The Potential of Flos sophorae immaturus as a Pigment-Stabilizer to Improve the Monascus Pigments Preservation, Flavor Profiles, and Sensory Characteristic of Hong Qu Huangjiu.

Hong Qu Huangjiu (HQW) is distinguished by its inclusion of Monascus pigments, meaning that photosensitivity strongly affects the sensory quality of the wine. In this study, the effects of Flos sophorae immaturus (FSI) on the stability of Monascus pigments, the flavor profiles, and the sensory characteristics of HQW were investigated. After sterilization, the addition of FSI increased the preservation rate of Monascus pigments in HQW by up to 93.20%, which could be accounted for by the synergy of rutin and quercetin in FSI. The total content of the volatile flavor compounds in HQW increased significantly as the added amounts of FSI were increased, especially 3-methyl-1-butanol, 2-methyl-1-propanol, and short-chain fatty acid ethyl esters (SCFAEE). Sensory evaluation and partial least-squares regression revealed that the concentration of FSI significantly affected the aroma characteristics of HQW but had little effect on the mouthfeel. The addition of 0.9 mg/mL FSI yielded a satisfactory HQW with high scores in terms of mouthfeel and aroma. The strong correlation between fruit-aroma, full-body, and SCFAEE suggests that FSI might alter the aroma of HQW by enhancing the synthesis of SCFAEE. Summarily, treatment with FSI represents a new strategy for improving the stability of photosensitive pigments and thus adjusting the aroma of HQW or similar beverages.

Corrigendum: Flavor Formation in Chinese Rice Wine (Huangjiu): Impacts of the Flavor-Active Microorganisms, Raw Materials, and Fermentation Technology.

[This corrects the article DOI: 10.3389/fmicb.2020.580247.].

Polysaccharides can improve the survival of Lactiplantibacillus plantarum subjected to freeze-drying.

Freeze-drying is one of the most commonly used methods of bacteria preservation. During this process, cryoprotectants can greatly reduce cellular damage. Micromolecular cryoprotectants have been widely adopted but have limited selectivity and protective effects. Therefore, explorations of other types of cryoprotectants are needed. This study aimed to explore the possibility of the macromolecular cryoprotectants and combinations of cryoprotectants to maintain bacterial activity. We found that the survival rate of Lactiplantibacillus plantarum AR113 after freeze-drying was 19% higher in the presence of soy polysaccharides than with trehalose, the best-performing micromolecular cryoprotectant. Moreover, a 90.52% survival rate of L. plantarum WCFS1 was achieved using the composite cryoprotectant containing soy polysaccharide and trehalose, which increased by 31.48 and 36.47% compared with adding solely trehalose or soy polysaccharide, respectively. These results demonstrate that macromolecular and micromolecular cryoprotectants have similar effects, and that combinations of macromolecular and micromolecular cryoprotectants have better protective effects. We further observed that the composite cryoprotectant can increase Lactobacilli survival by improving cell membrane integrity and lactate dehydrogenase activity. Our finding provides a new type of cryoprotectant that is safer and more effective, which can be extensively applied in the relevant food industry.

Flavor Formation in Chinese Rice Wine (Huangjiu): Impacts of the Flavor-Active Microorganisms, Raw Materials, and Fermentation Technology.

Huangjiu (Chinese rice wine) has been consumed for centuries in Asian countries and is known for its unique flavor and subtle taste. The flavor compounds of Huangjiu are derived from a wide range of sources, such as raw materials, microbial metabolic activities during fermentation, and chemical reactions that occur during aging. Of these sources, microorganisms have the greatest effect on the flavor quality of Huangjiu. To enrich the microbial diversity, Huangjiu is generally fermented under an open environment, as this increases the complexity of its microbial community and flavor compounds. Thus, understanding the formation of flavor compounds in Huangjiu will be beneficial for producing a superior flavored product. In this paper, a critical review of aspects that may affect the formation of Huangjiu flavor compounds is presented. The selection of appropriate raw materials and the improvement of fermentation technologies to promote the flavor quality of Huangjiu are discussed. In addition, the effects of microbial community composition, metabolic function of predominant microorganisms, and dynamics of microbial community on the flavor quality of Huangjiu are examined. This review thus provides a theoretical basis for manipulating the fermentation process by using selected microorganisms to improve the overall flavor quality of Huangjiu.

Membrane Fluidity of Saccharomyces cerevisiae from Huangjiu (Chinese Rice Wine) Is Variably Regulated by OLE1 To Offset the Disruptive Effect of Ethanol.

An evolution and resequencing strategy was used to research the genetic basis of Saccharomyces cerevisiae BR20 (with 18 vol% ethanol tolerance) and the evolved strain F23 (with 25 vol% ethanol tolerance). Whole-genome sequencing and RNA sequencing (RNA-seq) indicated that the enhanced ethanol tolerance under 10 vol% ethanol could be attributed to amino acid metabolism, whereas 18 vol% ethanol tolerance was due to fatty acid metabolism. Ultrastructural analysis indicated that F23 exhibited better membrane integrity than did BR20 under ethanol stress. At low concentrations (<5 vol%), the partition of ethanol into the membrane increased the membrane fluidity, which had little effect on cell growth. However, the toxic effects of medium and high ethanol concentrations (5 to 20 vol%) tended to decrease the membrane fluidity. Under high ethanol stress (>10 vol%), the highly tolerant strain was able to maintain a relatively constant fluidity by increasing the content of unsaturated fatty acid (UFA), whereas less-tolerant strains show a continuous decrease in fluidity and UFA content. OLE1, which was identified as the only gene with a differential single-nucleotide polymorphism (SNP) mutation site related to fatty acid metabolism, was significantly changed in response to ethanol. The role of OLE1 in membrane fluidity was positively validated in its overexpressed transformants. Therefore, OLE1 lowered the rate of decline in membrane fluidity and thus enabled the yeast to better fight the deleterious effects of ethanol.IMPORTANCE Yeasts with superior ethanol tolerance are desirable for winemakers and wine industries. In our previous work, strain F23 was evolved with superior ethanol tolerance and fermentation activity to improve the flavor profiles of Chinese rice wine. Therefore, exploring the genomic variations and ethanol tolerance mechanism of strain F23 could contribute to an understanding of its effect on the flavor characteristics in the resulting Chinese rice wine. The cellular membrane plays a vital role in the ethanol tolerance of yeasts; however, how the membrane is regulated to fight the toxic effect of ethanol remains to be elucidated. This study suggests that the membrane fluidity is variably regulated by OLE1 to offset the disruptive effect of ethanol. Current work will help develop more ethanol-tolerant yeast strains for wine industries and contribute to a deep understanding of its high flavor-producing ability.

Effects of boiling, ultra-high temperature and high hydrostatic pressure on free amino acids, flavor characteristics and sensory profiles in Chinese rice wine.

Traditional sterilization leads to poor vinosity of Chinese rice wine (CRW). Effects of boiling, ultra-high temperature (UHT) and high hydrostatic pressure (HHP) on CRW quality were investigated. Thermal treatment resulted in a decrease of total free amino-acids (FAA), whereas HHP-treatment caused an increase. However, UHT and HHP treatments had little effect on FAA with sweet and umami-like flavor. HHP-treated CRW contained 7.35% higher content of flavors relative to untreated wine, while thermally-treated CRW revealed 4.68-8.61% losses. Based on principal component analysis, CRW processed at 400 or 600 MPa for 10 min exhibited similar flavor to the untreated wine, which was highly associated with long-chain fatty acid ethyl esters (C13-C18). Moreover, partial least squares regression demonstrated that sensory attributes of cereal aroma and astringency were highlighted after thermal treatment, while fruit aroma, continuation and full body were dominant after HHP treatment. HHP treatment effectively enhanced the quality of CRW, which could be applied in other alcoholic beverages.

The effect of vacuum freeze-drying and radiation on allogeneic aorta grafts.

Vacuum freeze-dried aorta is a satisfactory material for blood vessel grafting. Previous studies have focused on immunity, however, vacuum freeze-drying is a complicated process of heat and mass transfer, and adopting a programmed cooling process may more completely preserve the mechanical properties of the blood vessels. Irradiation, as a method of removing pathogens, lowers the antigenic activity of the blood vessels. In our study, vacuum freeze-drying combined with radiation was used as a treatment for porcine aorta prior to grafting, aimed at deactivating endogenous retrovirus, shielding masses of endothelial cells and lowering the immunogenicity of the blood vessels. As for the mechanical properties, compared with normal aorta, the maximum axial tensile stress (ATS) decreased by 20%, the maximum circumferential tensile stress (CTS) increased by 30% and the maximum puncture stress (PT) decreased by 20%. Our results revealed that 2 months after of grafting, the host cells had migrated into the graft tissue and propagated to initiate endothelialization, the inflammatory reaction was abated and the PT had returned to normal levels.

[Structural change analysis of pig aorta before and after freeze-drying].

Pig aortic vessels were processed by vacuum freeze-drying and then the aotic vessels were scanned and compared by CT, microscopic and texture analyzer. These processes presented a new method for preserving the vessels. Morphological changes of the vessels were tracked by Micro-CT, and mechanical properties were compared by texture analyzer combining with microscopic observation for structures and tissues. Results showed that the wall of the vessels became thinner by freeze-drying. After rehydration, the membrane structure was generally maintained, and the elastic fibers were more orderly arranged so that they were close to fresh vessels. In the area of mechanical property, the maximum puncture stress and axial tensile stress of rehydrated blood vessels were stronger than that of the fresh, while circumferential tensile stress was weaker than that of the fresh. Finally, analysis also showed that the freeze-dried vessel was basically remained the original morphological structure. The pores in vessel fiber and stratification during drying may be beneficial to the host cell invasion and angiogenesis, so it is expected to be a new effective means to save the blood vessels. Currently, four pigs have been transplanted with the rehydrated vessels, and all of the four have survived for more than 3 weeks.

Effect of pre-freezing rate on porosity ratio and mechanical property of pig aorta.

Vacuum freeze-dried blood is a good material for vascular grafts. However, studies on this technology are few, particularly on physical performance change of freeze-dried blood vessel at different pre-freezing rate. In our study, pig aortas were non-invasively scanned by micro-CT in each stage of freeze-drying at different pre-freezing rates, then comparing the porosity ratio and grey level under different conditions with each other to analysis the influence of different methods on the aorta. The mechanical properties of rehydrated pig aorta and fresh one were compared by texture profile analyzer to investigate the influence of different pre-freezing rates on mechanical properties in pig aorta. Our results showed that the proper pre-freezing rate for freeze-drying were 1 C/min. The changing rates of porosity rate and the average gray scale value were 16.6% and 3.64% respectively after freeze-dried. The puncture tolerance (PT) and circumferential tensile stress were increased about 20% and 30% respectively, and the axial tensile stress (ATS) were decreased about 20% in rehydrated aorta compared with fresh aorta. We otherwise conclude that under optimized process conditions, freeze-dried aorta with proper porosity rate and mechanical properties approximate fresh aorta could be preparation.

Micro-computed tomography observation of sublimation interface and image analysis on sublimation process during freeze-drying.

The freeze-drying process is complicated with complex heat and mass transfer during sublimation. The sublimation interface of freeze-drying has become more attractive and meaningful recently. In this study, apple slices undergoing sublimation were scanned by a Micro-CT scanner. The cross-sectional images were reconstructed with those scanning images respectively. The technique of grey value analysis was used to recognize the procedure. The results showed that, from direct scanning images and 2-D reconstructed images, a 3-D moving mode of sublimation interface which contracted to the centre of the sample could be seen, sublimation process proceeded from edge to center gradually. The grey value of ice crystals was determined to be 154 through gauss calculation. By comparing frozen sample with freeze-dried one, the ice crystals regions in the beginning became the porous regions after drying, grey values increased correspondingly. Samples shrunk slightly after drying for 3 to 7 hours, which could be distinguished by the change in grey values.

Microscopic study of crystal growth in cryopreservation agent solutions and water.

Ice formation inside or outside cells during cryopreservation is evidently the main factor of cryoinjury to cells. In the study described here a high voltage DC electric field and a cryomicroscopic stage were used to test DMSO and NaCl solutions under electric field strengths ranging from 83 kV/m to 320 kV/m. Dendritic ice crystals became asymmetric when the electric field was activated. This change in the ice crystal shape was more pronounced in the ionic NaCl solution. In addition, ice growth of distilled water without an electric field was tested under different cooling rates.