Jayasankar Subramanian

Complex formation of blueberry (Vaccinium angustifolium) anthocyanins during freeze-drying and its influence on their biological activity.

Biological activity of polyphenols is influenced by their uptake and is highly influenced by their interactions with the food matrix. This study evaluated the complex formation of blueberry polyphenols with fruit matrixes such as pectin and cellulose and their effect on the biological and antiproliferative properties of human colon cell lines HT-29 and CRL 1790. Free or complexed polyphenols were isolated by dialyzing aqueous or methanolic blueberry homogenates. Seven phenolic compounds and thirteen anthocyanins were identified in blueberry extracts. Blueberry extracts showed varying degrees of antioxidant and antiproliferative activities, as well as α-glucosidase activity. Fruit matrix containing cellulose and pectin, or purified polygalacturonic acid and cellulose, did not retain polyphenols and showed very low antioxidant or antiproliferative activities. These findings suggest that interactions between polyphenols and the food matrix may be more complex than a simple association and may play an important role in the bioefficacy of blueberry polyphenols.

Upregulation of Phosphatidylinositol 3-Kinase (PI3K) Enhances Ethylene Biosynthesis and Accelerates Flower Senescence in Transgenic Nicotiana tabacum L.

Phosphatidylinositol 3-kinase (PI3K) is a key enzyme that phosphorylates phosphatidylinositol at 3’-hydroxyl position of the inositol head group initiating the generation of several phosphorylated phosphatidylinositols, collectively referred to as phosphoinositides. The function of PI3K in plant senescence and ethylene signal transduction process was studied by expression of Solanum lycopersicum PI3K in transgenic Nicotiana tabacum, and delineating its effect on flower senescence. Detached flowers of transgenic tobacco plants with overexpressed Sl-PI3K (OX) displayed accelerated senescence and reduced longevity, when compared to the flowers of wild type plants. Flowers from PI3K-overexpressing plants showed enhanced ethylene production and upregulated expression of 1-aminocyclopropane-1-carboxylic acid oxidase 1 (ACO1). Real time polymerase chain reaction (PCR) analysis showed that PI3K was expressed at a higher level in OX flowers than in the control. Seedlings of OX-lines also demonstrated a triple response phenotype with characteristic exaggerated apical hook, shorter hypocotyls and increased sensitivity to 1-aminocyclopropane-1-carboxylate than the control wild type seedlings. In floral tissue from OX-lines, Solanum lycopersicum phosphatidylinositol 3-kinase green fluorescent protein (PI3K-GFP) chimera protein was localized primarily in stomata, potentially in cytoplasm and membrane adjacent to stomatal pores in the guard cells. Immunoblot analysis of PI3K expression in OX lines demonstrated increased protein level compared to the control. Results of the present study suggest that PI3K plays a crucial role in senescence by enhancing ethylene biosynthesis and signaling.

Investigation of Antioxidant Content and Capacity in Yellow European Plums

ABSTRACT Phenolic content and antioxidant capacity of five Yellow European plums (Prunus domestica) were studied using heat reflux extraction. Fresh plums were extracted at 50°C and 70°C, while freeze dried plums were extracted at 50°C, 60°C, and 70°C. Quantification of phenolic compounds such as ascorbic acid, neochlorogenic acid, and chlorogenic acid, was performed using high performance liquid chromatography. Antioxidant activity was determined by evaluating the scavenging ability of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric (Fe3+) free radicals. Total phenolic content and ferric reducing antioxidant potential were highest for freeze dried samples extracted at 60°C whereas extraction at 70°C resulted in the lowest yield. Neochlorogenic acid was the predominant phenolic compound in each plum genotype followed by ascorbic acid and chlorogenic acid. This study demonstrates that there is an adequate amount of health promoting phytochemicals within European plums, hence extraction of these compounds have potential for use towards functional food, nutraceutical, and pharmaceutical industries.

Identification and Characterization of Genes Involved in the Fruit Color Development of European Plum

European plum fruit (Prunus domestica) are normally blue-black to dark purple. However, some genotypes remain green/yellow after ripening. We hypothesized that in such genotypes anthocyanin biosynthesis is genetically disturbed. To examine this hypothesis, six european plum genotypes with diverse fruit colors were investigated for the expression pattern of several anthocyanin biosynthetic genes (ABGs)—e.g., phenylalanine ammonia-lyase, chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR), anthocyanin synthase (ANS), and UDP-glucose:flavonoid 3-O-glucosyltransferase 1 and 2 (UFGT 1 and 2). Expression profiles indicated that ABGs, especially Pd-CHS and UFGT 2, were significantly downregulated in the green/yellow fruit compared with the dark-purple fruit. Furthermore, the quantification of total polyphenols and individual flavonoid compounds showed substantial differences between the off-colored and the purple genotype. To further examine the contribution of each of the ABGs in color development, the open reading frame (ORP) of Pd-CHS, Pd-DFR, Pd-ANS, and Pd-UFGT 2 was ectopically expressed in tobacco (Nicotiana tabacum). The characterization of transgenic plants showed that the petals of plants expressing Pd-CHS were darker in color and had higher anthocyanin content than control or even other transgenic types, suggesting the significant contribution of CHS in determining anthocyanin production levels and hence fruit coloration. The results of this study provides better understanding of color development in european plum, which can be rewarding in developing european plum cultivars with desired colors through classical or modern breeding tools.

Performance of five haskap (Lonicera caerulea L.) cultivars and the effect of hexanal on postharvest quality

Abstract: Growers are challenged to provide premium, ripe haskap fruit to market while limiting the negative attributes associated with over-ripening. Hexanal is an inhibitor of phospholipase D, an enzyme involved in membrane degradation, and has shown promise in extending the longevity of fruit. This study investigated the performance of a hexanal-based preharvest spray for enhancing the quality and shelf life of haskap fruit, an emerging crop in Canada. At two locations in 2015, 2016, and 2017, five cultivars were sprayed with a control treatment or a 0.02% hexanal formulation at 2–3 wk before harvest. Fruit was stored at 4 °C and assessed for quality at successive times. Although inconsistent, results suggest a hexanal spray may impart a small benefit to the postharvest quality of haskap fruit. Secondary objectives included describing important agronomic characteristics of haskap and assessing the potential of a hexanal preharvest spray for enhancing fruit retention. Hexanal did not reduce fruit drop and had no effect on quality at harvest. Fruit contained high levels of soluble solids and titratable acids, were very dark in colour, and did not degrade in quality as rapidly as softer fruit crops such as strawberry or raspberry.

Phospholipase D inhibition by hexanal is associated with calcium signal transduction events in raspberry

Raspberry (Rubus spp.) is an economically important crop with a restricted growing season and very limited fruit shelf-life due to its extreme tenderness. In order to prolong its shelf life, an aqueous composition containing hexanal as the key active ingredient (HC) was applied as a preharvest spray during fruit development. The effects of HC were assessed using physiological, biochemical and anatomical parameters on the treated fruits and compared with the effects of mock inoculation which lacked hexanal. Sugars and acidity did not show a significant change in response to HC treatment, while the pulling force (the tension required to detach the berry from the receptacle) significantly improved in the HC-treated fruits, compared to control. Scanning electron microscope (SEM) analysis revealed a high correlation between the presence of rigid epidermal hairs and a stronger degree of attachment between berries and their receptacle in the HC treated fruits. Further, electron micrographs also showed abnormal crystalline depositions on the epidermal drupelets of the treated berries. Energy Dispersive X-ray Spectroscopy (EDS) analysis showed those crystals to be largely composed of calcium. HC treatment also resulted in the reduction of transcript level of three phospholipase D genes, as well as altered expression pattern of five members of the annexin gene family, and four calmodulin-binding transcription activators. Quantification of PLD activity showed that hexanal inhibited PLD activity in treated berries. The potential crosstalk between hexanal, phospholipase D activity and calcium and this crosstalk’s role in delaying fruit softening and in prolonging storage life of fruits shelf life is discussed.

Effect of preharvest application of hexanal and growth regulators in enhancing shelf life and regulation of membrane-associated genes in strawberry

The role of hormones during fruit development and ripening in strawberry (Fragaria × ananassa) is poorly understood. In this study, two strawberry cultivars (‘Jewel’ and ‘Wendy’) were chosen based on their shelf life quality, which were intermediate and excellent, respectively. Hexanal and growth regulators were applied to the fruit as two preharvest sprays. Fruits treated with “Enhanced Freshness Formulation” (a formulation with hexanal as a key ingredient) showed improvement in the shelf life of both cultivars. Auxin application reduced loss of fruit firmness and abscisic acid was able to accelerate the ripening process without having a significant effect on the relevant fruit quality parameters. The regulation of gene expression during ripening in relation to hexanal and hormones was examined in 21 genes potentially involved in cell wall degradation. Gene expression profiles showed similar patterns in the two cultivars, with more prominent amplitude in ‘Wendy’. The expression of hormone-responsive genes responded in an antagonistic manner to exogenous hormone applications, supporting their role in ripening and fruit development. Hexanal application induced a clear reduction in the transcript level of two phospholipase D genes and other key enzymes involved in cell wall degradation. These findings indicate that ripening in strawberry is associated with the expression of specific genes and the modulation of this gene expression by hexanal supports its role in increasing fruit shelf life.