Physicochemical Properties and Shelf-Life of Regular-Fat Sausages with Various Levels of Grape Tomato Powder Prepared by Different Drying Methods

Grape tomatoes were purchased from the local market and washed, chopped, and homogenized before drying by a freeze-dryer (FT5505, Ilshin, Daejeon, Korea) at –50°C and 7 mm Torr vacuum and a hot, dry oven (LDO-250F, Labtech, Jeonju, Korea) at 100°C (Kim and Chin, 2016), respectively. The time and yield of freeze-drying and oven-drying at 100°C were 72 h and 9 h, and 9.59% and 8.2%, respectively. Then, the powder was sieved by two particle sizes (≥300 μm, ≤150 μm) and stored at −70°C.

Pork ham and back fat were purchased from the local market (Samho, Gwangju, Korea). After 60% lean meat and 20% fat were ground by an M-12s grinder (Fujee Plant, Busan, Korea), they were mixed with non-meat ingredients (18% ice water, 1.3% salt, 0.4% sodium tripolyphosphate (STPP), 0.25% cured blend, 0.05% sodium erythorbate, 0.1% ascorbic acid, and different kinds of tomato powder) (Table 1). Then, approximately 40 g of the meat batter was stuffed into 50 mL of centrifuge tube and centrifuged at 1,500×g for 2 min. The sausage mixtures were cooked in a water bath at 75°C for 30 min. All samples were taken out from tubes, then vacuum-packaged by food sealed plastic bags and stored in a refrigerator (10±1°C) for 28 days. The whole experiment was performed triplicates. The pork RFSs were manufactured with the addition of GTP except for control (without addition of powder) and REF (with addition of 0.1% ascorbic acid), according to the procedure of Lee and Chin (2009).

The pH values of the samples were determined by a pH meter (Mettler-Toledo, Schwarzenbach, Switzerland). Each sample was cut into 6 pieces and lightness (L*), redness (a*), and yellowness (b*) were measured by a Minolta color reader (Model # CR-10, Minolta, Tokyo, Japan). For the microbial count, 10 g of sanitized and homogenized sample was mixed with 90 mL of sterilized water (0.9%) using a Stomacher Lab Blender and serial dilutions were made. Then, about 0.1 mL of the diluted sample was dispersed onto the surface of violet red bile (VRB) and total plate count (TPC) agar and incubated at 37°C for 24–48 h.

Moisture, crude fat, and crude protein (%) were conducted by following the AOAC guidelines (AOAC, 2005). The moisture contents were analyzed by dry-oven methods, whereby the materials were dried at 102°C for 16–24 h. The crude fat content was determined by the Soxhlet extraction method and crude protein analysis was performed by the Kjeldahl protein determination.

A universal testing machine (Model 3344, Canton, MA, USA) was used to perform texture profile analysis according to a method described by Caine et al. (2003). The sausage samples (1.30 cm length and 1.30 cm diameter) were compressed with a 500-N load cell at an operational speed of 300 mm/min. The TPA values were expressed in terms of the hardness (gf), springiness (cm), gumminess (kg/mm), chewiness (kg/mm), and cohesiveness (ratio) of sausages. Ten samples were used for single texture profile analysis result of every sausage.

Accurately 1.5 g sample was weighed and wrapped using the 3 pieces of 1/4 filter paper and then centrifuged (1,500×g) for 15 min (VS-5000N, Vision Scientific, Bucheon, Korea). Weights of both the filter paper and samples were measured again. The expressible moisture content of the samples was calculated as follows:

Where ΔT was the thimble weight difference before and after centrifugation. A was the initial weight of the sample.

The oxidative rancidity was evaluated by TBARS (Sinnhuber and Yu, 1977). Each sausage sample mixed with 2.5% trichloroacetic acid (TCA, 3 mL) and 1% thiobarbituric acid (TBA, 17 mL) in a capped tube was accurately measured in grams. Then, the tubes were put into a boiling water bath for 30 min. The supernatant of each solution was mixed with 5 mL of chloroform and centrifuged at 670×g for 5 min (VS-5000N, Vision Scientific). Then, approximately 3 mL of petroleum was added to each supernatant and centrifuged. Finally, the clear solutions were analyzed by spectrophotometry (UV-1601, Shimadzu, Kyoto, Japan) at a wavelength of 532 nm.

The sausage samples were analyzed at 0, 3, 7, 14, 21, and 28-day intervals during 10°C chilled storage. Data were analyzed by two-way analysis of variance (ANOVA) using the SPSS 21.0 program for Windows. Duncan’s multiple range test was used to determine significant differences at the 5% level.

Table 2 shows the pH and color values of the RFSs with various amounts of GTP as affected by the different drying methods. Since the interaction between the treatments and storage time were not different (p>0.05), the data were pooled by treatment within each storage time and storage time within the treatment. The addition of GTP tended to decrease the pH values and the addition of oven-dried powder reduced the pH more than freeze-dried GTP. The reduced pH of the RFSs with the addition of tomato powder might be due to the tomato powder itself (Candogan, 2002). The reason why the oven-dried powder reduced the pH more than the freeze-dried powder was that the Maillard reactions of the tomato powder during heating caused a browning reaction that decreased the pH (Baloch et al., 2000). Although the pH values of all treatments decreased on day 3, they increased thereafter toward to the end of storage. Candogan (2002) reported that the pH of tomato paste-added patties increased with storage time and the changes in pH might be due to microbial growth during the refrigerated storage. However, a decrease in the pH values during storage of frankfurters containing tomato paste was observed by Deda et al. (2007) who suggested that the decrease in pH was obviously due to an increase of lactic acid bacteria, which might grow during storage. However, no lactic acid bacteria might grow in this study due to little change in the pH values.

REF and CTL had higher lightness (L*) values and lower redness (a*) and yellowness (b*) values. The addition of GTP tended to decrease lightness, but increased redness and yellowness. In the comparison of two drying methods, O turned darker and yellower than the F. Candogan (2002) reported that lycopene, the red substance and the corresponding pigment antioxidant, was affected by increasing tomato paste levels from 5% to 15%, which could result in beef patties that were yellower, redder, and darker. Since the O already underwent a series of Maillard reactions due to drying at high temperatures, the addition of O to the sausages turned them to be yellow and darker color (Cosmai et al., 2013). Salem (2013) reported that pH was a very important factor that was related to the meat color, water-holding capacity, and texture of meat. He also reported that beef patties mixed with optimum amounts of tomato peel powder had better color values, more acceptable by consumers. During the storage time, the addition of GTP affected the pH and color of the sausages and the oven-dried powder affected these more than freeze-dried powder.

The proximate analyses of sausages with different amounts and drying methods of GTP are shown in Table 3. Processing and chemical changes are affected by the nutritional composition, such as protein, fat, and moisture during storage. During the storage period, neither moisture nor crude fat showed differences, but crude protein (%) was slightly increased compared to the control. Kim et al. (2011) did the study on low-fat sausages added with tomato powder, who found that protein content increased with the increased addition of tomato powder, simultaneously, fat and moisture were without any changes. They reported that increased protein contents were not only the tomato powder was added, but also because tomato has 10.3% of crude protein contents, which was agreement with our studies. Although the protein contents were different statistically, the proximate composition of the RFSs was not actually affected by GTP addition due to the small changes of the protein contents, regardless of the different drying methods and levels of GTP.

Table 4 shows the textural properties of RFSs added with GTP and no interaction between treatments and storage time was found in the textural properties. The textural characteristics of cooked meat products are generally considered to be heat-induced changes in connective tissue, soluble proteins, and myofibrillar proteins (Zayas and Naewbanij, 1986). The hardness and chewiness values were decreased by the addition of GPT and the addition of FGTP into the sausages tended to decrease these characteristics more than oven-dried grape tomato powders (OGTP). During the storage time, textural hardness and gumminess increased as the storage time increased. Na et al. (2012) reported that the addition of tomato powder decreased the texture of sausages. Thus, the addition of tomato peel and powder had different effects on texture due to their different functional characteristics. However, the opposite result was observed in a previous study from Salem (2013) who reported that hardness increased when tomato powder was added because of the increase in tomato peel fiber. The increase in hardness could be explained by the presence of insoluble acid detergent fiber, which is composed mainly of cellulose and lignin in tomato peel (Kim et al., 2011; Knoblich et al., 2005). Springiness was affected by the addition of F1GTP and O2GTP. However, no changes in springiness were found in O1 and F2. During the storage time, springiness decreased on 3 days of storage, increased on 21 days of storage and pleateau thereafter. Gumminess changed slightly, only increasing a little on day 3 days of storage and decreased with the addition of F2GTP. Chewiness decreased with the addition of GTP, but no differences were observed during storage time. Cohesiveness decreased with the addition of GTP, except for O2GTP, which was increased during storage. During the storage time, cohesiveness tended to decrease with increased storage time. Thus, except for a few cases, most textural characteristics were affected by the addition of GTP, especially FGTP rather than OGTP and storage time.

Since interaction between storage time and treatments was observed (p<0.05), the data were separated by treatment within a storage time or storage time within a treatment (Table 5). Thiobarbituric acid-reactive substances (TBARS), which is used as an index for measuring the oxidative rancidity of meat and meat products, increased as storage time increased. The TBARS of REF was the lowest, and it was followed by the O1 at the initial day. However, the TBARS of O1 had the lowest value from 3 to 28 days of storage among all treatments. In addition, the TBARS of the OGTPSs was lower than that of freeze-drying at the same level of GTP. GTP dried by oven-drying had more total phenolics than those processed by freeze-drying, which could improve the oxidant activity. However, Dorta et al. (2012) did study on antioxidant activities of mango peel and seed by different drying treatments and they reported that mango seeds and peels could be stabilized by freeze drying without reducing antioxidant activities rather than the oven-drying. They explained that drying methods affected the contents of phenol and anthocyanin, which contribute to antioxidant activities. Drying is a useful technique for a longer shelf-life of fruits and vegetables with better antioxidant and antimicrobial activities, and freeze-drying can remove water from frozen material mainly by sublimation to preserve the product quality (Ratti, 2001). Oven-drying reduced the vitamin C content and increased the water-soluble R-tocopherol Trolox analog antioxidant content (Lavelli et al., 1999). Thus, GTP might be useful to the lipid antioxidant for RFSs during storage, especially the O1GTP is most influential among all treatments except for REF.

The microbial counts of total bacteria and Enterobacteriaceae, and expressible moisture (EM) of the GTPSs are listed in Table 6. EM decreased with the addition of GTP except for F2, and the EM in all treatments showed a gradually decreasing trend during storage. However, no differences were observed except for the O2. These results indicated that the water-holding capacity during storage might maintain or increase in the O2. Kerr et al. (2005) reported that the EM means the degree of juiciness retention in cooked sausages, and they also claimed the EM might be low with high cooking loss. In this study, the cooking losses (%) for the CTL, REF, F1, F2, O1, and O2 groups were 6.7%, 6.8%, 6.8%, 7.6%, 7.5%, and 7.1%, respectively, which showed opposite trends to the EM.

During storage, the total microbial counts increased rapidly up to 28 days of storage. The addition of GTP tended to reduce the microbial counts. The TPC of the O1 was not detected until 7 days of storage (<10² cells/g), and had the lowest TPC among all treatments. Thus, the O had better antimicrobial activities than that of other sausages, and the O1 had the best effect on microbial inhibition. TPC was reduced by the addition of GTP and oven-dried tomato powder had better antimicrobial effects with lower microbial counts than freeze-dried GTP. This observation was consistent with those of Kim et al. (2011) and Østerlie and Lerfall (2005), who reported that the lower pH of sausages with tomato powder reduced the microbial counts, demonstrating effective antimicrobial activity. Similarly, dried fruits and vegetables inhibited the growth of spoilage microorganisms because lower water content and powerful antimicrobial enzymatic or non-enzymatic browning reactions also could have occurred in the material matrix (Argyropoulos et al., 2011; Zhang et al., 2006). No microbial counts for Enterobacteriaceae (VRB) were observed during the storage time. Thus, the application of OGTP to meat products could be beneficial because of its antimicrobial activity.