Freeze-dried Apple Research Articles

Influence of Pulsed Electric Field Pretreatment on Vacuum Freeze-dried Apples and Process Parameter Optimization

Vacuum freeze-drying can be utilized to obtain high-quality dried products, but its application in the food processing industry is restricted by its relatively high energy consumption. However, this problem can be solved with Pulsed Electric Field (PEF) pre-processing. Using a three-factor quadratic orthogonal regression design, this study assessed the effects of changes in various parameters ofPEF pretreatment (pulse intensity, pulse duration and pulse number) on the properties of freeze-dried apple slices (productivity per unit area, flavonoid content and chromatic aberration). In comparison with freeze-dried apple slices that were not exposed to PEF pretreatment, those exposed to PEF showed a 30% increase in productivity per unit area, a decrease of nearly 50% in chromatic aberration and unchanged flavonoid content. Our research provides a theoretical basis for the application of PEF as a pretreatment for freeze-dried foods that can be used to overcome the high energy consumption of the freeze-drying process and improve product quality.

Antioxidant potential of atmospheric freeze-dried apples as affected by ultrasound application and sample surface

ABSTRACTAtmospheric freeze drying (AFD) yields products of a similar quality to the conventional vacuum freeze-drying technique, but reduces the operating cost. However, it involves very low drying rates. The sample surface/mass ratio is one of the process variables that can be taken into account to reduce drying time. Moreover, power ultrasound (US) can also be used to intensify this process because of its effects on external and internal mass transfer resistance. However, both factors may affect not only the drying time but also the final product quality. Therefore, the aim of this study was to address the influence of both ultrasound application and the sample surface/mass ratio on the drying process and the antioxidant potential of atmospheric freeze-dried apple. For that purpose, two sample geometries with different surface/mass ratio were considered: slabs (30 × 30 × 10 mm3) and cylinders (diameter: 9 mm and height: 30 mm). The samples were freeze dried (−10°C) with ultrasound application (21.7 kHz) at different power levels (0, 10.3, 20.5, and 30.8 kW/m3). The total phenolic content (TPC), antioxidant capacity (AC), and ascorbic acid content (AA) were measured in the dried apple. The drying time was significantly shorter for cylindrical samples than for slabs, probably due to their higher surface/mass ratio. The application of US increased the drying rate, this increase being greater for the slab than for the cylindrical particles used in this study. In general, AFD reduced the TPC, AC, and AA, the final content being significantly greater for slabs than for cylinders. This fact can also be related to the lower surface/mass ratio in the case of slabs. US application further reduced TPC, AC, and AA content, probably due to some cellular damage produced by the acoustic waves and to the oxygen transfer improvement. Nevertheless, the bigger particles (slabs) dried with ultrasound needed a 10% of drying time than the smaller ones (cylinders) dried without ultrasound. Moreover both kind of samples presented similar antioxidant potential.

Development, validation and evaluation of an analytical method for the determination of monomeric and oligomeric procyanidins in apple extracts

There is a lack of data for individual oligomeric procyanidins in apples and apple extracts. Our aim was to develop, validate and evaluate an analytical method for the separation, identification and quantification of monomeric and oligomeric flavanols in apple extracts. To achieve this, we prepared two types of flavanol extracts from freeze-dried apples; one was an epicatechin-rich extract containing ∼30% (w/w) monomeric (−)-epicatechin which also contained oligomeric procyanidins (Extract A), the second was an oligomeric procyanidin-rich extract depleted of epicatechin (Extract B). The parameters considered for method optimisation were HPLC columns and conditions, sample heating, mass of extract and dilution volumes. The performance characteristics considered for method validation included standard linearity, method sensitivity, precision and trueness. Eight laboratories participated in the method evaluation. Chromatographic separation of the analytes was best achieved utilizing a Hilic column with a binary mobile phase consisting of acidic acetonitrile and acidic aqueous methanol. The final method showed linearity for epicatechin in the range 5–100μg/mL with a correlation co-efficient >0.999. Intra-day and inter-day precision of the analytes ranged from 2 to 6% and 2 to 13% respectively. Up to dp3, trueness of the method was >95% but decreased with increasing dp. Within laboratory precision showed RSD values <5 and 10% for monomers and oligomers, respectively. Between laboratory precision was 4 and 15% (Extract A) and 7 and 30% (Extract B) for monomers and oligomers, respectively. An analytical method for the separation, identification and quantification of procyanidins in an apple extract was developed, validated and assessed. The results of the inter-laboratory evaluation indicate that the method is reliable and reproducible.

Effect of pulsed electric field treatment on water distribution of freeze-dried apple tissue evaluated with DSC and TD-NMR techniques

Abstract This work aimed to study pulsed electric fields (PEF) effect on the water distribution of freeze-dried apple. Apple (var. Cripps Pink) was treated in 15% trehalose and 1% ascorbic acid solution (388 μS/cm) at 3 Hz and various electric field strengths 0.3; 0.6; 0.9 and 1.2 kV cm − 1 for 5, 10 or 15 pulses. The samples were frozen at − 45 °C and freeze-dried. The analyses were performed after rehydration. Differential Scanning Calorimetry (DSC) and Nuclear Magnetic Resonance in the domain of time (TD-NMR) were performed to assess thermal properties of freezable water and water distribution in apple tissue, respectively. PEF changed the integrity and continuity of the cell structure shown by the water redistribution between different compartments. The water in vacuoles and extracellular spaces had higher TD-NMR relaxation times as water molecules can diffuse in larger volumes before relaxing, even if the overall solutes concentration in the tissue increases.

Opacity Studies in Dehydrated Fruits in Relation to Proton Mobility and Supramolecular Aspects

Water content is one of the variables affecting light scattering in foods, which on time determine gloss, translucence, and transparency. The objective of this study was to evaluate the effect of freeze-drying, humidification, and storage time on the changes of light distribution inside fruit tissues and their relationship with glass transition and proton mobility. Sliced and powdered freeze-dried apple, pear, and melon humidified at different relative humidities were employed. All the studied materials were translucent when fresh and became opaque after the freeze-drying process. In freeze-dried sliced fruits, the cellular structure contributed to maintain air inside the matrices, and then the opacity of the materials was almost constant, independently of the relative humidity. In the powdered materials, the compacted structure retained less air than sliced samples, and the powders were translucent due to the lower number of light-matter interfaces than in the porous-dried fruits, leading to a lower internal diffusion. The opacity decrease when increasing the water mass fraction followed a variation parallel to the Tg curve. Opacity decrease occurred at T-Tg values above 38 °C and was coincident with the observation of a proton population of higher mobility than that observed below the water content hydration limit value. Proton mobility at a molecular scale could thus be related to supramolecular events affecting food appearance, and this information may help to develop food products with the desired appearance.

Ascorbate and Apple Phenolics Affect Protein Oxidation in Emulsion-Type Sausages during Storage and in Vitro Digestion.

The effect of sodium ascorbate and apple phenolics on the oxidative stability of emulsion-type sausages during storage and digestion was investigated. Emulsion-type sausages containing 0.05% sodium ascorbate or 3% freeze-dried apple pomace were subjected to chilled illuminated storage and subsequent in vitro digestion. Lipid oxidation was assessed as TBARS, and protein oxidation was evaluated as thiol oxidation, total carbonyls, and γ-glutamic and α-amino adipic semialdehyde. Proteolysis was measured after digestion to evaluate protein digestibility. The results suggest the presence of protein-ascorbate and protein-phenol interactions, which may decrease protein digestibility and may interfere with spectrophotometric methods for measuring oxidation.

Comparison of different extraction solvents for assay of the polyphenol content in the peel and pulp of 21 apple cultivars from Macedonia

Apples (Malus domestica Borkh.) contain a large array of phenolic compounds belonging to flavonoids and non-flavonoids. This study systematically evaluates the polyphenolic content of 21 apple cultivars from the Republic of Macedonia, both commercial and autochthonous, applying spectrophotometric methods for the determination of total polyphenolic compounds, total flavonoids, total anthocyanins and total flavan-3-ols. The reliability of these methods was checked by confirming the method linearity and accuracy with standards and spiked samples. The efficiency of acetone, water, methanol and a mixture of methanol/water (90 : 10, V/V) as extraction solvents was compared. Evident differences between extracts obtained from freeze-dried apple peel and pulp, extracted with different solvents, and analyzed with the four spectrophotometric tests, were observed and discussed. The most satisfactory extraction efficiency was achieved using methanol/water (90 : 10, V/V) mixture. The results obtained from the methanol/water extracts illustrate evident differences between polyphenol contents and reveal the diversity in polyphenols, total flavonoid and flavanol composition between the assayed commercial and autochthonous cultivars. The maximum abundance of polyphenols was noticed in the peel of Tetovka and Livadarka cultivars (15.63 mg/g GAE and 14.85 mg/g GAE, respectively) and in the pulp of Pasalma, Tetovka and Livadarka cultivars (12.55 mg/g GAE, 11.45 mg/g GAE and 11.22 mg/g GAE, respectively).

Microbial analysis and survey test of gamma-irradiated freeze-dried fruits for patient's food

Abstract This study examined the microbiological and organoleptic qualities of gamma-irradiated freeze-dried apples, pears, strawberries, pineapples, and grapes, and evaluated the organoleptic acceptability of the sterilized freeze-dried fruits for hospitalized patients. The freeze-dried fruits were gamma-irradiated at 0, 1, 2, 3, 4, 5, 10, 12, and 15 kGy, and their quality was evaluated. Microorganisms were not detected in apples after 1 kGy, in strawberries and pears after 4 kGy, in pineapples after 5 kGy, and in grapes after 12 kGy of gamma irradiation. The overall acceptance score, of the irradiated freeze-dried fruits on a 7-point scale at the sterilization doses was 5.5, 4.2, 4.0, 4.1, and 5.1 points for apples, strawberries, pears, pineapples, and grapes, respectively. The sensory survey of the hospitalized cancer patients ( N =102) resulted in scores of 3.8, 3.7, 3.9, 3.9, and 3.7 on a 5-point scale for the gamma-irradiated freeze-dried apples, strawberries, pears, pineapples, and grapes, respectively. The results suggest that freeze-dried fruits can be sterilized with a dose of 5 kGy, except for grapes, which require a dose of 12 kGy, and that the organoleptic quality of the fruits is acceptable to immuno-compromised patients. However, to clarify the microbiological quality and safety of freeze-dried fruits should be verified by plating for both aerobic and anaerobic microorganisms.

Optimization of the extraction of apple monomeric phenolics based on response surface methodology: Comparison of pressurized liquid–solid extraction and manual-liquid extraction

Response surface methodology (RSM) was performed in order to evaluate the optimal extraction conditions for flavan-3-ol monomers ((+)-catechin and (−)-epicatechin), phloridzin, chlorogenic acid, hyperoside, isoquercitrin, quercitrin, ideain and total phenolic content (TPC) from Braeburn freeze-dried apples, using a pressurized liquid solid (PLS) extractor. The aim of this study was to evaluate the effect of four independent extraction factors, including nature of extraction solvent (pure methanol, acetone–water (70:30, v/v)), sample mass (50–550mg), extraction duration (1–15min) and number of extraction cycles (1–3), on these polyphenol concentrations (HPLC–DAD analysis). Methanol was the most suitable extraction solvent for the studied phenolic compounds. Optimal conditions varied with phenolic compound and must be chosen as a compromise. For an extraction in favour of chlorogenic acid, hyperoside, quercitrin and ideain, we recommended the following experimental conditions using the pressurized liquid solid extraction (PLE) method: two successive extractions with pure methanol from 50mg freeze-dried apple-samples for 15min, using three extraction cycles. In comparison with manual methods, benefits from the increase of polyphenol concentrations, the reduction of extraction time and organic solvent amounts were observed with the PLE method.

Effects of Sugar Addition on Total Polyphenol Content and Antioxidant Activity of Frozen and Freeze-Dried Apple Purée

The objective of this study was to investigate the influence of simple sugar addition including (glucose, G; fructose, F; sucrose, S; and trehalose, T) on the total polyphenol content (TPC) and antioxidant activity (AOA) of apple purée processed by freezing and freeze-drying and stored for 6 months. The apple polyphenol profile was mostly preserved in the freeze-dried samples with sugar addition during 6 months of storage, whereas the polyphenol profile in frozen samples consists only of quercetin glycosides, of which rutin had the largest share. After 6 months, the highest level of polyphenols was detected in frozen 'Idared' and 'Fuji' apple purée with addition of T 5% (12.2 and 16.7 mg/100 g FW, respectively), whereas in freeze-dried apple purée the highest TPC was in 'Idared' and 'Fuji' with addition of T 1% (16.3 and 13.6 mg/100 g FW, respectively). Results indicate that sugar addition before processing could have potential for enhancing product quality.

Optimization of Microwave-Osmotic Pretreatment of Apples with Subsequent Air-Drying for Preparing High-Quality Dried Product

Prepared apple (Red Gala) cylinders were subjected to microwave-osmotic dehydration treatment under continuous flow medium spray (MWODS) conditions and then air-dried to a final 20% moisture content. The dried samples were evaluated for color and textural properties, and rehydration capacity. The MWODS pretreatments were based on a central composite rotatable design and a response surface methodology using five levels of sucrose concentration, temperature, and contact time at a constant flow rate of 2800 mL/min. The air-drying was carried out at 60°C, 15±1% relative humidity, and 0.64±0.02 m/s air velocity. The results were compared to untreated air-dried (AD) (worst-case scenario) and freeze-dried (FD) (best-case scenario) apples without the MWODS treatment. Color properties were affected regardless of the type of treatment. Conventional AD apples were darker in color, whereas MWODS-treated samples were lighter with higher L∗ and b∗ values, higher Hue and Chroma values but lower a∗ value and ΔE. Further the color parameters of MWODS-treated samples were closer or equal to the FD apples. The texture properties were also affected by the osmotic variables with MWODS treatment resulting in softer and chewier products. The AD samples were hard, and FD apples were brittle.

Implication of water activity and glass transition on the mechanical and optical properties of freeze-dried apple and banana slices

The interactions between water content, matrix structures and chemical and physical events in complex foods are usually regarded in terms of water activity and glass transition. In this work, the water content and water activity values that define important changes in the textural and optical properties of freeze-dried banana and apple slices have been related to the critical water content and water activity that cause the glass transition in both products. From the obtained results, it may be concluded that both approaches, glass transition and water activity, may be considered to prevent changes in the mechanical properties, while only the concept of water activity is needed to control the browning reactions that take place in the fruits.

Physico-Chemical and Mechanical Properties of Apple Disks Subjected to Osmotic Dehydration and Different Drying Methods

The effect of sucrose infusion (SI) pretreatment and dehydration methods (freeze and air drying) on physical and textural properties of apple disks were analyzed. Dried samples were humidified between 11% and 43% relative humidity (RH) at 20 °C. Control samples (air- and freeze-dried) behaved similarly regarding water sorption and glass transition temperature. SI process caused important changes in the water sorption behavior of air-dried samples. Nuclear magnetic resonance relaxation times values (T2) for freeze-dried apples were higher than those for air-dried samples. Samples subjected to previous SI always presented lower T2 values because they had lower water contents. The dehydration method also affected the mechanic behavior. Air-dried samples exhibited higher Fmax values during puncture assay than those obtained for freeze-dried samples. SI samples showed higher Fmax values for both drying methods. The crust formed during air drying generated crispier materials along the whole RH range, while freeze-dried matrices were more deformable with the increase in RH. SI pretreatment also allowed diminishing browning development. The results obtained are useful in the choice of processing technologies of organoleptically acceptable dehydrated fruits for direct consumption or for their incorporation into compound foods.

Effect of Calcium Ion and Microwave Power on Structural and Quality Changes in Drying of Apple Slices

Effects of impregnated calcium ion and microwave (MW) power on texture, rehydration, shrinkage, color, and other selected indexes of freeze-dried apple slices were investigated. Apple slices were dried by freeze drying and microwave freeze drying (MFD) separately. Vacuum impregnated (VI) and non-vacuum-impregnated apple slices were dried at various microwave power levels. Non-vacuum-impregnated apple slices were found to preserve their mechanical structure better than the VI-treated ones. Microwave application resulted in decreased protopectin fraction as well as total pectin content. As microwave power varied from 1.2 to 2.0 W/g, the total pectin content decreased from 0.810 to 0.521 (expressed as g galacturonic acid/100 g fresh sample). The effect of microwave power in decreasing the drying time was significant. The color of MFD apple slices varied to a minor extent with MW power level over the range of parameters studied.

In Vitro Measures Used to Predict Anticancer Activity of Apple Cultivars and Their Comparison to Outcomes From a Rat Model of Experimentally Induced Breast Cancer

Experiments reported herein tested the hypothesis that cultivars of apple (Malus domestica Borkh.) would demonstrate anticancer activity in vivo as predicted by in vitro measures. Freeze dried powders of Red Delicious (RD), Fuji (FJ), Golden Delicious (GD), and Granny Smith (GS) apple cultivars were evaluated. Significant differences were noted among cultivars in total phenolics (P < 0.0001), flavonoids (P < 0.0003), oxygen radical absorbance capacity (P < 0.0001), and growth inhibition in the MDA-MB-468 human breast cancer cell line relative to vehicle-treated cells (P < 0.0001). These findings were extended to predict inhibition of the postinitiation phase of 1-methyl-1-nitrosourea-induced mammary carcinogenesis by freeze-dried whole apple powders of the same cultivars. Although rats fed apple-containing diets did not have lower incidence or multiplicity of cancers than rats fed control diet, a finding consistent with epidemiological reports on fruit and breast cancer risk, differences among cultivars were noted, with the greatest difference in cancer multiplicity between GS and RD (1.46 vs. 2.47 cancers/rat; P = 0.0159). The rate of cell proliferation in mammary carcinomas differed between GS and RD (P < 0.001), whereas the apoptotic rate did not. These findings suggest altered methodology for screening apples for anticancer activity and that more diverse apple cultivars with higher phytochemical content should be evaluated.

INFLUENCE OF STORAGE CONDITIONS ON FREEZE-DRIED APPLE FORTIFIED WITH VITAMIN E

The effect of different storage conditions (temperature: 4, 20 and 30 °C; time: 30, 60, 90 and 180 days;package: with and without vacuum), is evaluated in terms of the stability of vitamin E, color and textureof freeze-dried apple fortified with vitamin E, using matrix engineering as a methodology for obtainingfunctional foods. The vitamin’s quantification was carried out using gas chromatography. The color’s bycoordinates CIE- L*a*b*, hue and chroma and texture by penetration test. Degradation of vitamin E wasmodeled using a first order kinetics. However the kinetic constants weren’t fitted by Arrhenius equation,due to an abrupt change in them between 4 and 20ºC, the effect of the transition from glassy to rubberystate in the product. At 4ºC, the color was acceptable at 180 days, whereas browning is observed at 20ºCand 30ºC, and is higher according to temperature and time. Vacuum packaging showed a negative effectin the samples color, probably due to the mechanical effects. Textural changes, caused by progressivemoisture gain, are related to permeability of packaging material, generating loss of crunch, which waswell evaluated at the initial control time (30 day).

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 Apple Dried by Different Methods

Apple var. Idared cut into cubes was dried by convection and freeze-dried. Dried cubes were equilibrated to variable water activities by storage over saturated salt solutions (range 0–0.33). Rehydration was done for one hour in water at 20°C. Increase in both mass and volume of cubes was followed during rehydration. Changes in height of a cube were recorded using a minimal displacement gauge. Electron transmission microscopy was used to measure cell wall thickness in raw and rehydrated material. Modes of drying affected the behavior of apple cubes upon rehydration. Convective dried apple imbibed water and swelled during rehydration, and a collapse of structure was observed at the beginning of the wetting process. Analysis of both mass and volume increase showed that at the beginning of rehydration capillaries and pores were filled with water and thereafter swelling of biopolymers occurred. Cell walls imbibed water, but their thickness after one hour of rehydration was half of that of raw apple. Freeze-dried apple increased in mass much faster than these dried by convection. Rehydration caused collapse of structure, which was not rebuilt during further wetting. On the other hand, cell walls swelled significantly during rehydration and reached thickness almost that of raw apple. It was inferred that freezing injured tissue, which after drying contained numerous discontinuities. Hence, swelling of domains, which did not form a continuous structure, was not propagated and expressed by the increase in volume on a macroscopic scale. Initial water activity of both investigated materials affected collapse of structure during rehydration. The higher the water activity, the faster the collapse.

Preliminary Results of Extraction, Separation and Quantitation of Arsenic Species in Food and Dietary Supplements by HPLC-ICP-MS

Various extraction procedures were investigated using reference materials and samples to evaluate extraction efficiency and effectiveness. Inductively coupled plasma mass spectrometry (ICP-MS) was used to measure total arsenic and to quantitate arsenic species when coupled to an HPLC (high pressure liquid chromatography). Arsenic species were extracted from rice flour (NIST SRM 1568a) with water/methanol mixtures using accelerated solvent extraction (ASE). Total arsenic extraction efficiency ranged from 42 to 64%, for water and various methanol concentrations. From spinach (NIST SRM 1570), freeze-dried apple, and rice flour (NIST SRM 1568a), arsenic species were extracted with trifluoroacetic acid (TFA) at 100 °C. Total arsenic extraction efficiency was 90% for spinach, 75% for freeze-dried apple, and 83% for rice flour. Enzymatic extraction with alpha-amylase and sonication resulted in extraction efficiency of 104% for rice flour, 98% for freeze-dried apple, and 7% for spinach. Chromatograms of arsenic species extracted by the optimum extraction methods were obtained, and the species were quantified. Arsenite (As(III)), arsenate (As(V)), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) were found in the apple sample, and DMA and As(V) in the rice flour sample. As(V) and MMA were found in three herbal dietary supplement samples.

Effects of transglutaminase, tyrosinase and freeze-dried apple pomace powder on gel forming and structure of pork meat

Effects of microbial transglutaminase (mTG), mushroom tyrosinase and an apple powder containing transglutaminase (TG) and polyphenol oxidase (PPO) on the structure of industrial pork meat homogenate were studied. Apple powder and mTG both increased the value of storage modulus ( G′). Mushroom tyrosinase was not able to affect gel forming with the used dosages and treatment conditions. All the enzymes studied were able to improve gel hardness of unheated meat homogenate at 4 °C to a certain extent. In gel hardness measurements added cysteine affected positively on the apple powder—treated pork meat and negatively on mTG—and tyrosinase-treated meat. Surprisingly cysteine addition nullified also the action of mTG. Hence powdered apple pulp, a recovered co-product of an industrial process, may contain suitable enzyme activities for food protein stabilization.