Some aspects of potato appearance and texture. III. Sampling tubers for cation analysis

Individual unpeeled Kennebec tubers were analyzed after being subdiviled in various ways for sampling. The individual portions were wetashed whith a nitric-perchloric mixture and three cations were determined by Atomic Absorption Spectrophotometry. Representative samples of the tubers could be obtained by using subsamples of a blend or by using two opposite sectors cut longitudinally where each sector comprised 1/16th of the tuber. The latter method gave the greatest uniformity among the subsamples. Magnesium was uniformly distributed in the tubers studied, while calcium and potassium were more concentrated in the area external to the vascular tissue and in the stem and the bud ends of the tubers. The inequality of calcium distribution was extremely great.     

The importance of cell size in influencing the texture of the cooked potato. I. Preliminary observations

Summary The relationship between intercellular adhesion and the total surface area of cells per unit volume of tuber was investigated with samples from seventeen varieties grown in the field and eight varieties grown in pots. A direct relationship was found with a correlation coefficient of 0.63 (significant atP=0.001).

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Zusammenfassung die Beziehung zwischen Zellgr?sse und interzellularer Adh?sion wurde an Mustern von acht Sorten (Avenir, Gladstone, King Edward, Majestic, Maris Piper, Orion, Record undRedskin) untersucht, die in T?pfen in zwei N?hrl?sungen herangezogen wurden. Die gleichen Sorten wurden auch im Feld zusammen mit neun andern Sorten (Arran Pilot, Arran Victory, Dr McIntosh, Dumbar Standard, Golden Wonder, Pentland Crown, Pentland Dell, Ulster Glade undUlster Supreme) angebaut und untersucht. Die interzellulare Adh?sion wurde durch Messungen der Druckfestigkeit mittels des Wolodkewitsch Tenderometers bestimmt. Die Zellgr?sse wurde anhand von schwach vergr?sserten Mikrophotographien gemessen. Zwischen der interzellularen interzellularen Adh?sion und der gesamten Oberfl?che der Zellen in 1 mm³ des Knollengewebes wurde ein direkter Zusammenhang festgestellt (Abb. 1). Der Korrelationskoeffizient für diese zwei Faktoren war 0,63 was beiP-0,001 signifikant ist. Schwankungen in der Zellgr?sse k?nnen nur zum Teil für die unterschiedlich interzellulare Adh?sion verantwortlich gemacht werden. Es wird angenommen, dass dies auf den Einfluss von Polyuronid, Calzium und St?rke zurückzuführen ist. Der Einfluss von Interaktionen zwischen Zell gr?sse und diesen Bestandteilen auf die interzellulare Adh?sion wird untersucht.

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Résumé Les auteurs ont recherché la relation entre la grandeur des cellules et l'ahérence intercellulaire sur des échantillons de huit variétés (Avenir, Gladstone, King Edward, Majestic, Maris Piper, Orion, Record etRedskin) développées dans deux solutions nutritives différentes, ainsi que dans les mêmes variétés développées au champ; l'examen de la dite relation a également porté sur des échantillons de neuf autres variétés développées au champ (Arran Pilot, Arran Victory, Dr McIntosh, Dunbar Standard, Golden Wonder, Pentland Crown, Pentland Dell, Ulster Glade etUlster Supreme). L'adhérence intercellualaire est déterminée en mesurant la résistance à la compression au moyen du tendromètre Wolodkewitsch. La grandeur des cellules est déterminée par microphotographie de faible grossissement. Les auteurs ont trouvé une relation directe entre l'adhérence intercellulaire et la surface totale des cellules présentes dans 1 mm³ de tubercule (Fig. 1). Le co?fficient de corrélation entre ces deux facteurs est de 0,63 et est significatif au seulP=0,001. Les variations dans la grandeur des cellules ne jouent qu'un r?le partiel dans la variation de l'adhérence intercellulaire. Il est supposé que ceci peut-être d? à l'efet des polyuronide, calcium et amylose. Une-recherche est en cours sur l'effet des interactions entre la grandeur des cellules et leurs constituants sur l'adhérence intercellulaire.

     

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.     

Some aspects of total losses during storage and reconditioning of potato tubers

Summary Total losses during storage and reconditioning of several Polish varieties and strains in comparison with the American varietyKennebec are discussed. Several varieties or strains show such high losses that they are not acceptable for processing after storage. Susceptibility to loss is an attribute which must be taken into account when assessing varieties.     

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.     

Quality of potato tubers as affected by freezing: I. texture,ascorbic acid and enzymatic discoloration

The effect of freezing on the turgor, ascorbic acid content and enzymatic discoloration of Katahdin and Atlantic potatoes was studied. Tubers were exposed to a temperature of ?20°C for 24 hrs. then thawed for 1 hr. at 20°C before analysis. Frozen tubers were then compared with unfrozen controls. Both varieties lost turgor following freezing and exuded a sticky liquid with increased thawing time. At the end of 3 hrs. thawing, a sponge-like texture was observed in both varieties. In both varieties freezing resulted in a significant reduction (p<.01) in ascorbic acid and phenolic content (p<.01). Enzymatic discoloration was also significantly reduced (p<.01) in both varieties.     

The textural analysis of cooked potato. 2. Swelling pressure of starch during gelatinisation

Summary It has been disputed whether, when potato starch gelatinises and absorbs water, it generates an osmotic or matric pressure that makes the potato cells become round and separate from one another. Starch suspensions heated at 100°C in dialysis bags absorbed water, suggesting that starch swelling pressure does exist. It was quantified by heating starch suspensions at 85°C in a chamber which absorbed water through a membrane and contained an argon bubble whose volume was measured. This gave starch swelling pressures around 100 kPa, increasing non-linearly with starch concentration. A comparable estimate (a few hundred kPa) of starch swelling pressure within cooked potato tissue was obtained from the fact that it largely prevented the tissue contraction expected due to loss of turgor pressure in the first 1.5 min of boiling. A slight expansion thereafter was attributed to the combined effect of starch swelling pressure and cell wall and middle lamella degradation.     

Quality of potato tubers as affected by freezing: II. lipids and minerals

The effect of freezing on the chemical composition of Katahdin and Atlantic potatoes was studied. Tubers were exposed to a temperature of ?20°C for 24 hrs., then thawed for 1 hr. at 20°C prior to analysis. Frozenthawed tubers were compared with unfrozen controls for total lipid, phospholipid, fatty acid and mineral content. Following freezing, a significant (p<.01) decrease was observed in crude lipid and phospholipid content of both cortex and pith sections. Generally, an increase in palmitic acid and a decrease in linolenic acid occurred in the phospholipid fractions of both varieties. A decrease in both macro and micro mineral content also occurred following freezing.     

Impact of amylose content on starch retrogradation and texture of cooked milled rice during storage

Milled rice from 11 varieties, with amylose levels from 1.2 to 35.6% dry base, were collected to study the impacts of amylose content on starch retrogradation and textural properties of cooked rice during storage. The relationship between amylose content and different properties was determined using Pearson correlation. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by differential scanning calorimetry. ΔH_r values were found to be positively correlated with amylose content (0.603 ≤ r ≤ 0.822, P < 0.01) during storage. Textural properties were determined by a Texture Analyser. The hardness of cooked rice showed a positive correlation with amylose content (0.706 ≤ r ≤ 0.866, P < 0.01) and a positive correlation with ΔH_r of cooked rice (r = 0.650, P < 0.01) during storage. The adhesiveness showed a negative correlation with amylose content (−0.929 ≤ r ≤ −0.678, P < 0.01) and a negative correlation with ΔH_r of cooked rice (r = −0.833, P < 0.01) during storage. Hardness showed a negative correlation with adhesiveness (r = −0.820, P < 0.01). These results indicated that amylose content has significant effects on starch retrogradation and textural properties of cooked rice. The cooked rice with high amylose content is easy to retrograde, the cooked rice with low amylose content retrograded slowly. Sarch retrogradation contributes to the changes of textural properties of cooked rice during storage.     

Textural quality of cooked potatoes: II. Relationship of steam cooking time to cellular strength of cultivars with similar and differing solids

The relationship of steam cooking time with cellular strength of cultivars Chieftain, Kennebec, Russet Burbank and White Rose was compared within and among solids concentrations. Nitrogen fertilization had no discernible effect on cell wall strength. Cell strength of Kennebec and Russet Burbank was similar regardless of solids concentration or cooking time. However, cell strength of Chieftain and White Rose differed with solids concentration and cooking time. Knowledge of cell strength and its characteristics with cooking time appear important for understanding the differences in textural quality that exists between cultivars.     

Proximate composition and some functional properties of extrusion cooked soybean and sweet potato blends.

Mixtures of sweet potato flour and soy flour were made in a pilot mixer. They were moisturized with 18, 25, and 30% water and extruded in a single screw extruder at 80 rpm, using a die of 6mm. Extrusion temperature was maintained at 100 +/- 3 degrees C. Effects of adding soy flour into sweet potato flour, as well as variation in feed moisture on the composition and some functional properties of the extrudates were investigated. Increase in sweet potato content increased carbohydrate values. Protein increased with increase in soy flour. Feed moisture did not significantly (p < or = 0.05) affect extrudate composition. Increase in sweet potato content and feed moisture increased expansion ratio. Bulk density decreased with decrease in feed moisture, but increased with increase in soy flour. Starch content increased as sweet potato content increased. Degree of gelatinization increased with sweet potato content. Lower feed moisture enhanced gelatinization. Water absorption index (WAI) increased as sweet potato content increased. Feed moisture had a slight effect on WAI and water solubility index (WSI). Amylose increased with increase in sweet potato content. Increase in soy flour led to an increase in yellowness (b*) of extrudates.     

Some unique benefits with sudangrass for improved U.S. #1 yields and size of Russet Burbank potato

Three studies provided additional knowledge of beneficial effects of sudangrass for yield and quality increases of the Russet Burbank potato. Two of these studies showed significant increases of both U.S. #1 and smooth tubers > 280 g following green manures of sudangrass. These sudangrass (HS-33) effects did not differ from a sorghum-sudan hybrid (Trudan-8). When a sudangrass green manure was compared with a fallow treatment, results of the first study showed mean yield increases of 36% for U.S. #1 tubers > 280 g and yields of a second study by 34% for U.S. #1 tubers. This same sudangrass treatment outperformed green manures of either Austrian winter pea, barley, or sweet corn by increased U.S. #1 yields that ranged from 27% to 61%. By several lines of evidence, these benefits were found to extend beyond the effect of Verticillium suppression. Soil N was significantly increased following green manures of sudangrass, and these increases were in turn negatively correlated with wilt incidence and positively correlated with yields of both U.S. #1 tubers and tubers > 280 g. Additional benefits also included significant increases of tuber grade percentages for marketable tubers and of smooth tubers > 280 g. Benefits from sudangrass green manures beyond the effects of Verticillium suppression became further evident following a greenhouse study that involved field soil and sudangrass that had been grown in the same field. This study corroborated both field experiments by showing increased yields with green manures of sudangrass that approximated 5.5 t ha^-1 dry wt. As with the field studies, these yield benefits also extended beyond the effects of Verticillium suppression and were closely associated with significant increases ofFusarium equiseti, F. oxysporum, andF. solani. Throughout all studies, sudangrass green manures significantly increased microbial activities with increased populations ofFusarium spp. and increased concentrations in soil of mineralizable N, organic P, K, Mn, along with the percent soil organic matter -all factors that could have contributed to significant increases of yield and quality.     

Texture of cooked potatoes. Relationship between compressive strength,pectic substances and cell size of Redskin tubers of different maturity

Potato Research - Loss of compressive strength and breakage of disks and solubilization of pectic material occurred sooner as tubers matured. These changes occurred with shorter cooking times in...