After slaughtering, the oxidation of lipids and proteins deteriorates meat quality, and impairs color, texture, flavor thus shortens shelf life. Recent research published by Surai (2002), Li et al. (2010), Delles et al (2014) and Estevez (2015) illustrated that dietary supplementation with certain vitamins and antioxidants like organic Selenium (Se), can alleviate peroxidation.

Organic Se has been widely recognized as an efficient de novo antioxidant. Inside body, Se exists in two forms: selenomethionine (SeMet) as storage form, and selenocysteine (SeCys) as functional component of various selenoproteins (Roman et al. 2014), many of them are antioxidants. SeCys has to be synthesized de novo because it cannot be stored. Se supplements, either in the form of mineral Se or other non-SeMet molecules such as SeCys, will be excreted if not required for selenoprotein synthesis at any particular time to deal with stresses. Therefore, the capability of various Se sources to improve meat quality parameters is largely linked to their bioavailability and efficiency of depositing Se in animal tissues.

The rate of Se-deposition in tissues

A rapid biological test has been developed (Couloigner et al., 2015) to monitor Se deposition in the muscle of young chicks, by feeding the same diet with various Se supplementations at 0.2 ppm over a period of 0-7 day. Compared with other mineral and yeast products, Selisseo® (SO), as a pure form of organic selenium containing 100% hydroxy- selenomethionine (OH- SeMet), has demonstrated the highest efficiency to transfer SeMet into breast muscle (Figure 1).

The higher Se deposition rate of OH-SeMet in body tissues was further confirmed by Wang (2016) who supplemented with selenite, Se-Yeast and OH-SeMet for the whole broiler life cycle (42 days) and reported organic Se (Se-yeast and OH-SeMet) resulted in significantly higher Se deposition in liver and breast muscle. Furthermore, OH-SeMet is 64% more efficient than Se-Yeast (Table 1).

Figure 1: Chicken breast muscle total Se (mg/kg DM) after feeding various Se forms for 7 days post-hatch

Figure 2: Drip loss (%) in chicken breast and thigh muscle, trial conducted by Texas A&M University poultry research farm

Drip Loss

After slaughtering, carcass drip loss is one of important meat quality parameters that represents significant economic losses. Research has revealed drip loss is due to oxidation of proteins in the muscle. Proper management through both technological and nutritional means, can render significant savings for processing plants as well as retailers.

Early research indicated that adding selenium in chicken diets can improve meat quality by decreasing drip loss and lipid peroxidation during meat storage. Choct et al. (2004) reported that by adding seleno-yeast at 0.25 ppm, the drip loss of chicken breast meat measured at 24 h post- mortem can be reduced from 1.19% to 0.78%. The decrease of drip loss of breast muscle suggests an improvement of waterholding capacity (WHC) of chicken meat, which can lead to longer shelf-life and technological yield of meat during manufacturing process.

A study was conducted recently by Texas A&M University poultry research farm. The study used 720 broilers, fed with basal diet or Se supplementation at 0.3 ppm for 7 weeks, to measure drip losses of breast and thigh. The results (Figure 2) showed that compared with sodium selenite (SS), OH-SeMet (SO) numerically reduced drip loss in chicken breast muscle by 0.37 percentage unit or 5%, and thigh muscle by 0.2 percentage unit or 4.6%, respectively.

Similarly, the trial mentioned previoulsy conducted by Wang (2016) also confirmed that supplementation with organic Se can reduce drip losses in chicken breast muscle (Table 1). Compared with the negatie control (drip loss 5.03%), the addition of sodium selenite (SS) and Se-yeast (SY) at 0.3 ppm numerically reduced drip losses. The addition of OH-SeMet (SO 0.3 ppm) reduced drip by 1.31 percentage units or 26%. It was noted that even at lower inclusion level (0.1 and 0.2 ppm), OH-SeMet remained effective in reducing drip losses (data not shown).

Besides drip loss, the results in table 1 also indicate the addition of OH-SeMet significantly increased breast muscle pH and numerically reduced cutting force.

Similarly, supplementing organic Se into pig diets can also reduce drip loss and increase pH of pig muscle (Li et al. 2010). The authors reported dietary addition of 0.3 ppm Se as Se-yeast reduced drip loss from 3.42 to 3.09%, and if increased Se to 3 ppm, further reduced drip loss to 2.52% (P< 0.01). They illustrated drip loss was related to gene (Sepw1) expression in pigs and found the increased levels of organic Se not only decreased drip loss (P<0.05) but also the concentration of thiobarbituric acid reactive substances in the muscle. Increased dietary intake of organic Se quadratically increased (P<0.01) the mRNA level of Sepw1 gene among the 12 selenoprotein genes examined in muscle. Statistical analysis showed drip loss was negatively correlated with the mRNA level of Sepw1 gene, suggesting that the enhanced water- holding capacity of meat was associated with the increased expression of Sepw1 gene.

Figure 3: Panel expert visual grading of turkey thigh meat. Grade 1 to Grade 4 means no meat discoloration, minor, moderate and major discoloration (n = 243 meat units per treatment, error bar = SEM, P<0.05)

Figure 4: Evaluation of biomarkers on turkey thigh meat (n = 6 replicate per treatment, error bar = SEM, P<0.05)

Shelf-life

After slaughtering, carcass discoloration during storage may lead to consumer rejection thus economical losses. It appears that meat color stability is connected to a number of factors, such as genetic selection, nutrition, environment, slaughtering condition, processing technique, packaging, storage and distribution of the products. In order to study potential of OH- SeMet, Briens et al. (2016) collaborated with INRA to evaluate the responses of supplementing 0.2 ppm OH-SeMet to male turkeys during the last 4 weeks before slaughtering. Compared with the control, daily visual grading by a panel of experts confirmed that supplementing OH- SeMet (0.2 ppm) could maintain scores of thigh till day 13, significantly better (stored in standard package: protective film of polyvinylchloride, 70% O2, 30% N₂ atmosphere, 4˚C) (Figure 3).

Several biomarkers were also examined to assess oxidative mechanisms involved in discoloration process. Thigh turkey meat in test group showed significant better results: higher ultimate pH, higher glutathione peroxidase (GPx) activity and lower malondialdehyde (MDA) content (Figure 4), suggesting a slower lipid peroxidation processes thanks to better animal Se status by OH-SeMet.

Calculations based on visual grading have concluded that OH-SeMet can improve meat color stability and on average, meat producers are able to extract valuable savings from up to 1.5 extra days of shelf life extension without noticeable discoloration.

Protect fat through a synergestic action of Vitamin E and selenium

The synergistic action of Se and VitE leads to securing meat quality properties for a longer period of time at the retailers: a better color and lipid stability, and lower drip losses. Moreover, the use of hydroxy-methionine instead of Dl-Met leads to a better synthesis into cysteine and consequently a higher synthesis of glutathione, thereby leading to a better antioxidant protection of meat.

Increasing the dose of both VitE and Se as SeMet would give an extra boost that could help face more challenging oxidative conditions (meat storage during summer/hot periods, non-optimal processing and storage of meat).

In conclusion, the research presented above, has well demonstrated that dietary supplementation with organic Se (SeMet or OH-SeMet) can enhance Se deposition in animal tissues thus provide more Selenoproteins functioning as de novo antioxidants that break down Reactive Oxygen Species and slow down oxidation, leading to lower drip loss, better meat quality and longer shelf- life.

Reference under request

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