Pork hams (Landrace×Yorkshire, grade A) were purchased from the local market (Samho Co., Gwangju, Korea). After taking off the lean and excess connective tissue, the meat was ground and mixed with non-meat ingredients (1.3% salt, 0.4% sodium tripolyphosphate, 0.25% cured blend, 0.05% sodium erythorbate, and 1% soy protein isolate). The meat batter was stuffed into polyvinylidene dichloride film and cooked in a water bath at 75°C for 30 min. After chilling, LFSs were coated with films and stored at 10°C under refrigeration for 35 days.

The SA was purchased from the Tureban company (Goyang, Korea). The CTP was purchased from seed fruit and vegetable products company (Dunhuang, Gansu, China). A film-forming solution including SA (2%) was dissolved in calcium chloride solution (0.01 g/100 mL) with glycerol (same amount as SA) and dried in a dry-oven at 50°C for 24 h. Cross-linking was completed by pouring 50 mL of calcium chloride into film for 30 s followed by drying at room temperature for 6 h. Except that, 1% CTP was additionally added to prepare for a tomato SA film.

The pH of samples was determined randomly with a pH meter (Mettle-Toledo, Schwarzenbach, Switzerland). The color values consisting of lightness (Commission Internationale de l’Eclairage [CIE] L*), redness (CIE a*), and yellowness (CIE b*) of samples were measured by the color reader (Model CR-10. Minolta, Tokyo, Japan). For the microbial count, 10 g ground sample was mixed with 90 mL saline water (0.9%) using a Stomacher Lab Blender and serial dilutions were prepared. Then, about 0.1 mL of diluted sample was dispersed onto the surface of violet red bile (VRB) and total plate count (TPC) agar (Bingol and Bostan [15]). Subsequently, VRB and TPC agars were incubated at 37°C for 24 h.

Moisture, crude fat content, and fat content were assessed at 0, 3, 7 14, 21, 28, and 35 days by the method of AOAC [16]. Crude fat content was determined by the Soxhlet extraction method and crude protein analysis was carried out by following Kjeldahl technique.

Universal Testing Machine (Model 3344, Canton, MA, USA) was used to perform texture profile analysis (TPA) according to the method described by Bourne [17]. Sausage samples (1.30 cm length and 1.30 cm diameter) were compressed with a 500-N load cell at operational speed of 300 mm/min. TPA values were expressed in terms of hardness (gf), springiness (cm), gumminess, chewiness, and cohesiveness of LFSs.

Approximately 1.5 g of sample was wrapped in 3/4 filter paper (one piece of filter paper was separated into 4 pieces uniformly). Then, the sample was centrifuged (3,000 rpm) for 15 min (VS-5000N, Vision Scientific Co. Ltd., Bucheon, Korea). Weight of both filter paper and samples was measured again. The expressible moisture (EM) content of samples was calculated as follows:

ΔT was the Thimble weight difference before and after cen trifugation. A was the initial weight of the sample.

The oxidative rancidity was evaluated based on the thiobarbituric acid reactive substances (TBARS) value [18]. Each sample was mixed with 2.5% trichloroacetic acid (3 mL) and 1% 2-thiobarbituric acid (17 mL) in a cap tube. Then, tubes were put into 90°C boiling water bath for 30 min. Next, supernatant of each solution was mixed with 5 mL chloroform and centrifuged at 2,000 rpm for 5 min (VS-5000N, Vision Scientific Co. Ltd., Korea). Subsequently, approximately 3 mL petroleum was added to each supernatant and further centrifuged. Finally, clear solutions were analyzed by spectrophotometer (UV-1601, Shimadzu, Kyoto, Japan) at a wavelength of 532 nm.

The data on the effects of three different treatments during 35 days of storage at 10°C on physicochemical properties and antioxidant activities of LFSs were collected and subjected to two-way analysis of variance with treatments and storage time as factors using SPSS 21.0 program for windows. If the interaction between two factors were significant, then the data were separated out by treatment and storage time, which was analyzed at the significant level of 0.05, respectively.

pH and color values of LFSs are shown in Table 1. During storage, no changes in pH values of pooled control and treatments were observed during storage time, since the treated sausages and control didn’t detect microbial counts until 28 days of storage (< 2^e Log colony-forming unit [CFU]/g). LFSs wrapped with 2% SA film were same pH as LFSs without film (control [CTL]), but LFSs wrapped with 2% SA and 1% CTP film (TSA film) were lower pH than those of control, which might be due to the addition of tomato powder. Although the pH of sausage decreased with the wrapping with TSA-film statistically, the differences in pH was not enough to affect the sausage quality of sausage since the difference in pH was minimal. However, Deda et al [19] reported that the pH reduction of frankfurter containing tomato paste was a result of an increase in lactic bacteria during storage. Surface color is the most important factors affecting consumer acceptance, purchasing decisions, and satisfaction. Sausage color values were primarily related to the film. LFSs with TSA film had lower lightness (L*) value, but higher yellowness (b*) value than CTL. Redness (a*) values of all treatments exhibited no change regardless of wrapping. Based on the results, it was apparent that improvement in red and yellow color was due to the wrapped films, which led to increased preference of consumers for the products. Yuan et al [20] reported that chitosan films with added pomegranate peel extracts reduced the lightness and increased the redness. The increment of yellowness was affected by the lycopene in tomato powder, which imparted a peculiar red color [21]. During storage time, the redness and yellowness trended to increase, but lightness didn’t change. Candogan [21] did the similar study on beef patties added with different levels of tomato paste and he found that during storage, lightness and redness of patties added with tomato paste decreased but yellowness increased. He also reported that changes of color values were due to antioxidant activities of lycopene and the pigments present inside tomato paste.

Crude fat, crude protein, and moisture of CTL, SA, and TSA were 2.05, 2.23, and 2.26; 16.30, 17.04, and 17.45; 80.3, 78.8, and 78.6, respectively (Table 2). During the storage period, moisture and crude fat contents (%) exhibited no differences, except for a gradual decrease in crude protein level. Although moisture and crude fat contents (%) of all treatments were almost similar, regardless of wrapped films, protein content (%) of LFSs wrapped with TSA film was higher than CTL and similar to LFSs wrapped with SA film; However, no differences in protein content (%) was observed between CTL and LFSs wrapped with SA film (p>0.05). Elbakheet et al [22] reported that significant differences in fat content, ash content, and fiber content (%) were not observed among different samples during storage. Also, protein content, fat content, ash content, and crude fiber content exhibited an increase with increased addition of replacement of wheat germ flour. Increased protein content (%) in LFSs wrapped with film was observed, especially in LFSs wrapped with TSA film. However, moisture or fat content (%) was not different among the different treatments. Based on proximate analyses, it can be concluded that LFSs wrapped with film affected the proximate analyses due to water absorption from sausages by the film thereby, resulting in increased protein content. On the other hand, no changes in fat (%) were observed, since the sausages had very low-fat content (%).

The results of texture profile analyses of LFSs during storage are shown in Table 3. LFSs wrapped with the film were harder than CTL, but those wrapped with TSA exhibited texture similar to the ones wrapped with SA. Ruiz-Ramírez et al [23] reported that hardness of textural was affected by pH and water content. In this study, the increases in hardness (gf) could be explained based on lower expressive moisture (Figure 1A) and pH (Table 1). Additionally, it has been widely recognized that water absorption by film affects textural hardness (gf). The water content in LFSs was absorbed by the film thereby resulting in increased hardness (gf). However, springiness (mm), gumminess (kg/mm), chewiness (kg/mm), and cohesiveness (ratio) of all LFSs were not different among the treatments. Sánchez-Ortega et al [24] found that films could extend the shelf life because physicochemical properties (such as texture, moisture) of meat or meat products changed due to the gas barrier properties of film. They also reported that application of film also changed the sensory evaluation due to the changed physicochemical properties of the sausages. Our study was agreement with theirs and film or coating technique should increase the shelf life or quality and safety of meat or meat products without changes in sensory characteristics. Although film absorbed water from sausages, it didn’t much affect the sausage quality due to the mechanical properties (moisture content, solubility in water, water vapor permeability) of films [24,25]. Alginate coating could reduce microbial counts and form acceptable flavor, tenderness and appearance [26]. Thus, application of films to LFSs might change the textural hardness and may also affect the sensory characteristics.

As shown in Table 4, TPCs of treatment covered by TSA film were detected from 28 days of storage days and were found to be lower than CTL and LFSs covered by SA film. The lower microbial count in sausages wrapped with the TSA-film might be attributed to lower pH value, which resulted in reduced microbial growth. Decreased pH inhibited the anaerobic growth of enterobacteria and prevented meat spoilage as supported by previous studies. Grau [27] reported that lower pH value of muscle could support more undissociated lactate, which is an effective inhibitor. Vergara and Gallego [28] studied different compositions of gas present in the package during the 17 days of storage of lamb meat, and reported that pH values near 5.8 among the lower pH values favored bacterial growth and meat spoilage, which the relationship between bacteria and pH value was clearly reported. Another study also reported that modified atmosphere packaging with aloe gel or inclusion of thymol or eugenol enhanced the content of bioactive compounds including phenolics and lycopene, which in turn reduced the incidence of microbial spoilage [29]. These results indicated that LFSs wrapped with TSA film exhibited antimicrobial effect. It is proposed that TSA film can be used for enhancing the shelf-life of meat products.

As shown in Figure 1A, EM of LFSs wrapped with TSA film was lowest among the treatments at day 3 and lower than CTL before day 14. Since EM is related to water holding capacity and water activity, and it could be affected by the barrier properties of film such as water absorption [30]. Figure 1B shows the result of TBARS values as affected by LFSs wrapped with different films. The TBARS values of all samples gradually increased during storage and those of LFSs wrapped with TSA film was lower than the CTL (p<0.05) before day 14. However, no differences in TBARS between LFSs wrapped with SA film and CTL were observed except for those on day 14 (p>0.05). The TBARS value exhibited a gradual increasing tendency and below rancid value (1.0) during or at the end of storage. Thus, LFSs wrapped with TSA film might have antioxidant activity as compared to other treatments. Similar results were accounted for by Siripatrawan and Noipha [31], who reported that pork sausages with green tea film extended shelf-life. During storage, higher TBA was observed in control samples rather than LFSs wrapped with chitosan film and chitosan green tea film due to antioxidant activity of chitosan as well as its lower oxygen permeability characteristic [31,32]. These results suggested that lipid oxidation of sausage could be affected by bioactive film and antioxidant grape tomato powder. In this study, antioxidant activity of LFSs wrapped with TSA film showed better results than CTL. Also, it is proposed that TSA film could be used to enhance the antioxidant activities of meat products.