Thesis (M.Sc.)--Chulalongkorn University, 2009

Garlic oil contains bioactive components that are sulfide derivatives, which possess antimicrobial activity against various gram-negative and gram-positive bacteria. However, the oil is volatile and heat sensitive. The objective of this research was to develop antimicrobial microparticle of garlic oil using maltodextrin (DE 10) as carrier by spray drying technique, in order to apply in salad dressing that is not commercially sterilized and packed under presence of oxygen. This research is divided in to 3 parts. Firstly, the optimal proportion of initial feed emulsion was determined. Determination of critical micelle concentration (CMC) of polysorbate (Tween®) 20 and Tween®80 in 20 g/dL maltodextrin was carried out. It was found that CMC of Tween®20 and Tween®80 was 0.49% w/w. Thus, Tween®20 was selected as the emulsifier for subsequent studies. For determination of optimal emulsion preparation, emulsions containing Tween®20 at various concentrations (0.6%, 0.8% and 1% w/w) in 20 g/dL maltodextrin and 0.1:1 0.15:1 and 0.2:1 oil-to-maltodextrin ratio were prepared. Homogenization was carried out at 13,000, 19,000 and 24,000 rpm for 5 and 10 min. It was observed that all prepared emulsions were stable at room temperature (~25℃) for 48 hours. Oil droplet size ranged from 0.126 to 0.281 µm. The emulsion containing 0.2:1 oil-to-maltodextrin ratio homogenized at 19,000 rpm for 5 min had good stability, contained smaller oil droplet size (0.124 to 0.216 µm), and gave rise to higher encapsulation efficiency (18.45% oil retention). This condition was thus chosen for preparing the emulsion feed. In the second part, the optimal condition for spray drying was investigated. The inlet air temperature was varied from 120℃ to 200℃, and the initial feed was spray-dried at 25 mL/min at 3 bars. Most microcapsules were spherical with small holes dispersing on their surface. The microcapsules had the surface average diameter; D[3,2], from 9 to 13 µm and had smooth surface, except those spray-dried at 120℃ that had rough surface. Moisture content and water activity of microcapsules decreased with increasing the inlet air temperature. The solubility was not significantly different (p>0.05). The microcapsules contained 1.34 to 3.69% total oil. They contained di- and tri- sulfides from 0 to 0.05 and 0 to 0.01 mg/g, respectively. The microcapsules could inhibit the growth of Staphylococcus aureus at minimum inhibitory concentration (MIC) of 0.1 g/g, but showed no inhibition against Salmonella Typhimurium and Escherichia coli. The garlic oil release from the microcapsules prepared from 0.6% w/w Tween®20 and 0.2:1 oil-to-maltodextrin ratio spray-dried at 180℃ was of the burst release characteristic. The addition of garlic oil microcapsules could extend the storage life of salad dressing for up to 1 day at 25℃ and reduced 1.4 log CFU/g total bacteria at day 2. The salad dressing containing garlic oil microcapsules had higher L* and a* than the control sample. From the sensory assessment by 50 assessors, the salad dressing containing the microcapsules was darker, had higher smoothness and lower viscosity.