Abstract:The common method of reducing sugar in food was using nonnutritive sweeteners, but nonnutritive sweeteners would bring undesirable bitter or metallic taste and safety risks. Research showed that adding aroma substances to some foods could enhance the sweetness perception of foods, indicating that using aroma to increase sweetness to achieve the objective of food sugar reduction. Firstly, the important factors affecting the sweetening effect of aroma were summarized from two aspects:the type of odorant and the concentration of sweetener. Then, the mechanism of aroma sweetening was elaborated from three aspects:the olfactory perception mechanism, the brain nerve and taste perception mechanism, and the psychological perception mechanism of the front and back nasal pathways, and the application of molecular simulation in analyzing the binding and release process of sweeteners and taste receptors was summarized. Thirdly, the sensory analysis methods for evaluating the sweetening effect of aroma were summarized, and the differences among three sensory analysis methods, namely descriptive sensory analysis, time intensity analysis and sensory time dominance analysis, were compared. Then the application progress of aroma sweetening in food industry was summarized. Finally, the research directions of aroma sweetening and the methods of analyzing the mechanism of odor enhancing taste were prospected, in order to provide new ideas for the research of reducing sugar by aroma.

Abstract:Volatile sulfur compounds widely exist in a variety of foods and have the characteristics of very low threshold, which are characteristic flavor components that make an important contribution to food sensory quality, and play an important role in forming the unique flavor characteristics of food. Different kinds of sulfur compounds show different food flavor characteristics, and different contents of sulfur compounds have significant differences in the impact on the sensory quality of food. Therefore, the flavor characteristics and formation mechanism of sulfur compounds in six common foods which are greatly affected by sulfur compounds in sensory flavor were studied. The main sulfur compounds in milk are methyl mercaptan and dimethyl trisulfide, which usually smell like cooking. 2-Methyl-3-furan mercaptan is the key sulfur compound of beef, which presents roast flavor and meat flavor. The roast flavor of furfural mercaptan and the fruit flavor of 3-mercaptohexane-1-alcohol are the key flavor components in alcoholic drinks. 1,2,3,5,6-Pentathioheterocyclic heptane is a key compound showing the unique smell of Lentinus edodes. Dipropyl disulfide, dimethyl trisulfide and allicin are the key sulfur compounds in flavor formation of scallion, onion and garlic, respectively. Dimethyl sulfide and dimethyl trisulfide are the main reasons for the pungent flavor of rapeseed oil. Sulfur compounds are mainly formed by the degradation of sulfur-containing precursors by microorganisms or enzymes, and some sulfur compounds are also produced in Maillard reaction. A comprehensive introduction to the types of sulfur compounds in six common foods, their effects on food sensory quality and their formation mechanism, and the flavor of sulfur compounds in common food and the general rules of their effects on food sensory quality were summarized, aiming to provide reference for further research on formation mechanism and flavor characteristics of sulfur compounds in food.

Abstract:Thiazoles are important flavor of sulfur-containing heterocyclic class, which have always been favored by flavorists due to their dense aroma and intensive characteristics. With the continuous development of analytical technology, more and more thiazole compounds had been identified in food. 39 thiazole flavors (29 thiazoles and 10 thiazolines) have been evaluated and recognized as safe by the Flavor and Extract Manufacturers Association of the United States, and 29 thiazole flavors are allowed to be used in food according to flavor compound list in GB 2760—2014. Recent studies on permissible usage, aroma characteristics and natural occurrence of 39 thiazole flavors were introduced in this paper. The possible formation pathways of thiazole flavor compounds in food processing were reviewed, including thermal degradation of sulfur-containing compounds and Maillard reaction. During food processing, sulfur-containing amino acids underwent thermal degradation reactions such as deamination and decarboxylation at high temperatures to form thiazole and its derivatives. In addition, thiamine could also be degraded into a variety of volatile flavor substances containing sulfur and nitrogen when heated, and the thiazole degradation products mainly included 4-methyl-5-(β-hydroxyethyl) thiazole, 4-methylthiazole, 4,5-dimethylthiazole, 4-methyl-5-ethylthiazole, etc. The typical synthetic methods and reaction mechanisms of thiazole compounds were introduced from three aspects:traditional chemical synthesis, photochemical synthesis and electrochemical synthesis. Finally, it was pointed out that breaking through the bottleneck problems such as insufficient development and innovation of new flavors, backward traditional production technology and serious environmental pollution in the synthetic flavor industry would be the key points to promote the rapid and stable development of our country's synthetic flavor industry in the future.

Abstract:To explore the effects of covalent modification of tannin acid (TA), maltodextrin (MD), and polydextrose (PD) on functional characteristics and structure of soybean protein isolate (SPI), TA, MD and PD were sequentially covalently grafted onto SPI by alkali treatment and wet Maillard reaction, and binary conjugate (SPI-TA) and ternary conjugates SPI-TA-MD and SPI-TA-PD were obtained successively. The degree of covalent grafting of SPI-TA with MD and PD was investigated by the determination of reactive groups, and the formation of covalent bond in binary or ternary conjugates was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The structural changes of SPI in binary and ternary conjugates were studied by UV-visible spectra and Fourier transform infrared spectroscopy. The effects of TA, MD and PD on the functional properties of SPI were studied by evaluating solubility, emulsification, foaming performance, antioxidant activity, thermal stability and surface hydrophobicity. The results showed that the covalent binding of TA, MD and PD with SPI changed the structure of SPI and reduced the content of β-sheet in the secondary structure of SPI. The grafting equivalent of TA was (35.56±1.32)μmol/g, the grafting degree of MD and PD was 46.54% and 32.26%, respectively. Ternary conjugates showed significantly higher solubility, emulsification, antioxidant activity, foaming performance, surface hydrophobicity and thermal stability compared with SPI(P<0.05). The results could not only provide a theoretical basis for improving the functional properties and further understanding of the modification mechanism of SPI, but also provide a new food-grade raw material for the design of food functional ingredients delivery system, especially pine seed oil emulsion delivery system.

Abstract:In order to investigate the influence of ultrasonic modified protein on the gel structure and digestive properties of corn starch (CS), soybean isolated protein (SPI) treated with different ultrasonic time was added to corn starch, and the structure of ultrasonic modified protein and CS compound gel system was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffractometry and rheometer, and its in vitro digestive characteristics were analyzed.The results showed that compared with the original CS, the short-range orderliness, intramolecular and intermolecular hydrogen bond strength, and enthalpy (ΔH) of pasting of CS decreased, when soybean isolate protein modified with different ultrasonic time was added to the starch, and the ΔH of pasting tended to decrease gradually with the increase of ultrasonic time, and the ΔH of the compound gel system decreased by 27.27% when the ultrasonic time reached 30min. The interaction between the ultrasonic-modified protein and the CS was mainly through hydrophobic forces. The X-ray diffraction pattern of the compound gel system showed typical V-shaped structure characteristics, suggesting that the addition of the modified protein improved the starch digestion characteristics, and the content of both slow-digesting starch (SDS) and resistant starch (RS) increased gradually with the increase of ultrasonic time compared with the original starch, and the SDS and RS mass fractions increased by 7.01% and 3.41%, respectively.This study might provide a theoretical basis for the application of modified proteins in starch-based foods.

Abstract:With the rapid development of plant-based food consumption market, legume protein, as a sustainable protein resource and a substitute for animal protein, plays an important role in the health food industry. Protein assembly, as an effective strategy to drive protein itself and its interaction with macromolecules, is very important in the efficient processing of legume protein food. The mechanism of aggregation and assembly of legume proteins promoted by pH, temperature, ions, cross-linking enzymes, and macromolecules as well as the relationship between assembly behavior and protein processing properties were summarized. The pH will determine the type and distribution of the surface charge of the protein, change the secondary structure of the protein, and promote the assembly of the protein. The increase in temperature will not only expose some groups of legume protein but also increase the rate of diffusion and collision of the protein, thus accelerating the assembly. The type and strength of ions affect the distribution of water around the protein and the occurrence of assembly induced by electrostatic interaction between proteins. Cross-linking enzymes catalyze intramolecular or intermolecular cross-linking of legume proteins, thus driving legume proteins for aggregation and assembly. Polysaccharides and phenols change the structure of proteins by binding with legume proteins, providing conditions for protein aggregation and assembly. In addition, the effects of assembly behavior of legume proteins on the processing properties of legume proteins, including emulsification, foaming, gel, and film-forming properties were described, and the relationship between microscopic changes and processing properties was analyzed. Finally, the development direction of further efficient utilization of legume protein was prospected, which might provide a theoretical foundation for the better development of high-quality legume protein products.

Abstract:Ana o 3 is one of the main allergens of cashew nuts (Anacardium occidentale Linn.). Using raw cashew nuts as raw materials, the crude protein was extracted by crushing and degreasing, low-salt extraction. Then, the target protein was separated by freeze-drying, anion exchange chromatography, ultrafiltration concentration. Electrophoresis of small proteins, liquid chromatography-tandem mass spectrometry (LC-MS/MS) and Western Blotting were performed for protein identification. In addition, ultraviolet spectroscopy and circular dichroic spectroscopy were used to analyze the structural changes of cashew allergen Ana o 3 heated at 160℃ for 10,15, 20,25, 30min, to evaluate the stability of the cashew allergen Ana o 3 after separation and purification. The results showed that this study successfully established a method for rapid and efficient purification of cashew allergen Ana o 3. The purity of the protein obtained by this method was higher than 95%. According to the circular dichroism spectrum, the α-helix conformation of cashew allergen Ana o 3 gradually transformed into the β-sheet conformation during the heating process at 160℃, the content of β-turn changed little, and the content of random curl increased slightly. It indicated that the secondary structure of this protein was relatively stable. The ultraviolet spectrum showed that the absorbance of the ultraviolet characteristic absorption peak of cashew allergen Ana o 3 increased after heating, indicating that heating treatment might denature cashew allergen Ana o 3, unfold the structure, expose more tryptophan and tyrosine residues, and loosen the spatial structure. The results of protein electrophoresis and Western Blotting analysis also demonstrated that cashew allergen Ana o 3 was degraded and the epitopes were destroyed after heating treatment. The research was expected to offer a method for the preparation of high-purity cashew allergen Ana o 3, lay a basis for the study of cashew allergy, and provide a theoretical basis for the stability research of cashew allergens during thermal processing.

Abstract:To improve the surface anti-adhesion property of food storage and processing materials against Shewanella putrefaciens biofilm of aquatic products, the ZnO-PDMS films were prepared by tape casting method with polydimethylsiloxane (PDMS) as filmogen, ZnO micro-nanoparticles with different micro-nanophology prepared by hydrothermal synthesis method as modifiers, and antibiofilm property and mechanism of the ZnO-PDMS films against Shewanella putrefaciens biofilm were studied. The results showed that the hydrophobic and oleophobic properties of PDMS films were affected by micromorphology of modified ZnO micro-nanoparticles. Using pompon-shaped and flower-shaped ZnO micro-nanoparticles as modifiers, ZnO-PDMS superamphiphobic films were prepared, and their contact angles of water and oil were both beyond 150°. There was a positive correlation between antibacterial adhesion and amphiphobic of the films. With the extension of culture time, Zn²⁺ released from ZnO film, damaged the bacterial cell membrane and inhibited ATP and AKP enzyme activity in the cell, resulting in bacterial metabolic disorder and death. Compared with PDMS films modified by rod-shaped and pompon-shaped micro-nanoparticles, flower-shaped ZnO-PDMS film had stronger anti-adhesion and antibacterial property. Formation and growth of Shewanella putrefaciens biofilm could be effectively inhibited by the ZnO-PDMS film with both surper-amphiphobic and antibacrobic properties. This study aimed to provide technical support for development of antibiofilm materials.

Abstract:Tea polyphenols have been widely used in the food field due to their excellent antioxidant and antibacterial properties. By preparing tea polyphenols-pullulan-gelatin composite bioactive films, the effects of the mass fraction of tea polyphenols (0%, 2%, 4%, 6%, 8%, and 10%, based on the total dry weight of gelatin and pullulan) on the physicochemical properties, antioxidant and antibacterial properties of the films were studied. FTIR and SEM results showed that intermolecular interactions between tea polyphenols and pullulan and gelatin were appeared, especially when the mass fraction of tea polyphenols was 6%, the film structure became denser. Physical and chemical experiment results showed that, with the increase of the mass fraction of tea polyphenols, the tensile strength and elongation at break of the composite films first increased and then decreased, while the water vapor permeability first decreased and then increased. Meanwhile, the UV resistance increased and the films became darker and yellower. However, the addition of tea polyphenols did not significantly improve the thermal performance of the composite films. In addition, for the composite films, their maximum scavenging rate of DPPH radical was 87.44% and the maximum inhibition rate of Escherichia coli and Staphyloccus aureus were 95.73% and 85.22%, respectively. At the same time, the composite films could realize slow-release of tea polyphenols. The preparation of tea polyphenols-pullulan-gelatin composite films was aimed to provide a useful reference for the development of good bioactive packaging films.

Abstract:To explore the influence of vacuum pre-cooling co-treated with atomized ε-polylysine (ε-PL) on the quality of pakchoi (Brassica chinensis L.), the effects of vacuum pre-cooling, vacuum pre-cooling co-treated with atomized water or ε-PL on the changes in the appearance quality, antioxidant substance, nutrient composition, and harmful substance contents of pakchoi during low temperature circulation and shelf life were analyzed. The results showed that vacuum pre-cooling alone maintained the better quality of pakchoi compared with control, but caused serious water loss and wilting of leaf surface, and the water loss rate after precooling reached 4.45%, while vacuum pre-cooling combined with atomized water group could reduce the water loss rate by 61.27%. In contrast, vacuum pre-cooling co-treated with atomized ε-PL could not only decrease the water loss caused by vacuum pre-cooling alone, but also obviously delay the yellowing degree of postharvest pakchoi. The total chlorophyll mass ratio in vacuum pre-cooling co-treated with atomized ε-PL group was 0.74g/kg at the end of shelf-life, which was 2.87,2.00, and 1.56 times higher than that of control group, vacuum pre-cooling group, and vacuum pre-cooling combined atomized water group, respectively. Moreover, vacuum pre-cooling co-treated with atomized ε-PL significantly slowed down the decrease of antioxidant such as carotenoids, ascorbic acid, folic acid, and total phenols, maintained higher levels of titratable acid, soluble sugar, and soluble protein, and effectively inhibited the accumulation of nitrite and malondialdehyde. Vacuum pre-cooling co-treated with atomized ε-PL could effectively delay the yellowing and senescence process, and maintain better nutritional quality of postharvest pakchoi.

Abstract:In order to investigate in depth the melon spirits prepared by two classical distillation methods, Cognac method (double distillation) and Armagnac method (retort distillation), the aroma of the spirits were analyzed and compared using four different methods:quantitative descriptive analysis (QDA), qualitative and quantitative of flavor substance analysis, odor activity value (OAV) analysis and aroma extract dilution analysis (AEDA). The results of QDA showed that the two spirits presented different styles, with significant differences (P<0.01) in the four descriptors of preference, fruitiness, cucumber odor and fatty odor. Both also had some similarities, i.e., preference, floral and fruitiness were lower, cucumber odor and fatty odor were prominent. The qualitative and quantitative analysis indicated significant differences in the concentration of 53 out of 80 aroma substances, and the composition of total esters, alcohols, aldehydes and acids in the two spirits differed in proportion. Among them, the total alcohols were the highest in the Cognac spirits, accounting for 35.95% of the total aroma substances, while the Armagnac spirits contained the highest esters, accounting for 44.14%. In the aroma substances with significant differences in concentration, 32 had a contribution to overall aroma (OAV>1). (Z)-6-Nonen-1-ol was the aroma substance with the highest OAV, exceeding 4000 in both spirits. 52 Aroma substances were detected in the AEDA experiment, 24 of which had differences in flavor dilution factor (DF). (Z)-2-Nonenal, (E,E)-2,6-nonadienal, etc. all had higher DF and their DF were higher in Cognac than in Armagnac. Quantitative analysis of 21 key differential aroma substances (OAV > 1 and DF > 3) such as (Z)-2-nonenal, etc. in the samples of different alcohol contents showed that the content of these aroma substances in the initial fractions was significantly different. The significant differences in the key aroma substances of the initial distillates fractions resulted in flavor differences between the two spirits. It is hoped that the research provided some theoretical basis and data support for an in-depth understanding of the flavor of melon spirits.

Abstract:Taking Lentinus edodes (L. edodes) stipe as raw material, acetylated L. edodes stipe polysaccharide was prepared by acetic anhydride modification method. The effects of different purification degree on degree of acetylated substitution and structural characteristics of polysaccharides were studied, and the hypoglycemic activities of polysaccharides and acetylated polysaccharides were evaluated. The results showed that after purification, the purity of the polysaccharide extracted from L. edodes stipe and its corresponding acetylated polysaccharide increased from 36.42% and 41.87% before purification to 88.57% and 81.27%, respectively, while the yield of polysaccharide significantly decreased from 83.25% and 48.83% before purification to 21.85% and 35.42%, respectively. There was no significant effect of purification on the degree of acetylated substitution of polysaccharides, and the degree of acetylated substitution of different purified polysaccharides were about 0.3. Fourier transform infrared spectrum showed that the structure of polysaccharide was not destroyed by purification, and the characteristic absorption peak of acetyl group was found after acetylation modification. Congo red experiment showed that different purified polysaccharides and their corresponding acetylated polysaccharides had triple helix structure, but the red shift amplitude decreased with the continuous purification. Polysaccharides of L. edodes stipe and their corresponding acetylated polysaccharides had dose-dependent inhibitory activity on α-amylase and α-glucosidase, and acetylation could significantly increase the inhibitory activity of polysaccharides on α-glucosidase, indicating that acetylation modification improved the hypoglycemic activity of polysaccharides. In conclusion, purification could significantly improve the purity of polysaccharide and its corresponding acetylated polysaccharide extracted from L. edodes stipe and had no significant effect on the structure of the polysaccharide. Acetylation modification could further improve the hypoglycemic activity of polysaccharides.

Abstract:With a variety of probiotic properties such as lowering cholesterol, maintaining flora balance and enhancing immunity, lactic acid bacteria (LAB) is an important microorganism in the food industry. Strain development is frequently used to improve the performance and functionality of industrially important microbes. A brief overview of the characteristics and applications of three improved techniques of LAB, including traditional improvement, transposon mutagenesis and CRISPR was summaried. Traditional techniques for LAB improvement include adaptive evolution, random mutagenesis and protoplast fusion, which can improve LAB but are complex and ineffective. Transposon mutagenesis, a technique based on the inactivation of genes by blocking transcriptional or translational processes, is often used in the construction of LAB mutant libraries, which is efficient and simple, but is dependent on DNA strand breaks, with a low safety profile and being not applicable to a wide range of host characteristics. CRISPR editing technology is widely used in LAB, which enables simultaneous editing of multiple loci and is a powerful tool for gene silencing and transcriptional regulation, but the technique relies on DNA strand breaks and homologous recombination and has a high off-target rate. In addition, the construction and perspective of currently emerging CRISPR-associated transposon (CAST) editing systems are also discussed. The CAST enables efficient, accuracy, marker-free insertion of large fragments (>10kbp) of donor DNA without relying on double strand break and homologous recombination, having an extremely low off-target rate, showing great advantages in high accuracy targeting and efficient integration techniques, providing a reference in high accuracy and efficient LAB gene editing in future. This review could provide relevant theoretical guidance for the subsequent genetic improvement and function analysis of LAB gene.

Abstract:Breast milk is the most natural and ideal food for infants and young children. In order to make protein nutrition of infant formula powder closer to breast milk, it is of great importance to evaluate the difference of amino acid models between breast milk and formula powder. 1028 samples of breast milk from 15-180 days postpartum and 12 samples of formula powder for infants aged 0-6 months were collected, and various amino acid components were determined by amino acid analyzer. New amino acid models of breast milk were calculated by frequency matrix of breast milk samples, the cosine similarity analysis method was used to analyze the cosine similarity of amino acid models of infant formula powder with optimized breast milk, original breast milk and WHO breast milk. Nine essential amino acids and all the 18 amino acids were used respectively to compare the similarity of infant formula powder with optimized amino acid models of breast milk. Result showed that cosine similarity of the amino acids model of optimized breast milk, original breast milk and WHO breast milk had similar tendency with infant formula powder, indicating that cosine similarity comparison could give objective evaluation for nutrition value of infant formula powder. For the 9 essential amino acids, formula F had a high similarity to breast milk, while formula A had a low similarity to breast milk. For all the 18 amino acids, formula H and formula D had a high similarity to breast milk, while formula F had a low similarity to breast milk. The results of amino acid comparison showed that nutritional evaluation results of formula powder were affected by the difference of amino acids composition. In conclusion, the cosine similarity method could objectively evaluate the amino acid nutritional value of formula powder and Chinese breast milk, which provided a new evaluation method for the development and application of infant powder.

Abstract:Flavor can provide, supplement and stabilize the flavor in modified milk. Due to the characteristic of “self-limiting” and low dosage, less attention has been paid to its potential safety risk. The contents of 19 concerned flavor ingredients in 100 commercial modified milk samples from 25 brands were analyzed through SPME-GC-MS/MS in MRM mode which was evaluated methodologically. Benzaldehyde (100%), 2,3-butanedione (96%), linalool (88%) and hexyl alcohol (86%) were detected at higher rate. Vanillin (18886.03μg/kg), ethyl maltol (6271.15μg/kg), maltol (2522.64μg/kg) and benzyl alcohol (1937.60μg/kg) were detected at high average levels with the detection rates at 47%, 71%, 40% and 30%, respectively. The contents of flavor ingredients in different samples were greatly varied, even if in the samples with same taste from different brands. The exposure level and safety risk of the 19 concerned flavor ingredients were assessed accordingly based on the survey results of the daily intake of modified milk in different populations. Both the exposure analysis of the whole population and different populations showed that the per capita daily intake (PCI) of ethyl maltol and vanillin exceeded the threshold of toxicological concern (TTC) in some cases, which varied among different populations, but the overall risk was low. There was no safety risk for the rest of concerned flavor ingredients under the current intake of modified milk.

Abstract:The deformation process of food in oral processing and the relationship between oral processing ability and the formation of swallowable pellets had aroused extensive attention. However, it was difficult to directly observe the food oral processing of testers, obtain the relevant data of chewing experiment, and to repeatedly quantify the oral processing ability, which made it difficult to measure the chewing efficiency. In order to solve these problems, based on the oral simulation platform developed in the early stage, paraffin and peanuts were used as test samples to carry out chewing experiments through oral simulation platform and testers, respectively, and the mastication efficiency index of collected pellets were analyzed and compared for. Data analysis showed that there was a significant correlation between in vivo and in vitro chewing tests and chewing times, and there were significant differences in peanut d₅₀ and paraffin masticatory efficiency index MEI between in vivo and in vitro groups under different chewing times (P<0.05). When the chewing times reached the number of times required for swallowing, the masticatory efficiency indexes of the obtained pellets in vitro and the samples collected from the oral cavity of the testers had high consistency. Based on the oral simulation platform, which could simulate human food oral processing and produce food pellets, food chewing experiments were carried out to determine the chewing efficiency, in order to effectively replace the experimental personnel, reduce the experimental cost and increase the repeatability of the experiment.

Abstract:Egg freshness grade evaluation is an important technical indicator in process of egg quality inspection. Egg samples from different storage environment were prepared, the hyperspectral image information and spectral information of eggs were collected, and the image features and spectral features were extracted. The image features and spectral features were integrated with parallel integration method, and the features were extracted based on successive projections algorithm and gray-level co-occurrence matrix method. The support vector machine egg freshness discriminant model was built. The model was optimized by particle swarm optimization algorithm, the accuracy rate of training set reached up to 85%, and the accuracy rate of prediction set reached up to 76.67%. In order to solve the occasional misjudgment of single model, the progressive features integration method was used, and the multi-model consensus strategy and deep residual network ResNet 50 analysis method were introduced. The multi-model consensus strategy based on successive projections algorithm-histogram of oriented gradients features extraction method was built, the accuracy rate of training set of the model increased to 89%, and the accuracy rate of prediction set increased to 88%. Meanwhile, the deep residual network ResNet 50 model based on successive projections algorithm-histogram of oriented gradients features extraction method was built, the accuracy rate of training set of the model increased to 89%, and the accuracy rate of prediction set increased to 86.67%. The image features and spectral features integration modelling analysis indicated that both parallel integration method and progressive integration method had a certain identifiability for egg freshness grade discrimination, and the multi-model consensus strategy of progressive integration method showed better discrimination effect.