Method for prolonging normal-temperature storage period of seasonal low-salt black carp intervened fish blocks

Abstract

According to the method for prolonging the normal-temperature storage period of seasonal low-salt black carp intervention-processed fish cubes, an essential oil mixture is adopted to conduct preservation treatment on the black carp intervention-processed fish cubes, the use amount of the essential oil mixture is 0.4%-0.5% of the mass of the fish cubes, and the essential oil mixture comprises, by mass, 50%-60% of purple perilla essential oil, 20%-25% of dendrobium officinale flower essential oil and 20%-25% of saffron essential oil. And the drying, slitting and packaging processes of the black carp intervened fish blocks are technically innovated and improved, so that the normal-temperature storage period of the seasonal low-salt black carp intervened fish blocks is greatly prolonged.

Description

Technical Field

[0001] The invention relates to the field of food processing, in particular to a method for prolonging the room-temperature storage period of seasonal low-salt black carp processed fish pieces. Background Art

[0002] Zhejiang is a major black carp production province in China, with an annual output of more than 60,000 tons. Black carp is large in size and has a small share of the fresh market. Black carp is mainly pickled and dried in winter. Especially in Hangzhou, Jiaxing, Huzhou, Shaoxing and other places in Zhejiang, there is a custom of pickling black carp during the New Year and other festivals. However, this traditional dried black carp has the following key problems: 1. Traditional black carp is mainly processed by high-salt pickling, with backward technology, extensive high-salt pickling process, more arbitrary and empirical, and prominent standardization issues; 2. The product has a high salt content, unstable quality, low quality, and prominent quality and safety issues; 3. Traditional dried black carp is a whole fish that has not been cut, which conflicts with people's low-salt pre-prepared healthy consumption habits in modern society, resulting in a smaller consumer group for this traditional dried black carp, and the market potential cannot be tapped, which is inconsistent with the new era's healthy consumption trend and the requirements of Healthy China.

[0003] Aiming at the above key problems of the traditional dried black carp industry, the inventor has carried out scientific research for many years and successfully developed the key technology of reducing salt in flavored dried black carp processing, achieving the goals of product standardization, low salt (salt content <5%) and pre-cutting. In order to ensure the traditional flavor and New Year consumption customs, the low-salt black carp cuts developed are seasonal raw products. The seasonal season specifically refers to the winter around the Spring Festival in the Yangtze River Delta region such as Zhejiang, Jiangsu, Shanghai, and Anhui (the temperature is generally below 20°C). No preservatives are used, and no high-temperature sterilization or chlorine-containing fungicides are used. This is because high-temperature sterilization will cause the texture and flavor of the dried black carp to lose the old pickled flavor, and fungicides are likely to bring odors, destroying the coordination of traditional flavors.

[0004] Since low-temperature refrigeration in cold storage will affect the color and cured flavor of traditional dried black carp, low-salt dried black carp chunks must also maintain the same process requirements of room temperature storage and transportation as traditional products. However, once the temperature is relatively high in the seasonal winter, such as exceeding 25°C, the seasonal low-salt dried black carp chunks will experience more problems such as swelling, odor, and other spoilage when stored at room temperature, which greatly affects the seasonal storage needs and flavor of the seasonal low-salt dried black carp chunks. Summary of the invention

[0005] The purpose of the present invention is to provide a method for prolonging the room-temperature storage period of seasonal low-salt dried black carp fish pieces, the dried black carp fish pieces are preserved by an essential oil mixture, and the drying, cutting and packaging processes of the dried black carp fish pieces are technically improved, thereby greatly prolonging the room-temperature storage period of the seasonal low-salt dried black carp fish pieces.

[0006] To achieve the above purpose, the technical scheme provides a method for extending the room temperature storage period of seasonal low-salt dried black carp fish fillets, comprising the following steps: preserving the dried black carp fish fillets with an essential oil mixture, wherein the amount of the essential oil mixture is 0.4% to 0.5% of the mass of the fish fillets, and the essential oil mixture comprises 50% to 60% of perilla essential oil, 20% to 25% of dendrobium officinale essential oil and 20% to 25% of saffron essential oil in a mass ratio.

[0007] This scheme uses an essential oil mixture to preserve fish chunks and secondary dried fish chunks. The seasonal low-salt prefabricated fish chunks treated with the essential oil mixture have a good antibacterial effect and can play a good preservation role.

[0008] In some embodiments, the essential oil mixture is evenly sprayed and applied on the surface of the prepared black carp fish pieces for preservation.

[0009] In some embodiments, the sum of the mass ratios of perilla essential oil, dendrobium officinale essential oil and saffron essential oil in the essential oil mixture is 100%, wherein the mass ratio of perilla essential oil is one of 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% and 60%, the mass ratio of dendrobium officinale essential oil is one of 20%, 21%, 22%, 23%, 24% and 25%, and the mass ratio of saffron essential oil is 20%, 21%, 22%, 23%, 24% and 25%.

[0010] About the Perilla essential oil in this recipe’s essential oil blend: It is rich in perillaldehyde, limonene and other ingredients. Perillaldehyde has significant antibacterial activity and can inhibit the growth of a variety of bacteria (such as Staphylococcus aureus, Escherichia coli, etc.) and molds (such as Aspergillus niger, Penicillium, etc.). In pre-made fish blocks, these microorganisms are one of the main factors leading to the spoilage of fish blocks. For example, Staphylococcus aureus may multiply and produce toxins on the surface of fish blocks, and the antibacterial ingredients of perilla essential oil can prevent its growth, thereby extending the shelf life of fish blocks; ingredients such as limonene are natural antioxidants. The fat and protein in fish blocks are easily oxidized during storage, producing unpleasant odors and harmful substances. The antioxidant components in perilla essential oil can remove free radicals, slow down the oxidation of fat, and maintain the flavor and nutritional quality of fish blocks.

[0011] About the Dendrobium Officinale essential oil in this essential oil blend: Dendrobium officinale essential oil contains a variety of bioactive ingredients, such as eucalyptol and trans-2-decenal, which have inhibitory effects on microorganisms. They can destroy the cell membrane structure of microorganisms or interfere with the metabolic process of microorganisms, thereby inhibiting the growth and reproduction of microorganisms on the surface of prefabricated fish blocks, reducing the consumption and deterioration rate of internal substances in the fish blocks. Because fish blocks are biological materials, their own physiological activities during storage will also affect their preservation effects. This regulation can extend the shelf life.

[0012] About the Saffron Essential Oil in this Recipe’s Essential Oil Blend: Saffron essential oil contains ingredients such as saffron aldehyde and linoleic acid, which have good antioxidant and bactericidal properties. It can work synergistically with perilla essential oil to enhance the ability to scavenge free radicals, better inhibit the reproduction of microorganisms, and protect the fat and protein in fish chunks from oxidation.

[0013] In some embodiments, the dried and cut herring fillets are uniformly sprayed with the essential oil mixture, and then dried for a second time until the water activity is ≤ 0.8, and then the dried herring fillets are uniformly sprayed with the essential oil mixture for a second time.

[0014] In addition, when the dried and cut herring pieces are uniformly sprayed with the essential oil mixture, the amount of the essential oil mixture is 0.4% to 0.5% of the dried herring pieces. When the dried herring pieces are uniformly sprayed with the essential oil mixture for a second time, the amount of the essential oil mixture is 0.1% to 0.2% of the dried herring pieces.

[0015] In addition, the essential oil of this scheme is prepared by a steam distillation extraction process or a carbon dioxide supercritical extraction process. Specifically, the perilla essential oil in the essential oil mixture is prepared by a steam distillation extraction process or a carbon dioxide supercritical extraction process from perilla leaves, wherein the perilla essential oil contains ≥40% perilla aldehyde, and the ratio of perilla aldehyde to limonene is 5-6; the Dendrobium officinale essential oil in the essential oil mixture is prepared by a steam distillation extraction process or a carbon dioxide supercritical extraction process from Dendrobium officinale flowers, wherein the Dendrobium officinale essential oil contains 7% to 10% eucalyptol and 4% to 5% trans-2-decenal; the saffron essential oil in the essential oil mixture is prepared by a steam distillation extraction process or a carbon dioxide supercritical extraction process from saffron petals, and the saffron essential oil contains 10% to 12% crocinaldehyde and 2% to 4% linoleic acid.

[0016] The scheme provides a method for extending the storage period of seasonal low-salt dried black carp prepared fish pieces at room temperature, comprising: (1) Killing: Kill the raw fish by cutting it open from the back to obtain the fish body with scales, mucus and blood; (2) marinating: ginger, pepper, bay leaf powder and edible salt are uniformly mixed in a certain proportion to form a composite marinade, and 5% to 10% of the weight of the fish body is used to marinate the fish body to obtain marinated fish; (3) Cleaning: cleaning the pickled fish to obtain cleaned fish; (4) Low-salt pickling: Soak the cleaned fish in desalted water twice its mass for 4 to 6 hours, stirring the desalted water from time to time during the process, and changing the desalted water 2 to 3 times during the whole process to obtain low-salt pickled fish; (5) Primary drying: The low-salt pickled fish is dried once by sun drying, mechanical hot air drying, or a combination of sun drying and mechanical hot air drying to obtain primary dried herring with a moisture content of 60% to 65%. The mechanical hot air drying temperature is 25°C to 42°C; (6) Arrangement and cutting: trim the exposed sharp parts of the dried black carp and cut them into pieces of 10 g to 50 g; (7) Essential oil gradient treatment: spray the fish block evenly with the essential oil mixture, mix well and seal for 40 min to 60 min to obtain pretreated fish block, wherein the amount of the essential oil mixture is 0.4% to 0.5% of the weight of the fish block, and the essential oil mixture includes 50% to 60% of perilla essential oil, 20% to 25% of dendrobium officinale essential oil and 20% to 25% of saffron essential oil in a mass ratio; (8) Secondary drying: The pretreated fish pieces are subjected to secondary drying using mechanical hot air at 40°C to 42°C to obtain secondary dried fish pieces with a moisture content of 40% to 45% and a water activity (Aw) ≤ 0.8; (9) Secondary essential oil treatment: spraying the surface of the secondary dried fish block with an essential oil mixture for a second time, mixing, and softening for 20 min to 30 min to obtain a low-salt prefabricated fish block, wherein the amount of the essential oil mixture is 0.1% to 0.2% of the mass of the secondary dried fish block, and the essential oil mixture comprises 50% to 60% of perilla essential oil, 20% to 25% of dendrobium officinale essential oil, and 20% to 25% of saffron essential oil in a mass ratio; (10) Packaging: mixing the low-salt pre-made fish chunks with the dried distiller's grains, bagging, and vacuum-sealing the bags to obtain seasonal low-salt pre-made fish chunks; (11) Storage: Store the packaged seasonal low-salt pre-prepared fish fillets at room temperature, and the storage temperature should be ≤25°C.

[0017] In (1) disembowelment, the raw fish is disemboweled by opening it from the back, making parallel cuts of 2 cm to 3 cm on both sides of the mid-bone, removing the gills and internal organs, and obtaining the fish body with scales, mucus and blood.

[0018] In (2) pickling, the components of the compound pickle are as follows by mass percentage: 5-8% ginger powder, 3-5% pepper powder, 2-5% bay leaf powder, and 82-90% edible salt, and the sum of the percentages of the components is 100.

[0019] In addition, during (2) pickling, the fish bodies on the upper layer should be turned over regularly every 1 to 2 days, and the fish bodies on the lower layer should be placed upside down and compacted. The pickling environment temperature should be controlled below 15°C and the pickling time should be 3 to 5 days.

[0020] In the pickling step, the compound pickling agent of the present invention helps to accurately control the flavor of the fish. Ginger powder, pepper powder and bay leaf powder give the fish a unique flavor during the pickling process, and edible salt plays a key role in dehydration and antibacterial during the pickling process.

[0021] In (3) cleaning, the pickled fish is cleaned with drinking water to remove the pickle and mucus remaining on the surface to obtain the cleaned fish.

[0022] In (4) low-salt pickling, the salt content of desalted water is 1%.

[0023] In (5) one-time drying, the low-salt salted fish is dried by sun drying, mechanical hot air drying, or a combination of sun drying and mechanical hot air drying. Compared with a single drying method, this variety of options can be flexibly operated according to actual conditions. For example, when the weather is good, sun drying can save energy and give the dried fish a unique flavor; when the weather is bad or fast drying is required, mechanical hot air drying can play a role to ensure the continuity of production. The combined use can combine the advantages of the two, first sun drying to a certain degree and then using mechanical hot air drying, so that the dried fish is dried more evenly.

[0024] In this scheme, the moisture content is controlled at 60%~65% after the first drying, and at 40%~45% after the second drying, and the water activity (Aw) is ≤0.8. This precise moisture control is critical to extending the storage period of prefabricated fish blocks. Appropriate moisture content can prevent excessive growth and reproduction of microorganisms, because most microorganisms require certain moisture conditions for growth. By reducing the water activity, the physiological activities of microorganisms are inhibited, thereby achieving the purpose of extending the shelf life. The mechanical hot air drying temperature is 25℃~42℃ during the first drying and 40℃~42℃ during the second drying. The appropriate temperature can ensure that the moisture in the fish blocks is effectively evaporated, and the nutritional components and flavor of the fish blocks will not be destroyed due to excessive temperature. For example, high temperature may cause excessive protein denaturation, fat oxidation and other problems, while the appropriate temperature can retain the quality of the fish blocks to the greatest extent while drying.

[0025] In (6) sorting and cutting, the sharp parts exposed on the body of the dried herring include exposed fish bones, fish fins, fish tails, etc. In the sorting and cutting step, the sharp parts such as fish bones, fish fins, fish tails, etc. exposed on the body of the dried herring are trimmed off first. This not only improves the safety of the fish pieces, prevents consumers from being stabbed during consumption and prevents the packaging bag from being punctured, but also improves the appearance of the fish pieces. The dried fish is then cut into 10g ~ 50g fish pieces. This standardized cutting is convenient for consumers to eat and cook, and fish pieces of appropriate weight can be selected for different eating scenarios.

[0026] In (7) essential oil gradient treatment and (9) secondary essential oil treatment, the amount of essential oil mixture is strictly controlled to avoid excessive dosage from covering up the original pickled flavor of the dried herring.

[0027] In the packaging step (10), the low-salt prefabricated fish pieces are mixed with dried distiller's grains and then bagged. The amount of dried distiller's grains used is 5% to 10% of the mass of the seasonal low-salt prefabricated fish pieces. The dried distiller's grains are prepared by drying the distiller's grains of glutinous rice wine, and the water content is ≤10%. Since the dried distiller's grains contain some alcohol, they can play a certain bactericidal role.

[0028] In (11) storage, packaged seasonal low-salt pre-prepared fish fillets are often sold in winter or around the Spring Festival, and under storage conditions of 25°C, the storage period of seasonal low-salt pre-prepared fish fillets is extended from 28 days to 63 days.

[0029] Compared with the prior art, this technical solution has the following characteristics and beneficial effects: In response to the technical problem that seasonal low-salt herring prepared fish chunks are prone to spoilage at room temperature, the inventors carried out a series of emergency technical research activities and successfully developed a method for extending the room-temperature storage period of seasonal low-salt herring prepared fish chunks. The fish chunks were preserved using a specially configured essential oil mixture. Under storage conditions of 25°C, this method can extend the storage period of low-salt herring prepared fish chunks from 28 days to 63 days, maintaining the traditional salted and cured flavor of traditional dried herring, and meeting the seasonal demand for storing and selling flavored low-salt herring prepared fish chunks for 2 months at room temperature during the winter and Spring Festival. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 3 is a diagram showing changes in sensory scores of a control group and an essential oil group during storage at 25°C according to the present invention.

[0031] Figure 2 3 is a graph showing the changes in hardness of the control group and the essential oil group during storage at 25°C according to the present invention.

[0032] Figure 3 3 is a graph showing the change in water activity of a control group and an essential oil group during storage at 25° C. according to the present invention.

[0033] Figure 4 It is a graph showing the change in total colony count during storage at 25° C. for a control group and an essential oil group according to the present invention.

[0034] Figure 5 3 is a graph showing changes in coliform bacteria in a control group and an essential oil group during storage at 25°C according to the present invention.

[0035] Figure 6 3 is a graph showing changes in peroxide values ​​of a control group and an essential oil group during storage at 25°C according to the present invention.

[0036] Figure 7 2 is a graph showing the changes in acid value of a control group and an essential oil group during storage at 25° C. according to the present invention. DETAILED DESCRIPTION

[0037] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0038] Example 1 The minimum inhibitory concentration (MIC) of different essential oils on three representative microorganisms was analyzed. Different essential oils were used to treat Staphylococcus aureus, Escherichia coli and Aspergillus niger. The results of the minimum inhibitory concentration of different essential oils on these three representative microorganisms are shown in Table 1 Table 1 Results of minimum inhibitory concentration (MIC) of different essential oils against three representative microorganisms .

[0039] The lower the minimum inhibitory solubility, the better the minimum inhibitory effect at the same concentration. The results in Table 1 show that the inhibitory effect of perilla essential oil on Gram-positive bacteria Staphylococcus aureus and fungus Aspergillus niger is better than that on Escherichia coli; the inhibitory effect of Dendrobium officinale flower essential oil on Gram-negative bacteria Escherichia coli and fungus Aspergillus niger is better than that on Staphylococcus aureus, and the inhibitory effect of saffron essential oil on Escherichia coli and Aspergillus niger is better than that on Staphylococcus aureus. The three essential oils have advantages and disadvantages in their inhibitory effects on the three representative microorganisms. The composite essential oil scheme of perilla essential oil (50%) + Dendrobium officinale flower essential oil (25%) + saffron essential oil (25%) provided by the present invention has a good inhibitory effect on the three representative bacteria, and can play a synergistic effect after composite.

[0040] Example 2: Essential oil group (1) Killing: Kill the raw fish by cutting it open from the back, making parallel cuts 2 cm to 3 cm on both sides of the mid-bone, removing the gills and internal organs, and obtaining the fish body with scales, mucus and blood.

[0041] (2) Pickling: ginger, pepper, bay leaf powder and edible salt are uniformly mixed in a certain proportion to form a compound marinade, and the mixture is marinated according to step (1) with 8% of the fish weight as the marinade. Fish of different sizes are marinated separately. The fish are turned over regularly every 1 day, and the fish on the upper layer are inverted and placed on the lower layer and compacted. The pickling environment temperature is controlled below 15°C. The fish are pickled for 4 days to obtain pickled fish.

[0042] The components of the compound marinade are as follows by mass percentage: 6% ginger powder, 4% pepper powder, 3% bay leaf powder, and 87% edible salt.

[0043] (3) Cleaning: The fish pickled in step (2) is cleaned with drinking water to remove impurities such as the marinade and mucus remaining on the surface, thereby obtaining cleaned fish.

[0044] (4) The fish cleaned in step (3) is rinsed and desalted with desalted water having a 1% salt content. The fish cleaned in step (3) is placed in desalted water with a mass twice that of the water and soaked for 5 h. During the desalting process, the desalted water is stirred at irregular intervals. The desalted water is replaced twice during the whole process to obtain low-salt pickled fish.

[0045] (5) Primary drying: the low-salt pickled fish in step (3) is dried once by natural air drying in the sun, mechanical hot air drying, or a combination of natural air drying in the sun and mechanical hot air drying, and the primary dried herring is obtained after drying, and the moisture content is controlled at 60% to 65%. The mechanical hot air drying temperature is 40° C. to 42° C.

[0046] (6) Arrange and cut the dried black carp prepared in step (5) and cut the exposed fish bones, fins, tail and other sharp parts into pieces of 10 to 15 g.

[0047] (7) Essential oil gradient treatment: spray the fish blocks prepared in step (6) with the essential oil mixture evenly, mix well, and seal for 50 minutes to obtain pre-treated fish blocks. The amount of the essential oil mixture is 0.4% of the weight of the fish blocks. The amount should not be too high, otherwise it will cover up the original pickled flavor of the dried black carp, resulting in an unharmonious flavor. The essential oil mixture contains 50% of perilla essential oil, 25% of dendrobium officinale essential oil, and 25% of saffron essential oil.

[0048] (8) Secondary drying: the fish blocks pretreated in step (7) are subjected to secondary drying using mechanical hot air at 40° C. to 42° C., and the secondary dried fish blocks are obtained after drying, and the moisture content is controlled at about 42%, and the water activity (Aw) is ≤0.8.

[0049] (9) secondary essential oil treatment, the fish pieces secondary dried in step (8) are sprayed with the essential oil mixture for the second time, mixed, and softened for 25 minutes to obtain low-salt prefabricated fish pieces, the amount of the essential oil mixture is 0.15% of the mass of the secondary dried fish pieces, and the amount should not be too high, otherwise it will cover up the original pickled flavor of the dried black carp, resulting in an unharmonious flavor. The essential oil mixture contains 50% of perilla essential oil, 25% of dendrobium officinale essential oil, and 25% of saffron essential oil.

[0050] (10) Packaging: mixing the low-salt prefabricated fish blocks prepared in step (9) with dried distiller's grains, bagging, and vacuum sealing the bags to obtain seasonal low-salt prefabricated fish blocks (essential oil group). The amount of dried distiller's grains used is 6% of the mass of the seasonal low-salt prefabricated fish blocks. The dried distiller's grains are prepared by drying glutinous rice wine distiller's grains, and have a water content of ≤10%.

[0051] (11) Storage: The seasonal low-salt pre-prepared fish pieces (essential oil group) packaged in step (10) are stored at 25°C.

[0052] Example 3: Control group: (1) Killing: Kill the raw fish by cutting it open from the back, making parallel cuts 2 cm to 3 cm on both sides of the mid-bone, removing the gills and internal organs, and obtaining the fish body with scales, mucus and blood.

[0053] (2) Pickling: ginger, pepper, bay leaf powder and edible salt are uniformly mixed in a certain proportion to form a compound marinade, and the mixture is marinated according to step (1) with 8% of the fish weight as the marinade. Fish of different sizes are marinated separately. The fish are turned over regularly every 1 day, and the fish on the upper layer are inverted and placed on the lower layer and compacted. The pickling environment temperature is controlled below 15°C. The fish are pickled for 4 days to obtain pickled fish.

[0054] The components of the compound marinade are as follows by mass percentage: 6% ginger powder, 4% pepper powder, 3% bay leaf powder, and 87% edible salt.

[0055] (3) Cleaning: The fish pickled in step (2) is cleaned with drinking water to remove impurities such as the marinade and mucus remaining on the surface, thereby obtaining cleaned fish.

[0056] (4) The fish cleaned in step (3) is rinsed and desalted with desalted water having a 1% salt content. The fish cleaned in step (3) is placed in desalted water with a mass twice that of the water and soaked for 5 h. During the desalting process, the desalted water is stirred at irregular intervals. The desalted water is replaced twice during the whole process to obtain low-salt pickled fish.

[0057] (5) Drying: the low-salt pickled fish in step (3) is dried by natural air drying in the sun, mechanical hot air drying, or a combination of natural air drying in the sun and mechanical hot air drying to obtain low-salt dried black fish, wherein the moisture content is controlled at about 42%, and the mechanical hot air drying temperature is 40° C. to 42° C.

[0058] (6) Arrange and cut: trim the exposed fish bones, fins, tail and other sharp parts of the low-salt dried black carp in step (5), and cut it into fish pieces of 10 g to 15 g to obtain low-salt prefabricated fish pieces.

[0059] (7) Packaging: The low-salt pre-made fish fillets prepared in step (5) are bagged and vacuum-sealed to prepare seasonal low-salt pre-made fish fillets (control group).

[0060] (8) Storage: the seasonal low-salt pre-made fish pieces (control group) packaged in step (7) were stored at 25°C.

[0061] Test Example 1: After the prefabricated fish pieces in the essential oil group and the control group were vacuum-packed, the key characteristic indicators were compared and analyzed within 4 hours.

[0062] (1) Sensory evaluation The sensory evaluation was completed in the food sensory evaluation room. The evaluation team selected 10 members with rich experience in food industry, 5 men and 5 women. The team members were in good health and had strong discrimination of color, aroma and taste. The evaluators completed the evaluation independently and rinsed their mouths with water before evaluating each sample. The sensory evaluators discussed and evaluated and scored the sensory quality of the samples from three aspects: shape, color and smell of the black carp processed fish block products. The sensory evaluation scoring standards are shown in Table 2: Table 2 Sensory evaluation scoring criteria for low-salt dried black carp prefabricated fish pieces .

[0063] After evaluation by 10 professional sensory personnel, the sensory score of the essential oil group was 95.4±2.1 points, and the sensory score of the control group was 96.2±2.5 points. The evaluation results showed that there was no significant difference in the sensory scores between the essential oil group and the control group ( p＞ 0.05), the appearance and color of the essential oil group and the control group were basically the same; the control group had a strong traditional pickled and cured flavor, and the essential oil group also had a strong traditional pickled and cured flavor, with a slight aroma of essential oil, and a harmonious smell without odor.

[0064] (2) Analysis of microbial indicators. The results are shown in Table 3.

[0065] Table 3 Comparison of microbial indicators of pre-prepared fish nuggets between the essential oil group and the control group

[0066] Note: Different lowercase letters in the table indicate significant differences between the two groups ( p <0.05) As shown in Table 3, the total number of colonies and coliform bacteria in the essential oil group were significantly lower than those in the control group ( p<0.05), indicating that essential oil treatment can effectively reduce the background microorganisms of low-salt prefabricated fish blocks and help to prolong the storage period at room temperature.

[0067] (3) Analysis of key physical and chemical indicators. The results are shown in Table 4.

[0068] Table 4 Comparison of key characteristic indicators of pre-made fish pieces between essential oil group and control group

[0069] Note: Different lowercase letters in the table indicate significant differences between the two groups ( p <0.05) As shown in Table 4, the texture hardness of the oil in the refined group was significantly higher than that in the control group ( p <0.05), the fish pieces are less likely to fall apart during storage. The water activity of the essential oil group was 0.746, and that of the control group was 0.849, indicating that the essential oil treatment effectively reduced the water activity of the prefabricated fish pieces, which is beneficial to the preservation of freshness during storage. During the analysis, the prefabricated fish pieces in the essential oil group and the control group were all freshly processed, and the degree of fat oxidation and rancidity was basically the same, and there was no significant difference in acid value and peroxide value ( p＞ 0.05). There was no significant difference in salt content and water content between the refined oil group and the control group ( p＞ 0.05).

[0070] Test Example 2: The prefabricated fish blocks in the essential oil group and the control group were stored at 25°C, and the changing patterns of key characteristic indicators of the prefabricated fish blocks and their storage process as well as the advantages of the technology were compared and analyzed.

[0071] (1) Sensory evaluation of fish chunks and analysis of hardness changes Sensory evaluation scores Figure 1 ,Depend on Figure 1 It can be seen that: 1) The sensory scores of the pre-made fish pieces in the essential oil group and the control group reached the excellent quality standard, and there was no significant difference ( p＞ 0.05).

[0072] 2) After storage at 25°C for 14 days, the sensory score of the control group product was 82 points, which was reduced to the qualified quality standard; after 28 days, the sensory score was 76 points, which further dropped to the qualified quality standard line; at 35 days, bulging and juice oozing appeared, with obvious mucus on the surface and obvious corruption odor. It had lost its commercial quality and was completely corrupt and deteriorated, with a sensory score of 0. According to the sensory score, the shelf life of the control group when stored at 25°C is 28 days.

[0073] 3) The sensory score of the essential oil group product was 86 points when stored at 25℃ for 35 days, which was an excellent sensory quality standard. It was then downgraded to a qualified quality standard. The sensory score was 76 points at 63 days, which had dropped to the qualified quality standard line. At 70 days, bulging, juice oozing, obvious mucus on the surface, and obvious corruption odor appeared, and it had lost its commercial quality, with a sensory score of 15 points. According to the sensory score, the shelf life of the low-salt prefabricated fish fillets in the essential oil group at 25℃ was 63 days, which was 1 times longer than that of the control group, showing significant technical progress and advantages.

[0074] The hardness was evaluated on the 28th day for the control group and on the 63rd day for the essential oil group using a CT3 texture analyzer. Figure 2 ,Depend on Figure 2 It can be seen that the texture hardness of the oil in the refined group is significantly higher than that in the control group ( p <0.05), the fish pieces are less likely to fall apart during storage and the meat is firm.

[0075] (2) Analysis of water activity changes The results of the analysis of the changes in water activity of the pre-prepared fish pieces in the essential oil group and the control group during storage at 25°C are shown in Figure 3 ,Depend on Figure 3 The results show that: 1) Changes in water activity in the control group: The water activity of the prefabricated fish pieces just after processing was 0.849. The water activity continued to rise during storage and rose to 0.921 on the 28th day, which was not conducive to inhibiting the growth of microorganisms.

[0076] 2) Changes in water activity in the essential oil group: The water activity of the prefabricated fish pieces was 0.746 just after processing, and it only rose to 0.769 on the 28th day, which was significantly lower than that of the control group; it was 0.915 on the 63rd day, which was still lower than that of the control group on the 28th day.

[0077] 3) Conclusion: This indicates that essential oil treatment can effectively reduce the water activity of prefabricated fish fillets, which is beneficial to inhibiting microbial reproduction and preserving freshness during storage.

[0078] (3) Analysis of microbial changes The results of the analysis of the changes in the total number of colonies and coliform microbial indicators of the pre-prepared fish pieces in the essential oil group and the control group during storage at 25°C are shown in Figure 4 and Figure 5 The results in Table 3 have shown that essential oil treatment can effectively reduce the total colony count and background content of coliform bacteria and other microorganisms in low-salt prefabricated fish blocks, which is beneficial to reduce the content of microorganisms during storage. Figure 4 and Figure 5 The results show that: 1) Changes in the total number of colonies in the control group: After 28 days of storage, the total number of colonies increased from 1.32×10 6 CFU / g increased to 1.78×10 10CFU / g, increased by 1.35×10 4 times; coliform bacteria increased from 1.38×10 3 CFU / g increased to 1.82×10 7 CFU / g, increased by 1.32×10 4 times.

[0079] 2) Microbial changes in the essential oil group: ① After 28 days of storage, the total number of colonies increased from 1.07×10 4 CFU / g increased to 2.82×10 6 CFU / g increased by 264 times; the coliform bacteria increased from 1.02×10 2 CFU / g increased to 1.62×10 4 CFU / g, an increase of 159 times. ② After 63 days of storage, the total number of colonies increased to 5.25×10 9 CFU / g, an increase of 4.91×10 5 times; the coliform group increased to 1.91×10 5 CFU / g, increased by 1.87×10 3 times.

[0080] 3) Conclusion: Essential oil treatment can significantly reduce the total number of colonies and the number of coliform bacteria in the storage process of prefabricated fish blocks, effectively inhibit the reproduction of microorganisms, and show significant antibacterial technical advantages. On the 28th day of storage, the increase in the total number of colonies in the essential oil group was only 0.019 times that of the control group, and the increase in the number of coliform bacteria was only 0.012 times that of the control group. (4) Analysis of changes in peroxide value and acid value Changes of peroxide value and acid value of pre-prepared fish pieces in the essential oil group and the control group during storage at 25°C Figure 6 and Figure 7 As shown by Figure 6 and Figure 7 The results show that: 1) The pre-cooked fish pieces in the refined oil group and the control group were freshly processed, and the degree of fat oxidation and rancidity was basically the same, and there was no significant difference in acid value and peroxide value ( p＞ 0.05).

[0081] 2) During storage at 25℃, the peroxide value of the pre-prepared fish chunks in the control group increased from 1.65 mmol / kg on the 0th day to 28.13 mmol / kg on the 28th day, and the peroxide value of the essential oil group increased from 1.66 mmol / kg on the 0th day to 12.16 mmol / kg on the 28th day. The peroxide value of the control group was 131.33% higher than that of the essential oil group.

[0082] 3) The acid value of the pre-prepared fish fillets in the control group increased from 0.38 mg / g on the 0th day to 0.74 mg / g on the 28th day, and the essential oil increased to 0.61 mg / g. The acid value of the control group was 21.31% higher than that of the essential oil group. The peroxide value of the essential oil group on the 63rd day was 26.13 mmol / kg, which was slightly lower than that of the control group on the 28th day. The acid value of the essential oil group on the 63rd day was 0.76 mg / g, which was basically the same as that of the control group on the 28th day.

[0083] 4) From the above data analysis, it can be seen that the technical solution provided by the present invention can significantly delay the oxidative rancidity of low-salt prefabricated fish blocks during storage, and has significant technical advantages.

[0084] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for prolonging the storage period of low-salt black carp processed fish pieces at room temperature, characterized in that: The following steps are involved: The dried black carp fillets are preserved by using an essential oil mixture, wherein the amount of the essential oil mixture is 0.4% to 0.5% of the weight of the fish fillets, and the essential oil mixture includes 50% to 60% of perilla essential oil, 20% to 25% of dendrobium officinale essential oil and 20% to 25% of saffron essential oil in a mass ratio.

2. The method for prolonging the storage period of the aged low-salt black carp processed fish pieces at room temperature according to claim 1, characterized in that: Essential oils are prepared by steam distillation extraction or supercritical carbon dioxide extraction.

3. The method for prolonging the storage period of the aged low-salt black carp processed fish pieces at room temperature according to claim 1, characterized in that: Perilla essential oil contains ≥40% perillaldehyde, and the ratio of perillaldehyde to limonene is 5~6; Dendrobium officinale essential oil contains 7%~10% eucalyptol and 4%~5% trans-2-decenal; Saffron essential oil contains 10%~12% saffronaldehyde and 2%~4% linoleic acid.

4. The method for prolonging the storage period of the aged low-salt black carp prepared fish pieces at room temperature according to claim 1, characterized in that: Spray the essential oil mixture evenly on the surface of the cut herring fillets for preservation.

5. The method for prolonging the storage period of low-salt black carp processed fish pieces at room temperature according to claim 1, characterized in that: The dried and cut herring cut pieces are uniformly sprayed with the essential oil mixture, and then dried for a second time until the water activity is ≤0.8, and then the dried herring cut pieces are uniformly sprayed with the essential oil mixture for a second time.

6. The method for prolonging the storage period of the aged low-salt black carp processed fish pieces at room temperature according to claim 5, characterized in that: When the dried and cut herring fillets are uniformly sprayed with the essential oil mixture, the amount of the essential oil mixture is 0.4% to 0.5% of the dried herring fillets.

7. The method for prolonging the storage period of low-salt black carp processed fish pieces at room temperature according to claim 5, characterized in that: When the essential oil mixture is evenly sprayed on the herring prepared fish pieces for the second time, the amount of the essential oil mixture is 0.1% to 0.2% of the herring prepared fish pieces.

8. A method for prolonging the storage period of low-salt black carp processed fish pieces at room temperature, characterized in that: Includes steps: (1) Killing: Kill the raw fish by cutting it open from the back to obtain the fish body with scales, mucus and blood; (2) marinating: ginger, pepper, bay leaf powder and edible salt are uniformly mixed in a certain proportion to form a composite marinade, and 5% to 10% of the weight of the fish body is used to marinate the fish body to obtain marinated fish; (3) Cleaning: cleaning the pickled fish to obtain cleaned fish; (4) Low-salt pickling: Soak the cleaned fish in desalted water twice its mass for 4 to 6 hours, stirring the desalted water from time to time during the process, and changing the desalted water 2 to 3 times during the whole process to obtain low-salt pickled fish; (5) Primary drying: drying the low-salt pickled fish by natural air drying in the sun, mechanical hot air drying, or a combination of natural air drying in the sun and mechanical hot air drying to obtain primary dried herring, with the moisture content controlled at 60% to 65%, and the mechanical hot air drying temperature at 25°C to 42°C; (6) Arrangement and cutting: trim the exposed sharp parts of the dried black carp and cut it into fish pieces; (7) Essential oil gradient treatment: spray the fish block evenly with the essential oil mixture, mix well and seal for 40 min to 60 min to obtain pretreated fish block, the amount of the essential oil mixture is 0.4% to 0.5% of the weight of the fish block, and the essential oil mixture includes 50% to 60% of perilla essential oil, 20% to 25% of dendrobium officinale essential oil and 20% to 25% of saffron essential oil in a mass ratio; (8) Secondary drying: The pretreated fish pieces are subjected to secondary drying using mechanical hot air at 40°C to 42°C to obtain secondary dried fish pieces with a moisture content of 40% to 45% and a water activity of ≤0.8; (9) Secondary essential oil treatment: spraying the surface of the secondary dried fish block with an essential oil mixture for a second time, mixing, and softening for 20 min to 30 min to obtain a low-salt prefabricated fish block, wherein the amount of the essential oil mixture is 0.1% to 0.2% of the mass of the secondary dried fish block, and the essential oil mixture comprises 50% to 60% of perilla essential oil, 20% to 25% of dendrobium officinale essential oil, and 20% to 25% of saffron essential oil in a mass ratio; (10) Packaging: mixing the low-salt pre-made fish chunks with the dried distiller's grains, bagging, and vacuum-sealing the bags to obtain seasonal low-salt pre-made fish chunks; (11) Storage: Store the packaged seasonal low-salt pre-prepared fish fillets at room temperature, and the storage temperature should be ≤25°C.

9. The method for prolonging the storage period of the aged low-salt black carp processed fish pieces at room temperature according to claim 8, characterized in that: In the pickling step (2), the components of the compound pickle are as follows by mass percentage: 5-8% ginger powder, 3-5% pepper powder, 2-5% bay leaf powder, and 82-90% edible salt, and the sum of the percentages of each component is 100.

10. The method for prolonging the storage period of the aged low-salt black carp prepared fish pieces at room temperature according to claim 8, characterized in that: The amount of dried distiller's grains used is 5% to 10% of the mass of seasonal low-salt prefabricated fish blocks. The dried distiller's grains are prepared by drying the distiller's grains of glutinous rice wine, and the water content is ≤10%.

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