AGEN2002 Lecture Notes - Lecture 5: Anaerobic Glycolysis, Hemicellulose, Pectin
15 May 2018
School
Department
Course
Professor
5. Biochemistry & Physiology of F&V
Quality attributes in F&V
• Preharvest – genetic, agronomic, environmental
• Harvest – maturity, physical damage
• Immediate postharvest – temperature, handling
• Postharvest storage – packaging, temperature
• Non-technical – skilled personnel, extension
Products of photosynthesis - polysaccharides
• Starch (stored in roots, stems, bulbs, seeds, smaller quantities in leaves)
• Cellulose, pectin, hemicellulose
o Pectin & hemicellulose have a key role in texture & viscosity (forms a network that
‘cements’ cellulose microfibrils in the cell wall)
o Pectin breaks down during ripening & softening processes (hydrolytic cleavage of
long chains increases solubility, makes bonds between adjacent cell walls looser)
• Sucrose (glucose+fructose disaccharide)
o Most stored as sugar than starch (Sucrose is transport sugar)
Plant metabolism
• Catabolism: destructive, releases energy (kinetic)
o E.g. respiration
o Drives plant cellular biochemistry (production of key metabolites & organic acids)
o Results in loss of dry matter (substrate is degraded)
• Anabolism: constructive, require energy input
o E.g. Photosynthesis, cell wall formation
o Starch/sugar storage influences shelf-life
o Integrity of polysaccharides influences textural quality
Respiratory pathways
• Glycolysis can be aerobic/anaerobic
o Presence of O2: pyruvate enters TCA (Krebs) cycle
o Absence of O2: ethanol/lactic acid produced à off-flavours (e.g. alcoholic melons)
• Young tissues: actively growing, require high inputs of energy
• Developing organs have higher respiration rate than mature ones
Effect of temperature on respiration rate
• Within certain temperature (usually 0-20’C), respiration rate x2 for every 10’C rise in temp
• Cold chain: simplest & most effective way to maximise shelf life (reduce respiration rate)
Effect of gas atmosphere on respiration rate
• Low O2 retards respiration (but too low = anaerobic glycolysis, off-flavors)
• High CO2 retards respiration & control pathogenic growth
Document Summary
Quality attributes in f&v: preharvest genetic, agronomic, environmental, harvest maturity, physical damage. Immediate postharvest temperature, handling: postharvest storage packaging, temperature, non-technical skilled personnel, extension. Products of photosynthesis - polysaccharides: starch (stored in roots, stems, bulbs, seeds, smaller quantities in leaves, cellulose, pectin, hemicellulose, pectin & hemicellulose have a key role in texture & viscosity (forms a network that. Plant metabolism: catabolism: destructive, releases energy (kinetic, e. g. respiration, drives plant cellular biochemistry (production of key metabolites & organic acids, results in loss of dry matter (substrate is degraded, anabolism: constructive, require energy input, e. g. Photosynthesis, cell wall formation: starch/sugar storage influences shelf-life. Effect of temperature on respiration rate: within certain temperature (usually 0-20"c), respiration rate x2 for every 10"c rise in temp, cold chain: simplest & most effective way to maximise shelf life (reduce respiration rate)
