Lipids of potato tubers. II. Lipid-degrading enzymes in different varieties of potato tuber

The levels of two lipid-degrading enzymes, namely a hydrolytic enzyme (lipolytic acyl hydrolase) and an oxidising enzyme (lipoxygenase) were measured in tubers from 23 varieties of potato at harvest. Twenty-two varieties had very high levels of the hydrolytic enzyme, ranging from 5 to 50 jumol of substrate hydrolysed/ min/g of fresh weight of tuber. One variety, Desiree, contained a much lower level of this enzyme (0.06 to 0.2 units/g fresh weight). All varieties contained high levels of lipoxygenase activity in the range of 1 to 25 μmol of 0₂ consumed/min/g fresh weight of tuber, with linoleic acid as substrate. The combined action of these enzymes in the degradation of potato tuber lipids is discussed.     

复配精油纳米乳雾化处理对马铃薯发芽的抑制作用及机理探讨

该文采用水蒸馏法提取4种伞形科植物芫荽、莳萝、葛缕子和孜然的种子精油,将上述精油进行复配和纳米乳化处理,并用所得的复配精油纳米乳雾化处理马铃薯,研究其对马铃薯发芽的抑制效果,以及对马铃薯块茎活性氧和关键抗氧化物质含量及抗氧化酶活性影响。结果表明,复配精油纳米乳雾化能够明显抑制马铃薯块茎发芽,降低块茎过氧化氢含量,显著提高块茎的烟酰胺腺嘌呤二核苷酸磷酸(nicotinamide adenine dinucleotide phosphate,NADPH)和还原型谷胱甘肽含量,降低马铃薯块茎中总黄酮及总酚的含量;复配精油纳米乳雾化显著提高块茎部分关键抗氧化酶[过氧化氢酶(catalase,CAT);超氧化物岐化酶(superoxide dismutase,SOD);过氧化物酶(peroxidase,POD);多酚氧化酶(polyphenol oxidase,PPO)]的活性。由此可知,复配精油纳米乳通过调节马铃薯块茎关键抗氧化酶的活性和抗氧化物质含量来降低活性氧含量,从而延长马铃薯块茎的休眠期,达到抑制其发芽的效果。     

INFLUENCE OF TEMPORARY ANOXIA BY SUBMERGING IN WATER ON LIGHT-INDUCED GREENING AND GLYCOALKALOID FORMATION OF POTATO TUBERS

Temporary anoxia created by submerging potato tubers in water completely inhibited light-induced greening and glycoalkaloid formation of Russet Burbank, White Rose and Pontiac cultivar. Preanoxia vacuum treatment of the tuber has the same effect but hastened rottenness of the tubers. Anoxia treatment also inhibited the respiration of potato tissue. Partial exposure of the surface of anoxia tubers to air reduced the inhibition. The inhibition of the light-induced greening by anoxia condition was due to inhibition of tuber respiration. The light absorption by the water used to create anoxia condition did not contribute to the inhibition of light-induced greening. The duration which tubers could tolerate anoxia condition depended upon the cultivar and the physical condition of the tubers. Incorporation of 100 to 1000 ppm sodium hypochlorite or daily replacing with fresh water effectively improved incubation stability and reduced rottenness.     

寡雄蛋白处理对马铃薯块茎活性氧代谢及病程相关蛋白的诱导

以\     

Cooking kinetics of potato tubers determined by vibration techniques

A laser Doppler vibrometer (LDV) was used for remote sensing of potato cooking behavior. Non-destructive determinations of characteristic tuber resonant frequencies (modes M₁ and M₂) displayed in the amplitude–frequency plots (AFP) prior, during, and after steam cooking of the whole tubers were used to establish cooking kinetic coefficients for four different potato varieties. All measurements for a single potato were taken along the extended portion of the tuber at the same location. We found that potato softening during cooking is consistent with the kinetic equation of the first order and that the “two point” test, based on the determination of the AFP prior to and after cooking for 25 (or 15 in one case) min, yields a good estimation of the kinetic coefficient. The results suggest that the application of this method is limited to smaller tubers; the sloughing and cracking of larger tubers induced by longer cooking times confound the measurements.     

Impact of hot water treatment on sprouting,membrane permeability,sugar content and chip colour of reconditioned potato tubers following long‐term cold storage

BACKGROUND: The efficacy of hot water treatment in facilitating successful reconditioning of processing potato (Solanum tuberosum L.) cultivar Hermes following 6 months cold storage at 4.5 °C was examined. Tubers were subjected to hot water treatments (HWTs) at 52.5, 55.0, 57.5 and 60.0 °C for 0–60, 0–50, 0–40 and 0–20 min, respectively, and then reconditioned for 20 days at 16 °C before evaluated for sprouting, fresh weight loss, membrane permeability, sugar content and processing quality. RESULTS: The study demonstrates that in order to achieve complete inhibition of sprouting during potato reconditioning HWTs must exceed the thermal tolerance threshold of the tubers. Short‐duration HWT was effective in retarding sprout growth and tuber dehydration without significantly affecting storage parenchyma membrane permeability, tuber sugar content or processing quality. On the contrary, prolonged HWT caused extensive heat damage, loss of membrane integrity and induced an increase in tuber sucrose and reducing sugar content resulting in deterioration of chip colour in proportion to treatment duration. CONCLUSION: Although HWT at 52.5–60 °C following long‐term cold storage did not improve the processing quality of potato tubers after 20 days of reconditioning, future work is needed to evaluate the effect of short‐duration HWT on the permissible extent of reconditioning and subsequent processing quality. Copyright © 2008 Society of Chemical Industry     

A simplified procedure for quantification of potato glycoalkaloids in tuber extracts by H.p.l.c.; comparison with ELISA and a colorimetric method

An improved high-performance liquid chromatography (h.p.l.c.) procedure for determination of glycoalkaloid levels in potato tubers has been developed in which Sep-Pak cartridges replace the commonly used alkaline precipitation for clean-up of tuber extracts. Glycoalkaloids are extracted from fresh tuber tissue into an aqueous medium, the extract is submitted to clean-up and α-solanine and α-chaconine are quantitatively separated on a reversed phase column with ethanolamine modifier added to the mobile phase. Potato tubers were comparatively analysed for their glycoalkaloid content by this and two other methods: a recently developed immunoassay (ELISA) and a colorimetric procedure representing the traditional chemical approach. Agreement between the h.p.l.c. and the other methods was good.     

ACTINOMYCIN D INDUCTION OF TERPENE STRESS METABOLITES IN POTATO TUBER SLICES

Relatively large amounts of rishitin and lubimin accumulate in potato tuber slices following treatment with actinomycin D (AD). Optimum elicitation of these terpenes occurred at an (AD) concentration of μM. Terpene accumulation was evident within 24 h after treatment and progressed for up to 96 h at which time rishitin levels exceeded 100 μg/g fresh weight, discs. Slices prepared from tubers previously held at 25°C were less responsive to (AD) induction of terpenes than those from tubers previously stored at 4°C. Treatment of discs with 50 μM cycloheximide following (AD) treatment blocked further accumulation of terpenes indicating a requirement for continual protein synthesis. (AD) (20 μM) treatment caused a slight reduction in protein synthesis for the first 48 h following treatment after which it caused an increase in protein synthesis compared to controls. (AD) also affected respiration of discs in a manner which paralleled its effect on protein synthesis. Cyanide resistant respiration was more pronounced in (AD) treated discs than control discs. The data are discussed with reference to the mechanism by which (AD) elicits terpene biosynthesis in potato tubers discs.     

GLYCOALKALOID CONCENTRATION IN BY-PRODUCTS of POTATO STARCH EXTRACTION AS MEASURED BY MATRIX-ASSISTED LASER DESORPTIONIIONIZATION MASS SPECTROMETRY

Starch, potato protein concentrate, and potato pulp were produced in order to determine the fate of endogenous toxic glycoalkaloids during potato processing. Potato protein concentrate was precipitated from potato fruit water using acid and heat. Glycoalkaloid concentrations were determined using matrix- assisted laser desorption/ionization mass spectrometry. No correlation was observed between tuber protein concentration and yield of potato protein concentrate (r = 0.257). Glycoalkaloids could not be detected in starch extracted from tubers with a glycoalkaloid concentration of 6.6 mg/i 00 g (fwb). Dry potato protein concentrate and dry potato pulp produced from the same tubers contained 60 and 50 mg glycoalkaloid/100 g, respectively. the apparent partitioning of glycoalkaloids into the protein concentrate and pulp indicates toxicity might be a concern for these products, given that a maximum acceptable level of 20 mg glycoalkaloid/100 g is often cited for tubers.     

RHEOLOGICAL AND TEXTURAL CHARACTERISTICS OF RAW AND PAR-COOKED TAEWA (MAORI POTATOES) OF NEW ZEALAND

The quality characteristics of raw and par-cooked (partially cooked) tubers from four different Taewa cultivars were evaluated and compared with a modern potato cultivar (Nadine). Significant differences in dry matter, starch content, color and specific gravity were observed among the raw tubers from the different cultivars. Moemoe and Tutaekuri Taewa cultivars showed higher dry matter content (21.97 and 21.57%, respectively) whereas the lowest specific gravity of 1.057 was observed for Nadine. Par-cooked chef-ready tubers were prepared from each cultivar and evaluated for quality during 21 days of storage at 4C. Tutaekuri raw as well as par-cooked tubers had higher fracturability and hardness whereas Nadine par-cooked tubers had higher adhesiveness than other cultivars. Rheological parameters such as storage modulus ( G' ), loss modulus and loss tangent (tan δ ) were dependent on the dry matter and starch contents of the tubers. The highest peak G' values of 24,930 Pa and 19,700 Pa were observed for Tutaekuri and Moemoe potato cultivars, respectively.

PRACTICAL APPLICATIONS

Ready-to-microwave par-cooked tubers with a refrigerated shelf life of 21 days were developed without using any chemical preservatives. The rheology of the tuber tissue was studied using a dynamic rheometer for the first time. The technique allows the continuous monitoring of the changes occurring in the potato tissue during the heating and cooling cycles. Significant correlations between the textural characteristics of raw and cooked tubers and the dynamic rheological characteristics of fresh tubers were observed. The technique may be helpful in predicting the viscoelastic characteristics of raw potatoes and the changes in the texture of cooked tubers during refrigerated storage.     

不同真空包装净菜菌相组成及生长趋势比较

主要以真空包装山药段、南瓜、红薯块、土豆块、芋艿、香芋块、紫薯块为原料,比较不同种类的鲜切净菜的初始和腐败时的菌相组成和生长趋势。实验结果表明:净菜中的主要微生物包括酵母菌属、乳酸菌属、肠杆菌科、假单胞菌属和微球菌属。山药段、南瓜、红薯块、土豆块、芋艿、紫薯中酵母菌初始数量较多,在培养一段时间后,均呈现增长趋势;净菜中的乳酸菌数量初始都超过了2.0lgcfu/g,并且都呈现了显著的增长;净菜初始的肠杆菌科含量都超过了3.0lgcfu/g;但山药段、土豆块、芋艿、紫薯块中的肠杆菌科呈增长趋势,而香芋块、南瓜和红薯块中的肠杆菌科出现了下降趋势;香芋、芋艿的假单胞菌属、微球菌属生长迅速,山药段、南瓜、红薯、土豆块、紫薯块中的微球菌属都呈现下降的趋势。      

Digital imaging for evaluation of potato after-cooking darkening and its comparison with other methods

After‐cooking darkening (ACD) phenomenon occurs when potato tubers develop greyish dark colour after boiling, frying, or steaming. The pigment responsible for ACD is a complex of chlorogenic acid and iron, which is formed during cooking and oxidised during cooling. The evaluation of ACD is thus based either on the amount of chlorogenic acid in raw tubers or the greyish colour intensity on cooked tuber surfaces. This study introduced a new method, the digital imaging method, for evaluation of potato ACD. The comparison of this new method with visual evaluation and the measurement of chlorogenic acid using HPLC were also presented. The digital imaging method is based on the direct measurement of the degree of dark colour on cut tuber surfaces, expressed by pixel levels. The new method is faster, more reliable and simpler when compared with any methods presently used. It is particularly applicable to handling large sample numbers.     

Review on tropical root and tuber crops I. Storage methods and quality changes

The root and tuber crops, including cassava, sweet potato, yams, and aroids, enjoy considerable importance as a vegetable, staple food, or raw material for small‐scale industries at a global level, particularly in the less developed tropical countries. The perishability and postharvest losses of root and tuber crops are the major constraints in the utilization of these crops. Several simple, low‐cost traditional methods are being followed by fanners in different parts of the world to store different root and tuber crops in the fresh state. An account of different storage practices and constraints is reviewed in this article. Some of these methods have been studied and evaluated by different research workers. Several modern techniques, including refrigerated cold storage, freezing, chemical treatments, wax coating, and irradiation, for storing fresh tropical tubers are also reviewed. The pre‐ and postharvest factors to be considered for postharvest storage of different root and tuber crops are incorporated into the review.     

Isolation and characterization of Mexican chayote tuber (Sechium edule Sw.) starch

Starch was isolated from Mexican chayote tubers (Sechium edule Sw.) and the yield, physicochemical, rheological, and molecular characteristics were investigated. Commercial potato was used for comparison. Starch yield was 49% with a purity of 89.1%. AM content of chayote tuber starch was 26.3%. Birefringence was shown in chayote tuber starch and granules had diverse shapes such as spherical, oval, and polygonal, with size between 10 and 25 µm. B‐type XRD pattern was shown by chayote tuber starch. Chayote tuber starch had higher peak viscosity (PV) than potato starch and the maximum PV for chayote tuber starch was obtained at lower temperature. Flow properties of chayote tuber starch showed higher hysteresis than potato at the same concentration. In chayote tuber and potato starches, G′ > G″ at both temperatures. Chayote tuber starch presented slightly lower gelatinization temperatures, but slightly higher enthalpy of gelatinization than potato starch, and similar retrogradation rate (due to the enthalpy value of the phase transition) were found in both tuber starches. Chayote tuber starch presented higher Mw and Rz values than potato starch. Chayote tuber could be an alternative for starch isolation with specific physicochemical and molecular characteristics.     

The effects of boiling and leaching on the content of potassium and other minerals in potatoes

ABSTRACT:  The white potato ( Solanum tuberosum L.) is a valuable source of potassium in the human diet. While most consumers benefit from high levels of potassium in potato tubers, individuals with compromised kidney function must minimize their potassium intake. This study was undertaken to determine the effects of leaching and boiling on levels of potassium and other minerals in potato tubers. Leaching alone did not significantly reduce levels of potassium or other minerals in tubers. Boiling tuber cubes and shredded tubers decreased potassium levels by 50% and 75%, respectively. Reductions in mineral amounts following boiling were observed for phosphorus, magnesium, sulfur, zinc, manganese, and iron. There was no difference between the leaching and boiling treatment and the boiling treatment. In addition, mineral levels in tubers of 6 North American potato cultivars are reported. Significant differences in mineral levels were detected among cultivars, but they were too small to be nutritionally important. Individuals wishing to maximize the mineral nutrition benefits of consuming potatoes should boil them whole or bake, roast, or microwave them. Those who must reduce potassium uptake should boil small pieces before consuming them.     

高效液相色谱法测定8 个彩色马铃薯品种中花青素种类和含量

采用高效液相色谱法,以表皮和薯肉为研究对象,定量分析8 个彩色马铃薯品种块茎中花青素的种类和含量。研究发现,彩色马铃薯块茎中最多含有6 种花青素,即飞燕草色素、矢车菊色素、矮牵牛色素、天竺葵色素、芍药色素和锦葵色素。紫色马铃薯块茎中主要花青素为矮牵牛色素、芍药色素和锦葵色素,红色马铃薯块茎中主要花青素是天竺葵色素和芍药色素。飞燕草色素和芍药色素广泛存在于彩色马铃薯（紫色和红色）块茎的表皮中,而红色马铃薯块茎中未检测到锦葵色素。品种之间差异显著（P＜0.05）,其中紫云1号的总花青素含量最高。块茎表皮的花青素含量约是薯肉的6～176 倍,且大部分品种的表皮花青素种类比薯肉多。彩色马铃薯块茎的表皮富含丰富的花青素,是天然色素和抗氧化剂的重要来源。     

Nonyl alcohol vapour in potato stores during sprout suppression. II.—Physical factors in the uptake of nonyl alcohol vapour by potato tubers

A study was made of some physical factors which influence the uptake by potato tubers of nonyl alcohol, used for sprout suppression in commercial storage. The saturation concentration of nonyl alcohol vapour in air was determined over the relevant temperature range. Investigation of the interactions between potato tubers and mixtures of air, nonyl alcohol vapour and water vapour showed that the tubers reached equilibrium with the alcohol vapour most rapidly in dry air at the higher of two temperatures investigated. The weight of alcohol taken up by the tuber was greater in dry air and was proportional to the square of the applied alcohol vapour concentration. A sudden rise in humidity caused a rapid release of some alcohol from a treated tuber, while a drop in humidity caused a rather slower uptake. The results suggest that part of the nonyl alcohol is absorbed by the bulk of the potato and part adsorbed on the surface of the skin. The relevance of the results to commercial potato storage practice is discussed.     

The effect of the time and mode of application of gibberellic acid on the growth and yield of potato plants derived from true potato seed

The effect of the time and mode of treatment (single or repeated applications) of gibberellic acid (GA₃) on the growth and tuberisation of plants grown from true seed (TPS) of potato Chacasina F₁ was studied. Plant height, fresh and dry weight of stems and leaf dry weight increased in response to single or repeated GA₃ applications. Leaf colour was not affected by single applications of GA₃, whereas repeated applications caused a reduction in colour intensity. The numbers of secondary shoots and leaves per plant as well as total leaf area were largely unaffected by GA₃, although repeated applications from early in the growth cycle increased these parameters under conditions of decreasing photoperiod. When applied as a single dose during spring, GA₃ caused an increase in the number of tubers per plant, with a concomitant decrease in tuber dry matter content, irrespective of application date. In autumn the number of tubers per plant increased following single applications of GA₃ up to 50 days after transplantation, whereas tuber dry matter decreased. By contrast, repeated applications of GA₃ in both seasons increased tuber number only when initiated early in the growth cycle. The mean weight of tubers per plant was variably affected by GA₃ application, depending on the season, time and mode of application. It is suggested that the foliar application of GA₃ to plants from TPS at an early stage of vegetative development may be of value for seed tuber or micro‐tuber production, primarily by increasing the number of tubers produced per plant. Copyright © 2006 Society of Chemical Industry     

EFFECT OF SELENIUM FERTILIZATION ON THE CONCENTRATION OF SELENIUM, OTHER MINERALS, AND ASCORBIC ACID IN POTATOES

The effect of selenium fertilization on the concentration of selenium, other minerals, and ascorbic acid of Katahdin potato tubers was studied during each of two years. Sodium selenite was banded to the soil at rates of 5.6 (2.5), 11.2 (5.0) and 16.2 (7.5) kg/ha (ppm of soil). The tuber selenium concentration was increased significantly (p<0.01) from 0.47 ppm to 0.93 ppm fresh weight. However, selenium levels in the soil greater than 5.0 ppm did not result in further increases in the selenium concentration of tubers. No significant effects due to selenium fertilization were observed for the concentration of other minerals and ascorbic acid. Similar trends were observed during both years of the study. In areas where the soil is low in selenium, addition of this element could prove useful in increasing the selenium content of potatoes, a very important vegetable in the American diet.     

Changes in anthocyanin,flavonoid and phenolic acid concentrations during development and storage of coloured potato (Solanum tuberosum L) tubers

Changes in the anthocyanin concentration of coloured potato tubers have been investigated in cultivars with coloured skin and coloured or white flesh. The biosynthesis of anthocyanins coincided with tuber initiation in cultivars with intensely coloured mature tubers and, after a slight increase as the smaller tubers increased in size, anthocyanin concentrations remained relatively constant. Thus, because tubers were increasing in weight, anthocyanin was being synthesised to maintain a more or less constant concentration. In cultivars with less coloured tubers, the developing tubers remained white for a longer time, with anthocyanin concentrations increasing gradually up to a maximum at a certain tuber weight depending on the cultivar. The concentration of flavonoids was lower than that of anthocyanins but followed a similar pattern. Phenolic acid levels were about twice those of the anthocyanins and reached their maximum at a slightly lower tuber weight than anthocyanins and flavonoids. During cold storage (4°C) the anthocyanin concentration in coloured tubers increased, whereas tubers stored at higher temperatures did not show this increase. The increased colour in cold‐stored tubers is discussed in terms of its relationship to ‘cold sweetening’ and the increased concentration of sugars in cold‐stored tubers. The distribution of anthocyanins altered during tuber development and also during cold storage. In very small developing tubers the anthocyanins appeared first at the stem end of the tuber whilst the bud end remained white. As the anthocyanin concentration increased during tuber development, it increased over the whole tuber, but the concentration at the stem end was always higher than that at the bud end, until the tuber reached maturity, when the concentration became approximately equal at both ends. After cold storage, tubers had a higher concentration of anthocyanin in the bud end than the stem end; the opposite to that found in developing tubers. © 1999 Society of Chemical Industry