Static in vitro digestion model adapted to the general older adult population: an INFOGEST international consensus.

Understanding the mechanisms of food digestion is of paramount importance to determine the effect foods have on human health. Significant knowledge on the fate of food during digestion has been generated in healthy adults due to the development of physiologically-relevant in vitro digestion models. However, it appears that the performance of the oro-gastrointestinal tract is affected by ageing and that a model simulating the digestive conditions found in a younger adult (<65 years) is not relevant for an older adult (>65 years). The objectives of the present paper were: (1) to conduct an exhaustive literature search to find data on the physiological parameters of the older adult oro-gastrointestinal tract, (2) to define the parameters of an in vitro digestion model adapted to the older adult. International experts have discussed all the parameters during a dedicated workshop organized within the INFOGEST network. Data on food bolus properties collected in the older adult were gathered, including food particle size found in older adult boluses. In the stomach and small intestine, data suggest that significant physiological changes are observed between younger and older adults. In the latter, the rate of gastric emptying is slowed down, the pH of the stomach content is higher, the amount of secretions and thus the hydrolytic activities of gastric and intestinal digestive enzymes are reduced and the concentration of bile salts lower. The consensus in vitro digestion model of the older adult proposed here will allow significant progress to be made in understanding the fate of food in this specific population, facilitating the development of foods adapted to their nutritional needs. Nevertheless, better foundational data when available and further refinement of the parameters will be needed to implement the proposed model in the future.

Relationship among oral health status, bolus formation and food comfortability during consumption of model cheeses in elderly.

The aim of this study was to investigate the impact of oral impairment on chewing behaviour, food bolus properties and food comfortability during elderly consumption of model cheeses. Seventy-two elderly persons (aged 66 to 88) was recruited and classified into two groups according to dental status (poor vs. satisfactory). They showed a wide range of salivary flow rates whatever their dental status (stimulated: 0.2-3.8 mL min-1, resting: 0.1-0.8 mL min-1). Standardized bites of four model cheeses with an identical composition but different textures (soft, hard, processed and whipped) were tested. The time and number of chewing cycles required to form a bolus were measured. The rheological properties of the bolus were studied, as was saliva moistening. Food comfortability was assessed by means of a questionnaire composed of 5 sections (1-oral comfort, 2-bolus formation, 3-pain, 4-texture and 5-flavour perception). The chewing parameters measured were not modified by the oral health. However, elderly with poor dentition formed harder boluses than elderly with satisfactory dentition. Moreover, for elderly with poor dentition, the quantity of saliva incorporated into the bolus was correlated with the stimulated salivary flow rate, which was not the case for elderly with satisfactory dentition. General oral comfort and its different attributes were poorly associated with the oral health of the elderly. A multifactorial analysis performed on an average cheese showed that food comfortability is independent of changes in the hardness and moistening of the bolus, regardless of dental status. In particular, poor dental status increases the hardness of the bolus without modifying its comfortability.

Oral processing and comfort perception of soft cereal foods fortified with pulse proteins in the elderly with different oral health status.

This study investigated the oral processing and bolus formation mechanisms of two soft cereal products fortified with pulse proteins, sponge-cake (FSC) and brioche (FB), in the elderly population, and their relationship with the perception of oral comfort. Twenty subjects aged 65 and over participated in the study. They were classified in two groups according to dental status (poor vs. satisfactory) and presented varying stimulated salivary flow rate (SSF). Bolus properties (hydration ratio, apparent viscosity and particle size) were characterized after three chewing stages. Results showed that subjects with a poor dental status (DS) had a longer chewing duration for FB, while individuals with a higher SSF had a shorter duration for FSC. Compared to FSC, more saliva was added to the FB boli, and the viscosity and particle size of FB bolus were also higher. Based on the bolus particle size evolution during chewing, FB was considered to be more difficult to fragment than FSC, this latter showing a dramatic particle size reduction from the beginning of chewing. From the viscosity data, a model was used to represent the variations of the bolus structure index during chewing and a coefficient of interaction of saliva with food was defined. For both products, the perception of comfort depended more on the DS than on SSF. Bolus apparent viscosity was related to the perception of oral comfort in FSC, while the chewing duration and the bolus particle size at the beginning of chewing contributed to explain oral comfort in FB. Finally, the comparison of these results with those obtained previoulsy with standard (i.e. non enriched) sponge cake and brioche suggested that the proposed protein fortification did not challenge the oral comfort perception by the elderly.

Relationships of oral comfort perception and bolus properties in the elderly with salivary flow rate and oral health status for two soft cereal foods.

The aim of this study was to investigate food oral processing and bolus formation in the elderly population, and their relationship with the perception of oral comfort, for two soft cereal products of different composition: sponge-cake and brioche. Twenty subjects aged 65 and over participated in the study. They were classified in two groups according to dental status (poor vs. satisfactory) and presented various stimulated salivary flow rate (SSF) in each group. Food bolus properties (hydration ratio and apparent viscosity) were characterized after three chewing stages for both groups. Results showed that chewing duration did not depend on food product but rather on physiology: subjects with a poor dental status had a shorter chewing duration. For each chewing stage, sponge-cake boli showed a higher hydration ratio than brioche boli, which showed higher apparent viscosity. For sponge-cake, perception of oral comfort was primarily driven by SSF rate, irrespective of the dental status. In the case of brioche, oral comfort was also partially explained by SSF in the case of subjects with poor dental status. This result suggests that perception of oral comfort in brioche could be driven by product related attributes rather than oral health. For both foods, a phenomenological model of bolus viscosity as a function of stimulated salivary flow and chewing duration was proposed.

Bolus quality and food comfortability of model cheeses for the elderly as influenced by their texture.

The aim of this study was to examine the influence of the texture of dairy products on bolus properties and food comfortability as perceived by elderly persons. Four cheese models identical in terms of their nutritional composition but different by the type of texture (Soft, Hard, Processed and Whipped) were developed to resemble market cheese. Study was performed with a panel of 38 elderly persons without dental impairment but with variable rate of saliva flow. The time of chewing required to form the bolus was measured. The rheological properties of the bolus obtained were studied as well as the quantity of saliva incorporated. Food comfortability was assessed by means of a questionnaire asking about in-mouth comfort, bolus formation, pain, and perceived texture and flavor. Results showed that food comfortability was positively correlated to the ease of forming the bolus which depended on the food texture. Thus, the bolus formed with the Whipped product which required more saliva, was harder than the other three products and so judged the least comfortable. This product was characterized by a dry and sticky texture. On the other hand, the Soft and Processed products led to a softer food bolus that was more easily formed, and thus were judged as more comfortable. Their textures were perceived as soft, fatty and melting. This work highlights the importance of considering food bolus formation and related properties when looking for the link between food product characteristics and the enjoyment of eating in the case of the elderly population.

Association between Salivary Hypofunction and Food Consumption in the Elderlies. A Systematic Literature Review.

OBJECTIVES: This systematic literature review aims to summarize the existing scientific evidence about the association between a reduced salivary function and food consumption in elderly people. METHODS: A validated search strategy in two databases (PubMed and ISI Web of Knowledge) was carried out and retrieved papers together with their reference lists were screened by two independent reviewers. The quality of the included studies was critically appraised via the Quality Assessment Criteria for Evaluating Primary Research Papers. RESULTS: From the originally identified studies (n=391), only 15 articles (all cross-sectional studies) met the pre-fixed inclusion/exclusion criteria. The methodological quality of the included studies was in general good, although only 3 from 15 obtained the maximum score. The control of confounding factors was the quality variable more poorly rated in the selected studies. Salivary hypofunction was associated with a decrease of the objective chewing and swallowing abilities and taste perception. Moreover, most of the selected studies showed a relationship between salivary hypofunction and food consumption (in terms of appetite loss, unbalanced dietary intake and malnutrition), although no causality could be established. CONCLUSIONS: This study highlights the fact that salivary hypofunction definition and measurements are different across the studies. Therefore, future research efforts should focus on establishing a gold standard to define and identify salivary hypofunction throughout life and on performing longitudinal studies controlling for confounding factors to establish causality.

Model cheese aroma perception is explained not only by in vivo aroma release but also by salivary composition and oral processing parameters.

The aim of the present paper was to determine, from four model cheeses differing in fat content and firmness and consumed by fourteen well characterised subjects, the respective impacts of in vivo aroma release, bolus rheology, chewing activity, mouth coating and salivary composition on dynamic aroma perception. The originality of the approach is that it considers all the parameters together and is able to evaluate their relative contribution using multi-block partial least square (MB-PLS) regression. The fruity aroma perception of the more hydrophilic compound (ethyl propanoate) was related to its dynamic release parameters before swallowing whereas the blue cheese aroma perception of the more hydrophobic compound (nonan-2-one) was related to its dynamic release parameters after swallowing and was highly impacted by mouth coating. Moreover the MB-PLS approach made it possible to evidence the combined effects of saliva composition and cross-modal interactions to understand why in some cases dynamic aroma perception could not be explained by dynamic in vivo aroma release data. Subjects with a low sodium content in saliva perceived fruity aroma which is not congruent with saltiness as less intense and salt- congruent (blue cheese) aroma as more intense, which was explained by their higher sensitivity to salt. Subjects with high lipolysis activity perceived fruity aroma which is not congruent to fat as less intense and fat-congruent (blue cheese) aroma as more intense, which should be explained by the link between lipolysis activity and fat sensitivity. These results could be considered for the reformulation of foods towards specific populations taking into account nutritional recommendations.

Salivary composition in obese vs normal-weight subjects: towards a role in postprandial lipid metabolism?

In the pathophysiological context of obesity, oral exposure to dietary fat can modulate lipid digestion and absorption, but underlying in-mouth mechanisms have not been clearly identified. Therefore, we tested the hypothesis that salivary components related to dietary fat sensitivity would differ according to body mass index (BMI) and postprandial lipid metabolism in young men. Saliva was collected from nine normal-weight (BMI=22.3±0.5 kg m(-2)) and nine non-morbid obese (BMI=31.7±0.3 kg m(-2)) men before an 8-h postprandial metabolic exploration test involving the consumption of a 40-g fat meal, in which obese subjects revealed a delayed postprandial lipid metabolism. Nine salivary characteristics (flow, protein content, lipolysis, amylase, proteolysis, total antioxidant status, lysozyme, lipocalin 1 and carbonic anhydrase-VI) were investigated. We show that, under fasting conditions, salivary lipolysis was lower in obese vs normal-weight subjects, whereas proteolysis and carbonic anhydrase VI were higher. We reveal through multivariate and Mann-Whitney analysis that differences in fasting salivary lipolysis and proteolysis between both groups are related to differences in postprandial lipid metabolism including exogenous fatty-acid absorption and ß-oxidation. These results suggest a potential role of salivary composition on postprandial lipid metabolism and bring novel causal hypotheses on the links between salivary composition, sensitivity to dietary fat oral income and postprandial lipid metabolism according to BMI.

Inter-individual retronasal aroma release variability during cheese consumption: Role of food oral processing.

The aim of our study was to explain inter-individual differences on in vivo aroma release during cheese consumption by oral physiological parameters. To reach this objective, 34 subjects were recruited. Their salivary flow, oral volume and velum opening were determined. Six cheddar-based melted cheeses with different fat levels and firmness were flavoured with nonan-2-one (NO) and ethyl propanoate (EP). During their consumption (free protocol), in vivo retro nasal aroma release was followed by Atmospheric Pressure Chemical Ionisation-Mass Spectrometry (APCI-MS). Chewing activity was evaluated by electromyography recordings. Bolus saliva content, mouth-coating, and bolus rheology were also determined. Based on the quantity of aroma released before and after swallowing, subjects can be clustered into three groups: the first one (HRG) is characterized by a large quantity of aroma release whatever the aroma compound; the second one (MRG) showed a large release for EP and a lower one for NO; the third group (LRG) was characterized by a low quantity of aroma release whatever the compound. Whatever the group of subjects, fat and firmness effects differed according to the aroma compound. EP release increased with firmness and fat content, whereas NO release was not affected by firmness and decreased when fat content increased. Physiological parameters which better differentiated the three groups of subjects according to their release behaviour were chewing activity, mouth coating and frequency of velum opening. Subjects from HRG were differentiated from LRG subjects by a higher chewing activity, and more frequent velum opening. Subjects from MRG presented a lower mouth coating explaining their lower release of NO, the more hydrophobic compound. This study shows that the total amount of aroma released in the nasal cavity during food consumption depends not only on the characteristics of the product but also on the oral physiology of the subjects and on their food oral processing.

Main individual and product characteristics influencing in-mouth flavour release during eating masticated food products with different textures: mechanistic modelling and experimental validation.

A mechanistic model predicting flavour release during oral processing of masticated foods was developed. The description of main physiological steps (product mastication and swallowing) and physical mechanisms (mass transfer, product breakdown and dissolution) occurring while eating allowed satisfactory simulation of in vivo release profiles of ethyl propanoate and 2-nonanone, measured by Atmospheric Pressure Chemical Ionization Mass Spectrometry on ten representative subjects during the consumption of four cheeses with different textures. Model sensitivity analysis showed that the main parameters affecting release intensity were the product dissolution rate in the mouth, the mass transfer coefficient in the bolus, the air-bolus contact area in the mouth and the respiratory frequency. Parameters furthermore affecting release dynamics were the mastication phase duration, the velopharynx opening and the rate of saliva incorporation into the bolus. Specific retention of 2-nonanone on mucosa was assumed to explain aroma release kinetics and confirmed when gaseous samples were consumed.

Solid cheese consumption: quantification of oral coating.

Mouth coating, defined as the residual food that sticks to the oral surface after food ingestion, plays an important role in both the delivery of food components and mouth feel and after-feel perceptions. The aim of this work was to adapt a rapid and simple instrumental method to the quantification of food remaining after the in vivo ingestion of a solid food. This method was investigated in 12 non-trained subjects who consumed four melted cheeses differing in terms of their fat and water contents. Mouth coating was determined by fluorescence measurements using curcumin, an oil-soluble dye that had been added to the cheeses during their preparation. The results obtained showed that this method was reproducible, reliable and discriminating and could be used for solid cheeses covering a broad range of textures.

Contribution of exofacial thiol groups in the reducing activity of Lactococcus lactis.

Lactococcus lactis can decrease the redox potential at pH 7 (E(h7)) from 200 to -200 mV in oxygen free Man-Rogosa-Sharpe media. Neither the consumption of oxidizing compounds or the release of reducing compounds during lactic acid fermentation were involved in the decrease in E(h7) by the bacteria. Thiol groups located on the bacterial cell surface appear to be the main components that are able to establish a greater exchange current between the Pt electrode and the bacteria. After the final E(h7) (-200 mV) was reached, only thiol-reactive reagents could restore the initial E(h7) value. Inhibition of the proton motive force showed no effect on maintaining the final E(h7) value. These results suggest that maintaining the exofacial thiol (-SH) groups in a reduced state does not depend on an active mechanism. Thiol groups appear to be displayed by membrane proteins or cell wall-bound proteins and may participate in protecting cells against oxidative stress.

Gaseous environments modify physiology in the brewing yeast Saccharomyces cerevisiae during batch alcoholic fermentation.

AIMS: To investigate the impact of different gaseous atmospheres on different physiological parameters in the brewing yeast Saccharomyces cerevisiae BRAS291 during batch fermentation. METHODS AND RESULTS: Yeasts were cultivated on a defined medium with a continuous sparging of hydrogen, helium and oxygen or without gas, permitting to obtain three values of external redox. High differences were observed concerning viable cell number, size and metabolites produced during the cultures. The ethanol yields were diminished whereas glycerol, succinate, acetoin, acetate and acetaldehyde yields were enhanced significantly. Moreover, we observed major changes in the intracellular NADH/NAD(+) and GSH/GSSG ratio. CONCLUSIONS: The use of gas led to drastic changes in the cell size, primary energy metabolism and internal redox balance and E(h). These changes were different depending on the gas applied throughout the culture. SIGNIFICANCE AND IMPACT OF THE STUDY: For the first time, our study describes the influence of various gases on the physiology of the brewing yeast S. cerevisiae. These influences concern mainly yeast growth, cell structure, carbon and redox metabolisms. This work may have important implications in alcohol-related industries, where different strategies are currently developed to control better the production of metabolites with a particular attention to glycerol and ethanol.

Microbial production of 4-hydroxybenzylidene acetone, the direct precursor of raspberry ketone.

AIMS: To investigate the enzymatic aldol reaction between acetone as a donor and 4-hydroxybenzaldehyde as a receptor to generate 4-(4-hydroxyphenyl)-but-3-ene-2-one or 4-hydroxybenzylidene acetone, the direct precursor of 4-(4-hydroxyphenyl)-butan-2-one or raspberry ketone, using different species of filamentous fungi and bacteria. METHODS AND RESULTS: Different classes of micro-organisms were tested in a medium containing mainly acetone and 4-hydoxybenzaldehyde. Of the micro-organisms tested, only bacteria were able to synthesize significant amounts of 4-hydroxybenzylidene acetone, ranging from 15 to 160 mg l(-1) after 21 h of bioconversion, as a function of the bacteria tested. CONCLUSIONS: The biological production of 4-hydroxybenzylidene acetone has been described with bacteria possessing 2-deoxyribose-5-phosphate aldolase (DERA, EC 4.1.2.4). This result suggests that DERA is involved in the catalytic aldolization of precursors for the production of 4-hydroxybenzylidene acetone. SIGNIFICANCE AND IMPACT OF THE STUDY: Raspberry ketone or frambinone represents a total market value of between euro6 million and euro10 million. The possibility of producing its direct precursor through a simple process using bacteria is of considerable interest to the flavour market and the food industry as a whole. This paper broadens the spectrum for the use of aldolase to achieve the biological synthesis of compounds of interest.

Addition of oxidizing or reducing agents to the reaction medium influences amino acid conversion to aroma compounds by Lactococcus lactis.

AIMS: The aim of this research was to investigate the impact of extracellular redox potential (Eh) on amino acid conversion to aroma compounds by Lactococcus lactis that is commonly used as a starter in the cheese industry. METHODS AND RESULTS: The study was realized in vitro by incubating resting cells of L. lactis in reaction media in which E(h) was modified by the addition of oxidizing or reducing agents. Oxidative condition (+300 mV) favoured the production of aldehydes and volatile sulfur compounds responsible for malty, floral, fruity, almond and cabbage aroma. This production was mainly the result of a chemical oxidation of the alpha-keto acids produced by amino acid transamination. In contrast, reducing condition (-200 mV) stimulated the production of carboxylic acids such as phenylacetic, methylthiopropionic and isovaleric acids, which contribute to the very-ripened-cheese aroma as well as the production of hydroxy acids. CONCLUSIONS: Eh of the medium highly influences the nature of aroma compounds produced from amino acid catabolism by the resting cells of L. lactis. SIGNIFICANCE AND IMPACT OF THE STUDY: E(h) is a parameter that is not controlled during cheese production. Its control throughout cheese making and ripening could permit control of aroma formation in cheese.

Yeast as an efficient biocatalyst for the production of lipid-derived flavours and fragrances.

Responding to consumer' demand for natural products, biotechnology is constantly seeking new biocatalysts. In the field of hydrophobic substrate degradation, some yeast species known some years ago as non-conventional, have acquired their right to be considered as good biocatalysts. These Candida, Yarrowia, Sporobolomyces ... are now used for themselves or for their lipases in processes to produce flavours and fragrances. In this paper we present some examples of use of these biocatalysts to generate high-value compounds and discuss the new trends related to progress in the development of molecular tools or the mastering of the redox characteristics of the medium.

Glucosamine measurement as indirect method for biomass estimation of Cunninghamella elegans grown in solid state cultivation conditions.

Glucosamine measurement has been tested as the indirect method to estimate the biomass produced by Cunninghamella elegans during solid state cultivation (SSC). The independence of this cell constituent content from the age and the conditions of the culture have been verified. The influence of the medium composition, in particular the nature of the carbon source on glucosamine amount is presented. Glucosamine can be considered as a well-adapted biomass indicator, with the necessity to establish for each medium tested a prior correlation between biomass and glucosamine amount. This correlation should be defined in submerged conditions before applying the biomass estimating method in SSC.

Identification of beta-oxidation and thioesterase activities in Staphylococcus carnosus 833 strain.

Staphylococcus carnosus 833, inoculated into sausage meat, increased the level of methyl ketones, which contributed to the cured aroma. These ketones can arise from incomplete beta-oxidation followed by two enzymatic activities: a thioesterase and a decarboxylase. In this study we identified the beta-oxidative pathway (through the measure of 3-hydroxyacyl-CoA dehydrogenase activity) and the thioesterase activity in extracts of S. carnosus cells grown in the presence of different methyl esters. The beta-oxidative system was induced by methyl esters and highest induction was found with a 12-carbon substrate. It was specific for medium chain length fatty acyl CoA substrates. Its maximal activity was observed at the end of stationary growth phase. HPLC analyses of acyl-CoA after incubation of cell extracts with palmitoyl-CoA showed that the beta-oxidation system released preferentially long chain hydroxyacyl-CoAs, enoyl-CoAs, and acyl-CoAs. The time-course of intermediate formation indicated a precursor product relationship indicative of a model of free intermediates which could be further deacylated by a thioesterase. The thioesterase activity was enhanced when S. carnosus was grown in the presence of methyl esters with at least 12 carbons and this enzyme was specific for short chain acyl-CoAs. The maximal activity was reached at the stationary growth phase.

Metabolism of ricinoleic acid into gamma-decalactone: beta-oxidation and long chain acyl intermediates of ricinoleic acid in the genus Sporidiobolus sp.

In order to study differences in gamma-decalactone production in yeast, four species of Sporidiobolus were cultivated with 5% of methyl ricinoleate as the lactone substrate. In vivo studies showed different time courses of intermediates of ricinoleic acid breakdown between the four species. In vitro studies of the beta-oxidation system were conducted with crude cell extracts of Sporidiobolus spp. and with ricinoleyl-CoA (RCoA) as substrate. The beta-oxidation was detected by measuring acyl-CoA oxidase, 3-hydroxyacyl-CoA dehydrogenase activities, and acetyl-CoA production. The time courses of the CoA esters resulting from RCoA breakdown by crude extract of Sporidiobolus spp. permit the proposal of different metabolic models in the yeast. These models explained the differences observed during in vivo studies.

Addition of reducing agent dithiothreitol improves 4-decanolide synthesis by the genus Sporidiobolus.

Two species of the genus Sporidiobolus, S. johnsonii and S. ruinenii, were used to study the effect of the reducing agent, dithiothreitol (DTT), on 4-decanolide production using ricinoleic acid as the substrate. The results indicate that the addition of DTT into the cultures significantly enhanced 4-decanolide biosynthesis by the two species.