Studie On Variation Of Quality Changes Of The Harvested Wheat

In order to study the influence of storage conditions and wheat types on physical and chemical quality changes of wheat, zhengmai9023 (strong gluten), taikong6 (middle gluten) and zhengmai004 (wheak gluten) were used as experimental materials. The artificil simulated ageing was carried out in different temperature and humidity. Fatty acid value, falling number value, SDS of sedimentation value, reducing sugar content, germination rate, peroxidase (POD) activity, malondiadehyde (MDA) content and electrical conductivity were tested and evaluated. The relativity between the indexes and storage time, storage temperature, types of wheat also the relationship of the indexes were researched. Headspace solid-phase micro-extraction (HS-SPME), together with gas chromatography and mass spectrum (GC-MS), was used to extract, identify and analyze the volatile compounds from wheat sample of different gluten content. Changes of wheat volatile components during storage were analysed, the research results showed as following:(I) Fatty acid value, falling number value and reducing sugar content of wheat samples were increased while SDS of sedimentation value was decreased with extending storage time. Fatty acid value was sensitive to temperature changes as well as falling number value and sedimentation value were influenced by types of wheat. There was a big correlation of biochemical indexes and storage time. Sedimentation value had extremely significant correlation with fatty acid value(P≤0.01)and falling number value as similar to reducing sugar content but sedimentation value and reducing sugar content had no correlation.(II)Germination rate, peroxidase activity of wheat samples were decreased while malondiadehyde content and electrical conductivity were increased gradually. There was a significant difference of germination rate in different storage time and it was affected by wheat types. Extremely significant correlation of physiological indexes was observed(P≤0.01). Storage time was the most significant environmental factor which effect wheat physiological quality changes, secondly were wheat types and storage conditions.(III) Headspace solid-phase micro-extraction (HS-SPME) was used to extract the volatile compounds from wheat sample using 50μm DVB/CAR/PDMS coating assembly fiber. The results showed that 20 g sample was extracted for 60 min at 75℃with HS-SPME (50μm DVB/CAR/PDMS coating), and desorpting for 5 min at 260℃. The volatile compounds in wheat were hydrocarbons, aldehydes, alcohols, ketones, organic acids, esters, as well as heterocyclic compounds. Aldehydes were the main volatile compounds. Hexanal content is the highest one with an average of 9.584%, followed by Hexadecanal, with an average of 3.530%. Total content of volatile compounds increased with extending of storage time. Aldehydes, alcohols, ketones compounds of different gluten content decreased and hydrocarbons compounds increased while organic acids, esters and heterocyclic compounds varied during the storage.