Investigating The Influence Of Storage Conditions On Pummelo Essential Oil And Transformation Of Main Compounds

Citrus essential oils(CEOs)were important by-products of citrus fruit processing.Because of its fresh fragrance and bioactivities,CEOs became one of the most important fragrance materials,and had been widely applied in the food,cosmetics and pharmaceutical industries.CEOs were mainly composed of monoterpenes,while there were other compounds i.e.aldehydes,alcohols and esters,which were apt to deterioration in relation to the environment changes,which hindered its application.In this study,Guanxi pummelo essential oil(PEO)prepared by cold-press method was applied to investigate the effects of environmental factors(i.e.sunlight,storage temperature and oxygen)on the chemical constitution and aroma of citrus essential oil via GC-MS analysis and sensory evaluation,and the transformation pathway of limonene and aldehydes induced by UV-irradiation and air exposure was further explored.The main results were as follows:(1)46 volatiles was detected in Guanxi PEO by GC-MS,the most aboundant compounds was terpenes.The results showed that terpenes was the most abundant compounds in PEO which accounted for about 96% of the volatiles,among which limonene(476,150 ?g/m L)was the most abundant compound in PEO.The results of sensory evaluation and odour activity value(OAV)showed that PEO showed fresh aroma profile,and the fresh and lemon flavor of PEO mainly came form the limonene and aldehydes,and the floral of PEO came form the linalool.(2)The results of sensory evaluation showed that sunlight-exposed PEO showed the reduced flavor of herbaceous and lemon notes and increased flavor of oily off-flavor odor,while the heat-treatment and oxegen could increase the overripe flavor and reduced the fresh odour of PEO,respectively.This result of GC-MS and OAV showed that the strong oily note of the sunlight-exposed PEO was attributed to the increasing concentration of linalool oxides and limonene oxides,while the lack of neral and geranial could significantly lead to the decreasing of fresh odour.UV sunlight was further confirmed to be the critical contributor causing the chemical reactions for the aroma changes.(3)Co-treatment of UV-irradiation and air exposure caused remarkable changes in limonene,whereas either sunlight irradiation or air exposure alone showed little effect in a short time as 40 h.After co-treatment,limonene was transformed into limonene oxides,carvone,carveols,p-mentha-2,8-dienols,(2R,4R)-p-mentha-6,8-diene 2-hydroperoxide,and(2S,4R)-p-mentha-6,8-diene 2-hydroperoxide via four reaction branches,initiating and sustaining through free radical reactions.(4)The chemical structures had a significant influence on the transformation of aldehydes,and the saturated aliphatic aldehydes were most likely to happen to degradation.Aliphatic aldehydes and citral were transformed to organic acid via free radical reactions induced by UV-irradiation and oxidation initiated.Citral could also transform to cyclocitral after UV-irradiation due to free radical reactions and double bonds recombination.As aldehydes transformation contributed to 78.9% of total OAVs reduction of PEO,which was the main reason to the aroma change of PEO.Depending on the result of flavoring model sample(FMS),the degradation of aldehydes acconted for the significant decrease in minty,herbaceous and lemon notes of PEO.These results showed that sunlight,high temperature and oxygen could cause remarkable change on volatiles and aroma of PEO.UV in the sunlight was revealed to be the critical contributor that caused the volatiles concentration and aroma changes.Both limonene and aldehydes in PEO were turning to degradate in a short time at the presence of UV-irradiation and air exposure,and resulting in significant change on volatiles and aroma of PEO.This study provides important information for the production of CEO and aldehyde related products.