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Meat Science 99 (2015) 38–43
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Meat Science
journal homepage: www.elsevier.com/locate/meatsci
Influence of household cooking methods on amino acids and minerals of
Barrosã-PDO veal
Anabela F. Lopes a,1, Cristina M.M. Alfaia a,1, Ana M.C.P.C. Partidário b, José P.C. Lemos a, José A.M. Prates a,⁎
a
b
CIISA, Faculdade de Medicina Veterinária, Universidade de Lisboa, Avenida da Universidade Técnica, Pólo Universitário do Alto da Ajuda, 1300-477 Lisboa, Portugal
Unidade de Investigação de Tecnologia Alimentar, INIAV, Estrada do Paço do Lumiar, 22, Campus do IAPMEI, Ed. S, 1649-038 Lisboa, Portugal
a r t i c l e
i n f o
Article history:
Received 6 October 2013
Received in revised form 20 August 2014
Accepted 22 August 2014
Available online 30 August 2014
Keywords:
Veal
Cooking methods
Amino acids
Minerals
Retention
a b s t r a c t
The effect of commonly household cooking methods (boiling, microwaving and grilling) on amino acid and
mineral (Fe, Mg, K and Zn) contents was investigated in the longissimus lumborum muscle of Barrosã-PDO veal.
Fifteen Barrosã purebred calves at 7–8 months of age and an average weight of 177 ± 37 kg were slaughtered.
Cooking had a strong effect (P b 0.05) on yield, being higher (67.5%) in boiling compared to microwave and
grilling (64.0% and 64.5%, respectively). Grilling increased most of the percentage retention of individual
amino acids (N100%), in particular for leucine. No significant differences (P N 0.05) were observed for iron and
zinc retentions among the cooking methods, while the retention of magnesium and potassium was strongly
affected, mainly after boiling. Our findings indicate that the different cooking methods clearly affect the chemical
composition and nutritional value of meat, which may have a strong impact on the intake of essential nutrients.
© 2014 Elsevier Ltd. All rights reserved.
1 . Introduction
Red meat is generally recognized as valuable food with relevant
nutritional properties due to its content of high-quality proteins, with
a balanced content in amino acids, particularly in essential amino
acids. In fact, from the twenty amino acids constituting proteins, eight
have to be supplied by the diet (isoleucine, leucine, lysine, methionine,
phenylalanine, threonine, tryptophan and valine) in order to ensure an
adequate physical development and well-being (Aristoy & Toldrá, 2009;
Wu, 2009). Amino acid content and composition play an important role
in meat quality by providing nutritive value and flavor (Cai et al., 2010).
Meat is also a major dietary source of complex B vitamins, especially
vitamin B12, zinc, selenium, phosphorus and iron, thus contributing
significantly to the daily intake of these essential micronutrients
(Cabrera, Ramos, Saadoun, & Brito, 2010). The nutritional importance
of meat also lies in its essential trace element content, specifically in
iron, which is present in the form of heme (hemoglobin and muscle
myoglobin), accounting for its high bioavailability in red meats
(Alegría, Barberá, Lagarda, & Farré, 2009). Moreover, iron has a crucial
role in human health. Iron deficiency is one of the biggest nutrient deficiency concerns in Europe, which can lead to anemia as well as to disturbances in child growth and development (Lozoff & Georgieff, 2006).
Meat becomes more edible and digestible when subjected to
cooking (Alfaia, Lopes, & Prates, 2013). During cooking, meat undergoes
⁎ Corresponding author. Tel.: +351 213652890; fax: +351 213652895.
E-mail address: [email protected] (J.A.M. Prates).
1
Authors contributed to the work equally.
http://dx.doi.org/10.1016/j.meatsci.2014.08.012
0309-1740/© 2014 Elsevier Ltd. All rights reserved.
both physical and chemical changes, such as a decrease in the nutritional value, which are strongly dependent on protein denaturation and
water loss (Mora, Curti, Vittadini, & Barbanti, 2011; Tornberg, 2005). It
is well known that an increase in core temperature in meat will promote
collagen shrinkage, reduce water holding capacity and increase cooking
loss that influences its final quality and acceptability (Chiavaro, Rinaldi,
Vittadini, & Barbanti, 2009). Cooking loss is a combination of liquid and
soluble matter and with increasing temperature, water content decreases while fat and protein contents increase, thus indicating that
the main part of cooking loss is water (Heymann, Hedrick, Karrasch,
Eggeman, & Ellersieck, 1990). Heating time, temperature, cooking
method and muscle composition are all important variables, which
may influence the final desirable characteristics of the meat (Alfaia
et al., 2010; Christensen, Purslow, & Larsen, 2000). Although meat
changes induced by cooking have been studied for many years and
extensively discussed (Offer, 1984; Tornberg, 2005), only few reports
have specifically dealt with the influence of different cooking conditions
on the amino acid and mineral contents (Wilkinson, Lee, Purchas, &
Morel, 2014). Moreover, the nutrient composition of cooked meats
available in Food Composition databases is quiet limited.
Consumers are increasingly aware of the relationships between diet,
health and well-being resulting in choices of foods which are healthier
and more nutritious (Banovic, Grunert, Barreira, & Fontes, 2010). Beyond the choice of healthy foods, there is also a concern for healthy
cooking. In fact, a better understanding of the complexity of heat treatments used to cook meat and its influence on their nutrients may
increase consumer's expectations and acceptance of more convenient
and healthy cooking choices (Font-i-Furnols, & Guerrero, 2014). Meats
A.F. Lopes et al. / Meat Science 99 (2015) 38–43
with Protected Designation of Origin (PDO) are recognized and valued
by the consumers due to their distinctiveness and quality. The PDO
policy intends to guarantee to consumers a trustful supply that respects
both sanitary rules and the features perceived by consumers as signs of
quality (Monteiro et al., 2013). In line with this, the maintenance of
meat quality throughout cooking is particularly important for PDO
meats.
Therefore, the present study assessed the effect of three cooking
methods (microwave oven, boiling and grilling) on amino acid and
mineral (iron, magnesium, potassium and zinc) contents of BarrosãPDO veal. The influence of cooking methods, widely used in household
processing, on amino acids and minerals of meat is compared on the
basis of nutrient retention. Finally, the contribution of meat cooked
under different methods for the recommended daily intake of amino
acids and minerals was also evaluated.
2 . Materials and methods
2.1 . Animals and meat sampling
Fifteen Barrosã purebred calves produced in the Northwest of
Portugal were kept according to the traditional production pasturebased system following the rules established in the Barrosã-PDO product specifications (Commission Regulation no. 1263/96 of 01/07, EEC).
After weaning, the animals were slaughtered between January and February 2008, at 7–8 months of age and an average weight of 177 ± 37 kg.
Meat samples were taken from the longissimus lumborum (LL) muscle,
between the L1 and L4 ribs, two to three days after slaughter (+1 °C),
and vacuum packed and frozen at − 80 °C until application of heat
treatments.
2.2 . Cooking methods and preparation of samples
Frozen muscle samples were thawed overnight at 4 ± 2 °C. Once the
meat was thawed, each sample was sliced into cuts with 1.5 cm thickness (5 × 5 × 1.5 cm), weighed (around 38 g) and subjected to each
of the following cooking methods: microwaving, boiling and grilling,
while the raw cuts were sampled directly as the uncooked control.
Microwave oven (Mod. AVM 559, Whirlpool, USA) samples were
placed in a Pyrex container. Cooking was performed in a 2450 MHz at
750 W using two heating cycles of 45 s and turned over between cycles.
Boiling was performed in a water bath with samples completely
submerged for 40 min at 81 °C. In electric grill (Mod. ES/FOFTES), the
samples were placed on the center of the thermal resistance and
approximately 4 cm from heat source and cooked for 30 min at
225 °C. The samples were turned every 5 min. The cooking temperature
and time used for each method resulted from a series of tests, which
showed the best value for temperature/time cooking samples without
a trace of blood. The final cooking temperature was determined beforehand by inserting thermocouples (Type K — Lufft C100 Series Digital
Instruments, USA) into the approximate geometric center of each steak.
39
(1980). After hydrolysis, 25 mL of HCl 0.01 M was added and the extract
was filtered and evaporated in a rotary evaporator (R110 BUCHI) at
60 °C to a final volume of 5 mL. Then, 500 μL was withdrawn and the
pH was adjusted by the addition of approximately 1 mL of NaOH 1 N.
Then, 100 μL of internal standard (norleucine, 1 mg/mL) and 800 μL of
ethanol were added to 100 μL of the extract. The extracts were centrifuged at 14,500 rpm for 2 min. The supernatant was led to dryness at
70 °C under a nitrogen stream. The derivatization was carried out
using 250 μL of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) plus
1% trimethylchlorosilane (TMCS), during 2.5 h at 130 °C (Multi-Blok
Heater Lab-line). After derivatization, 300 μL of acetonitrile was added
(Quaresma et al., 2003).
2.4.2 . Gas chromatography analysis
The separation of amino acids was achieved by gas chromatography
(Hewlett 5890 Packard Series II) with flame ionization detection. A DB17 fused-silica capillary column (Agilent Technologies, Palo Alto, CA,
USA) with 30 m × 0.25 mm was used. The analysis conditions were as
follows: column temperature programmed from 80 °C (3 min), up to
210 °C with a rate of 5 °C/min; injector and detector temperatures,
275 °C and 300 °C, respectively. Helium was the carrier gas (70 kPa).
The amino acids were identified by their retention times and by comparison with a standard amino acid solution (Sigma-Aldrich AA-S-18).
Quantification was based on the internal standard method.
2.5 . Determination of minerals
The determination of ash content was carried out according to the
procedures described in AOAC (2000). The mineral elements (iron,
magnesium, potassium and zinc) were determined by atomic absorption spectrophotometry (PU 9100X Philips) based on the method proposed by Hermida, Gonzalez, Miranda, and Rodríguez-Otero (2006).
2.6 . Determination of retention
The retention of amino acids and minerals was calculated according
to Murphy, Criner, and Gray (1975), using the following equation:
TR (%) = (A × B / C × D) × 100, where A — nutrient content (g) of
cooked meat; B — meat weight (g) after cooking; C — nutrient content
(g) of raw meat and D — weight (g) of raw meat.
2.7 . Statistical analysis
As variance heterogeneity was detected for most parameters, the
data were analyzed using the PROC MIXED with variance heterogeneity
analysis of SAS (2009) software package (version 9.2; Statistical Analysis Systems Institute, Cary, NC, USA). The statistical model evaluated
included the treatment effect as repeated measure. Data were reported
as mean ± standard error (SE). Least squares means (LSMEANS), with
the option PDIFF adjusted with Tukey–Kramer, were determined to
compare groups. Differences were considered significant at a P-value
below 0.05.
2.3 . Determination of yield
3 . Results and discussion
After cooking and cooling (30 min at 20–22 °C), the samples were
wiped with a paper towel to remove visible exudates and the cooking
yield was calculated by the weight difference before and after cooking.
2.4 . Determination of amino acids
2.4.1 . Hydrolysis and derivatization of samples
Meat cooked samples were lyophilized (−60 °C and 2.0 hPa) until
constant weight using a lyophilisator Edwards Modulyo (Edwards
Hight Vacuum International, UK). Dry samples (0.2 g) were hydrolysed
with 5 mL of HCl 6 N solution (containing 1% phenol, w/v) for 24 h at
110 °C according to the procedure described by Pellet and Young
3.1 . Final cooking temperature and cooking yield
Meat is considered cooked when the temperature reached inside the
sample is kept at 65–70 °C for 10 min (Bender, 1992). Furthermore, the
end of the cooking process is generally indicated by change of the meat
color and by the development of flavors. In current study, the internal
endpoint temperature of meat was significantly different (P b 0.001)
among the three cooking processes (Table 1). The highest value was observed for microwaving (93.9 ± 0.32 °C), followed by boiling (74.1 ±
0.54 °C) and grilling (70.0 ± 1.21 °C). This internal endpoint temperature for each heating treatment enabled the meat to attain a medium
40
A.F. Lopes et al. / Meat Science 99 (2015) 38–43
Table 1
Final internal temperature and yield of longissimus lumborum muscle from Barrosã-PDO
veal after three different cooking methods (n = 15).
PA
Treatments
Microwaving
Temperature (°C)
Yield (%)
Boiling
a
93.9 ± 0.323
64.4ab ± 1.04
b
74.1 ± 0.542
67.5b ± 0.882
Grilling
70.0c ± 1.21
64.0a ± 1.08
***
*
Least square means (±SE); Astatistical probability of treatment: *, P b 0.05; ***, P b 0.001;
means in the same row with different superscripts are significantly different (P b 0.05).
(grilling) or a well (boiling and microwaving) degree of doneness
(Lorenzen et al., 1999). Similar findings were found for beef cooked
under microwaving, boiling and grilling (Alfaia et al., 2010).
The cooking yields of LL muscle of Barrosã-PDO veal are also shown
in Table 1. Cooking yields were also affected by the cooking process used
(P b 0.05). Boiling had a higher cooking yield (67.5%) compared to
grilling and microwave oven (64.5% and 64.0%, respectively). Temperature and sample size are generally accepted to be key factors connected
with weight loss. Bengtsson et al. (1976) observed that as internal temperature increased, cooking yields decreased. Our results also showed
that cooking yields decreased with increasing endpoint temperatures
due to moisture loss (e.g. evaporation, moisture drip) or fat gains/losses
during cooking (Roseland et al., 2012). Offer and Knight (1988) reported that cooking involves heat and mass transfer by diffusion of water
through the meat and evaporation from the meat surface, and through
physical expulsion caused by constriction of muscle bundles. The
authors hypothesized that meat surface dehydration led to the development of crust formation in grilling and microwave heating with less
pronounced loss of liquids, as was previously suggested by other authors (Vittadini, Rinaldi, Chiavaro, Barbanti, & Massini, 2005).
3.2 . Effect of cooking methods on amino acid content and composition
The total content (g/100 g meat) and composition (% of total amino
acids) of fifteen amino acids in raw and cooked LL muscle from BarrosãPDO veal are presented in Table 2. The data showed that amino acid
content in Barrosã-PDO veal increased significantly (P b 0.001) after
cooking, which was the result of water loss. Cooking significantly
decreased moisture content (P b 0.001), as expected, from 75% in raw
state up to 59% and, consequently, to a significantly higher amino acid
contents, with no significant differences (P N 0.05) among treatments.
Moisture content results (Table 2) were in agreement with the cooking
yield values of each treatment.
Regarding amino acid composition in normalized terms (each amino
acid as a percentage of total amino acids) and in decreasing order, the
foremost amino acids in raw and cooked meat were glutamic acid
(17–19%), leucine (12%) and aspartic acid (10–11%), except for grilling.
In grilled veal-PDO, the predominant amino acids were leucine (23%),
followed by glutamic and aspartic acids (16% and 9.2%, respectively).
In contrast, methionine, glycine, proline and tyrosine had the lowest
values (b 2.8%). Cystine, asparagine, glutamine and tryptophan were
not detected, which is in agreement with the findings of Moughan
(2003), who stated that these amino acids are destroyed by thermal
hydrolysis. A similar trend was observed in pork, where glutamic acid
and aspartic acid were the amino acids present at a higher level, whereas proline, serine, glycine and alanine showed the lowest values (e.g.
Okrouhlá et al., 2006; Purchas, Morel, Janz, & Wilkinson, 2009). From
the 15 amino acids analyzed, only 6 changed significantly as a result of
cooking, namely glutamic acid (P b 0.05), leucine (P b 0.001), methionine (P b 0.001), serine (P b 0.01), threonine (P b 0.05) and valine
(P b 0.01). Recently, Wilkinson et al. (2014) showed that 12 of the 17
amino acids measured in samples of pork longissimus muscle changed
significantly with cooking, with all amino acids increasing, except for
histidine and taurine. Throughout cooking, meat proteins are denatured
by the heat with subsequent loss of water-holding capacity of the proteins (Tornberg, 2005), but most of the loss appears to be water enhanced higher contents of other components in cooked meat.
3.3 . Effect of cooking methods on ash and minerals
The values of ash for raw and cooked LL muscle from Barrosã-PDO
veal are shown in Table 3. The ash value, an indicator of total mineral
content, obtained for raw meat (0.98 g/100 g) is in agreement with
the results (0.6–1.1 g/100 g) of Farfán and Sammán (2003). However,
Hoffman, Kroucamp, and Manley (2007) found higher levels in
longissimus dorsi muscle of springbok meat (1.1 to 1.4 g/100 g). Cooking
led to significant differences in ash content among treatments
(P b 0.001). Microwaving (1.4 g/100 g) and grilling (1.8 g/100 g) increased the ash content of meat, while boiling decreased its content
compared with the raw meat. Since microwave cooking and grilling
proceed in the absence of water (dry cooking methods), these cooking
methods allowed for a high retention of ash than boiling (wet cooking
method). Dal Bosco, Castellini, and Bernardini (2001) also found a
Table 2
Effect of cooking methods on moisture content (g/100 g meat), amino acid content (g/100 g meat) and composition (% total amino acids) of longissimus lumborum muscle from BarrosãPDO veal (n = 15).
PA
Treatments
Raw
Moisture
Total amino acids
Amino acid composition
Alanine
Arginine
Aspartic acid
Glutamic acid
Glycine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Proline
Serine
Threonine
Tyrosine
Valine
Microwaving
75.1a ± 0.430
18.4a ± 1.67
8.11
4.88
10.0
18.7a
2.01
7.25
11.7a
2.07
1.50ab
4.42
2.39
8.22a
8.43ab
2.48
8.67ab
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.516
0.443
0.586
0.958
0.302
0.233
0.407
0.523
0.167
0.235
0.202
0.632
0.296
0.931
0.549
61.6bc ± 0.736
31.3b ± 2.27
8.09
5.06
9.78
16.8ab
2.52
7.36
11.9a
3.37
1.68a
5.13
2.68
8.32ab
7.96ab
1.72
7.91ab
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.456
0.322
0.395
0.805
0.193
0.224
0.461
0.472
0.112
0.504
0.242
0.739
0.299
0.275
0.208
Boiling
Grilling
62.9b ± 0.799
31.2b ± 1.82
8.29
4.83
11.1
17.9ab
2.21
7.77
12.0a
2.20
1.59a
4.11
2.44
7.49a
8.34a
1.63
8.08a
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.228
0.395
0.255
1.03
0.242
0.257
0.372
0.544
0.141
0.206
0.175
0.279
0.179
0.249
0.161
59.4c ± 0.727
37.2b ± 2.19
***
***
7.22
3.98
9.24
15.7b
2.51
6.87
23.0b
1.66
1.05b
3.99
2.37
6.35b
7.52b
1.41
7.17b
ns
ns
ns
*
ns
ns
***
ns
***
ns
ns
**
*
ns
**
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.345
0.323
0.739
0.488
0.294
0.232
1.97
0.397
0.096
0.181
0.229
0.220
0.239
0.330
0.197
Least square means (±SE); Astatistical probability of treatment: ns, P N 0.05; *, P b 0.05; **, P b 0.01; ***, P b 0.001; means in the same row with different superscripts are significantly
different (P b 0.05).
A.F. Lopes et al. / Meat Science 99 (2015) 38–43
Table 3
Effect of cooking methods on ash (g/100 g meat) and mineral (mg/100 g meat) contents
of longissimus lumborum muscle from Barrosã-PDO veal (n = 10).
PA
Treatments
Raw
Ash
a
Microwaving
b
0.98 ± 0.064 1.40 ± 0.041
Boiling
Grilling
c
0.77 ± 0.014 1.76d ± 0.047 ***
Minerals
Iron
1.69 ± 0.143 2.13 ± 0.147 2.49
28.5b ± 1.38
20.4c
Magnesium 13.0a ± 0.74
316a ± 10.5
129b
Potassium
289a ± 20.3
Zinc
3.44a ± 0.310 4.89b ± 0.372 5.39b
±
±
±
±
0.393
0.52
6.73
0.338
3.14
30.1b
157c
5.79b
±
±
±
±
0.657
0.79
6.77
0.495
ns
***
***
***
Least square means (± SE); Astatistical probability of treatment: ns, P N 0.05; ***,
P b 0.001; means in the same row with different superscripts are significantly different
(P b 0.05).
decrease in ash content of rabbit meat after boiling and roasting. Similar
ash values for cooked meat (1.3 to 1.9 g/100 g) were reported by Farfán
and Sammán (2003).
The mineral (iron, magnesium, potassium and zinc) contents
for raw and cooked LL muscle from Barrosã-PDO veal are also presented in Table 3. The major minerals present in raw and cooked
meats were potassium (129–289 mg/100 g), followed by magnesium (13.0–30.1 mg/100 g), zinc (3.44–5.79 mg/100 g) and iron
(1.69–3.14 mg/100 g), which altogether represented about 31% of
total ash. The mean values for potassium, magnesium, zinc and
iron in raw meat varied greatly among the species (Gerber,
Scheeder, & Wenk, 2009). The mean potassium content in raw
Barrosã-PDO veal (289 mg/100 g) was higher than that found in
pork (172–175 mg/100 g), poultry (248–259 mg/100 g) and mutton (275 mg/100 g) (Sainsbury, Schonfeldt, & Van Heerden, 2011),
but inside of the range (299 to 350 mg/100 g) described for beef
(Driskell, Kim, Giraud, & Hamouz, 2011). The magnesium contents
found in this study are lower than those described in some other reports
(Driskell et al., 2011; Gerber et al., 2009; Ramos, Cabrera, Puerto, &
Saadoun, 2009). Regarding the contents of iron and zinc for BarrosãPDO veal, the values were similar to those (1.6–3.9 mg/100 g and 3.2–
5.9 mg/100 g, respectively) found in previous works (Driskell et al.,
2011; Gerber et al., 2009; Lombardi-Boccia, Lanzi, & Aguzzi, 2005).
Even so, the iron and zinc concentrations provided by veal were higher
than those found in pork and chicken (Gerber et al., 2009; LombardiBoccia et al., 2005). This variability in mineral composition is due to
many factors, such as muscle type (Gerber et al., 2009; Hermida et al.,
2006) age (Doornenbal & Murray, 1981), breed (Farfán & Sammán,
2003), genre (Doornenbal & Murray, 1981), diet (Driskell et al., 2011),
production region (Hoffman et al., 2007), genetic factors (Leonhardt &
Wenk, 1997) and species (Lombardi-Boccia et al., 2005).
Table 3 also shows the outcome of minerals in cooked meat. Cooked
meat showed higher mineral contents compared to the raw samples
due to the moisture loss upon cooking, except for potassium. In addition, cooking processes affected the various minerals in different ways.
The content of iron did not change after cooking (P N 0.05). Red meat
(beef, lamb and pork) is the main source of heme Fe, which is the iron
form having the highest bioavailability (Carpenter & Mahoney, 1992).
According to Purchas, Simcock, Knight, and Wilkinson (2003) the
general pattern is the soluble heme iron to decrease from the uncooked
state to the cooked state as cooking temperature increased. In the
current study, it appears that the decrease of soluble heme iron was
approximately matched by an increase in the proportion of insoluble
heme iron due to heat denaturation of the myoglobin molecule
(Purchas, Rutherfurd, Pearce, Vather, & Wilkinson, 2004). In addition,
a study carried out on heme iron concentration in meats showed that
heat treatments do not cause losses in total iron content but modify
the heme:non-heme iron ratio (Lombardi-Boccia, Dominguez, &
Aguzzi, 2002). The mean values of zinc and magnesium in BarrosãPDO veal increased significantly (P b 0.001) in cooked samples compared to raw meat. The contents of magnesium were significantly
41
higher in microwave oven and grilling, which is consistent with higher
loss of moisture. By contrary, the content of potassium decreased significantly after boiling, probably due to the leaching of minerals into
cooking water. As reported by Badiani et al. (2002), boiling leads to
some leaching of nutrients from meat to the cooking medium, while
in dry cooking methods, such as grilling and microwave, the water
loss by evaporation induces a concentration of minerals. Gerber et al.
(2009) also showed that cooking processes involving water, such as
boiling, affected mineral content the most.
3.4 . Retention of moisture, amino acids, ash and minerals
In order to evaluate the increase or loss/degradation of meat components during cooking, the retention of nutrients was calculated. The
effect of cooking methods on moisture and minerals retention values
is shown in Table 4. Water showed the greatest loss (retention of 51–
56%) during cooking compared to minerals. The retention of moisture
was significantly affected by heating methods (P b 0.01) being significantly lower in grilling (51%) than in boiling (56%). Boiling showed
the lowest water loss due to the incorporation of water during the
cooking process. As expected, all the amino acids were retained
(above 100%) after cooking due to water loss but without any statistically significant differences (P N 0.05) among heat treatments (104–
180%), except for leucine (data not shown). Leucine was significantly
higher for grilled meat than for both microwave and boiled meat
(P b 0.001). Since grilling proceeded at a higher temperature (225 °C
during 30 min) and in the absence of water, this cooking method probably allowed for a high retention of amino acids due to a higher water
loss. A hundred percent retention is expected, unless amino acids are
partially degraded (protein denaturation) or lost in the cooking juice.
Recently, Wilkinson, Lee, Purchas & Morel (2014) found that the
amino acid retention in samples of pork longissimus muscle was generally less than 90% cooked to either 60 °C or 75 °C in a water bath for
90 min, with slightly higher values at the lower cooking temperature.
Table 4 also shows the influence of cooking on retention of ash and
minerals from LL muscle of Barrosã-PDO veal. The heat treatments
changed the ash retention from 46.5% to 105%. The ash retention was
higher in grilling (105%) than in microwaving (89.9%) and boiling
(46.5%), which was expected given the former's superior cooking
yield. Dal Bosco et al. (2001) and Maranesi et al. (2005) found similar
ash retention values (72–98%) for cooked rabbit and lamb meats,
respectively. Serrano, Librelotto, Cofrades, Sáches-Muniz, and JiménezColmenero (2007) also reported that ash retention in cooked beef
steak ranged from 73.0% to 93.4% in microwaving and from 82.3% to
97.7% in electric grill. Minerals were reasonably well retained by
cooking, except potassium. The retention values of iron and zinc varied
between 78.9–105% and 88.9–97.0%, for microwaving and grilling,
respectively. Lombardi-Boccia et al. (2005) also found that retention of
iron and zinc varies from 83 to 88% in beef. Although only a few studies
have been performed on mineral retention of cooked meats, a broad
Table 4
Effect of cooking methods on mineral retention values (%) of longissimus lumborum muscle
from Barrosã-PDO veal (n = 10).
PA
Treatments
Microwaving
Moisture
Ash
Minerals
Iron
Magnesium
Potassium
Zinc
ab
52.9 ± 1.22
89.9a ± 3.20
78.9
138a
68.4a
88.9
±
±
±
±
5.49
7.01
2.55
6.25
Boiling
Grilling
b
56.3 ± 0.874
46.5b ± 1.07
50.7a ± 1.26
105c ± 3.61
**
***
87.8
93.4b
26.5b
93.2
105
135a
31.6b
97.0
ns
***
***
ns
±
±
±
±
14.0
2.09
1.41
6.41
±
±
±
±
19.3
4.49
1.82
7.63
Least square means (±SE); Astatistical probability of treatment: ns, P N 0.05; **, P b 0.01;
***, P b 0.001; means in the same row with different superscripts are significantly
different (P b 0.05).
42
A.F. Lopes et al. / Meat Science 99 (2015) 38–43
agreement exists that zinc, copper and iron largely remain in the meat
sample during cooking (Gerber et al., 2009; Lombardi-Boccia et al.,
2005). In our study, no significant differences were detected for iron
and zinc retentions among the cooking methods (P N 0.05). In contrast,
the retention of magnesium and potassium were significantly affected
by cooking (P b 0.001) mainly after boiling. Thus, the dry cooking
methods (microwave and grilling) allowed for a higher retention of
the mineral content in cooked meats, which is in agreement with data
described by Lombardi-Boccia et al. (2005) and Gerber et al. (2009).
Previously, Lassen and Ovesen (1995) stated that, when properly
used, microwave cooking does not affect the mineral contents of food
to a larger extent than conventional heating. There is a tendency
towards greater retention of many micronutrients with microwaving,
which tends to make microwave cooking healthier, probably due to
the reduced preparation time.
3.5 . Dietary reference intake contribution
Generally, the consumption of 100 g of raw bovine meat would be
enough to supply the daily adult's requirement of amino acids and minerals. However, nutrient requirements vary in specific groups of people,
as for example in children and/or in pregnant or lactating women,
because they have added needs (WHO/FAO/UNU, 2007). In modern
societies, meat is usually cooked prior to consumption, and the effect
of cooking on these nutrients is poorly documented (Gatellier et al.,
2009). Meat processing procedures, such as cooking, may affect the
physicochemical state of proteins and the bioavailability of their
amino acids (Santé-Lhoutellier, Astruc, Marinova, Grève, & Gatellier,
2008; Tornberg, 2005). According to the WHO/FAO/UNU (2007) report,
the mean values for the essential amino acid requirements in adults are
39, 20, 26 and 15 mg/kg body weight/day for leucine, isoleucine, valine
and threonine, respectively. Based on these values, an adult with 60 kg
will require 2340, 1200, 1560 and 900 mg of leucine, isoleucine, valine
and threonine per day, respectively. Facing these recommendations, a
daily consumption of 100 g of cooked Barrosã-PDO veal will provide
the amount required of these amino acids. Concerning minerals, the
same cooked veal portion only provided a significant amount of iron
and zinc (at least 15% of the nutrient reference values for adults, 14
and 10 mg supplied by 100 g, respectively). In contrast, the contents
of magnesium and potassium only provided less than 15% of the adult
daily reference intakes (375 mg and 2000 mg supplied by 100 g, respectively) (Regulation EU 1169/2011). Minerals are one of the classes of
essential nutrients in the human diet. Deficiency or excess of certain
essential nutrients are a concern for human health. As suggested by
the present study, the cooking method may strongly influence mineral
content of meat and, as a consequence, affect their intake by meat
consumers.
4. Conclusions
The data indicate that amino acid contents of meat were more affected by cooking methods than amino acid composition. The increase in
amino acid contents in cooked veal is a consequence of water loss
during the heating process. In contrast, only amino acid composition
was influenced by the different cooking methods. Through cooking, it
was demonstrated that modifications were dependent on the heating
method and on the time/temperature evolution. The major amino
acids found in raw and cooked veal were glutamic acid, leucine and
aspartic acid. Moreover, glutamic acid, leucine, methionine, serine, threonine and valine were the amino acids mostly affected by heating.
Among the cooking methods, grilling seems to be the treatment that
changed the most amino acid composition. The percentage retention
of individual amino acids was all above 100%, although with a value
particularly high for leucine after grilling.
Furthermore, the results indicate that cooking conditions also induce
changes in mineral composition, affecting the bioavailability and
content of these micronutrients in meat. Potassium was the mineral
most affected by cooking. No significant differences were observed for
iron and zinc retentions among the cooking methods, while the retention of magnesium and potassium was deeply affected, mainly after
boiling. It is suggested that heating processes involving water allow
for a low retention of the mineral content in cooked meats. However,
the magnitude of mineral loss is dependent on the cooking medium
and on the utilization of drip following cooking.
Overall our data indicate how the different cooking methods affect
the chemical composition and nutritional value of meat. This information may help consumers to choose the best procedure to cook meat
in order to preserve its nutritional quality. This information is of particular relevance for added value meats, such as PDO meats.
Conflict of interest
There is no conflict of interest.
Acknowledgments
Sampling assistance (CAPOLIB — Cooperativa Agrícola de Boticas,
CRL) and FCT doctorate fellowship (SFRH/BD/2007/35976) to Anabela
F. Lopes are acknowledged.
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