Heterologous Expression and Characterization of a Ferulic Acid Esterase from Aspergillus aculeatus with Potential Use in Sunflower Seed Processing

Hydrolytic activity for chlorogenic acid (CGA) has been recognized as an important side activity of some types of ferulic acid esterases. The purpose of this work was to enhance the efficient expression of ferulic acid esterase (FAE) and to explore its application in the processing of sunflower seed. Two novel FAEs from Aspergillus aculeatus (AaSD14) were expressed in genetically engineered E. coli BL21 (DE3), and their properties, including temperature, pH, metal ions and substrate specificity, were characterized after purification. Competitive CGA hydrolysis activity was observed in these recombined ferulic acid esterases (reFAEs) with reFAE1 of 246.37 U/g and reFAE2 of 340.95 U/g, which were 56.6 and 78.4 times higher than that of the wild strain (4.35 U/g), respectively. Meanwhile, the fermentation cycle was greatly shortened to 2.0 d. These reFAEs were recognized as type C FAE through substrate specificity assays. Treatment of sunflower seed protein (SSP) using reFAE2 resulted in a remarkable color change, from green to milk-white, confirming the activity of CGA biodegradation. Therefore, it shows certain potential in the processing of sunflower seed and other related foodstuffs.

Effects of Ferulic Acid Esterase-Producing Lactic Acid Bacteria and Storage Temperature on the Fermentation Quality, In Vitro Digestibility and Phenolic Acid Extraction Yields of Sorghum (Sorghum bicolor L.) Silage

Two lactic acid bacteria (LAB) strains with different ferulic acid esterase (FAE) activities were isolated: Lactobacillus farciminis (LF18) and Lactobacillus plantarum (LP23). The effects of these strains on the fermentation quality, in vitro digestibility and phenolic acid extraction yields of sorghum (Sorghum bicolor L.) silage were studied at 20, 30 and 40 °C. Sorghum was ensiled with no additive (control), LF18 or LP23 for 45 days. At 40 °C, the lactic acid content decreased, whereas the ammonia nitrogen (NH3-N) content significantly increased (p < 0.05). At all three temperatures, the inoculants significantly improved the lactic acid contents and reduced the NH3-N contents (p < 0.05). Neither LP23 nor LF18 significantly improved the digestibility of sorghum silages (p > 0.05). The LP23 group exhibited higher phenolic acid extraction yields at 30 °C (p < 0.05), and the corresponding yields of the LF18 and control groups were improved at 40 °C (p < 0.05). FAE-producing LABs might partially ameliorate the negative effects of high temperature and improve the fermentation quality of sorghum silage. The screened FAE-producing LABs could be candidate strains for preserving sorghum silage at high temperature, and some further insights into the relationship between FAE-producing LABs and ensiling temperatures were obtained.

The Effect of Xylooligosaccharide, Xylan, and Whole Wheat Bran on the Human Gut Bacteria

Wheat bran is a cereal rich in dietary fibers that have high levels of ferulic acid, which has prebiotic effects on the intestinal microbiota and the host. Herein we explored the effect of xylooligosaccharide, xylan, and whole wheat bran on the human gut bacteria and screened for potential ferulic acid esterase genes. Using in vitro fermentation, we analyzed the air pressure, pH-value, and short-chain fatty acid levels. We also performed 16S rRNA gene and metagenomic sequencing. A Venn diagram analysis revealed that 80% of the core operational taxonomic units (OTUs) were shared among the samples, and most of the xylooligosaccharide treatment core OTUs (319/333 OTUs) were shared with the other two treatments’ core OTUs. A significant difference analysis revealed that the relative abundance of Dorea, Bilophila, and Sulfurovum in wheat bran treatment was higher than that in xylan and xylooligosaccharide treatments. The clusters of orthologous groups of proteins functional composition of all samples was similar to the microbiota composition of the control. Using metagenomic sequencing, we revealed seven genes containing the conserved residues, Gly-X-Ser-X-Gly, and the catalytic triad, Ser-His-Asp, which are thus potential ferulic acid esterase genes. All the results indicate that xylan and/or xylooligosaccharide, the main dietary fibers in wheat bran, plays a major role in in vitro fermentation by the human gut microbiota.