Determination Of Undesirable Odour Components In Silver Carp(Hypophthalmichthys Molitrix) Surimi And The Effects Of Typical Ingredients On Their Volatilization

As one of the four important freshwater fish in China,silver carp(Hypophthalmichthys molitrix)is a source of food protein with high nutritional value.However,it is not very popular among consumers due to its thin meat and many bony spurs,and strong earthy and fishy smells that are difficult to remove,making it unsuitable for fresh consumption.So silver carp is generally used as an economic raw material for preparing surimi.In the context of the healthy China strategy,fish are in increasing demand as a source of good quality protein.China’s surimi industry has been in a bottleneck period from quantitative expansion to qualitative improvement.The heavy fishy odour of freshwater surimi is one of the industrial challenges affecting the quality and efficiency of surimi.Currently,most studies mainly used gas chromatography-mass spectrum(GC-MS)and other instruments to analyze volatile compounds with high odour activity value(OAV)in surimi to determine the source of fishy odour components.But volatile compounds with OAV greater than 1 only represented their contribution to the overall odour,and did not necessarily indicate that they were the source of undesirable odours.The identification of undesirable odour compounds in existing literature was not clearly explained.In addition,existing research focused on the removal of the fishy odour from raw materials of freshwater fish,but the interaction between different components could affect the release of undesirable odour components in actual product systems,and studies solely from the perspective of deodorization of raw materials might not be comprehensive enough.Therefore,this thesis mainly focused on the determination of undesirable odour components of silver carp surimi and their content changes in surimi products.The main research results were as follows:Firstly,through data mining and instrument analysis,the volatile odour compounds of silver carp surimi were comprehensively obtained,and a database of volatile compounds of silver carp surimi was constructed.The results showed that,based on data mining in Python,91 volatile components were obtained to describe the overall odour characteristics of freshwater fish.There were 27 main odour characteristic descriptors,and the relationship between characteristic odour components and odour characteristics of freshwater fish was obtained.The "fatty" odour was related to compounds such as pentanal,octanal,nonanal,(E)-2-nonenal,and decanal;The "fishy" odour was related to compounds such as hexanal,heptanal,(E)-2-octenal,(E,E)-2,4-heptadienal,(E)-2-decenal;The "grassy" odour correlated with compounds such as hexanal,octanal,nonanal and 1-hexanol;While the "mushroom" odour was mainly associated with volatile compounds such as 1-octen-3-ol.Based on the detection by SPME-GC-MS,there were 65 volatile compounds in silver carp surimi,including 23 aldehydes,13 alcohols,10 ketones,7 alkanes,etc;Based on the method of OAV,18 odour active substances(OAV > 1)were identified,and their relative odour contribution(ROC)was also evaluated.It was found that the ROC of hexanal,octanal,nonanal,and 1-octen-3-ol was higher,indicating that these substances played an important role in the odour contribution.Common substances were retained based on word frequency size and OAV > 1,21 volatile compounds were selected in the initial screening for the next step in determining undesirable odour.Secondly,by constructing a background model for low-odour surimi and combining odor recombination and omission experiments,the undesirable odour compounds of silver carp surimi were determined.The main volatile components related to undesirable odours in silver carp surimi were hexanal(fishy,grassy),octanal(fatty,grassy),(E)-2-octenal(fishy),nonanal(fatty,grassy),(E)-2-nonenal(fatty),(E,E)-2,4-heptadienal(fishy),1-hexanol(grassy),and 1-octen-3-ol(mushroom).These 8 undesirable odour compounds were select to conduct the next study on the effects of typical ingredients of surimi on their volatility.Finally,the effects of starch and vegetable oil on the volatilization of undesirable odour components from frozen surimi products were studied.The results showed that,when the proportion of starch was 5%,10%,and 15%,the contents of undesirable odour components all decreased,and the differences were not large,indicating that starch contributed to the inhibition of undesirable odours such as "fishy" and "fatty" smells.At the same time,the addition of vegetable oils at 2% and 3% ratios increased the contents of undesirable odour components,indicating that vegetable oil ingredients would aggravate "fishy","fatty" smells and other undesirable odours.Sensory evaluation was basically consistent with the analytical results of SPME-GC-MS,which further confirmed that the addition of starch and vegetable oil had some effects on the smell of fish balls.In addition,the content of undesirable volatile components in fish balls decreased significantly after cooking,but there was no difference between the overall change pattern and that after thawing.