Hot and cold water infusion aroma profiles of Hibiscus sabdariffa: fresh compared with dried.

UNLABELLED: Calyxes from the Roselle plant (Hibiscus sabdariffa L.) were used to prepare cold (22 °C for 4 h) and hot (98 °C for 16 min) infusions/teas from both fresh and dried forms. Aroma volatiles were extracted using static headspace SPME and analyzed using GC-MS and GC-O with 2 different columns (DB-5 and DB-Wax). Totals of 28, 25, 17, and 16 volatiles were identified using GC-MS in the dried hot extract (DHE), dried cold extract (DCE), fresh hot extract (FHE), and fresh cold extract (FCE) samples, respectively. In terms of total GC-MS peak areas DHE ≫ DCE > FHE ≫ FCE. Nonanal, decanal, octanal, and 1-octen-3-ol were among the major volatiles in all 4 beverage types. Thirteen volatiles were common to all 4 teas. Furfural and 5-methyl furfural were detected only in dried hibiscus beverages whereas linalool and 2-ethyl-1-hexanol were detected only in beverages from fresh hibiscus. In terms of aroma active volatiles, 17, 16, 13, and 10 aroma active volatiles were detected for DHE, DCE, FHE, and FCE samples, respectively. The most intense aroma volatiles were 1-octen-3-one and nonanal with a group of 4 aldehydes and 3 ketones common to all samples. Dried samples contained dramatically higher levels of lipid oxidation products such as hexanal, nonanal, and decanal. In fresh hibiscus extracts, linalool (floral, citrus) and octanal (lemon, citrus) were among the highest intensity aroma compounds but linalool was not detected in any of the dried hibiscus extracts. PRACTICAL APPLICATION: Hibiscus teas/infusions are one of the highest volume specialty botanical products in international commerce. The beverage is consumed for both sensory pleasure and health attributes and is prepared a number of ways throughout the world. Although color and taste attributes have been examined, little information is known about its aroma volatiles and no other study has compared extractions from both fresh and dried as well as extraction temperature differences. This is also, apparently, the first study to identify the aroma active volatiles in hibiscus beverages using GC-olfactometry. Manufacturers and consumers will now have a better understanding of why hibiscus teas prepared in different ways from either fresh or dried forms have a different flavor quality and intensity.

Effects of dense phase carbon dioxide pasteurization on the physical and quality attributes of a red grapefruit juice.

Red grapefruit juice was treated with continuous dense phase carbon dioxide (DPCD) equipment to inactivate yeasts and molds and total aerobic microorganisms. A central composite design was used with pressure (13.8, 24.1, and 34.5 MPa) and residence time (5, 7, and 9 min) as variables at constant temperature (40 degrees C), and CO(2) level (5.7%) after experimentally measuring CO(2) solubility in the juice. Five log reduction for yeasts and molds and total aerobic microorganisms occurred at 34.5 MPa and 7 min of treatment. A storage study was performed on the fresh juice DPCD treated at these conditions. degrees Brix, pH, titratable acidity (TA), pectinesterase (PE) inactivation, cloud, color, hue tint and color density, total phenolics, antioxidant capacity, and ascorbic acid were measured after the treatment and during 6 wk storage at 4 degrees C. During storage, the DPCD-treated juice showed no growth of total aerobic microorganisms and yeasts and molds. Cloud increased (91%) while percent PE inactivation was partial (69.17%). No significant (alpha= 0.05) differences were detected between treated and untreated samples for degrees Brix, pH, and TA. Treated juice had higher lightness and redness and lower yellowness. No significant differences (alpha= 0.05) were detected for the hue tint values while the color density value was higher for the treated samples compared to the untreated. The treatment and the storage did not affect the total phenolic content of the juice. Slight differences were detected for the ascorbic acid content and the antioxidant capacity. The experimental results showed evidence that the treatment can maintain the physical and quality attributes of the juice, extending its shelf life and safety.

Measurement of high-pressure carbon dioxide solubility in orange juice, apple juice, and model liquid foods.

An experimental system to measure the carbon dioxide (CO(2)) solubility in liquids at different pressures was designed and tested. Pressure and temperature were controlled in the system, and the design assured an accurate measurement of solubility. Experimental measurements of CO(2) solubility were performed in pure water, model solutions (ascorbic acid-sugars-water, citric acid-sugars-water), and in commercial orange juice (OJ) and apple juice (AJ), as a function of pressure (7.58 to 15.86 MPa) at constant temperature (40 degrees C). Aspen simulation software was used to predict the solubility in simple cases. All experimental results and predictions from simulations were compared with literature data. Measurements of CO(2) solubility in pure water were not significantly different than the literature. CO(2) solubility (g/100 g of liquid) results in the model liquids and in the juices were lower than for pure water, due to the presence of solutes. The software simulation was able to predict the CO(2) solubility in the model systems at low pressures.

Image analysis based quantification of bacterial volume change with high hydrostatic pressure.

Scanning electron microscopy (SEM) images of Staphylococcus aureus 485 and Escherichia coli O157:H7 933 were taken after pressure treatments at 200 to 400 MPa. Software developed for this purpose was used to analyze SEM images and to calculate the change in view area and volume of cells. Significant increase in average cell view area and volume for S. aureus 485 was observed in response to pressure treatment at 400 MPa. Cell view area for E. coli O157:H7 933 significantly increased at 325 MPa, the maximum pressure treatment tested against this pathogen. In contrast to S. aureus, cells of E. coli O157:H7 exhibited significant increase in average view area and volume at 200 MPa. The pressure-induced increase in these parameters may be attributed to modifications in membrane properties, for example, denaturation of membrane-bound proteins and pressure-induced phase transition of membrane lipid bilayer.

Quantifying nonhomogeneous colors in agricultural materials part I: method development.

Measuring the color of food and agricultural materials using machine vision (MV) has advantages not available by other measurement methods such as subjective tests or use of color meters. The perception of consumers may be affected by the nonuniformity of colors. For relatively uniform colors, average color values similar to those given by color meters can be obtained by MV. For nonuniform colors, various image analysis methods (color blocks, contours, and "color change index"[CCI]) can be applied to images obtained by MV. The degree of nonuniformity can be quantified, depending on the level of detail desired. In this article, the development of the CCI concept is presented. For images with a wide range of hue values, the color blocks method quantifies well the nonhomogeneity of colors. For images with a narrow hue range, the CCI method is a better indicator of color nonhomogeneity.

Quantifying nonhomogeneous colors in agricultural materials. Part II: comparison of machine vision and sensory panel evaluations.

The average colors of mangos and apples were measured using machine vision. A method to quantify the perception of nonhomogeneous colors by sensory panelists was developed. Three colors out of several reference colors and their perceived percentage of the total sample area were selected by untrained panelists. Differences between the average colors perceived by panelists and those from the machine vision were reported as DeltaE values (color difference error). Effects of nonhomogeneity of color, and using real samples or their images in the sensory panels on DeltaE were evaluated. In general, samples with more nonuniform colors had higher DeltaE values, suggesting that panelists had more difficulty in evaluating more nonhomogeneous colors. There was no significant difference in DeltaE values between the real fruits and their screen image, therefore images can be used to evaluate color instead of the real samples.

Microbial inactivation kinetics during high-pressure carbon dioxide treatment: nonlinear model for the combined effect of temperature and pressure in apple juice.

Isobaric and isothermal semi-logarithmic survival curves of natural microflora in apple juice treated with high-pressure carbon dioxide at 7, 13, and 16 MPa pressures and 35, 50, and 60 degrees C temperatures were fitted with a nonlinear equation to find the values of the coefficient b(P), b(T), n(P), and n(T). Profiles of the model parameters were obtained as a function of pressure and temperature. The model fitted with good agreement(R(2) > 0.945), the survival curves. An empirical equation was proposed to describe the combined effects of pressure and temperature. The equation, derived from a power law model, was written in the form: log(10) S(t) = -log(e) [C(0)+C(1) x exp (K(T) x (T-T(C))-C(2) x exp (K(P) x (P-P(C))) x t (C(3)xT(2)+C(4)xT+C(5)). The proposed model fitted the experimental data well. At 7 MPa and 50 and 60 degrees C, 13 MPa and 35 and 60 degrees C, 16 MPa and 35 degrees C, the model provided (log)10 reduction residual values (observed value-fitted value) lower than 0.284 showing a good agreement between the experimental and the predicted survival levels.

Carbon monoxide treatments to impart and retain muscle color in tilapia fillets.

Carbon monoxide (CO) has been used for improving the color of muscle foods. In the current study, we compared the postmortem treatment of tilapia fillets with 100% CO and euthanasia of live tilapia with CO for their ability to stabilize the color of white and red muscle of tilapia fillets. Both postmortem CO treatment and CO euthanasia were effective in increasing the redness (a* value) and lightness (L* value) of tilapia white and red muscle. Fillets obtained from CO-euthanized tilapia showed significantly higher a* and L* values during 1 mo of frozen storage at -20 degrees C and subsequent thawing and storage at 4 degrees C for 18 d. The amount of CO present in the red and white muscles decreased during the 18 d of storage at 4 degrees C. There was no significant difference in the pH, drip, or thaw loss of CO-treated tilapia fillets compared to the untreated fillets.

Effect of high pressure treatment on the quality of rainbow trout (Oncorhynchus mykiss) and mahi mahi (Coryphaena hippurus).

High pressure processing (HPP) is becoming a promising seafood preservation method. The objective was to investigate the effect of HPP on quality of rainbow trout and mahi mahi during cold storage. Skinless fillets treated with different pressures (150, 300, 450, and 600 MPa for 15 min) and stored at 4 degrees C were analyzed at 1, 3, and 6 d storage. Red muscle was analyzed for lipid oxidation products by measuring thiobarbituric reactive substances (TBARS) and whole muscle was analyzed for total aerobic count, texture profile analysis, and color. A pressure of 300 MPa effectively inactivated the initial microbial population in rainbow trout (6-log reduction). However, inactivation of the initial population on mahi mahi was only about 4-log reduction at the same pressure. Microbial growth was significantly retarded after HPP. Color results showed that redness (a* value) of rainbow trout at 300 MPa and above was significantly (P < 0.05) lower compared to mahi mahi. TBARS values for rainbow trout increased with increased pressure, whereas the same trend was not seen for mahi mahi where maximum oxidation was found at 300 MPa and then declined. This study demonstrates the usefulness of HPP in seafood processing and the influence of species variation on processing parameters. The optimum HPP conditions for influencing lipid oxidation, microbial load, and color changes were found to be 300 MPa for rainbow trout and 450 MPa for mahi mahi.

Changes in brown eggshell color as the hen ages.

The color of eggshells from eggs laid by commercial-type Hy-Line brown hens 25 wk of age was studied over a period of 10 mo. Color measurements were made by a color machine vision system and were analyzed using a mixed model to calculate between and within hen variances and to investigate the effect of time on shell color. Hens laid eggs with lighter colored shells as the flock aged, as evidenced by the lightness (L*) values increasing in time. A decrease in pigmentation was associated with a decrease in the amount of redness (a*) in the eggshell. When L* and a* values were corrected for egg weight, the rate of change in the L* and a* values decreased, indicating that size of the egg was a major factor affecting the color of the eggshell. These findings quantified the observations that older hens lay lighter colored eggs due to an increase in egg size associated with no proportionate change in the quantity of pigment deposited over the shell surface. Using a 2-stage sampling analysis and the variances between and within hens, sample sizes required to estimate the color of eggshells within 5% of the true mean were calculated. Accordingly, 11 eggs would need to be collected from each of the 51 hens housed for a study of brown eggshell color using the L*, a*, and b* (yellowness) coordinates.

Bacterial Effect of High Pressure CO2 Treatment on Foods Spiked with Listeria or Salmonella.

Studies were carried out to assess the use of high pressure CO2, treatment for controlling pathogenic microorganisms in model food systems. Listeria monocytogenes suspended in distilled water was completely killed after CO2 treatment at 6.18 MPa (61.2 atm) and 35°C for 2 h. Contrary to CO2 treatment, the use of N2 at these experimental conditions failed to exert bactericidal effect. High pressure CO2 treatment at 13.7 MPa (136.1 atm) and 35°C for 2 h was shown to effectively kill Salmonella in spiked chicken meat (>95%) and egg yolk (> 100%), and kill Listeria in spiked shrimp (> 99%), orange juice (> 99%), and egg yolk (> 99.4%). Such treatment was, however, less effective in killing Salmonella in a whole egg- Salmonella mixture. Furthermore, this treatment caused a twofold increase in bacterial numbers in a whole egg- Listeria mixture. N2 gas under similar experimental conditions did not kill the spiked bacteria in these four food systems. High pressure CO2 treatment technique could possibly be applied to reduce microbial load in some food systems.