Influence of HPP conditions on selected lamb quality attributes and their stability during chilled storage

Innovative Food Science and Emerging Technologies 19 (2013) 66–72

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Influence of HPP conditions on selected lamb quality attributes and their stability during chilled storage Ruth A. McArdle a, Begonya Marcos a, 1, Anne M. Mullen a, Joseph P. Kerry b,⁎ a b

Teagasc Food Research Centre, Ashtown, Dublin 15, Ireland Food Packaging Group, School of Food and Nutritional Sciences, University College Cork, Cork, Ireland

a r t i c l e

i n f o

Article history: Received 16 August 2011 Accepted 8 April 2013 Editor Proof Receive Date 15 May 2013 Keywords: High pressure processing Minimal processing Lamb Meat quality

a b s t r a c t The aim of this research was to determine the effects of combined pressure and temperature treatments on ovine quality after processing and during storage. Lamb M. pectoralis profundus samples were pressurised at 200, 400 and 600 MPa at temperatures 20 °C, 40 °C and 60 °C. Both of the pressure and temperature regimes applied had significant effects (p b 0.001) on texture, pH, colour and lipid oxidation. Pressurisation at 200 MPa had a lower (p b 0.001) impact on colour and pH parameters compared to higher pressurisation levels. High pressure processing (HPP) at higher temperatures (60 °C) resulted in lower Warner Bratzler shear force (WBSF) values compared to processing at 20 and 40 °C. Thiobarbituric acid reactive substances (TBARS) values during storage showed an increase of TBARS values with time of storage in all samples studied. Samples pressurised at 400 & 600 MPa at 60 °C resulted in the highest TBARS values at each time analysed. Industrial Relevance: The growing demand by consumers for more natural, minimally processed convenient food products that are safe, has stimulated food industry interest in high pressure processing (HPP). HPP offers a commercially viable alternative to heat and, used in combination with temperature, also appears to be a promising approach for producing shelf life-stable foods (Balasubramaniam & Farkas, 2008). This has stimulated renewed interest in HPP as an alternative to conventional heat processing. The objective of the study was to examine the impact of pressure–temperature processing on ovine quality parameters after processing and over an extended shelf life. A low value lamb muscle M. pectoralis profundus (brisket) was used to investigate the possibility of adding value to and increasing processing opportunities for this muscle type. © 2013 Elsevier Ltd. All rights reserved.

1. Introduction There has been a growing demand among consumers for ready to eat meat products, which are microbiologically safe and possess superior sensory attributes and nutritional quality, with an accompanying shelf-life extension (Mandava, Dilber, & Fernandez, 1995). This has stimulated renewed interest in technologies that provide an alternative to conventional heat processing. One such technology is high pressure processing (HPP) which improves the microbiological quality of food, by inactivating microorganisms with minimal changes to taste and nutrient content (Balasubramaniam & Farkas, 2008). It has been reported that pressurisation of beef can alter texture (Bouton, Ford, Harris, Macfarlane, & O'Shea, 1977; Jung, Ghoul, & de Lamballerie-Anton, 2000) colour (Carlez, Veciana-Nogues, & Cheftel, 1995) and lipid oxidation (Cheah & Ledward, 1996). Lipid oxidation is one of the most important parameters that influence the quality and

⁎ Corresponding author. E-mail address: [email protected] (J.P. Kerry). 1 Author Begonya Marcos is presently with IRTA, Food Technology, Finca Camps i Armet, E-17121 Monells, Girona, Spain. 1466-8564/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ifset.2013.04.003

acceptability of meat (Gray, Gomaa, & Buckley, 1996). High pressure can accelerate lipid oxidation in meat products (Cheah & Ledward, 1996). The effect of high pressure on meat system constituents depends on numerous factors including pH, ionic strength, and presence of other compounds. Temperature is one of the most important factors, as the effect HPP on meat constituents depends on the temperature at which pressurisation occurs, and the effect of temperature depends on the pressure (Jiménez Colmenero, 2002). Pressurisation is also accompanied by a moderate temperature increase known as adiabatic heating. This temperature increase (heat of compression) depends on the final pressure, the temperature at which pressurisation is taking place and the composition of the food material. Food materials have specific heat compression values, for example water increases at 3 °C/100 MPa and fats and oil increase at approximately 8 °C/100 MPa (Balasubramaniam & Farkas, 2008). While researchers have assessed the impact of HPP on the quality of meat, such studies have tended to focus on beef and chicken meat products (Carlez et al., 1995; Cheah & Ledward, 1996; Fernandez, Perez -Alvarez, & Fernandez - Lopez, 1997; Jung et al., 2000; Ma, Ledward, Zamri, Frazier, & Zhou, 2007; Macfarlane, McKenzie, & Turner, 1984; Marcos, Aymerich, & Garriga, 2005; Shigehisa, Ohmori, Saito, Taji, & Hayashi, 1991) with limited information available on

R.A. McArdle et al. / Innovative Food Science and Emerging Technologies 19 (2013) 66–72

the effect of high pressure processing on lamb products. The objective of the study was to examine the impact of pressure–temperature processing on ovine quality parameters after processing and over an extended shelf life. A low value lamb muscle M. pectoralis profundus (brisket) was used to investigate the possibility of adding value to and increasing processing opportunities for this muscle type. 2. Materials and methods

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Instron universal testing machine model 5543 (Instron Ltd., High Wycombe, UK) and Instron Series IX Automated Material Testing System software for windows (Instron Corporation, High Wycombe, Bucks, HP 123SY) were used. Four cores (1.25 cm in diameter) were taken parallel to longitudinal orientation of the muscle fibres for each sample. Cores are sheared at a crosshead speed of 200–250 mm/min. Five replicates of each treatment were analysed.

2.3. pH of lamb samples

2.1. Sample preparation and high pressure treatment of M. pectoralis profundus Lamb M. pectoralis profundus muscles were obtained from a local distribution plant. Briefly, carcasses from 25 lambs (b 12 months) were slaughtered and hung within 1 h of slaughter at 0 °C for 2 days. Muscles were excised, individually vacuum packed in polyamide polyethylene bags a vacuum packaging machine, J-V006W (Jaw Feng Machinery Ltd., Chia Yi County, Taiwan). Samples were treated for 20 min at 200, 400 and 600 MPa, and temperatures of 20, 40 and 60 °C in a high pressure vessel (100 mm internal diameter, 254 mm internal height, Pressure Engineered System, Belgium) filled with a mixture of water and rust inhibitor (Dowcal N, 60% v/v in distilled water). Samples were stored at 2 °C and were transferred to the pressurisation vessel immediately before processing. Temperature in the sample chamber was monitored during processing. Compressive heating during pressurisation led to a temperature variation of ±2 °C (Table 1). Non treated (NT) samples were kept as a control. Sampling for all quality measurements was done the day after treatment (day 1). Additional samples were also taken for colour, TBARS, FAA and microbial analysis (after 15, 30 days of storage).

The pH was measured after 1 day of storage (at 4 °C) following HPP using a glass probe pH electrode, EC-2010-11 (Refex sensors Ltd., Westport, Ireland) by direct insertion into the meat. An average of three measurements was made for each sample. Five replicates of each treatment were analysed.

2.4. Quality measurements during shelf life 2.4.1. Colour analysis of lamb Samples were exposed to air for 10 min prior to analysis. Colour measurements were taken from the cut surface following sampling according to the procedure of Stewart, Zipser, and Watts (1965) using the CIE L*a*b* system with a dual beam xenon flash spectrophotometer (Ultra Scan XE, Hunter lab). CIE L* (lightness), a* (redness) and b* (yellowness) values were recorded. The UltraScan XE was standardised before analysis using a black and white tile. The illuminant (D65, 10°) consisted of an 8° viewing angle and a 10 mm port size. An average of three measurements was taken for each sample. Five replicates of each treatment were analysed after storage at 4 °C for 1, 15 and 30 days.

2.2. Quality measurements after HPP 2.5. Measurement of lipid oxidation of lamb 2.2.1. Cook loss determination and Warner Bratzler Shear Force (WBSF) of lamb samples One day after treatment, muscles were cut across the fibre into steaks of 2.5 cm in thickness and cooked in plastic bags in a water bath set at 72 °C, until an internal temperature of 70 °C was reached. A temperature probe, HI 9061 (Hanna Foodcare Digital Thermometer, Bedfordshire, England) placed in the geometric centre of a steak was used to monitor temperature. Samples were allowed to cool and excess moisture was removed with tissue paper. The weight of each sample was recorded before and after cooking. Cook loss was expressed as the percentage of the weight difference. Five replicates of each treatment were analysed. Following cook loss determination samples were stored at 5 °C overnight, after which WBSF analysis was carried out according to the procedure of AMSA (1995). An

Table 1 Compressive heat temperatures of pressurised lamb M. pectoralis profundus. Treatment 20 20 20 40 40 40 60 60 60

°C, °C, °C, °C, °C, °C, °C, °C, °C,

200 400 600 200 400 600 200 400 600

Compressive heat temperature ( °C) MPa MPa MPa MPa MPa MPa MPa MPa MPa

23.7 25.8 27.9 44.8 47.7 49.1 61.3 62.8 69.4

± ± ± ± ± ± ± ± ±

2 2 2 2 2 2 2 2 2

°C °C °C °C °C °C °C °C °C

Values are mean values of twenty measurements. One measurement was taken every minute during pressurisation.

Thiobarbituric acid reactive substances (TBARS) values were measured as an index of lipid oxidation according to the method of Siu and Draper (1978). The TBARS number is expressed as mg of malondialdehyde (MDA) per kilogram of sample. Two independent extracts from each sample was carried out. Five replicates of each treatment were analysed after storage at 4 °C for days 1, 15 and 30.

2.6. Fatty acid analysis Total lipids were extracted using the method of Folch, Lees, and Stanley (1957). Fatty acid methyl esters (FAME) were prepared according to the method of Slover and Lanza (1979). The FAME were analysed by gas chromatography (Varian Star CX3400 GC with a flame ionisation detector, Varian Ltd., Walton-on-Thames, UK) and separated using a FAME column (100 m × 0.25 mm i.d., 0.2 μm film thickness, Chrompack, London). The injector and detector ports were set at 270 °C and 300 °C, respectively. The oven temperature program was initially set at 40 °C for the first 2 min, and then employed a variable temperature ramp up to 220 °C where it remained for 3 min followed by an increase up to 240 °C, where it remained for 10 min. The carrier gas was hydrogen and the flow rate of 1.6 ml/min was measured at the initial temperature. Fatty acid methyl esters were identified by comparison of retention times with standards (Sigma Chemical Co. Ltd., Poole, UK). Fatty acids were quantified using tricosanoic acid methyl ester (C23:0), added prior to saponification, as an internal standard. Column response and linearity were checked using a mixture of fatty acids (C16:0, C18:0, C18:1n9, C18:2n6, relative to internal standard C23:0, Sigma Chemical Co. Ltd., Poole, UK). Five replicates of each treatment were analysed after storage at 4 °C for days 1, 15 and 30.

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2.7. Microbiological analysis Meat samples (10 g) were added to 90 ml of maximum recovery diluent (Oxoid, Basingstoke, England) and homogenised. After appropriate dilutions total viable counts (TVC) were enumerated by pour plating on plate count agar (Oxoid) and incubated at 30 °C for 72 h. Lactic acid bacteria (LAB) were enumerated by plating on MRS agar (Oxoid) and incubated at 37 °C for 24 h; Enterobacteriaceae were enumerated by plating on Violet Red Bile Glucose agar (Merck) and incubated at 30 °C for 24 h. The presence of Listeria, Salmonella and Campylobacter were investigated according to ISO 11290–1:1996, ISO 6579:2002 and ISO 10272–1:2006, respectively. All counts were expressed as log colony forming units per gram of meat (Log 10 CFU/g meat). 2.8. Statistical analysis Data was analysed using the general linear model (GLM) procedure from the statistical analysis system (SAS) package (SAS 9.1 version, SAS Institute Inc., Cary, NC, USA) with animal as a random effect. Two different models were applied. The first model included treatment (NT, 200 MPa–20 °C, 200 MPa–40 °C, 200 MPa–60 °C, 400 MPa–20 °C, 400 MPa–40 °C, 400 MPa–60 °C, 600 MPa–20 °C, 600 MPa–40 °C, 600 MPa–60 °C) as a fixed effect, and was used to assess the effect of processing on meat quality parameters (model 1). The second model only considered pressurised samples (i.e. not the control), included pressure, temperature, pressure × temperature interaction as fixed effects, and was used to compare the effect of the pressurisation conditions applied on meat quality traits (model 2). Non-significant interactions between temperature and pressure were excluded from the second model, and the main effects of pressure and temperature levels on meat quality were assessed. Differences were assessed using the Tukey test. The level of significance was set at p b 0.05. 2.9. PCA Relationship between physicochemical and sensory variables was evaluated using Pearson's correlation coefficient. Furthermore, principal component analysis (PCA) was performed, to describe the relationships between variables and biotypes, by XI STAT (2009 version). 3. Results and discussion 3.1. Effects of pressure and temperature on Warner Bratzler Shear Force (WBSF) values As previously described two models were used in the analysis of the data. Using model 1 no significant differences (p > 0.05) in WBSF values were observed between the NT and the pressurised lamb samples with the exception of samples treated at 200 MPa–60 °C, which had lower WBSF values (Table 2). This suggests that the level of pressure and temperature appeared to have a tenderising effect on the meat sample. A study carried out by Bouton et al. (1977) shoed pressurisation at 150 MPa (1 h) at low temperatures (b 30 °C) had no impact on tenderness. However increasing the temperature to 55–60 °C resulted in more tender beef (Bouton et al., 1977). Ma and Ledward (2004) also reported a large decrease in hardness in beef M longissimus dorsi treated at 200 MPa at 60 °C when compared to samples treated at the same pressure at 20 °C. This was attributed to increased enzyme activity in meat proteins due to pressurisation at 50–60 °C leading to the breakdown of myofibrillar proteins. Among pressurised samples, no interaction (p > 0.05) between pressure and temperature was found for WBSF data, indicating that both parameters had an independent effect on texture (model 2). This independent effect of both pressure and temperature was also found in pressure–temperature treated beef samples (McArdle, Marcos,

Table 2 Quality measurements of non-treated, pressurised lamb M. pectoralis profundus. Treatment

WBSF (N)

pH

Cook loss %

Non-treated 20 °C, 200 MPa 20 °C, 400 MPa 20 °C, 600 MPa 40 °C, 200 MPa 40 °C, 400 MPa 40 °C, 600 MPa 60 °C, 200 MPa 60 °C, 400 MPa 60 °C, 600 MPa SE p

37.63ab 34.54abc 35.37ab 41.10a 33.46abc 31.76bc 40.55ab 25.78c 31.85bc 34.17abc 1.95 b0.001

5.69c 5.71c 5.88ab 5.91a 5.78bc 5.94a 5.94a 5.93a 6.00a 6.03a 0.03 b0.001

29.56bc 39.74a 30.34bc 32.99abc 26.55c 32.89abc 37.88ab 31.77abc 33.82abc 36.79ab 1.82 b0.001

WBSF = Warner Bratzler shear force. Results are mean values of five replicates. SE: standard error. Different letters within a column indicate differences among values.

Kerry, & Mullen, 2010). Samples treated at the highest-pressure level of 600 MPa had higher (p b 0.001) WBSF values when compared to samples treated at 200 and 400 MPa, independent of the pressurisation temperature (Table 3). No significant difference was observed between samples pressurised at 200 and 400 MPa. McArdle, Marcos, Kerry, and Mullen (2011) also found pressurisation of beef (M pectoralis profundus) at 600 MPa resulted in higher WBSF (p b 0.001) values compared to samples treated at 400 MPa, independent of the pressurisation temperature. Ma and Ledward (2004) observed higher hardness in beef M longissimus dorsi pressurised at 600 MPa than at 400 MPa for 20 min at 40 and 60 °C. In another study, Zamri, Ledward, and Frazier (2006) reported increased hardness in chicken M. pectoralis fundus treated at 600 MPa compared to 400 MPa over a temperature range of 20–50 °C. The increased toughness with pressure has been attributed to an increasing incidence of sarcomeres, in which thick filaments have been compressed onto the Z-line, thus removing the I-band as a zone of weakness (Macfarlane, McKenzie, & Turner, 1980). Samples pressurised at 60 °C resulted in lower (p b 0.001) WBSF values when compared to samples treated at 20 and 40 °C, independently of the level of pressure applied (Table 3). This is in agreement with previous work carried out on HPP treated beef, which reported a decrease in WBSF values with increasing temperature in pressurised beef M. pectoralis profundus treated in a range of 200–600 MPa at 35, 45 & 55 °C (McArdle et al., 2011). Jimenez-Colmenero, Cofrades, Carballo, Fernandez, and Fernandez-Martin (1998) found that heating pork batters under pressure (70 °C at 200/400 MPa) resulted in accelerated enzymatic breakdown of a higher molecular weight molecule known to be myosin.

Table 3 Effect of pressurisation conditions (temperature and pressure levels) on the quality parameters of pressurised lamb M. pectoralis profundus. Treatment

WBSF (N)

Temperature 20 °C 36.99a 40 °C 35.25a 60 °C 30.60b SE 1.12 p b0.001 Pressure 200 MPa 31.26b 400 MPa 32.99b 600 MPa 38.60a SE 1.12 p b0.001

pH

L*

a*

b*

Cook loss %

5.83b 49.22b 6.04 12.74b 34.35 5.88b 52.95a 5.19 14.14a 32.43 5.99a 54.95a 4.97 14.82a 34.12 0.02 0.77 0.37 0.27 1.18 b0.001 b0.001 NS b0.001 NS 5.81b 42.84b 6.63a 11.12b 32.68 5.94a 57.10a 4.68b 15.02a 32.34 5.96 a 57.19a 4.89b 15.55a 35.88 0.02 0.77 0.37 0.27 1.18 b0.001 b0.001 b0.001 b0.001 b0.04

NS: non-significant. Results are mean values of fifteen replicates. SE: standard error. Different letters within a column indicate differences among values.

R.A. McArdle et al. / Innovative Food Science and Emerging Technologies 19 (2013) 66–72

3.2. Effects of pressure and temperature on cook loss The ability of meat to retain water is an important quality attribute both commercially and also in terms of consumer acceptance. Using model 1 no significant effect was observed between NT sample and the other treatments (Table 2) with the exception of samples treated at 200 MPa at 20 °C. This could be due to a combination of the start temperature and the relatively low temperature increase during pressurisation (Table 1). An interaction (p b 0.05) between pressure and temperature was found (model 2), with a tendency towards higher cook losses as the pressure increased from 200/400 MPa to 600 MPa (Table 3). McArdle et al. (2010) also found higher cook losses in beef M pectoralis profundus as the pressure increased from 200 to 300 MPa. Jung et al. (2000) found that pressurised beef (520 MPa) samples at 10 °C showed higher cook loss when compared to the NT samples. The authors attributed the increase in cook loss to shrinkage as a decrease in sarcomere lengths was also reported. 3.3. Effect of pressure and temperature on pH values Pressurisation of samples at 200 MPa at 20 and 40 °C had no significant effect on pH values, while pressurising at the higher pressure and temperature levels resulted in an increase (p b 0.001) in pH (model 1; Table 2). Similarly, McArdle et al. (2010) observed no increase of pH values of beef treated at 200 MPa at 20 and 40 °C, while pressure treatments at higher pressures induced an increase of pH values of beef. Similar trends were also reported in raw sausage batter pressurised above 200 MPa (Mandava et al., 1995) where the authors attributed the pH increase to protein denaturation. The increase of muscle pH induced by HPP has also been attributed to the redistribution of ions that is facilitated by the increased ionisation that occurs at elevated pressures (Macfarlane et al., 1980). They also suggested that an increase in pH after treatment might be due to the release of imadazolium groups by histidine by the unfolding of actomyosin during pressurisation (Macfarlane et al., 1980). No interaction (p > 0.05) between pressure and temperature was observed for pH values (model 2). Pressurising at 400 and 600 MPa resulted in the highest (p b 0.001) pH values when compared to samples pressurised at 200 MPa, independent of the pressurisation temperature (Table 3). These results confirm previous findings in bovine M. pectoralis profundus where pressurisation at 400 MPa resulted in higher pH values when compared to samples treated at 200 MPa (McArdle et al., 2011). In bovine M. semitendinosus pressurised in the range of 100–500 MPa at 15 °C, the pH increased as the level of pressure increased (Kim, Lee, Lee, Kim, & Yamamoto, 2007). However, at pressures of 300 MPa or more, no further pH increases were reported. The pH of samples pressurised at 60 °C was higher (p b 0.001) when compared to samples pressurised at 20 and 40 °C, with no significant difference observed between samples treated at 20 and 40 °C (Table 3). Ma and Ledward (2004) reported an increase in the pH of beef M longissimus dorsi as the heat increased from 40 to 60 °C. It has been suggested that the increase in pH after heating is caused by a decrease in available acidic groups as a result of conformational changes associated with protein denaturation (Hamm & Deatherage, 1960). Ma and Ledward (2004) hypothesised that although the structures established by high pressure and heating may be different, the mode of unfolding are similar. Protein unfolding is thought to be much less intense in pressurised samples in comparison to cooked samples (Messens, Van Camp, & Huyghebaert, 1997). This would explain the higher increase in pH values observed in heat treated samples compared to HPP samples. 3.4. Effects of pressure and temperature on colour measurements No significant difference in L*a*b* values were observed between NT and samples pressurised at 200 MPa at 20 °C (Table 4). Samples

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processed at the higher pressure/temperature levels had higher (p b 0.001) L* and b* values (Table 4) manifesting as a ‘whitening’ effect. Jung, Ghoul, and de Lamballerie-Anton (2003) reported an increase in L* values in beef M. biceps femoris samples after HPP (350–600 MPa at 10 °C). Other authors have suggested that this “whitening/brightening” effect of pressure could be attributed to globin denaturation, heme displacement or release, and ferrous atom oxidation (Cheftel & Culioli, 1997). No interaction between pressure and temperature was observed for L*, a* and b* values. Samples pressurised at 400 and 600 MPa induced an increase (p b 0.001) of L* and b* and a decrease (p b 0.001) of a* values compared to samples treated at 200 MPa, independently of the pressurisation temperature (Table 3). Similarly, Kim et al. (2007) reported an increase in L* and b* values in bovine M. semitendinosus muscle pressurised above 200 MPa. Pressurisation at the higher temperatures of 40 and 60 °C induced an increase in L* and b* values when compared to samples pressurised at 20 °C (Table 3). Lopez-Caballero, Carballo, and Jimenez-Colmenero (2002) found that pressurised (300 MPa) pork at 35 and 50 °C had higher L* values when compared to samples pressurised at 20 °C. The increase of temperature induces further denaturation of globin and causes ferrous iron to become oxidised to its ferric form which results in the reported discolouration of meat (Bou et al., 2008). Monitoring of lamb samples during 30 days of refrigerated storage showed that throughout storage lower L* values were observed for NT and the 200 MPa–20 °C were lower (p b 0.001) compared to other treatments. Lamb redness (a*) was lowest (p b 0.001) in samples pressurised with 400 MPa at 40 °C and 400/600 MPa at 60 °C all times during storage. The observed decrease of a* values due to HPP has been attributed to reduced myoglobin content and metmyoglobin being formed at the expense of oxymyoglobin (Carlez et al., 1995). Samples pressurised at the higher pressure levels (400 and 600 MPa) had consistently higher b* values throughout chilled storage, while no significant difference was found between samples treated at 200 MPa (at 20, 40 and 60 °C) and the non treated control at each time point studied (Table 4). 3.5. Effects of pressure and temperature on TBARS measurements Lipid oxidation is one of the primary causes of quality deterioration in foods and especially in meat products (Morrissey, Sheehy, Galvin, Kerry, & Buckley, 1998). Although the preservative effects of HPP on meat are well known, at sufficiently high pressure meat becomes more susceptible to lipid oxidation (Angsupanich & Ledward, 1998). Increased lipid oxidation after HPP, may be due to conformational changes of hemoproteins, which result in greater exposure of the catalytic heme group to unsaturated fatty acids (Bou et al., 2008). Interaction between pressure and temperature was significant, so differences on TBARS values of the interactions were analysed (model 1). As expected NT samples showed the lowest TBARS values (Table 4). After HPP no significant difference was observed between samples pressurised at 200 MPa (20 °C) and the NT samples. At 20 °C HPP at 400 MPa induced a smaller increase of TBARS values than processing at 600 MPa (Table 4). Similarly, Cheah and Ledward (1996) also found that pressurisation of minced pork at 20 °C resulted in an increase of TBARS values as the pressure increased from 400 to 600 MPa. Pressurisation at both 400 and 600 MPa at 60 °C showed the highest increase in TBARS values, followed by pressurisation (400 and 600 MPa) at 40 °C. Pressure and temperature had a synergistic effect on lipid oxidation. It is also interesting to note that as the temperature increased from 20 to 60 °C an increase in TBARS values was found at every pressure level used. These results suggest the importance of temperature control during HPP at lower pressures. TBARS values during storage increased with time of storage in all samples studied (Table 4). At each time point analysed, NT samples together with samples treated at 200 MPa and 20 °C, consistently had

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Table 4 Quality measurements of non-treated, pressurised lamb M. pectoralis profundus. Treatment

L*

a*

1 Non-treated 20 °C, 200 MPa 20 °C, 400 MPa 20 °C, 600 MPa 40 °C, 200 MPa 40 °C, 400 MPa 40 °C, 600 MPa 60 °C, 200 MPa 60 °C, 400 MPa 60 °C, 600 MPa SE p

15 f

34.9 40.2ef 52.8bc 54.7ab 41.5de 58.8ab 58.6ab 46.9cd 59.7a 58.3ab 1.95 b0.001

30 d

35.5 40.9cd 52.4b 54.2ab 40.9cd 59.6a 59.1a 45.4c 59.1a 57.1ab 1.25 b0.001

b*

1 f

34.7 39.1e 52.9bc 55.1ab 41.8de 59.2ab 58.5ab 47.4cd 60.3a 57.6ab 1.35 b0.001

15 a

7.4 6.2abc 6.4abc 5.5abc 6.8abc 3.9c 4.9abc 6.9ab 3.8c 4.3bc 0.63 b0.001

30 a

6.9 5.4ab 5.1bab 3.7bc 5.4ab 3.6bc 3.6bc 5.2ab 3.3c 4.5bc 0.45 b0.001

TBARS mg MDA/kg meat

1 a

6.4 4.6ab 3.9ab 2.2bc 4.1ab 3.3bc 3.9bc 4.4ab 3.5c 4.1bc 0.47 b0.001

15 e

10.0 9.6e 14.1bc 14.5ab 11.4de 15.3ab 15.7ab 13.3cd 15.7ab 16.4a 0.47 b0.001

30 e

9.6 9.8e 15.9b 15.9b 10.6de 15.8bcd 15.3bcd 12.6cd 15.8bc 17.6a 0.35 b0.001

1 c

11.2 10.2c 15.3ab 15.2ab 11.1c 15.2ab 15.6ab 11.3bc 15.6a 16.3a 0.44 b0.001

15 e

30 f

0.18 0.36e 0.59d 1.27c 0.72d 1.60b 1.73b 1.10c 2.01a 2.14a 0.04 b0.001

0.46 0.76e 1.33d 1.60c 0.77e 1.75c 1.72c 1.70c 2.18b 2.97a 0.042 b0.001

1.30fg 1.18g 1.43f 1.72e 1.65e 1.88d 2.33c 2.44c 2.59b 2.89a 0.03 b0.001

L* = lightness, a* = redness, b* = yellowness, TBARS = thiobarbituric acid reactive substances. NS: non-significant. Results are mean values of five replicates. SE: standard error. Different letters within a column indicate differences among values.

the lowest oxidation measurements with samples pressurised at 400 & 600 MPa at 60 °C, exhibiting the highest TBARS values at all time points analysed.

profiles were also monitored during 30 days of storage with no significant differences observed during the shelf life of meat (data not shown). 3.7. Effects of pressure and temperature on microbiological composition

3.6. Effects of pressure and temperature on fatty acid composition Fatty acid composition of meat is important for quality traits of meat such as nutritional value, flavour, and textural properties. It varies widely depending on species degree of trimming, nature of processing/cooking and on the preservation techniques employed (Gerber, Scheeder, & Wenk, 2009). The fatty acid composition of non treated lamb M. pectoralis profundus is summarised in Table 5. Similar to other livestock species reared for meat production, major fatty acids in muscle lipids were oleic (C18:1), palmitic (C16:0) and stearic (C18:0). The most abundant fatty acid was oleic acid (C18:1) and this is in good agreement with other findings (Park & Washington, 1993; Sweetie, Ramesh, & Arun, 2006). The polyunsaturated/saturated fatty acid (PUFA/SFA) ratios for lamb is typically 0.1 but it can be higher in some muscles (e.g. Wood et al., 2003). Factors that affect this ratio include animal breed, sex and nutrition (Cividini, Levart, & Zgur, 2008; Enser et al., 2000). The PUFA/SFA ratios of both NT and pressurised samples were in the range of 0.21– 0.54%. The PUFA/SFA ratio is used to assess the nutritional quality of the lipid fraction in foods. Nutritional guidelines have recommended a PUFA/SFA ratio to be above 0.4–0.5 (Wood et al., 2003). The PUFA/SFA ratios of pressurised samples were significantly higher when compared to non treated samples, with the exception of the milder treatments (20 °C at 200 and 400 MPa) (Table 6). Ono, Berry, and Paraczay (1985) found an increase in the PUFA/SFA ratio in cooked samples when compared to raw meat. They hypothesised that unsaturated fatty acid especially PUFAs are less affected by cooking as they are part of the membrane structure and that proportional change in fatty acid composition may be explained by the breakdown of SFAs. Pressurising with higher temperatures may breakdown SFAs in a similar way to cooking. The ratio of omega 3 to omega 6 PUFAs (n6:n3) ratio is also important, as it is a risk factor in cancers and coronary heart disease (Enser, Richardson, Wood, Gill, & Sheard, 2000). The recommendation is for a ratio of less than 4 (Wood et al., 2003).The n6:n3 ratio is particularly beneficial in ruminant meats, especially from animals that have consumed grass which contains of 18:3 (Wood et al., 2003). High pressure had no significant effect on n6:n3 ratios with the exception samples treated at 400 MPa at 40 °C (Table 6). Moreover, the n6:n3 ratios in all treated samples remained within recommended levels, with ratios of both NT and pressurised samples in the range of 1.03–2.12%. Fatty acid

The efficiency of high pressure processing for inactivating vegetative bacteria in food has been widely reported (Farkas & Hoover, 2000; Kalchayanand, Sikes, Dunne, & Ray, 1998; Marcos, Aymerich, Monfort, & Garriga, 2008; Patterson & Kilpatrick, 1998). After 15 days of refrigerated storage, NT and pressurised samples showed Enterobacteriacae and LAB counts to be under the detection limit. Lower levels of TVCs for samples pressurised at the higher pressure–temperature combinations Table 5 Fatty acid composition (% of total fatty acids) of non-treated lamb M. pectoralis profundus. Fatty acid

Non treated lamb (% of total fatty acids)

C14:0 C14:1 C15:0 C15:1 C16:0 C16:1 C17:0 C17:1 C18:0 C18:1n9t C18:1n9c C18:2n6c C18:3n6 C18:3n3 C20:0 C20:1n9 C20:2 C20:3n6 C20:4n6 C22:0 C22:1n9 C23:0 C22:2 C24:0 C24:1n9 C22:6n3 SFA MUFA PUFA P/S n6/n3

0.00 0.09 0.09 0.28 23.00 0.02 0.66 0.04 14.26 0.01 32.63 2.01 0.92 3.02 0.62 3.67 1.53 0.10 0.30 0.04 3.87 10.65 0.18 0.58 1.02 0.30 54.10 34.87 11.04 0.21 1.10

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.05 0.05 0.07 0.11 0.78 0.11 0.91 0.04 1.08 0.01 1.66 0.14 0.10 0.22 0.14 0.34 0.16 0.16 0.18 0.29 0.62 0.38 0.05 0.81 0.39 0.09 1.37 1.54 0.52 0.02 1.03

Results are mean values of five replicates ± standard error.

R.A. McArdle et al. / Innovative Food Science and Emerging Technologies 19 (2013) 66–72

71

Table 6 Fatty acid classes of non treated and pressurised lamb M. pectoralis profundus after one day of chilled storage. Fatty acid

Treatment (% of total fatty acids) NT

20 °C 200 MPa

SFA 54.10a 50.92 a MUFA 34.87 38.44 PUFA 11.04d 10.64de 0.21e P/S 0.21e n6/n3 1.10b 1.48ab

20 °C 400 MPa

20 °C 600 MPa

40 °C 200 MPa

40 °C 400 MPa

40 °C 600 MPa

60 °C 200 MPa

60 °C 400 MPa

60 °C 600 MPa

49.81a 39.96 10.24e 0.21e 1.38b

42.92c 43.50 13.58cd 0.32d 1.15b

45.82bc 36.75 17.43bc 0.38cd 1.27b

45.70bc 38.39 15.92c 0.35cd 2.12a

39.53c 40.50 19.98ab 0.51ab 1.90ab

39.39c 39.49 21.13a 0.54a 1.34b

41.78c 40.34 17.89abc 0.43bc 1.52ab

45.30bc 36.47 18.23abc 0.40c 1.03b

SE

p

1.37 1.54 0.52 0.02 0.13

b0.001 NS b0.001 b0.001 b0.01

NS: non-significant. Results are mean values of fifteen replicates. SE: standard error. Different letters within a column indicate differences among values.

Principal component analysis (PCA) was conducted to analyse the correlations between the studied variables and to assess the different effects of the HP treatments applied on meat quality. The sample score and correlation loading plots for F1 vs F2 are shown in Fig. 1(a,b). The analysis shows that the first two components explained 82.77% of the total variation. It can be seen in Fig. 1(b) that function 1 (F1) is linked with L*a*b*, pH and TBARS values. Function 2 (F2) is related to WBSF and cook loss. The squared cosine values (Table 7) confirm that pH, L*, a*,b* and TBARS are strongly correlated to the F1 axis while WBSF is correlated to the F2 axis. Cook loss, though would be best viewed on a F2/F3 map. In relation to the F1 axis, samples pressurised at 200 MPa with the exception of samples treated at 200 MPa at the 60 °C are located on the left of the plot along with the non-treated sample. In contrast samples treated at the higher pressure and temperature levels are located on the right hand side of the figure i.e. to the right of F1 zero point. The correlation loading plot (Fig. 1(b)) illustrates quality parameters studied in the work. In this plot TBARS, pH and L* are clustered together while a* is on the opposite side of the F1 direction showing its negative correlation to L*, TBARS and pH. The location of the NT and mild HPP samples (200, 20 °C and 40 °C) in the sample score plot may be explained by their high a* values. In contrast the location of samples treated at the higher pressure and temperature levels may be explained by their high L*, TBARS and pH values. Samples treated at 200 MPa at 60 °C and 400 MPa at 20 °C are situated relatively close to the F1 zero point. Factors which influenced the location of these treatments were their colour and lipid oxidation values (both of which were intermediate). When the sample locations were analysed in relation to the F2 axis, samples treated with 600 MPa at both 40 and 20 °C are located at the top of the plot. It is also interesting to note that NT samples are also in the upper half of the plot while samples at 200 MPa at 60 °C are located in the lower half of the plot and therefore related with WBSF values. To summarise, when lamb samples were HPP at mild pressure levels (200 MPa) at 60 °C a tenderising effect was observed. At the same temperature, increased pressure levels resulted in increased TBARS, pH and colour changes and increased WBSF.

Acknowledgements This research was funded by the Irish Department of Agriculture, Fisheries and Food, through the Food Institutional Research Measure and by the Teagasc Walsh Fellowship programme.

a

2

Observations (axes F1 and F2: 82.77 %) 40oC, 600 MPa 20oC, 600MPa 20oC, 200MPa

1

F2 (17.46 %)

3.8. Principal component analysis on lamb quality attributes

values and most notably a decrease in WBSF values. PUFA/SFA ratios were significantly higher in pressurised samples compared to NT samples, with some treatments (200, 400, 600 MPa at 40 and 60 °C) having PUFA/SFA ratio within the recommended levels. These results show that HP technology could be applied as a pre-treatment for obtaining prepared “ready” meals.

Non treated 60oC, 600MPa

0 20oC, 400MPa 40oC, 400MPa 60o C, 400MPa

-1 40oC, 200MPa

-2 60oC, 200MPa

-3

-4

b

The importance of pressurisation temperature has been shown with higher temperatures resulting in increases in L*, lipid oxidation

-2

-1

0

1

2

3

Variables (axes F1 and F2: 82.77 %) 1

WB

0 .75 C o o k lo ss

0 .5 0 .2 5 0

b* L*

a*

TB A R S

-0 .2 5

pH

-0 .5 -0 .75 -1 -1

4. Conclusion

-3

F1 (65.31 %)

F2 (17.46 %)

(20 °C at 400/600 MPa, 40 °C at 400/600, 60 °C at 200/400/600 MPa) was found when compared to NT and mild HPP samples (20 and 40 °C at 200 MPa) after 15 days of storage (data not shown). Carlez, Rosec, Richard, and Cheftel (1994) found that pressurising at 400 and 450 MPa caused a 3 to 5 log cycle reduction in total flora count and induced a lag phase of 13–15 days during storage. Garriga, Grèbol, Aymerich, Monfort, and Hugas (2004) also showed that HPP at 600 MPa caused a reduction (>2 log cycles) in aerobic counts in marinated beef.

-0 .75 -0 .5

-0 .2 5

0

0 .2 5

0 .5

0 .75

1

F1 (65.31 %) Fig. 1. Principal component analysis (PCA) plots quality parameters of non-treated, pressurised lamb M. pectoralis profundus (a) PCA scores plots of different treatments (b) correlation loading plot for quality parameters analysed.

72

R.A. McArdle et al. / Innovative Food Science and Emerging Technologies 19 (2013) 66–72

Table 7 Squared cosines of the variables of quality parameters of non-treated, pressurised lamb M. pectoralis profundus. Variables

F1

F2

F3

F4

pH WB Cook loss L* a* b* TBARS

0.874 0.002 0.171 0.941 0.827 0.826 0.931

0.058 0.840 0.304 0.001 0.001 0.013 0.005

0.008 0.154 0.506 0.026 0.086 0.147 0.000

0.057 0.000 0.017 0.003 0.084 0.002 0.001

Values in bold correspond for each variable to the factor for which the squared cosine is the largest.

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