Study On The Preparation Of Basic Flavorings By Solid Substrate Fermentation And Enzymatic Hydrolysis Of Pinctada Martensii

The Solid-state fermentation conditions of Pinctada martensii cultivated with Aspergillusoryzae were optimized. The off-flavor compounds of Pinctada martensii were detected byGC-MS and GC-O. The changes of nutritional substrates and off-flavor compounds weremonitored during the fermentation process. Ultimately the hydrolysates of Pinctada martensiimeat koji were richer in umami taste, less off-odor and better antioxidant than the commercialprotease hydrolysates.The effects of stewing conditions, addition of carbon, initial moisture contents of the koji,culture time and temperature on the protease activity of koji were investigated. Optimumkoji-making conditions of solid-state fermentation were obtained. Pinctada martensii washeated at121℃for10min, added25%flour (w/w), the initial moisture content of koji was51.89%, inoculated with0.5‰Aspergillus oryzae spores, then the koji was cultured at32℃for46h. Under the above conditions, the neutral and acid protease activity of koji were1494U/g and390U/g, respectively. The various biochemical changes were detected and comparedin different growth conditions, such as physical indicators (total weight, moisture content,total sugar, soluble sugar, reducing sugar, organic acids, total nitrogen, amino nitrogen, totalvolatile basic nitrogen, free amino acids) and activity of enzymes (neutral protease, acidicprotease, alkaline protease, α-amylase and glucoamylase). These results showed that1) thetotal weight, moisture content, total sugar, total nitrogen decreased during the process, and theconsumption of carbon sources was responsible for the loss of dry matter. The nutritionalmaterial consumption was closely correlated with the different growth periods of Aspergillusoryzae. During the fermentation time of24-36h, reducing sugar and amino acids were rapidlyabsorbed. The consumption of glutamic acid was the largest. The activity of protease reachedthe peak point during40-46h of koji fermentation.Volatile compounds in Pinctada martensii were investigated by GasChromatography-Mass pectrometry (GC-MS). A total of83volatile compounds wereidentified and quantified in this study.48,51,45,42,54compounds were found in freshPinctada martensii meat, heated Pinctada martensii meat, Pinctada martensii koji, hydrolyzate,heated hydrolyzate, respectively. Meanwhile, the key odor-active compounds were analyzed by GC-O method. The main off-flavor compounds were pentanal,3-methyl-2-butenal,hexanal, heptanal, benzaldehyde,1-octen-3-ol,(E)-2-octenal, nonanal,2-phenylpropenal,benzenecarboxylc acid and2-decenal. The aldehyde compounds with off-odor decreased by98.82%during koji-making process.Crude proteases (CP) from Pinctada martensii koji, four commercial proteases(Protamex,Papain, PTN6.0S, Flavorzyme) and nonprotease were employed to hydrolyse PinctadaMartensii. CP was found to be a more effective protease with protein recovery of68.36%thanthe tested commercial proteases. Moreover, CP produced the highest degree of hydrolysis(DH,64.27%) than others. The test of molecular weight distribution indicated that CPhydrolysate was mainly consisted of <3KDa fraction, especially <1KDa fraction (84.65%)was observed to be the highest of commercial hydrolysates. CP hydrolysate possessed higherumami amino acid (38.27%) than other hydrolysates. As a result, the sensory evaluationshowed that CP hydrolysate had a better taste than other hydrolysates. Antioxidative activitieof hydrolysates was1.93times as Papain and5.70times as Flavorzyme. Meanwhile, Oxygenradical absorbance capacity (ORAC) reached the maximum of2834.67μmol trolox/g, whichwas1.13times as much as the equal quality of the glutathione.