Identification Of Aroma-active Compounds And Modeling Of Aroma Quality Evaluation Of Citrus Fruits

Citrus is widespread consumer’s fruits crops because of its unique flavor and high nutritional value.Aroma is one of the important qualities of citrus fruits,and different species citrus fruits have their own unique aroma quality.Aroma quality of citrus fruits is determined by types,content,proportion of aroma-active compounds.Despite numerous studies have been conducted on aroma compounds of citrus fruits,studies aimed at evaluating the aroma quality of citrus fruits was surprisingly scarce in the domestic and foreign.At present,the most frequently used method is sensory evaluation method,but their result is affected by some subjective factors,and it is hard to quantify.Therefore,in order to objectively and scientifically evaluate the aroma quality of citrus fruits,a model was established to evaluate the aroma quality of citrus fruits.The model was explored a new way to evaluate the aroma quality of citrus fruits.In this study,aroma compounds in peel and pulp of thirteen citrus cultivars,representing five citrus types,and including sweet orange(Newhall navel orange),pummelo(Liangpingyou,Shatianyou,Guanximiyou,Humiyou and Qiangdele),loose-skin mandarins(Satsuma mandarin,Ougan,shatang mandarine,Lugan and red tangerine),lemon(Eureka lemon)and kumquat(Huapi kumquat),were characterized by headspace solid phase microextraction combined with gas chromatograph-mass spectrometer(HS-SPME-GC-MS)method.Based on odor activity value method(OAV),comparing the contribution of aroma compounds to overall aroma of citrus fruits.Meanwhile,combining with multivariable analysis evaluated the aroma quality of citrus fruits.The main results were as followed:(1)Optimization of solid phase microextraction(SPME)parameters of citrus volatile profile was performed to use the single factor method and response surface method.The results showed that optimization of SPME conditions were as followed: 6.21 min of preheating time,45 min of extraction time,42 °C of extraction temperature,and 3.4 min of desorption time.(2)The aroma compounds were identified in the peel and pulp of thirteen citrus cultivars by HS-SPME-GC-MS method,which monoterpenes were main aroma compounds.The main aroma compounds of thirteen citrus cultivars were d-limonene,β-myrcene,linalool,decanal,γ-terpinene,geranial,neral,β-pinene,α-terpieol,(-)-4-terpineol and so on.(3)Clear differences in the concentration and types of aroma compounds between each of the citrus cultivars suggested that their metabolism of aroma compounds was affected by genetic background.The types of aroma compounds were higher in peel of Newhall navel orange(114 compounds)and Huapi kumquat(99 compounds),while lower types in Shatianyou pomelo(63 compounds)and Liangpingyou pomelo(60 compounds).And the concentration of aroma compounds were higher in Eureka lemon(46782.81μg/g FW)and red tangerine(46334.05μg/g FW),while lower concentration in Shatianyou pomelo(15319.32μg/g FW)and Liangpingyou pomelo(14518.33μg/g FW).(4)Those aroma compounds were regarded to contribute greatly to the aroma quality of different citrus types by OAV method and multivariate analysis.Geraniol acetate,(-)-carvone,β-myrcene,trans-β-ocimene were greatly contributed to aroma quality of Huapi kumquat peel;geranial,geraniol acetate,citronellal and neral were greatly contributed to Eureka lemon peel;octanal,geranial,citronellal and valencene were greatly contributed to Newhall navel orange peel;dodecanal,β-citronellal,octanal,β-myrcene and geraniol acetate were greatly contributed to loose-skin mandarins peel;nootkatone,geranial,geraniol acetate and β-myrcene were greatly contributed to pomelo peel.These aroma-active compounds contributed the unique aroma quality of citrus fruits.(5)The result of principal component analysis(PCA)and hierarchical clustering analysis(HCA)based on fifty-six aroma-active compounds showed the citrus cultivars of same type were gathered together and the citrus cultivars of different types were discriminated.The result of PCA and HCA was achieved an effective classification for citrus cultivars based on aroma-active compounds.(6)A model was established based on multivariate analysis for evaluating the aroma quality of citrus fruits with aroma-active compounds as variables.Then the aroma quality of citrus fruits from different production areas was evaluated by their corresponding model.The results showed Suichuan Huapi kumquat(JG-SC)was higher aroma quality than Rongan Huapi kumquat(JG-RA)and Youxi Huapi kumquat(JG-YX);Wanzhou Eureka lemon(NM-WZ)was higher aroma quality than Tongnan Eureka lemon(NM-TN)and Anyue Eureka lemon(NM-AY);Ganzhou Newhall navel orange(QC-GZ)was higher aroma quality than Fengjie Newhall navel orange(QC-FJ),Yizhang Newhall navel orange(QC-YZ)and Zigui Newhall navel orange(QC-ZG).