Consumers always demand the best products regarding quality and nutrition. The trend of choosing products without preservatives, excessive heat treatments, and additives are also gaining popularity. To fulfill the desires of consumers new technologies are introduced in every food industry. Ultrasound is an emerging processing and analytical technique in food processing. It shows great results in the processing of different products regarding reduction in processing time, product purity, simplifying the complex procedure, and nonthermal processing. Most of the world is running out of energy sources and ultrasound will provide them the best alternative regarding processing assistance. Keeping these uses in view, this report comprises the use of possible ultrasound implementation in fish processing and analytical procedures to minimize the disadvantages of different conventional procedures. The working mechanisms of ultrasonication in different products, their advantages, and possible combinations are also discussed in this report. The challenges faced by the industry in applying ultrasound in the fish industry are also mentioned in this report.
Key Words: Ultrasound, Analytical techniques, Quality, Nutrition.
The use of technology always desires of human beings to facilitate in work. It is the same in food processing. Food safety, nutrient loss during processing, and more time consumption is the issue for these types of industries. The human ear can listen up to less than 20kHz, more than this point human ear cannot feel the sound waves. Ultrasounds have a frequency of 20kHz or more. Ultrasound provides a great opportunity to achieve goals regarding food safety, nutrition, and more fast processing (Boateng and Nasiru, 2019). Ultrasound is also very effective to use an analytical technique. Thermal processing usually destroys much of the nutrition in the food which is not acceptable for consumers. As we know this is an emerging technology that is why not much adaptation is being in use by industries. Ultrasound waves are very flexible to choose from regarding their velocity, attenuation, frequency spectrum when it passes through a medium. Their use in seafood processing for different processes depends on the wavelength according to the process and need (Arvanitoyyanis et al, 2015). Ultrasound is considered a more efficient and reliable method to use for cell disruption. These waves create shear force and break the cell wall. This phenomenon can be used to extract the oil from fish and other seafood (Ravishankar, 2019). Ultrasound waves are not only used as an alternative to the thermal process it also can be used in place of washing, this process is also very interesting as it also reduced the amount of wastewater because more than half of the wastewater comes from the product washing (Ultrafish, 2017). The use of ultrasound is also increasing in the field of checking the fat-lean portions of the fish prior to catch and death. Water holding capacity is a big concern of the meat and fish industry, in studies, it is shown that the meat treated with ultrasound has more WHC and for a longer period of processing (Boateng and Nasiru, 2019). All above mention facts show that ultrasound is non-toxic, reliable, and nutrition-safe treatment for foodstuff, but still is not practiced for fish and other seafood products. As we know that the future concern of everyone will be nutrition and sustainable food so the old and toxic methods of processing can create headaches for both industry and consumers. The main component in fish is its protein. During processing when we provide heat to the amine dense product it creates some time carcinogens which is a big concern of consumers. So, it is possible to apply ultrasound in fish and other seafood processing operations to overcome the problems associated with conventional processing methods.
Lower Power Ultrasound
Lower Power Ultrasound (LPU) in a combination with spectroscopy and nuclear magnetic resonance are mostly used process for food analysis. The variety of wavelengths in ultrasound allows checking the properties of food, and foreign bodies in food. The basic principle of LPU is that sound waves go through the food body and make compressions and decompressions. The combination of the waves and matter alters the velocity and attenuation of the sound waves by absorption and/or scattering mechanisms. Frequency and wavelength determine the velocity of sound, in this way high-frequency sound will be shorter in wavelength and low sound have long-wavelength (Awad et al, 2012).
High Power Ultrasound
High power ultrasound (HPU) provides mechanical, biochemical, and chemical effects, it changes the physicochemical properties and enhances the quality of many food systems in processing(Jayasooriya et al, 2004). Mechanical word shows that it has applications in the extraction of flavors & oils, degassing, destruction of foam in foods. Whereas in chemical and biochemical sterilization of process-related tools to remove biofilms from the surface of food processing equipment. In HPU temperature, pressure and intensity are very important to know alongside velocity and energy ( Awad et al, 2012).
Ultrasound Measurement Techniques
The major two techniques used for ultrasound measurement are pulse-echo and continuous wave ultrasound. Ultrasound is generated by transforming the electric current into ultrasound of controlled frequency. But some time pith and catch techniques were also applied to measure ultrasounds. In pulse-echo (Fig.1), a sample cell with a transducer and oscilloscope is used to measure ultrasound. There is a signal producer is used to make an electric pulse which converts into ultrasound pulses by the transducer, these pulses then pass through the sample and collide with the wall of the sample container, then come back to the transducer and again converts into electric signals and save on oscilloscope. Sample cell length (L) is the same as half the distance travel by the pulse of ultrasound, this can be calculated by reference material of known ultrasound velocity. Velocity (V) is measured by time (T) delay between successive echoes by V=2L/T (Awad et al., 2012).
Fig.1 Pulse-echo system (Awad et al., 2012)
Continued wave technique (Fig.2) also called through transmission, uses two transducers at both ends. This system has a pulse generator that generates the pulse having a specific frequency and wavelength. Before measurements of electric pulse, a function generator is attached with the pulse generator to adjust it. in the first transducer, ultrasound waves are produced, and then these waves pass through the sample cell between the two transducers. The original and final electrical pulses are monitored by oscilloscope connected to sample cell and function generator. Measurements sensitive to temperature like in melting and crystallization processes are done with having a controlled water bath around the sample cell. The ultrasound velocity value can be calculated through the path length. This can be calculated by measuring the length (L) of the sample cell with reference sample like distilled water because the ultrasound wave velocity (V) of reference distilled water at different temperatures is known. By measuring time delay (ΔT) between original and propagated pulses, the cell length can be measured L=V/ ΔT (Awad et al., 2012).
Fig.2. Continues Wave Technique (Awad et al., 2012)
The pitch and catch system consists of two transducers in which the first one generates a sound pulse and is called transmitting transducer while the second transducer receives and detects. In this system, an ultrasonic pulse is sent through the sample which is generated at a certain frequency. This pulse is then received at the opposite side or after reflection from the wall of the container (Buckin et al., 2002). The depth of flaws in a material can be measured accurately by using this system.
Possible Applications in Fish Processing
Ultrasound is currently, applied in food processing like in fruits and vegetables, meat, chicken, cereals, and fat products. But when we consider the use of ultrasound in fish processing, found it very limited. Many projects are under work at this point like Ultrafish, a project of EU started in Spain because of its potential in fish processing like it has in other food categories. The possible areas where the application of ultrasound can be possibly described below.
The physicochemical properties of foods can be determined by using ultrasonic methods. It is also useful to determine the composition, structure, and physical stat of foodstuff (McClements, 1994). Fish commercialization is totally dependent on the composition verities because Fish mainly have protein, water, fat, minerals. But these all components depend on different factors like species, age, season, and sex. Ultrasound has the advantage that it is more quick, nondestructive, accurate, automated, and can be performed in the laboratory and online. On the other hand, conventional methods are not that much up to mark when compare to ultrasonication. In ultrasonic composition analysis, it is not needed to prepare a sample as we do in general laboratory methods. Ultrasonic characteristics of fish tissues rely on temperature and composition. In solid-non-fat contents, ultrasonic velocity increases at almost all temperatures, but it becomes complex in fat areas (Ghaedian et al., 1998). Commercially fillers are a very important part of fish so the water content of fish fillets can be determined rapidly and accurately by using ultrasonic velocity. The amount of fat and minerals remain constant in cod fillets which makes it easy to determine the amount of protein in cod fillets (Ghaedian et al., 1997). It also means that only by varying the temperature both in the lean and fatty parts of the meat we can check the composition easily (Awad et al., 2012).
Enzymes play a vital role in fish freshness. So, it is important to control their activity to some extent so it will not harm the fish. Power ultrasound is applied to inactivate enzymes in foods. The principle of ultrasonication to inactivate the enzymes is cavitation. Cavitation provides mechanical and chemical effects against enzymes. Pressure and temperature are also used to achieve inactivation. Ultrasound produces cavitation bubbles and then by creating strong shock waves to cause strong shear force. This powerful condition allows sonication to break down the hydrogen bonding and other forces in polypeptide bonds. This will change the structure of enzymes and they will lose their activity (Mawson et al.,2010). But for different enzymes, the method of applying sonication is also different. Mostly mano-thermo-sonication (MTS), in which mild heat application with ultrasound and moderate pressure is used. MTS is very useful to those enzymes that need high temperatures for inactivation like protease. MTS requires less time and low temperature than the only thermal process for enzyme inactivation. When ultrasound is used with treatment like pressure then it is called mono-sonication and if only heat is applied then called thermo-sonication (Vercet et al.,2001). The use of ultrasonication in this field is mostly used in liquid foods section more than in solid due to cavitation process which can easily create in liquids. But mano-thermo-sonication and thermo-sonication will be of great importance in the fish industry if more research is applied to them.
Microbes and Ultrasonication
Microbes are the main cause of food-borne diseases. Fish can also become hazardous to eat if it contains pathogens more than critical limits. Mostly, in industries, conventional heat process like pasteurization and sterilization is applied to get rid of microbes. These techniques successfully destroy microbes, but they also cause nutrition loss, flavor degradation, change in product properties (Dolatowski et al.,2007). Ultrasonication has the prospect to be applied for the inactivation of microbial populations. The mechanism of ultrasonication is that waves rapture the cell membrane and when mild heat is applied with this the required result is achieved. Some bacteria show strong standing against waves, so that is why before the application of ultrasonication it is important to know the characteristics of targeted bacteria and then according to this choose the treatments like mono-sonication, thermo-sonication, or mano-thermo-sonication. Listeria is a species of bacteria mainly found in fish and fish products. In a study, it is recorded that if thermo-sonication is applied on the food products having 24 kHz and 55 °C for 2.5 minutes then we can reduce listeria more than the conventional pasteurization process. In E.coli’s case, the process requires pressure also along with heating and sonication, so it then becomes mano-thermo-sonication with 20 kHz, 40-61 °C, and 100-500 kPa for 0.25-4 minutes. Another important pathogen salmonella can also control by thermo-sonication with 24kHz and 52-58oC specifications for 2-10 minutes. (Chemat et al., 2011). Destruction of spores by thermal methods is not easy. They are resistant to high temperatures and pressures. Most of the time survived during processing and can cause negative effects on product shelf life and the reputation of the manufacturer. Bacillus and Clostridium spores are very resistant to pathogenic microbes. 100oC temperature for 4hours is required to destroy the spores of bacillus thermophilus. Manosonication is found helpful in this regard. By applying treatment at 500kPa for 12 minutes inactivated around 99% spores of bacillus. Inactivation is also increased with an increase in the amplitude of the waves. When 20kHz is used with 300kPa and 90µm then the inactivation of spores will be 75%. But it can increase up to 99% by just increasing amplitude to 150µm. Same as this if we increase the thermal temperature with 300kPa and 20kHz then inactivation also gets increased (Chemat et al., 2011). The food-borne diseases reported in Europe and USA mostly occur due to cryptosporidium and protozoa-type microbes. They are found in water and most of the time do not eliminate from processing water even by treatment of that water with chlorine disinfectant technique. Ozone and ultrasound were both found very helpful to eliminate the chances of this contamination (Chemat et al., 2011). The use of ultrasound alone in pathogens removal is not much feasible. But with a combination of ultrasound, pressure and thermal treatment more possible log reduction of bacterial growth is possible within a short time as compared to conventional treatments. So, the future of ultrasound as bacterial removal is relying on thermo-sonication, mano-sonication, and thermo-mano-sonication (Piyasena et al., 2003).
Drying is the oldest method of preservation used for fish and other food commodities. This method increases shelf life by removing water from the product and this way water which is a vital requirement for spoilage causing microbes and enzymes to become unavailable and food remains fit for human consumption. The methods often used in fish industries are time-consuming. They require days to weeks to complete procedures. Due to this original taste and color of the product also got changed. Some alternative method like freeze-drying is adopted by some industries in Europe but it is very expensive and affects the price of the product. Direct or indirect contact of ultrasound applications was found suitable for food drying in a combination with mild heat (Charoux et al., 2017). The diffusion or dehydration of the product is enhanced by compression, rarefaction, and pressure applied by using ultrasound waves (Mason, 2002). During clip fish drying processing it is noted that 43% time reduced by applying 25kHz intensity of ultrasound waves with any other technique. Just like the use of ultrasound in pathogens removal, in drying ultrasonication is applied with other techniques to achieve the target as soon as possible. So, that is why the influence of ultrasound depends on the selection of different parameters for drying like mode of ultrasound application, other combined drying techniques, the intensity of waves, conditions applied, and type of material (Musielak et al., 2016). Fish drying will become safer to do if ultrasound is applied during drying as it will cut down the processing time and the chance of quality deterioration of fish products will be minimum with no side effects at low cost.
Freezing is also a very popular method of preservation in the food sector. Many fish processes demand frozen fish to be delivered as raw material. Freezing has a very good effect on product quality and shelf life. The loss of nutrients and flavor is much lower than other techniques. According to Awad 2012, freezing is done by converting water into crystals. The quick-freezing method helps to gain small crystals, but the slow methods create large crystals that will damage the structure of the product (Awad et al.,2012). But the rapid freezing techniques, very expensive to apply. It also increases the price of products. High power ultrasound is used successfully to control crystallization and nucleation procedure, it also remains noncontact and has no side effects on the product chemically (Acton & Morris, 1993). HPU is still not applied in fish industries, but it is used applied in potatoes freezing with slow freezing methods and results are more than satisfying (Awad et al., 2012). So, as fish require freezing during almost it’s all procedures, we can reduce the cost of rapid freezing by applying HPU with a simple slow method which will not affect the quality and structure of the fish and fish products.
Thawing is a very critical and slow step in frozen fish processing. HPU application on cod thawing gives very good results (Miles et al., 1999). Cod flesh received 500kHz frequency with 0.5W intensity which takes 2.5 hours for thawing this time is less than the usual water methods and it also did not change the quality characteristics of cod (Miles et al., 1999). In another experiment 1500kHz, HPU was applied on the cod block with 60W intensity. It helps to decrease 71% time as compared to usual water methods (Chemat et al., 2011).
Brining is a very vital step in fish processing for many ready-to-eat products. It does not only add taste but also gives a preservation effect. Simple bringing solution applications take much time, and we need to use more salt. Conventional brining is not much remained under control as it is not performed uniformly on the whole product. Brining is a process in which salt of the solution goes into the flesh and water of the flesh comes out. This is a two-way process. It is noted in pork flesh that if we apply saturated NaCl solution with different ultrasonication energy with great agitation, it showed that the NaCl penetration is higher in sonicated than non-sonicated. It also reduces the penetration time of NaCl. The brining assisted with ultrasound also helps to distribute brine in all the products equally, but this all depends on the size of flesh, sound energy, and agitation frequency (Chemat et al., 2011). The mass transferability of ultrasound also shows that it can be useful in fish brining and other marination procedures which require a lot of time to get ready for final processing and packaging.
Fish is a natural source of the best omega3 fatty acids. The fish flavor is also used in many products just to give a smooth fish flavor. Typically, fish oil and flavor are extracted by harmful chemicals and high energy costs. This method has many drawbacks so that is why the concern of extraction technology converted towards green extraction technologies assisted by harmless technologies like microwave, ultrasound, ultrafiltration, and flash distillation process. Ultrasound is becoming very popular in extraction methods and it is called the ultrasound-assisted extraction (UAE) method used with high power ultrasound. The mechanism of UAE is that when waves are applied on the medium it creates compression and rarefaction so by this application oil is extracted from fish without the use of any chemical material (Chemat et al., 2011). But still, the very little approach is shown about this system. Only a few articles are available about the UAE oil extraction method. Asian swamp eel is used in an experiment to extract oil with the help of the UAE method. The parameters set for the procedure are 25kHz, 200W, and 60 minutes with only 500 ml of ethanol. The procedure was recorded successfully. In another work on the same species was done with the same frequency but 400W, 50 °C, and for 57 minutes. It gave 94.82% extraction (Ivanovs and Blumberga, 2017). the main advantage of ultrasound-assisted extraction is that
• It is very easy to use
• Require very little time to complete extraction
• Less solvent requirement
• More penetration ability into the material
But the problem with this method is that it requires high power consumption and that is why difficult to scale up (Ivanovs and Blumberga, 2017: Chemat et al., 2011).
Ultrasound waves can be used infiltration to avoid blockage of the filter membrane. It makes solid particles move around and this way they will not settle down and their cake layer will not create on the membrane (Chemat et al., 2011).
Fig.1 Ultrasound-assisted filtration (Chemat et al., 2011)
This filtration assistance can be applied in fish sauce processing and other liquid filtrations during processing. Fish fillet cutting is a process of high concern regarding product quality. If cutting of fillets is not accurate as wanted for the product it can become a headache during processing. Conventional knives produce more waste and are less accurate. Ultrasonic cutting is used in some soft and fragile products like cake and cheese. Ultrasound cutting has a knife-type blade attached with a shaft to an ultrasonic source. Although in fish processing high-pressure water jet cutting becoming more popular these days but the energy consumption of the ultrasound method is far less than water jet cutting (Chemat et al., 2011).
Challenges with Ultrasound Application
The main challenge in the application of ultrasound is the lack of standardization for the different procedures in fish and food processing at the commercial-scale level. It shows a great result on the experimental level but its scale-up procedure still requires studies. Only 20-40kHz frequency is available still in use for the commercial level which is not enough for many procedures. In the liquid phase when applied small gas bubbles make it difficult for the waves to propagate through the medium (Rastogi, 2011). It is also difficult to convince consumers that ultrasound-treated foods are not harmful for consumption.
Ultrasound waves provide non-destructive, easy application, and fast processing procedures. This technique will not harm the environment. We can use it as a preservation technique by applying it against microbes and enzymes. The approach of ultrasound against microbes is destructive and its inactivation ability of enzymes without any quality and nutritional deterioration makes it more acceptable for new generation value-added products. Although this method has not completely become an alternative to conventional methods still this can make procedures much easier and reduce time by applying it with a combination of different conventional techniques. It is also required to satisfy customers about ultrasound that it is a harmless and green technology. If the comparison is done between ultrasonication and conventional processing, ultrasound has more benefits but still, a lot of studies are needed to minimize its capital investment, its scale-up standardization, and other challenges associated with it.
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Submit To: Ólafur Ögmundarson (Associate Professor, Norwegian University of Life Sciences NMBU, Norway)
Submit By: Muhammad Umar (Norwegian University of Life Sciences NMBU, Norway)
Student No: 110155
Course: MAT703F Marine Resources-Research and Innovation
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