Ultrasound assisted extraction of food and natural products. Mechanisms,techniques, combinations,protocols and applications. A review

This review presents a complete picture of current knowledge on ultrasound-assisted extraction (UAE) in food ingredients and products, nutraceutics, cosmetic, pharmaceutical and bioenergy applications. It provides the necessary theoretical background and some details about extraction by ultrasound, the techniques and their combinations, the mechanisms (fragmentation, erosion, capillarity, detexturation, and sonoporation), applications from laboratory to industry, security, and environmental impacts. In addition, the ultrasound extraction procedures and the important parameters influencing its performance are also included, together with the advantages and the drawbacks of each UAE techniques. Ultrasound-assisted extraction is a research topic, which affects several fields of modern plant-based chemistry. All the reported applications have shown that ultrasound-assisted extraction is a green and economically viable alternative to conventional techniques for food and natural products. The main benefits are decrease of extraction and processing time, the amount of energy and solvents used, unit operations, and CO₂ emissions.     

Individual and interactive effect of ultrasound pre-treatment on drying kinetics and biochemical qualities of food: A critical review

One of the earliest and most prevalent processing methods to increase the shelf-life of foods is drying. In recent years, there has been an increased demand to improve product quality while lowering processing times, expenses, and energy usage in the drying process. Pre-treatments are therefore effectively used before drying to enhance heat and mass transfer, increase drying efficiency, and lessen degradation of final product quality. When food is dried, changes are expected in its taste, color, texture, and physical, chemical, and microbial properties. This has led to the need for research and development into the creation of new and effective pre-treatment technologies including high-pressure processing, pulsed electric field, ultraviolet irradiation, and ultrasound. Sound waves that have a frequency >20 kHz, which is above the upper limit of the audible frequency range, are referred to as “ultrasound”. Ultrasonication (US) is a non-thermal technology, that has mechanical, cavitational, and sponge effects on food materials. Ultrasound pre-treatment enhances the drying characteristics by producing microchannels in the food tissue, facilitating internal moisture diffusion in the finished product, and lowering the barrier to water migration. The goal of ultrasound pre-treatment is to save processing time, conserve energy, and enhance the quality, safety, and shelf-life of food products. This study presents a comprehensive overview of the fundamentals of ultrasound, its mechanism, and how the individual effects of ultrasonic pre-treatment and the interactive effects of ultrasound-assisted technologies affect the drying kinetics, bioactive components, color, textural, and sensory qualities of food. The difficulties that can arise when using ultrasound technology as a drying pretreatment approach, such as inadequate management of heat, the employment of ultrasound at a limited frequency, and the generation of free radicals, have also been explained.     

Effects of multi-frequency ultrasound on the freezing rates,quality properties and structural characteristics of cultured large yellow croaker (Larimichthys crocea)

This research evaluated the effects of multi-frequency ultrasound assisted freezing (UAF) on the freezing rate, structural characteristics, and quality properties of cultured large yellow croaker. The freezing effects with triple ultrasound-assisted freezing (TUF) at 20, 28 and 40 kHz under 175 W was more obvious than that of single ultrasound-assisted freezing (SUF) at 20 kHz and dual ultrasound-assisted freezing (DUF) at 20 and 28 kHz. The results showed that UAF significantly increased the freezing rate and better preserved the quality of frozen large yellow croaker samples. Specifically, the quality parameters of the TUF-treated samples were closer to those of the fresh samples, with greater texture characteristics, a larger water holding capacity (lower thawing loss and cooking loss), lower K values and lower thiobarbituric acid reactive substances values. Light microscopy observation images revealed that the ice crystals formed by TUF were fine and evenly distributed, resulting in less damage to the frozen large yellow croaker samples. Therefore, multi-frequency UAF could improve the quality properties of the large yellow croaker samples.     

Recent advances in the application of ultrasound in dairy products: Effect on functional,physical, chemical,microbiological and sensory properties

Alternative methods for improving traditional food processing have increased in the last decades. Additionally, the development of novel dairy products is gaining importance due to an increased consumer demand for palatable, healthy, and minimally processed products. Ultrasonic processing or sonication is a promising alternative technology in the food industry as it has potential to improve the technological and functional properties of milk and dairy products. This review presents a detailed summary of the latest research on the impact of high-intensity ultrasound techniques in dairy processing. It explores the ways in which ultrasound has been employed to enhance milk properties and processes of interest to the dairy industry, such as homogenization, emulsification, yogurt and fermented beverages production, and food safety. Special emphasis has been given to ultrasonic effects on milk components; fermentation and spoilage by microorganisms; and the technological, functional, and sensory properties of dairy foods. Several current and potential applications of ultrasound as a processing technique in milk applications are also discussed in this review.     

Ultrasound applications in drying of fruits from a sustainable development goals perspective

This review focuses on the many contributions of ultrasound technologies for fruit drying toward the United Nations Sustainable Development Goals (SDG). Along this review, several aspects attained from the application of ultrasound technologies are correlated with the SDGs. The main ultrasonic technologies applied for fruit drying, such as ultrasonic bath, probe ultrasound, air-borne ultrasound air-drying, and ultrasound-assisted contact air-drying, are presented. An in-depth discussion on ultrasound contributions, its advantages, disadvantages, and limitations are made. The effects of ultrasound on water diffusivity in several fruits are presented by correlating this effect with drying time and cost of energy. Ultrasound-assisted fruit drying, like other food processing technologies, directly impacts Zero Hunger, but ultrasound technologies contribute to much more than delivering long shelf-life food. This technology can be used to produce healthy foods and provide well-being, which will be discussed by correlating the effects of ultrasound-assisted air-drying with the concentration of nutritional compounds. Ultrasound-assisted fruit drying reduces wastewater toxicity and energy consumption and improves productivity, potentially improving workplaces and salaries. A walk through the technology is presented from Zero Hunger to No Poverty.     

New ultrasonic assisted technology of freezing,cooling and thawing in solid food processing: A review

Solid foods include fish, shrimp, shellfish, and other aquatic products, fruits, and vegetables. These products are commonly used for food freezing, cooling, and thawing. However, traditional freezing, cooling, and thawing of solid food technologies have limitations in quality, such as protein denaturation and water loss in food. Ultrasound-assisted technology has become a useful method in solid food processing due to improved preservation quality of solid food. This paper comprehensively reviews the mechanism and application of ultrasonic in solid food processing technology. Although the application of ultrasound-assisted ultrasound in solid food processing is relatively comprehensive, the energy saving of food cold processing is essential for practical application. This paper analyzes the optimization of ultrasonic in solid food processing, including orthogonal/multi-frequency technology and the combination of ultrasonic and other technologies, which provides new ideas for freezing, cooling, and thawing of solid food processing.     

Application of ultrasound in combination with other technologies in food processing: A review

The use of non-thermal processing technologies has been on the surge due to ever increasing demand for highest quality convenient foods containing the natural taste & flavor and being free of chemical additives and preservatives. Among the various non-thermal processing methods, ultrasound technology has proven to be very valuable. Ultrasound processing, being used alone or in combination with other processing methods, yields significant positive results on the quality of foods, thus has been considered efficacious. Food processes performed under the action of ultrasound are believed to be affected in part by cavitation phenomenon and mass transfer enhancement. It is considered to be an emerging and promising technology and has been applied efficiently in food processing industry for several processes such as freezing, filtration, drying, separation, emulsion, sterilization, and extraction. Various researches have opined that ultrasound leads to an increase in the performance of the process and improves the quality factors of the food. The present paper will discuss the mechanical, chemical and biochemical effects produced by the propagation of high intensity ultrasonic waves through the medium. This review outlines the current knowledge about application of ultrasound in food technology including processing, preservation and extraction. In addition, the several advantages of ultrasound processing, which when combined with other different technologies (such as microwave, supercritical CO₂, high pressure processing, enzymatic extraction, etc.) are being examined. These include an array of effects such as effective mixing, retention of food characteristics, faster energy and mass transfer, reduced thermal and concentration gradients, effective extraction, increased production, and efficient alternative to conventional techniques. Furthermore, the paper presents the necessary theoretical background and details of the technology, technique, and safety precautions about ultrasound.     

Mechanisms for improving mass transfer in food with ultrasound technology: Describing the phenomena in two model cases

The aim of this work was to demonstrate how ultrasound mechanisms (direct and indirect effects) improve the mass transfer phenomena in food processing, and which part of the process they are more effective in. Two model cases were evaluated: the hydration of sorghum grain (with two water activities) and the influx of a pigment into melon cylinders. Different treatments enabled us to evaluate and discriminate both direct (inertial flow and “sponge effect”) and indirect effects (micro channel formation), alternating pre-treatments and treatments using an ultrasonic bath (20 kHz of frequency and 28 W/L of volumetric power) and a traditional water-bath. It was demonstrated that both the effects of ultrasound technology are more effective in food with higher water activity, the micro channels only forming in moist food. Moreover, micro channel formation could also be observed using agar gel cylinders, verifying the random formation of these due to cavitation. The direct effects were shown to be important in mass transfer enhancement not only in moist food, but also in dry food, this being improved by the micro channels formed and the porosity of the food. In conclusion, the improvement in mass transfer due to direct and indirect effects was firstly discriminated and described. It was proven that both phenomena are important for mass transfer in moist foods, while only the direct effects are important for dry foods. Based on these results, better processing using ultrasound technology can be obtained.     

Effect of ultrasound-assisted freezing on the physico-chemical properties and volatile compounds of red radish

Power ultrasound, which can enhance nucleation rate and crystal growth rate, can also affect the physico-chemical properties of immersion frozen products. In this study, the influence of slow freezing (SF), immersion freezing (IF) and ultrasound-assisted freezing (UAF) on physico-chemical properties and volatile compounds of red radish was investigated. Results showed that ultrasound application significantly improved the freezing rate; the freezing time of ultrasound application at 0.26 W/cm² was shorten by 14% and 90%, compared to IF and SF, respectively. UAF products showed significant (p < 0.05) reduction in drip loss and phytonutrients (anthocyanins, vitamin C and phenolics) loss. Compared to SF products, IF and UAF products showed better textural preservation and higher calcium content. The radish tissues exhibited better cellular structures under ultrasonic power intensities of 0.17 and 0.26 W/cm² with less cell separation and disruption. Volatile compound data revealed that radish aromatic profile was also affected in the freezing process.     

Continuous and pulsed ultrasound-assisted extraction of carob’s antioxidants: Processing parameters optimization and identification of polyphenolic composition

Polyphenols in carobs have recently attracted great attention due to their wide range of biological and health promoting effects. A comprehensive study was conducted to find an optimum method for the extraction, purification and characterization of these valuable bioactive substances. Under this framework, the ultrasound-assisted extraction (UAE) of polyphenols from carob pulp was optimized by the maximization of the yield in total phenolics using response surface methodology. In particular, the effects of solid-solvent ratio, solvent concentration, extraction time, sonication amplitude, and sonication mode were investigated and optimized using a complete experimental design. In comparison to conventional extraction techniques, UAE offered a higher yield of antioxidants and a shorter processing time. Solid-phase extraction was evaluated as a clean-up strategy prior to the electrophoretic analysis of extracts. The results from the analysis of real samples revealed the predominance of gallic acid and highlighted the great influence of the ripening stage on carobs composition.     

Ultrasound-assisted extraction of three bufadienolides from Chinese medicine ChanSu

In this study, the application of ultrasound-assisted extraction (UAE) method was shown to be more efficient in extracting anti-tumor bufadienolides (bufalin, cinobufagin and resibufogenin) from important animal medicine of ChanSu than the maceration extraction (ME) and soxhlet extraction (SE) method. The effects of ultrasonic variables including extraction solvent, solvent concentration, solvent to solid ratio, ultrasound power, temperature, extraction time and particle size on the yields of three bufadienolides were investigated. The optimum extraction conditions found were: 70% (v/v) methanol solution, solvent to solid ratio of 10ml/g, ultrasound power of 125W, temperature of 20°C, extraction time of 20min and particle size of 60-80 mesh. The extraction yields of bufalin, cinobufagin and resibufogenin were 43.17±0.85, 52.58±1.12, 137.70±2.65mg/g, respectively. In order to achieve a similar yield as UAE, soxhlet extraction required 6h and maceration extraction required much longer time of 18h. The results indicated that UAE is an alternative method for extracting bufadienolides from ChanSu.     

Mechanisms underlying the effects of ultrasound-assisted alkaline extraction on the structural properties and in vitro digestibility of Tenebrio molitor larvae protein

Edible insects have been considered as a sustainable and novel protein source to replace animal-derived proteins. The present study aimed to extract Tenebrio molitor larvae proteins (TMP) using ultrasound-assisted alkaline extraction (UAE). Effects of different UAE times (10, 20, 30, 40, and 50 min) on the structural properties and in vitro digestibility of TMP were comparatively investigated with the traditional alkaline extraction method. The results revealed that ultrasonication could effectively alter the secondary/tertiary structures and thermal stability of TMP during UAE. The molecular unfolding and subsequent aggregation of TMP during UAE were mainly attributed to the formation of disulfide bonds and hydrophobic interactions. Moreover, TMP extracted by UAE had higher in vitro digestibility and digestion kinetics than those extracted without ultrasound, and the intermediate UAE time (30 min) was the optimal ultrasound parameter. However, longer UAE times (40 and 50 min) lowered the digestibility of TMP due to severe protein aggregation. The present work provides a potential strategy for the extraction of TMP with higher nutritional values.     

Ultrasound-assisted extraction of anthraquinones from roots of Morinda citrifolia

This study investigated the use of ultrasound-assisted extraction (UAE) to improve the extraction efficiency of the classical solvent extraction techniques such as maceration and soxhlet extraction to extract anti-oxidant activity compounds, anthraquinones, from the root of Morinda citrifolia. The effects of different extraction conditions were determined, i.e., temperature of (25, 45, 60 °C), ultrasonic power, solvent types, and compositions of ethanol in ethanol–water mixtures. The results show that the yield increases with increasing extraction times and extraction temperatures. The percent recovery of anthraquinones using ultrasound was found to be highly dependent on the type of solvents (acetone > acetonitrile > methanol > ethanol). Furthermore, the use of ethanol–water solution as extraction solvent increased the yield of anthraquinones due to the relative polarity, the swelling effect of plant tissue matrix by water, and increased sound absorption. To achieve the same recovery as that achieved by UAE, soxhlet extraction and maceration required much longer time.     

Ultrasound and deep eutectic solvents: An efficient combination to tune the mechanism of steviol glycosides extraction

Ultrasound-assisted extraction is widely recognized as an eco-friendly technique due to low solvent consumption and time extraction as well as enhanced extraction efficiency with respect to conventional methods. Nevertheless, it would be convenient to avoid the usually used organic solvents to reduce the environment pollution. In this regard, Deep Eutectic Solvents (DES) represent nowadays a green and sustainable alternative for the extraction of bioactive compounds from natural sources. In this study, an efficient extraction of stevioside and rebaudioside A from Stevia rebaudiana coupling ultrasound with DES was developed. A solvent screening was performed using the predictive approach COnductor-like Screening MOdel for Real Solvent (COSMO-RS). The effect of three independent variables, namely % of water, temperature, and sonication amplitude, were investigated by the response surface methodology (RSM). Comparing ultrasound-assisted extraction (UAE) with conventional extraction, it has been demonstrated that the amount of steviol glycosides through UAE is almost three times higher than that obtained by the conventional method. Possible physicochemical factors involved in the UAE mechanism were discussed.     

Comparison between the use of polyether ether ketone and stainless steel columns for ultrasonic-assisted extraction under various ultrasonic conditions

The ultrasound-assisted extraction (UAE) was conducted using the stainless steel (SS) and polyether ether ketone (PEEK) columns and analyzed with high-performance liquid chromatography (HPLC) to understand the mechanism of ultrasound-assisted chromatography (UAC). Empty SS and PEEK columns were used to extract dyes from a fabric under identical conditions with several parameters including the initial ultrasonic bath temperatures (30 °C and 40 °C), ultrasound power intensities (0, 20, 40, 60, 80, and 100 %), ultrasound operation modes (normal and sweep), and ultrasound frequencies (25 kHz, 40 kHz, and 132 kHz) to compare their extraction capabilities. After 30 min of extraction, the amount of extract was determined by HPLC. The PEEK material was significantly affected by ultrasonic radiation compared to the SS material, especially at a higher temperature (40 °C), power intensity (100 %), and frequency (132 kHz) with sweep mode. At a maximum power density of 45 W/L, the extraction effectiveness ratio of PEEK to SS was in the range of 1.8 - 3.9 depending on the specific frequency, initial temperature, and with or without temperature control. The most optimal ultrasound frequencies, in terms of enhancing extraction effectiveness, are in the order of 132 kHz, 40 kHz, and 25 kHz. Unlike the SS material, the PEEK material was more affected by temperature and acoustic effects under identical conditions, especially at 132 kHz ultrasound frequency. In contrast, at lower frequencies of 40 kHz and 25 kHz, no significant differences in the acoustic effects were observed between the PEEK and SS materials. The findings of this study contribute to elucidating the roles of column materials in UAE and UAC.     

Prospects and application of ultrasound and magnetic fields in the fermentation of rare edible fungi

Ultrasound has the potential to be broadly applied in the field of agricultural food processing due to advantages such as environmental friendliness, low energy costs, no need for exogenous additives and ease of operation. High-frequency ultrasound is mainly used in medical diagnosis and in the food industry for the identification of ingredients and production line quality testing, while low-frequency ultrasounds is mainly used for extraction and separation, accelerating chemical reactions, auxiliary microbial fermentation and quality enhancement in food industry. Magnetic fields have many advantages of convenient use, such as non-toxic, nonpolluting and safe. High-intensity pulsed magnetic fields are widely used as a physical non-thermal sterilization technology in food processing, while weak magnetic fields are better at activating microorganisms and promoting their growth. Ultrasound and magnetic fields, due to their positive biological effects, have a wide range of applications in the food processing industry. This paper provides an overview of the research progress and applications of ultrasound and magnetic fields in food processing from the perspectives of their biological effects and mechanisms of action. Additionally, with the development and application of physical field technology, physical fields can now be used to provide significant technical advantages for assisting fermentation. Suitable physical fields can promote the growth of microbial cells, improve mycelial production and increase metabolic activity. Furthermore, the current status of research into the use of ultrasound and magnetic field technologies for assisting the fermentation of rare edible fungi, is discussed.     

Ultrasonics in food processing

In recent years, the physical and chemical effects of ultrasound in liquid and solid media have been extensively used in food processing applications. Harnessing the physical forces generated by ultrasound, in the absence and presence of cavitation, for specific food processing applications such as emulsification, filtration, tenderisation and functionality modification have been highlighted. While some applications, such as filtration and emulsification are "mature" industrial processes, other applications, such as functionality modification, are still in their early stages of development. However, various investigations discussed suggest that ultrasonic processing of food and dairy ingredients is a potential and viable technology that will be used by many food industries in the near future.     

Application of ultrasound technology in processing of ready-to-eat fresh food: A review

With the increase in food standardization and the pace of modern life, the demand for ready-to-eat foods is growing. The strong processing conditions of traditional technology often accelerate the rate of deterioration of quality, and microbes are the safety hazard of ready-to-eat foods. Ultrasound technology is an environmentally friendly technology that hardly causes thermal damage to raw materials. In this paper, the ultrasound technology is used in the disinfection, sterilization, enzyme inactivation, desensitization, dehydration, curing, tenderization and cooking process of fresh food from the perspective of microbial safety and quality of fresh food. The cavitation effect of ultrasound can improve the mass transfer rate of infiltration processes such as dehydration and curing, promote the oxidation of lipids and proteins for enrich the flavor of meat products, improve the microbiological safety and reduce the sensitization by destroying the integrity of the microbial cells and the conformation of the protein. In addition, ultrasound as an auxiliary processing technology can reduce the damage of traditional production technology to reserve the quality and nutritional value of food. Ultrasound has proved to be an efficient and green processing technology for ready-to-eat food.     

Green extraction of lutein from marigold flower petals,process optimization and its potential to improve the oxidative stability of sunflower oil

Marigold flower petals are considered the richest source of lutein which possesses immense applications in the food and health sector. The study was undertaken to improve the stability of sunflower oil by enriching it with lutein extracted from marigold flower petals using safe and green technology. The extraction of lutein was optimized using Box-Behnken design by ultrasound-assisted extraction (UAE) employing sunflower oil as a solvent. The impact of three independent variables i.e., ultrasonic intensity, solid to solvent ratio, and extraction time were evaluated on the amount of lutein extracted and its antioxidant activity. Highest amount of lutein (21.23 mg/g) was extracted by employing ultrasonic intensity of 70 W/m2, extraction time of 12.5 min, and solid to solvent ratio of 15.75%. FT-IR spectra of lutein extracted by ultrasound and conventional extraction show similar peaks depicting that ultrasound does not have any impact on the functionality of lutein. Sunflower oil incorporated with lutein at 1000 PPM and the synthetic antioxidant (TBHQ) showed good oxidative stability than oil with 500 PPM lutein and no lutein during accelerated storage for a month. The oxidative stability was shown by different oil samples in the following order: TBHQ = 1000PPM lutein˃500PPM lutein ˃control oil. It was concluded that the ultrasound technique extracts lutein efficiently from marigold flowers and this lutein was effective in improving the oxidative stability of sunflower oil under accelerated storage conditions.     

Green ultrasound-assisted extraction of carotenoids from pomegranate wastes using vegetable oils

The objective of this work was to develop a new process for pomegranate peels application in food industries based on ultrasound-assisted extraction of carotenoids using different vegetable oils as solvents. In this way, an oil enriched with antioxidants is produced. Sunflower oil and soy oil were used as alternative solvents and the effects of various parameters on extraction yield were studied. Extraction temperature, solid/oil ratio, amplitude level, and extraction time were the factors investigated with respect to extraction yield. Comparative studies between ultrasound-assisted and conventional solvent extraction were carried out in terms of processing procedure and total carotenoids content. The efficient extraction period for achieving maximum yield of pomegranate peel carotenoids was about 30 min. The optimum operating conditions were found to be: extraction temperature, 51.5 °C; peels/solvent ratio, 0.10; amplitude level, 58.8%; solvent, sunflower oil. A second-order kinetic model was successfully developed for describing the mechanism of ultrasound extraction under different processing parameters.