Effects of different drying methods on phenolic contents,antioxidant, and tyrosinase inhibitory activity of peach blossoms

Fresh peach blossoms of two varieties were dried by using different methods, which include shade drying, freeze drying, microwave drying and hot air drying (at 30, 60, 90, 120 °C). The effects of different drying methods on phenolic contents, antioxidant and tyrosinase inhibitory activity were evaluated. Among the seven drying treatments, microwave drying yielded the highest contents of total phenolics, flavonoids, anthocyanins, proanthocyanidins and individual phenolic compounds in dried peach blossoms, while hot air drying at 30 °C gave the lowest retention of total phenolics, flavonoids, anthocyanins. As compared with shade drying and freeze drying, hot air drying at 60, 90, 120 °C resulted in higher retention of phenolic content. The highest antioxidant activity in dried peach blossoms was obtained by microwave drying, while hot air drying at 30 °C gave the lowest. The effect of different drying methods on antioxidant activity of dried peach blossoms was consistent with that of phenolic content. The highest tyrosinase inhibitory activity was achieved by hot air drying at 120 °C for variety ‘yingchun’ and 90 °C for variety ‘huangjinmeili’, but there was no significant difference among hot air drying at 60, 90, 120 °C for both varieties. The tyrosinase inhibitory activities of peach blossoms by microwave drying and freeze drying were comparable and much lower than that of shade drying. The results indicated that microwave drying was a desirable method for the preservation of phenolic compounds and antioxidant activity in peach blossoms, while shade drying and hot air drying at high temperature were favorable for tyrosinase inhibitory activity.     

A novel infrared freeze drying (IRFD) technology to lower the energy consumption and keep the quality of Cordyceps militaris

A novel laboratory scale apparatus using infrared lamps replacing the electric heating plate for the freeze drying of Cordyceps militaris was developed in this study. The drying time, energy consumption, nutritional properties, antioxidant activities and main volatile compounds of Cordyceps militaris dried by infrared freeze drying (IRFD) and traditional freeze drying (TFD) at different drying temperatures (40, 50, 60 and 70 °C) were compared. Results indicated that drying at 40, 50 and 60 °C resulted in higher retention of cordycepin, total phenolics, hydroxyl radical scavenging activity, reducing power, 3-octanone, 3-octanol and 1,3-octadiene when compared with those dried at 70 °C. IRFD could reduce 7.21–17.78% of the drying time and 11.88–18.37% of the energy consumption at a constant drying temperature in comparison of TFD. In terms of quality, IRFD and TFD had similar retention effects on cordycepin, adenosine, hydroxyl radical scavenging activity and reducing power. Consequently, the results suggest that IRFD should be a promising approach for achieving high-quality dried products.Industrial relevance.IRFD could reduce 7.21–17.78% of the drying time and 11.88–18.37% of the energy consumption at a constant drying temperature in comparison of TFD without compromising the quality of the dried product. This study can help food processing industries to produce high quality freeze dried Cordyceps militaris and many other foods with an energy efficient freeze drying process.     

Bioactive compound retention in Echium amoenum Fisch. & C. A. Mey. petals: Effect of fluidized bed drying conditions

The dried petals of Echium amoenum Fisch. & C.A. Mey. are used for the treatment of many diseases but there are not any reports about the effects of drying conditions on their bioactive compounds. A complete 3² factorial design was used, where the independent variables were drying temperature (40°C–60°C) and air flow rate (0.5–1.0 m/s). The bioactive compounds studied were total phenolic, total flavonoid and anthocyanin contents, and antioxidant activity. The desirability index was used to predict the optimal drying conditions. Both independent variables were statistically significant. The optimal drying conditions were air velocity of 0.86 m/s at 60°C. The results show that the drying conditions play an important role in determining the final quality of the product, content of its bioactive compounds, and minimum drying time.     

Hot air drying of tea flowers: effect of experimental temperatures on drying kinetics,bioactive compounds and quality attributes

The drying process is important for the quality and value of tea flower products. In the present work, the effects of different hot air drying (HAD) temperatures from 60 to 120 °C on drying kinetics, bioactive compounds (catechins, flavonol glycosides and triterpenoid saponins) and quality attributes (volatile compounds, colours and antioxidant properties) of tea flowers were systematically evaluated. The results showed that higher drying temperature resulted in a shorter drying time but with greater loss of bioactive compounds and quality attributes. Flowers subjected to HAD at 60 °C showed the highest bioactive contents and quality attributes of all HAD samples and the quality of HAD 60 °C samples were close to that of freeze-dried samples. Taking account of the production efficiency and energy consumption, the tea flowers dried at 60 °C for 180 min was preferred. These findings provide a guide for the processing of tea flowers with the aim of improving the overall quality of the product.     

Effect of vacuum‐drying,hot air‐drying and freeze‐drying on polyphenols and antioxidant capacity of lemon (Citrus limon) pomace aqueous extracts

The aim of this study was to investigate the effect of freeze‐drying, hot air‐drying and vacuum‐drying at 70, 90 and 110 °C, on dried lemon pomace polyphenols and antioxidant capacity. The total phenolic content and antioxidant capacity were higher in lemon pomace dried by hot air or under vacuum than those dried by freeze‐drying and increased as the temperature increased. The highest total flavonoid content was recorded in the pomace dried under vacuum at 70 and 90 °C. Lemon pomace dried by freeze‐drying had the highest neohesperidin content, whereas pomace dried under vacuum at 70 °C had the highest rutin and p‐coumaric acid content. The highest gallic acid content was recorded in the pomace dried by hot air at 110 °C. The results of this study indicate that drying technique should be carefully selected according to the bioactive compounds aimed to be extracted.     

Changes in bioactive compounds and antioxidant activity during convective drying of murta (Ugni molinae T.) berries

Murta (Ugni molinae T.) berries were air‐dried at five temperatures (40, 50, 60, 70 and 80 °C), and the changes in β‐carotene, phenolic acids, total phenolic and flavonoid contents and antioxidant capacities (DPPH and ORAC) were investigated. The berries showed a high content of β‐carotene, which decreased during drying temperature between 40 °C and 80 °C. Free and bound phenolic acids were also determined, showing gallic acid to be the prevalent phenolic acid. Total phenolic and flavonoid contents in the dried berries showed a higher decrease at lower temperature due to longer drying time. The radical‐scavenging activity also showed higher antioxidant activity at higher drying temperatures (70–80 °C) than at lower drying temperatures (40–50 °C). Total phenolic content (TPC) and flavonoids showed good correlation with antioxidant capacity. Murta berries proved to be an excellent source of antioxidants and bioactive compounds and are therefore a potential ingredient for new functional food products.     

Effect of drying temperature on polyphenolic content and antioxidant activity of apricots

This study was carried out in order to check for the influence of drying parameters on the phenolic compounds and antioxidant activity on two apricot cultivars (Pelese and Cafona) using two sets of air drying temperatures: (1) air temperature at 55 °C; (2) air temperature at 75 °C. Whole fresh and dried fruits were assessed for: phenolics, ascorbic acid, antioxidant activity and redox potential (all parameters were calculated on a dry matter basis). Analysis of data shows that the decrease in chlorogenic and neochlorogenic acid in Cafona cultivar is higher at the lower drying temperature. Catechin showed the same behaviour of hydroxycinnamic acids in both cultivars, while the decrease in the other compounds was significantly more marked in the sample dried at 75 °C. The antioxidant activity increased significantly in Cafona fruits and this increase was confirmed by a diminution of the redox potential.     

Influence of drying treatments on the physical and chemical properties of cucumber

This work aimed at determining the properties of cucumber exposed to convective air drying and freeze-drying. The samples were analysed in terms of colour, texture, chemical properties (moisture content, fibre, ash, vitamin C and sugars), phenolic compounds and antioxidant activity in fresh and after drying. The trials in the convective chamber were done at 40 and 60 °C, in the drying tunnel at 60 °C and in the freeze dryer at ?50 °C. The results showed that the antioxidant activity and the phenolic compounds were not affected by any of the drying treatments tested, since the values were quite similar in the fresh product as compared to the dried cucumbers. With respect to colour, the freeze drying treatment was identified as the one originating less colour change, when compared with the colour of the fresh product. Finally, texture was less affected by drying in the chamber at 40 °C and freeze drying.     

Comparison of electrohydrodynamic and hot-air drying of the quince slices

Electrohydrodynamic is one of the new methods of drying with low energy consumption, which has attracted much attention from the investigators in recent years. In this study, the quince slices have been dried by an electrohydrodynamic method with variable voltage (at three levels of 5, 7, 9 kV) and by a hot- air drying with variable temperature (at three levels of 50, 60 and 70 °C). The effect of two drying methods on drying kinetics, energy consumption, potent antioxidant activity and phenolic compounds of quince slices is investigated. Statistical results showed that the total phenolic compounds and the antioxidant capacity of the dried quince slices by the hot-air process is 1.37 and 1.15 times as much as those in electrohydrodynamic process, respectively, and the average energy by hot-air drying is 48.66 times as much as the average energy consumption of electrohydrodynamic method.     

基于风味成分分析的不同干燥方式玫瑰花茶鉴别技术研究

风味物质是玫瑰花茶的重要活性成分之一。基于顶空气相-离子迁移谱（Headspace-gas chromatography-ion mobility spectroscopy, HS-GC-IMS）技术分析了玫瑰花茶在热泵能低温干燥（RT1）、常温干燥（RT2）、真空低温干燥（RT3）和真空冷冻干燥（RT4）四种不同干燥方法下的气味指纹图谱,采用主成分分析法分析其风味物质的差异。气相-离子迁移谱结果表明,共鉴定出64个信号峰和53种挥发性化合物。玫瑰花茶中具有较高强度峰的化合物包括12种醇、20种醛、10种酮、6种酯、3种烯烃、1种呋喃和1种醚。不同干燥方式的玫瑰花茶中的黄酮含量差异不大,真空低温干燥的玫瑰花茶中总酚和总花色苷含量最高。主成分分析结果表明,前2个主成分的累计贡献率为82%,能够很好地代表原始数据的特征,不同干燥方式下玫瑰花茶风味物质含量差异较大。其中,RT4玫瑰花茶样品中的风味物质更为丰富。     

Effect of drying conditions on bioactive compounds and antioxidant activity of broccoli (Brassica oleracea L.)

The effect of air‐drying parameters on antioxidant activity and changes in antioxidant compounds of broccoli (Brassica oleracea L.) were studied. Broccoli samples were dried to 70 g kg^?1 moisture content using temperatures ranging from 50 to 100 °C and air flow‐rates from 1.20 to 2.25 m s^?1, resulting in drying times from 25 to 90 min. Temperature, owing to its positive effect on the oxidation kinetics, was negatively correlated with ascorbic acid and free and total polyphenol contents but not with kaempferol, even though the sample dried at the highest temperature showed the lowest kaempferol content. The air flow‐rate was positively correlated with the total (TPP) and free (FPP) polyphenol contents because it led to a reduction in the drying time. No correlation was found between air flow‐rate and kaempferol content. Air flow‐rate and temperature positively affected the antioxidant activity by reducing the drying time. High‐temperature, short‐time processes maximised the antioxidant activity of broccoli owing to the negative effect of drying time on antioxidant activity. The antioxidant activity of broccoli was positively and significantly correlated with the FPP content but not with TPP and kaempferol. The evaluation of hydroxymethylfurfural content as an indicator of the occurrence of a Maillard reaction in dried broccoli did not support the hypothesis of a contribution of MRPs to the antioxidant activity of dried broccoli. Copyright © 2006 Society of Chemical Industry     

Influence of hot-air temperature on drying kinetics,functional properties,colour, phycobiliproteins,antioxidant capacity,texture and agar yield of alga Gracilaria chilensis

Effect of air temperature on drying kinetics, functional properties, phycobiliproteins (PE and PC), colour, antioxidant capacity, total phenolic content, texture and agar yield during drying of algae Gracilaria chilensis were studied. Drying curves were satisfactorily simulated with the Weibull model at 40, 50, 60 and 70 °C. Both, Rehydration Ratio and Water Holding Capacity decreased with increasing temperature. Low drying temperatures showed higher PE and PC concentration than higher temperatures (e.g. 60 and 70 °C). In particular, dehydration at 50 °C presented the higher values of these two pigments. The three chromatic coordinates (L1, a1 and b1) were influenced by the treatments showing the highest ?E value at 50 °C. Antioxidant activity as well as texture were notably influenced by increasing drying temperatures. At 70 °C, a maximum agar yield of 40 g/100 g was obtained. Results indicated that agar yield and quality of dried algae showed opposite behaviours leading to a compromise decision on operating conditions involved in the overall process. According to these results, optimization of the process based on economical aspects of the final dried product is required.     

Changes produced in the aroma compounds and structural integrity of basil (Ocimum basilicum L) during drying

The influence of drying on the aroma compounds, from a chemical and sensory standpoint, and on the structural integrity of basil (Ocimum basilicum L) was evaluated. The drying methods tested were oven drying at 45 °C, air drying at room temperature and freeze‐drying. The volatile compounds of fresh and dried basil were extracted and concentrated by simultaneous distillation/extraction and analysed by gas chromatography/mass spectrometry. In all, 27 volatile components were identified, linalool being the major component, followed by eugenol. The total quantity of volatiles of fresh basil decreased considerably during oven drying and freeze‐drying, whereas air drying of basil at room temperature brought about only small losses of volatile components. The cell damage produced on basil leaves during drying was evaluated by scanning electron microscopy. From a sensory standpoint, fresh basil was described as having a fresh, herbaceous and floral odour, while the dried samples had a mentholated, spicy, hay‐like and earthy odour. Copyright © 2004 Society of Chemical Industry     

Phenolic compounds and antioxidant activity are differentially affected by drying processes in celery,coriander and parsley leaves

Convective drying (CO) is the most common technique for drying herbs, although it may diminish phenolic compounds content. Microwave drying (MW) has been suggested as an alternative, although its effects on phenolic compounds remain to be explored. The aim of this study is to compare the effects of different convective temperatures (40, 80 and 120 °C) and microwave powers (100, 500 and 1000 W) on drying time, polyphenols classes (HPLC-DAD) and antioxidant capacity in celery, coriander and parsley leaves. Microwave procedure reduced drying time (MW: 3 h–7 min; CO: 25–1.5 h) resulting more effective than CO. Increasing temperatures led to an initial decrease in total phenolic content (TPC) and antioxidant activity followed by an increase, potentially by the release of bound phenolic acids. Regarding MW, the highest polyphenol content was generally observed at 500 W, probably due to the hydroxycinnamic acid's rise. Antioxidant capacity was similar at 500 and 1000 W. There was a good agreement between TPC and antioxidant capacity. Consequently, MW seems a good alternative to reduce drying time. However, the maintenance or improvement of phenolic activity depends on the food matrix. Indeed, the best drying system and conditions to preserve phenolic compounds were variable depending on the herb type: celery (CO at 40 °C), coriander (both CO at 40 °C and MW at 500 W) and parsley (MW at 100 W).     

不同干燥条件下猪肉脯风味指纹图谱的研究

目的 应用气相离子迁移谱（Gas Chromatography-Ion Mobility Spectrometry, GC-IMS）对肉脯不同干燥条件下的挥发性有机物（Volatile Organic Compounds, VOCs）进行分析,实现基于风味指纹信息的肉脯干燥温度和时间关键参数的反向预测。方法 采用单因素分析方法并借助GC-IMS技术对不同干燥温度与时间下肉脯样品的VOCs变化进行了检测和分析,对选取的GC-IMS图谱特征区域信号进行主成分分析,并结合偏最小二乘回归方法分别对干燥温度和时间进行预测识别。结果 肉脯在干燥过程中产生的VOCs主要包括：醇类、醛类、酮类、酸类、杂环化合物以及含硫化合物等6类,GC-IMS风味指纹谱结合化学计量学方法能够准确预测烘干阶段肉脯的工艺参数。结论 本研究对研究工艺条件对肉脯风味的影响提供了一种新的分析方法,也为肉制品的品质鉴别提供了理论基础。     

干燥方式对香芋片挥发性物质的影响

目的:提高香芋片干燥技术及提取效率。方法:采用水蒸气蒸馏法及气相色谱—质谱联用技术,对比热风干燥(HAD)、直触超声强化热风干燥(CU-HAD)、远红外辐射干燥(FIRD)、直触超声强化远红外辐射干燥(CU-FIRD)和冷冻干燥(FD)香芋片的挥发性成分组成及特征差异,并进行主成分分析。结果:干燥前及不同干燥方式加工后的香芋片共检测出149种挥发性成分,其中烷烃类54种、酯类20种、苯环类16种、醇类12种、酮类11种、烯烃类11种、醛类8种、酸类4种、其他类化合物13种。不同干燥方式处理的香芋片挥发性成分以苯环类、酯类为主。以HAD处理的香芋片挥发性成分最少,仅有42种,FIRD次之,以CU-HAD处理的香芋片虽然挥发性成分较多,但多数为烃类化合物,对香芋风味贡献值较小,以CU-FIRD和FD处理的香芋片的整体成分较接近,但CU-FIRD耗时最短,结合主成分分析得出CU-FIRD对香芋片挥发性成分的保留与加工效果最好。结论:将直触超声技术和远红外辐射加热联合应用对香芋风味的保护作用要好于单一超声和单一远红外辐射的效果。     

Antioxidative effect of Ecklonia cava dried by far infrared radiation drying

Far infrared radiation drying (FIRD) of Ecklonia cava was tried in order to reduce drying time and save money in an industrial processing of wet seaweeds. FIRD was carried out at temperature range of 40–80°C with the examination of antioxidant activities as compared to freeze drying (FD). FIRD showed the shorter drying times and higher polyphenolic contents than FD. Most FIRD extracts had IC₅₀ values than FD extracts. Among them, absolute methanolic extract (ME) from E. cava dried by FIRD at 40°C (FIRD40-ME) possessed the highest radical scavenging activity. Moreover, FIRD40-ME enhanced cell viability and H₂O₂ scavenging activity in Vero cell. Thus, FIRD40-ME was separated by high performance liquid chromatography (HPLC) and radical scavenging activities of the separated compounds were directly evaluated by on-line coupled ABTS·+ radical scavenging detection system. From the result, it was found that dieckol was the major antioxidant compound. These results illustrate that antioxidant activity of FIRD were more effective than FD and industrial application of FIRD process can be useful in seaweeds.     

干燥方法对茯苓产品显微性状、营养成分及抗氧化活性的影响

选取真空冷冻干燥(FD)、40℃恒温干燥(CD-40)、60℃恒温干燥(CD-60)、100℃恒温干燥(CD-100)、120℃恒温干燥(CD-120)、日晒(SD)、空气能仿生变温干燥(AD)7种方法对茯苓进行干燥,比较干燥后茯苓产品的茯苓菌丝体的显微性状、水溶性多糖含量、水溶性蛋白含量、醇溶性蛋白含量和水提液的抗氧化活性。结果表明:与FD相比,SD、AD的茯苓菌丝体呈疏松排列,CD的茯苓菌丝体呈糊状黏结状态;AD的茯苓产品的抗氧化活性最高;与FD相比,AD的水溶性多糖含量变化不显著、水溶性蛋白极显著增加(P<0.01)、醇溶性蛋白显著减少(P<0.05)。综合分析,AD为最佳的茯苓干燥方法,可解决茯苓无硫加工产业化的需求。     

Loss of essential oil of tarragon (Artemisia dracunculus L.) due to drying

The effect of hot air‐drying on the essential oil constituents and yield in French and Russian tarragon (Artemisia dracunculus L.) leaves was studied. The tarragon leaves were dried at air temperatures ranging from 40 to 90 °C. The drying stopped when the moisture content of the samples reached 10% or for some of the treatments reached 7, 20 and 30%. The essential oil of the fresh and dried leaves was isolated by hydrodistillation and analysed by capillary gas chromatography and gas chromatography–mass spectrometry. The decrease of oil during the drying process was highest at 60 °C drying temperature. For French tarragon the decrease in the amount of oil was significantly lower at 90 °C. The effect of the relative humidity of the drying air at each temperature was not significant. The main compounds were estragole in French tarragon (69%) and sabinene in Russian tarragon (40%). The drying process changed the relative percentage of the constituents in the oil; for instance, the relative percentages of estragole decreased and sabinene increased in French tarragon. Copyright © 2006 Society of Chemical Industry     

干燥方式对真姬菇菌柄和菌盖挥发性风味物质的影响

采用电子鼻结合顶空固相微萃取-气相色谱-质谱技术探究热风干燥（60、70、80℃）、冷冻干燥、自然干燥对真姬菇菌柄和菌盖挥发性风味物质的影响,并通过相对气味活度值（relative odor activity value,ROAV）分析各风味物质对干燥样品总体风味的贡献。结果表明：通过电子鼻检测发现这10组样品传感器数值存在明显差异且电子鼻可以对其风味很好地区分。热风干燥（60、70、80℃）、冷冻干燥、自然干燥的菌盖分别鉴定出32、41、40、53、48种风味物质,而菌柄分别鉴定出34、33、33、43、44种风味物质。相同干燥方式处理的菌盖挥发性风味物质含量高于菌柄,相较于自然干燥和冷冻干燥,热风干燥生成了较高含量的新型风味物质。由ROAV分析得出25种风味物质,其中三甲胺、异戊醛、1-辛烯-3-醇风味贡献较大。进一步对这25种风味物质进行主成分分析,建立综合函数品质评价模型,发现热风干燥80℃时制得菌盖样品（g-80℃）评分最高,说明其风味品质最好。