Novel and Precise Method to Isolate,Identify, and Quantify Volatile Compounds in Headspace of Pear Juice Enriched with α-Cyclodextrin

The combination headspace solid phase micro-extraction?+?gas chromatography–mass spectrometry?+?gas chromatography with flame ionization detector was successfully used in quantitative determination of the instrumental odor of pear juice. Esters, aldehydes, alcohols, and terpenes were the major chemical families of the pear juice odor. Twenty-six were identified and quantified, with propyl acetate, hexyl acetate, 2-methyl-1-butanol, and butyl acetate being the major compounds. α-Cyclodextrins (CD) significantly improved the color of pear juice, leading to higher values of L* and lower of scores of a*, b*, and ΔE*. However, α-CD also reduced the total concentration of volatiles in the headspace of the juice by creating inclusion complexes with volatiles; after 40 min of oxidation, total volatiles were 8.2 and 3.4 mg L^?1 in control and α-CD-treated juices, respectively. But in summary, the global quality (joint consideration of the main sensory attributes) was improved by the addition of α-CD (6.9 compared to 5.2).     

Effect of calcium carbonate,calcium citrate,tricalcium phosphate,calcium gluconate and calcium lactate on some physicochemical properties of soymilk

Soymilk fortified with 25 mm Ca (Ca carbonate, Ca citrate, triCa phosphate, Ca gluconate or Ca lactate) was compared with the properties of unfortified soymilk (control). Calcium carbonate, Ca citrate and triCa phosphate did not significantly affect [Ca²⁺], absolute viscosity and particle size of soymilk, but Ca gluconate and Ca lactate significantly increased these properties. The pH of soymilk was significantly increased by adding Ca carbonate but significantly reduced by adding Ca gluconate and Ca lactate. Dry sediment of soymilk increased significantly with the addition of all Ca salts excluding triCa phosphate. Freezing point depression increased significantly only for Ca gluconate and Ca lactate, mainly owing to their higher solubility.     

Microbiological,physicochemical and rheological properties of fermented soymilk produced with exopolysaccharide (EPS) producing lactic acid bacteria strains

Growth of Lactobacillus plantarum 70810, Lactobacillus rhamnosus 6005 and a commercial yogurt starter culture in soymilk was investigated in the present study. It was found that the fermented soymilk using L. plantarum 70810 had significantly higher viable cell counts, water holding capacity (WHC, 88.27%), apparent viscosity (1840.35 mPa s) and exopolysaccharide (EPS) amount (832.15 mg/L) than the other two starter cultures in soymilk. Direct observation of microstructure in fermented soymilk indicated that the network structures of EPS-protein could improve the texture of fermented soymilk. Considering that the beneficial effects of L. plantarum 70810 in fermented soymilk, volatile compounds in fermented soymilk were further identified. Then the growth and fermentation characteristics of L. plantarum 70810 including changes in viable cell counts, pH, titratable acidity, apparent viscosity and EPS production during storage were investigated. In comparison to original soymilk base, the concentrations of the characteristic flavor compounds for fermented soymilk using L. plantarum 70810 increased, whereas hexanal, 2-pentylfuran and 2-pentanone in relation to beany flavor of soymilk decreased. In addition, fermented soymilk using L. plantarum 70810 maintained high viable cell count (>10⁸ cfu/mL), apparent viscosity (966.43 mPa s) and amounts of EPS (635.49 mg/mL) during storage at 4 °C for 21 days.     

Feasibility of using dialysis for determining calcium ion concentration and pH in calcium-fortified soymilk at high temperature

Abstract: Dialysis was performed to examine some of the properties of the soluble phase of calcium (Ca) fortified soymilk at high temperatures. Dialysates were obtained while heating soymilk at temperatures of 80 and 100 °C for 1 h and 121 °C for 15 min. It was found that the pH, total Ca, and ionic Ca of dialysates obtained at high temperature were all lower than in their corresponding nonheated Ca‐fortified soymilk. Increasing temperature from 80 to 100 °C hardly affected Ca ion concentration ([Ca²⁺]) of dialysate obtained from Ca chloride‐fortified soymilk, but it increased [Ca²⁺] in dialysates of Ca gluconate‐fortified soymilk and Ca lactate‐fortified soymilk fortified with 5 to 6 mM Ca. Dialysates obtained at 100 °C had lower pH than dialysate prepared at 80 °C. Higher Ca additions to soymilk caused a significant (P≤ 0.05) reduction in pH and an increase in [Ca²⁺] of these dialysates. When soymilk was dialyzed at 121 °C, pH, total Ca, and ionic Ca were further reduced. Freezing point depression (FPD) of dialysates increased as temperature increased but were lower than corresponding soymilk samples. This approach provides a means of estimating pH and ionic Ca in soymilks at high temperatures, in order to better understand their combined role on soymilk coagulation.     

Extraction and Preconcentration of Some Triazole Pesticides in Grape Juice by Salting Out Homogeneous Liquid–Liquid Extraction in a Narrow-Bore Tube Prior to Their Determination by Gas Chromatography–Flame Ionization Detection

A fast and simple extraction and preconcentration method for some triazole pesticides has been developed using a homogeneous liquid–liquid extraction method performed in a narrow-bore tube. The extraction is based on phase separation of a water-miscible organic solvent from aqueous solution in the presence of a salting out agent. In this work, the homogeneous solution of water and acetonitrile (water-soluble extraction solvent) was broken by addition of 30 %, w/v, sodium chloride (salting out agent). After sonication, a small volume of acetonitrile was collected on top of the tube and the extracted analytes in the collected phase were determined by gas chromatography–flame ionization detection. The effect of various experimental parameters including kind and volume of the water-soluble organic solvent, amount of salt, length and diameter of tube, and pH of sample solution was investigated. Under the optimum conditions, calibration graphs were linear over the range of 3–5,000 μg L^?1. Relative standard deviations were less than 5.4 % for six repeated determinations (C?=?100 μg L^?1). Furthermore, the limits of detection (S/N?=?3) and quantification (S/N?=?10) were obtained in the ranges of 0.60–4.8 and 1.9–16 μg L^?1, respectively. This method is very simple and rapid, requiring less than 10 min for sample preparation. It has been successfully utilized for the analysis of triazole pesticides in the grape juice samples.     

Soybean variety and storage effects on soymilk flavour and quality

Soymilk prepared from five soybean cultivars, grown in Ontario, were analysed for protein, oil, mineral composition, viscosity, colour, lipoxygenase (LOX) activities and flavour profile. Among the five soybean cultivars, the Vinton 81 variety contained the highest protein and the lowest fat. The yield of soymilk from all five cultivars was similar. Major differences were observed in viscosity and in the composition of both the soymilk and the okara. Higher protein and fat extractability was found in soymilk made from S08‐80 and Vinton 81 varieties. Their okara protein contents were also among the highest. Minimum extractability was observed with S03W4 cultivar. Soymilk made from S 03W4 and Vinton 81 cultivars had the whitest colour (lowest ΔE values). Viscosity values were the highest for S08‐80, FG1 and S20‐20 varieties. Headspace solid‐phase microextraction gas chromatography was used to analyse volatile compounds in soymilk. A total of fourteen volatiles were identified, among which aldehydes and their corresponding alcohols were the major compounds. Similar volatile compounds were identified in all the samples analysed but at different concentrations. The highest LOX activity was observed in the Vinton 81 and S20‐20 soybean cultivars, which had the highest total volatile and hexanal contents. A positive correlation (correlation coefficient = 0.82) between enzymatic activity and the total volatiles was observed. Vinton 81 cultivar was subjected to storage (at 18 °C and 50% relative humidity) for a period of 10 months. Soymilk was prepared at different times during storage. The results showed that the soymilk colour, LOX and total volatiles were significantly (P < 0.05) affected by the storage of the soybeans over time.     

CHANGES IN SOYMILK QUALITY AS A FUNCTION OF COMPOSITION AND STORAGE

ABSTRACT

Three soymilk products formulated with different concentrations of fat, sugar and starch were evaluated for changes in their physical properties and volatiles profile over time (3 months) under different temperatures (4, 22 and 38C) of storage. Samples were tested for pH, color, viscosity and volatile flavor changes. The pH and color of the soymilks decreased significantly during the first month of storage and then remained stable over time. Color and viscosity of the soymilk products were affected by both the soymilk composition and storage treatment. The high‐fat soymilk sample (product C) had the whitest color (lower ΔE) and the lowest viscosity. Storage at 38C negatively affected the color. The viscosities of the soymilk products stored at 4C were the lowest among the treatments. The major volatiles identified in all soymilk products were hexanal, heptanal, octanal, nonanal, hexanol, 1‐octen‐3‐ol, benzaldehyde, 2‐pentyl furan and 2‐ethyl furan. The intensities of the volatile compounds in the soymilk products increased during the first weeks of storage, particularly when stored at 38C. The intensities, however, decreased gradually over time. Among the three formulated soymilk products, the sweetened sample (product B) gave the lowest flavor intensities under all three temperatures of storage. Overall, storage at 4C and addition of sugar preserve best the soymilk quality.

PRACTICAL APPLICATIONS

Soy products are well appreciated for their nutritional and potential health benefits. Soy beverage consumption is increasing among North American consumers because of improvements in soy beverage quality and processing technologies. There is, however, a demand for new value‐added soy‐based drinks with improved “functional” (health‐benefiting) properties. Soy beverage could be an excellent carrier for “functional” or “nutritive” ingredients such as minerals, vitamins and omega 3 oils; however, addition of such ingredients may affect the stability of the product and requires the development appropriate of technologies for their incorporation. Results from this project provide new knowledge on the storage stability and quality of three different soy product formulations. The information could be useful in the establishment of optimal conditions for processing of functional soy beverages, for use by the food industry.

     

Predicting the Heating Temperature of Soymilk Products Using Fluorescence Fingerprints

A novel measurement technique using fluorescence fingerprints (FFs) was developed to measure the degree of heat treatment applied to soymilk. FFs are a set of fluorescence spectra acquired at consecutive excitation wavelengths. Soymilk was heated at 50, 60, 70, 80, or 90 °C, for 10 min, and the samples were measured both in the liquid and freeze-dried forms. Partial least squares (PLS) regression models were constructed to predict heating temperature from the FFs of liquid soymilk and freeze-dried soymilk. Heating temperatures were predicted from soymilk FFs with root-mean-square errors of prediction (RMSEP) and R ²P of 7.20 °C and 0.92 and from freeze-dried soymilk FFs with RMSEP and R ²P of 9.00 °C and 0.89, respectively. The fluorescence of aromatic amino acids and Maillard products mainly contributed to the prediction models. FF measurement proved to be effective for the objective control of the soymilk heating process.     

Modelling and Comparison of Wheat Flour Extrusion Cooking Behaviours in Two Different Twin-Screw Extrusion Systems

The aim of this study was to investigate the extrusion cooking behaviours of two wheat flour samples (W1DK, W2CH) in two different twin-screw extrusion systems, where the wheat flour samples were characterised by rapid visco analyser (RVA) measurements. A new method is proposed to model and compare the wheat flour extrusion behaviours in the two systems through the RVA measurements, an extrudate bulk density model and a melt viscosity calculation. A new method is suggested to calculate the melt viscosity in the extrusion process. The average viscosity value of the W1DK sample was 64% higher than that of the W2CH sample in the RVA measurements. The comparison results show that the high viscosity for W1DK obtained from the RVA corresponds to a high reduced melt viscosity (η _r , (1/s)^γ) for W1DK, i.e., η _r ?=?0.25–2.61 (1/s)^γ (η _r ?=?0.042–0.082 (1/s)^γ for W2CH), a high specific mechanical energy (SME) for W1DK, i.e., SME?=?8.16–11.28 kJ/kg (SME?=?5.57–9.99 kJ/kg for W2CH) and a low extrudate bulk density (ρ _B ) for W1DK, i.e., ρ _B ?=?185–488 g/L (1 g/L?=?1 kg/m³) (ρ _B ?=?406–510 g/L for W2CH) in the two extrusion systems. The RVA viscosity and the calculated melt viscosity can be used to identify a recipe characteristic in terms of torque and extrudate bulk density in the two extrusion systems. A comparison has also been made for the bulk density model and response surface methodology in the extrudate bulk density prediction.     

Freshness assessment of gilthead sea bream (Sparus aurata) by machine vision based on gill and eye color changes

The fish freshness was evaluated using machine vision technique through color changes of eyes and gills of farmed and wild gilthead sea bream (Sparus aurata), being employed lightness (L^*), redness (a^*), yellowness (b^*), chroma (c^*), and total color difference (ΔE) parameters during fish ice storage. A digital color imaging system, calibrated to provide accurate CIELAB color measurements, was employed to record the visual characteristics of eyes and gills. The region of interest was automatically selected using a computer program developed in MATLAB software. L^*, b^*, and ΔE of eyes increased with storage time, while c^* decreased. The a^* parameter of fish eyes did not show clear a trend with storage time. The L^*, b^*, and ΔE of fish gills increased with storage time, but a^* and c^* decreased. Regression analysis and artificial neural networks approaches were used to correlate the eyes and gills color parameters with the time of storage and a strong correlation was found between color parameters and storage day. Gills color changes were more precise than those found for eyes in order to evaluate the fish freshness. However, the gills cover should be removed for taking the images and thus, the method is destructive and time-consuming. Therefore, the color parameters of fish eyes can be used as a green, low cost and easy method for fast and on-line assessing of fish freshness in food industry.     

Effects of Pulsed Electric Field Processing on Quality Characteristics and Microbial Inactivation of Soymilk

Effects of pulsed electric fields (PEF) on quality characteristics and microbial inactivation of soymilk were studied with different PEF parameters. PEF did not affect significantly the values of pH, “a” (an indicator of redness ranging from “?a” to “+a”, ?a?=?green, +a?=?red) and electric conductivity. The values of “L” (white if “L”?=?100, black if “L”?=?0) increased slightly, whereas values of viscosity and “b” (an indicator of yellowness ranging from “?b” to “+b”, ?b?=?blue, +b?=?yellow) decreased slightly as PEF time increased from 0 to 547 μs. Cysteine, tyrosine, phenylalanine, and serine reduced with the increase of PEF time. The relative activities of soybean lipoxygenase (SLOX) decreased with PEF time increasing from 0 to 1,036 μs. When PEF time and strength increased, the inactivation of Escherichia coli and Staphylococus aureus increased significantly (p?<?0.05), achieving a maximum of 5.20 and 3.51 log₁₀ cycles reduction at PEF time 547 μs and pulsed electric strength 40 kV/cm, respectively. The inactivation of E. coli, S. aureus, and SLOX as a function PEF time followed Weibull distribution. This study demonstrated that PEF could inactivate efficiently E. coli, S. aureus, and SLOX without affecting the quality characteristics of soymilk. Thus, this technique could be an advantageous alternative to heat treatment for pasteurization of soymilk.     

Determination of Major Sialic Acids in Dairy Products by Electrophoretic Stacking Technology with Contactless Conductivity Detection

Synergistic stacking technique by combining field-amplified sample injection with moving chemical reaction boundary was developed for the sensitive determination of two major sialic acids, N-acetylneuraminic acid (NANA) and N-glycolylneuraminic acid (NGNA) based on capillary electrophoresis with capacitively coupled contactless conductivity detection. A series of experimental parameters affecting electrophoretic separation, detection sensitivity, and hydrolysis efficiency of sialic acids were investigated. Under the optimum conditions, NANA and NGNA could be well separated from the common monosaccharides and disaccharides as well as other potential coexisting inorganic and organic anions in a running buffer of 30 mmol L^?1 NaOH–10 mmol L^?1 Na₂HPO₄/0.8 mmol L^?1 CTAB. This developed method has been applied to determine the target analytes in dairy products. In terms of its high sensitivity (LODs 1.7–2.2 ng mL^?1, namely, 5.5–7.2 nmol L^?1), good linearity (r > 0.999), acceptable recovery (93–107%), and reliability of acid hydrolysis step, this proposed method provides a simple, rapid, sensitive, and environmentally friendly alternative for the analyses of the main sialic acids in dairy products without derivatization.     

Use of a Core-Shell Column for the Development of a Green LC Method for Thiol Determination in Fresh Fruits Following Derivatization with Methyl Propiolate

A novel HPLC method has been established for the determination of thiols in fruit samples, introducing, for the first time, methyl propiolate as an advantageous precolumn derivatization reagent for cysteine (CYS), glutathione (GSH), and N-acetylcysteine (NAC). The formed derivatives were detected at 285 nm, following isocratic separation on a core-shell column (Ascentis Express C18, 50?×?2.1 mm i.d., 2.7 μm) with a mobile phase of 15 mmol L^?1 (ΝΗ₄)₂ΗPO₄/H₃PO₄ (pH?=?2.2)/methanol (92:8?v/v), containing 1 mmol L^?1 EDTA, at a flow rate of 0.2 mL min^?1. Derivatization parameters were optimized including pH and concentration of buffering medium, amount concentration of methyl propiolate, derivatization time, and temperature, by the univariate approach. Under optimal conditions, the developed analytical scheme offers a total analysis time of less than 10 min, limits of detection in the range 0.1–0.5 μmol L^?1, and satisfactory linearity up to 100 μmol L^?1 for all analytes. The method proved also to be equally selective and robust. Endogenous thiols were determined in melon, watermelon, and avocado, using the standards addition approach, after minimal sample preparation, with no use of organic solvents. The accuracy was evaluated by recovery experiments resulting in the range of 86.4–118.5 %.     

Automated Sequential Injection Method for Determination of Caffeine in Coffee Drinks

An automated sequential injection analysis spectrophotometric assay for the determination of purine alkaloids in coffee drinks was developed. The sample was treated with a carrez reagent for matrix suppression followed by filtration; subsequently, alkaloids were separated from organic acids using a short C18 monolithic column (10 × 4.6 mm). The flow rate of the separation step was 10 μL s^?1 with 10% v/v of methanol as the mobile phase. The sum of alkaloids evaluated as caffeine was detected at 274 nm. The influence of the main parameters affecting the quantification of purine alkaloids was optimized. One sample analysis lasted 15 min when aspirated in triplicate. The linear range was 1–15 mg L^?1, and the determination coefficient (r ²) was 0.9969. The limit of detection and limit of quantitation were 0.128 and 0.425 mg L^?1, respectively. The repeatability evaluated as the relative standard deviation (RSD) was 3.58% (n = 12, 10 mg L^?1). Under optimal conditions, the method was successfully applied to determine purine alkaloids in different real samples including soluble coffee, coffee from an espresso machine, and brewed coffee drinks.     

Effects of brine concentration and temperature on color of vacuum pulse osmotically dehydrated sardine sheets

The effects of brine concentration (0.15-0.27 g NaCl/g) and temperature (30-38 °C) on the color parameters (L, a, b, ΔE) of vacuum pulse osmotically dehydrated sardine sheets were investigated. The results showed that osmotic dehydration has a significant effect on color of sardine sheets. Redness (a-value) and yellowness (b-value) decreased through dehydration time while lightness (L-value) and total color difference (ΔE) increased. The decreases in redness and yellowness were lesser with increasing temperature and brine concentration while increases in lightness and ΔE were higher. These changes would be predicted by simple models as a function of the temperature, brine concentration, and dehydration time.     

Ultra high pressure homogenization of soymilk: Microbiological,physicochemical and microstructural characteristics

The effect of ultra high pressure homogenization (UHPH) at 200 and 300 MPa on soymilk was studied. A soymilk base product (BP) and ultra high temperature (UHT) treated soymilk were compared with UHPH treated soymilk. UHPH at 200 and 300 MPa reduced initial counts, spores and enterobacteria counts. Particle size analysis evidenced the intense reduction of particle size caused by UHPH, although the formation of aggregates was detected at 300 MPa. Colour differences between UHPH and BP or UHT soymilks were found. Treated soymilk (300 MPa) showed the lowest values of L¹, a¹ and b¹ coordinates. UHPH processed samples were more stable (showed less particle settling) than BP and UHT soymilks and these differences were also observed at days 30 and 60 of storage at 4 °C. Differential scanning calorimetry analysis indicated that soymilk proteins were partially denatured by 200 MPa, whereas UHPH treatment at 300 MPa showed the same extent of denaturation as UHT soymilk. Images of transmission electron microscopy showed the distribution and general characteristics of the colloidal particles and structures of UHPH, BP and UHT which were generally in accordance with the physicochemical parameters studied.     

Kinetics of salmon quality changes during thermal processing

The kinetics of reactions leading to changes in salmon quality during thermal processing were evaluated. Small samples (D 30 mm × H 6 mm) cut from pink salmon (Oncorhynchus gorbuscha) fillets were sealed in aluminum containers (internal dimension: D 35 mm × H 6 mm) and heated in an oil bath at 100, 111.1, 121.1, and 131.1 °C for different time intervals up to 180, 150, 120, 90 min, respectively. A fractional conversion model was used to describe the increase in cook loss during heating; and a quadratic relationship to correlate cook loss with area shrinkage ratio. Color changes (CIE L¹, b¹ and ΔE) involved whitening and browning phases. In the browning phase, the changes of CIE L¹, b¹ and ΔE followed a zero-order reaction. The progressive change of texture with time as indicated by shear force during heating went through four different phases, and the second (rapid tenderizing) and third phases (slow toughening) were modeled using a first-order reaction kinetic model. The decay of thiamin during heating was modeled with two different relationships: a second-order reaction in which the temperature dependence of the rate constant followed an Arrhenius relationship; and a Weibull-log logistic model recently proposed.     

Tannic acid modulated the wall compactness of cinnamaldehyde-loaded microcapsules and enhanced inhibitory effect on Aspergillus brasiliensis

The evaluation of antifungal properties in cinnamaldehyde (CA)-loaded microcapsules is significant to clarify potential food applications in various food matrices and systems. The impact of tannic acid (TA) crosslinking on the release and the antifungal properties of CA microcapsules was investigated based on gelatin/gum Acacia complex coacervates. The inhibition zone diameter of microencapsulated CA against Aspergillus brasiliensis was dependent on the TA addition and retained 26.1 ± 0.1 mm after 180-day storage at 25 °C. Specifically, TA enhanced hydrogen bond interactions between the microcapsule wall materials and favoured a sustained release of CA during the incubation with Aspergillus brasiliensis. Meanwhile, confocal laser scanning microscopic observation revealed that the microstructure of multinuclear microcapsules was more compact and intact under the crosslinking of 0.4% TA. The comparation of microscopic morphology and membrane potential of Aspergillus brasiliensis exerted a synergistic antifungal effect between CA and TA crosslinked microcapsules.     

Sensitive and Selective Determination of Riboflavin in Milk and Soymilk Powder by Multi-walled Carbon Nanotubes and Ionic Liquid [BMPi]PF<Subscript>6</Subscript> Modified Electrode

A novel electrochemical method to detect riboflavin was proposed using a multi-walled carbon nanotubes and ionic liquid N-butyl-N-methyl-piperidinium hexafluorophosphate composite film modified glassy carbon electrode (MWNTs-[BMPi]PF₆/GCE). A well-defined CV behavior with a pair of sensitive and well-shaped redox peak was observed, and the response value of riboflavin at MWNTs-[BMPi]PF₆/GCE is much higher than that at MWNTs/GCE in 0.1 mol L^?1 HAc-NaAc buffer solution (pH 4.5). The electrochemical approach based on a sensitive DPV analytical signal exhibits an excellent analytical performance with a wide linear range (2.6 × 10^?8 to 1.3 × 10^?6 mol L^?1) and low detection limit (4.7 × 10^?9 mol L^?1) for the riboflavin. Moreover, the proposed method possesses a potential practical application value and can be employed for the quantitative analysis of trace riboflavin with a recovery of 95.8–102.4 % in food samples such as milk and soymilk powder.