Flavor Improvement Of Enzymatic Extracts From Pinctada Martensii Entrails By Maillard Reaction

Pinctada martensii entrails, a by-product produced during the production of marine pearl in south China, is an important low-valued protein resource which is not yet fully utilized. Its enzymatic hydrolysate, which is tasty, nutritive and possesses various physiological activities, is ideal for the development of natural functional seafood seasoning. However, there are still many defects in the flavor of the enzymatic hydrolysate, such as a strong fishy smell, a poor aroma and a weak mellow taste. In this thesis, the optimum condition for flavor improvement of the enzymatic extracts from Pinctada martensii entrails by Maillard reaction was studied and its effects on volatile and non-volatile flavor were evaluated with the combination of sensory evaluation, chemical analysis and instrument analysis, expecting to provide theory foundation for the development of high-grade seafood seasoning using Pinctada martensii entrails.The effects of factors, namely the kinds of reducing sugar, the ratio of the sugar in their combinations, the addition amount of reducing sugar, the initial pH value, the reaction time and the moisture content of enzymatic extracts, on the flavor of enzymatic extracts were investigated by single factor experiments based on sensory evaluation and Maillard reaction degree. And then the Maillard reaction condition was optimized by the orthogonal experiments based on the preceding results. The results showed that the optimum reaction parameters are as follows:3%(w/v) glucose,70%(w/w) moisture content, pH 6.5, reaction time 22 min, reaction temperature 100℃.The flavor profiles of the extracts before and after Maillard reaction were analyzed by flavor profile test, the results showed that the fishy smell was weakened quite effectively, the shellfish flavor was intensified and some other flavors were produced, therefore the volatile flavor of the extracts was improved by the Maillard reaction.The fingerprints of the extracts before and after Maillard reaction were acquired by electronic nose technology and were analyzed by principal component analysis, soft independent modeling of class analogy and statistical quality control, the results, which coincided with the results of flavor profiles, revealed that the characteristic flavor of the extracts was well remained, but its overall flavor changed greatly.Qualitative and quantitative analysis of the volatiles in the extracts before and after Maillard reaction were conducted by HS-SPME-GC-MC technique and the odour active value(OAV) of each volatile was calculated, the results showed that the amout of volatiles in enzymatic extracts increased from 39 to 44, the content of volatiles in enzymatic extracts increased from 58.42μg/100 mL to 222.20μg/100 mL and the amout of odour active compounds in enzymatic extracts increased from 11 to 14. Considering organoleptic perception, the odour active compounds could be classified under "shellfish meaty" "nutty", "fishy, grassy", "sweet, fruity", "toasty", "caramel" aroma and other organoleptic perception. Comparing with the extracts, the OAV of volatiles which contribute to "fishy, grassy" and "sweet, fruity" aroma in the Maillard reaction products decreased to 1/3 and 2/5, respectively; the OAV of volatiles which contribute to "shellfish meaty" and "nutty" aroma increased to 6.9 times and 20.3 times, respectively; the OAV of volatiles which contribute to "toasty" and "caramel" aroma increased from 0 to 32.0 and 152.1, respectively; the OAV of volatiles which contribute to other aroma increased to 14.3 times. These results coincided with the results of flavor profiles.The taste profiles of the extracts before and after Maillard reaction were analyzed by flavor profile test, the results showed that the prominent characteristics of the extracts before Maillard reaction in taste were that the umami taste was very strong and the bitter taste was less weak; after Maillard reaction, the bitter taste was weakened obviously, the mellow taste and after taste were enhanced obviously, the umami taste was enhanced somewhat, so the overall taste was improved.The non-volatile taste active compounds, including free amino acids, ATP related compounds, glycine betaine, glycogen, organic acid and mineral salts and peptides in the extracts before and after Maillard reaction, were analyzed by chemical and instrumental analysis, and the effects of Maillard reaction on the taste of the extracts were evaluated by taste active values (TAVs) and equivalent umami concentration (EUC) methods. The constitution model of the taste active compounds in extracts didn't change after Maillard reaction, according to the contribution to the overall taste, the taste active compounds could be classified as the ones which constituted core of the taste (Glu, Val, Met, Ala, AMP, glucose, succinic acid, Na+ and Cl-), the ones which elaborated the characteristic taste (Gly, Arg, IMP, glycine betaine, K+ and PO43-) and the ones which enhanced the overall flavor(glucogen, lactic acid, short peptides, Mg2+ and the rest of free amino acids). But the roles of the taste active compounds in the taste of Maillard reaction products changed in different levels with their changes in content. The content of free amino acids which have bitter taste(except for Arg) reduced, therefore the bitter taste was weakened; the content of free amino acids, which have sweet taste, and glucose reduced, therefore the sweet taste was weakened; the content of Glu, Asp and IMP reduced, the EUC reduced from 28.07g MSG/100mL to 22.86 g MSG/100mL, the TAV of the EUC reduced from 936 to 762, therefore the synergy between amino acid and nucleotide became weaker; the content of glucogen reduced, its balance role in taste became weaker; the content of lactic acid, succinic acid and Arg increased, their flavor enhancement roles(the flavor including the characteristic taste)became stronger; thermal degradation products and(or) Maillard reaction products of the peptides in the molecular weight range of 964 to 4657 Da, played the flavor enhancement roles. Considering the changes of the taste profiles, we can predict that the above changes of taste active compounds, which were caused by Maillard reaction, improved the non-volatile flavor of the extracts.