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

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

* 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^th day 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^th day 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 3x10³ cfu/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 10² cfu/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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