Terpenes are compounds that include monoterpenes, sesquiterpenes, diterpenes, and terpenes, where isoprene is the basic structural unit of multiple oxygenated hydrocarbons. Terpenes are often found in plants, especially in some Zingiberaceae or tulips, and they have been obtained by direct extraction, chemical synthesis, and microorganisms. They exhibit anti-bacterial, anti-viral, anti-oxidant, and analgesic activity, aid digestion, and have other biological activities. Terpenes are widely used as factors in food health and as anti-cancer treatments. They are used especially as active substances in fermented Chinese baijiu products and gives Chinese baijiu its fruity aroma. To a certain extent, terpenes affect the quality of baijiu. In pharmaceutical products, terpenes, especially limonene and elemene, have strong biological activity that reduces the mitosis of tumor cells, induces tumor cell apoptosis, and inhibits tumor cell growth. However, the low yield of terpenes limits its application. Therefore, we review the sources of terpenes, focus on the biosynthesis pathway of sesquiterpenes, and explore the latest research progress on terpenes that play a biologically active and functional role in fermented products and pharmaceutical products, especially in the development and utilization of the Chinese baijiu industry. We provide new research ideas for the improvement and optimization of terpenes in various industries.

Pulcherriminic acid is a cyclic dipeptide found mainly in Bacillus and yeast. Due to the ability of pulcherriminic acid to chelate Fe³⁺ to produce reddish brown pulcherrimin, microorganisms capable of synthesizing pulcherriminic acid compete with other microorganisms for environmental iron ions to achieve bacteriostatic effects. Therefore, studying the biosynthetic pathway and their enzymatic catalysis, gene regulation in the process of synthesis of pulcherriminic acid in Bacillus can facilitate the industrial production, and promote the wide application in food, agriculture and medicine industries. After initially discussing, this review summarizes current research on the synthesis of pulcherriminic acid by Bacillus, which includes the crystallization of key enzymes, molecular catalytic mechanisms, regulation of synthetic pathways, and methods to improve efficiency in synthesizing pulcherriminic acid and its precursors. Finally, possible applications of pulcherriminic acid in the fermented food, such as Chinese Baijiu, applying combinatorial biosynthesis will be summarized.

The solid-state fermentation process of strongly flavored Baijiu is complicated by the co-fermentation of many different microorganisms in the fermentation pools. The traditional fermentation pools of strong flavor Baijiu are sealed with mud, and this sealed-pit mud is not easy to maintain; therefore, the pit cap is prone to cracks and to caving in. The destruction of the sealed-pit mud may lead to instability in the composition and an abundance of microorganisms in the fermentation process that results in fluctuations of product quality. Thus, the production method of replacing the mud cap with a new steel cap is gradually attracting the attention of scientific and technical workers in the industry. However, so far, there have been relatively few reports on the use of steel lids for sealing pits for fermentation and brewing. In this study, the volatile flavor components of 270 Baijiu samples from mud-sealing and steel-sealing pits of a Chinese Baijiu distillery were studied qualitatively and quantitatively using Gas Chromatography–Mass Spectrometry (Abbreviated as GC-MS). Our statistical methods included Hierarchical Cluster Analysis (Abbreviated as HCA), Principal Component Analysis (Abbreviated as PCA), and Discriminant Analysis (Abbreviated as DA). A statistical analysis was carried out on the yield of strongly flavored Baijiu, and we made a comprehensive evaluation of the Baijiu produced under the two pit-sealing modes with regard to flavor and economic efficiency. The yield of strong flavored Baijiu was 6.7% higher with steel-sealing pits compared with mud-sealing pits. Cluster analysis categorized the strongly flavored Baijiu samples into two categories initially: (1) samples produced using mud-sealing pits and (2) samples using steel-sealing pits. Our analysis also indicated that the 28 compounds used for quantification were selected correctly. Surprising to the experimental staff, the overall score for the steel-sealing pits was greater than that of the mud-sealing pits based on PCA. Using DA, the prediction results were 100% accurate. In summary, through a comparative analysis of the flavor and yield, which are the two main factors that affect the quality of Baijiu in a distillery, and systematic combination at both experimental and theoretical levels, the differences between the Baijiu production by steel-sealing and the traditional mud-sealing were clear. Regardless of the impact of age, the detectable flavor components of Baijiu from the mud-steeling pits were very consistent with those of the steel-sealing pits in terms of richness or concentration. However, steel-sealing pits were significantly superior to mud-sealing pits with respect to output, consistency in quality, and cost (human and economic) savings.

Plant chitinase, a member of the pathogenesis-related proteins and glycoside hydrolase family 19, plays a crucial role in plant resistance to pathogenic fungi. In this study, we isolated a chitinase gene encoding PaChi from Picea asperata, containing an open reading frame of 768 bp that encodes 255 amino acid residues. PaChi includes the chitin-binding domain, catalytic domain, and active site characteristic of class IV chitinases. Homologous modeling and phylogenetic analysis indicated that PaChi exhibits the highest structural similarity and closest genetic relationship with the chitinase of Norway spruce, suggesting potential functional similarities. RT-qPCR analysis demonstrated that PaChi expression is relatively high in the roots of P. asperata. Additionally, PaChi transcription levels were significantly upregulated during the early stages of Lophodermium piceae infection, indicating active involvement in the defense response of P. asperata against L. piceae infection. SDS-PAGE analysis revealed that the recombinant PaChi has a molecular weight of approximately 27 kDa. The purified recombinant PaChi exhibited a chitinase activity of 4.61 U/mg, with optimal pH and temperature at 7.0 and 40 °C, respectively. Notably, purified recombinant PaChi significantly affected the mycelial morphology of L. piceae, inclusion body concentration and cell swelling. These findings lay the groundwork for further understanding the molecular mechanisms by which PaChi is involved in biological stress.

Visual evaluation techniques for Chinese Baijiu remain an active research area. We identified a novel dendritic crystal pattern formed after the droplet evaporation of Feng-flavor Baijiu. Interestingly, this pattern showed an obvious correlation with aging in Jiuhai container (storage vessels for aging) (R² = 0.904, p < 0.01), suggesting its potential as a visual quality indicator of Feng-flavor Baijiu. During droplet evaporation, the local solution preferentially reaches a supersaturated state at the three-phase contact line, initiating nucleation and crystallization that ultimately assemble into a dendritic crystal pattern with a coffee-ring structure. Further analysis revealed that the crystals are mainly composed of metal ions such as calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), and potassium (K⁺), which primarily originate from a unique aging container known as the Jiuhai container. Furthermore, we observed that trace components such as acids and esters can significantly inhibit or promote the formation of dendritic crystals, contributing to distinct dendritic crystal patterns across various quality grades (Ⅰ to Ⅴ) of Feng-flavor Baijiu samples. More interestingly, crystallization simulation experiments showed that dendritic crystal patterns formed in blended Feng-flavor Baijiu but not in other blended-flavor Baijiu samples. Consequently, the characteristic dendritic crystal patterns generated by droplet evaporation could serve as potential visual indicators for evaluating the quality of Feng-flavor Baijiu.