A Proposed Food Breakdown Classification System to Predict Food Behavior during Gastric Digestion

The pharmaceutical industry has implemented the Biopharmaceutics Classification System (BCS), which is used to classify drug products based on their solubility and intestinal permeability. The BCS can help predict drug behavior in vivo, the rate‐limiting mechanism of absorption, and the likelihood of an in vitro–in vivo correlation. Based on this analysis, we have proposed a Food Breakdown Classification System (FBCS) framework that can be used to classify solid foods according to their initial hardness and their rate of softening during physiological gastric conditions. The proposed FBCS will allow for prediction of food behavior during gastric digestion. The applicability of the FBCS framework in differentiating between dissimilar solid foods was demonstrated using four example foods: raw carrot, boiled potato, white rice, and brown rice. The initial hardness and rate of softening parameter (softening half time) were determined for these foods as well as their hypothesized FBCS class. In addition, we have provided future suggestions as to the methodological and analytical challenges that need to be overcome prior to widespread use and adoption of this classification system. The FBCS gives a framework that may be used to classify food products based on their material properties and their behavior during in vitro gastric digestion, and may also be used to predict in vivo food behavior. As consumer demand increases for functional and “pharma” food products, the food industry will need widespread testing of food products for their structural and functional performance during digestion.     

Particle Size Distribution of Brown and White Rice during Gastric Digestion Measured by Image Analysis

The particle size distribution of foods during gastric digestion indicates the amount of physical breakdown that occurred due to the peristaltic movement of the stomach walls in addition to the breakdown that initially occurred during oral processing. The objective of this study was to present an image analysis technique that was rapid, simple, and could distinguish between food components (that is, rice kernel and bran layer in brown rice). The technique was used to quantify particle breakdown of brown and white rice during gastric digestion in growing pigs (used as a model for an adult human) over 480 min of digestion. The particle area distributions were fit to a Rosin–Rammler distribution function. Brown and white rice exhibited considerable breakdown as the number of particles per image decreased over time. The median particle area (x₅₀) increased during digestion, suggesting a gastric sieving phenomenon, where small particles were emptied and larger particles were retained for additional breakdown. Brown rice breakdown was further quantified by an examination of the bran layer fragments and rice grain pieces. The percentage of total particle area composed of bran layer fragments was greater in the distal stomach than the proximal stomach in the first 120 min of digestion. The results of this study showed that image analysis may be used to quantify particle breakdown of a soft food product during gastric digestion, discriminate between different food components, and help to clarify the role of food structure and processing in food breakdown during gastric digestion.     

Bioaccessibility of carotenoids from plant and animal foods

The frequent consumption of carotenoid-rich foods has been associated with numerous health benefits, such as the supply of provitamin A. To exert these health benefits, carotenoids need to be efficiently liberated from the food matrix, micellized in the small intestine, taken up by the enterocytes and absorbed into the human blood stream. Enormous efforts have been made to better understand these processes. Because human studies are costly, labor-intense and time-consuming, the evaluation of carotenoid liberation and micellization at the laboratory scale using simulated in vitro digestion models has proven to be an important tool for obtaining preliminary results prior to conducting human studies. In particular, the liberation from the food matrix and the intestinal micellization can be mimicked by simulated digestion, yielding an estimate of the so-called bioaccessibility of a carotenoid. In the present review, we provide an overview of the carotenoid digestion process in vivo, the currently used in vitro digestion models and the outcomes of previous bioaccessibility studies, with a special focus on correlations with concomitantly conducted human studies. Furthermore, we advocate for the on-going requirement of better standardized digestion protocols and, in addition, we provide suggestions for the complementation of the acquired knowledge and current nutritional recommendations. © 2018 Society of Chemical Industry     

Simulating human carbohydrate digestion in vitro: a review of methods and the need for standardisation

Numerous in vitro carbohydrate digestion methods exist for analysis of the likely glycaemic properties of foods. Generally these methods encompass simulations of oral, gastric and intestinal digestion processes, but the way in which physiological conditions are implemented across methods differs considerably. Some differences are in the mode of comminution, inclusion and duration of a gastric digestion, and choice of amylolytic enzyme. Incubation temperature, pH, duration and stirring mode also differ between methods. Such differences, particularly the method used to mimic chewing, can have a substantial influence on the relative estimate of glycaemic potency for a given food. To achieve estimates of high predictive power, and global relevance, a validated, standardised in vitro digestion method must be developed. This article provides a systematic review of commonly used and referred to in vitro carbohydrate digestion methods. Methodological discrepancies between protocols are identified thus defining the route a systematic standardisation investigation should take.     

Advances in the in vitro digestion and fermentation of polysaccharides

In vitro digestion models are widely used to study the structural changes, digestion and release of food components under simulated gastrointestinal conditions. As compared to the in vivo digestion tests, the in vitro digestion reflects the digestion and utilisation of food after ingestion and has the advantages of being time consuming, inexpensive, reproducible and free from moral and ethical restrictions. This study reviewed the current research studies on the in vitro simulated digestion of polysaccharides conducted in the last 5 years and focused on the oral, gastric and intestinal digestion models, with the aim of providing a basis for the further testing of changes in the content, structure and active ingredients of polysaccharides before and after digestion.     

In vitro human digestion models for food applications

In vitro digestion models are widely used to study the structural changes, digestibility, and release of food components under simulated gastrointestinal conditions. However, the results of in vitro digestion models are often different to those found using in vivo models because of the difficulties in accurately simulating the highly complex physicochemical and physiological events occurring in animal and human digestive tracts. This paper provides an overview of current trends in the development and utilisation of in vitro digestion models for foods, as well as information that can be used to develop improved digestion models. Our survey of in vitro digestion models found that the most predominant food samples tested were plants, meats, fish, dairy, and emulsion-based foods. The most frequently used biological molecules included in the digestion models were digestive enzymes (pancreatin, pepsin, trypsin, chymotrypsin, peptidase, α-amylase, and lipase), bile salts, and mucin. In all the in vitro digestion models surveyed, the digestion temperature was 37 °C although varying types and concentrations of enzymes were utilised. With regard to digestion times, 2 h (the stomach, small intestine, and large intestine each) was predominantly employed. This survey enhances the understanding of in vitro digestion models and provides indications for the development of improved in vitro digestion models for foods or pharmaceuticals.     

In vitro digestibility of starch in cooked potatoes as affected by guar gum: Microstructural and rheological characteristics

Potatoes from different New Zealand cultivars (Nadine, Moonlight, Red Rascal, Agria) were analysed for starch digestibility in vitro (under simulated gastric and small intestinal conditions). The extent of starch hydrolysis (%) for all the potato cultivars ranged between 85% and 95% at the end of in vitro digestion. Nadine potatoes, which were waxy in texture, showed higher starch hydrolysis (%) whereas these levels did not differ significantly among the other three cultivars. Confocal laser scanning microscopy and scanning electron microscopy were performed on the digests in order to study the microstructural changes occurring during digestion in cooked potatoes. The micrographs clearly showed that starch was quickly hydrolysed by the enzymes present in simulated intestinal fluid (SIF) whereas the cell walls remained intact during simulated digestion process. Addition of guar gum (0.5%) to cooked potatoes reduced their starch hydrolysis (%) by ∼15% during the in vitro digestion. Online viscosity measurements were also performed on the cooked potatoes during simulated small intestinal digestion using a dynamic rheometer. Cooked potato viscosity dropped considerably upon the action of enzymes from SIF on starch as the digestion progressed. The presence of 0.5% guar gum facilitated the cooked potato matrix to maintain viscosity similar to undigested cooked potato sample throughout the in vitro digestion, which might have resulted in lower starch hydrolysis (%).     

Effects of simulated gastric and intestinal digestion on chitooligosaccharides in two in vitro models

Chitooligosaccharides (COS) with different degree of polymerisation (DP) have different physiological activities such as anti-tumour and anti-hyperlipidemia activities. However, the digestive process might lead to the change of DP of COS as well as cause the change of physiological activities in vivo. In this study, two in vitro digestion models (static and dynamic) were used to investigate digestion behaviours of COS and the influencing factors during digestion with or without food matrix. The results showed that COS with DP 2–5 were indigestible and COS with DP 6–10 degraded with time during gastric and intestinal digestion. Pepsin, pancreatin and lipase were the main factors leading to degradation. Food matrix could protect COS with DP 6–10 from degradation during gastric digestion. However, the degradation of COS with DP 6–10 accelerated and the degradation of COS with DP 5 occurred during intestinal digestion with food matrix due to pancreatin, lipase and bile salt.     

Effects of salt-induced changes in protein network structure on the properties of surimi gels: computer simulation and digestion study

Surimi is considered a new base ingredient in special dietary foods because of its excellent gel formation properties and nutritional value. Cross-linked network structures are the basis for the formation of protein hydrogels. In this work, protein network structure induced by NaCl was investigated to evaluate its effects on texture property and digestibility of surimi gels. Micro-protein frameworks were investigated by scanning electron microscope combined with computer simulation, which indicated that the network structure became fine and smooth as a result of salt treatment. The digestibility of surimi with NaCl was higher than that of blank samples in simulated gastric juice in first 30 min, whereas the digestibility showed no significant difference (P = 0.257) in intestinal juice after 180 min. This work aids in understanding of the contribution of salt to the mechanism of surimi gels formation, and its effects on digestion, thus supporting potential applications in special dietary food.     

Modelling the breakdown mechanics of solid foods during gastric digestion

Solid food disintegration within the stomach has a major role on the rate and final bioavailability of nutrients within the body. Understanding the link between food material properties and their behaviour during gastric digestion is key to the design of novel structures with enhanced functionalities. However, despite extensive research, the establishment of proper relationships has proved difficult. This work builds on the hypothesis that to bridge this knowledge gap a better understanding of the underlying mechanisms of food disintegration during digestion is needed. The purpose of this study is to propose a new protocol that, by uncoupling the physicochemical processes occurring during gastric digestion, allows for a more rigorous understanding of these mechanisms. Using steamed potatoes as a product model, this study aims to develop a viable methodology to characterize the role of gastric juice and compressive forces on the breakdown mechanics of solid foods during digestion. From a general viewpoint, this work not only reveals the importance of the parameter used to describe the size distribution of food particles on the interpretation of their breakdown behaviour, but also provides a new framework to characterize the mechanisms involved. Results also illustrate that food breakdown during gastric digestion might well not follow a unimodal behaviour, highlighting the need to characterize their performance based on parameters describing broad aspects of their particle size distribution rather than single point values. Arguably simplistic on its approach, this study illustrates how an improved understanding of the role of chemical and physical processes on the breakdown mechanics of solid foods can facilitate valid inferences with respect to their in-vivo performance during digestion. In particular, it shows that while the contraction forces occurring in the stomach can easily disintegrate the potato matrix at the molecular level, the continuous exposure to gastric juices will promote their disintegration into progressively smaller debris. A discussion on the challenges and future directions for the implementation of a more general and standardized protocol is provided. Not intended to reproduce the breakdown behaviour of foods during gastric digestion, but rather to characterize the mechanisms involved, the proposed protocol would open new opportunities to identify the material properties governing the performance of different foods upon ingestion.     

A cellulase digestion technique for predicting the dry matter digestibility of grasses

A digestion technique using a commercially-available crude cellulase preparation from Trichoderma viride is described. The enzyme showed cellulase, hemicellulase and proteolytic activity when tested on herbage or herbage polysaccharides. A high correlation (r = 0.92, P < 0.001, residual standard deviation 2.5) was found between a simple one stage enzyme digestion and in vivo dry matter digestibility for a range of grass species and varieties. In vitro dry matter digestibility and detergent fibre were also determined on the same samples and the results correlated with in vivo dry matter digestibility. The cellulase method is rapid and reproducible and particularly well suited for the evaluation of plant material in breeding programmes.     

Solvent extraction and in vitro simulated gastrointestinal digestion of phenolic compounds from purple sweet potato

The total content of phenolic compounds in purple sweet potato (PSP) was determined and the release of such compounds from PSP in gastrointestinal digestion was studied in vitro. The extraction conditions for the maximum recovery of free phenol (FP) and bound phenol (BP) from PSP were determined by response surface methodology (RSM). The maximum recovery of FPPSP was 14.16 ± 0.87 mg GAE per g short for dry weight (DW), which was obtained using 60% (v/v) ethanol maceration with a liquid–solid ratio of 57.21:1 (mL g⁻¹) at 51.93 °C for 2.12 h. The maximum recovery for BPPSP was 7.54 mg GAE per g DW, which was obtained upon hydrolysis with 1.87 mol L⁻¹ NaOH at a liquid–solid ratio of 35.93:1 (mL g⁻¹) for 4.74 h. The maximum phenolic content was released after 1 and 2 h for the in vitro gastric and intestinal digestion respectively. The release of the phenolics was promoted by pepsin and gastric acid during gastric digestion, while it was further promoted by trypsin during intestinal digestion.     

Sulphated and carboxymethylated polysaccharides from Lycium barbarum L. leaves suppress the gelatinisation,retrogradation and digestibility of potato starch

Processing starch with polysaccharides promotes broader applications, and it is important to consider all possible structural interactions among the molecular ingredients. In this study, polysaccharides isolated from Lycium barbarum L. were chemically modified by sulphation (SLP) and carboxymethylation (CLP), and the effects on the gelatinisation, retrogradation, and digestibility properties of the potato starch were investigated. After chemical modification, the slope of the curve between the molar mass and molecular radius of polysaccharides decreased, revealing that the relatively rigid rod-like structure of native polysaccharide (0.78) changed to SLP's random linear chain (0.53) and CLP's spherical conformation (0.23), and the water solubility increased from 63.6% to 70.4% (SLP) and 84.1% (CLP) in distilled water at 25 °C. Moreover, testing polysaccharides as an additive indicated that both derivatives significantly decreased the peak viscosity, breakdown, and setback viscosity during potato starch pasting. Furthermore, the possible interactions could be further examined by structure analyses, suggesting the polysaccharide and SLP hydrogen bonds interacted with the surfaces of starch granules, while CLP penetrated the interiors of pasted starch granules, destroyed the helixes and backbone structure of starch, and formed type V crystallinity with amylose. The results of in vitro digestion analysis revealed that polysaccharides could decrease the amount of resistant starch and increase the amount of slowly digestible starch, which might be related to the inhibition of starch gelatinisation. These results facilitate the application of chemical derivatives in starch-based functional foods and understand the interaction mechanism between potato starch and polysaccharides.     

Acid‐formed pectin gel delays major incomplete kiwi fruit allergen Act c 1 proteolysis in in vitro gastrointestinal digestion

BACKGROUND: It is thought that food sensitisers must be able to reach the intestine in order to sensitise patients. Pectin is a gel‐forming plant polysaccharide that can protect allergens from in vivo gastric digestion and in vitro pepsin digestion. The aim of this study was to examine if pectin gel formed in the acidic environment of the stomach can protect labile allergen from in vitro gastrointestinal digestion. RESULTS: Pectin forms a gel in the acidic conditions of gastric fluid up to a concentration of 1.0 ± 0.14 g L^?1. Four allergenic fruits (kiwi, cherry, apple and banana) form gels in the same manner at the dilutions 14.8 ± 0.4; 8.4 ± 0.2, 9.4 ± 0.35 and 29.1 ± 0.2, respectively. The time necessary for dissolution of 50 g L^?1 pectin gel in intestinal fluid was found to be 70 ± 0.2 min. Pectin gel formed in situ was able to protect Act c 1 from pepsin digestion for 1 h and from further intestinal digestion for one additional hour. CONCLUSION: Pectin gel in an acidic environment protects Act c 1 from pepsin digestion and dissolves slowly in the slightly basic environment of the intestine allowing the survival of fruit allergen for additional time and possible interaction with the gut immune system. Copyright © 2008 Society of Chemical Industry     

Physicochemical characterisation and α‐amylase inhibitory activity of tea polysaccharides under simulated salivary,gastric and intestinal conditions

Tea polysaccharides (TPS) are one of the main components of tea with various bioactivities. Digestion could result in the changes of the physicochemical properties and bioactivities of polysaccharides. The objective of this study was to determine the changes in physicochemical properties and α‐amylase inhibitory activities of TPS after simulated digestion. The structure of TPS determined by UV, IR and SEM showed that no obvious changes after salivary digestion, but significant changes after gastrointestinal digestion were observed. After intestinal digestion, the contents of reducing sugar were increased from 0.650 ± 0.011 to 1.594 ± 0.078 mm , and the centre molecular weight was decreased from 540.57 to 375.35 KDa. The molar ratio of monosaccharide was changed after digestion. And α‐amylase inhibition rate was significantly increased (P < 0.05). The results could provide information on the digestibility of TPSin vitro and contribute to the development of related functional foods or medicines.     

Effects of baking on protein digestibility of organic spelt products determined by two in vitro digestion methods

Consumption of organic foods is steadily increasing because it is believed to be healthier than conventional foods. This study was designed to investigate protein digestibility of organic spelt bread, biscuit, cookie and muffin in comparison to their corresponding normal wheat products. Three types of fermented bread products namely, yeast leavened, sour and yeast/sour dough were evaluated. Protein digestibility was assessed based on two methods, three-enzyme one-step and two-enzyme two-step digestion in vitro. The one-step digestion method produced results that were comparable with in vivo (rat) methods whereas the two-step digestion method was more reliable in determining differences among the examined wheat products. Organic spelt used in the present study was comparable to common wheat in protein content averaging 15.4 g/100 g dry matter. Slight differences were observed between organic spelt and common wheat products in protein digestibility determined by the two digestion methods. However, significant differences were found among each wheat products. In general, after baking protein digestion was significantly increased. Spelt and common wheat bread products had similar protein digestibility within each type of bread with sour dough breads had the highest protein digestibility. Biscuit, cookie and muffin products possessed lower protein digestibility than breads. In general, variations in protein digestibility due to baking were more noticeable than that found between the two wheats.     

Development of an in vitro mechanical gastric system (IMGS) with realistic peristalsis to assess lipid digestibility

A new in vitro mechanical gastric system (IMGS) was fabricated which incorporates: a J-shaped stomach, a mechanical system with realistic peristaltic frequency and force magnitude, and a reproduction of the gastric pH curve. To evaluate the impact of a more realistic gastric peristalsis on the intestinal lipolysis of protein-stabilized O/W emulsions, the emulsions were subjected to two different in vitro digestion methodologies: (i) gastric digestion in the IMGS and intestinal digestion in a stirred beaker (SB), and (ii) gastric and intestinal digestion assays carried out in SBs. At the end of the intestinal digestion, the total amount of free fatty acids released was significantly higher for the first methodology (IMGS-SB) in comparison with the second one (27.5% vs. 23.0%), probably due to the higher physical instability induced by the IMGS in the gastric contents. These results reaffirm that O/W emulsion stability plays a crucial role in controlling the final extent of lipolysis of this kind of food-grade emulsions.     

The effect of methanal (formaldehyde) treatment of casein on its digestion in vivo and in vitro

The effect of methanal (HCHO) treatment of casein on its in vitro and in vivo digestion was investigated. As the quantity of HCHO bound to casein increased, the in vitro rumen degradability decreased but no further reduction occurred above 10.6 g HCHO kg^?1 treated casein DM. The proportion of the original HCHO (25.4 g HCHO kg^?1 treated casein DM) remaining bound to casein at pH values 3.0 to 6.0 was approximately 0.5; the proportion remaining bound at pH 2.0 was significantly less (0.39). N solubility and in vitro digestion of casein by pepsin/HCl and/or intestinal proteolytic enzymes was significantly reduced by treatment with HCHO (10.6 g HCHO kg^?1 treated casein DM). When fed to rats the dry matter (DM) and true N digestibilities decreased significantly as the ratio HCHO;casein increased; the digestibility of the N-free component of the diet remained unchanged. The quantity of available lysine in the diets and their true biological value (BV) decreased as the level of bound HCHO increased; there was significant linear relationship between BV and available lysine. The apparent disappearances of amino acids from the small intestine of sheep, when untreated or HCHO treated caseins (12.3 g HCHO kg^?1 DM) were infused into the duodenum, were not affected by the pH of the infusate (pH 2.5 or 6.8) but were significantly reduced by HCHO treatment. It is concluded that exposure of HCHO-treated casein to low pH values does not completely release bound HCHO from casein and that the intestinal digestion of casein to which HCHO remains bound is reduced when compared to untreated casein. All amino acids determined showed similarly reduced apparent intestinal absorptions due to HCHO treatment. It is suggested that the lower BV of HCHO-treated caseins was due to reduced metabolic availability of lysine.     

Fermented coconut jelly as a probiotic vehicle,physicochemical and microbiology characterisation during an in vitro digestion

There is little information on the survival of probiotics in plant-based foods after simulated gastric and intestinal conditions, likewise the microstructure arrangement in the no-dairy fermented food. This work aimed to study if the agar–agar in a fermented coconut jelly confers protection to probiotics, phenolic and antioxidant compounds during in vitro digestion. Samples containing higher agar–agar amounts tend to retain (P < 0.05) antioxidant and phenolic compounds in their network better, even after the in vitro digestion. Also, a compact and homogeneous microstructure was observed by the Confocal Laser Scanning Microscopy. The texture profile analysis shows that 1% of agar samples presented the maximum hardness (P < 0.05) due to more bonding points and intermolecular interactions. Finally, the survival of probiotics remained above the recommended values (10⁶–10⁷ CFU g⁻¹) after the in vitro digestion of a product with probiotic potential.     

Starch-based nanoparticles: Stimuli responsiveness,toxicity, and interactions with food components

In recent years, starch-based nanoparticles have attracted great interest due to their small size, good biocompatibility, and environmental friendliness, as well as their potential applications in foods, drug delivery carriers, and biodegradable edible films. Compared with nonstarch polysaccharides, starch can be enzymatically hydrolyzed into glucose in vivo, so it can be used as an enzyme-responsive carrier. The recent research progress of starch-based nanoparticles, including starch nanoparticles, starch nanospheres, starch micelles, starch vesicles, starch nanogels, and starch nanofibers, are reviewed in this paper. The main focus is on their responsiveness, digestibility, toxicity, interactions with other components, and applications. Starch-based nanoparticles are nontoxic and responsive to pH, temperature, light, and other stimuli. It can interact with proteins, antioxidants, and lipids through electrostatic interactions and hydrogen bonding interactions. Starch-based nanoparticles have a wide range of applications, including enhancing the mechanical properties of films and gels, stabilizing emulsions, as a fluorescent indicator, a catalyst, and a nanocarrier to control the release of active ingredients and drugs.