Change in content of sugars and free amino acids in potato tubers under short-term storage at low temperature and the effect on acrylamide level after frying

Changes in the sugar and amino acid contents of potato tubers during short-term storage and the effect on the acrylamide level in chips after frying were investigated. The acrylamide content in chips began to increase after 3 days of storage at 2 degrees C in response to the increase of glucose and fructose contents in the tubers. There was strong correlation between the reducing sugar content and acrylamide level, R(2)=0.873 for fructose and R(2)=0.836 for glucose. The sucrose content had less correlation with the acrylamide content because of its decrease after 4 weeks of storage at 2 degrees C, while the reducing sugar in potato tubers and the acrylamide in chips continued to increase. The contents of the four amino acids, i.e., asparatic acid, asparagine, glutamic acid and glutamine, showed no significant correlation with the acrylamide level. These results suggest that the content of reducing sugars in potato tubers determined the degree of acrylamide formation in chips. The chip color, as evaluated by L* (lightness), was correlated well with the acrylamide content.     

Effects of physiological changes in potato tubers (Solanum tuberosum L.) after low temperature storage on the level of acrylamide formed in potato chips

Acrylamide in potato chips made from tubers stored at 2 or 20 degrees C for two weeks after harvest was analyzed by GC-MS. The acrylamide level in the former chips was higher than ten times of that in the latter, which was highly correlated with both glucose and fructose levels in the tubers.     

Fatty acids, membrane permeability, and sugars of stored potato tubers

The relationships of potato (Solanum tuberosum L.) tuber membrane permeability and membrane lipid composition to sugar accumulation were examined. Tubers from four potato cultivars were stored for 40 weeks at 3°C and 9°C. Rates of tuber membrane electrolyte leakage, total fatty acid composition, free fatty acid composition, and sugar content were measured throughout the storage period. Storage of tubers at 3°C caused dramatic increases in total fatty acid unsaturation, membrane permeability, and sugar content compared to tubers stored at 9°C. Cultivars with higher levels of fatty acid unsaturation had lower rates of membrane electrolyte leakage and lower sugar contents. We propose that high initial levels or high induced levels of membrane lipid unsaturation mitigate increases in tuber membrane permeability during storage, thus positively influencing the processing quality of stored potato tubers.     

Effect of temperature on invertase, invertase inhibitor, and sugars in potato tubers

The accumulation of reducing sugars in potato tubers exposed to low temperatures occurs with concomitant formation of the enzyme invertase. During the initial period of cold treatment when reducing sugars increase rapidly, invertase formation proceeds until the level of enzyme exceeds that of an endogenous macromolecular invertase inhibitor, resulting in a basal invertase activity. As the rate of sugar accumulation decreases and the sugar level becomes nearly constant, total invertase decreases, the basal activity disappears, and a low excess of inhibitor develops. On transfer of cold-stored tubers to warmer temperatures, sugars and invertase decrease sharply and a large excess of inhibitor develops. These changes in sugars, invertase and inhibitor occur reversibly when the tubers are subjected to alternating temperatures.     

冷藏对米蛾卵液中游离氨基酸变化的影响

赤眼蜂的工厂化繁育常使用米蛾卵作为中间寄主卵,为了满足赤眼蜂生产的需要,需对米蛾卵进行冷藏,但冷藏米蛾卵影响赤眼蜂的生长发育。利用核磁共振技术(NMR)测定了新鲜米蛾卵(U)、新鲜杀胚米蛾卵(CK)、杀胚米蛾卵在4℃条件下冷藏15 d(N15)、30 d(N30)、45 d(N45)和60 d(N60)后,米蛾卵卵液游离氨基酸种类和含量的变化。结果共鉴定到24种游离氨基酸及其衍生物,包括昆虫发育必需的10种氨基酸。U和CK之间的游离氨基酸组分没有显著差异,N15、N30和N45游离氨基酸总量随冷藏时间的延长而显著升高,N60中的氨基酸总量与N45比较没有显著增加。对24种游离氨基酸及其衍生物的含量进行主成分分析,结果表明丙氨酸、谷氨酰胺、鸟氨酸、天冬氨酸、组氨酸、赖氨酸、丝氨酸、焦谷氨酸等8种氨基酸的含量随冷藏时间的增加而有着显著的变化,其中,丙氨酸变化幅度最为明显,随着冷藏时间的增加,含量从0.1624 mmol/L增加到8.6192 mmol/L;组氨酸在N30、N45和N60处理之间显著下降,从0.7553 mmol/L降低到0.2495 mmol/L。因此,冷藏会导致米蛾卵内游离氨基酸含量发生一定变化,这可能是冷藏米蛾卵影响赤眼蜂生长发育的重要原因之一。     

转基因棉花中糖类和游离氨基酸含量的变化对棉蚜泌蜜量及蜜露主要成分的影响

以3个转基因棉和2个亲本对照棉花品种为研究材料,分别测定了这5种棉花植株体内主要糖分与游离氨基酸含量;同时,分别用这5个棉花品种的叶片饲养棉蚜Aphis gossypii Glover并测定其蜜露分泌量及其主要营养成分。结果表明,转基因棉花“国抗22”叶片中葡萄糖、蔗糖、麦芽糖的平均含量及可溶性糖总量分别比亲本对照棉“泗棉3号”减少61.76%、 89.05%、77.86%和23.61%,转基因棉花“苏抗103”和“中抗310”叶片中葡萄糖、蔗糖、麦芽糖的平均含量及可溶性糖总量分别比亲本对照棉“苏棉12”下降14.15%、32.80%、92.22%、11.46% 和4 6.81%、93.19%、61.11%、43.91%,游离氨基酸总量及各种氨基酸、果糖、鼠李糖、海藻糖的含量在不同转基因棉与亲本对照棉花品种间也存在很大差异,其中一些处理间的差异达显著或极显著水平。这表明外源基因的导入已经影响到了转基因棉花品种中主要糖分与游离氨基酸的合成。棉蚜取食转基因棉花品种“国抗22”后,蜜露的日平均分泌量比取食对照品种“泗棉3号”减少40.54%,取食其他两个转基因棉花品种“苏抗103”和“中抗310”后蜜露的分泌量也比取食对照棉花品种“苏棉12”降低22.67%和30.0%,但棉蚜取食转基因棉花后蜜露中游离氨基酸的总量均高于对照棉花品种,蜜露中可溶性总糖、蔗糖和各种氨基酸含量在取食转基因棉和常规棉花品种间存在一定差异。     

Analysis of the compartmentation of glycolytic intermediates, nucleotides, sugars, organic acids, amino acids, and sugar alcohols in potato tubers using a nonaqueous fractionation method

The compartmentation of metabolism in heterotrophic plant tissues is poorly understood due to the lack of data on metabolite distributions and fluxes between subcellular organelles. The main reason for this is the lack of suitable experimental methods with which intracellular metabolism can be measured. Here, we describe a nonaqueous fractionation method that allows the subcellular distributions of metabolites in developing potato (Solanum tuberosum L. cv Desiree) tubers to be calculated. In addition, we have coupled this fractionation method to a recently described gas chromatography-mass spectrometry procedure that allows the measurement of a wide range of small metabolites. To calculate the subcellular metabolite concentrations, we have analyzed organelle volumes in growing potato tubers using electron microscopy. The relative volume distributions in tubers are very similar to the ones for source leaves. More than 60% of most sugars, sugar alcohols, organic acids, and amino acids were found in the vacuole, although the concentrations of these metabolites is often higher in the cytosol. Significant amounts of the substrates for starch biosynthesis, hexose phosphates, and ATP were found in the plastid. However, pyrophosphate was located almost exclusively in the cytosol. Calculation of the mass action ratios of sucrose synthase, UDP-glucose pyrophosphorylase, phosphoglucosisomerase, and phosphoglucomutase indicate that these enzymes are close to equilibrium in developing potato tubers. However, due to the low plastidic pyrophosphate concentration, the reaction catalyzed by ADP-glucose pyrophosphorylase was estimated to be far removed from equilibrium.     

Effect of low temperature on the activity of phosphofructokinase from potato tubers

The aim of this work was to compare the coldlability of phosphofructokinase (EC 2.7.1.11) from tubers of potato cultivars (cvs.) known to differ in their propensity to accumulate sugars at low temperature. When stored at 4°C for six weeks, the sugar content of tubers ofSolanum tuberosum L. cv. Record doubled whereas the amount of sugar in tubers of cv. Brodick and an advanced breeding clone (13676) decreased slightly. Tubers from each line contained four forms of phophofructokinase. Over the range 12°–16°C the temperature coefficients of the four forms of phosphofructokinase from cvs. Record and Brodick were similar. In cv. Record the temperature coefficients of three of the enzyme forms were significantly higher at 2°–6°C than at 12°–16°C, whereas those from cv. Brodick were unchanged. These results are consistent with the proposal that inactivation of phosphofructokinase at low temperature results in the accumulation of hexose phosphates leading to increased sucrose synthesis.     

Effects of natural amino acids and sugars on activity of infusiorian cyclases

Natural amino acids and sugars in unicellular eukaryotes are known to regulate adenylyl cyclase (AC) and guanylyl cyclase (GC) systems that control the most important cell processes. The goal of the present work consisted in study of effects of natural amino acids and sugars and some of their derivatives on AC and GC activities of infusoria Tetrahymena pyriformis and Dileptus anser. Methionine, arginine, lysine, and tryptamine stimulated basic AC activity of T. pyriformis, whereas alanine, tyramine, and cysteine decreased it. Methionine, glycine, alanine, thyrosine, arginine, and to the lesser degree tryptamine and histidine stimulated AC of D. anser. The GC activity of T. pyriformis rose in the presence of tryptamine, tryptophane, histidine, arginine, and lysine, whereas glycine and aspartic acid, on the contrary, decreased it. Tryptamine, tryptophan, leucine, glutamic acid, serine, histidine, and alanine stimulated the GC activity of D. anser. Glucose, fructose, and sucrose stimulated the basal AC activity of both infusorians and GC of T. pyriformis, with glucose and sucrose increasing AC of T. pyriformis twice, while that of D. anser 4.5 times. Lactose stimulated AC and GC of T. pyriformis and was inefficient with respect to the D. anser cyclases, whereas mannose and galactose did not affect the enzyme activities in both infusorians. The study of the chemotactic response of the infusorians to amino acids and sugars indicates that involved in realization of this response can be signaling pathways both dependent on and independent of cyclic nucleotides. Thus, it has been established for the first time that several amino acids and sugars affect functional activity of enzymes with cyclase activity of the infusorians T. pyriformis and D. anser. This confirms the hypothesis that at early stages of evolution the large specter of comparatively simple natural molecules has a hormone-like action.     

Oxylipin profile and antioxidant status of potato tubers during extended storage at room temperature

Potato tubers (cv. Bintje) (Solanum tuberosum L.) were stored under extreme conditions at 20 °C for 350 days without sprout inhibitors in order to assess whether aging- and/or senescence-related processes occurred. Under these extreme storage conditions, multiple sprouting followed by the formation of daughter tubers occurs. At the same time, an increase in respiration intensity, as evidenced by cytochrome c oxidase activity (E.C. 1.9.3.1), is observed, leading to a potential increase in reactive oxygen species (ROS) production. As polyunsaturated fatty acids are priority targets of oxidative attacks, the damage to lipids was assessed by oxylipin profiling in both free and esterified forms. Oxylipin profiling showed a predominance of linoleic acid-derived oxylipins and of 9-hydroxy and 9-hydroperoxy fatty acids in both free and esterified forms. No significant accumulation of individual oxylipin was observed 350 days after harvest. To further understand the absence of lipid breakdown products accumulation, the main enzymatic and non-enzymatic antioxidants were assessed. Antioxidant enzyme activities [superoxide dismutase (E.C. 1.15.1.1), catalase (E.C. 1.11.1.6.), ascorbate peroxidase (E.C. 1.11.1.11)] were enhanced during the advanced phase of aging. The main non-enzymatic antioxidant compound, ascorbate, decreased markedly in the early stages of storage, followed by a slower decline. Total radical scavenging activity was also maintained at the end of the storage period. Our results indicate that the enhanced aging process occurring during storage at room temperature does not seem to be associated with the changes classically encountered during leaf senescence or seed aging and that the observed degenerative processes do not surpass the protective potential of the tubers.     

Effects of dithiothreitol on dopa oxidase activity from potato tubers

A filtrate, prepared from potato tuber by grinding in an isotonic medium, has been separated into a particulate and a ‘soluble’ fraction by ultracentrifugation. Following dialysis and lyophilization, both fractions catalysed the oxidation of l-DOPA, with approximately 30% of the l-DOPA: oxygen-oxidoreductase (EC 1.14.18.1; DOPA oxidase) activity being associated with the particulate fraction. When dithiothreitol (DTT, 10^?2M was included in the grinding medium, much lower yields of DOPA oxidase were obtained and 80% appeared to be associated with the particulate fraction. DTT proved to be a powerful inhibitor of DOPA oxidase. With concentrations of DTT causing only partial inhibition, the kinetics of the inhibited rate of dopachrome formation from l-DOPA were complex. When oxygen consumption was measured inhibition was not transient. The degree of inhibition was inversely related to the DOPA oxidase activity, indicating interaction of a product of this activity with DTT. Direct determination of -SH groups in DTT using 5,5′-dithiobis(2-nitrobenzoic acid (DTNB) showed that they were all oxidised during the initial phase of inhibition of dopachrome formation. It is concluded that the first phase of inhibition involves oxidation of DTT by an intermediate between l-DOPA and dopachrome. The second phase of inhibition also appeared to require -SH groups initially, since trans-4,5-dihydroxy-1,2-dithiane (oxidized DTT) caused very little inhibition at all.     

The role of free sugars and amino acids in the regulation of biomass partitioning and plant growth

Theoretical plant growth models postulate an important role for growth substrates such as sugars and amino acids. To test this experimentally, spinach plants were grown under controlled conditions and with nitrogen added daily, following different exponential addition schemes. Plants were harvested during exponential growth. Free amino acid levels or free sugar levels were only weakly correlated with growth and biomass partitioning. Factor analysis showed however that the product of free sugar concentration and amino acid concentration yielded a parameter adequately reflecting the plant's nutritional state.It is concluded that growth and biomass partitioning under limiting N conditions cannot be modelled solely based on N substrate levels.     

新鲜土壤样品储存温度和时间对不同形态氮素的影响

土壤氮素形态及含量具有重要的生态学研究意义,而土壤样品的储存对土壤氮素含量的准确测定有很大影响.为了选择合理的土壤样品储存方法,本研究以福建省建瓯市万木林保护区罗浮栲林土壤为研究对象,测定在不同温度(25、4和-20 ℃)、不同储存时间(0、7和30 d)下土壤铵态氮、硝态氮、总氮、可溶性有机氮、氨基酸氮含量和微生物生物量氮,以及冷冻后常温培养过程中的氮素含量.结果表明: 在7 d的储存时间内,除氨基酸氮以外,常温培养样品下其余的氮素含量均有所增加;与新鲜样品相比,冷藏、冷冻样品的所有氮素含量之间均无显著性差异,且氮素含量变化较常温培养下更加稳定.因低温储存样品有刺激氮矿化的效果,在30 d储存时间内,与新鲜样品相比,除可溶性有机氮外,冷藏、冷冻样品的所有氮素含量均显著升高;两种冷储存方法之间无显著差异.因此,新鲜样品带回实验室后应及时处理;如需要冷储藏,时间不要超过半个月.如果需要较长的储存时间,则需将样品放置于更低的温度(-40或-80 ℃).在对储存土壤样品进行培养试验之前,需要进行预培养处理.在预培养过程中,除硝态氮含量呈现先下降再迅速升高的趋势外,其余氮素均随着培养时间逐渐趋近于新鲜土壤样品含量,在培养一周左右恢复到与新鲜土壤样品氮含量最为接近的状态.结合已有研究,对野外取样和风干样品需要5～14 d的预培养,冷储存样品预培养时间不应少于一周.     

The effect of sugars and free amino acids from the freshwater prawn Macrobrachium rosenbergii hemolymph on lectin activity and on oxidative burst

We determined the effect of low molecular weight components (LMWC) from healthy juvenile and adult Macrobrachium rosenbergii hemolymph on lectin activity and oxidative burst (OB) in hemocytes. In an attempt to identify the LMWC that affect the lectin's hemagglutinating activity or oxidative burst, we determined the hemolymph carbohydrates and free amino acids (FAA) concentration. The LMWC (<2000 Da) were obtained after dialysis of the hemolymph. Our results showed that LMWC from juveniles exerted a greater inhibition on lectin than LMWC from adult hemolymph. Production of superoxide radicals by hemocytes was lower in the presence of juvenile (p<0.05) as compared to adult LMWC. FAA composition of the hemolymph and of LMWC from adults showed higher proportion of alanine (which corresponded to 25% of total FAA) and proline (>20%); whereas, in juveniles, the main FAA identified were glycine (>40%) and alanine (26%). N-Acetyl-D-glucosamine (GlcNAc) was the main sugar residue in the hemolymph and LMWC from juveniles; its concentration was 2.4 times higher than glucose (Glc), whereas, in adults, Glc was the main free sugar residue. Our results suggest that the proportion of FAA and carbohydrates in the hemolymph of M. rosenbergii seems to be correlated with the maturation process; furthermore, the high proportion of free GlcNAc and glycine regulate, in the juvenile stage, lectin activity and cellular oxidative mechanisms, respectively.     

Photosynthetic assimilation of 14C into amino acids in potato (Solanum tuberosum) and asparagine in the tubers

Asparagine is the predominant free amino acid in potato tubers and the present study aimed to establish whether it is imported from the leaves or synthesised in situ. Free amino acid concentrations are important quality determinants for potato tubers because they react with reducing sugars at high temperatures in the Maillard reaction. This reaction produces melanoidin pigments and a host of aroma and flavour volatiles, but if free asparagine participates in the final stages, it results in the production of acrylamide, an undesirable contaminant. ¹⁴CO₂ was supplied to a leaf or leaves of potato plants (cv. Saturna) in the light and radioactivity incorporated into amino acids was determined in the leaves, stems, stolons and tubers. Radioactivity was found in free amino acids, including asparagine, in all tissues, but the amount incorporated in asparagine transported to the tubers and stolons was much less than that in glutamate, glutamine, serine and alanine. The study showed that free asparagine does not play an important role in the transport of nitrogen from leaf to tuber in potato, and that the high concentrations of free asparagine that accumulate in potato tubers arise from synthesis in situ. This indicates that genetic interventions to reduce free asparagine concentration in potato tubers will have to target asparagine metabolism in the tuber.     

Decreased amount of reducing sugars in transgenic potato tubers and its influence on yield characteristics

This work focuses on the comparison of field characteristics and amounts of reducing sugars in cold-stored tubers of transgenic plants derived from two potato cultivars. The bacterial gene coding for phosphofructokinase under the tuber-specific promoter was used to support the glycolysis in stored tubers. While the tubers from untransformed control plants steadily accumulated reducing sugars during cold storage, the tubers from transformed plants regardless the genotype were characterized by subsequent decrease in the sugar content. After long period of cold storage the greatest reduction in the reducing sugar content was by more than 60 % compared to control. Before the storage, however, the content of reducing sugars was in 80 % of transgenic lines higher than in control ones. The plants evaluated in field trials for their appearance showed any changes in growth characteristics in about 25 % of the transgenic lines. Despite the introduced modification of sugar metabolism the yield of transgenic plants with normal appearance did not differ significantly from the yield of control plants.