Differential effects of glucose and fructose on hexose metabolism in dog spermatozoa

Incubation of dog spermatozoa with 10 mmol l(-1) glucose or fructose rapidly increased the intracellular content of glucose 6-phosphate and fructose 6-phosphate, although the effect of fructose was greater. These effects were correlated with increases in ATP, ribose 5-phosphate and glycogen contents, and in the rates of formation of L-lactate and CO2. In all cases, except for ATP and glycogen, the effect of fructose was greater than that of glucose. The total hexokinase activity of the crude extracts of dog spermatozoa was more sensitive to fructose than to glucose at lower concentrations (0.1-3.0 mmol l(-1)). Both monosaccharides induced a fast and intense increase in the overall tyrosine phosphorylation of dog spermatozoa, although their specific induced-phosphorylation patterns differed slightly. Glut 3 and Glut 5 hexose transporters were the main hexose transporters in dog spermatozoa; however, other possible SGLT family-related hexose transporters were also localized. These data indicate that, at concentrations from 1 mmol l(-1) to 10 mmol l(-1), fructose has a stronger effect than glucose on hexose metabolism of dog spermatozoa. These differences appear to be related to variations in the sensitivity of hexokinase activity. Moreover, the differential hexose metabolism induced by the two sugars had distinct effects on the function of dog spermatozoa, as revealed by the diverse patterns of tyrosine phosphorylation.     

Metabolic studies of a fructose-intolerant yeast by in vivo 31P-nuclear magnetic resonance spectroscopy

The metabolic effects of the administration of fructose to a yeast expressing the cDNA for rat liver ketohexokinase have been investigated by ³¹P-nuclear magnetic resonance spectroscopy. Cessation of growth suffered by the yeast on exposure to 5 and 25 mM-fructose was accompanied by a large accumulation of fructose 1-phosphate at the expense of cytoplasmic orthophosphate and nucleoside triphosphate. Shifts in resonances were consistent with a drop in cytoplasmic pH. Arresting growth with 1 mM-fructose, however, did not result in these changes, although a large accumulation of fructose 1-phosphate occurred which may have been supported by the mobilization of polyphosphates.     

Influence of the carbohydrate source on beta-glucan production and enzyme activities involved in sugar metabolism in Pediococcus parvulus 2.6

The influence of carbohydrate source on growth, exopolysaccharide (EPS) production and on the activity of the enzymes implicated in energy generation and UDP-glucose synthesis in Pediococcus parvulus 2.6 was evaluated. The highest EPS production was obtained on glucose, while fructose was a poor substrate for EPS synthesis. HPLC and NMR analysis on monomer composition and structure of the EPS showed that this strain produced the same beta-glucan, regardless of the carbohydrate source. The alpha-phosphoglucomutase specific activities were dependent on the carbohydrate source and a high correlation between the activity of this enzyme and the amount of EPS was found in glucose- and maltose-grown cultures. alpha-UDP-glucose pyrophosphorylase activity, necessary for the activation of glucose, was very low, but significantly higher on glucose as sugar source. In vitro phosphorylation assays and transport activities showed that glucose is taken up by a proton motive force-dependent permease, while fructose is internalized by an inducible phosphotransferase system, which renders fructose-6-phosphate. The levels of 6-phosphofructokinase activity and alpha-phosphoglucomutase activities determined on fructose were higher and lower, than those found on glucose or maltose, respectively. This suggests that fructose-6-phosphate is mainly diverted to glycolysis and explains the low EPS synthesis on fructose. Results indicate that alpha-phosphoglucomutase and/or alpha-UDP-glucose pyrophosphorylase might be the bottlenecks for EPS biosynthesis, opening the field for metabolic-engineering strategies aimed to improve EPS production.     

1-MCP处理对不同期采收的阿克苏富士苹果在采后贮藏期糖代谢的影响

以阿克苏富士苹果为试材,通过测定在贮藏过程中(0~150d),果实蔗糖、葡萄糖、果糖和山梨醇含量,以及蔗糖磷酸合成酶(SPS)、蔗糖合成酶(SS-S、SS-C)、酸性转化酶(AI)、中性转化酶(NI)和山梨醇脱氢酶(SDH)的活性,研究采后苹果果实糖代谢及相关酶活性的变化规律并分析了1-MCP处理对它们的影响。结果表明:在采后贮藏期间1-MCP处理在一定程度上抑制了贮藏过程中富士苹果果实蔗糖、葡萄糖、果糖和山梨醇含量的增加,且对不同采收期果实酶活性的影响效果不同,果实中蔗糖、山梨醇含量以及SDH活性呈下降趋势,果糖含量、葡萄糖含量、与SPS、SS-S活性呈先下降后上升趋势,AI与NI在贮藏过程中出现明显峰值,且1-MCP处理可以显著提高这一峰值。     

Effect of fructose on the hexosamine turnover in the rat crystalline lens

Rats were given isocaloric rations containing starch (control) and varying amounts of fructose as carbohydrates. Hexosamines were isolated from the lens, glycoproteins--from the blood serum, and their turnover was studied. A drastic deceleration of hexosamine turnover in the lens was observed at high-fructose diets (20 and 40% of fuel value), while glycoprotein turnover in the blood plasma was not changed as compared to the control, glucose-6-phosphate dehydrogenase in red blood cells was decreased, insulin level was lowered, and glucose level in the blood serum rose insignificantly. It has been suggested that fructose may be cataractogenic in animals.     

Co-crystallization of Sucrose at High Concentration in the Presence of Glucose and Fructose

ABSTRACT: Co-crystallization of sucrose from a highly concentrated sucrose syrup (≤ 7% moisture, w/w) at 131 °C with 0, 5, 10, 15, and 20% of fructose, glucose, or a mixture of fructose and glucose was investigated. The crystallization of sucrose was delayed in presence of these lower molecular weight sugars. The DSC melting endotherm of co-crystallized samples exhibited a decrease in crystalline sucrose in the sample as a function of increased level of glucose and fructose. The mechanical strength of co-crystallized granules was found to be related to the moisture content and the amount of glucose or fructose content in the sample. The samples containing 10, 15, and 20% glucose in co-crystallized product demonstrated crystallization of glucose in its monohydrate form during 1 mo of storage.     

CHANGES IN SUGARS AND LYSINE IN BABY FOODS DURING STORAGE

The effect of storage on sugar content (fructose, glucose, sucrose) and free lysine in vegetable, meat, fish and fruit baby foods for a period of two years and at temperatures of 5, 15 and 25C were studied. The results showed that under these storage conditions a decrease occurred in fructose, glucose and sucrose for vegetable, meat and fish foods. A drop in sucrose was found in the fruit sample, together with an increase in fructose and glucose. The increase of reducing sugars in this sample is attributed to the hydrolysis of sucrose, an effect which is favorable because of storage temperature. A drop in free lysine was found for the four types of samples; this decrease was dependent on storage temperature but mainly on the time of storage. After one year, the levels of lysine were decreased by half or more at all temperatures. Although infants can get lysine from other sources such as milk and cereals, the lysine loss can be important leading to negative nutritional consequences if infants mainly eat baby foods stored at least for one year. The loss of reducing sugars and of lysine showed that during storage of these products a Maillard browning reaction between reducing sugar and lysine occurred.     

NADP-linked dehydrogenases in secreted milk

The activities of glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, malic enzyme, lactate dehydrogenase and malate dehydrogenase have been determined in secreted milk from sows, rats and rabbits. Within each species, although there was considerable variation in the absolute activities of these enzymes, the relative activities were similar to those observed for, or previously published for mammary homogenates. The only exception was milk glucose 6-phosphate dehydrogenase which tended to lose activity upon prolonged storage in the mammary gland. These results suggest that the pattern of milk enzymes can be an accurate reflection of that occurring in the mammary gland.     

Biochemical changes in the water-soluble carbohydrates during the development of chicory (Cichorium intybus Linn) roots

Qualitative and quantitative changes in the water-soluble carbohydrates have been studied during the development of chicory roots. Besides sucrose, glucose and fructose, some inulin-type glucofructosans have been detected at all stages of development of the roots. The contents of the total water-soluble carbohydrates, free glucose and bound fructose increase whereas bound glucose decreases with the advancement in the growth of the roots. The ratio of the concentration of bound fructose to that of bound glucose increases with the ageing of the roots and reaches its maximum value around the month of June, indicating thereby that the maturity of the plant is characterised by an increase in the content of glucofructosans at the expense of sucrose.     

Influence of freezing process on free sugars content of papaya and banana fruits

Changes in individual sugar content (fructose, glucose and sucrose) during freezing and frozen storage have been evaluated by HPLC on papaya (Carica papaya grupo Solo var Sunrise), fruits proceedings from female and hermaphrodite flowers, and banana (Musa cavendishii var enana). Effects of thermal treatments, such as blanching and microwaving, prior to freezing banana fruit were examined. Both an increase in total sugar levels of papaya samples during freezing and a decrease in sucrose, by invertase, were found followed by an increase in fructose and glucose. A slight decrease in total sugars of banana samples during freezing and storage has been observed, with no significant differences between the pretreatments applied. © 1998 SCI.     

Influence of Storage Duration and Temperature on Sweet Potato Sugar Content and Chip Color

Sugar concentration and chip color of three orange-flesh and two white-flesh sweet potato cultivars were determined after various lengths of storage at different temperatures. Lightest colored chips were produced from roots chipped immediately after harvest and from cultivars which contained the lowest levels of glucose and fructose. Storage of roots at 32°, 15.6°, or 7°C after harvest resulted in increased sucrose, glucose and fructose concentrations and darker colored chips. Manipulation of storage temperature was not successful in lowering reducing sugar concentration in any cultivar.     

贮藏温度对采后龙眼果实糖代谢及其相关酶活性的影响

研究采后不同贮藏温度(25、15、4℃)对'石硖'龙眼果实糖组分及相关酶活性的影响.测定龙眼果肉可溶性固形物含量(SSC)、3种主要糖含量和糖代谢相关酶活性的变化,对不同贮藏温度各个时期样品进行主成分分析和载荷因子分析,并对各指标进行相关性分析.结果表明:25℃贮藏的龙眼SSC下降最快,贮藏8 d即从23.5％降至22...     

An enzyme‐based method for the rapid determination of sucrose,glucose and fructose in sugar beet roots and the effects of impact damage and postharvest storage in clamps

A high‐throughput enzyme‐coupled assay is described for the determination of sucrose, glucose and fructose in sugar beet roots. This method is sensitive, rapid and inexpensive and has been used to highlight the increases in sucrose loss following root stresses such as freezing or aggressive harvesting. Sugar beet roots lose 12.5% of their sucrose following an episode of impact damage greater than 2 J, rising to 19.7% loss after 8 J, with concurrent increases in glucose and fructose. Increases in glucose and fructose are particularly pronounced following a period of clamp storage (up to 2.3 and 3.3 µg mg^?1 fresh weight, respectively). © 2001 Society of Chemical Industry     

Bioactive amines and carbohydrate changes during ripening of ‘Prata'' banana (Musa acuminata × M. balbisiana)

Green bananas were harvested at the full three-quarter stage, conditioned in polyethylene and stored for 35 days at 16 ± 1 °C and 85% relative humidity. Peel colour changed with time. The yellow colour ideal for consumption was achieved at 21 days and, after 28 days, brown specks started to appear. There was a significant increase in the pulp-to-peel ratio. The green fruit had high starch and low soluble sugars levels. Starch levels decreased significantly throughout ripening. At the seventh day of storage sucrose was prevalent, however, fructose and glucose levels increased while sucrose remained constant, decreasing after 28 days. Starch loss followed a first order reaction. Formation of glucose and fructose followed zero order kinetics with higher rate for fructose. The bioactive amines detected were putrescine, spermidine and serotonin. Serotonin decreased significantly after the 14th day of storage. Putrescine levels were similar up to 21 days and decreased significantly thereafter.     

Fructo-oligosaccharide changes during the storage of dehydrated commercial garlic and onion samples

The composition of fructo-oligosaccharides (FOS), together with glucose, fructose and sucrose, has been determined in commercial dehydrated samples of onion ( Allium cepa L.) and garlic ( Allium sativum L.). No qualitative differences were detected among the FOS identified in both onion and garlic. Results show a lower FOS content in garlic than in onion in all samples analysed. In garlic samples, FOS with degree of polymerisation from 3 to 7 were identified and quantified for the first time. In addition, a study on the effect of the storage in these carbohydrates has been carried out under controlled conditions (50 °C, a _w 0.44). The storage seemed to promote important changes in the content of glucose and fructose, which could participate in the Maillard reaction and in the composition of sucrose and FOS, whose hydrolysis was noticeable during the storage time. Therefore, all these chemical changes should be considered to evaluate the quality of these foods.     

Reducing sugars effect on available lysine loss of casein by moderate heat treatment

In order to investigate the effect of various reducing sugars on the available lysine loss by Maillard reaction, four model systems were prepared by mixing casein with glucose, fructose, lactose or maltose, followed by storage at 37 °C, 50 °C and 60 °C. The available lysine contents were monitored periodically. Highest and lowest reaction rates were observed in the model systems containing glucose and fructose, respectively, at the three temperatures. The two disaccharides behaved very similarly, with reaction rates between those of the monosaccharides studied. The activation energies of glucose, lactose and maltose systems were similar (116–132 kJ mol⁻¹), while that of fructose was somewhat higher (166kJ mol⁻¹). This difference was supposed to be in part due to the different mechanism of tautomerization of fructose, highly dependent on temperature. Therefore, though the potential nutritional damage at moderate temperatures is lower when fructose is used instead of other reducing sugars, its higher activation energy can reverse the effect at higher temperatures.     

Sustained oscillations in free-energy state and hexose phosphates in yeast

In a population of intact cells of the yeast Saccharomyces cerevisiae the dynamics of glycolytic metabolism were investigated under the condition of sustained oscillations. At 5-s intervals cells were quenched in −40°C methanol, extracted and the intracellular concentrations of glycolytic metabolites, adenine nucleotides and phosphate were analysed. Oscillations were found for the glycolytic intermediates glucose 6-phosphate, fructose 6-phosphate and fructose 1,6-bisphosphate. At variance with earlier reports on transient glycolytic oscillations, some intermediates further down the glycolytic pathway did not oscillate significantly, even though NADH did. In addition, the adenylate energy charge and the free energy of ATP hydrolysis oscillated significantly. Dynamic coupling through the latter may be responsible for this effective compartmentation of glycolytic dynamics.     

STABILITY OF ANTHOCYANINS, PHENOLS AND FREE RADICAL SCAVENGING ACTIVITY THROUGH SUGAR ADDITION DURING FROZEN STORAGE OF BLACKBERRIES

Influence of sugar and mixtures of sugar on color retention of two varieties of blackberries, Thornfree and Cacanska bestrna, were investigated during storage at − 18C for 12 months. After harvest, blackberries were coated with sugars (sucrose, fructose and glucose) and different sugar (sucrose  +  fructose  +  glucose, fructose  +  glucose, fructose  +  sucrose) mixtures. Anthocynin content, total phenol content and free radical scavenging activity of prepared samples were evaluated. Ratio of fruit : sugar was 1:1. The highest anthocyanin retention was in blackberry samples with glucose addition and the lowest in samples with sucrose addition, in both cultivars. Blackberry samples with sucrose addition had even lower retention than samples without sugar addition. Samples with an addition of other sugars had higher retention of anthocyanin than samples stored without sugars.

PRACTICAL APPLICATION

Possibility of phenols retention of blackberries due to sugar addition, during cold storage was investigated. Results showed that glucose had the most positive effect on anthocyanins retention as well as total phenolic compounds content. For that reason, certain amount of sucrose in fruit preserves can be replaced by addition of glucose, and for that reason retention of phenolic compounds can be higher and, as could be expected, more effective against oxidative stress in human body due to intake of product formulation with glucose.     

Effects of cultivar,root weight,storage and boiling on carbohydrate content in carrots (Daucus carota L)

The effects of cultivar (n = 4), root weight (n = 4), storage (5 months) and boiling (7 min) and their interactions on the content of dry matter and carbohydrates were studied and ranked in carrots. Boiling had the greatest effect and had an influence on all variables except the ratio between sucrose and the monosaccharides glucose and fructose. The choice of cultivar was also of great importance as regards glucose, fructose and sucrose content, while dietary fibre and dry matter were much less affected, or even unaffected, by this factor. Root weight and storage were consistently of less significance than boiling and cultivar. Thus dietary fibre solubility, fructose content and the ratio between sucrose and the monosaccharides glucose and fructose were independent of the root weight, while storage had no impact on the dry matter content. After storage the cultivar Lonto had lost more dry matter than the other cultivars (10% versus mean 1% for the others, P = 0.009) and the sugar ratio between sucrose and the monosaccharides glucose and fructose had increased in the cultivar Amarant, while it decreased in the other cultivars (P < 0.001). Furthermore, Amarant had a lower loss of sugars (35%) following boiling than the other cultivars (mean 39%, P = 0.002). Storage and boiling interacted concerning soluble and insoluble dietary fibre, fibre solubility and glucose content. It is concluded that the various factors (especially boiling and cultivar) gave rise to such differences in carbohydrate content and composition that they might be of nutritional importance. The results may thus provide a basis for selecting raw material when studying possible health effects of carrots. Copyright © 2004 Society of Chemical Industry     

Color changes during storage of honeys in relation to their composition and initial color

The causes of darkening in honey have been attributed to Maillard reaction, fructose caramelization and reactions of polyphenols, however, no systematic studies exist on this subject. The influence of composition and initial color on the rate of darkening of several Argentine honeys submitted to storage at 37°C during 90 days was evaluated through spectrocolorimetric measurements. The most suitable color functions to evaluate darkening of honeys [lightness (L_ab*), browning index (BI), metric chroma (C_ab*), metric hue (H_ab*) and 1/Z] increased linearly as storage time increased, after an initial induction period of very low browning development. The slope of the linear browning development zone with time was an index of browning rate, and it was analyzed in relation to the initial color and the composition of honeys (moisture content, total nitrogen, total lipids and polyunsaturated fatty acids, fructose and glucose content). Of the analyzed variables, the initial color was the parameter which better defined the rate of darkening of honeys.