Degradation, chlorophylls

Abridged Spectrophotometry. It is not always necessary to obtain complete spectrophotometric curves in order to measure physical characteristics related to color. The procedure can often be considerably simplified by some abridged form of spectrophotometry. Measurements may be made only at critical wave lengths or wave-length bands, as has been done to determine chlorophyll degradation (1, 8). In such instances the real problem that faces the investigator is to establish the critical wave lengths. 

Chlorophyll Degradation during Plant Senescence and Fruit... 

Heaton, J.W. and Marangoni, A.G., Chlorophyll degradation in processed foods and senescent plant tissues. Trends Food Sci. TechnoL, 1, 8, 1996. 

Mangos, T.J. and Berger, R.G., Determination of major chlorophyll degradation products, Z. Lebensm. Unters. Forsh. A, 204, 345, 1997. 

Matile, P, Hortensteiner, S., and Thomas, H., Chlorophyll degradation, Annu. Rev. Plant Physiol Plant Mol. Biol, 50, 67, 1999. 

Hortensteiner, S., The loss of green color during chlorophyll degradation by a prerequisite to prevent cell death Planta, 219,191, 2004. 

The photoprotective role of carotenoids is demonstrated in plant mutants that cannot synthesize essential leaf carotenoids. These mutants are lethal in nature since without carotenoids, chlorophylls degrade, their leaves are white in color, and photosynthesis cannot occur. Generally, the carotenoids are effective for visible light but have no effects in ultraviolet, gamma, or x-radiation. The reactions are listed as follows ... 

FIGURE 4.1.1 Possible chlorophyll degradation pathways in plant tissues or in processed foods. Pheophorbide a monooxygenase is specific for pheophorbide a. RCC = red chlorophyll catabolite. FCC = fluorescent chlorophyll catabolite. NCC = non-fluorescent chlorophyll catabolite. 

Studies of chlorophyll degradation in heated broccoli juices over the 80 to 120°C range revealed that chlorophylls degrade first to their respective pheophytins and then to other degradation products in what can therefore be described as a two-step process. Both chlorophyll and pheophytin conversions followed a first-order kinetics, but chlorophyll a was more heat sensitive and degraded at a rate approximately twice that of chlorophyll This feature had been observed by other authors. Temperature dependence of the degradation rate could adequately be described by the Arrhenius equation. ... 

Traditionally, dried or powdered plant material is used and extracts can be obtained by mixing the material with food-grade solvents like dichloromethane or acetone followed by washing, concentration, and solvent removal. The result is an oily product that may contain variable amounts of pheophytins and other chlorophyll degradation compounds usually accompanied by lipid-soluble substances like carotenoids (mainly lutein), carotenes, fats, waxes, and phospholipids, depending on the raw material and extraction techniques employed. This product is usually marketed as pheophytin after standardization with vegetable oils. 

Funamoto, Y. et al.. Effects of heat treatment on chlorophyll degrading enzymes in stored broccoli (Brassica oleracea L.), Postharvest Biol.TechnoL, 24, 163, 2002. 

Weemaes, C.A. et al., Kinetics of chlorophyll degradation and color loss in heated broccoli juice, J. Agric. Food Chem., 47, 2404, 1999. 

Boekel, M.J.S., Kinetic modeling in food science a case study on chlorophyll degradation in olives, J. Sci. Food Agric., 80, 3, 2000. 

LaBorde, L.R and Von Elbe, J.H, Chlorophyll degradation and zinc complex formation with chlorophyll derivatives in heated green vegetables, J. Agric. Food Chem., 42, 1100, 1994. 

Despite being a fast and relatively low-cost method, thin layer chromatography shows low resolution as it involves a large surface in contact with air, promoting photoxidation. Acidity of silica gels should be neutralized because it may trigger chlorophyll degradation by pheophytinization. ... 

Hdrtensteiner, S. et ah, Evolution of chlorophyll degradation the significance of RCC reductase, Plant Biol, 2, 63, 2000. 

The use of 1-methylcyclopropene (1-MCP) to extend the shelf life of cherry tomato (.Lycopersicon esculentum var. Cerasiforme) delayed the ethylene-induced climacteric peaks in mature green and breaker fruits, chlorophyll degradation, and accumulation of lycopene and carotenoids (Opiyo and Tie-Jin 2005). Higher 1-MCP concentrations inhibited the accumulation of lycopene and carotene such that the color of the fruit did not reach that of control fruit. 

Ethylene coordinates the expression of genes responsible for enhanced respiratory metabolism, chlorophyll degradation, carotenoid synthesis, conversion of starch to sugars, increased activity of cell wall-degrading enzymes, aroma volatile production, and so on. All these events stimulate a series of biochemical, physiological, and structural changes making fruits mature and attractive to the consumer. 

The ripening of nonclimacteric fruits is usually considered as a process that as a whole does not require ethylene. Nevertheless, endogenous ethylene is involved at some steps of development of these fruits. In general, chlorophyll degradation in nonclimacteric fruits is believed to be ethylene stimulated, whereas the synthesis of pigments can depend on ethylene action or not. ... 

Chlorophylls are hydrophobic compounds made of four modified pyrole rings with an Mg atom and an attached long C20 hydrocarbon tail (Fig. 8.1). In pepper, unripe fruit colors can vary from ivory, green, or yellow. The green color is accumulation of chlorophyll in the chloroplast while ivory indicates chlorophyll degradation as... 

Species That Produce Pigments in Response to Ozone. Ozone causes pigment changes in many plant species. Chlorophyll degradation occurs and chlorosis results. In one plant, Rumex crispus L., chlorophyll concentrations did not decrease but anthocyanin synthesis was increased after exposure to ozone ( ). 

If the eight peripheral substituents are made up of three kinds, for example two ethyls, two propionates and four methyls (with one methyl on each pyrrole subunit) then 15 isomers are possible, and these are related to the original primary type isomers as shown in Scheme 2. Further complications, many of which can be found in chlorophyll degradation products, lead to a third (larger) set of type isomers which can be directly related to those in Scheme 2. 

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