Determination of fluorine in milk samples via calcium-monofluoride by electrothermal molecular absorption spectrometry

The determination of fluorine in milk samples via the molecular absorption of calcium mono-fluoride (CaF) was performed using a HR-CS-ETAAS. For this purpose, calcium was pipetted to graphite furnace together with samples. The amount of Ca and the graphite furnace program were optimised. Fluorine was determined in pyrolytically coated platforms at 606.440 nm applying a pyrolysis temperature of 700 °C and a molecule forming temperature of 2250 °C. Finally, applying standard addition technique, F contents of several milk samples were determined. The results obtained by linear calibration and standard addition techniques were significantly different which can be attributed to non-spectral interferences in milk due to matrix concomitants. Therefore, in order to tolerate the errors, the F contents of several milk samples were determined applying standard addition technique. However, since the ingredients of milk samples change for different kinds, the F in each sample was determined from its own standard addition curve. The range of F content for the milk samples were 0.027–0.543 μg mL⁻¹. The limit of detection and characteristic mass of the method were 0.26 and 0.13 ng of F, respectively.     

Tungsten permanent chemical modifier with co-injection of Pd(NO3)2 + Mg(NO3)2 for direct determination of Pb in vinegar by graphite furnace atomic absorption spectrometry

A tungsten carbide coating on the integrated platform of a transversely heated graphite atomizer (THGA^®) used together with Pd(NO₃)₂ + Mg(NO₃)₂ as modifier is proposed for the direct determination of lead in vinegar by graphite furnace atomic absorption spectrometry. The optimized heating program (temperature, ramp time, hold time) of atomizer involved drying stage (110 °C, 5 s, 30 s; 130 °C, 5 s, 30 s), pyrolysis stage (1000 °C, 15 s, 30 s), atomization stage (1800 °C, 0 s, 5 s) and clean-out stage (2450 °C, 1 s, 3 s). For 10 μL of vinegar delivered into the atomizer and calibration using working standard solutions (2.5–20.0 μg L⁻¹ Pb) in 0.2% (v/v) HNO₃, analytical curve with good linear correlation (r = 0.9992) was established. The characteristic mass was 40 pg Pb and the lifetime of the tube was around 730 firings. The limit of detection (LOD) was 0.4 μg L⁻¹ and the relative standard deviations (n = 12) were typically <8% for a sample containing 25 μg L⁻¹ Pb. Accuracy of the proposed method was checked after direct analysis of 23 vinegar samples. A paired t-test showed that results were in agreement at 95% confidence level with those obtained for acid-digested vinegar samples. The Pb levels varied from 2.8 to 32.4 μg L⁻¹. Accuracy was also checked by means of addition/recovery tests and recovered values varied from 90% to 110%. Additionally, two certified reference materials were analyzed and results were in agreement with certified values at a 95% confidence level.     

Steady-shear flow of semidilute guar gum solutions with sucrose, glucose and sodium chloride at different temperatures

Steady-shear flow curves of aqueous solutions of guar gum at 0.22% at different temperatures (5-65 °C), guar gum (0.22%) with sugars (sucrose or glucose) at different sugar/water ratio (0.10, 0.20 and 0.40) at 5 °C, guar-sugar (at 0.40 sugar/water ratio) at different temperatures (5-65 °C) and guar gum and guar-sucrose (0.40 sucrose/water ratio) with NaCl (1%) at 5 °C, were determined using a controlled-stress rheometer over a wide range of shear rate (1-1000 s⁻¹). Apparent viscosity increased with decreasing temperature and increasing sugar content independent of sugar type. Synergic effect on apparent viscosity due to sugar addition was found and was correlated with sugar content. Salt addition decreased slightly the apparent viscosity and increased the shear-thinning behaviour of the guar gum solution. Steady-shear flow curves were satisfactorily described by the Cross model. Semi-empirical correlations of Cross model parameters with sugar content and temperature were obtained.     

Effects of temperature on Agrocybe chaxingu quality stored in modified atmosphere packages with silicon gum film windows

The effects of three storage temperatures (1, 3, and 5 °C) were determined on the quality of the edible mushroom Agrocybe chaxingu stored in modified atmosphere packages (MAP) with and without (control) silicon gum film windows. Results showed that the storage temperature had clear effects on headspace gas concentrations of O₂, CO₂ and ethylene, sensory characteristics, respiration rate, ascorbic acid content, soluble solid content and electrolyte leakage. The higher storage temperature (5 °C) resulted in more rapid changes in the different quality parameters for the stored mushroom except in the case of storage at 1 °C where chilling injury occurred. The MAP with silicon gum film windows at 3 °C provided the best atmosphere for mushroom A. chaxingu as shown by a fact that the MAP packs with windows at 3 °C had better quality than the control.     

Study of spray drying of the Aloe vera mucilage (Aloe vera barbadensis Miller) as a function of its rheological properties

Spray Drying (SD) was used to obtain Aloe vera powder from fresh plants. The powder was reconstituted in an aqueous medium and its rheological properties, particle size distribution (PSD), thermal properties (differential scanning calorimetry, DSC), and morphology (scanning electron microscopy, SEM) were evaluated in order to find an alternative to natural gum to be used in the food industry. Rheological measurements were conducted at 25 °C in aqueous concentrations of 3 g/100 mL and 6 g/100 mL. A 2³ factorial design was used with three central points to evaluate yield, efficiency and the rheological properties of reconstituted powders, results were compared with a liophilized (FD) sample of A. vera mucilage. Experimental results showed that the shear viscosity decreased with the increase of the inlet air temperature and the speed of atomization, and it increased with increasing feed flow in SD. Additionally, most powders obtained in all treatments have an average particle diameter of ∼10 μm with a modal distribution (PSD). The best conditions of SD in order to obtain a good thickening agent were: 150 °C inlet temperature, 1.5 L/h feed rate and atomization speed of 275,000 rpm, and with rheological properties very close to those of the FD sample.     

Quantitative analysis of volatiles in transesterified coconut oil by headspace-solid-phase microextraction-gas chromatography–mass spectrometry

A simple and fast headspace-solid-phase microextraction (HS-SPME) method coupled with gas chromatography–mass spectrometry (GC–MS) was developed for the analysis of volatile compounds in transesterified coconut oil by applying solvent dilution. Solvent dilution conditions (solvent type and solvent amount) and HS-SPME sampling parameters (adsorption temperature and time) were optimised through monitoring the adsorption result of the selected volatiles (octanoic acid esters) in transesterified coconut oil samples. The incubation of methanol (800 μl)-diluted oil (200 μl) sample at 60 °C for 30 min led to the best result. The method was further validated by determining the calibration linear range, correlation coefficient (R²), accuracy, precision, limit of detection and limit of quantification through spiking standards into the blank matrix consisting of coconut oil and methanol. This method may also be applicable for detection and determination of volatile compounds in other transesterified oil samples.     

Temperature-dependent quality characteristics of pre-dehydrated cookies: Structure,browning, texture, in vitro starch digestibility,and the effect on blood glucose levels in mice

The purpose of this study was to elucidate the physical and biochemical properties of pre-dehydrated cookies baked at various temperatures. Cookie dough was vacuum-dried, and then baked at 120–180 °C for 18 min. All samples showed lower spread ratio than non-dehydrated cookie baked at 180 °C (control). Browning of the samples baked at 180 °C and 160 °C was higher than that of the control. In contrast, little browning was observed in the sample baked at 120 °C. The fracture force of samples baked at 140 °C and 120 °C agreed well with the control. From these results, the sample baked at 140 °C was employed for subsequent studies. In vitro starch digestibility suggested that the sample baked at 140 °C had higher slowly digestible starch content than the control. From postprandial blood glucose levels in mice, it was found that the sample significantly reduced the blood glucose peak observed at 30 min post-administration.     

Surface tension and refractive index of guar and tragacanth gums aqueous dispersions at different polymer concentrations,polymer ratios and temperatures

Surface tension and refractive index of guar gum (GG) (up to 0.97% w/w) and tragacanth gum (TG) (up to 1.41% w/w) aqueous dispersions were determined for systems with only one and both gums (mixtures) (up to 1.25% w/w). Experimental determinations were carried out from 5 to 30 °C for surface tension and from 10 °C to 40 °C for refractive index. For mixtures, the effect of polymer ratio (1:3, 1:1 and 3:1) was analyzed at different total gum concentration and temperature. GG showed lower surface activity and refractive index than TG at the same experimental condition. Models for the estimation of surface tension and refractive index as function of gum concentration and temperature were proposed and satisfactorily tested. Both physical and optical properties, in the tested gum concentration range, allowed the determination of different behaviour for both gums because of a critical aggregation concentration for TG dispersions while this phenomenon was not observed for GG.     

The determination of total germanium in real food samples including Chinese herbal remedies using graphite furnace atomic absorption spectroscopy

This paper outlines the development of a method for the determination of total germanium in foodstuffs utilising graphite furnace atomic absorption. It was found that by varying the drying times interferences could be minimised. Metals including calcium, cobalt, copper, magnesium, nickel, lead and zinc were tested for potential interferences. It was found experimentally that none of the listed metals interfered with this method. The optimal furnace conditions were determined to be; drying for 80 s (85 °C for 30 s, 95 °C for 40 s and 120 °C for 10 s), ashing at 700 °C for 8 s and atomisation at 2600 °C for 3.3 s followed by a tube clean for 2 s at 2800 °C and a lamp current of 5 mA for analysis at 265.2 nm. The method was found to have a linear range of 3.3–125 μg/l with a limit of detection and a characteristic mass of 0.051 and 0.053 ng germanium, respectively. The samples chosen for analysis include vegetables, fruit juices, Chinese herbal remedies and over the counter formulations. It was found that the aloe vera tablet, ginseng tablet and ginger tablet contained 20.83, 5.48 and 9.96 μg/g. Other foods found to contain germanium were potato, garlic and carrot, having 1.85, 2.79 and 0.60 μg/g of germanium. The food found to contain the highest concentration of germanium was Soya mince having 9.39 μg/g.     

Effect of edible coatings on the quality of frozen fish fillets

The objective of this study was to determine the changes in the quality of coated trout fillets after coating with edible materials. Fillets were coated and stored at −18 °C for a period lasting up to 7 months. Coating materials were applied in three different stages (first, second, and last coatings). The coated fillets were fried and analyzed for oil absorption and moisture content throughout the storage period. Sensorial attributes and the physical-biochemical changes were also measured before the frying process in each month. It was observed that it is more advantageous to use gluten as the first coating, xanthan gum as the second coating, and wheat (W) and corn (C) flours in the ratio of 1:1 or 2:1 as the last coating. In terms of the fillet quality, the following results were obtained in the analyses conducted before frying. The lowest pH found was 6.25 in zein-containing samples and 6.30 in guar-containing samples. The effects of the last coatings on pH were unimportant (P > 0.05). The lowest thiobarbituric acid levels found were 2.07 mg kg in the fillets coated with casein mixture, 2.44 mg kg in the fillets coated with xanthan gum, and 2.25 mg kg in the fillets coated with W:C flour mixture in the ratio of 2:1. The lowest total volatile basic nitrogen levels found were18.06 mg 100 g in the fillets coated with casein mixture, 18.62 mg 100 g in the fillets coated with xanthan gum, and 18.47 mg 100 g in the fillets coated with W:C flour mixture at 1:1 ratio. In the sensorial analysis, the coated samples were much more preferred than those not coated. As a result of the effects of all the materials, the coating layers on the meat surface provided more resistance against mass transfer during storage.     

Osmotic dehydrofreezing of strawberries: Polyphenolic content, volatile profile and consumer acceptance

We evaluated dehydrofreezing in strawberries in terms of retention of healthy compounds (i.e. polyphenolics) and sensory qualities for direct consumption in substitution of fresh fruit. Different osmodehydration (OD at 30 °C and 5 °C), vacuum osmodehydration (VOD at 30 °C) and immersion chilling freezing (ICF) processes were applied in sucrose syrup. Samples were analyzed for dry matter, soluble solids, pH, titratable acidity, mass transfers, polyphenolic content by HPLC-DAD/MSD, volatile profile by SPME-GC/MSD and consumer acceptance. The results of sensory evaluation, in particular, confirmed the cryoprotective effects of osmotic processes of fruits with respect to untreated frozen control samples. The OD samples at 5 °C presented a water loss to solid gain ratio comparable to OD at 30 °C and VOD samples. Moreover, while osmo-dehydrofreezing at relatively high temperatures caused a slight depletion of phenolic compounds, the samples osmodehydrated at 5 °C showed higher polyphenolic retention. Data on aromatic compounds showed that some compounds increased (e.g. ethanol and acetaldehyde), while others did not appear to be affected by the pre-treatments.     

Kinetics of oil uptake during frying of potato slices:: Effect of pre-treatments

Oil uptake in fresh, blanched and, blanched and dried potato slices was studied during frying. Potato slices blanched in hot water (85 °C, 3.5 min) and potato slices blanched (85 °C, 3.5 min) and then dried until to a moisture content of ∼60 g/100 g (wet basis) were deep fried in sunflower oil at 120, 150 and 180 °C. A control treatment consisted of unblanched potato slices without the pre-drying treatment (fresh samples). It was studied applying two empirical kinetic models in order to fit the oil uptake during frying: (i) a first order model; (ii) a proposed model, with a linear time behavior for short times, while time independent for long times. Oil uptake was high even for short frying times at the different temperatures tested suggesting that oil wetting is an important mechanism of oil uptake during frying. For control slices, oil uptake increased approximately by 32% as the frying temperature decreased from 180 to 120 °C at moisture contents ?1 g water/g dry solid. No apparent effect of frying temperature in oil uptake was observed at moisture contents ?0.5 g water/g dry solid in fried slices previously blanched and dried. The two kinetic models studied fitted properly the values of oil uptake during frying, with similar correlation coefficient r².     

Histamine production by Enterobacter aerogenes in tuna dumpling stuffing at various storage temperatures

Enterobacter aerogenes was studied for its growth, and promoting the formation of total volatile base nitrogen (TVBN) and histamine in tuna dumpling stuffing stored at various temperatures from −20 °C to 37 °C. The bacterial number rapidly increased in low (2.0 log CFU/g) or high (5.0 log CFU/g) inoculated concentrations at temperature above 15 °C and reached the highest bacterial count at 37 °C. In addition, the low spiked sample stored at 37 °C for 12 h and the high spiked sample stored at 25 and 37 °C for 12 h, formed histamine at above 50 mg/100 g of the potential hazard level in most illness cases. However, bacterial growth was controlled by cold storage of the samples at 4 °C or below, but histamine formation was stopped only by frozen storage. Once the frozen stuffing samples were thawed and stored at 25 °C, histamine started to accumulate rapidly.     

Biogenic amine changes in barramundi (Lates calcarifer) slices stored at 0 °C and 4 °C

The biogenic amines formation in barramundi (Lates calcarifer) slices kept for 15 days at 0 °C and 4 °C were investigated using nine biogenic amines, total plate counts and biogenic amines formers. Significant differences in biogenic amines concentrations of barramundi slices stored at 4 °C and at 0 °C after 3 days of storage were observed. All amines, except tryptamine, 2-phenylethylamine, tyramine and agmatine in the slices increased with time during storage at both temperatures. At the end of the storage period, histamine concentrations were 82 mg/kg and 275 mg/kg for samples kept at 0 °C and 4 °C, respectively. At day 15, the total plate count was approximately 8.6 log CFU/g for sample kept at 0 °C and 9.7 log CFU/g for samples kept at 4 °C. Histamine-forming bacteria (HFB) in all samples ranged from 5.4 to 6.1 log CFU/g at 0 °C and 4 °C, respectively. The observed shelf-life of barramundi slices were 6–9 days.     

Effect of whey and pea protein blends on the rheological and sensory properties of protein-based systems flavoured with cocoa

Whey and pea protein combined in different proportions (100W:0P, 75W:25P, 50W:50P, 25W:75P, 0W:100P) were used to prepare protein-based systems flavoured with cocoa and containing κ-carrageenan or κ-carrageenan/xanthan gum as thickeners. Steady and dynamic shear rheological properties of samples were measured at 10 °C and sensory differences were evaluated. Protein-based systems exhibited a shear-thinning flow behaviour that was fitted to the simplified Carreau model. Samples showed different viscoelastic properties, ranging from fluid-like to weak gel behaviour. For both types of system (with and without xanthan gum) viscosity, pseudoplasticity and elasticity rose on increasing the pea protein proportion in the blend. The sample with only whey protein obeyed the Cox-Merz rule, while in the rest of the samples complex viscosity was higher than apparent viscosity. Regarding sensory properties, the protein blend ratio mainly affected sample thickness, which rose as pea protein proportion increased. However, at the same time, the chocolate flavour and sweetness decreased and the off-flavour increased.     

Pyrolytic formation of polyaromatic hydrocarbons from steroid hormones

Four steroid hormones, namely androsterone, cholesterol, estrone and estradiol, have been pyrolysed at 300, 400 and 500 °C and the pyrolysates from these have been analysed by GC–MS. The results indicate that these formed different products under the pyrolysis and most of them evolved into polycyclic aromatic hydrocarbons during their residence in the pyrolysis chamber at high temperatures. The products from the pyrolysates, at all temperatures, were analysed for similarities and differences using multivariate data analysis. The products possessed some similarities on pyrolysis at 300 °C but were entirely different when pyrolysed at 500 °C. Androsterone and cholesterol formed a higher percentage of substituted PAH than did estrone and estradiol. These compounds included carcinogens, such as phenanthrene, methylphenanthrene, fluorene and its derivatives. The side chain of cholesterol had no effect on the products formed, while the presence of the aromatic ring in estrone and estradiol led to a higher percentage of phenol and its derivatives in the pyrolysates. Furthermore, estrone was subjected to flash pyrolysis and the products formed were compared with those which resulted from the long time pyrolysis: flash pyrolysis produced small amounts of PAH.     

Temperature and moisture dependent dielectric properties of legume flour associated with dielectric heating

Dielectric properties data are important in developing thermal treatments using radio frequency (RF) and microwave (MW) energy and are essential in estimating heating uniformity in electromagnetic fields. Dielectric properties of flour samples from four legumes (chickpea, green pea, lentil, and soybean) at four different moisture contents were measured with an open-ended coaxial probe and impedance analyzer at frequencies of 10-1800 MHz and temperatures of 20-90 °C. The dielectric constant and loss factor of the legume samples decreased with increasing frequency but increased with increasing temperature and moisture content. At low frequencies and high temperatures and moisture contents, negative linear correlations were observed between the loss factor and frequency on a log-log plot, which was mainly caused by the ionic conductance. At 1800 MHz, the dielectric properties data could be used to estimate the legume sample density judging from high linear correlations. Loss factors for the four legume samples were similar at 27 MHz, 20 °C and low moisture contents (e.g. <15 g/100 g). At the highest moisture content (e.g. 20 g/100 g) soybean had the highest loss factor at 27 MHz and 20 °C, followed by lentil, green pea, and chickpea. The difference in loss factor among the four legumes did not show clear patterns at 915 MHz. Deep penetration depths at 27 MHz could help in developing large-scale industrial RF treatments for postharvest insect control or other applications that require bulk heating in legumes with acceptable heating uniformity and throughputs.     

Surface coating of l-glutamine solid microparticles for enteric delivery

The objective of this work was to produce enteric delivery systems to minimize gastric degradation of bioactives, using l-glutamine microparticles as a model, by surface-coating with a layer of enteric polymer (hydroxypropyl methylcellulose phthalate). Suspensions of solid glutamine microparticles in a methanol solution with enteric polymer and different concentrations of plasticizer (glycerol or triethyl citrate) and medium chain fatty acids (MCFA) were spray-dried at 55 °C. Spray-dried powders were characterized for in vitro release kinetics in simulated gastric (pH 1.2) and intestinal (pH 6.8) fluids at 37 °C. At a MCFA:polymer mass ratio of 2:1, formulations with plasticizer used at 30% of polymer mass resulted in <30% glutamine release after 2 h and <40% after 4 h at pH 1.2. At pH 6.8, complete release of glutamine was observed for most samples after 4 h. Our work demonstrated a simple approach for enteric delivery of food and pharmaceutical compounds.     

Effects of heat treatment and high pressure on the subsequent lactosylation of β-lactoglobulin

The effects of a previous heat treatment (60 and 80 °C, 30 min) and high-pressure (400 MPa, 25 and 60 °C, 1 h) on the subsequent lactosylation of β-lactoglobulin (50 °C, 44% RH, 120 h) were investigated. A control of native β-lactoglobulin was also stored under the afore-mentioned conditions. The structural changes caused during these treatments were studied by the loss of amino groups, SE-HPLC and native-PAGE and the degree of lactosylation was evaluated by means of furosine determination. After thermal and high-pressure treatments, the greatest structural changes were observed in the case of samples of β-lactoglobulin treated at 80 °C, 30 min and 400 MPa, 60 °C, 1 h. During storage, the highest lactosylation degree was found in native β-lactoglobulin. In heat-treated samples, the increase of lactosylated lysines was lower than the decrease of free amino groups, probably due to the cross-linking reactions. A similar decrease of free amino groups of β-lactoglobulin was observed immediately after 400 MPa, 60 °C, 1 h and 80 °C, 30 min; however, the level of lactosylation during the storage period was lower in the former, indicating different types of conformational changes in the two treatments. These differences lead to a higher effectiveness of heat-treatment than high-pressure in denaturating β-lactoglobulin for subsequent lactosylation under the tested conditions (of temperature, time, high-pressure and storage).     

The influence of different stabilizers and salt addition on the stability of model emulsions containing olive or sesame oil

Stabilizers are widely used in low-fat emulsion production. However, food industry pays attention to ingredients, such as resistant starch (RS) that also present substantial benefits to human health. Low-fat model emulsions of either olive or sesame oil that also contained xanthan gum (XG), whey protein concentrate (WPC), and undigested (resistant) starch (RS) were produced and stored at 5 °C. Salt was added in selected samples. A multiple light scattering technique was applied for investigating destabilization phenomena. Microscopic observations and droplet size measurements took place. Rheological properties performing a heating–cooling cycle experiment (5–25–5 °C) were measured. Olive oil emulsions presented the greatest stability and the lowest droplet size. RS plays the role of solid particle stabilizer, mainly entrapped in the matrix of the continuous phase. By salt addition stability was significantly improved, whereas droplet size was decreased. Those samples had a more pronounced elastic character and significantly greater viscosity values than their counterparts without salt.