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Xin Zhao Dept. of Horticulture, March 30, 2005 PowerPoint Presentation
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Xin Zhao Dept. of Horticulture, March 30, 2005
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  1. Are Organic foods more nutritious? — Comparison of nutritional quality of organic vs. conventional fruits and vegetables Xin Zhao Dept. of Horticulture, March 30, 2005

  2. What is organic agriculture “An ecological production management system that promotes and enhances biodiversity, biological cycles and soil biological activity. It is based on minimal use of off-farm inputs and on management practices that restore, maintain and enhance ecological harmony”(NOSB) “Biodiversity, integration, sustainability, natural plant nutrition, natural pest management, and integrity”

  3. Labeling of organic foods ●100 percent organicExclusively produced using organic methods ●OrganicAt least 95% of the ingredients (by weight, excluding water and salt) in a processed product have been organically produced. The remaining contents can only be natural or synthetic ingredients allowed on the national list. ●Made with organicingredientsProduced with 70-95% organic ingredients, with up to three specific organic ingredients or food groups listed on the front panel. ●Less than 70% organic ingredientsOrganic items can only be listed in the ingredient panel, no mention of organic on the main panel.

  4. “100 Percent Organic” or “Organic” ●Exclusion of genetic engineering, irradiation, or sewage sludge in any ingredients for100 percent organic, organic, or made with organic products ●Use of USDA Organic seal is voluntary ●Actual percent of organic content may be displayed on all products, regardless of label category

  5. Organic food — One of the fastest growing segments of food industry ●U.S. organic food retail sales grew 20-25% annually since 1990(Dimitri and Greene, 2002 ) ●Organic food is one of the top ten trends among U.S. consumers(Sloan, 2003) ●Sales of organic foods are expected to reach almost $20.9 billion in 2010(Nutrition Business Journal)

  6. Organic food category share in 2003 Organic Trade Association, 2004

  7. Consumer’s attitude (Recent trend) ●Health has been cited as the primary reason for purchasing organic foods ●In the U.S., organic consumers would consider the following: safety > freshness > general health benefits > nutritional value > environmental issues > flavor Egoistic or Altruistic? Perceived health benefits are more strongly related to attitude and behavior of organic consumers compared with perceived environmental benefits

  8. Quality value of fruits and vegetables • Sensory attributes • external apperance (shape, color, size) • taste and flavor • - texture • Essential nutrients • water - proteins • fats - carbohydrates • vitamins - minerals • Bioactive non-nutritive compounds • glucocinolates • phenolics (phenolic acids, • flavonoids) • carotenoids • indoles • … • Undesirable attributes • - nitrate, solanin, … • pesticide residues • - microbiological contamination

  9. Bioactive non-nutritive compounds • glucocinolates • phenolics (phenolic acids, • flavonoids) • carotenoids • indoles • - … Phytochemicals ●Prevention of cancer and coronary heart disease ●Closely related to plant secondary pathways ●Secondary metabolites are involved in plants’ immune systems, protecting them from disease, insect attack, UV damage, nutrient deficiency, and other environmental stresses.

  10. Four general categories of plant secondary metabolites ●Phenolics e.g., flavonoids, phenolic acids ●Terpenee.g.,carotenoids, steroids, limonoids ●Alkaloidse.g., indole, glycoalkaloids ●Sulfur containing compoundse.g., glucosinolates, allicin

  11. Glycolysis Pentose phosphate pathway Shikimate pathway Acetate pathway Phenolic compounds Synthesis of phenolic compounds PAL enzyme Flavonoids

  12. ?Are organically produced food crops more nutritious The National Organic Program USDA makes no claims that organically produced food is safer or more nutritious than conventionally produced food. Organic food differs from conventionally produced food in the way it is grown, handled, and processed.

  13. Comparison of essential (primary) nutrients in organic vs. conventional foods(focused in studies prior to mid 1990’s) Nitrate level was consistently lower in organically produced vegetables

  14. ?Are organically produced food crops rich in phytochemicals

  15. Line of evidence • Polyphenol concentrations were 10 percent significantly higher than non-organic potatoes. (Hamouz et al., 1999) • Organic apples had 18.6 percent more phenolic compounds (mainly flavonols) than fruits from non-organic orchards. (Weibel, 2000) • Antioxidant phenolic compounds were 26 percent higher in organically produced wines. (Levite et al., 2000) • Organic vegetable soups contained nearly six times as much salicylic acid as non-organic soups. (Baxter et al., 2001) • Organically grown vegetables showed 20-120% higher antioxidative activity and 1.3-10.4 times higher flavonoid concentration, compared with conventional vegetables. (Ren et al., 2001)

  16. Line of evidence • Chlorogenic acid in potatoes was the affected by the organic treatments. (Thybo et al., 2002) • An increase of polyphenols found in organic peach and pear implied the improved antioxidant defense system of the organically grown plants. (Carbonaro et al., 2002) • Total phenolics were higher in organically and sustainably produced marionberry, strawberry and corn, and total phenolic content was the highest in sustainable agricultural system. (Asami et al., 2003) • Lycopene, total carotenoids, and total antioxidant activity were higher in catsup produced by organic food companies (Ishida and Chapman, 2004)

  17. Related theories C/N ratio hypothesis ●Increase in N availability will increase amino acids, protein and N- containing secondary metabolites such as alkaloids. ●Decrease in N availability will increase starch, cellulose and non-N- containing secondary metabolites such as phenolics and terpenoids. Growth-differentiation balance hypothesis ●There is a physiological trade-off between growth and differentiation. Chemical defense responses take place at the cost of new plant growth. ●Too much biomass production in plants may lead to a reduction in the functioning of other processes and consequently the chemical and nutritional composition of plants.

  18. Phytochemicals are primarily produced during maturation More phytochemicals in plants Low N supply Early maturation Organic Farming Stress-induced phytochemicals No herbicides, pesticides It was hypothesized that organically grown fruits and vegetables contain higher phytochemical levels than their conventional counterparts

  19. Other explanations ●Varietal differences - Reduced level of secondary compounds is one consequences of crop plant domestication. - Cultivated food crops usually contain fewer natural toxins (including phytochemicals) than their wild counterparts. - Organic farmers are more likely to select varieties with greater resistance to pest or disease

  20. Comparison of organic and conventional production systems Organic production Conventional production Plant protection by pesticides Plant protection by plant induced defense mechanisms Plant nutrients supplied as salts Plant nutrients supplied organically bound Soil biological process Soil chemical process Lundegardh and Martensson, 2003

  21. Some results from our study ●Experimental design Split-split plot design ●Whole plot: Environment = high tunnel vs. open field ●Subplot: Fertilizer source = organic vs. conventional ●Sub-subplot: Cultivar

  22. ●Phenolic acids and aglycone flavonoids Phenolics in lettuce and collard greens Phenolics in pac-choi

  23. Pac choi a P≤ 0.05 b Organic Conventional ●Total phenolic content

  24. Sensory evaluation of organic vs. conventional spinach Fresh 1-week old

  25. Limitations of current research ●Lack of investigations of confounding factors in organic farming system ●Focused on whole system or fertilizer application ●Confounding factors may includegenetics, soil type and condition, location, fertilization method and application rate, temperature, irrigation, sunlight, climate, season, postharvest practice, … ●Flawed design, and few systematic studies

  26. Suggested studies on how to improve the phytochemical content of foods 1) Synthesis and degradation of phytochemicals during crop production and postharvest handling 2) Food processing methods and phytochemical synthesis and degradation 3) Effect of manipulation of particular phytochemicals on other traits 4) Identification of most contributing production factors 5) Evaluation of phytochemical content throughout the plant growth and development 6) Consideration of the entire food system Goldman et al., 1999

  27. Limitations of current research ●Controversy about health benefits of plant secondary metabolits ●Phytochemicals may exhibit paradoxical roles in cancer prevention depending on the dosage, showing anticancer effects at low doses while behaving as carcinogens at high doses. ●Simply boosting the level of one or two phytochemicals in foods may not be essentially beneficial. ●Phytochemical-enriched organic foods need to be tested on animals and humans for their health promoting effects.

  28. Limitations of current research ●Incomplete understanding of plant-insect interactions ●Organic fertilizers showed suppressive effects on insect pests in various crops. ●The form and range of flavonoids in plants could influence insect feeding behaviors, but the complex mechanisms remain unkown. ● Increase of foliar phenolics may even be beneficial for insect fitness. ● What is the underlying difference in plant-insect interactions between organic and convention systems?

  29. Limitations of current research ●Little interpretation of mechanisms at molecular level ●Few studies have tried to reveal molecular mechanisms for the elevation of phytochemical levels in organically produced crops.

  30. “ Such a complex issue with many different parts needing to be researched” “ Hard to perform a fair comparison and analysis between the two systems” “Organic is most likely here to stay” “ We need answers to many questions about it” So, more research needs to be conducted! Mixon, 2003

  31. Thank you