Influence of osmotic dehydration and freezing on the volatile profile of kiwi fruit

The effect of osmotic dehydration on the volatile fraction of kiwi fruit was studied, as well as the effect of freezing and frozen storage. Osmotic treatments were carried out in sucrose solutions until the kiwi fruit reached 30°Brix, at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD), by using 45 and 65°Brix sucrose. Volatile compounds of fresh, dehydrated and frozen-stored (at −18 °C for 1 month) samples were obtained by simultaneous distillation-extraction, and analyzed by GC-MS. Osmotic dehydration provoked formation of esters and a decrease in aldehydes and alcohols, depending on the dehydration treatment applied, which is similar to what occurs during kiwi ripening. A severe reduction of all volatile compounds occurred after one month in frozen storage, which smoothes the changes induced by osmotic treatments. Only small differences between dehydrated and non-pretreated frozen/thawed samples could be recognized.     

Preservation of spinach by isochoric (constant volume) freezing

Efforts are currently directed towards improving the quality of vegetables after freezing and thawing. One of the methods under investigation is isochoric freezing. In this study, we evaluated isochoric freezing for preserving the quality of baby-leaf spinach. We compared the properties of thawed spinach frozen to −4°C in an isochoric system with those of fresh spinach, thawed spinach frozen to −4°C in an isobaric system and thawed spinach that were commercially frozen. Spinach leaves frozen under isobaric conditions lost mass and thickness, making them softer and translucent. They also lost much of their nutrient content. In comparison, isochoric freezing maintained cell integrity and turgidity. Thawed leaves remained crunchy with characteristics similar to fresh leaves. Isochoric freezing also preserved nutritional content better than isobaric freezing, although significant nutrient losses still occurred.     

Effects of the methods of pre-treatment before freezing on the retention of chlorophylls in frozen leaf vegetables prepared for consumption

The investigation included kale, New Zealand spinach and spinach. The evaluation covered the raw material; the raw material after blanching; the raw material after cooking; and frozen products prepared for consumption after 0, 4, 8 and 12 months of refrigerated storage. Both the traditional method of freezing (blanching before freezing) and the modified method of freezing (cooked before freezing) were used in the experiment, as well as two storage temperatures, T = −20 °C and T = −30 °C. The content of chlorophylls in fresh kale was four times that in New Zealand spinach and 1.5 times that in spinach. With the exception of New Zealand spinach, blanching and cooking significantly reduced the content of chlorophylls. In kale products prepared for consumption, the content of chlorophylls decreased in each successive stage of the investigation. In products of New Zealand spinach and spinach, the losses were usually not significant. After 12 months of refrigerated storage, frozen kale products prepared for consumption retained 52–65% of total chlorophylls compared with the content in the raw material; products of New Zealand spinach and spinach retained 66–71%. In kale and New Zealand spinach, the content of chlorophyll a decreased more rapidly than that of chlorophyll b, while in spinach the converse was true. The kale products obtained using the modified method contained more chlorophylls, while in the two spinach species their content was lower. The lower storage temperature resulted in a higher retention of chlorophylls in vegetables.     

Changes in optical and mechanical properties during osmodehydrofreezing of kiwi fruit

The influence of osmotic dehydration and freezing–thawing on optical (colour and translucency) and mechanical properties of kiwi slices were analysed. Osmotic treatments were carried out in sucrose solutions up till the soluble solids in kiwi fruit reached 30 °Brix, both at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD). Analyses were carried out on fresh and dehydrated samples before and after frozen storage (at −18 °C for 1 and 30 days). Reflexion spectra (400–700 nm) were measured to obtain the Kubelka–Munk coefficients and CIE-L*a*b* colour co-ordinates. Mechanical properties were analysed through the compression test. A transparency gain was observed in PVOD treated samples and in frozen–thawed samples, which implied a reduction in product clarity and chrome. Colour hue did not change notably, due to either osmotic treatments or freezing. Samples treated with 45 °Brix osmotic solution at atmospheric pressure were the best preserved in mechanical properties after freezing–thawing.     

Effect of Osmotic Dehydration and High Temperature Fluidized Bed Drying on Properties of Dehydrated Rabbiteye Blueberries

Rabbiteye blueberries were dried using an experimental high temperature fluidized bed (HTFB) dehydrator and the properties of the dried product were evaluated. 15 m/sec air velocity was required for fluidization and at 170°C the moisture content (MC in kg water/kg dry matter) of thawed blueberries was reduced from 5.8 to 0.7 after 8 min. After osmotic dehydration in sucrose, MC was 1.3, and 4 min in the HTFB drier at 150°C reduced MC to 0.28. Reduction of water activity to 0.5 after HTFB required cabinet drying at 60°C and 4 m/ set for 2.13 and 2.75 hr for the untreated and osmotically dehydrated berries, respectively. HTFB simultaneously dried and puffed the berries, resulting in reduced bulk density compared to berries produced using conventional drying. Osmotic dehydration prior to HTFB imparted a raisin-like texture to the product.     

Optimisation of processing variables affecting the osmotic dehydration of pomegranate arils

For the optimisation of osmotic dehydration by response surface methodology, the experiments were conducted according to Central Composite Rotatable Design (CCRD) with three variables at five levels. The low and high levels of the variables were 40 and 50 °C for osmotic solution temperature, 45 and 55°Bx for sucrose solution concentration, 60 and 100 min for duration of dipping in osmotic solution, respectively. The fruit to solution ratio was kept 1:4 (w/w) during all the experiments. Before dipping the arils in sucrose solution, the freezing of the whole pomegranate at ?18 °C was carried out to increase the permeability of the outer cellular layer of the arils. The arils were further convectively dehydrated at 60 °C air temperature up to final moisture content of 10% (wb) to make it a shelf stable product. The optimum conditions for osmotic solution concentration, temperature and process duration were 55°Bx, 40 °C and 100 min, respectively.     

接触脱水膜干燥对南美白对虾干复水特性的影响

接触脱水膜（contact dehydrating sheet,CDS）是一种适用于鱼肉等富含蛋白质食品干燥的新型冷脱水技术。为研究低温脱水对南美白对虾干复水特性的改善作用及其内在原因,本实验研究了CDS脱水至不同水分质量分数虾干的蛋白质结构变化及复水过程中复原率、持水力和水分状态的分布情况,并和热风干燥（hot air drying,HAD）的虾干进行比较。结果表明：采用CDS脱水法制备的不同水分质量分数（60%、45%、30%,以湿基计）虾干复原率、持水力均高于相对应的HAD脱水虾干组,其中水分质量分数为30%时,CDS脱水虾干的复原率、持水力分别为85.22%、69.17%,明显高于HAD脱水虾干（62.55%、65.73%）。低场核磁共振分析表明CDS脱水处理的水分质量分数为30%的虾干复水后虾仁的结合水、不易流动水、自由水比例均比HAD处理组更接近鲜虾。表面疏水性和蛋白质结构分析表明CDS脱水虾干蛋白的表面疏水性变化程度比HAD脱水低,蛋白质二级结构变化比HAD脱水虾干小。因此,CDS脱水法能维持蛋白质结构的完整性,复水后的虾干有更好的复原率、持水力,使产品品质更接近鲜虾,可以作为对虾及其他高值水产品的脱水干燥新途径。     

Multi-Objective Optimization of Osmotic–Ultrasonic Pretreatments and Hot-Air Drying of Quince Using Response Surface Methodology

In this study, application of a multi-objective optimization technique based on response surface methodology has been presented. Quince slices were dehydrated using osmotic dehydration with sucrose solutions at different concentration (40 and 60 Brix), processing time (1, 1.5, and 2 h), and ultrasonication time (0, 15, and 30 min) were the factors investigated with respect to water loss, solid gain, and weight reduction. Response surface methodology was used to determine the optimum processing conditions that yield maximum water loss and weight reduction and minimum solid gain during osmotic dehydration of quinces. Dehydrated quince slices at optimized osmo-ultrasound condition were then subjected to air-drying at 60 and 80 °C. Rehydration ratio, shrinkage, and moisture content of dried samples were regarded as responses to the non-thermal and air-drying conditions. Multi-objective optimization led to obtaining the best condition for production of dried quince slices with lowest moisture content, and shrinkage.     

Changes in quality characteristics of tofu with freezing treatment of soybeans

The aim of this study was to investigate the influence of length of freezing time (?18°C for 5 or 24 h) on the quality characteristics of tofu. The yield and moisture content of tofu obtained from frozen soybean were lower than control tofu. Tofu made from frozen soybeans showed higher hardness, gumminess and chewiness than the control. Freezing treatment also made the microstructure of the tofu more uniform than the control. However, after 24-h freezing, hardness decreased and the microstructure of tofu appeared to form pores. Sensory evaluation showed that mouth-feel decreased with an increase of freezing time. Among all of tofu frozen at ?18°C, 5-h freezing treatment showed the highest overall acceptability. These results indicate that the length of time that soybeans are frozen before making tofu affects the quality of tofu.     

Effect of Pretreatments on Quality Characteristics of Dehydrated Ivy Gourd (Coccinia indica L.)

Ivy gourd (Coccinia indica L.) is an important tropical vegetable cultivated in India. It belongs to the Cucurbitaceae family and is attributed with neutraceutical properties such as hypoglycemic effect and contained a fair amount of ascorbic acid. The effect of blanching and different pretreatments on the quality characteristics of dehydrated ivy gourd slices was optimized. The treated ivy gourd slices were dehydrated in a cross flow hot air drier at 50 ± 1 °C to a final moisture content of 4.6%. The dehydration ratio of dried ivy gourd slices ranged from 17.1:1 to 18.7:1. Ivy gourd slices blanched at 98 °C in water, dipped in 0.2% potassium metabisulphite (K₂S₂O₅) solution and dried at 50 ± 1 °C for 5–6 h resulted in best product. Dehydrated ivy gourd slices obtained from the optimized treatment had good color, texture with rehydration ratio of 1:8.6. Equilibrium relative humidity of dehydrated slices was 34.18% with an initial moisture content of 4.6% at 28 ± 1 °C. Dehydrated slices were packed in low density polyethylene (LDPE) and metallized polyester polyethylene (MPP) pouches and stored at room temperature (27–35 °C) for 6 months. The dehydrated slices were analyzed for changes in physicochemical composition and sensory quality characteristic such as color and appearance, texture and overall quality during storage. Dehydrated ivy gourd slices remained acceptable during storage of 4 and 6 months in LDPE and MPP pouches, respectively, at room temperature.     

Original article: Effect of sucrose and glycerol mixtures in the osmotic solution on characteristics of osmotically dehydrated mandarin cv. (Sai‐Namphaung)

This study investigated the effects of a series of osmotic solutions consisting of sucrose and glycerol on the quality of osmotically dehydrated mandarin, namely mandarin cv. (Sai‐Namphaung). Mandarin samples were peeled and osmotically dehydrated at 55 °C with agitation at 3.5776 × 10^?1g in five osmotic solutions containing various mixtures of 60% sucrose and 60% glycerol (9:1, 8:2, 7:3, 6:4 and 5:5 w/w, respectively). The osmotically dehydrated mandarin was further dried using hot‐air drying at 70 °C for 360 min. Increasing the glycerol ratio in the mixtures significantly (P ≤ 0.05) increased water loss and solid gain during osmotic dehydration, and significantly (P ≤ 0.05) affected kinetic rate constants during drying. An increase in the glycerol ratio in the mixtures caused a significant decrease in the quality factors of hardness, moisture content, water activity and reducing sugar. However, the increase resulted in an increase in the darkness of the dried mandarin, compared with increasing the sucrose ratio in the mixtures (P ≤ 0.05). The increase had an insignificant (P > 0.05) effect on vitamin C content.     

Water sorption and cooking time of red kidney beans (Phaseolus vulgaris L.): part I – Effect of freezing and drying conditions on water sorption and cooking time

Water sorption and cooking time of kidney beans were determined. The beans were manually harvested at 19.2 ± 0.1% moisture content and stored at ?20 and ?10 °C for about half a year. The beans were further dried at 30, 40 and 50 °C inside a thin‐layer drier for 7.5 h or under room conditions for 4 week. The freezing storage temperature before the beans were dried did not influence their cooking time and water sorption. The saturated kernel volumes decreased approximately 7% after drying. The beans decreased their sphericity during water sorption and had a larger swelling ratio in the thickness direction than in other directions. Lower initial moisture content, especially with a higher drying temperature, decreased water sorptivity and resulted in higher percentage of uncooked kernels if the beans were not soaked before cooking. However, there was no relationship between initial moisture content and uncooked percentage if the beans were soaked before cooking. High drying temperature resulted in hard‐to‐cook (HTC) phenomenon.     

Effect of cold pre‐treatment duration before freezing on frozen bread dough quality

The effect of cold pre‐treatment (CT) duration prior to freezing on the quality of a standard bread dough was investigated. Doughs held at 0 °C or 10 °C for 1 h or 3 h before air‐blast freezing were compared with standard dough frozen after 0.5 h at 0 °C (0 °C/0.5 h) and fresh (unfrozen) dough. Cumulative gas production measured in a risograph was used to quantify the dough quality after storage at ?18 ± 0.1 °C for 1, 7 or 17 days. Relative to fresh dough, gas production significantly reduced after freezing for all treatments. The doughs with CT at 0 °C for 1 or 3 h or 10 °C for 1 h had significantly higher gas production after freezing and less rapid decline in gas production during frozen storage than the doughs with the 0 °C/0.5 h CT. The 10 °C/3 h CT gave no gas production benefit after freezing and had the most rapid decline in gas production during frozen storage.     

Effect of freezing conditions and storage on ice crystal and drip volume in turbot (Scophthalmus maximus): Evaluation of pressure shift freezing vs. air-blast freezing

Turbot fillets were frozen either by pressure shift freezing (PSF, 140 MPa, −14°C) or by air-blast freezing (ABF), and then stored at −20°C for 75 days. Smaller and more regular intracellular ice crystals were observed in fillets frozen by PSF compared with air-blast frozen ones. Ice crystals area in PSF samples was approximately 10 times smaller than that of ABF samples, on average. The PSF process reduced thawing drip compared with air-blast freezing. Conversely to this classical freezing process, the storage time did not adversely influence the thawing drip of PSF samples. In addition, PSF appeared to reduce cooking drip after 45 days of storage at −20°C. Differential scanning calorimetry analysis showed a significant reduction of the total enthalpy of denaturation for the pressure shift frozen samples compared to fresh and conventional frozen samples. Besides, a new melting transition appeared on the thermogram of PSF samples at approximately +40°C.     

HIGH TEMPERATURE DRYING CHARACTERISTICS AND MOISTURE ADSORPTION ISOTHERMS OF BLACK PLUM (VITEX DONIANA) SYRUP AND SYRUP-STARCH

Modified sweeteners were formulated from mixtures of Black plum syrup and phosphorylated corn starch concentrations of 20, 30, and 40% (w/w). Each mixture was coated on an aluminium plate at 1 mm thickness, dehydrated at 60°, 70°, 80° and 90°C, and evaluated for drying and moisture sorption characteristics. Results showed that the mixtures exhibited falling rate drying characteristics. The rate of dehydration increased in the order 20% > 30% > 40% starch at constant temperature. The incremental choice of 10% starch and drying temperature except at 70° and 80°C had significant effect (p < 0.05) on drying rate. The moisture isotherm curves of the pre-dried mixtures were sigmoid in shape. Their monolayer values or upper critical moisture contents necessary for shelf-stability were significantly different from each other for the samples pre-dried at 60°C. The effect of drying temperatures on equilibrium moisture content was only significant at 90°C (p < 0.05).     

Preparation, Evaluation and Analysis of a French-Fry-Type Product from Sweet Potatoes

A French-fry-type product was prepared from ‘Jewel’ and ‘Centennial’ sweet potatoes. Samples were prepared from freshly harvested, cured, and stored, cured roots. The roots were peeled, sliced into strips and blanched in hot water. The blanched strips were partially dehydrated by one of five treatments and then frozen at ?30°C. Frozen strips were fried in hot peanut oil and evaluated by a sensory panel. Strips prepared by dehydration in a hot air tunnel at 120°C for 5 min were favored by the sensory panel. Blanching removed significant amounts of dry matter and resulted in partial hydrolysis of the starch by endogenous enzymes. Sensory color scores were not affected by reducing sugar content. Sensory flavor scores were related to total sugar content.     

Effect of Surface Freezing on Ascorbic Acid Retention in Water Blanched Potato Strips

The average retention of ascorbic acid in potato strips (10 × 10 × 80 mm) blanched in water at 50°C and 65°C over various blanching times, with and without surface freezing pre-treatment was determined. The strips were frozen in Freon Freezant-12 for 15 sec, with the freezing front penetrating 0.4–0.5 mm. Average retention of ascorbic acid in the surface-frozen potato strips was significantly lower than that in fresh strips and lower at 65°C than at 50°C. At an equal average retention of ascorbic acid, at 50°C the fresh strips required a blanching time four times higher than that for the surface-frozen strips; at 65°C it was twice as high.     

Osmotic-Convective Dehydrofreezing Process for Drying Kiwifruit

Osmotic and convective dehydrofreezing were studied to determine sugar concentration, ascorbic acid loss, and texture changes in dried and dehydrofrozen kiwifruit. Two concentrations of sucrose (60° and 72° Brix) were used as osmotic solutions after convective air drying. Time needed to reach desired moisture was reduced with combined drying compared with osmotic drying. Firmness was evaluated by the maximum force from a back extrusion test. A reduction in maximum force was observed after freezing, as compared with fresh and dried fruit. Addition of ascorbic and citric acid as antioxidants in the osmotic solution prevented browning, and significant loss of ascorbic acid during osmotic drying. Air drying at 30°C produced distinguishable color changes.     

Freezing Characteristics and Storage Stability of Broccoli (Brassica oleracea L. var. botrytis L.) Under Osmodehydrofreezing and Ultrasound-Assisted Osmodehydrofreezing Treatments

Freezing characteristics (freezing time, latent heat of fusion of ice, and freezable water content) and quality parameters (drip loss, color, firmness, and l-ascorbic acid content) of broccoli (osmodehydrofrozen and ultrasound-assisted osmodehydrofrozen) during frozen storage were investigated. Freezing time, latent heat of fusion of ice, and freezable water content of osmodehydrated samples decreased significantly compared to samples which were not under osmotic dehydration. The changes of drip loss, color, firmness, and l-ascorbic acid content of osmodehydrofrozen and ultrasound-assisted osmodehydrofrozen broccoli during frozen storage were inhibited markedly compared to samples which were not submitted to osmotic dehydration before freezing. Compared to osmotic dehydration, the ultrasound-assisted osmotic dehydration shortened the needed dehydration time and better preserved the firmness and l-ascorbic acid content after osmotic dehydration pretreatment. In addition, the ultrasound-assisted osmotic dehydration minimized the drip loss and loss of l-ascorbic acid content and better maintained the color and firmness when stored at ?25 °C for 6 months. These findings indicate that it is promising to apply ultrasound-assisted osmodehydrofreezing in freezing and frozen storage of food.     

Effects of Freezing Rate, Frozen Storage Temperature and Storage Time on Tenderness Values of Beef Patties

All-beef and soy-extended patties were frozen to ?18°C in either 24, 48, 72 or 96 hr and stored at ?23°, ?18° or ?7°C for 6, 9, 12, 18 or 24 months. Freezing produced considerable reductions in both sensory and instrumental measures of tenderness with the effects being greater for the slower freezing rates. Thus, just after freezing, and prior to storage, tenderness was found to be higher in patties subjected to faster freezing compared to slower rates of freezing. Storage at ?7°C reduced sensory scores for tenderness and increased stress in relation to strain during shearing. Extending patties with soy reduced the effects of freezing rate, storage temperature and storage time on tenderness.