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Oligofructans are potential biological substances that due to their distinctive properties have a positive health-promoting effect. This research aimed to produce oligofructans using sugarcane juice fermentation with Bacillus subtilis TISTR 001 and to study the prebiotic properties in vitro. The results showed that the maximum total oligofructans in the form of free fructose was 2.57% (w/v) at the 84th hour of fermentation with 0.17 g/g reducing sugar and a production yield of 0.031 g/L/h and maximum levansucrase activity of 1.57 × 10 6 U/mL at that time. The oligofructans contained in the fermented juice had potential functional ingredients that exhibited prebiotic properties that could resist the digestion of enzymes in the gastrointestinal tract under in vitro conditions with digestion of only 6.92%. In addition, the fermented juice promoted the growth of prebiotics, especially Bifidobacterium bifidum TISTR 2129 and inhibited the growth of pathogens using both single culturing and co-culturing with probiotics.

This research investigated the effects of inorganic compounds or metal ions (calcium ion, Ca2+; potassium ion, K+; magnesium ion, Mg2+) on ethanol production efficiency invertase, an enzyme produced by Saccharomyces cerevisiae, in sucrose solution, which was the substrate for yeast fermentation. The results showed that all metal ions (concentration 0.20 and 0.60 % (w/v)) acted as inhibitors on invertase activity in the order Ca2+ > K+ > Mg2+. Subsequently, these ions inhibited sugar conversion, reducing sucrose utilization and less glucose and fructose consumption based on the high content of remaining sugars in the culture medium. The reduction of the substrate was due to the consumption and an increased growth rate of S. cerevisiae, which all resulted in low efficiency of ethanol production and an increase in glycerol content. The glycerol content was increased due to yeast cells' developed mechanism or adaptation to enhance cell survival following metal ion contamination, especially from Ca2+ and K+; furthermore, the glycerol content significantly increased during the changed conditions, such as when the sugars were nearly all consumed. The kinetic parameters such as specific growth rate (µ-1), substrate consumption rate (Qs), and ethanol production of the research work were also undertaken. In conclusion, metal ion contamination in the sucrose substrate of yeast fermentation resulted in low efficiency of ethanol production, specific growth rate, and substrate consumption rate decrease with the Ca2+ ion (concentration 0.20 - 0.60 % (w/v)) acting more harshly as an inhibitor of ethanol production than the other ions, particularly where there was a high concentration of contamination.

The inconsistent quality of molasses directly influences ethanol production, particularly due to contamination by metal ions that causes severe problems and reduces production efficiency. This research focused on calcium (Ca2+), potassium (K+), and magnesium (Mg2+) ions that are common in molasses. The key objective was to understand clearly the effect of ions on ethanol fermentation and Saccharomyces cerevisiae performance. Individual ions and ion mixtures were studied in sucrose solution and in molasses. The results showed that severe stress could be ordered as Ca2+>K+>Mg2+ and the adverse effect was greater when the ion concentration increased. Ca2+ was a strong inhibitor while trace amounts of Mg2+ produced a positive effect. To achieve the greatest efficiency in ethanol production using molasses in the substrate preparation, Ca2+ should not exceed 0.18% (w/w) prior to fermentation and the final sugar concentration should be 20–25% (w/v), as adjusting the addition of sucrose will result in a suitable yeast medium. Pretreatment and dilution were the best practices for ion removal, with Ca2+ being clearly decreased. Furthermore, determination of the composition and ion concentration in molasses are essential initial steps that must be routinely applied to ensure that the knowledge gained and the efficient techniques investigated can both be used to improve ethanol production.