Comparison of the cooking behaviour of the potato cultivars Nicola and Irene with respect to pectin breakdown and the transfer of ions

Summary The potato cultivars Nicola and Irene were investigated with respect to cell sloughing, specific cell surface area, release of pectic material and transfer of ions using a model cooking study. Both cell sloughing and the release of pectic material were higher for the mealy-cooking cultivar Irene. As the respective cell size distributions measured were the same for both cultivars, the difference in release of pectic material could not be explained by a difference in the specific cell surface areas between the cultivars. Additionally, it was recorded that during cooking only 20% of the calcium present in non-cooked tissue was transferred into the cooking medium, whereas more than 70% of potassium and citrate were transferred. The ratios D_a.citr2−/D_a.K+ and D_a.Ca2+/D_a.K+ for water and cooked potato tissue revealed that in water, potassium ions diffused faster than citrate and calcium ions. However, in cooked potato tissue both citrate and calcium ions diffused faster than potassium ions.     

Leaching of solutes and sloughing of potato tuber tissue

Thin slices of tissue from low (1.075–1.078 and high (1.092–1.094) specific gravity tubers were soaked in distilled water (100g/250ml) for 0, 1, 2, 3, 4, and 6 hours. Following the soak periods, the soak water and remaining tissues were separated and analyzed. Analyses of the soak water included pH, electrical conductivity, total solids, K, P and citric acid. The tissue analyses included total ash, alkalinity of ash, Ca, Mg, total N and phytate P. Other tissue samples were soaked the same periods of time and used to evaluate the amount of sloughing that occurred during cooking. All constituents studied diffused into the water during the soak periods. The greatest loss from the slices occurred in the first 2 to 3 hours and were similar for both specific gravity groups. After 6 hours the average amounts of material in the soak water were: total solids — 23%, P — 68%, phytate P —55%, K — 71%, total ash — 62%, total nitrogen — 56%, Ca — 35% and Mg —50%. Citric acid diffused into the soak water during the first 3 hours and the amount in the water then decreased. This apparent change may be due to metabolism of the acid. The sloughing of tissue decreased with the length of the soak period. The decrease in sloughing was highly correlated (P<1 %) with the length of the soak period, increases in electrical conductivity of the soak water, and with the leaching of all constituents measured.     

Cooking quality of some Dutch potato varieties

Summary The relationships among three methods for evaluating texture (sloughing during cooking, hardness of cooked potato dice and shear press value of French fries) and some chemical constituents (Ca, Mg, K, free pectin, phytin and citrate) were investigated, using the main specific gravity classes of seven Dutch potato varieties. The interplay of these constitutents (except K) in the softening of the texture during cooking was expressed as follows: Only the shear press value showed a relationship with the specific gravity. None of the textural-properties was geverned by the PC PMC number or by water uptake of raw slices. The same properties were determined after 50 and 100 days storage at 10 and 4 C. A decrease in sloughing and hardness, but an increase in shear press value occurred. PCMPC number also increased, but remained quite low, explaining its lack of influence on texture.     

Diffusion-processed sweet potato pulp,a new product with broad appeal

Peeled sweet potato slices of two standard varieties were soaked for 120 min, drained, boiled for 20 min, and mashed. The pulp was prepared in 6 simple dishes and tested organoleptically by a trained taste panel. The pulp was also prepared and evaluated by 30 families. Sugar and protein contents were compared to those of untreated uncooked sweet potato, and untreated cooked sweet potato. Diffusion processing lowers the content of all sugars, but subsequent cooking increases reducing sugar content. Processing also removes water soluble phenolic substances and results in less polyphenolic discoloration before and after cooking. Protein and starch contents are also reduced, the former by diffusion, and the latter by diffusion and by erosion on boiling. Dishes made from the pulp were highly acceptable, more moist in texture, less sweet, and more attractive than dishes from non-processed sweet potatoes. People who do not like to eat sweet potatoes found diffusion processed pulp highly acceptable as a staple food.     

The textural quality of cooked potatoes. I. The relationship of cooking time to the separation and rupture of potato cells

Mealy mashed potatoes were obtained from potato slabs steam cooked as little as 8 min. The potato slabs were undercooked by the fork test. The bud-end slabs were softer than the stem-end slabs and the compressive force to rice the potato was high. Histologically, potatoes cooked 8–18 min showed no distention of cell walls and the rupture of cells was caused by the ricing of the potato tissue. Measurement of released free starch from the ruptured cells showed the potato cell was more susceptible to rupture as the cooking time increased. Potatoes cooked 9–12 min showed no significant differences in amount of cell rupturing. The results indicated the possibility that the pectic material in the middle lamella underwent a change, which was complete at cooking time of 9–12 min, to permit forced separation of the cells without undue damage to the cells. With longer cooking time, there was breakdown of the pectic material in the primary and secondary wall increasing the susceptibility of cells to rupture.     

The textural analysis of cooked potato. 1. Physical principles of the separate measurement of softness and dryness

Summary The texture of cooked potatoes was described by two physical parameters: softness, resulting from both cell cleavage and cell separation, and dryness, depending on the ratio of cell separation to cell cleavage. The softness of potato tissue was measured by determining its resistance to cutting with a thin stainless steel wire. Softness increased rapidly with cooking time, particularly when the cultivar was predicted tobe soft in texture by published taste panel trials. Raw potato tissue released intercellular fluid from fractured surfaces due to cell cleavage. After cooking less fluid was released, i.e. the texture became drier, as cell separation increased. The erosion of cells from cooked potato tissue by a high-pressure jet of water was used to measure dryness quantitatively. Erosion increased during cooking. Carrot tissue, whose cells do not separate on cooking, did not erode, but anomalous results with apple tissue suggested that measurement of dryness in this way might not be fully independent of softness.     

Some aspects of cooked potato texture and appearance. II. Potato cell size stability during cooking and freezing

Slices of potato tuber tissue were cooked in water on microscope slides on a Koffler hot stage. At various temperatures during heating and cooling photographs of sets of potato cells were made. After cooling the tissue was frozen. Further photographs were made after thawing and reheating to 75C. The sizes of the individual cells were measured on the photographs. No swelling of the cells was observed under any of the conditions imposed. The hypothesis that starch gelatinization causes distention of potato cell walls during cooking was not supported by the results. Several suggestions were made for other roles of the starch in potato texture.     

Cell Wall Reinforcement in the Potato Tuber Periderm After Crop Treatment with Potassium Phosphite

The potato periderm is the outer tissue of potato tubers that protects the tuber from pathogen attack, dehydration, and wounding during harvest and storage. It is of secondary origin and replaces the epidermis early during tuber development. The outer layers of the periderm consist of cells with suberized walls. Phosphite compounds (Phi) are inorganic salts from phosphorous acid, and in previous works, we demonstrated that they are effective in protecting potato plants from biotic stress caused by different pathogens and also against UV-B radiation. The aim of the present work was to study the effect of Phi on the post-harvest potato periderm structure, cell wall components, and related enzymes. In three years of field experiments, potassium phosphite (KPhi) applications were compared with an untreated control. KPhi was applied to seed tubers before planting combined with foliage application of a conventional fungicide, to seed tubers and foliage without conventional fungicide, or to seed tubers combined with foliage application of KPhi plus a conventional fungicide. Observations of periderm sections showed increases in suberin and pectin depositions in post-harvest tubers from KPhi-treated plants compared to tubers from non-treated plants. In addition, peroxidase activity increased in the periderm tissue. The activity of laccases and superoxide dismutase was measured in the protein extract of the periderm, and an increase due to KPhi treatment was detected. The results presented here suggest that early KPhi treatment to seed tubers followed by foliage treatment leads to reinforcement of the cell wall of periderm cells, which represents a benefit for future response to stresses.     

Influence of hydrothermal treatment on rheological and cooking characteristics of fresh egg pasta

The effect of D.I.C. processing conditions on rheological and cooking properties of commercial fresh egg pasta was studied. The mechanical properties of pasta before and after cooking were evaluated by empirical test and characterised by maximal apparent force (F_max) and apparent relaxation coefficient (ARC). Structural (apparent density) and cooking quality were evaluated by determining mass ratio (W/Wo), optimal cooking time (OCT), swelling index (SI), solid, soluble and total cooking losses (TCL) and compared to untreated pasta. The hydrothermal treatment caused a reduction in firmness and relaxation capacity of treated pasta. The increase of processing conditions induced a decrease of F_max and the processing time has an influence when it is associated to the low pressures. The values of ARC vary from 51% (untreated pasta) to 37% (D.I.C. treated pasta). The increase of processing time from 30 to 60 s does not seem to have a significant influence on ARC. The apparent density of treated pasta is a function of processing pressure and time but it is always lower than untreated pasta density. Treated pasta had a higher quality score based on water sorption and SI and matter losses (TCL values and solid and soluble losses) as compared to untreated pasta.     

Potato berry blackening and premature drop due to boron deficiency

A number of methods are used in potato programs to achieve successful crosses. The cut stem technique is used in many of them and it usually achieves good results. However sometimes berries turn black, produce sterile seed and drop off prematurely. No pathogen was associated with the disease. Six water sources were compared including potable water, water from a deep tubular well, water from a superficial well, Hoagland’s nutrient solution, distilled and deionized water. Flowering stems of cv Yungay were cut, pollinated with pollen from clones R 128.6 and placed in bottles with water from different sources. Hoagland’s nutrient solution and water sources with highest boron content produced lowest incidence of blackened berries. An additional experiment testing 6 macrometabolic and 6 micrometabolic elements including B produced the following results: Treatments containing B produced normal berries; whereas treatments without B produced around 90% of blackened berries and/or drop off. It was thus demonstrated that this abnormality was caused by B deficiency which could be corrected by addition of 2 ppm of boric acid. Solutions containing greater than 5 ppm caused phytotoxicity in leaves of flowering stems.     

Effects of potato/wheat flours ratio on mixing properties of dough and quality of noodles

The effects of potato flour/wheat flour (PF/WF) ratio on the mixing properties of dough and the quality of noodles were investigated. Substitution of wheat flour with potato flour caused the increases in the water absorption and the protein weakening value (C1-C2) of formulated flours, as well as the decrease in the corresponding dough mixing parameters including dough development time (DDT), dough stable time (DST), initial mixing time (C2), maximum torque during heating (C3), minimum torque of hot paste (C4) and the amount of retrogradation (C5-C4), indicating that the addition of PF weakened dough strength but improved degradation resistance. The textural, cooking, sensory characteristics and microstructure of noodle samples were evaluated. The results indicate that adhesiveness, springiness, broken ratio and cooking lose increased progressively with increasing PF content while the score of sensory evaluation continued to decrease. However, hardness, cooking yield and optimum cooked time for the samples of PF content range from 10% to 20% showed a distinctive variation. Environmental scanning electron microscopy (ESEM) confirmed changes in noodle microstructure as PF addition affected gluten network development. In general, noodles with PF content below 40% were acceptable.     

A non-destructive method for rapid evaluation of boiling quality of potato tubers

A non-destructive method for rapid evaluation of boiling quality of potatoes has been developed. The method is based on the degree of sloughing, after-cooking darkening and colour of tuber fractions (cores of 1.3 cm in diameter) cooked in test tubes at 118°C for 25 min. Using sixteen potato cultivars, with 20–30% dry matter content, boiling quality results obtained by the new method were compared to sloughing and after-cooking darkening values obtained by boiling quartered tubers in aluminum sauce pans on a standard electric stove. The correlation coefficient between sloughing data obtained by the two methods was 0.912 (P< -0.001). The new method has proven to be simple, reproducible and highly suitable for evaluating a large number of potato samples. This should make it attractive for routine use by potato breeders.     

Antispasmodic effect of Piper nigrum fruit hot water extract on rat ileum

The aim of this study was to investigate the effect of black pepper fruit hot water extract (BPE) on rat ileum contractility and the mechanism(s) of its action. The extract was prepared by adding black pepper powder to boiling distilled water followed by evaporated the solvent. Ileum was dissected from male adult rat (Wistar) and in Tyrode solution the tissue contractions were recorded by an isotonic transducer under 1 g tension. The cumulative concentrations of the BPE (0.0625-1 mg mL(-1)) reduced the ileum contractions induced by KCl (60 mM) or carbachol (10 microM) concentration dependently (p<0.001). In Ca2+-free Tyrode solution with high potassium (60 mM), BPE, (0.0625-1 mg mL(-1)) attenuated the contractions induced by cumulative concentrations of CaCl2 (0.225-2.7 mM) concentration dependently (ANOVA, p<0.05). The incubation of the tissue preparation (20 or 30 min) with L-NAME (100 microM), naloxone (1 microM) or propranolol (1 microM) did not reduce the extract antispasmodic effect on KCl-induced ileum contraction. The extract spasmolytic effect was attenuated neither by glibenclamide (10 microM) nor by tetraethylammonium (1 mM). Present results suggest that the spasmolytic effect of the extract on rat ileum was possibly mediated via Ca2+ influx.     

Microstructural and chemical investigation of subsurface hardened potatoes (Solanum tuberosum L.)

Summary Microstructural changes related to subsurface hardening of pre-peeled potatoes were investigated using cv. Sava potatoes peeled using an industrial peeler, a laboratory knife peeler or a hand knife peeler. The pre-peeled potatoes were packed in polymer bags and stored at 18°C for six days until cooking. Potato hardness and microstructure of the tissue was investigated. Cellulose and suberin in hard potato tissue increased linearly with increase in mechanical impact in a damage barrel. The area of cell walls and especially cell corners of mechanically damaged potatoes showed white autofluorescence in blue light. The number of layers of bricklike and autofluorescent parenchyma increased significantly with increasing hardness. Subsurface hardening was related to percentage cells with fluorescent gelatinised cell mass and curly cell walls in a depth of the potato tissue corresponding to the depth of maximum hardness.     

The textural analysis of cooked potato. 3. Simple methods for determining texture

Summary Separate methods were developed for measuring softness, i.e. ease of cutting, and dryness, i.e. the tendency to cell separation. Pieces of potato tissue 30 mm long and 10 mm square were cooked in boiling water for 5, 10 or 15 min. To measure softness, the force required to cut the tissue with a thin stainless steel wire, inserted into a razor cut 1 mm deep, was recorded. To measure dryness, the tuber segments were crushed between two plates to half their original thickness and the crushed tissue separated on a 1 mm sieve. The <1 mm fraction consisted largely of single cells and was measured by its packed volume. Both softness and dryness increased with cooking time in a range of six cultivars. There was some correlation between them, and a closer correlation between dryness and specific gravity. The results agreed with previous organoleptic texture determinations.     

Changes in the nutrient composition of potatoes during home preparation: I. Proximate composition

The effects of various home cooking methods on the proximate composition of four potato varieties were investigated. The results revealed significant increases in the dry matter content of tubers during oven-baking and microwave cooking. With one exception, cooking unpeeled tubers in boiling water did not significantly alter their proximate composition. Boiling peeled tubers resulted in a significant decrease in the total ash content. Except for one variety, there was a significant decrease in crude fiber in boiled peeled and oven-baked potatoes. Changes in protein values were erratic.     

Effects of various water or hydrothermal treatments on certain antinutritional compounds in the seeds of the tribal pulse,Dolichos lablab var.vulgaris L.

Effects of soaking, cooking and autoclaving on changes in polyphenols, phytohaemagglutinating activity, phytic acid, hydrogen cyanide (HCN), oligosaccharides and in vitro protein digestibility were investigated in seeds ofDolichos lablab var.vulgaris. Both distilled water and NaHCO₃ solution soaking and autoclaving significantly reduced the contents of total free phenolics (85–88%) compared to raw seeds. Autoclaving (45 min) reduced the content of tannins by upto 72%. Soaking seemed to have limited effect in eliminating phytohaemagglutinating activity, whereas autoclaving (45 min) seemed to eliminate the haemagglutinating activity completely. The reduction in content of phytic acid was found to be some what greater in distilled water soaking (28%) compared to NaHCO₃ solution soaking (22%). Only a limited loss in content of phytic acid was observed under cooking as well as autoclaving. Loss of HCN was greater under autoclaving (87%) compared to the other processes studied. Of the three sugars analysed, soaking reduced the level of verbascose more than that of stachyose and raffinose. Autoclaving reduced the content of oligosaccharides more efficiently (67–86%) than ordinary cooking (53–76%). Autoclaving improved the in vitro protein digestibility (IVPD) significantly (13%). Of all the different water and hydrothermal treatments studied autoclaving seemed to be the most efficient method in improving IVPD and eliminating the antinutrients investigated except phytic acid.     

Effect of titanium surface calcium and magnesium on adhesive activity of epithelial-like cells and fibroblasts

In the present study, we investigated the hydrothermal treatment of titanium with divalent cation solutions and its effect in promoting the adhesion of gingival epithelial cells and fibroblasts in vitro. Gingival keratinocyte-like Sa3 cells or fibroblastic NIH3T3 cells were cultured for 1 h on experimental titanium plates hydrothermally-treated with CaCl(2) (Ca) or MgCl(2) (Mg) solution, or distilled water (DW). The number and adhesive strengths of attached cells on the substrata were then analyzed. The number of Sa3 cells adhering to the Ca- and Mg-treated plates was significantly larger than in the DW group, but the strength of this adhesion did not differ significantly between groups. In contrast, NIH3T3 cell adhesion number and strength were increased in both the Ca and Mg groups compared to the DW group. Fluorescent microscopic observation indicated that, in all groups, Sa3 had identical expression levels of integrin β4 and development of actin filaments, whereas NIH3T3 cells in the Ca and Mg groups displayed much stronger punctate cytoplasmic signals for vinculin and more bundle-shaped actin filaments than cells in the DW group. As a result, it was indicated that the hydrothermal treatment of titanium with Ca or Mg solution improved the integration of soft tissue cells with the substrata, which may facilitate the development of a soft tissue barrier around the implant.     

Soft-rot Resistance of Coloured Potato Cultivars (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.): The Role of Anthocyanins

Coloured potatoes (Solanum tuberosum L.) rich in anthocyanins are gaining increasing interest on the markets, mainly due to beneficial health effects. Potato varieties containing colour pigments are therefore utilized more and more in actual breeding programmes. In this study, 10 purple-fleshed potato cultivars were compared in their resistance to soft rot caused by Pectobacterium carotovorum (Pc) with 10 white/yellow-fleshed potato cultivars. The results revealed that coloured potato cultivars exhibited on average better resistance to soft rot than white/yellow-fleshed potato cultivars. On tuber halves of purple-fleshed cultivars, the extent of rotting caused by Pc was on average 28.6% lower than on white/yellow-fleshed cultivars. The greater resistance of coloured potatoes coincided with the presence of anthocyanins, higher concentrations of soluble phenols and elevated polyphenol oxidase activity in tuber tissue. These three components were significantly correlated with the extent of rotting caused by Pc. However, coloured and white/yellow-fleshed cultivars were not very different in phenylalanine ammonia-lyase and peroxidase activity. There were also no significant differences in concentrations of dry matter, starch, crude protein and glycoalkaloids. Key findings reveal that total soluble phenols and anthocyanins contributed crucially to resistance expression in tuber tissue of coloured potato cultivars.     

Repellency of selected biorational insecticides to potato psyllid, Bactericera cockerelli (Hemiptera: Psyllidae)

Bactericera cockerelli has recently become a major concern because of its direct feeding and vectoring of bacterial diseases in many solanaceous crops. The repellency of four biorational insecticides, MOI-201 (a Chinese medicine plant extract), Requiem (a plant extract of Chenopodium ambrosioides), BugOil (a mixture of four plant essential oils), and SunSpray oil (a mineral oil), to B. cockerelli adults was tested on tomato. In a no-choice test, all the insecticides had significant repellency to adults and deterred oviposition as compared with untreated controls. Of the four insecticides, the two oils showed a stronger repellency to adults and deterred oviposition more strongly than Requiem or MOI-201. In a choice test, all insecticides had significant repellency to adults and deterred oviposition compared to untreated controls. Of the four tested insecticides, <1 adults and no eggs were found on the leaves treated with SunSpray Oil, BugOil or Requiem 3 d after treatment. The repellency rates of these three insecticides were 77.2–95.4%. MOI-201 also repelled adults significantly and deterred oviposition compared to untreated controls even though it was the least effective insecticide among the four evaluated. In conclusion, all four insecticides tested showed significant repellency to B. cockerelli adults and deterred oviposition, especially the two oils. The overall repellency to potato psyllid adults can be arranged in a descending order of SunSpray oil > BugOil > Requiem > MOI-201. These insecticides could be used in integrated pest management programs targeted against the potato psyllid on solanaceous crops.