Microstructural,cooking and textural characteristics of potato (Solanum tuberosum L) tubers in relation to physicochemical and functional properties of their flours

Potato tubers from six different cultivars were freeze‐dried, ground into flour and analyzed for thermal, pasting and textural characteristics (using differential scanning calorimetry, Rapid Visco analyzer and Instron universal testing machine, respectively) to study the relationship between flour characteristics and cooked potato mealiness. The potatoes with higher sensory mealiness scores resulted in flours having lower transition and pasting temperatures, higher amylose content, setback, peak and final viscosity. The flour gels from the mealier potatoes also exhibited higher values of textural parameters such as hardness, cohesiveness, chewiness and springiness. The microstructure of the tuber parenchyma (studied using scanning electron microscopy), cooking and sensory characteristics of potatoes were found to be related to the pasting and textural characteristics of their flours. Potato cultivars with lower mealiness scores, loosely packed cell arrangement, with comparatively large‐size cells and thinner cell walls showed lower values of textural parameters for both raw and cooked potatoes. This information may prove useful for the selection of potato cultivars with desirable textural and flour‐making properties for specific end‐uses. Copyright © 2005 Society of Chemical Industry     

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.     

Study on the water state,mobility and textural property of Chinese noodles during boiling

The water mobility, state and textural properties of Chinese fresh noodles (CFNs) and Chinese dried noodles (CDNs) made from same wheat cultivar were measured during boiling using low-field nuclear magnetic resonance (LF-NMR), low-field nuclear magnetic Imaging (LF-NMI) and a textural analyser. ‘The oil immersion method’ was applied to gain the clear images from LF-NMI measurement. The distributions of the three water states (T₂₁, T₂₂ and T₂₃) in the noodles were distinguished. The results indicated that water mobility in noodles was closely related to the gelatinisation of noodle starch. Compared with CFNs, CDNs need a longer cooking time for water mobility and starch gelatinisation. The results of the cooked noodle profiles showed that the cooked CDNs (8 min) had an undesirable textural properties compared with the cooked CFNs (2 min). The longer cooking time of CDNs is responsible for its undesirable texture since the textural properties change during the longer cooking time.     

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.     

Effects of Different Drying Conditions on Water Absorption and Gelatinization Properties of Pasta

Three flat pasta types dried by low temperature (LT), high temperature (HT), and very high temperature (VHT) drying profiles were analyzed. The starch properties of these pastas, cooked at different temperatures for different times, were investigated. The starch properties were examined by observing starch swelling with a scanning electron microscope (SEM), identifying the phase difference with an ultrasonic device, and determining the water absorption and gelatinization rate with the BAP method and X-ray diffraction. The SEM images revealed expanded and gelatinized starch granules during cooking pasta and increased with drying temperature. The water absorption of pasta increased with cooking temperatures and times, and the trend was LT > HT > VHT-dried pasta. The gelatinization rate of pasta increased with cooking time and temperature. The X-ray diffractograms of pasta cooked less than 12 min showed typical A-type X-ray diffraction patterns, while in pasta cooked for 12 min, V-type diffraction was observed. Uncooked pasta showed an enhanced peak at about 2θ?=?20°, which indicated the generation of high levels of amylose–lipid complexes. The present study found that these changes occurred during drying and may affect pasta starch characteristics.     

Composition, soaking, cooking properties and thermal characteristics of starch of chickpeas, wrinkled peas and smooth peas

We investigated both the distribution of protein, ash and starch in legume (chickpeas, smooth and wrinkled peas) cotyledons, and the soaking and cooking characteristics, including gelatinization and retrogradation, of the starch. There were large differences in composition between different types of legumes and also between the outer and inner parts of legume cotyledons. Wrinkled peas exhibited much higher water absorption during prolonged soaking and there were higher hardness value determined for cooked seeds compared with chickpeas and smooth peas. While the hardness of cooked seeds decreased continuously as cooking time increased to 110 min, all legume starch was fully gelatinized after cooking for 70 min.     

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.     

Gelatinization of Sweet Potato,Tania and Yam Tuber Starches

Morphological changes that occur in starch granules of sweet potato, tania and yam tubers from native to cooked states, were studied both by electron microscopy and differential scanning calorimetry. In the first stages of heating, the same event was observed in all samples: a central cavity appeared at hilum level of the starch granules just before granule expansion started. Differences in gelatinization behaviour between these three starches were enhanced by mechanism by which amylose leached out. In the sweet potato starch granules, amylose was released through micropores formed in the starch granules during the phase of expansion whereas in tania starch granules, both micropores and pin-holes were observed. In yam starch granules, amylose escaped only by pin-holes formed across the starch granules. When cooking was achieved, spongy-like structures were observed in cooked sweet potato parenchyma cells while folded gelatinized granules remained in yam. In cooked tania tuber, both types of cell contents were observed. Sweet potato, tania and yam starches presented DSC endotherms at 72.7, 69.9 and 74.4°C with enthalpy change of 13.6, 12.9 and 20.9J/g, respectively.     

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     

Involvement of Polyphenols in the After-Cooking Darkening of Gamma Irradiated Potatoes

Peeling of potatoes prior to boiling reduces the intensity of gamma irradiation induced after-cooking darkening of the tuber flesh. Polyphenols in the flesh of cooked whole tubers, pre-peeled tubers and in the cooking water were determined to examine its role in the darkening. Pre-peeling results in increased leaching of polyphenols from the flesh into the cooking water thus reducing the amount available for the formation of iron-phenolics complex responsible for darkening. The results indicate a strong correlation between low polyphenol levels and the reduction in after-cooking darkening of pre-peeled potatoes.     

Structuring and texturing gluten-free pasta: egg albumen or whey proteins?

The effects of adding egg albumen or whey proteins to pasta made from parboiled rice flour (PR) were investigated. Pasta quality was evaluated in terms of color, furosine content, and cooking properties (water absorption, cooking loss, and consistency at the optimal cooking time). The surface heterogeneity of the cooked and uncooked materials was studied, and some starch properties (pasting properties and starch susceptibility to α-amylase hydrolysis) were assessed, along with the features of the protein network as determined by conditional solubility studies and with ultrastructural features of the cooked products. Egg albumen improved pasta appearance and gave a product with low cooking loss, firmer, and nutritionally more valuable than the other ones. In albumen-enriched pasta, small starch granules appear homogeneously surrounded by a protein network. In the uncooked product, the protein network is stabilized mostly by hydrophobic interactions, but additional disulfide interprotein bonds form upon cooking. Thus, addition of 15 % liquid albumen to PR results in significant improvement of the textural and structural features of rice-based gluten-free pasta.     

Optimization of low-temperature blanching for retention of potato firmness: Effect of previous storage time on compression properties

Low-temperature blanching (LTB) of potatoes (cv. Kennebec), both without further processing and prior to cooking or freezing + cooking, significantly increased firmness retention as measured from compression parameters. The increase in firmness with respect to that of unblanched potatoes diminished in the order: blanched at 60 °C for 60 min and cooked > blanched at 60 °C for 60 min frozen and cooked > blanched at 60 °C for 60 min. Potato tubers were kept in refrigerated storage, and firmness, PME activity and dry matter (DM) content were periodically sampled over a period of 80 days. In the early stages of storage, PME activity lost 40% of its original value after 60 min at 60 °C, indicating that the contribution of starch breakdown products to the firmness of cooked and frozen cooked potatoes predominated over the effect of enzyme activity. With increasing time in storage, PME activity measured in the fresh tissue increased by 95% of its original value after 35 days; this resulted in changes in the pectic polymers which made for a firmer texture and different PME behaviour versus LTB temperature and time. A central composite rotatable design was used to study the effects of variation in levels of temperature (52.93–67.07 °C) and time (31.72–88.28 min) on compression parameters and PME activity. Stationary points showing maximum mechanical resistance had critical temperatures and times in the ranges of temperature (58–60 °C) and time (66–75 min) used for each independent variable. Results show a high correlation between PME activity and tissue firmness, suggesting that the contribution of the changes in the composition of the cell wall to the firmness of frozen cooked potatoes increased with increasing time in storage and reached a maximum in the intermediate stages of storage (35 days). Engineering stress (_u) proved to be the most appropriate compression parameter for detecting the firming effect that the PME activity produced on the frozen-cooked potato tissues as a consequence of LTB under these conditions.     

THE THERMAL PROPERTIES OF POTATOES AND CARROTS AS AFFECTED BY THERMAL PROCESSING1

The effects of processing on the thermal properties of white potatoes and carrots were studied. The test samples were blanched, boiled, cooked and canned. Whole potato tubers were baked to study the effects of starch gelatinization. The thermal conductivity (k) and density (ρ) were measured and the specific heat (c_p) and thermal diffusivity (α) were calculated. Results showed that in general, α initially decreased and then increased during processing. Test samples were found to have a gain in α when their moisture content increased by more than 9%. The α of potatoes decreased after canning and increased after boiling. In carrots, a similar trend was also observed but to a lesser degree. The k of potatoes was unaffected after blanching or cooking. In all the processing baking study showed that gelatinization significantly decreased the k of potatoes.     

Effect of cooking time on the quality, minerals and vitamins of spaghetti produced from two Italian durum wheat varieties

Spaghetti was made from two Italian durum wheat varieties and cooked for 10, 15 and 20 min. Percentages of water absorption and cooking loss were determined. Measurable amounts of soluble nitrogen, starch, minerals and vitamins were found in the water used for cooking.
Minerals and vitamins were determined in cooked spaghetti. The percentage reduction of metals increased with increasing cooking time, but trace elements decreased after 10 min of cooking and then became stable at the longer times. It is preferable to cook spaghetti for 15 min.     

Changes occurring in potatoes during cooking and reheating as affected by salting and cool or frozen storage – a LF-NMR study

Low field nuclear magnetic resonance (LF-NMR) was measured continuously during cooking of salted and unsalted potatoes to investigate the effect of salt on the cooking process. The cooked potatoes were subjected to cool storage (1, 2, 24 and 48 h) or frozen storage (1, 3, 5 or 14 days). Upon storage they were reheated in the LF-NMR instrument to investigate the effect of different storage regimes and salt on the state of water in potatoes during a continuous reheating process. In salted potatoes, a broader distribution of T₂ times leaning towards longer relaxation times were observed for extra-cellular/cytoplasmic water at low temperatures during cooking. This could indicate that the extra-cellular space is increased due to salting. In samples subjected to cool and frozen storage an additional free water component was found, which reflects that syneresis occurs as a result of retrogradation. In the frozen samples, the T_2,1 and T_2,2 water populations merge, illustrating an increased cell wall permeability or freeze damage of the cell walls. This is more evident in the unsalted samples showing that the cell walls are stabilized by salt during freezing. In conclusion, the results showed that LF-NMR could monitor the changes during starch gelatinization, starch retrogradation and melting of retrograded starch in salted and non-salted potatoes.     

基于高温流化技术改良红小豆的蒸煮品质

以红小豆为原料,采用高温流化技术（流化温度215 ℃、流化处理时间55 s、进料速率62 kg/h）对其进行处理,通过分析红小豆籽粒结构、淀粉结构、糊化特性以及水分吸收、迁移和分布情况,探究高温流化技术改良红小豆蒸煮品质的机理。结果表明,红小豆经过高温流化处理后,籽粒致密结构变得疏松、子叶相邻细胞间毛细孔直径增大、部分淀粉颗粒结构破损。在98 ℃近沸水中蒸煮时,原料红小豆蒸煮60 min时的糊化度与高温流化红小豆蒸煮30 min时的糊化度相当;经过高温流化处理之后,红小豆的糊化黏度更低,回生趋势更小;蒸煮60 min时,高温流化红小豆吸水率为90.06%,比原料红小豆提高34.84%,吸水性能明显改善;高温流化红小豆颗粒内部的水分迁移速率明显加快且分布更均匀;高温流化红小豆煮饭的感官评分更高。综上,高温流化改良红小豆蒸煮品质的途径主要是通过拓宽籽粒水分进入的通道、破坏吸水屏障来提高吸水性能,从而使淀粉吸水更充分、糊化更彻底,同时也改善了其煮饭的口感风味。     

KINETICS of QUALITY CHANGE DURING COOKING and FRYING of POTATOES: PART I. TEXTURE

Kinetics of texture change during cooking and frying of potatoes were evaluated in this study. Potatoes were cut into cylinders (diameter × height: 20 mm × 20 mm for cooking, and 10 mm × 20 mm for frying) and cooked in a temperature controlled water bath at 80–100C or fried in a commercial fryer at 160–190C for selected times. the cooked samples were water cooled while the fried samples were air cooled immediately after the treatment. Test samples were then subjected to a single cycle compression test in a computer interfaced Universal Testing Machine and three textural properties (hardness, stiffness and firmness) were derived from the resulting force‐deformation curves. Texture parameters of cooked potatoes decreased with progress of cooking time and the rate of texture changes associated with each temperature was found to be consistent with two pseudo first‐order kinetic mechanisms, one more rapid than the other. Textural values of fried potatoes were found to increase with frying time and also followed a first order kinetic model. Temperature sensitivity of rate constants was adequately described by Arrhenius and z‐value models.     

Transfer of heat and moisture during microwave baking of potatoes

Microwave baking of potatoes comprised two phases. In the first phase the internal temperature of the potatoes rose to approximately 100 °C with little loss of water vapour. The uniformity of internal heating during this phase was assessed by identifying gelatinised starch. Starch gelatinisation began near the outer surface after 1.5 min of cooking and was complete by 2.5 min. During the second cooking phase the thermal energy absorbed was used to evaporate water. When immersion in boiling water was substituted for this second phase of microwave cooking, it took significantly longer for the internal texture to soften adequately for the potatoes to be considered cooked. This suggests that microwave cooking influences texture independently of the thermal profile of the cooking process. Damage by escaping steam is suggested as a mechanism. © 2002 Society of Chemical Industry     

Effect of processing on potato starch: in vitro availability and glycaemic index

The content of digestible starch (DS) and resistant starch (RS) in processed potatoes was assessed. In addition, the effect of domestic cooking on the in vitro digestibility of starch in this tuber, which may influence the glycaemic response, was studied. Resistant starch in raw potato is high, however different RS values were obtained when processed, ranging from 1.18% in boiled potatoes to 10.38% in retrograded flour. In general, cooked potatoes have high levels of DS. Starch digestibility is improved after processing and it is affected by the cooking methods. Boiled and mashed potatoes showed the highest rate of digestion, on the contrary raw potato was hardly digested. The estimated Glycaemic Index (GI) from the degree of starch hydrolysis within 90 min was in accordance with the reported GI values, for potatoes processed in the same way.     

RHEOLOGICAL AND CALORIMETRIC INVESTIGATIONS OF STARCH-FISH PROTEIN SYSTEMS DURING THERMAL PROCESSING2,,3

During the thermal processing of starch-surimi systems, significant rheological changes due to the sol-gel transformation of fish proteins and the gelatinization of starch were observed by rigidity scanning. Differential scanning calorimetry (DSC), produced results which corresponded well with rheological changes. Starch gelatinization in cooked fish-starch gels was studied by DSC. The effects of starches on the textural properties of cooked gels were dependent on their gelatinization characteristics, such as gelatinization temperature, degree of swelling and water uptake of the granules. Gels producing higher failure stress values were obtained after starch gelatinized; however, no significant effect on failure strain was observed by the addition of starch. Pregelatinized starch had detrimental effects on the gelation of fish protein, and more water was absorbed by this starch compared to non-pregelatinized starches. Resulting gels were weaker and less deformable.