Phenolics in cereals, fruits and vegetables: Occurrence, extraction and analysis

Applications of solid-phase microextraction in food analysis.

To evaluate the antibacterial activity of 21 plant essential oils against six bacterial species. The selected essential oils were screened against four gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris) and two gram-positive bacteria Bacillus subtilis and Staphylococcus aureus at four different concentrations (1:1, 1:5, 1:10 and 1:20) using disc diffusion method. The MIC of the active essential oils were tested using two fold agar dilution method at concentrations ranging from 0.2 to 25.6 mg/ml. Out of 21 essential oils tested, 19 oils showed antibacterial activity against one or more strains. Cinnamon, clove, geranium, lemon, lime, orange and rosemary oils exhibited significant inhibitory effect. Cinnamon oil showed promising inhibitory activity even at low concentration, whereas aniseed, eucalyptus and camphor oils were least active against the tested bacteria. In general, B. subtilis was the most susceptible. On the other hand, K. pneumoniae exhibited low degree of sensitivity. Majority of the oils showed antibacterial activity against the tested strains. However Cinnamon, clove and lime oils were found to be inhibiting both gram-positive and gram-negative bacteria. Cinnamon oil can be a good source of antibacterial agents.

/pdf/in-vitro-antibacterial-activity-of-some-plant-essential-oils-115needhff.pdf

In vitro antibacterial activity of some plant essential oils.

A rapid aqueous acid extraction thiobarbituric acid method for measuring malondialdehyde as a marker of lipid peroxidation in animal tissue, food, and feedstuff samples has been developed. Sample is homogenized with aqueous trichloroacetic acid in the presence of hexane and butylated hydroxytoluene, and the homogenate is centrifuged. Following reaction with thiobarbituric acid reagent, malondialdehyde is directly quantified on the basis of the third-derivative absorption spectrum of the pink complex formed. Further purification is not required because the derivative transformation of the conventional analytical band at around 532 nm virtually eliminates spectral interferences arising from other compounds. The effect of antioxidants and the optimum conditions for the reaction have been established, and the analytical performance of the new method has been evaluated. The applicability of the method on various animal tissue, food, and feedstuff samples has been also tested. Owing to its simplicity and increased sensitivity and specificity, the method may be preferred over other methods for estimating the extent of lipid peroxidation.

Rapid, sensitive, and specific thiobarbituric acid method for measuring lipid peroxidation in animal tissue, food, and feedstuff samples

Consumers increasingly demand convenience foods of the highest quality in terms of natural flavor and taste, and which are free from additives and preservatives. This demand has triggered the need for the development of a number of nonthermal approaches to food processing, of which high-pressure technology has proven to be very valuable. A number of recent publications have demonstrated novel and diverse uses of this technology. Its novel features, which include destruction of microorganisms at room temperature or lower, have made the technology commercially attractive. Enzymes and even spore forming bacteria can be inactivated by the application of pressure-thermal combinations, This review aims to identify the opportunities and challenges associated with this technology. In addition to discussing the effects of high pressure on food components, this review covers the combined effects of high pressure processing with: gamma irradiation, alternating current, ultrasound, and carbon dioxide or anti-microbial treatment. Further, the applications of this technology in various sectors— fruits and vegetables, dairy, and meat processing—have been dealt with extensively. The integration of high-pressure with other matured processing operations such as blanching, dehydration, osmotic dehydration, rehydration, frying, freezing / thawing and solid-liquid extraction has been shown to open up new processing options. The key challenges identified include: heat transfer problems and resulting non-uniformity in processing, obtaining reliable and reproducible data for process validation, lack of detailed knowledge about the interaction between high pressure, and a number of food constituents, packaging and statutory issues.

/pdf/opportunities-and-challenges-in-high-pressure-processing-of-3p4mjmljox.pdf

Opportunities and Challenges in High Pressure Processing of Foods

The kinetics of ascorbic acid loss and nonenzymatic browning in clarified orange juice (serum) were investigated in an anaerobic environment from 70.3 to 97.6°C and from 11.7 to 80.6°Brix. Data were fitted to first-order kinetic models. Rate constants of ascorbic acid degradation in serum were not different from rate constants in whole juice. Activation energies were 30 kcal/mol and largely independent of solids concentration. Rate constants of browning pigment formation were 30-50% greater in serum. Activation energies were 19-25 kcal/mol and increased slightly with solids concentration.

Kinetics of ascorbic acid loss and nonenzymatic browning in orange juice serum: experimental rate constants.

The enzyme pectinesterase (PE) reduces the quality of citrus juices. Current inactivation of the enzyme is accomplished by heat, resulting in a loss of fresh fruit flavor in the juice. We explored the use of pressurized treatments of orange and grapefruit juices to bypass the use of extreme heat during processing. PE inactivation using isostatic high pressure in the range of 500−900 MPa was accomplished in orange and grapefruit juices. The higher pressures (>600 MPa) caused instantaneous inactivation of the heat labile form of the enzyme but did not inactivate the heat stable form of PE. Treatment times caused significantly different (α = 0.05) total PE activity losses in orange but not in grapefruit juices, and PE inactivation at different pressures was significantly different in both juices. Heat labile grapefruit PE was also more sensitive than orange to pressure. Dp values for orange PE inactivation at 500 and 600 MPa were 83.3 and 2.4 min, respectively; while the zp value between 500 and 600 MPa was ...

Inactivation of pectinesterase in orange and grapefruit juices by high pressure

Pseudomonas gladioli was isolated by an enrichment culture technique using limonene as the sole source of carbon. Fermentations were conducted for 4–10 days in shake flasks at 25°C using a pH 6.5 mineral salts medium and 1.0% (+)-limonene. Major conversion products were identified as (+)-α-terpineol and (+)-perillic acid. Quantitative analysis of α-terpineol and perillic acid during the fermentation revealed that α-terpineol was resistant to further degradation by the bacterium, while perillic acid was readily degraded.

Bioconversion of (+)-limonene by Pseudomonas gladioli.

A procedure was developed to measure adsorption (scalping) of limonene by low density polyethylene. The polymer was mounted on an oxygen electrode. Limonene absorption produced an increase in oxygen permeability which appeared proportional to limonene concentration. Diffusion coefficients calculated from permeation curves were similar to diffusion coefficients calculated on a weight change basis.

Oxygen permeability of low density polyethylene as a function of limonene absorption: an approach to modeling flavor "scalping".

The ability of low density polyethylene (LDPE) to absorb citrus flavor compounds was examined The LDPE sample was mounted on an oxygen electrode As volatiles were absorbed, oxygen permeation through the polymer increased Limonene, ethyl butyrate, myrcene, and α-pinene were readily absorbed by LDPE Octanal, citral, linalool, and α-terpineol were absorbed at much lower levels Time-course changes in readings were used to calculate diffusion coefficients of volatiles in the polymer Diffusion coefficients were proportional to the volatile's solubility in the polymer

Absorption of citrus flavor volatiles by low density polyethylene

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