| The meat soup is appreciated as a favorite dish around the world,due to its unique aroma and delicious taste.Traditional clay stewpots(TS)have been used for a long time to cook meat soup as they impart delicious taste.Moreover,with the development of industry,the preparation of meat soup is mainly based on electrical stewpot which is more intelligent and rapid.Additionally,meat soup cooked in commercial electrical stewpots(CS)has different problems,such as loss of meat flavor or development of peculiar smell,which make its quality hard to control and almost impossible to guarantee.In this study,the main objective was first to investigate the flavor differences of pork bone soup prepared in TS and CS and identify the main factors affecting the meat soup flavor.The processing parameters of electrical stewpot were optimized for the preparation of pork bone soup with high quality and short cooking time.Moreover,partial least squares regression(PLSR)was used to discover the key factors influencing the pork bone soup flavor.Furthermore,the changes of volatile compounds in pork bone soup during cooking process in different heating modes were analyzed.Additionally,the flavor formation mechanism was clarified and the off-flavor compounds were identified.Then,the main chemical reaction sources of volatile compounds in pork bone soup were elucidated by model test.As such,a convenient and rapid analysis method to discriminate pork bone soup flavor in different pork origins,heating conditions and heating modes was established by flash gas chromatography electronic nose(flash GC E-nose).Effects of TS and CS on the flavor quality of pork bone soup were compared.The sensory results showed that pork bone soup cooked in TS had higher meaty aroma,lower off-flavor scores and higher acceptance level,while the long heating time of CS would lead to the flavor deterioration.Twenty-nine odor active compounds were identified in pork bone soup by gas chromatography-mass spectrometry/olfactometry(GC-MS/O),and there were 26 and 14 odorants identified in samples prepared with TS and CS respectively.These results combined with the gas chromatography-mass spectrometry(GC-MS)had revealed a high relative content of odor-active compounds,aldehydes,alcohols,ketones,esters,hydrocarbons,nitrogen-containing substances,furans and other unknown compounds in pork bone soup cooked in TS.Results also showed that the flavor profiles of pork bone soups in different stewpots mainly depended on their specific heating modes,including the heating rate of 2.358°C/min for TS and 0.581°C/min for CS and a total heating time of 120 min in TS and 240 min in CS.Moreover,high scores of the meaty attribute and high relative content of odor-active compounds such as aldehydes and ketones,were obtained in pork bone soup prepared in electrical stewpot by controlling its heating parameters.Furthermore,low temperature modulation modes were applied and the effect of heating modes on pork bone soup flavor generation in electrical stewpot was investigated.One of the electrical stewpot samples showed good sensory characteristics compared with other samples and its corresponding heating parameters were as follows: heating rate of 2.419°C/min,constant temperature time of 20 min,low temperature of 80°C and its holding time of 50 min(C4).The significant impact of odor-active compounds,taste compounds and heating parameters on sensory attributes through PLSR was investigated.Results showed that benzaldehyde,6-methyl-5-hepten-2-one,2-nonanone,2-undecanone and hexanoic acid had a significant and positive correlation with meaty note.Fatty attribute was significantly and positively correlated with octanal and 6-methyl-5-hepten-2-one.Octanal and decanal were significantly and negatively correlated with the off-flavor attribute.Glu was significantly and positively correlated to meaty note;whereas,Phe was significantly and negatively correlated to meaty note.There was no significant influence for the two attributes,fatty attribute and kokumi.Off-flavor attribute showed significant and negative correlation with Glu and His.The heating rate,low temperature and low temperature time had been found significantly associated with sensory attributes;especially low temperature time was significantly and negatively correlated with the off-flavor note.Results indicated that low temperature modulation modes could help to reduce the off-flavor in meat soup.The changes of volatile compounds from four pork bone soup samples during heating process prepared in the TS,CS,low temperature modulation mode C4,C12 with the same heating rate and total heating time as C4,but maintaining high temperature at 100°C were studied and evaluated by GC-MS.Results showed that TS had high heating rate and short total heating time.With the increase of heating time,the aldehydes content in TS increased first,then decreased,and increased afterward.The content of ketones,nitrogen-containing compounds and furans increased.While CS had low heating rate and long total heating time.The content of aldehydes,ketones and esters in the CS samples first increased and then decreased,and the reduction of their content was obvious.Cooking at high temperature(100°C)would lead to the evaporation and loss of volatile compounds,the overreaction of lipid oxidation and Maillard reaction,resulting in some irritating compouds of acids and ketones.The content of aldehydes,ketones and esters obtained at the end of heating time in the C4 sample were higher than those in the C12 sample.Low temperature modulation modes could contribute to generate and retain the main aroma components by increasing heating rate,shortening the heating time,adding automatic decreasing temperature phase and low temperature phase.Result further clarified that low temperature modulation modes could improve the flavor profile of pork bone soup.The optimized heating mode was applied to industrial application and production by Midea Electrical Heating Appliances Manufacturing Co.,Ltd.Correlation analysis between the volatile compounds and the off-flavor attribute by PLSR showed that(E)-hexenal,hydroxyacetone,3-hydroxy-2-butanone,?-butyrolactone,acetic acid,hexanoic acid,naphthalene and 2-pentylfuran had a significant and positive contribution to the off-flavor note.Furthermore,the chemical reaction sources of the volatile components released from the stewed pork bone soup were analyzed.The model test results of pork bone soup without ginger and salt,lipid oxidation and Maillard reaction of fat-free pork bone soup showed that the volatile compounds of hexanal,octanal,nonanal,decanal,benzaldehyde,(E)-2-nonenal,(E)-2-decenal,(E,E)-2,4-decadienal,(E)-2-octenal,(Z)-2-heptenal,1-octen-3-ol,2-nonanol,2-nonanone,2,3-octanedione,?-lactone,ethyl palmitate,(E)-9-octadecenoic acid ethyl ester,Methyl stearate,phthalic acid diisobutyl ester,hexanoic acid,acetic acid,heptanoic acid,octanoic acid,nonanoic acid,2-pentylfuran and 2,4-bis(1,1-dimethylethyl)-phenol in pork bone soup were derived from lipid oxidation.Benzaldehyde,2-undecanone and pyridine were derived from Maillard reaction.Whereas,the volatile components of 3-methyl-1-butanol,1-dodecanol,1-hexadecanol,indole,2-acetylthiazole and 5-dodecyldihydro-2(3H)-furanone were came from the interaction between lipid oxidation and Maillard reaction.These results indicated that the aroma of pork bone soup was mainly derived from lipid oxidation.Monitoring the flavor changes during cooking process can offer a direction for quality control of meat products.The effect of different pork origins,heating rate and total heating time on the flavor profile of pork bone soup was also investigated through GC-MS.Results indicated that there were significant differences between the samples.As such,flash GC E-nose was applied to discriminate the volatile profiles emitted by pork bone soups prepared from different pork sources and exposed to different processing conditions.Results showed that pork origins,heating rate,cooking time and heating mode were the key factors influencing the flavor profile of meat soup,thus,it was possible to separate samples into different clusters using flash GC E-nose signals.The present study demonstrated that flash GC E-nose was a useful and rapid approach to monitor the changes in flavor profile among samples.The influence of low temperature modulation modes(TM1-TM6)on chicken broth sensory attributes and flavor profile was further studied.Sensory results indicated that the suitable heating mode for chicken broth preparation were as follows: the heating rate was 2.62°C/min,the low temperature time was 22 min,the low temperature was 90°C,and its holding time was 35 min(TM1).Chicken broth processed using TM1 had the best flavor with higher chicken meat-like and lower off-flavor scores.Moreover,GC-MS and GC-MS/O results revealed that the TM1 samples had the most abundant odorants,and the relative content of aldehydes,alcohols and ketones in the TM1 samples was higher than other samples.The umami-taste components from TM1 samples such as umami amino acids and inosine 5?-monophosphate(IMP)had the highest amount.Additionally,the relationship between sensory evaluation and odor-active compounds were evaluated by PLSR,which indicated that heptanal,benzaldehyde,(Z)-2-decenal,(E,E)-2,4-decadienal,1-pentanol,2-undecanone,2-pentylfuran and one unknown compound were significantly and positively correlated with chicken meat-like note.Whereas,fatty aroma were significantly and positively correlated with octanal,(E,E)-2,4-decadienal and 1-pentanol.(E,E)-2,4-Decadienal and 2-undecanone had a significant and negative correlation with off-flavor attribute.In our study,we have also investigated the effect of different heating modes on the flavor profile of fish(crucian carp)soup which was evaluated through sensory evaluation,GC-MS and GC-MS/O analysis.Sensory results indicated that the suitable heating mode for fish soup preparation were as follows: the heating rate was 2.44°C/min,the low temperature time was 20 min,the low temperature was 90°C,and its holding time was 60 min(TM2).The crucian carp soup prepared under these conditions had a stronger intensity of fish flavor and fatty aroma,also,the fish soup had a lighter off-flavor.A total of 26 odorant compounds were identified by GC-MS/O with direct-time intensity method in crucian carp soups prepared with CS and TS.The aldehydes,alcohols,ketones,ester and phenolic compound were considered to have an important influence on the aroma of fish soup.The results of GC-MS analysis showed that different heating modes had a significant effect on the flavor profile of the fish soup.Compared with other heating modes,the sample prepared in TM2 had the highest content of aldehydes,ketones and ester.Correlation analysis between sensory attributes and odor-active compounds of fish soups through PLSR revealed that octanal,decanal,2-heptanol,1-octen-3-ol,octanol,6-methyl-5-hepten-2-one and 2-undecanone were significantly and positively correlated with fish flavor,while ethanol and dodecanol were significantly and negatively correlated with fish flavor.The compounds of(E)-2-octenal,2-heptanol,1-octen-3-ol and hexadecanoic acid ethyl ester showed a significant and positive influence on fatty note.Whereas,octanal and 2-heptanol was significantly and negatively correlated with the fishy smell note.In addition,all detected odor-active compounds showed non-significance with off-flavor. |
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