Postharvest Color Changes in Red Rose Petals1
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Proc. Fla. State Hort. Soc. 9^:137-139. 1985. POSTHARVEST COLOR CHANGES IN RED ROSE PETALS1 F. J. Marousky and T. C. Carlyle (6) used a Hunter Color-Color Difference Meter (HCCD) U.S. Department of Agriculture to measure rose petal color. Marousky (7) used a HCCD Agriculture Research Service to measure poinsettia bract color. These workers reported Gainesville, FL 32611 the HCCD has the advantage of discerning subtle color differences not perceptible to the human eye. Additional index words. Rosa hybrida, floral preservative, 8- The objective of this study was to determine the color hydroxyquinoline citrate, sucrose, colorimeter, an change in petals of aging cut red roses held in water or a thocyanin. sucrose based floral preservative. Abstract. Cut 'Better Times' roses (Rosa hybridal.) were har Methods and Materials vested in the bud stage and held with stem ends in water or Freshly harvested 'Better Times' roses (Rosa hybrida) a floral preservative (200 mg 8-hydroxyguinaline citrate plus were obtained from a commercial grower. Individual sep 20 g sucrose). Color, anthocyanin, pH, and area of petals als were just beginning to reflex away from the flower bud. were determined initially and after 3 days. A Hunter Color- Flowers were brought to the laboratory shortly after har Color difference meter was used to objectively measure petal vest, trimmed and placed in water (deionized) or floral color. Petals on stems held in preservative turned blue, but preservative (200 mg 8-hydroxyqinoline citrate plus 20 g not as intensely as petals on stems held in water. An sucrose/liter). Each flower was held in an individual con thocyanin concentration in aging petals did not change from tainer. There were 6 flowers (each considered as a replica initial levels. Petal color variations were due to internal tion) per treatment. Flowers were held at 26°C under 150 physiological changes and petal expansion, not to an ft-c irradiance supplied by cool-white fluorescent tubes for thocyanin concentrations. 'Cara Mia' and 'Forever Yours' red 12 hr each day. Relative humidity was not controlled but roses did not blue when held in water. Flowers held in preser varied from 60 to 80%. Petal color was measured on a vative had less red saturated petals than petals from fresh Hunter Color-Color Difference Meter (HCCD) as outlined flowers or from flowers held in water. by Marousky (7). A thin black cardboard with an opening 3 cm in diameter was centered over the large sample open Petal bluing is regarded as a characteristic of deteriora ing and the instrument was standardized with a white tile tion in cut red roses (4). Weinstein (13) suggested that petal (L = 94.9, a = -1.2, b = +2.2). One of the 3 most abaxial bluing was due to pH increase resulting from increased petals was randomly selected and the adaxial surface was free cellular ammonia accompanying proteolysis. Weins placed on the circular opening and covered with a black tein showed petal glucose was depleted in 66 hr and cardboard. This same petal was used for area and an suggested amino acids were preferentially utilized as a re thocyanin determinations. Petal area was determined on a spiratory substrate. The increase in ammonia coincided Licor Model LI-3000 leaf area meter. Individual petals with the respiratory loss of free amino acids. Kuc (5) were placed in 20 ml methanol containing 1% HCL and showed rose petals remained red when ammonia levels re refrigerated overnight. Eluted anthocyanin solutions were mained below the equivalency of organic acid levels, but poured into a 25-ml volumetric flask and brought up to rose petals turned blue when ammonia levels exceeded the volume. This dilution was read directly on a spec- acid equivalency level. Asen et al (2) showed bluing in red trophotometer set at 525 nm. Petal pH was determined rose petals was due to a copigment complex of cyanidin similar to the method used by Coorts et al (3). One of the 3,5 diglucoside and quercetin and kampferol glycosides. 3 most abaxial petals was placed in a Waring blendor with They showed high anthocyanin concentration and copig 10 ml deionized water and macerated for 1 min. The pH ment phenomenon were affected by slight changes in pH. of the slurry was determined. Data were collected initially Many workers have reported carbohydrate based pre and after flowers had aged for 3 days. servatives prevented petal bluing (2, 3, 8, 10, 11). Stoltz 'Cara Mia' and 'Forever Yours' were obtained from a (11) showed petals did not blue or become deficient in commecial grower and handled similarly as 'Better Times' carbohydrates when preservatives containing glucose or roses. Color data were collected for these 2 cultivars. Sam sucrose were used. He hypothesized that protein hydro ples of petal tissue (1-cm diameter discs) were removed lysis occurred only under conditions of carbohydrate star from 'Forever Yours' roses and fixed overnight in FAA (5 vation and preservatives prevented carbohydrate depletion ml formalin, 5 ml glacial acetic acid, and 90 ml 50% or substituted for naturally occurring carbohydrates. ethanol). Tissue was dehydrated in an alcohol series and Much of the work describing bluing of red rose petals subjected to critical point drying. Tissue was sputter coated has been evaluated visually. Visual color acuity is very sub with gold, viewed, and photographed in a Cambridge jective and is dependent on the psychological attitude of Scanning Electron Microscope. the observer and the light source. Lindstrom and Markakis Results and Discussion 'Mention of a trademark, warranty, proprietary product, or vendor does not constitute a guarantee by the U.S. Department of Agriculture Petals from freshly harvested 'Better Times' roses had and does not imply its approval to the exclusion of other products or a slightly bluish caste (Table 1). These results are similar vendors that may also be suitable. 2Research accomplished cooperatively with Department of Ornamen to those reported by Lindstrom and Markakis (6). 'Better tal Horticulture, IFAS, Univ. of Florida, Gainesville, FL. Times' roses held and aged in water for 3 days had petals Proc. Fla. State Hort. Soc. 98: 1985. 137 Table 1. Hunter Color values, area, anthocyanin and pH of petals of 'Better Times' roses held in water and floral preservatives for 3 days. Hunter color values Area Treatments L a b (cm) Anthocyaniny PH Initial 29.7az +51.2c - 1.9a 15.1a 135a 5.11a After 3 days in: Water 33.3a +38.1a -12.9c 18.4b 133a 5.51c Preservativex 33.2a +45.5b - 6.8b 21.5c 128a 5.23b zMean separation within columns by Duncan's multiple range test, 5% level. yOptical density x 103. x200 mg 8-hydroxyquinoline citrate plus 20g sucrose/liter. which were more saturated in blue (-b value) and less satu in water for 3 days increased in area but not to the same rated in red (a value). Petals from roses held in preserva extent as petals from roses held in preservative (Table 1). tive were light red but were bluer than petals from fresh Since reflectance of red rose petals is closely related to roses. However, petals from roses aged in preservative anthocyanin concentration per area (5), decreased petal were not as blue as petals from roses aged in water. redness of roses held in preservative was due to petal ex Petals of 'Better Times' roses aged in water or preserva pansion and not to a loss of anthocyanin. The geometry of tive contained similar levels of anthocyanin as fresh petals the rose petal epidermal cells could change light reflec (Table 1). Ahuja et al (1) reported that cyanin in outer tance. Sacalis (9) showed sucrose induced a "balloon" effect petals of 'Happiness' and 'Pink Coronet' decreased as flow to rose petal epidermal cells. Our work shows rose petals ers opened and expressed pigment concentrations as in preservative expanded more than those in water (Table amount per unit fresh weight. They suggested cell enlarge 1). This expansion was also observed at the cellular level. ment during flower opening probably reduced the number (Fig. la, lb). The "balloon" effect was apparent on petals of cells per unit weight. Weinstein (13) and Yasuda (12) from roses held in preservative but not on those in water. indicated anthocyanin concentration in flowers was best The abaxial surface of rose petals (Fig. 2) had a different expressed as amount per unit area. Petals from roses held configuration and would have different color values on the HCCD, but no measurements were made. The high degree of bluing in rose petals held in water or preservative is due in part to the increase in pH (Table 1) Aging petals on cut red roses rapidly increased in am monia (5, 11, 13). The increase in ammonia was due to proteolysis. The free ammonia increased cellular pH lead ing to a bluing of the anthocyanin pigment. Asen et al (2) reported cyanidin 3,5, diglycoside was colorless at pH 4 to 5. However as cyanin complexes with quercitin derivatives and the pH increased, the spectrum shifted into the blue range. Fig. 1. Scanning electron micrographs of adaxial petal surfaces of Fig. 2. Scanning electron micrograph of abaxial petal surface of 'Forever Yours' roses a) held in water, b) held in floral preservative 'Forever Yours'. (2300x mag). 138 Proc. Fla. State Hort. Soc. 98: 1985. Table 2. Hunter color values of petals of 'Cara Mia' and 'Forever Yours* Literature Cited roses held for 3 days in water and floral preservatives. Ahuja, K. G., H. L. Mitchell, and W. J. Carpenter 1963. Quantitative Hunter color values determination of anthocyanidin from petals of rose cultivars 'Pink Coronet' and 'Happiness.' Proc.