Effect of addition of cryoprotectants on the mechanical properties, colour and sensory attributes of fresh and frozen/thawed mashed potatoes

Cryoprotectants such as hydrocolloids (amidated low-methoxyl (ALM) and high methoxyl (HM) pectins), kappa- and iota-carrageenans (k-C and i-C), xanthan gum (XG)) and dairy proteins [whey protein (WP), sodium caseinate (SC)] were added to mashed potatoes to investigate ways of improving the effects of freezing and thawing. It was found that each hydrocolloid and protein, depending on concentration, affected the mechanical properties [instrumental textural profile analysis (ITPA), cone penetration (CP) test], the total colour difference (ΔE*) with respect to fresh control (FC) and the sensory attributes of fresh (F) and frozen/thawed (F/T) mashed potatoes in a different way. In the F/T samples, adding 5 and 8 g kg⁻¹ ALM, 3, 5 and 8 g kg⁻¹ k-C, 1.5, 3, 5 and 8 g kg⁻¹ i-C and 1.5, 5 and 15 g kg⁻¹ WP significantly increased ITPA consistency. Also, adding 2.5 and 5 g kg⁻¹ XG significantly increased ITPA consistency of the F/T product. In both F and F/T samples, k-C provided the highest ITPA consistency and also high CP average force evidencing a stronger synergistic effect in κ-C/denatured milk protein systems, although the excessive thickening and stickiness provided was judged undesirable by the panellists. Adding 8 g kg⁻¹ HM pectin had a disruptive effect on the mashed potatoes and decreased both ITPA consistency and CP average force. In all cases, freezing and thawing reinforced the gel structure of the products as compared to F and FC counterparts. The ΔE* values were higher in F samples containing ALM and HM pectins. Dairy proteins affected the taste and odour of the mashed potatoes and were judged unacceptable in the sensory analysis. Samples containing 0.5 and 1.5 g kg⁻¹ added XG were preferred organoleptically due to the creamy mouthfeel it produced. ITPA consistency correlated well with sensory texture attributes.     

Rheological,thermal and sensory properties of whey protein concentrate/pectin‐fortified mashed potatoes made from dehydrated flakes

The effect of different amounts of whey protein concentrate (50–150 g kg^?1), low and high methoxyl pectin (5–15 g kg^?1) on the rheological, thermal, structural properties and sensory quality of mashed potatoes prepared from dried mashed potatoes flakes was investigated. The response surface technique was used to analyse the effects of whey protein concentrate and pectin simultaneously on the consistency index, flow behaviour index, apparent viscosity and Casson plastic viscosity. Both whey protein concentrate and pectin decreased the consistency of the mashed potatoes weakening its structure in all concentrations assayed. Results suggest that whey protein concentrate interacts with high methoxyl pectin through non‐covalent interactions. Based on the sensory evaluation results, up to 100 g kg^?1 whey protein concentrate with 15 g kg^?1 of low methoxyl pectin and 15 g kg^?1 of high methxyl pectin could be incorporated to dried mashed potatoes flakes without losing significantly the sensory quality of the product.     

Oscillatory Rheological Properties of Fresh and Frozen/Thawed Mashed Potatoes as Modified by Different Cryoprotectants

Five different hydrocolloids (amidated low-methoxyl [ALM] and high-methoxyl [HM] pectins, kappa- and iota-carrageenans [κ-C and ι-C], and xanthan gum [XG]) and two dairy proteins (whey protein [WP] and sodium caseinate [SC]) were added at five different concentrations to fresh (F) and frozen/thawed (F/T) mashed potatoes to investigate ways of improving the effects of freezing and thawing. It was found that each hydrocolloid and protein, depending on the concentration, affected the viscoelastic properties of F and F/T mashed potatoes in a different way. Color, drip loss (DL), total soluble solid (TSS) content, and overall acceptability (OA) were also determined. All systems showed weak gel behavior, although the F samples exhibited higher values of G′ and G″ as compared to F/T counterparts. However, the effects were highly dependent on the type and level of biopolymer added. F and F/T mashed potatoes with added WP presented higher values of G′ and G″, and values were lowest in both when XG was added. After freezing and thawing, the addition of ingredients (3 to 5 g kg⁻¹ ALM and HM, 3 to 8 g kg⁻¹ κ-C, and 1.5 g kg⁻¹ WP) had the effect of thickening the mash and thus improving freeze/thaw stability. Processed samples were darker than F samples, although this darkening was not detected by the panelists. Color was affected less by κ-C or ι-C than by the other ingredients added. ALM pectin, κ-C and ι-C, XG, and SC all exhibited water-holding capability, whereas HM and WP did not. The product yielded by XG was softer than controls without added cryoprotectants in both F and F/T samples, but samples containing 0.5 and 1.5 g kg⁻¹ added XG were judged more acceptable than the F control because of the creamy mouth-feel it produced.     

Polycyclic aromatic hydrocarbons (PAHs) in traditional and industrial smoked beef and pork ham from Serbia

Smoked beef and pork ham samples were analysed during process of smoking (after packing and storing) for the presence of the 16 EU priority PAHs via Fast GC/HRMS method. This study showed that there are differences in PAH contents between final smoked beef ham samples from traditional smokehouse (TS) (3.9 μg kg⁻¹) and industrial smokehouse (IS), (1.9 μg kg⁻¹). Also there is a difference in PAH contents in final smoked pork ham samples (4.9 μg kg⁻¹, TS; 4.2 μg kg⁻¹, IS). In beef and pork ham samples from the same smokehouse different PAH contents were observed during smoking. The highest content of examined PAHs in all beef and pork ham samples during smoking showed benzo[c]fluorene (BcL) (beef ham: from 0.3 μg kg⁻¹ to 1.5 μg kg⁻¹; pork ham: from 0.2 μg kg⁻¹ to 2.1 μg kg⁻¹).The maximum level for benzo[a]pyrene (BaP) of 5 μg kg⁻¹ in smoked meat products was not exceeded in any samples. Correlation statistic analysis (P < 0.05) of obtained contents from samples both from TS and IS showed that BaP is a good marker both for 16 EU priority PAHs and 12 IARC probably and possibly carcinogenic PAHs (IS: R _BaP/Σ16PAHs = 0.95, R _BaP/Σ12PAHs = 0.96; TS: R _BaP/Σ16PAHs = 0.71, R _BaP/Σ12PAHs = 0.88).     

Enhancement of freezing stability in mashed potatoes by the incorporation of kappa‐carrageenan and xanthan gum blends

BACKGROUND: To ameliorate the detrimental effects of freezing and thawing, blends of κ‐carrageenan (κ‐C) and xanthan gum (XG) were added to frozen/thawed mashed potatoes (F/TM potatoes). Product was tested by textural and rheological measurements, other quality parameters and sensory analyses. The effects of variation in levels of κ‐C (1.5–4.5 g kg^?1) and XG (0.5–2.5 g kg^?1) concentrations were studied. RESULTS: Instrumental measurements and sensory analyses indicated that 4.5 g kg^?1κ‐C and 2.5 g kg^?1 XG provided better thickening. κ‐C provided the appropriate texture, while XG imparted creaminess to the product, which could be associated with an increase in the amount of XG–water interactions. Addition of κ‐C had a major impact on textural properties, gel strength and viscoelastic behaviour, whereas XG influenced steady properties, colour, water‐holding capacity (WHC) and overall acceptability (OA). CONCLUSION: The OA of F/TM potatoes was mostly improved by addition of cryoprotectant blends, which is ascribed to improvement of F/TM potatoes texture by retarding starch retrogradation, increasing WHC, and enhancing the principal characteristics determining consumer acceptance. Creaminess was the most crucial factor for OA of the products. Addition of both polysaccharides at a low concentration (each cryoprotectant at 1.5 g kg^?1) is recommended. Copyright © 2009 Society of Chemical Industry     

Square-Wave Adsorptive Stripping Voltammetry for Trace Determination of Dimoxystrobin and Azoxystrobin in Potatoes and Grapes

Square-wave voltammetry was used for trace determination of azoxystrobin and dimoxystrobin in potatoes, grapes, and grape juice. Experimental conditions have been optimized to achieve simultaneous determination of these analytes using the hanging mercury drop electrode. Supporting electrolyte was HCl 0.1 mol L⁻¹, and other optimized conditions were deposition potential (−300 mV), deposition time (30 s), amplitude (150 mV), frequency (150 Hz), and step height (2 mV). Azoxystrobin and dimoxystrobin redissolution peaks presented their maxima, respectively, at −928 mV and around −650 mV. Linear and homoscedastic analytical responses (r ² > 0.99) have been observed. Limits of quantification as low as 119 μg L⁻¹ (in grape juice) and 45 μg kg⁻¹ (in potatoes and grapes) were found. A previous solid-phase extraction was necessary to eliminate interferences from potato and grape samples. For grape juice, no sample treatment was required. Satisfactory recoveries (from 72.3% to 96.7% for dimoxystrobin and from 81.7% to 102.3% for azoxystrobin) were found. Interferences from other strobilurins (piraclostrobin and picoxystrobin) were evaluated.     

Determination of Melamine in Liquid Milk and Milk Powder by Titania-Based Ligand-Exchange Hydrophilic Interaction Liquid Chromatography

A simple and rapid high-performance liquid chromatography (HPLC) procedure for the analysis of melamine in liquid milk and milk powder has been developed. Decrease of acetonitrile percentage and phosphate buffer concentration in mobile phase, and lowering of buffer pH and column temperature would benefit the retention of melamine on titania. Taking advantage of the ligand-exchange and hydrophilic interaction mixed retention mode on bare titania column, neither complex pretreatment nor ion-pair reagent was required. The whole analysis for one sample including sample pretreatment and HPLC analysis could be accomplished within 30 min. The method presented good linearity (R ² = 0.9998) in a wide range of 0.02–10 μg mL⁻¹. The limit of detection (3σ) and limit of quantification (10σ) of the method were 6 and 20 μg L⁻¹, respectively, which were equivalent to 15 and 50 μg kg⁻¹ melamine in liquid milk, 60 and 200 μg kg⁻¹ melamine in milk powder, respectively. Such sensitivity could be compared with those obtained by HPLC with solid-phase extraction or HPLC coupled with tandem mass spectrometry and was adequate for the screening of melamine in tainted dairy products. The repeatability (RSDs) of the retention times and peak areas of 11 replicate detections of 1.0 μg mL⁻¹ melamine were 0.32% and 2.5%, respectively. The intermediate precision on three consecutive days (RSDs, n = 6) of the retention times and peak areas were 1.1% and 2.3%, respectively. The recovery of spiked melamine in dairy samples ranged from 95.2% to 105%. The simplicity, sensitivity and rapidity of the proposed method make it an effective alternative detecting technique for melamine.     

Co-production of Lactic Acid and <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> Cells from Whey Permeate with Nutrient Supplements

Lactic acid and cell production from whey permeate by Lactobacillus rhamnosus with different nutrient supplements were investigated in this study. Yeast extract was identified as the most effective nutrient affecting lactic acid production. Increase in inoculum size from 0.05% to 1% (v/v) resulted in a substantial increase in lactic acid productivity from 0.66 to 0.83 g L⁻¹ h⁻¹ (P < 0.001). The optimal temperature for lactic acid production was 37 °C, while the highest cell production was obtained at 42 °C. When whey permeate and yeast extract concentrations were 6.8% (w/v) and 3 g L⁻¹, respectively, lactic acid productivity reached 0.85 g L⁻¹ h⁻¹ after 48-h cultivation, which is 3.40 times of those without nutrient supplements.     

Correlation between sensory and chemical markers in the evaluation of Brazil nut oxidative shelf-life

Sensory analysis is one of the most suitable processes for measuring oxidative damage and determining the shelf-life of nuts, but it is an expensive and time-consuming methodology. Thus, our objective was to correlate sensory data and chemical markers obtained during the accelerated oxidation of Brazil nuts and to determine the chemical parameters values associated with the sensory shelf-life of the nuts as established by the consumers. Brazil nuts were kept at 80 °C for 21 days. At intervals of 2 days, the oxidized odor of the samples was analyzed by nine trained panelists using a discriminative scale, and the oil was extracted to quantify the chemical parameters. A high (r > 0.95) and significant correlation (p < 0.05) was observed between the sensory data and the hydroperoxide concentration (PV), para-anisidine value (pAV), hexanal content, and α- and γ-tocopherol concentrations. When compared with fresh samples, sensory identification of oxidized odor occurred on the 4th day, noticeably earlier than changes in chemical markers (12th day). Consumers rejected the nuts after 12 days of storage, which corresponded to PV = 18.8 meq kg⁻¹ oil, pAV = 7.68, hexanal = 48.95 μmol 100 g⁻¹ oil, α-tocopherol = 15.01 mg kg⁻¹ oil, and γ + β-tocopherol = 73.88 mg kg⁻¹ oil. Our study suggests that simple spectrometric methods, such as PV and pAV, can be used to estimate the oxidative shelf-life of nuts based on sensory analysis.     

On-line Solid-Phase Extraction Coupled to Liquid Chromatography–Ion Trap Tandem Mass Spectrometry for Determination of Penicillins in Catfish

A highly selective method was developed for the simultaneous determination of eight penicillins in catfish using automated on-line solid-phase extraction coupled to liquid chromatography–tandem mass spectrometry (XLC–MS/MS). The type of cartridge, equilibration sample volume, volume of solvent to carry the sample into the cartridge, and elution times were studied in order to optimize the XLC operating conditions. MS/MS conditions were also adjusted for better peak resolution. The present method was validated in agreement with the criteria of Commission Decision 2002/657/EC, showing a linear range from 2 to 350 μg kg⁻¹ and regression coefficient higher than 0.995 for the studied penicillins. Decision limits, calculated in the case of substances with no permitted limit, were lower than 0.6 μg kg⁻¹, and detection capability values were lower than 2.0 μg kg⁻¹. Samples spiked at 2.0, 10.0, and 50.0 μg kg⁻¹ showed high recovery (72–92%) and precision values lower than 20% except for amoxicillin. The present method was also applied for the analysis of penicillins in 30 catfish samples bought in local markets.     

Optimization and Modeling of Process Parameters for Lipase Production by Bacillus brevis

Statistical evaluation of fermentation conditions and nutritional factors by Plackett–Burman two-level factorial design followed by optimization of significant parameters using response surface methodology for lipase production by Bacillus brevis was performed in submerged batch fermentation. Temperature, glucose, and olive oil were found to be the significant factors affecting lipase production. Maximum lipase activity of 5.1 U ml⁻¹ and cell mass of 1.82 g l⁻¹ at 32 h were obtained at the optimized conditions of temperature, 33.7 °C; initial pH, 8; and speed of agitation, 100 rpm, with the medium components: olive oil, 13.73 ml l⁻¹; glucose, 13.98 g l⁻¹; peptone, 2 g l⁻¹; Tween 80, 5 ml l⁻¹; NaCl, 5 g l⁻¹; CH₃COONa, 5 g l⁻¹; KCl, 2 g l⁻¹; CaCl₂·2H₂O, 1 g l⁻¹; MnSO₄·H₂O, 0.5 g l⁻¹; FeSO₄·7H₂O, 0.1 g l⁻¹; and MgSO₄·7H₂O, 0.01 g l⁻¹. The lipase productivity and specific lipase activity were found to be 0.106 U (ml h)⁻¹ and 2.55 U mg⁻¹, respectively. Unstructured kinetic models and artificial neural network models were used to describe the lipase fermentation. The kinetic analysis of the lipase fermentation by B. brevis shows that lipase is a growth-associated product.     

Determination and Evaluation of the Mineral Composition of Chinese Cabbage (Beta vulgaris)

Inductively coupled plasma optical emission spectrometry was used to determine the elements present in Chinese cabbage (Beta vulgaris). The accuracy of the method was confirmed by analysis of a certified reference material of spinach leaves. The study involved 57 samples that were collected in 13 Brazilian cities. Average concentrations of elements found per gram of Chinese cabbage were as follows: 3.44 mg g⁻¹ sodium, 5.09 mg g⁻¹ potassium, 1.25 mg g⁻¹ phosphorous, 0.85 mg g⁻¹ calcium, 0.49 mg g⁻¹ magnesium, 2.79 μg g⁻¹ manganese, 9.50 μg g⁻¹ iron, 0.74 μg g⁻¹ copper, 14.28 μg g⁻¹ zinc, and 6.44 μg g⁻¹ strontium. Principal component analysis and hierarchical cluster analysis demonstrated that there is no systematic difference in the mineral composition between the cabbage samples that were analyzed.     

Properties of <Emphasis Type="Italic">Aspergillus subolivaceus</Emphasis> free and immobilized dextranase

Aspergillus subolivaceus dextranase is immobilized on several carriers by entrapment and covalent binding with cross-linking. Dextranase immobilized on BSA with a cross-linking agent shows the highest activity and considerable immobilization yield (66.7%). The optimum pH of the immobilized enzyme is shifted to pH 6.0 as compared with the free enzyme (pH 5.5). The optimum temperature of the reaction is resulted at 60 °C for both free and immobilized enzyme. Thermal and pH stability are significantly improved by the immobilization process. The calculated K _m of the immobilized dextranase (14.24 mg mL⁻¹) is higher than that of the free dextranase (11.47 mg mL⁻¹), while V _max of the immobilized enzyme (2.80 U μg protein⁻¹) is lower than that of the free dextranase (11.75 U μg protein⁻¹). The immobilized enzyme was able to retain 76% of the initial catalytic activity after 5.0 cycles.     

Development of an ELISA Reverse-Based Assay to Assess the Presence of Mycotoxins in Cereal Flour

The first successful application of the ELISA reverse method and device (ER m&d), in the context of food safety and traceability, was developed in our laboratories to detect and quantify CP4EPSPS and Cry1AB genetically modified related proteins in soy and maize samples, respectively. To prove the versatility and the transferability of the technology, the ER was here applied to assess the presence of mycotoxins in cereals. Appropriate protocols were developed to assess the presence of deoxynivalenol and ochratoxin A and the ER was tested on contaminated wheat samples. In particular, deoxynivalenol (DON) and ochratoxin A (OTA) were detected in a range of values from 430 to 5,000 μg kg⁻¹ and from 1.7 to 10 μg kg⁻¹, respectively. The assays were optimized to reach a limit of quantification equal to 550 and 1.8 μg kg⁻¹ for DON and OTA, respectively.     

Physicochemical and microbiological description of Caxiri – a cassava and corn alcoholic beverage

Caxiri is a fermented alcoholic beverage made from cassava, corn and sweet potatoes by indigenous people in Brazil. Saccharomyces cerevisiae Rhodotorula mucilaginosa, Lactobacillus fermentum, Bacillus subtilis and L. helveticus were the main microbial species detected. Maltose was the main carbohydrate found (19.12 g L^?1), and lactic acid (15.09 g L^?1) and ethanol (92.16 g L^?1) were also found in high concentrations. Gas chromatography‐flame ionisation detector was used to identify thirteen volatile compounds. Among these volatiles, the higher concentrations were decanoic acid (123.04 μg L^?1) for the acids, diethyl malate (88.32 μg L^?1) for the esters, furfural (109.31 μg L^?1) for the aldehydes, 2‐phenylethanol (1022.76 μg L^?1) for the alcohols and 1,1‐diethoxyethane (226.24 μg L^?1) for the others. This study contributes to increasing knowledge of the microbiota present in the alcoholic fermentation produced from cassava, corn and sweet potatoes.     

Effect of debittering and solid-state fermentation processes on the nutritional content of lupine (Lupinus mutabilis Sweet)

There is a growing interest in vegetable-based sources of proteins. Despite its high nutrient content, lupine has been rarely exploited as a protein source due to the presence of high levels of non-nutritive compounds such as alkaloids, which impart a bitter taste. Here, we evaluated the effect of debittering and solid-state fermentation on the nutritional contents of three lupine varieties (Lupinus mutabilis Sweet). These processes induced significant changes (P < 0.05) in the nutritional composition of the three lupine varieties (INIAP-450, INIAP-451 and Criollo) and increased the protein levels to 644.55 g kg⁻¹ (Criollo variety) and the levels of several constituent amino acids such as valine (54.62 g kg⁻¹), methionine (42.47 g kg⁻¹), isoleucine (59.27 g kg⁻¹) and leucine (76.32 g kg⁻¹). The ether extract of INIAP-450 showed increased levels (up to 244.03 g kg⁻¹); especially, monounsaturated fatty acids (559.78 g kg⁻¹) and polyunsaturated fatty acids (293.17 g kg⁻¹) were observed. The omega-6/omega-3 ratio in the debittered grain oil reached the minimum requirement established for good-quality oils (5/1). However, the levels of other components decreased, showing levels up to 13.04 g kg⁻¹ (total starch) in the Criollo variety, 22.62 g kg⁻¹ (resistant starch) in INIAP-450, 6.53 g kg⁻¹ (potassium) in INIAP-451, 46 g kg⁻¹ (iron) in INIAP-451 and 29.75 g kg⁻¹ (zinc) in INIAP-450.     

Determination of Degradation Rate of Acaricide Fenpyroximate in Apple, Citrus, and Grape by HPLC-DAD

Fenpyroximate, a widely used acaricide around the world, was recently registered for control of mites in Egypt. Hence, only limited data are available on the dissipation rate of fenpyroximate under field conditions. In this study the dissipation rate of fenpyroximate after one application on apple, citrus and grape was estimated. Samples were prepared by an optimized quick, easy, cheap, effective, rugged, and safe (QuEChERS) analytical method before quantification by high performance liquid chromatography with diode array detector (HPLC-DAD). The initial deposit of fenpyroximate residue of 1.63, 0.33, 0.49 and 1.75 mg kg⁻¹ on apple, citrus, grape fruits and grape leaves, respectively after 7 days of application degraded to 0.14 mg/kg (91.41%), 0.09 mg kg⁻¹ (72.7%), 0.08 mg kg⁻¹ (83.6%) and 0.07 mg kg⁻¹ (96.0%), respectively. Pre-harvest interval (PHI) and maximum residue limit (MRL) were: 7 days and 0.3 mg kg⁻¹ for apple, 3 days and 0.2 mg kg⁻¹ for citrus, 3 days and 0.2 mg kg⁻¹ for grape fruits, and 14 days and 0.2 mg kg⁻¹ for grape leaves. Dissipation rate for all fruits followed first order kinetics with half-lives (t _1/2) of 2.03, 2.42, 1.56 and 2.75 days for apple, citrus, grape fruits and grape leaves, respectively. We suggested that a waiting period of at least 3 days before harvesting the citrus and grape fruits and 7 days for apple and 17 days for grape leaves after fenpyroximate application at recommended dose that may be considered quite safe from point of health hazards due to the toxic effect of residues.     

Stability and Degradation Kinetics of Bioactive Compounds and Colour in Strawberry Jam during Storage

The effect of storage time and temperature on degradation of bioactive compounds such as ascorbic acid, anthocyanins, total phenols, colour and total antioxidant capacity of strawberry jam were investigated. The results indicated that lightness (L) value decreased significantly (p < 0.05) over 28 days of storage at 4 and 15 °C, with lower values measured at higher temperatures. Anthocyanins, ascorbic acid and colour degradation followed first-order kinetics where the rate constant increased with an increase in the temperature. The reaction rate constant (k) increased from 0.95 × 10⁻² day⁻¹ to 1.71 × 10⁻² day⁻¹ at 4 and 15 °C for anthocyanins. Similarly, k increased from 2.08 × 10⁻² day⁻¹ to 4.54 × 10⁻² day⁻¹ at 4 and 15 °C for ascorbic acid. In general, total antioxidant activity for strawberry jam samples stored for 28 days at 4 and 15 °C exhibited lower values as compared to control (day 0). The results showed greater stability of nutritional parameters at 4 °C compared to 15 °C.     

Quantitative Determination and Confirmation of Five Synthetic Glucocorticoid Residues in Milk Powder by Gel Permeation Chromatography–Liquid Chromatography–Tandem Mass Spectrometry

A new method for multi-residue determination of five synthetic glucocorticoids (betamethasone, dexamethasone, prednisone, prednisolone, and hydrocortisone) in milk powder is developed. The glucocorticoids in the samples were extracted with tert-butyl methyl ether under ultrasonication incubation, and then cleaned up through gel permeation chromatography. After C18 LC gradient elution separation using acetonitrile with 0.1% formic acid as a mobile phase, the eluents were determined by liquid chromatography–tandem mass spectrometry with multiple reaction monitoring and positive ionization modes. The effective separation for the five glucocorticoids was achieved. The limit of quantification of the method for testing five glucocorticoids in milk powder was in the range from 0.2 to 0.5 μg kg⁻¹, which was lower than the maximum residue limits established by European Union for glucocorticoids in foods. Experiments on spiked samples of milk powder showed that the mean recoveries at addition level of 1.0, 3.0, and 5.0 μg kg⁻¹ were in the range of 71.2% and 103%, and the relative standard deviation ranged from 4.7% to 16.8%. The calibration curves for these drugs between 1.0 and 100 μg l⁻¹ showed good linearity, with correlation coefficient (r) more than 0.999. The real sample test showed that this method is sensitive and accurate. It can be used for qualitative and quantitative determination of studied glucocorticoid residues in milk powder samples.     

A rheological characterisation of mashed potatoes enriched with soy protein isolate

The effect of the addition of soy protein isolate (SPI) (0, 15, 30, 45 and 60 g kg⁻¹) on viscoelastic properties, large deformation measurements and microstructure of fresh (FM) and frozen/thawed (F/TM) mashed potatoes was investigated. Rheological data showed weak gel behaviour for both FM and F/TM potatoes without and with added SPI together with a significant decrease of system viscoelasticity (G′ and G″) with increasing SPI volume fraction, primarily attributed to the no interaction between the amylose/amylopectine matrix and the dispersed SPI particles or aggregates as revealed by scanning electron microscopy (SEM). Micrographs also showed that SPI formed white coarse aggregates. A freeze/thaw cycle produced a more significant decrease in viscoelastic functions, due to superior aggregation of denatured SPI and reduced water activity. In F/TM samples, high correlations between small and large deformation measurements were found. Results may be useful for technological applications in SPI-enriched mashed potatoes.