Design, Construction, and Testing of an Automated NIR In-line Analysis System for Potatoes. Part I: Off-line NIR Feasibility Study for the Characterization of Potato Composition

An off-line near-infrared reflectance (NIR) feasibility study was conducted to explore the critical steps in the NIR determination of the major potato constituents (dry matter, starch, and protein) in relatively large (10 kg) potato samples. The results were important for the design of an automated industrial analysis system for potatoes with in-line NIR. The 10-kg potato samples were pulped with an industrial rotary saw blade rasp. A critical step in the NIR measurements was the occurrence of phase separation in the potato pulp. Phase separation manifests itself directly after pulping the potatoes and significantly affects the NIR spectrum. Therefore, during the NIR measurements, the potato pulp had to be stirred continuously. The NIR spectra (1,100–2,500 nm) were measured by applying an optical fiber NIR probe (EDAPT-1) connected to the NIR spectrophotometer (Technicon Infralyzer IA 500). NIR models for the concentration of dry matter, starch, and coagulating protein in potatoes have been developed. With the partial least squares regression procedure, promising NIR models were calculated. The NIR models were validated using an independent validation set of potato samples. The root mean square error in prediction of the samples in the validation set was 0.5% (w/w) for dry matter, 0.63 (w/w) for starch concentration, and 0.06% (w/w) for the coagulating protein.     

温度对马铃薯α淀粉老化的影响

采用挤压膨化技术制作马铃薯α淀粉,并利用酶水解法及X-射线衍射法等研究了在同一贮藏时间内,不同贮藏温度对膨化马铃薯α淀粉老化变化的影响,探讨了影响机理。研究结果表明,贮藏温度从23℃±1℃降低到-18℃±1℃时,贮藏期为180d的样品α度也从87.8%明显降低到80.2%,样品的结晶度从8.4%上升为16.45%;说明样品α度的高低与贮藏温度的高低成正比,而样品的老化程度高低与贮藏温度的高低成反比。     

Production of potato starch with low waste

The use of fine grinding and air classification of dehydrated potatoes with sieving and minimum washing to produce potato starch is described. A substantial reduction in the amount of waste water over that required by conventional wet milling procedures was obtained. The procedure proposed would reduce wastes by 90%.     

Somaclonal variation in tuber traits of potato

Summary About 13,000 somaclones of 17 cultivars and clones of potato were obtained from in vitro callus cultures and individually planted in a greenhouse, followed by tuber generations grown in the field. These plants were subjected to the multistage selection procedure commonly used in potato breeding. Over a period of five years and three field generations the tuber number, size, shape, eye depth, starch content, starch yield and tuber appearance of these somaclones were assessed and compared with that of the controls. These characters varied depending on donor genotype and trait. The frequency of variants was assessed and there were acceptable proportions of desirable abberrants and invariants among the somaclones. Depending on trait the average gain rate for all donor genotypes ranged between 0.2 and 2.3% for-deviants, between 12.2 and 15.5% for invariants and between 0.1–1.4% for +deviants. It is concluded that this technique should be used into potato breeding programmes to improve commercially important characteristics of specific cultivars and breeding clones.     

Some studies on carbohydrates in potato tubers

Summary Starch and pulp were isolated from three cultivars of potato tubers grown in four localities. The starch content in the pulp was determined by an enzymatic method which is shown to be more accurate than a polarimetric method. On an average, 94% of the starch was isolated and 5% remained in the pulp. The change in low-molecular weight carbohydrates in the potato tubers during storage for 2, 4, 7 and 11 weeks at 9 C was studied. Generally there was an increase of sucrose, glucose, fructose andmyo-inositol during the first 2–4 weeks of storage, followed by a diminishing decrease.     

The recovery of maleic hydrazide from processed potato products

Summary A method used for estimating extractable maleic hydrazide (MH) concentrations in fresh potato material, concentration range 5–17 mg kg⁻¹, was found not to be suitable for processed potato products (10–33% recoveries) although, boiling potato pieces enhanced recovery by 20%. Each step of the determination was examined and a modified procedure developed with particular emphasis on the extraction of MH from the dried potato matrix, and the quality of the HPLC column used. Potato slices and model systems based on filter papers plus additives were used. Recoveries from fried potato slices were 74±6%. Based on the effect of glucose in reducing extractable MH recoveries, it is suggested that the remainder of the MH (20–25%) is converted into a conjugated structure on reaction with dehydrated sugar (Diels-Alder reaction).     

The Inter-genebank potato database and the dimensions of available wild potato germplasm

The Association of Potato Inter-genebank Collaborators (APIC) constructed a database of all wild potato holdings of the most important potato genebanks in Europe, the United States, Peru, and Argentina. The Inter-genebank Potato Database (IPD) now contains data of 11,819 wild potato accessions conserved in seven potato genebanks. The collector’s number is the key identifier used to merge all databases into the IPD. A total of 7,112 different wild potato accessions were identified, which comprise 5,306 accessions with known collector’s numbers. The IPD passport database showed that almost 30% of accessions held in APIC genebanks are from Argentina, a country that comprises less species diversity than Peru and Bolivia. These latter countries are represented by 24% and 20% of accessions, respectively. APIC genebanks maintain 188Solarium taxa out of more than 230 recognized by the latest comprehensive treatment of potatoes(Solarium sect.Petota) by Hawkes (1990). About 60% of the accessions comprise only 20 taxa represented by 785 to 92 accessions each. Conversely, 2% of the accessions comprise 72 taxa and are represented by five or fewer accessions each. About 70 taxa are not available in any genebank. The IPD evaluation database comprises 5,603 records with data from more than 33,000 evaluations of wild potato accessions. Fifty-five traits are summarized, including the reactions of the accessions to 12 pathotypes or races or strains of 12 fungi, four bacteria, 12 viruses, one viroid, 13 nematodes, and seven insects; response to heat and cold stress; and content of dry matter, starch, vitamin C, amylase, reducing sugars, and glycoalkaloids. About 30% of the wild potato populations screened showed various levels of resistance to most of the diseases and pests evaluated. The IPD database is available on the Internet at www.potgenebank.org.     

Rapid extraction and solubilization of potato starch with Dimethylsulfoxide

Dimethyl sulfoxide (DMSO) solubilization of starch from lyophilized potato tissue is equally quantitative and more convenient than solubilization in dilute alkali, especially when analysis of a large number of samples is necessary. Starch extraction with DMSO decreases the handling time of each sample by eliminating sonication, filtration, and centrifugation steps required by the NaOH solubilization technique.     

The technology of potato granule manufacture

The production of potato granules, a dehydrated mashed potato product, is in line with a growing trend in the processing of foods toward concentration and improved convenience for use. Several methods for producing potato granules have been developed during the past 30 years. The only one of these methods currently in commercial use in this country is the “add-back” process. This process involves a recycling (adding back) of dried potato granules and mixing the recycled material with freshly mashed potatoes to form a friable moist mixture below 40 per cent moisture content. The moist mixture is held for a period during which moisture equilibration takes place and a reduction in starch solubility and swelling capacity occur. After drying under suitable conditions, the individual cells remain separated and substantially undamaged. Physical damage to the product may cause release of free soluble starch, which manifests itself as an undesirable rubberiness in the reconstituted product. Investigations have revealed relationships of several variables in the process to this specific attribute of quality and to others (e.g., product yield and package density) and have provided useful information for process adjustment to improve the acceptability of potato granules.     

Relation of potato compsition to potato size and blackening tendency

A compositional study was conducted on six potato samples representing various degrees of stem-end blackening. The aim of the study was to determine compositional variation with potato size. The compositional characteristics, of stem-and bud-end tissue of various potato sizes, of the six samples were determined. The larger the potato the greater was the tendency for the stem-end to have the following characteristics: (i) low citric acid content, (ii) high K/citric acid, and (iii) relatively low citric acid/polyphenolic content. It was also shown that differences in stem-end blackening tendency between potato samples, as well as differences in blackening within the same sample could be correlated with these same compositional characteristics.     

The nutrient and glycoalkaloid content of a new potato meal

The nutrient and glycoalkaloid content of a new potato meal produced as a by-product of starch manufacture using low temperature dehydration was determined. Comparisons were made between the new potato meal and the previously manufactured meal which was prepared by high temperature dehydration. The glycoalkaloid content of the new potato meal was 15.53mg α-chaconine and 4.75mg α-solanine per 100g meal compared to 15.79mg α-chaconine and 7.83mg α-solanine in the potato meal produced by high temperature dehydration. The new potato meal contained 2% more protein and 1.9, 3.4 and 1.2 times more niacin, riboflavin and thiamin, respectively than the previous by-product. The potassium and phosphorus concentrations were approximately 2.0 and 0.2%, respectively. Other minerals were found in lesser concentrations with the sodium content being only 7.4mg/100g potato meal. A 28g serving would provide approximately 5, 7 and 4% of the RDA for protein, niacin and thiamin, respectively.     

Electrophoretic characterization of North American potato cultivars

A total of 112 named cultivars and advanced breeding lines were assayed through horizontal starch electrophoresis to test the utility of isozyme loci as a means to objectively identify potato cultivars. Both leaf and tuber tissue were sampled in thirteen enzyme systems. Two buffer systems (Histidine-citrate, pH 5.7 and Lithium-borate, pH 8.3) were used to resolve 16 isozyme loci, of which 14 were scorable without progeny testing. A total of 43 scorable allozymes were detected. All cultivars or advanced breeding lines that were the result of hybridization were discriminated by their sum electrophoretic pattern, whereas, sports (i.e., Russet Burbank vs. Burbank) or line selections (i.e., Norgold Russet “M1” vs. “M2”) have patterns that are identical to the original mother clone. The allelic diversity within and among cultivars indicate that horizontal starch electrophoresis offers an objective means to discriminate sexually-derived potato cultivars.     

The textural analysis of cooked potato. 2. Swelling pressure of starch during gelatinisation

Summary It has been disputed whether, when potato starch gelatinises and absorbs water, it generates an osmotic or matric pressure that makes the potato cells become round and separate from one another. Starch suspensions heated at 100°C in dialysis bags absorbed water, suggesting that starch swelling pressure does exist. It was quantified by heating starch suspensions at 85°C in a chamber which absorbed water through a membrane and contained an argon bubble whose volume was measured. This gave starch swelling pressures around 100 kPa, increasing non-linearly with starch concentration. A comparable estimate (a few hundred kPa) of starch swelling pressure within cooked potato tissue was obtained from the fact that it largely prevented the tissue contraction expected due to loss of turgor pressure in the first 1.5 min of boiling. A slight expansion thereafter was attributed to the combined effect of starch swelling pressure and cell wall and middle lamella degradation.     

Rapid estimation of the amylose/amylopectin ratio in small amounts of tuber and leaf tissue of the potato

Summary Small amounts of potato tuber and leaf tissues are extracted in perchloric acid. After staining with I₂-KI solution absorbancies at 618 and 550 nm are measured. The amylose/amylopectin ratio can be estimated from the ratio of the absorbancies by using a formula or a graph in which the specific absorptions of the two compounds are introduced. Weighing of samples is not required. The method can be used for the estimation of the starch composition of minitubers and is especially suitable for the detection of mutants with an altered starch composition.     

A rapid method for the determination of sulphur dioxide in sulfited potato flakes

A simple and rapid method is presented for the determination of sulfite in dehydrated potato flakes. Special extraction and filtration techniques are used to prevent potato cell rupture and subsequent release of the starch. Presence of cooked starch would interfere greatly with filtration of the extract. An iodimetric titration and simple calculation yield reproducible results with little effort or time.     

Simplified extraction method for ELISA and PCR detection of potato leafroll luteovirus primary infection in dormant potato tubers

This report describes a simple, rapid and inexpensive procedure for sampling large numbers of dormant tubers for analysis of potato leafroll luteovirus (PLRV) infection. The procedure uses a common electric drill to simultaneously remove and macerate tuber-eye samples for detection of PLRV by the enzyme-linked immunosorbant assay (ELISA) and the polymerase chain reaction (PCR). By using these sampling and analysis approaches, 19 of 20 different PLRV isolates were detected in dormant tubers from plants with primary infections. Results from the dormant tuber analysis, were verified by planting the tubers and testing leaf tissue by ELISA and PCR. Similar sampling and testing done on healthy dormant tubers and sprouts from the tubers consistently gave negative results as expected.     

The degree of starch phosphorylation as influenced by phosphate deprivation of potato (Solanum tuberosum L.) plants

Summary The levels of starch phosphorylation in potato tubers were investigated in relation to fertilization with phosphorus (P) of field-grown and greenhouse-grown plants. The field-grown plants received 0, 15 or 30 kg P ha⁻¹. Starch from plants grown without P-fertilizer contained 15.6 nmol P (mg starch)⁻¹ whereas starch from plants grown with 30 kg P ha⁻¹ contained 20.6 nmol P (mg starch)⁻¹. The greenhouse-grown plants were cultured in inert media and received nutrient solutions containing 0, 3, 12 or 24 mg P l⁻¹, respectively. Plants grown with no P-fertilizer produced tuber starch with phosphorylation levels reduced to approximately 30% of the level found in plants grown with an ample supply of P. Thus, the level of starch phosphorylation can be modified by limiting the P-supply through the root system. Application of foliar P-fertilizer to the greenhouse-grown plants had no significant effect on the phosphorylation of the tuber starch.     

Use of jet injection to determine potato cultivar susceptibility to potato viruses A and Yc

Summary The use of a high pressure jet injector to inoculate virus rapidly was compared with graft inoculation to determine cultivar susceptibility to potato virus A (PVA) and potato virus Y^c (PVY^c). Tubers were injected with virus infected potato sap, plant reactions recorded, and virus recovered using a bioassay test and enzyme linked immuno-sorbent assay. The injection method compared well with a traditional grafting procedure for PVY^c susceptibility tests but was unsuitable for testing susceptibility to PVA.     

Hydrogen peroxide increases potato tuber and stem starch content, stem diameter, and stem lignin content

Field-grown potato plants were sprayed twice weekly, from 21 to 90 days after planting, with 5 or 50 mM hydrogen peroxide (H₂O₂) solutions. Relative to water-sprayed controls, the H₂O₂ treatments significantly enhanced tuber starch accumulation by between 6.7% and 30%, as determined by specific gravity or the anthrone spectrophotometric method. Pronounced effects of similar H₂O₂ treatments on aerial stem anatomy and starch content were also found in glasshouse experiments. H₂O₂ treated stems were up to 27% thicker than controls, mainly due to enlarged medullar parenchyma cells. Histochemical observations indicated that there were more starch grains in cortex and pith tissue of H₂O₂-treated stems. H₂O₂ also increased the number and size of xylem tracheary elements in the vascular bundles and the number of interfascicular fibers. Quantification using image analysis confirmed that stems of H₂O₂ treated plants contained up to 3.4-fold more starch and 62% more lignin. This new chemical treatment to promote starch accumulation has potential utility in potato crop production and research.     

Evaluation of procedures for detection of pectolyticErwinia spp. on potato tubers

The effectiveness of a tuber incubation method for detection ofErwinia carotovora var.atroseptica andE. carotovora var.carotovora in potato tubers was compared with a lenticel sampling procedure. In the first method, tubers were injured by puncturing lenticels with sterile toothpicks, then wrapped in moist paper towels and polyvinylidene film, and placed in closed chambers flushed with N₂. In later experiments, wrapping tubers in two layers of polyvinylidene film and incubation in air was found to be as effective as the single layer of polyvinylidene and incubation in chambers flushed with N₂. Isolations were made on a selective crystal violet pectate (CVP) medium from homogenized samples of tissue removed from soft rot lesions developing around injured lenticels. In the second method, 10 lenticels/tuber were aseptically removed with a scalpel and homogenized in distilled water; the suspension was plated on CVP. The first method was less tedious and slightly more effective than the lenticel sampling method. In a preliminary survey, these methods were used to detectErwinia infestations in small samples of certified seed potato tubers from Maine, Minnesota, Montana, New York, North Dakota, and Wisconsin. PectolyticErwinia spp. were detected in at least one sample from each state except Montana. The percentage of tubers withErwinia infestations varied from 0–100% among samples. Characterization ofErwinia isolates showed that bothE. carotovora var.carotovora andE. carotovora var.atroseptica were present. PectolyticErwinia spp. on symptomless potato seed tubers may serve as inoculum sources for blackleg and soft rot diseases.