panellists overall preferred the colour of VC samples in comparison to the WI controls with scores only slightly lower (P > 0.05) at 140 and 145% injection levels. Instrumental colour analysis (Table 3) agreed with these results as a -values decreased as injection level increased, leading to a less pronounced
red colour to the beef product. In general, people prefer cooked meat products to have the appearance of being well done with little or no pink or red colouration. Overall acceptability of VC samples was improved by increasing injection level in primary processing (P < 0.05). Best overall acceptability was at an injection level of 130% and this was signi®cantly better than the WI control samples (P < 0.05). It should be noted that as in previous research (Mc Donald et al., 2000) VC samples were comparable to WI samples at initial injection levels of 120%. The greatest in¯uence on the overall acceptability of the VC samples was the high percent salt in samples as injection level increased which signi®cantly decreased acceptability (P < 0.05). 3.3. Chemical analysis Compositional analysis (Table 5) indicated that injection level did not have a signi®cant eect on the mean moisture content of the VC samples (P > 0.05) although moisture loss due to VC was up to 3.35% higher than WI cooling which compares favourably with earlier research (Mc Donald et al., 2000). It was expected that increased injection levels would increase overall moisture contents in the VC samples and this would signi®cantly aect the protein and fat contents. It was observed that the lowest mean moisture content (70.09%) was in the 120% injection samples and increased up to a maximum of 71.04% in 145% injection samples. This subsequently impacted on percentage protein values in the samples which decreased in relative terms as percentage moisture increased, although not signi®cantly (P > 0.05). Increased protein and decreased moisture contents relative to VC samples will have an impact on sample texture. WI cooled samples had a signi®cantly higher (P < 0.05) mean moisture content than all VC samples (Table 5). These results aggress with previous research, which indicated that in comparison to more conventional cooling systems VC cooked beef
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
145
Table 5 Chemical analysis of the cooked beef productA Cooling method
% MoistureB
VC 120% VC 125% VC 130% VC 135% VC 140% VC 145% WI 120%
70.34 70.63 70.64 70.86 71.41 72.06 73.44
(0.11)a (0.17)a (0.09)a (0.09)a (0.15)b (0.21)c (0.22)d
% Protein 22.34 22.05 21.05 20.75 20.53 19.42 21.38
(0.11)a (0.10)a (0.05)a (0.05)a (0.11)a (0.36)b (0.13)c
% Fat 3.77 3.84 3.56 3.81 3.26 3.42 3.68
% Ash
(0.10)ac (0.06)a (0.06)ac (0.14)ac (0.18)bc (0.16)ac (0.14)ac
3.35 3.43 4.47 4.63 4.73 4.94 3.39
(0.03)a (0.02)a (0.04)b (0.03)b (0.02)b (0.02)c (0.02)a
% Salt 2.33 2.94 3.40 3.78 4.10 4.48 2.22
(0.08)a (0.05)b (0.05)c (0.04)d (0.05)e (0.04)f (0.07)a
Water activity 0.96 0.96 0.96 0.96 0.95 0.95 0.98
(0.00)a (0.00)a (0.00)a (0.00)a (0.00)a (0.00)a (0.00)b
A a±f means in the same column with dierent superscripts are dierent (P < 0.05). Standard error of means in brackets. VC/WI vacuum cooled and water immersion cooling followed by % injection level. B Mean moisture content.
products have lower moisture contents (Mc Donald et al., 2000). Analysis of moisture contents at dierent positions in the VC samples revealed the presence of a moisture gradient with signi®cant dierences between moisture contents at the surface, intermediate (half way point) and core (P < 0.05). As expected the surface had the lowest moisture content in all VC samples with moisture contents increasing towards the core region. Within the meat structure, the process of VC is dierent to that at the surface. Water vapour will both evaporate due to depressed pressure and condense on cooler parts of the beef simultaneously. Furthermore, conductive cooling from the cooler surface to the internal regions will also facilitate evaporative cooling. Therefore, moisture content as demonstrated by analysis will be greater within the meat matrix. Percentage dierences between moisture contents for the core, surface and intermediate regions were 10.35% and 3.95%, respectively (P < 0.05). In comparison the WI samples had no signi®cant dierences (P > 0.05) in moisture content between dierent regions. However, it was observed that moisture content was slightly higher at the surface perhaps due to the samples been cooled in a plastic bag. Diusion of water and water vapour through the meat during VC is the result of dierences in concentration and pressure and will only occur if the meat is porous (Crank, 1975; Labuza & Hyman, 1998). Monitoring of diusion rates from dierent regions during VC could be examined by perhaps using magnetic resonance imaging (Chen, Long, Ruan, & Labuza, 1997). Moisture loss from the core and other regions of the samples will continuously occur in order to reach thermodynamic equilibrium with the surrounding beef components and the vacuum chamber environment (Labuza & Hyman, 1998). If VC were continued beyond ®nal cooling temperature a point would be reached where the whole structure of the meat would equilibrate to mean moisture content. Changes in the moisture content of a multi-domain cooked beef product can aect not only yield (Table 1), but also its physical and chemical composition (Table 5)
along with its safety and shelf-life (Labuza & Hyman, 1998). The excessive loss of moisture at the surface of the samples is unacceptable. To improve the acceptability of VC beef products a means must be found to equilibrate moisture loss from dierent regions during VC. Pre-spraying of the product surface with water prior to VC has been shown to reduce water losses in vegetables and in some cases increase yield (Sun, 1999a,b). Perhaps this could be used with cooked beef products, however there are concerns about product safety due to contamination of the meat from the water used in spraying (Mc Donald, 1999). The eect of increasing injection level in VC samples was the signi®cant increase of percentage salt (P < 0.05). This in turn had objectionable eects with some taste panellists in terms of sample ¯avour. Increasing salt concentrations lead to an increase in percentage ash content and a decrease in water activity (P < 0.05) as was expected with increasing salt concentrations (Table 5). Thus, to implement the use of increased injection levels care will be needed in considering the eects of salt on the sensory attributes of the product if the use of injection level to improve quality in VC samples is to be of any real commercial bene®t. 3.4. Instrumental texture and colour The injection level had a signi®cant eect (P < 0.05) on both the texture and colour of the VC samples in comparison to each other and the WI control samples (P < 0.05). At injection levels of 120% Warner±Bratzler results for VC and WI samples were 20.59 and 17.38 N, respectively and comparable to previous research which indicated that WI had the lowest shear force results and best texture in comparison to VC samples (Mc Donald et al., 2000). As injection level increased shear values decreased in VC samples indicating a more tender beef product (Table 3). These results were substantiated by sensory analysis (Table 4) which indicated that panellists found VC samples with greater than a 125% injection level superior to WI samples in terms of tenderness (P < 0.05). Overall results indicate that both VC and
146
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147
injection level aect cooked beef tenderness. Increasing injection level in VC samples will help oset the eects of water loss on texture in the samples thus resulting in more tender products. Furthermore, a higher level of salt and sodium tripolyphosphate in higher injection samples may have contributed towards a higher water binding and better texture in VC samples (Lamkey, Mandigo, & Calkins, 1986). Self et al. (1990) indicated that VC did not aect cooked chicken breast tenderness, although no instrumental analysis was carried out in this research. The overall dark nature of the cooked beef product makes dierences in colour dicult to distinguish visually. However, instrumental measurement of colour (Table 3) indicated that injection level aected the internal colour of the cooked beef product (P < 0.05). Increasing injection level resulted in samples appearing lighter in colour as indicated by a higher L -value. The lighter colour as injection level increases is likely due to increased water which results in lower concentrations of meat pigments and decreases light penetration (Lawrie, 1998). Lower a -values in VC samples as injection level increased were preferred by panellists which indicated a less pronounced red/pink or undercooked colour in comparison to WI samples (P < 0.05). 4. Conclusions The results indicate that injection level can signi®cantly improve the quality of a VC beef product. An optimum injection level of 130±135% of sample green weight allows for a VC cooked beef product, which is comparable in quality to a high quality cooked beef product cooled using WI. However, the ingredients in the injection solution, particularly the salt and sodium polyphosphate will have to be carefully monitored to prevent adverse eects on sensory attributes such as ¯avour. This research has provided information, which may be used to improve the acceptance and implementation of VC as a practical cooling operation in the production of cooked meat products such as beef. Further research will investigate the eects of injection level on the quality of a rapid vacuum cooled cooked beef product using a brine solution with a constant salt and phosphate concentration. Acknowledgements This research has been part-funded by grand aid under the European Regional Development Fund, which is administered by the Department of Agriculture, Food and Forestry, Ireland. Thanks are given to Mr. Patrick Ward (Teagasc, National Food Centre, Ireland) for his help and guidance in the preparation of the
samples for this research. Special thanks are also given to Mr. Michael Cooney (Department of Food Science, University College Dublin) for his assistance in the analysis of the samples.
References AMSA (1995). Research guidelines for cookery, sensory evaluation and instrumental tenderness measurements of fresh meat. Chicago: National Livestock and Meat Board. Anon (1981). Rapid vacuum cooling. Food Processing Industry, 9, 49. Anon (1984). American meat institute. Good manufacturing practices. Guidelines for the production of fresh and cured cooked beef. Washington DC: AMI. Anon (1986). Losses of food and nutrients in food processing. In R. Passmore, & M.A. Eastwood, Human nutrition and dietetics (pp. 231±235). New York: Churchill Livingston. Anon (1989). Chilled and frozen. Guidelines on cook-chill and cookfreeze catering systems. London: HMSO Publications Centre. Anon (1991). Guidelines on cook-chill systems in hospitals and catering premises. Irish food safety advisory committee. Dublin: Government Publication Sale Oce. Anon (1998a). United States Department of Agriculture Code of Federal Regulations-Animals and Animal Products. In Requirements for the production of cooked beef, roast beef and cooked corn beef (pp. 270±271). 9 CFR Ch. III (318.17). Anon (1998b). Determination of ash in meat and meat products (reference method) ISO 936 (BS 4401). AOAC (1960). Ocial methods of analysis (9th ed., Sec. 960.39). Arlington, Virginia: Association of Ocial Analytical Chemists. AOAC International. (1990). Ocial methods of analysis (15th ed., Sec. 950.46A, 935.47, 935.48, 992.15). Arlington, Virginia: Association of Ocial Analytical Chemists. Boles, J. A., & Swan, J. E. (1997). Eects of brine ingredients and temperature on cook yields and tenderness of pre-rigor processed roast beef. Meat Science, 45, 87±97. Burfoot, D., Self, K. P., Hudson, W. R., Wilkins, T. J., & James, S. J. (1990). Eect of cooking and cooling method on the processing times, mass losses and bacterial condition of large meat joints. International Journal of Food Science and Technology, 25, 657±667. Chen, Y. L. (1986). Vacuum cooling and its energy use analysis. Journal of Chinese Agricultural Engineering, 32, 43±50. Chen, P. L., Long, Z., Ruan, R. R., & Labuza, T. P. (1997). Nuclear magnetic resonance studies of water mobility in bread during storage. Lebensmittel ± Wissenschaft und ± Technologie, 30, 178± 183. Crank, J. (1975). The mathematics of diusion (2nd ed.). Oxford: Clarendon. Eilert, S. J. (1996). Phosphate type, concentration and preblend duration to improve water holding capacity of beef connective tissue. Journal of Muscle Foods, 7, 255±269. Evans, J., Russell, S., & James, S. (1996). Chilling of recipe dish meals to meet cook-chill guidelines. International Journal of Food Refrigeration, 19, 79±86. Everington, D.W. (1993). Vacuum technology for food processing. Food Technology International Europe, 71±74. Frost, C. E., Burton, K. S., & Atkey, P. T. (1989). A fresh look at cooling mushrooms. Mushroom Journal, 193, 23±29. Hofmans, G. J. P., & Veerkamp, C. H. (1976). Vacuum cooling of broiler carcasses. In B. Erdtsieck, Proceedings of the Second European Symposium on Poultry Meat Quality, European Federation Branch of the World Poultry Science Association. Ima®don, G. I., & Spanier, A. M. (1994). Unravelling the secret of meat ¯avour. Trends in Food Science and Technology, 5, 315±321.
K. McDonald et al. / Journal of Food Engineering 47 (2001) 139±147 James, S. J. (1990). Process engineering in the food industry ± 2: convenience foods and quality assurance (pp. 88±97). London: Elsevier Applied Sciences. James, S. J. (1996). The chill chain from carcass to consumer. Meat Science, 43, S203±S216. Labuza, T. P., & Hyman, C. R. (1998). Moisture migration and control in multi-domain foods. Trends in Food Science and Technology, 9, 47±55. Lamkey, J. W., Mandigo, R. W., & Calkins, C. R. (1986). Eect of salt and phosphate on the texture and colour stability of restructured beef steaks. Journal of Food Science, 51, 873±875, 911. Lawrie, R.A. (1998). Lawrie's meat science (pp. 130±137, 212±257). Cambridge, England: Woodhead Publishing. Lee, B. J., Hendricks, D. G., & Cornforth, D. P. (1998). Eect of sodium phytate, sodium pyrophosphate and sodium tripolyphosphate on physico chemical characteristics of restructured beef. Meat Science, 50, 273±283. Mc Donald, K. (1999). Safety in the cooling of large cooked meats. The Food Science. Times, 2, 3±12. Mc Donald, K., & Sun, D. W. (2000a). Vacuum cooling technology for the food processing industry. Journal of Food Engineering, 45, 55± 65. Mc Donald, K., & Sun, D. W. (2000b). The formation of pores and their eects in a cooked beef product on the eciency of vacuum cooling. Journal of Food Engineering (in press). Mc Donald, K., Sun, D. W., & Kenny, T. (2000). Comparison of the quality of cooked beef products cooled by vacuum cooling and by conventional cooling. Lebensmittel ± Wissenschaft und ± Technologie., 31, 21±29. Murphy, R. Y., & Marks, B. P. (1999). Apparent thermal conductivity, water content, density, and porosity of thermally processed ground chicken patties. Journal of Food Processing and Engineering, 22, 129±140.
147
Noble, R. (1985). A review of vacuum cooling of mushrooms. Mushroom Journal, 149, 168±170. Pepper, F. H., & Schmidt, G. R. (1975). Eect of blending time, salt, phosphate and hot-boned beef on binding strength and cook yield of beef rolls. Journal of Food Science, 40, 227±230. Self, K. P., Nute, G. R., Burfoot, D., & Moncrie, C. B. (1990). Eect of pressure cooking and pressure rate change during cooling in vacuum on chicken breast quality and yield. Journal of Food Science, 55, 1531±1535, 1551. Shackelford, S. D., Koohmaraie, M., Whipple, G., Wheeler, T. L., Miller, M. F., Crouse, J. D., & Reagan, J. O. (1991). Predictors of beef tenderness: development and veri®cation. Journal of Food Science, 56, 1130±1135, 1140. Siegel, D. G., Theno, D. M., Schmidt, G. R., & Norton, H. W. (1978). Meat massaging: the eects of salt, phosphate and massaging on cooking loss, binding strength and exudate composition in sectioned and formed ham. Journal of Food Science, 43, 331±333. Sun, D. W. (1999a). Comparison of rapid vacuum cooling of leafy and non-leafy vegetables. ASAE Paper No. 996117, ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. Sun, D.W. (1999b). Eect of pre-wetting on weight loss and cooling times of vegetables during vacuum cooling. ASAE Paper No. 996119, ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. Sun, D. W., & Brosnan, T. (1999). Extension of the vase life of cut daodil ¯owers by rapid vacuum cooling. International Journal of Refrigeration, 22, 472±478. Sun, D. W., & Wang, L. (2000). Heat transfer characteristics of cooked meats using dierent cooling methods. International Journal of Refrigeration, 23, 508±516. Trout, G. R., & Schmidt, G. R. (1984). Eect of phosphate type and concentration, salt level and method of preparation on binding in restructured beef rolls. Journal of Food Science, 49, 687±694.