The effect of temperature in the range of −0.8 to 4°C on lamb meat color stability
Xin Li, Yan Zhang, Zheng Li, Meng Li, Yongfeng Liu, Dequan Zhang
PII: S0309-1740(16)30420-X
DOI: doi:10.1016/j.meatsci.2017.07.010
Reference: MESC 7316
To appear in: Meat Science Received date: 23 October 2016 Revised date: 7 June 2017 Accepted date: 13 July 2017
Please cite this article as: Xin Li, Yan Zhang, Zheng Li, Meng Li, Yongfeng Liu, Dequan Zhang , The effect of temperature in the range of −0.8 to 4°C on lamb meat color stability, Meat Science(2017), doi:10.1016/j.meatsci.2017.07.010
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The effect of temperature in the range of -0.8 to 4 °C on lamb meat colour stability
Xin Li1, Yan Zhang1, 2, Zheng Li1, Meng Li1, Yongfeng Liu2, Dequan Zhang1, *
1 Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences/Key Laboratory of Agro-Products Processing, Ministry of Agriculture, Beijing 100193, P. R. China
2 College of Food Engineering and Nutritional Science, Shaanxi Normal University, Shanxi Xian 710119, P. R. China
*Corresponding author: Dequan Zhang
Address: Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences, No. 1 Nongda South Road, Xi Beiwang, Haidian District, Beijing 100193, P. R. China
E-mail: [email protected] Tel.: +86-10-62818740
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Abstract
This study investigated effects of controlled freezing point storage (CFPS, -0.8 °C) on lamb color stability compared with storage at 4 °C (control). The muscle samples (n = 5) of longissimus thoracis et lumborum from both carcass sides were assigned
randomly to the two storage treatments and stored for 10 days. The a*, b*, R630/580 and Chroma values of samples stored in CFPS were significantly higher than that of samples in control from day 2 to day 10 (P < 0.05). Higher relative content of
oxymyoglobin but lower relative content of metmyoglobin were observed in samples stored in CFPS treatment than those in control over 10 days of storage (P < 0.05).
Meat samples stored in CFPS group had a significantly higher NADH content and metmyoglobin reductase activity than that in control group. In conclusion, ovine muscle stored in CFPS treatment for 10 days demonstrated better color stability in comparison with those in 4 °C storage.
Keywords: lamb; color; controlled freezing point storage; myoglobin; NADH;
metmyoglobin reductase activity 1. Introduction
Color of fresh meat is considered as the most important quality characteristic for consumers. It is recognized as an indicator of freshness especially in red meat and therefore influences consumer’s purchase decision. As one of the world’s largest producers of meat, the total production of raw meat in China is more than 78 Mt in which mutton accounts for 5% and is developing rapidly (Zhou, Zhang, & Xu, 2012).
It can be predicted that color stability of lamb will play an important role in the development of the meat industry in China. Meat color is influenced by many factors such as the concentration of pigments, the chemical states of myoglobin (Mb) and the physical characteristics of the meat. Therefore, many studies have been carried out to detect the biochemical and physical factors influencing color and color stability of meat (Suman, Hunt, Nair, & Rentfrow, 2014; Warner, R.D., Kearney, G., Hopkins, D.L., & Jacob, R.H., 2017).
Myoglobin is the key pigment in muscle responsible for meat color. When it is exposed to air, Mb combines with oxygen to form ferrous oxymyoglobin (OxyMb),
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which is bright red in color and presumed by consumers to indicate freshness. The extended contact of Mb with oxygen leads to the formation of the oxidized form, ferric metmyoglobin (MetMb), which is brown and unattractive (Jeong et al., 2009).
During storage, the accumulation rate of MetMb on the surface of meat is governed by many intrinsic factors (e.g. animal age, breed, sex, diet, pH, metabolic type of the muscle) and extrinsic factors (e.g. temperature, oxygen availability, type of lighting, growth of surface microbial, and type of packing) or by a combination of these factors (Jeong et al., 2009; Renerre, 1990). Metmyoglobin can convert to deoxymyoglobin (DeoxyMb) and/or OxyMb in the presence of NADH enzymatically or
non-enzymatically (Bekhit & Faustman, 2005). Reduced nicotinamide adenine dinucleuotide (NADH) plays an important role in MetMb reducing process. Although the general mechanism of the MetMb reduction system is well established, the effect of storage temperature on NADH, an ultimate reducing substrate for the
metmyoglobin reductase activity (MRA), has not been clearly established (Kim, Keeton, Smith, Berghman, & Savell, 2009).
Temperature is one important factor that impacts meat color and variation of temperature at rigor and storage result in different color stability (Hopkins, Lamb, Kerr, van de Ven, & Ponnampalam, 2013; Rosenvold and Wiklund, 2011; Young, Priolo, Simmons, & West, 1999). Controlled freezing-point storage (CFPS), also known as subzero or super chilling storage, provides an alternative and promising technique for preservation of fruit, vegetable and meat products without resorting to freezing. It is common to store meat at CFPS condition in countries that export meat overseas during the shipping period. However, the effect of CFPS on meat quality during display is not well known. Therefore, it would help to detect how meat quality influenced by CFPS treatment during display and it might improve meat quality and shelf life of raw meat products. The CFPS provides a storage condition that leads to substantial retardation of biochemical and microbial activity of muscle tissue without physically damaging the muscle cells due to ice crystal formation compared with freezing (Zhu, Ma, Yang, Xiao, & Xiong, 2016). The CFPS is characterized by a fast chilling rate stemming from the high heat-exchange capacity and a small temperature
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variation range because of strict control in comparison with regular refrigerated storage at 4 °C (Ando, Nakamura, Harada, & Yamane, 2004). Due to a low turnover rate of product and other production factors, meat is often subjected to a long production chain. The CFPS condition offers great flexibility for meat retailers and processors to meet the requirement of this situation in comparison with refrigerated storage and freezing (Zhu et al., 2016).
In our early experiment about the effects of CFPS on muscle tenderization and
glycolysis, a more bright red color (increased a* value and relative content of OxyMb) was observed on samples stored at CFPS in comparison with samples in other
treatments (data not shown). However, knowledge about the effects of CFPS on meat color stability during a period of storage and possible mechanism is limited. The objective of this study was therefore to explore the effects of CFPS treatment on lamb color stability during storage for 10 days compared with normal refrigerated storage at 4 °C.
2. Materials and methods 2.1 Animals and sampling
Five sheep carcasses from Small- tail Han sheep and Fat-tail Han sheep crossbred were collected randomly from a local slaughterhouse. The animals were eight-month old (a common slaughter age for lambs in China) with the same gender, feeding strategies, consignment and pre-slaughter conditions. The animals were slaughtered on the same day following the standard commercial slaughtering procedures of the slaughter house without electrical stimulation. The muscle samples of longissimus thoracis et lumborum (LTL) from both sides of each carcass were obtained
immediately after slaughter and transported to the laboratory on ice within 2.5 h postmortem to make sure that samples between treatments have the same rate of temperature decline at post mortem.
The core temperature of one LTL muscle during the initial 85 min postmortem was measured by inserting a temperature probe into the muscle to detect the controlled freezing point of LTL muscle. The muscle was quickly chilled in freezer at -18 °C.
The controlled freezing point of ovine LTL muscle was determined as the subtle
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increased temperature below zero before further decreasing of the temperature.
The LTL muscles from both sides of the same carcass were allocated randomly into two treatments: control (4 °C) and CFPS (-0.8 °C). Each LTL muscle was divided equally into six pieces from anterior to posterior side and each piece was 5 cm in length. The samples were overwrapped by polyvinyl chloride film with oxygen transmission rate of 10600 cm3/(m2·24 h·atm), moved to control or CFPS treatment and stored for 10 days in darkness. One piece of meat from each animal in each treatment was collected randomly after 0, 2, 4, 6, 8 and 10 days of storage for meat color and pH measurement and then frozen quickly in liquid nitrogen and stored at -80 °C for chemical analysis. The temperatures of the storage treatments were
monitored by thermometer during the whole storage to confirm the storage treatments fulfill the temperature requirement of the experimental design.
2.2 pH
The pH values were measured using a portable pH probe (Testo 205 pH meter, Lenzkirch, Germany). The calibration of electrode was carried out before
measurement using standard buffer of pH 4 and pH 7 at the same temperature as the samples. Three measurements at different locations were recorded on each sample (n
= 5). The starting time point was measured from bleeding and the pH of day 0 storage was measured within 15 min after bleeding.
2.3 Color
The meat surface color was measured at four random locations on cross section of meat samples (n = 5) using a Minolta CM-600d spectrophotometer (Konica Minolta Sensing Inc., Osaka, Japan) with 8 mm diameter measuring aperture size, illuminant D65, 10° standard observer and CIE L*, a*, b* color score. The color was measured through oxygen permeable PVC film. Meat samples for day 0 storage were collected immediately after slaughter and the meat color was measured on the fresh-cut surface after 1.5 h blooming in air. The Chroma value was calculated as (a*2 + b*2)1/2 and the Hue angle was calculated as arctan (b*/a*). The reflectance values between 360 nm and 740 nm were recorded by the Minolta spectrophotometer with 10 nm intervals.
The surface color stability was estimated by ratio of reflectance at 630 nm and 580 nm
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(R630/580).
The myoglobin redox forms were calculated via selected wavelengths (AMSA, 2012).
Briefly, the reflectance values at the isobestic wavelengths 474 nm, 525 nm, 572 nm were integrated by the reflectance values at 470 and 480 nm, 520 and 530 nm, 570 and 580 nm. The reflex attenuance values (A) at 474, 525, 572 and 730 nm were calculated according to the formula A = log10 (1/R). The relative content of different redox forms of myoglobin were calculated as follows: MetMb (%) = [1.395 - (A572 - A730)/(A525 - A730)] ×100, DeoxyMb (%) = 2.375 × [1 - (A474 - A730)/(A525 - A730)] × 100, OxyMb (%) = 100 – DeoxyMb (%) – MetMb (%).
2.4 Metmyoglobin reductase activity
2.4.1 Preparation of equine metmyoglobin substrate
The method by Bekhit et al. (2003) was used with slight modifications. Equine myoglobin was dissolved in 2.0 mM phosphate buffer pH 7.0 and centrifuged at 10000 ×g, 25 °C for 10 min. The solution was naturally oxidized at 25 °C for 24-30 h.
The concentration was adjusted to 0.75 mM with 2.0 mM phosphate buffer pH 7.0 on the basis of spectrophotometric measurement at 525 nm (ɛ525 = 7700 l/mol·cm).
2.4.2 Metmyoglobin reductase extract from the tissue
Metmyoglobin reductase extracts were obtained according to the method described by Reddy and Carpenter (1991) with slight modifications. Briefly, 5 g frozen muscle and 30 ml cold 2.0 mM phosphate buffer (pH 7.0) was homogenized at 13,500 rpm for 30 s. The homogenate was then centrifuged at 35,000 g at 4 °C for 30 min (Himac CP 100 WX Preparation Ultracentrifuge, HITACHI, Japan). The supernatant was filtered using two layers of hospital gauze to remove fat. Oxyhemoproteins in the extract were oxidized with excess potassium ferricyanide (0.5%), dialyzed (using 8000-14000 MW cut-off membrane) against three 1 L changes of 2.0 mM phosphate buffer (pH 7.0) for 24 h and then centrifuged at 15,000 g for 20 min at 4 °C and the volume of the
supernatant adjusted to 30 ml with 2.0 mM phosphate buffer (pH 7.0).
2.4.3 Metmyoglobin reductase activity assay
Metmyoglobin reductase activity was determined according to the method by Reddy et al. (1991) with slight modifications. The assay mixture consisted of the following
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solutions: 5 mM disodium EDTA, 50 mM phosphate buffer (pH 7.0), potassium ferricyanide, water, MetMb, enzyme extract and NADH. The reaction was carried out at 30 °C and initiated with addition of NADH. Enzyme activity in muscle extracts was measured by the change in absorbance at 580 nm during the reaction time. The linear phase at the initial time was used for calculation. One unit of MRA was defined as the amount which would reduce 1 nmol of MetMb per min.
2.5 NADH content
The NADH content was determined using the method by Li et al. (2012) with slight modifications. The NADH in muscle tissue (1.5 g) was extracted using alkaline extraction. Subsequently, about 13.5 ml of triethanolamine-HCl-phosphate mixture was added to neutralize each sample to pH 7.8. The samples were centrifuged at 21, 000 ×g for 10 min at 4 °C (Himac CR 22 GII High-Speed Refrigerated Centrifuge, HITACHI, Japan) after flocculating the denatured protein at room temperature. The supernatant was filtered using two layers of hospital gauze to remove fat layer and get a clear supernatant fluid. The NADH content assay mixture consisted of 150 μl of 17.5 μg/ml dichlorophenolindophenol (DCPIP), 3 μl of 1 mg/ml phenazine
methosulfate (PMS), 6 μl ethanol, 30 μl of 0.1 M pH 7.4 sodium phosphate buffer, 6 μl muscle extract supernatant and 3 μl alcohol dehydrogenase. The change of
absorbance at 600 nm was measured (Spectra Max 190, Molecular Devices, American) for 20 min to determine the NADH content based on the reduction of DCPIP to its colorless form. The NADH content (nmol/g) in fresh muscle tissue was calculated using the equation obtained from the standard curve.
2.6 Statistical analysis
The results were expressed as mean ± standard deviation (SD). Statistical analysis was carried out using IBM SPSS Statistic 17.0 software (SPSS Inc., Chicago, IL, USA).
The model of Repeated Measures was used with storage time as Within-Subject
Factor and storage treatment as Between-Subject Factor. The method REML was used.
The Duncan's multiple range tests was used to estimate the levels of statistical significance (P < 0.05).
3. Results
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3.1 pH
The pH of samples stored in control and CFPS was affected by storage treatment, time and their interaction effects (P < 0.05, Fig. 1). The pH of samples stored under CFPS and control showed the same trend that decreased initially and then kept stable. The pH of samples stored in CFPS treatment was higher (P < 0.05) than that in control on day 4, 6 and 8, but no differences were observed on day 0, 2 and 10. The pH of
samples on day 0 was higher than on the other storage time within each treatment (P <
0.05).
3.2 Color
Meat surface color stability of LTL muscle samples stored in control and CFPS were presented in Table 1. The meat color parameters, including L*, a*, b*, R630/580, Chroma and Hue angle were affected by storage treatment, time and their interaction effects (P < 0.05).
The a*, b*, R630/580 and Chroma values of samples stored in CFPS were
significantly higher than that of samples in control from day 2 to day 10 (P < 0.05) indicating a more stable color of samples in CFPS group. The L* values for samples of CFPS group were lower than those stored in control group on day 2, 4 and 8. The Hue angle of samples in CFPS group was lower than those stored in control group on day 4, 6, 8 and 10. No difference on meat color was observed between samples stored in CFPS and control treatments on day 0.
There were significant (P < 0.05) increase in L*, a* and b* values after 2 days of storage compared to the initial values in both storage treatments. The L* and a* values of samples stored in CFPS were stable during 2-10 days of storage. The b* values of samples in CFPS group during day 4 to day 10 storage were lower than day 2 but higher than the initial values on day 0. The L* value of samples in control were significantly (P < 0.05) lower on day 6 and 10 than day 2 and 4. The a* and b* values of samples in control group were lower during day 6 to day 10 than day 2 and 4. For b* values of samples in control group, it was higher during day 6 to day 10 than day 0.
The Chroma, Hue angle and R630/580 values exhibited a similar trend between two treatments that they showed significant (P < 0.05) increases on day 2 except R630/580
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of samples in control group. The R630/580 and Chroma values of samples in CFPS were stable during day 2 to day 6 but decreased on day 8 and day 10 (P < 0.05). For Hue angle of samples in CFPS treatment, the results on day 4 to day 10 were lower than that on day 2 but higher than day 0. The R630/580 of meat under control
treatment decreased (P < 0.05) on day 4 and then kept stable throughout days 4 to day 10. The Chroma results of samples stored in control were higher on day 2 and 4 than day 0 and then decreased during the following storage time. The highest Hue angle for samples in control was observed on day 10 during storage.
3.3 Relative proportions of myoglobin redox forms
The relative proportions of myoglobin redox forms of samples stored in control and CFPS were affected by storage treatment, time and their interaction effects (P < 0.05, Fig. 2). Higher relative content of OxyMb but lower relative content of MetMb were observed in samples stored in CFPS treatment than those in control over 10 days of storage (P < 0.05). The relative contents of DeoxyMb were higher in samples in control than in CFPS treatment on day 6 and day 8 (P < 0.05). The relative contents of DeoxyMb, OxyMb and MetMb of meat under two different storage temperature had no difference (P > 0.05) on day 0.
The relative content of DeoxyMb in control decreased (P﹤0.05) on day 2 and then increased on day 6 (P﹤0.05), while it was stable for samples stored in CFPS
treatment during the storage. The relative contents of OxyMb in two groups increase during the first four days of storage and then decreased on day 6. The relative content of MetMb for meat under control treatment increased significantly from day 6 to day 10 and it decreased (P < 0.05) on day 4 and followed by increasing (P < 0.05) on day 6 to the same level as day 0 until the end of storage for samples in the CFPS
treatment.
3.4 Metmyoglobin reductase activity
The metmyoglobin reductase activity of samples stored in control and CFPS was affected by storage treatment, time and their interaction effects (P < 0.05, Fig. 3).
Meat samples in CFPS group had higher MRA than in control group on day 4, 8 and 10 of storage. Meat samples in the two groups exhibited a decreasing trend in MRA as
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extension of storage time. The MRA of samples in control treatment decreased on day 4 of storage whereas the decrease was detected on day 8 for samples in CFPS
treatment.
3.5 NADH content
The NADH content of samples stored in control and CFPS was affected by storage treatment, time and their interaction effects (P < 0.05, Fig. 4). Meat of samples stored in CFPS group had a significantly higher NADH content than that in control group throughout the storage period (P < 0.05, Fig. 4). The NADH contents of muscle in the two storage treatments decreased (P < 0.05) during the 10 days of storage. The NADH content of samples in CFPS kept decreasing throughout the whole storage time. For samples stored in control treatment, a stable NADH contents were observed during day 4 to 8.
4. Discussion
For all parameters measured in this study, no significant difference was observed on day 0 between samples at the CFPS and control treatments, which indicated that the differences obtained during the storage were due to the different storage treatment instead of samples.
Controlled freezing point storage preserves foods at non-freezing temperature-zone between the freezing point of water and that of an individual food material in order to prolong the storage life of fresh food and provide good quality retention (Guo, Ma, Sun, & Wang, 2008). Fennema, Powrie, and Marth (1973) reported that the initial freezing points (i.e. the temperature where ice starts to form in the product) of most foods are between -0.5 ºC and -2.8 ºC. The freezing point of ovine LTL muscle in this study was -2 ºC according to the measurement of muscle temperature decreasing line and the temperature of CFPS treatment was therefore set at -0.8 ºC. The variation of meat color during the 10 days storage could be mainly attributed to the difference of temperature under the two treatments (4 ºC v.s. -0.8 ºC) and the consequent influences on muscle metabolism.
In this study, the pH of samples at both storage treatments reach the ultimate values on day 2 postmortem without difference between each other. During storage, the pH
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of samples in CFPS treatment were higher than those in control treatment during day 4-8 which might be due to the generation of basic compounds, such as ammonia and trimethylamine resulting from autolytic and microbial reactions (Delbarre-Ladrat et al., 2006). Meat pH is one of the most important factors affecting fresh meat color (AMSA, 2012) and a high ultimate pH value is associated with redder color (Ylä-Ajos
& Puolanne, 2007). Moreover, the initial freezing point temperature of muscle is also influenced by pH (Farouk, Kemp, Cartwright, & North, 2013).
The meat surface color of samples stored in CFPS treatment was much better than those in control treatment as indicated by the color results and visual impression (pictures not shown) during storage. The a* values of samples stored at CFPS treatment was greater than those in control treatment, i.e. the meat stored in CFPS showed redder color than in control treatment. Temperature is the most important extrinsic factor influencing the storage life of fresh meat except for storage time (Jeyamkondan, Jayas, & Holley, 2000). Rosenvold et al. (2011) reported that color stability of lamb loins decreased significantly when the storage temperature was increased from -1.5 °C to 2 °C and even one week at 2 °C at the end of the storage period had a substantial negative impact on the retail color display life. The lowest temperature that can be maintained indefinitely without the muscle freezing is -1.5 °C and maximum storage life can be achieved when meat is held at this temperature.
The ratio of reflectance at 630 nm and 580 nm (R630/580) on meat surface was calculated to estimate the change in meat color due to the formation of MetMb, and therefore can be used as an indicator of surface color stability. A high ratio indicates fewer discoloration and thus greater color stability. The R630/580 is related to consumer’s perception of meat color that a threshold value of 3.3 is required to have meat samples accepted by consumers (Khliji, van de Ven, Lamb, Lanza, & Hopkins, 2010). The R630/580 ratios of samples in this study were lower than 3.0 and this might due to the small aperture size (8 mm) used in this study (Yancey & Kropf, 2008). The higher R630/580 ratios of samples stored at CFPS treatment in this study indicated better color stability than those in control treatment and its discoloration appeared later. Chroma value is an indication of saturation or vividness of color (color
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intensity) and Hue angle is considered as an indicator of discoloration (Kim et al.
2009). Color stable meat tended to have a lower Hue value than that of color unstable ones and it gives a more realistic perspective on meat browning than single color coordinates. In this study, it demonstrated that meat under CFPS had lower Hue values than those under control during day 4-10 indicating controlled freezing point storage inhibiting meat discoloration.
The relative contents of DeoxyMb, OxyMb and MetMb in meat depend on the oxygen availability, autoxidation rate of myoglobin and MetMb reducing capacity.
Transformation of myoglobin between different redox states is the key factor affecting meat color (Mancini & Hunt, 2005). The higher a* values obtained in samples stored in CFPS treatment was associated with the formation of OxyMb (Li et al., 2012). The formation of MetMb can be indicated by R630/580 which is called OxyMb/MetMb ratio as a proxy (Hopkins et al., 2013). The results in this study indicated that
controlled freezing point storage inhibited the accumulation of MetMb effectively and meat stored under controlled freezing point exhibited more stable color. Increased storage temperature has a large impact on retail color display life due to a more rapid rate of metmyoglobin formation at higher temperatures (Kim et al, 2013).
Metmyoglobin reductase activity in meat is complicated and under the influence of many factors. Reddy et al. (1991) found significant difference in MRA between beef muscles with different color stabilities. Madhavi & Carpenter (1993) reported that MRA was higher in beef longissimus dorsi compared to the less color stable psoas major. In this study, samples stored in CFPS treatment had higher MRA on day 4, 8 and 10 than those in control treatment. This result is in accordance with the better color stability obtained in the samples at CFPS treatment. There is one more factor that might relate to MRA is pH. In this study, the pH of samples stored in CFPS treatment was higher than those in control treatment during day 4-8 storage.
Metmyoglobin reducing activity increases with increasing pH (Bekhit & Faustman, 2005). The pH condition of CFPS in this study might be more proper for color stability.
The presence of NADH has been shown to be essential for reduction of MetMb in
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muscle through both enzymatic and non-enzymatic reduction pathways (Bekhit &
Faustman, 2005). Since the enzymatic reduction system is specific for NADH, the role of NADH as a coenzyme and electron carrier in the conversion of ferric myoglobin to its ferrous form is now generally accepted. Mikkelsen, Juncher, &
Skibsted (1999) reported that no MetMb reduction without NADH in porcine muscle, whereas they found inclined rate of MetMb reduction by increasing the amount of NADH content in their in vitro test. Kim et al. (2006) also reported increased MetMb reduction of equine MetMb with incremental content of NADH. For samples stored at CFPS treatment, the NADH content was higher than those in control treatment during day 2-10 storage.
It is still under discussion that whether MRA or NADH is the crucial factor
determining meat color. Theoretically, both of them make contributions on meat color stability and specifically they are two components of metmyoglobin reductase system in mitochondrial. NADH–cytochrome b5 reductase, suggested as the main reducing enzyme (Arihara, Itoh, & Konda, 1989; Bekhit, Geesink, Morton, & Bickerstaffe, 2001), is absolutely specific for NADH. In the MetMb reducing system, NADH acts as a coenzyme and electron carrier in the conversion of ferric myoglobin to its ferrous form (Renerre, 1990). Therefore, both MRA and NADH were measured in samples stored in CFPS and control treatments in this study. The results of meat color stability influenced by storage temperature in this study confirmed the findings of Rosenvold et al. (2011), besides, a further investigation on MRA and NADH contents were carried out in this study. The higher MRA and NADH contents of samples stored in CFPS treatment than those in control treatment throughout the 10 days storage can be a strong evidence to support the explanation of better color stability obtained in samples stored in CFPS treatment. Improvement of color stability is crucial for meat industry both of fresh meat and raw meat for processing. The CFPS therefore could be a possible solution of good meat color stability although technology on control of temperature is needed to improve.
5. Conclusions
The controlled freezing point storage has been applied on fruit, vegetable and aquatic
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products storage, however, published report on its application on fresh red meat storage is limited. In this study, ovine muscle stored in CFPS treatment for 10 days demonstrated better color stability in comparison with those in 4 °C storage.
Therefore, controlled freezing point storage could be used as an option storage method for color improvement of fresh red meat. The samples in this study were overwrapped by polyvinyl chloride film during storage and effects of different packaging conditions (e.g. MAP) could be investigated in next study as packaging could affect potential effects of storage procedure by interacting with storage treatments.
Acknowledgements
The authors thank the financial support from the “National Agricultural Science and Technology Innovation Program” and the “Special Fund for Agro-scientific Research in the Public Interest (201303083)” in China.
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Figure captions
Fig. 1. pH of lamb longissimus thoracis et lumborum (LTL) after different storage treatments and times (n = 5). CFPS: controlled freezing point storage, -0.8 °C; Control:
4 °C. *indicates significant difference between storage treatments of CFPS and control (P < 0.05). Different uppercase letters within CFPS group indicate significant
difference (P < 0.05) between storage times. Different lowercase letters within control group indicate significant difference (P < 0.05) between storage times. The results were expressed as mean ± standard deviation (SD).
Fig. 2. Relative pigment contents of lamb LTL after different storage treatments and times (n = 5). *indicates significant difference between storage treatments of CFPS and control (P < 0.05). Different uppercase letters within CFPS group indicate significant difference (P < 0.05) between storage times. Different lowercase letters within control group indicate significant difference (P < 0.05) between storage times.
The results were expressed as mean ± SD.
Fig. 3. Metmyoglobin reductase activity (MRA) of lamb LTL after different storage treatments and times (n = 5). *indicates significant difference between storage treatments of CFPS and control (P < 0.05). Different uppercase letters within CFPS group indicate significant difference (P < 0.05) between storage times. Different lowercase letters within control group indicate significant difference (P < 0.05) between storage times. The results were expressed as mean ± SD.
Fig. 4. NADH concentration of lamb LTL after different storage treatments and times (n = 5). *indicates significant difference between storage treatments of CFPS and control (P < 0.05). Different uppercase letters within CFPS group indicate significant difference (P < 0.05) between storage times. Different lowercase letters within control group indicate significant difference (P < 0.05) between storage times. The results were expressed as mean ± SD.
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Fig. 1
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Fig. 2
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Fig. 3
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Fig. 4
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Table 1. Meat color of lamb longissimus thoracis et lumborum (LTL) after different storage treatments and times (n = 5).
CFPS: controlled freezing point storage, -0.8 °C; Control: 4 °C. Means within a row lacking a common letter (a-d) differ at P < 0.05. Means of the same parameter within a column lacking a common letter (x, y) differ at P < 0.05.
Temperature treatment
Storage time (day) P-value
0 2 4 6 8 10 Temperature Time Interaction
L* CFPS 37.9 ± 1.62b 42.3 ± 0.64ay 41.6 ± 0.97ay 42.8 ± 1.64a 41.2 ± 1.08ay 41.3 ± 2.11a < 0.001 < 0.001 0.014 Control 38.1 ± 1.36c 45.2 ± 0.88ax 45.3 ± 1.54ax 43.3 ± 1.47b 43.7 ± 1.12abx 42.5 ± 1.02b
a* CFPS 8.3 ± 1.11b 12.6 ± 0.29ax 13.1 ± 0.80ax 12.9 ± 0.94ax 11.5 ± 1.62ax 12.1 ± 1.35ax < 0.001 < 0.001 < 0.001 Control 7.7 ± 0.49b 10.9 ± 0.72 ay 10.0 ± 1.09ay 7.7 ± 0.82by 7.3 ± 0.94by 6.4 ± 1.47by
b* CFPS 6.4 ± 0.97c 15.7 ± 0.50ax 13.7 ± 1.19bx 13.6 ± 0.71bx 12.6 ± 1.95bx 12.7 ± 0.97bx < 0.001 < 0.001 0.004 Control 6.5 ± 0.88c 12.7 ± 0.94ay 12.0 ± 0.95ay 9.5 ± 0.29by 9.4 ± 1.45by 9.5 ± 0.84by
R630/580 CFPS 2.5 ± 0.24d 2.9 ± 0.05ax 2.7 ± 0.13abcx 2.9 ± 0.19abx 2.6 ± 0.23cdx 2.6 ± 0.12bcdx < 0.001 < 0.001 0.003 Control 2.4 ± 0.13ab 2.6 ± 0.16ay 2.2 ± 0.33bcy 1.9 ± 0.23cy 2.0 ± 0.25cy 2.1 ± 0.08cy
Chroma CFPS 10.5 ± 1.37c 20.1 ± 0.35ax 18.9 ± 1.36abx 19.2 ± 1.65abx 17.0 ± 2.47bx 17.5 ± 1.59bx < 0.001 < 0.001 0.003 Control 10.1 ± 0.90c 16.8 ± 1.13ay 15.4 ± 1.26ay 12.2 ± 0.62by 11.9 ± 0.69bcy 11.5 ± 1.41bcy
Hue CFPS 37.6 ± 2.98c 51.1 ± 1.32a 46.1 ± 1.45by 46.3 ± 1.71by 47.5 ± 2.03by 46.5 ± 1.70by < 0.001 < 0.001 0.003 Control 40.3 ± 2.60c 49.5 ± 1.21b 49.9 ± 1.84bx 50.9 ± 2.87bx 52.3 ± 1.67bx 56.7 ± 4.74ax
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Highlights
Lamb color stability in controlled freezing point storage (CFPS, -0.8 °C) was studied.
Better meat colour stability was obtained in CFPS than in control (4 °C).
NADH content was higher for meat samples stored in CFPS than that in control.
Metmyoglobin reductase activity was higher for samples stored in CFPS than control.
