DNA damage protection and antioxidant activities of peptides isolated from sour meat co-fermented by P. pentosaceus SWU73571 and L. curvatus LAB26

ABSTRACT

DNA damage and antioxidant activities of sour meat peptides were evaluated using chemiluminescence and spectroscopic methods. All sour meat peptides exhibited DNA damage protection and free radical scavenging activities against DPPH radicals, hydroxyl radicals and superoxide anions in a dose-dependent manner, and showed the strongest inhibition of hydroxyl radicals and the weakest inhibition of superoxide anion radicals. The IC₅₀ values of sour meat peptides from inoculating fermentation were 2.11, 4.23, 0.097 and 9.85 mg/mL for the inhibition of DNA damage and scavenging capacities of DPPH radicals, hydroxyl radicals and superoxide anion radicals, respectively, and were significantly lower than those of traditional fermentation (P < 0.05). Compared to traditional fermentation, co-fermentation of P. pentosaceus SWU73571 and L. curvatus LAB26 significantly enhanced inhibition of DNA damage and antioxidant activities of peptides (P < 0.05), revealing good microbial sources as a natural starter for the improvement of antioxidant capacity of fermented meat products.

RESUMEN

Utilizando quimioluminiscencia y métodos espectroscópicos, el presente estudio evaluó los daños ocasionados al ADN y las actividades antioxidantes de los péptidos aislados de la carne agria. Según la dosis empleada, todos los péptidos aislados de la carne agria mostraron protección del daño ocasionado al ADN y eliminación de los radicales libres DPPH, hidroxilo y anión superóxido. Además, en los péptidos se constató la mayor inhibición del radical de hidroxilo y la menor inhibición del radical de anión superóxido. Tras la fermentación por inoculación, los valores IC₅₀ de los péptidos aislados de la carne agria fueron 2.11, 4.23, 0.097 y 9.85 mg/mL para la inhibición de daños al ADN y la capacidad de eliminación de radicales DPPH, hidroxilo y anión superóxido, respectivamente, resultando ser significativamente inferiores a los registrados en la fermentación tradicional (P < 0.05). En comparación con la fermentación tradicional, la co-fermentación empleando P. pentosaceus SWU73571 y L. curvatus LAB26 aumentó significativamente la inhibición del daño ocasionado al ADN y las actividades antioxidantes de los péptidos (P < 0.05). Esto indica que existen buenas fuentes microbianas como iniciador natural para mejorar la capacidad antioxidante de los productos cárnicos fermentados.

KEYWORDS:

• DNA damage
• antioxidant activity
• peptide
• sour meat
• co-fermentation

PALABRAS CLAVE:

• Daño al ADN
• actividad antioxidante
• péptido
• carne agria
• co-fermentación

1. Introduction

During metabolism in body, reactive oxygen species, such as hydroxyl radical, superoxide anion radical and hydrogen peroxide, are spontaneously generated in living organisms, which break a balance between the antioxidant capacity of cells and generation of reactive oxygen species (ROS), resulting in oxidative stress (Botsoglou et al., 2009; Xu et al., 2011). Reactive oxygen species could be related to several degenerative diseases such as diabetes mellitus, stroke and cancer (Ablola et al. 2018; Y. Zhu et al., 2018). Functional components such as functional peptides, oligosaccharides/polysaccharides and functional enzymes from fermented products (fermented ham, fermented sausage, dry-cured loins, fermented milk and sour meat) play a significant role in the prevention of those diseases.

Meat fermentation plays an important role in processing, preservation and storage of meat and meat products, including the taste improvement of meat. During the fermentation process, many enzymes such as microbial enzymes, endogenous enzymes and digestive enzymes from non-starter and starter cultures could promote enzymatic hydrolysis for bioactive peptides through different pathways (Gallego et al., 2018a). The generation of bioactive peptides enhances the function and nutritional quality of fermented meat during the fermentation process. Moreover, the oxidation processes also drive the generation of peptides. Bioactive peptides have proven different types of bioactivities, including antioxidant activity (Escudero et al., 2013a; Wattanasiritham et al., 2016), antihypertensive activity (Escudero et al., 2013b), antimicrobial activity (Naimah et al., 2018), angiotensin-converting enzyme (ACE)-inhibitory activity (Gallego et al., 2018a), cholesterol-lowering activity (H. Zhang et al., 2012), anticancer activity (Chi et al., 2015) and multifunctional activity (Zambrowicz et al., 2015). In recent years, peptides from fermented meat have been receiving an increasing attention for natural functional products and medicine development due to good protein source of meat. However, much attention is paid to antioxidant and ACE-inhibitory activities of peptides from fermented meat (C. Z. Zhu et al., 2016; Dellafiora et al., 2015; Gallego et al., 2018b; Mejri et al., 2017; Xing et al., 2018). These fermented meat products are mainly obtained through traditionally natural fermentation. Inoculating fermentation of meat products for bioactive peptides is still clearly unknown. In order to select functional starter cultures for meat fermentation, some microorganisms with producing bioactive peptides are also studied, and they are mainly lactobacilli species (such as Lactobacillus sakei and Lactobacillus curvatus), Bifidobacteria and Bacillus (Moayedi et al., 2018; Stadnik & Keska, 2015). Microorganisms involved in traditional fermented meat mainly are Lactobacillus, Staphylococcus, Weissella and Tetraggenococcus, including Lactobacillus sakei and Lactobacillus curvatus (Chen et al., 2014). Previous Study has reported the improvement of fermented sausage extracts in antioxidant activity through the inoculation of Lactobacillus curvatus and Lactobacillus paracasei (Zhang et al., 2017).

In this study, two lactic acid bacteria (LAB) strains of Pediococcus pentosaceus (P. pentosaceus) SWU73571 and Lactobacillus curvatus (L. curvatus) LAB26 have proven their antioxidant, exopolysaccharide-producing and cholesterol-lowering activities (Zhan, 2015; Zhang et al., 2016). These LAB strains were used for sour meat fermentation. Furthermore, natural fermentation and inoculating fermentation for sour meat were carried out for peptides extraction, and DPPH radical scavenging activity using L5 S UV-Vis spectrophotometer (Shanghai INESA Analytical Instrument, Ltd., China) and chemiluminescence evaluation for DNA damage protection, hydroxyl radical and superoxide anion radical scavenging activities of sour meat peptides using BPCL Ultra-Weak Luminescence Analyzer (Institute of Biophysics, Chinese Academy of Sciences, China) were performed to prove the improvement of functional capacity of peptides due to the application of LAB starter cultures.

2. Materials and methods

2.1. Strains

Two strains used in this study were Pediococcus pentosaceus SWU73571 and Lactobacillus curvatus LAB26 were isolated from traditional fermented sour meat of the Dong minority in China, maintained at 4°C in a refrigerator and renewed twice for experimental use.

2.2. Preparation of starter cultures

Two strains Pediococcus pentosaceus SWU73571 and Lactobacillus curvatus LAB26 were incubated at 37°C and centrifuged, and their concentrations were regulated to 10⁷ cfu/mL by 0.85% normal saline for inoculating fermentation.

2.3. Sour meat manufacture

Forty-five percent glutinous rice, 1% minced ginger and chilli were mixed to prepare grains, and prepared double-starter culture was mixed with grains for preparing inoculated grains. Fresh pork meat was cut into dices (5 cm × 5 cm × 5 cm), cured with 8% salt, and then inoculated with inoculated grains and sealed into a pottery jar. And then, the jar was put in 15°C environment with relative humidity (RH) 96% for 180-day fermentation. Traditional product was just from a natural fermentation under the same fermented conditions without the addition of starter culture.

2.4. Peptide extraction

Sour meat peptide extraction was carried out using the method described by Escudero et al. (2012). Sour meat was trimmed to remove fat, minced and homogenized with 90 mL of 0.2 mol/L phosphate buffer (pH 7.2). The homogenate was remained at 4°C for 20 min and centrifuged at 4°C and 12000 g for 20 min. The supernatant was added with threefold volumes of 40% ethanol solution to deproteinize, remained at 4°C for 12 h, centrifuged at 4°C and 12000 g for 10 min, and filtered using 0.45 μm microporous filters (Molecular weight cut-off, 10 kD). The filtrate was concentrated on a rotary evaporator and freeze-dried to sour meat peptides powder.

2.5. Antioxidant activity of sour meat peptides

2.5.1. Measurement of DNA damage protection capacity

The measurement of DNA damage protection capacity of sour meat peptides was carried out based on the copper sulfate-phenanthroline-ascorbic acid-hydrogen peroxide-DNA (CuSO₄-Phen-Vc-H₂O₂-DNA) chemiluminescence system in accordance with the method reported by Ma et al. (1998) with a slight modification. Copper sulfate and 1,10-phenanthroline were dissolved in acetate buffer (0.1 mol/L, pH 5.2) to 7.5 × 10⁻⁵ and 5.25 × 10⁻⁴ mol/L, respectively, for CuSO₄-Phen solution, and then 3 μg/mL DNA was incubated in the CuSO₄-Phen solution. The reagents were added into the sample cell in the following order: 100 μL different concentrations (0, 1, 5, 10, 50 mg/mL) of sour meat peptides solution, 800 μL CuSO₄-Phen-DNA solution, 100 μL 4.2 × 10⁻³ mol/L Vc and 200 μL 3% H₂O₂. The luminescence intensity was tested at 20°C and 900 V every 3 s for a total test time of 540 s. The background was detected without the addition of H₂O₂.

2.5.2. Measurement of 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity

The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity was measured according to the method described by Ye et al. (2010) with a slight modification. In brief, 4 mL of 0.1 mol/L DPPH radical solution was incubated with different concentrations of sour meat peptides. The mixture system was shaken and incubated at room temperature in dark for 30 min, and then the absorbance at 517 nm was measured (A_s). There was absolute ethanol in place of the sample as a blank (A_b) and 4 mL absolute ethanol in place of 4 mL of 0.1 mol/L DPPH radical solution as a sample blank (A_sb). The radical scavenging activity was calculated according to the following equation:

$Scavengingactivity\left(\mathrm{\%}\right)=\left[A_b-\left(A_s-A_{sb}\right)\right]/A_b\times 100$

2.5.3. Measurement of hydroxyl radical scavenging activity

The hydroxyl radical scavenging activity was determined in accordance with the copper sulfate- phenanthroline-ascorbic acid-hydrogen peroxide system (Su et al., 2016). The reagents were added into the sample cell in order: 50 μL sour meat peptide solution with different concentrations (0, 0.05, 0.10, 0.50 and 1.00 μg/mL), 50 μL CuSO₄ (1 mmol/L), 50 μL 1,10-phenanthroline (1 mmol/L), 700 μL borate buffer (50 mmol/L, pH 9.0), 100 μL ascorbic acid (1 mmol/L) and 50 μL H₂O₂ (0.15%). The luminescence intensity was tested at 20°C and 900 V every 3 s for a total test time of 399 s. The background was detected without the addition of H₂O₂.

2.5.4. Measurement of superoxide anion radical scavenging activity

Radical scavenging activity of sour meat peptides was performed based on the pyrogallol-luminol chemiluminescence system reported by Guo and Wang (1989). Luminol was mixed with 0.05 mol/L sodium hydroxide to a concentration of 0.05 mol/L stock solution and was then diluted to a concentration of 1 mmol/L working solution with double-distilled water before the use. Pyrogallol was dissolved in 1 mmol/L hydrogen chloride solution to a concentration of 0.01 mol/L solution and was then diluted to a concentration of 6.25 × 10⁻⁴ mol/L before the use. The 1 mmol/L luminol and 0.05 mol/L carbonate buffer (pH 10.2, containing 0.1 mmol/L ethylene diamine tetraacetic acid) were mixed by a ratio of 2:1 to luminol solution. A series of concentrations (0, 1, 5, 10 and 50 mg/mL) of 10 μL sour meat peptide solution, 50 μL pyrogallol (6.25 × 10⁻⁴ mol/L) and 940 μL luminol solution were added into the sample cell in order. Luminescence intensity was tested at 20°C and 900 V every 2 s for a total test time of 300 s. The background was detected without the addition of pyrogallol.

2.6. Statistical analysis

All data were conducted with the Analysis of Variance (ANOVA) using SPSS 16.0 software (version 16.0, SPSS Inc., USA). All experimental results were presented by mean ± standard deviation. Probability values (p = .05) were considered significant to indicate differences. The Duncan’s multiple comparison (p = .05) was used to indicate significant difference.

3. Results

3.1. DNA damage protection

In CuSO₄-Phen-Vc-H₂O₂-DNA system, two peaks appeared on the kinetic curves of chemiluminescence (Figure 1). The first peak was generated because hydroxyl radicals from Fenton reaction attacked Phen, and the second peak was generated due to DNA damage caused by hydroxyl radicals, where supercoiled plasmid DNA exposed to hydroxyl radicals derived from the Fenton’s reaction could result in the formation of open circular DNA. When different concentrations of sour meat peptides ranging from 1 to 50 mg/mL were added into the system, a delayed and inhibited light emission was observed, and the luminous intensity decreased in the presence of peptides from both traditional and inoculating fermentation, indicating inhibition effect of sour meat peptides on DNA damage. Sour meat peptides from inoculating fermentation showed a significant increase in the inhibition of DNA damage at the same concentration of peptides when compared to traditional fermentation (P < 0.05). At 10 mg/mL, the inhibition rate of DNA damage to sour meat peptides from inoculating fermentation (78.19%) was significantly higher than that from traditional fermentation (51.47%) (P < 0.05). There was a significant difference in the half-inhibition concentration (IC₅₀) of sour meat peptides between traditional fermentation (9.20 mg/mL) and inoculating fermentation (2.11 mg/mL) (data not shown). When the peptide concentration was up to 50 mg/mL, the DNA damage inhibition of sour meat peptides from inoculating fermentation was up to 89.89% while that from traditional fermentation was also over 70%, just up to 75.45%, indicating more effective inhibition of DNA damage.

Figure 1. Inhibition of different concentrations of sour meat peptides to DNA damage. All measurements are expressed as the mean ± standard deviation. (n = 3). Different lowercase letters (a, b, c and d) differ significantly (P < 0.05) at the same fermentation, and different uppercase (A and B) differ significantly (P < 0.05) between traditional fermentation and inoculating fermentation.

Figura 1. Inhibición del daño ocasionado al ADN ante diferentes concentraciones de péptidos de carne agria. Todas las mediciones se expresan como la media ± desviación estándar (n = 3). Las distintas letras minúsculas (a, b, c y d) indican valores significativamente diferentes (P < 0.05) en la misma fermentación y las distintas letras mayúsculas (A y B) indican valores significativamente diferentes (P < 0.05) entre la fermentación tradicional y la fermentación por inoculación

4. 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity

To evaluate the effect of sour meat peptides from traditional and inoculating fermentation on antioxidant activity, the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity was measured. The results shown in Figure 2 indicated that the DPPH radical scavenging activities of sour meat peptides from traditional fermentation and inoculating fermentation increased with the increase of peptide concentrations ranging from 1 to 5 mg/mL. The DPPH radical scavenging activity of butylated hydroxyltoluene (BHT) was significantly the highest, followed by that from inoculating fermentation and that from traditional fermentation (P < 0.05). At 5 mg/mL, the DPPH radical scavenging activity (54.74%) of sour meat peptides from inoculating fermentation was significantly higher than scavenging activity (43.79%) of peptides from traditional fermentation (P < 0.05). The IC₅₀ value of sour meat peptides from inoculating fermentation was 4.23 mg/mL, indicating higher scavenging activity than that (5.74 mg/mL) from traditional fermentation (data not shown).

Figure 2. Scavenging activities of different concentrations of sour meat peptides to 1,1-diphenyl-2-picrylhydrazyl radical. All measurements are expressed as the mean ± standard deviation. (n = 3). Different lowercase letters (a, b, c, d and e) differ significantly (P < 0.05) at the same fermentation, and different uppercase (A, B and C) differ significantly (P < 0.05) between traditional fermentation and inoculating fermentation.

Figura 2. Actividades de eliminación del radical 1,1-difenil-2-picrilhidrazilo ante diferentes concentraciones de péptidos de carne agria. Todas las mediciones se expresan como la media ± desviación estándar (n = 3). Las distintas letras minúsculas (a, b, c, d y e) indican valores significativamente diferentes (P < 0.05) en la misma fermentación y las distintas letras mayúsculas (A, B y C) indican valores significativamente diferentes (P < 0.05) entre la fermentación tradicional y la fermentación por inoculación

4.1. Hydroxyl radical scavenging activity

As shown in Figure 3, all of the kinetics from the reactions reached the maximal luminescence before 100 s and then stabilized. Sour meat peptides from both traditional and inoculating fermentation indicated the scavenging activity on hydroxyl radicals in a dose-dependent manner with a concentration range of 0.05–1.00 mg/mL. With the peptide concentration increasing, the hydroxyl radical scavenging activities of all sour meat peptides gradually increased. The scavenging activity of peptides from inoculating fermentation was significantly higher than that of traditional fermentation at the same concentration (P < 0.05). At 0.10 mg/mL, hydroxyl radical scavenging activity of sour meat peptides from inoculating fermentation reached 51.66%, while that from traditional fermentation just reached 44.96% in the system. When sour meat peptide concentration reached 1 mg/mL, hydroxyl radical scavenging activities of sour meat peptides from traditional fermentation and inoculating fermentation were 76.02% and 85.61%, respectively, indicating effective hydroxyl radical scavenging capacity. The IC₅₀ values of sour meat peptides from traditional fermentation and inoculating fermentation were 0.247 mg/mL and 0.097 mg/mL, respectively (data not shown).

Figure 3. Scavenging activities of different concentrations of sour meat peptides to hydroxyl radical. All measurements are expressed as the mean ± standard deviation. (n = 3). Different lowercase letters (a, b, c and d) differ significantly (P < 0.05) at the same fermentation, and different uppercase (A and B) differ significantly (P < 0.05) between traditional fermentation and inoculating fermentation.

Figura 3. Actividades de eliminación del radical hidroxilo ante diferentes concentraciones de péptidos de carne agria. Todas las mediciones se expresan como la media ± desviación estándar (n = 3). Las distintas letras minúsculas (a, b, c y d) indican valores significativamente diferentes (P < 0.05) en la misma fermentación y las distintas letras mayúsculas (A y B) indican valores significativamente diferentes (P < 0.05) entre la fermentación tradicional y la fermentación por inoculación

4.2. Superoxide anion radical scavenging activity

The superoxide anion radical scavenging activities of sour meat peptides from traditional fermentation and inoculating fermentation are shown in Figure 4. Like the other antioxidant activities, the superoxide anion radical scavenging activities of peptides from both traditional fermentation and inoculating fermentation also exhibited a dose-dependent effect within a concentration range of 1–50 mg/mL. Sour meat peptides from inoculating fermentation exhibited higher scavenging activity of superoxide anion radicals when compared to that of traditional fermentation, but no significant difference was found between them at a concentration of 5 mg/mL sour meat peptides (P > 0.05). At 10 mg/mL, superoxide anion radical scavenging activity of sour meat peptides from inoculating fermentation reached 51.45%, but that from traditional fermentation just reached 19.81%. When sour meat peptide concentration reached 50 mg/mL, the scavenging activities from both traditional fermentation and inoculating fermentation were 48.55% and 68.89%, respectively. Sour meat peptides could scavenge superoxide anion radicals effectively with the IC₅₀ value of 52.99 mg/mL from traditional fermentation and with the IC₅₀ value of 9.85 mg/mL from inoculating fermentation (data not shown).

Figure 4. Scavenging activities of different concentrations of sour meat peptides to superoxide anion radical. All measurements are expressed as the mean ± standard deviation. (n = 3). Different lowercase letters (a, b, c and d) differ significantly (P < 0.05) at the same fermentation, and different uppercase (A and B) differ significantly (P < 0.05) between traditional fermentation and inoculating fermentation.

Figura 4. Actividades de eliminación del radical anión superóxido ante diferentes concentraciones de péptidos aislados de carne agria. Todas las mediciones se expresan como la media ± desviación estándar (n = 3). Las distintas letras minúsculas (a, b, c y d) indican valores significativamente diferentes (P < 0.05) en la misma fermentación y las distintas letras mayúsculas (A y B) indican valores significativamente diferentes (P < 0.05) entre la fermentación tradicional y la fermentación por inoculación

5. Discussion

During meat fermentation, proteolysis of meat proteins occurs due to microbial enzymes and endogenous enzymes and enhances the production of bioactive peptides. Antioxidant peptides derived from different sources exhibit varying scavenging capacities in free radicals. Antioxidant capacity of a peptide depends on its molecular size, amino acid composition and chemical properties (Cheung et al., 2012; Farvin et al., 2010; Sampath Kumar et al., 2011). Few studies have reported antioxidant activity of fermented meat peptides from either natural traditional fermentation or inoculating fermentation (Wei et al., 2017; Ye et al., 2010), but much attention was paid to bioactive peptides from dry-cured meat products such as dry-cured ham and dry-cured sausage (Gallego et al., 2018a; Xing et al., 2018). At the end of meat fermentation (180 days), the total bacterial counts of natural fermentation and fermentation with inoculum were 6.53 log cfu/g and 7.94 log cfu/g, respectively (data not shown). Sour meat peptides showed dose-dependent effects on DNA damage protection and free radicals with increasing mass concentration of peptides, and those peptides differed in scavenging capacities to different free radicals, which were similar to Zheng et al. (2016). The study of free radical-induced DNA damage was performed to evaluate the inhibitory effect of sour meat peptides and to compare the difference between traditional fermentation and inoculating fermentation. When compared to sour meat peptides from traditional fermentation, peptides from inoculating fermentation exhibited significantly higher inhibitory effects on DNA damage, indicating the LAB inoculating fermentation could improve the inhibitory effect of sour meat peptides on DNA damage induced by hydroxyl radicals. DNA protective effect of an antioxidant peptide from hoki frame protein hydrolysate (Glu-Ser-Thr-Val-Pro-Glu-Arg-Thr-His- Pro-Ala-Cys-Pro-Asp-Phe-Asn) on pBR 322 plasmid DNA was investigated at various concentrations (2.78–55.5 μmol/L) that demonstrated the protective effect on hydroxyl radical-induced DNA damage (Kim et al., 2007). In a similar study, the 1–5 kDa peptide fractions from Mytilus edulis hydrolysates by gastrointestinal digestion enhanced the protective effect on hydroxyl radical-induced pBR 322 plasmid DNA damage in a dose-dependent manner (Park et al., 2014).

The DPPH radical, a stable nitrogen radical, has been widely used to evaluate radical scavenging capacities of natural antioxidants derived from different sources. Sour meat peptides exhibited the ability to scavenge DPPH radicals with the IC₅₀ of 5.74 mg/mL from traditional fermentation and with the IC₅₀ of 4.23 mg/mL from inoculating fermentation, indicating that LAB inoculating fermentation could enhance DPPH radical scavenging capacity of sour meat peptides. A κ-casein derived peptide from the milk fermented with Lactobacillus delbrueckii subsp. bulgaricus displayed DPPH radical scavenging activity (Kudoh et al., 2001). Proteases produced by Bacillus subtilis are reported to hydrolyze rapeseed proteins, leading to the production of amino acids and peptides during fermentation (He et al., 2012). Hydroxyl radical as an extremely reactive radical could induce DNA damage when supercoiled plasmid DNA was exposed to hydroxyl radicals (Abbas et al., 2014). The removal of hydroxyl radicals is one of the most effective defense mechanisms of a living body against various diseases (Sheih et al., 2009). It was reported that the IC₅₀ values of DPPH radical, hydroxyl radicals and superoxide anions of bile salt binding peptides were 2.50, 2.04 and 2.79 mg/mL, respectively (Wei et al., 2017); however, the IC₅₀ of hydroxyl radical scavenging activity of bile salt binding peptides was obviously lower than those from both natural traditional fermentation (0.247 mg/mL) and inoculating fermentation (0.097 mg/mL) in our study. Superoxide radical derived from mitochondrial electron transport systems is usually considered as an initial radical, further leading other cell-damage radicals, such as hydroxyl radical, hydrogen peroxide or singlet oxygen (Jha et al., 2016). Some peptides can protect cells against the toxic effect of superoxide anions through reacting with those radicals (Ajibola et al., 2011). Sour meat peptides exhibited superoxide anion radical scavenging activities with the IC₅₀ of 52.99 mg/mL from traditional fermentation and with the IC₅₀ of 9.85 mg/mL from inoculating fermentation. This illustrated that sour meat peptide from LAB inoculating fermentation exhibited higher superoxide anion radical scavenging activity than that from traditional fermentation. Some species of lactic acid bacteria could enhance the proteolysis of meat proteins and the formation of bioactive peptides. For example, the degree of proteolysis depending on the strain used in cheese is directly related to antioxidant capacity (Gupta et al., 2009). Peptides with molecular weight less than 5000 exhibit well-scavenging effect on free radicals, and peptides with long peptide chain exhibit low scavenging efficiency of free radicals (Shi et al., 2014). The mixture starter of Pediococcus pentosaceus SWU73571 and Lactobacillus curvatus LAB26 promoted hydrolysis of proteins and the formation of short-chain peptides, and further improved DNA damage protection and antioxidant activities of sour meat peptides, which was in agreement with findings in yogurt fermented with Lactobacillus strains reported by Sah et al. (2014).

6. Conclusion

In this study, sour meat peptides from both traditional fermentation and inoculating fermentation exhibited DNA damage protection and free radical scavenging activities against 1,1-diphenyl-2- picrylhydrazyl radical, hydroxyl radicals and superoxide anions in a dose-dependent manner, and showed the strongest inhibition of hydroxyl radicals and the weakest inhibition of superoxide anion radicals. Compared to sour meat peptides from traditional fermentation, those from LAB inoculating fermentation had higher inhibition of DNA damage and free radical scavenging activities. The results clearly indicated that sour meat peptides derived from co-fermentation with Pediococcus pentosaceus SWU73571 and Lactobacillus curvatus LAB26 could enhance the inhibition of DNA damage and antioxidant activities, revealing good microbial sources as a natural starter for the improvement of antioxidant capacity of fermented meat products, natural antioxidants and therapeutic agent aiming at treating oxidative damage-derived diseases.

Disclosure statement

No conflict of interest was reported by the authors.

Additional information

Funding

This study was funded by the National Natural Science Foundation of China program [31260379 and 31960485].