The improved bioavailability of zein/soybean protein isolate by puerarin in vitro.

As the largest emitter of greenhouse gases, the livestock and poultry industry is facing the challenge of increasing production to meet global demand while reducing environmental impacts. Improving feed digestibility by optimizing feed structure (e.g., exogenous additive) is one of the green breeding measures to alleviate carbon pressure. In this study, the interaction mechanism and in vitro digestibility properties of puerarin (PUE) with feed proteins (zein and soy protein isolate (SPI)) to form Zein-PUE and SPI-PUE complexes were investigated mainly by multispectral and molecular docking techniques. Results indicated that the addition of PUE improved the physicochemical properties of proteins (e.g., solubility and disulfide bond contents). Then, the spectral results showed that the binding processes were spontaneous, and the protein structure tended to loose and disordered after binding, and more hydrophobic residues were exposed to the hydrophilic microenvironment. Moreover, on the basis of molecular docking revealed that PUE bound to zein by hydrogen bond, electrostatic and hydrophobic interactions, while with SPI by hydrogen bond and hydrophobic interaction. Finally, in vitro digestion experiments demonstrated that the bioavailability of Zein-PUE and SPI-PUE complexes increased by 1.15 % and 2.11 %, respectively. Overall, PUE is a promising feed additive beneficial for enhancing protein digestibility and bioavailability.

Immobilization of α-galactosidase in polyvinyl alcohol-chitosan-glycidyl methacrylate hydrogels based on directional freezing-assisted salting-out strategy for hydrolysis of RFOs.

Raffinose family oligosaccharides (RFOs) in food are the main factors causing flatulence in Irritable Bowel Syndrome (IBS) patients and the development of effective approaches for reducing food-derived RFOs is of paramount importance. In this study, polyvinyl alcohol (PVA)-chitosan (CS)-glycidyl methacrylate (GMA) immobilized α-galactosidase was prepared by the directional freezing-assisted salting-out technique, aimed to hydrolyze RFOs. SEM, FTIR, XPS, fluorescence and UV characterization results demonstrated that α-galactosidase was successfully cross-linked in the PVA-CS-GMA hydrogels, forming a distinct porous stable network through the covalent bond between the enzyme and the carrier. Mechanical performance and swelling capacity analysis illustrated that α-gal @ PVA-CS-GMA not only had suitable strength and toughness for longer durability, but also exhibited high water content and swelling capacity for better retention of catalytic activity. The enzymatic properties of α-gal @ PVA-CS-GMA showed an improved Km value, pH and temperature tolerance range, anti-enzymatic inhibitor (melibiose) activity compared to the free α-galactosidase and its reusability was at least 12 times with prolonged storage stability. Finally, it was successfully applied in the hydrolysis of RFOs in soybeans. These findings provide a new strategy for the development of α-galactosidase immobilization system to biological transform the RFOs components in the food for diet intervention of IBS.

Vishniacozyma victoriae: An endophytic antagonist yeast of kiwifruit with biocontrol effect to Botrytis cinerea.

Botrytis cinerea is a pathogenic fungus to fruit, biocontrol is a promising approach to relieve this issue. In this study, Vishniacozyma victoriae is an endophytic yeast extracted from kiwifruit, was used to enhance the resistance of host to B. cinerea. The results showed that lesion diameter of the kiwifruit inoculated with B. cinerea was 55.16 %, 50.57 %, and 48.07 % lower than that of inoculated with V. victoriae + B. cinerea on 4th, 8th, and 12th day, respectively. On 12th day, the total organic acid content and energy charge of kiwifruit inoculated with B. cinerea were 19.25 % and 7.95 % lower than those inoculated with V. victoriae + B. cinerea. These indicated that V. victoriae used the organic acids and energy of host to colonize in the wound, which prevented B. cinerea from contacting the host. Accordingly, V. victoriae is a promising biocontrol yeast to inhibit the infection of B. cinerea on kiwifruit.

Chitosan quaternary ammonium salt/gelatin-based biopolymer film with multifunctional preservation for perishable products.

The postharvest physiological and metabolic activities caused fruits and vegetables (F&V) quality deterioration. Therefore, developing an efficient preservation strategy is a promising approach to relieve this issue. In this study, a modified metal-organic framework (MOF; i.e., Cer@MHKUST-1) was encapsulated into a blended matrix of chitosan quaternary ammonium salt (CQAS)/gelatin to fabricate a multifunctional (water-locking, ethylene-removing, and antibacterial) packaging biopolymer-based film (i.e., CMCGF), the characteristics and preservative effects of the packaging were investigated. Results indicated that the physicochemical (e.g., mechanical, gas/light barrier, wettability) properties of CMCGF were improved compared with the control film (i.e., CGF). CMCGF have a higher ethylene adsorption performance of 65-69 cm3/g STP compared with CGF (7.8 cm3/g STP). Cu ions released from CMCGF destroyed the cell wall and membrane, resulting in the death of bacteria, and the antibacterial efficiency of CMCGF against E. coli and S. aureus was 97-100 % and 98-100 %, respectively. Postharvest storage experiments on tomato and winter jujube confirmed the high-efficiency preservation effect of CMCGF packaging. Therefore, CMCGF provides a multifunctional approach to extending the shelf-life of perishable products to decrease food wastage.

Biodegradable active packaging: Components, preparation, and applications in the preservation of postharvest perishable fruits and vegetables.

The consumption of fresh fruits and vegetables is restricted by the susceptibility of fresh produce to deterioration caused by postharvest physiological and metabolic activities. Developing efficient preservation strategies is thus among the most important scientific issues to be urgently addressed in the field of food science. The incorporation of active agents into a polymer matrix to prepare biodegradable active packaging is being increasingly explored to mitigate the postharvest spoilage of fruits and vegetables during storage. This paper reviews the composition of biodegradable polymers and the methods used to prepare biodegradable active packaging. In addition, the interactions between bioactive ingredients and biodegradable polymers that can lead to plasticizing or cross-linking effects are summarized. Furthermore, the applications of biodegradable active (i.e., antibacterial, antioxidant, ethylene removing, barrier, and modified atmosphere) packaging in the preservation of fruits and vegetables are illustrated. These films may increase sensory acceptability, improve quality, and prolong the shelf life of postharvest products. Finally, the challenges and trends of biodegradable active packaging in the preservation of fruits and vegetables are discussed. This review aims to provide new ideas and insights for developing novel biodegradable active packaging materials and their practical application in the preservation of postharvest fruits and vegetables.

A potential spoilage bacteria inactivation approach on frozen fish.

Frozen products are more susceptible to microbial spoilage during thawing. Therefore, the development of a thawing technology with effective bacteriostasis is still urgent in food science. In this study, red sea bream was used as the research object, S. putrefaciens was incubated on the surface of fish fillets, and ultrasound plus high voltage electric field (US&HVEF) was performed to investigate the antibacterial activity. On this basis, the effect of US&HVEF thawing on the quality characteristics of fillets was further studied. The results indicated that US&HVEF showed a better antibacterial performance toward S. putrefaciens, with the lethality of 96.73%. Furthermore, US&HVEF could minimize thawing loss, preserve fillets texture, stabilize the secondary and tertiary conformation of myofibrillar protein (MFP), and inhibit the MFP aggregation and oxidation. Accordingly, this study shows that food safety also involves spoilage bacteria prevention except for quality and proves that US&HVEF technology has great potential in food thawing.

Investigation of the antifreeze mechanism and effect on quality characteristics of largemouth bass (Micropterus salmoides) during F-T cycles by hAFP.

The interaction between herring antifreeze protein (hAFP) and ice crystals was studied by molecular dynamics simulation in this paper. On this basis, the effect of hAFP on the quality attributes of largemouth bass after three freezing-thawing (F-T) cycles was studied. Scanning electron microscope was conducted to analyze the microstructure changes of muscle fibers. The content of dityrosine/total sulfhydryl/carbonyl and the Ca2+-ATPase activity were measured to explore the degree of protein oxidation. Raman and intrinsic fluorescence spectra were used to measure the protein secondary structure and tertiary conformation. Results showed that hAFP protected the organisms from freezing by binding to the ice crystals, decreasing the freezing point and inhibiting the recrystallization. Furthermore, hAFP combined with chitosan magnetic (CS@Fe3O4) nanoparticles or vacuum impregnation hAFP was shown to be an effective method to reduce the mechanical damage of ice crystals to samples, and decrease the oxidation degree of samples during F-T cycles.

Corrigendum: Viscoelastic and Functional Properties of Cod-Bone Gelatin in the Presence of Xylitol and Stevioside.

[This corrects the article DOI: 10.3389/fchem.2018.00111.].

Effect of vacuum impregnation of red sea bream (Pagrosomus major) with herring AFP combined with CS@Fe3O4 nanoparticles during freeze-thaw cycles.

This study examined the effect of herring antifreeze protein (hAFP) combined with chitosan magnetic nanoparticles (CS@Fe3O4), applied through vacuum impregnation, on protein conformation and moisture state of red sea bream during freeze-thaw cycles. DSC and dynamic rheology were used to analyze physicochemical changes. Raman, intrinsic fluorescence and second derivative UV spectrometry were used to explore the structural changes of myofibrillar proteins. Surface hydrophobicity, particle size and zeta-potential were used to analyze protein aggregation and denaturation. AV, POV, and TBA were used to determine the degree of lipid oxidation. LF-NMR and MRI were used to test water migration and distribution. The results indicated that pretreatment of red sea bream through vacuum impregnation with hAFP combined with CS@Fe3O4 solutions could minimize freeze-thaw damage, prevent protein and lipid oxidation. Therefore, these results confirm the importance of hAFP as a valuable food additive in frozen foods.

Effects of xylitol and stevioside on the physical and rheological properties of gelatin from cod skin.

Jelly and confectionery products are high in sugar and calories. Xylitol and stevioside are natural low-calorie sweeteners and they can be used as an alternative; however, their effects on fish gelatin are unknown. The gelatin was extracted from cod skins and added to xylitol or stevioside (0, 2, 6, 10, 14, and 20% (w/v)) to form gel products. This paper investigated how xylitol and stevioside affected the physical and rheological behaviors of fish gelatin, such as color, gel strength, texture profile analysis, storage modulus (G'), loss modulus (G″), and viscosity. Results showed that the change of color and viscosity in gel products were similar when various concentrations of xylitol or stevioside were added to the fish gelatin. But the effects of xylitol/stevioside on texture profile analysis and G', G″ were different, which might due to the structure variation in xylitol and stevioside. The linear structure of xylitol resulted in ionic interaction, hydrogen bonding, van der Waals forces, and hydrophobic association between xylitol and fish gelatin. Therefore, xylitol is a promising sweetener substitute, which was probably related to its greater solubility and number of -OH groups.

Viscoelastic and Functional Properties of Cod-Bone Gelatin in the Presence of Xylitol and Stevioside.

The physical, rheological, structural and functional properties of cod bone gelatin (CBG) with various concentrations (0, 2, 4, 6, 10, and 15%) of low-calorie sweeteners [xylitol (X) and stevioside (S)] to form gels were investigated. The gel strength of CBGX increased with increased xylitol due presumably to hydrogen bonds between xylitol and gelatin, but with CBGS the highest gel strength occurred when S concentration was 4%. Viscosity of CBGS samples were higher than CBGX due to S's high molecular mass. The viscoelasticity (G' and G''), foaming capacity and fat binding capacity of CBGX were higher while foam stability was lower. The emulsion activity and emulsion stability of CBGX were a little lower than CBGS at the same concentration. The structure of X is linear making it easier to form a dense three-dimensional network structure, while the complex cyclic structure of S had more difficulty forming a network structure with cod bone gelatin. Therefore, X may be a better choice for sweetening gelatin gels.