An assessment of binary mixture interactions for nine sweeteners

Binary mixtures of acesulfame K, aspartame, sodium cyclamate,fructose, glucose, stevioside, sodium saccharin, sucrose andxylitol were assessed using factorial mixture designs. A simpleadditive model was used to generate predictions for the sweetnessof the mixtures and these predicted responses were comparedto the observed sweetness ratings of the mixtures. It was foundthat the mixtures tended to exhibit superadditivity at low concentrations,additivity at intermediate concentrations and subadditivityat high concentrations. Synergistic and suppressive effectsin the mixtures were evaluated by comparing mixture responsesto the sweetness ratings of ‘self-mixtures’. Self-mixturedata were generated by treating a mixture of a substance withitself as if it were a mixture of two different substances.Synergism was defined as a mixture response that was greaterthan the sweetness of the component self-mixtures, and suppressionwas defined as a mixture response that was less than the sweetnessof the component self-mixtures. Of the 31 binary mixtures studied,18 showed synergism, two showed suppression and 11 did not differsignificantly from their components. It is hypothesized thatmultiple sweetness receptors or release from bitter suppressionmay account for the synergistic effects.     

Carbon catabolite repression of invertase during batch cultivations of Saccharomyces cerevisiae: the role of glucose, fructose, and mannose

When Saccharomyces cerevisiae are grown on a mixture of glucose and another fermentable sugar such as sucrose, maltose or galactose, the metabolism is diauxic, i.e. glucose is metabolized first, whereas the other sugars are metabolized when glucose is exhausted. This phenomenon is a consequence of glucose repression, or more generally, catabolite repression. Besides glucose, the hexoses fructose and mannose are generally also believed to trigger catabolite repression. In this study, batch fermentations of S. cerevisiae in mixtures of sucrose and either glucose, fructose or mannose were performed. It was found that the utilization of sucrose is inhibited by concentrations of either glucose or fructose higher than 5 g/l, and thus that glucose and fructose are equally capable of exerting catabolite repression. However, sucrose was found to be hydrolyzed to glucose and fructose, even when the mannose concentration was as high as 17 g/l, indicating, that mannose is not a repressing sugar. It is suggested that the capability to trigger catabolite repression is connected to hexokinase PII, which is involved in the in vivo phosphorylation of glucose and fructose. Received: 5 May 1998 / Received revision: 3 August 1998 / Accepted: 8 August 1998     

Sugar Absorption and Sucrose Inversion by Excised Tomato Roots

The growth of excised tomato roots in sucrose is accompaniedby the appearance in the medium of glucose and fructose. Thequantitative relations between this appearance of glucose andfructose in the medium, total sugar absorption by the roots,and the decrease in the sucrose concentration of the mediumdo not suggest any causal relationship between sucrose uptakeand glucose and fructose appearance in the medium. Excised tomato roots exhibit surface invertase activity witha pH optimum at 4.0–4.4. Alterations of external pH, whichdid not affect sucrose absorption, drastically altered the levelsof glucose and fructose appearing in the medium. Glucose is preferentially absorbed from mixtures of glucoseand fructose, and by adjustment of the ratio of the two sugars,a mixture can be obtained from which equimolar absorption ofthe two sugars occurs. Root growth in this mixture is, however,very poor compared with that occurring in presence of sucrose. The results are discussed in the light of earlier studies onsucrose uptake by cultured tomato roots.     

Synthesis of tastes other than the 'primaries': implications for neural coding theories and the concept of 'suppression'

It has been demonstrated that mixtures of ‘primary’tastes may be perceived as singular rather than as multiple(Erickson and Covey, 1980). This finding may be accounted forin two different and testable ways. First, suppression: oneof the tastes in the mixture may be suppressed by the other(i.e., in a mixture of A and B, A suppresses the taste of B);the prediction which follows from this hypothesis is that asolution of A (the suppressing component) should be indistinguishablefrom the AB mixture. Secondly, synthesis: the singularity ofthe mixture may arise from the formation of a new taste, andin this case both components should be distinguishable fromtheir mixture. The present data indicate that the latter istrue in some cases. Since the taste of these mixtures must beother than the primary tastes used to form them, these findingsquestion the presumption that only four ‘primaries’are adequate to describe the range of tastes.     

Sporulation in Rhizopus sexualis and Some Other Fungi Following a Period of Intense Respiration

Rhizopus sexualis grown at 20° C. on liquid I per cent.malt or glucose-asparagine medium showed a peak of respiratoryactivity between 40 and 55 hours-after inoculation. Rate ofrespiration then fell until it reached a steady low level whichcoincided with maximum mycelial growth. Zygospore initiationoccurred at or just after the peak of respiration. At a low temperature (9° C.) or with high concentrationsof glucose the respiration peak was less marked and no zygosporesdeveloped. Single ‘plus’ or ‘minus’strains of the heterothallic species Mucor hiemalis and Phycomycesblakesleeanus showed a pattern of respiration and mycelial growthsimilar to that of R. sexualis but no zygospores were formed.Zygospores did not develop without a preliminary period of intenserespiration, but such a peak period could occur without beingfollowed by zygospore formation. A strain of Sordaria fimicola was grown at 25° C. on a syntheticmedium with 5.0 per cent. sucrose or glucose as source of carbon.Respiration reached a peak at approximately 4 and 5 days respectively,the actual peak value being twice as large on sucrose as onglucose. Dry weight of mycelium was greater on glucose thanon sucrose. Perithecia were formed only on the sucrose medium.Visible peri-thecial initials were first seen shortly afterthe occurrence of the respiratory peak. Mature perithecia werepresent 3 days later. The possible significance of these results is discussed.     

The taste, odor and hedonic quality of polyglycerols

Twenty subjects judged the taste and odor intensity and thetaste and odor pleasantness/unpleasantness of five concentrationsof sucrose, glycerol, a commercial triglycerol, a syntheticlinear diglycerol and a synthetic linear triglycerol. Judgmentsof intensity were made using the method of magnitude estimation;judgments of pleasantness/unpleasantness were made using a graphicline scale. Only the two linear polyglycerols had appreciableodor intensity. Both were described as having an ‘acrid’or ‘burnt caramel’ quality. The odor exponent forthe linear triglycerol was extremely high (1.44) and may beattributed to its intensely unpleasant quality. Sucrose wascharacterized solely by sweet taste, glycerol and the commercialtriglycerol by sweet and bitter tastes, the linear diglycerolby sweet, bitter and sour tastes, and the linear triglycerolby bitter and sour tastes. The relationships between perceivedtaste intensity and concentration were well described by powerfunctions, although the slope of the psychophysical functionfor the linear triglycerol was markedly lower than that forthe other compounds. The relative order of taste intensitieswas: linear triglycerol > sucrose > glycerol = lineardiglycerol > commercial triglycerol. Judgments of taste (andodor) pleasantness/unpleasantness showed only sucrose and glycerolto have positive hedonic qualities. All the polyglycerols werejudged unpleasant at all concentrations. Differences in thetaste and odor characteristics of the commercial and synthetictriglycerols were attributed to the commercial product beinga mixture of over 20 compounds. Although the synthetic lineardi- and triglycerols are effective in lowering water activity,these data suggest that more purified crystalline forms mustbe synthesized before they can be used effectively as humectantsfor intermediate moisture foods.     

Effects of Inorganic Phosphate on the Utilization of Sucrose by Suspension-cultured Catharanthus roseus Cells

The metabolic fate of [U-¹⁴C]sucrose in suspension culturesof Catharanthus roseus cells was monitored for 96 h after thecells were transferred to fresh complete (‘+Pi’)or to phosphate-deficient Murashige and Skoog (‘–Pi’)medium. Sucrose was hydrolysed extracellularly to glucose andfructose. The rate of uptake of sugars by the cells was 1.5–3times higher in ‘+Pi’ culture than in ‘–Pi’culture. Little difference in the rate of incorporation of radioactivityinto the ethanol-soluble fraction was found between the ‘+Pi’and ‘– Pi’ cultures during the initial 24h of culture, but after 48 h the rate in ‘ +Pi’cultures was higher than that in ‘–Pi’ cultures.Incorporation of radioactivity into ethanol-insoluble macromoleculeswas always significantly higher in the cells in ‘+Pi’cultures than in those in ‘–Pi’ cultures.The results suggest that Pi strongly affects the utilizationof sugars by cultured plant cells through the stimulation oftransport of sugars as well as through the activation of metabolism. Catharanthus roseus, Madagascar periwinkle, suspension culture, inorganic phosphate, sucrose, transport, metabolism     

The State of Aggregation of Casein Affects the Storage Stability of Amorphous Sucrose, Lactose, and Their Mixtures

The effect of the state of aggregation of casein (micellar or non-micellar, as milk protein concentrate [MPC] or sodium caseinate [Na-caseinate], respectively) on water sorption, plasticization, and crystallization of freeze-dried matrices containing sucrose, lactose or their blends were studied. The Guggenheim–Anderson–de Boer (GAB) equation satisfactorily fitted to the water sorption data. In most cases, sugar crystallization—studied by water sorption behavior, x-ray diffraction, and non-isothermal calorimetry—occurred significantly slower in systems containing Na-caseinate compared to MPC. The type of casein did not affect the temperature range where the glass transition (T _g) was observed. Sugar/Na-caseinate mixtures showed higher instant crystallization temperatures (up to 20°C) than sugar/MPC mixtures. X-ray diffraction showed that: (a) crystallinity increased with increasing relative vapor pressure (RVP) > 44%; (b) lactose crystallized mainly as α-lactose monohydrate regardless of casein type; and (c) that sucrose crystals predominated the patterns of the sucrose/lactose mixtures. Results suggested that the way proteins organize in space (i.e., aggregation state) affected their interactions with neighboring sugar and water molecules, which led to differences in sugar crystallization behavior. Poster presented at the 4th International Workshop on Water in Food in Brussels March, 2006. Funded by CONACyT (Mexico) and Dippin’ Dots Inc., KY, USA.     

Purification of food-grade oligosaccharides using immobilised cells of Zymomonas mobilis

Immobilised cells of the bacterium Zymomonas mobilis were used to remove glucose, fructose, and sucrose from food-grade oligosaccharide mixtures. Unpurified fructo-, malto-, isomalto-, gentio-, and inulinoligosaccharides, containing total carbohydrate concentrations of 300 g l(-1), were added to immobilised cells, in 100 ml batch reactors. No pH control or nutrient additions were required. Contaminating glucose, fructose, and sucrose within the mixtures was completely fermented within 12 h. The fermentation end products were ethanol and carbon dioxide. A minor amount of sorbitol was also produced as a fermentation by-product in the inulin-oligosaccharide mixture. No degradation of the oligosaccharides in the mixtures was observed.     

Regulation of sucrose and starch metabolism in potato tubers in response to short-term water deficit

To investigate the effect of water stress on carbon metabolism in growing potato tubers (Solanum tuberosum L.), freshly cut and washed discs were incubated in a range of mannitol concentrations corresponding to external water potential between 0 and −1.2 MPa. (i) Incorporation of [¹⁴C]glucose into starch was inhibited in water-stressed discs, and labeling of sucrose was increased. High glucose overrode the changes at low water stress (up to −0.5 MPa) but not at high water stress. (ii) Although [¹⁴C]sucrose uptake increased in water-stressed discs, less of the absorbed [¹⁴C]sucrose was metabolised. (iii) Analysis of the sucrose content of the discs confirmed that increasing water deficit leads to a switch, from net sucrose degradation to net sucrose synthesis. (iv) In parallel incubations containing identical concentrations of sugars but differing in which sugar was labeled, degradation of [¹⁴C]sucrose and labeling of sucrose from [¹⁴C]glucose and fructose was found at each mannitol concentration. This shows that there is a cycle of sucrose degradation and resynthesis in these tuber discs. Increasing the extent of water stress changed the relation between sucrose breakdown and sucrose synthesis, in favour of synthesis. (v) Analysis of metabolites showed a biphasic response to increasing water deficit. Moderate water stress (0–200 mM mannitol) led to a decrease of the phosphorylated intermediates, especially 3-phosphoglycerate (3PGA). The decrease of metabolites at moderate water stress was not seen when high concentrations of glucose were supplied to the discs. More extreme water stress (300–500 mM mannitol) was accompanied by an accumulation of metabolites at low and high glucose. (vi) Moderate water stress led to an activation of sucrose phosphate synthase (SPS) in discs, and in intact tubers. The stimulation involved a change in the kinetic properties of SPS, and was blocked␣by protein phosphatase inhibitors. (vii) The amount of ADP-glucose (ADPGlc) decreased when discs were incubated on 100 or 200 mM mannitol. There was a strong correlation between the in vivo levels of ADPGlc and 3PGA when discs were subjected to moderate water stress, and when the sugar supply was varied. (viii) The level of ADPGlc increased and starch synthesis was further inhibited when discs were incubated in 300–500 mM mannitol. (ix) It is proposed that moderate water stress leads to an activation of SPS and stimulates sucrose synthesis. The resulting decline of 3PGA leads to a partial inhibition of ADP-glucose pyrophosphorylase and starch synthesis. More-extreme water stress leads to a further alteration of partitioning, because it inhibits the activities of one or more of the enzymes involved in the terminal reactions of starch synthesis. Received: 26 August 1996 / Accepted: 5 November 1996     

SHORT COMMUNICATION Factors Affecting Protoplast Culture ofCucumis melo'Green Delica'

Hypocotyls, cotyledons and etiolated half-expanded leaves ofCucumismelo‘Green Delica’ were used as explants for protoplastisolation and culture. Protoplasts isolated from cotyledonsand etiolated half-expanded leaves cultured in Durand, Potrykusand Donn (DPD) medium supplemented with 0.9 µMbenzylaminopurine(BAP), 3.6 µM2,4-dichlorophenoxyacetic acid (2,4-D) and1% sucrose, using the agarose bead culture method, were ableto form cell walls and subsequently go through cell division.Pretreatment of half-expanded leaf explants in the dark for14 d provided the best material for protoplast isolation andcell division. Approximately one third of protoplasts from etiolatedhalf-expanded leaves formed microcolonies. For hypocotyl protoplasts,none of the treatments used were suitable to induce cell division.There was no significant difference between sucrose, glucose,and sucrose plus glucose, in culture media on the plating efficiencyof leaf protoplasts ofC. melo‘Green Delica’; however,bigger colonies were formed in media supplemented with 1% sucrose.No shoot or whole plant regeneration was achieved. However,the methods reported here provide further information onC. meloprotoplastculture.Copyright 1998 Annals of Botany Company Cucumis melo,protoplast culture, 2,4-D, BAP, yeast extract, casein hydrolysate.     

Effects of selective adaptation on coding sugar and salt tastes in mixtures

Little is known about coding of taste mixtures in complex dynamic stimulus environments. A protocol developed for odor stimuli was used to test whether rapid selective adaptation extracted sugar and salt component tastes from mixtures as it did component odors. Seventeen human subjects identified taste components of "salt + sugar" mixtures. In 4 sessions, 16 adapt-test stimulus pairs were presented as atomized, 150-μL "taste puffs" to the tongue tip to simulate odor sniffs. Stimuli were NaCl, sucrose, "NaCl + sucrose," and water. The sugar was 98% identified but the suppressed salt 65% identified in unadapted mixtures of 2 concentrations of NaCl, 0.1 or 0.05 M, and sucrose at 3 times those concentrations, 0.3 or 0.15 M. Rapid selective adaptation decreased identification of sugar and salt preadapted ambient components to 35%, well below the 74% self-adapted level, despite variation in stimulus concentration and adapting time (<5 or >10 s). The 96% identification of sugar and salt extra mixture components was as certain as identification of single compounds. The results revealed that salt-sugar mixture suppression, dependent on relative mixture-component concentration, was mutual. Furthermore, like odors, stronger and recent tastes are emphasized in dynamic experimental conditions replicating natural situations.     

A moment-by-moment comparsion of sucrose and saccharin drinking by the rat

Comparisons were made between the ingestion patterns in ratsto a 0.2% sodium saccharin solution and to a 32% sucrose solutionin both short-term (30 min, one solution only) and long-term(23 h, solution versus water) tests. The resolution of measurementin the short- and long-term tests was 0.5 and 30 s respectively.Analysis programs for both procedures allowed for a quantificationof the ingestion patterns over time, showing details of thelick bursts in the short-term tests and ingestion bouts in the23-h tests. Although the quantities of sucrose and saccharinconsumed in the long-term tests were equal, the drinking patternsfor water, saccharin and sucrose were markedly different duringthe three testing periods, (i) There were fewer drinking boutsto the sucrose than to the saccharin or water, (ii) The averagebout of sucrose was much larger than the saccharin or waterbouts, (iii) The inter-bout intervals for sucrose were muchlonger than those for saccharin, (iv) Nearly half of the sucroseintake occurred during the ‘lights-on’ portion ofthe 23-h drinking period as compared to less than one-thirdfor saccharin or water, (v) Food intake when saccharin was presentwas equal to normal food intake when only water was available.However, in the presence of sucrose, the number and the sizeof feeding bouts decreased resulting in a 36% reduction in foodintake. Similar results were found in the short-term tests whencomparing sucrose and saccharin ingestion in that the quantitiesconsumed were not reliably different, but the ingestion patternswere, (i) The rats had many more bursts of licking saccharinthan sucrose, (ii) The saccharin bursts were much shorter thanthose for sucrose, (iii) Saccharin licking occurred off andon throughout the 30-min testing period while sucrose was consumedat a rapid rate at first and then terminated in 10–15min from the period onset. Inferences about the different tastesof saccharin and sucrose to the rat arc drawn from the detailedpattern analyses.     

Simultaneous utilization of glucose and sucrose by thermophilic fungi.

The utilization of mixtures of glucose and sucrose at nonlimiting concentrations was studied in batch cultures of two common thermophilic fungi, Thermomyces lanuginosus and Penicilium duponti. The sucrose-utilizing enzymes (sucrose permease and invertase) in both fungi were inducible. Both sugars were used concurrently, regardless of their relative proportion in the mixture. At the optimal growth temperature (50 degrees C), T. lanuginosus utilized sucrose earlier than it did glucose, but at a suboptimal growth temperature (30 degrees C) the two sugars were utilized at nearly comparable rates. The coutilization of the two sugars was most likely possible because (i) invertase was insensitive to catabolite repression by glucose, (ii) the activity and affinity of the glucose transport system were lowered when sucrose was included in the growth medium, and (iii) the activity of the glucose uptake system was also subject to repression by high concentrations of glucose itself. The concurrent utilization of the available carbon sources by thermophilic fungi might be an adaptive strategy for opportunistic growth in nature under conditions of low nutrient availability and thermal fluctuations in the environment.     

The Production of Bacillus cereus Enterotoxins Is Influenced by Carbohydrate and Growth Rate

Enterotoxin production is a key factor in Bacillus cereus food poisoning. Herein, the effect of the growth rate (μ) on B. cereus toxin production when grown on sucrose was studied and the Hemolytic BL enterotoxin (HBL) and nonhemolytic enterotoxin (Nhe) production by B. cereus was compared according to carbohydrate at μ = 0.2 h⁻¹. The anaerobic growth was carried out on continuous cultures in synthetic medium supplemented with glucose, fructose, sucrose, or an equimolar mixture of glucose and fructose. Concerning the HBL and Nhe enterotoxin production: (1) the highest enterotoxin production has occurred at μ = 0.2 h⁻¹ when growing on sucrose; (2) HBL production was repressed when glucose was consumed and the presence of fructose (alone or in mixture) cancelled glucose catabolite repression; (3) the consumption of sucrose increased Nhe production, which was not affected by the catabolite repression. Furthermore, analysis of the fermentative metabolism showed that whatever the μ or the carbon source, B. cereus used the mixed acid fermentation to ferment the different carbohydrates. The enterotoxin productions by this strain at μ = 0.2 h⁻¹ are highly influenced by the carbohydrates that do not involve any fermentative metabolism changes.     

‘Osmotic pump‘ feeding by coreids

Species of Coreidae (Heteroptera) cause ‘water soaked’ lesions in their food plants. Such insects typically feed from parenchyma in and surrounding vascular tissues and also cause acropetal wilting and necrosis of small diameter shoots. Feeding byMictis profana (Fabr.) in South Australia on the shoots ofAcacia iteaphylla F. Muell. ex Benth. was found to cause a local, concurrent increase in both water content and free amino acid concentration, consistent with phloem unloading. Coreids, unlike other groups of phytophagous Heteroptera, secrete a salivary sucrase (α-D-glucohydrolase, EC 3.2.1.48) as probably the sole salivary carbohydrase, and tissues attacked byM. profana showed more sucrose hydrolysing activity than unattacked. The salivary enzyme is postulated to cause unloading of solutes into the apoplast due to the osmotic effects of conversion of endogenous sucrose to glucose and fructose, allowing the insect to suck the leaked contents of many cells from a single locus. The term ‘osmotic pump feeding’ is proposed for such a process. In demonstrations of its feasibility, infiltration of shoots with mixtures of glucose and fructose stoichiometrically equivalent to isosmotic sucrose increased the amounts of tissue sap and amino acid that could be sucked from the tissues; similarly, invertase and 1 M sugars forced into the extracellular space of stem sections increased the amino acids offloaded into the bathing solutions.     

Confusion in the use of the taste adjectives 'sour' and 'bitter'

Subjects from Britain and America were tested on their skillat applying the taste adjectives ‘sweet’, ‘sour’,‘salty’, and ‘bitter’ to clearly distinguishablesolutions of sucrose, citric acid, NaCl and quinine sulphate,respectively. The main error that occurred was calling citricacid ‘bitter’ while the tendency to call quininesulphate ‘sour’ was not so common; this is the wellknown sour-bitter confusion. A sour-salty confusion was alsonoted as well as a tendency to call citric acid ‘sweet’.All these confusions were rectified by mere definition usingstandards. Skill at applying taste adjectives was not alwaysfound to be consistent over time. More errors occurred at lowersolution concentrations, even though stimuli were clearly distinguishable;indistinguishability of stimuli may account for some confusionsin other studies. ^*Present address: Department of Psychology, University of Bristol,Bristol BS8 1HH, England.     

Effects of Rapidly and Slowly Permeating Osmotica on Macromolecule and Sucrose Synthesis

Metabolic effects induced by low water potentials were separatedfrom those induce by low turgor and hydration, by comparingresponses of plant cells to rapidly and slowly permeating osmotica. Metabolic processes selected for study were those which areclaimed to be very sensitive to water deficits. ‘Glucose-stimulated’respiration, and sucrose and starch synthesis, were measuredin Chlorella pyrenoidosa and protein synthesis in vacuolatedand non-vacuolated segments of Zea mays roots. Mannitol, a slowlypermeating osmoticum, stimulated sucrose synthesis and reducedrates of other metabolic processes, including starch and proteinsynthesis. In contrast, metabolism changed little during exposureto low water potentials induced by ethylene glycol, which rapidlypermeates cells. The experiments demonstrated that water and solute potentialsas low as—20 atm had only very small effects on metabolism,strongly suggesting that water deficits act principally viadecreases in turgor and hydration.