Microstructural characterization of deep-fat fried formulated products using confocal scanning laser microscopy and a non-invasive double staining procedure

The aim of this work was to characterize the inner microstructure of different fried formulated products to understand its relationship to oil absorption. Two product categories, which were either based on potato-flakes or wheat gluten, were analyzed. A non-invasive double staining procedure to perform a two channel observation using confocal scanning laser microscopy was set-up. The dough was directly stained during preparation with fluorescein-5-isothiocyanate (FITC), laminated and fried in oil stained with Nile Red. Thereafter, samples were observed without further intrusion. Pore size, porosity and oil were quantified using image analysis. A direct relationship between porosity and oil absorption was found in gluten-based products, but, no relationship was detected in potato-flakes-based ones. Further, gluten-based products were less porous but retained, in general, more oil. Parameters such as pore tortuosity and/or connectivity, as well as oil wettability, might explain such differences. In addition, the developed microscopy technique developed herein may be used in other food systems.     

Effect of microwave pretreatment on mass transfer during deep-fat frying of chicken nugget

The effect of a microwave pretreatment at different time duration on the mass transfer of chicken nuggets during deep-fat frying was studied. Coated chicken nugget samples pretreated in a microwave oven for 1-2 min were fried at 160 °C for times ranging from 0 to 300 s to evaluate the mass transfer as compared to the samples without a microwave pretreatment. Microwave pretreatment had a significant effect on moisture loss and oil uptake of chicken nuggets during deep-fat frying.     

Microstructural evolution of whipped cream in whipping process observed by confocal laser scanning microscopy

It is useful to carefully observe the evolution of foam structures to elucidate the factors affecting cream during whipping. In this study, confocal laser scanning microscopy and a double dyeing technology were used to investigate the microstructural evolution of a rigid foam structure in whipped cream. The location of fat and proteins were determined according to the signals they produce at different characteristic wavelengths. Protein membranes on the surface of air bubbles were clearly observed. A simple yet comprehensive characterization of the whipping process was established according to the micrographs and supported by relevant theories. The formation of a rigid foam structure depends on foaming of the protein in the plasma phase and partial coalescence of fat globules. The formation of protein foam in the cream, creation of net structure, and system breakage and collapse phenomena occurring throughout the whole whipping evolution process was depicted and distinguished visually by different colors.     

Dough microstructure: Novel analysis by quantification using confocal laser scanning microscopy

The effect and the correlation of water addition to flour on the microstructure and viscoelastic properties of wheat flour dough were investigated using confocal laser scanning microscopy and a spectrum of rheological methods. Dough with water addition in the range of 52.5-70.0 g water 100 g⁻¹ flour was investigated using a stickiness test, uniaxial elongation test, and fundamental rheology like small amplitude oscillatory shear measurement and a creep recovery test. A method for quantifying the microstructure of dough protein gained by CLSM was established with image processing and analysis. The complex shear modulus decreased rapidly with water addition due to the plasticization effect of water molecules and increased mobility in the continuous phases. Elastic behavior, determined as loss factor tan ?? and relative elastic part J_el decreased. Rheological tests showed high linear correlations with each other (r of |0.66|-|0.98|). Image analysis measurements (average size, area fraction, perimeter, circularity, and fractal dimension) showed high linear correlations (r of |0.66|-|0.85|) with water addition and rheological attributes like the complex shear modulus (r = 0.85) and J_el (r = 0.86). CLSM in combination with image processing and analyzing has proven to be an applicable and powerful tool for examining and quantifying dough protein microstructure. Hence, it was possible to prove the dependency of rheology on the microstructure of dough.     

Porosity determination of deep‐fat‐fried coatings using pycnometer (Fried batter porosity determination by pycnometer)

The effect of processing conditions such as frying time and temperature, and batter formulation on pore development in deep‐fat fried chicken nuggets coatings were studied using helium pycnometer method. Chicken nuggets with preformed and laboratory prepared batter coatings were fried at temperatures between 170 and 190 °C for a time range between 0 and 240 s. There was significant (P < 0.05) effect of frying temperature and batter formulation on porosity. Porosity increased with frying time and temperature, and ranged between 2.15 and 47.92% for the preformed batter and 9.96 and 54.76% for the formulated batters. Apparent and bulk densities of the preformed batters increased and decreased with frying time, respectively, but both declined gradually with increasing frying temperature. As the level of rice flour in the formulation increased, apparent and bulk densities also increased. Batter formulation and frying temperature significantly (P < 0.05) influenced the variation in moisture and fat content of the fried batter. Porosity demonstrated positive and negative correlation with fat uptake and moisture loss, respectively, for all the batter coatings.     

Functionality of batters containing different starch types for deep-fat frying of chicken nuggets

The effect of various starch types (amylomaize, corn, waxymaize, pregelatinized tapioca) on quality attributes (texture, moisture content, oil content, color, coating pick up, cooking yield, volume and porosity) of deep-fat fried chicken nuggets were studied. Chicken samples, 0.04 m in diameter and 0.015 m in thickness, taken from the breast portion, were coated with batters composed of a 3:5 solid to water ratio by immersion. The solid content of batter formulations contained equal amounts of corn and wheat flour, 5.0% starch, 1.0% salt and 0.5% leavening agent. As control, batter without starch addition, was used. Samples were fried at 180°C for 3, 6, 9 and 12 minutes. Crispness and oil content of chicken nuggets increased, whereas moisture content decreased with increasing frying time. Starch addition to the formulations increased crispness of the product significantly at the last stages of frying. The highest porosity and oil content was obtained when corn starch was used. Pregelatinized tapioca starch was found to provide a product with the lowest oil content, the highest moisture content, coating pick up and volume.     

Quality changes in chicken nuggets fried in oils with different degrees of hydrogenatation

Quality changes in chicken nuggets fried in different mixtures of hydrogenated and non-hydrogenated canola oils were studied. Colour, texture, oil and moisture contents of the chicken nugget samples fried at 190 °C for 30, 60, 90, 120, 180, 240 and 300 s were investigated. The proportions of hydrogenated to non-hydrogenated frying oils used in the study were 0%, 20%, 40%, 60%, 80% and 100%.Results indicate that increase in frying time resulted in decreased product lightness (L*) whereas redness (a*) and yellowness (b*) increased. The maximum load to puncture increased with increasing frying time. In addition, oil content increased slowly with frying time, and moisture content decreased as expected. Both frying times and oil types have significant effects on the quality parameters investigated. First-order kinetic equation was used to describe colour changes as well as oil and moisture contents of the samples. Oil and moisture contents had negative correlation relationship. With increasing degree of oil hydrogenation, the surface colour of the fried chicken nuggets samples were lighter, texture increased, oil and moisture contents decreased.     

Quantitative analysis of confocal laser scanning microscopy images of heat-set globular protein gels

Gels of the globular protein β-lactoglobulin were made by heating solutions at pH 7 and different NaCl concentrations (C_s). The influence of the ionic strength on the gel structure was studied by confocal laser scanning microscopy (CLSM). For C_s < 0.2 M the images were homogeneous, but at higher NaCl concentrations micro-phase separation was observed. The protein concentration in the two phases was determined from the images. It is shown how CLSM images can be quantitatively analysed in terms of the pair correlation function of the protein concentration fluctuations, yielding results that can be directly compared to those obtained from light scattering. The transition between so-called finely stranded and particulate gels is explained by a switch from net repulsive to net attractive interaction between growing protein aggregates.     

Food surface texture measurement using reflective confocal laser scanning microscopy

ABSTRACT:  Confocal laser scanning microscopy (CLSM) was used in the reflection mode to characterize the surface texture (roughness) of sliced food surfaces. Sandpapers with grit size between 150 and 600 were used as height references to standardize the CLSM hardware settings. Sandpaper particle sizes were verified by scanning electron microscopy (SEM). The mean amplitude (in micrometers) of surface variation along line segments of the scanned sandpaper topographical image sets showed very close agreement between the measured result and the grit particle size (based on the U.S. Coated Abrasive Manufactures Inst. {CAMI], standard). The verified instrument settings were then used to measure the surface texture of mechanically sliced food surfaces, including cooked ham, salami, and cheese. Sliced food surface texture parameters of Ra (average height of a line segment), Rs (surface area ratio), Pa (average height on a region of interest), and Pq (root-mean-square height on a region of interest) were evaluated by this method. Values of the surface roughness of sliced ham, salami, and cheese were found to be comparable to the range of dimensions of selected sandpapers. The CLSM method may be useful for other surface texture measurements, and to investigate the impact of food surface texture on microbial adhesion or attachment, which might play a significant role in microbial transfer from one surface to another.     

Characterisation of pore properties of deep‐fat‐fried chicken nuggets breading coating using mercury intrusion porosimetry technique

The objective of this study was to characterise the pore properties of deep‐fat‐fried chicken nuggets coating under different processing conditions namely frying temperatures (170, 180 and 190 °C) and time (0–240 s) using porosimetry technique. Porosity range obtained was between 39.93 and 68.99%. Porosity of the freeze‐dried samples decreased with frying time. The main effect of temperature on porosity was significant (P < 0.05). Porosity showed a high positive and negative correlation with moisture and fat contents, and the correlation coefficients ranged between 0.88 and 0.96 and 0.78 and 0.8, respectively. Bulk density increased with frying time, while apparent density was relatively the same. Pore distribution showed bimodality. There was no significant effect of temperature on pore size distribution. Over 70% of the pore volume is made up of pores greater than 1 μm. Pore volume ranged between 0.54 and 1.5 cm³ g^?1, and it decreased with frying time. Mean pore diameter was between 0.006 and 389 μm, while with frying time, it ranged between 0.25 and 8.32 μm. Total pore area was between 2.53 and 16.53 m² g^?1. Hysteresis phenomenon showed that some of the pores were not perfectly cylindrical in shape.     

Direct observation of bacterial exopolysaccharides in dairy products using confocal scanning laser microscopy

The objective of this work was to develop a methodology for direct visualization of bacterial exopolysaccharides (EPS) in fully hydrated dairy products. The new method involved staining EPS with wheat germ agglutinin labeled with Alexa fluor 488 or staining with concanavalin A 488. Samples were observed using confocal scanning laser microscopy. Distribution of EPS produced by Lactococcus lactis (CHCC 3367), a combination of Streptococcus thermophilus (CHCC 3534) and Lactobacillus delbrueckii ssp. bulgaricus (CHCC 769) and Lactobacillus delbrueckii ssp. bulgaricus RR in milk was compared in stirred and unstirred fermented milk. The EPS and proteins were observed as distinct entities, with EPS present in the protein network pores. EPS was observed in greater amounts in milk fermented by the ropy L. lactis culture than in milk fermented by the less ropy strain of S. thermophilus. Stirring the fermented milk caused aggregation of EPS into more extended structures. The more ropy the culture, the longer and larger the strands formed during stirring. The method was also applied to Feta cheese made with an EPS-producing strain of S. thermophilus. EPS was observed in the cheese as thick sheets filling pores in the protein network.     

Visualisation of starch granule morphologies using confocal scanning laser microscopy (CSLM)

Confocal scanning laser microscopy (CSLM) is a powerful tool for the visualisation of starch granules from their botanical source, during processing into their final application. CSLM allows the visualisation of the starch gelatinisation process and of granule remnants in starch pastes in their original environment and without modification. In this study, CSLM has been used to study the granule morphology of starch from different botanical sources. CSLM is a suitable technique to obtain, under mild conditions, 2D and 3D images of the granules. The samples for observation by CSLM do not require complicated preparations such as drying and metal coating as in the case of electron microscopy. Moreover, the CSLM technique is not limited to the observation of native starch granules, as the gelatinisation process and the remnants of granules in starch pastes can be monitored in their original environment. In this way, starch granules can be visualised from their botanical sources to the final application with a single microscopic technique. © 2002 Society of Chemical Industry     

Visualization of a recombinant gene protein in the baculovirus expression vector system using confocal scanning laser microscopy

Expression of the recombinant protein beta-galactosidase in the Spodoptera frugiperda Sf-9 insect cell line infected by the Autographa californica nuclear polyhedrosis virus expressing beta-galactosidase (AcNPV-betagal) was visualized using confocal scanning laser microscopy with fluorescent staining of both the recombinant protein and the cell nucleus. The average size of the insect cells and the intracellular DNA concentration both increased markedly, respectively reading 3.8- and 2.3-fold the values before infection. The average beta-galactosidase activity began to increase at 20-24 h post infection and finally reached 1.9 x 10(4) units/ml. As the post infection time increased, the stained nucleus images expanded and spread broadly. Beta-galactosidase was first identified by fluorescent staining at 12 h post-infection, filled the cell at 27 h, began to be released at 36 h, and finally spread out of the cell. The locations of the nucleus and expressed beta-galactosidase were identified from computerized tomograms and 3-dimensional images.     

激光扫描共聚焦显微镜对小鼠乳腺中PAI-1表达的定量分析

对昆明种白小鼠乳腺发育进行了组织学观察,并利用激光扫描共聚焦显微系统对脂肪细胞相关因子纤溶酶原激活物抑制剂-1(PAI-1)的表达进行了免疫荧光检测。结果表明,PAI-1不仅分布在脂肪组织,在导管和腺泡上皮以及周围基质区域也有表达。整个乳腺发育过程中PAI-1有3次明显上调,它的表达与脂肪细胞的多少无关,而是发生在乳腺组织结构剧烈变化的时期。PAI-I表达增强抑制纤溶酶系统对乳腺细胞外基质的降解,限制了脂肪细胞的生长,从而调节乳腺发育。但是,退化期PAI-1表达上调并不能逆转乳腺退化的趋势,这可能是乳汁持续积累的结果。     

Assessment of off-flavor development in restructured chicken nuggets using hexanal and TBARS measurements and sensory evaluation

The hexanal contents of chicken nuggets treated with various anti-oxidants were evaluated in relation to the development of warmed-over flavor (WOF) during frozen storage. Of the antioxidant treatments tested, the sodium tripolyphosphate (STPP)/tertiary butylhydroquinone combination showed the greatest effect by decreasing hexanal production by 95%. Combinations of STPP/oleoresin rosemary, (0.5 g kg^?1 and 1 g kg^?1) decreased the hexanal contents by 85% and 91%, respectively. A higher correlation coefficient (pooled, within treatments) between hexanal contents and sensory scores for WOF (r = 0.68) relative to that between hexanal contents and thiobarbituric acid reactive substances values (r = 0.14) was obtained. A pooled, correlation coefficient within treatments and storage times (r = 0.56), was found between TBARS and sensory scores. It was concluded that the use of correlation coefficients calculated without pooling groups of data within each significant experimental factor to interrelate the results of different analyses may be inappropriate.     

Microstructure of milk gel and cheese curd observed using cryo scanning electron microscopy and confocal microscopy

Cryo scanning electron microscopy (cryo SEM) and confocal laser scanning microscopy (CLSM) were used to visualise changes in the microstructure of milk, rennet-induced gel and curd during the manufacture of Cheddar cheese. Our results show that cryo preservation did not alter the microstructure of the sample when it was fixed by rapid freezing in slush liquid nitrogen due to the formation of amorphous ice. Artefacts such as the formation of ice crystals could be observed in samples when immersed directly into liquid nitrogen (−196 °C) at atmospheric pressure. These ice crystals changed the shape of sample pores increasing their size to >20 μm. The etching time, thickness of gold coating, accelerating voltage and type of detector used for cryo SEM observation were varied in order to minimise the formation of such artefacts and optimise conditions for imaging. Chains and clusters of casein micelles and fat globules were best observed in the gel and the cooked curd when the samples were freeze fractured and etched for 30 min, coated with a mixture of gold and palladium alloy approximately 6 nm thick at −140 °C and observed using a backscattered electron detector at 15 kV. The structure of the gel, curd and cheese was also observed using CLSM. Spherical fat globules were mostly present in the serum pores of the gel prepared from unhomogenised milk but were found embedded in the aggregated chains of the casein network within the gel prepared from homogenised milk when observed using CLSM. The porosity measurements obtained using cryo SEM were similar to those obtained using CLSM. These two complementary techniques can potentially be used to assist studies for the control of cheese texture and functionality.     

Characterization of fibrillar collagen types using multi-dimensional multiphoton laser scanning microscopy

In dermal photodamage the ratio of the collagen types III to I changes. This makes the investigation of the fibrillar collagen type characteristics interesting for skin research. In this study collagen types were characterized using 5-dimensional multiphoton laser scanning microscopy (5D-IVT) that can be applied in vivo. Second harmonic generation (SHG) signals and fluorescence lifetimes of the collagen autofluorescence were analysed. Collagen type I generates a higher SHG intensity and a longer fluorescence lifetime compared to collagen type III. Thus, the SHG intensity decrease found in photodamaged skin might be explained by the increase in collagen type III. Calculating the in vivo relevant increase of collagen type III gives a negligible difference in fluorescence lifetime not qualifying this method for the determination of collagen type changes in dermal photodamage in vivo in human skin. However, for pathologies that exhibit higher differences in collagen types 5D-IVT analysis might be a suitable method.     

A novel technique for differentiation of proteins in the development of acid gel structure from control and heat treated milk using confocal scanning laser microscopy

The incorporation of caseins and whey proteins into acid gels produced from unheated and heat treated skimmed milk was studied by confocal scanning laser microscopy (CSLM) using fluorescent labelled proteins. Bovine casein micelles were labelled using Alexa Fluor 594, while whey proteins were labelled using Alexa Fluor 488. Samples of the labelled protein solutions were introduced into aliquots of pasteurised skim milk, and skim milk heated to 90 degrees C for 2 min and 95 degrees C for 8 min. The milk was acidified at 40 degrees C to a final pH of 4.4 using 20 g glucono-delta-lactone/l (GDL). The formation of gels was observed with CSLM at two wavelengths (488 nm and 594 nm), and also by visual and rheological methods. In the control milk, as pH decreased distinct casein aggregates appeared, and as further pH reduction occurred, the whey proteins could be seen to coat the casein aggregates. With the heated milks, the gel structure was formed of continuous strands consisting of both casein and whey protein. The formation of the gel network was correlated with an increase in the elastic modulus for all three treatments, in relation to the severity of heat treatment. This model system allows the separate observation of the caseins and whey proteins, and the study of the interactions between the two protein fractions during the formation of the acid gel structure, on a real-time basis. The system could therefore be a valuable tool in the study of structure formation in yoghurt and other dairy protein systems.     

Evaluating taste contribution of brown sugar in chicken seasoning using taste compounds,sensory evaluation,and electronic tongue

In this study, the taste contribution of brown sugar in chicken seasoning was evaluated. Chicken seasonings containing brown sugar (AB), white sugar (AW), and liquid sugar (AL) were compared by the detection of taste compounds, sensory evaluation, and electronic tongue measurements. The correlation model of the three kinds of data was built by partial least squares regression (PLSR). The contents of the taste compounds in sample AB was higher than in sample AW and lower than in sample AL. Sample AB had the strongest “umami” and “full-body” taste and the highest response values for the UMS and GPS sensors. Combined with the PLSR results, brown sugar could be used to balance the taste of chicken seasoning. In conclusion, brown sugar had a positive effect on flavor quality and could help to improve chicken seasoning recipes.