The technology of the pork-meat made Law-Salted Sausages enriched by the additive of soy isolate and treated by high pressure

Abstract

The dissertation is devoted to the technology of reduced-salt pork batters using soy protein isolate and high pressure processing. In the introduction obtained that excessive salt intake could lead to hypertension, cardiovascular and cerebrovascular diseases and other chronic diseases, the salt reduction has become a global consensus for the control of chronic diseases. The World Health Assembly formally adopted “a relative 30% reduction in salt intake by 2025” as one of nine voluntary global targets for the prevention and control of Non-communicable diseases. At present, nearly half of the countries in the world have launched national salt reduction guidelines or actions, and developed their own industrial salt reduction guidelines. However, the traditional emulsion meat products contain higher salt, because salt soluble protein dissolution at a high salt concentration (> 0.3 mol/L) is a key step in the formation of the good gel structure. Directly decreases the concentration of salt, reduces the amount of salt soluble protein extraction and dissolution, degradation of heat-induced meat gel structure. It is necessary to find new technologies for reduced-salt emulsion meat products that can solve the problem of the emulsion meat products having a higher cooking loss, and worse gel properties when reduced salt content. The high pressure processing can effectively change the protein structures and techno-functional properties in the meat products, and retain the nutrition and flavour. The ability of high pressure processing to inactivate microorganisms and denature proteins has been known for over one hundred years. The changes in protein structures, conformations, and gel properties are closely related to the pressure levels, time and temperature, so the high pressure processing condition is an important research direction. The application of high pressure processing offers some interesting opportunities in the processing of muscle-based food products, such as the high pressure can affect the texture and gel-forming properties of meat batters and myofibrillar proteins, the tenderize, colour and other properties of muscle. The processing effects on muscle based products are highly dependent on the primary effects of pressure, time and temperature on the relevant thermodynamic and transport properties of meat systems. Especially, high pressure processing improves the properties of muscle, comminuted meat and myofibrillar proteins, and the use of moderate pressure treatment of pre-rigor meat seems to have potential since the meat will be tender and look normal colour. Reasonable high pressure processing enhances the water holding capacity and texture of comminuted meat, but the products lack the cooked appearance and potential for accelerated loss of flavour. Meanwhile, it improves the quality of reduced-salt meat products through affecting the non-covalent bond, covalent bond and protein conformation of myofibrillar proteins, the water holding capacity and texture of myofibrillar proteins will be increased produce by the moderate pressure treatment. The protein content of soy protein isolate is more than 90%, it is a high-quality plant protein food raw material. Its functional properties can be divided into three categories: interface properties, hydration properties, and properties related to protein-protein interactions, including precipitation, aggregation, and gel properties. On this basis, hundreds of countries in the world have developed thousands of food products containing soy protein in recent years. The globulin of soy protein has a closely globular structure, the molecular weight is small, and active group packages within the molecule, and some methods of modification are difficult to effectively change the structure and improve its functional characteristics. The changes in techno-functional properties of soy protein by high pressure processing, such as emulsion properties, water holding capacity, and gel properties are increased or decreased with the changes in the pressure levels, time and temperature. Soy protein and its modified products are widely used in meat products, protein drinks, dairy products, baked products and other foods due to their prominent functional properties. They play an important role in supplementing protein, supplementing the nutrition of multiple types of protein, reducing the intake of animal protein, and giving food health care functions. Especially, the proper pressure treatment of soy protein increases the water holding capacity, improves gel and emulsion properties by affecting the non-covalent bond, covalent bond and protein conformation, and also reduces the allergenicity of soy proteins in infant formula. Thus, the application of high pressure processing and soy protein isolate to modify the properties of meat products, increases the water- and fat- holding capacity and qualities of reduced-salt pork batters, and it also meets the basic principle of food processing. Therein, the relevance and feasibility of using high pressure processing and soy protein isolate combinations for producing reduced-salt pork batters to improve the water- and fat- holding capacity, and qualities have been proved. The result provides a theoretical basis for our experimental design. Purpose of the research is scientific substantiation and development of the production and processing of reduced-salt pork batter products using the technology of high pressure processing and soy protein isolate combination, and to explore the mechanism of reduced-salt pork batter products by high pressure processing and soy protein isolate combination. Subject of research contain chilled pork longissimus lumborum, pork myofibrillar protein, reduced-salt pork batter, soy protein isolate, high pressure processing, high pressure and soy protein isolate combination, pasteurized reduced-salt pork batter produced using high pressure and soy protein isolate combination and stored at cold temperature. Object of research is the production of reduced-salt pork batter using the technology of high pressure processing and soy protein isolate combination, which has better water holding capacity, gel properties, sensory quality and longer shelf-life, obtains a novel method to produce high quality reduced-salt pork batter, such as reduced-salt sausages and meatball. In the second section, the methodological approaches adopted in the dissertation work include theoretical research, raw materials and ingredients, experiment methods, practical testing, technology promotion, and subordinate various methods of research for the only goal decision set in the dissertation work scientific problem. In the third section, the chilled pork meat and soy protein isolate were used as raw materials, three batters with 0%, 2%, and 4% soy protein isolate were prepared under 200 MPa for 10 min, respectively. The changes of colour, cooking yield, emulsion stability, rheological property and protein secondary structure attributes of pork meat batters (1% sodium chloride) treated by high pressure processing with different soy protein isolate were analysed, the effect of high pressure processing and soy protein isolate combinations on the water holding capacity, techno-functional properties and protein conformation of reduced-salt pork meat batters were investigated. The result showed that the effect of high pressure processing and soy protein isolate combinations on the gel properties, rheological property and protein conformation of pork batters were significant differences. The pH, L* and b* values, cooking yield and hardness, cohesiveness and chewiness, and G' values at 80 °C were significantly increased (P < 0.05) when soy protein isolate was added, but the a* value, TR, WR and FR were significantly decreased (P < 0.05). Meanwhile, the TR, WR and FR, G' values at 80 °C were significantly decreased (P < 0.05) with the increase in soy protein isolate. Thus, the 2% soy protein isolate addition could improve the water holding capacity and texture of pork batters treated under 200 MPa. The result of low-field NMR showed that the cooked pork batters made with soy protein isolate were bound tightly, because of the changes of fast relaxing protein and slowly relaxing water protons. The initial relaxation times of T2b, T21 and T22 were quicker (P < 0.05) in the cooked pork batters with soy protein isolate than that of the sample without soy protein isolate, and the cooked pork batters had the smallest peak ratios of T22, and the largest peak ratio of T21. The result caused the water tightly associated with protein and macromolecular constituents to decrease, the mobility of water was reduced, and increased the water holding capacity and bounded water content. Added soy protein isolate and treated by high pressure processing delayed the thermal denaturation of meat proteins and declined the pre-gel effects generated by the denaturation of myosin tails from 53 °C to 59 °C. The α-helix structure changed into β-sheet, β-turn and random coil structures when soy protein isolate was added, and the random coil structure content was significantly increased (P < 0.05) with the increase in soy protein isolate. Especially, the content of random coil structure was significantly increased (P < 0.05) from 11.42 ±0.26% to 14.22±0.29% with the increase in soy protein isolate. Overall, the 2% soy protein isolate addition could improve the techno-functional properties and emulsion stability of reduced-salt pork meat batters treated with high pressure processing. The fourth section presents the results of our own research on the effects of soy protein isolate on gel properties and water holding capacity of reduced-salt (1% sodium chloride) pork myofibrillar protein under high pressure processing. The pork myofibrillar protein and soy protein isolate were used as raw materials, and three reduced-salt pork myofibrillar protein systems with 0%, 2%, 4% soy protein isolate were prepared under 200 MPa for 10 min, respectively. The texture, rheological property, sulfhydryl groups, and the water distribution state of reduced-salt pork myofibrillar protein systems with different soy protein isolate (0, 2% and 4%) under high pressure processing (200 MPa, 10 min) were measured. The result showed that the L* value, cooking yield, hardness, total and reactive sulfhydryl, surface hydrophobicity, and the G' value at 80 °C of pork myofibrillar protein were significantly increased (P < 0.05) when soy protein isolate was added; however, the springiness, cohesiveness, and chewiness of gels with 4% soy protein isolate were lower than of gels with 2% soy protein isolate. Three reduced-salt pork myofibrillar protein systems exhibited a typical G' curve of pork myofibrillar protein after high pressure processing with three phases evident from 20 °C to 80 °C. At 80 °C, the G′ values of the treatments were 2380 Pa, 2791 Pa, and 3113 Pa, respectively. The rheological findings indicated that the thermal stability of the myofibrillar protein was increased when soy protein isolate was added. The initial relaxation times of T2b, T21, and T22 were shortened (P < 0.05) when soy protein isolate was added, but they were decreased with the increase in soy protein isolate; meanwhile, the peak ratios of P2b and P22 were significantly decreased (P < 0.05) when soy protein isolate was added, whereas the peak ratio of P21 was significantly increased (P < 0.05), implying that the bound and free water was declined, and the immobilized water was increased. Overall, the 2% soy protein isolate could enhance the gel characteristics and water-holding capacity of pork myofibrillar protein under 200 MPa. In the fifth section, the pork meat and soy protein isolate were used as raw materials, five reduced-salt (1% sodium chloride) pork batters with 2% soy protein isolate were prepared under 0.1-400 MPa for 10 min at 10±2 °C, respectively. The effects of different pressures on the techno-functional properties, water distribution and mobility of reduced-salt pork batters supplemented with soy protein isolate were examined, and the pH, gel properties, rheology, water distribution and mobility of reduced-salt pork batters were measured. The result showed that compared with the sample of 0.1 MPa, the pH, cooking yield, texture properties and G′ values at 80 °C were significantly increased (P < 0.05) in the batters treated by different pressures from 100 MPa to 400 MPa, a corresponding of the initial relaxation times of T2b, T21 and T22 were faster (P < 0.05), implying that the water in the cooked batters treated by different pressures were tied closer. Meanwhile, all the curves of the changes on G′ were similar, and they had a typical curve of dynamic rheology with three phases caused by the meat proteins denaturation during heating. Therein, the samples treated by 200 MPa and 300 MPa had the highest L* value, cooking yield, texture properties and G′ values at 80 °C, while the initial relaxation times of T2b, T21 and T22 were shortest (P < 0.05), and the peak ratio of P21 was the largest and the P22 was the smallest. To the contrary, the samples of 0.1 MPa and 100 MPa had the smallest peak ratio of P21 and the largest peak ratio of P22. Thus, excessive pressures led to the gel structure being worse and more water moving, causing the free water to increase and the immobilized water to decrease. Overall, treatment by 200 MPa and 300 MPa could improve the gel properties of reduced-salt batters with soy protein isolate, lower the water mobility and increase the immobilized water. In the sixth section, the pork meat and soy protein isolate were used as raw materials, and two pasteurized reduced-salt (1% sodium chloride) pork batters with soy protein isolate (0 and 2%) were prepared under 200 MPa for 10 min at 10±2 °C according to the operation key points of “Production process and operation key points of produce reduced-salt pork batter using the technology of high pressure and soy protein isolate combination”, respectively. The effects of soy protein isolate and high pressure processing combined on gel qualities of pasteurized reduced-salt pork batter stored at cold temperature were studied, through analysing the changes in storage loss, total, TBARS, pH, colour and texture characteristics of pasteurized reduced-salt pork batters with different soy protein isolate treated under 200 MPa during the cold storage (0-60 days). The results showed that storage loss, TBARS, pH, L* value, and hardness of pork batters were increased significantly (P < 0.05) with the increase in the cold storage time, except the samples with 2% soy protein isolate were stored at the 1st and 30th days. Meanwhile, the total plate count of samples were not detected before the 30th day, while significantly increased at the 60th day. The range of storage loss, microbial, TBARS, pH, colour and texture properties variations from the samples without soy protein isolate were larger than that of 2% soy protein isolate. Overall, adding 2% soy protein isolate could improve the gel properties, water- and fat- holding capacity, and reduce the microbial reproduction of pasteurized reduced-salt pork batter during cold storage. Especially, applying the technology of soy protein isolate and high pressure processing combined to produce the pasteurized reduced-salt pork batter, its cooking yield, texture properties and gel structure were increased significantly (P < 0.05), and successfully reduced the salt content to 1%. According to the above research, “The technological scheme of production in pasteurized reduced-salt pork batter using the technology of soy protein isolate and HPP combined”, “The composition of the technological system and the purpose of its structural operation elements”, and “Technological scheme of pasteurized reduced-salt pork batter using the technology of soy protein isolate and HPP combined” were formulated. They provided a basis for the popularization and application of this technology in enterprises. The technology has carried out mass production in 3 factories in China to produce reduced-salt (1% sodium chloride) emulsion meat products, such as meatballs, Taiwan sausage and breakfast sausage. Apply the technology to produce the pasteurized reduced-salt pork batter, its cooking yield, texture properties and gel structure were significantly increased, and successfully reduced the salt content to 1%. Meanwhile, the technology has produced good socio-economic effectiveness. Such as, producing 1 ton of product can reduce electricity by about 20~30 kilowatt hours and 0.8~1.5 tons of running water compared with traditional processing; the salt content of this product is approximately 1%, which is about 40% lower than that of traditional products. According to our calculations, when consumers eat 100 g of this type product, which can reduce their salt intake by 0.8 g, and the content of protein is increased by 0.60%~0.85%; it takes 5%~8% less time to produce a ton of product, resulting in higher productivity, increased workshop and equipment utilization, and reduced workshop and equipment depreciation; the cooking yield of product was increased by 3.66%~5.53%. Finally, producing 1 ton of meatballs can save you $96.42~$118.66; producing 1 ton of Taiwan sausage can save you $80.37~$96.07; producing 1 ton of Taiwan sausage can save you $96.42~$103.12. From the above, we can know that the pork meat batters with soy protein isolate treated by high pressure processing should be adopted for lowering sodium content in the meat processing industry. The Appendix provides the Operation key points of “Production process and operation key points of produce reduced-salt pork batter using the technology of high pressure and soy protein isolate combination”, and the Application Testify of 3 factories in China (Henan Zhongpin Food Industry Co. LTD; Hua County Ji Xianda Food Co. LTD; Nanjing Huang Professor Science and Technology Food Co. LTD) to produce reduced-salt (1% sodium chloride) emulsion meat products, such as meatballs, Taiwan sausage and breakfast sausage.