Effects of Green Tea and Grape Seed and TBHQ on Physicochemical Properties of Baladi Goat Meats

Abstract

The effect of natural extracts of green tea or commercial grape seed in combination with synthetic tert methyl-butylhydroquinone at different concentrations on lipid oxidation and the redness of goat meats stored at 5°C for 9 days was evaluated. Fresh boneless Baladi goat meats were ground and mixed at varying concentrations of green tea or grape seed extract alone or combined with tert methyl-butylhydroquinone. The color values of raw goat meat and the thiobarbituric acid-reactive substance values of raw and cooked goat meats were determined following 0, 3, 6, and 9 days of storage at 5°C. The antioxidant activity of the plant extracts and the tert methyl-butylhydroquinone ranged from 4.6–10.2 h induction time using an oxidative stability instrument. Thiobarbituric acid-reactive substance values ranged from 0.21 to 1.21 and 0.31 to 4.57 mg malondialdehyde/kg (goat meat) for the raw and cooked goat meats, respectively. Tert methyl-butylhydroquinone and plant extracts significantly decreased lipid oxidation of the goat meats, with a higher level of addition being more effective in minimizing lipid oxidation. Grape seed extract significantly increased the redness, while green tea extract decreased it; no effect of tert methyl-butylhydroquinone on the redness of goat meats was observed. This study has shown that inclusion of natural extracts of green tea and grape seed in goat meat could reduce lipid oxidation during its storage.

Keywords:

• Goat meat
• Plant extracts
• Antioxidant
• Green tea
• Grape seed
• Physicochemical properties

INTRODUCTION

Goats are ruminants that can well adapt to harsh environments, require only limited feeds, and need marginal land to be raised on. Because of these reasons, goats have traditionally been a major animal form in Jordan, and goat meat, especially the Baladi goat meat, is the most commonly consumed high-protein product in Jordan. Goat meat is unique in flavor and palatability and leaner than other meats. Goat meat is also a good source of desirable fatty acids, since goats deposit higher amounts of polyunsaturated fatty acids than other ruminants.[1] Goat meat has an immense market potential, as it could become an ideal choice for health conscious consumers.[2] There is also a worldwide tendency for rapid increase in demand for goat meat.[3]

Over the past decade, consumer demands have been on the rise for more “natural” flavor and color on processed foods with a shelf life sufficient to survive the distribution chain and home storage before consumption. As a processed food, Baladi goat meat also faces the issue of shelf life extension and storage quality maintenance. While contamination by microbes after slaughtering and during processing is of most concern to producers and consumers alike, the physicochemical properties of goat meat, such as color, pH, water holding capacity, lipid, and protein contents, etc., are, however, important to evaluate the storage stability and quality of Baladi goat meats.

Seideman et al.[4] reported that meat color is one of the most important quality attributes for consumer acceptance, which can be affected by the concentration and chemical states of heme pigments of individual animals. Thiobarbituric acid-reactive substance (TBARS) has been reported to be the simplest method to quantify malondialdehyde oxidized in meat and meat products.[5] The undesirable off-flavor in meat may be related to two chemical changes: breakdown of sulphur-containing amino acids and autoxidation of fats. Antioxidants have been documented to minimize lipid oxidation in processed food at levels reported safe for human consumption.[6] Synthetic antioxidant, such as tert methyl-butylhydroquinone (TBHQ) has been widely used to retard lipid oxidation[7] and functions as oxygen scavengers in fat-containing foods, such as meats.[8] However, the concern of synthetic antioxidants with carcinogenicity and toxicological concerns led to the search for natural antioxidants as alternatives. In the last decade, the interest on natural antioxidants and plant extracts to inhibit safety and negative consumer perception of synthetic antioxidants have been concerned.[9] Green tea is rich in flavonoids that have antioxidant properties.[10] Grape seed extracts contain large amounts of phenolic compounds and antioxidants.[11,12] Rababah et al.[13] found that grape seed and green tea extracts had the highest antioxidant activities compared within several plant extracts. Ahn et al.[6] reported that using antioxidants and plant extracts could reduce the TBARS values in raw meats during storage. Horax et al.[14] reported that selected plant extracts, including green tea, could be effectively used to minimize oxidative changes during storage. However, little information is available in the literature on antioxidative effects and physicochemical changes of such materials when used in muscle foods, especially goat meats. Consequently, the effect of green tea and grape seed extracts on minimizing the physicochemical property changes of goat meats during storage calls for investigation. The objective of this study was, therefore, to evaluate the effectiveness of TBHQ and the natural extracts of green tea and grape seed alone or in combination on the physicochemical properties of Baladi goat meats stored at 5°C for 0, 3, 6, and 9 days.

MATERIALS AND METHODS

Materials

Baladi goat meats used in this study were provided by a local meat farm, and green tea (Celestial Seasoning, Inc., Boulder, CO, USA) was purchased from a local supermarket. Commercial grape seed extract powder was obtained from Mega Natural Inc. (Madera, CA, USA). TBHQ (Tenox 20A with 20% TBHQ) was purchased from the Eastman Chemical Company (Kingsport, TN, USA).

Methods

Green tea extract preparation

Green tea extracts were prepared as described by Rababah et al.[13] In brief, green tea leaves were ground in a coffee grinder (Braun Aromatic KSM2, Brarn Canada Div., Gillette Canada Company Missis-sauja, ON, Canada) for 1 min. Ground tea powder was mixed with water (1:10) and boiled for 10 min. The extract in the supernatant was recovered through vacuum filtration. The filtrate was then frozen to −20°C and freeze-dried at <100 millitorr vacuum. The resulting extract was stored at 5°C until use.

Measurement of oxidative stability index (OSI) of goat fat substrate mixed with TBHQ, grape seed, and green tea extracts

The purpose of measuring the OSI of the goat fat was to investigate the efficacy of plant extracts, which have the beneficial antioxidant activities to prevent lipid oxidation, on mitigating the rancidity of goat fat and, therefore, extending the shelf life of goat meats. Lipid oxidative experiments of goat fat blended with TBHQ (200 ppm), the grape seed and tea extracts (500, 3000, and 6000 ppm individually or combinations of grape seed and tea extracts at the same concentration), and the goat fat (control) were conducted in triplicate in an oxidative stability instrument (Metrohm model 743, Herisau, Switzerland). The goat fat was obtained by melting the fat portion of the goat meat in water bath at 60°C. Each mixture of goat fat and the plant extracts or TBHQ was homogenized for 3 min using a Hamilton Beach Scovel homogenizer (NSF, USA) prior to transferring into the OSI tubes. Sample tubes were held in a thermostatic block in the OSI machine at 110°C, and a stream of air at 210 g/cm² was bubbled through the sample. The air pressure was allowed to equilibrate at 176 g/cm². The volatiles released from the sample passed through rubber tubing into a tube containing deionized water and a conductivity probe. A water trap was placed between a sample tube and a conductivity tube to facilitate condensation of water from the sample and aid free flow of volatiles into the conductivity tube. The probe measured change in conductivity of deionized water due to collected volatiles. The induction period was the time, in hours, before detectable levels of volatile organic acids were trapped in the deionized water. The software analyzed the data and generated an induction period as the OSI number. A longer induction period indicated a better oxidative stability of the sample.

Ground goat meat

The goat meats were obtained from six Baladi male goats with an age of 6 months and an average weight of 35 kg. The meats were purchased from a local meat farm, taken within 1–2 h of slaughter and kept at 5°C. At 24 h postmortem, bones, connective tissue, and separable fat were manually removed from the carcasses. The six processed carcasses were divided into three batches with two carcasses each. The lean meats from the two carcasses in one batch were combined and ground twice with a grinder (MFC, Börsen Platz, Frankfast, Germany) to form one experimental unit. Each experimental unit was divided into nine sub-units. Each sub-unit received one of the following treatments: (1) mixing with green tea extracts at 3000 and 6000 ppm levels; (2) mixing with grape seed extract at 3000 and 6000 ppm levels; (3) mixing with combined green tea and grape seed extracts at 3000 and 6000 ppm levels, respectively; (4) mixing with TBHQ at 200 ppm level; and (5) mixing with de-ionized water. In addition, non-marinated goat meat, referred to as “as is,” was also used as the control.

Baladi goat meats marinated with plant extracts and TBHQ

The goat meats were marinated via a tumbling method with TBHQ, green tea extract, grape seed extract, and the combination of green tea and grape seed extracts. As mentioned earlier, the plant extracts and TBHQ were added to ground goat meats at the predetermined levels, i.e., 3000 and 6000 ppm alone or in combinations for both extracts and 200 ppm for TBHQ based on 8.5% goat fat, following the procedure below. Two kilograms of meat was tumbled with 80 ml of plant extracts and TBHQ solutions for 20 min. Also, goat meats were marinated with deionized water in addition to the control (for comparison purposes). A quantity of 200-gram portions of each treated meat were placed in a plastic bag, over-wrapped with oxygen-permeable polyvinyl chloride film, and stored in a 5°C refrigerator for 0, 3, 6, and 9 days. Samples were evaluated for TBARS (raw and cooked) and color (raw) for redness (a*). For every targeted day of storage time, three plastic bags of goat meat of each level of each treatment and the controls were taken randomly for analyses. The remaining samples were kept at 5°C for the next targeted day.

TBARS analysis for raw and cooked meat samples

A modified fluorometric method was used to determine TBARS value in the raw and cooked goat meats to evaluate lipid oxidation.[5] Two-gram portions of meat samples were liquefied with 40 ml of deionized water in a blender (Osterizer Galaxie Dual Range 14, Oster Corp., Milwaukee, WI, USA) for 1.5 min. To 1.0 mL of homogenate, 200 μL of 8.1% sodium dodecyl sulfate, 1.5 mL of 2 M HCl, 1.5 mL of 20 mM thiobarbituric acid, and 50 μL of 7.2% butylated hydroxytoluene were added and vortexed. The samples were then heated in a 90°C water bath for 15 min, and cooled in cold water for 10 min. After cooling, 1.0 mL of deionized water and 5.0 ml of n-butanol/pyridine (15:1) were added. The solutions were centrifuged (J2-21 Centrifuge, Beckman, Fullerton, CA, USA) at 3000× g and 20°C for 15 min. A blank was made using 1.0 ml of deionized water in place of the samples. The clear upper layer solutions were removed and readings were taken using a spectrofluorophotometer at 520 nm. The calculation was made from the observed fluorescent intensity of samples using an equation of a standard curve of malondialdehyde (MDA) as follows:

where F = fluororescent intensity.

Color measurement

The color of meat samples was measured by a Color Tec-PCM^Tm (Pittsford, New York, USA) and recorded using the L*a*b* color system. The L*a*b* color system consists of a luminance or lightness component (L*) and two chromatic components: the a* component for green (-a) to red (+a) and the b* component from blue (−b) to yellow (+b) colors. The colorimeter was calibrated using a standard white plate. Values of the white standard were L = 97.10, a = +0.13, b = +1.88, c = 1.88, and h^o = 86.1. Color was measured four times for each sample. Three bags were used for each treatment, and then the measurements were averaged.

Statistical Analysis

Data was analyzed using factorial analysis of variance procedure (mixed procedure) of SAS Version 8.2 software package (SAS Institute Inc., 2002).[15] The model included the main effects and interactions of nine treatments and four storage times. Multiple t tests were used to separate means at 95% significance level for each test.

RESULTS AND DISCUSSION

Oxidative Stability Index of Goat Fat Mixed with Plant Extracts or TBHQ

Antioxidant activities of the plant extracts and their combinations at three levels (500, 3000, and 6000 ppm), TBHQ (200 ppm), and the control using OSI are shown in Table 1. The results (Table 1) showed that the induction times of plant extracts were much lower than TBHQ (36.1 h) and ranged from 4.2 to 9.7 h (Table 1), but higher than that of the control (2.2 h). The induction time of green tea and grape seed extract or the combined extracts (grape seed and green tea extracts) at 500 ppm level were 4.2, 4.5, and 4.3, respectively, and no significant differences were observed at 500 ppm (p < 0.05) between single and combined extracts. The results of induction time (Table 1) showed that there are significant differences at higher levels (6000 ppm) of green tea (7.5) and grape seed extract (9.4) or the combined extracts (9.7) compared with lower level (3000 ppm), which were 5.3, 5.9, and 6.2 induction time (h), respectively. Lower antioxidant activity was detected in green tea extracts compared with grape seed extracts. These results agreed with the findings by Rababah et al.[11,13] who found that using higher levels of plant extracts increased the induction time (h). Fatihanim et al.[16] found that compared to the control, plant extracts increased the induction time and were capable of protecting the oil from further oxidation. Also, Pitchaon and Suphan[17] found that compared with the control, plant extract increased the induction time and affected the antioxidant activity.

Table 1 Induction time (h) of goat fats blended with TBHQ, grape seed, and green tea extracts, and their combinations as measured by oxidative stability instrument. ^†

Sample	Level (ppm)	Induction time (h)
Grape seed extract	6000	9.4 ± 0.1^b
Grape seed extract	3000	5.9 ± 0.1^d
Grape seed extract	500	4.5 ± 0.1^f
Green tea extract	6000	7.5 ± 0.1^c
Green tea extract	3000	5.3 ± 0.1^e
Green tea extract	500	4.2 ± 0.1^f
Green tea + grape seed	6000	9.7 ± 0.2^b
Green tea + grape seed	3000	6.2 ± 0.2^d
Green tea + grape seed	500	4.3 ± 0.1^f
TBHQ	200	36.1 ± 0.9^a *
Control	—	2.2 ± 0.1^g
^†All values are dry basis. Values are means of three replicates.
*Column values with the same letters were not significantly different ( p < 0.05).

The results demonstrated that an oxidative stability instrument can be used effectively to determine antioxidant activities in lipid-based products, such as goat fat. Also, the results of grape seed and green tea extracts and their combination at higher levels (3000 and 6000 ppm) showed higher antioxidant activities; therefore, these two levels were selected for marination of goat meats to minimize the physicochemical changes.

TBARS Analysis for Raw and Cooked Meat Samples

Tables 2 and 3 show the effect of storage time at 5°C of plant extracts and TBHQ marinated raw and cooked goat meats and controls on TBARS (mg malondialdehyde/kg goat). The results showed that TBARS values for 0–9 days of storage ranged from 0.21–1.21 and 0.31–4.57 mg malondialdehyde/kg goat meat for raw and cooked meats, respectively. In general, there were significant differences (p < 0.05) of TBARS values between plant extracts or TBHQ and the controls of raw and cooked meats. The addition of plant extracts or TBHQ reduced TBARS values of raw and cooked meats (Tables 2 and 3). Compared to controls, the TBARS values of plant extracts-marinated meats were generally lower and decreased with increasing plant extracts concentration. TBHQ was the most effective antioxidant to decrease lipid oxidation followed by grape seed and green tea extracts at 6000 ppm level and 3000 ppm level, respectively. The higher level (6000 ppm) of each extract (grape seed and green tea extracts) or their combinations was more effective in minimizing lipid oxidation than the lower level (3000 ppm), and this could be due to higher antioxidant activities at the higher level of plant extracts. Rababah et al.[13] reported that the higher level of plant extracts had longer induction times (h) values than the lower level using oxidative stability index. Grape seed extracts were slightly more effective in decreasing TBARS values during storage compared with green tea extracts. It has been found that grape seed extracts contain higher antioxidant activities than green tea extracts.[13]

Table 2 Effect of storage time (days) and plant extracts or TBHQ on TBARS (mg malonaldehyde/kg meat) of raw goat meats stored at 5°C

		Days
Treatment	Level ppm	0	3	6	9
Control “as is”	—	0.21^a4 *	0.44^a3	0.53^a2	1.19^a1
Water control	—	0.22^a4	0.45^a3	0.54^a2	1.21^a1
Green tea extracts	3,000	0.22^a3	0.22^b3	0.39^b2	0.67^b1
Green tea extracts	6,000	0.21^a2	0.21^b2	0.23^c2	0.58^c1
Grape seed extracts	3,000	0.21^a3	0.23^b3	0.39^b2	0.59^c1
Grape seed extracts	6,000	0.21^a2	0.21^b2	0.23^c2	0.51^cd1
Grape seed + green tea	3,000	0.21^a3	0.25^b3	0.42^b2	0.65^b1
Grape seed + green tea	6,000	0.21^a2	0.23^b2	0.23^c2	0.56^c1
TBHQ	200	0.21^a2	0.21^b2	0.21^c2	0.40^d1
*Means followed by different letters (a–d) in the same column or different numbers (1–4) in the same row are significantly different (p < 0.05).

Table 3 Effect of storage time (days) and plant extracts or TBHQ on TBARS (mg malonaldehyde/kg meat) of cooked goat meats stored at 5°C

		Days
Treatment	Level ppm	0	3	6	9
Control “as is”	—	0.32^a4 *	1.87^a3	2.69^a2	4.54^a1
Water control	—	0.33^a4 *	1.88^a3	2.71^a2	4.57^a1
Green tea extracts	3,000	0.32^a3	0.74^b2	0.94^b1	1.03^b1
Green tea extracts	6,000	0.34^a3	0.41^c23	0.50^c2	0.77^c1
Grape seed extracts	3,000	0.31^a3	0.73^b2	0.92^b1	1.01^b1
Grape seed extracts	6,000	0.31^a3	0.38^c23	0.46^cd2	0.74^c1
Grape seed^+ green tea	3,000	0.32^a3	0.72^b2	0.94^b1	1.02^b1
Grape seed^+ green tea	6,000	0.32^a3	0.41^c3	0.55^c2	0.77^c1
TBHQ	200	0.32^a2	0.34^c2	0.39^d12	0.48^d1
*Means followed by different letters (a–i) in the same column or different numbers (1–4) in the same row are significantly different (p < 0.05).

The reduction of lipid oxidation of meat samples marinated with plant extracts could be due to either inhibition of formation of free radicals during the initiation step or interruption of the propagation of the free radical chain reaction by acting as an electron donor.[7,18] Also, mitigating lipid oxidation by plant extracts could be attributed to scavengers of free radicals in meat samples.[19–21]

Color Measurement

The redness (a*) values of plant extracts and TBHQ-marinated raw goat meats and controls are shown in Table 4. They ranged from 10.2 to 22.5. As storage time advanced from 3 to 9 days, the redness of the goat meat decreased for the controls and marinated meat samples. This reduction in redness values could be due to oxygenation of meat myoglobin.[2,22] This finding agreed with Nassu et al.[23] who reported that addition of plant extracts to the goat meat decreased the redness with longer storage time. Compared with the controls, the results (Table 4) showed that grape seed extract addition significantly (p < 0.05) increased the redness. On the other hand, green tea extracts decreased the redness and no effect of TBHQ was observed. The observed variablity in redness values of infused meat samples by two plants extracts (grape seed and green tea extracts) could be related to the nature of pigments in these plants.

Table 4 Effect of storage time (days) and plant extracts or TBHQ on redness (a*) of raw goat meats stored at 5°C

		Storage (day)
Treatment	Level ppm	0	3	6	9
Control “as is”	—	20.4^b4	17.1^b3	14.4^b2	12.5^b1
Water control	—	19.3^b4	16.4^b3	14.1^b2	12.3^b1
Grape seed extracts (GS)	3,000	21.4^a4 *	18.4^a3	15.7^a2	13.1^a1
Grape seed extracts	6,000	22.5^a4	19.3^a3	16.2^a2	13.4^a1
Green tea extracts (GT)	3,000	17.5^c4	15.2^c3	13.3^c2	11.1^c1
Green tea extracts	6,000	16.2^d4	14.3^d3	12.2^d2	10.2^d1
GS+ GT	3,000	20.7^b4	16.4^b3	14.6^b2	12.6^b1
GS+ GT	6,000	21.8^a4	18.1^a3	15.3^a2	13.2^a1
TBHQ	200	19.2^b4	16.2^b3	14.2^b2	12.4^b1
*Means followed by different letters (a–d) in the same column or different numbers (1–4) in the same row are significantly different (p < 0.05).

CONCLUSIONS

The findings of this study demonstrated that storage increased lipid oxidation. Infusing synthetic antioxidant and plant extracts into goat meat minimized lipid oxidation in raw and cooked goat meat. The oxidative stability instrument systems can be used effectively to determine antioxidant activities of plant extracts in goat meats. TBHQ was the most effective antioxidant in retarding lipid oxidation of goat meat. Grape seed and green tea extracts/combinations at a higher level (6000 ppm) were more effective than at a lower level (3000 ppm) in minimizing lipid oxidation. Infusion of goat meat with TBHQ and selected plant extracts is an effective method to minimize lipid oxidation caused by storage.

ACKNOWLEDGMENT

The project was funded by the Deanship of Research/Jordan University of Science and Technology and the USAID Middle East Regional Cooperation 227 program under project number PCE-G-00-00-00026.