Optimising pulsed microwave‐vacuum puffing for Shiitake mushroom (Lentinula edodes) caps and comparison of characteristics obtained using three puffing methods

Shiitake mushroom (Lentinula edodes) caps were puffed using pulsed microwave‐vacuum puffing (PMVP), microwave‐vacuum puffing (MVP) and microwave puffing (MP). The response surface method was used to optimise the process parameters for using PMVP to puff mushroom caps. The experiments were conducted using a central composite design to determine the visual appearance and initial moisture content (30–50%) of the mushroom caps. The initial moisture content and microwave power intensity showed highly significant linear relations with the expansion ratio and sensory evaluation. The optimal conditions for puffing mushroom caps were initial moisture content, microwave intensity, vacuum pressure and pulse ratio of 35%, 40 W g^?1, 77.5 ± 1.5 kPa and 1.35, which resulted in an optimal expansion ratio and sensory score of 163.2% and 6.83, respectively. The caps puffed using PMVP showed better textures, sensory scores and microstructures than those puffed using either MP or MVP.     

复水温度对香菇复水特性及品质的影响

香菇是中国产量最高和市场消费量最大的食用菌。干制是香菇的主要加工方式,而干香菇需复水后才能作为原料被烹调或进一步加工。本研究将热风干燥的香菇分别在25,45,65℃和85℃下复水,研究香菇复水过程中复水比、外观、质构和风味品质的变化。结果表明,在45℃复水270 min,干香菇吸水后表面的褶皱较为舒展,微观结构显示其菌丝恢复膨胀且伸展。同时,其复水比稳定保持在3.88,剪切力(1 290.28 g)、弹力(0.66 g)和复原力(0.34 g)适中,咀嚼性(656.02 g)最大,说明香菇复水完全且质地柔软适中,易被切开。此外,45℃复水香菇所含特征含硫化合物的含量较高,以1,2,3,5,6-五硫杂环庚烷(67.02%)和1,2,4-三硫环戊烷(39.06%)为主,风味较浓郁。综上,复水温度显著影响香菇复水后的食用品质,将干香菇在45℃复水270 min可获得品质较好的复水香菇。     

INFLUENCE OF PLATE TEMPERATURE AND MODE OF REHYDRATION ON TEXTURAL PARAMETERS OF PRECOOKED FREEZE-DRIED BEEF

The effects of various plate temperatures and rehydration procedures in texture of precooked freeze-dried beef, were evaluated. Frozen precooked commercial beef was freeze-dried at 20, 40, 60 and 80C during 24 h. The rehydration procedure involved two main variables: distilled water at room-temperature and at 80C, for 30 min. The texture profile analysis was performed with a TA-XT2 Texture Analyzer (SMS) for freeze-dried rehydrated samples and compared to frozen precooked beef. The results showed that with a same drying period, the 60C plate temperature and rehydrated in distilled water at room-temperature resulted in a better product texture, in regards to texture parameters hardness and chewiness.     

Effect of air-drying temperature on physico-chemical properties,antioxidant capacity,colour and total phenolic content of red pepper (Capsicum annuum, L. var. Hungarian)

Red pepper has been recognised as an excellent source of antioxidants, being rich in ascorbic acid and other phytochemicals. Drying conditions, particularly temperature, leads to pepper modifications that can cause quality degradation. In this work, the effects of process temperatures between 50 and 90 °C on physico-chemical properties, rehydration, colour, texture, vitamin C, antioxidant capacity and total phenolics during the drying of red pepper were studied. The rehydration ratio decreased with temperature and the maximum water holding capacity was achieved at 50 °C. Both vitamin C content and the total phenolic content decreased as air-drying temperature decreased. The radical scavenging activity showed higher antioxidant activity at high temperatures (i.e. 80 and 90 °C) rather than at low temperatures (i.e. 50, 60 and 70 °C). Chromatic parameters (L*, a*, b*, C* and H°), non-enzymatic browning compounds and extractable colour were affected by drying temperature, which contributed to the discolouring of pepper during this process.     

Structural properties of dehydrated products during rehydration

The following structural properties of dehydrated apple, banana, carrot and potato were examined during rehydration: true density, apparent density, porosity and specific volume. Samples were dehydrated using five different drying methods: conventional, vacuum, freeze, microwave and osmotic; after which they were rehydrated in an air dryer at 50 °C and 80% air humidity. Structural properties were examined during rehydration to various moisture contents, ranging from 0.01 to 3.5 kg kg^–1 (dry basis). The dehydrated products did not recover their structural properties after rehydration as a result of structural damage that occurred during drying and the hysteresis phenomenon which took place during rehydration. Porosity of the rehydrated products was higher during rehydration than during dehydration. A generalized structural model was used to describe the structural properties, and of the four parameters that were incorporated, only the shrinkage coefficient, which represents volume expansion, changed on rehydration.     

Effect of pulsed vacuum and ultrasound osmopretreatments on glass transition temperature, texture, microstructure and calcium penetration of dried apples (Fuji)

The effect of pulsed vacuum and ultrasound pretreatments on glass transition, texture, rehydration, microstructure and other selected properties of air- and freeze-dried apples (Fuji) were investigated. Apple cylinders (15 mm height × 15 mm diameter) were first osmoconcentrated in a 60 g/100 g high-fructose corn syrup solution containing 7.5 g/100 g Gluconal Cal^® combined with agitation, pulsed vacuum (PV), or ultrasound for 3 h, then hot-air or freeze dried. Changes in glass transition temperature, hardness, crispness, and rehydration rate were measured, microstructure was observed using scanning electronic microscopy (SEM), and calcium ions distributions were analyzed by a laser ablation inductively coupled mass spectrometry (LA-ICP-MS). Under the same drying method, ultrasound led to a higher glass transition temperature, lower water activity, moisture content and rehydration rate, severer structure collapse, less cavities and calcium uptake than PV did. Different osmoconcentration pretreatment had no significant (P < 0.05) effect on the hardness, crispness, shrinkage and rehydration rate. Compared to hot-air drying, freeze-dried apples showed the porous structure, minimal shrinkage, softer texture, better rehydration capacity, lighter color, and slightly lower glass transition temperature.     

Rehydration of active dried yeast: impact on strength and stiffness of yeast cells measured using microelectromechanical systems

This study investigated the rehydration of active dried yeast and the impact of temperature and wort density on the strength and stiffness of individual cells using a microelectromechanical system. Dried yeast was rehydrated using a variety of methods, including direct pitching into wort (13.6°P) at 12, 22 and 30°C, as well as propagation using YEPD media (4.2°P). Cell viability was found to broadly correlate with measurement of cell strength and stiffness. Both wort density and temperature affected viability and physical characteristics of the cells after 1 h of rehydration. Yeast cells rehydrated at low temperature and high wort density burst at a lower force (0.26 ± 0.02 μN) than cells rehydrated using high temperature and low density media (0.50 ± 0.10 μN). Cells rehydrated at higher temperatures or using low density media showed no significant difference in strength and stiffness when compared with high viability, actively fermenting yeast. Changes in yeast physiology, owing to stress responses, may contribute to the observed differences in mechanical properties. These findings have application in brewery design, as pumping, centrifugation, storage and associated shear impart mechanical stress upon yeast cells. © 2018 The Institute of Brewing & Distilling     

Effect of integrated application of gamma irradiation and modified atmosphere packaging on physicochemical and microbiological properties of shiitake mushroom (Lentinus edodes)

Shiitake (Lentinula edodes) mushrooms were packed in biorientated polypropylene (BOPP) bags and exposed to different doses of gamma irradiation (1.0, 1.5, and 2.0 kGy) within the packaging, heat sealed and stored at 4 °C for 20 d. Of the three doses, 1.0 kGy was most effective in maintaining a high level of firmness. Samples treated with 1.0 kGy also exhibited smaller initial declines in soluble protein, higher increases in total sugar content and lower levels of malondialdehyde accumulation. Furthermore, 1.0 kGy promoted the accumulation of phenolics compound and showed higher antioxidant ability during storage. At higher doses, 2.0 kGy resulted in a higher microbial reduction, but showed negative effects on texture, chemical properties and functional components. All the gamma irradiation were effective in retarding mushroom sensory deterioration. Thus, application of gamma irradiation in combination with MAP can extend the storage life of shiitake mushroom up to 20 d.     

Effect of air temperature on drying kinetics and quality characteristics of osmo-treated jumbo squid (Dosidicus gigas)

The present study investigated the influence of air temperature on the drying kinetics, color, rehydration, total volatile basic nitrogen (TVBN), antioxidant capacity and texture of osmosed jumbo squid fillets during convective dehydration at 50, 60, 70, 80 and 90 °C. The Logarithmic and Two-term models could be used to describe the squid experimental drying curves. Discoloration of product was more noticeable at high drying temperatures where combined effects of non-enzymatic browning as well as protein denaturation modified the original color of the squid samples. Rehydration indexes showed a decrease while texture presented an increase with increasing air-drying temperature probably due to changes in food protein matrix. Total volatile basic nitrogen increased with process temperature. Antioxidant activity presented a decrease with temperature, especially at high drying temperatures. Results of this study demonstrated that the drying kinetics together with the reported quality attributes of the dried squid can be used to improve the final characteristics of the product.     

The effect of blanching on the quality of dehydrated broccoli florets

Different blanching treatments were applied to broccoli florets prior to dehydration in order to improve product quality. The pretreatments used were a conventional blanching in water at 99ǃ °C, and a stepwise blanching (a blanching at low temperature followed by a short blanching at high temperature after a holding time) using different temperatures for the first step (50, 55, 60, 65 and 70 °C). Five rehydration temperatures were used (25, 40, 55, 65 and 80 °C). Rehydration rate (D_eff and W_e), chlorophyll content and texture of the rehydrated product were evaluated. Rehydration was modelled according to Fick's diffusion equation. A good agreement between the model and the experimental data was obtained when D_eff and W_e values were identified for each temperature (average explained variance 96.9%). Samples stepwise blanched at 60 °C showed, on the average, the lowest W_e values. Stepwise blanching at 60-65 °C and rehydration at 25-55 °C were the combinations that gave the firmest product. Stepwise blanching at 50 °C together with the conventional blanching (99ǃ °C) and rehydration between 25 and 65 °C were the combinations that allowed preservation of the highest chlorophyll content. From these results, it seems difficult to obtain firm samples with a high chlorophyll content without additives.     

Centrifugal osmotic dehydration and rehydration of carrot tissue pre-treated by pulsed electric field

This paper studies the centrifugal osmotic dehydration (OD), rehydration and texture of carrot tissue treated by pulsed electric field (PEF). The influence of centrifugal acceleration (0-5430g), salt addition (NaCl/sucrose solutions 0/65, 7/44 and 15/50% w/w), and temperature (20-40 °C) on the OD kinetics was investigated in the presence and absence of PEF (E=0.60 kV/cm, treatment duration t_PEF=0.05 s). The centrifugal OD of samples untreated and treated by PEF was compared with OD under stirring (250 tr/min).Centrifugal force, PEF and salt addition increase the amount of water removed during OD. However, the centrifugal force decreases the intake of solids by the product.The application of PEF enhances both water loss (WL) and solid gain (SG) during OD (under stirring or centrifugation), increases the rehydration capacity of carrot tissue, but somewhat decreases the firmness of rehydrated product.The combination of centrifugal field with PEF and salt addition can be advantageous for reducing the OD duration. The textural study shows that the product obtained with OD is less affected by thermal treatment than the directly dried product.     

Quality Changes of Dehydrated Restructured Fish Product from Silver Carp (Hypophthalmichthys molitrix) as Affected by Drying Methods

Restructured fish slices from silver carp (Hypophthalmichthys molitrix) were dried using air drying (AD), freeze drying (FD), and vacuum drying (VD) (4 mm thickness) and microwave-vacuum drying (MVD) (2, 4, 6, and 8 mm thickness). Quality attributes of the dried products were compared in terms of their rehydrated characteristics, change in dimensions, color, texture, sensory values before and after rehydration, and change in volatile compounds. AD, FD, and VD resulted in the different levels of shrinkage while MVD caused some expansion in diameter and thickness in the 4-, 6-, and 8-mm-thickness samples. Rehydration caused significant swelling in AD, FD, and VD products (p?<?0.05) but insignificant change in MVD products (p?>?0.05). Drying methods significantly affected the color and texture of both dried and rehydrated products (p?<?0.05), but slice thickness had no significant effect on the color in MVD products (p?>?0.05). MVD products rehydrated faster and had higher rehydration ratio as well as lower water hold capacity, hardness, springiness, cohesiveness, and chewiness than others. In sensory evaluation, MVD products alone exhibited acceptable crispness and favorable odor. The rehydrated dried products were acceptable by the sensory panelists and were preferred in the order: FD, VD, AD, MVD. Gas chromatography-mass spectrometry revealed that drying significantly decreased the n-alkanals and 1-octen-3-ol content (p?<?0.05) and produced new aldehydes including 2-methyl-propanal, 3-methyl-butanal, and furfural in MVD products. This study demonstrated that drying restructured fish meat can be potentially used to develop the new dried fish products using optimal drying conditions.     

Effect of puffing conditions on physical properties and rehydration characteristic of instant rice product

The aim of this work was to study the effects of puffing conditions on the properties of instant rice and to obtain optimal processing condition for product with rehydration time within 5 min. Thai jasmine rice was soaked, cooked and dried at 80 °C in a tray dryer before being puffed at different moisture contents (15–20% wb), temperatures (200–220 °C) and time intervals (20–30 s). The rice puffed at higher moisture contents and puffing temperatures for longer time exhibited higher volume expansion ratios and shorter rehydration times. Presumably, case hardening of the grain surface occurred. Instant rice that can be rehydrated in 5 min with more acceptable hardness than the commercial instant rice was obtained. Regression models to predict the quality of instant rice were developed using response surface methodology.     

干燥方式对复水香菇感官、质构及营养品质的影响

为获得复水性较好的干香菇,研究了热风干燥（hot-air drying,HAD）、中短波红外干燥（infrared radiation drying,IRD）和真空冷冻干燥（freeze drying,FD）香菇的复水特性及复水后的综合品质。结果表明：FD香菇具有均匀的多孔结构,使得干香菇的复水速率明显高于HAD香菇和IRD香菇,复水60?min即可达最大复水体积比（9.22）,且复水香菇的外观与鲜样接近。同时,复水后FD香菇的剪切力（1?352.99?g）和咀嚼性（232.54?g）最小,表明其质地柔软、易被切分。此外,FD复水香菇和其他两种复水香菇具有相似的电子鼻响应值曲线,表明其香气无差异。复水时FD香菇的蛋白质和VB2的溶出率最高,分别为0.42?mg/g和0.71×10－3?mg/g,说明FD复水香菇富含营养成分,且加工时较易溶出。综上,FD可作为一种较好的干燥方式来制备复水性较好的高品质香菇。     

Effects of cooking, drying and pretreatment methods on texture and starch digestibility of instant rice

Instant rice produced from a conventional process consisting of the cooking, washing and drying steps possesses poorer eating quality compared with that of freshly cooked rice. The objective of this work was therefore to study the effects of cooking, pretreatment and drying methods on microstructure, textural properties and starch digestability of instant rice after rehydration; jasmine white rice was chosen as a test material. Conventional boiling method and electric rice cooking were selected as the methods to prepare cooked rice. In the case of boiling, cooked rice was frozen at −20 °C or cooled at 4 °C for 24 h prior to drying, while the cooked rice from an electric rice cooker was washed with ambient or cool water for 30 s prior to drying. After pretreatment the cooked rice was dried either by freeze drying or hot air drying at 80 °C. Based on the scanning electron microscopic results it was found that the cooking, pretreatment and drying methods all affected the rice morphology. The hardness and stickiness of instant rice after rehydration were lower for samples prepared from the rice cooker than those of freshly cooked rice, while both textural properties appeared to be improved significantly for the samples from boiling. The texture of the freeze-dried products was not different from that of the air-dried one. The freezing pretreatment provided the texture and glycemic index of instant rice after rehydration similar to those of the freshly cooked rice. On the other hand, the cooling pretreatment resulted in the harder texture and higher glycemic index of the samples.     

Viscoelastic behaviour of dehydrated products during rehydration

Viscoelastic behaviour of dehydrated products during rehydration of apple, banana, carrot and potato was examined under uniaxial compression tests. Samples were dehydrated with four different drying methods: conventional, vacuum, freeze and osmotic-freeze drying and after that they were rehydrated in an air dryer at 50°C and 80% air humidity. Compression tests were performed during rehydration for various moisture contents, ranging from 0.01 to 1.5 kg/kg dry basis. The viscoelastic behaviour of dehydrated products during rehydration were examined comparing the values of the four parameters incorporated into the stress–strain model, during rehydration with those of dehydrated products. The four examined parameters: maximum stress, maximum strain, elastic parameter and viscoelastic exponent seem to show a hysteresis phenomenon. It can be concluded that dehydrated product do not keep their viscoelastic behaviour after rehydration due to structural damages that occur during drying. More specifically, freeze dried materials present the highest hysteresis after rehydration, losing their elasticity and becoming more viscous. Osmotic pretreatment seems to help freeze dried materials to keep their elastic nature, probably due to solids gain. Air and vacuum dried materials showed the smallest hysteresis tendency, keeping their viscoelastic characteristics during rehydration close to those of dried materials.     

Determination of microwave drying and rehydration kinetics of green peppers with the bioactive and textural properties

The aim of this study was to determine the effect of microwaves on drying and rehydration kinetics of green pepper varieties (sweet, green, and bell) and the bioactive and textural properties of dried and rehydrated peppers. Drying was performed at 90, 180, and 90 + 180 W and dried peppers were rehydrated at 25, 50, and 70°C. The best drying fits were obtained using the equations of both Sigmoid and Hii et al. for drying, and two term exponential decay was the most appropriate model for rehydration. The lowest and highest final rehydration ratio values were obtained for the peppers dried at 180 and 90 W, respectively at each temperature and pepper variety. Among peppers, bell pepper showed the lowest color change (ΔE) and it was the most potent to recover initial color in rehydration. Peppers had softer texture in both drying and rehydration treatment. Total phenolic content of peppers was reduced around 56–65% compared to the fresh pepper by drying and this decrement was reached up to 87% in rehydrated peppers. Results showed that drying at 180 W and rehydration at 70°C provided faster drying and rehydration as well maintained the quality characteristics of green peppers.     

Effect of drying method on the moisture sorption isotherms for Inonotus obliquus mushroom

Moisture sorption isotherms of Inonotus obliquus mushroom were studied over a selected temperature range (20-50 °C). Sigmoid sorption isotherms were observed for these samples. The sorption data were analyzed using various conventional models. The Oswin model was found to be the best model for predicting the equilibrium moisture content of mushroom in the range of water activity 0.08-0.96. The monolayer moisture content decreased as temperature increased and was affected by the drying method used. The net isosteric heat of sorption was determined using the Clausius-Clapeyron equation and the value decreased with increase in moisture content of mushroom.     

Ohmic heating blanching of Agaricus bisporus mushroom: Effects on polyphenoloxidase inactivation kinetics,color, and texture

The effect of ohmic heating blanching (OHB) on the inactivation kinetics of polyphenol oxidase (PPO), color, and texture from Agaricus bisporus mushroom treated at different temperatures (67–90 °C) for 1 to 5 min was investigated in the present work. OHB and conventional blanching (CB) treatments were able to inactivate mushroom PPO. However, the inactivation kinetics results showed a lower energy activation (E_a) value during OHB (16.03 ± 1.34 KJmol-1) compared to conventional blanching (20.07 ± 1.85 KJmol-1). Significant differences were observed in color (L*, h° and ΔE) and mushroom texture between the blanching treatments. Nevertheless, both treatments caused minimal physicochemical changes. Therefore, OHB is a promising technology for mushroom blanching because it promotes PPO inactivation in less time and reduces the impact on the color and texture of mushrooms compared to CB.     

Kinetics of water absorption and soluble‐solid loss of hot‐air‐dried carrots during rehydration

Cubes of carrots dried at 60, 70, 80 and 90 °C were rehydrated at 20 and 95 °C. Kinetics of water gain and soluble‐solid loss were monitored and described by Peleg model. Dry matter holding capacity, water absorption capacity and rehydration ability were derived to assess the rehydration process. It was found that leaching flow was higher for the samples dried at higher temperatures. Rehydration ability and dry matter holding capacity of the samples rehydrated at 95 °C were higher than those observed for the samples soaked at 20 °C. Swelling of carrots during rehydration neither depended on temperature of drying nor on the temperature of the water. The results indicate that the use of low drying temperatures is suitable for preserving the quality attributes of carrots after rehydration.