CHEN Jianjian,1,* LIU Yuan,2 SHI Jingang3
1 Laboratory of Food Oral Processing, Zhejiang Gongshang University
2 Department of Food Science and Engineering, College of Agriculture and Biology, Shanghai Jiao Tong University
3 EPC Natural Products Co.,Ltd.
Abstract
As an independent sub-discipline of food science, food sensory has gone through more than half century history. The success of food sensory research can be seen by many landmark achievements and the establishment of various sensory theories. However, approaches of traditional sensory research were largely based on that of food material research which failed to take into full consideration of the impacts of human physiology, sensory psychology, brain behaviour. This papery begins by asking some very basic questions of food sensory, which leads to authors’ reflection on some fundamental principles of food sensory research from different perspectives. A large part of discussion is on the current challenges and possible new breakthroughs of food sensory research. Authors hope that views and discussion presented in this paper will inspire further thinking and even a wide range debate about future direction and opportunities of food sensory science.
Keywords: Food sensory, food flavor, food texture, food oral processing, sensation and perception
Sensory perception is not exclusive to humans; many animals (or even some plants) have this ability. Animals' perception of the external environment is often a matter of life and death, and they are always in the throes of excitement and fear of Fight or Flight, and the slightest misjudgment of the environment may lead to their doom. Therefore, the perception ability of animals is one of the most basic abilities for their survival. The human sensory perception of the external world has evolved to a state of perfection. Humans not only have a complete system of five senses, but also have an unparalleled brain information processing and cognitive ability. Of course, there are certain perceptual abilities that are inferior to those of animals. In terms of vision, humans can only perceive a very limited range of electromagnetic waves through the eyes, both so-called visible light, and cannot use ultrasound to perceive their surroundings and locate them like bats and dolphins, or have the infrared image perception of snakes, or see ultraviolet light like reindeer. However, the five human sensory organs have integrated a comprehensive, multidimensional, and mutually coordinated system of precise perception [1], which allows humans to perceive the color, form, and distance of the external world through vision, the chemical nature and composition of the external world through smell and taste, the sound waves of the external world through hearing, and thus judge external events from a distance, and the physical and mechanical nature of the external environment through touch [2]. The sense of touch allows the perception of the physical and mechanical properties of the external environment [2]. It is on the basis of this system that human sensory perception of food operates, complemented by reward mechanisms developed during the long evolutionary process (the brain mechanism is still poorly understood) to form preferences for food.
Food sensory science is generally considered to be a separate discipline under food science. Although systematic research on food sensory has been conducted for more than half a century and many landmark results have been achieved, we still know very little about the principles of food sensory perception. The principles of sensory perception in physics, physiology, psychology, and neuroscience of the brain are still unclear, and many related fields still need to be further investigated. In this paper, we will discuss the challenges and possible breakthroughs in food sensory science research from some basic concepts of food sensory, in order to attract colleagues in food sensory science research and promote the rapid development of food sensory science in China.
1. Is sensation a nature of food?
In our daily life and in the literature, we are not unfamiliar with the term "sensory properties", and we accept and appreciate this term: it treats human sensory experience as a property of food materials, alongside its physical, chemical and microstructural properties. However, the scientific validity and accuracy of the term "sensory properties" is questionable for three reasons.
First, food sensory is the human experience of eating food material, which is obviously subjective and individual. Secondly, if "sensory properties" is a property of food, it should have a numerical value and a scale like other material properties, while subjective descriptions or values of intensity and preference given through sensory experience do not have a scale in most cases. Third, "sensory properties" do not have the objective measurability of ordinary material properties. We know that there are two types of material properties, one is the strength property, whose measurement value has nothing to do with the quantity of the material itself, such as the specific gravity of the material; one is the breadth property, whose measurement value has a direct relationship with the quantity of the material, such as the volume of the material. Both of them should have exclusive and measurable characteristics. The measurement of material properties can be performed with different technical methods in different experimental settings, but the results obtained should be unique and repeatable. Whether Zhang San uses instrument A, or Li Si uses instrument B, the results should be consistent. But "sensory properties" obviously do not have this characteristic, it varies from person to person.
So if sensory is not the nature of food, then what is it? According to the authors, sensory is a human perception of the nature of a material, an experience, so it may be more appropriate to call it sensory experience. Sensory experience is strongly influenced by the person (physiological and psychological), time, environmental conditions, etc., and is characterized by subjectivity and variability. This is the reason why the results of sensory analysis tend to show a normal distribution. Figure 1 shows the population distribution of sensory perception, with a typical Gaussian distribution, for example, the preference for a certain food, generally very much and very little, is distributed at the two ends of the Gaussian curve, while the sensory preference of most of the population is distributed in the middle.
Figure 1. Normal distribution characteristics of the results of sensory analysis of the population. The sensory perception of the same food by the population varies greatly from very negative to very positive with individual differences, while most of the consumers are distributed around the peak in the middle. This is the basic basis for sensory analysis experiments in personnel selection, training and data analysis.
Of course, the term "sensory nature" has been commonly used and accepted in everyday life and in much of the academic literature, and has become an accepted concept. However, we must be clear that the so-called "sensory properties" are very specific and fundamentally different from the general material properties [3].
2. Can sensory experience of food be objectively measured?
In the design, development and production of food products, there is an urgent need for industry to relate sensory experience of food products to consumer preferences. As a result, a lot of energy and material resources have been invested in the development of various measuring devices and instruments and the creation of new methods, such as the well-known food texture meter, electronic nose, and electronic tongue, to name a few. Obviously, such devices are still in the characterization and measurement of the properties of food materials, rather than human sensory experience. It is just that the measurement of such instruments is different from the traditional material property characterization, such as simulating the human oral diet environment as the measurement condition, which is indeed a big step forward in terms of technology. Nevertheless, we still have a long way to go for real measurement of sensory experience, and some even doubt that human sensory experience can be objectively measured. Doubts about the objective measurability of sensory experience of food are based on two very important facts: first, the derivative nature of the senses and second, the concomitant nature of the senses.
During the long civilizational process of human beings, a splendid and colorful food culture has been formed. In order to better express the appreciation of delicacies and to identify the subtle differences in sensory experiences of different foods, humans have created a rich vocabulary to describe the specific sensory characteristics and pleasurable feelings of food. These words are descriptive, regional and developmental, and some of them can only be understood but not communicated. For example, crunchiness is a characteristic sensory quality of certain solid foods, bringing a chewable, relaxing and pleasant sensation to consumers, and is highly appreciated by them. There are three most common words in Chinese to describe the crispness of such foods: "crisp", "crispy", and "loose". These three words can be used individually or in combination, such as "crispy", "crunchy", "flaky", etc. The intrinsic sensory meanings of these words are similar. Although their intrinsic sensory meanings are similar, there are very subtle differences. Table 1 lists the main material properties of these three sensory words, from which the reader can see the commonalities and differences between them.
Table 1: Basic sensory meanings and material properties of "crisp", "flaky" and "loose".
Sensory terms Material property characteristics1 Material property characteristics2 Material property characteristics3 Food examples
Crisp Irrecoverable structural fracture and sound when applied stress exceeds the threshold of the food material Stress threshold is high; food tends to split in half, or a few large particles; generally less likely to be accompanied by deformation Few crunchy sounds, either dry or watery foods Apples, crisp pears, roasted peanuts, cookies, hard candies, etc.
Crisp When the applied stress exceeds the threshold of the food material, it produces irrecoverable structural fracture and sound Stress threshold is low; often collapses and breaks, food becomes many small particles, even powder; sometimes accompanied by small deformation A large number of small, crisp sounds such as a foot on snow; food has a high degree of void; generally high fat content, low water content Many baked foods
Loose Irrecoverable structural fracture when applied stress exceeds the threshold of the food material and produces sound Low stress threshold; broken particles are either large or small, accompanied by significant deformation Sound characteristics are not particularly pronounced; food has high air content, low density, and low water content Marshmallow
As can be seen in Table 1, the crisp, crunchy and fluffy texture senses are very similar but have clear and subtle differences, reflected in their corresponding food material characteristic properties, including their microstructural properties, mechanical properties, density, void shape, void size, water/oil content and other factors. However, it is clear that none of these physical and structural properties directly corresponds to the sensory characteristics of crispness, flakiness, and fluffiness, and therefore it is also difficult to measure them directly and quantitatively with instruments. The only approach that can be taken at this time is to use primary material property measurements or combinations of multiple material properties to predict sensory experience, but it is clear that the combination of physical models corresponding to sensory experience is not set in stone, but is likely to vary from person to person.
Food senses can be essentially divided into primary senses (both direct senses) and derived senses. Sensory derivation is characterized by multiplicity and multilayered nature [4]. It can be predicted that as human food culture continues to develop, more and more subtle descriptive words will be derived from the human sensory experience of food. An example is the Japanese word for "kokumi", which must be more complex (or richer) in its sensory connotation and difficult to characterize by a physical quantity. In recent years, verbal terms such as "cool" and "cool" have been widely used by young consumers to describe the senses of some new beverages, and are likely to become new sensory descriptors in the future.
There is another category of senses that is very specific and is actually a concomitant experience in the eating process. For example, "astringency" has been used as the most important sensory characteristic in tea quality analysis [5]. Although there is a large body of literature on the subject of astringency, I believe that it is debatable whether astringency can be considered as a sensory characteristic. There are two reasons for this: first, it lacks the physical or chemical properties of the corresponding material, and although current research suggests that polyphenols may be the functional component that leads to raw acidity, the nature of its sensory stimulation is not clear. Second, it lacks corresponding sensory channels; none of the five senses of sight, hearing, taste, smell, and touch seem to correspond to raw oxygen. There are many indications that the production of raw fluid is likely the result of the physiological response of the body to food stimulation (e.g., increased saliva production, changes in saliva composition, etc.) and is a concomitant sensory experience. The objective measurement of such sensory experiences is made more difficult by the difficulty of identifying a traceable physical, chemical, or physiological variable.
Therefore, it can be argued that food sensory experience as a subjective human experience of food material properties can be described in words, but because of the derivative and concomitant characteristics of food sensory experience and the multiplicity of material properties corresponding to the senses, objective measurement of food sensory experience is not as straightforward as determining the specific gravity or temperature of a material. How to objectively and accurately measure the sensory experience of food has always been a problem that the food industry is eager to solve. Based on the above analysis, to establish an objective measurement method for food sensory experience, we need to consider two aspects: first, we need to determine whether the nature of sensory experience is the experience of a single material attribute or a combination of multiple material attributes; whether it is a primary sensory or a derived sensory, or a companion experience [4]. If the experience is a direct experience of a single material property (e.g., sweetness of sugar water), the intensity of the sensory experience can be predicted by direct measurement of the material property, and the corresponding relationship is well described by Stevens' law. In the case of multiple material property experiences or derived sensory experiences, it is necessary to first specify their corresponding material properties, and then analytically determine the form of the combination of material properties corresponding to that sensory experience. The physics, physiology, and psychology principles behind it are yet to be studied in greater depth. In the case of concomitant experiences, the principles of generation are more complex and the instrumentation is more difficult to measure.
3. The main challenges of current sensory science research
The current challenges of sensory science research can be considered from two perspectives: breakthroughs in the basic theory of sensory science research and the technological needs of the food industry. Although sensory science research has made great progress after more than half a century of development and formed a basic food sensory theory system, the direction of advancement and how to find the next theoretical breakthrough have become the confusion of many sensory science researchers. The authors believe that new breakthroughs in sensory science research should be considered in the following areas: (1) the eating experience has obvious dynamic characteristics, how to understand and control the dynamic changes of sensory stimuli during the eating process, how to interpret the changes of food microstructure and the interaction between food and saliva during the eating process to guide the optimal design of food structure; (2) the receptor principle of sensory stimuli, how to understand the transformation of sensory (2) the receptor principle of sensory stimuli, how to understand the transformation of sensory stimuli to sensory signals and the underlying physical and physiological principles; (3) the brain synthesis mechanism of sensory information and its psychological and neuroscientific principles; (4) sensory pleasure as one of the intrinsic drivers of human diet, how to understand the brain reward mechanism of diet and regulate human eating behavior. From the perspective of the technological needs of the food industry, there are two main challenges: first, how to accurately understand the combination and coordination of different sensory stimuli in food design to achieve the best pleasure effect; second, how to establish objective assessment techniques for consumer sensory experience. The food industry has been expecting to be able to replace consumer sensory analysis with simple instrumental measurement techniques, but the results have not been significant so far. Based on the above discussion, a few specific examples are shared below.
(1) Multiple sensory stimuli and their interaction
It is an undisputed fact that there are multiple sensory stimuli, including physical, chemical, optical, acoustic, etc. It is well established that a person can have a corresponding sensory experience to individual sensory stimuli, forming the famous sensory laws such as Weber, Fechner, Stevens, etc. However, the reality is that multiple stimuli are often present at the same time during eating and drinking, thus generating interactions of multiple stimuli and thus sensory experiences that do not correspond directly to the individual stimuli [6, 7]. As shown in Figure 2, sensory stimuli C1, C2, and C3, may produce corresponding sensory experiences G1, G2, and G3, but more often produce sensory properties Ga, Gb, and Gc that do not correspond directly to the stimuli.Many researchers in sensory science have made different hypotheses about the interaction process of multiple sensory stimuli, and many different views exist. For example, is it a single step from stimulus to sensory experience or multiple steps? If it is a multi-step process, at which stage does the sensory interaction (or derivation) occur? Does the sensory stimulus interact to become another stimulus (e.g., a combination of stimuli C1, C2, and C3 becomes stimuli Ca, Cb, and Cc), or does the stimulus information interact and derive during information processing in the brain (e.g., G1, G2, and G3 interact and derive to become Ga, Gb, and Gc)? What is the physical model of sensory interaction, is it a simple algebraic superposition or is it based on complex derivative functions? (see Figure 2)
Figure 2. Interactions in the case of multiple stimuli and possible sensory derivations. Multiple stimuli can produce multiple corresponding sensory experiences, but often produce derived sensory properties that do not correspond directly to the individual stimuli.
(2) The nature and function of oral fluid laminae
The oral fluid layer is a layer of mucus adsorbed on the surface of the oral cavity, which serves to moisten and protect the surface tissues of the oral cavity, wrapping around the sensory receptors, between the food mass and the surface of the oral cavity during eating and drinking, becoming a de facto third phase between the food mass and the surface tissues of the body (see Figure 3). The oral fluid lamina consists mainly of salivary components, but there are increasing indications that the oral lamina differs significantly from saliva in terms of composition, microstructure, interface and colloidal properties [8].
Figure 3 During eating, broken food particles are moistened and wrapped by saliva to form food masses with some cohesion, which are separated from the oral surface (in this figure, the tongue surface with papillae) by the oral fluid laminae.
At present, our preliminary understanding of the oral fluid layer is mainly in two aspects. One is its lubricating function. This is the reason why oral friction studies have received a lot of attention in recent years. The oral lamina can eliminate the pain caused by the friction between the tongue and other oral surfaces during speech, allowing the tongue to shape freely and produce a variety of beautiful sounds and tones. For eating and drinking, the oral fluid layer serves to reduce the friction between the food mass and the oral surface to reduce the abrasion and burning pain of the tongue surface, while on the other hand, the oral fluid layer also ensures the tongue's ability to effectively manipulate the food mass to ensure effective chewing and safe swallowing. Theories and experiments on oral soft friction have been reported in recent years in a series of literature [9, 10].
Another important perception of oral fluid thinning is the identification of food astringency mechanisms. Astringency was once thought to be a taste (called astringency) that was a chemical sensation. It is now clear that astringency is actually a tactile sensation, caused by the exposure of the tongue surface due to the precipitation of constituent proteins in the oral lamina, which leads to a change in tactile sensation. It is manifested in a significant increase in the coefficient of friction of the oral surface [11].
Matter migration control is another very important property of the oral fluid laminae that directly affects the taste as well as the odor sensation of foods. Traditional food flavor studies have basically defaulted to the idea that flavor components directly contact oral receptors once they are released from food, ignoring the key controlling factors such as solubilization of flavor small molecules in the laminae, interaction with structural components of the laminae, and migration in the laminae. Accurate interpretation of the migration mechanism in the oral lamina is essential for oral sensory perception studies of food flavors, and is a very important guide for the design of reduced sugar and salt foods.
3. The main challenges of current sensory science research
The current challenges of sensory science research can be considered from two perspectives: breakthroughs in the basic theory of sensory science research and the technological needs of the food industry. Although sensory science research has made great progress after more than half a century of development and formed a basic food sensory theory system, the direction of advancement and how to find the next theoretical breakthrough have become the confusion of many sensory science researchers. The authors believe that new breakthroughs in sensory science research should be considered in the following areas: (1) the eating experience has obvious dynamic characteristics, how to understand and control the dynamic changes of sensory stimuli during the eating process, how to interpret the changes of food microstructure and the interaction between food and saliva during the eating process to guide the optimal design of food structure; (2) the receptor principle of sensory stimuli, how to understand the transformation of sensory (2) the receptor principle of sensory stimuli, how to understand the transformation of sensory stimuli to sensory signals and the underlying physical and physiological principles; (3) the brain synthesis mechanism of sensory information and its psychological and neuroscientific principles; (4) sensory pleasure as one of the intrinsic drivers of human diet, how to understand the brain reward mechanism of diet and regulate human eating behavior. From the perspective of the technological needs of the food industry, there are two main challenges: first, how to accurately understand the combination and coordination of different sensory stimuli in food design to achieve the best pleasure effect; second, how to establish objective assessment techniques for consumer sensory experience. The food industry has been expecting to be able to replace consumer sensory analysis with simple instrumental measurement techniques, but the results have not been significant so far. Based on the above discussion, a few specific examples are shared below.
(1) Multiple sensory stimuli and their interaction
It is an undisputed fact that there are multiple sensory stimuli, including physical, chemical, optical, acoustic, etc. It is well established that a person can have a corresponding sensory experience to individual sensory stimuli, forming the famous sensory laws such as Weber, Fechner, Stevens, etc. However, the reality is that multiple stimuli are often present at the same time during eating and drinking, thus generating interactions of multiple stimuli and thus sensory experiences that do not correspond directly to the individual stimuli [6, 7]. As shown in Figure 2, sensory stimuli C1, C2, and C3, may produce corresponding sensory experiences G1, G2, and G3, but more often produce sensory properties Ga, Gb, and Gc that do not correspond directly to the stimuli.Many researchers in sensory science have made different hypotheses about the interaction process of multiple sensory stimuli, and many different views exist. For example, is it a single step from stimulus to sensory experience or multiple steps? If it is a multi-step process, at which stage does the sensory interaction (or derivation) occur? Does the sensory stimulus interact to become another stimulus (e.g., a combination of stimuli C1, C2, and C3 becomes stimuli Ca, Cb, and Cc), or does the stimulus information interact and derive during information processing in the brain (e.g., G1, G2, and G3 interact and derive to become Ga, Gb, and Gc)? What is the physical model of sensory interaction, is it a simple algebraic superposition or is it based on complex derivative functions? (see Figure 3)
Figure 2. Interactions in the case of multiple stimuli and possible sensory derivations. Multiple stimuli can produce multiple corresponding sensory experiences, but often produce derived sensory properties that do not correspond directly to the individual stimuli.
(2) The nature and function of oral fluid laminae
The oral fluid layer is a layer of mucus adsorbed on the surface of the oral cavity, which serves to moisten and protect the surface tissues of the oral cavity, wrapping around the sensory receptors, between the food mass and the surface of the oral cavity during eating and drinking, becoming a de facto third phase between the food mass and the surface tissues of the body (see Figure 3). The oral fluid lamina consists mainly of salivary components, but there are increasing indications that the oral lamina differs significantly from saliva in terms of composition, microstructure, interface and colloidal properties [8].
Figure 3 During eating, broken food particles are moistened and wrapped by saliva to form food masses with some cohesion, which are separated from the oral surface (in this figure, the tongue surface with papillae) by the oral fluid laminae.
At present, our preliminary understanding of the oral fluid layer is mainly in two aspects. One is its lubricating function. This is the reason why oral friction studies have received a lot of attention in recent years. The oral lamina can eliminate the pain caused by the friction between the tongue and other oral surfaces during speech, allowing the tongue to shape freely and produce a variety of beautiful sounds and tones. For eating and drinking, the oral fluid layer serves to reduce the friction between the food mass and the oral surface to reduce the abrasion and burning pain of the tongue surface, while on the other hand, the oral fluid layer also ensures the tongue's ability to effectively manipulate the food mass to ensure effective chewing and safe swallowing. Theories and experiments on oral soft friction have been reported in recent years in a series of literature [9, 10].
Another important perception of oral fluid thinning is the identification of food astringency mechanisms. Astringency was once thought to be a taste (called astringency) that was a chemical sensation. It is now clear that astringency is actually a tactile sensation, caused by the exposure of the tongue surface due to the precipitation of constituent proteins in the oral lamina, which leads to a change in tactile sensation. It is manifested in a significant increase in the coefficient of friction of the oral surface [11].
Matter migration control is another very important property of the oral fluid laminae that directly affects the taste as well as the odor sensation of foods. Traditional food flavor studies have basically defaulted to the idea that flavor components directly contact oral receptors once they are released from food, ignoring the key controlling factors such as solubilization of flavor small molecules in the laminae, interaction with structural components of the laminae, and migration in the laminae. Accurate interpretation of the migration mechanism in the oral lamina is essential for oral sensory perception studies of food flavors, and is a very important guide for the design of reduced sugar and salt foods.
(3) Mechanism of postnasal olfactory sensory
The existence of postnasal olfactory odor perception has been confirmed by many studies and is generally accepted by the academic community [12, 13]. The importance of the postnasal olfactory senses also lies in their potential influence on the taste senses, and there is growing evidence that nasal aroma sensation during eating strongly influences or alters the taste sensations in the mouth. The mechanism of nasal sniffing, however, is still obscure. Many studies have defaulted to the transfer of odor molecules during postnasal sniffing as a simple process of material migration from the oral cavity to the nasal cavity by pulmonary respiration (as shown in Figure 4a). If the transfer of odor molecules is so simple, there is every reason to believe that the stimulation of odor molecules in the nasal cavity should have a strong "yes-no" rhythm with pulmonary breathing (as shown in Figure 4b). That is, when exhaling, the odor molecules released from the mouth enter the nasal cavity with the pulmonary airflow, thus producing the aroma sensation; while when inhaling, the air is inhaled from outside the body, and there should be no odor perception at this time. However, our personal experience tells us that there is no such rhythmic switching of the postnasal olfactory senses, but rather a continuous and sustained sensation. This indicates that there is some kind of buffering or relaxation of odor components in the postnasal sensory process. What is the mechanism behind this phenomenon? Is it influenced by the physical mechanism of molecular migration or is it due to the physiological relaxation of the nasal odor receptors? This is a very interesting question, the answer of which can reasonably explain the control mechanism of the postnasal olfactory senses during the diet, and also provide reliable theoretical and technical support to enhance the postnasal olfactory senses in food industry product design.
Figure 4. Postnasal olfactory odor perception. (a) Migration of odor molecules from the oral cavity to the nasal cavity; (b) According to the theory that pulmonary respiration brings odor molecules into the nasal cavity, postnasal olfactory odor perception should have an "on-off" characteristic.
(4) Development of bionic sensing technology
The human perception of food is carried out through the sensory organs, among which the perception of smell and taste is mainly achieved by the specific binding of odor-presenting substances with the corresponding receptors. Most of the common intelligent sensory systems on the market today are based on metal oxide or electrochemical sensors, which respond to certain characteristic structural components mainly by detecting the chemical properties of the sample rather than the odor or taste properties, regardless of whether these components are aromatic or not, and regardless of the flavor presented by the mixed components. With the rapid development of receptor isolation and purification techniques and biosensing technologies, food sensing processes have been studied based on receptors under ex vivo conditions. For example, sensors prepared based on fresh taste receptors are able to produce a rapid response to the fresh taste substance (MSG) in a relatively short period of time and the signal intensity is synergistically potentiated by IMP, indicating that the receptors still maintain biological properties consistent with those of animal taste receptors under ex vivo conditions and can be used to study food perception processes in vitro [14]. Although there are currently bionic sensors for single-component or few-component interaction detection, these sensors are still many problems away from practical applications. The short survival time of the receptor in vitro limits the life cycle and lifetime of the prepared sensors; the receptor-ligand binding process is very fast and the signal changes are very weak, and there is a shortage of methods and equipment related to the accurate acquisition of sensor signals; the detection accuracy of bionic sensors is much higher than that of the human body, and their effective detection range is narrower and cannot be applied to the detection of food-grade samples; how to simulate the human body with a small number of bionic sensors The detection accuracy of bionic sensors is much higher than that of human body, and their effective range is narrower than that of food-grade samples. By solving the above problems, we can greatly promote the development of bionic sensors, which in turn can provide technical support for in vitro research on food sensory processes and the development of corresponding intelligent sensing devices.
4. Prospects of food sensory science research
In the past years, the main concerns of international and domestic food sensory science research can be broadly summarized into two aspects: first, the analysis of food microstructure properties and composition, food flavor researchers are more concerned with food composition, while food texture researchers are more concerned with the microstructure properties of food. This type of research focuses on the formation, content, characteristics, and interactions with carriers of food structure and flavor components. A series of physical analysis techniques including chromatography, mass spectrometry, microstructural analysis, and mechanical property determination have also been established in the process. After years of efforts, the food sensory research focusing on composition and microstructure analysis should be said to have reached a relatively mature level, which is well suited to meet the needs of the food industry. Second, a series of more objective and reliable assessment terms and methods for human sensory experience, commonly known as sensory analysis, have been established, including personnel screening, training, scenario control, testing methods, and data analysis. Food microstructure analysis and compositional analysis provide a solid material basis for sensory science research, while the standardization of sensory assessment terms and methods provides objective and comparable measures of human experience. However, the research ideas and logic of these two concerns do not touch the core essence of human senses, and cannot explain the great individual differences among consumers, nor the sensory differences caused by situational changes in individuals themselves.
In response to these limitations, food sensory science research, with food-human interaction as the core concern, has received widespread academic attention in recent years. In this context, food oral processing research has become an emerging frontier in the field of food science [15, 16], aiming to reveal the underlying mechanisms of food sensory experience, including food physics, human (oral) physiology, sensory psychology, and neurological principles of the brain. Based on such perceptions, Figure 5 shows multiple interfaces in the human food sensory perception process, which are both physical and virtual [17]. Many scientific issues and questions are embedded in these interfaces. If our sensory research can cut through these interfaces, we should be able to understand and discover well the relevant principles that determine the interaction between food and human body and achieve new breakthroughs.
Figure 5. Oral dynamics of dietary and sensory processes and the corresponding interfaces. The right side shows the multidimensional dynamics of eating processes, while the left side shows some physical or virtual interface behaviors associated with these processes. Within these interface behaviors, numerous dietary and sensory principles are embedded. This figure is based on a modification of the literature [17].
Multidisciplinary intersection is a sure way to achieve new breakthroughs in food sensory research. Figure 6 lists some of the relevant supporting disciplines for food sensory science, ranging from food physics and food materials science, to sensory physiology, sensory psychology, and brain neuroscience. The rise of food oral processing research is a clear example of multidisciplinary intersection. The essential principles of food sensory can be studied and revealed in a comprehensive and multi-layered manner only by cutting from different perspectives such as the interaction between food materials and human physiology/psychology. At the same time, it is undeniable that philosophy, aesthetics, sociology, etc. also have direct or indirect influence on food and senses.
As the subject of food perception, human is easily influenced by physiological, psychological, cultural, environmental and other factors, thus causing inaccuracy in the results of artificial sensory evaluation. With the rapid development of bionic technology, the application of bionic sensors in food perception evaluation has gained increasing attention. Food perception process research is carried out in vitro to enrich food perception theory from a macroscopic perspective on big data analysis, food preference evaluation, etc.
Figure 6. Multidisciplinary intersection is the future of food sensory science research. The figure lists the relevant supporting disciplines and research areas for food sensory science research. From the intersection of these fields, food oral processing research is formed.
This paper presents some thoughts on some basic issues of food sensory research, which are only based on the author's rudimentary understanding. The views and discussions in this paper are not intended to give answers to these questions, but to generate more discussions and thoughts among colleagues, so as to jointly promote the development of food sensory science in China, and make China's sensory science research go to new heights and achieve the goal of leading international research as soon as possible. The goal is to promote the development of food sensory science in China, so that China's sensory science research can reach new heights and achieve the goal of leading the world.
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