Factors influencing apparent digestibility coefficient (ADC) of nutrients from a plant proteinbased diet supplemented with microbial phytase were investigated in a series of experiments with rainbow trout (Oncorhynchus mykiss). The influence of phytase level, water temperature, feed particle size and addition of a protease/non-starch polysaccharidase (PNSP) enzyme cocktail were tested in a phytase-supplemented (2000 FTU kg-1) diet. Finally, the influence of Ca/P ratio, addition of 1,25-hydroxycholeocalciferol, or inclusion of lactic acid (LA) in diets with and without phytase was evaluated. Addition of microbial phytase improved ADC of dry matter (DM), protein, ash and minerals (P, Ca, Mg, Fe and Zn) (P < 0.05). Reducing feed particle size potentiated the effect of phytase on P and ash ADC, as did the addition of a PNSP enzyme cocktail; the latter also significantly improved DM ADC in both control and phytase-supplemented diets. Increasing the Ca/P ratio reduced the effect of phytase on P and ash ADC. Addition of 1,25-dihydroxycholecalciferol and LA had no effect on DM, P and ash ADC in control diets and tended to reduce the phytase-induced increase in P ADC.

This study was undertaken to investigate the effects of adding microbial phytase to plant protein-based diets for rainbow trout (Oncorhynchus mykiss). A plant protein-based basal diet was formulated to be isonitrogenous, isolipidic and isoenergetic to a nutrient-dense, fish meal-based control diet (Starter salmonid diet; Ontario Ministry of Natural Resources (MNR), University of Guelph). The basal plant protein-based diet was supplemented with 3000FTU microbial phytase kg−1 included either in a free form or encapsulated in chitosan-alginate microcapsules. A second control group was fed the basal plant protein-based diet supplemented with monosodium phosphate to NRC requirements. Apparent digestibility coefficients (ADC) were determined for dry matter, energy, protein, ash, P, Ca, Mg, Mn, Cu, Zn and Fe. The above diets were fed to triplicate tanks of rainbow trout for 56 days; growth and feed efficiency were monitored at 2-week intervals. At the start of the study and at 28-day intervals, fish were sampled to determine composition of the whole carcass and tissues and blood concentration of inorganic P. Proteolytic enzyme activity in intestine was measured on days 0, 4 and 28. Feeding the fishmeal-based control diet increased (P<0.001) ADC for a number of macro- and micro-nutrients, growth rate, feed efficiency, and tissue ash and P concentrations compared with the plant protein-based diet; however, supplementation of the plant protein-based diet with microbial phytase improved (P<0.001) the ADC for energy, protein (P<0.05), ash, P and a number of macro- and micro-nutrients. Fish growth, feed efficiency, concentrations of tissue ash and P, and retention of P (P<0.001) and N (P<0.05) were also increased by supplementation of the plant protein-based diet with microbial phytase; values for these parameters approached those of the fish meal control diet in the final 28 days of the experiment. In the same period, inclusion of microbial phytase resulted in lower (P<0.05) total, solid and dissolved P excretion versus all other treatment groups. There was no effect (P>0.05) of phytase supplementation on proteolytic enzyme activity. Encapsulation of microbial phytase tended (P<0.10) to diminish its ability to liberate P. The data suggest that microbial phytase can effectively increase the apparent digestibility and bioavailability of a range of nutrients from plant protein-based diets for rainbow trout, resulting in increased growth performance and tissue mineralization. Encapsulation of phytase reduces this effect, likely due to hindered interaction between the enzyme and dietary phytate-P.

A series of experiments was performed to evaluate the influence of a number of physico–chemical factors on the diffusion of a model protein, bovine serum albumin (BSA), from dried chitosan-coated alginate microcapsules. Diffusion of BSA was quantified during the microcapsule manufacture processes (gelation, washing, rinsing) and during incubation in conditions simulating the pH encountered during the gastric (0.1 N HCl; pH 1.5) and intestinal (200 mM Tris–HCl; pH 7.5) phases of digestion. Factors tested included alginate and chitosan concentration, calcium chloride (CaCl2) concentration in the gelation medium, loading rate, chitosan molecular mass and pH of the gelation medium. Microcapsule size and gelation time were altered in order to determine their effects on protein retention. Alginate and chitosan concentration significantly influenced BSA retention during microcapsule manufacture and acid incubation, as did calcium chloride concentration in the gelation medium (P<0.05). BSA retention during manufacture was not significantly altered by protein loading rate or pH of the encapsulation medium, however, protein retention during acid incubation decreased significantly with increasing protein loading rate and encapsulation medium pH (P<0.05). Microcapsules that were washed with acetone following manufacture demonstrated significantly increased protein retention during acid incubation (P<0.05). In microcapsules that had been acetone-dried to a point whereby their mass was reduced to 10% of that immediately following encapsulation, protein retention was over 80% following 24-h acid incubation vs. only 20% protein retention from non acetone-dried microcapsules. The presence of calcium in the neutral buffer medium significantly reduced BSA diffusion in a concentration-dependent manner (P<0.05).

Ownership of energy saving items in the home is surprisingly low in Ireland. Logistic regression analysis of data derived from a survey of households reveals significant reasons for not investing in such items. The reasons are somewhat similar to those found by Brechling and Smith for the United Kingdom. Lack of information, non-appropriability, small potential saving, restricted access to credit and transactions costs play an important role, leaving only a minority of non-owners who are model-inconsistent and who are possibly non-optimisers. Some policy implications are outlined.