Ultrahigh Performance Liquid Chromatography Analysis of Volatile Carbonyl Compounds in Virgin Olive Oils

The enzymatic and chemical oxidation reaction in olive oil produces many volatile carbonyl compounds that contribute to the complex flavor of olive oil. A novel ultrahigh performance liquid chromatography (UHPLC) method with dynamic headspace sampling and 2,4-dinitrophenylhydrazine (DNPH) derivatization were established to determine the volatile carbonyls in virgin olive oil. Quantification of nine characteristic carbonyls (acetone, hexanal, <i>E</i>-2-hexenal, octanal, <i>E</i>-2-octenal, nonanal, <i>E</i>-2-nonenal, <i>E</i>,<i>E</i>-2,4-nonadienal, and <i>E</i>,<i>E</i>-2,4-decadienal) was achieved using cyclopentanal as an internal standard. This method provides comparable linearity (<i>R</i>² = 0.9917–1.0000) and repeatability (less than 7.6% relative standard deviations) with solid phase microextraction gas chromatography (SPME-GC). The relative standard deviations (%RSD) of all applied carbonyl standards were lower than 7.6%. The limits of detection (LOD) and quantification (LOQ) were in the ranges of 1.6–150.1 and 4.8–906.1 μg/kg. The recoveries obtained for olive oil samples were in the range of 81.0–115.3%. To show the potential of this method on the quantification of other volatile carbonyls that were not included in this study, GC–electron ionization mass spectrometry (GC–EI/MS) was employed to identify the derivatized carbonyls (carbonyl (2,4-DNPH) hydrazones) while peak assignments were made on the basis of elution sequences and peak areas. This method provided feasibility of using LC to determine volatile carbonyls in oil matrices, which can be applied to exam the degree of lipid oxidation and evaluate the sensory properties of VOO and other edible oils

Physical and Antimicrobial Properties of Peppermint Oil Nanoemulsions

The mixture of peppermint oil (PO) with medium-chain triacylglycerol was emulsified in water and stabilized with a food-grade biopolymer, modified starch, to form PO nanoemulsions. The effects of emulsifying conditions including homogenization pressure, the number of processing cycles, and oil loading on the mean diameters and viscosities of nanoemulsions were characterized by dynamic light scattering, optical microscopy, and rheological measurements. The formulated PO nanoemulsions with mean diameters normally <200 nm showed high stability over at least 30 days of storage time. Their antimicrobial properties related to those of PO have also been evaluated by two assays, the minimum inhibitory concentration (MIC) and time-kill dynamic processes, against two Gram-positive bacterial strains of Listeria monocytogenes Scott A and Staphylococcus aureus ATCC 25923. Compared with bulk PO, the PO nanoemulsions showed prolonged antibacterial activities. The results suggest that the nanoemulsion technology can provide novel applications of essential oils in extending the shelf life of aqueous food products

Effects of Timing and Severity of Salinity Stress on Rice (<i>Oryza sativa</i> L.) Yield, Grain Composition, and Starch Functionality

The aim of this work was to examine agronomic, compositional, and functional changes in rice (<i>Oryza sativa</i> L. cv. Nipponbare) grains from plants grown under low-to-moderate salinity stress in the greenhouse. Plants were grown in sodium chloride-containing soil (2 or 4 dS/m² electrical conductivity), which was imposed 4-weeks after transplant (called Seedling EC2 and EC4) or after the appearance of the anthers (called Anthesis EC2 and EC4). The former simulates field conditions while the latter permits observation of the isolated effect of salt on grain filling processes. Key findings of this study are the following: (i) Plants showed adaptive responses to prolonged salt treatment with no negative effects on grain weight or fertility. Seedling EC2 plants had more panicles and enhanced caryopsis dimensions, while surprisingly, Seedling EC4 plants did not differ from the control group in the agronomic parameters measured. (ii) Grain starch increased in Seedling EC4 (32.6%) and Anthesis EC2 (39%), respectively, suggesting a stimulatory effect of salt on starch accumulation. (iii) The salinity treatment of 2 dS/m² was better tolerated at anthesis than the 4 dS/m² treatment as the latter led to reduced grain weight (28.8%) and seed fertility (19.4%) and compensatory increases in protein (20.1%) and nitrogen (19.8%) contents. (iv) Although some salinity treatments led to changes in starch content, these did not alter starch fine structure, morphology, or composition. We observed no differences in reducing sugar and amylose content or starch granule size distribution among any of the treatments. The only alterations in starch were limited to small changes in thermal properties and glucan chain distribution, which were only seen in the Anthesis EC4 treatment. This similarity of compositional and functional features was supported by multivariate analysis of all variables measured, which suggested that differences due to treatments were minimal. Overall, this study documents the specific response of rice under defined conditions, and illustrates that the plasticity of plant response to mild stress is complex and highly context-dependent, even under greenhouse conditions in which other potential environmental stress impacts are minimized