Formation Of Characteristic Flavor Precursors Via Enzymatic Hydrolysis-mild Thermal Oxidation Of Tallow

Moderate oxidation lipid has an important role for the preparation of thermal process meatflavor. With different oxidation states of lipid added to the same thermal reaction system, theflavor of thermal reaction products will make a big difference. A lot of researchers havestudied the control oxidation of lipid, however, most of them only discussed the processoptimization, rarely involved in the identification of characteristic meat flavor precursors.This paper used “enzymatic hydrolysis-mild thermal oxidation” method to obtain oxidizedtallow, and determined the characteristic flavor precursors of oxidation tallow. The maincontents are the following:Based on the results of enzymatic indicators and sensory evaluation of thermal reactionproducts, the optimal lipase was selected from seven commercial lipases. Then the singlefactor test and orthogonal experiment were used to confirm the optimum conditions ofenzymatic hydrolysis. The results showed that the optimum conditions were as follows:reaction time8hours, substrate concentration70%(w/w), the dose of lipase70U/g tallow,initiative pH6.5and reaction temperature45oC. Subsequently, under the optimum conditionsof enzymatic hydrolysis, we controlled the mild oxidation process through adjusting theoxidation time, temperature and flow of air. Nine kinds of oxidized tallow with differentoxidation states including the raw lipid were added into the thermal reaction system to obtainflavor samples. Based on the results of sensory evaluation analysis, beeflike flavor sampleswith the addition of moderate oxidation tallow showed very strong meaty, beefy, tallowy andsimulate attributes and were very weak in burnt and off-flavor notes compared to othersamples. Based on PCA, sensory evaluation, electronic nose and SPME/GC-MS analysis, theoxidation states of tallow significantly affected the flavor of beeflike flavor samples. In orderto prepare characteristic beeflike flavors, the optimum oxidation conditions were as follows:oxidation temperature90-100oC, oxidation time5h, flow of air75L/h·(100g enzymatichydrolysis tallow mixture), and the corresponding parameters were PV70.45-100.17meq/kg,AV134.28-137.22mg KOH/g and p-AV23.79-49.11.This paper identified volatile compounds of enzymatic hydrolysis-mild thermal oxidationtallow and beeflike flavor samples by SPME/GC-MS analysis, and determined thearoma-active compounds of beeflike flavor samples through GC-O analysis based ondetection frequency method. A total of34aroma-active compounds were identified, mainlyconsisting of heterocyclic sulphur or nitrogen compounds and aldehydes. Among the34aroma-active compounds, acetic acid, nonanal,3-(methylthio) propionaldehyde,2-methyl-3-furanthiol and bis(2-methyl-3-furyl)disulfide were the most potent odourants.The characteristic flavor precursors were identified through PLSR analyses between GC-Oresponses, quantitative descriptive sensory data and GC-MS profiles of oxidized tallow.Combined with mathematical correlation analysis and theoretical derivation, twenty-ninecompounds were believed to be the potential characteristic flavor precursors. Among these,tetra-decanoic acid, D-limonene,1,7-heptandiol,2-butyltetrahydrofuran,(Z)-4-undecenal,(Z)-4-decenal,(E)-4-nonenal and5-pentyl-2(3H)-furanone were unique products generated from enzymatic hydrolysis-mild thermal oxidation of tallow. The others were commonproducts generated from pure thermal oxidation of tallow in our previous study.