THE EFFECT OF WATER-SOLUBLE ROSEMARY EXTRACT, SODIUM ERYTHORBATE, THEIR MIXTURE AND PACKAGING METHOD ON THE QUALITY OF TURKEY MEATBALLS

Abstract

The effect of antioxidants (water-soluble rosemary extract, sodium erythorbate and their mixture), packaging method (VP and MAP-20% CO2 / 80% N^sub 2^) and storage time on the quality of turkey meatballs were studied. The applied antioxidants delayed lipid oxidation and improved the sensory quality of turkey meatballs. The rate of lipid oxidation was lower in vacuum packaged samples than in MA-stored samples. Water-soluble rosemary extract was less effective than sodium erythorbate in delaying lipid oxidation, regardless of the packaging method, and it protected samples against redness fading during modified atmosphere storage. Sodium eiythorbate slowed down the hydrolytic process in turkey meatballs more effectively during vacuum storage than during MA storage. [PUBLICATION ABSTRACT]

Headnote

ABSTRACT

The effect of antioxidants (water-soluble rosemary extract, sodium erythorbate and their mixture), packaging method (VP and MAP-20% CO2 / 80% N^sub 2^) and storage time on the quality of turkey meatballs were studied. The applied antioxidants delayed lipid oxidation and improved the sensory quality of turkey meatballs. The rate of lipid oxidation was lower in vacuum packaged samples than in MA-stored samples. Water-soluble rosemary extract was less effective than sodium erythorbate in delaying lipid oxidation, regardless of the packaging method, and it protected samples against redness fading during modified atmosphere storage. Sodium eiythorbate slowed down the hydrolytic process in turkey meatballs more effectively during vacuum storage than during MA storage.

- Key words: antioxidants, lipid oxidation, microbial quality, physicochemical quality, sensory properties, turkey meatballs -

INTRODUCTION

Over the past decade, poultry-based products have become increasingly popular worldwide due to their high nutritional quality. Such products are available either fresh or precooked, and after subsequent packaging they are usually stored under refrigeration. Since poultry is perishable food, the main concern of the meatprocessing industiy is to extend the shelf-life of poultry products. The susceptibility of poultry meat to microbial spoilage presents a potential health hazard, since it may harbor pathogenic microorganisms. Spoilage is commonly detected by a sensory and/or microbiological analysis (PATSIAS et ed., 2006).

Poultry meat contains high amounts of polyunsaturated fatty acids, which makes it susceptible to oxidation (LUCERA et al, 2009). Oxidation is one of the major causes of chemical spoilage, resulting in rancidity and deterioration of the nutritional quality, color, flavor, texture and safety of foods (ANTOLOVICH et al, 2002). This irreversible change contributes to the development of unacceptable organoleptic characteristics in both fresh and frozen processed meat products. Oxidative processes are also associated with discoloration of meat products, as lipid oxidation results in the formation of pro-oxidants capable of reacting with oxymyoglobin, which leads to the development of metmyoglobin (LUCERA et al, 2009).

There has been an increasing interest recently in the use of spices and aromatic herbs which, owing to their strong antioxidant and antimicrobial properties, are often considered superior to many of the currently used natural and synthetic antioxidants. The above properties result from the presence of vitamins, flavonoids, terpenoids, carotenoids, phytoestrogens and minerals, and they render spices and some herbs or their antioxidant components as preservative agents in food (SUHAJ, 2006).

Rosemary (Rosmarinus officinalis) is a plant of the family Labiatae, whose major and most active components are carnosol, carnosic acid and rosmarinic acid. Rosematy is an important contributor to the oxidative stability of meat products (MARTÍNEZ et al, 2006). Water-soluble rosemary extract is a natural product containing phenolic diterpenes, which suggests that it may possess antioxidant activity. However, the practical application of extracts is limited due to the strong flavor they impart to foods as well as to their interactions with some food ingrethents (BURT, 2004). For these reasons the preservative effect of extracts may be achieved by using them in lower concentrations and in combination with other preservation technologies such as low temperature and vacuum or modified atmosphere packaging (LUCERA et al, 2009). Several Authors reported that some compounds in rosemary extracts could have antibacterial activity (CUVELIER et al, 1996; DEL CAMPO et al, 2000)

Packaging methods including vacuum packaging (VP) and modified atmosphere packaging (MAP) have been investigated as technologies to increase the shelf-life of poultry products by inhibiting spoilage and the growth of pathogenic microorganisms (NTZIMANI et al, 2008). Modified atmosphere packaging (MAP) has gained considerable popularity over the last decades as a modern non-thermal method of food preservation. The proper combination of gases (CO2, N2 and O2) in the headspace of food packs results in suppression of the microbial flora of perishable foods such as meat products, developed under aerobic conditions, and it helps to maintain their sensory attributes (PATSIAS et al, 2006).

MATERIALS AND METHODS

Materials

Thigh muscles of male British United BIG6 turkeys (Frednowy, Poland) were purchased from the Indykpol Company (Olsztyn, Poland). Water-soluble rosemary extract (0791 Stabilotion WS) containing 9+1% phenolic diterpenes (carnosic acid, carnosol, rosmanol) was purchased from the RAPS GmbH &CO.KG Company (Kulmbach, Germany). Sodium eiythorbate was supplied by the Parchn Group Company (Xingangshan Town, Dexingxing City, Jiangxi Province, China).

Preparation of samples, packaging and storage

Two different experiments were carried out, according to the following designs:

Experiment 1

After cutting and chilling, 1 kg portions of turkey meat were packaged in polyethylene bags and deep-frozen at-25°C at the "Indykpol" Poultry Processing Plant in Olsztyn. After three days, half of the material was placed in the refrigerator at 3°C, where it was defrosted over 20 hours and assigned to the first experiment. Defrosted meat was cut into 4-6 cm pieces and ground in a meat grinder, type MMU-IOZ (Naklo, Poland) with a 4 mm mesh. Ground turkey meat was divided into four groups. Following the addition of wheat flour roll soaked in water (13%), beaten eggs (5%), flour (2%) and salt (1% in relation to total mass weight) to meat (80%), the mass was mixed in a multifunctional food processor (Bauknecht, Warsaw Poland). Experimental treatments were as follows: no additives (control - C), sodium eiythorbate (SE) - 0.3 g/kg of total mass weight, water-soluble rosemary extract (WR) - 0.3 g/kg and a mixture of WR and SE (MIX) - 0. 15 and 0. 15 g/kg, respectively. The amount of water-soluble rosemary extract (WS) added to turkey meatballs was determined based on the recommendations of the supplier regarding meat products, and previous research which investigated the sensory acceptability of the proposed amount in the final product. As a result, WS was added at the lowest concentration. The amount of sodium erythorbate was determined based on the recommendations of the supplier and the amount of WS, in order to compare their effects.

Water-soluble rosemary extract was mixed with part of the meat mass before mixing with the total mass. Sodium erythorbate was dissolved in water (200C) in the amount of 15 g/ 100 mL, and it was slowly added to the meat mass while mixing. While preparing a mixture of SE and WR, the ingrethents were added individually. Next the mass was formed into 90 g ± Ig meatballs (8 cm in diameter, 1 cm in thickness).

Eighty-four meatballs randomly selected from each treatment were placed on the oven tray (twelve meatballs at a time) and were cooked in the BECK FCV 4 EDS steam-convection oven (BECK GmbH, Jagsthausen, Germany) with a measuring probe. Steam and hot air were used for heat treatment (air temperature - 1800C, steam saturation - 30%). The treatment was continued until a temperature of 82°C was reached inside the product. The patties analyzed after cooking were stored overnight at 0°C. The remaining samples were cooled to room temperature and vacuum packaged (VP-Experiment 1) with the MULTIVAC A 300 packaging unit (Multivac, Wolfertschwenden Germany) into bags of a five-layer PE-LD/adh/PA/ADH/ PE-PD film (total thickness - 0.08 mm, PA layer thickness - 0.024 mm, oxygen permeability - 40 cm^sup 3^/m^sup -2^24 h *bar^sup -1^ water vapor permeability - 10 g m 224 h^sup -1^ bar 1J, The samples were stored at 3° ± 1°C.

Experiment 2

After 14 days of storage, the other half of turkey meat was placed in the refrigerator at 3°C, where it was defrosted over 20 hours and assigned to the second experiment. Meatballs were prepared following the same procedure as in experiment 1. After cooking and cooling to room temperature, the samples were packaged under modified atmosphere (a gas mixture of 80% N2 and 20% CO2, MAP) with the MULTIVAC A 300 packaging unit (Multivac, Wolfertschwenden Germany) into identical bags as in experiment 1 and were stored at 3° ± 1°C.

Three randomly selected packages were collected every 5 days of storage from each experiment and from each treatment for an analysis of CIE L*, a* and b*, pH, AV, malondialdehyde (MDA) and water activity, and a sensory analysis. After 15 and 30 days of storage, one additional package was opened for a microbial analysis.

Analytical Methods

Lipid oxidation analysis

Lipid oxidation was assessed in 10 g of turkey meatballs by the 2-thiobarbituric acid (TBA) method of TARLADGIS et al (1960) modified by PIKUL et al (1989), after 0, 5, 10, 15, 20, 25 and 30 days of storage at 4°C. TBARS values were calculated from a standard curve of malondialdehyde and expressed as mg malondialdehyde (MDA) kg-1 product. TBARS determination was conducted in triplicate on each of three samples per treatment. The antioxidant potential, expressed in terms of the percentage of antioxidant activity, was calculated using the equation:

% AOA= [TBARS value of the control sample - TBARS of the experimental sample] ? 100/ [TBARS value of the control sample]

Acid value (AV)

The acid value (AV) indicates how much fatty acid has accumulated as a result of lipolysis. It was determined in fat extracted from the products after 0, 5, 10, 15, 20, 25 and 30 days of storage at 4°C, in accordance with the Polish Standard PN-EN ISO 660 (Animal and vegetable fats and oils 2005). AV determination was conducted in triplicate on each of three samples per treatment.

pH

For pH determination, 10 g samples of the products stored for 0, 5, 10, 15, 20, 25 and 30 days at 4°C and 90 mL of distilled water were homogenized in a blender (type MPW-302) for 60 s. The pH of the mixture was measured using a pH-meter; model ATC PICCOLO 2 (Woonsocket USA), standardized at pH 4 and pH 7 (PEXARA et al, 2002). pH was measured directly after homogenization and it was read after stabilization. pH determination was conducted in triplicate on each of three samples per treatment.

Water activity

An adequate amount of a ground sample was placed in a measuring container and three measurements were performed on the products after 0, 5, 10, 15, 20, 25 and 30 days of storage at 4°C, using a water analyzer (type AWC 203-C, Novasina, Pfäffikon, Switzerland), after reaching equilibrium at 200C, according to the manufacturer's instruction. The samples were brought to room temperature prior to evaluation. Water activity determination was conducted in triplicate on each of two samples per treatment.

Color evaluation

The color of the samples was determined with a spectrophotometer (Dr Lange Spectro-color), d/8° with a 10 mm measuring aperture and SPECTRAL-QC computer software after calibration using Dr Langeblack and white standards. The results are given in the color-coordination system CIE Lab [where L* measures relative lightness (L* = 0 darkness, L* = 100 lightness), a* - relative redness (+60 = red, -60 = green) and b* - relative yellowness (+60 yellow, -60 = blue)]. Color was measured on the meat surface 30 min after the package had been opened. The measurement was repeated at six randomly selected points on each of three samples per treatment.

Microbiological analysis

A 10 g ground sample of each product was taken aseptically and placed in a sterile stomacher bag containing 90 mL of Ringer liquid. The sample in the bag was blended in a laboratory blender (Stomacher 400, Seward Laboratory, London, UK) for 2 min, and submitted to serial dilutions with the same diluents. For the determination of mesophilic and psyehrotrophie bacteria, appropriate serial dilutions were plated on plate count nutrient agar, and were incubated at 300C for 72 h (mesophilic bacteria) and at 6.5°C for 7 days (psyehrotrophie bacteria) prior to enumeration. Coliforms were enumerated by plating on violet red bile lactose agar (Merck, Warsaw, Poland) and then they were incubated at 300C for 48 h. The counts of fungi were determined on YGC - Agar (Merck) after 96 h incubation at 25°C. To determine the presence of sulfate IV reducing Clostridium sp., adequate dilutions were inoculated into a liquid meat-liver agar medium, were heated at 80°C for 15 minutes and incubated at 37°C for 48 h. All microbial counts were reported as a logarithmic value of colony forming units per gram of sample. Microbial populations in the samples were determined in triplicate before thermal processing, after thermal processing and after 15 and 30 days of storage at 3° ± Io C. Samples taken from three randomly selected meatballs per treatment were homogenized.

Sensory quality

Meatballs were subjected to a sensory evaluation by the flavor profile method (MEILGAARD et al, 1999). The sensory panel consisted of five panelists trained in accordance with the Polish Standard ISO 11035 (Identification and selection of descriptors, 1999). All judges were trained to be familiar with the flavor attributes to be measured (meaty, typical of poultry meat, aromatic, typical of roasted meat, spicy-rosemary, sour, WOF). The sensory assessment was performed after 0, 5, 10, 15, 20, 25 and 30 days of storage at 4°C. Two sensory evaluation sessions were conducted per day. The 2nd session comprised the replicates of the 1st session. The sessions were conducted at one-hour intervals. For flavor evaluation, two meatballs per treatment were cut into approximately uniform pieces. Samples were served in random order to each panelist on a white porcelain dish, coded with random numbers. At the beginning of each session, the panel was presented with the reference samples for the extremes of scales of the flavor attributes to be measured. The intensity of particular attributes was determined on a five-point scale: 0-lack of perception; 1 -hardly noticeable perception; 2-slightly noticeable perception; 3-moderately noticeable perception; 4strongly noticeable perception; 5-very strongly noticeable perception.

Statistical analysis

Both experiments were performed in a completely randomized 4x7 factorial design. The experimental factors included four additives and seven storage times. Data obtained for the initial characterization of the tested additives and storage time were subjected to a two-way analysis of variance (ANOVA), after the normality and homogeneity of variance had been confirmed. Since significant interactions were found, independent one-way ANOVA tests were carried out on each variable (additives and storage time). When the ANOVA showed the differences to be significant, the obtained values were evaluated by Tukey's test. Additive treatments were compared each day. The level of significance was determined at P<0.05. The relationships between the investigated properties were determined using Pearson's correlation. The correlations between sensory attributes and lipid changes (MDA, AV) were performed using Spearman's non-parametric rank correlation test. The statistical analysis was carried out using STATISTICA 7.1 software (StatSoft Inc. 2008).

RESULTS AND DISCUSSION

The effect of water-soluble rosemary extract and sodium eiythorbate on lipid stability

Determination of lipid oxidation

An analysis of variance showed (Table 1) that the analyzed additives and storage time significantly (P<0.001) affected the MDA content in samples stored under vacuum and modified atmosphere conditions. Vacuum-packaged turkey meatballs (Table 1) without active compounds (C) showed the highest MDA values throughout storage. MDA concentrations in all samples decreased significantly after 5 days of storage, and during further storage MDA content changed significantly, but the observed changes were ambiguous. The decrease in the MDA content noted after 5 days of storage could result from the fact that the rate of MDA reaction with protein was faster than the rate of MDA formation, or the formation of secondary products of lipid oxidation that do not react with TBA. ULU (2004) reported that malonaldehyde is highly reactive and remains bound to other food ingrethents. After 30 days of vacuum storage, the MDA content of all samples was significantly higher, compared with the first period of storage. Similar changes in TBA values were also noted by NASSU et al (2003) in a study investigating the effect of natural antioxidants in fermented goat sausages during a storage period of 80 days, and according to the Authors they were due to the fact that malonaldehyde did not accumulate as a stable end product.

Until day 25 of MA storage (Table 1), lipid oxidation in control (C) samples was more intense than in treated samples. At the last stage of storage, samples containing water-soluble rosemary extract and a mixture of sodium erythorbate and water-soluble rosemary extract were characterized by a higher MDA content, compared with C and SE samples. The inhibitory effect of water-soluble rosemary extract on lipid peroxidation in cooked turkey products might be due to the free radical scavenging and transition metal chelating activities of WR components (HUANG et al, 1996). YU et al (2002) found that water-soluble rosemary extract prevented lipid oxidation in cooked turkey products during refrigerated storage. FERNÁNDEZ-LÓPEZ et al (2005) demonstrated that rosemary extracts (water- and oil-soluble) were effective in retarding lipid oxidation in cooked beef meatballs during 12 days of storage at 8°±1°C. According to BRAGAGNOLO et al (2005, 2007), the addition of rosemary to minced chicken meat prior to high-pressure treatment was effective in preventing the formation of "pressed-over-flavor" upon subsequent cooking and lipid oxidation during refrigerated storage. The positive effects of rosemary and sodium eiythorbate used alone have been well documented with respect the prevention of lipid oxidation, whereas, to the Author's best knowledge, there are no reports on the combined use of rosemary and sodium eiythorbate. In the present experiment, MDA content was lower in vacuum-stored turkey meatballs than in MA-stored samples. This could be caused by a higher amount of oxygen in MA-packaged samples, in comparison with vacuum-packaged ones, because complete removal of oxygen is extremely difficult. These findings agree with those reported by other Authors (NOLAN et aL9 1989; SMIDDY et al., 2002). SHEARD et al (2000) consider MDA concentrations higher than 0.5 mg/kg as threshold values for rancidity perception by consumers, whereas according to Ockerman (as cited in GEORGANTELIS et al, 2007) meat products with MDA concentrations higher than 1 mg/kg are considered rancid. In the present study, control samples were perceived as rancid after 20 days of vacuum storage and throughout MA storage. The MDA content of all samples with additives and with sodium eiythorbate was close to the threshold value during vacuum storage and during MA storage, respectively. In MAP samples with water-soluble rosemary extract and with a mixture water-soluble rosemary extract and sodium eiythorbate, MDA content did not exceed 1 mg/kg until day 15 and 25 of storage, respectively.

Antioxidant activity

The individual and interactive effects of sodium eiythorbate and water-soluble rosemary extract on the inhibition of lipid oxidation in turkey meatballs are showed in Table 1 . Antioxidant activity was not stable during vacuum and MA storage. Samples containing sodium eiythorbate showed higher antioxidant activity than those containing water-soluble rosemary extract, which could be caused by low phenol concentrations in this extract. It was found that sodium eiythorbate used in combination with water-soluble rosemary extract showed lower antioxidant activity during vacuum storage than each of the additives applied alone. A similar tendency was observed during MA storage, except on day 15 and 20 when water-soluble rosemary extract combined with sodium eiythorbate showed higher antioxidant activity than water-soluble rosemary extract applied alone. After 30 days of MA storage, water-soluble rosemary extract and a mixture of sodium eiythorbate and water-soluble rosemary extract exhibited a prooxidative effect. As shown in Table 1, sodium eiythorbate and water-soluble rosemary extract were more effective as individual antioxidants than their mixture. WILKINSON et al (2001) reported that sodium eiythorbate delayed lipid oxidation in freeze-dried beef and chicken. BALEV et al (2005) demonstrated that the addition of sodium eiythorbate suppressed the accumulation of secondary derivatives of lipid peroxidation in dry-fermented sausages, and that sodium eiythorbate was more effective than rosemary. The prooxidative effect of the MIX additive observed at the final stage of storage in the present study could be caused by a too low concentration of sodium eiythorbate in MIX samples, which therefore could show its prooxidative effect. Sodium eiythorbate was probably utilized as a reducing agent and could be expected to behave similarly to its isomer, ascorbate. Ascorbate has been reported to act as an antioxidant or prooxidant depending on its concentration, the presence of metal ions, and tocopherol concentrations (SCHAEFER et al., 1995). In consequence, the results of studies investigating the use of ascorbate as an antioxidant are ambiguous. DECKER and XU (1998) demonstrated that ascorbate can act as a prooxidant at low (0.020.03%) concentrations and as an antioxidant at high (0.5%) concentrations. The prooxidative effect of water-soluble rosemary extract could result from the interaction between phenol diterpens contained in this additive and other active components. According to HERNANDEZ-HERNANDEZ et al (2009), antioxidant activity does not depend only on total phenol concentrations, but also on their polarity and molecular structure, MADSEN et al (1995) reported that the effect of certain potential antioxidants might vary considerably depending on a complex interaction between various factors including the type and concentration of active compounds and the nature of the food system.

Hydrolytic changes

Both the additives and storage time significantly affected (P<0,001) the acid value of turkey meatballs (Table 2), During vacuum storage, acid value showed a rising tendency in C and WR samples, while changes in the acid value of SE and MIX samples were significant, but ambiguous. There was a significant additive ? time interaction in AV (P<0, 00 1) , The smallest changes in acid value were noted in samples with sodium eiythorbate, as compared with C, WR and MIX samples.

During storage, the rate of the hydrolytic process was slower in MAP turkey meatballs than in VP samples. After 10 days of MA storage, the acid value of control samples decreased significantly, and during subsequent storage periods it showed a rising tendency. The acid value of SE and MIX samples did not change significantly until day 20, after 25 days it increased significantly and remained at a similar level at the final stage of storage. The acid value of WR samples showed an ambiguous tendency during MA Storage. These results are partly consisted with the findings of previous studies (BALEV et al., 2005; KARPIÑSKATYMOSZCZYK, 2006). BALEV et al (2005) found that the addition of sodium eiythorbate slowed down lipolysis in dryfermented sausages during the drying process. According to KARPIÑSKA-TYMOSZCZYK (2006), sodium eiythorbate was a more effective inhibitor of hydrolytic changes in poultry meatballs than sage. FERNÁNDEZ-FERNÁNDEZ et al (2002) reported that the hydrolytic process took place in chorizo sausages stored under modified atmosphere (100% CO2, 100% N2 and 50% CO2/ N2) and vacuum, but more slowly in MA-packaged samples.

pH

The effect of the analyzed additives on pH values in vacuum packaged turkey meatballs is presented in Table 2. In C and WR samples, pH values decreased with prolonged storage time. The decrease in pH values during storage could be caused by an increase in the quantity of free fatty acids as a result of hydrolytic changes. The pH of MIX samples showed small, but significant changes. At the final stage of storage (25-30 days), pH values were significantly lower (6.54) than after 5 days of storage (6.67), and in the remaining periods of storage pH values were similar (6.57 - 6.65). There was a significant additive x time interaction for pH values (P<0.001). At the final stage of storage (25-30 d), SE and MIX samples had higher pH values than WR and C samples.

In MA packaged samples, pH values were affected only by storage time (Table 2). The pH of samples with additives (SE, WR, MIX) was in the range of 6.42 - 6.54, and no significant differences were observed during storage. The pH values of samples without additives increased significantly during the initial phase of storage, i.e. after 5 days (from 6.41 to 6.58), and during further storage they remained at a similar level (6.50 - 6.55). ROJAS and BREWER (2007) demonstrated that the pH values of cooked beef and pork patties during refrigerated storage were not affected by the antioxidants (oleoresin rosemary extract, grape seeds and water-soluble orégano extract). PEXARA et al (2002) reported that the pH values of cooked sliced turkey fillets decreased during storage at 4°C, but to a lesser degree in VP than in MAP samples.

Water activity

Both the additives and storage time affected (P<0.05) water activity in vacuum-packaged turkey meatballs (data not shown). During 25 days of storage, water activity in control samples did not change significantly (0.954 - 0,964) and after 30 days of storage it was significantly higher (0.966) than after 10 days (0.954) and similar to the initial value (0 days- 0.962). Water activity in WR samples did not change significantly (0.956-0.969) and in MIX samples it decreased over the first 15 days of storage (from 0.973 to 0.951), after 20 days it increased significantly to 0.966, and during subsequent storage it remained at the same level (0.965 - 0.967). The most profound, but ambiguous changes were observed in water activity in SE samples (0.952 - 0.972). Significant differences in water activity between samples were observed only initially (0 days) and after 5 and 25 days of storage. Samples with additives showed higher water activity than control samples. In the experiment with MA stored samples, water activity was affected (P<0.05) only by storage time (data not shown) and it did not change significantly in samples with additives (0.964 - 0.978), Water activity in control samples decreased significantly after 5 days of storage (from 0.978 to 0.965) and during further storage it remained at the same level (0.965 - 0.967). Slighter changes in water activity were observed in MA-packaged turkey meatballs compared with vacuum-packaged samples. RUBIO et al (2006) also found that water activity decreased during storage of sliced cured beef packaged under vacuum, but it did not vary in gas-packaged (20% CO2/ 80% N2) samples.

Color evaluation and the correlation between color and rancidity

Table 3 shows mean L*, a*, and b* values during storage of turkey meatballs packaged in vacuum and modified atmosphere. During vacuum storage, surface L* values (lightness) increased on day 30 in SE and MIX samples and on day 20 in WR samples, and they did not change in control samples. During MA storage, L* values did not change significantly in C samples and increased on day 10 and 20 in MIX and SE samples, respectively. Lightness (L*) values in WR samples increased significantly after 20 days of storage, and then they decreased to a similar level as immediately after cooking (0 days). The effect of the tested additives on the color lightness (L*) of cooked turkey meatballs was noted only in vacuum-packaged samples after 20 days of storage, and samples with water-soluble rosemary extract were characterized by the highest L* values, ANTON et al (1993) reported that the increase in L* values could be related to the increase in metmyoglobin formation. Some Authors reported that color lightness in meat and meat products depends on several factors such as water-holding capacity (FERNANDEZ-LOPEZ et al, 2000) fat content (FISHER et al, 2000), and free water content (JUDGE et al, 1989).

Redness (a*) values were affected (P<0,001) by the additives in turkey meatballs packaged by both methods and by storage time only in MA packaged samples (table 3), During MA storage, the redness of control samples decreased gradually, In SE and MIX samples, a* values decreased significantly only after 10 days of storage. Initially (0 days) samples with water-soluble rosemary extract were characterized by the lowest redness and the value of this color component did not change significantly during storage. There was a significant interaction between the additive and storage time for a* values in both experiments. During vacuum storage, water-soluble rosemary extract applied alone and in combination with sodium erythorbate caused a decrease in the redness of turkey meatballs At the end of MA storage samples with additives showed higher values of redness than control samples. In the present study water-soluble rosemary extract protected turkey meatballs against redness fading during MAP storage. These results correspond with those reported by YU et al (2002) who found that cooked turkey products containing water-soluble rosemary extract had higher a* values than of the control during refrigerated storage. A preserving effect of rosemary extract on red meat color has been demonstrated by other Authors (AKSU et al, 2005; MANCINI et al, 2005; SEYDIM et al, 2006).

Storage time affected b* values (yellowness, P<0.05) only in VP samples (Table 3). In SE samples, yellowness decreased only during vacuum storage and this decrease was significant at the final stage of storage. The effect (P<0.01) of the tested additives was observed only in turkey meatballs stored under modified atmosphere. Samples with additives showed higher b* values than control samples, but a significant differences was found only after 10 days of storage. This difference may be explained by the effectiveness of the antioxidants added to turkey meatballs.

Microbial analysis

The results of a microbial analysis are presented in Table 4. In raw samples, total mesophilic bacteria counts in Experiment 1 (turkey meatballs destined for VP) ranged from 5.5 x 10^sup 3^ to 1.1 x 10^sup 5^, and their counts were similar (around IO4) in all samples in Experiment 2 (turkey meatballs destined for MAP). Thermal processing caused a reduction in the counts of mesophilic bacteria in all samples. After 15 days of vacuum storage, the counts of mesophilic bacteria did not change significantly only in WR samples (50 cfu/g) and they increased significantly in C (10^sup 4^), SE (10^sup 4^) and MIX samples (10^sup 2^). After 30 days of storage, the counts of mesophilic bacteria increased to 105 in samples with additives, and they remained at the same level as after 15 days of storage in control samples. During MA storage, the counts of mesophilic bacteria increased steadily in C and SE samples, from 102 to 105 cfu/g and from <100 to 105 cfu/g, respectively. The counts of mesophilic microorganisms in WR samples did not change after 15 days of storage and they increased to 105 cfu/g after 30 days. In MIX samples, the population size of mesophilic bacteria reached 60 cfu/g after 15 days and it increased to 10^sup 2^ cfu/g after 30 days of MA storage.

According to NTZIMANI et al (2010), the limit of acceptability for poultry product is 10^sup 7^ cfu/g mesophilic microorganisms. The present results show that turkey meatballs stored under vacuum and modified atmosphere for 30 days were of an acceptable quality. The lowest counts of mesophilic microorganisms (102cfu/g) were noted in MIX samples stored under modified atmosphere. In control turkey meatballs, the counts of the above bacteria were lower in samples stored under vacuum than in those stored under modified atmosphere. Water-soluble rosemary extract had an inhibitory effect on mesophilic bacteria for 15 days of vacuum and MA storage, while a mixture of water-soluble rosemary extract and sodium erythorbate exerted an inhibitory effect for 15 days of MA storage.

The counts of psychrotrophic bacteria in raw turkey meatballs were 10^sub 4^ cfu/g in control samples and 10^sub 3^ cfu/g in samples with additives. Thermal processing reduced the counts of the above bacteria to below 10 cfu/g in samples assigned to VP and to 10^sup 2^ cfu/g in samples assigned to MAP. During vacuum and MA storage, the levels of psyehrotrophie bacteria increased in C and SE samples. The counts of psyehrotrophie bacteria in WR samples remained at the same level during MA storage. After 15 days of vacuum storage. They reached 20 cfu/g and increased to 102 cfu/g after 30 days. In MIX samples, the numbers of psyehrotrophie bacteria did not change after 15 days of vacuum storage and they decreased over the same period during MA storage to reach the final count of 102 cfu/g on day 30. The tested additives inhibited the growth of psyehrotrophie bacteria during manufacturing and vacuum and MA storage. Water-soluble rosemary extract and its mixture with sodium eiythorbate were more effective in this respect than sodium eiythorbate applied alone.

Fungal contamination of raw turkey meatballs reached 100-700 cfu/g and 30-140 cfu/g in samples assigned to VP and MAP, respectively. Thermal processing decreased fungal counts to below 10 cfu/g and no fungal growth was noted in VP and MAP samples over refrigerated storage.

The total counts of coliforms in raw turkey meatballs were 60 - 200 cfu/g in samples assigned to VP and <10 - 17 cfu/g in samples assigned to MAP. It is possible that the bacteria were transmitted during the preparation of meatballs. They were completely destroyed during thermal processing. All additives inhibited the growth of coliforms during vacuum storage, while in control samples their counts increased to 10^sup 4^ cfu/g after 30 days. Turkey meatballs were free of sulfate reducing Clostridium sp.

To the author's best knowledge, there are no reports addressing the combined use of rosemary extract and sodium eiythorbate in the preservation of meat products. An inhibitory effect on microbial growth has been observed in some meat products following the application of rosemary (DEL CAMPO et al., 2000; DJENANE et al., 2002, 2003; CAMPO et al, 2003; FERNÁNDEZ-LÓPEZ et al, 2005; ZHANG et al, 2009) and sodium erythorbate (BARRINGER et al, 2005; KARPIÑSKATYMOSZCZYK, 2006).

Sensory quality

After thermal processing all samples destined for vacuum packaging were characterized by similar intensity of meaty (3.8-4.0), typical of poultry meat (4.0-4.5), fatty (1.0) and typical of roasted meat flavors (3.5). During storage only in control samples significant decreased intensity of meaty (to 2.7), typical of roasted meat (to 2.0) and aromatic flavors (to 2.0). The typical of poultry meat flavor significantly decreased only in WR samples at the end of storage (to 3.0). Samples differed in scores for meaty flavor only on day 30, and for the typical of roasted meat flavor - on day 20, 25 and 30. The intensity of the above flavors was higher in samples with additives (2.5-3.0) than in control samples (2.0). Initially (storage time 0) all samples stored under modified atmosphere were characterized by similar intensity of meaty (3.7-4.0), typical of poultry meat (4.0-4.5), fatty (1.0) and typical of roasted meat flavors (3.5) and their intensity did not change significantly during storage.

Turkey meatballs with additives i.e. with water-soluble rosemary extract applied alone or in combination with sodium erythorbate, were characterized by higher intensity of the aromatic flavor (2.5-4.0 and 3.0 - 3.5 respectively in VP and 3.5-4.0 and 3.0 - 3.5 respectively in MAP) than control turkey meatballs (2.0-3.0 in VP and 2.5 - 3.0 in MAP) and samples with sodium erythorbate (2.8-3.0 in VP 2.5-3.0 in MAP). WR and MIX samples had a rosemary flavor of low intensity (1.7-2.5 and 1.0-1.5 respectively in VP and 1.72.5 and 1.0-1.5 respectively in MAP). WOF appeared during storage in all vacuum-packaged samples, after 15 days in C (1.0) and WR samples (0.5), after 20 days in SE samples (0.5) and at the end of storage in MIX samples (1.0). WOF intensity increased during subsequent storage, and after 30 days it was slightly noticeably only in control samples. WOF was detected at a later stage of storage under modified atmosphere in samples with additives (where it had lower intensity) and in control samples. Water-soluble rosemary extract and a mixture of sodium erythorbate and water-soluble rosemary extract were effective in slowing down WOF development in turkey meatballs during vacuum and MA storage.

Rosemary extract used as an antioxidant contributed to the maintenance of the sensory quality of turkey meatballs, during both VP and MAP storage. The effect of rosemary was determined by the type of packaging. Samples stored under modified atmosphere had better sensory quality than those stored under vacuum. This property of rosemary extract has been reported in other food products. The addition of rosemary in the formulation of turkey sausages also gave rise to an improvement of their sensory quality (BARBUT et al, 1985). According to SANCHEZ-ESCALATE et al (2001), beef patties with rosemary extract kept the characteristic fresh meat odor for a longer time than control samples. LIU et al (2009) demonstrated that the addition of rosemary seemed not only to enhance the aroma of fresh chicken sausages, but also to retard the off-odor produced by fat oxidation.

The relationship between changes in lipids and sensory quality

In MAP samples, MDA content significantly affected WOF (r = 0.41). Similar results were obtained by others Authors (NOLAN et al, 1989, AHN et al, 2002, GIMÉNEZ et al, 2004, MARTINEZ et al, 2006). In vacuum-packaged samples, acid value was positively correlated with WOF (r = 0.52) and negatively with meaty flavor (r = -0.59), typical of poultry meat flavor (r = -0.63) and typical of roasted meat flavor (r = -0.57). The acid value of MAP samples was negatively correlated with aromatic flavor (r = -0.40) and typical of roasted meat flavor (r = -0.41). In samples packaged by both methods (VP and MAP), spicy flavor was positively correlated with aromatic flavor (r = 0.73 and r = 0.94, respectively) and negatively with meaty flavor only in MAP samples (r = -0.45). In VP samples, WOF was negatively correlated with meaty (r = -0.70), typical of poultry meat (r = -0.75), aromatic (r = -0.63) and typical of roasted meat (r = -0.87) flavors, while in MAP samples a negative correlation was observed between WOF and meaty flavor (r = -0. 39) .

CONCLUSION

The results of this study indicate that the addition of water-soluble rosemary extract (at a level found acceptable in a sensoiy analysis) to turkey meatballs retarded the formation of TBARS, but it was less effective than sodium erythorbate and offered protection against redness fading during MAP storage. Sodium erythorbate delayed the hydrolytic process in vacuum-packaged turkey meatballs. In MAP samples, a mixture of water-soluble rosemary extract and sodium erythorbate exerted a weaker antioxidant effect and a stronger antimicrobial effect, compared with the additives used alone. Turkey meatballs with water-soluble rosemary extract were characterized by the best sensoiy quality, in particular when stored under modified atmosphere. Further research could investigate the combined application of rosemary and sodium erythorbate in different meat products as well as the use of different quantities of the additives than those used in this study, with the aim to optimize their antioxidant and antimicrobial effects.

The Author is grateful to Ania Fankidejska and Mariusz Szczepanski for their technical assistance.

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