Hot air drying of yacon (Smallanthus sonchifolius) and its effect on sugar concentrations

This work aimed to experimentally study the drying behaviour of yacon tubers with and without steam blanching. Drying was carried out for 5 h and 30 min in a forced air dryer at 50 °C, 60 °C and 70 °C. The results indicated that the shortest drying time was obtained at 70 °C for blanched samples, and that the equilibrium water activity values were significantly lower for the blanched samples at all temperatures. The yacon dried without prior blanching showed lowest concentrations of reducing sugars when dried at 70 °C, significantly lower than those dried at 50 °C and 60 °C. This indicates hydrolysis of the fructo-oligosaccharides at 70 °C, a fact verified by the significant increase in reducing sugars content from 36.65 ± 0.54–44.10 ± 0.96% and reduction in the non-reducing sugars from 31.62 ± 0.55–26.18 ± 0.29%.     

Dietary fiber,fructooligosaccharides, and physicochemical properties of homogenized aqueous suspensions of yacon (Smallanthus sonchifolius)

Yacon roots are a promising source of inulin­type fructans (35 g/100 g dry matter) with a total amount of dietary fiber of about 45 g/100 g dry matter. The polydispersity of the particle size distribution of yacon aqueous suspension was reduced with increasing the degree of homogenization due to two phenomena: aggregation of particles, and disruption of large particles. Non­homogenized yacon suspensions exhibited large cell clusters that were disrupted into small cell clusters, single cells, and aggregates. The most concentrated suspension exhibited mainly aggregates.The volume fraction of the suspensions decreased significantly with increasing the degree of homogenization. This was attributed to a denser packing of small particles and aggregates in between large particles thus allowing the water within the structure to be released.Yacon suspensions exhibited high elastic modulus (750 Pa) at low water insoluble solids content (0.9% WIS). Additional results suggested that inulin­type fructans contributed to the elastic properties of yacon suspensions.The yacon suspensions studied in this work can be considered as semi­concentrated suspensions, i.e. the plot elastic modulus of the suspensions versus concentration exhibited a region immediately after the transition region. Particle interactions seem to be of great importance in this region in the particular case of yacon suspension since the elastic modulus (G′) reached 750 Pa at low water insoluble solids content (< 1%).     

Single-layer drying characteristics and colour kinetics of red chilli

Single‐layer drying experiments were conducted under controlled conditions of temperature, relative humidity (RH) and air velocity to find out the effects of drying conditions and blanching on the drying rate and colour of Thai red chilli. Drying rate increased with an increase of drying air temperature and a decrease of RH. Air temperatures above 65 °C affected the colour of red chilli. Red chilli should be dried at an air velocity equal to or just above 0.50 m s^?1. Above this value, the drying rate becomes independent of air velocity. RH and air velocity have no effect on the colour of red chilli. Faster drying rate and higher colour value was found for the blanched sample rather than the unblanched sample. The Newton and the Page equations were fitted to the experimental data. The Newton equation was found to describe the single‐layer drying of red chilli better than the Page equation.     

Modelling the change in colour of broccoli and green beans during blanching

The green colour of vegetables changes considerably during heat treatments like blanching. Green beans from two different countries and growing seasons, and the stems and florets of broccoli were heat-treated from 40 up to 96°C. The colour was monitored with the CIE-Lab system. Expressing the green colour as −a*/b* proved to considerably reduce the observed variance within measuring samples. It can be considered as a kind of internal standardisation. The colour was modelled by a simplified kinetic mechanism of two consecutive reactions: one that increases colour, one that degrades colour. First, all data sets were analysed separately using non-linear regression. The obtained percentage variance accounted for (R²_adj) ranged from 75.7 to 90.8%. Allowing separate initial conditions but with the kinetic parameters in common, the data of the same vegetable type (green beans and broccoli separately) could be pooled and analysed together (R²_adj=87.4 and 77.2%, respectively). The kinetic parameters obtained were so similar that a complete pooled and generic analysis was possible even for green beans and broccoli together. These findings greatly validate the developed model and indicate that the formation and degradation of visible colour in vegetables is governed by processes related to the colouring compounds (like chlorophyll and chlorophilides), irrespective of the vegetables under study.     

Dependence of fructooligosaccharide content on activity of fructooligosaccharide-metabolizing enzymes in yacon (Smallanthus sonchifolius) tuberous roots during storage

ABSTRACT:  Tuberous roots of yacon ( Smallanthus sonchifolius ) accumulate about 10%, on a fresh weight basis, of inulin-type fructooligosacharides (FOSs), known as a food ingredient with various healthy benefits. However, we have a great difficulty to ensure these benefits because FOSs with a lower degree of polymerization (DP) decreased remarkably, and fructose increased when the tuberous roots were stored after harvesting even under previously recommended storage conditions of low temperature with high humidity. In the present study, to elucidate the involvement of FOS-metabolizing enzymes in FOS reduction during storage at 90% relative humidity and 8°C, we extracted a crude protein from yacon tuberous roots and measured the activities of invertase (β-fructofuranosidase, EC 3.2.1.26), sucrose:sucrose 1-fructosyltransferase (1-SST, EC 2.4.1.99), fructan:fructan 1-fructosyltransferase (1-FFT, EC 2.4.1.100), and fructan 1-exohydrolase (1-FEH, EC 3.2.1.80). The enzyme activities acting on sucrose, both invertase and 1-SST, were weakened after storage for a month. In addition, the activity of 1-FEH acting on short FOSs such as 1-kestose (GF₂) and 1-nystose (GF₃) was higher than that of 1-FFT. These results suggest that the continuous decline in FOSs of low DP during storage was dependent mainly on the 1-FEH activity. On the other hand, FOSs with a DP of ≥ 9 only slightly decreased in stored yacon tuberous roots during storage, though distinct 1-FEH activity was observed in vitro toward a high-DP inulin-type substrate, indicating that highly polymerized FOSs content was unlikely to be closely connected with the 1-FEH activity.     

雪莲果热泵干燥特性及品质研究

研究雪莲果样品厚度、装料量、干燥温度、风速和旁通比对雪莲果热泵干燥特性及质量变化的影响。结果表明：雪莲果干燥速率随着样品厚度和装料量的增加而降低,随着干燥温度和风速的升高而增加。雪莲果热泵干燥过程绝大部分以降速干燥为主伴随相对较短时间的恒速干燥,而有些干燥速率曲线只存在降速干燥阶段。综合考虑单位能耗除湿率、色泽差异、收缩率、复水比,雪莲果热泵干燥最适参数范围：样品厚度2～4 mm、装料量1～2 kg/m2、干燥温度25～35 ℃、风速1.5～2.0 m/s。而旁通比对雪莲果热泵干燥进程影响不显著。     

Vacuum impregnation of apple slices with Yacon (Smallanthus sonchifolius Poepp. & Endl) fructooligosaccharides to enhance the functional properties of the fruit snack

This work aimed to incorporate prebiotic FOS from yacon in apple slices using vacuum impregnation (VI). Three FOS concentrations (10.3, 14.1 and 18.9 g per 100 g of dry matter (DM)), two temperatures (25 and 35 °C), reuse of extracts and stability of the impregnated slices were evaluated. The highest impregnation level (30.5 g per 100 g DM) was obtained at 35 °C with 14.1% FOS extract while levels of common sugars were reduced. Total phenolics and ABTS antioxidant capacity (AC) slightly decreased while ORAC AC was reduced by 55%. Reuse of the impregnation solution in successive cycles after restoring the FOS level maintained the FOS concentration and profile (GF2–GF7), sugars and phenolic antioxidants. FOS in apple slices remained stable during 4 week storage, while a_w, colour and fracture point changed during storage. This work demonstrated the feasibility of yacon FOS to improve the functional properties of dehydrated apple slices.     

Prebiotic effects of yacon (Smallanthus sonchifolius Poepp. & Endl), a source of fructooligosaccharides and phenolic compounds with antioxidant activity

Montepulciano is one of the most famous and important red-berried grapes of Italy. This article presents and discusses a comparative study of aroma profile and phenolic content of the Montepulciano wine from the Marches and the Abruzzo regions. The volatile composition of wines was determined by using headspace solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). The PDMS fibre was chosen. The dominating esters in Montepulciano wines were ethyl hexanoate, ethyl decanoate, and ethyl octanoate, whereas phenyl ethanol and 3-methyl-1-butanol were dominating alcohols.Phenolic compounds, namely gallic acid, p-coumaric acid, trans-ferulic acid, caffeic acid, trans-resveratrol, (+)-catechin and (−)-epicatechin, were examined using HPLC-MS with direct injection of wine samples. The total phenolic content of the analysed wines was in the range of 30.4-61.9 mg l⁻¹. The presence of high amounts of esters seems to characterise the volatiles of Montepulciano wines from the Marches, whereas a high level of alcohols was found in Montepulciano wines from Abruzzo. Moreover, multivariate chemometric techniques, such as cluster analysis and principal component analysis, supported this thesis. Headspace solid phase microextraction and gas chromatography-mass spectrometry were used to analyse 20 commercial wine samples (Montepulciano monovarietal red wines) from the Marches (10 samples) and Abruzzo (10 samples).     

Effect of blanching on microwave freeze drying of stem lettuce cubes in a circular conduit drying chamber

Effects of boiling water and microwave blanching methods on the dielectric properties, electrical conductivity as well as microstructure of stem lettuce cubes (as a model for plant tissue) were studied. The study also focused on how different blanching methods affect microwave freeze-drying (MFD) in a circular conduit drying chamber and conventional freeze drying (FD) of stem lettuce cubes. Results showed that the electrical conductivity of samples blanched by microwave was two times higher than that of boiling water blanched ones and five times higher than that of unblanched samples. Apart from that, dielectric constant (ε′) and loss factor (ε″) of the stem lettuce cubes decreased significantly after freezing. MFD duration of microwave blanched samples was approximately 4.5 h, reduced by 30% compared to boiling water blanched ones. MFD process in a circular conduit yielded products of high quality compared to that in a tray.     

热风干燥过程中小白杏色泽的变化及其动力学研究

为降低小白杏因干燥引起的褐变,保证产品干燥后色泽良好,同时为小白杏干燥设备选型及工艺确定提供理论依据,选择热风干燥的方式,以新疆小白杏为原料,以亮度值(L)、红绿值(a)、黄蓝值(b)、总色差(△E)和褐变指数(BI)为考察指标,研究了热风干燥温度(40,50,60℃)和风速(2,3,4m/s)对新疆小白杏色泽的影响,并在该基础上建立新疆小白杏热风干燥色泽变化动力学模型,有效预测、调节杏褐变程度。结果表明:小白杏在不同风速、不同干燥温度条件下均发生了较为明显的颜色变化,不同热风干燥温度对干燥时间和干燥后杏干色泽均有显著影响,而不同干燥风速对干燥后杏干色泽影响不显著。在不同热风干燥温度和不同风速条件下干燥小白杏的L值和b值随着干燥时间的延长逐渐降低,而a值、△E值和BI值均逐渐升高。小白杏热风干燥过程中颜色参数的反应速率常数k值随着干燥温度的升高而呈现出一定的规律性变化,其中k值受热风温度的影响较大,受风速的影响较小。根据拟合决定系数R2的比较结果,通过动力学方程模拟,得出0阶模型能更好地描述和预测不同风速和不同干燥温度条件下小白杏在热风干燥过程中的颜色变化,而在不同风速和干燥温度条件下小白杏褐变动力学模型模拟效果较好的是1阶模型。该研究为小白杏干燥工艺及杏干产品感官品质控制提供了理论依据。     

Kinetics of colour change of bamboo shoot slices during microwave drying

The effect of microwave power on colour change kinetics of bamboo shoot slices was investigated during microwave drying. Colour changes were quantified by tri‐stimulus Hunter L (whiteness/darkness), a (redness/greenness), and b (yellowness/blueness) system. These values were also used for calculation of total colour change (ΔE), chroma, hue angle, and browning index (BI). Microwave drying as expected changed colour parameters because of browning. The values of L and b decreased, while values of a and ΔE increased during drying. Mathematical modelling of colour change kinetics indicated that L, b, chroma and BI could be defined using a first‐order kinetic model, while a, ΔE and hue angle could be defined using a zero‐order kinetic model. Considering together colour deterioration and quality of dried bamboo shoot slices at higher power reveals the need of process standardisation for getting good quality product.     

Changes in pigment profile and surface colour of fig (Ficus carica L.) during drying

In this study, anthocyanins in three fresh fig varieties (Ficus carica L.) cultivated in Turkey were characterised and quantified by HPLC/DAD and HPLC/MS. In addition, the carotenoid composition of Sar?lop and Sar?zeybek, yellow fig varieties, was determined, and then the ripening‐ and drying‐related changes in carotenoids and surface colour of figs were monitored during conventional sun‐drying. Four different anthocyanins, cyanidin‐3‐glucoside, cyanidin‐3,5‐diglucoside, cyanidin‐3‐rutinoside (major anthocyanin) and pelargonidin‐3‐glucoside, were identified in samples. Lutein, zeaxanthin, β‐cryptoxanthin and β‐carotene were carotenoids in yellow fig varieties. Approximately 80% of carotenoid compounds in yellow fig varieties degraded at the end of drying (i.e. seventh day). L (lightness), a (redness and greenness) and b (yellowness and blueness) colour parameters were measured by Hunter Lab system. Great changes in carotenoid composition and surface colour were observed at ripening stage on tree. A significant reduction in L and b values that refers to browning in figs was made in the first 3 days of drying process.     

Effect of blanching and drying treatments on quality of bamboo shoot slices

The enzymes activity, texture, pectin, microstructure and colour change in bamboo shoots (Dendrocalamus latiflorus) were examined to evaluate the effect of blanching and drying treatments on quality of bamboo shoot slices (BSS). Peroxidase (POD), phenylalanine ammonia‐lyase and polyphenol oxidase in BSS will become completely inactive at 95 °C for 6‐, 9‐ and 12‐min blanching treatments, respectively. The hardness and protopectin (PP) content decreased after the blanching treatment. Meanwhile, the content of water‐soluble pectin increased initially and then decreased gradually during the blanching. After the blanching treatment, the L* and a* of BSS decreased, while b* increased, ΔE > 2. The hardness of rehydrated BSS decreased by 43.57% after freeze drying (FD), which, however, decreased more after hot air drying (HAD). The pectin of rehydrated BSS was also determined to explain the hardness change in BSS. The BSS acquired similar microstructure of fresh samples after FD, while microstructure of BSS was severely damaged after HAD. The colour of BSS changes significantly after drying treatment. However, FD can maintain better colour of BSS than HAD. The results may provide a reference for industrial production of BSS.     

Stability of quercetin derivatives in vacuum impregnated apple slices after drying (microwave vacuum drying,air drying,freeze drying) and storage

Microwave vacuum drying (MVD) was investigated for apple slices enriched with quercetin derivatives by vacuum impregnation (VI). Additional freeze drying (FD) and air drying (AD) were conducted. Compared to native apples, the impregnated tissue resulted in higher moisture content, elevation of weight and significant browning, due to the incorporated VI solution. The total quercetin content and quercetin glycoside composition were not affected by MVD and FD. The vacuum conditions protect the polyphenols from oxygen dependent degradation and browning reactions. AD resulted in an average quercetin glycoside loss of 44% and undesirable changes, particularly discoloration. The degradation is caused by both non-enzymatic and enzymatic reactions. The pulsed microwave energy intake improved the drying result in structure and led to a faster drying process of 130 min. The bulk density of MVD apple chips (0.69 g/ml) ranged between 0.33 g/ml for FD and 0.75 g/ml for AD. The final moisture content was the lowest after FD (6.8 g/100 g), followed by 9.0 g/100 g after MVD and 12.7 g/100 g after AD. The shelf life was significantly influenced by storage temperature and time. After 12 month at 20 °C, the total quercetin content decreased by 21%.     

Influence of drying conditions on colour,betacyanin content and antioxidant capacities in dried red-fleshed dragon fruit (Hylocereus polyrhizus)

In this study, drying of red-fleshed dragon fruit at different temperatures (40, 50, 60, 70 and 80 °C) and air velocities (1.0 and 1.5 m s⁻¹) was conducted under the specific humidity of 25 g H₂O kg⁻¹ dry air. The results showed that drying at higher temperatures resulted in shorter drying times. However, temperature and air velocity did not significantly affect the total betacyanin contents and antioxidant capacities in dried products. Seven betacyanins identified by LC-MS were betanin, isobetanin, phyllocactin, isophyllocactin, betanidin 5 –O-(6′O-3-hydroxybutyryl)-β-glucoside, isobetanidin 5 –O-(6′O-3-hydroxybutyryl)-β-glucoside and decarboxylated phyllocactin. In addition, the temperature increased the isomerisation of betacyanins. The most preferable condition for preserving the colour and betacyanin contents of red-fleshed dragon fruit was the drying at a temperature of 80 °C and air velocity of 1.5 m s⁻¹ since it could shorten the drying time and give a bright red colour to the dried product as well as it had no significant impact on the betacyanins.     

雪莲果系列制品的研制

为提高雪莲果的利用价值和开发新的功能性食品,以新鲜雪莲果为原料,榨汁后滤液喷雾干燥制备雪莲果汁粉,滤渣制备雪莲果渣粉。考察了护色剂对雪莲果汁粉及出粉率的影响,并对产品中低聚果糖的含量进行了测定。再以玉米胚芽油为芯材,雪莲果汁及其他材料为壁材,采用微胶囊技术研发新型的功能性雪莲果汁粉末油脂。结果表明:0.20%的柠檬酸护色效果较好,制备的雪莲果汁粉末油脂表面油含量2.11%,包埋率92.6%,冲溶后的乳状液有雪莲果香且稳定性好。     

Effect of different drying methods on drying characteristics,colour, total phenolic content and antioxidant capacity of Goldenberry (Physalis peruviana L.)

In this study, the effects of convective, microwave and microwave–convective drying methods on the drying characteristics, colour, total phenolic content and antioxidant capacity of goldenberry fruits were investigated. To select the most appropriate thin‐layer drying model for drying treatments, nine mathematical drying models were fitted to the experimental data. Based on the statistical tests used for evaluation, the Midilli et al. and Wang and Singh models were considered the best models to describe the drying behaviours of goldenberry fruits in all drying methods. The colour values (L*, a* and b*) of fresh fruit were decreased by drying. Compared with the fresh sample, the dried samples exhibited a 64–75% and 65–75% decrease in total phenolic content and antioxidant capacity, respectively. Among the different drying treatments, the values closest to those of fresh samples with respect to colour values, total phenolic content and antioxidant capacity were achieved with the 160 W microwave drying method.     

雪莲果多糖降血脂及降血糖活性的研究

本文采用预防性高血脂动物模型实验方法考察雪莲果中提取多糖的降血脂活性。分别对小鼠的体重,血清总胆固醇(TC),三酰甘油(TG),低密度脂蛋白胆固醇(LDL-C)和高密度脂蛋白胆固醇(HDL-C)进行了测定。结果发现:雪莲果多糖对小鼠体重增长无显著性影响;雪莲果粗多糖和纯多糖极显著降低高血脂小鼠血清TC、TG和LDL-C含量(p0.01);雪莲果纯多糖显著提高小鼠血清中HDL-C含量(p0.05),并且纯多糖能极显著降低小鼠肝脏TG和TC含量(p0.01)。表明雪莲果中糖类成分对高脂饮食所致小鼠血脂升高有明显抑制作用,且纯多糖的效果优于粗多糖,能有效预防高血脂症。采用小鼠高血糖模型降糖实验方法考察雪莲果多糖的降血糖活性。结果显示:雪莲果粗多糖低、中剂量组空腹血糖值显著降低(p0.05),证明雪莲果多糖体内降血糖效果。