Changes in Total Plate Counts and Quality of Pig Small Intestine by Different Washing and Packaging Methods

The small intestine samples from crossbred pigs (about 105 to 110 kg body weights) collected at a commercial slaughterhouse (Korea) were used in the present investigation. The slaughters of the pigs were carried out under the commercial slaughtering process including: electrical stunning, bleeding, scalding, dehairing, washing, skinning and evisceration. Immediately after slaughter, the small intestine (duodenum and jejunum parts) samples were collected, trimmed off of visible fats and connective tissues and washed with tap water to remove food remnants and feces. Thereafter, the small intestines (about 100 kg) were cut into fragments (approximately 1 m in length) which were then used for packaging and acetic acid washing treatments.

For packaging treatments; the samples (approximately 16 kg each) were used for each packaging method; aerobic packaging (AP), skin packaging (SP) and vacuum packaging (VP). In each packaging method, the assigned samples were divided into small equal portions (1 kg each) which were then packaged by the above mentioned methods. After packaging, the packaged samples were divided into different storage groups (1, 4, 7, and 10 d, about 4 kg samples/group). The storage was done in a cooling room at 4℃.

For washing treatment; the samples (12 kg each) were rewashed with acetic acid solutions at different level (0%, 0.5%, 1%, and 2% v/v). The washing was done by immersing the samples in the acetic acid solution (5 liters per each kg sample) and washed for 2 min. Thereafter, the samples were rinsed with tap water for 1 min and absorbed with wiper papers, placed into plastic pouches (about 1 kg sample/bag), sealed and stored at 4℃ for 1, 4, 7, and 10 d as shown the Table 1.

The total plate counts (TPC) in pig small intestine were determined following the procedures of Korea Food & Drug Administration (KFDA) Food Code (2008). Twenty-five grams of pig small intestine were taken and added with 225 mL of peptone water (1 g/L peptone), and were then homogenized for 1 min in a stomacher (400 VW, Bag Mixer, France). A serial dilution was made for the homogenized samples using peptone water. The diluted samples (1 mL each) were plated onto the Petrifilm Aerobic Plate Counts (3M Health Care, MN, USA) and incubated at 37℃ for 48 h in an incubator. All the red colonies appearing on the plates were counted as the TPC and expressed as log colony forming units/g (CFU/g).

pH values were determined by homogenizing 3 g of each sample with 27 mL distilled water using a homogenizer (T25basic, IKA, Malaysia). The pH values were measured using a pH-meter (S20K, Mettler Toledo, Swiss).

The surface color of pig small intestine was measured using a chromameter (CR-400, Minolta, Japan) standardized with a white plate (Y=93.5, X=0.3132, y=0.3198). Five measurements were taken on different locations of the outer surfaces of the samples and results were expressed according to the Commission International de l’Eclairage (CIE) system and reported as CIE L* (lightness), CIE a* (redness), and CIE b* (yellowness).

Thiobarbituric acid reactive substances (TBARS) content was determined to evaluate the lipid oxidation levels in samples, following the procedure of Buege and Aust (1978). The samples (5 g each) added with distilled water (15 mL), saturated butylated hydroxyansole (50 μL) and 20 mL of thiobarbituric acid (0.02 M)/ trichloroacetic acid (15% w/v) (TBA/TCA at 1:1 ratio) were homogenized at 11,000 rpm for 15 s using an Ultra­Turrax T25B. The volume of the sample homogenate was adjusted to 50 mL with the TBA/TCA solution and immediately placed on ice. The tube containing homogenate was immersed in a 90℃-water bath for 15 min. After removal from the water bath, the sample tubes were immediately placed on ice to cool for 20 min and centrifuged at 3,000×g for 10 min using an Avanti J­E centrifuge (Beckman Coulter Inc., CA, USA). About 1.5 mL of supernatant was taken and the absorbance was measured at 531 nm using an UV– visible spectrophotometer (ProteomeLab Du­800, Beckman Coulter, Inc., USA). The TBARS content was calculated on the sample weight basis and expressed as mg malondialdehyde/kg (MDA/kg) sample. Three repetitions were applied for each sample in each treatment.

All experiments were repeated thrice. Data was collected for the determination of pH, color, TPC, and thiobarbituric acid reactive substances. The data was analyzed using a one-way ANOVA of SAS software (SAS Institute Inc., Cary, North Carolina, USA) followed by Duncan’s multiple range tests to determine significant difference between the treatments (p<0.05).

The changes in TPC of pig small intestine washed with different concentrations of acetic acid during cold storage are presented in Table 2. The TPC in all the treatments were significantly (p<0.05) increased with increased storage days. The TPC were significantly (p< 0.05) higher in the control as compared to those in the treatments at the end of storage (10^th d). However, no significant differences in the TPC occurred among treatments with acetic acid solutions. The results showed that prior to the storage, washing the pig small intestine with 0.5% acetic acid solution was more effective in inhibiting the growth of TPC.

The effect of packaging methods on the TPC in the pig small intestine during cold storage are presented in Table 3. The TPC in all the samples significantly (p<0.05) increased as increasing the storage time. The TPC was significantly (p<0.05) higher in the AP-treated samples than in the SP- and VP-treated samples after 7 d storage. However, there were no significant differences in the TPC among all treatments after 10 d storage. These results suggest that the use of SP or VP method was more effective in improving the microbiological safety for the fresh pig small intestine during cold distribution.

It is suggested that the internal organs of animals should be removed within 30 min after bleeding. Bijker (1981) illustrated a drastic increase in the bacterial growth curve when products were stored at 4℃ compared to that of similar products stored at 2℃. Even at 2℃, bacterial counts in beef, pork, and lamb organs were altered during 5 d of storage (Hanna et al., 1982). The freezing of liver, kidney, and heart for 4 d did not significantly decrease the bacterial counts in these products (Hanna et al., 1982). Kang et al. (2014) suggested that small intestine is required a lot of washing times to remove blood, indigestible feed, and feces, etc. These authors have demonstrated that the reduction of initially high bacterial numbers is very important for shelf-life extension and freshness maintenance of pig small intestine.

Shelf-life can be defined as the period of time a product can be stored without becoming sensorial unacceptable or becoming a health risk. The predominant reason for meat spoilage is microbial activity, oxidation and enzymatic autolysis (Dave and Ghaly, 2011). In some cases, spoilage is caused by one specific microorganism (Gram and Dalgaard, 2002; Kalchayanad et al., 1993), but spoilage mainly depends on the composition of a heterogeneous microflora. However, other reasons for spoilage exist, since even sterile vacuum-packed meat has a limited shelf-life and becomes bitter over time, probably due to the proteolytic deterioration of meat proteins by intrinsic enzymes (Meinert et al., 2009). Odorous impression (scale anchored to the extremes ‘fresh’ and ‘spoiled’) is suitable attribute for describing spoilage of pork, beef (Meinert et al., 2009), and chicken (Franke et al., 2017), because the development of deviating raw meat odor and psychotropic growth follows the same pattern (Meinert et al., 2009).

Preservation of meat and meat products is essential for the meat industry. Several thermal and non-thermal methods are known and have been tested for decontaminating effects on bacteria in packed products to obtain an increased shelf-life and safety (Aymerich et al., 2008). In the present study, however, our treatment methods (packaging under different conditions and washing with acetic acid solutions) partly showed the beneficial effects on improving shelf-life and safety of pig small intestine during cold storage.

Table 4 shows the changes in pH values of pig small intestine as affected by different packaging methods during cold storage. The pH values of the AP-treated samples significantly (p<0.05) decreased with increased storage time whereas, no constant tendency was found in the SP- and VP- treated samples with increased storage time. The SP-treated samples had significantly (p<0.05) higher pH value than the SP- and VP-treated samples during storage. After 7 d of cold storage, the pH value of VP-treated samples was lower than those of the AP- and SP-treated samples (p<0.05). Therefore, the VP method seemed to be more effective in maintaining the pH environment of small intestine during cold distribution. Kang et al. (2014) demonstrated that after 7 d of cold storage, pH levels of white viscera with small and large intestine were favorable for microbial growth. From this reason, the small intestine requires a more careful washing process than the other pork by-products.

Table 5 shows the changes in color traits of pig small intestine as affected by different packaging methods during cold storage. The treatment and storage time did not cause any changes in CIE L* values. The samples treated with AP and SP had significantly (p<0.05) higher CIE a* and CIE b* values than the ones treated with VP after 7 d storage. These results suggest that lower oxygen content in the VP treated samples made them become paler in color.

The changes in TBARS of pig small intestine by different packaging methods during cold storage are shown in Table 6. There were no changes in TBARS values for all the treatments as increasing the storage time. However, the TBARS values in the AP-treated samples were significantly (p<0.05) higher than those of the SP- and VP-treated samples after 7 days storage. These results suggest that the SP and VP methods were effective in preventing the lipid oxidation in the small intestine during storage. In the meat industry, adding value to meat by-products by applying the technological and scientific innovations to make the low valued by-products into the products with highly economic profitability is necessary to support the meat production sector (Ockerman and Basu, 2004a; Ockerman & Basu, 2004b; Pearl, 2004).