Development of a gelled form of lactic-fermented green shell mussel (Perna canaliculus)
Bohari, Murtuza Hamza
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New Zealand?s isolation makes it a natural home to many unique species. One of them is the now cultivated New Zealand green shell mussel (Perna canaliculus) which is sought after by seafood lovers around the world. This mussel is by far the largest seafood export from New Zealand accounting for about 85% and exported to 78 countries in 2011. This research was conducted to create a variant of an existing value-added product: lactic-fermented comminuted mussel meat. This product has been named Perna. The existing knowledge relates to a spreadable form of Perna, which is currently undergoing commercial evaluation. This work is mainly about developing a gelled form of Perna using hydrocolloids, specifically carrageenans and gelatine. The proposition was that a gelled, sliceable form of Perna would expand its culinary potential. The spreadable form would be used for crackers and breads, while a slice of Perna could be part of an entr?e in domestic cuisine or food service. However, as the project progressed it became clear that unacceptable variations in pH of Perna were affected by the time the mussels were cooked in boiling water prior to comminution and fermentation. Because of the fundamental importance of this variation in terms of odour/flavour, the first part of the thesis explores the chemistry of how pH could be better controlled. It was found that the buffering capacity of mussel proteins changed with cooking. Although no explanations were obtained at a biochemical level, the empirical outcome was that cooking live mussels between 7 to 10 minutes would predictably result in a desired final pH of around 4.5 that yields superior organoleptic properties such as pleasant smell, taste and texture. Moving to gelation as a goal, it was found that kappa and iota carrageenans were incapable of forming useful gels in Perna, the former producing excessive syneresis and latter a soft, spongy product. Experiments with gelatine were initially unsuccessful, inadvertently because of the low gelatine concentrations tested. After a more concentrated gelatine colloidal suspension of about 8% was incorporated into the mussel mince, a useful gel was finally created, although the texture was crumbly. However, this final success is considered an excellent starting point for sliceable product refinement.