Smoked Odor Characteristics Of Phenol Compounds And Their Contribution To The Smoked Flavor Of Chinese Bacon

Since ancient times smoke was used as a food preservation method.The smoking process has a considerable influence on the sensory characteristics of smoked products that are demanded by consumers.Currently,the aim of smoke processing,besides extending shelf-life,is mainly to develop the unique smoked flavor.Determining the smoked flavor attributes and their flavor compounds is a prerequisite to maintain the traditional smoked flavor characteristics by modern smoking process.It is of great important for the improvement of quality and safety.However,previously researches on smoked flavor attributes and their flavor compounds were not systematic and in-depth.The characteristics for smoked foods are associated with raw materials,woods,smoking process,climate and storage conditions.Smoked flavor is not a single smoky characteristic,but rather includes all characteristics which produced by smoking process.However,these sensory characteristics contributing to smoked flavor were not identified.Phenolic compounds are regarded as the main source of smoked flavor and aroma.Many studies were focused on of the change of phenolic compounds content during smoking process,or the correlation between sensory characteristics and chemical composition.However,available information on smoked odor characteristics of phenol compounds and their contribution to the smoked flavor of foods is limited.Thus,a smoked characteristics lexicon developed was used to describe the odor characteristics of phenol compounds at various concentrations.Sensory characteristics of combinations of two kinds of phenolic compounds also were evaluated.The correlation model of odor characteristics and the volatile compounds in Chinese bacon samples was establishe by partial least squares regression(PLSR).The main research contents and results are as follows:1.A general lexicon associated with smoking process was establish by a high trained panel.Fourteen attributes included: smoky,ashy,woody,musty/dusty,musty/earthy,burnt,acrid,pungent,petroleum-like,creosote/tar,cedar,bitter,metallic,and sour,were generated to describe the smoked flavor.Every attribute in the lexicon has a definition and between one and three references.The principal components analysis showed that three principal components were necessary which explained 72.55% of the variance.All 14 attributes are necessary to fully describe those explain those three principal components.Agglomerative hierarchical clustering based on the flavor characteristics of ten smoked productes and five non-smoked products,showed that the lexicon distinguished between smoked and unsmoked products.So we can assume that these smoked attributes on the lexicon refer to the smoke flavor,not the base products.This lexicon can be applied to identify differences in the smoked flavor of specific products,describe those differences and determine the key odor active compounds in a way that improves flavor understanding.2.Odor characteristics of various concentrations of phenolic compounds were evaluated after screening whether the phenolic compounds associated with smoked aroma.Among the 19 phenolic compounds,only 2,6-dimethylphenol was not associated with any smoky characteristics.Smoked attributes were determined in ten alkylphenols,six guaiacols,and two syringols at various concentrations.The panel evaluated these eighteen phenolic compounds associated with smoked aroma at seven concentrations included 1 mg/kg,10 mg/kg,100 mg/kg,1 g/kg,5 g/kg,10 g/kg ? 100 g/kg.A total of 126 samples were identified.Phenolic compounds did not present smoked odor characteristics at all concentrations.Ten samples,such as 1 mg/kg 2,5-dimethylphenol,were not describe as smoked odor characteristics.Most of phenolic compounds were described as smoky at low concentration,generally at 1 mg/kg and 10 mg/kg.This shows the powerful impact of phenolic compounds on smokiness in foods.In general,as phenolic compounds concentration increased,more odor attributes were found and the odor attributes became more intense.However,some phenolic compounds did not have the higher score at the higher concentration.The smoky intensity changed with concentrations were irregularly.Four group isomers of phenolic compounds had different odor characteristics and intense.3.How combining two phenolic compounds affects smoked characteristics and intensity were determined by high trained panel.Two compounds,100 mg/kg 4-ethylguaiacol and 100 mg/kg 2,6-dimethoxyphenol were used to combine with other phenolic compounds.Those compounds were chosen because the dimethoxyphenol compound had a unidimensional odor that was only smoky with no other odor character at 100 mg/kg and the ethylguiacol compound showed a multidimensional odor with smoky and other odors,such as woody,at 100 mg/kg.The smoky character remained in all combinations of 100 mg/kg 4-ethylguaiacol and 100 mg/kg 2,6-dimethoxyphenol.However,the woody character did not retain in some combinations of 100 mg/kg 4-ethylguaiacol.When 100 mg/kg 4-ethylguaiacol or 100 mg/kg 2,6-dimethoxyphenol combined with one non-smoky phenolic compound,many additional smoked characteristics,such as ashy,woody,burnt,acrid,pungent,were presented in the combinations.The combination of two non-smoky compounds also may present smoked odor characteristics.All 4 combinations of two non-smoky compounds containing 100 ppm 2,6-dimethylphenol presented smoked odor characteristics.However,half of the 4 combinations containing 1 ppm 2,6-dimethoxyphenol were not determined to have any odor character and the other half presented many odor characteristics related to smoked flavor.Odor characters and intensities of most combinations with two phenolic compounds were changed from those smelled individually.Combinations did not show particular consistency in their effects.4.Odor characteristics of Chinese bacon from different geographical regions were evaluated by a high trained panel.Thirteen odor attributes inclued smoky,woody,ashy,acrid,sour aromatic,sweet aromatic,meaty,cured,cooked,soy sauce,alcohol,oil-heated,rancid,were used to describe and distinguish these Chinese bacon samples.The principal components analysis showed that three principal components were necessary which explained 82.10% of the variance.All 13 attributes are necessary to fully describe those explain those three principal components.Odor characteristics of Chinese bacon were classified four groups.All odor characteristics associated with smokingprocess,such as smoky,woody,ashy and acrid,were grouped together.The second group associated with seasonings,such as soy sauce,sweet aroma and alcohol.The third group usually had meaty,cooked,sour aromatic and cured,these characteristics generally associated with raw materials and process.The forth group included oil-heated and rancid,which generate by oil.Hunan-style bacon and Guizhou-style bacon had the highest intensities of smoked odor characteristics,which did not present in Guangdong-style bacon.Odor attributes commonly present in Guangdong-style bacon are soy sauce,sweat aromatic,and alcohol.The results displayed that DA was available in distinguishing Chinese bacon from different geographical regions.5.The volatile compounds of eight Chinese bacon samples with different odor characteristics were investigated by SPME-GC-MS.A total of 103 volatile compounds were identified.More volatile compounds were detected in smoked bacon than non-smoked Guangdong bacon.The main compounds in Guangdong bacon were esters and ethanol,phenol compounds were not detected.There were more kinds and contents of phenols,furans,hydrocarbons,aldehydes and ketones in Smoke bacon.Six alkylphenols and six guaiacols were detected in smoked bacon samples.6.The contribution of volatile compounds on Chinese bacon odor characteristics was carried out by PLSR.The results suggested that phenolic compounds,furans,?-Cedrene,d-limonene,3,4-dimethoxytoluene had positive correlation with four smoked attribues.Alhough present smoked odor characteristics individually,some phenolic compounds,such as 4-methylphenol,had negative correlation with four smoked attribues of Chinese bacon.