3D Microstructure of supercritical fluid extrudates. II: Cell anisotropy and the mechanical properties

The mechanical properties of biopolymeric cellular foams are often governed by their microstructure. 2D and 3D microstructural data of supercritical fluid extrudates were obtained with X-ray microtomography and correlated with the mechanical properties determined using compression and three-point bending tests. Cell size from transverse cross-sections of SCFX extrudates decreased with radial distance from the center. In the longitudinal direction, the cell shapes were more elliptical than spherical and were aligned along the extrusion direction. These findings indicated the presence of a certain degree of anisotropy in SCFX extrudates in both directions. Both piece density and the ratio of cell wall thickness to cell diameter were observed to be good predictors of compressive and flexural mechanical properties, including jaggedness parameters. Compressive modulus data suggested that cell shape anisotropy due to cell elongation in the longitudinal direction actually affected the mechanical properties of SCFX extrudates. X-ray microtomography was found to be useful to investigate 2D and 3D morphology of SCFX extrudates, including cell shape and cell size anisotropy.     

Microstructural characterization of multiphase chocolate using X-ray microtomography

In this study, X-ray microtomography (μCT) was used for the image analysis of the microstructure of 12 types of Italian aerated chocolate chosen to exhibit variability in terms of cocoa mass content. Appropriate quantitative 3-dimensional parameters describing the microstructure were calculated, for example, the structure thickness (ST), object structure volume ratio (OSVR), and the percentage object volume (POV). Chemical analysis was also performed to correlate the microstructural data to the chemical composition of the samples. Correlation between the μCT parameters acquired for the pore microstructure evaluation and the chemical analysis revealed that the sugar crystals content does not influence the pore structure and content. On the other hand, it revealed that there is a strong correlation between the POV and the sugar content obtained by chemical analysis. The results from this study show that μCT is a suitable technique for the microstructural analysis of confectionary products such as chocolates and not only does it provide an accurate analysis of the pores and microstructure but the data obtained could also be used to aid in the assessment of its composition and consistency with label specifications. PRACTICAL APPLICATION: X-ray microtomography (μCT) is a noninvasive and nondestructive 3-D imaging technique that has several advantages over other methods, including the ability to image low-moisture materials. Given the enormous success of μCT in medical applications, material science, chemical engineering, geology, and biology, it is not surprising that in recent years much attention has been focused on extending this imaging technique to food science as a useful technique to aid in the study of food microstructure. X-ray microtomography provides in-depth information on the microstructure of the food product being tested; therefore, a better understanding of the physical structure of the product and from an engineering perspective, knowledge about the microstructure of foods can be used to identify the important processing parameters that affect the quality of a product.     

Microstructure,textural and sensorial properties of durum wheat bread as affected by yeast content

In this study, breads varying in yeast content and therefore leading to distinct cellular structures are investigated. Firstly, X-ray microtomography is used to characterize not only the final cellular structure, but also the process of development of microstructure during the fermentation stage. With μCT, image analysis of the full 3-D microstructure, measuring the size, shape, networking/connectivity and distribution of various phases was possible. These measurements represent the full 3-D microstructure, which is not always possible by 2-D image analysis using statistical techniques. Secondly, the textural properties of the baked bread were obtained by compression tests and finally, the sensorial quality of the final product is also evaluated and correlated with the above properties. Results showed that an increase of the yeast content increased the percentage volume of pores and decreased the force required for compression of the bread sample and the tenacity. Moreover, a larger quantity of smaller sized pores led to a firmer bread structure. Regarding the sensorial properties, none of the investigated microstructural parameters were significantly correlated with the overall quality of the bread. In fact, the overall quality was more strongly affected from other parameters such as odor and appearance attributes.     

A Novel Approach to Study Biscuits and Breadsticks Using X-Ray Computed Tomography

Abstract: In this study X-ray microtomography (μCT) was used for analysis of the microstructure of 6 different types of Italian biscuits and 3 types of Italian breadsticks. Appropriate quantitative 3-D parameters describing the microstructure were calculated, such as the structure thickness (ST), the object structure volume ratio (OSVR), the degree of anisotropy (DA), and the percentage object volume (POV). Sensory analysis was also performed to discriminate samples on the basis of texture characteristics. A correlation between microstructural data (OSVR for biscuits and OSVR, POV, and DA for breadsticks) and sample crunchiness was also found. Results obtained from the current study showed that analysis at a microscopic level could be useful to the food industry, as the accurate calculation of number, dimension, and distribution of pores in the products could be used to improve the sensorial properties of food. Further study by μCT could be carried out to correlate microstructure to specific ingredients and process conditions to allow obtaining more tailored food.     

Evaluation of microstructural properties of coffee beans by synchrotron X-ray microtomography: a methodological approach

Synchrotron radiation microtomography was used as a nondestructive imaging technique to investigate the microstructural properties of green and roasted coffee beans. After image acquisition, 2D images have been reconstructed and 3D images of the beans have been then obtained. Qualitative and quantitative analysis of the images allow to fully characterize the morphological and structural features of the coffee beans. Roasting causes meaningful changes in the microstructure of the coffee bean tissue with the development in the entire bean of a porous structure with pores of different shape and size depending on the zone of the bean and cracks occurring mainly in the more external regions and between parenchyma and mucilage. The highly contrasted X-ray images have been analyzed to determine the pore size and its distribution in different regions of the coffee beans by selecting Volume-of-Interest (VoI). The use of phase-contrast hard X-rays imaging techniques represents an interesting tool of investigation of the internal structure, morphology, as well as the quality of whole coffee beans. Moreover, the high potentiality of 3D X-ray imaging and the approach used in this study could be applied in understanding the effects of roasting process conditions on the evolution of microstructural properties of the bean that may affect the stability as well the grinding and brewing performances. PRACTICAL APPLICATION: Synchrotron radiation microtomography is an elegant nondestructive imaging technique to investigate the microstructural properties of porous cellular matrices like the green and roasted coffee beans. The quantitative analysis of the resulting 2D and 3D images allows a more comprehensive and objective characterization of the sample under investigation as a whole or of extracted Volumes-of-Interest in the bean. This imaging technique could have a major role in understanding the effects of roasting process conditions on the microstructural properties of the bean.     

Fat microstructure of yogurt as assessed by x-ray microtomography

In this work, the x-ray microtomography (μCT) technique was used for the analysis of fat microstructure and quantification of fat in 7 types of yogurts. The dynamic mechanical properties of the yogurt samples also were studied using a controlled-strain rotational rheometer and correlated to the fat microstructure. Five types of commercially produced and 2 homemade yogurts, chosen to exhibit variability in terms of visible structure of fat, were used for this experiment. Appropriate quantitative 3-dimensional parameters describing the fat structure were calculated. With regard to the microstructural and rheological relationship, results from the correlation carried out show that a correlation exists among some microstructural and rheological parameters of the yogurt samples. The results from this study also show that μCT is a suitable technique for the microstructural analysis of fat as it not only quantifies the fat deposits present, but also determines the deposits’ spatial distribution.     

Effect of the incorporation of antioxidants on physicochemical and antioxidant properties of wheat starch–chitosan films

Blend edible films were prepared from wheat starch (WS) and chitosan (CH) with glycerol as plasticizer. Four active ingredients (antioxidants) were added, namely basil essential oil, thyme essential oil, citric acid and α-tocopherol. The starch:antioxidant mass ratio was 1:0.1. Prior to characterisation, the films were conditioned at 25 °C–53%RH as to their structural, mechanical, optical and barrier properties. The antioxidant capacity of the active ingredients was determined by means of a spectrophotometric method. The incorporation of antioxidants led to a heterogeneous film microstructure, mainly in those containing α-tocopherol, which affected the surface roughness. Yellowness was induced in films when α-tocopherol was added and no notable colour changes were observed in the other cases, although all the antioxidants increased the transparency of the films. Despite of the fact that the mechanical properties were barely affected by the incorporation of antioxidants, citric acid promoted an increase in the elastic modulus but a decrease in film stretchability. The water vapour barrier properties of the films were only slightly improved when citric acid and α-tocopherol were added, whereas the oxygen barrier properties were significantly improved in all cases. The greatest antioxidant capacity of the films was reported for films containing α-tocopherol, which exhibited the highest antioxidant power.     

丝瓜茎汁液复合饮料的工艺研究

本实验以丝瓜为主要原料,以白砂糖、柠檬酸、丝瓜伤流液及菠萝汁等为辅料,开发一种具有保健功能的丝瓜茎汁液复合饮料。以饮料的感观质量为评价指标,采用单因素实验,考察白砂糖、柠檬酸、菠萝等对饮料品质的影响。在此基础上,采用四因素三水平正交试验L9(34),确定该饮料的最佳配方,其结果为丝瓜12%、白砂糖8%、柠檬酸0.070%、菠萝6%、丝瓜伤流液15%。该天然饮料营养丰富、风味独特,具有清热化痰、凉血解毒等保健作用。     

Coffee beans microstructural changes induced by cultivation processing: An X-ray microtomographic investigation

The present work reports on the microstructural characterisation of four types of different processed coffee beans, Coffea arabica, Arabica monsooned, Coffea canephora and Robusta monsooned, by means of X-ray microtomography technique (μCT). A three dimensional (3-D) quantitative analysis was carried out on the microstructure the bean samples before and after roasting. The 3-D microstructure information provides a better understanding of the structure of the beans and from an engineering perspective; knowledge about the microstructure can be used to identify the important processing parameters that affect the quality of coffee. With regards to the microstructure, the porosity increase can summarise the overall effects of the roasting process on coffee beans. Results demonstrate the success of μCT for the quantification of the microstructural alterations of the coffee beans induced by their different cultivation processes before and after the roasting process.     

Physicochemical Properties of Microencapsulated ω‐3 Salmon Oil with Egg White Powder

The objective of this study was to produce microencapsulated omega(ω)‐3 fatty acids (PUFAs) fortified egg white (EW) powders and to characterize their nutritional and physical properties. Stable emulsions (E‐SO‐EW) containing 3.43 (g/100 g) salmon oil (SO), 56.21 (g/100 g) EW, and 40.36 (g/100 g) water and a control (E‐EW) containing EW and water were prepared. E‐SO‐EW and E‐EW were separately spray dried at 130, 140, and 150 °C inlet air temperatures. This resulted in 3 microencapsulated SO fortified EW powders (SO‐EW), and 3 dried EW powders (DEW). The powders were analyzed for microencapsulation efficiency (ME), color, fatty acids methyl esters, protein, fat, moisture, ash, amino acids, minerals, microstructure, and particle size. The EPA and DHA content of SO and the ME of the powders were not affected by the inlet air temperature. The crude protein content of SO‐EW powders was approximately 24 (g/100 g) lower than dried EW powders. Leucine was the most abundant essential amino acid found in all the powders. Most of the powders’ median particle size ranged from 15 to 30 μm. The study demonstrated that microencapsulated ω‐3 salmon oil with high quality EW protein can be produced by spray drying.     

Coffea arabica beans microstructural changes induced by roasting: An X-ray microtomographic investigation

The present work reports on a microstructural characterization of Coffea arabica beans in the course of roasting by means of X-ray microtomography technique (μCT). In fact, the aim of this study is to demonstrate the capability of μCT as a useful tool for the characterization of microstructure of C. arabica beans at different roasting times: from green to very dark. μCT is a non-invasive technique that has the ability to image low moisture materials by using the differences in X-ray attenuation arising, mainly, from differences in density within the specimen. Green coffee beans were roasted and sampled at the following roasting times; 2, 3, 4 and 5 min. Several parameters such as percentage object volume (POV), density, total volume and pore size distributions were calculated for each roasting time and their variations discussed. The results from this study show how the microstructure of the coffee bean evolves with increasing roasting time, for example, the increase in total pore volume, the increase in porosity and density due to the rupture of bonds in the internal structure of the coffee beans during roasting. μCT has proven to be a suitable technique for microstructural analysis of roasted foods such as coffee bean and provides an accurate analysis of the pores and microstructure during the roasting process.     

低糖荔枝果酱工艺优化研究

研究低甲氧基果胶(LMP)质量分数、氯化钙质量分数、柠檬酸质量分数和果冻粉质量分数对低糖荔枝果酱品质的影响,并采用响应曲面法进行工艺优化。结果表明:低糖荔枝果酱最优工艺条件为低甲氧基果胶质量分数0.71%、氯化钙质量分数0.052%、柠檬酸质量分数0.48%和果冻粉质量分数0.15%。在此优化条件下制备的低糖荔枝果酱感官评分实测值为14.6,与预测值(14.7)接近;产品可溶性固形物含量44.8%、总酸度0.65%、黏度3.382Pa·s、硬度3.35N,具有酸甜适口、口感细腻润滑的特点。     

Effects of external shear forces on crystallisation kinetics of model fat blends

The effects of different shearing conditions on the crystallisation of cocoa butter (CB) with the addition of other confectionery ingredients (sugar and lecithin) were investigated. Differential scanning calorimetry (DSC), X‐ray diffraction (XRD) and polarised light microscopy (PLM) were conducted to measure the thermal, polymorphic and microstructural properties, of these mixtures, respectively. Both shearing conditions and ingredients have a pronounced impact on the thermal and polymorphic behaviour of CB, and its microstructure. In the absence of shear, the addition of lecithin delayed the polymorphic transformation in CB and results in slightly bigger crystal clusters. When both sugar and lecithin are added to nonsheared CB, they retard the formation of stable polymorphism. Moreover, sugar particles tended to agglomerate in the absence of lecithin under static conditions. With the application of shear, a more homogenous microstructure of the samples was observed. Shear significantly increases the crystallisation rate, polymorph transformation and the formation of a higher number of smaller crystals at both the presence and absence of lecithin.     

Drying of foods using supercritical carbon dioxide — Investigations with carrot

The use of supercritical carbon dioxide (scCO₂) for the removal of moisture from cylindrical pieces of carrot has been investigated. The experiments were carried out at 20 MPa pressure and the effects of temperature and co-solvent (ethanol) addition were examined. At the investigated conditions, comparisons with air-drying indicated that drying kinetics and the associated drying mechanisms differed between the techniques. The microstructural characteristics of carrot pieces that had been dried using the different techniques were compared using X-ray microtomography and light microscopy. Carrots dried in the supercritical fluid environment were seen to retain their shape much better than air-dried carrots which underwent shrinkage. Samples dried in ethanol-modified scCO₂ possessed less dense structures and consequently displayed more favourable rehydrated textural properties than the air-dried equivalents.

Industrial relevance

Drying is a common unit operation in food processing, but the rehydrated product is often of very poor quality. Comparatively little work has been done on optimising drying for quality of the final, rehydrated product. Supercritical drying is a possible way of maintaining product microstructure, and this paper describes experiments in which the supercritical drying of carrot is studied and compared with conventional processes.     

不同类型晾晒烟种质资源的化学成分和几种致香成分分析

  目的  筛选品质优良的晾晒烟种质资源。  方法  35份晾晒烟种质资源种植于云南省玉溪市研和镇,取经晾晒调制后的中部烟叶,经相关分析和聚类分析比较其常规化学成分和淀粉、多酚、石油醚提取物、多元酸、高级脂肪酸等成分含量。  结果  各主要成分含量范围(及最高值类别):总氮1.62%~3.44%(晒烟)、烟碱2.30%~9.76%(晒烟)、钾0.73%~3.42%(黄花烟)、多酚1.51%~6.43%(晒烟)、石油醚提取物2.66%~8.94%(雪茄烟)、草酸7.09 mg/g~50.21 mg/g(晒烟)、苹果酸41.97 mg/g~173.39 mg/g(黄花烟)、柠檬酸16.02 mg/g~126.45 mg/g(黄花烟)等。35份晾晒烟种质可聚为5类:第1类为黄花烟资源,钾、苹果酸、柠檬酸等含量高;糖、酚、石油醚提取物、草酸、丙二酸等含量低;第2类有马里兰烟、晒烟和雪茄烟,其石油醚提取物含量高,苹果酸和柠檬酸等含量较高;第3类多为晒烟,多酚含量高;第4类总氮、烟碱含量高,草酸含量较高,第5类总糖、还原糖、淀粉等含量高,两糖差、糖碱比、氮碱比高,苹果酸、柠檬酸等含量低。      

COMPOSITIONAL CHANGES OF STRAWBERRY DUE TO DEHYDRATION, COLD STORAGE AND FREEZING–THAWING PROCESSES

Strawberry is an excellent source of food ingredients, although compositional changes might occur in improperly controlled processing, affecting product quality. In this article, changes in sugar composition (glucose, fructose and sucrose), citric acid, water and total soluble content, as induced by partial dehydration and freezing–thawing processes, were analyzed in strawberries (var. Camarosa). Osmotic dehydration (OD) with 65 °Brix sucrose solution, air drying (AD) at 45C, or combined treatments (OD–AD) were applied to reduce strawberries’ water content to 70–85%. Fresh and dehydrated samples were frozen (?40C, 24 h) and stored (?18C, 30 and 180 days). All samples processed by OD and OD–AD showed a significant sugar gain, and depending on the dehydration treatment, total or partial sucrose hydrolysis was observed. Dehydration treatments caused small losses of citric acid. During the freezing–thawing process, drip loss and enzymatic action also cause changes in sugar concentration, especially in OD‐treated samples.     

葡萄籽的预处理及其在饮料中的应用探究

为提高葡萄酒发酵废弃物葡萄籽的利用率,将其功能性成分提取出来并应用于饮料中。在不同温度下,对葡萄籽提取液活性炭脱色效果进行研究,同时以酸度（以柠檬酸和苹果酸1：1的混合酸添加）、糖度、浓缩葡萄汁为参数进行单因素试验,探究以葡萄籽提取物为原料调配饮料的最优条件,得出该饮料的最佳配方：混合酸（柠檬酸：苹果酸=1：1）2.4g/L、蔗糖8.0%、浓缩葡萄汁3.0%。     

Physico-chemical,orosensory and microstructural properties of meat products containing rye bran,pea fibre or a combination of the two

Functionality of dietary fibres depends on their interaction with the food matrix to where they are added and gastrointestinal conditions. The present study investigated the physico-chemical, orosensory and microstructural properties of meatballs and sausages containing different fibre ingredients (six recipes in total). The fibre-rich meat products had a dietary fibre content of 3.0 g per 100 g. Viscosity and water-holding capacity (WHC) were determined after an in vitro simulated digestion model. Fourteen subjects assessed chewing time. Microstructural characteristics were determined by CT scanning. Sausages had a longer chewing time and higher water content, but a lower WHC than meatballs. In contrast, the differences in viscosity were low. Moreover, the microstructural characteristics differed between sausages and meatballs and the differences seemed to be influenced by the fibre type. In conclusion, fibre ingredients affect meat quality-related properties in terms of chewing time and microstructure when added to meatballs or sausages.     

Factors influencing quantities of sugars and organic acids in blackcurrant concentrates

 Use of endogenous non-volatile flavour components, i. e. sugars and organic acids, in fruit juice products is desirable. A study of 133 blackcurrant concentrates from three seasons examined variation in sugars and acids arising from storage of fruit at freezing or sub-ambient temperature, seasonal differences, geographical origin and choice of conventional thermal-evaporative or freeze concentration technology. Compared with freeze concentrates, conventional concentrates had significantly higher contents of total sugars and acids, notably malic acid, and higher fructose/glucose, lower malic/citric acid and similar sugar/acid ratios. Concentrates from frozen fruit generally had smaller amounts of fructose, total sugars and fructose/glucose ratios than those from fresh fruit, as well as less citric, ascorbic and total acids and lower sugar/acid ratios. Principal component analysis of 40 randomly chosen concentrates showed that variance is dominated by differences in fructose, total sugars and ascorbic acid contents and sugar/acid ratios. Geographical origin and concentration technology were major sources of variance but changes in post-production sub-ambient storage could not be excluded. Received: 4 July 1997 /  Revised version: 14 October 1997     

磷酸单酯淀粉糊透明度影响因素的研究

研究了磷酸单酯淀粉的透明度以及NaCl、蔗糖、柠檬酸等食品成分和老化作用对透明度的影响。结果表明，NaCl对淀粉糊的透明度影响不大，而蔗糖、柠檬酸则能提高糊液的透明度，老化使淀粉糊的透明度下降，初期下降迅速，中后期下降减缓。