2014 Volume 20 Issue 6 Pages 1235-1244
We investigated the effects of 22 kinds of rice flours with different characteristics on the textural properties and whiteness of heat-induced fish meat gel without preheating. Amylose (AM), setback viscosity (SV), peaking time (PT), and crude protein (CP) positively affected the breaking force of fish meat gel. In contrast, breaking strain had a positive correlation with PT and CP, but a negative correlation with median particle size (MPS). Heat-induced gels with two added rice flours, prepared with a jet mill or a hammer mill, provided no significant differences in breaking force and breaking strain compared with gels containing rice starch. These flours were characterized by higher CP, AM, SV, and PT, as well as lower MPS, compared with the other flours. The whiteness of the gels with rice flour, except for one sample, was significantly higher than that of gels containing rice starch. Therefore, particle size, AM, PT, protein content, and SV of rice flour are important factors for producing high quality fish meat gel.
Rice (Oryza sativa L.) is the most important food in Japan because it is a staple food and the only main food crop that can be domestically supplied. The Japanese self-sufficiency rate for food is low: only 39% of the calories consumed in Japan in 2010 came from non-imported food (Ministry of Agriculture, Forestry and Fisheries, 2012), so food self-sufficiency is a major problem in Japan. However, the consumption of rice has been steadily decreasing in Japan,i so the use of rice flour in baked foods, noodles, and batter has increased to promote demand for rice (Nakamura et al., 2010; Nakamura and Ohtsubo, 2010).
Various additives have been used in fish meat products, such as kamaboko, to reduce its cost, and improve and/or enhance its texture (Ramírez et al., 2011). Starch is one of the main additives and is commonly added to these products at a level of 4% – 12% (Hunt et al., 2009). Starch affects the textural properties of fish meat products because of its physico-chemical properties, such as water-holding capacity, and its mechanical strength during gelatinization upon heating (Yamashita and Yoneda, 1989; Yamazawa, 1991; Hunt et al., 2009). Starch is the major component of rice, accounting for approximately 80% of its total weight. Potato starch, corn starch, and wheat starch are the most popular additives used for surimi based products (Okada, 2008; Hunt et al., 2009). Japan imports most of the corn and wheat for starch production (Ministry of Agriculture, Forestry and Fisheries, 2014a). In contrast, the raw material for potato starch is supplied within Japan. However, failure of the potato crop may result in the need for other domestic additives. Wheat allergy and celiac disease triggered by wheat protein such as gluten are important problems worldwide (Hiscgenhuber et al., 2006). Patients with these diseases avoid eating even fish products containing wheat starch. Therefore, rice may become an acceptable, harmless additive in Japanese processed foods because of the low risk of causing an allergic reaction (Shih, 2003). In Japan, the price of domestic rice is higher than that of imported cereal crops such as corn and wheat (Ministry of Agriculture, Forestry and Fisheries, 2014b).ii Recently, however, the price of rice has been steadily decreasing in Japan (Fujino, 2005), indicating that rice may become more price competitive with imported cereal crops in the future. In addition, rice flour production is environmentally friendly compared with rice starch production, which requires alkaline steeping (Bao and Bergman, 2004). Thus, rice flour is considered a promising new additive for fish meat products and a contributor to the increase in rice consumption. However, there are few reports on the use of rice flour in fish meat products. We have reported that up to 3% rice flour improves the textural properties of fish meat gel, as does rice starch, and suppresses the softening of fish meat gel (the modori phenomenon) (Tanimoto and Tomioka, 2013).
Rice flours are traditionally prepared in Japan from soaked rice grains using a roll mill. Various milling methods are currently applied for making rice flour. Rice flour properties, such as particle size distribution and damaged starch content, depend on the milling method (Nishita and Bean, 1982; Arisaka et al., 1992; Araki et al., 2009). These characteristics may affect the textural properties of fish meat gel with rice flour. Yoon and Lee (1990) reported that surimi gel containing 11 – 20 µm powdered cellulose particles has a higher penetration force because of its water-absorbing ability. Yamashita and Yoneda (1989) also reported that the jelly strength of surimi gel containing small granules (<10 µm) of potato starch was higher than that containing medium (10 – 40 µm) or large (>40 µm) granules. In addition, the swelling power (water-absorbing ability) of starch is a major factor that influences the gel-reinforcing effect (Yamashita and Yoneda, 1989; Yamazawa, 1991; Hunt et al., 2009). Furthermore, Hunt et al. (2009) suggested that a starch granule containing a higher ratio of amylopectin to amylose improves gel strength compared with a starch granule of similar size with a lower ratio of amylopectin to amylose. In contrast, amylose content contributes to an increased higher penetration force due to its increased susceptibility to retrogradation (Kim and Lee, 1987).
The aim of the present study was to evaluate several characteristics (crude protein content, total starch content, amylose content, damaged starch content, swelling power, and median particle size) of rice flour that may affect textural properties of heat-induced fish meat gel without preheating. We also investigated the relationship between gel properties of fish meat gel and pasting properties of rice flour, and studied the effects of the characteristics of rice flour on the whiteness of fish meat gel.
Materials Frozen walleye pollock (Theragra chalcogramma) surimi (FA grade) was provided by Supreme Alaska Seafoods Inc., Seattle, WA, USA. The surimi contained 4% sucrose, 4% sorbitol, and 0.3% sodium tripolyphosphate as a cryoprotectant. The water content of the surimi was 74.3 ± 0.04% (average ± standard deviation) as measured by the method previously reported (Tanimoto and Tomioka, 2013). Twenty-two different rice flours and a rice starch were used as additives for fish meat gel. Table 1 shows the pretreatment and milling methods for preparation of rice flours used in this study and these rice cultivars. Rice starch derived from the Japonica rice cultivar planted in Japan was provided by Johetsu Starch Corp., Niigata, Japan.
| Flour no. | Pretreatment | Milling method | Rice cultivar |
|---|---|---|---|
| 1 | Soaking | Hammer milling | n/a |
| 2 | Soaking | Jet milling | n/a |
| 3 | Soaking/Pectinase | Jet milling | n/a |
| 4 | Soaking | Roll milling/Jet milling | n/a |
| 5 | n/a | Pin milling | n/a |
| 6 | n/a | n/a | n/a |
| 7 | n/a | Roll milling | n/a |
| 8 | n/a | Roll milling | n/a |
| 9 | n/a | Roll milling | n/a |
| 10 | n/a | Jet milling | n/a |
| 11 | n/a | Jet milling | n/a |
| 12 | Soaking | n/a | n/a |
| 13 | - | Pin milling | Koshihikari |
| 14 | - | Pin milling | Koshihikari |
| 15 | Soaking | Jet milling | n/a |
| 16 | Soaking | Roll milling | n/a |
| 17 | Soaking | Hammer milling | n/a |
| 18 | Soaking | Hammer milling | n/a |
| 19 | Soaking | Hammer milling | Koshihikari |
| 20 | Soaking | Hammer milling | Kinuhikari |
| 21 | Soaking | Hammer milling | n/a |
| 22 | Soaking | Pin milling | n/a |
-, no pre-treatment; n/a, not available.
Determination of water content, crude protein content, and total starch content Water content was measured according to the Association of Official Analytical Chemists Official Method (AOAC Official method 925.10) with a slight modification; the samples were dried for 3 h at 135°C (Delwiche S, 2003). Nitrogen content was measured by a CN corder (Macro Corder JM1000CN, J- Science Lab., Kyoto, Japan) based on the Pregl-Dumas method (Patterson, 1973). Hippuric acid was used as a standard. A conversion coefficient of 5.95 for crude protein content was used.iii Total starch content was determined according to the method of the American Association of Cereal Chemists (AACC method 76.13) using a kit supplied by Megazyme International Ireland Ltd., Co. (Wicklow, Ireland) (American Association of Cereal Chemists, 2000a).
Damaged starch and amylose content The damaged starch content was determined according to the method of the American Association of Cereal Chemists (AACC method 76 – 31) using a starch damage assay kit (Megazyme International) (American Association of Cereal Chemists, 2000b). Amylose content was measured according to the method of Juliano et al. (1981) with slight modification. After 1.0 mL of 95% ethanol was added to 100 mg of rice flour, the mixture was allowed to stand for 20 h at room temperature. A 9.0-mL aliquot of 1.0 N NaOH was added to the solution, followed by dilution with distilled water up to a volume of 100 mL, then a 0.5-mL aliquot of this sample was mixed with 0.1 mL of 1.0 N acetic acid, 0.2 mL of 0.2% I2 in 2.0% KI, and 9.2 mL of distilled water. After 20 min at room temperature, the absorbance of the mixture was measured at 620 nm. Potato amylose (Type III, Sigma Co., St. Louis, MO, USA) and rice waxy amylopectin (Johetsu Starch Corp.) were used to prepare a standard curve.
Preparation of fish meat gel Frozen surimi was partially thawed at 3°C overnight. Salted surimi paste containing rice flour or starch was prepared by mixing intermittently using a domestic food processor (Model MK-K80P; Panasonic Corp., Osaka, Japan) for 10 min. The weight ratios (%) of the final concentration of surimi, rice flour or starch (13.8% moisture basis), water, and NaCl in the paste were 75.0%, 10.0%, 12.3%, and 2.7%, respectively. The adding amount of rice flour and starch was set based on the value which provided significant differences in textural properties of fish meat gels in a previous study (Tanimoto and Tomioka, 2013). The total weight of salted surimi was 200 g. The temperature of the surimi pastes was 8°C – 9°C immediately after mixing. The pastes were stuffed into a 9-cm circumference polyvinylidene chloride casing, then cooked at 90°C for 30 min. After cooking, the gels were cooled immediately for 30 min with tap water and stored at 20°C overnight prior to analysis.
Textural properties of the fish meat gels Textural properties of the fish meat gels were measured according to the method of the Codex Alimentarius Commission with a slight modification.iv Cylinder-shaped samples measuring 30 mm in height were prepared. The breaking force and strain of the fish meat gel were measured using a texturometer (tensipresser® MY BOY II; Taketomo Electoric Inc., Tokyo, Japan) equipped with a spherical plunger (diameter 5 mm). The probe was pressed into the surface of a gel specimen at a constant speed (1 mm/sec) at 20°C until the gel was punctured. Breaking force and strain were recorded as the force (kg) and the distance (m) when the gel sample was punctured by the probe, respectively.
Determination of color The fish meat gels were subjected to color measurement using a colorimeter (CR-400; Konica Minolta Optics, Inc., Tokyo, Japan). L* (lightness), a* (redness/greenness), and b* (yellowness/blueness) values were measured, and whiteness was calculated using the method described by Park (1994), as follows:
 |
Determination of swelling power Swelling power was measured using the method described by Yamashita and Yoneda (1989). A 20-mL aliquot of 2.7% (w/w) NaCl solution was mixed with 0.20 g of rice flour in a stoppered test tube. The test tube was heated at 90°C for 30 min. After heating, the sample was immediately cooled for 30 min using tap water and stored at 20°C for 23 h. The volume of the swollen sample was measured, and the volume per sample weight (mL/g) was used to evaluate swelling power.
Determination of median particle size The median particle size of the rice flour and rice starch was measured using a laser diffraction particle size analyzer (Heros & Rodos, Sympatec, Clausthal-Zellerfeld, Germany). The samples were fed into a laser diffraction sensor, HELOS (Helium-Neon Laser Optical System) using a universal dry dispersing unit, RODOS. This sensor detected the diffraction patterns of the sample particles. The median particle size of the samples was computed from these diffraction patterns.
Pasting properties of rice flour The pasting properties of rice flour were measured using a Rapid Visco Analyzer (RVA) model 3D (Newport Scientific, Warriewood, Australia). A 3.5-g (14.0% moisture basis) portion of sample and 25 mL of distilled water were mixed in a viscograph cup. A programmed heating and cooling cycle was followed, as outlined in the procedure of Toyoshima et al. (1997). The suspension was heated from 50°C to 93°C (at 50°C for 1 min and for 4 min to reach 93°C). The temperature was maintained at 93°C for 7 min, cooled from 93°C to 50°C in 4 min, and allowed to stand at 50°C for 3 min. Pasting properties were evaluated based on the peak viscosity, trough viscosity, breakdown viscosity, breakdown %, final viscosity, setback viscosity, peak time, and pasting temperature.
Statistical analysis Statistical analyses were performed using the Excel Tokei 2010 statistical software (SSRI Co. Ltd., Tokyo, Japan) and SPSS Statistics 17.0 (SPSS Inc., Chicago, IL, USA). One-way analysis of variance with Dunnett's or Tukey-Kramer post-tests was used to analyze the data and test for differences among mean values. The significance level was set at p < 0.05. Pearson's correlation coefficients were calculated between textural properties and whiteness of the fish meat gel and rice flour characteristics. The significance level was set at p < 0.05.
Textural properties and whiteness of fish meat gel Table 2 shows the textural properties and whiteness of fish meat gel with various rice flours. Breaking force and strain ranged from 588.4 × 10−3 kg to 714.6 × 10−3 kg and from 8.38 × 10−3 m to 9.77 × 10−3 m, respectively. The breaking force of twelve fish meat gels with rice flours (nos. 1, 3, 6, 7, 10, 11, 15, 17, 18, 19, 20, and 21) were not significantly different compared with gels with rice starch. The breaking strain values with rice flours (nos. 15 and 17) were not significantly different from that of gels with rice starch. All gel samples with rice flour had significantly higher breaking force values compared with fish meat gel without rice flour (p < 0.05). This result confirmed that the addition of rice flour to fish meat gel enhanced the breaking force, as did rice starch in our previous study (Tanimoto and Tomioka, 2013). However, the addition of rice flour as well as rice starch to fish meat gel did not elongate the breaking strain, in contrast to the earlier study (Tanimoto and Tomioka, 2013). In addition, the improved gel properties were different between the two studies. These discrepancies are considered to be due to various factors such as the method for preparing fish meat gel and the gel forming ability of surimi used. Gel samples with rice flours prepared by jet milling and hammer milling had significantly higher breaking force than gel samples made by pin milling (p < 0.05) (Table 3). The breaking strain of the gel with rice flours by jet milling and hammer milling was significantly higher than those by other milling methods (p < 0.05) (Table 3). The whiteness of gel samples with rice flour varied from 73.9 to 76.3. The values with rice flours used in this study, except for no. 13, were significantly higher than that with rice starch (p < 0.05). Jet milled samples had significantly higher whiteness compared with those milled using a pin mill (p < 0.05) (Table 3). The change ratio (1.03; maximum value / minimum value) of the whiteness of gel samples with rice flour is lower than those of breaking force and strain (1.17 and 1.21, respectively). This result indicated that the difference in rice flour characteristics affected textural properties of the fish meat gels more significantly compared with the whiteness.
| Flour no. | Breaking force (kg) | Breaking strain (m) | Whiteness (−) |
|---|---|---|---|
| 1 | 690.2 ± 46.1† | 9.31 ± 0.54*† | 75.4 ± 0.4*† |
| 2 | 628.1 ± 33.6*† | 9.23 ± 0.27*† | 76.0 ± 0.3*† |
| 3 | 644.7 ± 22.7† | 9.32 ± 0.19*† | 75.3 ± 0.3*† |
| 4 | 619.9 ± 25.7*† | 9.04 ± 0.27*† | 75.8 ± 0.4*† |
| 5 | 588.4 ± 53.0*† | 8.57 ± 0.60*† | 75.5 ± 0.2*† |
| 6 | 669.8 ± 28.3† | 9.33 ± 0.25*† | 75,4 ± 0.3*† |
| 7 | 645.9 ± 27.9* | 9.04 ± 0.27*† | 75.6 ± 0.5*† |
| 8 | 613.7 ± 45.7*† | 8.67 ± 0.33*† | 75.3 ± 0.4*† |
| 9 | 626.3 ± 40.1*† | 8.94 ± 0.36*† | 75.5 ± 0.3*† |
| 10 | 686.9 ± 25.0† | 9.52 ± 0.22* | 75.5 ± 0.3*† |
| 11 | 683.6 ± 20.9† | 9.32 ± 0.29*† | 75.7 ± 0.2*† |
| 12 | 598.7 ± 52.5*† | 8.77 ± 0.63*† | 76.3 ± 0.4*† |
| 13 | 604.4 ± 41.6*† | 8.38 ± 0.29*† | 73.9 ± 0.6† |
| 14 | 607.8 ± 26.2*† | 8.44 ± 0.31*† | 75.2 ± 0.2*† |
| 15 | 714.6 ± 46.8*† | 9.65 ± 0.42 | 76.2 ± 0.4*† |
| 16 | 629.7 ± 28.0*† | 8.77 ± 0.41*† | 74.9 ± 0.2*† |
| 17 | 710.0 ± 38.3† | 9.77 ± 0.28 | 75.4 ± 0.4*† |
| 18 | 639.3 ± 28.3† | 9.25 ± 0.28*† | 75.4 ± 0.3*† |
| 19 | 643.6 ± 30.2† | 9.12 ± 0.26*† | 75.0 ± 0.4*† |
| 20 | 678.9 ± 11.9† | 9.50 ± 0.12* | 75.6 ± 0.1*† |
| 21 | 684.2 ± 31.6* | 9.28 ± 0.43*† | 75.4 ± 0.4*† |
| 22 | 628.7 ± 47.7*† | 8.82 ± 0.38*† | 75.0 ± 0.4*† |
| Starch | 684.4 ± 59.4† | 10.13 ± 0.72 | 73.7 ± 0.4† |
| Surimi onlv | 207.0 ± 6.1 | 9.94 ± 0.36 | 76.9 ± 0.3 |
Values are means ± standard deviation (n = 3). Values of breaking force and breaking strain are × 10−3. Asterisks indicate that the flours had significant differences compared with starch (p < 0.05). Daggers indicate that the flours and starch had significant differences compared with surimi only (p < 0.05).
| Millig Method | Breaking force (kg) | Breaking strain (m) | Whiteness (−) |
|---|---|---|---|
| Jet | 671.6 ± 34.8a | 9.41 ± 0.17a | 75.7 ± 0.4a |
| Pin | 607.3 ± 16.6b | 8.55 ± 0.19b | 74.9 ± 0.7b |
| Hammer | 674.4 ± 27.6a | 9.37 ± 0.23a | 75.4 ± 0.2ab |
| Roll | 628.9 ± 13.2ab | 8.85 ± 0.17b | 75.3 ± 0.3ab |
Values are means ± standard deviation (n ≥ 4). Values of breaking force and breaking strain are × 10−3. Different small letters in the same column indicate significant differences (p < 0.05).
Moisture content, crude protein content, total starch content, amylose content, and damaged starch content The moisture content of the rice flours ranged from 10.7% to 13.8% (Table 4). The desired moisture content of rice flour for novel use (rice bread, noodles, and cake) is set at 15% or less in Japan.v The moisture content of these rice flours appeared to meet these criteria.
| Flour no. | Moisture content (%) | Crude protein content (%, db) | Total starch content (%, db) | Amy lose content (%) | Damaged starch content (%) | Swelling power (mL/g) | Median particle size (µm) |
|---|---|---|---|---|---|---|---|
| 1 | 12.9 ± 0.0 | 6.9 ± 0.0 | 88.2 ± 0.8 | 21.0 ± 1.0 | 13.7 ± 1.0 | 23.6 ± 0.8 | 74.2 ± 0.2 |
| 2 | 12.3 ± 0.0 | 7.1 ± 0.1 | 85.6 ± 2.9 | 17.1 ± 1.1 | 8.2 ± 0.5 | 23.6 ± 0.5 | 34.9 ± 0.0 |
| 3 | 12.3 ± 0.1 | 5.8 ± 0.1 | 88.5 ± 1.4 | 18.1 ± 0.9 | 2.3 ± 0.1 | 25.4 ± 0.6 | 42.5 ± 0.1 |
| 4 | 12.0 ± 0.1 | 6.S ± 0.1 | 88.2 ± 2.4 | 18.0 ± 0.5 | 2.1 ± 0.1 | 26.3 ± 0.3 | 45.0 ± 0.2 |
| 5 | 12.4 ± 0.0 | 7.1 ± 0.0 | 87.6 ± 2.2 | 16.9 ± 1.4 | 9.2 ± 0.7 | 25.7 ± 0.7 | 80.9 ± 0.1 |
| 6 | 12.3 ± 0.0 | 6.8 ± 0.0 | 88.6 ± 1.9 | 21.6 ± 1.0 | 5.1 ± 0.3 | 26.0 ± 1.0 | 59.6 ± 0.9 |
| 7 | 10.7 ± 0.0 | 6.5 ± 0.1 | 89.1 ± 1.3 | 22.1 ± 0.9 | 10.2 ± 0.8 | 26.7 ± 0.5 | 83.8 ± 0.8 |
| 8 | 11.6 ± 0.0 | 7.1 ± 0.1 | 88.3 ± 2.6 | 20.4 ± 1.0 | 11.2 ± 1.0 | 27.5 ± 0.4 | 82.8 ± 1.8 |
| 9 | 11.6 ± 0.0 | 6.9 ± 0.1 | 88.2 ± 1.9 | 20.2 ± 1.3 | 7.8 ± 0.7 | 27.9 ± 0.3 | 89.8 ± 0.5 |
| 10 | 11.2 ± 0.1 | 7.5 − 0.1 | 86.0 ± 0.5 | 19.9 ± 0.9 | 5.1 ± 0.8 | 29.7 ± 0.5 | 39.7 ±0.7 |
| 11 | 11.6 ± 0.0 | 7.1 ± 0.1 | 88.9 ± 2.6 | 21.4 ± 1.2 | 3.3 ± 0.4 | 27.3 ± 1.3 | 35.9 ± 0.3 |
| 12 | 12.8 ± 0.1 | 7.1 ± 0.1 | 91.0 ± 2.2 | 19.1 ± 0.7 | 14.1 ± 1.5 | 26.3 ± 0.4 | 45.8 ± 0.7 |
| 13 | 13.5 ± 0.1 | 5.9 ± 0.1 | 89.3 ± 2.5 | 21.0 ± 0.6 | 12.4 ± 1.1 | 25.6 ± 0.8 | 111.3 ± 2.7 |
| 14 | 12.2 ± 0.0 | 6.6 ± 0.1 | 88.2 ± 1.9 | 17.7 ± 0.4 | 7.6 ± 1.0 | 28.8 ± 0.6 | 89.4 ± 0.2 |
| 15 | 12.5 ± 0.0 | 7.5 ± 0.1 | 88.9 ± 2.0 | 22.1 ± 0.4 | 10.0 ± 1.4 | 29.7 ± 0.7 | 39.5 ± 0.6 |
| 16 | 13.4 ± 0.1 | 7.3 ± 0.1 | 88.7 ± 1.5 | 20.9 ± 0.6 | 6.3 ± 0.8 | 25.6 ± 1.5 | 162.8 ± 0.3 |
| 17 | 12.4 ± 0.0 | 7.6 ± 0.1 | 87.5 ± 0.5 | 23.3 ± 0.3 | 10.6 ± 1.5 | 22.9 ± 0.4 | 40.6 ± 0.4 |
| 18 | 13.0 ± 0.0 | 7.7 ± 0.1 | 87.6 ± 0.2 | 19.7 ± 0.4 | 8.9 ± 1.3 | 20.4 ± 0.3 | 27.3 ± 0.2 |
| 19 | 13.8 ± 0.0 | 6.7 ± 0.1 | 88.1 ± 1.6 | 18.1 ± 0.5 | 11.6 ± 1.1 | 22.8 ± 0.5 | 39.1 ± 0.7 |
| 20 | 13.1 ± 0.0 | 7.3 ± 0.0 | 87.7 ± 1.6 | 19.6 ± 1.3 | 8.1 ± 0.7 | 22.1 ± 0.5 | 36.7 ± 0.9 |
| 21 | 12.8 ± 0.1 | 7.5 ± 0.1 | 86.5 ± 1.7 | 21.0 ± 1.0 | 14.2 ± 0.9 | 20.7 ± 0.2 | 96.6 ± 2.0 |
| 22 | 12.2 ± 0.0 | 6.8 ± 0.1 | 89.0 ± 0.9 | 21.0 ± 0.8 | 7.7 ± 0.7 | 24.5 ± 0.3 | 115.9 ± 0.9 |
| Starch | 13.2 ± 0.0 | 0.5 ± 0.0 | 95.6 ± 0.6 | 22.7 ± 0.9 | 1.5 ± 0.3 | 22.0 ± 0.4 | 7.9 ± 0.4 |
Values are means ± standard deviation (n = 3).
The crude protein content, total starch content, amylose content, and damaged starch content of the rice flours are shown in Table 4. The crude protein content of the rice flours ranged from 5.8% to 7.7%. The total starch content of the rice flours ranged from 85.6% to 91.0%. In contrast, the total starch content of rice starch was 95.6%. Amylose content of rice flours ranged from 16.9% to 23.3%. The damaged starch content of rice flours ranged from 2.1% to 14.2%. The value of rice flours milled using a jet mill was significantly smaller than those using a hammer mill (p < 0.05) (Table 5). Several studies have reported that damaged starch content depends on the type of milling device and differences in the milling conditions such as dry, wet milling, or pectinase pretreatment (Nishita and Bean, 1982; Arisaka et al., 1992; Araki et al., 2009).
| Millig Method | Moisture content (%) | Crude Protein content (%, db) | Total starch content (%, db) | Amylose content (%) | Damaged starch content (%) | Swelling power (mL/g) | Median particle size (µm) |
|---|---|---|---|---|---|---|---|
| Jet | 12.0 ± 0.6a | 7.0 ± 0.7a | 87.6 ± 1.6a | 19.7 ± 2.1a | 5.8 ± 3.3a | 27.1 ± 2.7a | 38.5 ± 3.1a |
| Pin | 12.6 ± 0.6a | 6.6 ± 0.5a | 88.5 ± 0.8a | 19.1 ± 2.2a | 9.2 ± 2.2ab | 26.2 ± 1.9a | 99.4 ± 16.9b |
| Hammer | 13.0 ± 0.5a | 7.3 ± 0.4a | 87.6 ± 0.6a | 20.4 ± 1.8a | 11.2 ± 2.5b | 22.1 ± 1.3b | 52.4 ± 26.9a |
| Roll | 11.8 ± 1.1a | 7.0 ± 0.3a | 88.5 ± 0.4a | 20.9 ± 0.9a | 8.9 ± 2.3ab | 26.9 ± 1.0a | 104.8 ± 38.8b |
Values are means ± standard deviation (n ≥ 4). Different small letters in the same column indicate significant differences (p < 0.05).
Swelling power and median particle size The swelling power of the rice flours ranged from 20.4 mL/g to 29.7 mL/g (Table 4). The values of many rice flours (nos. 1 – 16 and 22) used in this study were significantly higher compared with that of rice starch (p < 0.05). The swelling power of rice flours prepared by hammer milling was significantly lower than that of rice flours made by other milling methods (p < 0.05) (Table 5). Median particle size ranged from 27.3 µm to 162.8 µm (Table 4). Rice flours milled using a jet mill and a hammer mill had significantly smaller median particle sizes than those milled using a pin mill and a roll mill (p < 0.05) (Table 5).
Pasting properties Table 6 shows the pasting properties of the rice flours. Peak viscosity, trough viscosity, breakdown viscosity, final viscosity, and setback viscosity ranged from 296.5 mPa·s to 483.1 mPa·s, from 169.7 mPa·s to 262.0 mPa·s, from 126.3 mPa·s to 274.1 mPa·s, from 265.9 mPa·s to 388.6 mPa·s, and from 96.2 mPa·s to 151.1 mPa·s, respectively. In contrast, the breakdown %, peak time, and pasting temperature varied from 41.8% to 56.8%, from 377 sec to 427 sec, and from 66.4°C to 73.4°C, respectively. Rice flours milled using a pin mill had significantly higher breakdown viscosity than those milled using a hammer mill (p < 0.05) (Table 7). The pin mill and the roll mill resulted in significantly higher breakdown % compared with the hammer mill (p < 0.05) (Table 7). In addition, peak times for the rice flours milled using a jet mill and a hammer mill were significantly longer than those using a pin mill (p < 0.05) (Table 7). The other pasting properties were not different among the milling methods.
| Flour no. | Peak viscosity (mPa·s) | Trough viscosity (mPa·s) | Breakdown viscosity (mPa·s) | Breakdown % | Final viscosity (mPa·s) | Setback viscosity (mPa·s) | Peak time (sec) | Pasting temperature (°C) |
|---|---|---|---|---|---|---|---|---|
| 1 | 403.1 ± 3.6 | 212.0 ± 2.9 | 191.1 ± 2.8 | 47.4 ± 0.5 | 348.5 ± 2.8 | 136.6 ± 2.8 | 408 ± 4 | 67.8 ± 0.1 |
| 2 | 392.3 ± 6.3 | 210.0 ± 7.4 | 182.3 ± 6.6 | 46.5 ± 1.6 | 323.7 ± 6.4 | 113.7 ± 1.2 | 420 ± 0 | 71.0 ± 0.3 |
| 3 | 482.7 ± 7.1 | 262.0 ± 8.6 | 220.7 ± 1.5 | 45.7 ± 1.0 | 388.6 ± 9.8 | 126.5 ± 3.7 | 397 ± 5 | 72.5 ± 0.7 |
| 4 | 463.5 ± 17.0 | 215.8 ± 10.8 | 247.7 ± 6.2 | 53.5 ± 0.6 | 326.6 ± 8.3 | 110.8 ± 2.8 | 395 ± 2 | 72.1 ± 0.0 |
| 5 | 461.4 ± 12.3 | 212.8 ± 6.0 | 248.6 ± 10.2 | 53.9 ± 1.2 | 343.7 ± 8.9 | 130.9 ± 6.0 | 383 ± 2 | 70.8 ± 0.0 |
| 6 | 482.6 ± 8.7 | 233.9 ± 3.0 | 248.7 ± 5.8 | 51.5 ± 0.3 | 368.6 ± 5.1 | 134.6 ± 2.1 | 401 ± 2 | 70.3 ± 0.3 |
| 7 | 430.1 ± 15.3 | 192.7 ± 9.3 | 237.4 ± 6.4 | 55.2 ± 0.7 | 331.4 ± 5.4 | 138.8 ± 3.9 | 393 ± 5 | 66.4 ± 0.1 |
| 8 | 398.0 ± 4.7 | 172.1 ± 8.4 | 225.9 ± 3.7 | 56.8 ± 1.6 | 285.8 ± 12.2 | 113.7 ± 3.9 | 381 ± 5 | 69.4 ± 0.0 |
| 9 | 468.3 ± 12.3 | 208.3 ± 5.0 | 260.0 ± 13.6 | 55.5 ± 1.7 | 347.1 ± 6.5 | 138.9 ± 6.5 | 401 ± 5 | 69.4 ± 0.1 |
| 10 | 429.2 ± 8.1 | 204.1 ± 6.5 | 225.1 ± 11.6 | 52.4 ± 1.9 | 327.6 ± 5.2 | 123.5 ± 1.7 | 407 ± 2 | 70.5 ± 0.4 |
| 11 | 457.9 ± 13.0 | 213.6 ± 3.0 | 243.5 ± 12.9 | 53.2 ± 1.4 | 360.3 ± 4.5 | 146.7 ± 4.2 | 427 ± 2 | 69.9 ± 0.0 |
| 12 | 296.5 ± 5.6 | 169.7 ± 1.4 | 126.3 ± 6.6 | 42.6 ± 1.5 | 265.9 ± 3.7 | 96.2 ± 2.7 | 425 ± 5 | 68.1 ± 0.5 |
| 13 | 399.8 ± 6.3 | 195.6 ± 1.3 | 204.2 ± 6.3 | 51.1 ± 0.8 | 337.3 ± 4.8 | 141.7 ± 4.5 | 383 ± 2 | 66.5 ± 0.1 |
| 14 | 483.1 ± 4.8 | 208.9 ± 2.6 | 274.1 ± 5.3 | 56.7 ± 0.7 | 338.7 ± 4.5 | 129.7 ± 3.8 | 377 ± 5 | 70.5 ± 0.4 |
| 15 | 400.1 ± 6.8 | 185.1 ± 3.4 | 215.0 ± 10.0 | 53.7 ± 1.6 | 331.1 ± 3.5 | 146.0 ± 3.7 | 401 ± 6 | 67.1 ± 1.3 |
| 16 | 438.0 ± 10.0 | 233.8 ± 7.8 | 204.3 ± 11.5 | 46.6 ± 2.0 | 372.9 ± 9.7 | 139.1 ± 5.4 | 408 ± 4 | 67.1 ± 0.1 |
| 17 | 385.7 ± 5.2 | 214.5 ± 2.6 | 171.0 ± 5.7 | 44.3 ± 1.0 | 365.6 ± 4.9 | 151.1 ± 2.8 | 421 ± 2 | 67.2 ± 0.1 |
| 18 | 419.5 ± 12.4 | 219.3 ± 5.5 | 199.4 ± 16.3 | 47.5 ± 2.7 | 331.4 ± 5.5 | 112.1 ± 2.8 | 421 ± 8 | 73.4 ± 0.4 |
| 19 | 428.1 ± 11.3 | 204.8 ± 8.5 | 223.3 ± 8.4 | 52.2 ± 1.5 | 318.5 ± 11.5 | 113.7 ± 3.8 | 389 ± 6 | 72.0 ± 0.1 |
| 20 | 431.9 ± 3.2 | 229.8 ± 15.4 | 202.1 ± 18.6 | 46.8 ± 4.0 | 350.2 ± 10.7 | 120.4 ± 9.6 | 416 ± 4 | 72.4 ± 0.4 |
| 21 | 368.4 ± 9.8 | 212.2 ± 7.9 | 153.9 ± 5.9 | 41.8 ± 1.7 | 358.9 ± 10.7 | 146.7 ± 3.3 | 427 ± 5 | 67.6 í 0.4 |
| 22 | 426.3 ± 8.3 | 191.9 ± 9.0 | 234.3 ± 3.9 | 55.0 ± 1.4 | 321.3 ± 12.6 | 129.4 ± 4.7 | 391 ± 2 | 69.6 ± 0.4 |
| Starch | 402.1 ± 8.5 | 161.0 ± 1.1 | 241.1 ± 7.5 | 60.0 ± 0.6 | 264.9 ± 3.0 | 103.9 ± 2.2 | 391 ± 2 | 71.6 ± 0.0 |
Values are means ± standard deviation (n = 3).
| Millig Method | Peak viscosity (mPa·s) | Trough viscosity (mPa·s) | Breakdown viscosity (mPa·s) | Breakdown % | Final viscosity (mPa·s) | Setback viscosity (mPa·s) | Peak time (sec) | Pasting temperature (°C) |
|---|---|---|---|---|---|---|---|---|
| Jet | 432.4 ± 38.2a | 215.0 ± 28.5a | 217.3 ± 22.3ab | 50.3 ± 3.9ab | 346.3 ± 27.7a | 131.3 ± 14.5a | 410 ± 12a | 70.2 ± 2.0a |
| Pin | 442.6 ± 36.9a | 202.3 ± 10.1a | 240.3 ± 29.1b | 54.2 ± 2.4a | 335.2 ± 9.7a | 132.9 ± 5.9a | 383 ± 5b | 69.3 ± 2.0aa |
| Hammer | 406.1 ± 25.2a | 215.4 ± 8.5a | 190.1 ± 24.5a | 46.7 ± 3.5b | 345.5 ± 17.6a | 130.1 ± 17.0a | 414 ± 14a | 70.0 ± 2.8a |
| Roll | 433.6 ± 28.9a | 201.7 ± 26.0a | 231.9 ± 23.2ab | 53.5 ± 4.7a | 334.3 ± 36.6a | 132.6 ± 12.6a | 396 ± 11ab | 68.1 ± 1.5a |
Values are means ± standard deviation (n > 4). Different small letters in the same column indicate significant differences (p < 0.05).
Relationships between textural properties and whiteness of fish meat gel and rice flour characteristics Table 8 shows the Pearson's correlation coefficients between textural properties and whiteness of the fish meat gel and rice flour characteristics. Breaking force was positively correlated with amylose content, setback viscosity, peak time, and crude protein content (r = 0.617, p < 0.01; r = 0.512, p < 0.05; r = 0.496, p < 0.05; r = 0.433 p < 0.05). Breaking strain had positive correlations with peak time (r = 0.606, p < 0.01) and crude protein content (r = 0.462, p < 0.05), but negative one with median particle size (r = −0.631, p < 0.01). The whiteness was also positively correlated with peak time (r = 0.500, p < 0.05) and crude protein content (r = 0.492, p < 0.05), but negatively with median particle size (r = −0.583, p < 0.01). Fish meat gel containing rice flour (nos. 15 or 17) showed no significant differences in breaking force and breaking strain compared with gels containing rice starch (Table 2). These rice flours were characterized by higher crude protein, amylose, setback viscosity, and peak time and lower median particle size compared with the other rice flour samples (Tables 3 and 4). These tendencies support the results of the significant correlation between textual properties of fish meat gel and various characteristics of rice flour (table 8).
| Breaking force | Breaking strain | Whiteness | |
|---|---|---|---|
| Moisture content | −0.063 | −0.094 | −0.365 |
| Crude protein content | 0.433 * | 0.462 * | 0.492 * |
| Total starch content | −0.279 | −0.378 | −0.053 |
| Amylose content | 0.617 ** | 0.374 | −0.105 |
| Damaged starch content | −0.012 | −0.162 | −0.087 |
| Swelling power | −0.111 | −0.218 | 0.162 |
| Mediam particle size | −0.369 | −0.631 ** | −0.583 ** |
| Peak viscosity | −0.065 | −0.061 | −0.236 |
| Trough viscosity | 0.199 | 0.311 | −0.160 |
| Breakdown viscosity | −0.198 | −0.258 | −0.202 |
| Breakdown % | 0.238 | 0.130 | 0.408 |
| Final viscosity | 0.420 | 0.347 | −0.273 |
| Setback viscosity | 0.512 * | 0.215 | −0.289 |
| Peak time | 0.496 * | 0.606 ** | 0.500 * |
| Pasting temperature | −0.121 | 0.168 | 0.206 |
* and ** indicate significant at p < 0.05 and 0.01.
This study aimed to determine suitable rice flour properties for use as an additive for fish meat gel. We found that breaking force was positively correlated with amylose content (p < 0.01) and setback viscosity (p < 0.05) (Table 8). The high amylose content of starch promotes retrogradation (Kim and Lee, 1987; Bao and Bergman, 2004). The amylose fraction in starch determines firmness of the gels, whereas amylopectin determines gel elasticity (Hunt et al., 2009). The setback on RVA is caused by retrogradation of starch, particularly amylose (Wani et al., 2011). In fact, amylose content in the rice flour was significantly correlated (0.654, p < 0.01) with setback viscosity in this study. Hence, the correlation between breaking force and amylose content is suggested to be due to the increased hardness of rice flour induced by its retrogradation under decreasing temperature. Breaking force, breaking strain, and whiteness were positively correlated with peak time and crude protein content (p < 0.05). Juliano (1979) reported that protein content is one of the main factors affecting the stickiness and hardness of cooked rice. Arai and Watanabe (1994) suggested that the contribution of protein to the hardness of cooked rice is due to its inhibition of starch gelatinization. A longer peak time may be due to the lower rate of water absorption and swelling of starch granules. In fact, crude protein content in the rice flour was significantly correlated (r = 0.596, p < 0.01) with peak time in this study. However, rice noodles had negative correlations between the protein content, and the maximum tensile strain and storage modulus (Li et al., 2007). Thus, rice flour protein did not directly affect the properties of fish meat gel but had an indirect influence on the properties by suppressing starch gelatinization. In addition, the mechanical strength of starch granules affects the jelly strength of fish meat gel (Okada and Yamazaki, 1959; Hunt et al., 2009). Therefore, the correlation results of amylose content, crude protein content, setback viscosity, and peak time with breaking force is suggested to be due to the mechanical strength of rice flour gel in fish meat.
The amylopectin component in starch contributes to granule swelling in fish meat gel and increases gel strength (Hunt et al., 2009). The swelling power (water-absorbing ability) of starch is a major factor that influences the gel-reinforcing effect (Yamashita and Yoneda, 1989; Yamazawa, 1991; Hunt et al., 2009). However, breaking force did not correlate with swelling power significantly in this study (Table 8). In addition, we have reported that the swelling power of rice flour and rice starch does not explain the differences in their gel reinforcing effects (Tanimoto and Tomioka, 2013). These observations suggest that the change in the swelling power of rice flours ranging from 20.4% to 29.7% (Table 4) did not affect textural properties of fish gel compared with other characteristics. When a surimi gel was prepared with starch that has a low gelatinization temperature, the resulting higher gel strength is attributed to starch granule swelling (Hunt et al., 2009). In fact, potato starch has relatively lower gelatinization temperature compared with those of corn and wheat starches (Jiranuntakul et al., 2011). The addition of potato starch provided higher gel strength fish meat gel compared with fish meat gels containing corn and wheat starches (Okada and Yamazaki, 1959). However, both breaking force and strain did not correlate with the pasting temperature of the rice flours significantly in this study (Table 8). In addition, the pasting temperature of the rice flours did not have significant correlation with swelling power in this study. Therefore, the changes in the pasting temperature as well as the swelling power of rice flours (Tables 4 and 6) did not affect the textural properties of fish gel compared with other characteristics.
Breaking strain was negatively correlated (p < 0.01) with median particle size (Table 8). To our knowledge, there is no report on the relationship between the breaking strain of fish meat gel with an additive and its particle size. Yoon and Lee (1990) reported that surimi gel containing 11 – 20 µm powdered cellulose has higher penetration force due to its water-absorbing ability. Konoo et al. (1997) reported that the breaking strength of gel with starch did not vary with the particle size and its distribution. This is in agreement with the current results showing insignificant correlation between breaking force and median particle size (Table 8). On the other hand, Yamashita and Yoneda (1989) also reported that the jelly strength of surimi gel containing small granules (<10 µm) of potato starch is higher than that containing medium (10 – 40 µm) or large (>40 µm) granules. When the addition of an additive to fish meat gel does not increase the gel's breaking strength, the increase in its jelly strength is due to the elongation of its breaking strain. This supports the result that the particle size of rice flour affects the breaking strain of fish meat gel in this study.
Arisaka (1992) and Nishita and Bean (1982) reported that the distribution of rice flour particle size is affected by the milling method. We also found that median particle size of the rice flours milled using a jet mill and a hammer mill was significantly smaller than those milled using a pin mill and a roll mill (p < 0.05) (Table 5). In addition, rice flours milled using a jet mill and a hammer mill had significantly longer peak times compared with those using a pin mill (p < 0.05) (Table 7). Rice flours prepared with a jet mill and a hammer mill provided a significantly higher gel breaking force than flours prepared by pin milling (p < 0.05) (Table 3). In addition, fish meat gel with rice flour had highly positive correlation between breaking force and breaking strain (0.895; p < 0.05). Jet milling and hammer milling resulted in significantly higher breaking strain compared with pin milling and roll milling (p < 0.05) (Table 3). Two rice flours (nos. 15 and 17) which showed no significant differences in breaking force and breaking strain when mixed with gel samples compared with gels containing with rice starch are milled by jet milling and hammer milling, respectively. Thus, the jet mill and the hammer mill are suitable milling methods to prepare rice flour as an additive for fish meat gel compared with the other milling methods. These results could be because of the smaller particle size and longer peak time of the rice flour.
We clarified the relationship between the textural properties and whiteness of heat-induced fish meat gel containing rice flour and rice flour characteristics. Among 22 fish meat gel samples containing rice flours, two gel samples showed no differences in breaking force and breaking strain compared with gels containing rice starch. Amylose content, setback viscosity, peak time, and crude protein content were important rice flour characteristics for making a fish meat gel with higher breaking force. However, the smaller median particle size, longer peak time, and higher crude protein content led to higher breaking strain and whiteness. Therefore, the median particle size, amylose content, peak time, setback viscosity, and crude protein content of rice flour are important properties required for making a superior fish meat gel. Setting (Suwari) phenomenon of fish meat leads to an increase in the textural strength and elasticity of heat-induced gel preheated below 40°C (Martin-Sánchez et al., 2009) In contrast, modori is a gel-weakening phenomenon of fish meat at around 50°C – 60°C (Martin-Sánchez et al., 2009). Fish meat gel processing must regulate these phenomena. Various food additives to fish meat gel affect these phenomena (Martin-Sánchez et al., 2009; Yamashita et al. 1999). Therefore, further studies are in progress to confirm the effect of rice flour on setting and modori of fish meat gel using the optimum rice flour.
Acknowledgements This study was supported in part by a Grant-in-Aid for the Iijima Memorial Foundation for the Promotion of Food Science and Technology. The authors would like to give heartfelt thanks to Dr. Taizo Masuda (Prefectural University of Hiroshima) for his guidance in analyzing crude protein in rice flour. The authors are grateful to Dr. Kanenori Takata (National Agricultural Research Center for Western Region) for his guidance in determining the median particle size of the rice flours.
