Light is important in the production of phenolic compounds because key enzymes in phenolic biosynthesis are induced by light, and because products of photosynthesis are used in the synthesis of phenolic compounds. It is known that light intensity decreases with increasing depth in apple tree canopies. The objective of this experiment was to determine how leaf position on a limb affects the total foliar phenolic content. Leaves from `Stark Spur Supreme Red Delicious' on C6 and M26 rootstocks were collected on 28 July and 2 Aug. 1996. Each tree was divided into two sides, east and west. Each side was divided into 3 areas; exterior, middle, and interior. From each area, leaves were collected and PAR, SLW, assimilation, total N, and total phenolics were measured. Leaf position on a limb was a significant parameter for all of the measured variables. PAR, SLW, assimilation, total N, and total phenolics were highest in leaves at the exterior of the canopy. The total foliar phenolic content of the exterior canopy leaves was 20% higher than that found in the interior canopy leaves. There was a significant correlation between SLW and total phenolic content/cm2(r 2 = 0.77; P < 0.05). Assimilation may be a limiting factor in phenolics production in apple trees because of the correlation between assimilation and total phenolic content/cm2 (r2=0.56, P < 0.05).
M. Elena Garcia, C.R. Rom, J.B. Murphy and K. Kugler
Justine E. Vanden Heuvel*, Jessica L. Robidoux and Catherine C. Neto
Carbon supply reduction was used to investigate the relationship between total non-structural carbohydrate (TNSC) concentration in the vegetative tissue and the production of phenolic compounds in the fruit of grapevines. Potted, greenhouse-grown DeChaunac vines were partially defoliated on one of three dates (berry set, veraison, or 7 days pre-harvest) during the growing season. Light environment of the fruit clusters was not affected by defoliation. Seven days following defoliation, half of the vines were destructively harvested for carbohydrate analysis, while the remaining vines were kept for fruit analysis at maturity. Defoliation of vines at berry set and veraison significantly reduced TNSC concentration in the leaf tissue. Partial defoliation of vines at berry set reduced total flavonols by 24%, total anthocyanins by 33%, and total phenolics by 13% in the fruit compared to the control vines. At veraison, partial defoliation of vines reduced total flavonols by 8%, anthocyanins by 43%, and did not affect total phenolics. While flavonol and total phenolic content was not affected by defoliation 7 days prior to harvest, total anthocyanins were increased by 39%, although leaf TNSC concentration was not affected. Concentration of total flavonols and anthocyanins were positively correlated with TNSC in the leaves (r = 0.53 and r = 0.73, respectively) while total phenolic content was not correlated with TNSC. These results indicate that development of anthocyanins and flavonols in fruit is linked to carbohydrate availability from vegetative tissues during berry set and veraison.
Kim E. Hummer
analysis. Ellagic acid was present as free and glycosylated forms and ellagitannins; other reportedly anticarcinogenic compounds were also present. Table 2. Total anthocyanin (ACY), berry count, and total phenolics (TPH) of blueberries, black currants
A.R. Gonzalez, T. Wang, D.J. Makus and A. Mauromoustakos
Respiration and quality changes were measured in white and green asparagus stored at 20°C. Green asparagus had a higher respiration rate and weight loss than white. Respiration rates decreased and stabilized after 2 days storage in both green and white asparagus. Total phenolics and pulp pH were higher in green than in white asparagus. No significant difference was observed in titratable acidity. Total phenolics and pH decreased while titratable acidity increased during storage of both types of asparagus. Ascorbic acid levels were higher in green spears but soluble solids were higher in white spears. Both ascorbic acid and soluble solids decline during storage. Total chlorophyll content of green asparagus decreased during storage. White asparagus had little chlorophyll. Green color, measured by CDM –a values, followed the same pattern as total chlorophyll.
M.S. Padda and D.H. Picha
Sweetpotatoes may be potentially high in concentration of certain phytochemical compounds, including phenolics. Low temperature stress-induced phenolic compounds may enhance the nutraceutical value of sweetpotatoes. However, extended exposure to low temperature results in chilling injury. Cured and non-cured roots of `Beauregard' sweetpotatoes were exposed to low temperature storage (5 °C) for up to 4 weeks. The total phenolics and individual phenolic acid contents were determined at weekly intervals using Folin-Denis reagent and reversed-phase HPLC, respectively. Total phenolics and individual phenolic acids increased with length of low temperature exposure. Non-cured roots had a higher phenolic content than cured roots after 4 weeks. A 3-day exposure period to room temperature (22 °C) following removal from low temperature storage typically resulted in increased phenolics. In a comparison of different tissue locations, the highest phenolic content was found in peel tissue and the lowest in the pith tissue. The major individual phenolic acid in all root tissues was chlorogenic acid.
Shiow Wang* and Wei Zheng
The effects of preharvest methyl jasmonate (MJ) application on fruit quality, flavonoid content and antioxidant capacity (ORAC) in black raspberry cv. Jewel (Rubus occidentalis L) were studied under field conditions. Raspberries treated with 0.1 mm methyl jasmonate had 20% higher soluble solids content, 20% higher total sugars, 16% higher fructose, 34% higher glucose and 30% lower titratable acids, 31% lower malic acid and 17% lower citric acid than untreated fruit. El-lagic acid, quercetin 3-glucoside, kaempferol 3-glucoside, kaempferol 3-glucuronide, cyanidin 3-glucoside and cyaniding 3-rutinoside were found in raspberry fruit extract. Cyanidin 3-rutinoside was the most dominant anthocyanin and was the major contributor to antioxidant activity in Jewel raspberries. MJ treatments significantly enhanced the content of anthocyanins by 92%, total phenolics by 53%, flavonoids by 98% and the antioxidant capacities by 74% in the fruit. The ORAC value was positively correlated with anthocyanins and total phenolics. In this study, the correlation coefficient for ORAC (y) vs anthocyanins (x) was 0.977 (y = 0.056x + 27.874), and that for ORAC (y) vs. total phenolics (x) was 0.988.
Teddy Morelock*, Luke Howard and J. Brad Murphy
Spinach (Spinacia oleracea L.) is a highly nutritious leafy green vegetable that contains high levels of vitamins A, C, E and folate as well as minerals such as iron and calcium. Spinach is high in carotenoids, specifically lutein and β-carotene. Spinach has also been shown to have high ORAC (oxygen radical absorbency capacity) values and to have a high total flavonoids content (100 mg·kg-1). Leaves were collected from 11 commercial cultivars and 15 advanced breeding lines which were grown at the Univ. of Arkansas vegetable substation near Kibler, Arkansas. Samples were placed in polyethylene bags in ice chests and transported to the Univ. of Arkansas within 2 hours and samples were stored at -20 °C until analysis were performed. Both growing season and genotype had an effect on both ORAC and total phenolics. Over-winter spinach, which is planted in the fall and harvested in the spring, had higher total phenolics as well as higher ORAC than fall-planted fall-harvested spinach. Univ. of Arkansas breeding lines had higher average levels of total phenolics and ORAC than commercial cultivars. These data indicate that it should be possible to breed for higher antioxidant capacity in spinach. In a separate study involving the same cultivars wide variation in lutein content was observed with the cultivars F380 and Fallgreen having the highest levels. Data indicate wide variation in lutein and that breeding for increased lutein content is possible.
M.S. Padda and D.H. Picha
Antioxidant activity and phenolic content in sweetpotato root and leaf tissues were quantified at different developmental stages. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical method was used to measure antioxidant activity and total phenolic content was quantified by spectrophotometry using Folin-Denis reagent. Individual phenolic acids were quantified using reversed phase high performance liquid chromatography. Antioxidant activity and phenolic content decreased with root development and leaf maturity. Roots at the initial stages of development (about 4 g root weight) had a higher antioxidant activity and phenolic content compared to fully developed roots. Phenolic content in fully developed roots was significantly higher in the cortex tissue than internal pith tissue. The highest total phenolic content and antioxidant activity was found in cortex tissue at the initial stage of development (10.3 mg chlorogenic acid eq/g dry tissue weight and 9.7 mg Trolox eq/gdry tissue weight, respectively). Sweetpotato leaves had a significantly higher phenolic content and antioxidant activity than roots. Immature unfolded leaves had the highest total phenolic content (88.5 mg chlorogenic acid eq/g dry tissue weight) and antioxidant activity (99.6 mg Trolox eq/g dry tissue weight). Chlorogenic acid was the major phenolic acid in root and leaf tissues with the exception of young immature leaves in which the predominant phenolic acid was 3,5-dicaffeoylquinic acid.
Malkeet S. Padda and David H. Picha
Three different style cuts of minimally processed sweetpotatoes (shredded, French-fry, and sliced) were stored at 0 °C and 5 °C for 4 and 8 days. Total phenolic content, individual phenolic acids, and free radical scavenging activity were determined using Folin-Denis reagent, reversed-phase HPLC, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) methods, respectively. Total phenolic content in sliced cut sweetpotatoes held at 5 °C was higher than in the shredded cut. Both sliced and French-fry cut sweetpotatoes held at 5 °C had significantly higher antioxidant activity than shredded cut sweetpotatoes. All treatments, except shredded sweetpotatoes held at 0 °C, had significantly higher total phenolic content and antioxidant activity after 4 and 8 days of storage. Minimally processed sweetpotatoes held at 5 °C accumulated more phenolic compounds and had a higher antioxidant activity than sweetpotatoes held at 0 °C. Chlorogenic acid followed by 3,5-dicaffeoylquinic acid were the predominant phenolic acids present in sweetpotatoes. The rate of increase in individual phenolic acid content with storage time was higher at 5 °C than at 0 °C. No tissue browning was observed in any of the cuts after 8 days of storage and the products were considered to be marketable.
M.S. Padda and D. H. Picha
Phenolic acids are one of several classes of naturally occurring antioxidant compounds found in sweetpotato. Simplified but reliable methodologies were developed to quantitate total and individual phenolic acids in sweetpotato roots. Total phenolic acid content was measured using both Folin-Denis and Folin-Ciocalteu reagents. The Folin-Ciocalteu reagent gave an overestimation of total phenolic acids due to the absorbance of interfering compounds (i.e., reducing sugars and ascorbic acid). The average total phenolic acid content in `Beauregard' sweetpotatoes was 60.9 mg/100 g fresh weight. Individual phenolic acids were separated with two reversed-phase C18 columns of different dimensions and particle size. The columns tested were a 7 × 53 mm, 3 μm, Alltima Rocket (Alltech Assoc.) and a 3.9 × 150mm, 4 μm, Nova-Pak (Waters Corp.). Different mobile phases were also evaluated. The Alltima C18 column using a mobile phase of 1% (v/v) formic acid aqueous solution: acetonitrile: 2-propanol, pH 2.5 (70:22:8) provided the best separation of individual phenolic acids. Total analysis time was less than 5 minutes. Chlorogenic acid was the major phenolic acid found in sweetpotato root tissue (15.8 mg/100 g fresh weight). In a comparison of different tissue preparation states (fresh, frozen, freeze-dried), fresh tissue gave the highest concentration of total and individual phenolic acids. Among the 3 extraction solvents tested (80% methanol, 80% ethanol, and 80% acetone), 80% methanol and 80% ethanol gave higher, but similar, phenolic acid extraction efficiency.