title: VALORIZATION OF BY-PRODUCT OF WINDOWPANE OYSTER Placuna placenta SHELL PROCESSING
Creators: name: Rustia, Jessica
Publisher: name: University of Liverpool Repository
Year: 2024

description: The windowpane oyster, Placuna placenta, derives its trivial name from the use of its translucent shells to make windows, a common practice in SE Asia prior to the establishment of industrial glass production, and one maintained in historical buildings. Many objects are made from this material, such as ornaments and Christmas decorations. However, over exploitation has led to a decline of the oyster beds. This not only impacts on the revenue of oyster harvesting communities and the country, but also on local ecosystems and shoreline stability. There are two by-products from the oyster, the meat and the extensive slime. Some of the former is consumed locally, though much is either donated to aquaculturists as food or discarded, whereas the latter is always discarded.
This thesis aimed to establish the means to develop food products of commercial value from the windowpane oyster meat and to establish whether the slime might contain molecules with commercial potential. Achieving this aim would provide a blueprint to establish full exploitation of the oyster, enhancing local incomes and potentially increasing efforts to maintain and expand the oyster beds.
It was important understand the practices of oyster harvesters, their socio-economic status and attitudes to the development of new food products particularly since only historical data were available for the former. Consequently, a survey and documentation of practices was done in the province of Bataan, Philippines to assess existing practices regarding the fishery, “kapis” handicraft making and by-product management of the windowpane oyster shell processing industry and identify those which would be suitable for adoption or innovation. The respondents were all in a precarious socio-economic position, occupying the bottom two deciles of Filipino average income. The only parameter that cross correlated was gender and paid labour; men dominating paid labour and women performing many unpaid tasks, such as shucking the oysters. In contrast, parameters such as the frequency and quantity of shells gathered each week, the amount of meat consumed, and the quantity of shells used in handicrafts were not associated with the respondents' age, marital status, education level, or gender.
The windowpane oyster meat was underutilized by the respondents in Bataan, despite their precarious socio-economic position. This indicated that, despite being widely known as edible, and being consumed locally, there was a lack of knowledge and support for its processing in a manner suitable for the production of added-value foods that could be sold. However, the respondents were very positive regarding the adoption of new programs on the utilization of by-products or waste from the bivalve when introduced, including food products derived from the meat, because most of them felt that there is a market for windowpane oyster products and that the products are safe for consumption based on their personal experience.
Windowpane oyster meat collected on three separate occasions was then subjected to biochemical analysis to assess its nutrient composition and safety important parameters for making value-added foods. Results of proximate analysis and chemical tests of the fresh and precooked windowpane oyster meat demonstrated that this bivalve is an inexpensive and nutritious substitute not only to shellfish, but also poultry and red meats. It had a high amount of protein and important macro and microminerals and contained phenolics and carotenoids which contributed to its antioxidant activity. Although it had more saturated fatty acids than other bivalves, it also had considerable monounsaturated and polyunsaturated fatty acids important for human diet. Microbiological analyses demonstrated that the windowpane oyster meat was safe for human consumption, because of the low aerobic plate count and coliform count and absence of Escherichia coli, Salmonella species and Vibrio parahaemolyticus in the precooked meat. The results suggested that either pathogens were not initially present or could be destroyed by the precooking done. The levels of toxic heavy metals were all below the limits set by international agencies, Food Standards Agency-UK, FSANZ (2016), and FAO-LEX. The one exception was arsenic, the limits for which are only stated in the New Zealand FSANZ (2016) standards; in one of the three samples the levels of arsenic were above this limit. However, mixing of the samples would reduce the levels to within the limits. Moreover, this one sample deviated in many parameters from the other two, suggesting an unknown seasonal or local environmental effect. This highlighted that while the oyster meat is safe for the processing value-added food products, further analysis of samples at greater time resolution and from more locations would help understand the sources of such variation.
The windowpane oyster meat was used to develop three food products, based on the focus groups discussion conducted and on popularity of particular products amongst Filipinos. Thermally processed windowpane oyster “adobo” and marinara sauce can be considered healthy and safe for human consumption, with shelf life of at least a year based on the microbial analysis and commercial sterility tests that were done. The oysters and the other ingredients added affected the nutritional value and health benefits from the products. After lactic acid fermentation of the salted fresh windowpane oyster, pH and proximate composition changed depending on fermentation time. Drying and pulverization of the fermented oysters produced a stable product since this had a very low water activity. The windowpane oyster products were moderately liked following sensory evaluation by panels of respondents, and the data distribution indicated that there would be a market for these products. Thus, the respondents generally stated that if the thermally processed windowpane oyster “adobo” and marinara sauce are commercially available, they would probably buy the “adobo” and would definitely buy the marinara sauce. The products are promising because majority of the sensory panelists agreed that these are just about right in terms of the attributes evaluated. This work did highlight that blind testing versus the same products made with other native shellfish would provide valuable data since some of the sensory evaluation responses may have been affected by the fact that the respondents had never eaten windowpane oyster meat previously.
A preliminary fractionation of the windowpane oyster slime was undertaken using dialysis. This was followed by measurement of protein and uronic acid content, mild acid hydrolysis, fractionation on a C8 reverse phase bond elute column and SDS-PAGE. The data demonstrate that the slime contained some protein and considerable amounts of polysaccharides, as well as molecules that were acid labile and contained aromatics. Given the presence of uronic acids and proton NMR chemical shifts consistent with glycosaminoglycans, it seems likely that some of the polysaccharides may belong to this class of sugars. These data indicate that a programme to undertake an in-depth analysis of the slime would be likely to identify bioactive components of commercial value. Such a programme would combine activity assays, such as those for coagulation and fractionation to provide evidence for the structures of the molecules present and their amounts.