POSTHARVEST BIOCHEMISTRY

POSTHARVEST BIOCHEMISTRY

1. PLASMA MEMBRANE DEGRADATION ENZYMES

   • Plasma Membrane
     • Role of plasma membrane during ripening
       • 70% of total lipids in mammalian cells are phospholipids - acidic phospholipid (minor but have important role)
         • Monoacidic - has phosphate but no headgroup (carry one -ve charge that link the headgroup)
         • Phosphatic acid: carry two -ve charges on the phosphate( has phosphate but no headgroup)
         • phosphatidylinositol(Ptdlns) : one -ve charged phosphate linking an inostol headgroup to lipid backbone
   • Phospholipases
     • Lipase enzyme that hydrolyses phospholipid molecules
       • Phospholipase D
         • a) Phospholipase D(PLD) hydrolysed phosphatidylcholine (PC) into phosphatidic acid (PA) b) Phospholipase C(PLC) hydrolyses phosphatidylinositl diphosphate (PIP) into diacylglycerol(DAG)
           • Hexanal- strong PLD inhibitor
           • PLD- membrane degrading enzyme and initiates phospholipid degradation

2. ETHYLENE BIOSYNTHESIS INHIBITION

   • 1-methylcyclopropene (1-MCP)
     • prevent ethylene action
     • competitive inhibitor
     • stronger affinity than that of ethylene
     • irreversible binding
       • interferes ethylene action
       • delays ethylene biosynthesis
   • Silver thiosulfate (STS)
     • sodium thioshulfate + silver nitrate
     • prolong the vase life of cut flower
     • Ag+ ion blocks ethylene receptor site
       • delays senescence
     • not commercialized due to
       • complicated & sensitive with time of exposure
       • issue with waste management

3. GENETIC ENGINEERING

   • goal : add one/more new traits that are not already found in an organim
     • genetically modifed organism
   • process of manually adding new DNA to an organism
   • common techniques used
     • RNA interface (RNAi)
     • gene overexpression
     • anti-sense
   • plant genetic engineering
     • agrobacterium
     • gene gun

4. ETHYLENE BIOSYNTHESIS

   • Pathway of biosynthesis
     • Amino acid methionine convert to SAM (S-adenosylmethionine) through SAM synthase
       • SAM convert to ACC (1-aminocyclopropane-1-carboxylic acid) through ACC synthase (ACS)
         • ACC convert to ethylene through ACC oxidase (ACO)
   • System in Ethylene Biosynthesis
     • System I ethylene - Autoinhibition of ethylene synthesis.
     • System II ethylene - Ethylene production increases due to autocatalytic regulation.

5. ETHYLENE SIGNALLING

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