Effects of pretreatment ultrasound bath and ultrasonic probe,in osmotic dehydration,in the kinetics of oven drying and the physicochemical properties of beet snacks

Osmotic dehydration and ultrasound are pretreatments used in order to reduce costs and processing time in the drying of food. We investigated the effect of the ultrasonic bath and an ultrasonic probe in osmotic solution, as a pretreatment of the drying process in an oven, for beet snacks. Different conditions of pretreatments (TP: ultrasonic probe treatment; TB: ultrasonic bath treatment) were performed and analyzed for water loss (WL) and solid gain (SG). After the snacks were ready, we evaluated the drying kinetics, aw, Brix, color, texture, and anthocyanin content. No difference was observed between treatments for SG and WL. The pretreatments TP5, TP10 and TB20 decreased by 22.2% the drying time in the oven. Regarding the snacks, there was no difference in texture. The colors of TP5, TP10, and TB10 were similar to the control, as well as the a_w value of the TP5 and TP10. The TP5 had the highest anthocyanin content. The use of ultrasound probe in osmotic solution for 5 min, as a predrying treatment, is a viable technology as it reduces pretreatment and drying time without impairing the quality of the final product.

Practical applications

The use of ultrasound as a pretreatment in the drying of fruits reduces the drying time. Drying is an important process in obtaining new products, in addition to increasing shelf‐life.     

Far infrared assisted refractance window drying of apple slices: Comparative study on flavour,nutrient retention and drying characteristics

In the present investigation, far infrared (FIR) assisted refractance window (RW) drying (FIR+RW) of apple slices (2 and 5 mm) was evaluated in comparison with RW and hot air (HA). FIR+RW reduced drying time by 50 and 69% compared to RW and HA, respectively. Also, FIR+RW drying retained a significantly higher amount of phenolics, flavonoids, ascorbic acid, and antioxidant activity, as compared to HA. Increase in FIR temperature from 50 to 60 °C reduced drying time by 10–19% without having any deleterious effect on quality. Colour, flavour, and microstructure of FIR+RW dried slices were comparable to that of RW. Nearly 46% saving in energy consumption was observed for FIR+RW drying compared to HA. Results suggested that FIR+RW drying can be explored as a potential technique for drying of fruits in a shorter time, with better retention of flavour, nutrients and also enhance energy efficiency.Industrial relevanceDried apple slices have a good market potential as a raw material in many processed foods and can be an alternative to deep fat fried chips for health-conscious consumers. This work focuses on assessing the efficacy of developed FIR assisted RW drying system in terms of drying time, energy, and quality attributes (colour, nutritional, flavour, microstructure) in comparison with conventional drying methods. The results showed that FIR assisted RW drying technique has great industrial potential in saving processing time as well as energy with better retention of quality of dried products.     

红外干燥对芝麻品质的影响

利用红外技术对芝麻进行干燥,并采用压榨法制油,研究不同红外干燥参数对芝麻水分含量、发芽率、挥发性气体成分及芝麻油酸值、过氧化值的影响。结果表明:红外干燥对芝麻的发芽能力有显著的破坏作用,100℃红外干燥5 min发芽能力约下降至1/5,干燥25 min芝麻完全失去发芽能力。当红外干燥时间在10~25 min或干燥温度在70~130℃时,芝麻的水分含量均达到安全水分(7%)。随着干燥时间的延长或温度的升高,芝麻油酸值由21.35 mg KOH/g降低至4.11 mg KOH/g,过氧化值呈升高趋势(最大值0.71mmol/kg)。红外干燥的芝麻挥发性气体成分中含有烃类、酯类、醛类、醇类、酸类等,其数目依次降低;当干燥时间在15min以上或干燥温度在100℃以上时,酯类成分相对含量减少,而酸类和醇类成分相对含量有一定的增加。     

红外辐射干燥胡萝卜的试验研究

采用红外辐射干燥的方法,对胡萝卜片进行了不同条件下的干燥试验,研究红外辐射干燥法对不同干燥参数条件下胡萝卜片的含水率及颜色变化,结果表明物料的厚度、加热温度对干燥含水率变化影响较大,而物料的厚度、加热温度和辐照距离对胡萝卜片的颜色变化均很大。在胡萝卜片厚度为4.5mm,辐照距离为12cm,物料温度55℃时,在保证干燥品质较好的条件下,效率最高。     

Study the effect of sun, oven and microwave drying on quality of onion slices

Sun, oven (50 and 70 °C) and microwave oven (210 and 700 W) drying of onion slices were carried out to monitor the drying kinetics and quality degradation of the product. Page, “Modified Page” and “Midilli and Küçük” models exhibited high coefficient of determination (R²) values, ranging between 0.994 and 0.999. The calculated effective diffusivity (D_eff) values (m²/s) of onion slices for the sun, oven 50 °C and oven 70 °C, microwave 210 W and microwave 700 W drying process were 8.339 × 10⁻¹⁰, 7.468 × 10⁻¹⁰, 1.554 × 10⁻⁹, 4.009 × 10⁻⁸ and 4.869 × 10⁻⁸, respectively. Fresh and dried onion slices had high amounts of K (696.82-16357.55 mg/kg), Ca (69.64-340.03 mg/kg), Na (37.72-1895.43 mg/kg), Mg (3.31-964.77 mg/kg) and P (46.47-3384.07 mg/kg) minerals. The highest mineral values were determined in oven dried samples. Sun (L^∗ 58.00 ± 4.83, a^∗ 0.27 ± 0.10, b^∗ 14.36 ± 2.40) and microwave oven drying (210 W) (L^∗ 54.78 ± 7.54, a^∗ −0.71 ± 0.09, b^∗ 13.17 ± 1.05) revealed better colour values in the dried products. The phenolic contents of microwave oven dried samples (1664.39 ± 134.12 and 1623.59 ± 140.02 for 210 W and 700 W, respectively) were higher than those of the other dried onion slices.     

超声—远红外辐射干燥对香蕉片品质的影响

采用超声—远红外辐射干燥技术对香蕉片进行干燥,比较不同辐射温度(150,210,270 ℃)和超声功率(0,30,60 W)对香蕉片质构、复水比、收缩率、色差、感官品质、总酚含量、维生素C含量和抗氧化活性的影响.结果表明,辐射温度和超声功率对干燥香蕉片的理化品质均有影响.香蕉片质构、复水比和收缩率等品质以辐射温度270...     

Effect of ultrasound pre-treatment on the kinetics and thermodynamic properties of guava slices drying process

The present work aims to evaluate the influence of sonication pre-treatment on the drying kinetics of guava circular slices in electric oven. Circular guava slices with 6.0 mm thickness were pre-treated with ultrasound for 0 min, 10 min, and 20 min, respectively. Drying kinetics experiments were performed at the temperatures of 50, 70, and 90 °C using an electric oven at 1200 W. Drying kinetics experimental data were fitted using empirical models and a diffusive model with third type boundary conditions. Process activation energy and thermodynamic properties were also determined. Drying of pre-treated samples revealed higher drying rates and less process time. Both Page and the diffusion models were adequate to describe the drying phenomena presenting coefficients of determination higher than 0.99 and low chi-squared values. Results also revealed that sonication times increased moisture transport rates with uniform distribution along with the interior of the slices during drying. The activation energy and enthalpy presented negative values and a positive correlation with the sonication time, while entropy and Gibb's free energy presented positive values and a negative correlation to the sonication time.     

干燥方法对黄秋葵抗氧化能力的影响

为明确不同干燥方法对黄秋葵品质的影响,优选其干燥技术,以新鲜黄秋葵果实为原料,分别采用热风、冷冻、微波、自然干燥方法干制,测定不同干制方法得到的黄秋葵干果中膳食纤维、果胶、黄酮等物质的含量,评价不同干制方法所得果实的抗氧化能力。结果表明:干燥方法并不影响黄秋葵中总膳食纤维、总糖、总氮和灰分的含量。可溶性膳食纤维、果胶、黄酮与Vc含量均以冷冻干燥果实最高,依次为14.21%、7.38%、1.72%和322.7 mg/kg,与新鲜果实中含量均无显著性差异(P0.05);不同方法干制后黄秋葵中总酚含量降低。自然干燥的黄秋葵总还原力(FRAP值)最低为0.767 mmol/L,而其他干制样品与新鲜黄秋葵的总还原力(0.856 mmol/L)相近且无显著性差异(P0.05);冷冻干燥及新鲜果实对1,1-二苯基-2-三硝基苯肼(DPPH)自由基、羟自由基(·OH)的清除率较高,但新鲜果实对超氧阴离子(O-2·)的清除率则均高于干制后的黄秋葵。综合分析认为,冷冻干燥能较好保持新鲜黄秋葵的营养成分和抗氧化能力,可作为黄秋葵即食加工的首选方法;自然干燥成本低,处理量大,所得干果中果胶含量高,适用于食品精深加工用黄秋葵的干制处理。     

超声波辅助韧化改性甘薯淀粉的结构及理化特性

为研究超声波辅助韧化对甘薯淀粉特性的影响，在其韧化处理不同阶段施加超声波，并对其表观直链淀粉含量、相对分子质量、支链淀粉链长分布、淀粉颗粒形态、结晶结构、糊化、流变、凝胶性质等理化特性进行表征。结果表明，在韧化处理中施加超声波对支链淀粉侧链分布和淀粉颗粒形态特征无显著影响；超声波辅助韧化在一定程度上改变了甘薯淀粉的结晶结构，韧化中间阶段施加超声波使其相对结晶度从31.98%减少至25.71%；与单独韧化相比，超声波辅助韧化使甘薯淀粉具有更高的回升值（1220 cp）和更低的崩解值（1594 cp），同时使甘薯淀粉凝胶的G″与G′值升高，大幅提高了甘薯淀粉凝胶的弹性和黏性；超声波辅助韧化使甘薯淀粉的凝胶硬度、胶黏性和咀嚼性增加。