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1.
The effect of freezing on the turgor, ascorbic acid content and enzymatic discoloration of Katahdin and Atlantic potatoes was studied. Tubers were exposed to a temperature of ?20°C for 24 hrs. then thawed for 1 hr. at 20°C before analysis. Frozen tubers were then compared with unfrozen controls. Both varieties lost turgor following freezing and exuded a sticky liquid with increased thawing time. At the end of 3 hrs. thawing, a sponge-like texture was observed in both varieties. In both varieties freezing resulted in a significant reduction (p<.01) in ascorbic acid and phenolic content (p<.01). Enzymatic discoloration was also significantly reduced (p<.01) in both varieties.  相似文献   

2.
The effect of final mixing temperature (16 °C and 31 °C) on the structure stability of frozen bread dough was examined by low temperature-scanning electron microscopy and the quality of bread made from them assessed. The presence of ice-crystals were determined in both doughs after freezing, by low-temperature S.E.M. The microstructures showed a slight increase in size and decrease in number of angular voids, representing ice-crystals, after 14 weeks storage at −20 °C. Loaves baked from frozen dough with a final mixing temperature of 31 °C were poorer in both gassing power and overall loaf quality than 16 °C doughs, after 14 weeks storage.  相似文献   

3.
The effects of storage treatments and potassium fertilization on the phospholipid, triglyceride and free fatty acid content of Russet Burbank potatoes were determined. Thin-layer chromatography of the lipids indicated at least 18 types of lipids were present. Eight were phospholipids which were the predominant lipid class in the potatoes. Phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid comprise the major phospholipids. A large increase in phosphatidic acid and a decrease in phosphatidylcholine were observed in potatoes stored at 5.6 C (42 F). Potatoes fertilized with 240 lbs of potassium (calculated as K2O) had a higher content of triglycerides compared to potatoes with no fertilization. Potatoes stored at 5.6 C (42 F) exhibited a decrease in triglyceride and phospholipid content but the free fatty acids were increased. The various lipid contents of reconditioned potatoes were similar to those of freshly harvested potatoes.  相似文献   

4.
Summary Potato cultivars were grown in a glasshouse and plants periodically transferred to a growth chamber. When the ambient temperature in the growth chamber was raised from 15 to 40°C in steps of 5°C per hour, net photosynthetic rate decreased at temperatures above 20°C. At 40°C the rate was 37% of the rate at 20°C. A greater decrease in net photosynthetic rate occurred with plants of the cultivar Up-to-Date than with cultivars R100 and BP13. Low values of leaf diffusive resistance were recorded and changes in photosynthetic rate could not be explained by changes in this factor. When a constant ambient air temperature of 20°C was maintained while soil temperature was increased, net photosynthetic rate decreased.  相似文献   

5.
Oat roll is one of the traditional oat wholemeal foods. The purpose of this work was to investigate the effects of quick freezing at −20 °C, −40 °C and −80 °C for 90 min before frozen storage on the quality of frozen steamed oat roll. Quick freezing at −40 °C and −80 °C inhibited the increase of peak gelatinization temperature, enthalpy and the ordered degree of oat roll starch, therefore postponing starch retrogradation. The cross-section microstructure confirmed that reducing the quick-freezing temperature could prevent the increase of ice crystals size, ruptured structures and maintain the integrity of internal structure. As the storage time extend, the ice recrystallization led to an increase in size of ice crystals, while a decrease in their number. Frozen steamed oat roll starch had the highest swelling power at the quick-freezing temperature of −80 °C, that indicated strongest water absorption and binding ability when gelatinized again. Texture analysis demonstrated that hardness increased during frozen storage, quick freezing at −80 °C had the best texture properties. Therefore, declining the quick-freezing temperature could obtain a higher quality of frozen steamed oat roll, by means of delaying the starch retrogradation and minimising the size of ice crystals.  相似文献   

6.
Abscisic acid (ABA), sucrose, reducing sugars and proline contents were monitored over an eleven-month period in tubers of three potato cultivars that varied in tuber dormancy. ABA and proline levels increased after top pulling the haulms and were not affected by harvest date. Proline did not change in either a storage temperature or cultivar-specific manner. The highest concentrations of ABA were found in tubers stored at 2°C while the lowest concentrations occurred in tubers stored at 20°C. At 10°C, the end of tuber dormancy in the cultivars Kennebec and Nooksack (but not Sebago) coincided with the decline in ABA content. There was no evidence of a threshold concentration of ABA below which sprouting would occur. Tuber samples of 10 different cultivars were removed from 10°C and placed in 20°C storage (in darkness). Initial ABA concentrations (i.e., at the time of removal from 10°C storage) were positively correlated with duration of dormancy and negatively correlated with subsequent rates of sprout elongation at 20°C. Sucrose content was negatively correlated with duration of dormancy. Reducing sugars responded primarily to storage temperature and did not appear to be related to dormancy or sprouting.  相似文献   

7.
The effect of boiling and baking in either a convential or microwave oven on the lipid content of potatoes was investigated. The crude lipid content of potatoes was lowered significantly by all methods of cooking. The loss was highest in potatoes cooked in a microwave oven, least in boiled tubers, and intermediate in tubers baked in a conventional oven. Similar trends were observed for both cortex and pith tissues. Generally, the phospholipid content followed the same trend as the crude lipid, the exception being the cortex tissue of tubers baked in the conventional oven, in which the greatest loss of phospholipid occurred. Cooking did not significantly alter the fatty acid composition of tubers. A possible relationship between the degree of cell rupturing, known to be influenced by different mechanisms of heat transfer, and the amounts of tuber lipid associated with different cooking methods was discussed.  相似文献   

8.
The survival ofCorynebacterium sepedonicum, the bacterial ring rot pathogen of potatoes, on burlap surfaces held at constant freezing and above-freezing temperatures and under wide fluctuations of these temperatures was investigated by root-inoculating potato stem cuttings with aqueous suspensions prepared from these surfaces. The pathogen survived and remained infectious on burlap for 53 mo at all constant freezing temperatures, and its infectivity did not diminish throughout this period at either ?20 or ?40°C. At 42 months, viable ring rot bacteria were no longer detected at a constant temperature of 5°C. In a second experiment, ring rot bacteria survived and remained infectious on burlap for 23 months at fluctuating temperatures of ?40 to 5°C and ?40 to 25°C, but only survived for 12 months at 25°C. However, results of this study indicate that wide fluctuations between freezing and above-freezing temperatures caused decreased infectivity of the pathogen.  相似文献   

9.
Breeding and selection for frost resistant potatoes with high yield and good quality is very promising. This has been demonstrated in a frost resistance breeding program conducted at the International Potato Center, Lima, Peru. Yield trials were conducted using selected frost resistant clones at various Andean locations at elevations from 3,200 to 3,900 meters (14). During the growth season, several hail storms and frosts occurred at these locations. These freezes (?3°C to ?4°C) were very useful in elimination of the undesirable clones under natural conditions. Clones with yield from 1 to 2 kg/plant have been selected. A yield of 1 to 2 kg/plant was superior to most common cultivars grown in the Andes. The difference in frost resistance between a resistant and sensitive type of potato is about 3 to 4°C.Solanum tuberosum is a sensitive type which, in most cases, can survive at about ?2.0°C. Evidence indicates that the difference in resistance to freezing injury is due to the genotype’s capability to tolerate freeze-induced dehydration and to withstand the aggregation of proteins under freezing stress. It is likely that freezing injury is caused primarily by the loss of membrane integrity and, therefore, that membrane thermal stability is paramount in the tolerance to freezing stress.  相似文献   

10.
Changes in ascorbic acid levels were followed in apical and basal portions of Russet Burbank and Kennebec tubers during growth and development. Influence of nitrogen fertilization during growth and short-term storage on ascorbic acid level of the tuber was also studied. Changes in ascorbic acid content during growth showed two distinct phases, the first phase being characterized by an increase in ascorbic acid content with growth and development of the tuber, followed by a second phase which showed a decrease in ascorbic acid content with increasing maturity. The shift from the first phase to the second phase occurred earlier for Kennebec than for Russet Burbank. Increased nitrogen fertilization resulted in a delay of this shift from the first to the second phase. The apical portion of the tuber consistently showed higher ascorbic acid content than the basal portion. Kennebec tubers were higher in vitamin C content than tubers of Russet Burbank cultivar. High nitrogen fertilization resulted in less ascorbic acid content during growth. Storage of tubers for four weeks at 5.5°C also resulted in a marked decrease in ascorbic acid content of tubers. Nitrogen fertilizer rate during growth had no influence on the decrease in ascorbic acid content of tubers in storage.  相似文献   

11.
低温对水稻幼苗类囊体膜脂肪酸组分和膜脂过氧化的影响   总被引：5，自引：0，他引：5  
以高产杂交稻组合两优培九和常规杂交稻汕优63为材料,设10℃低温和25℃常温对照两个处理,研究了夜间低温对幼苗类囊体膜膜脂过氧化和脂肪酸组分的影响。低温处理后,两个组合叶片的叶绿素含量明显下降,但两优培九下降幅度较小。两个组合的低温处理组脂肪酸组分中的16:0和18:0含量下降,常温对照组的下降幅度较小;而低温处理组脂肪酸组分中的18:1、18:2和18:3含量均上升。脂肪酸的不饱和度均呈上升趋势,但两优培九不饱和度整体上比汕优63小。低温处理下,两个组合的MDA和超氧阴离子含量都呈上升趋势,但两优培九MDA含量上升幅度远远比汕优63小。由结果可知,两优培九在苗期对低温不敏感,抗冷性较强。夜间低温引起叶片的类囊体膜膜脂过氧化加剧,脂肪酸不饱和度上升,这两方面的变化有着密切的关系,且都与杂交稻的冷适应发展有紧密的联系。  相似文献   

12.
Whole grains of different cereals have traditionally been prepared with water and heat prior to dehulling, but knowledge of the effect on nutritional properties is limited. The aim of the present study was to investigate if phytate reduction occurred during hydrothermal treatment of whole grains. Wheat, rye, hulled and dehulled barley, hulled oats and naked oats were incubated with either water or acetate buffer (pH 4·8) at 55 °C for 24 h with the exception of oats, which were incubated at 37 °C. Phytate in wheat, rye and barley was reduced by 46–77% when water was used and by 84–99% when acetate buffer was used. The phytate reduction in oats was considerably less, 8–26%, but, after grinding and soaking, phytate was reduced by 72–77% in dehulled oats and by 88–94% in naked oats. Citric acid and citrate buffer was used for pH adjustment in some experiments, and their use resulted in less phytate reduction than when acetate and lactic acid were used. Wet-steeping of naked oats and naked barley in water at 53–57 °C for 20–30 min reduced the bacterial counts by 99·97%, and the addition of acid prevented bacterial growth during the incubations. It was concluded that cereals with reduced phytate content and good hygienic quality can be developed and produced using hydrothermal treatment of whole grains.  相似文献   

13.
Superheated steam (SS) at 170 °C for 5 min was used to inactivate lipase of common buckwheat grains in this study, which effectively retarded lipid hydrolytic rancidity and maintained lipid nutrition of common buckwheat. Higher stabilities based on lower free fatty acid accumulation and lipase activity were observed in SS-treated buckwheat samples during storage. Meanwhile, SS could suppress oxidation of unsaturated fatty acids (UFA) in buckwheat, significantly retard the increase of saturated fatty acids and the decrease of polyunsaturated fatty acids during storage. Moreover, the lipidomics profile results indicated that SS processing could retard the increased hydrolysis and oxidation of sulfoquinovosyl diacylglycerol, phosphatidylethanolamine, phosphatidylserine and lysophosphatidic acid during storage, while regulate the content of galactolipids. Thus, SS processing could effectively inactivate lipase, suppress UFA oxidation, change glycerolipids and glycerophospholipids subclass metabolism, and consequently retard hydrolytic rancidity and the loss of lipid nutrition in buckwheat during storage. SS processing was proved to effectively protect the quality of buckwheat during storage for the first time.  相似文献   

14.
Summary The effect of high tuber temperature (30 °C) on the growth rate and carbohydrate metabolism of tubers was studied with 3 cultivars differing in heat tolerance. Subjecting individual tubers to 30°C for 6 days caused cessation of tuber growth. During this period, non-treated tubers (20°C) on the same plant increased in volume. At 30°C, incorporation of14C-labelled assimilates into the ethanol-insoluble fraction (mainly starch) as well as the starch content was significantly reduced. In contrast, the incorporation of14C-labelled assimilates into the sugar fraction was not affected by high tuber temperature. At 30°C the activity of some of the enzymes involved in starch metabolism was depressed. Varietal differences in responses of tuber growth rate and carbohydrate metabolism to high tuber temperature were insignificant. From these preliminary results it is concluded that high soil temperatures may decrease starch content of potato tubers directly by inhibition of the conversion of sugars into starch.  相似文献   

15.
The response of four potato cultivars to various temperatures was evaluated in respect to respiration, sugar and phenolic content, and ion leakage from cut tissue sections. Respiration decreased with decreasing temperature from 20° to 0°C but after 24 hours at 0°C began to increase and reached a maximum after 10 days at 0°C, then drifted downward. No distinct break in an Arrhenius plot of the respiration data from 20° to 0°C was observed. Reducing and non-reducing sugars did not change initially between 20° and 0°C and did not increase until after 6 or 7 days at 0°C. The magnitude of the increase in sugars varied between cultivars. Only one cultivar significantly increased in phenolic content during chilling. Ion leakage remained constant from 20° to 0°C then showed a transient increase within 24 hours at 0°C. A sustained increase in leakage did not occur until after 10 days at 0°C. Cultivars varied in the rate and magnitude of the increase. The respiratory rise could not be attributed to an increase in sugar content or an increase in membrane permeability. Also, the initial increase in sugars preceded the sustained increase in ion leakage. Differences observed between cultivars in the parameters measured were not considered sufficient to explain differences in chilling sensitivity.  相似文献   

16.
《Plant Production Science》2013,16(2):110-116
Abstract

Germination percentages of wheat grains sampled at 3 grain-filling stages : yellow-ripe stage (water content 45-50%), dough-ripe stage (35-40%), and full-ripe stage (25-30%), and imbibed in water at 12°C and 20°C were examined in relation to the activities of α-amylase and endoprotease. Wheat varieties studied were Chihoku-komugi, which is susceptible to pre-harvest sprouting, and Satanta, which is resistant. Germination percentage was higher at 12°C than at 20°C in all grains sampled at all stages in both varieties, and was higher in Chihoku-komugi than in Satanta at 20°C. The activity of α-amylase in the grains at the yellow-ripe stage was higher at 12°C than at 20°C in both varieties, but that at the other 2 stages was higher only in Satanta. Endoprotease increased rapidly from 7 to 10 days after the start of imbibition, and exceeded 12 units only at 12°C in Chihoku-komugi grains at the dough and full-ripe stages. The results showed that α-amylase activity was lower than the value equivalent to 300 brabender unit (BU) in amylography when the germination percentage was 0%. Endoprotease activity exceeded 6 units when the germination percentage exceeded 90%.  相似文献   

17.
Long term performance of conductivity of p-toluene sulfonic acid (pTSA) doped electrochemically synthesized polypyrrole (PPy) films was estimated from accelerated aging studies between 80 °C and 120 °C. Conductivity decay experiments indicated that overall aging behavior of PPy films deviated from first order kinetics at prolonged aging times at elevated temperatures. However, an approximate value for the activation energy of the conductivity decay of PPy was calculated as E=47.4 kJ/mol, enabling an estimate of a rate constant of k=8.35×10−6/min at 20 °C. The rate of decrease of conductivity was not only temperature dependent but also influenced by the dopant concentration. A concentration of 0.005 M pTSA in the electrolyte resulted in a conductive film and when this film was exposed to 120 °C for a period of 40 h, the conductivity decayed to about 1/20 of its original value. The concentration of pTSA was increased to 0.05 mol/l and when the resulting film was aged in the same way, it showed a decrease in the conductivity to about 1/3 of its original value. Both microwave transmission and dc conductivity data revealed that highly doped films were considerably more electrically stable than lightly doped films. The dopant had a preserving effect on the electrical properties of PPy.  相似文献   

18.
A study was conducted to establish a growth rate response of potato plant (Solanum tuberosum L.) tops to exposure to 72-hr periods of six constant temperature treatments (10, 15, 20, 25, 30, 35°C) and to determine a thermal optimum for vegetative potato growth rates. The plants were maintained under “no stress” soil moisture conditions throughout the study. The temperature treatments were accomplished by inserting the plants into a growth chamber for 72 hours at selected temperatures. Maximum growth (as measured by percent change in leaf area) occurred at 25°C with temperature growth differences significant at the 5% level. Plant height measurements (percent change occurring during treatment time) showed maximum stem elongation at 30°C during an early growth stage and 25°C during stage 2 (4 weeks later). Predictive models developed from the data indicate maximum rates of leaf area increase in both growth stages occur at 24.7°C and that maximum rates of stem elongation occur at 31.3 and 27.4°C for growth stages 1 and 2, respectively. Leaf water potential and stomatal resistance measurements taken at the end of each treatment period indicated that no water stress occurred.  相似文献   

19.
To investigate the effect of temperature on the resistance characteristics of rice varieties with different resistance genes to brown planthopper(BPH),Nilaparvata lugens(Stl),the resistances of IR26(Bph1)and IR36(bph2)to BPH population in Hangzhou,China were monitored in greenhouse during September in 2007 and 2008 by using the standard seedling screening techniques(SSST)developed by the International Rice Research Institute(IRRI).Furthermore,the changes in resistance of IR26 and IR36 to BPH,soluble sugar and oxalic acid contents in 25-day-old rice plants of susceptible variety TN1 and resistant varieties IR26 and IR36 were detected at five temperatures(22℃,25℃,28℃,31℃ and 34℃).IR26 completely lost resistance both in greenhouse and at the five tested temperatures.IR36 still had moderate resistance at natural temperature,but its resistance decreased gradually when the temperature increased from 25℃ to 34℃,and fully lost its resistance at 31℃ and 34℃.The highest durable resistance of IR26 and IR36 were recorded at 25℃.The soluble sugar content in plants of the three tested rice varieties increased with temperature increase,and the oxalic acid content increased with the temperature increase at first,maximized at 25℃,and then declined.Two-way ANOVA indicated significant effects of temperature and rice variety on contents of soluble sugar and oxalic acid in rice plants.  相似文献   

20.
Summary Potatoes irradiated to control sprouting were dipped in: hot water (56°C, 5 min; 52°C, 10, 15 and 20 min); cold (25°C, 5 min) or hot (56°C, 5 min) salicylic acid (1000 and 2000 ppm); or sodium hypochlorite (0.1 and 0.2%, 5 min); or dusted with salicylic acid (1 and 2%), to try to reduce the incidence of bacterial soft rot (Erwinia sp.) during controlled temperature (10°C, 15°C) and ambient temperature (20–34°C) storage. All treatments, particularly hot water and hot salicylic acid dip, increased microbial spoilage, possibly as a result of handling damage during the treatments combined with the inhibition of wound periderm formation as a result of irradiation. Storing irradiated tubers in well ventilated containers reduced soft rot compared to storing them in sacks and after 6 months storage at 10, 15 and 20–34°C, 95, 90 and 77% respectively were healthy and marketable.  相似文献   

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