Am. J. Pot Res (2008) 85:455–465 DOI 10.1007/s12230-008-9053-z

Genotypic and Environmental Contributions to Baked Potato Flavor

Shelley H. Jansky

Published online: 24 September 2008 # Potato Association of America 2008

Abstract This study was carried out to determine the relative clones de especialidad. Los atributos de sabor incluyeron contributions of genotype and environment to baked potato calidad de harinoso, dulzura, intensidad de sabor, desabrido flavor variation in standard potato cultivars. In addition, y percepción general de sabor. Se encontraron diferencias relationships between individual flavor components and entre cultivares y ambientes de producción. Las papas overall quality perception scores were determined. The study almacenadas recibieron mayor puntaje en percepción de was carried out for 2 years using stored potatoes. In addition, calidad que las papas frescas. La condición de harinoso fue fresh potato tubers were evaluated in the second year. Taste el atributo del sabor más variable y fue influenciado por el panels evaluated potato varieties within four market classes, genotipo y el medio ambiente. La dulzura e intensidad de russets, whites, reds, and specialty clones. Flavor attributes sabor fueron asociadas positivamente con la percepción de included mealiness, sweetness, flavor intensity, off-flavor, and calidad. Se detectó también una fuerte asociación negativa overall quality perception. Differences among cultivars and entre la falta de sabor y la percepción de calidad. production environments were found. Stored potatoes re- ceived higher quality perception scores than fresh potatoes. Keywords Potato . Solanum tuberosum . Sensory analysis . Mealiness was the most variable flavor attribute and was Baked potato . Sensory panel influenced by both genotype and environment. Sweetness and flavor intensity were positively associated with quality perception. A strong negative association between off-flavor Introduction and quality perception was also detected. Per capita consumption of potatoes in the USA is higher Resumen Este estudio se realizó para determinar la than that of any other vegetable. In 2005, Americans ate contribución relativa del genotipo y el medio ambiente a 61 kg of potatoes per person, of which 21 kg (34%) were la variación del sabor de la papa horneada en cultivares purchased fresh (Economic Research Service, US Depart- estándar de papa. Además se determinó la relación entre los ment of Agriculture). Tomatoes ranked a distant second, componentes individuales del sabor y el puntaje de la with 41 kg consumed per year, of which 8 kg (19%) were percepción de la calidad general. El estudio se realizó por purchased fresh. The most popular way to prepare fresh dos años usando papas almacenadas. Además, tubérculos potatoes is by baking them (Lin and Yen 2004). While frescos de papa fueron evaluados en el segundo año. Los overall per capita consumption of potatoes is expected to paneles sensoriales evaluaron las variedades de papa dentro decrease in the future, the consumption of baked potatoes is de cuatro clases comerciales, rugosas, blancas, rojas y expected to increase. In fact, the largest growth of all potato products among adults is expected to occur for baked S. H. Jansky (*) potatoes (Lin and Yen 2004). Department of Horticulture, Potato breeding programs typically focus on yield, tuber USDA-ARS and University of Wisconsin-Madison, appearance, processing quality, and disease resistance as 1575 Linden Drive, Madison, WI 53706, USA selectable traits (Bradshaw and MacKay 1994; Ross 1986; e-mail: [email protected] Tarn et al. 1992). Flavor, on the other hand, is not an 456 Am. J. Pot Res (2008) 85:455–465 important selection criterion during cultivar development. quality decreases due to the production of organic acids Currently, most breeding programs only require the absence (Cieslik 1997). Levels of methional, an aroma compound, of off-flavor. In recent years, breeders and growers have vary across environments (Duckham et al. 2002; Oruna- expressed a desire to assess cultivar flavor and use this Concha et al. 2001). Because methionine contains sulfur, information in breeding programs to improve the market sulfur application rates may account for some differences in value of potatoes. methional levels (Duckham et al. 2002). Methoxypyrazines Components of flavor include taste, aroma, texture, and may be produced by the tuber or by soil bacteria umami (a Japanese word meaning delicious). The major (Pseudomonas taetrolens) and then absorbed by the tuber, taste (nonvolatile) components in potato tubers are glyco- so soil microbe populations may influence flavor (Buttery alkaloids, sugars, amino acids, lipids, acids, and nucleotides et al. 1973). In addition, high potassium levels in tubers (Maga 1994). Glycoalkaloids can produce a bitter flavor may enhance umami taste intensity (Ugawa and Kurihara when greater than 14 mg/100 g tuber fresh weight (Sinden 1994). Differences in production environment were found et al. 1976). The main contributions of sugars, amino acids, to influence the development of off-flavor in pre-cooked and lipids are the volatile compounds they produce after vacuum-packed potatoes, but specific environmental heating. However, sugars also contribute directly to sweet parameters influencing off-flavor were not determined taste. Phenolic compounds such as chlorogenic acid may (Jensen et al. 1999). contribute negatively to flavor, as a positive correlation Some studies have evaluated the effects of organic between phenolic content and bitterness/astringency has versus conventional production systems on sensory attrib- been reported (Mondy et al. 1971). However, Sinden et al. utes. Using triangle tests, Wszelaki et al. (2005) found that (1976) did not find a strong relationship between phenolic taste panelists were able to distinguish between conven- content and bitterness. Ribonucleotides act as precursors for tionally and organically grown boiled red potatoes if the umami compounds (flavor potentiators). Steamed or boiled skin was left on the tubers while boiling. If the skin was tubers with high levels of guanosine 5′-monophosphate removed during boiling, then differences could not be (GMP) had high quality perception scores in sensory detected. Hajslova et al. (2005) determined that cultivar and analyses (Morris et al. 2007). A positive synergistic effect production year are important influences on sensory quality on flavor occurs when 5′ ribonucleotides interact with of boiled potatoes, but that there is no clear influence of amino acids, especially glutamate. production system (organic versus conventional). In a Baked potatoes produce a complex array of volatile review of studies conducted to evaluate organoleptic quality compounds including lipids, Maillard reaction products, sulfur in organic versus conventional systems, no clear statements compounds, and methoxypyrazines (Oruna-Concha et al. could be made regarding the superiority of one type over 2001). Pyrazines are considered to be among the most the other (Woese et al. 1997). important and characteristic components of baked potato Sensory quality changes during the storage of potato flavor (Oruna-Concha et al. 2001). They are produced by the tubers. In 1981, True and Work (1981) noted that ‘Russet Maillard reaction, in which reducing sugars (glucose and Burbank’ ranked high and ‘Ontario’ ranked low for flavor fructose) interact with amino acids at high temperature. A preference in fresh baked potatoes, but differences were not strong positive relationship between pyrazine levels and baked detected in tubers stored at 8.2°C for 6 months. In a study potato flavor has been reported (Maga and Holm 1992). of pre-peeled boiled potatoes, cultivar and storage time (0, Potato texture is a complex trait, but much variation can 1.5, and 6 months at 4°C) were the primary factors be explained by determining the degree of a tuber’s explaining (68%) variability in taste, color, and texture mealiness or, at the opposite end of the spectrum, waxiness (Thybo et al. 2006). When potato tubers are cooked, fatty (van Marle et al. 1997). A mealy potato is dry and granular, acids degrade to produce aldehydes and ketones, which while a waxy potato is moist and gummy. Texture is contribute to flavor (Duckham et al. 2002). Total levels of influenced, at least in part, by characteristics of starch fatty acids and their flavor products increase during storage grains and cell walls (Martens and Thybo 2000; McComber (Duckham et al. 2002). It is interesting to note that, as et al. 1994; van Marle et al. 1997). Mealiness has been tubers acclimate to cold storage temperatures, their fatty found to be associated with high dry matter content (van acid profiles change. Consequently, both levels and types of Dijk et al. 2002). However, dry matter content does not fatty acids change during storage. There is variation among always explain mealiness. In one sensory analysis study, cultivars in the way their fatty acid profiles are altered ‘Ontario’ was judged to be less mealy than other cultivars during cold storage (Mondy et al. 1963). The types and in the trial, but its total solids content was similar to some levels of other volatile components of flavor also change of those cultivars (True and Work 1981). during storage, presumably due to alterations in enzyme There is evidence that production environment affects activities and levels of flavor precursors, such as sugars sensory quality. As tuber nitrogen levels increase, sensory (Duckham et al. 2002). Levels of glucose and fructose in Am. J. Pot Res (2008) 85:455–465 457 most cultivars increase during storage at less than 10°C testing began, the methods for testing human beings in this (Sowokinos 2001). study were determined to be exempt from review by Potato growers and breeders are interested in considering Institutional Review Board of the Graduate School at the flavor as a marketable trait. In order to breed for improved University of Wisconsin-Madison. A trained taste panel of flavor, the relative contributions of cultivar, production 16 to 20 members evaluated the flavor of tubers baked at environment, and storage environment must be understood. 200°C for 1 h from March 6 to 9, 2006. Each panel member Consequently, before initiating research efforts to enhance evaluated each sample for the five flavor attributes of each potato flavor, it is important to quantify these sources of of the 13 varieties grown at the Hancock production site. variation. This study was carried out to determine the Four separate tasting sessions (two per day) were held, one relative effects of cultivar and environment on baked potato for each market class. Each panel member was presented all flavor, and to determine the relationship between sensory (three to four) samples at one time on a plate. Samples were attributes and perceived desirable flavor. arranged in random order on the plate and coded with random three-digit numbers. The arrangement of samples on the plate was the same for all panel members. The panel Materials and Methods also evaluated the same characteristics in four of the varieties (‘Green Mountain,’‘Kerr’s Pink,’‘Russet Bur- Tuber Production Repeated experiments were conducted bank,’ and ‘Russet Norkotah’), across the four production with 13 conventional potato cultivars across four locations sites. Again, four taste testing sessions were held, one for in Wisconsin in 2005. The cultivars included three red each cultivar across the four sites. Scoring for all taste skinned varieties (‘Bison,’‘Red Norland,’ and ‘Red panels was carried out by placing a mark along a 150 mm Pontiac’), three round white varieties (‘Atlantic,’‘Green horizontal line on a score sheet. The distance of a mark Mountain,’ and ‘Kerr’sPink’), three russet or baking from the beginning of the score line (in mm) was used as a varieties (‘Bake King,’‘Russet Norkotah,’ and ‘Russet data point. A taste panel of 20 to 24 members repeated this Burbank’) and four specialty varieties (‘Banana,’‘German procedure from October 30 to November 2, 2006, and Butterball,’‘Yellow Finn,’ and ‘Yukon Gold’). The four March 19 to 22, 2007, using tubers harvested in the fall of locations were Sturgeon Bay (east-central Wisconsin, con- 2006. ventional production system), Hancock (central Wisconsin, conventional), Rosholt (central Wisconsin, certified organic), Statistical Analysis Single-factor repeated measures analy- and Baraboo (southern Wisconsin, certified organic). Tubers ses of variance were performed across different evaluation were harvested in September and stored at 5.5°C until late days and times (trials) to compare the effects of potato February. They were then removed from cold storage and clones and location on the five taste attributes (mealiness, kept at room temperature for 10 days before being used for sweetness, potato flavor intensity, off-flavor intensity, and sensory analysis. quality perception). All analyses were performed using In 2006, the same set of 13 cultivars was evaluated in PROC MIXED in SAS® PC Windows Version 9.1.3 repeated experiments and three additional cultivars were software. Outlier panelist ratings (those identified as being added to the studies (‘Millenium Russet,’‘Megachip,’ and consistently high or low) were removed by ranking original ‘Villetta Rose’). Experiments were conducted at Hancock, data scores and testing the sum of the ranks across all Rosholt, Baraboo, and Rhinelander (northern Wisconsin, varieties (or locations) with an upper and lower 5% tail for conventional). Rhinelander was substituted for Sturgeon the ranking limit. Levene’s homogeneity of variance test Bay because taste panel data (not shown) from a limited was performed on the original data with outliers removed to sample of cultivars grown at Rhinelander in 2005 showed determine transformation necessity. All analyses were some unusual taste attributes. Sturgeon Bay experimental performed on transformed data where necessary, but raw site was eliminated because of limitations in the number of data means are presented for ease of interpretation. If a samples that could be processed by the taste panel. significant F-test value from the ANOVA was obtained at p≤0.05, then differences of least squares means were used Sensory Analysis Based on published literature and previ- for pairwise multiple comparisons when determining potato ous experience, criteria that define potato flavor were clone or location differences. developed for the sensory evaluation. The taste panel For each of the three studies (spring 2006, fall 2006, survey included the five following criteria: mealiness (a spring 2007), one trial consisted of three to four clones in measure of texture), sweetness, potato flavor intensity (a one of the four market classes, russet/bakers, whites, reds, measure of the strength of the flavor perceived as “potato- and specialty (yellow-fleshed and/or fingerling) clones. All like”), off-flavor, and quality perception. The first four clones originated from a single location (Hancock). Clone criteria are objective, while the last is subjective. Before differences within each of the four trials (market classes) 458 Am. J. Pot Res (2008) 85:455–465 were analyzed separately for each taste attribute. A second cultivars differed for mealiness and quality perception, set of trials consisted of four clones grown at each of four white cultivars for mealiness, red cultivars for mealiness, locations. One trial was one clone grown at four locations. and quality perception, and specialty cultivars for sweetness Location differences for each trial (clone) were analyzed (Table 3). separately for each taste attribute. Differences among cultivars within a market class were detected for mealiness more than any other flavor variable with tubers grown at Hancock. These differences were Results and Discussion especially apparent in tubers stored until February or March. Texture differed among cultivars in seven out of Differences Among Cultivars Grown at Hancock eight trials using stored tubers. Differences in texture were also noted in two out of four trials using fresh tubers. Spring 2006 The only trial-attribute data set needing a Within russet potatoes, ‘Bake King,’ and ‘Russet Burbank’ transformation was mealiness in red cultivars. The were mealier than ‘Russet Norkotah,’ and ‘Freedom (mealiness)5 transformation stabilized the variance. Russet Russet.’‘Red Pontiac’ was mealier than the other red cultivars differed in mealiness and flavor; white cultivars cultivars. ‘Yukon Gold’ was the mealiest specialty cultivar. differed in mealiness; red cultivars differed in mealiness Sweetness did not consistently differ across market and sweetness, and specialty cultivars differed in mealiness classes. In fresh potatoes harvested in 2006, ‘Freedom (Table 1). Russet’ was not as sweet as the other russet cultivars, but that difference was lost in storage. There were no differ- Fall 2006 The only trial-attribute data set requiring a ences in sweetness among specialty cultivars at harvest in transformation was flavor in white cultivars. The square 2006, but after storage, ‘Yellow Finn’ was much sweeter root transformation stabilized the variance. Differences than ‘Banana.’‘Red Pontiac’ was sweeter than ‘Red were observed in russet cultivars for sweetness; in white Norland’ in the spring 2006 study, but that difference was cultivars for quality perception; in red cultivars for meal- not detected in the fall or spring evaluation of tubers iness, off-flavor, and quality perception, and in specialty harvested in the fall of 2006. When stored at cold cultivars for mealiness and quality perception (Table 2). temperatures, potato tubers undergo low temperature sweetening. Storage at 5°C results in a dramatic accumu- Spring 2007 The only trial-attribute data set requiring a lation of glucose, fructose, and especially sucrose (Coffin et transformation was unusual flavor in white cultivars. The al. 1987). The increase in sugars during storage varies by square root transformation stabilized the variance. Russet cultivar, so ‘Freedom Russet,’‘Yellow Finn,’ and ‘Red

Table 1 Mealiness, sweetness, intensity of potato flavor, intensity of off-flavor, and overall quality perception of four market classes (russets, whites, reds, and specialty cultivars) in the spring, 2006, taste panel

Cultivar Mealinessa Sweetness Flavor Off-flavor Quality perception

Bake King 86.7±23.9 ab 53.9±27.8 70.9±25.9b 35.3±25.8 78.1±23.3 Russet Burbank 79.5±27.8 ab 48.8±30.6 80.2±24.2ab 34.6±30.1 79.4±28.4 Russet Norkotah 67.0±27.0 b 58.9±29.4 84.7±20.7a 35.2±28.5 83.4±25.5

Atlantic 86.3±27.8aa 57.8±21.3 62.0±34.8 36.4±30.1 68.6±32.3 Green Mountain 96.2±20.4a 60.0±26.9 67.2±30.8 50.8±31.0 65.6±28.3 Kerr’s Pink 37.7±22.0b 66.6±31.0 73.5±23.3 50.7±36.7 70.3±31.1

Bison 42.6±18.2b 63.5±22.5ab 70.9±23.8 41.6±32.3 81.9±27.8 Red Norland 32.0±26.8b 57.4±30.5b 67.0±24.1 36.6±23.4 65.9±33.7 Red Pontiac 50.8±31.2a 75.9±30.7a 78.2±33.7 39.1±36.9 70.4±32.0

Banana 78.9±24.9a 50.2±24.8 75.5±26.8 43.2±34.6 76.0±30.5 German Butterball 55.9±28.4b 55.6±27.6 137.4±26.9 40.6±22.9 69.9±26.4 Yukon Gold 68.7±32.5ab 60.8±32.8 75.8±29.7 44.8±36.0 79.8±31.7 Yellow Finn 55.5±26.8b 55.9±27.3 69.7±25.9 36.1±27.5 74.4±21.5 a Mealiness: 0 = waxy, 150 = mealy; sweetness: 0 = not sweet, 150 = sweet; flavor: 0 = no potato flavor, 150 = strong potato flavor; off-flavor: 0 = no off-flavor, 150 = strong off-flavor; quality perception: 0 = undesirable, 150 = desirable b Clone means within each market class and flavor attribute followed by the same letter are not significantly different based on differences of least squares means at p=0.05 Am. J. Pot Res (2008) 85:455–465 459

Table 2 Mealiness, sweetness, intensity of potato flavor, intensity of off-flavor, and overall quality perception of four market classes (russets, whites, reds, and specialty cultivars) in the fall, 2006, taste panel

Cultivar Mealinessa Sweetness Flavor Off-flavor Quality perception

Bake King 73.1±39.1 59.5±26.3ab 69.0±29.5 35.3±34.4 85.4±23.6 Russet Burbank 66.3±25.0 57.2±32.9a 61.6±23.2 50.4±40.6 73.4±32.6 Russet Norkotah 53.6±44.1 57.8±28.8a 61.4±29.7 43.4±30.4 72.5±32.1 Freedom Russet 53.3±32.4 37.4±18.4b 61.1±31.8 56.5±41.7 64.7±30.0

Atlantic 59.8±28.3 52.3±27.5 76.4±25.6 33.8±29.2 79.2±29.6a Green Mountain 67.8±26.9 64.4±25.4 69.0±17.1 46.3±28.8 70.2±32.1ab Kerr’s Pink 59.6±31.2 57.8±26.7 58.8±24.4 56.4±37.2 59.8±30.2b Megachip 78.0±27.1 53.8±27.8 62.2±32.1 45.6±35.0 59.5±30.6b

Bison 42.4±33.3bc 48.3±26.9 58.2±22.6 31.4±24.8b 66.5±29.9b Red Norland 46.4±35.0ab 56.7±31.6 65.4±25.1 42.9±27.9ab 69.9±29.6ab Red Pontiac 59.2±18.6a 53.2±30.6 72.3±32.8 40.5±32.0b 90.9±41.4a Villetta Rose 30.8±27.5c 44.0±30.0 58.8±34.8 60.5±37.9a 50.7±36.1b

Banana 55.8±29.2 b 47.3±26.1 63.0±32.3 50.8±37.3 58.1±31.9b German Butterball 59.5±33.0 b 57.4±25.3 73.9±27.4 36.0±27.1 80.0±25.9a Yukon Gold 83.9±26.4a 48.2±26.0 72.2±30.7 38.0±32.6 68.7±31.9ab Yellow Finn 59.0±29.1b 48.7±27.3 76.1±23.6 45.1±29.1 73.0±28.4ab a Mealiness: 0 = waxy, 150 = mealy; sweetness: 0 = not sweet, 150 = sweet; flavor: 0 = no potato flavor, 150 = strong potato flavor; off-flavor: 0 = no off-flavor, 150 = strong off-flavor; quality perception: 0 = undesirable, 150 = desirable b Clone means within each market class and flavor attribute followed by the same letter are not significantly different based on differences of least squares means at p=0.05

Table 3 Mealiness, sweetness, intensity of potato flavor, intensity of off-flavor, and overall quality perception of four market classes (russets, whites, reds, and specialty cultivars) in the spring, 2007, taste panel

Cultivar Mealinessa Sweetness Flavor Off-flavor Quality perception

Bake King 60.5±33.5abb 56.2±35.5 57.3±28.1 41.6±34.1 66.5±30.6ab Russet Burbank 63.0±30.1a 61.0±28.2 69.8±25.1 43.1±30.6 80.7±30.8a Russet Norkotah 43.7±27.2c 72.1±29.3 62.2±34.2 43.6±30.5 58.0±27.9b Freedom Russet 46.9±32.4bc 66.7±33.0 60.0±29.9 40.3±37.8 71.7±30.7ab

Atlantic 79.8±28.7a 52.9±24.6 72.3±27.1 38.9±31.4 71.7±30.6 Green Mountain 67.8±30.2b 51.0±31.7 71.8±30.6 47.8±29.9 70.7±35.3 Kerr’s Pink 41.0±28.4c 63.2±30.3 79.6±28.3 56.5±42.5 71.2±37.5 Megachip 72.9±32.3ab 47.3±28.0 64.9±28.2 36.8±27.4 66.6±36.5

Bison 39.1±31.7b 62.3±33.1 62.3±29.4 35.2±25.6 76.3±34.4ab Red Norland 29.4±23.7b 70.0±35.1 64.9±25.8 42.2±29.3 67.6±34.6b Red Pontiac 65.7±27.4a 63.5±29.1 69.4±29.0 42.8±30.9 81.7±32.8a Villetta Rose 31.1±26.8b 60.1±31.2 59.5±32.6 54.4±36.6 63.9±40.0b

Banana 68.1±32.7 43.3±24.5b 59.8±29.5 52.2±29.2 62.8±32.1 German Butterball 58.3±33.5 51.3±23.5ab 64.6±26.5 47.3±34.2 76.0±26.3 Yukon Gold 72.4±34.5 51.1±28.1ab 70.9±29.5 41.6±30.4 75.1±28.4 Yellow Finn 56.2±30.0 64.5±31.0a 67.0±29.3 42.4±29.1 75.2±30.5 a Mealiness: 0 = waxy, 150 = mealy; sweetness: 0 = not sweet, 150 = sweet; flavor: 0 = no potato flavor, 150 = strong potato flavor; off-flavor: 0 = no off-flavor, 150 = strong off-flavor; quality perception: 0 = undesirable, 150 = desirable b Clone means within each market class and flavor attribute followed by the same letter are not significantly different based on differences of least squares means at p=0.05 460 Am. J. Pot Res (2008) 85:455–465

Pontiac’ may accumulate more sugars during storage than rather than baked. Perhaps the mealiness of ‘Red Pontiac’ the other cultivars with which they were compared. contributed to its favorable rating as a baking potato. In the The only differences in intensity of potato flavor and spring 2007 study, the flavor of ‘Russet Burbank’ was intensity of off-flavor were observed for russet cultivars in found to be better than that of ‘Russet Norkotah’ (Table 3). the spring 2006 and red cultivars in the fall 2006 study, This observation is in line with anecdotal evidence from the respectively. ‘Russet Norkotah’ had more potato flavor than potato industry. ‘Bake King.’ This result is interesting because ‘Bake King’ Because the genetic base of North American and was chosen for its reputation as a cultivar with good flavor European cultivars is very low (Douches et al. 1996; and ‘Russet Norkotah’ was chosen because of its purported Mendoza and Haynes 1974; Ross 1986)], it is perhaps not poor flavor attributes. ‘Villetta Rose’ had a stronger off- surprising that striking differences among cultivars were flavor than ‘Bison’ and ‘Red Pontiac.’ Taste panelists’ not detected. Genetic bottlenecks occurred when the potato descriptions of ‘Villetta Rose’ include acidic, sour, bitter, was brought to Europe from South America, and then when and metallic. Mineral analyses (P, K, Ca, Mg, S, Zn, B, Mn, it was brought to North America from Europe, and a third Fe, Cu, Al, and Na) of lyophilized raw tuber samples did time during selection for processing traits in the twentieth not identify any element that was higher in ‘Villetta Rose’ century. Breeders have necessarily focused on adaptation, than in ‘Bison’ and ‘Red Pontiac.’ In addition, when tuber appearance and disease resistance rather than flavor. lyophilized raw and baked tuber samples were rehydrated, South American land races are more genetically diverse and there were no significant pH differences among the three are likely to have undergone selection pressure for flavor. In cultivars. Perhaps differences in glycoalkaloid levels con- fact, a recent paper indicates that this germplasm base is a tributed to off-flavor in this trial. However, in a previous good source of flavor variability (Morris et al. 2007). study, the level of glycoalkaloids in ‘Villetta Rose’ was 9.26 mg/100 g fresh weight, which is well within the Differences Among Locations acceptable limit of 20 mg/100 g. Differences in overall quality perception were not Spring 2006 The only trial-attribute data set requiring a consistently detected for any of the market classes. ‘Red transformation was mealiness in ‘Green Mountain.’ The Pontiac’ received very high acceptance scores in the fall (mealiness)3 transformation stabilized the variance. Differ- 2006 and spring 2007 studies (Tables 2 and 3). It was ences between locations were observed in all four cultivars mealier than the other cultivars in those two studies as well. for mealiness and in ‘Kerr’s Pink’ and ‘Green Mountain’ Red cultivars are typically waxy or moist and are boiled for sweetness (Table 4).

Table 4 Mealiness, sweetness, intensity of potato flavor, intensity of off-flavor, and overall quality perception of four cultivars grown at four locations in the spring, 2006, taste panel

Cultivar Location Mealinessa Sweetness Flavor Off-flavor Quality perception

Russet Burbank Baraboo 52.1±26.1cb 56.1±25.3 67.5±26.9 37.2±25.6 69.6±29.5 Hancock 99.1±19.2a 45.7±27.2 64.1±30.5 41.4±30.8 67.7±32.2 Rosholt 83.6±25.6ab 58.9±26.1 70.4±27.0 35.5±26.7 70.9±31.7 Sturgeon Bay 66.8±26.2b 51.0±30.0 58.7±29.3 44.6±28.4 103.1±171.9 Russet Norkotah Baraboo 55.9±21.0bc 53.5±22.6 70.0±25.0 37.0±25.4 71.0±26.0 Hancock 68.0±26.5ab 60.8±23.4 71.3±25.9 45.5±34.7 70.0±33.3 Rosholt 47.3±20.2c 56.8±24.6 69.4±24.0 43.2±26.5 72.1±28.2 Sturgeon Bay 78.4±23.5 a 56.7±24.6 76.3±26.6 41.5±30.5 70.2±31.6 Kerr’s Pink Baraboo 41.9±30.4b 53.8±24.4ab 64.8±26.8 41.8±35.6 74.2±34.3 Hancock 49.6±27.8b 67.3±28.1a 67.0±22.6 42.6±30.5 71.3±24.0 Rosholt 41.8±20.1b 60.7±31.3a 65.5±26.0 32.7±23.3 78.4±22.2 Sturgeon Bay 76.2±26.9a 46.3±27.5b 72.2±27.6 54.2±33.2 61.0±35.1 Green Mountain Baraboo 73.6±24.4b 40.8±24.7b 66.7±25.2 53.6±34.4 63.0±29.3 Hancock 89.8±17.2a 57.4±27.7a 73.5±22.8 53.5±50.1 71.0±31.4 Rosholt 63.5±22.5b 61.6±35.1a 73.7±33.2 44.5±39.5 111.1±190.1 Sturgeon Bay 62.1±34.8b 68.6±28.3a 70.9±25.3 44.6±33.4 78.4±27.5 a Mealiness: 0 = waxy, 150 = mealy; sweetness: 0 = not sweet, 150 = sweet; flavor: 0 = no potato flavor, 150 = strong potato flavor; off-flavor: 0 = no off-flavor, 150 = strong off-flavor; quality perception: 0 = undesirable, 150 = desirable b Clone-location means within each trial and flavor attribute followed by the same letter are not significantly different based on differences of least squares means at p=0.05 Am. J. Pot Res (2008) 85:455–465 461

Table 5 Mealiness, sweetness, intensity of potato flavor, intensity of off-flavor, and overall quality perception of four cultivars grown at four locations in the fall, 2006, taste panel

Cultivar Location Mealinessa Sweetness Flavor Off-flavor Quality perception

Russet Burbank Baraboo 41.0±13.7 42.2±25.9 63.6±29.3 54.9±32.6 68.1±27.4 Hancock 57.2±34.1 43.2±21.3 52.7±24.4 39.3±28.9 56.0±34.5 Rhinelander 40.5±23.5 57.2±28.4 60.2±22.1 41.6±31.8 64.8±37.8 Rosholt 50.6±29.4 50.1±22.0 48.8±30.0 54.6±29.0 73.6±26.8 Russet Norkotah Baraboo 52.5±31.2bcb 53.0±33.0 63.0±24.2 49.0±34.5 67.1±31.3 Hancock 75.5±26.5a 50.3±28.5 62.1±29.8 30.4±24.6 64.8±31.2 Rhinelander 41.2±19.1c 47.4±19.0 54.6±26.3 39.5±28.9 69.0±26.1 Rosholt 57.0±29.8b 52.1±27.5 69.6±28.7 37.4±31.2 80.1±32.3 Kerr’s Pink Baraboo 50.4±28.7b 50.3±25.1 56.6±26.2 48.2±30.2 66.4±26.3 Hancock 68.6±26.8a 36.2±18.7 66.4±26.2 49.8±32.5 55.6±26.4 Rhinelander 60.1±25.6ab 40.5±26.5 62.8±28.7 49.6±34.2 65.2±31.3 Rosholt 48.8±19.7b 44.4±24.4 63.3±23.1 49.2±35.0 56.8±24.6 Green Mountain Baraboo 53.8±24.3b 49.8±28.1 72.4±23.8 53.5±32.3 65.2±24.1 Hancock 87.5±24.2a 38.3±22.9 59.3±24.0 46.0±27.3 60.8±26.5 Rhinelander 61.7±22.0b 38.9±23.5 71.1±22.0 43.9±24.7 70.4±24.6 Rosholt 58.1±27.5b 51.4±24.3 58.3±24.3 47.5±27.8 59.1±20.3 a Mealiness: 0 = waxy, 150 = mealy; sweetness: 0 = not sweet, 150 = sweet; flavor: 0 = no potato flavor, 150 = strong potato flavor; off-flavor: 0 = no off-flavor, 150 = strong off-flavor; quality perception: 0 = undesirable, 150 = desirable b Clone-location means within each trial and flavor attribute followed by the same letter are not significantly different based on differences of least squares means at p=0.05

Fall 2006 The only trial-attribute data sets requiring a Spring 2007 No data transformations were necessary. transformation were mealiness in ‘Russet Burbank’ and Differences were observed across locations in ‘Russet sweetness in ‘Russet’ Norkotah. The 1/(mealiness) and 1/ Burbank’ for mealiness, flavor, and off-flavor; ‘Russet (sweetness) transformations stabilized the variances. Differ- Norkotah’ for mealiness, sweetness, and flavor; Kerr’s Pink ences in mealiness were observed across locations in for mealiness, sweetness, flavor, and quality perception, ‘Russet Norkotah’, ‘Kerr’s Pink’, and ‘Green Mountain’ and Green Mountain for mealiness, sweetness and quality (Table 5). perception (Table 6).

Table 6 Mealiness, sweetness, intensity of potato flavor, intensity of off-flavor, and overall quality perception of four cultivars grown at four locations in the spring, 2007, taste panel

Cultivar Location Mealinessa Sweetness Flavor Off-flavor Quality perception

Russet Burbank Baraboo 51.0±30.4bb 62.5±33.5 78.4±23.8a 39.6±31.3ab 72.8±27.3 Hancock 82.7±22.4a 44.4±25.0 58.7±24.1b 24.7±26.6b 74.0±30.7 Rhinelander 59.4±26.8b 51.9±22.5 72.9±28.0a 48.4±39.0a 69.2±30.2 Rosholt 54.0±25.0b 49.8±27.1 69.0±29.7ab 31.0±28.0ab 76.3±29.6 Russet Norkotah Baraboo 62.9±31.6 a 56.6±19.3b 60.5±25.3bc 36.1±25.7 71.6±24.8 Hancock 63.8±28.4 a 60.3±24.2ab 69.9±28.7ab 34.9±26.4 78.3±28.8 Rhinelander 44.9±27.6 b 66.2±27.9a 75.4±20.1a 47.9±33.8 79.7±33.8 Rosholt 59.2±24.1a 54.9±26.2b 55.6±25.5c 45.1±31.7 76.1±25.1 Kerr’s Pink Baraboo 63.0±30.3ab 41.8±21.1ab 51.2±29.8b 46.7±35.3 55.2±28.2b Hancock 76.4±30.2a 35.9±20.6b 45.4±29.3b 39.4±32.4 64.7±25.5ab Rhinelander 52.0±27.1b 48.2±22.5a 68.6±23.1a 36.6±32.9 78.5±27.6a Rosholt 59.7±25.1b 49.4±26.8a 54.7±26.4ab 36.7±27.9 75.9±36.9a Green Mountain Baraboo 56.5±22.4c 57.8±31.2a 71.1±23.6 29.5±30.4 79.8±29.7ab Hancock 88.5±26.1a 40.9±29.2b 63.9±24.1 29.3±29.5 72.8±27.7b Rhinelander 61.2±25.6bc 61.7±27.8a 73.4±25.0 25.6±24.4 88.9±25.5a Rosholt 72.5±26.2b 49.3±27.1ab 68.6±22.3 24.9±22.6 86.9±26.3a a Mealiness: 0 = waxy, 150 = mealy; sweetness: 0 = not sweet, 150 = sweet; flavor: 0 = no potato flavor, 150 = strong potato flavor; off-flavor: 0 = no off-flavor, 150 = strong off-flavor; quality perception: 0 = undesirable, 150 = desirable b Clone-location means within each trial and flavor attribute followed by the same letter are not significantly different based on differences of least squares means at p=0.05 462 Am. J. Pot Res (2008) 85:455–465

Certainly, production environment contributes to potato those from the other two locations when differences were flavor. Taste panelists were able to detect differences in all detected in the spring 2007 trial (Table 6). Tubers from five attributes of potato flavor among samples of the same Hancock generally had lower quality perception scores, but cultivar grown at different locations. In fact, differences due differences were not always consistent or significant. While to production site were detected more often than differences the amount of applied nitrogen fertilizer was much higher at due to cultivar. While 19 of 60 taste panel comparisons Hancock (260 kg/ha) than the other sites (approximately detected differences due to cultivar (Tables 1, 2, and 3), 22 170 kg/ha), the level of potassium in the soil at Hancock of 60 detected differences due to production site (Tables 4, (64 ppm) was much lower than the other sites (Rhinelander 5, and 6). Differences between locations for mealiness were 102 ppm, Rosholt 149 ppm, and Baraboo 190 ppm). The detected in 11 out of 12 comparisons. Samples from synthesis of organic acids, including chlorogenic and Hancock were the mealiest in 10 out of those 12 ascorbic acids, has been reported to increase with increas- comparisons and tuber specific gravity was highest at ing levels of nitrogen fertilizer (Cieslik et al. 1994). Hancock in both years (data not shown). In fact, specific Chlorogenic acid levels are negatively associated with gravity was highly correlated with mealiness (p<0.0001), potato flavor (Thybo et al. 2006). On the other hand, with correlation coefficients of 0.88, 0.73 and 0.75 in the positive taste attributes have been reported to increase with spring 2006, fall 2006, and spring 2007 studies, respectively. increasing levels of potassium fertilizer (Ciecko et al. Consequently, production environment influences dry matter 2005). content, which in turn affects mealiness scores. These data A larger number of significant differences due to agree with previous studies in which dry matter content was production environment were detected in stored tubers (13 associated with texture (Murphy et al. 1967; van Dijk et al. of 20) than in fresh ones (three of 20) when a direct 2002). In another study, taste panelists were able to detect comparison could be made using tubers from the 2006 field textural differences in mashed potatoes from different sites, season (Tables 5 and 6). Specifically, differences in but not from different cultivars (Faulks and Griffiths 1983). sweetness, flavor, off-flavor, and quality perception were Following the 2006 production year, differences in sweetness not detectable in fresh tubers, but they were noticeable in were not apparent in fresh tubers, but occurred across stored tubers of ‘Russet Norkotah,’‘Kerr’sPink’ and locations in stored tubers of ‘Russet Norkotah,’‘Kerr’sPink’ ‘Green Mountain’ for sweetness; ‘Russet Burbank,’‘Russet and ‘Green Mountain’ (Tables 5 and 6). Tubers from Hancock Norkotah’ and ‘Kerr’s Pink’ for intensity of potato flavor; did not taste as sweet as those from the other production ‘Russet Burbank’ for off-flavor, and ‘Kerr’s Pink’ and locations. Differential accumulation of sugars during cold ‘Green Mountain’ for overall quality perception. It is storage may explain this observation, but the relationship to puzzling that location differences became more apparent production environment remains a tantalizing question. in stored potatoes. As suggested previously, differential In the spring 2007 study, flavor intensity differences accumulation of flavor compounds is likely to occur during were detected among locations for all cultivars except storage, but the relationship to production environment is ‘Green Mountain’ (Table 6). Potatoes grown at Rhinelander not clear. One possible explanation is that flavor is had a more intense flavor than at other sites. It is worth influenced by the soil or soil microbes that adhere to noting that there were no trends to indicate that tubers from unwashed tubers during storage. the organic sites (Baraboo and Rosholt) were more flavorful than those from the conventional sites. Side-by-side Differences Between Fresh and Stored Tubers comparisons of organic and standard production fields would provide a better test of this variable. However, these When all cultivars within a market class were bulked for results are consistent with previous studies that reported a analysis, there were no differences between taste panel lack of association between sensory quality and production scores in the fall of 2006 and the spring of 2007 for any of system (Hajslova et al. 2005; Woese et al. 1997). the five flavor attributes. However, when individual The only effect of production environment on off-flavor cultivars were analyzed by bulking across locations, differ- was observed for ‘Russet Burbank’ in the spring 2007 study ences were observed (Table 7). Stored tubers were mealier, (Table 6). Tubers from Rhinelander had a more intense off- sweeter, more flavorful, and they had lower levels of off- flavor than those from Hancock. Taste panelist comments flavors. It is not surprising, then, that stored tubers were on ‘Russet Burbank’ tubers from Rhinelander included given higher quality perception scores than fresh tubers. metallic, burnt, and bitter. Because differences in off-flavor During cold storage, tubers accumulate sugars (Coffin et al. were not apparent in other comparisons, it is difficult to 1987). This may directly impact flavor by making tubers determine the basis of these results. taste sweeter. Sugars may also indirectly enhance flavor by Tubers from the two most northerly sites, Rhinelander contributing to the Maillard reaction, which produces major and Rosholt, had a better overall baked potato taste than flavor components, including pyrazines (Maga and Holm Am. J. Pot Res (2008) 85:455–465 463

Table 7 Taste attributes of fresh versus stored tubers of four cultivars

Cultivar Mealinessa Sweetness Flavor Intensity Off-flavor Quality perception

Russet Burbank Fall 2006 65.3 44.6 65.3 47.7bb 63.9a Spring 2007 69.7 52.4 69.3 27.3a 82.1b Russet Norkotah Fall 2006 57 42.8 62.3 49.2 61.0a Spring 2007 62.8 43.8 55 39.8 68.6b Kerr’s Pink Fall 2006 56.5 50.7a 62.4 39.1 70.3 Spring 2007 57.7 59.4b 65.4 41.1 76.4 Green Mountain Fall 2006 47.3a 48.2 56.3a 47.6b 31.8 Spring 2007 61.8b 52.1 69.8b 36a 29.1 a Mealiness: 0 = waxy, 150 = mealy; sweetness: 0 = not sweet, 150 = sweet; flavor: 0 = no potato flavor, 150 = strong potato flavor; off-flavor: 0 = no off-flavor, 150 = strong off-flavor; quality perception: 0 = undesirable, 150 = desirable b Clone means within each trial and flavor attribute followed by the same letter are not significantly different based on differences of least squares means at p=0.05

1992; Oruna-Concha et al. 2001). Higher levels of consumers and highly variable among market types. Each Maillard/sugar-derived flavor compounds have been ob- taste panel member had a preconceived notion of an ideal served in stored tubers compared to fresh ones (Duckham et baking potato with regard to mealiness. Some prefer waxy al. 2002). In fact, total levels of flavor compounds tubers, while others prefer mealy tubers. Consequently, a increased during storage due to the mobilization of flavor mealy potato was not considered ideal by all taste panel compound precursors and the activation of lipid enzymes. members. On the other hand, moderate positive correlations were detected between quality perception and sweetness. Correlations Between Quality Perception and Objective This is especially intriguing because a long-held belief in Flavor Attributes the potato industry that consumers are not interested in potatoes that taste sweet (Solms and Wyler 1979). It is not In this study, four objective flavor attributes (mealiness, surprising that we observed a moderate positive correlation sweetness, potato flavor intensity, and off-flavor intensity) between potato flavor intensity and quality perception. were measured as components of the subjective attribute of Similarly, we expected a negative relationship between interest to potato breeders and producers, quality percep- intensity of off-flavor and quality perception. This was the tion. If a breeder could identify a component of flavor that strongest correlation, explaining up to 20% of the variabil- strongly influences quality perception, then s/he would be ity among taste panelists. Because potato flavor is bland, able to focus on that trait with the assumption that even low levels of off-flavor are likely to have a negative improvement would lead to a more desirable product. effect on taste panelists. While some of the correlations in Considering that differences in mealiness were relatively Table 8 were significant, none was high. One factor that easily detected by taste panelists, it may at first be likely had an influence on the strength of the correlations is surprising that correlations between mealiness and quality genetic variability among taste panelists. Some undoubted- perception were low and generally not significant (Table 8). ly taste bitter, for example, less readily than others. This This component of flavor is easily recognizable by would reduce the correlation between off flavor and acceptability. Studies are underway to evaluate the effect Table 8 Correlation coefficients between perception of quality of of taste panelist genotype on flavor scores. baked potato flavor and objective attributes for each sensory analysis study

Comparison Spring 2006 Fall 2006 Spring 2007 Conclusions

Mealiness −0.01 (0.86) 0.06 (0.11) 0.13 (<0.01) Because potato flavor results from a complex combination Sweetness 0.17 (<0.01) 0.30 (<0.01) 0.31 (<0.01) of positive and negative texture, aroma, and taste compo- Flavor intensity 0.07 (0.05) 0.31 (<0.01) 0.27 (<0.01) nents, it is difficult to find an individual trait that has a Off-flavor −0.21 (<0.01) −0.43 (<0.01) −0.45 (<0.01) major and consistent effect on flavor. In addition, both p value is in parentheses synergistic and antagonistic interactions between these 464 Am. J. Pot Res (2008) 85:455–465 compounds are likely to occur. While there is an abundance Coffin, R.H., R.Y. Yada, K.L. Parkin, B. Grodzinski, and D.W. of literature on the chemical components of flavor, Stanley. 1987. Effect of low temperature storage on sugar concentrations and chip color of certain processing potato information is lacking on the relationships between both cultivars and selections. Journal of Food Science 52: 639–645. cultivar and environment on baked potato flavor as detected Douches, D.S., D. Maas, K.R. Jartrzebski, and R.W. Chase. 1996. by taste panelists. Data from this study provide a Assessment of potato breeding programs in the USA over the last foundation for additional research toward the goal of century. Crop Science 36: 1544–1552. Duckham, S.C., A.T. Dodson, J. Bakker, and J.M. Ames. 2002. Effect breeding potato cultivars with enhanced flavor. Cultivar, of cultivar and storage time on the volatile flavor components of production environment, and storage environment affect baked potato. Journal of Agricultural and Food Chemistry 50: overall quality perception as well as components of flavor. 5640–5648. Variation due to production environment is as important as Faulks, R.M., and N.M. Griffiths. 1983. Influence of variety, site and storage on physical, sensory and compositional aspects of that due to genotype. This is partly due to a large effect of mashed potato. Journal of the Science of Food and Agriculture environment on flavor, but is probably also due in part to 34: 979–986. low genetic variability for flavor in conventional potato Hajslova, J., V. Schulzova, P. Slanina, K. Janne, K.E. Hellenas, and C. cultivars. Stored potatoes are typically more flavorful than Andersson. 2005. Quality of organically and conventionally grown potatoes: Four-year study of micronutrients, metals, fresh potatoes, presumably due to the production of flavor secondary metabolites, enzymic browning, and organoleptic compounds and enzymes during storage. Mealiness is the qualities. Food Additives and Contaminants 22: 514–534. most easily recognized component of flavor and is highly Jensen, K., M.A. Petersen, L. Poll, and P.B. Brockhoff. 1999. correlated with specific gravity, which is easy to measure Influence of variety and growing location on the development of off-flavor in precooked vacuum-packed potatoes. Journal of and already quantified by breeders because it is an Agricultural and Food Chemistry 47: 1145–1149. important quality for processing cultivars. Tremendous Lin, B.-H., and S.T. Yen. 2004. U.S. potato consumption: Looking variation in mealiness exists, especially among market ahead to 2020. Journal of Food Products Marketing 10: 49–65. classes, but also among production systems. While prefer- Maga, J.A. 1994. Potato flavor. Food Reviews International 10: 1–48. Maga, J.A., and D.G. Holm. 1992. Subjective and objective comparison ences for mealiness are variable, consumers prefer potatoes of baked potato aroma as influenced by variety/clone. In Food with a sweet taste, strong baked potato flavor, and lack of science and human nutrition, ed. G. Charalambous, 537–541. off-flavor. 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