Trends in synthetic and natural antioxidants for shelf life extension of meat and meat products
By F.S.H. Lu and A. Pham-Mondala
- Naturally sourced antioxidants have gained considerable attention in the food industry due to consumers’ preference for natural ingredients.
- An optimal combination of naturally sourced ingredients is important to retard spoilage and quality deterioration of meat from lipid oxidation, microbial growth, and other mechanisms.
- Our studies suggest that it is feasible to use naturally sourced antioxidants to maintain color and flavor stability, and subsequently to extend the shelf life of fresh, pre-cooked, cooked, and processed meat.
In meat, the presence of unsaturated fat in membrane phospholipids causes fat to oxidize during processing and storage. As a result, the quality of meat and meat products deteriorate when fat oxidizes and develops off-flavors. Lipid oxidation increases the conversion rate of oxymyoglobin (bright red color) to metmyoglobin (brown discoloration) and subsequently impacts the physical appearance of meat and meat products . Meat is also very susceptible to spoilage and microbial growth during slaughtering and post-slaughter handling. Therefore, meat suppliers use various food additives to extend the shelf life of meat and meat products. These typically include synthetic antioxidants such as BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene), propyl gallate, and TBHQ (tert-butylhydroquinone). Nevertheless, due to increasing demands for clean label solutions, extensive work has been conducted to identify novel and natural extracts with potential applications in meat and meat products.
Studies using natural extracts with potential applications in meat and meat products were reviewed by Kumar and colleagues. Examples of the natural extracts, active ingredients, and applications that have been studied can be seen in Table 1. .
TABLE 1. Antioxidants from natural sources with the potential applications in meat and meat products
|Natural sources||Active Ingredients||Applications|
|Oregano essential oil||Thymol, para-cymene, gamma-terpinene, carvacrol||Raw and cooked porcine/bovine meat|
|Sage essential oil||Eucalyptol, camphor, alpha-pinene||Raw and cooked porcine/bovine meat|
|Curry and mint leaves||phenolics||Raw ground pork meat|
|Rosemary and oregano leaves extracts||Phenolics, rosmarinic acid, carnosic acid, carnosol||Raw pork batter|
|Grape seeds and peels extract||phenolics||Raw and cooked ground chicken|
|Borage leaves extract||phenolics||Dry fermented sausage enriched with omega-3 polyunsaturated fatty acids|
|Sea buckthorn (berry residues)||polyphenols||Raw and cooked mechanically deboned chicken and turkey.|
|Defatted canola meal||Sinapic, ferulic, para-hydrobenzoic acid||Chicken meat homogenate|
|Red grape pomace extract||Total polyphenolics, total anthocyanins||Pork burger|
The most commonly used naturally sourced antioxidants are phenolic compounds such as phenolic acids, tocopherol, and flavonoids. Phenolics prevent lipid oxidation through different mechanisms—by functioning either as free radical scavengers, metal chelators, or singlet oxygen quenchers. The antioxidative potential of phenolics depends on their skeleton structure. The number and location of functional groups, such as free hydroxyl OH groups, is just one example. For instance, phenolics with a higher number of OH groups and ortho-3,4-dihydroxy structures will have higher antioxidative properties . In addition, some phenolics, such as carnosic acid from rosemary, and catechin from green tea, not only have OH groups that can donate hydrogen to free radicals, but also contain vicinal -OH groups that can chelate metals. Consequently, combinations of natural extracts can potentially deliver synergistic effects and improve antioxidant performance in preventing lipid oxidation. Such combinations can also reduce the effective dosage of each extract, thus minimizing impacts on flavor and color.
Fresh meat, including sausages, are a major category of meat retail sales, both in the United States and Europe. Fresh sausages contain a high level of fat and are prepared from fresh comminuted meat from different meat types such as pork, chicken, beef, and so on. Therefore, fresh sausages are highly perishable, especially when these products are refrigerated (2–5°C) in oxygen semi-permeable packaging. In some European countries, such as the United Kingdom, Australia, and New Zealand, sulfur dioxide (mainly in the form of Sodium metabisulphite, SMBS) is a commonly used antimicrobial agent and color preservative used to maintain the quality of fresh sausages, with the maximum permissible limit in Europe of 500 mg/kg of sulfur dioxide/sulfites. The use of SMBS in meat is not allowed in the United States, as it causes a significant loss of thiamin. Consequently, synthetic antioxidants such as BHA, BHT, and propyl gallate are commonly used to extend the shelf life of fresh sausages in the US market. Three main mechanisms responsible for the spoilage of sausages are lipid oxidation, microbial growth, and enzymatic autolysis (such as proteolysis and lipolysis). Of these, microbial growth is the main cause of spoilage for sausages [4, 5].
For this reason, naturally sourced ingredients comprising antioxidative and antimicrobial agents were developed in our laboratory to delay the spoilage of pork sausages from different mechanisms, and to meet the different needs of US, UK, and EU markets. A storage study was conducted to investigate the efficacy of a natural blend comprising rosemary extract and buffered vinegar to extend the shelf life of British pork sausages. British pork sausages (70% minced pork, 15% water, 13% rusk and flour) were treated either with 0.075% of SMBS or 1.0% of the natural additives. The sausages were stored at 2°C under polyvinyl chloride (PVC) overwrap packaging for 14 days. The obtained results showed that SMBS is only effective in stabilizing the color of pork sausages for the first few days, whereas naturally sourced ingredients were superior in maintaining the color of pork sausages even after 14 days of storage (Fig. 1a). In addition, these naturally sourced ingredients provided a performance comparable to that of SMBS in inhibiting the growth of spoilage bacteria (total plate count of 3.6 log 10 CFU/g versus 2.9 log 10 CFU/g quantified at 7 days of storage), yet had the lowest lipid oxidation level (as shown by the hexanal level in Fig. 1b). The degree of lipid oxidation in sausages was monitored through the hexanal level, and using other selected oxidation markers such as heptanal, 1-octen-3-ol, and nonanal (Fig. 1c).
FIG. 1. a) Color changes of pork sausages during 14 days of storage at 2°C; b) the hexanal level in cooked sausages after 7 days of storage at 2°C; c) the profile of secondary volatile oxidation products detected in oxidized pork sausage
Similarly, a study was conducted to investigate the efficacy of natural antioxidant combinations (0.5% rosemary extract combined with buffered vinegar, and 0.2% rosemary extract combined with green tea) in prolonging the shelf life of US pork sausage relative to that of synthetic antioxidants. (0.02% BHA and BHT based on fat content). To mimic sausages in the US supply chain, pork sausages (90% minced pork, 3% water) were frozen at -20°C for 3 months, followed by refrigerated storage at 3°C for 22 days. Judging from the data of total plate count (Fig. 2), the combination of rosemary extract and buffered vinegar provided the longest shelf life to pork sausages (more than 22 days), followed by the combination of rosemary extract and green tea (15 days) and the combination of BHT and BHA, which showed the shortest shelf life (7 days). Our studies showed that a natural combination of antioxidants performed better than synthetic antioxidants in extending the shelf life of fresh pork sausages.
Fig. 2. Total plate count of US pork sausages treated with a) BHA and BHT; b) rosemary and green tea extracts, c) vinegar and rosemary extracts during real-time shelf life study at 3°C for 22 days
As consumers typically associate the freshness of meat with redness, they may reject meat and meat products that are discolored. In the meat industry, modified atmosphere packaging (MAP) has been used extensively to preserve meat color. Our internal studies have proven that incorporation of rosemary extract alone could further improve the color and flavor stability of fresh ground beef packed under MAP condition (Fig. 3). Our studies also proved that the use of antioxidant combinations (rosemary and acerola extracts) could provide additional color and flavor stability to fresh ground beef compared to rosemary extract alone.
Fig. 3. Visual observation of ground beef packed under high oxygen MAP condition at 3–4°C for 12 days (away from light) without antioxidant (left) and with rosemary extract (right)
In contrast with raw meat, undesirable off-flavors and aromas in cooked meat are often described as having a “warmed over flavor” (WOF), and different antioxidants are required to delay the development of these off-notes in cooked meat systems. Trials were conducted in our laboratory to investigate the efficiency of a combination of antioxidants (rosemary and green tea extract) to reduce WOF flavor and aroma in cooked beef. Our findings showed that the flavor stability of cooked beef treated with rosemary and green tea extracts was improved as evidenced by a lower level of WOF flavor and aroma (Fig. 4). The details of the above-mentioned studies have been published by Pham-Mondala and colleagues elsewhere , and therefore are not further discussed in this article.
Fig. 4. Sensory profile of 95% lean cooked beef stored at 4°C for 3 days’ storage under PVC overwrap (obtained from 20 trained panelists)
As with raw and cooked meat, there is an increasing interest in using naturally sourced antioxidants to maintain the color and flavor stability of processed meat, such as dry fermented sausage. In United States, dry fermented sausage is usually formulated to contain 45% meat block and 42% fat in the finished product, with a moisture and protein ratio of 1.6:1, a pH less than 5, and a salt content of 4% by weight. Due to its high fat content, dry fermented sausage is highly susceptible to oxidation—especially when it is sliced and not stored under a protective atmosphere. Typically, nitrites in the form of sodium nitrite or potassium are used by the meat industry to stabilize cured meat flavor and color, and to limit the growth of anaerobic bacteria and other microbes [5, 7]. The current permissible level of nitrites in meat products is 156 ppm in the United States and 200 ppm in Canada. To provide an alternative to conventional curing using nitrites, our laboratory has evaluated the efficiency of using a natural cure (150 ppm sodium nitrite from pre-converted vegetable juice powder, 0.12% of acerola powder, rosemary, and green tea extracts) versus conventional cure (150 ppm sodium nitrite, 400 ppm ascorbic acid, 60 ppm BHA/BHT) in maintaining the quality and shelf-life of dry-fermented sausage. In this study, the sausages were packed under high oxygen MAP condition (80% O2 and 20% CO2) to accelerate oxidation. Storage was conducted at a refrigerated temperature of 3°C for 28 days. The obtained results showed that a natural cure with rosemary and green tea extracts was as effective as a conventional cure in reducing the oxidation level in the sausages, but with a better maintenance of color (changes of a* value, Fig. 5). Our studies demonstrated that it is feasible to use a natural cure in extending the shelf life of dry fermented sausages.
Fig. 5. The changes of a* values (redness) of dry fermented sausage stored under high oxygen MAP packaging (80 O2 and 20 CO2) at 31C for 28 days
In conclusion, our internal studies demonstrated that it is feasible to use naturally sourced food ingredients to maintain color, retard the development of off-notes, and limit microbial growth in meat and meat products. We also learned that combinations of naturally sourced food ingredients are more effective at extending the shelf life of complex meat systems, as they delay spoilage from different causes.
F.S.H Lu received her PhD in Food Science from the Technical University of Denmark, where she investigated the oxidative stability of omega-3 for food applications and won an AOCS honored student award for her widely published research. In 2014, Lu joined Mondelez UK as a lipid scientist, expanding her knowledge in analytical techniques for studying oxidative stability, antioxidants, and shelf life prediction. In 2017, she joined Kalsec Europe Ltd as a lead scientist, serving as a principle investigator for projects involving the use of antioxidants. Lu supports research in the areas of lipid oxidation, antioxidants, and shelf life extension of meat products for the European market. She can be contacted at firstname.lastname@example.org.
A. Pham-Mondala earned Ph.D. and MS degrees in Food Science, Nutrition, and Health Promotion from Mississippi State University. Her research focused on developing antioxidant combinations to extend the shelf life and quality of fresh meat products during processing and storage. In 2016, Pham-Mondala joined Kalsec Inc. as a senior scientist in Meat and Poultry Applications/Antioxidants. In this role, she supports the Meat, Poultry, and Pet Food Team on product development for meat and poultry applications, conducts research for developing all-natural innovative products and solutions in key food applications, and real-time analytical support to meet industry needs. She can be contacted at email@example.com.
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