Effect Of Lipid Oxidation On Flavor Quality Deterioration Of Raw Coffee Beans During Storage

In this paper,Hainan Xinglong coffee beans are used as raw materials to study the lipid oxidation process,shelf life prediction,sensory changes,active ingredients,enzyme activity changes,volatile components and electrons of coffee beans at 40 o C,50 o C and60 o C accelerated storage for 20 days.The storage model of coffee oil under 60 o C storage conditions was established to study the correlation between peroxide value,acid value,free fatty acids,malondialdehyde,fatty acids and volatile substances,and to explore the main factors that cause the quality deterioration of green coffee beans.This study provides a scientific basis for the effect of lipid oxidation on the quality loss of green coffee beans during accelerated storage.The main research contents are as follows:1.Effects of storage on lipid oxidation of raw coffee beansThe contents of acid value,iodine value,peroxidation value,total oxidation value,thiobarbiturate active substances and free fatty acids increased with the increase of storage time,while the contents of water content,p-anisidine value and unsaturated fatty acids decreased,indicating that lipid oxidation occurred during accelerated storage.The Arrhenius model was used to predict the shelf life of green coffee beans.Under the storage conditions of 40 ℃,50 ℃ and 60 ℃,the shelf life of green coffee beans was 57 d,44 d and 23 d.The frequency and absorbance of 3700-3150 cm-1,3010-2999 cm-1,1800-1700 cm-1 and 1300-1100 cm-1 bands were measured by Fourier spectroscopic instrument,which indicated that the lipid oxidation reaction occurred during storage.The results showed that the oxidation degree of coffee beans was higher than 40 ℃ and 50 ℃under 60 ℃ storage condition.2.Effects of accelerated storage on phenolic acids,alkaloids,phenolic compounds and biological activities in green coffee beans.Coffee beans in the process of accelerated storage L*,a*,b*,ΔE,phenolic acid and total phenol,total ketone content and DPPH antioxidant activity decreased,however,Browning index increased during storage.The color parameters were highly correlated with the content of Browning index,DPPH,total phenol and total flavonoids.The results showed that the quality of coffee beans under 60 ℃ storage was higher than 40 ℃ and50 ℃,and the nutritional value decreased with the extension of storage time.3.Effects of different storage conditions on enzyme activity and flavor of coffee beansThe activities of lipase,superoxide dismutase,lipid peroxidase and peroxidase increased significantly with the extension of storage time and were also proportional to the storage temperature.A total of 55 volatile substances were identified by headspace solid-phase microextraction and gas chromatography-mass spectrometry.With the increase of storage time,the contents of acids first increased and then decreased,the contents of esters gradually increased,and the contents of aldehydes first decreased and then increased.It was speculated that the characteristic compounds of the deterioration of the flavor quality of green coffee beans during accelerated storage were hexaldehyde,benzaldehyde,phenylacetaldehyde,acetic acid,caproic acid and benzoic acid.2.The oxidation of coffee oil was monitored by acid value,free fatty acids,peroxidevalue,thiobarbital acid,fatty acids and volatile compounds.Samples stored at 60 ℃ the oxidation stability of treatment after 20 d,peroxide value,malondialdehyde,free fatty acids,acid value,the oxidation index content increased,the increasing trend of total saturated fatty acids,unsaturated fatty acid amount is on the decline,and coffee oil deterioration and rancidity odor,hexanal,heptyl aldehyde in coffee oil,2,4-nonyl diene aldehydes,acetophenone,caproic acid,oleic acid,palmitic acid and stearic acid as the representative rancid flavor,combining the above index analysis,the index and the change of the quality of the coffee oil has a good correspondence.The decline of coffee oil quality during storage was mainly related to the formation of aldehydes,acids and volatile substances,and was also closely related to the oxidation and degradation of lipids.