Studies On The Preparation Of Basic Thermal Process Beef Flavorings By Maillard Reaction Of Model System

This thesis is composed of six chapters dedicated to meat flavor research. The first chapteris a literature review covering aspects related to development of thermal process meat(beef)flavorings and meat volatiles from their sources to their generation as well as factors influencingmeat aroma profile in Maillard reaction model system. The second chapter is the research ofpreparation and characterization of beef hydrolysates. The third and the fourth chapter consisted ofdevelopment of a synthetic basic meat flavorings through Maillard reaction of model systemconsisting of beef hydrolysates -L-cysteine-HCl -D-glucose by using surface responsemethodology and analysis of its reaction products. The rest two chapters consisted of two originalstudies investigating the effects of fat and taurine on volatile generation from Maillard reaction ofL-cysteine-HCl -D-glucose, respectively.Four commercial proteases (Neutrase , Alcalase > Flavourzym and Protamex) were evaluatedfor hydrolysis of beef protein. Hydrolysis conditions were optimized for the mixture ofFlavourzyme and Protamex by response surface methodology (RSM). Based on DH, optimumhydrolysis conditions were determined as follows: 4.8%substrate concentration, pH7.0,temperature 52.5 ℃ and 9h reaction time. The hydrolysis degree of beef protein reached amaximum degree of hydrolysis of 50.65% at the optimum hydrolysis conditions. The total amountof free amino acids reached 9.28%, 21.5%, 31.7% and 33.5% at DH% of 12%, 24%, 35% and43%, respectively. There was a strong positive relationship (R2=0.9621) with the total amount offree amino acids and DH% values of the samples. The molecular weight distribution of beefprotein hydrolysates hydrolyzed by Flavourzyme & Protamex at different DH were analyzed bysize exclusion-high-performance liquid chromatography. The content of peptides with molecularmasses below o.35kDa were 39.6%, 57.1%, 64.7% and 75% at DH% of 12%, 24%, 35% and 43%,respectively. The effect of beef hydrolysates with different DH on flavor properties of Maillardreaction products of model system were evaluated by fuzzy overall evaluation method. Resultsshowed that beef hydrolysates obtained at 24% DH characterized by a percentage (57.1%) ofpeptides with molecular masses below 0.35kDa and a percentage (20.1%) of free amino acids wasbest suitable for generation of meat flavor of Maillard reaction.Response surface methodology (RSM) was used to development a meat process flavoringsfrom the model system of enzyme-hydrolyzed beef protein-L-cysteine-HCI-D-glucose. Fivefactors were evaluated: concentration of L-cysteine-HCl, concentration ofoverall acceptability, the optimum reaction conditions for production of a meat flavoringswere 3.5x10-2mol/L of reduced sugar (D-glucose: D-xylose=l:l) , 2.75X 10-2mol /LofL-cysteine-HCl, initial pH 6.5, temperature 125 癈 and reaction time 135min.The Basicmeat(beef) flavoring generated from the model system of enzyme-hydrolyzed beefprotein-L-cysteine-HCl-D-glucose under the optimum conditions have good sensory propertieswith typical and full-bodied beef flavor.The volatile compounds of a meat flavorings made from the model system at the optimumreaction conditions were isolated by solid-phase microextraction(SPME), simultaneousdistillation extraction(SDE) and thermal desorption(TD). The extracts were analyzed by gaschromatograph-mass spectrometry (GC-MS). 110 volatile compounds were identified. Themixture of volatile compounds identified was characterized by a considerably high percentage(47%, based on the number of kinds of compounds) of heterocyclic compounds. 52 heterocycliccompounds identified consisted of oxygen-containing compounds (furans and furanones),sulfur-containing compounds (thiophenes, thiazoles and furans) and nitrogen-containingcompounds (pyrazines, pyrroles and oxazoles). Aliphatic compounds included sulfur-containingcomponents, hydrocarbons, alcohols, aldehydes, ketones and carboxylic acids. The total numberof sulfur-containing compounds up to 28 having a percentage of more than 25%. Somei m p o r t a n t m e a t f l a v o r c o m p o u n d s s u c h a s 2 -f u r a n m e t h a n e t h i o l ,2 -m e t h y l -3 -f u r a n t h i o l , m e t h y l ( 2 -m e t h y l -3 -f u r y l ) d i s u l f i d e ,bis(2-furfuryl)disulfide, bis(2-methyl-3-furyl)disulfide, 3-methyl-2-thiophenecarboxaldehyde,2-methylthiophene, 2-methyl-tetrahydrothiophen-3-one, 2-methyl-4,5-dihydrothiophene,thiazole, 2-methylthiazole, 4,5-dimethylthiazole, 2-acetylthiazole, ethylene sulfide,2,5-dimethyl-4-hydroxy-3(2H)-furanone, 2-acetylfuran, 2-methyltetrahydrofuran-3-one,2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, pyrazine, 2,6-dimethyl pyrazine and2-methylcyclopentanone, et al. were identified in a heated meat flavor model mixture, which areconsistent with previous findings in meats. The results suggested that the composition of themodel system and reaction conditions were appropriate and the results of analysis providedgood evidence for the sensory evaluation. Application of solid-phase microextraction,simultaneous distillation extraction and thermal desorption in the analysis of meat flavoringshad good complementarity. The simultaneous distillation extraction could reflected morecomprehensive flavor profile of meat flavoring.The reaction between L-cysteine-HCl and D-glucose at pH6.5 generated a complex mixtureof volatile compounds. 96 volatile compounds were identified. The mixture contained 58 kindsof heterocyclic compounds (60%) and 49 kinds of sulfur-containing compounds (51%). Thesulfur-containing compounds dominated by 29 Thiophenes containing 4thiophenethiols, 1 aclylthiophene, 1 thiophenecarboxaldehyde, 5 dihydro-3(2H)-thiophenones, 4thienothiophenes and 14 alkylthiophenes. 2-ethylthieno (2,3-b) thiophene has not been reportedin literatures.Two kinds of fat separately were added into the solutions of L-cysteine-HCl -D-glucose,which were heated to the temperature of 100 癈 for 3 hours at pH 6.5. The inclusion of beeftallow and sunflower oil considerably increased the number of volatile components, adding notonly the products of lipid oxidation, such as Trans-,trans-2,4-decadienal, but also compoundsspecific to the interaction of the lipid in the Maillard reaction. The amount of 2-acetyl-furan,2,5-dimethyl-3(2H)-furanone and 2,3-dimethyl-thiophene increased with increase of degree ofunsaturated of fat. 3-methyl-lH-pyrrole and l-(lH-pyrrol-2-yl)-ethanone only identified from thereaction of L-cysteine-HCl and D-glucose with fat. The addition of two kinds of fat caused thedisappearance or reduction of many heterocyclic compounds, like thiophenes, thiazoles andfurans. The plausible explanation for this phenomenon is that the products of lipid oxidationcompete with each other for ammonia or sulfur active precursors available in the system top r o d u c e s o m e n o n v o l a t i l e c o m p o u n d s o r n e w v o l a t i l e c o m p o u n d s .Taurine, Taurine-D-glucose and L-cysteine-HCl -D-glucose with or without taurine wereheated to the temperature of 100 癈 for 3 hours at both pH 4.5 and 8.0. Taurine withoutD-glucose reaction products produced no odor. Taurine was more easy to degradation atalkalescence pH condition. The degradation compounds of taurine mainly containedhydrocarbons, alkylbenzenes, aldehydes, alcohols and esters. The isolate from the interaction oftaurine and D-glucose possessed a typical sweet, caramel-like characteristic. Four kinds ofN-containing heterocyclic compounds were identified from the reaction system of taurine andD-glucose at pH 8. The results suggested that a free ammonia generated from the deamination oftaurine under the conditions used and taurine act as limited nitrogenous sources to facilitate theformation of nitrogen-containing flavor compounds. However, how exactly taurine provided thenitrogen source remained to be elucidated. There were no sulfur-containing compoundsidentified from taurine system and the reaction system of taurine and D-glucose. The resultssuggested that taurine can not substitute for L-cysteine acted as sulfur donor. Taurine affectedvolatile formation from the reaction of L-cysteine-HCl and D-glucose in complex manners.Taurine mitigated the green, nutty and sweet odor and made the meaty flavor more full andsoftness by facilitating the generation of thiophenes, pyrazines and furans. On the other hand,taurine inhibited the generation of of thiazoles.