Chilling Injury, Physicochemical Properties, and Antioxidant Enzyme Activities of Red Pitahaya (Hylocereus polyrhizus) Fruits under Cold Storage Stress

Low-temperature storage is extensively used to optimize the postharvest life of various fresh fruits.However,red pitahaya(Hylocereus polyrhizus)fruits are sensitive to chilling injury(CI),which leads to the limitation of low-temperature storage.In this study,red pitahaya fruits were stored at 2,4,6,8,and 10℃,respectively,for 27 days to determine the appropriate storage temperature.During the storage of red pitahaya fruits,storage at 8℃ was more effective in suppressing decay and maintaining quality than other low temperatures.Lowtemperature(2,4,and 6℃)storage decreased weight loss(WL)and maintained higher content of titratable acidity(TA),soluble sugars(SS),and total phenolics(TP)but different degrees of CI were detected.No CI was observed at 8℃ and 10℃.Red pitahay as stored at 8 and 10℃ were associated with better color evaluation,lower electrolyte leakage(EL),respiration rate,and lipoxygenase(LOX)activity,and higher fruit firmness,superoxide dismutase(SOD)activity,and catalase(CAT)activity.However,higher storage temperature(10℃)resulted in higher metabolic activity leading to lower quality and antioxidant capacities compared with 8℃.Therefore,our results demonstrated that red pitahaya stored at 8℃ exhibited a protective effect on fruit quality and resisted CI development during storage.

Effects ofβ-1,3-glucan and ascorbic acid on the nutritional-immune response and antioxidant signaling pathways of live tiger grouper during simulated transport

Transport in water is the most common method for transporting live fish in China,however,transport is a strong stressor.Transport stress could lead to a reduced immune and antioxidant system function of tiger grouper,resulting in sickness and death.Besides,tiger grouper were continuously stressed during transport,which resulted in quality deterioration.It is necessary that find a way to relieve the stress of transportation of tiger grouper.Ascorbic acid is not only a good anti-stress agent,but it is also an effective immunostimulant.β-1,3-glucan is a feed additive that can enhance the immune response of fish.Therefore,this study evaluated the effects ofβ-1,3-glucan and ascorbic acid on the nutritional-immune response and antioxidant signaling pathways of live tiger grouper during simulated transport.Results indicated that addingβ-1,3-glucan and ascorbic acid in transport-water muted the increase of alanine aminotransferase(ALT)and aspartate aminotransferase(AST)activity.In addition,β-1,3-glucan and ascorbic acid activated Nrf2 and mediated TOR expression and then up-regulate related mRNA expression of antioxidant and immune enzymes.We concluded that the application ofβ-1,3-glucan and ascorbic acid inhibit the increase of metabolism enzymes and inflammatory factors and activate immune and antioxidant signaling pathways to relieve oxidant stress,immune response,and apoptosis.Reducing the loss of amino acids provided nutrients to relieve oxidative stress and immune response,which demonstrated immune-nutritional response in live tiger grouper during simulated transport.These results may provide a new solution for alleviating the decline of immune and antioxidant function of tiger grouper caused by transportation stress.

The application of Melissa officinalis L.essential oil nanoemulsions protects sea bass(Lateolabrax japonicus)against myofibrillar protein and lipid oxidation during refrigeration

Objectives:The nutrient rich sea bass is prone to oxidation of lipid and protein during refrigeration.Materials and Methods:The research was to investigate the effect of different concentrations of Melissa officinalis L.essential oil(MOEO)nanoemulsions on myofibrillar protein(MP)and lipid oxidation in sea bass(Lateolabrax japonicus)during refrigeration at 4°C.Results:The results of thiobarbituric acid reactive substances and mitochondrial membrane potential showed that carboxymethyl chitosan/locust bean gum active coating solutions incorporating 2%MOEO nanoemulsions(C/L-2M)was the most effective in inhibiting lipid oxidation that occurred in sea bass under attack by reactive oxygen species.Low-field nuclear magnetic resonance results showed that C/L-2M maximally slowed the conversion of bound water to free water during storage.The oxidation of lipids and MP disrupted the secondary and tertiary conformations of MP and accelerated protein aggregation and degradation.Conclusions:C/L-2M slowed the oxidation of lipids and proteins by inhibiting the oxidation of reactive oxygen species.C/L-2M is a very promising preservative emulsion for the preservation of sea bass.

Development and characterization of mycelium bio-composites by utilization of different agricultural residual byproducts

Mycelium bio-composites was developed by incubating Pleurotus ostreatus fungi on different sub-strates from agricultural residual byproducts,including rice straw,bagasse,coir-pith,sawdust,and corn straw.The scanning electron microscope(SEM)results showed that the hypha of com-posite derived from bagasse was the densest,and the diameter of hypha was the biggest(0.77μm),which was presumably due to the existence of cellulose in bagasse in the form of dextran and xylan.The maximum and minimum compression strength for sawdust substrate and corn straw substrate were 456.70 and 270.31 kPa,respectively.The flexural strength for bagasse sub-strate and rice straw substrate were 0.54 and 0.16 MPa,respectively.The two composites derived from rice straw and bagasse exhibited higher hydrophobic properties than others.In comparison,mycelium bio-composite derived from bagasse showed the best comprehensive properties.Except for a little worse anti-creep ability and waterproof performance,other properties of mycelium bio-composites could be comparable to commercially expanded polystyrene(EPS)packaging mate-rial.Derived from this study,mycelium material provided a good way to use agricultural residual byproducts and could be a good alternative to non-biodegradable materials for packaging appli-cations.

Effect of the number of freeze-thaw cycles number on the quality of Pacific white shrimp (Litopenaeus vannamei): An emphasis on moisture migration and microstructure by LF-NMR and SEM

The objective of this study was to evaluate the effects of the number of freeze-thaw(F-T)cycles on moisture migration,protein degradation,microstructure and quality in Litopenaeus vannamei.The quality of samples with different F-T cycles were determined by low-field nuclear magnetic resonance(LF-NMR),magnetic resonance imaging(MRI)and scanning electron microscopy(SEM),combined with sodium dodecyl sulphate polyacrylamide gel electrophoresis(SDS-PAGE),texture properties analysis(TPA),color difference,polyphenol oxidase(PPO)activity,total volatile basic nitrogen(TVB-N),total viable count(TVC),and sensory evaluation.The results showed that F-T cycles caused a significantly increase in transverse relaxation time in T22 and T23 and a decreased brightness of pseudo-color diagram after 4 F-T cycles,indicating that water mobility increased as immobilized water was shifted to free water.The texture of samples declined as well,especially after 4 F-T cycles.The rapid growth of PPO activity caused a decrease in brightness(L*)and an increase in redness(a∗)after 3 F-T cycles.The increase of TVB-N,TVC,and sensory score explained the changes in shrimp quality which became obvious after 3 F-T cycles and unacceptable after 6 cycles.Meanwhile,fewer than 4 F-T cycles accelerated protein aggregation,while denaturation occurred after 4 cycles.Therefore,repeated F-T cycles could accelerate the changes of protein,microstructure,water distribution,and quality deterioration especially after 3 F-T cycles,with a threshold was 6 F-T cycles.

Effect of quercetin-containing preservatives and modified atmospheric packaging on the production of biogenic amines in Pacific white shrimp(Litopenaeus vannamei)

To investigate the productions of biogenic amines(BAs)in Pacific white shrimp treated by compound preservatives(P,0.05 g/L quercetin,0.025 g/L 4-hexylresorcinol,and 0.025 g/L cinnamic acid)in combination with modified atmosphere packaging(M,80% CO_(2)/10% O_(2)/10% N_(2)),four groups of samples treated with or without preservatives and alone or in combination with modified atmosphere packaging(A,A+P,M,M+P)during storage at 4℃for 12 days were analyzed.Most BAs increased in all samples,especially,putrescine and cadaverine.MAP inhibited the increase of most BAs(except for tyramine)and psychrotrophic bacterial counts.The inhibitory effect of the compound preservatives on bacterial growth and BAs was limited in aerobically-and MAP-stored samples,but they retarded the production of tyramine,which accumulated more rapidly in MAP.Lowest total BAs and bacterial counts were found in sample M+P(78.3 mg/kg and 5.82 log cfu/g,day 12),indicating that the combined treatment of the preservatives and MAP could reduce the risk of disorders caused by BAs.