Author: Michael James Roberts
Roberts, Michael James, 2009 Developing large rocklobsters, Jasus edwardsii, as a premium value-added product: Key sensory and biochemical characteristics of the flesh., Flinders University, School of Biological Sciences
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ABSTRACT The Southern Rocklobster, Jasus edwardsii, supports a commercial fishing industry worth $180 million AUD per annum, the majority of which is exported live to Asia. The current market demands for smaller rocklobsters can sometimes result in discounting of the larger individuals, a significant financial loss for the industry. Value adding of large rocklobster into processed product may help combat this loss; however, there is financial risk associated with the development of new products for new markets without first understanding the product variability. The aims of this thesis were to quantify raw product flesh characteristics using physical, biochemical and sensory approaches, determining the extent of variation in those characteristics, and finally to investigate the potential biological and post-harvest sources of that variation. One of the initial requirements was the establishment of previously undefined key descriptors of sensory properties for raw rocklobster flesh, which were texture (chewiness and crunch), flavour (metallic, lobster and sweetness) and appearance (pinkness and translucency) (Chapter 2). These were tested using a combination of triangle tests and a hybrid descriptive test using a trained sensory panel. The trained panel found no significant difference in the texture, flavour or appearance of raw flesh between large and small rocklobster (Chapter 4). However, differences in the sensory descriptors of flesh translucency, pinkness and lobster flavour were significantly influenced by frozen storage of the product and the section of tail from which a sample was sourced (Chapter 4). Biochemically, these differences were largely associated with variation in flesh adenylates, with AEC, IMP load, total adenylate pool and K value being identified as the key contributors. Of all the potential sources contributing to variation in flesh biochemical properties, post-harvest factors such as ‘batch’ (i.e. rocklobsters processed on a single day) had a dominant influence (Chapter 3). The difference detected in flesh characteristics between batches was greater than any seasonal pattern such as moult stage. Biological variables such as rocklobster condition and shell colour had no significant influence on flesh properties (Chapters 3 & 4). White rocklobsters are currently discounted in the live export trade; however this does not appear to be necessary for value added product owing to the lack of significant differences to red rocklobsters across a range of biochemical parameters (Chapter 3). Rocklobster physical condition (which has previously been associated with prior stress) was not shown to affect flesh biochemistry or sensory properties (Chapter 4). This result was not expected and may reflect the potential recovery of rocklobsters sampled in this study prior to processing. These findings suggest that commercial rocklobsters, which have had similar recovery, are unlikely to show reduced sensory properties. Recent commercial interest has focussed on holding rocklobster in tanks to provide year-round supply. As a result, the impacts of tank-holding and feeding on rocklobster flesh sensory properties were investigated (Chapter 5). Rocklobsters that were tank-held and fed for up to four months produced flesh with similar physical, biochemical and sensory properties to freshly caught rocklobster. Tank-holding therefore offers a viable solution to operators wanting a year-round supply of fresh product from a resource which is subjected to a restricted fishing season. A Japanese consumer panel was established to assess the greatest differences in flesh properties as detected by the trained sensory panel. The Japanese consumer panel assessed raw flesh from fresh, short and long-term frozen storage treatments (Chapter 4). This consumer panel detected similar differences in taste, texture and flavour as the trained panel, and whilst no significant overall preference was detected, half of the panellists showed a preference for rocklobster product that had been stored frozen for 18 months. The findings from this research are useful for the commercial industry as they indicate that raw rocklobster flesh has little variation associated with discounting factors such as size and shell colour. Although the greatest variation in flesh biochemistry was seen with frozen storage, even long term storage produced rocklobster flesh properties which were favourable for some panellists. The commercially caught Southern Rocklobster appears to have raw flesh properties well suited for a value added product.
Subject: Biological sciences thesis
Thesis type: Doctor of Philosophy
School: School of Biological Sciences
Supervisor: Dr. Kirsten Benkendorff