Abstract
The yeast Candida tropicalis DSM 7524 produces xylitol, a natural, low-calorie sweetener, by fermentation of xylose. In order to increase xylitol production rate during the submerged fermentation process, some parameters-substrate (xylose) concentration, pH, aeration rate, temperature and fermentation strategy-have been optimized. The maximum xylitol yield reached at 60–80 g/L initial xylose concentration, pH 5.5 at 37 °C was 83.66% (w/w) on consumed xylose in microaerophilic conditions (kLa = 2·h−1). Scaling up on 3 L fermenter, with a fed-batch strategy, the best xylitol yield was 86.84% (w/w), against a 90% of theoretical yield. The hyper-acidophilic behaviour of C. tropicalis makes this strain particularly promising for industrial application, due to the possibility to work in non-sterile conditions.
Highlights
Xylitol, a five-carbon sugar alcohol, occurs widely in nature but it is a normal intermediate in humans [1]
In absence of respirometric measurements, the amount of CO2 was approximately estimated assuming that the remaining amount of xylose not consumed for cells growth and for xylitol production was used by the yeast for respiration
The results demonstrated that our Candida had a maximum of xylitol yield, both on initial and consumed xylose (Yp/s initial = 71.52%–54.99% and Yp/s consumed = 71.52%–83.66%, respectively), in the range between 60 g/L and
Summary
A five-carbon sugar alcohol, occurs widely in nature but it is a normal intermediate in humans [1] Because of these characteristics and benefits, it is widely and increasingly used in the food and confectionary industries [2], and its dietary and chemical properties have been extensively studied [3]. Contrary to other widespresd non-caloric sweeteners, such as saccharine or aspartame, D-xylitol has Biomolecules 2015, 5 many properties similar to those of sucrose. It dissolves readily in water, it is as sweet as sucrose, despite having only approximately two-third of its calories, and is approximately twice as sweet as sorbitol and nearly three times as sweet as mannitol [4]. Since a research study conducted in Finland evaluating the effectiveness of xylitol on dental plaque reduction in 1970, xylitol has been widely researched and globally accepted as a natural sweetener approved by the U.S Food and Drug Administration (FDA) and the American Academy of Pediatric Dentistry [6]
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