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     

Textural and Rheological Properties of Cooked Potatoes

Cooked potato samples of different cultivars and specific gravities were analyzed for textural and rheological properties by sensory evaluation, texture profile analysis (TPA) and stress relaxation tests. Mealiness was correlated with the product of cohesiveness and adhesiveness, but not with other TPA parameters. Stress relaxation tests of cooked potatoes yielded a Maxwell model consisting of two viscous and three elastic elements. One of the elastic moduli was correlated with mealiness. Hardness by sensory evaluation correlated well with hardness and fracturability by TPA, and with the three elastic moduli in the relaxation model.     

Factors Related to Potato Mealiness

Four potato cultivars from 1984 and 1985 growing seasons were studied. Specific gravity did not correlate with potato size or shear strength, nor could it be used to predict sensory mealiness scores. Shear strength measures of the cooked potatoes showed that the Russet Burbank had a particularly strong structure at low deformations. Starches from the two more mealy cultivars, Russet Burbank and Norchip, had slightly lower gelatinization temperatures than those from the two waxy cultivars, Pontiac and LaSoda. Gelatinization temperatures were higher in potato juices than in water. Starches from the two mealy cultivars gave swelling powers between those of the two waxy cultivars, but yielded higher solubles. Pontiac potato starch exhibited anomalous behavior in its resistance to swelling and in development of viscosity in the amylograph.     

Physicochemical and sensory properties of fresh potato-based pasta (gnocchi)

This study dealt with the characterization and quality assessment of 3 kinds of potato-based pasta (gnocchi) made with steam-cooked, potato puree (water added to potato flakes), and reconstituted potatoes as main ingredients. The aim of the research was to evaluate the quality of the products in terms of physicochemical, textural, and sensory characteristics. Water content, water activity, color (L* and h°), and texture (texture profile analysis [TPA] and shearing test) were evaluated on both raw and cooked samples. In addition, on the recovered cooking water the loss of solid substances was determined and on the cooked gnocchi a sensory assessment was performed. Eight sensory attributes (yellowness, hardness, gumminess, adhesiveness, potato taste, sweet taste, flour taste, and sapidity) were investigated. Statistically significant differences among products were obtained, especially concerning textural properties. In fact, sample made with reconstituted potatoes and emulsifiers resulted the hardest (8.53 ± 1.22 N), the gummiest (2.90 ± 0.05 N), and the "chewiest" (2.90 ± 0.58 N) after cooking. Gnocchi made with potato puree or reconstituted potatoes significantly differed from the one produced with steam-cooked potatoes in terms of sensory properties (yellowness, hardness, flour taste, and sapidity). Pearson's correlation analysis between some textural instrumental and sensory parameters showed significant correlation coefficients (0.532 < r < 0.810). Score plot of principal component analysis (PCA) confirmed obtained results from physicochemical and sensory analyses, in terms of high discriminant capacity of colorimetric and textural characteristics.     

Physical properties of acetylated and enzyme-modified potato and sweet potato flours

ABSTRACT:  Textural profile, pasting behavior, gelatinization characteristics, sedimentation volume, and gel consistency of acetylated (Ac) and enzyme (glucoamylase)-modified (EM) potato and sweet potato flours have been investigated to determine their suitability in products such as baked goods, soup, and pudding. Dough hardness of Ac and EM samples was significantly higher than their native samples ( P < 0.01). Dough cohesiveness of modified potato did not change, while it decreased in modified sweet potato. With increase in moisture, textural properties of modified samples, in general, showed reduced values. Rapid Visco Analyser showed least pasting viscosities of Ac flours due to restricted swelling of starch granules while EM flours exhibited high viscosities. Acetylated samples showed reduced gelatinization temperature (GT), and enthalpy (ΔH) compared to native samples, whereas enzyme-treated samples showed no significant changes in GT, indicating their comparable crystallinity values with those of native samples. Modified flour samples had lower sediment volumes and gel consistency, and the gel consistency of EM flour correlated with its cold paste viscosity.     

Original article: Influence of flour mill streams on cake quality

Wheat‐milling process generates different flour streams that differ in particle size, composition and functional and cake‐making properties. Particle size, composition and pasting properties of flour fractions (two from break and three from reduction system) obtained during milling of three wheats varying in protein content were determined. Shape, textural, colour and sensory analyses were performed on cakes prepared with the different mill streams. The final break and reduction streams had the highest protein and ash contents, pasting temperatures and the lowest starch percentage. Cakes prepared with the last streams showed higher batter density and lower volume. These results could indicate good air incorporation but deficient air distribution. Last streams cakes showed a darker, more reddish and yellowish crumb that was significantly related to flour colour characteristics. Because of these differences, such cakes obtained the lowest sensory scores. In this study, it has been verified that, to adapt flours to cake preparation, the final streams should be eliminated. The particle size of each stream is the most determinant parameter to obtain cakes with better volume and texture, being the flours with small particle size the most adequate.     

Effect of Potato Starch Properties on Instant Noodle Quality in Wheat Flour and Potato Starch Blends

The properties of potato starch and their effect on the quality of Chinese‐style alkaline instant noodles made from wheat flour and potato starch blends were investigated. Starches were extracted from nine potato cultivars, and the phosphorus content of these starches was analyzed together with the median granule size and pasting and gelatinization properties. Instant noodles were manufactured using mixtures of wheat flour and these potato starches. A Rheoner instrument was used to evaluate three textural parameters, namely, the breaking force (BF), breaking energy (BE), and ratio of the breaking force to the breaking deformation (BF/BD), of instant noodles cooked by immersing into boiling water for 3 and 7 min. The phosphorus content, peak viscosity, and breakdown were significantly and positively correlated with the BF of the noodles cooked for 3 min and did not significantly correlate with that of those cooked for 7 min. Other quality parameters of potato starch did not affect the BF significantly. Other textural parameters of instant noodle quality, such as the BE and BF/BD, did not significantly correlate with any of the quality parameters of potato starch. The findings obtained with the use of wheat flour and potato starch blends suggest that phosphate, which is thought to enhance starch viscosity of potato starch, is important for making instant noodles with favorable texture in hardness.     

Physicochemical Properties of Starch and Flour from Different Rice Cultivars

The starches and flours from four different rice cultivars were evaluated for composition, crystallinity characteristics, blue value, turbidity, swelling power, solubility, pasting properties, and textural and retrogradation properties. The amylose content of starches and flours from different rice cultivars differed significantly. The results showed that the physicochemical properties of rice starch and rice flour were correlated to amylose content. The crystallinity degree of rice starch and flour depended on amylose content. The blue value, turbidity value, and gel hardness were positively correlated to amylose content; however, the swelling power, solubility, and gel adhesiveness were negatively correlated to amylose content. Furthermore, the pasting properties and gel textural and retrogradation properties of rice flours were related to the structure properties of rice starch. And the characteristics of starch, protein, and lipid significantly influenced the turbidity, pasting properties, and gel textural and retrogradation properties of rice flours.     

Physicochemical Properties of Sweet Potato Flour and Starch as Affected by Blanching and Processing

The effects of blanching on physicochemical properties of flours and starches prepared from two varieties of sweet potatoes (Mun‐Kai and Negro) were studied and compared. The pasting temperature and peak viscosity of starches, respectively, were 74 and 80 °C and 381 and 433 RVU. The pasting temperature (74.0‐94.8 °C) of flours was greater than that of starch, depending on the variety and blanching process. However, the peak viscosity (ca. 103‐120 RVU) of flours was lower than that of the corresponding starches. Partial gelatinization of starch granules was observed as a result of a 1‐min blanching. Composition of starch and flour was found to affect swelling power and solubility. The starch content of starches, flours from unblanched sweet potato and flours from 1‐min blanched sweet potatoes were 97; 66.3 and 74.9; as well as 36.6 and 40.4%, respectively. Amylose content of flours and starches varied from 17.2‐20.8%.     

Studies on noodle quality of potato and rice starches and their blends in relation to their physicochemical, pasting and gel textural properties

The physicochemical, pasting, and gel textural properties of potato and rice starches and their blends were studied in relation to their noodle making performance. Amylose content, swelling power and solubility values of potato starch were significantly (P ≤ 0.05) higher than for rice starch. Pasting properties showed higher peak, final and setback viscosity for potato starch as compared to rice starch. Texture profile analysis revealed that potato starch gel had higher hardness, cohesiveness and chewiness as compared to rice starch gel. Potato starch noodles showed higher cooked weight and cooking loss and were scored higher by sensory panellists especially with respect to transparency and slipperiness. On the other hand, rice starch noodles were more firm with lower cooking loss. Addition of potato starch to rice starch significantly (P ≤ 0.05) affected the noodle characteristics. Among the starch blends studied, blending of potato and rice starch in the ratio of 1:1 resulted in good quality noodles in terms of their lower cooking time, higher cooked weight, transparency and slipperiness. The results revealed the possibility of blending of potato starch with rice starch in equal proportions to produce noodles of acceptable quality.     

Textural and Gelatinization Characteristics of White,Cream, and Orange Fleshed Sweet Potato Tubers (Ipomoea Batatas L.)

Sweet potato is an important food crop having nutritive value in terms of starch, carotein, and minerals. The acceptability and overall quality of the products depend on their textural and rheological attributes. Cooking quality of the tubers could be related to the textural, pasting, and gelatinization properties, which vary depending on the flesh color of the tubers. Also, being a promising ingredient in many of the traditional and industrial products, the physico-chemical and functional properties of sweet potato flour are very much important for their selection for developing various value added products. The textural, gelatinization, and pasting characteristics of white, cream, and orange fleshed sweet potato tubers were analyzed and their thermal softening behavior was modeled by linear regression and fractional conversion techniques. Significant variations were observed in the properties among different varieties (p < 0.05). Kinetics of texture degradation on cooking were explained by first-order and dual-mechanism first-order models and the latter was found to be more suitable. The first three principal components explained about 85% of the total variation in texture profile parameters, gelatinization, and pasting properties. Though there was no similarity in the textural properties of the raw tubers among the varieties of same flesh color group, the quality of the cooked tubers and flours of different varieties in the same group are similar as revealed by the multivariate analysis.     

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.     

Suitability of TEMPO-oxidized oat β-glucan for noodle preparation

Native oat β-glucan (N-BG) and the oxidized derivative β-glucan (Oxi-BG) were incorporated into noodles and preparation characteristics (pasting, cooking, and textural properties) were investigated. N-BG caused an increase in the pasting parameters of wheat flour, and values were increased by Oxi-BG. Noodles containing either N-BG or Oxi-BG had higher cooked weights, cooked volumes, and water absorption values than controls. Raw noodles containing either N-BG or Oxi-BG showed high L values. Cooked noodles lacking BG exhibited higher L values. N-BG-containing noodles had textural properties similar to controls. Noodles prepared with Oxi-BG had higher textural parameter values than N-BG noodles, except for hardness.     

不同加工方式对马铃薯原粉特性的影响

以新鲜马铃薯为原料,制备得到马铃薯熟粉、冷冻干燥马铃薯原粉、未经烫漂的热风干燥马铃薯原粉及经烫漂的热风干燥马铃薯原粉,研究不同类别的马铃薯原粉在外观品质、理化特性、功能特性及复水特性等方面的性质。结果表明,不同加工方式下马铃薯原粉的基本理化性质及外观品质均存在显著差异,其中经烫漂的热风干燥马铃薯原粉色泽(L^*值为80.78)最佳,为淡黄色粉末,具有高淀粉、高纤维及低脂肪的特点,有利于用作减肥及降血脂健康食品的原料;功能特性结果表明,马铃薯熟粉具有较高的持水能力(3.03±0.01 g/g)、乳化性(21.58%±1.37%)及乳化稳定性(15.98%±0.73%);冷冻干燥马铃薯原粉具有较高的持油能力(3.42±0.08 g/g)和溶解性(16.49%±1.07%);经烫漂的热风干燥马铃薯原粉具有较高的乳化稳定性(16.67%±0.76%)、复水性(复水比为6.43)和复水稳定性(95.76%±0.85%)。同时,结合考察不同加工方式下马铃薯原粉的加工效率与能耗,结果发现,经烫漂的热风干燥原粉具有较高的加工品质且加工能耗低,可作为熟粉的替代品。本研究可为马铃薯不同产品特点选择合适的加工方式,并为马铃薯原粉的研制及代替熟粉的可行性奠定基础。     

Physico‐chemical characteristics of non‐irradiated and γ‐irradiated yams cultivars (Dioscorea rotundata,Dioscorea alata) and sweet potato (Ipomoea batatas (L) Lam)

Physico‐chemical (pasting) properties of non‐irradiated (fresh) and γ‐irradiated yam cultivars and sweet potato were determined using Rapid Visco Analyser (RVA). Generally, pasting characteristics of the commodities decreased significantly with increased γ‐irradiation dose. Non‐irradiated sweet potato showed significantly higher peak (45.79), trough (35.25), breakdown (10.54), final (75.21) and setback (39.96) viscosities (in RVU) than γ‐irradiated samples. Also, peak time (6.97 min) and pasting temperature (50.18 RVU) significantly reduced with increased γ‐irradiation dose of tubers. The pasting properties of non‐irradiated and γ‐irradiated sweet potato showed similar but clearer trend compared with yam flours. Also, non‐irradiated and γ‐irradiated Dioscorea rotundata and Dioscorea alata showed significantly higher values of each of the pasting characteristics than values noted in sweet potato. Aside from the TDr 03/00196, peak time did not vary significantly with γ‐irradiation dose.     

Effects of wheat flour supplemented with soy protein concentrate on the rheology,microstructure and water mobility of protein-fortified precooked noodles

Wheat flour was supplemented with different levels of soy protein concentrate (SPC) and applied to precooked noodles for protein fortification whose quality attributes were characterised in terms of rheology, microstructure and water mobility. The wheat flours with high levels of SPC showed lower enthalpy values and higher temperatures derived from starch gelatinisation. They also exhibited lower values of the pasting viscosity and dynamic viscoelastic parameters. The mixolab measurements demonstrated that the supplement with SPC was effective in raising the water absorption and dough stability of wheat flour. In addition, the use of SPC-supplemented wheat flours produced precooked noodles with tight and dense structures, which were confirmed by scanning electron microscopic analysis. These microstructural changes were consequently related to higher maximum resistance to extension and lower extensibility of the noodles. However, the SPC-supplemented wheat flours did not significantly affect the cooking loss of the noodles. Furthermore, three water components with different mobility were observed in the precooked noodles whose spin-spin relaxation times were distinctly reduced with increasing levels of SPC. Overall similarities in the sensory noodle attributes were detected as wheat flour was supplemented with SPC at a level of 8% (w/w).     

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.     

Comparative studies of some properties of undehulled, mechanically dehulled and manually dehulled cowpea (Vigna unguiculata Walp. L.) flours

A comparative evaluation was made of some physico‐chemical and rheological characteristics of undehulled, manually dehulled and mechanically dehulled cowpea (Vigna unguiculata Walp. L.) flours from brown and white varieties of the legume. The flours were used to prepare steamed bean paste, ‘Moinmoin’, which was analysed for some sensory parameters. Dehulling and dehulling methods had no appreciable influence on the physical characteristics and proximate composition of the flours, except ash content, which was slightly higher in undehulled flour samples. Amylograph pasting characteristics of the flours showed varying trends because of dehulling method and/or presence of seed coats. ‘Moinmoin’ samples prepared from the flours received similar ratings for all sensory attributes, with no significant differences (P < 0.01 and P < 0.05), except for the low‐rated (poorer) colour of the undehulled brown product.     

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

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

PRACTICAL APPLICATIONS

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