Fish oil encapsulated powder was prepared with four ratios (0.6:1, 0.8:1, 1:1 and 1.2:1) of fish oil:whey protein concentrate with addition of 100 ppm in dry matter antioxidant (α-tochopherol) and 25 ppm in dry matter nisin as an antimicrobial agent. The emulsion was homogenized, pasteurized and spray or freeze dried. The produced powder was freshly analyzed for moisture content, encapsulation efficiency and microstructure while degree of oxidation was determined every 15 days in the powder kept at 4°C for 90 days.
Spray dried powders have lower moisture content than freeze dried one. Moisture in both powders tended to decrease with the increasing of oil ratio.
Encapsulation efficiency showed the highest values (70.2 % for spray and 63.18% for freeze dried powder) at the ratio of (0.6:1), while it was decreased with the increasing of fish oil ratio up to (1.2:1). Encapsulation efficiency was dropped by about 13% and 10% from the ratio of 1:1 to the ratio of 1.2:1 in spray and freeze dried powder respectively. Spray dried powder had higher encapsulation efficiency than freeze dried. In addition, the ratio of (1:1) can be considered as the most suitable ratio could be applied as it allows reasonable concentration of omeg-3 in the same time, the encapsulation efficiency is acceptable. Many authors and foundations suggested 500 mg of ω-3 fatty acids as daily requirement, this amount can be covered by 4.38g of powder of 1:1 fish oil:WPC.
Oxidation stability was determined for fish oil as a control and for the encapsulated fish oil powder (EFOP) along 90 days storage at 4°C.
Degree of oxidation (TBAR values) was gradually increased in both fish oil (control) and EFOP with the advance of storage time. TBAR values of fish oil were dramatically increased throughout storage time (10 at zero time, and it become 325 nmolMAD/kg oil at day 90). On the other hand the increment of TBAR values in EFOP was not so remarkable (18 as minimum at zero time, and it become 53 as maximum nmol MDA/kg oil at day 90). Encapsulation of fish oil strongly delayed the oxidation development in the powder beside the influence of antioxidant (α-tochopherol) which was added. The third factor which considerably impaired oxidation is the low storage temperature (4°C).
Scanning electron microscope (SEM) showed that spray drying resulted in spherical particles of different sizes with collapse or shriveling, visible wrinkles or dimples on the surface, but no apparent pores. On the other hand, freeze dried powder showed a completely different morphology of particles. Relatively low magnification (x1500) showed the powder in plates-like layers without pores on the surface, while magnification of (x3500) was not clear enough to describe the image content. At the same magnification of (x3500), spray dried powder showed clear individual spherical particles with different sizes. Images of spray dried powder with magnifications of (x10000 and x15000) were very sharp and distinctive. The particles were mostly about 2um diameter with smooth surface and visible wrinkles. Magnification more than (x3500) for freeze dried powder was not successful to show any useful details.