Introduction

Fresh meat and meat products are the major protein source and are perishable. Maintenance of quality and delivery of safe food to consumers is a major challenge today. Edible films and coatings prepared from polysaccharides, proteins and lipid materials besides serving as gas and moisture barriers can also act as carriers for functional food additives such as antioxidants and antimicrobials. Alginate is one of the most important polysaccharide that is used to develop biodegradable films because of its capability to form a continuous matrix and is renewable with abundant resource (Talja et al., 2007). Bio-films and coatings, as carriers of foods additives (i.e. antioxidants, antimicrobials), have been particularly considered in food preservation due to their ability to extend shelf life (Sallam, 2007). Various essential oils could be incorporated as food additives into edible films to broaden their antimicrobial properties. Essential oils are complex mixtures of numerous compounds from various parts of the plants. Clove oil (Eugenol) has biological activities, such as antibacterial, antifungal, insecticidal, anti oxidant activities and is used traditionally as flavoring agent and antimicrobial material in food. Eugenol showed an inhibitory effect on the growth of L. monocytogenes, Campylobacter jejuni, S. enteritidis, E. coli and S. aureus (Cressy et al., 2003). Cinnamaldehyde, which was identified in cinnamon oil, is an effective inhibitor of the growth of yeasts, bacteria and molds as well as toxins produced by micro-organisms. It can completely inhibit the growth of a number of bacteria such as Staphylococcus spp., Micrococcus spp., Bacillus spp. and Enterobacter spp. (Masuda et al., 1998). These essential oils upon direct addition into the food may alter the flavour of the product, because of their strong odour.

With this background, the present work has been designed to develop and evaluate sodium alginate based edible films incorporated with essential oils i.e. clove oil and cinnamon oil on the quality of chicken balls with objectives of studying the apparent characteristics of these films on chicken balls and to study the physicochemical and microbiological characteristics of the chicken balls wrapped with above polymers at refrigerated (4±1^oC) and frozen (-18±1^oC) storage temperature at regular intervals.

Materials and Methods

Film forming solution was prepared with sodium alginate at a concentration of 2% (w/v) in distilled water and alginate was allowed to hydrolyze. Glycerine was used as plasticizer at 4 % level. Two additives namely clove oil and cinnamon oil each at 1% level were added slowly with continuous stirring to the above solution and three types of coating solutions were produced viz. solution without addition of EO and with sodium alginate alone (T₁), sodium alginate incorporated with 1% clove oil (T₂), and incorporated with 1% cinnamon oil (T₃) and solutions were homogenized in vortex mixer for 2 minutes. Films were formed by casting method and evaluated for their physical characteristics. The physical characteristics of films like thickness and grammature were evaluated. The thickness was measured following with digital micrometer and data was obtained from the average of ten random measurements from each film and the grammature was measured following the procedure outlined by Geraldine et al., 2008.To assess the antimicrobial activity of the films modified disc diffusion method of Bauer et al., 1966 was employed using MHA plates having lawn cultures of E.coli and S.aureus along with standard antibiotics i.e. Penicillin G and Streptomycin for S. aureus where as Gentamicin and Chloramphenicol for E.coli.

Meat balls were prepared with chicken (65%), salt (1.8%), fat (4.0%), binder (3.0%), spices (2.2%), condiments (4.0%) and water (20%). The balls were wrapped in these films. Chicken balls were evaluated for quality in terms of proximate composition, pH, water loss analysis, 2-thiobarbituric acid reactive substances value, peroxide value and total plate counts at refrigerated and frozen storage temperatures at regular intervals i.e., 5 days and 15 days respectively. The percentage moisture, fat, crude protein and peroxide value were estimated as per AOAC, 1995. The pH of the preparation was estimated by the method of Trout et al., 1992 and was measured by using digital pH meter (Oakton Instruments, USA). The water loss was estimated as described by Lu et al., 2009. The distillation method outlined by Tarladgis et al., 1960 was followed for the determination of TBARS values. Microbial quality was evaluated as per the procedure of APHA, 1984. The chicken balls were cooked and subjected to a six member taste panel for sensory evaluation to evaluate color, appearance, flavour, juiciness, tenderness and overall acceptability on a 9 point hedonic scale as per the scale suggested by Peryam and Pilgrim (1957).

Statistical Analysis

The data was subjected the statistical analysis using SPSS MAC, version 20.0, SPSS Chicago (US).The entire experiment was repeated six times to reduce the standard error.

Results and Discussion

The results of effect of edible polymer coatings of sodium alginate with cinnamon oil and clove oil on quality of chicken balls were presented in Tables 1, 2 and 3.

Table 1: Proximate and film characteristic (Mean ± S.E) values of chicken balls as influenced by different edible films

(P<0.05) means bearing at least one common superscript in the same row do not differ significantly. SA: Sodium alginate, CL: Clove oil, CI: Cinnamon oil

The T₂ and T₃ formulations of chicken balls showed significantly (P< 0.05) higher moisture content than the control and T₁. The higher moisture content might be due to the retention of moisture content which can be attributed to the incorporation of the hydrophobic essential oils affecting the ability of the film wrap to retain water (Ghasemlou et al., 2013) with in the product and the ability of wrapping materials to prevent water losses. These findings were in agreement with Chidanandaiah et al., 2009 and Ojagh et al., 2010.

Table 2: Physiochemical and microbial (Mean ±S.E) values of chicken balls as influenced by different edible film wraps

(P<0.05) means bearing different superscripts under different storage periods in the same row differ significantly. SA: Sodium alginate, CL: Clove oil, CI: Cinnamon oil.*spoiled

The proximate composition did not differ significantly between the treatments. pH, TBARS, peroxide value and percent water loss of wrapped and unwrapped chicken balls differed significantly. The wrapped balls revealed lower values when compared to unwrapped controls. Among the wrapped formulations the values were lower for essential oil incorporated counter parts. The edible coating significantly decreased weight loss in the meat samples during all days of display. Little or no exudates from the coated samples were visible, which is an important attribute.

Table 3: Sensory (Mean ± S.E) values of chicken balls as influenced by different edible film wraps

(P<0.05) means bearing different superscripts under different storage periods in the same row differ significantly. SA: Sodium alginate, CL: Clove oil, CI: Cinnamon oil.*spoiled

During storage, irrespective of formulations pH, percent water loss increased both at refrigerated and frozen storage temperatures. pH values and percent water loss were lower in T₂ and T₃ when compared with C and T₁. This lower values due the effect of phenolic compounds such as flavonoids and phenolic acids present in oils, which exhibit a wide range of antimicrobial effect and the hydrogen and covalent interactions between the alginate network and phenolic compounds (Ghasemlou et al., 2013) limiting the availability of hydrogen groups might be responsible for lower water losses (Shen et al., 2010). However the rate of increase in pH and water loss was lower for essential oil incorporated film wrapped chicken balls. The development of desiccated surface layer over wrap in cold storage might produced a further resistance to mass transfer thus bringing about a slow increase in water loss. The results were in accordance with the result of Yongling et al., 2011. The effect of wrapping on oxidative stability was evaluated. The inclusion of essential oil in wrapping film significantly affected the value. The difference might be due to the difference in chemical composition and the way and stage of inclusion of EO during preparation of film. The TBARS values of T₂ and T₃ were significantly (P<0.05) lower when compared to T₁ and C which might be due to the poly phenols acting as free radical scavengers (Perumulla and Hettiarachchy, 2011). The sodium alginate based film layers on the surface of the product might have resisted oxygen diffusion and retarded lipid oxidation. These results were in accordance with Chidanandaiah et al., 2009.The values of all treatments along with controls increased continuously during storage period irrespective of temperature of storage but the rate of increase was lower for T₂ and T₃ when compared to T₁ and C. This observation was similar to the results of Yongling et al., 2011. These results were in agreement with those of Rostami et al., 2010. The high values had not affected the palatability of the product but might be due to the vicinity of the product with the film wrap which is being incorporated with EO with a process into the wraps which involves heat effects. Total plate counts (TPC) were significantly (P<0.05) lower in wrapped samples when compared to the control samples. This might be due to the antimicrobial effect of oils in synergy with the ability of sodium alginate to produce strong gels resulting in formation of semi permeable layer reducing microorganism infiltration into the wrapped samples accompanied by lowering water activity. During storage the total plate counts increased with increasing storage period. However lower counts were noticed in treatment samples in comparison with controls. Further TPC of T₂ and T₃ were significantly (P<0.05) lower than the control and T₁.

There was an increase in the shelf life of five days at refrigerated storage temperature and 15 days at frozen storage temperatures. This marginal improvement in microbial quality might be due to the effect of phenolic compounds that are present in clove and cinnamon oils which were proved to possess certain antimicrobial activity in vitro. These results were in agreement with the reports of Chidanandaiah et al., 2009 and Yongling et al., 2011.The formulation of chicken balls wrapped with sodium alginate based film recorded significantly (P<0.05) higher sensory scores than the control chicken balls. These sensory results were in accordance with Chidanandaiah et al., 2009 and Yongling et al., 2011. Thickness of the films ranged from 360 to 363µ. Mean thickness of 362µ was formed which is indicative of the desirable characteristics of these films for future use as wraps or as pouches for primary packaging of the product. Incorporation of natural spice oils did not significantly (p>0.05) affect the resulting film thickness. This was in agreement with Ghasemlou et al., 2013.Grammature of the film ranges from 761 to 764g/m².Grammature is directly related to the mechanical resistance. In other words, greater grammature yields greater mechanical resistance. The values obtained were greater than Cassava Alginate Films (Henrique et al., 2007).

The results of modified disc diffusion test revealed that alginate films containing clove oil and cinnamon oil can effectively inhibit the growth of two tested bacteria with varying magnitude. Both gram positive and gram negative bacteria were sensitive to the potent essential oils. Cinnamon oil exhibited better effect when compared to the moderate effect seen with clove oil at 1% level. The zone of inhibition of clove and cinnamon oil incorporated films ranged from 9.75 to 19.45 mm in diameter.

Conclusion

The salient features of the study revealed that edible films with essential oils namely clove oil and cinnamon oil each at one per cent level had significant effect in reducing the fat oxidation, microbial infiltration and can improve the shelf life of the product without affecting the sensory quality. The study revealed the possibility of formation of edible film wraps as primary packaging materials from sodium alginate with incorporation of essential oils which can also serve to extend the shelf life of the product.

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