Freshly prepared, ready-to-cook chicken patties were procured from HACCP and ISO-certified processing plants. Each 200 g product was aseptically packaged separately in sterile low-density polyethylene pouches. After being sealed with heat, the packages were delivered to the Board of Radiation and Isotope Technology (BRIT), Sector 20, Turbhe, Navi Mumbai. The chicken patties were divided into four groups of 50 patties each, with one group serving as the control, while the remaining three were subjected to electron beam irradiation at doses of 3.0, 3.5, and 4.5 kGy. One sample consisting of 5 chicken patties (200 gm each) was selected, and homogenized into a single composite sample. From this composite sample, the portions as required for the various tests were aseptically taken for further analysis. This process was repeated for 5 replicates in each group. Likewise, the same procedure was followed for analysis of samples in all control and treatment groups. Further, all the samples were analysed on 10 different intervals (0, 7, 9, 14, 21, 28, 31, 34, 37, 39 and 41st day) throughout the study. The packaged samples were placed in aluminium trays and exposed to radiation from a linear electron beam radiofrequency accelerator on both sides (Energy: 4.5 MeV, Beam Power: 15 kW, Pulsed Linear Accelerator–Electron Beam Accelerator Facility). The beam current was maintained between 0–4.5 mA, and irradiation was conducted at a conveyor velocity of 1.8 m/min. Dosimetry for the irradiation of these samples was carried out using a Radiochromogenic film dosimeter (B-3). Because of the electron beam’s limited penetration power, the samples were arranged to have a maximum thickness of 3 cm. Throughout the experiment, the samples were kept at refrigeration temperatures (0–4 °C). Following irradiation, all treated samples were transported in an ice box to the institutes laboratory and stored in a refrigeration room at 0–4 °C until further analysis.

For microbial analysis, 10 g of sample from each packet was weighed aseptically and transferred to 90 mL of sterile Normal Saline Solution (NSS) in stomacher bags for homogenization in a stomacher (Seward Stomacher 80, Fisher Scientific, Loughborough, Leicestershire, England) for 60 sec. Using 9 mL of sterile Normal Saline Solution (NSS), ten-fold serial dilutions were carried out, up to a 10⁶ dilution. The Total Viable Count (TVC) was determined using the standard pour plate method, as outlined in IS 5402:2012. Furthermore, differential counts of specific pathogenic and spoilage organisms were evaluated in duplicate using various selective and differential media, using the spread plate technique. Method and media for the isolation and enumeration were as follows: Staphylococcus aureus-IS:5887 part 2-1976 method using Baird Parker agar, Listeria monocytogenes-IS 11290-1:1996 method using PALCAM agar, Bacillus cereus-IS:5887 part 6-2012 method using Bacillus cereus agar, E. coli IS:5887 part 1-1976 method using eosin methylene blue agar, Salmonella spp. -IS 5887 Part 3:1999 method using xylose lysine deoxycholate agar, Pseudomonas aeruginosa -IS 14843:2000 method using Pseudomonas isolation agar. The plates were incubated for 24 hours at 37 °C. The yeast and mould-IS:5403 part 1:1999 method using Sabouraud dextrose agar and incubated at 24–25 °C for 5–7 days. For further confirmation, the obtained isolates were subjected to biochemical tests as prescribed in the standards as mentioned above. The microbial analysis of the samples was performed at the storage time of 0, 7, 9, 14, 21, 28, 31, 34, 37, 39 and 41st day until spoilage of the samples were observed.

A trained, institute-approved panel of 6 personnel scientifically evaluated the sensory properties of the irradiated chicken patties. The panel consisted of members of different age groups, sexes, the veterinary faculty, and the departmental staff. Each parameter in the sensorial analysis was evaluated by a 9-point descriptive scale [12] where 9- Like extremely, 8- Like very much, 7- Like moderately, 6- Like slightly, 5- Neither like nor dislike, 4- Dislike slightly, 3- Dislike moderately, 2- Dislike very much and 1- Dislike extremely. The products underwent testing and evaluation based on appearance, color, flavor, texture, juiciness, and overall acceptability. Following the assessment, the mean values for each parameter were determined. The surface color of the chicken patties was analyzed using a Color Difference Meter (Spectrophotometer Colourflex EZ-45, Reston, VA, USA), measuring Hunter color values L*, a*, and b*.

The chicken patty samples with a TVC above 6 log CFU/g, a pH above 6.3, a TBA value above 1 mg malonaldehyde/kg, and a Tyrosine value above 1 mg/100 g were considered spoiled and were not further considered in the study.

A randomised block design within treatments was used to collect and analyse the experimental data for every storage day. The study consisted of 4 treatment groups with 5 patties each and 4 replicates in each storage interval. The results were analyzed by ANOVA in “WASP-Web Agri Stat Package-2.0”, developed by the ICAR Research Complex, Goa, India.

The microbiological quality of electron beam-irradiated and non-irradiated (control) chicken patties stored under refrigeration was assessed at various intervals to evaluate their shelf life. An increase in irradiation dose corresponds to a decrease in microbial count, as shown in Fig. 1. On day 0, the average TVC (log CFU/g) for the control samples was found to be 5.19 $\pm$ 0.17 and 4.23 $\pm$ 0.10, 4.18 $\pm$ 0.39 and 3.63 $\pm$ 0.13, for EB dosage of 3.0, 3.5 and 4.5 kGy, respectively. All control (non-irradiated) chicken patty samples were fully spoiled by the 9th day of storage, with an average Total Viable Count (TVC) of 6.33 $\pm$ 0.35 log CFU/g. For comminuted poultry meat products such as chicken patties, Food Safety and Standards Authority of India (FSSAI) sets an upper permissible limit of 5 $\times$ 10⁶ CFU/g (equivalent to 6.7 log CFU/g) for the Total Viable Count (TVC) above which the product is considered unacceptable for consumption. In contrast, samples treated with 3.0, 3.5, and 4.5 kGy reached spoilage on the 34th, 37th, and 41st days of storage, respectively, with average TVC values of 6.43 $\pm$ 0.24, 6.42 $\pm$ 0.26, and 6.34 $\pm$ 0.23 log CFU/g, respectively (Fig. 1). The reduction in the total viable count in the chicken patties samples observed in the present study agree with Li et al. [13], who reported a decrease in the microbiota after treatment with electron beam irradiation in ready-to-eat chicken claw samples, with an increase in irradiation dose. Ham et al. [14] observed a substantial decrease in the total bacterial count of beef patties as the irradiation dose increased. Likewise, Shin et al. [15] also reported that electron beam irradiation at 4 kGy led to a reduction in the microbial count of Bologna sausage.

Fig. 1.

Average microbiological count (log CFU/gm) and shelf-life of chicken patties treated with electron beam irradiation at the dose rate of 3.0, 3.5 and 4.5 kGy and stored at refrigeration temperature (0–4 °C). Control: non-irradiated chicken patties; P1: Chicken patties irradiated at the dose rate of 3.0 kGy; P2: Chicken patties irradiated at the dose rate of 3.5 kGy; P3: Chicken patties irradiated at the dose rate of 4.5 kGy. TVC, Total Viable Count.

The extended storage period of the samples up to 41 days at the effective dose rate of 4.5 kGy is in sharp contrast to the non-irradiated control samples wherein spoilage was observed on the 9th day of storage. The observed microbial inhibition is likely due to the ability of ionizing radiation to damage bacterial DNA and interfere with essential cellular processes [16]. Whereas, the initial count of S. aureus (log CFU/g) on the 0th day for the control chicken patties samples was 1.89 $\pm$ 0.20, and it further spoiled on the 9th day, with a corresponding average count of 3.22 $\pm$ 0.33.

None of the samples treated with 3.0, 3.5, and 4.5 kGy exhibited the presence of S. aureus. Similar reductions in S. aureus counts have been reported in previous studies. Deepika [17, 18, 19] and Khillare [20] observed a significant decline in S. aureus levels in pork sausages, salami, and raw pork samples following electron beam irradiation. Likewise, Cabeza et al. [8] found that treating ham slices with 2 kGy of electron beam irradiation led to a marked reduction in S. aureus counts. These findings align with the study by Chang et al. [21], who demonstrated that S. aureus in suspension culture was totally rendered inactive by 2 kGy of electron beam irradiation, whereas 4 kGy efficiently destroyed S. aureus cells in biofilms. Previous studies have reported that increasing the irradiation dose, particularly at higher levels, results in significant fragmentation of cellular components of S.aureus organisms. The bacterial inactivation maybe, therefore, attributed to the leakage of biomolecules like adenosine triphosphates (ATPs), nucleic acid and proteins occurring due to European Bioinformatics Institute (EBI) induced cell membrane damage [21]. All the control and irradiated chicken patties samples were also analyzed for detection of E. coli, Salmonella spp., Pseudomonas spp., Listeria spp., and B. cereus where none of the non-irradiated and irradiated chicken patties samples was found to be positive for these organisms. The control chicken patties samples showed average yeast and mold count as 2.62 $\pm$ 0.62 on the 9th day, whereas chicken patties samples treated with dosages 3.0, 3.5, and 4.5 kGy did not show any presence of yeast and mold count, thus indicating the safety of the product at its extended shelf-life.

A gradual increase in pH values was observed in all chicken patty samples during storage. As shown in Fig. 2, the initial pH values on day 0 for the control samples and those irradiated at 3.0, 3.5, and 4.5 kGy were 6.16 $\pm$ 0.04, 6.15 $\pm$ 0.11, 6.10 $\pm$ 0.06, and 6.08 $\pm$ 0.11, respectively. Spoilage was observed in the control and samples irradiated at 3.0, 3.5, and 4.5 kGy on the 9th, 34th, 37th, and 41st day, respectively, corresponding to pH values of 6.35 $\pm$ 0.02, 6.31 $\pm$ 0.04, 6.34 $\pm$ 0.05, and 6.37 $\pm$ 0.03. The observed increase in pH of chicken patty samples aligns with the findings of Deepika [17, 18, 19] and Khillare [20], who reported a similar pH increase in control and irradiated pork sausage, salami, and raw pork samples stored under refrigeration throughout the storage period. However, this was in contrast to a study conducted by Wahyono et al. [22] where the pH remained unchanged after Electron Beam irradiation on pork samples. This rise in the pH could possibly be due to microbial degradation of proteins and amino acids, forming compounds such as ammonia and amines [23].

Fig. 2.

Average of pH of chicken patties treated with electron beam irradiation at the dose rate of 3.0, 3.5 and 4.5 kGy and stored at refrigeration temperature (0–4 °C). Control: non-irradiated chicken patties; P1: Chicken patties irradiated at the dose rate of 3.0 kGy; P2: Chicken patties irradiated at the dose rate of 3.5 kGy; P3: Chicken patties irradiated at the dose rate of 4.5 kGy.

The TBA values observed on 0th day for control and irradiated chicken patties at the dose of 3.0, 3.5, and 4.5 kGy were 0.51 $\pm$ 0.17, 0.43 $\pm$ 0.25, 0.41 $\pm$ 0.18 and 0.42 $\pm$ 0.20, respectively. These values increased to 0.87 $\pm$ 0.28, 0.94 $\pm$ 0.32, 0.90 $\pm$ 0.37 and 1.11 $\pm$ 0.48 on the 9th, 34th, 37th, and 41st day, respectively (Fig. 3). The increase in TBA values in both irradiated and non-irradiated chicken patty samples during the storage period was consistent with the findings of Ham et al. [14] and Trindade et al. [24], who reported a similar rise in Thiobarbituric acid reactive substances (TBARS) values in processed meat products and beef burgers following electron beam irradiation as storage time progressed. The elevated TBA value in this study indicates the increase in the malonaldehyde value which is an oxidative product of poly unsaturated fatty acid present in the meat, thus suggestive of spoilage of the chicken patties [25].

Fig. 3.

Average TBA number (mg malonaldehyde/kg) of chicken patties treated with electron beam irradiation at the dose rate of 3.0, 3.5 and 4.5 kGy and stored at refrigeration temperature (0–4 °C). Control: non-irradiated chicken patties; P1: Chicken patties irradiated at the dose rate of 3.0 kGy; P2: Chicken patties irradiated at the dose rate of 3.5 kGy; P3: Chicken patties irradiated at the dose rate of 4.5 kGy. TBA, Thiobarbituric Acid.

The average tyrosine values (mg/100 g) of control and irradiated chicken patties samples at the dose rate of 3.0, 3.5, and 4.5 kGy on 0 days were 0.25 $\pm$ 0.06, 0.22 $\pm$ 0.09, 0.24 $\pm$ 0.11 and 0.24 $\pm$ 0.09, respectively. The tyrosine values gradually increased to 0.56 $\pm$ 0.13, 0.88 $\pm$ 0.25, 0.78 $\pm$ 0.40 and 1.18 $\pm$ 0.52 on 9th, 34th, 37th and 41st day (Fig. 4). The increase in tyrosine values observed in this study is consistent with the findings of Rane et al. [5], who reported a similar rise in tyrosine values in chicken nuggets as the storage period progressed. Since it assesses the amount of tyrosine and tryptophan found in the non-protein extract of meat, the tyrosine value serves as a marker of proteolysis of the meat [26]. The growth of spoilage bacteria in the meat leads to both lipolytic and proteolytic changes, resulting in the buildup of breakdown products like free amino acids and aldehydes. Notably, both elevated tyrosine and TBA values with declining sensory scores in the current study, particularly in terms of odor, taste, and overall acceptability suggests a direct relationship between biochemical spoilage markers and sensory deterioration.

Fig. 4.

Average of Tyrosine number (mg/100 g) of chicken patties treated with electron beam irradiation at the dose rate of 3.0, 3.5 and 4.5 kGy and stored at refrigeration temperature (0–4 °C). Control: non-irradiated chicken patties; P1: Chicken patties irradiated at the dose rate of 3.0 kGy; P2: Chicken patties irradiated at the dose rate of 3.5 kGy; P3: Chicken patties irradiated at the dose rate of 4.5 kGy.

The sensory scores of irradiated and control chicken patties exhibited a progressive decline across all attributes as storage time increased. Table 1 presents the sensory scores obtained for both control and irradiated chicken patty samples. The colour values of irradiated and control chicken patties at different refrigeration storage intervals are presented in Table 2. The L* values showed an increasing trend over the storage period, while the a* values of irradiated samples decreased with extended storage duration. Significant differences were observed in b* values between the treatment and control groups, with a further decline throughout refrigeration storage. The findings of the current study are consistent with those of Johnson et al. [27], who reported that chicken frankfurters treated with electron beam irradiation at 3 kGy maintained their sensory qualities with minimal changes during refrigerated storage for up to 32 days. Remarkably, a previous study reported that the sensory evaluation of irradiated and frozen minced turkey meat showed acceptable sensory scores even after storage up to 6 months [28]. Similar to the present study, no significant differences were found in the sensory evaluation scores between control and irradiated ground beef samples, with a 1 kGy dose exerting minimal impact on tenderness, juiciness, beef flavor, and aroma [29]. Similarly, the L* values for the present study increased throughout storage, which concurs with Rane et al. [5] who reported an increase in L* value in irradiated chicken nuggets. The findings of the present study are consistent with those of Wahyono et al. [22], who reported a decrease in the a* values of irradiated pork during storage. However, in contrast to our results, Carcel et al. [4] observed an increase in the a* values of electron-beam-irradiated chicken steaks and hamburgers with higher irradiation doses. The decline in b* values observed in this study aligns with the findings of Du et al. [9], who reported a similar decrease in the b* values of electron beam-irradiated cooked chicken breast fillets over time. Conversely, Carcel et al. [4] noted an increase in the b* values of electron beam-irradiated chicken steak and hamburgers with higher irradiation doses. These color changes, particularly the increase in lightness (L*) and decline in redness (a*), may be due to pigment oxidation and structural modifications induced by irradiation and prolonged storage [30].