In the recent climate change regime, industrial demand for renewable materials to replace petroleum-derived polymers continues to rise. Of particular interest is polyhydroxybutyrate (PHB) as a substitute for polypropylene. Accumulating evidence indicates that PHB is highly produced as a carbon storage material in various microorganisms. The effects of growth conditions on PHB production have been widely studied in chemolithotrophs, particularly in Rhodobacter. However, the results on PHB production in Rhodobacter have been somewhat inconsistent due to different strains and experimental conditions, and it is currently unclear how diverse environmental factors are linked with PHB production. Here, we report optimized growth conditions for PHB production and show that the growth conditions are closely related to reactive oxygen species (ROS) regulation. PHB accumulates in cells up to approximately 50% at the highest level under dark-aerobic conditions as opposed to light aerobic/anaerobic conditions. According to the time-course, PHB contents increased at 48 h and then gradually decreased. When observing the effect of temperature and medium composition on PHB production, 30 °C and a carbon/nitrogen ratio of 9:1 or more were found to be most effective. Among PHB biosynthetic genes, PhaA and PhaB are highly correlated with PHB production, whereas PhaC and PhaZ showed little change in overall expression levels. We found that, while the amount of hydrogen peroxide in cells under dark conditions was relatively low compared to the light conditions, peroxidase activities and expression levels of antioxidant-related genes were high. These observations suggest optimal culture conditions for growth and PHB production and the importance of ROS-scavenging signaling with regard to PHB production.

The green microalga Haematococcus pluvialis accumulates astaxanthin, a potent antioxidant pigment, as a defense mechanism against environmental stresses. In this study, we investigated the technical feasibility of a stress-based method for inducing astaxanthin biosynthesis in H. pluvialis using electric stimulation in a two-chamber bioelectrochemical system. When a cathodic (reduction) current of 3 mA (voltage: 2 V) was applied to H. pluvialis cells for two days, considerable lysis and breakage of algal cells were observed, possibly owing to the formation of excess reactive oxygen species at the cathode. Conversely, in the absence of cell breakage, the application of anodic (oxidation) current effectively stimulated astaxanthin biosynthesis at a voltage range of 2–6 V, whereas the same could not be induced in the untreated control. At an optimal voltage of 4 V (anodic current: 30 mA), the astaxanthin content in the cells electro-treated for 2 h was 36.9% higher than that in untreated cells. Our findings suggest that electric treatment can be used to improve astaxanthin production in H. pluvialis culture if bioelectrochemical parameters, such as electric strength and duration, are regulated properly.

Oil palm empty fruit bunch (OPEFB) is the largest biomass waste from the palm oil industry. The OPEFB has a lignocellulose content of 34.77% cellulose, 22.55% hemicellulose, and 10.58% lignin. Therefore, this material’s hemicellulose and cellulose content have a high potential for xylitol and ethanol production, respectively. This study investigated the integrated microaerobic xylitol production by Debaryomyces hansenii and anaerobic ethanol semi simultaneous saccharification and fermentation (semi-SSF) by Saccharomyces cerevisiae using the same OPEFB material. A maximum xylitol concentration of 2.86 g/L was obtained with a yield of 0.297 g/g_xylose. After 96 h of anaerobic fermentation, the maximum ethanol concentration was 6.48 g/L, corresponding to 71.38% of the theoretical ethanol yield. Significant morphological changes occurred in the OPEFB after hydrolysis and xylitol and ethanol fermentation were shown from SEM analysis.

The massive potential of pineapple fruit production can produce a sizable amount of waste, around 75% (w/w) of pineapple weight, contributing to global environmental problems. For this reason, biorefinery techniques are urgently needed to convert pineapple plantation waste into high-value-added bioproducts including bromelain, various sugars, xylooligoscharide, xylitol, and ethanol. The purpose of this study was to examine the effectiveness of converting pineapple plantation waste into bromelain, xylitol, and ethanol. In this study, the activity of the bromelain enzyme was tested in each part of the pineapple plant waste. The configuration of the hydrolysis and fermentation processes used to make ethanol and xylitol from the rest of the pineapple plant waste from bromelain extraction was also investigated. Bromelain is a proteolytic enzyme found in pineapple plants and can be isolated from every part of pineapple plant waste. Enzyme activity under several conditions, such as crude extract, pure extract, and dried extract, has been studied to determine the best conditions for the downstream process of this enzyme’s production in the future. The purification of bromelain involved the utilization of the precipitation method followed by dialysis, whereas the drying process of bromelain employed the freeze-drying method. The bromelain enzyme specific activity is shown to be highest in the pineapple stem, as observed in crude-extract (1.45 ± 0.06 CDU/mg), purified-extract (10.38 ± 0.06 CDU/mg), and dried-extract (12.05 ± 0.43 CDU/mg) conditions. Using the pineapple stem to extract bromelain can produce lignocellulosic waste, which is made up of 39.47% starch, 19.96% hemicellulose, 36.44% cellulose, and 6.05% lignin. The high content of starch, cellulose, and hemicellulose has the potential to be used as feedstock for ethanol and xylitol fermentation. In this study, ethanol and xylitol fermentation were carried out using two methods: separate hydrolysis and fermentation methods (SHF) and semi-simultaneous saccharification and fermentation methods (semi-SSF). As a result, fermentation using the semi-SSF method produced ethanol with a higher titer and yield (22.12 ± 0.05 g/L and 0.44 ± 0.00 g/g, respectively). However, the production of xylitol was found to be insignificant, regardless of whether it was obtained using SHF or semi-SSF. The purification of bromelain involved the utilization of the precipitation method followed by dialysis, whereas the drying process of bromelain employed the freeze-drying method.

Hydrolysis and fermentation processes are key stages in xylitol production from lignocellulosic materials. In this study, pineapple cores, one of the wastes from the canned pineapple industry, were used as raw material for xylitol production. Two methods was used for hydrolysis: enzymatically using commercial enzyme Cellic HTec2, and acid hydrolysis using 4% H₂SO₄. In contrast, the fermentation process was carried out with two selected yeasts commonly employed in xylitol fermentation, Debaryomycess hansenii, and Candida tropicalis. Before these two processes, the pineapple cores were characterized using the Van Soest method to determine their lignocellulosic content. The hemicellulose content was 36.06%, the cellulose content was 14.20%, and the lignin content was 10.05%. This result indicates that the hemicellulose content of pineapple cores has the potential to be used as a raw material in the production of xylitol. The hydrolysis efficiency of enzymatic hydrolysis was 21% higher than that of acid hydrolysis. The highest xylitol and biomass yield of 0.371 g_xylitol/g_xylose and 0.225 g_cell/g_xylose were observed by C. tropicalis using an enzymatic hydrolysate.