Fruit Quality and Consumer Acceptability of Three Plum Types
plums at more advanced stages of maturity can improve fruit quality and consumer acceptance but leads to a reduction in shelf life and greater potential for damage during shipping and distribution (Abdi et al., 1997; Candan et al., 2008; Crisosto et al., Variety 2004; Fajt and Usenik, 2010). By growing plums closer to their intended market, they can be marketed without the need for long-distance shipping, Trials which allows growers to harvest them at a later stage of maturity when quality is optimal. To create cultivars with im- proved fruit quality, the asian plum Fruit Quality and Consumer Acceptability of has been hybridized with the apricot plum (Prunus simonii), the myroba- Three Plum Types and 14 Plum Cultivars lan plum (Prunus ceracifera), and other species and for cold tempera- Grown in Maine for a Local Market ture tolerance, it has been hybridized with american and canadian plum Angela D. Myracle, Zakkary J. Castonguay, Amber Elwell, and (Prunus nigra) (Hansen, 1915; Okie and Ramming, 1999). This has Renae E. Moran1 resulted in interspecific plums derived from the asian plum that are referred to as asian or japanese plums, and Prunus salicina Prunus domestica Prunus americana ADDITIONAL INDEX WORDS. , , , american plum (Table 1). European postharvest, soluble solids, titratable acidity, texture, sensory evaluation plums with sufficient cold tempera- SUMMARY. Fruit quality and consumer acceptance were measured in 14 plum ture tolerance can be an option in cultivars. In 2015, six cultivars of asian plum (Prunus salicina) and one cultivar of zones 4 and 5 but differ in texture, american plum (Prunus americana) were harvested partially ripe and tree-ripe. In flavor, and appearance from asian and 2016, three types of plums, asian, american, and european (Prunus domestica), were american plums and are relatively un- harvested tree-ripe. Within most cultivars in 2015, partially ripe fruit were rated as known to most consumers. The asian highly as tree-ripe fruit using a hedonic rating from 1 to 9 with 1 being dislike plums ‘Shiro’ and ‘Methley’ are extremely and 9 being like extremely. ‘Obilnya’ and ‘Abundance’ were rated higher than ‘Shiro’ and ‘Methley’ at both stages of ripeness and higher than ‘Vanier’ at the grown for their consistently high partially ripe stage. ‘Early Golden’ and ‘Spring Satin’ were rated higher than ‘Shiro’ yield in cold regions but knowledge and ‘Methley’ at the tree-ripe stage. In 2016, seven cultivars (Obilnya, Kahinta, on the consumer acceptance of these Superior, Toka, Castleton, Early Italian, and Rosy Gage) were scored at the desired and other cold hardy plums needs consumer acceptance level. ‘Shiro’ and ‘Cacxak’s Best’ received overall acceptability further evaluation. Cultivation of scores below the level of acceptability. Plum type had minimal effect on scores for plums in eastern and northern grow- texture, sweetness, sourness, and overall liking. European cultivars received lower ing regions of the United States and color scores than american and asian plums. Soluble solids concentration (SSC) Canada requires cultivars that possess ranged from 6.7% to 13.6% in asian plums, from 14.8% to 19.8% in american plums, cold temperature tolerance, resistance and from 15.3% to 22.1% in european plums. Overall consumer acceptance of to bacterial leaf spot, and rain crack- american and european cultivars was as good as for asian cultivars. ing resistance (Norton et al., 1987), but these traits are not typically pres- nnual consumption of fresh firmness reaches 10 lbf, but plums ent in asian cultivars selected for long- plums in the United States is are not considered ready to eat until distance shipping. A0.6 lb per capita, which is they soften to 2–3 lbf (Crisosto, Consumer preference depends on lower than that of similar types of 1994; Kader and Mitchell, 1989; flavor, texture, and appearance, which fruit such as sweet cherry (Prunus Robertson et al., 1992). Harvesting vary with cultivar and maturity at avium) and peach (Prunus persica) that have an annual per capita con- sumption of 1.1 and 2.8 lb, respectively Units (U.S. Department of Agriculture, To convert U.S. to SI, To convert SI to U.S., 2017). Low consumption may be multiply by U.S. unit SI unit multiply by due to the lower quality that occurs 29.5735 fl oz mL 0.0338 with harvest at an early stage of fruit 2.54 inch(es) cm 0.3937 maturity, a necessary practice to pre- 0.4536 lb kg 2.2046 4.4482 lbf N 0.2248 vent bruising and premature ripening 1.6093 mile(s) km 0.6214 during long-distance shipping. Pro- 28.3495 oz g 0.0353 ducers harvest plums when flesh ( F – 32) O 1.8 F C( C · 1.8) + 32
230 • April 2018 28(2) harvest (Boyhan et al., 1996; Corollaro complex nature of quality, consumer consumer testing. Harvested fruit et al., 2014; Crisosto et al., 2003). testing is needed to identify cultivars were selected at two stages of matu- These traits can be measured with with high consumer appeal. The ob- rity on the same day, tree-ripe and sensory testing using the untrained jectives of this research were to de- partially ripe, according to skin color general public and a hedonic liking termine if the partially ripe stage of and firmness changes specific to each scale from 1.0 to 9.0 (Peryam and maturity is as acceptable as the tree-ripe cultivar. Because of the large variation Pilgrim, 1957). For plums sold in stage of maturity in several asian plum in maturity of fruit on the same tree, supermarkets, a hedonic degree of cultivars and to determine the con- firmness was assessed by gently hand- liking score greater than 5.0 (neither sumer acceptability of three plum types squeezing fruit to determine which like nor dislike) is considered consumer that possess cold hardiness in U.S. fruit were sufficiently ripe to harvest. accepted (Crisosto et al., 2004). How- Department of Agriculture hardiness Peel color was also visually assessed to ever, minimum acceptability scores as zone 5. select fruit for harvest. ‘Spring Satin’ low as 5.0 could potentially lead to was assessed at only the tree-ripe stage Materials and methods because of the disparity in ripening cultivar recommendations that have Fruit were acquired from several among the three cultivars selected for only slightly positive ratings of liking sources for consumer testing. Most the first consumer testing date. (Meredith et al., 1992). To ensure cultivars were grown at the University EXPERIMENT 2. During early successful marketing, food products of Maine Highmoor Farm in Mon- Aug. to mid Oct. 2016, 20–50 fruit are expected to score at least 7.0 (Stone mouth, ME (lat. 44 14#N, long. were harvested from two to five trees et al., 2012). 70 3#W), where trees were planted of each cultivar for a total of 100 fruit Soluble solids concentration, ti- as three randomized complete block per cultivar. An exception was ‘Early tratable acidity (TA), and flesh firm- designs. Two trees each of ‘Toka’, Italian’ which was purchased from ness are commonly used as indirect ‘Kahinta’, and ‘Superior’ were a supermarket the same day as con- measures of fruit quality. Consumer planted in 2006. Five trees each of sumer testing as a measure of a locally acceptance of plums tends to be more ‘Early Golden’, ‘Shiro’, ‘Methley’, available commercially grown euro- favorable as SSC increases from below ‘Spring Satin’, and ‘Vanier’ were pean cultivar. The first consumer test- 10% to above 14%, but TA becomes planted in 2007. Three trees each of ing was held on 16 Aug. with ‘Shiro’, important when SSC is below 12% ‘Obilnya’, ‘Rosy Gage’, ‘Castleton’, ‘Obilnya’, and ‘Early Italian’. The (Crisosto et al., 2004). Most of the and ‘Cacxak’s Best’ were planted in second testing was held on 9 Sept. commercially important cultivars emit 2008. Each of these plantings was when ‘Rosy Gage’, ‘Castleton’, and low amounts of aroma volatiles (Gomez located in separate locations on the ‘Superior’ were tested. The third test- and Ledbetter, 1994), so sweetness and same farm. On 9 Aug. 2015, ‘Abun- ing was held on 15 Sept. when sourness contribute most to plum dance’ was harvested from a commer- ‘Kahinta’, ‘Toka’, and ‘Cacxak’s Best’ flavor (Singh and Singh, 2008) and cial farm in Fairfield, ME, located 36 were tested. Harvested fruit were consumer acceptance (Crisosto et al., miles north of the Highmoor Farm. selected at the tree-ripe stage of ma- 2003). However, these traits are not ‘Early Italian’ was purchased from turity. Insufficient fruit were available as well characterized in american a supermarket on 16 Aug. 2016 and to consumer test ‘Spring Satin’, ‘Early plums. Texture is not well studied in was grown at an unknown location. Golden’, ‘Methley’, and ‘Vanier’, and plums but has an impact on accept- All trees were trained and pruned for fruit quality measurement of ability of sweet cherry (Chauvin et al., according to the open-center system. ‘Spring Satin’ and ‘Vanier’. 2009), peach (Olmstead et al., 2015), Trees were grown according to New CONSUMER TESTING. Consumer and northern highbush blueberry England commercial production prac- testing was conducted 1–3 d after [Vaccinium corymbosum (Gilbert tices (Cooley et al., 2015). All trees harvest with fruit that had been held et al., 2014)]. Many factors in addition were hand-thinned to a uniform crop at room temperature except ‘Spring to sweetness, sourness, and firmness load in mid-June. Satin’, ‘Shiro’, and ‘Methley’ in Expt. contribute to fruit quality such as EXPERIMENT 1. During early 1, which were cold-stored for 2 d at aroma, bitterness, astringency, and Aug. to mid Sept. 2015, 20–50 fruit 1 C. The consumer testing was held juiciness for which optimum ranges were harvested from two to five trees at the University of Maine Sensory are not yet established. Because of the of each cultivar for a total of 100 fruit Evaluation Center. This testing was
This research was funded in part by the Maine De- per cultivar except Toka where only approved by the University of Maine partment of Agriculture, Conservation and Forestry, 40 fruit were harvested because of Institutional Review Board for the and by the United States Department of Agriculture limited supply. The first consumer Protection of Human Subjects and Federal Formula Hatch Funds under project NE1336. testing was held on 4–5 Aug. with participants were compensated four We acknowledge the valuable assistance of Xue Du, Bouhee Zeng, Katherine Davis-Dentici, and Mary ‘Spring Satin’, ‘Methley’, and ‘Early dollars for their time. Participants Ellen Camire. Maine Ag. and Forest Expt. Stn. no. Golden’, the second testing on 10–11 were recruited at the University of 3591. Aug. with ‘Obilnya’ and ‘Shiro’, and Maine via fliers posted around cam- Mention of a trademark, proprietary product, or the third testing on 3–4 Sept. with pus and announcements through an vendor does not constitute a guarantee or warranty of the product and does not imply its approval to the ‘Vanier’ and ‘Abundance’. ‘Spring e-mail list maintained by the univer- exclusion of other products that may also be suitable. Satin’ plumcot was included because sity. Because of the variation in har- School of Food and Agriculture, University of Maine, of its strong resemblance to plums. vest dates of the plum cultivars, Rogers Hall, Orono, ME 04469 Sufficient numbers of ‘Toka’ fruit testing was conducted in three differ- 1Corresponding author. E-mail: [email protected]. were available for inclusion in fruit ent sessions. Each session was com- https://doi.org/10.21273/HORTTECH03958-18 quality measurements but not for pleted over a 2-d period or until there
• April 2018 28(2) 231 VARIETY TRIALS
Table 1. Plum and plum hybrid cultivars evaluated in this study and their filtered juice from a pooled sample respective type and species. of 5–10 fruit. The samples were pre- Cultivar Type Species Skin color Flesh color pared by blending pitted plums for 5 s in a centrifuge (5804R; Eppendorf, z Abundance Asian Prunus salicina Red Yellow Hamburg, Germany) for 10 min at Cacxak’s Best European Prunus domestica Purple Gold 3234 gn. The centrifuged samples Castleton European P. domestica Purple Gold were filtered through Whatman #4 Early Golden Asian P. salicina hybrid Yellow Yellow filter paper (GE Healthcare Lifescien- y Early Italian European P. domestica Purple Gold ces, Chicago, IL) in a Buchner funnel · Kahinta American P. salicina Prunus americana Red Gold with an applied vacuum. The samples · Methley Asian P. salicina Prunus ceracifera Purple Red were stored at –20 C until analysis. · Obilnya Asian P. salicina P. ceracifera Purple Orange Soluble solids concentration was Rosy Gage European P. domestica Pink/green Green measured in triplicate with a digital · · Shiro Asian (P. salicina Prunus simonii) Yellow Yellow refractometer (model PAL-3; Atago, · (P. cerasifera Prunus Bellevue, WA). Titratable acidity was munsoniana) measured using an automated titrator · Spring Satin Plumcot P. salicina Prunus armeniaca Purple Yellow (HI 84532; Hanna Instruments, Car- · · Superior American P. salicina (P. americana Red Gold rollton, TX) on all samples. Titratable P. simonii) acidity was measured in duplicate in · Toka American P. americana P. simonii Dark red Gold 2015 as long as the values were within · Vanier Asian P. salicina P. simonii Red Yellow ±0.05% of one another and in tripli- z‘Abundance’ plums were grown in a commercial orchard in Fairfield, ME. cate in 2016. In a subset of samples in y‘Early Italian’ plums were purchased from a local supermarket. Location of production was unknown. 2015, a manual burette titration was used to ensure accuracy of the auto- were 100 participants. During the questions. Demographic and frequency matic fruit juice titration values. Both second testing date in Expt. 1, there questions were presented before sam- methods showed similar accuracy. Ti- were only 84 participants since it co- pling and were followed by five hedonic tratable acidity was measured by both incided with the 2 weeks before start questions about color, sweetness, skin means using 5 mL of the prepared of fall semester, a time when most tartness, texture, and overall liking, juice sample and 45 mL of ultrapure faculty and staff were absent. The with 1 = dislike extremely and 9 = like water. The manual burette method sensory testing ballot was created extremely (Peryam and Pilgrim, 1957). used standard 0.1 normal sodium and executed using SIMS 2000 soft- Open-ended comments were optional hydroxide (NaOH) to bring the pH ware (Sensory Computer Systems, for each of the samples, allowing for to 8.1. Titratable acidity was represented Morristown, NJ). additional comments and comparisons as percent malic acid (MA) as this is the Plum samples were prepared in to be made. The hedonic questions predominant acid found in plums (Bae a negative pressure kitchen and dis- were repeated for each sample and et al., 2014). Percent MA was calculated tributed to participants through a presented in the same order. After using the following equation: small sliding window to their individ- sampling was complete, participants an- ual stations. The participants were swered a follow-up set of questions, percent acid = seated at a partitioned desk with which included a seven-point Likert lighting to emulate ‘‘Northern Day- scale (1 = strongly agree and 7 = ðÞmilliliters NaOH 3 ðÞ0:1 NaOH 3 ðÞ0:067 3 ðÞ100 light 65.’’ Samples were assigned a strongly disagree), which was used to grams of sample three-digit randomized code assigned assess likelihood of purchasing and fruit by SIMS. The plums were cut into size preference. Size preference was Fruit quality and consumer test- quarters or sixths, depending on the assessed using a tangible, to-scale pic- ing data collected in 2015 were ana- size of the plum, with the pit removed ture reference of plums at three sizes, lyzed for the main effect of type, but the skin attached. Panelists were 1.0, 1.5, and 2 inches in diameter, cultivar, and stage of maturity as well not otherwise involved in the study which represent the size of plums grown as their interaction using the general and were not informed of which in Maine. linear models procedure of SAS (ver- cultivars were under evaluation. For FRUIT QUALITY ANALYSIS. Flesh sion 9.1; SAS Institute, Inc., Cary, each cultivar and stage of maturity, firmness was measured the same day NC) and Tukey’s honestly significant two vertical slices of fruit with the peel as harvest on 5–10 fruit of each difference test for means separation. and that were free of blemishes were cultivar and stage of maturity with Data collected in 2016 were analyzed placed in white ceramic dishes labeled a hand-held Effigi-type penetrometer using the same method but for only with the assigned three-digit random- and an 8-mm tip (Fruit Hardness the main effects of cultivar and type. ized code. Participants were also given Tester model 803; General Specialty Because type was confounded with water, napkin, and a laminated sheet Tools and Instruments, Secaucus, cultivar, the interaction of these two with plum images printed to-scale to NJ). Pressure testing was performed effects could not be analyzed. assist in answering the sizing prefer- on two sides of the plums not next to Results ence question. the seam and after removing a section The same testing ballot was used of the peel. CONSUMER DEMOGRAPHICS. In for all tests and consisted of demo- Soluble solids concentration, both experiments, most of the partic- graphic, hedonic, and Likert scale pH, and TA were measured using ipants were female and the largest age
232 • April 2018 28(2) group represented was 18–24 years Golden. Among tree-ripe fruit, color Golden’ and ‘Vanier’ received higher (Table 2). Most of the participants scores were not as variable among scores for sweetness than partially ripe consumed plums infrequently, one to cultivars. ‘Early Golden’, ‘Methley’, fruit. For other cultivars, there was no four times per year. Responses regard- and ‘Obilnya’ received the highest difference between partially ripe and ing preference for fruit size indicated color scores, followed by ‘Abun- tree-ripe fruit. Among partially ripe that larger plums were preferred. Most dance’, ‘Spring Satin’, and ‘Vanier’. fruit, ‘Abundance’ and ‘Obilnya’ re- of the participants also indicated that ‘Shiro’ had the lowest color score ceived higher sweetness scores than the health benefits of food were im- among tree-ripe fruit. other cultivars. Among tree-ripe portant when making food choices. Hedonic scores for texture varied fruit, ‘Early Golden’, ‘Obilnya’, and CONSUMER TESTING. In Expt. 1, among cultivars (P < 0.01), but for ‘Spring Satin’ received higher scores hedonic scores were generally lower most cultivars, there was no differ- than ‘Methley’ and ‘Shiro’ but similar for most traits in ‘Shiro’ and ‘Meth- ence between the two stages of ma- scores to ‘Abundance’, which was ley’ than for other cultivars (Fig. 1). turity (P = 0.92). However, the also similarly scored as ‘Methley’ In most cultivars, consumers pre- interaction between cultivar and ma- and ‘Shiro’. ferred partially ripe fruit as much as turity was significant (P = 0.04). For Hedonic scores for skin tartness tree-ripe. However, the stage of ma- ‘Methley’, tree-ripe fruit received varied with cultivar (P < 0.01) and turity affected consumer acceptance lower scores than partially ripe fruit. stage of maturity (P < 0.01) with in ‘Early Golden’ and ‘Vanier’, in Among partially ripe fruit, ‘Obilnya’ a significant interaction (P < 0.01). which tree-ripe were preferred over received the highest texture score, The effect of maturity was cultivar partially ripe fruit. followed by ‘Abundance’ and ‘Early dependent. Scores were similar for Hedonic scores for color varied Golden’. Scores for ‘Methley’, the two stages of maturity in most among cultivars (P < 0.01) and stage ‘Shiro’, and ‘Vanier’ were lower than cultivars, but in Early Golden and of maturity (P < 0.01) with a signifi- for ‘Obilnya’ and ‘Abundance’ but Vanier, tree-ripe fruit scored higher cant interaction (P < 0.01). The effect were similar to ‘Early Golden’. In than partially ripe fruit. Among par- of maturity was cultivar dependent. tree-ripe fruit, ‘Abundance’, ‘Early tially ripe fruit, ‘Abundance’ and ‘Early Golden’ harvested tree-ripe re- Golden’, ‘Obilnya’, ‘Spring Satin’, ‘Obilnya’ scored higher than other ceived a higher color score than when and ‘Vanier’ received higher scores cultivars. Among tree-ripe fruit, harvested partially ripe. However, for than ‘Methley’, whereas ‘Shiro’ re- ‘Methley’ and ‘Shiro’ scored lower other cultivars, color scores did not ceived intermediate scores that were than other cultivars. vary among partially ripe and tree-ripe. similar to ‘Vanier’ and ‘Methley’. Hedonic scores for overall ac- Among partially ripe fruit, ‘Obilnya’ Hedonic scores for sweetness ceptability varied with cultivar (P < received the highest score for color, varied with cultivar (P < 0.01) and 0.01) and stage of maturity (P < 0.01) which was greater than for ‘Abun- stage of maturity (P < 0.01) with with no interaction (P = 0.08). The dance’, ‘Early Golden’, ‘Shiro’, and a significant interaction (P < 0.01). effect of maturity not was cultivar ‘Vanier’. ‘Shiro’ received lower color The effect of maturity was cultivar dependent. Tree-ripe fruit received scores than other cultivars except Early dependent. Tree-ripe fruit of ‘Early higher scores than partially ripe fruit.
Table 2. Demographic characterization of the three-session consumer panels for plum cultivar evaluation in 2015 (n = 100, 84, and 100 for each of the three sessions, respectively) and 2016 (n = 98, 100, and 100). Proportion of total (%) Variable Response category 2015 2016 Gender Male 39.6 38.6 Female 60.0 61.4 Prefer not to say 0.4 0.0 Age in years 18–24 44.6 45.0 25–38 30.9 35.2 39–59 20.0 14.4 60+ 4.6 6.7 Frequency of plum consumption Never 7.4 6.7 1–4 times per year 54.4 56.4 1–2 times per month 31.2 25.8 1–2 times per week 6.3 9.7 3 or more times per week 0.7 1.6 Preference for plum size (diameter)z 1 inch 2.5 2.5 1.5 inches 37.0 43.0 2 inches 60.6 54.5 Response to ‘‘I often think about the health benefits Agree strongly 46.0 43.6 of foods before I choose to eat them.’’ Agree somewhat 45.9 50.9 Neither likely or unlikely 3.9 2.3 Somewhat unlikely 3.5 2.6 Very unlikely 0.7 0.6 z1 inch = 2.54 cm.
• April 2018 28(2) 233 VARIETY TRIALS
Hedonic scores for texture varied among cultivars, but did not differ greatly among asian, american, and european plums. ‘Kahinta’, which re- ceived the highest texture scores, was rated as highly as all cultivars except Shiro, which received the lowest rat- ing. Texture ratings of ‘Superior’, ‘Toka’, and ‘Cacxak’s Best’ were not significantly different from that of ‘Shiro’. Scores for sweetness varied among cultivars and not among plum types. Scores were lower for ‘Shiro’ and ‘Cacxak’s Best’ than for other cultivars. Hedonic scores for tartness were variable among cultivars but did not differ among types. ‘Obilnya’ had the highest hedonic score for tartness, followed by ‘Kahinta’, ‘Superior’, ‘Toka’, ‘Early Italian’, and ‘Rosy Gage’. Scores for ‘Shiro’ and ‘Cacxak’s Best’ were lower than that for other cultivars except for Castleton, which scored similarly as Cacxak’s Best. Scores for overall liking varied with the cultivar and the type of plum. Among cultivars, Cacxak’s Best and Shiro received lower scores than other cultivars. American plums generally scored higher than european and asian plums for overall liking with some exceptions such as the asian cultivar Obilnya, which scored as highly as all the american cultivars. FRUIT QUALITY INDICATORS. In Expt. 1, flesh firmness varied primar- ily with cultivar and with stage of maturity with no interaction (Table 3). Firmness was greater in partially ripe fruit than in tree-ripe. When har- vested partially ripe, ‘Obilnya’ and ‘Vanier’ had the firmest fruit and Fig. 1. Hedonic acceptability rating of color, texture, sweetness, sourness, and ‘Methley’ had the least firm. In tree- overall liking in one plum–apricot cultivar (Spring Satin) and six asian plum ripe fruit, ‘Obilnya’, ‘Spring Satin’, cultivars harvested at two stages of fruit maturity, partially ripe and tree-ripe, and ‘Vanier’ had the greatest firm- in 2015; 1 = dislike extremely and 9 = like extremely. Bars with the same letters ness, followed by ‘Abundance’, ‘Early are not statistically significant at P £ 0.05 by Tukey’s honestly significant difference; * indicates a significant difference between stage of maturity within Golden’, ‘Methley’, and ‘Shiro’ which a cultivar. had the lowest firmness. Soluble solids concentration var- ied with cultivar and stage of maturity Among partially ripe fruit, ‘Abundance for color as much as cultivar. Hedonic with a significant interaction. In and ‘Obilnya’ received the highest scores for color were higher for asian ‘Early Golden’, ‘Obilnya’, ‘Abun- scores, ‘Early Golden’ an intermediate and american plums than for european dance’, ‘Vanier’, and ‘Toka’, SSC score, and ‘Methley’, Shiro’, and plums except ‘Shiro’, which also had was higher in tree-ripe fruit compared ‘Vanier’ the lowest. Among tree-ripe the lowest score among asian plums. with partially ripe fruit. In contrast, fruit, ‘Methley’ and ‘Shiro’ scored ‘Obilnya’, ‘Superior’, ‘Kahinta’, and ‘Methley’ and ‘Shiro’ had higher SSC lower than other cultivars. ‘Toka’ did not differ in color hedonic in partially ripe fruit compared with In Expt. 2, the cultivar had score and scored higher than euro- tree-ripe. Among partially ripe fruit, a larger effect on hedonic scores than pean cultivars. Among european ‘Toka’ had the highest SSC, followed plum type for most traits (Fig. 2). plums, cultivars received similar scores by ‘Methley’ and ‘Obilnya’. ‘Vanier’ However, plum type affected preference for color. and ‘Abundance’ were intermediate
234 • April 2018 28(2) Among partially ripe fruit, ‘Early Golden’ and ‘Obilnya’ had greater MA than other cultivars. ‘Methley’ and ‘Vanier’ had lower MA than other cultivars harvested partially ripe. ‘Early Golden’ and ‘Obilnya’ had the greatest MA in tree-ripe fruit, followed by ‘Shiro’ and ‘Toka’. Malic acid was lowest in ‘Abundance’, ‘Methley’, and ‘Vanier’, and interme- diate in ‘Spring Satin’. In most cultivars, the ratio of SSC to MA was greater in tree-ripe than in partially ripe fruit. However, in ‘Methley’, both stages had similar ratios and in ‘Shiro’, the ratio was lower in tree-ripe than in partially ripe fruit. In partially ripe fruit, SSC:MA was greatest in ‘Vanier’ and ‘Toka’ and was lowest in ‘Early Golden’. In tree-ripe fruit, ‘Spring Satin’ had the greatest SSC:MA and ‘Early Golden’ had the lowest. In Expt. 2, flesh firmness varied among cultivars and among plum types (Table 4). Firmness was greatest in ‘Superior’ and ‘Castleton’, intermediate in ‘Kahinta’ and ‘Rosy Gage’, and lowest in ‘Obilnya’, ‘Shiro’, and ‘Toka’. Asian cultivars had lower firmness than american and european cultivars. Firm- ness was not measured in all cultivars because of the limited number of fruit available. Soluble solids concentration var- ied with the cultivar and with the plum type. European cultivars had higher SSC compared with asian and most american cultivars, but the american plum Toka had SSC that was as high as in most european cultivars. The other american plums, ‘Kahinta’ and ‘Superior’, had SSC that was intermediate to european and asian cultivars. ‘Early Italian’ had the highest SSC and ‘Shiro’ the lowest. Malic acid varied among cultivars and plum types. ‘Superior’ had similar MA as ‘Early Golden’ and ‘Kahinta’, Fig. 2. Hedonic acceptability rating of color, texture, sweetness, sourness, and but greater than that in other culti- overall liking in asian (As), american (Am), and european (E) plum cultivars vars. ‘Obilnya’, ‘Early Italian’, ‘Rosy harvested tree-ripe in 2016; 1 = dislike extremely and 9 = like extremely. Bars with Gage’, and ‘Toka’ had intermediate the same letters are not statistically significant at P £ 0.05 by Tukey’s honestly MA.‘Methley’,‘Shiro’,‘Cacxak’s significant difference. Best’, and ‘Castleton’ had the lowest MA. American plums had greater MA in SSC and ‘Early Golden’ and ‘Shiro’ Malic acid varied among cultivars than european plums, and asian were lowest. Among tree-ripe fruit, and stage of ripeness with a significant plums were intermediate to the other SSC was greatest in ‘Toka’ and interaction. In most cultivars, MA two types, but this was not consistent ‘Spring Satin’; intermediate in was similar in both stages of maturity. for every cultivar within a type. ‘Methley’, ‘Obilnya’, and ‘Vanier’; However, in ‘Abundance’, ‘Toka’, ‘Toka’, an american plum, had lower and lowest in ‘Abundance’, ‘Early and ‘Vanier’, partially ripe fruit had MA than some asian and european Golden’, and ‘Shiro’. greater MA than tree-ripe fruit. cultivars.
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Table 3. Fruit quality attributes of one plum–apricot (P–A), one american (Am), and six asian (As) plum cultivars harvested at two stages of maturity, partially ripe (PR) and tree-ripe (TR), in 2015. Firmness (lbf)z SSC (%) MA (%) SSC:MA (ratio) Cultivar Type PR TR PR TR PR TR PR TR Abundancey As 3.0 abcx 2.1 abc* 9.6 de 9.9 f* 1.3 d 1.1 d* 7.2 8.8 Early Golden As 2.2 cd 1.3 bc* 8.9 f 9.4 g* 2.1 a 2.0 a 4.2 4.8 Methley As 1.4 d 0.7 c* 10.9 b 10.4 e* 1.3 d 1.2 cd 8.4 8.5 Obilnya As 4.2 a 2.5 ab* 10.6 c 11.5 c* 2.1 a 2.1 a 5.1 5.6 Shiro As 2.6 bcd 1.6 bc* 9.5 e 9.1 h* 1.6 b 1.7 b 5.9 5.4 Spring Satin P–A — 2.9 ab — 13.2 b — 1.3 c — 10.0 Toka Am — — 13.8 a 14.5 a* 1.7 b 1.6 b* 8.2 9.3 Vanier As 3.9 ab 3.3 a* 9.8 d 10.7 d* 1.5 c 1.1 d* 6.4 9.6 ANOVA P values for type III sums of squares Cultivar (C) <0.01 <0.01 <0.01 Maturity (M) <0.01 <0.01 <0.01 C · M 0.71 <0.01 <0.01 z1 lbf = 4.4482 N. y‘Abundance’ was purchased from a nearby farm in Fairfield, ME, but other cultivars were grown at the research farm in Monmouth, ME. xMeans separation within columns by Tukey’s honestly significant difference. Means followed by the same letter are not significant. *Indicates a significant effect of maturity stage within a cultivar. SSC = soluble solids concentration; MA = malic acid.
Table 4. Fruit quality attributes of asian (As), american (Am), and european (E) to very much. Most of the european plum cultivars harvested at the tree-ripe stage of maturity in 2016. and american cultivars also scored Cultivar Type Firmness (lbf)z SSC (%) MA (%) SSC:MA (ratio) near 7.0, indicating that consumers did not prefer one type more than Early Golden As — 10.6 j 2.0 ab 5.3 another and that cultivar had a greater Methley As — 11.7 i 1.4 e 8.7 impact on overall liking than plum y Obilnya As 2.2 c 13.6 h 1.9 bc 7.0 type. Shiro As 0.9 d 6.7 k 1.3 ef 5.1 In previous studies, hedonic Kahinta Am 3.8 ab 14.8 g 2.0 ab 7.3 scores for plums ranged from 3.3 to Superior Am 5.0 a 15.7 e 2.1 a 7.5 7.8 depending on cultivar, quality, Toka Am 1.8 cd 19.8 b 1.6 d 12.3 and stage of maturity (Crisosto x Cacak’s Best E — 15.3 f 1.0 g 15.2 et al., 2004; Meredith et al., 1992; Castleton E 5.0 a 17.3 d 1.2 f 14.0 Minas et al., 2013; Okie, 2005). The x Early Italian E — 22.1 a 1.9 c 11.8 fruit tested in this study were har- Rosy Gage E 3.3 bc 19.5 c 1.7 d 11.6 vested partially ripe and tree-ripe, < < < P value 0.01 0.01 0.01 — which may be the reason for mean Type overall scores being 5.0 or above. Asian 1.6 b 10.6 b 1.6 ab 6.5 Harvest at an earlier stage of maturity American 3.5 a 16.8 a 1.9 a 9.0 would likely have caused a greater European 4.2 a 18.5 a 1.4 b 18.2 disparity in consumer ratings. The < < < P value 0.01 0.01 0.01 — difference in maturity between the z1 lbf = 4.4482 N. two stages was relatively small, and yMeans separation within cultivar and within type by Tukey’s honestly significant difference. Means followed by the same letter within cultivar or within type are not significant. in a few cases, MA was not signifi- x‘Early Italian’ was purchased from a supermarket in Orono, ME, the same day as testing. Other cultivars were cantly different between the two grown at the research farm in Monmouth, ME. stages. The high scores for partially SSC = soluble solids concentration; MA = malic acid. ripe fruit in most cultivars indicate that producers can harvest fruit be- The ratios of SSC to MA were the northeastern United States and fore full ripeness to extend shelf life. A greatest in european plums except for Canada for local marketing. These shelf test was not included in this ‘Toka’ which had a ratio similar to two cultivars scored 6.0 or below for study but could affect consumer european cultivars. The ratio of SSC overall liking, indicating that con- acceptance. to MA was lowest in ‘Shiro’ and ‘Early sumers neither liked nor disliked them Plum types differed in fruit qual- Golden’, and was highest in ‘Cacxak’s or liked them slightly. The only other ity attributes. American cultivars gen- Best’. cultivar to score as low was Cacxak’s erally had greater SSC than asian Best, which was included because of its cultivars and were likely rated higher Discussion unpleasant aftertaste that made it an than expected because of this. Euro- Most of the cultivars in this study example of an unacceptable cultivar. By pean plums also had higher SSC than received consumer acceptance scores contrast, ‘Spring Satin’ and ‘Obilnya’ asian plums, which has been previ- that were higher than Methley and scored above 7.0, indicating that ously reported (Sahamishirazi et al., Shiro, two cultivars that are grown in consumers liked them moderately 2017; Usenik et al., 2008). It is not
236 • April 2018 28(2) clear why european plums received because Shiro would have been lower scores for color but could be underripe and Obilnya would have Literature cited due to the dark or dull appearance of been overripe if each had been har- Abdi, N., P. Holford, and W.B. McGlasson. the flesh. vested according to one standard 1997. Effects of harvest maturity on the Greater consumer acceptance firmness value. The low texture scores storage life of japanese plums. Austral. J. has been associated with a greater for ‘Toka’ were possibly because of Expt. Agr. 37:391–397. SSC:MA (Crisosto et al., 2003; mealy texture and peel thickness. Bae, H., S.K. Yun, J.H. Jun, I.K. Yoon, Guerra et al., 2010; Robertson However, these traits were not directly E.Y. Nam, and J.H. Kwon. 2014. Assess- et al., 1992; Usenik et al., 2014). measured by the untrained consumer ment of organic acid and sugar composi- However, this did not occur in our panel. tion in apricot, plumcot, plum and peach study in which SSC:MA was 14.0 in Additional qualities such as bit- during fruit development. J. Appl. Bot. ‘Castleton’ and 4.2 in ‘Early Golden’, terness, astringency, off-flavors, and Food Qual. 87:24–29. both of which received similar accept- aroma also play an important role in Boyhan, G.E., J.D. Norton, M.H. ability scores. ‘Cacxak’s Best’ had the consumer acceptance (Crisosto et al., Hollingsworth, J.A. Pitts, J.B. Witt, highest SSC:MA ratio but scored 2006; Guerra et al., 2010; Robertson H.W.Ivey,andJ.T.Owen.1996.Plum lower because of its aftertaste. In et al., 1992; Usenik et al., 2014) but variety trials in Alabama 1986–1995. Ala- plums, previous research indicates were not measured because of the bama Agr. Expt. Sta. Bul. 628. that SSC:MA can vary from 5.4 to constraints of an untrained consumer Candan, A.P., J. Graell, and C. 20.8 among many different cultivars testing population. Astringency of Larrigaudiere. 2008. Roles of climacteric (Lozano et al., 2009; Robertson the skin was not included in the ethylene in the development of chilling et al., 1992; Usenik et al., 2008) sensory questioning but may have injury in plums. Postharvest Biol. Tech- and from 13.2 to 37.5 in ‘Black been a factor in consumer acceptance nol. 47:107–112. Amber’ harvested at several stages of of some of the cultivars, particularly Chauvin, M.A., M. Whiting, and C.F. maturity (Crisosto et al., 2004), Vanier, and may have been a factor in Ross. 2009. The influence of harvest time a range two to four times as large as consumer rating of skin tartness. on sensory properties and consumer ac- what occurred in our study. The Aroma may be important to con- ceptance of sweet cherries. HortTech- lower SSC:MA in our study could sumer acceptance, particularly with nology 19:748–754. also be due to higher MA, a possible cultivars such as Early Golden and effect of the cool growing conditions of Toka. Plums are not considered to Cooley, D., W. Autio, D. Greene, J. be highly aromatic (Gomez and Clements, M. Conklin, T. Bradshaw, H. Maine compared with regions that are Faubert, G. Koehler, R. Moran, and G. warmer, such as California (Crisosto Ledbetter, 1994), but this may be ı Hamilton. 2015. 2015 New England tree et al., 2004) and Spain (D az-Mula because of the harvest and storage fruit management guide. Cornell Univ., et al., 2009). In addition, it is possible practices that lengthen shelf life. The Ithaca, NY. that flavor and aroma in these cultivars greater development of flavor and were more developed than in fruit that aroma in these cultivars that resulted Corollaro, M.L., F. Gasperi, and L.C. have undergone more substantial trans- from harvest at advanced maturity Grappadelli. 2014. An overview of sen- sory quality of apple fruit. J. Amer. Pomol. port or storage periods, and this may and testing soon after harvest was Soc. 68:141–157. have influenced consumer liking to likely an important factor contribut- a greater extent than SSC:TA. ing to consumer acceptance. For mar- Crisosto, C.H. 1994. Stone fruit maturity Texture is an important determi- kets that do not require harvest at an indices: A descriptive review. Postharvest nant in consumer acceptance but is early stage of maturity, selection of News Info. 5(6):65–68. typically indirectly measured as firm- cultivars with more complex flavors Crisosto, C.H., G.M. Crisosto, and E. ness. Plums are considered too soft may enhance consumer acceptance Bowerman. 2003. Understanding con- when firmness decreases to below 1 and increase plum consumption. sumer acceptance of peach, nectarine lbf (Robertson et al., 1992). This was American and european plums and plum cultivars. Acta Hort. 604: apparent in the case of ‘Methley’ and are relatively unknown to growers 115–119. ‘Shiro’, which received the lowest and consumers but have greater cold Crisosto, C.H., D. Garner, G.M. Crisosto, ratings for texture and had tree-ripe temperature tolerance than asian and E. Bowerman. 2004. Increasing firmness below 1 lbf. It was not clear if plums and would allow growers in ‘Blackamber’ plum (Prunus salicina Lindell) consumers had an upper limit for colder regions to produce locally consumer acceptance. Postharvest Biol. firmness preference because ‘Obilnya’ grown plums. As selection of fruit Technol. 34:237–244. and ‘Kahinta’ received high scores for cultivars becomes based on consumer Crisosto, C.H., G.M. Crisosto, and F. texture despite having firmness above acceptance, Shiro and Methley may Neri. 2006. Understanding tree fruit 3 lbf. However, flesh firmness at become less important in plum pro- quality based on consumer acceptance. optimum maturity varies with culti- duction in colder regions, although Acta Hort. 712:183–190. var, which prevents the use of one plums are currently a minor fruit crop ı standard for every cultivar (Crisosto, in northeast United States and Can- D az-Mula, H.M., P.J. Zapata, F. Guillen, D. Martınez-Romero, S. Castillo, M. 1994). This was the case in this study ada. Expansion of the local market Serrano, and D. Valero. 2009. Changes in in which flesh firmness varied by may be possible by growing cultivars hydrophilic and lipophilic antioxidant ac- cultivar from 1.4 to 4.2 lbf at the such as Obilnya, Abundance, Spring tivity and related bioactive compounds partially ripe stage and 0.7–3.3 lbf in Satin, Toka, Superior, Kahinta, Rosy during postharvest storage of yellow and tree-ripe fruit. The same standard Gage, and Castleton, as well as other purple plum cultivars. Postharvest Biol. could not be used for every cultivar cultivars not tested in this study. Technol. 51:354–363.
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Fajt, N. and V. Usenik. 2010. Plum cul- Meredith, F.I., S.D. Senter, W.R. Forbus, 1992. Physical, chemical and sensory tivar testing in the western part of Slov- Jr., and J.A. Robertson. 1992. Post- characteristics of japanese-type plums enia. 2010. Acta Hort. 874:275–280. harvest quality and sensory attributes of grown in Georgia and Alabama. J. Sci. ‘Byrongold’ and ‘Rubysweet’ plums. J. Food Agr. 60:339–347. Gilbert, J.L., J. Olmstead, T. Coluquhoun, Food Qual. 15:199–209. L. Levin, D. Clark, and H. Moskowitz. Sahamishirazi, S., J. Moehring, W. Claupein, 2014. Consumer-assisted selection of Minas, I.S., G.M. Crisosto, D. Holcroft, and S. Graeff-Hoenninger. 2017. Quality blueberry fruit quality traits. HortScience M. Vasilakakis, and C.H. Crisosto. 2013. assessment of 178 cultivars regarding 49:864–873. Postharvest handling of plums (Prunus phenolic, anthocyanin and sugar content. salicina Lindl.) at 10 C to save energy and Food Chem. 214:694–701. Gomez, E. and C. Ledbetter. 1994. preserve fruit quality using an innovative Comparative study of the aromatic pro- application system of 1-MCP. Postharvest Singh, S.P. and Z. Singh. 2008. Postharvest files of two different plum species: Prunus Biol. Technol. 76:1–9. oxidative behavior of 1-methylcyclopropene salicina Lindl. and Punus simonii L. J. Sci. treated japanese plums (Prunus salicina Food Agr. 65:111–115. Norton, J.D., T.L. Kamps, and T.E. Lindell) during storage under controlled Guerra, M., M.A. Sanz, and P.A. Casquero. Conaty. 1987. New plums for the south. and modified atmospheres. Postharvest 2010. Influence of harvest dates on quality, Proc. 7th Annu. Mtg. Shortcourse. Alabama Biol. Technol. 74:26–35. Fruit Veg. Growers Assn., Auburn, AL. storage capacity and sensory attributes of Stone, H., R. Bleibaum, and H.A. p. 65–78. european plum cv. Green Gage. Food Sci. Thomas. 2012. Sensory evaluation prac- Technol. Intl. 15:527–534. Okie, W.R. and D.W. Ramming. 1999. tices. 4th ed. Elsevier, Waageningen, The Hansen, H.E. 1915. Progress in plant Plum breeding worldwide. HortTech- Netherlands. nology 9:162–176. breeding. South Dakota Agr. Expt. Sta. U.S. Department of Agriculture. 2017. Bul. 159. Okie, W.R. 2005. ‘Spring Satin’ plumcot. Food availability. 1 Feb. 2017.
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