| On a global level, aquaculture represents the fastest growing agricultural sector. Industry expansion however, has been slowed as a result of environmental concerns related to wastes originating from intensive production. In particular, effluent from fish culture facilities has been cited as a point source of phosphorous loading, contributing to incidents of eutrophication of receiving water bodies. Experiments were undertaken to develop and characterize a novel strategy to encapsulate microbial phytase in order to protect its activity and enhance phosphorus availability in rainbow trout fed plant-based protein diets. Using the model protein bovine serum albumin, optimal conditions were defined for encapsulation in alginate-chitosan microcapsules. Under optimal conditions, a model protein was efficiency encapsulated, and was released in a pH-dependent manner. Furthermore, protein release was affected by microcapsule drying following production and the presence of calcium in the external medium. Using the optimal encapsulation conditions, internal and external gelation were compared as methods of microcapsule production. Internally-gelled microcapsules were revealed to be more porous than their externally-gelled counterparts, resulting in relatively low encapsulation efficiency.; The influence of three different feces collection methods and three external digestibility markers on apparent digestibility was evaluated. Both feces collection method and marker type affected apparent macro-nutrient digestibility measurements, whereas the influence of these factors on micronutrient apparent digestibility was not as evident. The addition of microbial phytase to a plant protein-based diet fed to rainbow trout resulted in significantly increased apparent digestibility of phosphorus and that of a number of divalent minerals, dry matter and protein. This response was affected by phytase level, water temperature, feed particle size, and the addition of non-starch polysaccharidase enzyme cocktail and increased calcium to phosphorus ratio. Rainbow trout were fed a plant protein-based diet for 8 weeks alone or supplemented with native or encapsulated phytase or mineral phosphorus. Growth, feed efficiency and tissue mineralization was reduced in fish receiving the basal diet. Unencapsulated phytase addition significantly increased phosphorus and nitrogen retention and reduced total, solid and dissolved phosphorus wastes. Encapsulation in alginate-chitosan microcapsules tended to reduce the beneficial effects observed with free phytase addition.; These results reveal that using an external method of ionotropic gelation, proteins may be efficiently encapsulated in alginate-chitosan coacervate microcapsules. Protein release is dependent on the pH and divalent ion content of the external medium. Microbial phytase is effective in augmenting the apparent digestibility and bioavailability of phosphorus and a number of additional nutrients in plant protein diets fed to rainbow trout. Phytase supplementation results in improved growth performance, tissue mineralization, phosphorus and nitrogen retention and reduced phosphorus excretion. Encapsulation of phytase in alginate-chitosan microcapsules does not improve the efficacy of microbial phytase, therefore, this encapsulation strategy is not particularly suited to the application of feed-grade phytase. |
