Food Sci. Biotechnol. 24(2): 471-480 (2015) DOI 10.1007/s10068-015-0062-7
RESEARCH ARTICLE
Optimization of Sterilization Conditions for Production of Retorted Meatballs Hee Soon Cheon, Su-Hee Choi, Changho Jhin, Won-Il Cho, Jun-Bong Choi, Hae-Hun Shin, Seungmin Lee, Hyunnho Cho, Hee-Jeong Hwang, KeumTaek Hwang, and Myong-Soo Chung
Received July 14, 2014; revised September 20, 2014; accepted September 24, 2014; published online April 30, 2015 © KoSFoST and Springer 2015
Abstract Sterilization conditions for meatballs in retort trays were determined. Microbiological safety, texture, and sensory attributes were analyzed for 27 sterilization conditions (33 factorial design) using temperature, time, and processing method. Temperature and sterility were monitored using an F0 sensor. Quality factors of water activity, viable cell counts, color, sensory characteristics, and texture were analyzed for retorted meatballs under each experimental condition. Quality attributes were significant (p<0.05) and differentially affected by temperature, time, and method. Linear effects were more important than quadratic and interaction effects. F0 and hardness for quadratic effects were significantly (p<0.01) predicted. F0, the sensory quality of chewiness, and color b values were significant (p<0.05) for interaction effects. Overall, F0 at the coldest point, the sensory quality of chewiness, the degrees of
Hee Soon Cheon, Changho Jhin, Hyunnho Cho, KeumTaek Hwang Department of Food and Nutrition, and Research Institute of Human Ecology, Seoul National University, Seoul 151-742, Korea Su-Hee Choi, Hee-Jeong Hwang, Myong-Soo Chung () Department of Food Science and Engineering, Ewha Womans University, Seoul 120-750, Korea Tel: +82-2-3277-4508; Fax: +82-2-3277-4508 E-mail:
[email protected] Won-Il Cho CJ Foods R&D, CJ Cheiljedang Corp., Seoul 152-051, Korea Jun-Bong Choi Graduate School of Hotel and Tourism, The University of Suwon, Hwaseong, Gyeonggi 445-743, Korea Hae-Hun Shin Division of Foodservice Industry, Baekseok Culture University, Cheonan, Chungnam 330-705, Korea Seungmin Lee Department of Food and Nutrition, Sungshin Women’s University, Seoul 142-732, Korea
lightness and yellowness, and hardness were significantly (p<0.01) influenced, more by temperature and time than by method. Response surface methodology revealed optimum sterilization conditions for meatballs. Keywords: rotary retort, retorted meatball, response surface methodology
Introduction Thermal sterilization is one of the most effective and widely used food-preservation technologies for maintenance of food safety. Thermal treatment allows preservation food products for longer periods of time and extension of the shelf-life based on inactivation of contaminant microorganisms. However, sterilization processes can also negatively affect the quality of foods. In particular, a lack of appropriately defined heat-treatment conditions can lead to overheating, which in turn will lower the sensory qualities of thermally sterilized food products. Moreover, thermal processing is an energy intensive process, and the associated general consumption of energy vastly increases production costs. Therefore, optimization of thermal heating processes is needed according to characteristics of particular food products in order to minimize both inherent energy consumption and deterioration of food quality characteristics with maximization of food safety based on elimination of spoilage microorganisms (1). Studies of thermal sterilization processes have been reported with a view to improvements in the safety of food end-products while maintaining food sensory and nutritional values (2). However, there have been relatively few studies of the quality of specific food products, such as retorted meatball, subjected to different thermal processing conditions.
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meatball products manufactured according to fixed specifications was sealed at 165ºC and 4 bars (400 kPa) of pressure for 1.7 s using a peelable lid film composed of 15 µm nylon (Ny), 25 µm Ny, 12 µm EVOH, and 30 µm EPL (CMPS017C).
An effective thermal sterilization method that reduces sterilization time and maintains food safety is agitation of food contents on a rotating retort, or use of preservatives. However, preservatives are not widely accepted by consumers. Rotary thermal processing is known to be more effective than stationary thermal processing as mechanical agitation during thermal processing increases heat transfer rates in food products, eliminates cold points, and reduces sterilization time by approximately 50% (3,4). Food products can be heated faster and more evenly using a rotary sterilizer (5). Although advantages of rotary thermal processing with respect to heat transfer are known, there are few experimental results regarding the effects of different sterilization conditions on the heat-transfer rate. Further research into optimum sterilization conditions of specific commercial retorted products is needed. The aim of this study was to optimize sterilization conditions for production of retorted meatballs, focusing on microbiological safety and textural and sensory qualities.
Experimental design Sterilization was performed under 27 different conditions of temperature and time and using different methods based on a 33-factorial design (Table 1B). Based on the results of preliminary sterilization experiments, the sterilization temperature and processing time were used as quantitative variables. Thus, for each variable, 3 different temperatures (117, 121, and 125ºC) and 3 different processing times (19, 28, and 37 min) were used. The sterilization method was also varied as a qualitative variable using 3 different types of sterilizer, including a water-spray retort (RCS-60SPXTG; Hisaka, Osaka, Japan) (coded as −1), and static and rotary modes of a watercascading retort (Stock Pilot-Rotor 900; Hermann Stock Maschinen Fabrik, Neumünster, Germany), hereafter referred to as water-cascading static and rotary retorts, respectively, coded as 0 and +1. The reference sterilizing condition was the water-cascading static retort operated at 121ºC for 28 min, since this retort uses conditions similar to retorts used for sterilization of commercially retorted meat products.
Materials and Methods Sample preparation Ingredients of retorted meatball products and specifications are shown in Table 1A. Meatballs are a type of Western food made from chicken and pork meat. Nine meatballs (99 g each) in tomato-based sauce with vegetables (total weight, 101 g) (Table 1A) were placed into thermoforming plastic containers (153× 121.4×31.9 mm) using a 3-layer configuration of polypropylene (PP)/ethylene vinyl alcohol (EVOH)/PP 0.8T (EVOH 4.8%). The plastic tray containing 200 g of
Sterilization process Sterilization was conducted according to the experimental design in random order. The waterspray retort and water-cascading retort were used for sterilization experiments. The rotating speed of the watercascading rotary retort was 6 rpm. The temperature history
Table 1. Specifications of the samples used for the experiments (A) and independent variables and their coded and actual values used in a 33-factorial design (B) (A) Type
Meatball product
Ingredient
Composition
Specification
Meatball
chicken, pork
11 g×9 per pack
Vegetables
onions, carrots garlic, green peppers white button mushrooms
Diced and stir-fried over a low heat Minced and stir-fried over a low heat Sliced and stir-fried over a low heat
Sauce
tomato ketchup, starch syrup, tomato paste, butter, flour, minor ingredients
Mixed and boiled at 100oC
(B) Independent variables Sterilization temperature Sterilization time
Sterilization method
Unit o
Factor
Specific ranges
C
X1
117
121
125
min
X2
19
28
37
X3
–1 (Water-spray retort)
Water-cascading retort
-
0 (Static)
+1 (Rotary)
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Optimization of Sterilization of Retorted Meatballs Table 2. Pressure conditions in water-spray (A) and water-cascading (B) retorts (A) Condition
Come-up time o
Temperature ( C)
25
Sterilization time
100
Pressure (kPa)
117
-
Time (min)
8
o
Temperature ( C)
25
100
Pressure (kPa) 8
o
Temperature ( C)
121
90
Pressure (kPa)
-
Time (min)
7
2
2
121 C
3 11
40 C 170
150 2
100 2
o
3 11
o
125 C
40 C
200 8
100 o
28 125
150
o
170 7
25
170
37
-
Time (min)
40oC
117 C 170
7
Cooling time
o
200
19
150 3
100 2
3 10
(B) Conditions
Come-up time (min)
Sterilization time (min)
Cooling time (min)
Pressure (kPa) (at 117, 121, and 125oC)
100
150
140
and sterility of meatballs during each sterilization process were monitored using an F0 sensor (Tracksense Pro, Ellab, Hilleroed, Denmark) and sterility was expressed as an F0 value calculated as: F0=Ft×10(T−121.1)/z Pressure conditions for the water-spray and cascading retorts were determined based on preliminary sterilization experiments (Table 2). Preliminary experiments were also conducted to determine the cold point in retort trays and sterilizers based on varying the spot monitored using the F0 sensor (Fig. 1, positions 1, 2, 3 (1/4, 1/2, and 3/4 points). The cold point was determined to be the middle (position 2) of the retort tray at the bottom of the retort sterilizer, and the coldest point of tray contents was assumed to be the center of the meatball, which has the lowest thermal conductivity in the meatball product. Under these conditions, F0 values of all meatball samples were recorded. Color measurement Changes in meatball color before and after sterilization were measured using a colorimeter (Color Quest XE, Hunter Associates Laboratory, Reston, VA, USA). Before analysis, calibration was conducted using black and white reference tiles. Measurement of meat color was carried out after tomato sauce was removed from meatballs by washing under flowing water for 2 min. The color difference (∆E) between meatballs produced under reference conditions and treated under different experimental conditions was quantified as: 2
2
∆E = (L1 – L0) + (a1 – a0) + (b1 – b0)
2
where L1, a1, and b1 are color parameters under different
Fig. 1. Positions monitored by the F0 sensor in order to determine the cold point in the retort tray containing meatball products. The yellow circles represent meat balls in the container; the blue lines represent the container.
sterilization conditions, and L0, a0, and b0 are the same parameters under reference conditions. Analysis of texture Meat texture was measured using a texture analyzer (TA-XT2i Stable Microsystems, Godalming, UK) after cutting meatball samples into 1×1×1 cm cubes. Texture profile analysis was performed, including hardness, chewiness, springiness, and cohesiveness at room temperature using a cylindrical aluminum probe (20 mm in diameter, No. P/20a) with a trigger force of 5 g and 80% strain at a pretest speed of 1.0 mm/s, a test speed of 1.0 mm/s, and a post-test speed of 1.0 mm/s. Chewiness was calculated as hardness×springiness×cohesiveness. Sensory evaluation Sensory evaluations were performed by a trained panel consisting of 10 students from the Department of Food Science and Engineering, Ewha Womans University. Sensory attributes of redness and chewiness were evaluated after panelists completed 3
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training sessions. All sample meatballs were the same size and each was served on a randomly coded plate after heating in a microwave oven for 2 min. Water was provided for cleansing of the palate after tasting of each sample. Panelists rated the intensity of sensory attributes from 1 (extremely weak) to 9 (extremely strong) for each sample. Finally, the overall acceptability of meatball products was evaluated on a 9 point hedonic scale using an untrained panel of 30 members (students of the Department of Food Science and Engineering, Ewha Womans University). Microbiological analysis The viability of microorganisms in meatballs was assessed using 10 g of meatball sample in sterile distilled water pummeled for 3 min at 9 strokes/s using a stomacher (HBM-400A; Tianjin Hengao Technology Development, Tianjin, China). The resulting mixture was
then diluted and spread onto agar (Plate Count Agar; Difco Laboratories, Detroit, MI, USA) and cultivated for 24 h at 37ºC in an incubator (HB-101S; Hanbaek Scientific, Bucheon, Korea), after which viable cells were counted. The number of viable cells was quantified as colonyforming units (CFU)/mL, and the number of countable colonies was 30-300 per culture plate. Response surface methodology and statistical analysis Multiple regression analysis, contour analysis, and construction of plots were performed using MATLAB (MathWorks, Natick, MA, USA). Linear, quadratic, and interaction effects of the 3 independent variables of sterilization temperature, processing time, and processing method on different quality attributes of meatballs were determined using SPSS software (SPSS, Chicago, IL, USA). Response surface methodology (RSM) was used to
Table 3. The quality attributes of the meatball products evaluated under various sterilization conditions through a 33-factorial experimental design Variable
1)
Temperature (X1; ºC)
Time (X2; min)
Method (X3)1)
117 117 117 117 117 117 117 117 117 121 121 121 121 121 121 121 121 121 125 125 125 125 125 125 125 125 125
19 19 19 28 28 28 37 37 37 19 19 19 28 28 28 37 37 37 19 19 19 28 28 28 37 37 37
–1 0 +1 –1 0 +1 –1 0 1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1
Y '12)
Y '21
Y '22
Y '23
1.57±0.173) 0.65±0.17 2.79±0.11 2.99±0.33 2.52±0.43 5.84±0.28 5.80±0.55 5.65±0.07 9.54±0.49 3.26±0.21 1.74±0.29 12.29±0.32 8.41±0.46 8.03±0.51 20.37±1.32 15.10±0.32 20.81±1.36 30.18±1.00 6.40±1.09 8.43±1.44 36.56±0.95 24.32±2.42 23.90±1.39 55.02±0.72 40.66±1.13 48.92±3.33 69.54±0.52
6.67±1.32 6.00±1.55 4.87±1.25 4.97±1.97 3.90±1.97 2.75±1.67 6.20±1.58 2.97±1.38 5.60±1.98 3.73±1.98 3.93±1.64 3.40±1.96 6.03±1.96 4.33±1.77 5.87±1.87 4.73±1.96 3.37±1.59 3.67±1.71 5.97±1.94 5.80±1.73 3.73±2.00 5.60±1.71 2.27±1.39 3.07±1.68 2.77±1.57 2.37±1.16 1.97±1.00
4.80±1.32 6.60±1.17 4.30±1.42 4.00±1.25 5.10±1.91 2.80±1.23 6.40±1.26 7.10±1.20 6.20±0.79 2.70±1.06 3.10±0.99 1.50±0.71 6.10±1.20 4.00±1.49 7.30±1.16 5.80±1.23 5.40±1.17 7.00±1.15 4.60±1.35 5.60±1.07 3.10±1.10 7.40±0.84 3.30±1.57 5.40±1.96 3.90±0.88 3.40±1.07 3.00±0.82
5.40±1.26 6.90±1.37 5.10±1.79 5.30±1.57 5.30±1.77 4.00±1.33 6.20±1.87 4.70±1.16 4.60±1.90 4.40±1.26 6.30±1.34 4.20±1.62 5.00±1.56 3.60±1.43 4.20±1.62 5.10±1.97 4.10±1.37 4.90±1.52 5.30±1.57 6.60±1.26 5.30±1.57 3.70±1.42 3.30±1.34 4.30±1.83 2.80±1.23 2.60±1.17 2.20±0.79
1)
0, water-cascading static retort; +1, water-cascading rotary retort; –1, water-spray retort Y '1, F0 value at the coldest point in retort tray; Y '21, Preference evaluation (overall acceptability); Y '22, Sensory evaluation (degree of redness); Y '23, Sensory evaluation (chewiness) 3) Data are mean±SD values 2)
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Optimization of Sterilization of Retorted Meatballs Table 3. Continued Variable Temperature (X1; oC)
Time (X2; min)
Method (X3)1)
117 117 117 117 117 117 117 117 117 121 121 121 121 121 121 121 121 121 125 125 125 125 125 125 125 125 125
19 19 19 28 28 28 37 37 37 19 19 19 28 28 28 37 37 37 19 19 19 28 28 28 37 37 37
–1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1
Y '312)
Y '32
Y '33
Y '34
55.74±1.07 52.50±0.08 49.87±1.32 51.70±0.91 52.98±0.77 54.41±1.01 50.90±1.43 50.83±0.95 47.25±1.64 53.19±1.68 53.53±0.50 51.90±2.24 50.78±1.01 49.75±0.40 47.59±1.64 47.99±0.89 48.65±1.23 42.96±1.09 51.48±0.65 51.61±1.11 50.42±1.10 48.33±0.51 50.13±0.27 45.28±1.51 46.17±1.90 46.91±1.05 46.89±1.49
16.91±1.55 18.86±0.34 18.87±1.03 19.76±0.67 17.97±1.15 17.50±1.13 18.79±1.47 18.51±0.65 20.69±0.88 17.91±2.10 17.11±0.92 17.92±1.82 18.11±0.33 19.47±1.10 18.18±2.11 19.39±0.48 17.87±1.45 18.76±1.45 19.08±1.16 18.53±1.07 15.66±0.61 19.35±0.65 18.92±0.61 17.09±0.41 17.82±1.41 18.27±1.27 17.99±0.84
30.65±1.51 30.45±0.43 29.89±0.46 31.13±0.70 29.59±0.95 31.90±0.75 30.11±1.15 30.18±0.97 30.29±1.38 31.15±0.76 29.78±0.57 32.02±1.31 30.09±0.87 29.39±0.71 29.49±1.41 28.73±0.41 27.62±1.54 26.60±1.31 31.55±0.81 31.12±0.86 28.23±0.50 29.05±0.33 29.78±0.36 27.22±1.12 26.20±2.16 27.64±0.77 26.73±1.06
6.64±1.06 3.01±0.50 0.80±0.46 2.63±1.13 3.59±0.67 5.65±1.59 1.52±1.14 1.65±1.01 2.92±1.27 4.16±1.52 4.47±0.76 3.73±1.52 1.84±0.67 0.00±0.62 2.52±1.63 1.88±0.92 2.63±1.52 7.38±1.04 2.79±0.90 2.71±1.17 4.04±1.63 1.46±0.44 0.78±0.80 5.51±1.67 5.07±1.66 3.55±0.99 4.17±2.13
1)
0, water-cascading static retort; +1, water-cascading rotary retort; –1, water-spray retort Y '31, Color (L); Y '32, Color (a); Y '33, Color (b); Y '34, Color (E)
2)
schematically identify relationships between independent variables and response variables. All data are expressed as mean values of 3 replicate measurements.
Results and Discussion Data analysis The total viable bacterial count of raw meatball products before sterilization was 1.43×104 CFU/ mL. After completion of the different sterilization processes (117, 121, 125ºC and 19, 28, 37 min), no viable cells were detected on any plates. With the exception of viable bacterial counts, the response variables (F0, sensory qualities, color values, and textural properties) varied according to the 3 independent variables of sterilization temperature, time, and method (Table 3). Results of multiple regression analysis are shown in Table 4. Linear effects were generally more significant than quadratic and interaction effects. In the case of quadratic
effects, only F0 values and hardness were significantly predicted at p<0.01. The F0 values, the sensory quality of chewiness, and color values of b were significantly (p<0.05) affected for interaction effects. Overall, the response variable F0 at the coldest point, the sensory quality of chewiness, and the degrees of lightness, yellowness, and hardness were significantly (p<0.01) influenced, more by the sterilization temperature and time than by the sterilization method. Relationships between response variables and independent variables were analyzed using RSM. Resulting equations and response surface plots, which expressed changes in response variables (Y) with sterilization temperature (X1) and time (X2), are shown in Fig. 2 and 3. The sterilization method (X3) significantly affected the dependent variables (p<0.05), but similar trends were found for the same sterilization method. The optimum sterilization conditions were determined by checking the validity of the sterilization conditions using multiple regression analysis and overlapping
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Table 3. Continued Dependent responses1)
Variable Temperature (X1; oC)
Time (X2; min)
Method (X3)2)
Y '4
Y '51
Y '52
Y '53
Y '54
117 117 117 117 117 117 117 117 117 121 121 121 121 121 121 121 121 121 125 125 125 125 125 125 125 125 125
19 19 19 28 28 28 37 37 37 19 19 19 28 28 28 37 37 37 19 19 19 28 28 28 37 37 37
–1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1
0.96±0.01 0.96±0.01 0.95±0.00 0.96±0.01 0.93±0.01 0.99±0.00 0.94±0.01 0.93±0.01 0.94±0.01 0.95±0.02 0.95±0.00 0.99±0.01 0.94±0.00 0.96±0.01 0.98±0.00 0.94±0.01 0.96±0.00 0.98±0.00 0.97±0.00 0.98±0.00 0.99±0.00 0.98±0.01 0.98±0.00 0.99±0.00 0.99±0.00 0.98±0.00 0.99±0.01
1159.6±179.4 1114.4±121.8 1126.8±92.6 743.6±43.9 817.9±111.1 700.2±13.6 670.1±56.7 707.5±36.0 721.0±50.5 1091.3±32.5 1045.0±83.6 775.9±36.5 693.7±55.7 709.2±117.9 637.3±65.9 558.5±16.5 576.7±30.0 527.8±64.2 1119.3±17.2 1480.8±271.3 1080.0±37.6 555.6±123.3 562.8±55.0 466.7±41.9 507.2±74.5 417.0±37.0 445.6±27.3
0.60±0.11 0.37±0.06 0.69±0.07 0.75±0.07 0.68±0.07 0.64±0.06 0.75±0.05 0.76±0.05 0.67±0.04 0.78±0.10 0.66±0.03 0.70±0.04 0.78±0.05 0.73±0.04 0.70±0.04 0.72±0.07 0.58±0.18 0.62±0.12 0.74±0.02 0.76±0.05 0.65±0.08 0.79±0.07 0.70±0.13 0.68±0.05 0.69±0.16 0.61±0.12 0.67±0.11
0.28±0.08 0.20±0.01 0.21±0.01 0.21±0.02 0.25±0.02 0.24±0.02 0.22±0.05 0.21±0.01 0.19±0.03 0.17±0.06 0.20±0.02 0.22±0.01 0.24±0.02 0.21±0.02 0.20±0.03 0.19±0.02 0.21±0.03 0.23±0.02 0.23±0.02 0.25±0.02 0.22±0.03 0.21±0.04 0.24±0.01 0.20±0.02 0.19±0.00 0.20±0.01 0.21±0.02
185.87±23.37 153.59±28.82 162.12±23.09 119.22±2.26 140.19±10.00 106.32±4.45 110.52±19.90 113.62±8.80 90.91±16.04 153.90±69.21 134.82±2.22 121.86±5.41 127.02±10.2 109.15±20.4 91.80±25.05 78.09±14.89 69.89±24.99 74.48±17.83 186.00±15.78 285.53±64.8 157.37±44.08 93.54±36.78 96.45±22.08 63.54±8.15 66.48±21.94 51.35±13.38 62.80±7.09
1)
Y '4, Water activity (Aw); Y '51, Texture (hardness); Y '52, Texture (springiness); Y '53, Texture (cohesiveness); Y '54, Texture (chewiness) 0, water-cascading static retort; +1, water-cascading rotary retort; –1, water-spray retort
2)
of contour plots corresponding to optimum criteria for response variables (Fig. 4). F0 value Commercially recommended F0 values for chicken and meat products are within ranges of 6.8 and 8.2 min, respectively (6). The F0 value for a sterilization time of 5-10 min was reported to be reasonable for the quality and safety assurance of high quality products (7). The food matrix can affect the heat-transfer rate, and different microorganisms have different degrees of heat resistance. Therefore, specific heat treatments are required for specific food items. Consequently, the optimum value of F0 was 7 min. Values of F0 varied with sterilization conditions from 0.65 to 69.54 min (Table 3). The value of F0 was affected by the sterilization temperature, time, and the processing method, being significant at p<0.01 (Table 4). Values of F0 were highest when meatball products were sterilized using the water-cascading rotary retort and increased with an
increasing sterilization temperature and time (Fig. 2A). The increase was rapid with an increasing processing time at high temperature. Considerable changes in F0 values were not observed when the temperature was low. Thus, temperature had a greater effect on sterilization than time. Increasing the heating temperature produces a more rapid increase in the rate of microorganismal death than the rate of nutrient destruction (8). This study confirms the advantages of high-temperature, short-time (HTST) sterilization processes. Sensory characteristics The sensory characteristic of chewiness was predicted with significance (p<0.05) using the overall model, including linear, quadratic, and interaction effects. Chewiness was controlled more by the sterilization temperature and time than by the processing method (Table 4). Chewiness tended to increase as the processing time decreased (Fig. 2B). The chewiness of meatballs sterilized at a high temperature for a long time tended to be greater than for meatballs sterilized at a low temperature for a long
Optimization of Sterilization of Retorted Meatballs
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Fig. 2. Response surface plot for F0 values at the cold point (A) and sensory scores of chewiness (B) of the meatball products as a function of sterilization temperature (X1) and time (X2) for the water-cascading rotary retort (+1) sterilization method. (A) F0 value; Response surface equation: Y=0.38444X12+0.21238X1X2+1.7069X1X3–95.1434X1+0.011722X22+0.0675X2X3–25.29X2+6.0744X32– 200.9985X3+5871.7484 (B) Sensory scores of chewiness; Response surface equation: Y=6.2478e–15X12–0.017824X1X2+0.066667X1X3+ 0.34074X1+0.0063786X22–0.017593X2X3+1.7236X2–0.26667X32–7.8185X3–29.6251
Fig. 3. Response surface plot for L (lightness) (A) and b (yellowness) (B) and the textural property (chewiness) (C) of the meatball products as a function of sterilization temperature (X1) and time (X2) for the water-cascading rotary retort (+1) sterilization method. (A) L (lightness), Response surface equation: Y=0.037222X 1 2 –0.010208X 1 X 2 +0.07125X 1 X 3 –9.1242X 1 – 0.0021331X22+0.0024074X2X3+1.0973X2–1.1628X32–9.7837X3+ 615.0707; (B) b (yellowness), Response surface equation: Y= 0.0068403X 1 2 –0.022963X 1 X 2 –0.10021X 1 X 3 –1.2439X 1 – 0.0043484X 2 2 +0.016574X 2 X 3 +2.894X 2 –0.0038889X 3 2 + 11.3117X3+80.2078; (C) Textural property (chewiness), Response surface equation: Y=1.1229X12–0.60588X1X2–0.12604X1X3– 256.4381X1+0.25016X22+ 0.53259X2X3+54.2225X2–14.2967X32– 10.186X3+15029.5563
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time. An increase in the F0 value resulted in a less desirable texture. Color Values of a and ∆E were not affected significantly (p>0.05) by sterilization temperature, time, and sterilization method. However, the color parameter values of L and b could be predicted with significance (p<0.05) using values of a and ∆E (Table 4). The effect of processing on the value of L (lightness) was significant (p<0.05) for all combinations of sterilization temperature and time. The L values of meatballs treated using the water-cascading static retort were highest among sterilization methods. The L values decreased as either the heating temperature or the processing time increased (Fig. 3A). Thus, the lightness of the meatball surface color treated at a high temperature for a long time was low. The surface color of meatballs was influenced more by sterilization temperature than by time. The Maillard reaction between starch added during manufacture and amino acids in meat under conditions of high temperature for a long time was considered to be the major cause of the decline in L values. Starch breaks down into dextrin, which reacts with basic amino acids, such as lysine, present in meat, to produce a brown pigment (melanoidin) that, in turn, causes a decline in L values. Nakanishi (9) also showed that browning of fish cakes occurred as a result of the amino-carbonyl reaction when F0 values were higher than 6 min. Meanwhile, another study showed that heat treatment under HTST conditions was an efficient method of increasing the marketability of meat products with respect to color (10). The optimum range of L values was
determined to be approximately 50-60, (dimensionless value) with reference to the mean L value of untreated and treated meatball samples. The 2 sterilization variables of temperature and time had a significant (p<0.01) effect on the value of b. Temperature had a greater effect than time. The value of b decreased with an increasing sterilization temperature and time (Fig. 3B). Thus, the yellowness of the meatball surface decreased as the reddish tomato sauce that remained on the meat turned brown with heating. However, since no significant (p>0.05) relationship was found between the b value and the preference for meatballs, this parameter was not considered important for establishment of optimum sterilization conditions. Textural properties No sterilization condition variables were significant (p>0.05) for meatball cohesiveness (Table 4). However, meatball hardness values for the overall model were significantly (p<0.05) affected by sterilization temperature and time. Meatballs became harder with a decreasing processing time and sterilization temperature (Fig. 3C). This change was more significant marked for temperature. The change in hardness was due mainly to heat treatment that caused conversion of collagen to gelatin and dissociation of muscle protein (11). Bertak and Karahadian (12) showed that extra heating destroys the gel network matrix, resulting in a lower shear strain and reduced hardness and chewiness. Palka and Daun (13) also reported that the tenderizing effect observed at high temperatures was probably caused by heat-induced gelatinization of meat collagen and changes in the muscle
Table 4. Regression analysis of dependent variables (Y, including F0 value, sensory characteristics, and Hunter’s color value) under various sterilization conditions for the meatball products Source
Model
Degrees of freedom
9
Sum of squares1)
Y '1 Y '21 Y '22 Y '23 Y '31 Y '32 Y '33 Y '34 Y '4 Y '51 Y '52 Y '53 Y '54
2)
8608*** 25.27 18.81 24.82*** 177*** 11.25 52.74*** 33.93 0.008*** 1765208*** 0.10* 0.004 52021***
Linear
Quadratic
Cross
R2
Temperature (X1; oC)
Time (X2; min)
Method (X3)*
3
3
3
-
4
4
4
6889*** 19.71** 12.52 16.70*** 164*** 5.49 41.53*** 4.52 0.007*** 1404758*** 0.028 0.002 40406***
453*** 2.55 0.77 2.02 10.42 0.31 0.81 11.64 0.001 263497*** 0.033 0.002 5626
1265*** 3.01 5.51 6.09** 2.60 5.44 10.39** 17.76 0.001 96953* 0.044* 0.001 5987*
0.979 0.493 0.269 0.697 0.768 0.416 0.751 0.403 0.719 0.896 0.549 0.245 0.790
5732*** 8.70 7.84 13.01*** 51.31** 6.24 25.63*** 7.83 0.006*** 182554** 0.053* 0.002 8439*
2364*** 9.00 13.59 15.24*** 98.36*** 4.40 33.10*** 19.34 0.001 1615700*** 0.058* 0.002 46070***
1777*** 10.58 2.88 2.65 30.67* 6.04 4.39 24.53 0.003** 63906 0.037 0.001 3498
1) Y '1, F0 value at the coldest point in retort tray; Y '21, Preference evaluation (overall acceptability); Y '22, Sensory evaluation (degree of redness); Y '23, Sensory evaluation (chewiness); Y '31, Color (L value); Y '32, Color (a value); Y '33, Color (b value); Y '34, Color (E value); Y '4, Water activity (Aw); Y '51, Texture (hardness); Y '52, Texture (springiness); Y '53, Texture (cohesiveness); Y '54, Texture (chewiness) 2) *p≤0.1; **p≤0.05; ***p≤0.01
Optimization of Sterilization of Retorted Meatballs
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Fig. 4. Contour map for the optimum sterilization conditions (gray color) of the meatball products for the water-spray (–1) (A) and the water-cascading static (0) (B) and the water-cascading rotary (+1) (C) sterilization method and response surface plots for the F0 values of meatball products as a function of sterilization temperature (X1), time (X2), and method (X3) (D).
cytoskeleton. In general, foods processed at higher temperatures, which results in a lower hardness value, are considered to be of lower quality (11,14). Consequently, the optimum range of hardness was approximately 710-1200, based on hardness values of untreated and meatballs treated under the reference conditions (hardness of untreated samples= 1233.47). The overall model, including linear, interaction, and quadratic effects of temperature, time, and processing method, significantly (p<0.01) affected the chewiness of meatballs (Table 4). The chewiness value of meatballs treated with the water-cascading static retort was highest of all sterilization methods. Chewiness increased sharply with a decreasing processing time and temperature (Fig. 3C). A reduction in chewiness due to an increase in the processing temperature or the F0 value has also been reported (13,15). The decreasing trend in chewiness values was thought to be due mainly to denaturation of proteins and destruction
of muscle cells that occured during thermal processing. Consequently, the optimum range of chewiness was 110160, based on measured chewiness values of both untreated and meatballs treated under reference conditions (chewiness of untreated samples=165.64). Determination of optimum sterilization conditions Contour analysis was conducted to determine the optimum sterilization conditions of meatball products. The optimum conditions for each sterilization method were determined based on superimposing significant (p<0.05) contour plotting lines of the selected quality attributes. Optimum conditions of the water-spray type retort were highly restricted due to low F0 values 22.20-23.00 min at 123.8-124.5ºC (Fig. 4A). Sensory attribute scores and preferences were high for meatball products treated with the water-spray retort. The optimum temperature and processing time for the
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water-cascading static retort were 122.1-125.0ºC and 22.70-24.30 min, respectively (Fig. 4B). The overall preference for meatball products treated with the watercascading static retort was lower than for meatballs sterilized using the water-spray and water-cascading rotary retorts (Fig. 4D). Contour analysis of the water-cascading static retort, excluding preference, showed that the overall trend of the contour map was virtually the same as for the waterspray retort. However, the acceptable range for sterilization using the water-spray retort was more restricted than for use of the water-cascading static retort, attributable to differences in the distribution of F0 values. At high temperatures, F0 values of the water-spray retort were lower than for the water-cascading static type, although they were higher at lower temperatures (Fig. 4D). Contour analysis for the water-cascading rotary retort revealed optimum sterilization time and temperature conditions of 19.00-22.50 min at 118.9-119.6ºC or 19.00-22.00 min at 118.9-121.8ºC (Fig. 4C). Meatballs treated using the watercascading rotary retort had the highest F0 value for all 3 sterilization methods (Fig. 4D), indicating that the heattransfer rate of the water-cascading rotary retort was fast enough for meatballs to achieve a high F0 value under lowtemperature, short-time conditions. This result is consistent with previous reports that the rate of heat transfer can be increased and the processing time reduced by rotation of the retort (2,5). Moreover, the response variables F0, L, hardness, chewiness, and preference scores of chewiness, were maximized using the water cascading rotary retort at 121.4ºC and 19 min, determined based on optimization performed using RSM analysis (data not shown). The maximum values of each of these quality attributes (F0, L, hardness, chewiness, and preference scores of chewiness) for meatballs treated at 121.4ºC and 19 min in the water cascading rotary retort were 12.73, 50.53, 997.88, 144.27, and 5.40, respectively. These sterilization conditions were included in the optimum range determined using contour analysis, Therefore, the optimum conditions were 121.4ºC for 19.00 min using the water-cascading rotary retort, and 125.0ºC for 22.75 min using the water-cascading static retort. Sterilization conditions for production of retorted meatballs were determined based on analysis of safety and sensory qualities of food products processed under different conditions. The quality attributes of the F0 value at the cold point, viable cell count, water activity, color, sensory characteristics, and textural properties of meatballs were significantly (p<0.05) affected by the sterilization temperature, the processing time, and the processing method. RSM and contour analysis revealed that the optimum sterilization
Cheon et al.
conditions for meatball products that simultaneously satisfied all specifications were 121.4ºC for 19.00 min using the water-cascading rotary retort and 125.0ºC for 22.75 min using the water-cascading static retort. The heat-transfer rate was relatively fast for sterilization of meatballs using the water-cascading rotary retort under conditions of 19.00-22.50 min at 118.9-119.5ºC or 19.0022.00 min at 118.9-121.8ºC. Therefore, product quality deterioration was minimized and microbiological safety was achieved. Disclosure The authors declare no conflict of interest.
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