In cold storage, fruits and vegetables still keep a low respiratory rate. Although cold storage is beneficial to maintain the quality of some fruits and vegetables, several factors (temperature and humidity fluctuations, heat inflow, air velocity, light, etc.) will accelerate moisture loss. Biopolymer films have attracted great attention for fruits and vegetables preservation because of their biodegradable and barrier properties. However, there is still a certain amount of water transfer occurring between storage environment/biopolymer films/fruits and vegetables (EFF). The effect of biopolymer films to inhibit moisture loss of fruits and vegetables and the water transfer mechanism in EFF system need to be studied systematically. Therefore, the moisture loss of fruits and vegetables, crucial properties, major components, fabrication methods, and formation mechanisms of biopolymer films were reviewed. Further, this study highlights the EFF system, responses of fruits and vegetables, and water transfer in EFF. This work aims to clarify the characteristics of EFF members, their influence on each other, and water transfer, which is conducive to improving the preservation efficiency of fruits and vegetables purposefully in future studies. In addition, the prospects of studies in EFF systems are shown.

The anthocyanin extracts (AE) from different sources were commonly used in preparing an indicator film to reflect food freshness, as AE contained rich anthocyanins which acted as the pH-sensitive ingredient. Therefore, this study aimed to compare the impact of AE sources (including rosella extract (RE), Lycium ruthenicum Murray (LE), and mulberry extracts (ME)) on the film properties and pH-sensitivity of konjac glucomannan/zein (KZ) composite film. Results showed that the three AEs had significantly different anthocyanin species and total contents, contributing to their different color changes in response to the pH changes. Some film property changes were not affected by the different AE, but mostly, different film property changing extents were observed, such as thickness, color, mechanical properties, hydrophilicity, antioxidant property, and water vapor permeability. This indicated that the hydrophilic plasticizing and void-filling effects of the anthocyanin were impacted by the anthocyanin structure. On the other hand, the impact of AE sources on the pH sensitivity and volatile ammonia sensitivity of the films was significantly different, mainly relating to both anthocyanin contents and composition. Finally, the KZ film with LE addition of 10% was suggested to be applied in the intelligent food packaging, as the addition of anthocyanin was relatively low and the film had both good pH sensitivity and film properties.

The strategy of emulsion coating was used for grape preservation. Camellia oil (CO) was incorporated with KGM/curdlan (KC) to fabricate KC-CO emulsion systems. KC-CO emulsions were analyzed by droplet size distribution and confocal laser scanning microscopy (CLSM), and KC-CO films were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), mechanical properties, dissolution, gas permeability, water contact angle (WCA). KC-CO coating was used for preservation of ‘Kyoho’ grapes. The results indicated that the addition of CO had a positive effect on KC system. CO could form a uniform emulsion with KC, and the droplets were evenly dispersed in the KC matrix. KC-CO films displayed a continuous microstructure, and elongation at break (EAB) was improved, while tensile strength decreased. The dissolution, water vapor permeability (WVP), and WCA were significantly enhanced, while the permeability of oxygen and carbon dioxide exhibited no advantage compared with KC film. KC-CO-10 possessed optimal properties and was selected as an emulsion coating for preservation. The results suggested that KC-CO-10 significantly maintained the appearance, total solid and acid content of ‘Kyoho’ grapes, and delayed the weight loss and firmness decrease. This study contributed to the understanding of polysaccharide-lipid emulsion system and the applications.

The mechanical, barrier properties, and water resistance of packaging materials are crucial for the preservation of fruits and vegetables. In this study, zein was incorporated as a hydrophobic substance into the konjac glucomannan (KGM)/curdlan (KC) system. The KC/zein (KCZ) showed good compatibility with the zein aggregates uniformly distributed in the network formed by an entanglement of KGM and curdlan micelles based on hydrogen bonds. The presence of zein inhibited the extension of the KC entangled structure and enhanced the solid-like behavior. The high content of zein (>6 %) increased zein aggregation and negatively affected the structure and properties of KCZ. The zein addition significantly improved the water vapor permeability, tensile strength, and elongation at break. The hydrophobicity of the KCZ films was significantly enhanced, accompanied by the water contact angle increasing from 81 degrees to 112 degrees, and the moisture content, swelling, and soluble solid loss ratio decreasing apparently. The K(56)C(40)Z(4) coating exhibited an excellent preservation effect to inhibit the respiration of cherry tomatoes, significantly reducing the water loss and firmness decline and maintaining the appearance, total solid, total acid, and ascorbic acid content. This work provided a strategy to fabricate hydrophobic packaging for the preservation of fruits and vegetables.

The low water solubility of zein severely limits its industrial application. In this study, the emulsifying performance and stability of zein were improved by electrostatically compounding different ratios of citrus pectin (CP) with zein to obtain zein-CP composite particles (ZCPs). When the mass ratio of CP to zein was 1: 2 (C1Z2), the composite particles showed the smallest particle size, and the C1Z2 stabilized Pickering emulsion (C1Z2-PE) exhibited excellent physical and environmental stability. The ZCPs stabilized emulsions were further cross-linked by transglutaminase (TGase) and Ca2+, resulting in the formation of emulsion gels with increased mechanical properties. Macroscopic and microscopic morphology analysis demonstrated the successful preparation of the emulsion gels. Through the rheological study and texture analysis, it was observed that the double cross-linked emulsion gels exhibited a remarkable improvement in apparent viscosity and gel hardness. This research offers a new strategy and technical reference for the development of new gel-based products.

To enhance the water-resistance and antibacterial properties of KGM films, mandarin oil (MO), was directly emulsified by pectin and then dispersed to the KGM matrix. The effect of MO concentration (0, 0.5, 1.0, 1.5, and 2 wt%) on the performance of the film-forming emulsions as well as the emulsion films was investigated. The results revealed that pectin could encapsulate and protect MO, and KGM as film matrix could further contributed to the high stability of the film-forming emulsions. The FT-IR, XRD, and SEM suggested that MO stabilized by pectin was uniformly distributed in the KGM matrix. The compatibility and good interaction between KGM and pectin contributed to highly dense and compact structure. Furthermore, increasing the concentration of MO effectively improved water-resistance, oxygen barrier, and antimicrobial activity of the KGM based films. The 1.5 wt% MO loaded KGM film had the highest tensile strength (72.22 MPa) and water contact angle (theta = 95.73 degrees), reduced the WVP and oxygen permeability by about 25.8 % and 32.8 times, respectively, prolonged the shelf life of strawberries for 8 days. As demonstrated, the 1.5 wt% MO-loaded KGM film has considerable potential for high-performance natural biodegradable active films to ensure food safety and reduce environmental impacts.

Citrus fruits have suffered serious losses in postharvest storage and transportation. A novel approach, fragmented konjac glucomannan-based Syringa essential oil (KSE) films, was used to maintain the quality of citrus fruits in storage. The KSE film was successfully prepared by using the encapsulating method via coacervation, with an encapsulation efficiency of 18.3% and loading capacity of 11.4%. GC–MS showed that eugenol, caryophyllene, and humulene were the main constituents of Syringa EO. SEM showed that EO drops or volatiles distributed in the KGM molecular matrix produced a concave structure during film formation. FTIR indicated no interaction or modification between KGM and Syringa EO, and EO was successfully encapsulated into the KGM films. The fragmented KSE films showed significant antifungal activity against Penicillium italicum, Penicillium digitatum, and Geotrichum citri-aurantii, inhibiting spore germination and mycelium elongation, resulting in suspected indentation, plasmolysis, and vacuolization. In storage, the fragmented KSE film packed in a non-woven bag apparently maintained the quality of citrus fruits, including sustaining fruit firmness and reducing vitamin C (VC), total soluble solids (TSS), and titratable acid (TA) loss. One of the modes of action for the quality maintenance of citrus fruits might be induced systemic resistance. This study might convey stronger impact in postharvest by newly developed packaging materials.

In this study, konjac glucomannan (KGM) and curdlan were used to fabricate composite coating (KC). The coating solutions were investigated using a rheological method, and the coatings were characterized by water solubility tests, water vapor permeability (WVP), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The preservation effect of KC coating on cherry tomatoes stored at room temperature was determined. Results indicated that the curdlan addition can adjust the hydrophilicity/hydrophobicity of KGM coatings. Curdlan addition enhanced intermolecular entanglement and film-forming property. Increasing curdlan content in KC coatings significantly decreased the moisture content, dissolution and swelling ratio, and WVP. The KGM-curdlan composites behaved as high-performance coatings with good compatibility and uniformity. The K3C2 coating showed the best uniformity, water barrier, and thermal stability. The application of K3C2 coating significantly reduced the weight loss, decay loss, and delayed the decreases of firmness, soluble solids, total acid, and VC contents of cherry tomatoes. The KGM/curdlan edible coatings have promising potential for prolonging the shelf life of cherry tomatoes and applications in fruits preservation in the future.

Natural polysaccharides with high viscosity, good thermal stability, and biocompatibility can improve the mechanical properties of inorganic silica aerogels and enhance their application safety. However, the effects of the preparation methods of polysaccharide-silica aerogels on their microstructure and application properties have not been systematically studied. To better investigate the effect of the microstructure on the properties of aerogel materials, two aerogels with different structures were prepared using Konjac glucomannan (KGM) and tetraethoxysilane (TEOS) via physical blending (KTB) and co-precursor methods (KTC), respectively. The structural differences between the KTB and KTC aerogels were characterized, and the thermal insulation and fire-retardant properties were further investigated. The compressive strength of the KTC aerogels with a cross-linked interpenetrating network (IPN) structure was three times higher than that of the KTB aerogels, while their thermal conductivity was 1/3 of that of the KTB aerogels. The maximum limiting oxygen index (LOI) of the KTC aerogels was 1.4 times, the low peak heat release rate (PHRR) was reduced by 61.45%, and the lowest total heat release (THR) was reduced by 41.35% compared with the KTB aerogels. The results showed that the KTC aerogels with the IPN have better mechanical properties, thermal insulation, and fire-retardant properties than the simple physically blending KTB aerogels. This may be due to the stronger hydrogen-bonding interactions between KGM and silica molecules in the KTC aerogels under the unique forcing effect of the IPN, thus enhancing their structural stability and achieving complementary properties. This work will provide new ideas for the microstructure design of aerogels and the research of new thermal insulation and fire-retardant aerogels.

The pore size distribution and pore number had a great impact on the air filtration performance of polysaccharide-based aerogels. In this study, konjac glucomannan (KGM)/curdlan (KC) aerogels were prepared by the vacuum freeze-drying method, and the microstructure, molecular interaction, mechanical property, thermal stability, and air filtration performance were investigated. Results indicated that KGM and curdlan showed good compatibility based on hydrogen bonds and formed complete aerogel with three-dimensional network structure. KC1.2 displayed the highest compressive stress and thermal stability. With the addition of curdlan, the pore size decreased and the pore number increased, which resulted in the improvement of filtration efficiency. However, the high number (up to 1200) of pores in KC1.2 caused a decrease of filtration efficiency, and KC1.2 showed high air resistance (up to 1000 Pa). For PM1.0 and PM2.5, all KC aerogels had high filtration efficiency of more than 80 %. Considering the filtration efficiency and air resistance, KC0.9 was regarded as the optimum material for air filtration. All KC aerogels maintained stable filtration efficiency and pore structure after fifteen filtration cycles, demonstrating a long service life. These results indicated that KC aerogel had great potential for application in air filtration.

目的 探究天然多糖魔芋葡甘聚糖(konjac glucomannan,KGM)/可得然胶(curdlan,CUD)复合气凝胶(KC)遭受环境微生物葡萄灰霉侵染时两者发生的相互作用.方法 以KGM和CUD为原料,采用溶胶预冷、真空冷冻干燥制备不同配比的KGM/CUD复合气凝胶(K1C0.6、K1C0.9、K1C1.2),用灰霉接种处理,检测气凝胶的重量变化率;运用扫描电镜、红外光谱和差示扫描量热仪分别分析气凝胶的微观形貌、分子变化和热稳定性;观察灰霉在气凝胶上的生长适应性.结果 经灰霉作用,KC气凝胶结构坍塌、皱缩,孔结构严重破坏;灰霉适宜于气凝胶环境的生长,生长旺盛,形态完整,萌发大量孢子;气凝胶被侵染的同时吸收大量水分,促进了作用进程;红外光谱推测,侵染后的气凝胶的多糖长链被降解为短链,无新基团产生;差示扫描量热仪(differential scanning calorimetry,DSC)分析表明,侵染后的气凝胶热稳定性明显下降.结论 葡萄灰霉侵染KC气凝胶,充分利用和降解多糖分子链,且适应于气凝胶环境,本研究将为天然多糖复合物的安全和质量检测提供理论依据.

为进一步开发植物精油在柑橘采后防腐保鲜中的应用,以肉桂精油为芯材,玉米糊精、阿拉伯胶、明胶为壁材,采用复合凝聚-冷冻干燥法制备肉桂精油微囊.通过扫描电镜和激光粒度仪考察精油微囊的微观形貌结构,采用傅里叶红外光谱和差示扫描量热法探究其分子间相互作用和热稳定性,运用琼脂扩散法和显微观察分析其抑菌作用.结果 表明,EDA1G2和EDA3(不含明胶)2种精油微囊呈近球形结构,对肉桂精油包埋性良好、分散均匀,平均粒径分别为49.2 μm和11.56 μm,粒径分布集中;红外光谱揭示肉桂精油被包埋在微囊中,且壁材和芯材间并不是简单的物理混合,也没有形成新的化学键,可能发生非共价键结合;DSC显示2种微囊热稳定性良好;肉桂精油和微囊均对指状青霉、意大利青霉和地霉菌株展现明显的抑菌作用,可显著抑制孢子萌发和菌丝伸长,意大利青霉的菌丝有解体的趋势,且EDA1G2对意大利青霉的抑制更为明显.该结果将为柑橘采后防腐保鲜中的研究和应用提供理论依据.

Citrus diseases are the dominant threat to citrus production and cause substantial economic losses. At present, chemical control is highly effective and is widely applied in the control of agricultural diseases. However, the chemicals used may have a negative impact on the environment and human life. Biological control is considered a safe and sustainable strategy and has attracted great attention for its potential for disease control. Bacillus species show broad-spectrum antimicrobial activity and have been widely used as agricultural biocontrol agents. This study aims to provide an overview of the research on and application of Bacillus species as potential biocontrol agents against citrus diseases. Bacillus species mainly act through the antagonistic mechanisms of production of antimicrobial substances (lipopeptides, antibiotics, and volatile organic compounds), induced systemic resistance and competition for nutrients and space (colonization). Few Bacillus-based biocontrol products are applied in citrus, so developing and commercializing Bacillus products is a promising area of study. Combined strategies based on Bacillus spp. are more effective than individual strategies alone and should be used in the control of citrus diseases. This study will contribute to Bacillus-based biocontrol in the citrus industry.

ABSTRACT Lineage-specific genes (LSGs) are defined as genes with sequences that are not significantly similar to those in any other lineage. LSGs have been proposed, and sometimes shown, to have significant effects in the evolution of biological function. In this study, two sets of Hanseniaspora spp. LSGs were identified by comparing the sequences of the Kloeckera apiculata genome and of 80 other yeast genomes. This study identified 344 Hanseniaspora-specific genes (HSGs) and 109 genes (‘orphan genes’) specific to K. apiculata. Three thousand three hundred thirty-one K. apiculata genes that showed significant similarity to at least one sequence outside the Hanseniaspora were classified into evolutionarily conserved genes. We analyzed their sequence features, functional categories, gene origin, gene structure and gene expression. We also investigated the predicted cellular roles and Gene Ontology categories of the LSGs using functional inference. The patterns of the functions of LSGs do not deviate significantly from genome-wide average. The results showed that a few LSGs were formed by gene duplication, followed by rapid sequence divergence. Many of the HSGs and orphan genes exhibited altered expression in response to abiotic stress. Studying these LSGs might be helpful for understanding the molecular mechanism of yeast adaption.

Green mold caused by Penicillium digitatum is a serious postharvest disease of citrus. In this study, we obtained a new strain with potent biocontrol activity to control green mold of citrus, and it was characterized as Bacillus sp. w176 by physiological, biochemical, and 16S rDNA analyses. Cell-free supernatant (CFS) of strain w176 in PDB culture was analyzed by Liquid Chromatography Tandem Mass Spectrometry (LCMS/MS). There were more than four different groups of possible metabolites including macrolactin, bacillaene, mycosubtilin, and surfactin. Additionally, both Bacillus sp. w176 and its CFS could effectively reduce disease incidence and lesion diameter of green mold of citrus in vivo. Bacillus sp. w176 and its CFS reduced green mold by round percentage of 89.3% and 54.46%, respectively. Moreover, both Bacillus sp. w176 and its CFS could similarly inhibit the expansion of green mold on citrus with similar effect compared to the fungicide prochloraz after three months of storage. Transmission Electron Microscope (TEM) examination showed that subcellular structure of P. digitatum was changed involving vacuolation, when it was incubated with CFS. Gene expression analysis indicated a change in redox and ribosome biogenesis stress-related genes transcript levels, when P. digitatum were treated with CFS. These results suggested that both Bacillus sp. w176 and its CFS might be valuable for disease control purpose. Our study may provide a novel biological agent to control the citrus green mold and improve our understanding of the possible biocontrol mechanisms of strain w176.

Blue mold in citrus is caused by Penicillium italicum. In this study, the P. italicum-specific primers were developed for rapid detection based on the conserved genes RPB1 and RPB2 among Penicillium genomes. The two primer pairs RPB1-a and RPB1-b proved to be specific to detect P. italicum. The PCR assay among 39 fungal isolates and the colonial, pathogenic morphologies and molecular methods validated the specificity and reliability of these two primer pairs. This report provided a method and P. italicum-specific primers, which might greatly contribute to citrus postharvest industry.

Kloeckera apiculata plays an important role in the inhibition of citrus postharvest blue and green mould diseases. This study was based on the previous genome sequencing of K. apiculata strain 34-9. After homologous comparison, scaffold 27 was defined as the mitochondrial (mt) sequence of K. apiculata 34-9. The comparison showed a high level of sequence identity between scaffold 27 and the known mtDNA of Hanseniaspora uvarum. The genome sequence of H. vineae T02/19AF showed several short and discontinuous fragments homologous to the mtDNA of H. uvarum. The shared and specific genes of K. apiculata, H. uvarum, and H. vineae were analysed by family using the TreeFam methodology. GO analysis was used to classify the shared and specific genes. Most of the gene families were classified into the functional categories of cellular component and metabolic processes. The whole-genome phylogram and genome synteny analysis showed that K. apiculata was more closely related to H. uvarum than to H. vineae. The genomic comparisons clearly displayed the locations of the homologous regions in each genome. This analysis could contribute to discovering the genomic similarities and differences within the genus Hanseniaspora. In addition, some regions were not collinearity-matched in the genome of K. apiculata compared with that of H. uvarum or H. vineae, and these sequences might have resulted from evolutionary variations.

Citrus fruit usually suffer significant losses during the storage and transportation stages. Green mold, a postharvest rot of citrus fruit caused by Penicillium digitatum, is one of the most serious fungal diseases. In this study, the antagonist strain DH-4 was identified as Bacillus amyloliquefaciens according to morphological observation and 16S ribosomal DNA analysis. In addition, it showed broad antifungal activity, especially the suppression of Penicillium spp. The culture filtrate of strain DH-4 exhibited apparent activity against P. digitatum in vitro and in vivo. In storage, the culture filtrate with DH-4 in it showed a better antiseptic effect. The antifungal substances in the culture filtrate, produced by strain DH-4, displayed stable activity in various extreme conditions. In addition, the antifungal substances in the culture filtrate were identified as macrolactin, bacillaene, iturins, fengycin, and surfactin by ultraperformance liquid chromatography (UPLC) electrospray ionization mass spectrometry analysis. The UPLC fractions containing these antifungal compounds were basically heat tolerant and all responsible for the antagonistic activity against P. digitatum. Transmission electron microscope observation indicated that the antifungal substances might cause abnormalities in the P. digitatum cellular ultrastructure, which could be the possible mode of action of B. amyloliquefaciens against P. digitatum. In addition, it was confirmed via scanning electron microscope analysis that the main way it inhibited P. digitatum was by secreting antimicrobial compounds without direct interaction. This study contributes to the understanding of the mechanism of B. amyloliquefaciens against citrus green mold as well as providing a potential application for the biocontrol of postharvest rot diseases in citrus fruit.

Specific primers targeting Penicillium digitatum were developed based on fungal genes RPB1 and cmd , which are conserved among the genomes of Penicillium spp. The specific primers were designed based on the mutational sites in the homologous regions of the conserved genes. The results indicated that primer pairs RPB1–1 and cmd-3 were specific enough to distinguish Penicillium digitatum (N1) from Penicillium chrysogenum (Q), Penicillium italicum (A10) and Penicillium expansum (L) when the DNA samples were diluted 100-fold. To further verify the effectiveness and specificity of the two primer pairs RPB1–1 and cmd-3, 38 strains of fungal isolates from sources related to citrus were detected using both primer pairs, and 14 candidate P. digitatum strains were identified. Then, the fourteen candidate P. digitatum strains were further identified as P. digitatum by morphological and molecular methods, which confirmed the detection accuracy and reliability of the specific primer pairs RPB1–1 and cmd-3 as molecular markers of P. digitatum. This work may significantly facilitate the rapid identification of P. digitatum in the citrus industry.

The yeast Kloeckera apiculata strain 34–9 is an antagonist that shows biological control activity against the postharvest fungal pathogens of citrus. An antifungal compound, 2-phenylethanol (PEA), has been identified from the extract of K. apiculata. To better understand the molecular processes underlying the response of citrus fruit tissue to K. apiculata, the extract and PEA, microarray analyses were performed on navel oranges using an Affymetrix Citrus GeneChip.