Meat Science 87 (2011) 46–53

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Antioxidant activity of bovine and porcine meat treated with extracts from ediblelotus (Nelumbo nucifera) rhizome knot and leaf

Bo Huang, Jingsheng He, Xiaoquan Ban, Hong Zeng, Xincheng Yao, Youwei Wang ⁎Institute of the Traditional and Chinese Medicine and Natural Products, College of Pharmacy, Wuhan University, Wuhan 430071, P. R. China

⁎ Corresponding author. Tel.: +86 27 68759323; fax:E-mail address: wyw@whu.edu.cn (Y. Wang).

0309-1740/$ – see front matter © 2010 The Americandoi:10.1016/j.meatsci.2010.09.001

a b s t r a c t

a r t i c l e i n f o

Article history:Received 12 January 2010Received in revised form 29 August 2010Accepted 1 September 2010

Keywords:AntioxidantNelumbo nuciferaWaste productsPorcineBovine

Lotus (Nelumbo nucifera) is an extensively cultivated vegetable in eastern Asia, particularly in China. Bothlotus rhizome knot (LRK) and lotus leaf (LL) are waste products of the lotus industry. Extracts from LRK and LLare proposed as antioxidants for meat. Porcine and bovine ground meat samples were subjected to threetreatments: CONTROL (with no additives), LRK (lotus rhizomes knot extract 3% w/w), and LL (lotus leafextract 3% w/w). Raw and cooked samples were stored at 4 °C and the antioxidant activity was determined at1, 3, 6 and 10 days. Antioxidant activity was significantly increased in all meat samples with the addition ofboth LRK and LL, but LRK was more effective against lipid oxidation. The results show the potential for usingLRK and LL extracts in the meat industry to prolong shelf life.

© 2010 The American Meat Science Association. Published by Elsevier Ltd. All rights reserved.

1. Introduction

Synthetic antioxidants such as butylated hydroxytoluene (BHT),butylated hydroxyanisole (BHA) and tertiary butyl hydroquinone(TBHQ) have been widely used by the food industry because they areboth powerful and inexpensive. However, BHA (Sherwin, 1990) andBHT (Chen, Pearson, & Gray, 1992; Sun & Fukuhara, 1997) are suspectedcarcinogens, and consumer concern has led to a decrease in their use inthe food industry (Namiki, 1990). Vitamins in meat also play a role inpreventing lipid oxidation. However, while vitamin oxidation mayprotect fatty acids from oxidation, the nutritional value of meat can benegatively affected by a general reduction in the availability of vitaminsA, D, E and C (Madhavi, Deshpande, & Salunkhe, 1996).

For the food industry, the use of natural antioxidants can beadvantageous because natural products do not require extensivesafety testing prior to use. Examples of natural products includeoregano, sage (Fasseas, Mountzouris, Tarantilis, Polissiou, & Zervas,2007), rosemary (Sebranek, Sewalt, Robbins, & Houser, 2005), blackpepper (Martínez, Cilla, Beltrán, & Roncalés, 2007), tea (Bañón, Díaz,Rodríguez, María, & Alejandra, 2007), and chickpea flour (Verma,Ledward, & Lawrie, 1984). However, natural products are often moreexpensive and less effective than synthetic antioxidants. As a result,special attention has been focused on the extraction of antioxidantsfrom inexpensive or residual sources from agricultural industries,such as potato peel (Singh & Rajini, 2008), grape seeds (Brannan,2009), citrus peel and seeds (Bampidis & Robinson, 2006), carrot

+86 27 68759010.

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waste (Eim, Simal, Rosselló, & Femenia, 2008) and tea leaves(Farhoosh, Golmovahhed, & Khodaparast, 2007).

Lotus (Nelumbo nucifera) is an ornamental plant that is also adietary staple in eastern Asia, particularly in China. The rhizome (lotusroots) knot is a common vegetable used as a traditional herbal remedyto stop bleeding. Lotus rhizome knots (LRK) contain high levels ofpolyphenolic compounds and distinctive antioxidative properties incomparison with commonly used plant extracts (Hu & Skibsted,2002). Lotus leaf (LL) contains several flavonoids (Mukherjee,Mukherjee, Maji, Rai, & Heinrich, 2009) and leaf extracts showedsignificant antioxidant effects in previous studies (Huang et al., 2010).Lotus leaves have long been used in China to package meat to prolongshelf life and improve taste.

Both LRK and LL are reported to possess significant antioxidantactivity due to the presence of polyphenolic compounds (tannins andflavonoids) (Editor Committee of National Chinese Medical ManageBureau, 1999; Liu, Hou, Jin, Guo, & Wang, 2009; Mukherjee et al.,2009). However, to the best of our knowledge, no investigation hasaddressed the use of LRK and LL as readily available and inexpensiveantioxidants in meat and meat products. Thus, the objective of thiswork was to assess the antioxidant activity of LRK and LL in both rawand cooked porcine and bovine meat. In addition, the mainpolyphenolic compounds in the two extracts were investigated.

2. Materials and methods

2.1. Chemicals

Standards (i.e., gallic acid and rutin) were purchased from theNational Institute for the Control of Pharmaceutical and Biological

by Elsevier Ltd. All rights reserved.

47B. Huang et al. / Meat Science 87 (2011) 46–53

Products (Beijing, PR. China). It was reported that tannins andflavonoids are the main polyphenolic compounds in LRK and LL,respectively. (Editor Committee of National Chinese Medical ManageBureau, 1999; Liu et al., 2009; Mukherjee et al., 2009). Gallic acid wasused as a standard for the determination of total tannins and rutin wasused as a standard for the determination of total flavonoids.α,α-diphenyl-β-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethyl-benzthiazoline-6-sulfonic acid (ABTS) were purchased from SigmaChemical Co. (St. Louis, MO, USA). All other chemicals used were‘AnalaR’ grade, obtained from China Medicine (Group) ShanghaiChemical Reagent Corporation (Shanghai, PR. China).

2.2. Preparation of the extracts

Minced fresh rhizome knots and dried leaves of N. nucifera wereextracted with distilled water at room temperature overnight. Theextracts were filtered, and the solvent removed by rotary evaporationat 35 °C. The residues were evaporated to dryness in vacuo and theresulting dry powder was stored at 4 °C. The yield of LRK and LLextracts were 6.6±0.3% and 10.3±0.6%, respectively.

2.3. Determination of total phenolics, tannins, and flavonoids in theextracts

Total phenolic content (TPC) of LRK and LL extracts (0.1 g for each)were determined using the Folin–Ciocalteau assay (Zoecklin, Fugel-sang, Gump, & Nury, 1995). Results were expressed as grams of gallicacid equivalents per 100 g of dry extract.

Total tannin content (TTC) of LRK and LL extracts (0.1 g for each)were estimated gravimetrically as the difference between totalphenolics and phenolics remaining after binding the tannins withpolyvinyl polypyrrolidone (PVPP) according to Makkar, Blummel,Borrowy, and Becker (1993). The concentrations of total tannins wereexpressed as grams of gallic acid equivalents per 100 g of dry extract.

Total flavonoid content (TFC) of LRK and LL extracts (0.1 g foreach) was determined by colorimetric assay (Moreno, Isla, &Sampietro, 2000). A calibration curve was generated with rutin asthe reference compound, and the results were expressed as grams ofrutin equivalents per 100 g of dry extract.

2.4. Chemical composition analysis by HPLC-DAD

HPLC analysis of LRK and LL extracts (0.1 g for each) wasaccomplished using an Agilent-1100 HPLC system with a diodearray detector (Agilent Technologies, Waldbronn, Germany),equipped with a quaternary pump, vacuum degasser, autosampler,and column heater-cooler (Agilent Technologies, Waldbronn,Germany). Spectroscopic data from all peaks were collected in therange of 200–400 nm, and chromatograms were recorded at 265 nmand 350 nm. The chromatographic separation was performed on areversed-phase C18 analytical column (3 μm, 150 mm×4.6 mm i.d.,Advanced Chromatography Technologies, Aberdeen, U.K.) with thecolumn temperature set at 45 °C. A linear gradient elution of water,containing 1% acetic acid (A) and MeCN (B) was used (0–25 min,solvent A was decreased from 100% to 0%, then solvent A wasincreased to 100% and held constant for 5 min). The flow rate was0.4 ml/min, and the injection volume was 20 μl.

2.5. Preparation of meat samples

Fresh porcine (Biceps femoris) and bovine (Biceps femoris) samples(1 kg) from one pig and cattle were obtained from the local marketand visible fat was removed. Samples from each meat were thendivided into three groups and were homogenized with 3% w/w ofeither LRK or LL in amulti-functional food blender (BSS260-D6, BaoshiElectrical Co., Ltd., Foshan, China). No extract was added to the control

samples (CONTROL). All samples (3 g, 5 cm diameter and 0.7 cmthick) were packed in polyethylene film from a local market andstored at 4 °C in darkness for 24 h and then tested for antioxidantactivity (day 1). After testing, each sample was split into two. Oneportion remained in the raw state and the otherwas cooked at 85 °C inan oven (DGX-9143-B-1, Shanghai, China) for 30 min (Fasseas et al.,2007). Both raw and cooked samples were assayed for antioxidantactivity as described below at 3, 6 and 10 days of storage at 4 °C indarkness, in a polyethylene film.

2.6. Assessment of lipid oxidation

The TBA assay followed the method of Fasseas et al. (2007) withslight modification. In brief, 0.03 g of sample was mixed with 0.6 mldeionised H2O, 0.9 ml of phosphoric acid (pH 2.0) and 0.9 ml 0.8%(w/w) of thiobarbituric acid (TBA) in 1.1% (w/w) sodium dodecyl-sulfate (SDS) in a test tube, and then vortexed and heated at 100 °C for60 min in a water bath. After cooling, butan-1-ol (3 ml) was addedand the solutionmixed. Samples were then centrifuged at 8960×g for10 min (TGL-16C, Anting Scientific Instrument Factory, Shanghai,China). The absorbance of the upper layer was determined at 532 nm(UV-1240, Shimadzu, Japan). Butan-1-ol was used as blank. Theresults were expressed as TBA values (the relative absorbance of eachsample on day 1).

2.7. DPPH free radical scavenging activity

The hydrogen atom or electron-donating ability of the meatsamples was measured from the bleaching of a purple-coloredmethanolic solution of DPPH (Gulluce et al., 2007). Free radicalscavenging activity was evaluated by the DPPH assay using themethod of Tepe et al. (2005). Samples (0.03 g) were constantly mixedwith 3 ml of 0.004% DPPH in methanol in a test tube at roomtemperature for 30 min. The samples were centrifuged at 1430×g for10 min (TGL-16C, Anting Scientific Instrument Factory, Shanghai,China). Absorbance of the supernatants was measured at 517 nm(UV-1240, Shimadzu, Japan), using methanol as blank. Measurementswere expressed as absorbance and decreasing values indicatedincreasing antioxidant activity.

2.8. ABTS free radical scavenging activity

Antioxidant activity of the samples was also measured using animproved ABTS (azinobisethylbenzthiazolinesulfonic acid) procedure(Re et al., 1999). TheABTS radical cation (ABTS+) solutionwas preparedthrough the reaction of 7 mM ABTS and 2.45 mM potassium persul-phate, after incubation at room temperature, in the dark for 16 h. TheABTS+ solution was then diluted with 80% ethanol to obtain anabsorbance of 0.700±0.005 at 734 nm. ABTS+ solution (3 ml; absor-bance 0.700±0.005) was added to 0.03 g of the samples and mixedvigorously (TS-1, Kylin-Bell Lab Instruments Co.,Ltd., Shanghai, China).The reaction mixture was allowed to stand at 30 °C for 30 min beforecentrifugation at 1430×g for 10 min (TGL-16C, Anting ScientificInstrument Factory, Shanghai, China). The supernatant's absorbance at734 nm (UV-1240, Shimadzu, Japan)was immediately recorded. Lowerabsorbance levels indicated higher antioxidant activity.

2.9. Reducing power assay

The potassium ferric cyanide reductionmethodmeasures the colorchange of the test solution from yellow to various shades of green andblue depending upon the reducing power of each sample. Meatsamples (0.03 g) were mixed with 2.5 ml of 200 mM sodiumphosphate buffer (pH 6.6) and 2.5 ml of 1% potassium ferric cyanide.The mixture was incubated at 50 °C for 20 min. Then, 2.5 ml of 10%trichloroacetic acid (w/v) was added and the mixture was centrifuged

Table 1Total phenols, tannins, and flavonoids in lotus rhizome knot (LRK) and lotus leafextracts (LL).

Sample TPC (g/100 g) TTC (g/100 g) TFC (g/100 g) TTC/TPC TFC/TPC

LRK 17.1±0.4 13.0±0.3 7.96±0.3 76.0 46.5LL 34.9±0.4 6.02±0.2 33.0±0.5 17.2 94.6

Values are expressed as mean±standard error. TPC, total phenolic content (gallic acidequivalents g/100 g); TTC, total tannin content (gallic acid equivalents g/100 g); TFC,total flavonoid content (rutin equivalents g/100 g).

48 B. Huang et al. / Meat Science 87 (2011) 46–53

at 1430×g for 8 min. The resulting supernatant was mixed with equalvolumes of deionized H2O and 1/5 volume of 0.1% ferric chloride. After10 min, the absorbance of the resulting solution was measured at700 nm (UV-1240, Shimadzu, Japan) (Barros, Baptista, & Ferreira,2007). Increased absorbance of the reaction mixture indicatedincreased reducing power.

2.10. Measurement of metmyoglobin

Metmyoglobin (metMb) accumulation in meat was measuredspectrophotometrically as described by Naveena, Sen, Muthukumar,Vaithiyanathan, and Babjiy (2006) with slight modification. Briefly, aportion (0.5 g) of meat was homogenized with 3 ml of cooled (b4 °C)0.04 M phosphate buffer at pH 6.8. The mixture was kept at 4 °C for1 h and subsequently centrifuged at 2240×g for 5 min. Thesupernatant was filtered and metMb formation was estimated fromthe absorbance at 503 nm. As metMb will be denatured and notsoluble in water after heating (Bernofsky, Fox, & Schweigert, 1959;Draudt, 1969; Leeward, 1992), metMb was not determined in thecooked samples.

2.11. Measurement of pH

To measure pH, 0.5 g samples were homogenized with 3 ml ofdistilled water and the homogenate was centrifuged at 2240×g for5 min. The supernatant was filtered and the pH of the supernatantmeasured with model PHS-3TC (Tianda Instrument Co., Ltd., Shang-hai, China) pH meter.

2.12. Color image

Color images of the surface of the meat samples were acquiredusing a digital CCD camera (L310W 13.6 mega pixels, Samsung Opto-Electronics Crop., Tianjing, China). Images were acquired in a closedbox equipped with a spiral light (Tornado CDL; illumination intensity,approximately 500 lx; dimensions, 47 mm in diameter, 80 mm inlength; Philips Corp.) to prevent outer light.

2.13. Sensory evaluation

Ten panelists scored the samples for overall acceptability at 1, 3, 6,and 10 days of storage. Panelists were also asked to provide additionalqualitative comments for each sample. The panelists included staffmembers and students in the Institute of Traditional ChineseMedicine& Natural Products, College of Pharmacy, Wuhan University. A ninepoint hedonic scale (9= like extremely; 8 = like very much; 7= likemoderately; 6 = like slightly; 5 = neither like nor dislike; 4 = dislikeslightly; 3 = dislike moderately; 2 = dislike very much; 1 = dislikeextremely) was used to score the samples.

2.14. Statistical analysis

All experiments were done in triplicate and results are reported asmean±standard error. ANOVA was used to assess the effects oftreatments (i.e., CONTROL, LRK, LL) and storage time (i.e., days 1, 3, 6and 10) using the Statistical Package for Social Sciences (SPSS) version12.0 (Norusis, 2004). Statistically significant effects were furtheranalyzed and means were compared using Duncan's multiple rangetest. Statistical significance was Pb0.05.

3. Results

3.1. Total phenolics, total tannins and total flavonoids in the extracts

Extracts obtained from LRK and LL were tested for TPC, TTC andTFC, and the ratios of TTC/TPC and TFC/TPC were calculated (Table 1).

In the LRK extract, both TPC and TFC were lower than in the LLextracts. TTC, however, was higher in LRK than in LL extracts. LRK hada higher TTC/TPC value and lower TFC/TPC value than LL.

3.2. HPLC-DAD analysis

HPLC-DAD was done to further delineate the different types ofphenolic compounds present in the extracts. Usually, flavonoidcompounds have two strong absorption peaks at 250–280 nm and350–370 nm, as shown in Fig. 1.

3.3. Assessment of lipid oxidation

Data from the TBA assay are presented in Fig. 2A as TBA values. Inraw samples, significantly (Pb0.05) greater levels (i.e., higher TBAvalues) of oxidation were found in the CONTROL and LL treatments inboth porcine and bovine samples than in the LRK group. Oxidationlevels in the LL treatment were significantly (Pb0.05) lower than inthe CONTROL after day 6 in both rawmeats. In the CONTROLs, storagetime had an effect onmeat oxidation, with higher levels after 6 days inboth meats.

In the cooked samples, the overall antioxidant activity wassignificantly (Pb0.05) higher for both treatments, with the LRKtreatment being the most effective. Overall, oxidation increased withstorage time in the CONTROLs of both cooked meats.

3.4. DPPH and ABTS free radical scavenging activity

According to the DPPH assay the LRK and LL treatments bothproduced significantly (Pb0.01) effective antioxidant activity (i.e.,lower absorbance) in both meat compared to CONTROL samples(Fig. 2B). The overall antioxidant activity was significantly (Pb0.05)higher for the LL than the LRK treatment in both raw and cookedsamples.

Data generated from the ABTS assay were similar to that from theDPPH assay (Fig. 2C). In raw samples, the antioxidant activity of the LLtreatment was significantly (Pb0.01) better than the LRK treatmentfrom day 3 in porcine and day 6 in bovine samples.

Both cooked porcine and bovine CONTROLs had significantly(Pb0.01) higher levels of oxidation than samples treated with LRKand LL. In contrast to the results for raw samples, the cooked LLsamples showed significantly (Pb0.01) higher antioxidant activitythan the LRK samples on days 3, 6 and 10 in porcine meat and days 6and 10 in bovine meat.

3.5. Determination of reducing power

Results from the reducing power assay (Fig. 2D) showed the LRKand LL treatments significantly (Pb0.01) increased reducing power(i.e., higher absorbance) compared to the CONTROLs in both rawmeats. Additionally, the reducing power in the raw LL samples wassignificantly (Pb0.01) higher than in the raw LRK ones.

In cooked samples, the reducing power assay produced results thatwere comparable with the corresponding raw ones.

Fig. 1. HPLC-DAD analysis of the LRK and LL extracts. LRK, lotus rhizomes knot extract; LL, lotus leaf extract.

49B. Huang et al. / Meat Science 87 (2011) 46–53

Overall, in both raw and cooked meats, the LRK and LL treatmentsshowed significantly higher reducing power than found in theCONTROL, and the absorbance was significantly higher in LL samplesthan in the LRK ones.

3.6. Metmyoglobin

According to the metmyoglobin assay of the raw samples, the LRKtreatment significantly (Pb0.01) retarded accumulation of metMb(i.e., lower absorbance) (Fig. 3A) before day 10 in raw porcinesamples, while no significant effects were seen in the raw bovinesamples. In contrast, significantly (Pb0.05) higher levels of metMbwere found in the LL samples on day 1, 3 in raw porcine and in all rawbovine meat samples compared with the CONTROL group.

3.7. pH

The pH of raw porcine samples treated with LL and LRK wassignificantly (Pb0.01) lower than the CONTROLs on day 6 (Fig. 4). Inraw bovine samples, the LRK samples had a significantly (Pb0.01)lower pH than the LL and CONTROLs on day 10. However, nosignificant changes were seen between the different treatments inboth cooked meats.

3.8. Color image and sensory analysis

Overall acceptability scores of porcine and bovine samples asaffected by LRK and LL extracts are presented in Table 2. The additionof LRK and LL changed the color of the meat samples and improvedacceptability (Fig. 5). The scores for LL treated samples weresignificantly higher than those of the LRK treated and CONTROLsamples, except for day 3 (raw) and 3 and 6 (cooked) in porcine meatand for days 1 and10 (raw) and 1and 3 (cooked) in bovine meat.

Overall, scores for the LRK treated samples and the CONTROLs werecomparable (PN0.05) in both raw and cooked meat types.

4. Discussion

Regarding the total phenolics, total tannins and total flavonoidscontent of LRK and LL extracts, the results agree with the previousresearch on the antioxidant activity of rhizome knot and leaf extractsfrom edible lotus (N. nucifera) that suggested a relationship betweenantioxidant activity and phenolic compound content (Hu & Skibsted,2002; Huang et al., 2010). LRK and LL extracts exhibited differentconcentrations of total phenols (tannins or flavonoids), which couldbe responsible for the differences noted between the TBA assay andDPPH, ABTS, and reducing power assays. LRK and LL treatmentsresulted in less oxidation than those found in the CONTROLs in bothmeats stored at 4 °C, with LRK demonstrating, by the TBA assay, thegreatest protective effect. Conversely, the DPPH, ABTS radicalscavenging and reducing power assays showed that LL treatmentgave the greatest antioxidant activity (Fig 2B,C, and D), perhapsbecause of the higher total phenolic content in LL extracts. Similardifferences between phenolic compound content and antioxidantactivity have been reported for water-soluble oregano and grape seedextracts in meat samples (Rojas & Brewer, 2007).

Tannins have absorption peaks at 250–280 nm (Wang, Zhang,Huang, & Qin, 2002). The use of the DAD detector makes it possible toanalyze and quantify different polyphenolic classes. The LRK extractshave a UV spectra, with an absorbance at 265 nm, and almost noabsorption at 350 nm. The LL extracts have UV spectra, with anabsorbance at 265 nm and 350 nm. The results further demonstratethat the LRK and LL extracts contain different types of phenoliccompounds. However, the detailed structures of the phenoliccompounds of LRK and LL extracts still need to be defined.

Fig. 2. Antioxidant activity levels in the meat samples (raw porcine samples, cooked porcine samples, raw bovine samples, cooked bovine samples) on storage, as determined by theTBA assay (A) DPPH assay (B), ABTS assay (C), reducing power assay (D). LRK, lotus rhizomes knot extract; LL, lotus leaf extract. Data represent means±respective standard errors.Bars with different superscripts (a–c) within the same sampling day differ significantly (Pb0.05).

50 B. Huang et al. / Meat Science 87 (2011) 46–53

Lipid oxidation is characterized by the formation of conjugateddienes, hydroperoxides and aldehydes (Kagan, 1988). Aldehydicproducts of lipid oxidation, especially MDA (malondialdehyde) canbe estimated by the reaction with TBA (thiobarbituric acid) and theTBA value is routinely used as an index of lipid oxidation in meatproducts (Raharjo & Sofos, 1993). The TBA value was decreased in allsamples on the addition of both LRK and LL, but LRK was moreeffective against lipid oxidation.

DPPH and ABTS assays both showed that LRK and LLtreatments significantly increased radical scavenging (Fig. 2Band C), in agreement with the previous studies (Hu & Skibsted,2002; Huang et al., 2010). Radical scavenging was also affected

over time in all untreated meat samples, perhaps becauseoxidation of the meat leads to the creation of compounds thatscavenge free radicals (Guillen-Sans & Guzman-Chozas, 1998).The DPPH radical assay is only suitable for lipid-solubleantioxidants, while the ABTS radical cation decolorization assayis applicable for both water-soluble and lipid-soluble antiox-idants (Re et al., 1999). This suggests that there are more water-soluble antioxidants in bovine than in porcine meat.

The presence of reductants (antioxidants) in meat causes thereduction of Fe3+/Ferric cyanide complex to the ferrous form.Therefore the Fe2+ complex can be monitored by measuring theformation of Perl's Prussian blue at 700 nm (Chung, Chang, Chao, Lin,

Fig. 3. metMb levels in the raw porcine (A) and bovine (B) samples on storage. LRK,lotus rhizomes knot extract; LL, lotus leaf extract. Data represent means±respectivestandard errors. Bars with different superscripts (a–c) within the same sampling daydiffer significantly (Pb0.05).

51B. Huang et al. / Meat Science 87 (2011) 46–53

& Chou, 2002). LL treatment gave a significantly higher absorbancethan the LRK treatment (Fig. 2D) due to the high polyphenolic contentof the LL extract. Similar observations have been reported for severalother plant extracts (Yen & Chen, 1995).

Fig. 4. pH of the raw and cooked porcine and bovine samples on storage. LRK, lotus rhizomeBars with different superscripts (a–c) within the same sampling day differ significantly (Pb

Table 2Mean scores of overall acceptability of porcine and bovine samples treated with lotus rhizo

Raw samples

Control LRK LL

PorcineDay 1 5.09±0.37a 5.91±0.37a 7.09±0.37Day 3 4.70±0.54a 6.50±0.37b 7.20±0.29Day 6 2.71±0.52a 4.14±0.55a 5.86±0.51Day 10 1.28±0.28a 1.57±0.20a 3.28±0.42

BovineDay 1 6.09±0.44a 6.18±0.42a 7.36±0.34Day 3 5.70±0.45a 6.30±0.26a 7.20±0.29Day 6 3.43±0.68a 5.00±0.72a 6.43±0.61Day 10 1.43±0.30a 2.28±0.42b 3.57±0.37

Values are expressed as mean±standard error. Within each treatment or storage time mea

Previous studies (Bao, Ushio, & Ohshima, 2008) have indicatedthat free radical scavengers could inhibit the formation of metMb.Reeder and Wilson (1998) proposed the following mechanism ofoxidative reactions between lipids and Mb:

deoxy Fe2+� �

Mb + LOOH→met Fe3+� �

Mb + LO● ð1Þ

met Fe3+� �

Mb + LOOH→ ferryl Fe4+� �

Mb + LO● ð2Þ

LO●→ epoxyL ð3Þ

epoxyL● + O2→LOO ð4Þ

epoxyL● + ferryl Fe4+� �

Mb→met Fe3+� �

Mb + epoxyLOH: ð5Þ

In fresh meat, Mb exists in three forms — deoxymyoglobin [deoxy(Fe2+)Mb], oxymyoglobin [oxy(Fe2+)Mb], and metmyoglobin [met(Fe3+)Mb]. DPPH and ABTS assays showed that LRK and LL havestrong radical scavenging capabilities. Phenolic compounds in LRKand LL could scavenge the LO• radical generated in meats (Eqs. 1and 2), providing a possible explanation for the mechanism of metMbinhibition. However, in this study, significantly higher apparentmetMb contents were found in the samples treated with LL than inthe CONTROL group. The higher absorbance at 503 nmmay have beendue to the natural color (light yellow) of the LL treatment solutions.

Although the addition of LRK and LL extracts showed changes tothe color of themeat samples, the sensory scores of LL treated sampleswere higher than of CONTROL and LRK treated samples, and LRKsamples exhibited similar sensory scores to CONTROLs. These resultssuggest that although LRK and LL extracts altered the color of themeatsamples they were considered acceptable by the panelists. However,

s knot extract; LL, lotus leaf extract. Data represent means+respective standard errors.0.05).

me knot (LRK) and lotus leaf extracts (LL).

Cooked samples

Control LRK LL

b 5.09±0.37a 5.91±0.37a 7.09±0.37bb 5.10±0.41a 5.90±0.35ab 6.60±0.40bb 4.28±0.97a 5.00±0.95b 6.43±0.48bb 2.86±0.40a 2.86±0.46a 4.71±0.57b

a 6.09±0.44a 6.18±0.42a 7.36±0.34ab 6.80±0.39a 6.60±0.34a 7.30±0.42ab 4.86±0.83a 5.14±0.74a 6.57±0.57bb 2.71±0.28a 3.43±0.43a 4.14±0.55b

ns with different superscripts (a–b) in a row differ significantly (Pb0.05).

Fig. 5. Color images of the surface of the different meat samples. LRK, lotus rhizomes knot extract; LL, lotus leaf extract.

52 B. Huang et al. / Meat Science 87 (2011) 46–53

further consumer sensory analysis is required to determine if the colorchange is acceptable.

5. Conclusions

The TBA assay can be effectively used to investigate oxidationoccurring during cooking and storage of meat, because the lipids aredramatically affected. This is in agreement with Kanatt, Chander, andSharma (2008) and Fasseas et al. (2007) The DPPH, ABT and reducingpower assays can be used to provide additional information regardingchanges that occur in porcine and bovine meat samples. Extracts fromboth the LRK and LL of the lotus plant are effective antioxidants andthe LRK extracts were more effective in inhibiting meat oxidation.Additional studies should be conducted to determine the compositionand structure of the active polyphenolic compounds in these wasteproducts from edible lotus.

Acknowledgements

This work was supported by the Key Program of NaturalScience Foundation of Hubei Province of China (No. 2008CDA045),the Fundamental Research Funds for the Central Universities

(20103010101000175), the Important National Science & TechnologySpecific Projects (No. 2009ZX09301-14) and the Special CommonwealProgram of China (No. 3-21).

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