Potato Discs Research Articles

Biological activities of Rumex dentatus L: evaluation of methanol and hexane extracts.

Rumex dentatus L. (Plygonaceae) extracts were evaluated for antibacterial, antifungal, cytotoxic, antitumor and allopathic potential. The leaf, stem and root extracts were prepared in methanol and hexane by simple maceration. The methanol extracts of root and shoot were found effective against all the bacterial strains tested. Zone of inhibition ranged between 9.7 to 12.1 mm. While the hexane extracts inhibited fungal growth (up to 80%) more efficiently than the methanol extracts. Concentration of different the extracts of R. dentatus effectively inhibited tumor induction on the potato discs produced by wild type Agrobacterium strains At10 and At6. The root extracts either in methanol or hexane showed LD50 values below 1000 ppm in brine shrimp mortality assay. The methanol extracts of leaf and stem inhibited radish seed germination (70 and 61% respectively) and root length more than the hexane extracts. The R. dentatus methanol extract showed presence of alkaloids, saponins, anthraquinones and tannins while flavonoids were also found in both methanol as well as hexane extract.

A Biaryl Xanthone Derivative Having Axial Chirality from Penicillium vinaceum

A new xanthone derivative having axial chirality was isolated from Penicillium vinaceum. Owing to the axial chirality, its structure, including absolute configuration, was determined by means of extensive spectroscopic data, such as UV, IR, MS, and 1D and 2D NMR spectra, and computational chiroptical methods. The new compound, (a R)-2'-methoxyvinaxanthone, has a structure containing two aromatic moieties with substituents hindering rotation about the biaryl axis. The compound gave positive results in a sea urchin egg test ( Paracentrotus lividus) and a crown gall tumor on potato disks test (Agrobacterium tumefaciens).

Patogenicidad de bacterias aisladas de plátano 'Hua Moa' con síntomas de pudrición blanda y aborto del racimo inoculadas en otros clones de plátano y guineo.

La producción del plátano (Musa spp.) en países de Centro y Sur América y el Caribe está limitada por enfermedades bacterianas. En Puerto Rico, la producción de clones de plátano hawaiiano 'Hua Moa' se ve afectada por una condición conocida como aborto del racimo o 'choke neck'. Esta condición en algunos casos está acompañada por síntomas de pudrición blanda, por lo que se cree puede estar relacionado con bacterias fitopatógenas. El propósito de este estudio fue identificar las bacterias relacionadas con la pudrición blanda de tejidos en plantas con la condición de aborto del racimo y determinar su virulencia en otros clones de plátano y guineo. Se aislaron bacterias de pseudotallos de Hua Moa en tres localidades de Puerto Rico, usando medios semiselectivos y agar nutritivo. Se determinó la patogenicidad en discos de papa y pseudotallos de plátano dentro de cámaras húmedas en condiciones in vitro. Las bacterias patogénicas se identificaron mediante el sistema BIOLOG®. En condiciones de invernadero se confirmó la patogenicidad de Burkholderia gladioli, Pseudomonas spinosa, Erwinia chrysanthemi y Pseudomonas aeruginosa en plátano (Maricongo, FIAH-121, Enano Común y Hua Moa) y de guineo (Grand Nain) usando una escala de 1 a 9. Todos los clones evaluados en condiciones de invernadero fueron susceptibles a E. chrysanthemi, posible agente causal de la pudrición blanda una vez se presenta el aborto del racimo. Burkholderia gladioli se informa por primera vez afectando a plátano y guineo. Esta bacteria fue más virulenta en Hua Moa y Grand Nain, con severidad 7 y 5, respectivamente, que en Maricongo, severidad 3. Pseudomonas spinosa y P. aeruginosa produjeron niveles de severidad menores de 4 comparado con E. chrysanthemi y B. gladioli que produjeron niveles de severidad mayores de 4. Esta investigación se realizó bajo condiciones in vitro y de invernadero y muestra que las principales bacterias relacionadas a la pudrición blanda en plantas con la condición de aborto del racimo en el campo son E. chrysanthemi y B. gladioli. Se recomienda realizar estudios de campo evaluando plantas hasta la etapa reproductiva para determinar si estas bacterias se relacionan además como agentes causales del aborto del racimo.

Kinetics of Heat and Mass Transfer and Color Development of Pre-Treated Sweet Potatoes During Frying

The potential utilization of sweet potatoes in the production of fries was examined. The influence of various pre-treatments (blanching, freezing, osmotic dehydration, and air-drying) on moisture loss, color development, and temperature rise in the product was investigated. Pre-treated sweet potato disks were fried in pure canola oil at 170°C for 0.5 to 5 min. Temperature rise within the product was similar for all pre-treatments except for samples frozen prior to frying. The maximum temperature range recorded was 166.7°C to 168.6°C for both the top and bottom surfaces. Air-drying, freezing, and osmotic dehydration (OD) in 3% NaCl solution accelerated moisture loss during frying. Both the frying time and pre-treatment influenced moisture content of the core, and final values ranged between 66.2% and 78.7%. Pre-treated samples had higher L, a*, and b* values, which became significant with longer frying periods and resulted in improved product color. Air-drying and OD may be considered as pre-treatments in the production of sweet potato fries.

Cytotoxicity of Native Sponges and Plants from the Colombian Caribbean Coast Against “Crown Gall” Tumors Induced by Agrobacterium tumefaciens

Agrobacterium tumefaciens is a Gram-negative rod able to induce crown-gall-like tumors in the potato discs. The cytotoxicity of extracts from Tabebuia and Xetospongia spp. was evaluated using this model. Two out of the six extracts tested (dichloromethane- and partial methanol-soluble extracts of Xetospongias spp.) showed the highest biological activity. Keywords: Tabebuia spp., Xetospongias spp., Agrobacterium tumefaciens, Ti plasmidum, Solanum tuberosum and, cytotoxicity

Effects of pre-treatments on the shrinkage and textural properties of fried sweet potatoes

This work studied the effects of various pre-treatments (blanching, freezing, air drying, osmotic dehydration and control) on the shrinkage and textural properties of fried sweet potatoes. Sweet potato discs were pre-treated and fried in pure canola oil at 170 °C for 0.5–5 min. Bulk density of the fried samples decreased while porosity increased with frying time. Effect of pre-treatment though not significant on bulk density but was significant ( P < 0.05 ) on product porosity. Control samples exhibited less shrinkage than pre-treated samples. Maximum change in diameter of samples ranged between 6.7% and 10.2% depending on pre-treatment. Maximum change in sample thickness was observed by 120 s of frying and the highest value was 18.3%. Pre-treated samples had higher difference in thickness compared to the control samples. Change in sample volume increased with frying time reaching a maximum at 120 s after which it either decreased or levelled off. Generally, pre-treatment improved the textural properties of fried samples in product hardness, springiness, chewiness, cohesiveness and adhesiveness.

Pulsed electric field enhanced drying of potato tissue

The influence of pulsed electric field (PEF) treatment on convective drying of potato tissue was investigated. The drying experiments for potato disks were done in the interval of drying temperatures 30–70 °C. The effects of pre-treatment before drying and PEF treatment in the course of the drying are discussed. The temperature dependencies of moisture effective diffusion coefficient D eff for intact, PEF-treated and freeze-thawed potato tissues are compared. It is shown that D eff is a function of the conductivity disintegration index Z σ . The moisture effective diffusion coefficient D eff is sensitive to the pre-treatment procedure, and the highest values of D eff are always observed for freeze-thawed pretreated samples. The data show that thermal pre-treatment of samples at high temperatures ( T = 70 °C) has practically no beneficial effect on the drying rate, though the same thermal pre-treatment at mild temperatures ( T = 50 °C) increases the moisture effective diffusion coefficient D eff and gives an effect that is comparable with that for the PEF pre-treated samples.

Cytotoxic and Antimycotic Activities of Essential Oil of Artemisia turanica Krasch from Iran

The cytotoxic and anti-fungal activities of Artemisia turanica essential oil were investigated. Also the composition of the essential oil of the plant was determined. For cytotoxic activity tests, a potato disc tumor inhibition method was exploited. For antifungal activity tests, a poisoned food technique against standard strains of Trichophyton rubrum, Trichoderma reesei, Microsporum gypseum and Aspergillus niger was adopted. The essential oils of A. turanica exhibited tumor growth inhibition (100 % ) inhibition at concentrations equal to 0.02 % (w/v) and higher. Thirteen components were identified in the essential oil of Artemisia turania. The main compounds consisted of 1,8-cineol (40.9 %), cis-verbenyl actate (19.0 %) and camphor (11.0 %). A dose activity relationship between the essential oil concentrations with inhibition of tumor growth on potato discs, and between the essential oil concentrations with antifungal activities was observed.

Evidence that SNF1-related kinase and hexokinase are involved in separate sugar-signalling pathways modulating post-translational redox activation of ADP-glucose pyrophosphorylase in potato tubers.

We recently discovered that post-translational redox modulation of ADP-glucose pyrophosphorylase (AGPase) is a powerful new mechanism to adjust the rate of starch synthesis to the availability of sucrose in growing potato tubers. A strong correlation was observed between the endogenous levels of sucrose and the redox-activation state of AGPase. To identify candidate components linking AGPase redox modulation to sugar supply, we used potato tuber discs as a model system. When the discs were cut from growing wild-type potato tubers and incubated for 2 h in the absence of sugars, redox activation of AGPase decreased because of a decrease in internal sugar levels. The decrease in AGPase redox activation could be prevented when glucose or sucrose was supplied to the discs. Both sucrose uptake and redox activation of AGPase were increased when EDTA was used to prepare the tuber discs. However, EDTA treatment of discs had no effect on glucose uptake. Feeding of different glucose analogues revealed that the phosphorylation of hexoses by hexokinase is an essential component in the glucose-dependent redox activation of AGPase. In contrast to this, feeding of the non-metabolisable sucrose analogue, palatinose, leads to a similar activation as with sucrose, indicating that metabolism of sucrose is not necessary in the sucrose-dependent AGPase activation. The influence of sucrose and glucose on redox activation of AGPase was also investigated in discs cut from tubers of antisense plants with reduced SNF1-related protein kinase activity (SnRK1). Feeding of sucrose to tuber discs prevented AGPase redox inactivation in the wild type but not in SnRK1 antisense lines. However, feeding of glucose leads to a similar activation of AGPase in the wild type and in SnRK1 transformants. AGPase redox activation was also increased in transgenic tubers with ectopic overexpression of invertase, containing high levels of glucose and low sucrose levels. Expression of a bacterial glucokinase in the invertase-expressing background led to a decrease in AGPase activation state and tuber starch content. These results show that both sucrose and glucose lead to post-translational redox activation of AGPase, and that they do this by two different pathways involving SnRK1 and an endogenous hexokinase, respectively.

Brominated Oxylipins and Oxylipin Glycosides from Red Sea Corals

AbstractEight new brominated oxylipins 1−8, including two glycosides, were isolated from the Red Sea invertebrates Dendrophyllia sp., Dendronephthya sp. (red variety), Dendronephthya sp. (yellow variety), and Tubipora musica. Their structures were elucidated mainly on the basis of NMR spectroscopic data. The relative and absolute configurations were determined by analysis of NOESY and CD data and by the modified Mosher method. The compounds gave positive results in a brine shrimp toxicity assay, a sea urchin eggs test (Paracentrotus lividus), and a crown gall tumor on potato disks test (Agrobacterium tumefaciens). (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003)

Crosses between isolates of Phytophthora infestans from potato and tomato and characterization of F1 and F2 progeny for phenotypic and molecular markers

Nineteen crosses were carried out in vitro between seven and nine isolates of Phytophthora infestans originating from potato and tomato, respectively. Oospores were produced abundantly in all but two crosses, but oospore germination was generally low (a few per cent) and depended on the combination of parental isolates. The highest fertility in F1 progeny was observed when at least one parental isolate originated from tomato, and the lowest in crosses of isolates from potato; half the crosses were not fertile. Forty‐three F1 and 51 F2 single‐oospore progeny of a selected cross, along with the 16 field isolates, were analysed phenotypically and with molecular markers. Phenotypic characterization included mating type; sensitivity to the phenylamide fungicide metalaxyl‐M; specific virulence on potato R‐gene differentials; and aggressiveness (infected leaf area) on potato and tomato leaf discs (host preference). Isolates and progeny were also assessed for mitochondrial DNA haplotype with RFLP–PCR (restriction fragment length polymorphism–polymerase chain reaction), and characterized with AFLP (amplified fragment length polymorphism) and SSR (simple sequence repeats, microsatellites). Parental isolates were sensitive and resistant to metalaxyl‐M, whereas all F1 were intermediate phenotypes. In the F2 progeny, the majority of isolates (43 of 51) were intermediate in sensitivity and four each were sensitive and resistant to metalaxyl‐M, respectively. In both F1 and F2 progeny, four isolates emerged through selfing. The A1 : A2 ratio was 25 : 18 in F1 and 24 : 21 (plus six self‐fertiles) among the F2 progeny. Many F1 progeny isolates were highly aggressive on both hosts, but 15 and 23% of isolates preferred tomato and potato, respectively. Among F2 progeny, few highly aggressive isolates were recorded and a quarter of isolates lost pathogenicity almost completely. Isolates preferring tomato increased, and those preferring potato significantly decreased in the F2 progeny. Inheritance of mitochondrial haplotype in F1 progeny was uniparental and mostly (25 of 27) from one parent only. Six and four different SSR genotypes were identified in F1 and F2 progeny, respectively, of which two were identical to the parents. The two microsatellite loci, 4B and 4G, segregated in the ratios 15 : 22 : 2 and 22 : 17 in F1 and 24 : 17 and 26 : 15 in F2 progeny, respectively, while the majority of AFLP markers segregated in either a 1 : 0, 1 : 1, 3 : 1 or 1 : 2: 1 ratio. There was no obvious association between AFLP and SSR genotypes, nor between genotypic and phenotypic traits.

Influence of heating conditions and starch on the storage modulus of Russet Burbank and Yukon Gold potatoes

The storage modulus of Russet Burbank (RB) and Yukon Gold (YG) potato discs (13.3 mm × 4.5 mm) was measured continuously during heating in water at temperatures ranging from 40 to 80 °C for 120 min using a dynamic mechanical analyser with a heating stage. The starch content of YG potatoes was higher than that of RB potatoes, but the raw starch granule size distribution of both varieties was similar. RB samples had the highest storage modulus values (25% higher than raw tissue) when heated in 60 °C water for 35 min. Image analysis revealed that the perimeters of starch granules in the potato samples increased by about 50% during heating for 30 min at 60 °C. Heating temperature and time and starch content influenced the storage modulus. © 2001 Society of Chemical Industry

Influence of heating conditions and starch on the storage modulus of Russet Burbank and Yukon Gold potatoes

AbstractThe storage modulus of Russet Burbank (RB) and Yukon Gold (YG) potato discs (13.3 mm × 4.5 mm) was measured continuously during heating in water at temperatures ranging from 40 to 80 °C for 120 min using a dynamic mechanical analyser with a heating stage. The starch content of YG potatoes was higher than that of RB potatoes, but the raw starch granule size distribution of both varieties was similar. RB samples had the highest storage modulus values (25% higher than raw tissue) when heated in 60 °C water for 35 min. Image analysis revealed that the perimeters of starch granules in the potato samples increased by about 50% during heating for 30 min at 60 °C. Heating temperature and time and starch content influenced the storage modulus.© 2001 Society of Chemical Industry

Effects of frying parameters on the colour development of fried potatoes

The effects of frying time and temperature on the colour development of potatoes during frying was studied. Potato disks 0.025 m in diameter and 0.005 m thick were used. Sunflower oil was used as a frying medium at temperatures 150 °C, 160°C, 170°C and 180°C. Colour parameters of Hunter L and b values followed first-order reaction kinetics during frying. The temperature dependence of the rate constants for Hunter L and b values showed good agreement with Arrhenius relation, the activation energies, Ea, being equal to 22.67 kcal/mol and 17.13 kcal/mol, respectively. Hunter a value increased as frying time and/or temperature increased. A multiple regression equation was developed for total colour change as a function of time and temperature. The increase in time and temperature increased total colour change.

Colorado potato beetle (Coleoptera: Chrysomelidae) feeding, development, and survival to adulthood after continuous exposure to Bacillus thuringiensis subsp. tenebrionis-treated potato foliage from the field.

Colorado potato beetle, Leptinotarsa decemlineata (Say), feeding, development, and survival to adulthood were examined after continuously exposing large larvae to Bacillus thuringiensis subsp. tenebrionis-treated potato foliage from the field. In laboratory assays, the overall consumption and the length of period to become prepupae were determined for larvae, which began as 3rd and 4th instars, that were offered potato leaf disks with naturally declining levels of B. thuringiensis residue. In small-cage field experiments, survival to adulthood and the period to adult emergence for beetles confined to potato plants treated with B. thuringiensis beginning as 3rd and 4th instars also were examined. Third instars remaining on plants after a B. thuringiensis application were unlikely to feed and 4th instars consumed only approximately 50% as much foliage as those fed untreated foliage. Many late instars subjected to B. thuringiensis-treated foliage failed to survive to adulthood; 58-83% of these beetles died during the larval stage. Reduced feeding and poor survival of late instars suggest that counts of large larvae after application do not provide a complete picture of the efficacy of the B. thuringiensis treatment. Late instar Colorado potato beetles that were exposed continually to naturally declining levels of B. thuringiensis-treated potato foliage took an average of 1.8-4.5 d longer to become prepupae and 4-8 d longer to emerge as adults compared with those provided with untreated foliage. Delayed emergence of adults that fed on B. thuringiensis-treated potatoes as late instars indicated that development was prolonged in these insects because of ingestion of a sublethal dose of B. thuringiensis.

Fungus Gnat Population Development in Coconut Coir and Sphagnum peat-based Substrates

Coir and peat-based substrates were tested for their effectiveness in inhibiting the development of fungus gnat populations. The first experiment was conducted in July under relatively high temperatures (20 to 35 °C) and a second experiment was conducted in April under relatively low temperatures (20 °C). Euphorbia pulcherrima Willd. ex Klotzch `Freedom' plants were planted into 18-cm-diameter containers filled with substrates containing 80% sphagnum peat or coir, with the remainder being perlite. Half of the containers of each substrate were inoculated with fungus gnat larvae and sealed with either cheesecloth or thrips screen for Expts. 1 and 2, respectively. After 6 and 8 weeks for Expts. 1 and 2, respectively, fungus gnat adult and larval populations were sampled. Adults and larvae were recovered from coir and peat-based substrates in both experiments. In Expt. 1, significantly more adults and larvae were recovered from coir-based than peat-based substrates. In Expt. 2, significantly more adults and larvae were recovered from the peat-based than coir-based substrates. In a third experiment, the peat- and coir-based substrates used in Expts. 1 and 2 were used as well as the Iowa State greenhouse substrate, which contained 40% Sphagnum peat, 40% perlite, and 20% loam (v/v). Helianthus annuus L. `Pacino' seeds were sown into 18-cm-diameter containers filled with the test substrates. Natural infestation was allowed to occur for 6 weeks, after which time potato disks were used to sample the fungus gnat larvae population. Larvae were recovered from all substrates, and there was no significant difference in the number of larvae collected from the three substrates. Based on the results of these experiments, we concluded that coir does not inhibit the development of fungus gnat larvae populations and, when presented with options, fungus gnats will infest coir-based substrates as readily as peat-based substrates.

Characterization of potato tuber lipoxygenase cDNAs and lipoxygenase expression in potato tubers and leaves

A collection of cDNAs was isolated from a λgt11 potato (Solanum tuberosum L.) tuber library by using a soybean lipoxygenase (LOX; linoleate:oxygen oxidoreductase, EC 1.13.11.12) sequence as a hybridization probe. These cDNA clones were classified by restriction patterns and sizes and two clones, plox1 and plox2, were selected for sequencing and further analysis. These clones were found to be virtually identical and contain full‐length cDNAs having a high degree of homology with other cloned LOX genes. plox1 contains a 2 806‐bp insert, with an open reading frame that encodes a protein of 861 amino acids (96.9 kDa), consistent with molecular mass estimates of the principal tuber LOX deduced from SDS‐PAGE. The deduced sequence contains iron‐binding domains that are conserved among LOXs. Restriction analysis of potato genomic DNA confirmed that potato LOX is comprised of a gene family with at least three members. The plox1 sequence hybridized to a transcript of 2.8 kb in gel blot analyses of total RNA extracted from potato tuber. Treatment of potato disks and leaves with methyl jasmonate or jasmonic acid increased LOX enzyme activity, as well as abundance of LOX mRNA, consistent with jasmonate's reported effect on LOX expression in plants. The fungal elicitor arachidonic acid (AA) strongly induced LOX enzyme activity in leaves and induced LOX mRNA transcripts in potato leaves and tuber disks. Infection of potato leaves with Phytophthora infestans induced LOX activity as well as LOX mRNA accumulation in both incompatible and compatible interaction types. LOX expression was compared with that of a wound‐inducible proteinase inhibitor (PINII) and a pathogenesis‐related protein (P4). Jasmonates induced PINII but not P4 transcript accumulation in potato leaves. In contrast, AA induced P4 but not PINII transcript accumulation in potato leaves. Infection with P. infestans resulted in a gene expression pattern similar to that observed with AA.

Nitrogen recycling during phenylpropanoid metabolism in sweet potato tubers

In the first step of the phenylpropanoid metabolic pathway, L-phenylalanine (L-Phe) is deaminated to form E-cinnamate, in a conversion catalyzed by phenylalanine ammonia-lyase (PAL; EC 4.3.1.5). The metabolic fate of the ammonium ion (NH4+) produced in this reaction was investigated in sweet potato (Ipomoea batatas) tuber discs. [15N]-Labeled substrates including L-Phe, in the presence or absence of specific enzyme inhibitors, were administered to sweet potato discs in light under aseptic conditions. 15N-Nuclear magnetic resonance spectroscopic analyses revealed that the 15NH4+ liberated during the PAL reaction is first incorporated into the amide nitrogen of L-glutamine (L-Gln) and then into L-glutamate (L-Glu). These results extend our previous observations in pine and potato that PAL-generated NH4+ is assimilated by the glutamine synthetase (GS; EC 6.3.1.2)/glutamate synthase (GOGAT; EC 1.4.1.13) pathway, with the NH4+ so formed ultimately being recycled back to L-Phe via L-Glu as aminoreceptor and donor.

Salmonella Contamination Associated with Bacterial Soft Rot of Fresh Fruits and Vegetables in the Marketplace.

Wash water from 66% of 401 samples of fresh fruits and vegetables collected in the marketplace and affected by bacterial soft rot were positive for suspected strains of Salmonella, i.e., black, hydrogen sulfide-positive colonies on Salmonella-Shigella agar incubated for 24 h at 37°C. By comparison, 30% of 402 healthy samples were positive. Incidence of suspected Salmonella in broth enrichment cultures was 59% in 533 soft rotted samples and 33% in 781 healthy samples. Thirty percent of 166 representative strains of suspected Salmonella, selected at random from 20 different commodities, were confirmed to be Salmonella by physiological and serological tests. Adjusting incidence values accordingly, Salmonella contamination was potentially present in at least 18 to 20% of soft rotted samples and in 9 to 10% of healthy samples. Wash water from 120 paired healthy and soft rotted fruits and vegetables contained an average of 1.0 × 105 and 3.7 × 106 CFU/ml, respectively, of suspected Salmonella-a ratio of 1:37. Average concentrations of suspected Salmonella in enrichment cultures of healthy and soft rotted samples were 7.5 × 107 and 2.7 × 109 CFU/ml, respectively, also in the ratio of 1:37. Fresh potato, carrot, and pepper disks coinoculated with the soft rot bacterium Erwinia carotovora and with Salmonella typhimurium, and incubated for up to 72 h at room temperature, contained approximately 10 times the concentration of S. typhimurium as did disks inoculated with Salmonella alone. Disks coinoculated with Pseudomonas viridiflava and S. typhimurium contained approximately three times the Salmonella populations as disks inoculated with Salmonella alone.

A Simple Technique to Improve the Firmness of Cooked Potato Tissue

Potato tissue samples with varying cell turgor pressures were prepared by soaking in mannitol solutions (0 to 0·5 M). Increased concentration of mannitol in the soaking solutions decreased the cell turgor pressure in potato tissues providing samples with varying degrees of turgidity or plasmolysis. Firmness changes in potato tissues of differing turgor pressure during cooking were examined using a Zwick universal testing machine and also by chewing tests. A modified device attached to a Zwick machine facilitated complete immersion of a potato disc in circulating boiling water, providing rapid and reproducible heat transfer in the tissue during firmness measurements. Tissue firmness expressed as the force required to cause 10% strain in the sample varied in potato discs treated with differing mannitol solutions. Potato discs soaked in 0 to 0·3 M mannitol solutions were more turgid at 20°C than other samples and showed higher tissue firmness. However, when discs of potato were heated in the range of 20–90°C, samples treated with 0·4 and 0·5 M mannitol solutions showed some increase in tissue firmness while all other samples exhibited a rapid decline. Bite-force measurements on potato discs also indicated a rapid loss of tissue firmness in turgid samples. Potato tissues when cooked after soaking in 0·4 or 0·5 M mannitol solution showed more intact and inflated cells than other samples. © 1997 SCI