The kinetic behaviour of the yeast
Candida guilliermondii FTI 20037 was evaluated on a bench bioreactor using rice straw hydrolysate as a substrate. The maximum xylitol concentration (45.4
g
l
−1) ...was attained after 45
h of fermentation, which corresponded to a xylitol volumetric productivity of 1.01
g
l
−1
h
−1. This value was improved in about 90% when compared to the results attained with aerated flasks (0.54
g
l
−1
h
−1). The kinetic results obtained in the present work reinforce the idea that rice straw hydrolysate constitutes an effective xylose source for xylitol production.
Semidefined media fermentation simulating the sugar composition of hemicellulosic hydrolysates (around 85 g l⁻¹ xylose, 17 g l⁻¹ glucose, and 9 g l⁻¹ arabinose) was investigated to evaluate the ...glucose and arabinose influence on xylose-to-xylitol bioconversion by Candida guilliermondii. The results revealed that glucose reduced the xylose consumption rate by 30%. Arabinose did not affect the xylose consumption but its utilization by the yeast was fully repressed by both glucose and xylose sugars. Arabinose was only consumed when it was used as a single carbon source. Xylitol production was best when glucose was not present in the fermentation medium. On the other hand, the arabinose favored the xylitol yield (which attained 0.74 g g⁻¹ xylose consumed) and it did not interfere with xylitol volumetric productivity (Q P=0.85 g g⁻¹), the value of which was similar to that obtained with xylose alone.
The stability of immobilized and native Esperase, a commercial serine protease, was studied by incubating the enzymes in four formulations containing the same amount of anionic and non-ionic ...surfactants. The results show that the activity of the immobilized enzyme is not affected by the presence of detergents while the native enzyme lost 50% of activity after 20 min of incubation in these four formulations. The washing performance of the detergents prepared with the immobilized Esperase was studied on cotton and wool fabric samples stained with human blood and egg yolk, using as control the detergent containing native Esperase. The best stain removal for cotton samples stained with human blood was achieved using the detergent with immobilized Esperase. Several physical tests confirmed that wool keratin was not degraded by the immobilized Esperase, validating the ability to use formulated detergents containing this immobilized enzyme for safe wool domestic washing.
We have shown that cutinase can be used to modify the surface of polyester, polyamide, and acrylic fibers. This enzyme can hydrolyze the esters groups of poly(ethyleneterephthalate) and the vinyl ...acetate, the comonomer of acrylic fibers. For the first time we have shown that cutinase is able to hydrolyze the amide bonds in polyamide 6.6. Hydroxyl and amine groups are formed at the fiber surface by enzyme action and detected by specific dyeing methods with reactive dyes.
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