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Meat Science 99 (2015) 38–43 Contents lists available at ScienceDirect 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. 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