Studies On The Relationship Between Total Antioxidantive Activity And Physiology Of Ripening And Senescence During Storage Of Fruits And Vegetables

Free radicals of active oxygen derived from oxidantive stress keep dynamic banlance with free radicals scavengers during the normal growing process of fruits and vegetables.However,during the postharvest storage of fruits and vegetables,the balance of oxidantive metabolism is destroyed and more free radicals are produced because of all kinds of adverse environment conditions,which will hurt fruits and vegetables and induce them senescence and death.But the freshly-harvested fruits and vegetables are living organisms ,and their metabolism still continue.They have the defense ability against free radicals.The defence system in fruits and vegetables includes enzyme and non-enzyme antioxidantive compounds.To summarize,the former is referred to as antioxidases,and the latter antioxidants.They scavenge free radicals by reacting with them and generating the compounds which are stable and harmless to fruits and vegetables.But certain single antioxidase or antioxidant don't defend serious oxidantive stress,only through teamwork of all kinds of antioxidase or antioxidant or activating whole defence system can fruits and vegetables resist oxidantive stress.That is,the changes of certain single antioxidase or antioxidant can't indicate the change of total defence system,and the change of total antioxidant activity (TAA) can reflect the change of total defence system of fruits and vegetables.The research takes grape,strawberry,spinach,celery and radish as the experimental materials,and studies the changes of total TAA which is measured according to the spectrophotometric method using DPPH as free radical generator. Samples are coated by tea polyphenol-based coating ,and TAA,superoxide dismulase (SOD) ,malondialdehyde (MDA) ,VC,chlorophyll (Chi) .textureand bulk density ,as indices of postharvest senescence ,are measured.We conclude that in initial storage period.the fruits and vegetables suffer slight stress,and free radicals can be scavenged by internal antioxidantive defence system,and new isoforms are synthesized when free radicals level exceeds the activity of endogenous antioxidants. Along with the senescence and the accumulation of free radicals,the ability of synthesis of new isoforms and antioxidant activity will decrease . Free radicals will accelerate the aging and death of fruits and vegetables after the level of free radicals increases to certain degree. At the same time, the fruits and vegetables coated by tea polyphenol (TP) can availably protect endogenous antioxidants and remain nutritional qulity and organoleptic properties and finally extend the functional life span,but not terminal life span.