Acid Precipitation versus Solvent Extraction: Two Techniques Leading to Different Lactone/Acidic Sophorolipid Ratios

Sophorolipids (SL) prepared from biotransformation of refined bleached deodorized (RBD) palm olein by Starmerella bombicola (ATCC 22214) occur as a mixture of homologs. Characterization of SL was performed using high-performance liquid chromatography with electrospray ionization mass spectrometry detection (HPLC-ESI-MS) under negative ion mode. Two different purification methods were compared: precipitation and solvent extraction. SL purified by precipitation and solvent extraction consisted of five major homologs with m/z values of 687, 645, 689, 705, and 661. The fractions of lactone and acidic SL via precipitation were 70.24 ± 1.4% and 29.76 ± 1.4%, respectively. SL isolated by solvent extraction contained 44.78 ± 1.9% lactone and 55.22 ± 1.9% acidic SL. Therefore, the purification method strongly impacted the composition of the SL products.     

小麦秸秆的预处理对球拟假丝酵母产槐糖脂的影响

考察小麦秸秆的预处理方式对球拟假丝酵母(Starmerella bombicola)利用其糖化液发酵产槐糖脂(SLs)的影响，并对发酵进行优化。分别选择稀酸预处理(DAP)、NaOH预处理(SHP)和SO3微热爆预处理(STMEP)对小麦秸秆进行预处理，使用纤维素酶酶解糖化后将糖化液用于SLs的发酵，采用补加葡萄糖和活性炭脱毒的方法提高SLs的产量。结果显示，SHP最利于小麦秸秆的酶解糖化，所得糖化液中葡萄糖含量达61.30 g/L，其次为STMEP和DAP，葡萄糖含量分别为48.33 g/L和40.00 g/L。STMEP糖化液中抑制物的总含量最低，其次为SHP和DAP。S. bombicola可以直接利用上述糖化液发酵产SLs，但发酵特性有所不同。SHP和STMEP糖化液更利于酸型槐糖脂(ASL)的积累，相比于化学合成培养基，其产量分别提高了74.27%和92.33%，达到100.45 g/L和110.86 g/L。补加葡萄糖和活性炭脱毒可以进一步提高SLs的产量。对于SHP糖化液，补加葡萄糖及其与活性炭脱毒的联合可将ASL的产量进一步提高至124.49 g/L；对于STMEP糖化液，则可将内酯型槐糖脂(LSL)的产量进一步提高至32.02 g/L，与化学合成培养基的LSL发酵水平相当。因此，小麦秸秆具备发酵产SLs的潜力，且不同预处理方式及发酵方式可用于获得不同类型的SLs，本研究有助于降低SLs的生产成本并拓展其应用领域。     

Starmerella bombicola: recent advances on sophorolipid production and prospects of waste stream utilization

Sophorolipids are among the most extensively studied microbial biosurfactants. Starmerella bombicola is the most productive strain known for sophorolipid production, with volumetric productivity of up to 3.7 g L⁻¹ h⁻¹. This review focuses on the two most important aspects that have an influence on sophorolipid commercialization. Firstly, the metabolic engineering achievements of S. bombicola in the last decade are summarized. Secondly, three improvements of the bioprocess are described, including alternative feedstock, fermentation strategy and specially designed bioreactor. Discussion is made on the waste sources that have been used as feedstock for sophorolipid production, and the review also emphasizes the potential of food waste as nutrient source. Fermentation strategies that correlate with the specially designed bioreactors for commercialization are also discussed in detail. © 2018 Society of Chemical Industry     

Influence of sequential inoculum of Starmerella bacillaris and Saccharomyces cerevisiae on flavonoid composition of monovarietal Sangiovese wines

The selection of Starmerella bacillaris strains to be used with Saccharomyces cerevisiae as mixed cultures has been recently suggested in order to produce wines containing lower ethanol and higher glycerol concentrations and to promote fructose degradation due to their fructophilic character. However, studies about effects of such mixed starter cultures on phenolic compounds, which are responsible for the colour and health-enhancing properties in red wines, are currently lacking. Therefore, in this work, the influence of sequential inoculated fermentation (SIF) with Starm. bacillaris and S. cerevisiae on phenolic content of monovarietal Sangiovese wine was evaluated by fermentations at laboratory scale. Axenic fermentations (AXFs) with S. cerevisiae were performed as control. S. cerevisiae attained higher cell densities in AXF compared with SIF. The experimental wines obtained by SIF showed significant lower ethanol and higher glycerol concentrations, whereas no significant difference was detected in colour intensity. The total phenol index reached significantly lower values in SIF. Furthermore, the wines produced by SIF contained higher concentrations of vitisin A that has a greater colour stability than the anthocyanin monomer. Finally, a lower content of both free anthocyanins and flavan-3-ols, key compounds for wine quality possessing also health-enhancing properties, was found in wines obtained by SIF. On the contrary, no significant difference was detected on flavonol concentration between SIF and AXF. This study highlighted that the use of sequential inoculum of Starm. bacillaris and S. cerevisiae can contribute to increasing the colour stability of red wines, even if at the expense of compounds with health properties.     

Vitis species,vintage, and alcoholic fermentation do not drive population structure in Starmerella bacillaris (synonym Candida zemplinina) species

The yeast species Starmerella bacillaris (synonym Candida zemplinina) is widely associated with oenological ecosystems and is frequently isolated from grape and grape must. Previous work showed that the genetic diversity of this species is high in wine environments and it is shaped by geographic location. Most analysed C. zemplinina strains, however, have been isolated from Vitis vinifera, disregarding the existence of other worldwide-distributed Vitis species used in winemaking. In this work, we address the impact of the Vitis species and geographic location on the genetic diversity of C. zemplinina. Microsatellite genotyping analysis was applied to two remarkable populations of C. zemplinina from Argentina and Portugal (Azores Archipelago), isolated from neighbouring V. vinifera and Vitis labrusca vineyards. The study also included a large population of previously characterized worldwide-isolated C. zemplinina strains. Genetic analyses confirmed that geographic localization significantly shaped the genetic diversity of C. zemplinina. No genetic differentiation on the basis of the Vitis species was recorded, indicating that C. zemplinina populations from neighbouring V. vinifera and V. labrusca vineyards are genetically homogeneous. In addition, no impact of the vintage was found on the C. zemplinina populations being both highly diversified and homogeneous during initial stages of alcoholic fermentation. Altogether, these results confirmed that winemaking-related factors (i.e., vintage, Vitis species, and alcoholic fermentation) do not impact the genetic diversity of C. zemplinina and that only geographic localization significantly shapes this yeast species.     

Jatropha oil and karanja oil as carbon sources for production of sophorolipids

Biosurfactants like sophorolipids (SL) are mild and environmentally friendly surfactants to be used in cosmetics and health care products. In addition to surfactant properties, SL also possess antimicrobial and skin healing properties. SL are produced by microbial fermentation using refined vegetable oils with glucose as a carbon source. This affects the economics of the production of SL. In the present work, non‐traditional oils like jatropha oil, karanja oil, and neem oil were used as newer feedstock for fermentative production of SL using Starmerella bombicola (ATCC 22214). In the fermentation, jatropha oil and karanja oil gave 6.0 and 7.6 g/L of SL (mainly lactonic form), respectively. HPLC, liquid chromatography–mass spectrometer, and ¹H NMR of crude SL obtained from fermentation broth showed lactonic form of two major SL. Oleic acid and linoleic acid were preferentially consumed over other fatty acids by the organism. Neem oil gave lower yield, i.e., 2.63 g/L of SL (mainly acidic form). Practical applications: Jatropha oil and karanja oil are one of the non‐traditional oils grown wildly in India that have large potential that is still to be explored. These oils contain non‐glycerides components that exclude their use as edible oil. These oils can be used as substrate for SL that can find novel applications like in soil remediation, skin care production, antimicrobial agents, low foaming detergents, and food additives. The current study has provided proof of concept work that has indicated the potential of these oils to be used as substrate for SL. It has opened new avenues and there is further scope to improve the yield by validating the process parameters like aeration rate, residual substrate recycle and pH control.