Study On Characteristic Flavor Of Deep-fried Oil Of Allium Fistulosum L.

Allium is widely cultivated in China and Southeast Asia as one of the most important vegetables,which contains volatile oil,vitamins and mucilage.Among which,green onion(Allium fistulosum L.)is a basic necessity for traditional Chinese cooking.Allium deep-fried is a process at the beginning of cooking which makes the flavor presenting matters being dissolved in the oil.During the cooking process,it is often to have a deep fried of the allium in a small amount of vegetable oil to give an unique flavor to the Chinese dishes and to cover the unpleasant flavor from other ingredients.In the development of food products,it is a normal practice for the producers to add the flavor of deep-fried allium into different products to cover the unpleasant flavors or to enhance the aroma.This flavor is widly used in savory food products as well.Therefore,it is important to study the flavor of the deep-fried oil of allium to provide a theoretical basis for the standardization and industrialization for Chinese traditional dishes.In this paper,a systematic study of the phy sical and chemical properties of the deep-fried alliums oil flavor were conducted in the aspects of processing technique and components identification method.Besides,some investigations in the formation mechanism of the flavor were explored.The major contents and conclusions were listed as follows:1.Determination of preparation process.Raw materials were selected.Quantitative and descriptive sensory evaluation method were used to establish the evaluation standard system of the deep-fried allium oil.The descriptive words were determined including green onion flavor(cooked),salty flavor,fried,oily,burnt,meaty,et al.Then a comprehensive evaluation of the oil flavor was conducted,including commercially available alliums(green onion(Allium fistulosum L.),garlic(A.sativum L.),onion(A.cepa L.),chives(A.ascalonicum L.),eleutherine bulbosa)and different oils(soybean oil,palm oil,olive oil,corn oil,sunflower seed oil,rapeseed oil and camellia oil).Green onion and soybean oil were sellected as the raw materials to make deep-fried oil.Besides,three important influence factors,namely initial temperature,final temperature and temperature rising rate on the deep-fried allium oil flavor were investigated,by using sensory evaluation,electronic nose and solid phase microextraction(SPME)-gas chromatography mass spectrometry(GC-MS).The determined optimum conditions were:initial temperature set at 140?,final temperature set at 165? and temperature rising rate set was 1.4?/min.2.Establishment of the flavor extraction method.The extraction conditions of solid phase microextraction(SPME)and solvent-assisted flavor evaporation(SAFE)were optimized,respectively.The optimized condition of SPME was 75 ?m Carboxen/PDMS as extraction fiber,100? as extraction temperature and 50 min as extraction time.The optimized condition of SAFE was 50? as water bath temperature and 1:4 as material ratio(m:V).Comparing with SPME,SAFE method had better performance in the aspects of low threshold value compounds(such as aldehydes,acids and thioethers)extraction,and was better to be used for the extraction of volatile flavor from deep-fried alliums oil.3.Study on the formation mechanism of the flavor.Changes of aroma compositions during the process of deep-fried oil of Allium fistulosum L.were investigated by using sensory evaluation,electronic nose and SAFE-GC-MS.The results showed that the flavor of the oil including burnt,fried,oily,vegetable and salty were strengthened during the process when the temperature rose from 140 ? to 165?.In this stage,contents of furan and furanone,sulfur-containing compounds,aldehydes and alcohols increased immediately and its location on the fingerprint was distinguished from other samples.The above phenomenon proved that this stage was considered as the most important period for the formation of the the unique flavor of the deep-fried oil.4.Identification of aroma active substances and the application of its unique flavor in industrial products.Aroma extraction dilution analysis(AEDA)and odor activity values(OAVs)were both applied to identify the aroma active compounds in the deep-fried oil by gas chromatograph and olfactometry(GC-O).The analysis showed that totally 22 aroma compounds and 11 aroma compounds were detected by AEDA and OAV,respectively.Moreover,furaneol(FD=19683,OAV=2784)and dimethyl trisulfide(FD=6561,OAV=214480)were proved as the key aroma active compounds by both of the two methods.After accurate quantitative analysis,aroma recombination experiments were conducted based on the results of AEDA and OAV,respectively.It showed that the aroma profile of AEDA was better than that of OVA.In conclusion,AEDA was more suitable for the identification of aroma active substances in the deep-fried oil of Allium fistulosum L.