S. Zgoulli

Volatile Constituents and Antimicrobial Activity of Lavandula stoechas L. Oil from Tunisia

Abstract An oil obtained from the dried leaves of Lavandula stoechas L. in 0.77% yield was analyzed by capillary GC and GC/MS. Fenchone (68.2%) and camphor (11.2%) were the main components of the 28 identifed molecules. This oil has been tested for antimicrobial activity against six bacteria, and two fungi. The results showed that this oil was active against all of the tested strains; Staphylococcus aureus was the more sensitive strain.

Modification of the thermoresistance to spray-drying of a cold-adapted subtilisin by genetic engineering

The thermoresistance of a cold-adapted subtilisin dried by spray-drying was studied. Proteolytic activity of this enzyme was measured before and after spray-drying. Without chemical additives, spray-drying yields ranged from 2-13%. The use of arabic gum and lactose in the composition of the enzyme solutions allowed the strengthening of the enzyme structures and increased water mobility in the product. Increase of water mobility led to a shorter residence time of the product in the spray-drier and a net yield increase was obtained (yield higher than 50%). The effect of two selective mutations on the thermoresistance to spray-drying of the cold-adapted subtilisin was also investigated. Mutation T85D (introduction of an additional link with an ion Ca2+ necessary for enzyme activity, by substitution of Asp for Thr 85) had no effect on the thermoresistance of the subtilisin to spray-drying. Mutation H121W (introduction of an additional aromatic link by substitution of Trp for His 121) reduced the drying yield from 66% (not modified subtilisin) to 52%. This higher thermosensitivity could be explained by an increase of the hygroscopic character of the modified subtilisin (mutation H121W).

Study of residual water types in freeze-dried Lactobacillus acidophilus by nuclear magnetic resonance

Relaxation time ( T 2 *) measurements were carried out on freeze-dried powders of Lactobacillus acidophilus . T 2 * values of 8.2 and 362 μs were obtained with an ajustment by a bio-exponential model of the recorded magnetization decrease. These different values allowed to differentiate between water type A and water type B. Dry matter modifications of the samples correlate with a change in the calculated ratio Water type B/Water type A. By this experiment one can also conclude that water type A is the only type of water still present in powders whose dry matters are higher than 961 g/kg.