Quality Evaluation of Live Eastern Oyster (Crassostrea virginica) based on Textural Profiling Analysis, Free Amino Acids Analysis, and Consumer Sensory Evaluation
Type of DegreeMaster's Thesis
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The consumption of live eastern oyster (Crassostrea virginica) has become an important part of the diet for consumers in the United States. Because large amounts of oysters are grown every year, it is necessary for oyster farmers to understand quality differences caused by different aquaculture methods, as well as quality changes over the time of cold storage. The objective of this study is to develop a set of systematic methods for quality evaluation of live eastern oysters. Qualities evaluation of three aquaculture-treated oysters (daily, weekly, and never) were by means of: 1) textural analysis, 2) free amino acids (FAAs) analysis and 3) consumer preferences by means of 1) textural analyzer, 2) high-performance liquid chromatography (HPLC), and 3) consumer sensory evaluation. Besides, linear regression analysis with stepwise selection method was conducted to establish relationship between instrumental parameters (textural parameters and FAAs concentrations) and consumer preferences (texture likeability, flavor likeability and overall likeability) obtained from sensory evaluation. For texture characteristics among three treatments, hardness, gumminess and chewiness were important parameters for oyster texture. Daily treatment had firmest body when people biting them caused by more times of desiccation during production. Weekly treatment had strongest adductor muscle and longest survival time. As to flavor characteristics, predominant FAAs (free glycine, free alanine, free glutamic acid, free arginine, free cysteine and free methionine) and bitter FAAs (free leucine, free tyrosine and free phenylalanine) were identified and considered as main parameters of oyster flavor. Daily treatment had more sweet and sulfurous flavor than other two treatments. However, consumers were not able to statistically distinguish differences among three treatments. For changes during storage, quality of oyster texture decreased during cold storage at 4°C. The recommended shelf-life was less than 21 days due to the apparent increases of bitter FAAs of body on day 21, and the best consumption time was within 7 days due to the increase of free leucine of adductor muscle on day 7. Consumers couldn’t figure out differences among fresh oysters (0 day of storage period), oysters stored for 7 days and 14 days. The results of linear regression analysis indicated the effect of flavor was stronger than texture on oyster consumption. Sweet FAAs of body and sulfurous FAAs of adductor muscle made positive (r = 0.010) and negative effect (r = -0.025) to flavor likeability, respectively. Sweet FAAs of body also made positive (r = 0.008) effect to overall likeability. Sweet FAAs of body and sulfurous FAAs of adductor muscle was indicators for eastern oyster flavor and overall sensory characteristics.