The Optimization Of Fermentation Process And The Effect Under Temperature Variation On The Quality Of Shrimp Sauce Fermented With By-Product

Litopenaeus vannamei was widely loved and sold well because its delicious taste,high nutritional value,high content in protein,vitamins,minerals and polyunsaturated fatty acids.Although there are numerous product types,such as shrimp sauce,dried shrimp,shrimp dumplings,frozen shrimp and instant shrimp,but the main product is prawn,the by-product was mostly discarded or being rough machining.The effective utilization and deep processing of by-product are still to be developed.How to increase the additional economic value of by-product,reduce the emission pollution and develop new kinds of condiments are more worthful of exploration.The nutritional components and flavor compounds in Litopenaeus vannamei's prawn and head of were studied in this experiment.The process parameters(liquid-solid ratio,salinity and koji amount)were optimized.The quality of shrimp sauce that prepared by the optimal fermentation conditions was detected.Finally,shrimp sauce's physicochemical index,flavor compounds and sensory index were detected to study the influence made by temperature variation during fermentation.Laying a theoretical foundation for developing a kind of shrimp sauce with high nutritional value,good flavor and reasonable proportion.The head and prawn of raw and cooked were used to explore the contents of basic nutrients and flavor compounds.The volatile flavor compounds were detected by the method of headspace solid phase microextraction coupled with gas chromatography-mass spectrometry,the flavor nucleotides were detected used high performance liquid chromatography,the content of free amino acid,water,crude protein,crude fat and crude ash were also detected.The crude protein content and essential amino acids in head were significantly higher than that of prawn.The crude protein content of raw and cooked head is 1.09 times and 1.07 times than that of prawn,the content of essential amino acids in raw and cooked head is 2.10 times and 4.15 times than that of prawn.The amino acids that contribute most to the taste of head are glutamate and alanine,which contribute most of prawn are glycine and arginine.59 species and 70 species volatile flavor compounds were separately detected in head and prawn,of which 2-ethylfuran and 2-hexanone were found only in the head contributing to the unique flavor of head.The influence of fermentation parameters(liquid-solid ratio,salinity and koji amount)on the quality of shrimp sauce was studied based on the content of amino-acid nitrogen.The salinity and the liquid-solid ratio are lower,the higher the amount of starter,the content of amino-acid nitrogen is higher in shrimp to a certain extent.The parameters of fermentation process were determined as follows: liquid-solid ratio(0.4:1,0.6:1,0.8:1),salinity(20%,24%,28%),koji amount(17%,19%,21%).The optimized fermentation technology of shrimp sauce was optimized by response surface test.The optimized process parameters were as follows: the ratio of liquid-solid was 0.63:1,the salinity was 25.25% and the koji amount was 19.16%,then the content of amino-acid nitrogen in obtained shrimp sauce was 0.70 g/100 mL.In order to detect the optimal fermentation process,it was found that the content of amino-acid nitrogen,total nitrogen and total acid were 0.68 g/100 mL,1.46± 0.21 g/100 mL and 0.65 ± 0.03 g/100 mL,which basically met the national standard of shrimp sauce.Temperature influences the quality of shrimp sauce by affecting the growth rate of mycelium,enzyme reaction rate and product synthesis rate.The optimum growth temperature of Aspergillus oryzae and protease produced by Aspergillus oryzae were separately 30 centigradeand 40 centigrade~50centigrade.The method of temperature variation fermentation was adopted in order to explore the effect of temperature on the physicochemical properties,flavor components and sensory indexes of shrimp sauce.The first 5 days were fermented at 30 centigrade,and 6 days to 30 days,respectively at 35,40,45,and 50 centigrade.The amino-acid nitrogen content,the salt free soluble solids and the specific gravity of shrimp sauce fermented at 50 centigrade were the highest,the reddish brown of shrimp sauce was the most deep,but did not reach the browning degree of commercial shrimp sauce.A total of 59 kinds of volatile flavor compounds were obtained in shrimp sauce under variable temperature by measuring with headspace solid phase microextraction combined with gas chromatography mass spectrometry.The main contribution to the formation of the unique odors were aldehydes,ketones and pyrazines.Under 35 centigrade,40 centigrade,45 centigrade and 50 centigrade,there are 5,2,and 6 kinds of unique volatile odor respectively.35 centigrade is more conducive to the formation of flavor,producing more pyrazine and ketones,and 1H-indole content is less.The most delicious and sweet amino acids were found in the shrimp sauce fermented under 35 centigrade.The most essential amino acids and free amino acids in the shrimp sauce fermented under 50 centigrade.In the sensory evaluation,the shrimp sauce fermented under 35 centigrade has the highest overall acceptability,strong taste,moderate salty taste,and the best overall effect.It basically reached the level of A grade shrimp sauce demands.