Food oral processing—A review

Food oral processing is an essential procedure not only for the consumption and digestion of foods but also for the appreciation and pleasure of food texture and food flavour. The consumption of a food inside mouth involves various oral operations, including first bite, chewing and mastication, transportation, bolus formation, swallowing, etc. Exact mechanisms and governing principles of these oral operations are still not fully understood, despite of continuous efforts made by scientists from food, psychology, physiology, dental and clinical studies, and other disciplines. This article reviews recent progresses and literature findings about food processing and transformation in mouth, with particular attention on the physiology and rheology aspects of oral operations. The physiological behaviour of human's oral device is discussed in terms of biting capability, tongue movement, saliva production and incorporation, and swallowing. The complexity of oral processing is analysed in relation to the rheology and mechanical properties of foods. The swallowing and oral clearing process is also examined for its criteria, triggering mechanism, bolus deformation, and the rheology of swallowing.     

In-mouth mechanisms leading to flavor release and perception

During eating, foods are submitted to two main oral processes-chewing, including biting and crushing with teeth, and progressive impregnation by saliva resulting in the formation of a cohesive bolus and swallowing of the bolus. Texture influences the chewing behavior, including mastication and salivation, and in turn, these parameters influence texture perception and bolus formation. During this complex mouth process, flavor compounds are progressively released from the food matrix. This phenomenon is mainly dependent on the food texture, the composition and in-mouth breakdown, and on saliva impregnation and activity, but an individual's anatomical and physiological aspects characteristics should also be taken into account. This article reviews the knowledge and progresses on in-mouth processes leading to food breakdown and flavor release and affecting perception. Relationships between food texture and composition, food breakdown, oral physiology, and flavor release are developed and discussed. This review includes not only the mechanical aspects of oral physiology but also the biological aspects such as the influence of saliva composition, activity, and regulation on flavor perception. In vitro and in silico approaches are also described.     

The role of oral processing in dynamic sensory perception

Food oral processing is not only important for the ingestion and digestion of food, but also plays an important role in the perception of texture and flavor. This overall sensory perception is dynamic and occurs during all stages of oral processing. However, the relationships between oral operations and sensory perception are not yet fully understood. This article reviews recent progress and research findings on oral food processing, with a focus on the dynamic character of sensory perception of solid foods. The reviewed studies are discussed in terms of both physiology and food properties, and cover first bite, mastication, and swallowing. Little is known about the dynamics of texture and flavor perception during mastication and the importance on overall perception. Novel approaches use time intensity and temporal dominance techniques, and these will be valuable tools for future research on the dynamics of texture and flavor perception.     

Texture and texture assessment of thickened fluids and texture‐modified food for dysphagia management

Thickened fluids and texture‐modified foods are commonly used in the medical management of individuals who suffer from swallowing difficulty (known as dysphagia). However, how to reliably assess texture properties of such food systems is still a big challenge both to industry and to academic researchers. This article aims to identify key physical parameters that are important for objective assessment of such properties by reviewing the significance of rheological or textural properties of thickened fluids and texture‐modified foods for swallowing. Literature reviews have identified that dominating textural properties in relation to swallowing could be very different for thickened fluids and for texture‐modified foods. Important parameters of thickened fluids are generally related with the flow of the bolus in the pharyngeal stage, while important parameters of texture‐modified foods are generally related with the bolus preparation in the oral stage as well as the bolus flow in the pharyngeal stage. This review helps to identify key textural parameters of thickened fluids and texture‐modified foods in relation to eating and swallowing and to develop objective measuring techniques for quality control of thickened fluids and texture‐modified foods for dysphagia management.     

The determining role of bolus rheology in triggering a swallowing

Swallowing is the final stage of an eating process. Even though individuals know exactly when and how to swallow, the controlling mechanisms and the determining criteria of bolus swallowing are still not yet clear. One hypothesis is that bolus rheology, i.e. its flow-ability and stretch-ability, determines the triggering of a swallowing and the main aim of this work was to test this hypothesis. A wide range of fluid foods, including 18 commercial products and 10 lab-constituted foods, were examined for easiness of swallowing by a panel of 19 subjects. Oral residence time, defined as the time from the ingestion till the completion of swallowing, was determined for each eating process. It was observed that the oral residence time had a linear relationship with the sensed difficulty of swallowing. That is a food sensed difficult-to-swallow tends to stay longer in the oral cavity. Rheological properties (both shear and stretching flow) of these foods and their simulated boluses (mixture of food and simulated saliva) have also been determined at body temperature. The apparent shear viscosity showed a positive correlation with the sensed difficult of swallowing. However, the stretching behaviour of a fluid food, characterised by the maximum stretching force and the work of stretching showed much improved correlation to the sensory perceived easiness of swallowing. It was concluded that bolus rheology, in particular its extensional stretch-ability, had the most important influence on the ease of swallowing.     

Swallowing profiles of food polysaccharide gels in relation to bolus rheology

Swallowing profiles of food polysaccharide gels were investigated in relation to bolus rheology. Polysaccharide gel from either gellan gum or a mixture of gellan gum and psyllium seed gum was used as a model food. Acoustic analysis and sensory evaluation were carried out to investigate the swallowing profiles using the same human subjects. Model bolus was prepared through instrumental mastication using a mechanical simulator to mimic the action of the human jaw in the presence or absence of artificial saliva and was subjected to dynamic viscoelasticity measurements to investigate the rheological properties. Bolus from the binary gel was shorter in time required to transfer through the pharyngeal phase due to mass flow and was scored higher in sensory perceived cohesiveness (bolus forming) than that from gellan gum gel. Model bolus from the binary gel showed a rheologically weak gel (or structured fluid) behavior and was higher in structural homogeneity than that from gellan gum gel. Also, dynamic viscoelasticity parameters of the binary gel were less dependent on the addition level of saliva. Results indicate that the viscoelasticity balance is a key for texture design of dysphagia foods in relation to the saliva miscibility.     

Characterization of bread breakdown during mastication by image texture analysis

The methods currently used to characterise food breakdown during mastication are not easily applicable to cohesive and heterogeneous products such as white bread (baguettes). During this study, we investigated the applicability of image texture analysis to characterising the kinetics of bread bolus formation during chewing. Food boluses were collected from five subjects chewing four different breads after 10, 20 and 30 chewing cycles or at swallowing. Images were acquired and analysed using the Grey level co-occurrence matrix (GLCM) method. Food boluses were successfully discriminated: 60–73% of the images were correctly classified into their respective chewing cycles. Incorrect classifications arose from overlapping between subsequent cycles. Among the texture features the contrast was identified as being the best marker of food degradation. Different kinetics of bolus formation were observed between breads. This method revealed specific patterns of food degradation between subjects, which could be explained by their mastication behaviour and chewing efficiency.     

常见亲水胶体对烘焙食品品质影响的研究进展（网络首发、推荐阅读）

亲水胶体具有良好的功能特性,如改善食品的乳化、胶凝、溶解性和质构等特性。在烘焙食品中,亲水胶体用于改善面团、面包和蛋糕特性,提高感官质量以及延长食品货架期。已经有研究报道了亲水胶体在面包、饼干、蛋糕和面食制备中的潜在用途。综述常见的亲水胶体（黄原胶、瓜尔胶、阿拉伯胶、K-卡拉胶、刺梧桐胶、海藻酸盐、甲基纤维素、羧甲基纤维素和羟丙基甲基纤维素）对焙烤食品的流变学、理化、质构以及其它品质特性的影响,亲水胶体的加入使得产品的颜色、外观、风味和整体可接受性显著改善。     

The contribution of texture contrasts and combinations to food acceptance across cultures

Texture has long been considered an important attribute for food acceptance. However, which specific textural characteristics contribute to overall acceptance of a food is not well understood. It has been suggested that texture contrasts and combinations are a universal feature in giving foods a desirable texture, yet this notion is largely based upon anecdotal data. This study uses multiple survey research methods to assess the importance of texture contrast and combinations across cultures (Poland, U.S.A., and Singapore). Participants (N = 288) completed a survey that included overt measures of food texture contrast importance as well as free response questions regarding texture. The overall importance of texture for food liking was not different across the populations. However, the participants from Singapore and Poland gave more importance to a desirable food having multiple textures than the U.S.A. cohort. When looking at free responses, participants were twice as likely to mention combinations (multiple textures) with a texture contrast when describing foods they liked, in comparison to foods they disliked. This was observed across all three cultures. However, the type and quantity of texture terms used within combinations were different among cultures. For instance, Singaporeans enjoyed more texturally diverse food combinations than the other two cultures. These findings highlight the importance of texture contrasts and combinations in three distinct cultures.     

Particle size distribution in the food bolus after mastication of natural foods

The main goal of mastication is to prepare a food bolus suitable for deglutition. The bolus preparation consists in food breakdown and processing during which oral sensations are generated. This study was performed to examine the particle size distribution in the bolus formed by chewing 10 natural foods. Ten young subjects with normal dentition were asked to chew the food and to expectorate the bolus just before swallowing, while masticatory parameters were recorded. The particle size distribution of each bolus was evaluated by wet sieving. The number of cycles, sequence duration and masticatory frequency varied among subjects and foods. The particle size distributions differed among foods but were similar among subjects. The median particle size d₅₀ gave a range from 0.82 to 3.04 mm allowing a food classification based on the state of the bolus. The d₅₀ value reflected the fracturability and may be useful to describe food behaviour in the mouth during bolus preparation.     

The effect of inhomogeneous quinine and hydrocolloid distributions on the bitterness of model gels

This study investigated the effect of inhomogeneous distributions of quinine on bitterness intensity of gelatine–agar composite gels. It also investigated the effect of inhomogeneous distributions of the gel’s hydrocolloid constituents (the gelatine and agar) on the bitterness intensity of the quinine. Fifty-two screened subjects participated in four paired comparison tests comparing inhomogeneous designs of quinine (with a homogeneous hydrocolloid distribution) and inhomogeneous designs of the hydrocolloids (with a homogeneous quinine distribution), against a homogeneous control of identical overall quinine and hydrocolloid composition. Using the same gel designs, a mastication trial was undertaken where ten subjects were asked to chew each gel system until the point of swallowing, and eleven subjects participated in a time-intensity trial where bitterness intensity was monitored during mastication and after expectoration. Paired comparison tests showed that the inhomogeneous distribution of quinine increased bitterness intensity, while inhomogeneous distributions of the hydrocolloids did not. Mastication was not influenced by changes in the distribution of quinine or the hydrocolloids. Time intensity curves showed the gels having an inhomogeneous distribution of quinine had greater bitterness intensity throughout mastication, however no differences in bitterness intensity were observed between any gel designs in the latter stages of aftertaste measurements. Time intensity curves also showed a slight delay in time to maximum bitterness intensity for the gels with inhomogeneous distributions of hydrocolloids. Results suggest a homogeneous distribution of bitter compounds is the most suitable structure for minimising bitterness perception.     

STUDY OF FOOD TEXTURES BY RECORDING OF CHEWING AND SWALLOWING MOVEMENTS

Abstract Chewing and swallowing patterns were recorded in three subjects eating freely pieces of foods of various initial textures in an attempt to assess objectively these food textures as sensory stimuli in the mouth. In each phase of masticatory and swallowing movements corresponding to each piece of food, variations were noted differentiating the 16 textures tested. The number of masticatory movements, the time of mastication up to complete swallowing, the time course of the force of mastication and the number and distribution of swallowing movements were found to be the most discriminating parameters. In considering them, foods might be placed on a scale from hard and dry to soft and fluid textures. The results confirm the validity of recording chewing and swallowing movements as a new method for describing the true dimensions of oral sensory stimulations by food textures.     

RHYTHMIC AND IRREGULAR MOVEMENT OF THE FIRST MOLAR WHILE EATING FOODS WITH DIFFERENT TEXTURES

The three-dimensional movement of a tooth, any tooth, while naturally eating, was measured by an apparatus developed in our laboratory. The movement of the first molar on the usually used side is reported here. The mastication movements are divided into two parts, namely the rhythmical chewing period during which there are mastication pressure loads on the molar and the irregularly pulsated moving period in preparation for the swallowing followed by the rhythmical one during which there is no more pressure on it. The amplitudes of the up and down movements of the molar are 10–22mm for the rhythmical chewing period which are bigger than those for the irregularly moving period. The rhythmical chewing periods are distributed around 10–40 s depending on 14 kinds of food texture, and also on the size of the food, in a fairly similar manner for the participants. The period is longer for tough foods and bigger samples. The irregularly pulsated moving periods are widely distributed, 2–45s, and depend both on the food texture and on the participant. The irregular moving periods are longer for foods which scatter in the mouth or adhere to the teeth when chewing. The ingestion difficulty of the food was divided into two groups. One is where it is difficult to break down the food with the teeth and the other is where it is difficult to prepare for swallowing.     

甘薯泥作为吞咽障碍食品的研究进展

质构改良食品作为吞咽障碍患者的安全食品,具有质地柔软、吞咽安全及满足患者营养需求的特点,不同国家对吞咽障碍食品的分级各不相同,大多都聚焦于食品本身的质构特性。近些年,吞咽障碍患者的饮食安全备受关注,开发吞咽障碍食品的研究逐渐增加。甘薯泥是新鲜甘薯经过一系列加工制成的泥状食品,保留了甘薯中绝大多数营养物质,具有柔软、营养成分高的特点,是适合吞咽障碍患者食用的质构改良食品的优质原料。但甘薯泥的质构特性受到多方面因素的影响,例如加工原料、加工工艺以及贮藏条件等,限制甘薯泥作为吞咽障碍食品在食品领域的应用。该文将对质构改良食品的分类、甘薯泥加工工艺及影响甘薯泥质构特性的研究进行综述,旨在为适合吞咽障碍患者食用的甘薯泥产品的研发及应用提供理论依据。     

SPEECH ANALYSIS TECHNIQUES: A POTENTIAL MODEL FOR THE STUDY OF MASTICATION SOUNDS

Acoustical characteristics of mastication sounds may provide information regarding the texture of food: however, methods are needed to study these sounds. Spectrographic analysis, a speech analysis technique, is a potential method for the study of mastication sounds. To illustrate this technique, spectrograms and waveforms are presented for sounds of foods that are reference standards for the hardness and fracturability scales of the Texture Profile Method. Spectrograms also are presented for the sounds of 3 vowels. Acoustical characteristics of these 2 types of sounds are described and compared from the spectrograms and waveforms.     

Rheological,tribological and sensory attributes of texture-modified foods for dysphagia patients and the elderly: A review

Texture-modified foods (TMFs) and thickened fluids have been used as a therapeutic strategy in the management of food intake in the elderly and people with dysphagia. Despite recent advances in describing rheological features of TMFs for dysphagia management, there is still paucity of research regarding the sensory attributes, therapeutic thickness levels and swallowing safety of these foods. Additionally, the relationship between mechanical and structural properties of TMFs throughout the oral processing is not yet fully understood. The present review discusses several properties of food boluses that are important during oral processing to allow for safe swallowing. Dynamic changes that occur during oral processing of TMFs will be reviewed. The use of hydrocolloids to improve the cohesiveness of TMFs and how this impacts the sensory properties of TMFs will be also discussed. Additionally, this review will suggest potential new research directions to improve textural and sensory properties of TMFs.     

Bolus Formation and Disintegration during Digestion of Food Carbohydrates

Abstract: The first step in the digestion process is mastication, or chewing, when food is broken down, lubricated with saliva, and formed into a cohesive mass known as the food bolus. Upon swallowing, the bolus moves to the stomach and undergoes further breakdown during gastric digestion. The subject of this review is the formation of the food bolus and its subsequent breakdown in the stomach. Bolus formation has been widely studied, especially in terms of food particle size and lubrication. However, information about bolus disintegration is limited, and this review focuses on the breakdown of bread and starch‐based foods. Bolus formation and disintegration are key steps in the overall digestion process, as they control the rate at which ingested food components and nutrients are absorbed and released into the body. Information on the rate kinetics of bolus disintegration is necessary in developing a quantitative understanding of the food digestion process.     

Hydrocolloids in fried foods. A review

Many food ingredients and additives can be used to improve fried food, but hydrocolloids are the principal category of functional agents that have been used for the past forty years. Hydrocolloids play two main roles in fried food development. One is to form a fine ‘invisible’ coating, practically on their own, when their main purpose is to avoid excessive oil absorption during the pre-frying and frying processes. In the other, when they are added to the batter among its other ingredients, they are used to avoid oil absorption too, but they also act as viscosity control agents, improve adhesion, pick-up control and freeze-thaw stability or help to retain the crispness of the battered/breaded fried foods. This article reviews the wide range of functions that hydrocolloids perform in fried foods.     

Food physics and oral physiology

This paper is a review of mastication and swallowing, prepared for the Food Summit on “Food Texture: Perception and Measurement”, organized by the Wageningen Centre for Food Sciences (WCFS) from 28 November–1 December, 1999. The paper emphasizes models that could link the physical state of food to oral forces acting on it. It deals with the processing of solid foods because (1) theory seems better advanced in this area and (2) the paper by van Vliet (this issue) deals with the area of liquids and semi-solids.     

EFFECTS OF PHYSICAL PROPERTIES AND ORAL PERCEPTION ON TRANSIT SPEED AND PASSING TIME OF SEMILIQUID FOODS FROM THE MID-PHARYNX TO THE HYPOPHARYNX

The results of two sensory analyses, using healthy young individuals as assessors and semiliquid foods with markedly different physical properties as samples, were compared. One analysis required the assessors to perceive the food texture by oral perception alone and to use it as a basis for predicting the ease of swallowing of the bolus samples (i. e., the mobility of the samples through the pharynx) without actually swallowing the samples. The other analysis required the assessors to evaluate the mobility of the bolus samples through the pharynx, by actually swallowing them. Comparison of the results implied that human beings predict how easy it is to swallow a bolus (i. e., the mobility of the bolus through the pharynx) by perceiving in the oral cavity the texture of the food. Examinations were also made on the relationship between the evaluation of mobility of the bolus through the pharynx obtained by sensory analyses, and the transit speed and passing time of the bolus samples obtained by videomanofluorography. It was recognized that the front end speed was fast for semiliquid food samples that were soft and easy to swallow (and therefore easy to move through the pharynx), whereas the front end speed was slow for semiliquid food samples that were hard and difficult to swallow (and therefore perceived as being difficult to move through the pharynx.) These findings suggest that human beings' perception of the ease of swallowing of semiliquid food is closely related to the front end speed of the bolus. No significant difference was found among samples, either in the tail end speed of the bolus samples, or in the passing time from the front end to the tail end of the bolus samples. These results imply that, through some kind of swallowing efforts, healthy individuals are controlling the passing time through the pharynx of boluses with markedly diflerent physical properties, so that the time remains constant.