PROLONG THE SHELF–LIFE OF CHILLED KOFTA USING EXTRACT OF GREEN TEA LEAVES

H. ISMAIL, TAKWA

doi:10.21608/avmj.2011.176656

PROLONG THE SHELF–LIFE OF CHILLED KOFTA USING EXTRACT OF GREEN TEA LEAVES

Assiut Veterinary Medical Journal

Article 4, Volume 57, Issue 130, July 2011, Pages 1-15 PDF (494.53 K)

Document Type: Research article

DOI: 10.21608/avmj.2011.176656

Author

TAKWA H. ISMAIL

Dept. of Food Hygiene, Animal Health Research Institute, Ismailia Lab., Egypt.

Abstract

The effects of various concentrations of green tea, Camellia sinensis, extract on the sensory, bacteriological and chemical quality of Egyptian traditional Kofta were studied. For this purpose, kofta samples were divided into five groups. First group was kept as a control, others groups were treated with 0.5%; 1.0%; 1.5% and 2.0% green tea extract (GTE). All samples were stored at 4 ْC whereas sensory, bacteriological and chemical evaluation of the samples were conducted at 0; 2; 4; 6 and 8 days post–storage. Flavour and taste were accepted by panelists with high score in samples treated with concentrations between 1and 1.5% GTE. There were marked discoloration changes of kofta samples treated with 2.0% GTE. Total psychrophiles counts reached the unacceptable count (5× 10⁶) at 6^th day in 0% control samples while reached 8× 10⁵; 4× 10⁵; 7× 10⁵ and 8×10⁴ at 8^th day in each treated samples with 0.5%; 1.0%; 1.5% and 2.0% GTE respectively. Green tea extract showed an inhibitory effect on C. perfringens, Enterobacteriaceae and Staphylococcus aureus counts with increased storage time in compared to control samples. Also, beef kofta samples treated with green tea extract showed lower pH and thiobarbituric acid reactive substance values all over the storage period compared to control. These results suggest that green tea extract treatment could be effectively used to extend the shelf–life of fresh kofta for up to 8 days when stored at 4 ْC.

Keywords

Key words: Green tea leaves; meat products; kofta

Full Text

Dept. of Food Hygiene, Animal Health Research Institute,

IsmailiaLab., Egypt.

Prolong the Shelf–life of Chilled Kofta Using Extract of Green Tea Leaves

(With 4 Tables)

Takwa H. Ismail

(Received at 2/5/2011)

إطالة فترة الصلاحية للکفتة المبردةباستخدام مستخلص أوراق الشاي الأخضر

تقوي حسين إسماعيل

تم دراسة تأثير إضافة ترکيزات مختلقة من مستخلص الشاي الأخضر إلي اللحم البقري الطازج المفروم والمجهز لعمل المنتج المصري المعرف بأسم الکفتة وذلک علي الجودة الحسية والبکتريولوجية والکيميائية. وتم تقسيم العينات إلي خمس مجموعات وخلط کل مجموعة بمستخلص الشاي الأخضر بترکيز صفر% (المجموعة الضابطة) 0.5% ,1%, 1.5%, 2% علي التوالي ثم حفظها عند درجة حرارة 4 درجة مئوية حيث تم الفحص خلال فترات من 0 ، 2 ، 4 ، 6 ، 8 يوماً. وأظهرت النتائج أن معالجة العينات بترکيز 1% ، 1.5% ، 2% من مستخلص الشاي الأخضر أعطي نتيجة ايجابية وتحسين المظهر العام والرائحة ولون المنتج لمدة تصل إلي 8 أيام من التخزين. وکان العدد الکلي للبکتريا المحبة للبرودة في العينات المعالجة حتى اليوم الثامن من التخزين أقل من ⁶10 خلية لکل جرام بينما فسدت عينات المجموعة الضابطة بعد 6 أيام تخزين. کما أظهرت الدراسة أن مستخلص الشاي الأخضر له تأثير خافض بشکل عام علي الأحمال البکتيرية لکل من العدد الکلي لميکروب کلوسترديم برفرنجيز والعدد الکلي لبکتريا الأمعائية والعدد الکلي للمکورات العنقودية الذهبية. وأظهرت النتائج انخفاضا في قيمة الرقم الهيدروجيني وقيم حامض الثايوباربتيورک في کل العينات المعالجة مقارنة بالمجموعة الضابطة. هذا وقد أوصت الدراسة بإمکانية استخدام الشاي الأخضر في حفظ منتج الکفتة المصرية حتى 8 أيام کبديل طبيعي للمواد الحافظة الکيميائية ولتحسين الجودة وإطالة فترة التخزين عند حفظها عند درجة حرارة أربعة درجات مئوية.

Summary

Key words: Green tea leaves, meat products, kofta.

Introduction

Egyptian traditional kofta is one of the comminuted meat products and its popularity in all classes of Egyptian society has attracted interest of the meat processors as a business opportunity. The changes in consumer attitudes toward the use of synthetic antimicrobial compounds for prolong their shelf-life and to ensure safety of meat products have been challenge food investigators to seek of naturally compounds those poses antimicrobial properties in foods.

Green tea, Camellia sinensis, extract (GTE) is a highly safe way preserving its value for use in meat, it has antioxidant, deodorant and antimicrobial functions. It is a natural preservative that prolong the shelf-life of foods, enhance quality and provide safer products (Diker et al., 1991; Ji- sun and Yangh, 2007).

Several studies have been revealed to the antimicrobial properties of green tea extract (Ahn et al., 1991; Sakanka et al., 2000; Noriyuki et al., 2001; Kim et al., 2004; Juneja et al., 2007). The extract of green tea leaves has organic compounds including polyphenolic and catchin compounds which has effect against some foodborne pathogens as E. coli, Clostridium perfringens, Staph. aureas and Salmonella enteritidis (Kuroda and Hara, 1999; Noriyuki et al., 2001; Friedman, 2007). Catechins can reduce the potential risk of Cl. perfringens during abusive cooling for beef and chicken. It has more inhibition effect on the extracellular release of verotoxin from enterohemorrhagic Escherichia coli (Sakanaka et al., 2000; Juneja et al., 2007).

The natural antioxidants as green tea extract decrease malonaldhyde formation which minimize the oxidize ability of fatty acids by chelating iron and copper which cause the disruption of metal-catalyzed free radical formation. It inhibits the formation of lipolytic and proteolytic degradation products and improve the sensorial and physical quality of the treated food (Chander et al., 2005; Hüseyin, 2006; Kumudavally et al., 2008; Dembele et al., 2010). Green tea extract as food additives improved the shelf-life of fresh mutton at ambient storage condition (25± 2 ºC and 85± 5% RH) and significantly inhibited spoilage microflora, including certain pathogens for up to 4 days, meanwhile control samples showed initial signs of spoilage between 20 and 24 hours (Kumudavally et al., 2008).

Therefore, this study was planned to evaluate the effect of different concentrations of green tea extract as food additives on the sensory, microbial and chemical quality of the traditional Egyptian meat product "Kofta" and their effect on extending the shelf-life of the product under chilling storage.

Materials and Methods

Egyptian traditional kofta are produced from a mixture of finely ground meat with cooking salt, onion, and garlic. This mixture is formed into balls ranging in size from a marble to a ping-pong ball and then cooked in griller.

Preparation of Green Tea extract:

One hundred gram of the grounded leaves was extracted by using technique of James et al. (2010). 500 ml of distilled water were poured in sterile conical flask then covered with aluminum foil and kept at room temperature for 48 hours. After which the extract was obtained by filtering using a filter paper. The extract was concentrated by drying in a water bath maintained at a temperature of 40ºC until brownish black residues were obtained and these were kept in sealed containers and refrigerated at 3± 1º C until required.

Experimental design:

Fresh beef was purchased from local market at Ismailia city (Egypt) on the day of preparation. Beef was cut and minced with a grinder through a 4 mm plate diameter. Beef was divided into five groups, each group included 25 samples (each 150g). The five groups were thoroughly mixed in sterile mixer with 0% (control group), 0.5%, 1%, 1.5% and 2% green tea extract (GTE) eventually. Each sample was made as traditional Egyptian meat product named “Kofta” then wrapped with saran wrap and placed in a chiller at 4ºC ± 1 for 0, 2, 4, 6 and 8 day. Five samples were periodically removed for sensory, bacteriological and chemical evaluation as follows:

1- Sensory evaluation:

The procedure recommended by ASTM (1969) was used for sensory evaluation. Panelists were asked to sign a consent form. Kofta samples were grilled on electric grill for 20 minutes then acceptance testing was used to determine how much each sample was liked based on 5 points according to the guidelines cited below for a set taste, flavour and colour, where 5 = like excellent and 1 dislike poor.

Score	Quality Items for Kofta Samples
5	Natural flavour, color and odour
4	No sensible change in natural flavor, color, and odour
3	Sensible discoloration. Slightly sour odour and incipient rancidity in flavour
2	No natural color, moderately off-odor and off- flavor
1	Sharply sour and extremely rancid flavour, extremely discolored.

Sensory Schema (ASTM, 1969).

2- Bacteriological evaluation:

The technique recommended by APHA (2001) was used for preparation of Kofta samples.25g of the sample were aseptically removed and homogenized in 225 ml of 1% sterile buffered peptone water for 2 min using a stomacher 400 lab Blender to provide dilution of 10^-1. From the original homogenate, 1 ml was aseptically transferred to a test tube containing 9 ml sterile buffered peptone water (1%), from which 10 fold serial dilutions up to 10^-8 were prepared. By using surface plate technique, 0.1 ml from each of the previously prepared dilution was plated as follows: on each duplicate Standard Plate Count Agar for total psychrophiles count (AOAC, 1990), on Lactose Sulphite Broth for C. perfringens (MPN/g) (Beerens et al., 1980), on Violet Red Bile Glucose Agar for total Enterobacteriaceae counts and on Baird Parker Agar with Egg Yolk-Tellurite Emulsion for Staphylococcus aureus count (APHA, 2001).

3- Chemical evaluation:

a- Determination of pH: According to the method reported by Benjakul et al. (1997) using pH meter (PH-Meter 761 Calimatic West Germany)

b- Determination of Thiobarbituric Acid Reactive substance (TBARS):

TBARS value was determined by the technique recommended by Vyncke (1970). The absorbance was measured against the blank at 538nm. TBARS value was expressed as mg malonaldehyde/kg samples.

Results

Table 1: Mean values of sensory evaluation of treated beef kofta samples after grilled at the first day.

GTE	Taste	Flavor
0.0%	3.8	3.9
0.5	4.11	4.2
1%	4.60	4.2
1.5%	4.3	4.1
2%	4.0	4.0

Score = 5 (natural): 1 (no natural)

GTE = Green Tea Extract

Table 2: Mean values of sensory evaluation of treated beef kofta samples during storage at 4Cº

Storage (day)	Control			0.5% GTE			1% GTE			1.5% GTE			2% GTE
	A	F	C	A	F	C	A	F	C	A	F	C	A	F	C
Zero	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5
2	3.7	3.9	3.5	4	4	4	4	4	4. 3	4.5	4.5	4.2	4.5	4.5	4
4	3	3	3	3.5	3.5	3.5	4	4	4	4	4	4	4	4	3.5
6	2	2	2.5	3.5	3.2	3.5	3.8	3.9	3.7	4	3.9	3.5	3.5	3.8	3.5
8	*S	*S	*S	2.8	2.7	2.5	3.5	3.5	3.5	3.7	3.8	3	3.5	3.5	3

A= General appearance F= flavour C = colour

Score: 5 (natural) 1 (no natural)

GTE = Green tea Extract

* S = Spoiled

Table 3: Effect of different concentrations of green tea extract on bacterial quality of beef kofta stored at 4 Cº (CFU/g).

Time /Day

T. Ps.C

C. perferingens

MPN/g

Enterobacteriaceae

Staph. aureus

Mean

S.E.±

Mean

S.E.±

Mean

S.E.±

Mean

S.E.±

Control

9X10³

3X10⁴

8X10⁵

5X10⁶

^*S

3X10²

2X10³

6X10²

4X10⁴

^*S

1.3

2.3

3X10³

8X10³

6X10⁴

8X10⁴

^*S

3X10²

5X10²

3X10³

2X10⁴

6X10³

9X10³

2X10⁴

1X10⁵

^*S

2X10²

10³

6X10³

2X10⁴

0.5%

6x10³

3x10⁴

5x10⁴

3x10⁵

8x10⁵

3x10³

2x10²

6x10³

10⁴

6x10⁴

1.4

2.3

1X10³

4X10³

1X10⁴

6X10⁴

8X10⁴

10²

2X10²

3X10²

4X10³

2X10³

9X10²

3X10³

1X10⁴

7X10³

8X10³

10²

8X10²

7X10³

2X10²

1.0%

3x10³

6x10³

9x10³

5x10⁴

4x10⁵

2x10²

3x10²

10²

1x10³

10⁴

1.3

4X10²

4X10³

1X10⁴

9X10³

3X10⁴

10²

2X10²

3X10²

6X10²

1X10³

4X10²

3X10³

6X10³

8X10³

2X10²

10³

2X10²

4X10²

3X10²

1.5%

2X10³

4X10³

6X10³

5X10⁴

7X10⁵

4X10²

10³

2X10³

4X10³

3X10⁴

2X10²

8X10²

4X10³

8X10³

3X10⁴

10²

2X10²

10³

6X10²

5X10²

4X10³

3X10³

5X10³

7X10³

3X10²

2X10²

10³

3X10²

10³

2.0%

5x10³

3x10³

4x10³

2x10⁴

8x10⁴

2x10²

10²

3x10²

4x10³

6x10³

3X10²

4X10³

2X10³

7X10³

2X10⁴

10²

6X10²

2X10²

10³

3X10³

5X10²

3X10³

8X10³

3X10³

10²

10³

2X10²

4X10²

10³

T.PS.C = Total psychrophilic count

^*S = spoiled

ND = not detected.

Table 4: Chemical values of treated beef kofta samples stored at 4Cº

Time/

day

TBARS (mg MD/ Kg)

0 %

0.5%

1.5%

0 %

0.5%

1.5%

6.08

± 0.02

5.59

± 0.01

5.46

± 0.032

5.52

± 0.041

5.43

± 0.032

2.056

± 0.39

1.1 68

± 0.22

1.113

± 0.12

0.690

± 0.09

0.558

± 0.21

6.06

± 0.08

5.64

± 0.04

5.60

± 0.042

5.58

± 0.06

5.83

± 0.09

2.032

± 0.43

1.618

± 0.33

1.408

± 0.22

0.992

± 0.07

0.777

± 0.25

5.94

± 0.092

5.68

± 0.03

5.39

± 0.063

5.33

± 0.034

5.15

± 0.052

1.693

± 0.09

1.397

± 0.43

1.317

± 0.22

1.288

± 17

1.035

± 0.13

6.23

± 0.06

5.82

± .062

5.72

± 0.065

5.70

± 0.030

5.93

± 0.042

2.169

± 0.27

1.432

± 0.11

1.400

± 0.32

1.311

± 0.27

1.274

± 0.26

^*S

6.01

± 0.031

5.98

± 0.032

5.90

± 0.02

5.88

± 0.026

^*S

1.633

± 0.28

1.580

± 0.34

1.423

± 0.11

1.412

± 0.32

* S = spoiled

TBARS = Thiobarbituric Acid Reactive Substanc

Discussion

Sensory Quality

The results obtained in Table 1 show the sensory scores of grilled kofta after one day of shelf-life. Flavour and taste of control samples were unfavorable and might not be appealing to panelists than other treated samples. Flavour and taste were accepted by panelists with high score in samples treated with concentrations between 1 and 1.5% GTE. These results agree with those showed by Nirmal and Benjokul (2010). Green tea had not deteriorative changes in the sensory quality of beef steaks when marinated in their extract for six hours at 5ºC (Qualhas et al., 2010)

The changes in sensory characteristics during 8 days storage at 4ºC recorded in Table 2 revealed that with extending the shelf-life of the samples, off-flavor was developed in all samples by various scores from low to high score parallel to concentrations of GTE from low to high concentrations. The early signs of off-flavor appeared in control and 0.5% groups at 6 day storage, and such off-flavour was developed in other treated groups after 6 days of storage. A marked discoloration changes of kofta samples treated 2.0% GTE was observed, this might be implicated to the possibly penetration of chlorophyll pigments and their subsequent interference with other biochemicaly active compounds in beef samples, which caused an undesirable change in meat colour (Sarah et al., 2010). These results agree with those showed by Kumudavally et al. (2008); Jin-ling et al. (2009); Nirmal and Benjakul (2010).

Bacteriological quality:

From the results given in Table 3, it is noticed that total psychrophilic count reached the unacceptable limit (10⁶ cfu/g) at 6^th day in control group according to Egyptian Organization for Standardization and Quality Control (EOS, 2005). Total psychrophilic counts reached 8x10⁵; 4x10⁵; 7x10⁵ and 8x10⁴ cfu/g at 8^thday in treated samples with 0.5%; 1.0%; 1.5% and 2.0 0% GTE respectively. The antimicrobial effects of green tea extract in meat is well confirmed by Maolinchun (2006); Kang et al. (2007) and Nirmal and Benjakul (2010). The polyphenols of green tea extract had strong effect on the growth of total viable bacteria and total psychrophilic counts at 5^th and 10^thday during ice storage of fish (Noriyuki et al., 2001).

The acceptable limit for anaerobic spore forming bacteria in meat products do not exceed 10² cfu/g according to EOS (2005). Clostridium perfringens could be detected in little number of control samples during 0 and 2 day only with a mean value of 4 and 7 respectively. but the pathogen did not recovered from other treated groups. The concentration of 2.0% GTE samples showed more antimicrobial effect on C. perfringens. Juneja et al. (2007) confirmed that green tea extract has higher catechin content which is effective in controlling C. perfringens population densities during cooling of ground beef.

Also Sakanaka et al. (2000) found that the heat resistance Bacillus stearothermmophilus and C. thermoaceticum spores were more rapidly decreased by the addition of green tea polyphenols at high temperature. The differences in the obtained results may be attributed to the findings of Traci and Dunca (1974) who mentioned that a loss in the viability of C. perfringens cells may occur if foods were frozen or held under prolonged refrigeration. The inhibitory effects of GTE against C. perfringens were reported by Ahn et al. (1991); Juneja et al. (2006).

Most members of Enterobacteriaceae family are mainly mesophilic while some strains can grow at 0ºC (Downes and Ito, 2001). The results in Table 3 confirmed the inhibitory effect of different concentrations of GTE compared to control sample. 1.0%, 1.5% and 2.0% GTE were more effective in lowering the Enterobacteriaceae counts compared to control and 0.5% GTE groups. These results agree with Byrne (2009) who showed that the population of the pathogenic bacteria in pork loins meat packed with green tea extract film (GTE) 2.8% were significantly reduced during storage at 4Cº from 5.47 log cfu/g to 4.47/log cfu/g after 10 days.

The inhibitory effect of green tea extract 2%, 4% and 6% against E. coli, Pseudomonas aeruginosa; Serratia spp.; Bacillus subtilis; Enteobacteriaceae; coliform counts and Listeria monocytogenes were reported by Jin-ling et al.(2009) and Nirmal and Benjakul, (2010).

The results showed that Staph. aureus counts of untreated samples (control) were higher than those of treated samples with GTE where the mean values of Staph. aureus of each treated samples (0.5% ; 1.0% ; 1.5% and 2.0%) were 8 x 10³; 8×10³ ; 7x10³; and 3x10³cfu/g respectively at 8 days while the control samples reached 1x10⁵ cfu/g at 6 day during chilling storage. The antibacterial activities of green tea extract (GTE) against Staphylococcus aureus were reported by Kim et al. (2004); Vasudeo and Sonika (2009) and Javier et al. (2010).

The Egyptian Standardization (EOS, 2005) of frozen ball listed that the permissible limits for Staph. aureus must be not exceed than 10²cfu/g. The inhibitory action of green tea polyphenols and catechin is probably due to their ability to complex with extracellular and soluble proteins and to complex with bacterial cell walls (Sakanaka et al., 1996).

Chemical quality

The pH value assessed as a crucial factor for determination of meat quality (Nam et al., 2001), might interfere with solubility activities of antioxidants by changing in their electrical charges (Decker et al., 2005). Changes in pH value of treated beef kofta samples and control are shown during 8 days storage in Table 4. A gradual increase in the pH value was detected until day 4 while the pH values of treated samples showed a degree of stability by an increase in the amount of green tea extract added. The increase in meat pH value at storage period may be due to an increase in valotile bases compounds produced by either endogenous or microbial enzymes, and decomposition of nitrogenous components and increase of ammonia and free amine group produced in meat (Cann et al., 1983; Sikorski et al., 1990; Benjakul et al. 2002).

pH values of vacuum infused fresh chicken breast meats with green tea extracts stored at 5ºC ranged from 5.98 to 6.16(Rababah et al., 2006-a). There was gradual changes in pH values of treated fish fillets samples with 1%; and 2.5% GTE from 6.51 to 6.81 during storage period at 4ºC (Sarah et al., 2010). Meanwhile, Maolinchun (2006) confirmed that 0.1% of tea polyphenols had no significant effects on pH values by dipping of fish in (GTE) for one hour at 3ºC.

The results obtained in Table 4 revealed that the mean value of TBARS reached 2.161 mg/kg in the control samples at 6^th day, while it reached 1.633; 1.580; 1.423 and 1.412 mg/kg in 0.5%; 1.0%; 1.5% and 2.0% (GTE) treated samples at 8^th day respectively. The acceptable limit for TBA in meat do not exceed 0.9 mg/kg according to EOS (2005). It is evident that TBARS increased gradually with the time of meat storage due to formation of maloneldehyde (Gray and Crakal, 1992).Malonaldhyde production in food may be affected by temperature, fat amount in the product, the degree of unsaturation of fatty acids (Devore, 1988).These findings agree with Hüseyin, (2006); Maolinchun, (2006); Ko and Yang, (2008); Jin-ling et al. (2009); Dembele et al. (2010); Nirmal and Benjakul (2010) which confirmed the positive correlation between higher concentrations of green tea extract (2%, 4% &6%) (Phenolic and catechins content) and antioxidant properties of these compounds to retard the formation of malonaldehydes and TBARS values, control of lipid oxidation and preventing undesirable change in chemical properties in meat samples.

Furthermore Rababah et al. (2006-a) Found that TBARS values of uncooked (raw) chicken breast meats treated with green tea extract for 0 to 12 day of storage at 5Cْ ranged from 1.12 to 3.5 mg of malonaldehyde/ 100g while (TBARS) ranged from 2.50 to 7.80 mg/100g and from 2.4 to 7.35 mg/100g of chicken breast meat cooked by microwave and conventional electric oven, respectively. On the other wise Sarah et al. (2010) found much more reduction of TBARS values in 2.5% and 5% GTE treated fish fillets stored up to 8 days at 4Cْ , relative to other samples where (TBARS) valued from 0 to 8 days (0.13± 0.01 to 0.97 ± 0.09) and (0.11± 0.02 to 0. 80 ± 0.25) for 2.5% and 5% GTE respectively, while 1% GTE were (0.14± 0.01 to1.84± 0.09). Rababah et al.(2006-b)also found that TBARS values from 0 to 12 days ranged from (16.1-38.0 mg/kg) and (16.4- 67.8 mg/kg) for non irradiated raw chicken breast meat infused with green tea extract (3.000 ppm) and control samples respectively during storage at 5Cº. Meanwhile Sarker et al. (2010) found that the mean TABA values in fresh broiler meat for control, 0.5% and 1.0% green tea samples were 2.31± 0.09 ; 1.69± 0.13 and 2.22 ± 0.19 umol/l00g, respectively.

In conclusion the addition of 1.0 to 1.5% green tea extract to traditional Egyptian kofta resulted in the best koftaquality with extending their shelf-life up to 8 day under chilling storage. Panelists accepted the flavour and taste of treated products with concentration up to 1.5%. At this concentration, green tea extract can minimize the undesirable changes in microbiological and chemical properties which may be developed during storage.

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