A major challenge in taste research is to overcome the flavour imperfections in food products and to build nutritious strategies to combat against obesity as well as other related metabolic syndromes. The field of molecular taste research and chemical senses has contributed to an enormous development in understanding the taste receptors and mechanisms of taste perception. Accordingly, the development of taste-modifying compounds or taste modulators that alter the perception of basic taste modalities has gained significant prominence in the recent past. The beneficial aspects of these substances are overwhelming while considering their potential taste-modifying properties. The objective of the present review is to provide an impression about the taste-modulating compounds and their distinctive taste-modifying properties with reference to their targets and proposed mechanisms of action. The present review also makes an effort to discuss the basic mechanism involved in oro-gustatory taste perception as well as on the effector molecules involved in signal transduction downstream to the activation of taste receptors.

Reduced plasma vitamin D (VD) levels may contribute to excessive white adipose tissue, insulin resistance (IR) and dyslipidaemia. We evaluated the effect of chronic oral VD supplementation on adiposity and insulin secretion in monosodium glutamate (MSG)-treated rats. During their first 5 d of life, male neonate rats received subcutaneous injections of MSG (4 g/kg), while the control (CON) group received saline solution. After weaning, groups were randomly distributed into VD supplemented (12 µg/kg; three times/week) and non-supplemented (NS) rats, forming four experimental groups (n 15 rats/group): CON-NS, CON-VD, MSG-NS and MSG-VD. At 76 d of life, rats were submitted to an oral glucose tolerance test (OGTT; 2 g/kg), and at 86 d, obesity, IR and plasma metabolic parameters were evaluated. Pancreatic islets were isolated for glucose-induced insulin secretion (GIIS), cholinergic insulinotropic response and muscarinic 3 receptor (M3R), protein kinase C (PKC) and protein kinase A (PKA) expressions. Pancreas was submitted to histological analyses. VD supplementation decreased hyperinsulinaemia (86 %), hypertriacylglycerolaemia (50 %) and restored insulin sensibility (89 %) in MSG-VD rats, without modifying adiposity, OGTT or GIIS, compared with the MSG-NS group. The cholinergic action was reduced (57 %) in islets from MSG-VD rats, without any change in M3R, PKA or PKC expression. In conclusion, chronic oral VD supplementation of MSG-obese rats was able to prevent hyperinsulinaemia and IR, improving triacylglycerolaemia without modifying adiposity. A reduced cholinergic pancreatic effect, in response to VD, could be involved in the normalisation of plasma insulin levels, an event that appears to be independent of M3R and its downstream pathways.

Previous research suggests that monosodium glutamate (MSG) may have a biphasic effect on appetite, increasing appetite within a meal with its flavour-enhancing effect, but enhancing subsequent satiety due to its proposed role as a predictor of protein content. The present study explored this by assessing the impact of a 450 g soup preload differing in MSG concentration (1 % MSG added (MSG+) or no MSG (MSG–)) and nutrient content (low-energy control or high-energy carbohydrate or high-energy protein) on rated appetite and ad libitum intake of a test meal in thirty-five low-restraint male volunteers using a within-participant design. Protein-rich preloads significantly reduced intake at the test meal and resulted in more accurate energy compensation than did carbohydrate-rich preloads. This energy compensation was stronger in the MSG+ protein conditions when compared with MSG+ carbohydrate conditions. No clear differences in rated appetite were seen in MSG or the macronutrient conditions alone during preload ingestion or 45 min after intake. Overall, these findings indicate that MSG may act to further improve energy compensation when provided in a protein-rich context.

Studies indicate a positive association between dietary salt intake and some diseases, which has promoted the tendency to reduce the sodium in foods. The objective of this study was to determine the equivalent amount of different sodium chloride replacements required to promote the same degree of ideal saltiness in butter and to study the sensory profile of sodium chloride and the substitutes using the analysis of Temporal Dominance of Sensations (TDS). Using the magnitude estimation method, it was determined that the potencies of potassium chloride, monosodium glutamate and potassium phosphate relative to the 1% sodium chloride in butter are 83·33, 31·59 and 33·32, respectively. Regarding the sensory profile of the tested salt substitutes, a bitter taste was perceived in the butter with potassium chloride, a sour taste was perceived in the butter with potassium phosphate and sweet and umami tastes were dominant in the butter with monosodium glutamate. Of all the salt substitutes tested calcium lactate, potassium lactate, calcium chloride and magnesium chloride were impractical to use in butter.

The effect of monosodium glutamate (MSG) supplementation in soup or broth on satiety is not well understood. In the present study, the relative effects of four chicken broths with or without added MSG on motivational ratings and energy intakes at the next meal were compared using a double-blinded, within-subject design. A total of thirty-five normal-weight women, aged 20–40 years, took part in four study sessions. The four broths were base chicken broth (63 kJ), broth with added MSG (1·19 g) and nucleotides (0·03 g), broth with added MSG (1·22 g), and broth with added fat (BAF; 681 kJ). The preloads were presented twice at 09.00 and 11.15 hours for a maximum cumulative dose of 2·44 g MSG. Motivational ratings were collected before and at 15 min intervals post-ingestion for a total of 210 min. A test lunch meal was served at 12.00 hours, and plate waste was measured. The addition of MSG to chicken broth did not increase energy intakes at lunch or affect motivational ratings over the entire testing session. Both hunger and desire to snack between the second preload exposure and the test meal were significantly reduced in the MSG condition relative to the base broth condition (both, P =  0·03). However, only the BAF significantly suppressed energy intakes at lunch compared with the base broth control condition. Supplementing chicken broth with MSG can increase subjective ratings for satiety but does not alter energy intake at the next meal relative to an equal energy broth without added MSG.

The incidence of obesity and type 2 diabetes mellitus (T2DM) is increasing, and new experimental models are required to investigate the diverse aspects of these polygenic diseases, which are intimately linked in terms of aetiology. Feline T2DM has been shown to closely resemble human T2DM in terms of its clinical, pathological and physiological features. Our aim was to develop a feline model of diet-induced weight gain, adiposity and metabolic deregulation, and to examine correlates of weight and body fat change, insulin homeostasis, lipid profile, adipokines and clinical chemistry, in order to study associations which may shed light on the mechanism of diet-induced metabolic dysregulation. We used a combination of partially hydrogenated vegetable shortening and high-fructose corn syrup to generate a high-fat–high-fructose diet. The effects of this diet were compared with an isoenergetic standard chow, either in the presence or absence of 1·125 % dietary monosodium glutamate (MSG). Dual-energy X-ray absorptiometry body imaging and a glucose tolerance test were performed. The present results indicate that dietary MSG increased weight gain and adiposity, and reduced insulin sensitivity (P < 0·05), whereas high-fat–high-fructose feeding resulted in elevated cortisol and markers of liver dysfunction (P < 0·01). The combination of all three dietary constituents resulted in lower insulin levels and elevated serum β-hydroxybutyrate and cortisol (P < 0·05). This combination also resulted in a lower first-phase insulin release during glucose tolerance testing (P < 0·001). In conclusion, markers of insulin deregulation and metabolic dysfunction associated with adiposity and T2DM can be induced by dietary factors in a feline model.

In a fed and orally stimulated state, whether the addition of monosodium glutamate (MSG) (alone or in combination with inosine monophosphate-5 (IMP-5)) to a high-protein (HP) meal leads to early satiety and a difference in energy intake at a second course was investigated. Ten men and twelve women consumed, in random order, a first-course meal consisting of: (1) water (control); (2) a HP meal with 0·6 % MSG and 0·25 % IMP-5; (3) a HP meal with no additives; (4) a HP meal with MSG only; (5) a sham-fed meal 2 (oral-stimulation). Appetite perceptions, plasma concentrations of glucagon-like peptide 1 (GLP-1), glucose and insulin, and energy intake at a buffet (i.e. a second course) were measured before and after each condition. Changes in appetite, and in GLP-1, glucose and insulin, were similar for the three fed HP conditions and all were greater (post hoc all P < 0·01) than the control and sham conditions. Energy intake was not different following the HP+MSG+IMP (1·86 (sem 0·3) MJ) as compared with the HP+MSG-only (2·24 (sem 0·28) MJ) condition (P = 0·08), or for the HP+MSG+IMP compared with the HP no-additives condition (1·60 (sem 0·29) MJ) (P = 0·21). Following the HP+MSG-only condition, 0·64 (sem 0·20) MJ more energy was consumed compared with the HP no-additives condition (P = 0·005). We conclude that the addition of MSG to a HP meal does not influence perceptions of satiety and it may increase energy intake at a second course. Cephalic responses after the sham condition were of similar magnitude to the control and therefore just tasting food is not enough to influence appetite and energy intake.

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 ≤ 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.

1. Sheep with oesophageal fistulas were used in sham-feeding experiments to assess how sham intakes were affected by (a) physical form of straw (finely and coarsely ground; ground and pelleted), (b) type of food (straw pellets v. lucerne (Medicago sativa) hay pellets) and (c) additions of monosodium glutamate (MSG) with or without NaCl to the various straw diets. Normal animals were also fed on diets with and without MSG. Sham intakes of fine-ground loose straw (25 g/30 min) were markedly less (P = 0.002) than those of ground and pelleted straw (711 g/30 min). However, MSG at 5–40 g/kg fine and coarse ground straw increased sham intakes by 146 (P = 0.04) and 164% (P = 0.01) respectively. These findings indicated that the intakes of poor-quality diets can be increased by compacting them or by improving their palatability with MSG, or both. Sham intakes of straw pellets in two experiments were 32 (P = 0.02) and 45% (P = 0.008) of those of lucerne pellets (436 v. 1366 and 737 v. 1640 g/30 min). However, MSG at 20 g/kg straw pellets increased sham intakes from 674 to 1100 g/30 min (P = 0.05). When the MSG was mixed with NaCl (20 g/kg), the intakes of straw pellets were increased from 1089 to 1512 g/30 min (P = 0.02). Thus, the addition of MSG with or without NaCl increased the intakes of straw pellets. The highest intakes of the straw pellets treated with MSG were similar to those for lucerne pellets. When MSG-treated ammoniated barley straw (10 g/kg) was fed to normal sheep, the MSG increased DM intakes by 10 % (719–789 g/d; P = 0.04). MSG sprayed onto grass hay (10 g/kg) did not, however, affect daily DM intakes by these sheep. In general, the findings indicate that the intake of straw by ruminants may be increased by compressing it to form pellets or cubes and by adding MSG.

The effect of monosodium L glutamate (MSG) on diet palatability and piglet performance during the suckling and weaning periods was studied in the course of five successive experiments involving a total of 230 litters during the suckling period and 120 pens of seven piglets during the post-weaning period. During the suckling period, the addition of 5 g MSG per kg diet led to a significant 0·36 proportional increase of creep food intake from the 18th day post farrowing. However, no increase in weaning weight was observed subsequent to the intake of the diet with added MSG. Moreover, in an experiment where MSG was added with an associated commercial flavour, no flavour enhancing effect of MSG was detectable. Few health problems were encountered at weaning and the number of scouring piglets was not related to one particular diet. During the first 13 days after weaning the addition of MSG to the diet increased daily food intake by proportionately 0·1 (P < 0·01) as well as growth rate by proportionately 0·07 (P < 0·01). Moreover, the addition of MSG to the diet was more effective with piglets of low weaning weight and thus contradicted the classical relationship between post-weaning performance and weaning weight. Finally, in an experiment where weaning occurred at lower ambient temperature, no improvement of post-weaning performance was observed following the addition of MSG.