Effect of continuous and intermittent ultrasound on drying time and effective diffusivity during convective drying of apple and red bell pepper

A new approach of ultrasound-assisted convective drying was tested in this study using a screen as product support and sound transmitting surface. Red bell pepper and apple cubes were dried at 70 °C in a laboratory scale hot-air drying oven. In addition to continuous ultrasound used for both products, intermittent ultrasound was applied for apple drying reducing net sonication time to 50% and 10%. Significant improvements of drying characteristics were observed for continuous sonication and intermittent ultrasound at 50% net sonication time. Experimental data were fitted with eight models, among which the Midilli model resulted in the best fit with R² > 0.9988 and reduced χ² ? 0.0002. The influence of ultrasound on drying time to reach 20% and 30% residual moisture content as well as on effective moisture diffusivities and drying periods is discussed.     

Laser light backscattering to monitor moisture content, soluble solid content and hardness of apple tissue during drying

Continuous monitoring of food properties during drying is of stark relevance for the food processing industry. The main task of this research is to apply laser backscattering technology to simultaneously predict variations in hardness, moisture content and soluble solids content (SSC) of apples during drying. A laser diode with a wavelength of 635 nm was used to non-destructively analyze photon migration in the apple tissue. The backscattering area in pixel numbers, representing the illuminated area after laser light injection, and light luminescence measured by grey values were used for estimating changes in internal quality parameters during drying. A decrease in moisture content caused a reduction in photon scattering determined by diminished light propagation in the fruit tissue. Additionally, scattering images showed less photon migration as the SSC increased due to the light absorption of light at 635 nm by fruit compounds. To estimate moisture content, calibration models gave the highest coefficients of determination (R² = 0.8 and 0.89) with standard errors of cross validation (SECV) of 11.6 and 9.8 for backscattering area and light luminescence, respectively. However, predictions obtained for SSC were slightly lower. Laser light measurement at 635 nm was found to be adequate for predicting changes in moisture content and SSC of apple during drying over different stages. On the contrary, photon scattering at 635 nm is not recommended as estimator of change in hardness during apple drying, based on the results.     

Prediction of beef quality attributes using VIS/NIR hyperspectral scattering imaging technique

Hyperspectral imaging images were used to predict fresh beef tenderness (WBSF: Warner-Bratzler Shear Force) and color parameters (L^∗, a^∗, b^∗). Sixty-five fresh strip loin cuts were collected from 33 carcass after 2 days postmortem. After acquiring hyperspectral images, the samples were vacuum packaged and aged for 7 days, and then the color parameters and WBSF of the samples were measured as references. The optical scattering profiles were extracted from the images and fitted to the Lorentzian distribution (LD) function with three parameters. LD parameters, such as the scattering asymptotic vale, the peak height, and full scattering width were determined at each wavelength. Stepwise discrimination was used to identify optimal wavelengths. The LD parameters’ combinations with optimal wavelengths were used to establish multi-linear regression (MLR) models to predict the beef attributes. The models were able to predict beef WBSF with R_cv = 0.91, and color parameters (L^∗, a^∗, b^∗) with R_cv of 0.96, 0.96 and 0.97, respectively.     

Drying kinetics and quality of beetroots dehydrated by combination of convective and vacuum-microwave methods

Beetroot cubes were dehydrated by convective drying in hot air at 60 °C and by the combination of convective pre-drying (CPD) until moisture content 1.6, 0.6 or 0.27 kg/kg db and vacuum-microwave finish drying (VMFD) at 240, 360 or 480 W. The control samples were obtained by freeze-drying (FD). The drying kinetics of beetroot cubes was described with an exponential function. VMFD significantly reduced the total time of drying and decreased drying shrinkage in comparison with convective method. A critical moisture content divided the temperature profile of samples during VMFD into increasing and falling periods. At the falling temperature period a significant increase in the colour parameters L^∗, a^∗ and b^∗ was found. VM treated samples as well as FD ones exhibited lower compressive strength, better rehydration potential and higher antioxidant activity than those dehydrated in convection. Increasing the microwave wattage and decreasing the time of CPD improved the quality of beetroot cubes dried by the combined method.     

Thin layer drying model for simulating the drying of Tilapia fish (Oreochromis niloticus) in a solar tunnel dryer

Mathematical models for predicting the plenum chamber temperatures developed by a solar tunnel dryer and the drying of Tilapia fish (Oreochromis niloticus) in the solar tunnel dryer was developed, and simulated in Visual Basic 6 (Microsoft Visual Basic 6.0™). Based on Student’s t-test, the simulated and actual data for both plenum chamber temperature and moisture ratio did not differ significant at 5% level of significance. In addition, the simulated and actual moisture ratios showed similar trends, and reduced exponentially with drying time. Further, the performances of models at 10% residual error interval were 83% and 81% for plenum chamber temperature and moisture ratio, respectively. Finally, strong linear correlations existed between simulated and actual data for plenum chamber temperature (R² = 0.961), and for moisture ratio (R² = 0.995). Therefore, the model can be used to predict the drying of Tilapia fish in a solar tunnel dryer.     

Use of viscera extract from hybrid catfish (Clarias macrocephalus × Clarias gariepinus) for the production of protein hydrolysate from toothed ponyfish (Gazza minuta) muscle

Proteolytic activity of viscera extract from hybrid catfish (Clarias macrocephalus × Clarias gariepinus) was studied. The optimal pH and temperature were 9.0 and 50 °C, respectively, when toothed ponyfish (Gazza minuta) muscle was used as a substrate. When viscera extract from hybrid catfish was used for the production of protein hydrolysate from toothed ponyfish muscle, extract concentration, reaction time, and fish muscle/buffer ratio affected the hydrolysis and nitrogen recovery (NR) (p < 0.05). Optimum conditions for toothed ponyfish muscle hydrolysis were 3.5% hybrid catfish viscera extract, 15 min reaction time and fish muscle/buffer ratio of 1:3 (w/v). High correlation between the degree of hydrolysis (DH) and NR (R² = 0.974) was observed. Freeze-dried hydrolysate had a high protein content (89.02%, dry weight basis) and it was brownish yellow in colour (L^∗ = 63.67, a^∗ = 6.33, b^∗ = 22.41). The protein hydrolysate contained a high amount of essential amino acids (48.22%) and had arginine and lysine as the dominant amino acids.     

Stiffness measurement of eggshell by acoustic resonance and PLS models

Non-destructive measurement of eggshell stiffness was carried out by means of acoustic resonance system. It was achieved by analysis of measured frequency response of eggshell excited with a light mechanical. Partial least squares (PLS), synergy interval PLS (si-PLS), genetic algorithm PLS (GA-PLS) and GA-siPLS algorithms were used comparatively to calibrate regression model. The performance of the final model was evaluated according to root mean square error of prediction (RMSEP) and correlation coefficient (R) in prediction set. Experimental results showed that GA-PLS and GA-siPLS models got acceptable performance with fewer frequency variables. The optimal GA-PLS model was achieved with R = 0.771 and RMSEP = 3.6, and the optimal GA-siPLS model was achieved with R = 0.7591 and RMSEP = 3.55 in prediction set. It will help to build a compact and robust model serving for on-line measurement of egg’s stiffness.     

Application of computer vision technique for on-line monitoring of shrimp color changes during drying

The effects of drying temperature and drying medium velocity on color change kinetics of shrimp viz. lightness (L^∗), redness (a^∗), yellowness (b^∗), total color difference (ΔE), chroma (CH), hue angle (H°), and browning index (BI) were on-lineally investigated. Drying experiments were carried out on dryer equipped with computer vision systems using hot air drying (HAD) temperatures of 50–90 °C and superheated steam drying (SSD) temperatures of 110–120 °C at drying medium velocities of 1–2 m/s. Zero-, first-order, and fractional conversion models were utilized to describe the color changes of shrimps and the fractional conversion model successfully tracked the experimental data. The results showed that the color parameters were significantly influenced by the studied parameters. Lightness of the samples decreased, while other color parameters increased as drying proceeded. Generally, increasing drying medium temperature decreased L^∗ and H°, whereas increased other color parameters. The color characteristic of the SSD finished products were acceptable than the HAD processed samples. Finally, dimensionless moisture content of shrimps during drying was accurately correlated to the color parameters and drying time using a quadratic regression model. Moisture ratio had strong relationship with the lightness change compared with the redness and yellowness variations.     

On-line application of visible and near infrared reflectance spectroscopy to predict chemical–physical and sensory characteristics of beef quality

The aim of this study was to assess the on-line implementation of visible and near infrared reflectance (Vis-NIR) spectroscopy as an early predictor of beef quality traits, by direct application of a fibre-optic probe to the muscle immediately after exposing the meat surface in the abattoir. Samples from M.longissimus thoracis from 194 heifers and steers were scanned at quartering 48 h postmortem over the Vis-NIR spectral range from 350 to 1800 nm. Thereafter, samples from M.longissimus thoraciset lumborum were analysed for colour (L^∗, a^∗, b^∗; 48 h postmortem), cooking loss (14 days postmortem), instrumental texture (Volodkevitch, 10 days aged meat; slice shear force, 3 and 14 days aged meat) and sensory characteristics. Vis-NIR calibrations, tested by cross-validation, showed high predictability for L^∗, a^∗ and b^∗ (R² = 0.86, 0.86 and 0.91; SE_CV = 0.96, 0.95 and 0.69, respectively). The accuracy of Vis-NIR to estimate cooking loss and instrumental texture ranged from R² = 0.31 to 0.54, suggesting relatively low prediction ability. Sensory characteristics assessed on 14 days aged meat samples showed R² in the range from 0.21 (juiciness) to 0.59 (flavour). Considering the subjective assessment of sensory characteristics the correlations of Vis-NIR measurements and several meat quality traits in the range from 0.46 to 0.95 support the use of on-line Vis-NIR in the abattoir. Improvement of predictability was achieved if only extreme classes of meat characteristics have to be predicted by Vis-NIR spectroscopy.     

Hybrid mixture theory based moisture transport and stress development in corn kernels during drying: Validation and simulation results

The moisture transport and stress development mechanisms were elucidated for corn kernels using numerical solution of three-scale fluid transport equation. The 3D kernel structure was captured using micro-CT scanning and imported into finite elements package. The experimental drying profiles were predicted with reasonable accuracy (R² = 0.88-0.99 and CV = 3.5-9.5%). During simulations, the region with highest moisture content was observed to be away from the geometric center covering parts of soft-endosperm and germ. The high moisture flux was observed under the pericarp, in soft-endosperm toward top and in region connecting soft-endosperm and germ. The germ due to its lower moisture diffusivity in comparison to hard and soft endosperms, retained higher moisture and exhibited lower moisture flux. These observations agreed with previous magnetic resonance imaging based studies. Intermittent drying simulations indicated that fan on/off strategies with suitable time step-size would be a viable option for drying corn with lower stress-cracking and additional energy savings.     

Prediction of colloidal stability in white wines using infrared spectroscopy

The feasibility of utilizing infrared spectroscopy for the prediction of haze formation in white wines resulting from heat and colloidal stability tests was investigated. One-hundred eleven white wines, representing multiple regions and varieties from the 2008 California vintage, were collected and analyzed. The near and mid-infrared spectra were measured and heat and colloidal (ethanol addition) stability tests were performed on the same wines. Partial-least squares regression analysis was then used to construct models predictive of the resulting nepholometric turbidity to the acquired spectra. Preliminary models obtained following application of spectral pretreatments today considered as “classical” (e.g., derivatives, standard normal variate, vector normalization, constant offset elimination) lacked robustness; two alternative algorithms designed to remove spectral information unrelated to the turbidity were then employed (orthogonal signal correction; direct orthogonal signal correction). While OSC pretreatment did not result in more robust models, DOSC considerably enhanced the goodness of the PLS model constructed to predict the ethanol test turbidity. Predictive modeling of the short-NIR spectra, following DOSC preprocessing, allowed the prediction of colloidal stability on an unknown test set with an R² = 0.80 and a RMSEP = 10.12 using three latent variables. When the data set was restricted to Chardonnay wines alone, the predictive ability improved, with R² = 0.85 and RMSEP = 8.90.     

Compositions,functional properties and antioxidative activity of protein hydrolysates prepared from round scad (Decapterus maruadsi)

Composition, functional properties and antioxidative activity of a protein hydrolysate prepared from defatted round scad (Decapterus maruadsi) mince, using Flavourzyme, with a degree of hydrolysis (DH) of 60%, were determined. The protein hydrolysate had a high protein content (48.0%) and a high ash content (24.56%). It was brownish yellow in colour (L^∗ = 58.00, a^∗ = 8.38, b^∗ = 28.32). The protein hydrolysate contained a high amount of essential amino acids (48.04%) and had arginine and lysine as the dominant amino acids. Na⁺ was the predominant mineral in the hydrolysate. The protein hydrolysate had an excellent solubility (99%) and possessed interfacial properties, which were governed by their concentrations. The emulsifying activity index of the protein hydrolysate decreased with increasing concentration (p < 0.05). Conversely, the foaming abilities increased as the hydrolysate concentrations increased (p < 0.05). During storage at 25 °C and 4 °C for 6 weeks, the antioxidative activities and the solubility of round scad protein hydrolysate slightly decreased (p < 0.05). Yellowness (b^∗-value) of the protein hydrolysate became more intense as the storage time increased but the rate of increase was more pronounced at 25 °C than at 4 °C.     

Physicochemical and functional properties of chitosans affected by sun drying time during decoloration

The typical production of chitosan from crustacean shell consists of demineralization, deproteinization, decoloration, and deacetylation. Selected physicochemical and functional properties of chitosans as affected by various decoloration times (4, 5, 6, 7 or 8 h) using sun drying were evaluated. Moisture content (6.67-6.89 g/100 g), degree of deacetylation (81.91-82.73%), and color L^∗ value (78.32-79.43) of chitosans were not affected by sun drying time. However, color a^∗ and b^∗ values decreased when sun drying time was over 4 h. The viscosity of chitosan solution (0.5 g/100 mL acetic acid) decreased gradually with increasing sun drying time, with a more pronounced effect observed at 8 h of sun drying. There was no change in water-binding capacity (WBC) of chitosans decolorized by sun drying between 4 and 6 h; however, further increase in sun drying time from 6 to 7 or 8 h increased WBC of chitosans. DPPH radical scavenging activity of chitosans increased with increasing sun drying time. This study demonstrated that white-colored chitosans could be produced by an alternative decoloration step using sun drying for 4 h following the deacetylation step. However, increasing sun drying time to 7 h produced chitosan with increased WBC and DPPH radical scavenging activity.     

Amaranthus hypochondriacus and Amaranthus caudatus germplasm: Characteristics of plants,grain and flours

In the present study, the plant, grain and flour characteristics of 48 Amaranthus hypochondriacus and 11 Amaranthus caudatus lines are reported. A. hypochondriacus grains had a higher thousand kernel weight (0.62–0.88 g), a creamish yellow colour (L∗ = 61.38–68.29, b∗ = 5.26–6.8 and a∗ = 19.71–23.84), whereas A. caudatus grains had a lower thousand kernel weight (0.46–0.70 g) and a reddish-brown colour (L∗ = 47.1–51.2, b∗ = 11.82–14.02 and a∗ = 7.72–13.29). The A. caudatus lines had a higher protein content, fat content and tendency for retrogradation, and lower α-amylase activity as compared to A. hypochondriacus lines. The Amaranthus lines with higher a∗-values and lower thousand kernel weight, L∗- and b∗-values, had a higher fat, crude fibre and protein content. The correlation of fat and crude fibre content with the thousand kernel weight, L∗-, a∗- and b∗-values, was significant. The A. hypochondriacus lines showed higher pasting temperature, and lower peak viscosity, breakdown and setback, as compared to the A. caudatus lines. The result reflected that the lines with higher α-amylase activity showed a lower peak viscosity, breakdown, final viscosity and gel hardness, and a higher pasting temperature.     

Characterization of anthocyanins in Kenyan teas: Extraction and identification

Characterization and quantification of anthocyanins in selected tea cultivars processed into black (aerated) and green (unaerated) tea products was carried out in this study. The anthocyanins were extracted from tea products processed from a number of newly bred purple leaf coloured Kenyan tea cultivars (Camellia sinensis) using acidified methanol/HCl (99:1 v/v). Extracted anthocyanins were purified by C₁₈ solid phase extraction (SPE) catridges and characterised by HPLC-UV-Visible. They were identified according to their HPLC retention times, elution order and comparison with authentic standards that were available. Total monomeric anthocyanins were determined by the pH-differential method. Although the tea cultivars gave different yields of anthocyanins, the unaerated (green) teas had significantly (p ? 0.05) higher anthocyanin content than the aerated (black) teas. This was attributed to the degradation of anthocyanins by polyphenol oxidase products (catechin O-quinones) formed during the auto-oxidation (fermentation) process of black tea manufacture. Of the six most common natural anthocyanidins, five were identified in the purified extracts from purple leaf coloured tea, in both aerated (black) and unaerated (green) teas namely; delphinidin, cyanidin, pelargonidin, peonidin and malvidin. The most predominant anthocyanidin was malvidin in both tea products. In addition, two anthocyanins namely, cyanidin-3-O-galactoside and cyanidin-3-O-glucoside were also identified. Tea catechins were also identified in the tea products derived from the purple coloured tea cultivars namely, epigallocatechin (EGC), catechin (+C), epicatechin (EC), epigallocatechin gallate (EGCG), and epicatechin gallate (ECG). Correlation between the total catechins versus the total anthocyanins and anthocyanin concentration in unaerated teas revealed significant negative correlations (r = −0.723^∗ and r = −0.743^∗∗, p ? 0.05 and p ? 0.01, respectively). However, in aerated (black) tea the correlations were insignificant (r = −0.182 and r = −0.241, p > 0.05).     

Stability and colour characteristics of PEF-treated cyanidin-3-glucoside during storage

The stability and colour characteristics of PEF (pulsed electric field)-treated cyanidin-3-glucoside (Cy-3-glu) was investigated during storage at 4, 24 and 37 °C. The degradation of Cy-3-glu was analyzed using a first reaction kinetics while its colour characteristics was evaluated using colour indices such as colour density (CD) and CIE L^∗a^∗b^∗ parameters. PEF had no post-effect on the stability and colour characteristics of Cy-3-glu during storage while the storage temperature had a significant effect (p < 0.05). The degradation of PEF-treated Cy-3-glu during storage conformed to the first-order reaction kinetics with regression coefficients R² greater than 0.9300. Corresponding to 4, 24 and 37 °C, the degradation rate constant k in Cy-3-glu significantly increased in the exponential order level of 10⁻⁴, 10⁻³ and 10⁻², while the t_1/2 (the time that 50% Cy-3-glu degradation would take) and D-value (the time that 90% Cy-3-glu degradation would take) of Cy-3-glu during storage decreased in the exponential order level of 10³, 10² and 10. The reduction of CD was closely related to the Cy-3-glu content in this study, the Cy-3-glu content was perfectly predicted using CD with a higher coefficient R² > 0.9999. A significant decrease in b^∗ and H⁰ value was obtained at all storage temperature (p < 0.05). A positive correlation was found between the Cy-3-glu content and b^∗ value or H⁰ value with a coefficients R² > 0.8400 during storage. ΔE increased significantly, ΔE was less than 2 at 4 °C while it was greater than 2 at 24 and 37 °C.     

Composition and color stability of carbon monoxide treated dried porcine blood

Color stability of swine blood was studied over 12 weeks of storage in plastic bags, after pH (7.40, 6.70, or 6.00) adjustment, saturation with carbon monoxide (CO) and spray-drying. CO-treated dried blood presented a redder color and higher reflectance between 610 and 700 nm, compared to a brownish-red color and lower reflectance of untreated samples. As indicated by reflectance spectra, blood pH adjustment did not influence (P > 0.05) the initial color of dried blood but influenced (P < 0.05) its color stability (browning index). During storage, CO-treated blood showed a reduction in reflectance percentages as well as in CIE L^∗ and a^∗ values, which was more pronounced in polyethylene (OTR = 4130 cm³/m²/day/atm) packaged samples. After 12 weeks of storage, CO-treated samples packaged in high OTR bags presented color indexes similar to those of the untreated dried samples. CO-treated samples packaged in nylon-polyethylene (OTR = 30–60 cm³/m²/day/atm) bags showed a smaller rate of discoloration and color difference (ΔE^∗) between the CO-treated and untreated samples. Even with some darkening, packaging CO-treated dry blood in low OTR bags still gives an acceptable reddish color after 12 weeks of storage while untreated dry blood has a brownish color just after drying.     

Stability and anti-glycation properties of intermediate moisture apple products fortified with green tea

Intermediate moisture products made from blanched apple flesh and green tea extract (about 6 mg of monomeric flavan 3-ols added per g of dry apple) or blanched apple flesh (control) were produced, and their quality attributes were investigated over storage for two months at water activity (a_w) levels of 0.55 and 0.75, at 30 °C. Products were evaluated for colour (L^∗, a^∗, and b^∗ Hunter’s parameters), phytochemical contents (flavan 3-ols, chlorogenic acid, dihydrochalcones, ascorbic acid and total polyphenols), ferric reducing antioxidant potential, 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl radical-scavenging activity and ability to inhibit formation of fructose-induced advanced glycation end-products.     

Weibull distribution for modeling air drying of coroba slices

Application of Weibull distribution model was investigated for describing the moisture content of coroba slices during air drying. One set of experiments was performed following a full factorial design at three levels for air temperature (71, 82 and 93 °C) and velocity (0.82, 1.00 and 1.18 m/s). The set was designed to assess the adequacy of the Weibull model to describe water losses. The high regression coefficients (R² > 0.99) and low reduced chi-square indicated the acceptability of Weibull model for predicting moisture content. Values of scale parameter ranged from 41.77 to 71.52 (min) and values of shape parameter ranged from 1.06 to 1.21. Temperature sensitivity of scale parameter increased with increasing air velocity from 0.82 m/s (E_a = 210.45 J/mol) to 1.00 m/s (E_a = 214.93 J/mol) and then decreased with increasing velocity to 1.18 m/s (E_a = 139.03 J/mol). The normalized Weibull model was investigated for determining the effective diffusion coefficient (D_e). The D_e values ranged approximately from 2.51 × 10⁻¹² m²/s to 4.27 × 10⁻¹² m²/s.     

Mathematical model of pork slice drying using superheated steam

Superheated steam has received much attention as an effective technique for drying purposes because it produces dried products with high quality attributes. Although currently there are a number of works reporting the development of a mathematical model of superheated steam drying, they do not use a numerical method to estimate the effective moisture diffusivity value (D_eff value) of the product. The purposes of this work, therefore, were to develop a semi-empirical model for estimating the D_eff value of pork, and for predicting the evolution of the moisture content and the center temperature of sliced pork during superheated steam drying. The model was based on mass and energy-balance equations and was divided into three periods: heating up, constant drying rate and falling drying rate period. It was solved using an explicit finite difference method and used a grid search method to estimate the D_eff value of pork. The predicted results were compared with the experimental data of superheated steam drying of seasoned and unseasoned pork with slice thicknesses of 1 and 2 mm at a drying temperature of 140 °C. The comparison results showed that the developed model could estimate the ranges of the D_eff value of pork fairly well (D_eff = 3.311-12.471 × 10⁻¹⁰ m²/s for seasoned pork, and 4.200-15.056 × 10⁻¹⁰ m²/s for unseasoned pork) and could reasonably predict the evolution of the moisture content of the sliced pork. The predicted center temperature of the sliced pork was higher than the experimental data in the heating up period and in the first 5 min of the falling drying rate period, but it agreed well in the constant drying rate period and after the drying time of 10 min. Moreover, it was found that the slice thickness and the seasoning had an influence on the drying curves only in the constant drying rate and falling drying rate period.