Effects of various processing methods on free and bound amino acid contents of potatoes

The effects of various processing methods on available lysine and total and free amino acid levels of low (1.065 – 1.075) specific gravity (LSG) and high (1.095 – 1.106) specific gravity (HSG) potatoes were investigated. LSG potatoes after canning and chip making showed approximately 40% loss of total amino acid contents. Such losses in drum dried potatoes were approximately 20% and that of french fries 4.5%. All processing methods adversely affected the available lysine content; chips and canned potatoes showing the maximum loss, followed by drum dried and french fried potatoes. Losses in HSG potato products showed a trend similar to that of LSG material, but on a considerably reduced scale.     

Non-starch polysaccharides and the texture of French fried potato

Gel Filtration of the non-starch polysaccharides extracted from high and low specific gravity potatoes gave similar elution patterns. It is suggested that excessive degradation of the high molecular weight polysaccharides in low specific gravity potatoes, during frying, is an important reason for the poor textural qualities of low specific gravity french fries.     

Pectic substances and the texture of french fried potatoes

French fries made from low specific gravity potatoes are poor in texture and soggy in appearance. High specific gravity potatoes, on the other hand, produce mealy, firm and good-textured french fries. A comparison of raw potatoes of high and low specific gravity for protopectin, the degree of esterification, water-soluble pectins and divalent cations revealed no significant differences. Low specific gravity potatoes, however, were found to contain significantly higher levels of free calcium and lower degree of esterification of water-soluble pectins. Similar comparisons of french fries made from these potatoes showed that low specific gravity fries had a higher degree of protopectin de-esterification, greater breakdown of protopectin and higher levels of free calcium. It was concluded that protopectin of low specific gravity potatoes possesses fewer and/or weaker cross linkages, is poorly polymerized, and a substantial percentage of it breaks down on frying. This weakens the cell wall and results in a french fry of poor texture.     

Chemical composition of potatoes. VII Relationship of the free amino acid concentrations to specific gravity and storage time

Prior to storage, Maine-grown Katahdin potatoes were sorted into five specific gravity classes. Samples of three classes (high, intermediate, and low) were stored in individual boxes at 38 F for eight months, 45 F for one month, and 50 F for one month. New York-grown Katahdins were sorted into specific gravity classes periodically after removal from storage. Both lots were analyzed periodically for free amino acids (including the amides). In general, an inverse relationship was found between total solids and free amino acids calculated on a dry weight basis in Maine-grown and New York-grown Katahdin potatoes. In most cases little difference was found on the fresh-weight basis. Changes in the amino acids during storage were quite random. The differences found in the amino acid values between samples due to sorting for specific gravity before and after placing in storage were minor.     

Biochemical and molecular control of cold-induced sweetening in potatoes

The benefits of being able to process potatoes directly into chips or fries from cold storage (2 to 4 C) include less shrinkage, retention of dry matter, decreased disease loss, extended marketability, and the elimination of the need for dormancy-prolonging chemicals. Unfortunately at low temperature, potato tubers undergo a phenomenon known as cold-induced sweetening where the rate of conversion of starch to reducing sugars (i.e., glucose and fructose) is accelerated. As raw potatoes are sliced and cooked in oil at high temperature, the accumulated reducing sugars react with free amino acids in the potato cell forming unacceptably brown- to black-pigmented chips or fries via a non-enzymatic, Maillard-type reaction. Potatoes yielding these unacceptably colored products are generally rejected for purchase by the processing plant. All commercial potato cultivars presently used for the production of potato chips and fries accumulate excess free reducing sugars when exposed to cold stress. If a “cold-processing potato” was available, energy savings would be realized in potato-growing regions where outside storage temperatures are cool. In regions where outside temperatures are moderately high, increased refrigeration costs may occur. This expense would be offset, however, by removal of the need to purchase dormancy-prolonging chemicals, by a decreased need for disease control and by improvement of long-term tuber quality. The primary goal of this review is to describe recent research of a biochemical and molecular nature that relates to the underlaying mechanisms regulating post harvest, cold-induced sweetening in potato tubers. No attempt was made to outline the extensive research conducted on the genetic manipulation of carbon metabolism between starch and free sugars during photosynthesis and/or during potato development in relation to source/sink interactions.     

The effect of scion and stock autografting and heterografting on specific gravity,sugar content and chip color of potatoes

A potato chipping selection F58050 with high specific gravity and low sugar content and a non-chipping cultivar Sable with low specific gravity and high sugar content were each autografted and cross-heterografted to assess source-sink relationships on specific gravity, sugar content and chip color of potatoes. Heterografting of Sable scions onto F58050 stocks reduced the specific gravity of F58050 tubers compared to autografts of F58050 (P<.05). Grafting of F58050 scions onto Sable stocks did not significantly increase the specific gravity of Sable tubers compared to autografts of Sable. Heterografting of Sable scions onto F58050 stocks resulted in significantly (P<.05) darker chip color but no significant increases in reducing sugar content of potatoes as compared to potatoes from autografts of F58050, both at harvest and after 3 months’ storage at 12 C. On the other hand, potatoes from heterografting of F58050 scion onto Sable stock showed a slight improvement in chip color and significantly (P<.05) lower reducing sugar content than potatoes from autografts of Sable.     

Potato- An Important Source of Nutritional Kynurenic Acid

Kynurenic acid (KYNA) is a metabolite of tryptophan which is formed along the kynurenine pathway. KYNA may possess neuroprotective, anti-inflammatory, antioxidant and antiproliferative properties. This study measured the concentration of KYNA in various varieties of potatoes and products made from potatoes. KYNA content was determined by means of the high-performance liquid chromatography with fluorescence detection. KYNA was found in all 16 studied varieties of potato tubers in amounts varying from 0.239 to 3.240 μg/g dry weight. The content of KYNA in potato tubers declined during long-term storage. The content of KYNA in French fries varied from 0.100 to 0.646 μg/g dry weight. KYNA content in potato crisps was 0.478 and 0.576 μg/g dry weight. Hence, all in all, we concluded that the amount of KYNA potentially delivered to the human body in potatoes and various foods produced from potatoes is high and might be compared to the amount of KYNA present in a maximum daily dose of popular herbs and herbal medicines.     

Chemical composition variations of tissues and processing characteristics in ten potato cultivars grown in Jordan

Ten certified potato cultivears (Ajax, Crystal, Kennebec, Labelle, Liseta, Mondial, Norchip, Signa Gold, Spunta and Vital) were grown at Jordan University Experimental Station in 1993. At harvest, tuber subsamples of each plot were analyzed for physical properties and chemical composition. Processed chips and fries were evaluated for appearance, color, aroma, texture, taste and overall acceptability. There was significant variation in tuber weight which ranged from 108.8 (Kennebec) to 148.7 g (Labelle), specific gravity which varied from 1.022 (Mondial) to 1.191 g/ml (Spunta), total solids which ranged from 18.9 (Ajax) to 23.9% (Vial), and chemical composition. Cultivars Liseta, Signa Gold, Mondial, Kennebec and Crystal produced highly acceptable chips and fries, while Ajax, Kennebec, Norchip and Spunta produced excellent fries only. All other cultivars produced less acceptable chips and fries.     

Effect of storage period, cultivar and two growing locations on the processing quality of french fried potatoes

The source of raw potato tubers and the tubers’ duration of storage have a significant effect on color and texture of french fries. Controlling these variations is crucial to ensuring a consistent, high-quality end product. Russet Burbank and Shepody potatoes grown at two sites in Manitoba, Canada were stored for 9 and 11 months in 1994, and for 1 and 3 months in 1995, to determine the effects of short-term storage period, cultivar, and two tuber-growing locations on fry color and texture. French fry texture was measured by a puncture test, and peak force and peak deformation used as indices of textural quality. Large peak forces and deformations were assumed to be indicative of improved textural quality. Hunterlab L (lightness) value was used to determine fry color, higher values being associated with improved color quality. Fries processed from 11-month-old tubers had improved color and textural quality compared to those processed from 9-month-old tubers. Fries processed after 3 months tuber storage were darker in color but firmer in texture than fries processed from tubers after 1 month of storage. Differences in texture and color between the two cultivars were more evident with prolonged storage; fries processed from Russet Burbank potatoes were superior in texture and lighter in color than fries made from Shepody potatoes. With respect to site, fries processed from potatoes grown at Portage had better texture but darker color than those processed from Carberry potatoes. It was postulated that the calcium content of the soils may be responsible for both these results.     

Determination of blanching conditions for frozen par-fried potatoes

A procedure is presented for determining systematically the optimum blanching conditions required for potatoes from low temperature storage that are to be used for frozen French fries. Processing includes a low-temperature blanch for partial cooking and leaching of excess sugar followed by a brief immersion in glucose solution, if needed, for uniform coloring during finish frying. The glucose solution, or plain water if additional glucose is not required, should be of high temperature if other processing steps do not provide sufficient heating for complete enzyme inactivation. The potatoes are then par-fried and frozen.     

Suitability of Organic Potatoes for Industrial Processing: Effect of Agronomical Measures on Selected Quality Parameters at Harvest and after Storage

Three factorial field experiments were conducted in two consecutive years (2003 and 2004) on two sites in order to examine the impact of preceding crop, pre-sprouting, N and K fertilization and cultivar on quality attributes of organically grown potatoes destined for processing into French fries or crisps. Tuber dry matter (DM) concentration, glucose and fructose concentrations, as well as the colour of crisps and the quality score of French fries, were assessed at harvest and after a 4-month storage period. Results suggest that tubers from organic potato cropping may be expected to have sufficiently high tuber DM concentrations (>19%) for processing into French fries without impairing the texture of the fries when concentrations exceed 23%. DM concentrations of tubers for crips (cv. Marlen) fell short of the required minimum of 22% when a combined N and K fertilizer was applied. The tuber DM concentration was significantly lower following peas than following a legume-grass/clover ley or cereals (oats or winter wheat), but only in one of two seasons. Pre-sprouting increased tuber DM concentration considerably, especially in the growing season with a high incidence of Phytophthora infestans (+1.2% absolute increase). Tuber DM concentration was significantly higher after storage in two of three experiments (+0.4 and 0.5% absolute increase). Cultivars belonging to the very early and early maturity type showed the largest relative increase in reducing sugars concentrations due to storage, ranging between 300 and 1,100%. The medium-early cv. Agria and medium-late cv. Marena proved to be best suited for processing into French fries under conditions of organic farming, as only minor deviations from the highest quality standards were established at harvest (quality index at 4.3 and 4.1, respectively). A consistently high crisp quality was achieved by the medium-early cv. Marlen, with L-values of 70.8 and 66.7 at harvest and after storage, respectively. Overall, results show that the quality variables were mainly affected by cultivar, season, storage and their interaction. The effect of agronomical measures, such as fertilization, preceding crop and pre-sprouting of seed-tubers, was rather small and their effect on internal tuber quality and quality of fried products may hardly be predictable. The quality standards for tuber raw stock can be accomplished best when adequate cultivars are chosen.     

Irrigation and soil temperature effects on Russet Burbank quality

Potato growers in the Pacific Northwest suffer large economic losses in seasons with above normal temperatures, due to excess reducing sugars in tubers, which cause dark-end French fries. Our objective was to study irrigation management effects on potato quality, particularly the factors causing dark-end French fries or sugar-end syndrome. Solid-set sprinkler irrigated plots were established on potatoes at Kimberly, Idaho during the 1987, 1988 and 1989 irrigation seasons, and at Parma, Idaho in 1987 and 1988. Irrigation treatments were high and low frequency (3/week and I/week) and two or three water application amounts referenced to estimated evapotranspiration (ET, ET+20%, and ET-20%). Neither frequency nor amount significantly affected yields. Irrigation frequency had more influence on potato quality than application amount. More frequent irrigation produced slightly higher quality tubers and lower incidence of dark-ends when fried. Soil temperature was inversely related to tuber grade quality and directly related to percentage of sugar-end tubers. Soil temperature was about 0.5 C lower under the high frequency than under the low frequency irrigation regime. On these silt loam soils, allowing available soil water to decline to 50 percent had no adverse affect on yield or quality.     

Potassium hydroxide for peeling potatoes

Evolutionary operations (EVOP) were used to obtain conditions for optimum peeling of potatoes with KOH. With peeling at temperatures near 93 C, 20.6% KOH with an immersion time of 1 min 40 sec resulted in good peeling. Peeling at temperatures near 68 C required a KOH concentration of 25% and immersion times near 6 min. The higher immersion temperatures and higher KOH concentrations allowed shorter immersion times while obtaining adequate peeling of the potatoes. Potatoes peeled with KOH and NaOH were made into French fries andd mashed potatoes. Taste panels using the triangle difference test could detect no flavor differences between NaOH and KOH peeled potatoes at the 5% significance level.     

Influence of intercellular space differences due to variety and storage upon tuber specific gravity-dry matter relationship

At each of two locations in two years, five varieties of potatoes were examined for specific gravity—intercellular space relationships. At harvest intercellular space differred consistently among varieties and decreased during two months' storage at 40 F. Changes in weight, volume, and intercellular space were used to explain that changes in tuber specific gravity may or may not reflect changes in dry matter content and that differences and changes in intercellular space are of sufficient magnitude to account for most of the discrepancies between recently published regressions of dry matter on specific gravity developed without correction for intercellular space. A coordinated study is proposed to establish the correctness of this postulation. Estimation of dry matter content of white potatoes from specific gravity determinations is a widely accepted practice. The accuracy of the estimation has been questioned because of the relatively large error of estimation (±1.5 to 2%) usually encountered (24), the wide divergence of regressions (1, 6, 15, 16, 18, 19, 23), and the frequency with which discrepancies have been noted between specific gravity and quality (14). Recent recommendations call for “Improved accuracy in the quick estimation of solids either by specific gravity or other means” and clarification of the “effect of temperature and period of storage on changes in ... specific gravity” (25). The tests reported here were undertaken to obtain corroborating evidence for the estimation of dry matter content of sweet potatoes from root specific gravity after correction for intercellular space (IS), (8, 12). Sweet potatoes, as well as several other commodities, contain relatively large amounts of IS (8, 11) but when this is accounted for, a reasonably consistent relationship exists that appears to be nearly identical to the regression for the specific gravity of sucrose solutions (8). The work with sweet potatoes showed that 1 ml of IS produced a buoyancy equivalent to the weight in water of 2.38 g of dry matter (12). Although white potatoes contain relatively small amounts of IS on the average, amounts of 1% (1ml/100ml) and more have been reported (2, 8, 15, 16). Nissen, in Denmark, reported that varieties differed in IS and that for greatest accuracy the IS should be accounted for (15, 16). Most workers in the United States, however, have ignored the influence of IS upon the accuracy of the methol of estimating dry matter content from tuber specific gravity, although several have speculated that IS contributed to variation in this relationship (1, 18). The tests reported here indicate that varieties may differ with reasonable consistency in IS at harvest in much the same manner as sweet potatoes (17), and that these differences and changes in IS during storage may be large enough to account for most of the discrepancies observed in the relationship between tuber specific gravity and dry matter content.     

Processing conditions influencing the physical properties of French fried potatoes

Summary Achieving optimal colour and texture in French fries requires careful control of the unit operations that convert the raw potatoes into fries. The effects of variation in blanching, drying and finish frying conditions on puncture properties (peak force and peak deformation) and Hunterlab L (lightness) values of French fries were investigated. Fries blanched by low-temperature long-time (LTLT) conditions had larger peak force, peak deformation and L value than fries processed by standard conditions. High-temperature short-time (HTST) blanching increased lightness but decreased peak force and peak deformation. For drying, the colour and textural quality of French fries processed by standard conditions were better than those processed by the drying alternatives. For finish frying, LTLT conditions increased peak force whereas HTST conditions increased lightness. Therefore, a compromise has to be made in processing conditions to optimise both colour and textural quality. Even after finish frying, compositional differences within potato tubers influenced texture, both between and within French fries.     

水溶性低分子壳聚糖的制备

考察了6种氧化体系对壳聚糖降解效果的影响，结果表明：H2O2／HCl／MnO2是壳聚糖的有效氧化降解体系，可使它降解生成水溶性低分子壳聚糖。研究了反应条件对水溶性壳聚糖分子质量和产率的影响，结果表明，分子质量随着反应温度的升高而增大，随脱乙酰度的增加而减小。随着反应时间的延长，水溶性壳聚糖的分子质量随之降低，产率却随之增加。H2O2和MnO2分别加入体系反应1．5h后，水溶性壳聚糖的分子质量下降到只有1476，而产率却高达94．6％。     

Factors influencing incidence of internal brown spot in Russet Burbank potatoes

Studies were conducted to determine factors influencing incidence of internal brown spot (IBS) in Russet Burbank potatoes. A significant decrease in the incidence of IBS occurred as planting date was delayed from March 31 to May 12. IBS increased during storage particularly at the higher storage temperature and in larger tubers. Foliar application of maleic hydrazide (MH) significantly reduced IBS from a high of 33% of tubers to less than 10%. The incidence of IBS in tubers was lower in the field as well as in storage from plants sprayed with MH. Tubers with high specific gravity had greater incidence of IBS than low gravity tubers. Results indicate that IBS is a physiological disorder influenced by factors affecting growth of tubers.     

Relationship of specific gravity to sugar accumulation in stored Norgold and Russet Burbank potatoes

Studies were made on the influence of growing season and low fertility on reducing sugar accumulation in storage of the stem and bud portions of Russet Burbank and Norgold Russet potatoes separated into different specific gravity groups. The stem portion of Russet Burbank had a significantly different intercept and slope of regression line (between specific gravity and reducing sugar accumulation) than the bud portions of the same tubers indicating higher reducing sugar accumulation in the stem portion as well as differences in behavior as to amount accumulated at the different specific gravity levels. No significant difference in sugar content or behavior at the different specific gravity levels was obtained between stem and bud portions of Norgold Russet. Growing season did not cause significant differences in total sugar content or slope of the regression lines within the stem or bud portions of Russet Burbank. Low fertility level resulted in significantly higher sugar accumulation in the stem portion of Russet Burbank as compared to adequate fertility and there was also a trend toward less influence of specific gravity on sugar accumulation at the lower fertility level. Low specific gravity Russet Burbank potatoes tended to be more variable in sugar accumulation from year to year and also had wider differences in sugar accumulation between stem and bud portions than high specific gravity potatoes.     

Stability of high specific gravity genotypes of potatoes under high temperatures

An initial population of PHU-STN hybrid diploid potatoes was screened in 1978 at the Mountain Horticultural Crops Research Station, Fletcher, N.C. for high specific gravity and tuber production. Sixty clones were selected for testing under high temperatures at two North Carolina coastal locations. Twenty-seven clones maintained a relatively high specific gravity and acceptable tuber production under these high temperatures. The other 33 either were low in specific gravity or produced few, if any, tubers. Specific gravity was lower at the two coastal locations than at the Mountain Horticultural Crops Research Station. The 27 relatively stable, high specific gravity clones were retested in 1980 along with seven additional clones included for the first time. Severe high temperatures resulted in low survival rates and low specific gravity. However, eight clones maintained a relatively high specific gravity in relation to the rest of the population.     

苦丁茶冬青多糖乙醇分级纯化及其理化性质研究

为了研究苦丁茶冬青多糖醇沉规律及产物理化性质。通过热水浸提和不同浓度乙醇分级沉淀,得到乙醇终浓度为20%、40%、60%和80%的4种苦丁茶冬青多糖组分,即ICP-1、ICP-2、ICP-3和ICP-4。比色法检测各多糖组分总糖、糖醛酸、蛋白质和总酚含量;高效凝胶渗透色谱法进行相对分子质量的测定;紫外和红外光谱扫描考察各组分的光谱性质。结果表明：ICP-1、ICP-2、ICP-3和ICP-4总糖含量分别为19.21%、34.91%、37.70%和30.21%,糖醛酸含量分别为5.04%、44.90%、24.20%和5.84%;凝胶渗透色谱图表明：ICP-2和ICP-3为高纯度均一组分,分子量为440.440与348.279 ku;4种多糖组分在280 nm处均有吸收峰,说明均为糖蛋白质化合物。红外结果显示,各组分均为吡喃糖环构型。以上结果表明,乙醇分级沉淀的方法可用于分级纯化制备组分均一、纯度较高的苦丁茶冬青多糖组分。