Low temperature post-harvest storage of New Zealand Taewa (Maori potato): Effects on starch physico-chemical and functional characteristics

Fresh tubers from four traditional Taewa (Maori potato) cultivars (Karuparera, Tutaekuri, Huakaroro and Moemoe) and one modern potato cultivar (Nadine) of New Zealand, were stored at 4 °C and 80–90% relative humidity for six months after harvest. Starch was isolated from tubers after every three month period, and its physico-chemical and functional properties measured. Considerable changes in these properties occurred during storage. The extent of changes varied significantly from cultivar to cultivar. Starch swelling power, solubility and light transmittance decreased during tuber storage while a slight increase was observed in starch amylose content. The starch granule size distribution shifted to smaller granule size during tuber storage. Scanning electron micrographs showed degradation/erosion and pitting on the surfaces of many of the starch granules isolated from stored tubers. Transition temperatures and enthalpies of gelatinization of the starches increased somewhat during tuber storage, suggesting that changes in the stability of starch crystalline structures had occurred. Pasting, viscoelastic and texture profile analysis (TPA) characteristics of starch gels were found to have been influenced by tuber storage time for all the cultivars, but to the greatest extent for Nadine and Huakaroro. Gels made from starches from the stored tubers had a reduced tendency towards retrogradation as evidenced by the decrease in syneresis (%) during gel storage at 4 °C.     

Parenchyma cell microstructure and textural characteristics of raw and cooked potatoes

Cooking, microstructural and textural characteristics from four New Zealand potato cultivars (Agria, Nadine, Moonlight, and Red Rascal) were studied. Potatoes from the waxy cultivar, Nadine, showed lowest dry matter and starch content and also had highest cooking time compared to the other cultivars. The total colour difference, ΔE, indicative of browning and darkening during storage (for 1 h) of the peeled potatoes was observed to be highest for Red Rascal, followed by Nadine and was lowest for Agria. Light (LM) and confocal scanning electron (CSLM) micrographs revealed Moonlight and Red Rascal raw potato parenchyma cellular structure to be well integrated, showing compact hexagonal cells. Raw tubers from these cultivars also exhibited higher hardness and cohesiveness, as observed using texture profile analysis (TPA). Moonlight potato parenchyma retained cell wall outline after cooking and its cells were observed to be completely filled with gelatinised starch matrix, whereas the cellular structure of Nadine potato parenchyma was completely disintegrated after cooking. TPA results of cooked potatoes agreed well with these microstructural observations, with Moonlight cooked potatoes showing highest cohesiveness and hardness. The cell wall of parenchyma cells was observed to degrade partially upon cooking of potatoes, resulting in loosening of the cell wall microfibrils, as observed using transmission electron microscopy (TEM) of a selected potato cultivar. Also, the cell wall decreased in thickness after cooking. The remains of the primary cell wall along with some electron dense granular structures were observed floating in the cytoplasmic starchy matrix in potato tuber parenchyma cells.     

Development and characterization of extruded snacks from New Zealand Taewa (Maori potato) flours

Crispy extruded snacks were prepared by mixing ungelatinized dried potato flours from four different Taewa cultivars and a modern potato cultivar with corn flour at two different ratios (25:75; 50:50), and their quality characteristics studied. All of the potato flours showed differences in colour, dry matter content, starch content and pasting characteristics. Among the extrudates prepared with 25% potato flours, Huakaroro snacks showed an L¹ value of 51.71, whereas pure corn flour snacks had the highest L¹ value of 61.22. The b¹ at both levels of potato flour incorporation were lowest for Tutaekuri snacks. The microstructural characteristics of the extrudates such as cell structure and cell wall thickness changed considerably when potato flour was incorporated (50%) in the extruder feed. Moemoe, Tutaekuri and 100% corn flour snacks had the highest toughness, whereas the highest crispness was observed for the Huakaroro snacks. Lower and higher cold peak viscosities of 91 and 597 cP were observed for corn and Tutaekuri extrudates (in powdered form), respectively. The extrudates with 50% potato flour had higher breakdown and lower final viscosity than those containing 25% flour. The peak G′ values were highest for 100% corn, Moemoe and Karuparera snack pastes.     

Textural and pasting properties of potatoes (Solanum tuberosum L.) as affected by storage temperature

Fresh tubers from five potato (Solanum tuberosum L.) cultivars were stored at different temperatures (4, 8, 12, 16 and 20 °C) and 80–90% relative humidity for 18 weeks after harvest to examine the effect of storage temperature on their textural and pasting properties. Texture profile analysis was performed on raw and cooked potatoes using an Instron universal testing machine to measure textural parameters such as fracturability, hardness, cohesiveness, adhesiveness and springiness. Both raw and cooked potato tubers showed a considerable reduction in all textural parameters upon storage, irrespective of the storage temperature employed. Raw potatoes showed a decrease in fracturability and hardness with increasing storage temperature, whereas their cooked counterparts showed the opposite trend. The extent of change in the textural properties of both raw and cooked potatoes also varied among the different cultivars. Fresh and stored tubers from all cultivars were freeze‐dried, ground into flours and analysed for amylose content and pasting properties. The amylose content of flours prepared from potatoes stored at 4 and 8 °C was observed to be considerably lower than that of flours prepared from potatoes stored at 16 and 20 °C. Pasting characteristics such as peak viscosity, setback and final viscosity increased with increasing storage temperature, while the reverse was observed for pasting temperature, when studied using a rapid visco analyser. Breakdown in viscosity of the flour pastes from all cultivars was considerably reduced during storage, irrespective of the storage temperature employed. Copyright © 2006 Society of Chemical Industry     

Physico‐chemical and sensory attributes in conjunction with multivariate analysis of two potato (Solanum tuberosum L.) cultivars after 90 days of storage: an exploratory authentication study

Two cultivars of potato (Spunta and Agria), were studied in terms of their physico‐chemical and sensory characteristics. These cultivars were cultivated in three geographical regions of Greece (Macedonia, North Greece; Thessaly, Central Greece; Peloponnese, South Greece) and were stored for 90 days after harvesting. The physico‐chemical characteristics of the tubers determined, were pH, total acidity, firmness, dry matter and content in Ν, in Κ, P, Cu, Mn, Zn and Fe. The sensory characteristics measured for raw tubers of potato after storage, were skin colour, skin brightness, internal colour, surface roughness, odour intensity, moistness, surface wrinkling and stains while the sensory characteristics measured for the boiled tubers of potato were odour intensity, moistness, special taste, sweet taste, aftertaste persistence, metal taste, pastiness, mastication, flavour intensity, elasticity and overall acceptability. The application of multivariate analysis (principal component analysis, cluster analysis and discriminant analysis), revealed a variety of relations between the various parameters and resulted in satisfactory grouping either per geographical region or per cultivar.     

Cultivar, Specific Gravity and Location in Tuber Affect Puncture Force of Raw Potatoes

Three potato cultivars were sorted into specific gravity groups. Slices of raw potato were subjected to a puncture test at six sites in the cortex tissue and eight sites in the pith tissue. The cortex tissue generally showed 25-65% higher puncture force than the pith tissue. With exception of pith tissue in Monona cultivar, puncture force increased with increasing specific gravity in cortex and pith for raw potato. Dry matter content increased with increasing specific gravity. The cortex tissue had 3-6% higher dry matter than pith tissue.     

Nutritional composition of UK retail potatoes,both raw and cooked

Over two seasons, four maincrop potato cultivars together with early varieties, were purchased from a range of retail outlets in three principal consumer areas (London, Birmingham and Glasgow). Samples were analysed for moisture, total nitrogen, non-protein nitrogen, fat, carbohydrates (sugars, starch and dietary fibre), vitamins and minerals. Analyses were carried out on both the raw and cooked (boiled, baked, roast and chipped) tubers every 12 weeks. Values for raw and cooked materials were compared with previously published figures, and cultivar, centre and seasonal effects were identified by analysis of variance. Nutrients found to be lower than the Food Composition Table data were riboflavin and niacin (50%), potassium (40%), iron, copper and zinc (20–30%); thiamin and total folate were 2–3 times higher, total ascorbate, initially similar, declined more rapidly after harvest. These differences were reflected in the values obtained for the cooked potato where the major difference was a reduction in the fat content of chips by about 40%. Cooking losses were similar to those in the Food Composition Tables. The main varietal effects were confined to the vitamins. Centre effects showed that potatoes from Glasgow had less ascorbate and dry matter but slightly more free sugars. The only significant seasonal effect was for total ascorbate where the second season was higher than the first.     

Morphological,thermal, rheological and noodle‐making properties of potato and corn starch

A comparison between the morphological, thermal, rheological and noodle‐making properties of corn starch and potato starches separated from five different potato cultivars was made. The granule size and shape of all starches differed significantly. Potato starch granules were comparatively larger than corn starch granules, while the transition temperatures were found to be higher for corn starch. Consistency coefficients and flow behaviour indices measured by back extrusion were higher for potato starches than for corn starch. Stickiness of cooked starch pastes was observed to depend upon their consistency coefficient. The gels made from all potato starches showed higher gel strength than those from corn starch. The gel strength of starches from both corn and potato increased during refrigerated storage. The amylose content, swelling power, solubility and light transmittance values of potato starches were significantly higher than those of corn starch. Noodles made from potato starches had higher cooked weight and cooking loss than corn starch noodles. Texture profile analysis revealed that potato starch noodles also had higher hardness and cohesiveness than corn starch noodles. Hardness of cooked noodles from all starches increased and cohesiveness decreased during storage. Noodles made from starches of higher viscosity exhibited higher hardness and cohesiveness. Textural differences among cooked starch noodles appeared to be associated with morphological, thermal and rheological properties of corn starch and potato starches. © 2002 Society of Chemical Industry     

In vitro digestibility of starch in cooked potatoes as affected by guar gum: Microstructural and rheological characteristics

Potatoes from different New Zealand cultivars (Nadine, Moonlight, Red Rascal, Agria) were analysed for starch digestibility in vitro (under simulated gastric and small intestinal conditions). The extent of starch hydrolysis (%) for all the potato cultivars ranged between 85% and 95% at the end of in vitro digestion. Nadine potatoes, which were waxy in texture, showed higher starch hydrolysis (%) whereas these levels did not differ significantly among the other three cultivars. Confocal laser scanning microscopy and scanning electron microscopy were performed on the digests in order to study the microstructural changes occurring during digestion in cooked potatoes. The micrographs clearly showed that starch was quickly hydrolysed by the enzymes present in simulated intestinal fluid (SIF) whereas the cell walls remained intact during simulated digestion process. Addition of guar gum (0.5%) to cooked potatoes reduced their starch hydrolysis (%) by ∼15% during the in vitro digestion. Online viscosity measurements were also performed on the cooked potatoes during simulated small intestinal digestion using a dynamic rheometer. Cooked potato viscosity dropped considerably upon the action of enzymes from SIF on starch as the digestion progressed. The presence of 0.5% guar gum facilitated the cooked potato matrix to maintain viscosity similar to undigested cooked potato sample throughout the in vitro digestion, which might have resulted in lower starch hydrolysis (%).     

A Method for Intercultivar Comparison of Potato Tuber Nutrient Content Using Specific Tissue Weight Proportions

ABSTRACT:  Potato tubers are a staple food item in the North American diet. Each potato cultivar has unique tuber appearance and nutritional composition. A method was developed to facilitate better cultivar selection for dietary purposes and obtain a better understanding of the nutrient distribution within specific tissues of potato tubers. This involved a procedure for estimating the percent weight contribution of the 3 major tissue components, including periderm or "skin," cortex, and pith for 20 potato cultivars. Weight determination was based on the volume (calculated through an ellipsoid formula) and density of each component tissue. Calculated percent weight and dry matter data for each tuber tissue provided conversion factor values that were tabulated for all cultivars. An example is provided to illustrate the application of this procedure in facilitating identification of cultivars with significantly greater or lesser protein content.     

Effect of physicochemical properties of starch on the tendency of potato tuber flesh to darkening and the processed product quality

The aim of the present research was to determine whether, and to what extent, the selected potato starch quality parameters affect the tendency of potato tuber flesh to darkening and the value of thermal processing products. The research was carried out after harvest and after 6 months of tuber storage at the temperature of +8°C and relative air humidity of 95%. The research material was made up of three mid‐early potato cultivars: two Polish cultivars, ‘Lena’ and ‘Mors’, and ‘Agria’, a German cultivar. The research was carried out in three vegetation periods in Poland (the Kujawy and Pomorze region) and in Germany (Lower Saxony). The starch grain size, gel stability after defrosting and raw and cooked tuber flesh tendencies to darkening were significantly modified by the genetic factor, while neither the site nor the year of cultivation affected these characters significantly. As a result of tuber storage, genetic conditions affected the share of large grains (>60 µm) more considerably than the storage conditions and time; unlike the starch gel stability, since a high variation in this character depended on the site of cultivation and place of storage. The potato tuber storage time increases the degree of darkening and the tendency leads to the French fries and chips quality deterioration. The results of the present research clearly show that the fraction of starch grains >60 µm was significantly positively correlated with raw and cooked tuber flesh darkening, whereas fraction <40 µm was significantly negatively correlated with these potato tuber characters.     

Influence of cooking and microwave heating on microstructure and mechanical properties of transgenic potatoes

The transgenic potato clones of cultivar Irga with improved resistance to a necrotic strain of potato virus Y (PVY(N)) were subjected to heat treatment in order to determine their technological quality. The technological quality was determined on the basis of differences between mechanical properties of unmodified potato and transgenic clones during cooking and microwave heating. The compression test was applied in order to evaluate the mechanical resistance of raw, cooked and microwave-treated potatoes. Compression resistance was expressed by fracture stress F (kPa), fracture strain D (mm/mm), and Young modulus E (kPa). The differences in microstructure of potato tubers (unmodified and modified) were investigated using scanning electron microscopy (SEM). The observed differentiation in the mechanical properties of heat-treated potatoes was less connected with genetic modification but most of all with a kind of the process used. The heat processes caused a distinct decrease in mechanical resistance in all the examined tubers. However, the process of microwave heating resulted in more significant changes in mechanical properties of tubers than cooking. Deformation of parenchyma cells during cooking was directly connected with starch, gelatinisation and gel formation. Microwave heating affected significantly cellular water evaporation which resulted in intercellular failure, collapsing of cells, and limitation of starch gelatinisation.     

Long-Term Storage Effects on the Physical Properties of the Potato

Determination of physical properties of agricultural products, such as the potato, and their variations during long-term storage, is an important feature in achieving high product quality and consumer acceptance. Physical properties of potatoes (Agria, Satina, and Caesar cultivars), including surface area, volume, moisture content, weight, and three main diameters of tuber, were measured and then other properties, such as sphericity, roundness, geometric mean diameter, volume mean diameter, aspect ratio, effective diameter, and real density during storage time, were calculated. The measurements were done every 15 days for a period of 22 weeks and analyzed based on a completely randomized block design in ten replications. Significant differences were observed among three potato cultivars according to major diameter, shape characteristics, mass, volume, and surface area of tubers. In this relation, Satina was larger in size compared to the two other cultivars. However, the Agria cultivar was closer to a sphere in shape. Also, it was found that the surface area of each potato could be estimated based on its mass and volume by a power law equation with a high coefficient of determination. According to the results, real density of tubers increased as a function of storage time based on a polynomial equation with R² = 0.99. During storage time, moisture content of tubers decreased according to a linear model and was probably the major rationale for decrease in tuber size. Density, size, and moisture content are the major physical characteristics of potato tubers, which change dramatically during long-term storage. Considerable differences in physical properties of different cultivars persuade researchers to carry out further studies on other popular potato cultivars.     

Biochemical and textural changes in trifoliate yam Dioscorea dumetorum tubers after harvest

Biochemical and textural changes were investigated in trifoliate yam Dioscorea dumetorum tubers, after harvest, in an attempt to study the chemical and physical changes associated with the raw and cooked tubers and how these relate to the hardening phenomenon of the tubers after harvest. A 2×2×3×4 factorial experiment, with cultivar, storage condition, treatment and storage time as their respective variables, was done. Samples were analysed for moisture, starch, reducing sugars, alcohol-soluble sugars, acid and neutral detergent fibre, cellulose, hemicellulose and lignin. The Warner–Bratzler test cell was used in a TA.XT2 Texture Analyser to measure the hardness of cooked tubers. The moisture and starch contents of the tubers decreased from 77.8 to 70.4% and 70.5 to 66.5 g/100g, respectively in a period of 72 h of storage, suggesting rapid dehydration after harvest and breakdown of starch. All the other chemical indices increased with storage time. These changes were influenced by the storage temperature and the treatment given to the tubers prior to storage. In general, samples stored at 4 °C showed smaller changes in the chemical indices than those at 28 °C, suggesting a temperature-dependence of the changes. Both cultivars of yam showed increase in hardness with storage time. A high correlation (r=0.9503–0.9913) was noted between the texture and the chemical indices of the white cultivars. Storage of the trifoliate yam, Dioscorea dumetorum, immediately after harvest, leads to reduction in moisture and starch contents and increase in sugars and structural polysaccharides. Low temperature storage may reduce the hardening phenomenon. A mechanism for the hardening phenomenon has been proposed.     

Carbohydrate content of potato (Solanum tuberosum L.) tubers treated with Isopropyl-N (3-chlorophenyl) carbamate under different storage conditions

Post harvest application of Isopropyl-N (3-chlorophenyl) carbamate considerably reduced the degradation of starch when potato tubers were stored in an evaporative cooling chamber. The starch degraded at a faster rate when tubers were kept under refrigerated and room storage conditions.     

Quality of Reduced-Fat Frankfurter Modified by Konjac–Starch Mixed Gels

ABSTRACT:  Konjac–potato starch mixed gels were incorporated into reduced-fat (18%) frankfurters and compared with reduced-fat (18% fat, C18) and high-fat (28% fat, C28) controls for textural, sensory properties, and storage stability. At the same konjac concentration, increasing starch level resulted in lower G' (storage modulus) and G" (loss modulus) of the konjac–potato starch mixtures leading to more elastic-mixed gels. No differences in textural hardness among gel-added treatments were noticed. C28 had the lowest sensory firmness and highest juiciness scores. C18 and gel-added treatments had similar juiciness and firmness scores, and all treatments did not differ in overall acceptability.     

Physicochemical properties of dry matter and starch from potatoes grown in Canada

In this study dry matter and starch were isolated from three potato cultivars (AC Stempede Russet, Russet Burbank and Karnico) grown at two locations (Fredericton and Benton) in New Brunswick, Canada. The chemical composition including total starch, dietary fibre, free glucose and protein content in potato dry matter and apparent amylose and total phosphorus content in potato starch were determined. Differential scanning calorimetry (DSC) was used to determine the thermal properties of gelatinization and retrogradation of potato dry matter and starch. The pasting properties of potato dry matter and starch were investigated by rapid visco analyzer (RVA). The resistant starch measurement method was employed to evaluate the digestibility in vitro of native and gelatinized potato starch. Molecular characteristics including chain length and chain length distribution of potato starch were also analyzed using high performance anion exchange chromatography (HPAEC). The analytical results suggest that differences in chemical composition and molecular chain length of potato starch may contribute to different functional properties of potato dry matter and starch of individual cultivars.     

VISCOELASTIC BEHAVIOUR DURING THE GELATINIZATION OF STARCH I. COMPARISON OF WHEAT, MAIZE, POTATO and WAXY-BARLEY STARCHES

Dynamic measurements were used to characterize the viscoelastic behavior during gelatinization of wheat, maize, potato and waxy-barley starches. During the experimental conditions used the curves of storage modulus (G') and loss modulus (G") versus temperature showed an initial peak for all starches, followed by a second peak at 90–95° C in the case of wheat and maize starches. Wheat starch gave a more viscous response than the other starches. The changes in G' and G" were correlated to the changes in gel volume and amylose leaching during the heating. The results were interpreted using a composite material as a model for the starch gel.     

Cassava varietal screening for cooking quality: Relationship between dry matter,starch content,mealiness and certain microscopic observations of the raw and cooked tuber

Thirteen cassava (Manihot esculenta L Crantz) varieties from three successive annual harvests were screened for the mealiness of the cooked tuber, and the elasticity and smoothness of the pounded paste. Six were selected for further studies based on their mealiness and the starch and dry matter contents were determined. The diameter of the starch granules of the selected varieties and those of an irradiated M₁ V₂ population were measured. Microscopic examinations of the raw and cooked cells of the irradiated M₁ V₂ population were made. Correlations among all the parameters were studied. Varietal and seasonal differences in cooking quality were observed. There was no consistent relationship between mealiness of the boiled tuber and the elasticity and smoothness of the pounded paste. Varieties that were mealy were high in dry matter and starch content. The starch granules of mealy varieties were larger than those of nonmealy ones. There were no differences between mealy and non-mealy varieties in the arrangement of the cells or ‘cell condition’, of the raw tubers. However, the cells of the cooked tubers were held less cohesively, ie there was more ‘cell disorganisation’, in mealy varieties than in non-mealy ones.     

不同类型甘薯品种主要经济性状和营养成分差异

对20个主栽甘薯品种的经济性状和营养成分含量分析,表明不同类型间的差异很大,同一类型不同品种间差异达到显著或极显著水平。粗淀粉含量和鲜薯产量呈极显著正相关(ρ=0.967),粗蛋白与粗纤维含量呈极显著正相关(ρ=1.000);粗蛋白含量与鲜薯产量、薯干产量、粗淀粉含量均呈负相关。粗纤维的检测结果,基本符合专业技术人员肉眼判断结果。系统聚类分析结果与甘薯专业委员会的分类结果有差异,但甘薯品种经济性状突出,营养成分基本均衡,遗传距离远的品种基本自成一类。徐薯18和南薯88这两个品种各方面经济性状突出,遗传配合力高,仍然可以作为当前北方薯区甘薯育种的骨干亲本。