| Garlic(Allium sativum L.)has been widely used as not only a spice but also an herbal remedy.Some therapeutic effects of fresh garlic have been broadly reported.In this thesis,the formation and changes of volatile organosulfur compounds during the processing of garlic paste and frozen garlic were investigated.It aims to make a significant breakthrough in quality assurance during garlic processing.In this study,water blanching pretreatment was used to obtain products with high content of organosulfur compounds and sensory quality.Different blanching conditions(thermal-mechanical sequence,blanching temperature and time)were used to process garlic paste.The effects of different processing parameters on the quality of garlic products were investigated.The changes of enzyme activities,microstructure and water status were used to reveal the mechanism of the formation of fuctional compounds and quality changes during thermal processing.Moreover,allicin in aqueous solution was to investigate the potential endogenous and exogenous factors(e.g.p H,temperature,concentration,solvent,organic acids,polyphenols and amino acids)that might affect allicin stability.These findings are expected to clarify the interaction relationships and mechanism of internal and external source factors on the formation and maintenance of volatile organosulfur compounds in the processing of garlic.The volatile organosulfur compounds in garlic were analyzed by high performance liquid chromatography(HPLC),the texture analyzer was used for texture analysis,the colorimeter was used for measuring the color properties,low field nuclear magnetic resonance(LF-NMR)was used for analyzing the changes of water status,the scanning electron microscope(SEM)and the optical microscope were used for the observation of microstructure.The main results of this research are listed below:(1)Volatile organosulufur compounds in garlicGarlic is famous for its unique pungent flavor,which is mainly attributed to a series of volatile organosulfur compounds.The HPLC analysis results showed that in fresh garlic the predominant volatile compound is allicin(5.59±0.26 mg g-1)and(E/Z)-ajoene(1.68±0.05mg g-1),followed by cyclic sulfides(2-vinyl-[4H]-1,3-dithiin and 3-vinyl-[4H]-1,2-dithiin,0.54±0.05 mg g-1),the contents of diallyl disulfides(0.14±0.01 mg g-1)and diallyl disulfides(0.22±0.02 mg g-1)are the least.The content of allicin and its degradations could be analysis with HPLC approached.HPLC analysis a reliable analytical method for the accurate quantifiaction of characteristic flavor compounds in fresh garlic.(2)Changes of volatile organosulfur compounds and quality properties during the processfrozen garlicIn a preliminary research,the blanching conditions were determined according to the formation of volatile organosulfur compounds and the loss of enzymic activities.No significant decreased in allicin content was observed when the garlic samples were blanched at 80°C for less than 60 s,90°C for 45 s and 100°C for 45 s.As prolonged the blanching time by 15?30s,the loss rate of allicin with different temperature treatment increased significantly.Moreover,in order to reach the inactivation of peroxidase,the optimal blanching temperature was 100°C.As compared with fresh garlic,the frozen garlic treated by 45 s,60 s and 80 s at 100°C retained91.24%,27.51%and 8.65%of allicin,respectively,while 81.83%,92.84%and 95.28%of peroxidase activity was inactivated.As compared with frozen garlic without blanching treatment,the browning index of blanched frozen samples was decreased by 49.97%.The hardness of frozen garlic improved by 48.01%in the samples treated with 45 s at 100°C.However,there is no significant difference in hardness between frozen fresh garlic and frozen garlic after 60 s and 80 s of blanching at 100°C.The results of pectin methylesterase activity,water status and microstructure showed that:blanching induced free water transported to intercellular space,the activity of pectin methyl esterase was not compeletly inactived after 45s blanching,provide a protective effect for texture properties.However,blanching for 60 s and80 s resulted in the inactivation of pectin methyl esterase,pectin occurred thermal degradation,and the ice crystal volume increased during freezing,which caused the hardness decreased.Therefore,adding blanching pretreatment and strictly controlling blanching intensity in frozen garlic processing,which is an effective strategy to ensure the flavor quality and the physicochemical quality of frozen garlic.(3)Changes of volatile organosulfur compounds and quality properties during the process of garlic pasteThe sequence of unit operations determined the pattern of garlic microstructure disruption,resulting in various enzymic and non-enzymic reactions.In blended-heated garlic samples,the allicin content decreased steadily.In heated-blended garlic,a high level of allicin content was maintained for the first 5,2 and 2 min at 75,85 and 95°C,respectively.Afterwards(blanching for 5?10 min),it decreased sharply by 29.56,90.63 and 94.79%.As allicin degradated in thermal processing,the contents of linear polysulfides(DADS and DATS)increased,the content of(E/Z)-ajoene and cyclic sulfides decreased,resulted in the total content of organosulfur compound decreaed.Moreover,the changes of alliinase activity corresponding to the changes of allicin contents in heated-blended garlic,the alliinase activity dereased or even completely inactivated after blanching treated for 5?10 min,which indicated alliinase activity was a crucial factor affecting the changes of volatile organosulfur compounds in heated-blended garlic.Allicin had generated before blanching threatment in blended-heated garlic,which indicated the changes of volatile organosulfur compounds were no longer affected by alliinase.Garlic greening discoloration occurred in the blended-heated garlic with large number of cell clusters with broken edge,and the total color difference(?E)values were 12.08?24.75.However,it's obseverd that smaller cell clusters with intact cells in blended-heated garlic,and the total color difference(?E)values were 2.12?8.42,which indicated the heated-heated treatment was helpful to maintain the color quality of garlic.In conclusion,it is recommended that garlic paste be prepared using heated-blended processing,with proper thermal processing.(4)Factors affecting the change of volatile organic sulfideThe solvent type,temperature and p H value are important external environmental factors affecting the stability of allicin.In different solvent,the decomposition rate of allicin are varies,The stability of allicin in water was higher than methanol or ethanol solvent,allicin showed the lowest stability in non-polar solvent(hexane,dichloromethane,ether and acetone).It's observed that in lower temperature and lower concentration,the stability of allicin were increased.Moreover,the degradation process of allicin was good fit with two-first order kinetics(R2>0.97).It's showed that the stability of allicin was higher in acid condition(p H3.0?6.0)than in alkaline condition(p H?7.0).Moreover,in alkaline condition,all of allicin degradations increased in alkaline condition in allicin aqueous solution,however,only linear polysulfides increased accompanied with(E/Z)-ajoene and cyclic sulfides decreased in garlic paste.It's indicated the complex components of garlic paste that affected the changes of volatile organosulfur compounds.Therfore,the effect of endogenous factors was further invested.Apigenin,myricetin and quercetin had no significant effect on the stability of allicin(P>0.05),however after they oxidazed to quinone they could increase the stability of allicin.Arginine and histidine could react with allicin,enriches linear polysulfides.Therefore,these amino acids could be an endogenous factor that potentially involved in the degradation of allicin in garlic.The reseach on the effects of endogenous and exdogenous factors on the volatile organosulfur compounds provides a theoretical basis for regulating and controlling the flavor compounds during garlic processing and storage. |
PDF Full Text Request