Effect of the addition of tomato paste on the nutritional and sensory properties of mortadella

Meat Science 93 (2013) 213–219

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Effect of the addition of tomato paste on the nutritional and sensory properties of mortadella G. Doménech-Asensi, F.J. García-Alonso, E. Martínez, M. Santaella, G. Martín-Pozuelo, S. Bravo, M.J. Periago ⁎ Department of Food Science and Technology (Food Science and Nutrition), Faculty of Veterinary Science, Campus de Espinardo, 30.071-Murcia, Spain

a r t i c l e

i n f o

Article history: Received 3 April 2012 Received in revised form 2 August 2012 Accepted 27 August 2012 Keywords: Tomato Lycopene Mortadella Lipid oxidation Nutritional value Sensory properties

a b s t r a c t The aim of this study was to evaluate the effect of the addition of tomato paste (TP) to sausage mortadella in order to improve the nutritional properties and reduce the lipid oxidation associated with the content of lycopene. First, three different mortadellas without colourant were made with 2, 6 and 10% of TP, to optimise technologically the amount of this ingredient. Then, commercial product was compared with 10% of TP mortadella; both products were made with natural colourant. After a proximate analysis only total protein decreased due to the addition of TP. Lycopene content in mortadella and the total antioxidant activity were proportional to the amount of TP added. The presence of TP provided stability during meat grinding, cooking and storage of mortadella by reducing the lipid oxidation. In addition, TP provided yellowness and softness; however, when TP was added together with red colourant, the redness remained constant in the mortadella without effects on the consumer overall acceptance. © 2012 Elsevier Ltd. All rights reserved.

1. Introduction Nowadays, consumers demand natural and healthy food products, including meat products, with better nutritional properties. To design healthy products, the food industry modifies the formulations and common ingredients of the meat products including additives. In this sense, some synthetic colourants are considered responsible for allergenic or adverse reactions (Larsen, 2008), and EU regulations on their use in foodstuffs have been taken into account (Regulation, 1333/2008). Therefore, consumers' preference for naturally derived colourants is associated with their image of being healthy and of good quality. However, the list of natural colours is small, and only few are available in sufficient quantities to be useful to food manufacturers. Carotenoids are one of the most important natural pigments, providing attractive colour in vegetables and several animal foods. In addition, carotenoids are recognised as excellent antioxidants and as beneficial compounds for human health due to their pro-vitamin-A activity and their ability to quench oxygen and peroxyl radicals (Maiani et al., 2009). Thus, an inverse association between the consumption of carotenoidrich products and the risk of certain forms of chronic diseases including several types of cancer and cardiovascular disease has been described (Maiani et al., 2009). Lycopene is the most abundant carotenoid in the ripened tomato, accounting for approximately 80–90% of the total pigments.

Abbreviations: TP, tomato paste; MDA, malondialdehyde; TAA, in vitro total antioxidant activity; ABTS, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid); TEAC, Trolox Equivalent Antioxidant Capacity assay. ⁎ Corresponding author. Tel.: +34 868884793; fax: +34 868 884147. E-mail address: [email protected] (M.J. Periago). 0309-1740/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.meatsci.2012.08.021

It mainly accumulates in the final period of ripening, and it is higher in processed products (e.g. tomato juice, tomato paste (TP) etc.) than in raw tomatoes (Giovanelli, Lavelli, Peri, & Nobili, 1999). Tomatoes are the most highly consumed vegetable in Spain, and they are an important source of these antioxidants in the Spanish diet due to their content of different bioactive compounds such as carotenoids, phenolic compounds and vitamins (García-Valverde, Navarro-González, García-Alonso, & Periago, 2011; Periago et al., 2009). In a recent study on dietary sources of vitamin C, vitamin E and specific carotenoids in Spain, tomatoes ranked first as a source of lycopene (71.6%), second as a source of vitamin C (12.0%) and β-carotene (17.2%) and third as a source of vitamin E (6.0%) (Garcia-Closas et al., 2004). Moreover, tomato consumption has been considered beneficial in reducing the risk of prostate cancer (Gann et al., 1999; Weisburger, 1998) and cardiovascular disease (Mordente et al., 2011) mainly due to the content of lycopene (Krinsky, 1989). More recent studies have revealed the radiation-protective activity of lycopene (Andic, Garipagaoglu, Yurdakonar, Tuncel, & Kucuk, 2009; Srinivasan et al., 2007; Srinivasan, Devipriya, Kalpana, & Menon, 2009) and the protective activity against aggressive drugs such as cyclosporine, adriamycin and doxorubicin (Atessahin, Ceribasi, & Yilmaz, 2007; Ferreira et al., 2007; Jamshidzadeh, Baghban, Azarpira, Bardbori, & Niknahad, 2008; Yilmaz, Atessahin, Sahna, Karahan, & Ozer, 2006). Considering the colour properties of tomato products and the beneficial effects on human health, their addition to meat products could reduce the necessity of synthetic colourants and yield products with a better nutritional profile due to the increase of plant-derived bioactive compounds (lycopene and phenolic compounds). Indeed, these compounds could exert an antioxidant effect on meat products, avoiding the oxidation processes of the fat and increasing the product's shelf

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life. Hence, many studies have suggested using TP, tomato powder, tomato peels and lycopene in raw meat and meat products such as beef patties (Candogan, 2002; Sanchez-Escalante, Torrescano, Djenane, Beltrán, & Roncalés, 2003), minced meat (Østerlie & Lerfall, 2005), hamburgers (García, Calvo, & Selgas, 2009; Selgas, Garcia, & Calvo, 2009), fermented sausages (Calvo et al., 2008), fresh sausages (Mercadante, Capitani, Decker, & Castro, 2010) and frankfurters (Deda, Bloukas, & Fista, 2007; Eyiler & Oztan, 2011). In general, these studies have shown that the presence of lycopene from different tomato matrices leads to a better colour in the meat products, improved nutritional quality, reduced lipid oxidation and increased stability during the shelf-life period, all while retaining overall acceptability. In different cultures, meat and meat products in the diet are presented in various ways and produced using different technological processes. However, their consumption has been associated with an increased risk of coronary heart disease and hypertension (Ashaye & Gaziano, 2011); hence, their presence in the human diet must meet nutritional guidelines. Nowadays, numerous studies have sought to demonstrate the possibility of changing the image of meat and meat products from the traditional image to one of healthy living thanks to the addition of vegetable extracts and fibres, the elimination of fats and the reduction of additives. Mortadella is a sausage of Italian origin, made of finely hashed or ground pork meat, which incorporates at least 15% small cubes of delicately flavoured pork fat. Mortadella is also enhanced with plant-food ingredients such as pepper, garlic and olives. It is a semi-cooked meat product with a commercial shelf life of 60 days at 4 °C. Considering that the primary quality parameters of meat and meat products for consumers are colour, appearance and texture, any modification of the ingredients of mortadella could change its properties and affect consumer acceptance. The aim of this study has been to evaluate the effects of the addition of TP as an ingredient in mortadella in order to improve the quality of this cooked meat product by increasing the nutritional properties and reducing the lipid oxidation process associated with the content of lycopene.

2. Materials and methods 2.1. Experimental design To carry out this study, different mortadellas were designed and produced in two consecutive phases. In the first phase, three new mortadella products were developed (group 1) with different concentrations of TP (2%, 6% and 10%). Mortadella samples were elaborated with the addition of mixture of additives but not antioxidant neither colourants, in order to determine the effect of the addition of TP on the colour parameters and to optimise technologically the amount of added TP. In a second phase, two products were developed (group 2): regular mortadella (R) and mortadella with 10% of TP (R + 10%). These products were formulated with similar additives but this time including a natural colourant (E-120), according to the standard commercial formulation for these sausages. The five experimental samples of mortadella (2%, 6%, 10%, R and R + 10%) were manufactured by the company Embutidos Campos de San Juan (Campo de San Juan, Moratalla, Murcia, Spain). TP (14–16° Brix) was provided by Conservas Vegetales de Extremadura S.A. (CONESA, Villafranca del Guadiana, Badajoz, Spain). All mortadella samples were analysed to determine the nutritional composition, lycopene content, in vitro total antioxidant activity (TAA), lipid oxidation expressed as malondialdehyde concentration (MDA) and instrumental parameters of texture and colour. All the analyses were conducted immediately after manufacture, and the stability of lycopene, TAA, MDA and colour parameters was also evaluated during the shelf-life period (at 1 and 2 months of storage). In addition, the overall acceptance of mortadella with 10% TP was determined in comparison with the regular product. Three replications were performed for each analysis.

2.2. Production of mortadella Raw meat (38.5 kg of first-class lean pork and 38.5 kg of secondclass lean pork) was minced and then mixed with 19 l of water, forming a stable matrix to which other commercial ingredients (mix of spices and additives) were added to make the mortadella according to the experimental groups. The group 1 mix (without colourants) contained salt, soy protein, potato starch, skimmed milk, spices, dextrose, sodium polyphosphate (E-452i), monosodium glutamate (E-621), trisodium citrate (E-331iii), sodium ascorbate (E-301) and sodium nitrate (E-250). The group 2 mix (with colourant) contained salt, dextrose, soya protein, spices, corn dextrin, sodium polyphosphate (E-452i), monosodium glutamate (E-621), trisodium citrate (E-331iii), sodium ascorbate (E-301), sodium nitrate (E-250) and cochineal (E-120) as a dye. TP was added as an ingredient in the formulation using the following concentrations: 2%, 6% and 10% in group 1 and 10% in one product of group 2. All ingredients were mixed under pressure for 20 min, and the mixture was then stuffed into a synthetic casing. Samples were heat processed at 100% RH until they reached an internal temperature of 72 °C. The mortadella samples were then rinsed for cooling with cooled water and stored at 4 °C for 60 days. The two groups were manufactured at different times, according to the two phases described above in the Experimental design section. The mixes added during manufacture were also different, because in group 1, samples were made without colourant, and the commercially available product differed slightly from the mix used in the mortadella of group 2 (mix with cochineal).

2.3. Nutritional composition The proximate composition of the mortadella samples was determined according to the AOAC standard methods (2011). Moisture was determined by desiccation until constant weight, total nitrogen and protein using the micro-Kjeldahl method, total fat by the Soxhlet method and ash by incineration of the samples at 525 °C for 24 h. Total carbohydrates were not determined due to their low expected presence in mortadella. 2.4. Lycopene analysis Lycopene extraction and quantification were carried out according to the method described by Sharma and Le Maguer (1996). One gram of mortadella was weighed into a 125-ml flask wrapped with aluminium foil to exclude light. Next, 50 ml of a mixture of hexane–acetone– ethanol (2:1:1) was added to the flask to solubilise the carotenoids. Samples were shaken for 30 min, and then 10 ml of distilled water was added. The solution was left to separate into distinct polar and non-polar (containing lycopene) layers. Lycopene concentration was determined by molecular absorption spectrophotometry at 472 nm, and the results were expressed in mg/100 g using the molar extinction coefficient of lycopene in hexane (3450). Three measures were taken for each sample, one within the first week of manufacture and the other two at 1 and 2 months during the shelf-life storage at 4 °C. 2.5. Colour analysis Colour measurements, including L* (lightness), a* (redness), and b* (yellowness) of the samples, were performed with a Konica Minolta R-400 colorimeter (Minolta Co., Osaka, Japan). Lab* values were taken from the surface of each mortadella sample calculating the hue angle and chroma metric. Three measures were taken for each sample, one within the first week of manufacture and the other two at 1 and 2 months during the shelf-life storage at 4 °C. Total colour difference during storage was determined by Delta E, for each mortadella sample.

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2.6. Lipid oxidation measurements (TBARS) The extent of oxidation was determined through the concentration of thiobarbituric acid reactive species (TBARS) (Tarladgis, Pearson, & Dugan, 1964), and the results were expressed in mm of malondialdehyde (MDA) in 100 g of product. Three measures were taken for each sample, one within the first week of manufacture and the other two at 1 and 2 months of storage at 4 °C. Ten grams of mortadella was homogenised with 50 ml of distilled water and 1 g of antioxidant (BHT) for 5 min in Ultra-Turrax (Ika-Werke®, Germany). Then, the homogenised mixture was carried to a Kjeldahl tube with 46.5 ml and acidified with 2.5 ml of clorhidric acid 4 N. Five drops of silicon and a few glass pearls were added. The samples were distilled for 4 min with a Kjeltec 2100 distillation unit (Foss®, Sweden). After this, 5 ml of each distillate was mixed with 5 ml of 2-tibarbituric acid 0.02 M and heated in a boiling-water bath at 100 °C for 35 min. After cooling to room temperature, the absorbance was measured using an Evolution 300 spectrophotometer (Thermo Scientific®, England) at 532 nm. The concentration of MDA was calculated according to the molar extinction coefficient between the reaction of TBA and MDA and expressed as mmol/100 g of sample.

colour, flavour, taste, texture, chewiness, presence of white areas and size of white areas. The intensity was determined using a 10-point scale (1 being the lowest and 10 the highest). Panellists were also inquired on acceptance of flavour and taste and overall acceptance using qualitative punctuation of “I dislike it very much”, “I dislike it”, “Indifferent”, “I like it” and “I like it very much”. The sensory evaluation was performed on the twentieth day of storage. Unsalted crackers and water were offered to the panellists between sample testing periods. 2.10. Statistical analysis Data were analysed using the statistical software package SPSS 15.0. Descriptive analysis was performed first in order to determine the arithmetic means and standard deviations of the three determinations of each parameter. Then, analyses of variance (ANOVA) were performed with confidence intervals of 95%, 99% and 99.9% followed by the post-hoc Tukey test to establish statistical differences between samples within each group. Finally, a Pearson's correlation coefficient test was performed to analyse the relationships between all analysed variables.

2.7. Antioxidant activity (ABTS method)

3. Results and discussion

TAA was measured using the Trolox Equivalent Antioxidant Capacity (TEAC) method described by Miller, Samson, Candeias, Bramley, and Rice-Evans (1996). The assay is based on the reduction of the radical cation of ABTS, which is generated by filtering an ABTS solution through manganese dioxide powder. To obtain the hydrophilic and lipophilic antioxidants of the samples, the procedure described by Prior et al. (2003) was used. Two grams of sample was homogenised twice with 10 ml of hexane, mixed for 15 min and centrifuged at 3500 rpm/15 min. Hexane was kept and then evaporated in a rotary evaporator. The extracts of the samples were dissolved with 10 ml of a solution of acetone:water:acetic acid (70:29.5:0.5) and vortexed for 30 s. Samples were centrifuged at 3500 rpm for 15 min, the supernatant was transferred to a volumetric flask and phosphate buffer was added up to 25 ml. Next, 100 μl of the sample was mixed with 1 ml of the ABTS solution, and the absorbance was measured at 734 nm after 2 min of the reaction. The antioxidant activity of the samples was calculated by determining the decrease in absorbance at 734 nm. Trolox was used as the standard, and results are expressed as mmol Trolox equivalents/kg of mortadella. Three measures were taken for each sample, one within the first week of manufacture and the other two at 1 and 2 months of the storage at 4 °C.

3.1. Chemical, texture and colour parameters of mortadella

2.8. Textural analysis Texture was determined by a texturometer (QTS Texture analyser CNS FARNELL (R)) equipped with a 25-kg load cell. This test was performed using three portions for each sample with 3 cm 2 of surface area and 2.5 cm of thickness at room temperature. Portions of 3 cm 2 were taken from the middle of the 2.5 cm-thick mortadella slides which were compressed to 50% of their original height. Five parameters were analysed: springiness (cm) (i.e. ability of the sample to recover its original form after the deforming force was removed), work of shearing (Ns) (i.e. work needed to move the blade through the sample), hardness (N) (i.e. maximum force required to compress the sample), chewiness (Ncm) (i.e. work required to masticate the sample for swallowing), and cohesiveness (ratio) (i.e. the extent to which the sample could be deformed prior to rupture). 2.9. Sensory analysis Sensory analysis of both mortadella samples of group 2 (regular and regular + 10% of TP) was performed with 50 members from the University of Murcia (staff and students) aged 20 to 55. The hedonic scale was used to evaluate the intensity and the acceptability of

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Table 1 shows the results for nutritional composition (protein, lipid, ash and moisture), lycopene content, lipid oxidation and antioxidant activity in different mortadella products and the effect of the addition of TP. Significant differences are shown among samples of the same group. The main nutritional components of mortadella are proteins and fats. The main source of protein is meat, so the protein levels were inversely proportional to TP, showing a significant decrease according to the amount of TP in both groups from 18.01 to 12.54% and 12.94 to 10.43%, respectively. However, the protein content was higher in the group 1 samples due to the addition of milk proteins, which were added as an additive. On the contrary, total fat, ash and moisture contents were barely modified with the addition of TP, remaining constant among the mortadella samples of the same group. As expected, the lycopene content of mortadella increased from 0.21 to 1.99 mg/100 g according to the percentage of TP in the formulation (Table 1). In group 2, mortadella without TP, no lycopene was detected, whereas the addition of 10% TP provided a mean content of 1.65 mg/100 g. The addition of TP at different concentrations (2, 6 and 10%) did not negatively affect technological processing, so regular mortadella with 10% TP was suitable as a meat product with the added benefit of the presence of lycopene. The content of lycopene in mortadella was higher than that reported by Calvo et al. (2008) in dry sausages after the addition of tomato peel. The lycopene in our mortadella samples is expected to be more available in the large intestine, since it is from TP in which the grinding and heat processing leads to a softening of the plant cell wall and the disruption of lycopene–protein complexes. Furthermore, the presence in meat products, together with the fat, has a positive effect, which facilitates the formation of micelles and the uptake of lycopene in the intestinal cells. Related to lipid oxidation, MDA levels were higher in group 2 (Table 1) without significant differences between mortadella samples. Significant differences were not found in group 1 either. To clarify these results, it has been noted that the samples were manufactured at two different times, using different ingredients. Hence, the variability will be related to the differences in the raw materials and the conditions during processing. Despite this variability, MDA values show that the addition of lycopene from TP did not exert a significant effect in preventing the rapid oxidative changes that occur in the initial steps of meat-product manufacture (i.e. during the grinding of raw materials and the cooking process). The compounds that could have reacted with the TBA during the rapid oxidation of the meat products resulted from the breakdown

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Table 1 Proximate composition, lycopene content, lipid oxidation and antioxidant activity of mortadella samples (different letters within each group show significant differences at p b 0.05), (nd: not detected). Parameters

Samples Group 1

Protein (%) Lipid (%) Ash (%) Moisture (%) Lycopene (mg/100 g) MDA (mm/100 g) AA (mm eq. Trolox/kg)

Group 2

2%

6%

10%

R + 10%

R

18.01 ± 0.96a 28.39 ± 0.55a 3.36 ± 0.35a 64.00 ± 0.24a 0.21 ± 0.004c 37.83 ± 1.34a 0.78 ± 0.006b

14.18 ± 0.49b 28.20 ± 0.55a 3.31 ± 0.13a 65.04 ± 0.71a 0.63 ± 0.001b 35.36 ± 2.25a 0.95 ± 0.01a

12.54 ± 0.68b 27.90 ± 1.89a 3.20 ± 0.08a 65.29 ± 1.37a 1.99 ± 0.04a 31.77 ± 0.45a 0.95 ± 0.01a

10.43 ± 0.31b 26.33 ± 1.56a 2.67 ± 0.07a 65.38 ± 1.08a 1.65 ± 0.02a 43.95 ± 2.41a 0.99 ± 0.01a

12.93 ± 0.56a 24.87 ± 0.21a 2.97 ± 0.09a 63.96 ± 0.11a nd 41.26 ± 1.53a 0.74 ± 0.06b

of phospholipids and developed in a few hours (Østerlie & Lerfall, 2005), showing similar amounts in all samples. To determine the effect of the addition of TP on the functional properties of mortadella, TAA was also evaluated in all samples. TAA ranged from values around 0.75 to 1.00 mM eq. Trolox/kg (Table 1), showing significant differences according to the concentration of TP. In this way, it was determined that TAA was directly related with the presence of TP and lycopene, showing a positive correlation (Pearson's correlation coefficient, r = 0.816, p b 0.01). No significant differences were found in the textural parameters of the group 1 mortadella samples (Table 2); thus, it can be stated that the addition of TP does not affect texture. Indeed, the samples of this group showed values higher than those of group 2. This could be related to the presence of potato starch and skimmed milk, which provide consistency to the final product due to the gelatinisation of starch and the coagulation of protein during cooking. On the contrary, the group 2 samples showed significant differences only for hardness, decreasing after the addition of TP. Calvo et al. (2008) and García et al. (2009) reported an effect of tomato peel addition, as a source of lycopene, on the textural properties of dry fermented sausage and beef hamburgers. The tomato peel led to increased hardness, however, after analysing the texture by sensorial tests, panellists did not detect the instrumental differences in the hardness between experimental and control samples. The effect of tomato peel in the meat products increased the lycopene content; but, a negative effect was noted in overall acceptance. This could have been associated with the increased hardness due to the dietary fibre content (mainly cellulose and lignin) in tomato peel (González-Navarro, García-Valverde, García-Alonso, & Periago, 2011). The addition of TP had a slight effect on the colour attributes in both mortadella groups; no significant effect on lightness (L*), redness (a*) or saturation index (chroma metric); and a significant (pb 0.05) effect (increase) on yellowness (b*) and hue angle (Table 3). In all samples of mortadella with TP, the hue angle value, measured immediately after manufacturing, showed mean values ranging from 17.40 to 26.41, indicating an orange colour. However, the R+10% sample showed a lower hue angle than the 10% sample of group 1; due to the addition of the natural red colourant cochineal, which led to higher redness (a*) values and lower yellowness (b*) values in samples of group 2 compared with samples of group 1. In general, the addition of lycopene to meat products,

through the addition of tomato peel and TP, led to changes in the typical red colour of the meat products by increasing the yellow colour and providing an orange tone (Calvo et al., 2008; Deda et al., 2007; Østerlie & Lerfall, 2005). The effect of lycopene on frankfurters has also been considered beneficial for the reduction of the amount of added nitrites (around 33%), yielding highly desirable products from a diet/health standpoint (Deda et al., 2007). 3.2. Evaluation of lycopene levels, lipid oxidation, antioxidant activity and colour parameters during shelf-life storage Fig. 1 shows means and standard deviations of lycopene content across time in all products. Lycopene levels were rather constant across time, with similar values in the 2% and 6% samples and with slight changes (not significant) during the shelf-life period in samples with the 10% concentration of TP. Calvo et al. (2008) studied lycopene levels in dry fermented sausages enriched with lycopene from tomato peel by adding different concentrations of tomato peel (0.6%, 0.9% and 1.2%). The lycopene levels found were 0.65, 0.82 and 1.05 mg/100 g of dried weight, respectively. After 21 days of maturing, lycopene levels decreased to 0.44, 0.64 and 0.96 mg /100 g dried weight, respectively. These changes are likely related to the oxidation reactions of lycopene with free radicals and other compounds created during sausage maturing and fermentation. In our study, mortadella samples were cooked at low temperatures and then refrigerated. Thus, the oxidative phenomenon of lycopene during manufacture and storage were insignificant, remaining constant during the shelf-life storage period of the product. During the product's shelf life, the fat oxidation of mortadella samples that occurs during long-term storage was evaluated. Lipid oxidation is a chemical phenomenon that cannot be avoided during the storage of meat products, but it can be diminished by adding antioxidant substances that provide more stability and avoid the rancidity of the fat. Meat products represent a great proportion of the human diet, and flavour, colour and taste play a decisive role in consumer acceptance. Changes in the sensory attributes of meat products could be due to the rancidity; hence, protection against lipid oxidation is very important during technological processing and storage. Lycopene can be considered a natural antioxidant, reducing the effect of lipid oxidation, as has been described by other authors examining different meat products (Mercadante et al., 2010; Østerlie & Lerfall, 2005; Sanchez-Escalante et al., 2003). Fig. 2

Table 2 Effect of the addition of tomato paste (TP) on the textural properties of mortadella samples (different letters within each group show significant differences at p b 0.05). Sample Group 1

Group 2

2% 6% 10% R+ 10% R

Hardness (N)

Gumminess (N)

Work of shearing (Ns)

Cohesiveness (ratio)

Chewiness (Nmm)

Springiness (mm)

63.46 ± 1.34a 63.61 ± 2.77a 64.46 ± 1.47a 37.45 ± 0.34b 41.42 ± 0.99a

33.50 ± 3.27a 24.46 ± 1.51a 24.93 ± 6.12a 19.79 ± 3.47a 17.95 ± 2.25a

−3.04 ± 1.04a −2.94 ± 0.78a −1.69 ± 1.49a −0.51 ± 0.28a −0.59 ± 0.60a

0.53 ± 0.05a 0.39 ± 0.03a 0.40 ± 0.13a 0.54 ± 0.10a 0.44 ± 0.05a

237.00 ± 45.47a 183.33 ± 14.43a 205.16 ± 8.38a 154.92 ± 19.31a 171.03 ± 20.13a

7.41 ± 1.43a 7.24 ± 1.16a 9.32 ± 0.54a 9.57 ± 0.36a 9.53 ± 0.09a

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Table 3 Effect of the addition of tomato paste (TP) on the colour parameters of mortadella samples and stability during shelf-life (different letters within each group, for the same time of storage, show significant differences at p b 0.05). Colour parameter

Group 1

Group 2

2% L*

0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 1 2

a*

b*

Chroma

Hue angle

Delta E

6% a

month months month months month months month months month months month months

10% b

61.10 ± 0.23 59.58 ± 1.03a 61.04 ± 1.02a 17.60 ± 0.62b 17.09 ± 0.81b 17.91 ± 0.20b 6.25 ± 0.25c 5.59 ± 0.33c 5.66 ± 0.24c 18.32 ± 0.24c 17.99 ± 0.71c 18.78 ± 0.24b 17.40 ± 1.26c 18.16 ± 1.62c 17.53 ± 0.58c 1.73 0.67

59.23 ± 0.43 58.48 ± 0.87a 59.92 ± 0.23a 17.56 ± 0.38b 18.66 ± 0.49ab 19.76 ± 0.33a 8.35 ± 0.01b 7.76 ± 1.01b 9.24 ± 0.19b 19.39 ± 0.37b 20.23 ± 0.06b 21.81 ± 0.38a 23.09 ± 0.53b 22.59 ± 1.18b 25.15 ± 0.09b 2.15 2.47

shows lipid oxidation values expressed as content of MDA. It should be noted that all mortadella formulations with lycopene (2%, 6%, 10% and R + 10%) in both groups showed relatively good oxidative stability compared with the regular mortadella sample (R). In fact, the MDA content in the regular product (R) increased significantly from initial values of 42.05 to 59.17 mm MDA/100 g after storage at 4 °C for 2 months. On the contrary, all samples with TP showed values in the range of 30–40 mm MDA/100 g during the shelf-life period; although between the three concentrations of TP, no significant differences were observed either. These results show that the addition of TP significantly affects lipid oxidation mainly due to the presence of lycopene, which scavenges peroxyl radicals, forming adducts and yielding a resonance stabilised carotenoid radical (Burton & Ingold, 1984). Moreover, the addition of TP also provides small quantities of phenolic compounds (mainly hydroxycinnamic acids and flavonoids) (Jacob, García-Alonso, Ros, & Periago, 2010), which can also exert an antioxidant activity by donating a hydrogen atom (Mortensen & Skibsted, 2000). Our results are in agreement with those reported by other authors who observed an antioxidant effect of lycopene from tomato in beef hamburgers (Candogan, 2002; Sanchez-Escalante et al., 2003), minced meat (Østerlie & Lerfall, 2005) and cooked sausages (Mercadante et al., 2010). Due to the addition of TP, the antioxidant activity of the mortadella samples was significantly higher than that in the regular sample (Table 1). In addition, there was a significant rise in the first month that then stabilised in the second month, 1.26, 1.24 and 1.27 mmol eq. Trolox/kg for 2%, 6% and 10% samples of group 1 and 1.22 and 1.14 mmol eq. Trolox/kg for regular product (R) and regular mortadella with 10% TP (R + 10%). Despite the fact that the antioxidant

R + 10% c

R a

57.71 ± 0.23 58.99 ± 1.43a 60.61 ± 1.72a 19.08 ± 0.26a 18.79 ± 0.59a 19.35 ± 1.15ab 9.48 ± 0.06a 11.54 ± 0.39a 10.99 ± 1.13a 21.32 ± 0.07a 22.05 ± 0.66a 22.27 ± 1.35a 26.41 ± 0.87a 31.55 ± 0.67a 29.60 ± 2.25a 2.44 3.28

53.67 ± 0.12 53.39 ± 2.19a 57.54 ± 1.72a 25.47 ± 0.43a 26.12 ± 1.26a 25.53 ± 0.90a 8.28 ± 0.05a 8.88 ± 1.37a 7.82 ± 0.48a 27.03 ± 0.25a 27.62 ± 0.90a 26.71 ± 0.87a 19.18 ± 0.33a 18.82 ± 3.35a 17.04 ± 1.15a 0.93 3.90

56.50 ± 0.23a 55.70 ± 0.20a 58.39 ± 0.79a 25.37 ± 0.19a 26.47 ± 0.56a 25.55 ± 0.45a 2.42 ± 0.18b 1.55 ± 0.40b 1.10 ± 0.59b 25.46 ± 0.16b 26.52 ± 0.57b 25.58 ± 0.46b 5.45 ± 0.28b 3.34 ± 0.80b 2.47 ± 1.33b 1.61 2.31

activity increased significantly during storage (Fig. 3), this behaviour cannot be attributed to the presence of tomato antioxidant compounds (lycopene and phenolic compounds that can act synergistically), since all samples reached similar values (around 1.2 mm eq. Trolox/kg) during the second month of storage. The addition of TP has a clear effect on the antioxidant activity of mortadella at the time of manufacture (r = 0.816, p b 0.01) and during the first month of storage (r = 0.68, p b 0.01) but not during the second month. It must be noted that in meat, there are other chemical components that may be involved in this property. Although the antioxidant activity of meat and meat products has not been studied extensively, some studies have evaluated this property in beef (Wu, Duckett, Neel, Fontenot, & Clapham, 2008) and in functional meat products (López-López et al., 2009). Thus, proteins contained in mortadella may have antioxidant properties (Prior et al., 2003; Wu et al., 2008), and it is known that dipeptide carnosine presents with hydrophilic antioxidant activity similar to ferulic acid (Wu et al., 2008). In addition, processing of meat (e.g. heating or cooking) increases proteolysis and thus may increase antioxidant activity (Wu et al., 2008). Moreover, during storage, the proteolysis phenomena may be responsible for the fact that antioxidant activity reached a similar value in all samples. Related to the colour stability none of the analysed parameters was significantly affected during the shelf-life storage period, including total colour difference (Delta E) (Table 3). According to Østerlie and Lerfall (2005), the colour attributes of ground beef are more stable in meat with tomato peel and meat with TP. In this study, colour parameters showed the same behaviour during the two months of storage at 4 °C,

MDA

Lycopene

70

2,5

mg/100 g

2%

1,5

6% 10% R+10%

1

R

0,5

MDAmm/100 g

60 2

50 2% 6%

40

10%

30

R+10% R

20 10

0

0 0

1 month

2 months

Fig. 1. Stability of lycopene during shelf-life of mortadella samples.

0

1 month

2 months

Fig. 2. Evolution of lipid oxidation across storage time in mortadella samples.

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Antioxidant activity mm eq. trolox/Kg

1,4 1,2 1

2% 6% 10% R+10% R

0,8 0,6 0,4 0,2 0 0

1 month

2 months

Fig. 3. Evolution of antioxidant activity across storage time in groups 1 and 2.

remaining constant the red colour in mortadella R + 10% TP and the orange colour in mortadellas of group 1 (Table 3).

3.3. Acceptability of mortadella with tomato paste Intensity and acceptability ratings of the sensory attributes (colour, taste and texture) were compared between samples of group 2, regular mortadella (R) and mortadella with tomato paste (R+ 10%), which results are shown in Figs. 4 and 5, respectively. 10

As Fig. 5 shows, mortadella with TP yielded significant higher scores than regular samples in colour intensity (7.02 versus 5.38); but no differences were observed for the taste (5.98) and texture scores (5.08 versus 5.29). Therefore, the panellists were not able to appreciate any change in the taste of the mortadella after the addition of TP or the changes in the texture (hardness) described above with the texturometer (Table 2). Once the different attributes used to evaluate the intensity were rated, the acceptability of mortadella by the consumer based on taste and flavour was assessed (Fig. 5). Related to the overall assessment based on flavour, it should be noted that both mortadella samples received 61% positive responses, ranging from level 4 (“I like it”) and level 5 (“I like it very much”). In terms of general acceptance based on taste, panel members gave 69% positive responses (i.e. ranging from “I like it” to “I like it very much”) for regular mortadella and 66% positive responses for mortadella with tomato (Fig. 5). It is important remark that mortadella with TP received more extremely positive responses (i.e. “I like it very much” (21%)) than regular mortadella (16%). Concerning overall acceptability, both samples received similar values. That is, 67% and 65% of panellists chose “I like it” or “I like it very much” in response to regular (R) and tomato mortadella (R+ 10%), respectively. Panellists were also asked about their preference between the mortadella samples, and 59% of the panellists preferred mortadella with TP, hence, the increase in the colour intensity did not influence overall acceptance.

4. Conclusions

9 8 7 6 R+10%

5

R

We conclude that the addition of 10% of TP to mortadella does not affect the manufacturing process. In fact, it yields a product with similar technological characteristics and improved nutritional and functional properties without significantly affecting the sensorial attributes of colour, taste, texture or overall acceptance. Moreover, the addition of TP improves the stability of mortadella during the shelf-life period by significantly reducing the lipid oxidation associated with storage.

4 3

Acknowledgement

2 1 0 Colour

Taste

Texture

Fig. 4. Intensity of colour, taste and texture scores of mortadella with tomato and regular mortadella.

We thank Campo de San Juan (Moratalla, Murcia, Spain) and Conservas Vegetales de Extremadura S.A. (CONESA, Villafranca del Guadiana, Badajoz, Spain) for providing the samples for this study. We also thank the University of Murcia and the Fundación Séneca Research Agency of the Murcia Government for the G. Martín-Pozuelo and S. Bravo fellowships, respectively.

100 90 80 70 60

I like it and I like it very much

50

indifferent

40 I dislike it and I dislike it very much

30 20 10 0 R

R+10% Flavour

R

R+10% Taste

R

R+10%

Overall acceptability

Fig. 5. Acceptability of taste and flavour and overall acceptability of mortadella with tomato and regular mortadella.

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