Effects of storage temperature on the contents of sugars and free amino acids in tubers from different potato cultivars and acrylamide in chips

To clarify the effects of storage temperature on potato components and acrylamide in chips, tubers from five cultivars were stored at various temperatures (2, 6, 8, 10, and 18 degrees C) for 18 weeks, and the contents of sugars, free amino acids in tubers, and acrylamide in chips after frying were analyzed. At temperatures lower than 8 degrees C, the contents of reducing sugars increased markedly in all cultivars, with similar increases in the acrylamide level and dark brown chip color. Free amino acids showed little change at the storage temperatures tested and varied within certain ranges characteristic of each cultivar. The contents of reducing sugars correlated well with the acrylamide level when the fructose/asparagine molar ratio in the tubers was <2. When the fructose/asparagine ratio was >2 by low-temperature storage, the asparagine content, rather than the reducing sugar content, was found to be the limiting factor for acrylamide formation.     

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.     

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.     

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.     

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.     

The effect of humus substances on the level of free amino acids in wheat plants

The presence of potassium humate (commercial sample of Humussäure Riedel-de Haën A. G., Seelze-Hannover) in distilled water led to an increase in the content of alanine, aspartic and glutamic acid in the overground parts of wheat plants as compared with the content of these substances in control plants grown in distilled water. In plants cultivated on nutrient solutions a higher level of alanine and glutamic acid and a considerably lower level of amides was found than in plants grown in distilled water and in water with humate. Generally the content of amino acids was higher in the overground parts than in the roots after a cultivation period of one week as well as of 14 day. In the overground parts of 1 days old plants the level of aspartic acid, asparagine and alanine was found to be higher and that of glutamine lower than in seven days old plants. In the roots of the examined plants a decrease of the amino acid content accurred almost in all cases after a cultivation period of 14 days as compared to one of 7 days.     

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.     

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。     

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.     

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.     

Effects of fungicides applied to seed potato tubers at harvest or after grading on fungal storage diseases and plant development

An assessment was made over 3 years of the efficacy of thiabendazole, 2–aminobutane and a formulation of a mixture of thiabendazole and 2–aminobutane in controlling gangrene, skin spot and dry rot when applied either at harvest or after grading at different dates during the storage season.
After harvest applications, the incidence of gangrene was least on tubers treated with the mixture and generally greatest with thiabendazole. When applied after grading the efficacy of the fungicides was not affected by date of grading. Although 2–aminobutane applications at harvest or after grading were equally effective in controlling gangrene, thiabendazole and the mixture were less effective after grading where gangrene was prevalent in a stock. Thiabendazole and the mixture gave good control of dry rot when applied at harvest but were less effective when applied after grading, particularly late in the storage season. Dry rot was sometimes more prevalent on tubers fumigated with 2–aminobutane, especially those treated after grading. Skin spot was more effectively controlled by the mixture and 2–aminobutane than by thiabendazole but, with applications after grading, the efficacy of all fungicides declined the later the date of grading.
Plants grown from tubers treated with the mixture or its 2–aminobutane glycollate constituent exhibited characteristics associated with genetic variation.     

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.