Effects of added glutamate on liking for novel food flavors

Flavor preferences conditioned by post-oral infusion of monosodium glutamate in rats

Monosodium glutamate (MSG), the prototypical umami source, can enhance preference for associated flavors in humans and rodents. Although MSG flavor preference has been attributed to its taste, vagally-mediated post-oral detection has also been demonstrated. Recent studies showed that water-restricted rats acquired a preference for a flavor paired with intragastric (IG) infusion of 60 mM MSG in rats. The present study extends this work by comparing MSG-based flavor conditioning in water- and food-restricted rats and testing the persistence of flavor preferences. Rats with IG catheters drank flavored solutions paired with volume-matched infusions of 60 mM MSG or water in daily 30-min sessions. Two training/test cycles were conducted, each with eight one-bottle training sessions followed by two two-bottle preference tests without infusions. Food- and water-restricted groups displayed similar preferences for the MSG-paired flavor. When non-reinforced testing was continued after the second cycle, the food-restricted group sustained its preference across three 2-day tests, but water-restricted rats lost their preference. Other food-restricted rats learned to prefer a flavor paired with intraduodenal infusion, indicating that gastric stimulation by MSG is not required. A third experiment showed that adding 2 mM of the nucleotide inosine monophosphate to the IG infusion of MSG did not significantly enhance flavor conditioning. Because MSG-based flavor preferences can be obtained with infusions that bypass the stomach, the site for detecting MSG reinforcement may be intestinal.

Gustatory and olfactory function in rheumatoid arthritis

OBJECTIVES

To evaluate the gustatory and olfactory functions of patients with rheumatoid arthritis (RA) compared to sex- and age-matched healthy subjects and to investigate a potential relationship between disease activity [using the 28-joint Disease Activity Score (DAS28)] and chemosensory capacity. Furthermore, to dissect possible impacts of standard anti-inflammatory medications on the gustatory and olfactory functions.

METHODS

Patients with established RA underwent standardized assessment of their gustatory and olfactory functions. The patients were also examined for their disease activity, had their specific blood-test results analysed, and were asked to answer a standardized questionnaire about their quality of life, the negative effects of their disease, and about comorbidities.

RESULTS

A total of 101 RA patients (75 women, 26 men, mean age: 57.9 ± 13.8 and 64.2 ± 10.9 years, respectively) were analysed. In relation to age- and sex-related subjects, both female and male RA patients had a significantly decreased taste score (p < 0.001) and also a significantly decreased olfactory score (p < 0.05), indicating that a substantial number of patients suffer from hypogeusia or hyposmia. This abnormality did not correlate with disease activity, the duration of the disease, disease-modifying anti-rheumatic drug (DMARD) or tumour necrosis factor (TNF) inhibitor use, and the loss of the chemosensory functions, together indicating that hypogeusia and hyposmia are frequent clinical manifestations in RA patients independent of the inflammatory activity of their disease.

CONCLUSION

The results indicate that there is a significant decrease in the olfactory and gustatory function in RA patients compared to those of healthy controls, which can seriously and substantially affect the quality of the patients' life.

Sensory attributes of dishes containing shrimp paste with different concentrations of glutamate and 5'-nucleotides

The shrimp paste called belacan is a traditional umami taste condiment extensively used in Malaysia that is rich in glutamate and 5'-nucleotides. The aim of this study was to determine the concentration of glutamate and 5'-nucleotides of various types of foods prepared with belacan and to measure their sensory attributes. The concentration of free glutamic acid found in different brands of belacan was 180-530mg/100g and in local dishes 601-4207mg/100g. The total amount of 5'-nucleotides in belacan samples ranged from 0.85 to 42.25μg/g. A Quantitative Descriptive Analysis (QDA) using a list of 17 sensory attributes showed a good correlation between belacan concentration in the final food and a range of positive sensory attributes, except for bitter, sweet, sour taste and astringency. Belacan also contains bitter, sweet and sour compounds that change the positive attributes of belacan at higher concentrations. The highest aroma attributes were linked to nasi goreng belacan (belacan fried rice) while the highest flavour attributes were found in sambal belacan. There was a 32 folds significant increase of umami attributes with the addition of belacan to final foods. The optimum amount of belacan was 0.45% for asam pedas (tamarind flavoured dish with belacan), 18% for sambal belacan (chilli belacan), 1.5-2.5% for kangkong goreng belacan (stir fried water convolous with belacan), and 2% for nasi goreng belacan.

Glutamate. Its applications in food and contribution to health

This article reviews application of glutamate in food and its benefits and role as one of the common food ingredients used. Monosodium glutamate is one of the most abundant naturally occurring amino acids which frequently added as a flavor enhancer. It produced a unique taste that cannot be provided by other basic taste (saltiness, sourness, sweetness and bitterness), referred to as a fifth taste (umami). Glutamate serves some functions in the body as well, serving as an energy source for certain tissues and as a substrate for glutathione synthesis. Glutamate has the potential to enhance food intake in older individuals and dietary free glutamate evoked a visceral sensation from the stomach, intestine and portal vein. Small quantities of glutamate used in combination with a reduced amount of table salt during food preparation allow for far less salt to be used during and after cooking. Because glutamate is one of the most intensely studied food ingredients in the food supply and has been found safe, the Joint Expert Committee on Food Additives of the United Nations Food and Agriculture Organization and World Health Organization placed it in the safest category for food additives. Despite a widespread belief that glutamate can elicit asthma, migraine headache and Chinese Restaurant Syndrome (CRS), there are no consistent clinical data to support this claim. In addition, findings from the literature indicate that there is no consistent evidence to suggest that individuals may be uniquely sensitive to glutamate.

Collecting, comparing, and computing sequences: the making of Margaret O. Dayhoff's Atlas of Protein Sequence and Structure, 1954-1965

Collecting, comparing, and computing molecular sequences are among the most prevalent practices in contemporary biological research. They represent a specific way of producing knowledge. This paper explores the historical development of these practices, focusing on the work of Margaret O. Dayhoff, Richard V. Eck, and Robert S. Ledley, who produced the first computer-based collection of protein sequences, published in book format in 1965 as the Atlas of Protein Sequence and Structure. While these practices are generally associated with the rise of molecular evolution in the 1960s, this paper shows that they grew out of research agendas from the previous decade, including the biochemical investigation of the relations between the structures and function of proteins and the theoretical attempt to decipher the genetic code. It also shows how computers became essential for the handling and analysis of sequence data. Finally, this paper reflects on the relationships between experimenting and collecting as two distinct "ways of knowing" that were essential for the transformation of the life sciences in the twentieth century.

Optimal preferred MSG concentration in potatoes, spinach and beef and their effect on intake in institutionalized elderly people

BACKGROUND

Elderly people may benefit from sensory stimulation to increase food intake since anorexia of ageing is prevalent among them. An optimal MSG concentration may increase the palatability of foods but this depends on the food and chemosensory status of the taster. Currently, the results on taste enhancing to increase intake are inconsistent.

OBJECTIVE

To find an optimal preferred MSG concentration in mashed potatoes, spinach and ground beef and to determine whether this concentration increases consumption of these foods among institutionalized elderly people.

DESIGN

Single blind within subject cross-over study performed at the laboratory and in the residents' own apartments.

PARTICIPANTS

33 elderly and 29 young people in the sensory study and 53 elderly people in the intake study.

MEASUREMENTS

Pleasantness of the foods was rated of the foods each with 0, 0.5, 0.8, 1.3 and 2.0 g of MSG/100g. Intake was measured by weighing back leftovers of 2 meals with MSG (0.5% in mashed potatoes, 2% in spinach and ground meat) and without MSG.

RESULTS

0.5% MSG (p < 0.05) was preferred in mashed potatoes but no optimal preferred concentration was found for spinach and ground beef, possibly because of their complex taste. Intake was not different between the foods with and without MSG or the total meal (all p > 0.68).

CONCLUSION

MSG (0.5% and 2%) does not guarantee a higher intake among elderly. The chemosensory heterogeneity of the elderly population requires more individual flavor enhancement to improve the dietary intake and sensory experience.

Effects of isoflurane and alpha-chloralose anesthesia on BOLD fMRI responses to ingested L-glutamate in rats

It is important to investigate the effect of anesthesia on blood oxygenation level-dependent (BOLD) signals in an animal model. Many researchers have investigated the BOLD response to visual, sensory, and chemical stimuli in anesthetized rats. There are no reports, however, comparing the differences in the BOLD signal change between anesthetized and conscious rats when a visceral nutrient signal arises. Here, using functional magnetic resonance imaging (fMRI), we investigated the differences in the BOLD signal changes after intragastric administration of l-glutamate (Glu) under three anesthesia conditions: conscious, alpha-chloralose-anesthetized, and isoflurane-anesthetized condition. Under the conscious and alpha-chloralose condition, we observed the significant BOLD signal increase in the medial prefrontal cortex (mPFC), insular cortex (IC), hippocampus, and several hypothalamic regions including the lateral and ventromedial nucleus. In chloralose group, however, gut Glu stimulation induced BOLD signal increase in the prelimbic cortex and orbital cortex, which did not activate in conscious condition. Meanwhile, under isoflurane-anesthetized condition, we did not observe the BOLD signal increase in these areas. BOLD signal intensity in the nucleus of the solitary tract (NTS), to which vagus nerve transmits the visceral information from the gastrointestinal tract, increased in all conditions. Importantly, under conscious condition, we observed increased BOLD signal intensity in several regions related to the metabolic state (i.e. hunger or satiety), such as the mPFC, ventromedial and lateral hypothalamus (LH). Our results suggest that alpha-chloralose and isoflurane anesthesia caused distinct effects on BOLD response to the gut l-Glu stimulation in several brain regions.

Undernutrition and anorexia in the older person

Minimizing frailty in older age is important to individuals and society, as the increasing prevalence of chronic disease is leading to greater disability and health care costs. Nutritional frailty can be defined as the disability that occurs in old age due to rapid, unintentional loss of body weight and sarcopenia (lack of lean mass). This article provides a brief overview of the prevalence and consequences of undernutrition, age-related changes to appetite, food intake, and body composition, the factors contributing to the development of anorexia and undernutrition, and recommended management strategies.

Early milk feeding influences taste acceptance and liking during infancy

BACKGROUND

We identified a model system that exploits the inherent taste variation in early feedings to investigate food preference development.

OBJECTIVE

The objective was to determine whether exposure to differing concentrations of taste compounds in milk and formulas modifies acceptance of exemplars of the 5 basic taste qualities in a familiar food matrix. Specifically, we examined the effects of consuming hydrolyzed casein formulas (HCFs), which have pronounced bitter, sour, and savory tastes compared with breast milk (BM) and bovine milk-based formulas (MFs), in which these taste qualities are weaker.

DESIGN

Subgroups of BM-, MF- and HCF-fed infants, some of whom were fed table foods, were studied on 6 occasions to measure acceptance of sweet, salty, bitter, savory, sour, and plain cereals.

RESULTS

In infants not yet eating table foods, the HCF group ate significantly more savory-, bitter-, and sour-tasting and plain cereals than did the BM or MF groups. HCF infants displayed fewer facial expressions of distaste while eating the bitter and savory cereals, and they and BM infants were more likely to smile while they were eating the savory cereal. In formula-fed infants eating table foods, preferences for the basic tastes reflected the types of foods they were being fed. In general, those infants who ate more food displayed fewer faces of distaste.

CONCLUSIONS

The type of formula fed to infants has an effect on their response to taste compounds in cereal before solid food introduction. This model system of research investigation sheds light on sources of individual differences in taste and perhaps cultural food preferences.

Mechanisms of neural response to gastrointestinal nutritive stimuli: the gut-brain axis

BACKGROUND & AIMS

The gut-brain axis, which transmits nutrient information from the gastrointestinal tract to the brain, is important for the detection of dietary nutrients. We used functional magnetic resonance imaging of the rat forebrain to investigate how this pathway conveys nutrient information from the gastrointestinal tract to the brain.

METHODS

We investigated the contribution of the vagus nerve by comparing changes of blood oxygenation level-dependent signals between 24 control rats and 22 rats that had undergone subdiaphragmatic vagotomy. Functional data were collected under alpha-chloralose anesthesia continuously 30 minutes before and 60 minutes after the start of intragastric infusion of L-glutamate or glucose. Plasma insulin, L-glutamate, and blood glucose levels were measured and compared with blood oxygenation level-dependent signals.

RESULTS

Intragastric administration of L-glutamate or glucose induced activation in distinct forebrain regions, including the cortex, hypothalamus, and limbic areas, at different time points. Vagotomy strongly suppressed L-glutamate-induced activation in most parts of the forebrain. In contrast, vagotomy did not significantly affect brain activation induced by glucose. Instead, blood oxygenation level-dependent signals in the nucleus accumbens and amygdala, in response to gastrointestinal glucose, varied along with fluctuations of plasma insulin levels.

CONCLUSIONS

These results indicate that the vagus nerve and insulin are important for signaling the presence of gastrointestinal nutrients to the rat forebrain. These signal pathways depend on the ingested nutrients.

High-sensitive glutamate biosensor based on NADH at Lauth's violet/multiwalled carbon nanotubes composite film on gold substrates

A highly sensitive amperometric L-glutamate biosensor based on the electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide has been developed on Lauth's Violet (known as thionine)/multiwalled carbon nanotubes (Th-MWCNTs) composite film, which is used as a mediator and an enzyme immobilization matrix. The glutamate biosensor, which is fabricated by immobilizing glutamate dehydrogenase (GLDH) on the surface of Th-MWCNTs, displayed a precipitous response (ca. 3 s), a low detection limit (15.9 nM), a wide linear dynamic range (0.1 to 500 microM), and high sensitivity of 281.6 microAmM(-1) cm(-2), higher biological affinity, as well as good stability and repeatability. Interferences from other biological compounds were also studied for the fabricated sensor. The Th-MWCNTs system exemplifies a simple and efficient approach to the assimilation of GLDH and electrodes, which can provide analytical access to a large group of enzymes for wide range of bioelectrochemical applications in health care fields.

Conditioned flavor preference learning by intragastric administration of L-glutamate in rats

The preference for foods or fluids in rats is partly dependent on its postingestive consequences. Many studies have investigated postingestive effect of high caloric substances, such as carbohydrate or fat. In this study, we examined postingestive effect of L-glutamate at the preferable concentration using conditioned flavor preference paradigm. Adult male rats with chronic intragastric (IG) cannula were trained to drink a flavored solution (conditioned stimulus; CS+) paired with IG infusion of nutrient solution and another flavored solution (CS-) with IG distilled water infusion on alternate days. The nutrient solution was 60mM monosodium L-glutamate, sodium chloride or glucose. Before and after conditioning, rats received 30min two-bottle choice tests for CS+ and CS- solution. All groups exhibited no significant preference for CS+ in pre-test period. By the last half of conditioning period, intake of CS+ solution was significantly higher than that of CS- in MSG group, but not in NaCl and glucose groups. After conditioned, the MSG group showed significantly higher intake and preference for CS+ solution (69.9%), while the NaCl and glucose group did not show any significant intake and preference for CS+ solution (50.9%, 43.5%, respectively). These results indicate that the amino acid L-glutamate at a preferable concentration has a positive postingestive effect as demonstrated by its ability to condition a flavor preference. The mechanism(s) for this positive effect could be through a direct effect on gut Glu receptors rather than the provision of calories or glucose from metabolized Glu; Further studies are needed to test these hypotheses.

Taste sensitivity for monosodium glutamate and an increased liking of dietary protein

The aim of the present study was to determine individuals' taste threshold for monosodium glutamate (MSG) alone and in combination with inosine 5'-monophosphate (IMP-5) and to examine if this threshold was related to an increase in sensory properties (including pleasantness of taste) and/or to one's preference for dietary protein over carbohydrate and fat. Using the triangle tasting method, the taste threshold was determined for thirty-six women and twenty-four men. Thresholds varied from zero to infinite as determined using a clear soup with added MSG in the concentration range of 0.1 to 0.8 % (w/w) MSG. Subjects rated fourteen sensory properties of the soup and also their 'liking', 'eating frequency' and 'preference' of twenty-two common high-protein, high-carbohydrate and high-fat food items. The taste threshold (and therefore sensitivity) of MSG was lowered from 0.33 (sem 0.24) to 0.26 (sem 0.22) % MSG when 0.25 % (w/w) IMP-5 was added. None of the sensory properties assessed was associated with the taste threshold of MSG +/- 0.25 % IMP-5 in the overall study population. However, the taste descriptor 'meatiness' was associated with the threshold data for individuals who could taste concentrations of <or= 0.4 % MSG. 'Liking' and 'preference' scores for protein were found to be related to the threshold of MSG +/- 0.25 % IMP-5. From this study population we conclude that the taste threshold of MSG in combination with IMP-5 does appear to predict one's 'liking' of as well as 'preference' for high-protein foods.

Acquired flavor acceptance and intake facilitated by monosodium glutamate in humans

Monosodium glutamate (MSG) is known to enhance liking for the flavor of savory foods, but whether associations between flavors and effects of MSG lead to changes in subsequent liking and intake for the flavor alone is unclear. To test this, 32 volunteers evaluated and consumed a novel savory soup with no added MSG before and after four training sessions where the same soup was consumed either unchanged (Control) or with added MSG. The addition of MSG during training increased both pleasantness and savory character of the soup and resulted in a larger increase in rated pleasantness of the soup in the MSG-trained relative to control condition when the soup was re-evaluated Post-training without MSG. There was also a significant increase in voluntary soup intake Post-training after the soup had been paired with MSG but not in the Control condition, and rated hunger increased more after tasting the soup Post-training in the MSG-trained but not Control condition. These findings demonstrate that co-experience of a savory flavor and MSG can result in increased subsequent liking and intake for the flavor in the absence of MSG, and possible explanations for how MSG reinforces learning are discussed.

Bitter taste markers explain variability in vegetable sweetness, bitterness, and intake

Intake of vegetables falls short of recommendations to lower risk of chronic diseases. Most research addresses bitterness as a sensory deterrent to consuming vegetables. We examined bitter and sweet sensations from vegetables as mediators of vegetable preference and intake as well as how these tastes vary with markers of genetic variation in taste (3.2 mM 6-n-propylthiouracil bitterness) and taste pathology (1.0 mM quinine bitterness, chorda tympani nerve relative to whole mouth). Seventy-one females and 39 males (18-60 years) reported prototypical tastes from and preference for Brussels sprouts, kale and asparagus as well as servings of vegetables consumed, excluding salad and potatoes. Intensity and hedonic ratings were made with the general Labeled Magnitude Scale. Data were analyzed with multiple linear regression and structural equation modeling. Vegetable sweetness and bitterness were independent predictors of more or less preference for sampled vegetables and vegetable intake, respectively. Those who taste PROP as most bitter also tasted the vegetables as most bitter and least sweet. The spatial pattern of quinine bitterness, suggestive of insult to chorda tympani taste fibers, was associated with less bitterness and sweetness from vegetables. Via structural equation modeling, PROP best explained variability in vegetable preference and intake via vegetable bitterness whereas the quinine marker explained variability in vegetable preference and intake via vegetable bitterness and sweetness. In summary, bitterness and sweetness of sampled vegetables varied by taste genetic and taste function markers, which explained differences in preference for vegetables tasted in the laboratory as well as overall vegetable intake outside the laboratory.