Bei LIU Haiying LUO Moyu NIE Fei WU Tianxin LI Peng WU Ting HU
Abstract ［Objectives］This study was conducted to improve the gel properties of freshwater surimi and its products.
［Methods］ Tuanfeng lotus seed powder was added to frozen silver carp, and the relationship between the addiamount of Tuanfeng lotus seed powder (1%, 2%, 3%, 4% and 5%) and the quality of surimi products was studied, so as to improve the quality of surimi products.
［Results］ The water holding capacity (86.71%±0.36%), hardness (3 566.64±51.15) g, chewiness (2 697.16±15.81) g and gel strength (692.54±23.19) of surimi products increased to the maximums when the addition amount of lotus seed powder was 3%. Meanwhile, the cooking loss rate was reduced to the minimum (13.00%±0.17%), and the sensory quality was the best, although the whiteness of surimi products decreased slightly with the increase of Tuanfeng lotus seed powder. Therefore, the quality of silver carp surimi products could be improved obviously when the dosage of Tuanfeng lotus seed powder was 3%.
［Conclusions］ This study provides more new ideas for improving the quality of silver carp surimi products, and simultaneously makes the development of lotus seed food more diversified.
Key words Tuanfeng lotus seed powder; Silver carp; Surimi products; Quality
Received: June 17, 2022 Accepted: August 18, 2022
Supported by Scientific Research Program Steering Group Project of Department of Education of Hubei Province (B2020166).
Bei LIU (2002-), female, P. R. China, major: food science and engineering.
*Corresponding author.
Surimi is a deep-processed product made of fish after washing, collecting, rinsing, dewatering, and shredding［1］. During processing of surimi products, impurities such as water-soluble protein can be removed, and muscle fiber protein, which is rich in high-quality protein, can be concentrated, so surimi products are rich in high-quality protein. In today’s society, surimi products are suitable for the market as they can be eaten immediately and are also simple to process. As a modern processed aquatic food, they can better meet people’s food requirements and have a very far-reaching development prospect［2-7］. Freshwater fish is low in price, and this advantage can be well used in the development and production of freshwater surimi products. However, the gel-forming ability of freshwater surimi is not as good as that of seawater surimi, which limits its practicality［8］. Therefore, how to improve the gel properties of freshwater surimi and its products is the focus of current research.
Tuanfeng lotus seeds are a geographically indicated product of Tuanfeng County, and the demand is increasing year by year. As a high-quality product, lotus seeds are rich in carbohydrates, vitamins and proteins, and have the characteristics of low fat, high protein and high starch. Through the implementation of the operation mechanism of "village-level company+cooperative+farmer", the planting area of Xianglian in Tuanfeng County and towns including Taodian, Lukou and Chencelou has expanded to more than 3 300 hm2, covering 70% of Huanggang’s counties, cities, and towns. Lotus seeds also occupy a certain position in the national economy of Hubei Province as crops, aquatic vegetables, and medicinal and edible products［9］.
At present, the method of adding exogenous additives is mostly used in the research on improving the quality of surimi products, mainly including tapioca starch, wheat starch, corn starch, potato starch and deep processing extracts of other agricultural products［10］. Lotus seeds have long been known as one of the most nutritious products, and their edible and health benefits have always been valued by people. Although foods related to lotus seeds are constantly being developed［11］, few are associated with surimi products. In this study, the optimum amount of Tuanfeng lotus seed powder in silver carp surimi products was determined by investigating the relationships of the whiteness value, cooking property, water holding capacity, TPA performance, gel strength and sensory quality of silver carp surimi products with the addition amount of Tuanfeng lotus seed powder. This study provides more new ideas for improving the quality of silver carp surimi products, and simultaneously makes the development of lotus seed food more diversified.
Materials and Methods
Materials and reagents
Frozen silver carp surimi: Honghu Jingli Aquatic Food Co., Ltd., Hubei Province (AAA grade); PDVC casing: Qingyun Yijie Plastic Products Co., Ltd., Shandong Province; salt, dried lotus seeds: Huangzhou Huangshang Shopping Center.
Instrument and equipment
HR7625 food processor: Philips Household Appliances (China) Limited, Hongkong, China; CR-10 colorimeter: Konica Minolta; H/T18MM desktop high-speed centrifuge: Hunan Herexi Instrument & Eqipment Co., Ltd.; TA-XT Plus physical property tester: Texture Technologies Co., Ltd., USA; HS153 halogen moisture meter: Mettler Toledo Corporation.
Experimental methods
Preparation of surimi gel
First, frozen surimi was thawed at 4 ℃ for 12 h. Then, 200 g of surimi was cut into cubes with a width of 2 cm, which were put into a chopper mixer and chopped for 30 s, and then added with a little sodium chloride (mass fraction 2.5%) and chopped for 30 s. Lotus seed powder was added according to the ratios of 0%, 1%, 2%, 3%, 4% and 5% (calculated by the mass of surimi, W/W), respectively, and then the water content of surimi was adjusted to 80%, and the surimi was chopped and mixed for 30 s again. After chopping and mixing, the surimi was filled into casing (Φ2), and both ends were sealed after filling. The surimi gel was prepared by a two-stage heating method, that is, first heating at 40 ℃ for 1 h and then heating at 90 ℃ for 0.5 h. The sausages were cooled in ice water for 20 min, and the surface moisture was wiped off the casing. Finally, the prepared sausages were refrigerated at 4 ℃ for 24 h for later use.
Calculation of whiteness value
After taking out the sample, the casing was removed, and the internal material was cut into thick slices with a height of 2 cm. The chroma was measured using a colorimeter. The whiteness value W (whiteness) was calculated according to equation ①:
W=100-(100-L)*2+a*2+b*2①
In the equation, L* indicates the lightness of the sample; +a* indicates that the chroma is reddish, and -a* indicates that the chroma is greenish; and +b* indicates that the chroma is yellowish, and -b* indicates that the chroma is bluish.
Determination of cooking loss
The prepared samples were cut into 2 mm cylinders, which were weighed to record the weight as W1, and sealed in a cooking bag. A constant-temperature water bath was adjusted to 90 ℃, and the sample was put in and heated for 20 min. After cooling, it was taken out, and the moisture was wiped off, and the weight was record as W2. The cooking loss rate was calculated from equation ②:
Cooking loss rate (%)=W1-W2W1×100②
Determination of water holding capacity
First, a thin sample slice about 3 g in weight and 2-3 mm in thickness was cut, and the weight was recorded as W1. The sample was wrapped with two pieces of filter paper (20 mm in diameter) and centrifuged (temperature 4 ℃, speed 4 000×g, time 15 min). After centrifugation, the sample was weighed (W2, g). Three groups were measured in parallel. The water holding capacity (WHC) was calculated according to equation ③:
WHC (%)=W2/W1×100③
In the equation: W1 is the weight of the sample slice before centrifugation, and W2 is the weight of the sample slice after centrifugation.
Determination of TPA properties
Surimi gel samples with a height of 2 cm were prepared, and the TPA properties were measured with a texture analyzer at room temperature. Specific test parameters were as follows: probe P/36R, compression ratio 50%, trigger force 5 g, speed before the test 1 mm/s, speed during the test 1 mm/s, and speed after the test 5 mm/s, and the probe vertically pressed the sample for 2 times. The hardness, springiness, cohesiveness, chewiness and resilience of the surimi gel could be obtained from the texture curve.
Determination of gel strength
Surimi gel samples with a height of 2 cm were prepared, and the gel strength was measured using a texture analyzer at room temperature. Specific test parameters were as follows: probe P/0.25 S, speed before the test 1 mm/s, speed during the test 1 mm/s, speed after the test 5 mm/s, and puncture distance 15 mm. The gel strength was calculated from equation ④:
Gel strength=Breaking force×Breaking distance④
Sensory analysis
The four indexes (color, smell, tissue state and taste) of the samples were scored by eight food professionals, with a total score of 100 points, and the final score was taken as the average score of the eight members. The evaluation criteria are shown in Table 1.
Data analysis
All data in the experiment were obtained in at least three replicates, and were plotted using GraphPad Prism 7.0. IBM SPSS Statistics 26 was used to perform one-way ANOVA and Ducan test (P<0.05), and data were expressed as mean±standard deviation.
Results and Analysis
Effects of Tuanfeng lotus seed powder with different concentrations on the whiteness value of surimi products
The effects of Tuanfeng lotus seed powder with different concentrations on the whiteness value of surimi products are shown in Table 2. It can be seen from Table 2 that with the increase of the amount of lotus seed powder added, the whiteness value of surimi products continued to decrease, which might be related to the pale yellow color of dried lotus seeds after grinding. In addition, starch molecules in lotus seeds absorbed water and expanded during the heating process, causing light reflection, and the starch after gelatinization absorbed water and had a high degree of transparency. The gelatinization degree of starch increased with the increase of the amount of lotus seed powder added, which led to increased transparency, increased transmitted light, decreased reflected light, and decreased whiteness［12］.
Bei LIU et al. Effects of Supplemental Amount of Tuanfeng Lotus Seed Powder on Quality of Silver Carp Surimi Products
Effects of Tuanfeng lotus seed powder with different concentrations on the water holding capacity of surimi products
The effects of Tuanfeng lotus seed powder with different concentrations on the cooking loss rate of surimi products are shown in Fig. 1. It can be seen from Fig. 1 that the water holding capacity of white surimi products increased first and then decreased with the increase of the addition amount of Tuanfeng lotus seed powder. When the addition of lotus seed powder was 3%, the water holding capacity of surimi products reached the maximum value (6.71%±0.36%). It could be seen that Tuanfeng lotus seed powder could significantly improve the water holding capacity of silver carp surimi products. According to the research of Pei et al.［13］, the water holding capacity of surimi products is obviously related to the swelling property of starch. Starch is the main carbohydrate in Tuanfeng lotus seeds［14］, and amylopectin, which is more swellable and has strong water absorption and gel binding ability, is high in lotus seed starch［15-16］. The water-holding capacity of surimi products increased with the swelling of Tuanfeng lotus seed powder when it absorbed water and dissolved. Meanwhile, under the influence of proteins in Tuanfeng lotus seeds, the cross-linking of surimi gel network structure enhanced the gel water holding capacity of surimi products［17］.
Effects of Tuanfeng lotus seed powder with different concentrations on the cooking loss rate of surimi products
The effects of Tuanfeng lotus seed powder with different concentrations on the cooking loss rate of surimi products are shown in Fig. 2. The nutrients and moisture contained in surimi products will be lost during the cooking process, that is, cooking loss. The greater the cooking loss, the greater the water loss of surimi products under heating conditions［18］. It can be seen from Fig. 2 that with the increase in the amount of lotus seed powder added, the cooking loss of surimi products first decreased and then increased, and was significantly lower than that of the control group. When the addition amount of Tuanfeng lotus seed powder was 3%, the cooking loss rate was the lowest (13.00%±0.17%), which was 5.61% lower than that of the control group. It was because that water molecules were firmly fixed in the surimi gel network under the combined action of fish meat protein molecules and starch substances, so that the loss of water was suppressed and the cooking loss rate was reduced［19］. The smaller the cooking loss rate, the higher the water holding capacity, which was consistent with the water holding capacity results.
Effects of Tuanfeng lotus seed powder with different concentrations on the TPA of surimi products
The effects of Tuanfeng lotus seed powder with different concentrations on the TPA of surimi products are shown in Table 3. It can be seen from Table 3 that the cohesiveness and resilience of surimi products continued to decrease with the increase of the amount of lotus seed powder added, while the hardness and chewiness increased first and then decreased. When the addition amount of Tuanfeng lotus seed powder was 3%, the hardness and chewiness of surimi products reached the maximum value. Tuanfeng lotus seed powder had a great effect on the gel properties of surimi products, mainly because the starch in lotus seed powder was gelatinized and expanded into the denatured protein gel network, thus changing the gel texture properties［20］. When the addition amount was 3%, the water holding capacity of the surimi gel was the largest, and the hardness was also the largest at this time.
Effects of Tuanfeng lotus seed powder with different concentrations on the gel strength of surimi products
The effects of Tuanfeng lotus seed powder with different concentrations on the gel strength of surimi products are shown in Fig. 3. As can be seen from Fig. 3, with the amount of lotus seed powder added increasing, the gel strength of surimi products first increased and then decreased. When the amount of lotus seed powder added was 3%, the gel strength reached the maximum. It might be because that after adding lotus seed powder, the starch in it was gelatinized after heating, so that the force between starch granules increased, and the surimi gel network structure was filled, which improved the gel properties of surimi and made the tissue structure become denser［21］. When the amount of lotus seed powder was 5%, the gel strength of surimi was lower than that of the control group. It was because that the amylopectin content in Tuanfeng lotus seed powder was large, and after heating the surimi, the amylose and amylopectin in the surimi gel were entangled together, and the water absorption and swelling of starch molecules hindered the extension of protein molecules, resulting in incomplete denaturation of proteins and a decrease in gel strength［22］. Therefore, when too much Tuanfeng lotus seed powder was added, the gel strength of surimi products decreased instead.
Effects of Tuanfeng lotus seed powder with different concentrations on the sensory evaluation of surimi products
Sensory evaluation was carried out on the surimi products added with different amounts of lotus seed powder, and the results are listed in Table 4. As can be seen from Table 4, with the increase of the addition amount of Tuanfeng lotus seed powder, the odor score was on the rise, which might be related to the fragrance of Tuanfeng lotus seed powder itself, which can effectively reduce the fishy smell of surimi products after adding. The color score showed a downward trend, because the color of Tuanfeng lotus seed powder was light yellow-green, and the proportion of starch was high, and water absorption and swelling caused light reflection. The tissue state and springiness scores showed a trend of increasing first and then decreasing. When the addition of Tuanfeng lotus seed powder was 3%, the scores of tissue state and springiness reached the maximum values, but when the addition of lotus seed powder continued to increase, the tissue state and springiness scores of surimi products decreased significantly. Comprehensively, adding 3% Tuanfeng lotus seed powder could effectively improve the sensory quality of surimi products.
Conclusions
When the addition amount of Tuanfeng lotus seed powder was 3%, the water holding capacity, hardness, chewiness, gel strength and sensory quality of surimi products all reached the maximum values, and the cooking loss rate decreased to the minimum, although the whiteness value decreased slightly. Therefore, the overall quality of silver carp surimi products could be improved by adding 3% of Tuanfeng lotus seed powder. This study not only provides new ideas for improving the quality of silver carp surimi products, but also expands new ways for the promotion and development of Tuanfeng lotus seeds.
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