Apple Discs Research Articles

Combination of ferulic acid with Aloe vera gel or alginate coatings for shelf-life prolongation of fresh-cut apples

Weight loss, microbial spoilage and enzymatic browning are the main quality-determining processes which limit the shelf-life of fresh-cut apples. In this study, two edible coatings based on Aloe vera gel (AV) and sodium alginate cross-linked with calcium lactate (AC), with the addition of 10 mg/mL ferulic acid (FA) as a functional ingredient, were developed in order to prolong the quality and safety of fresh-cut apple discs. Texture parameters, pH and Brix values and water activity did not undergo relevant changes related to the treatments. Except for weight loss, which was significantly lower for the coated samples, the addition of FA was found to be the most relevant factor for the other investigated parameters, including the total phenolic content and the antioxidant activity measured by ferric reducing antioxidant power (FRAP). Browning was delayed by the addition of FA and also by the AV coating, while non-coated and alginate coated samples showed the highest values in early stages. Although no effect on Saccharomyces cerevisiae was observed, FA treatments and alginate were effective in reducing Listeria monocytogenes populations by 2.3 ± 0.4 log CFU / g, which contributes to an enhanced product safety.

Probiotic survival and in vitro digestion of L. salivarius spp. salivarius encapsulated by high homogenization pressures and incorporated into a fruit matrix

High pressure homogenization allows encapsulating microorganisms. Microencapsulation of probiotic microorganisms may enhance their viability during food processing, storage and gastrointestinal passage. The aim of this work was to evaluate the probiotic survival and in vitro digestion of non-encapsulated and encapsulated Lactobacillus salivarius spp. salivarius by homogenization at 70 MPa, included into an apple matrix by vacuum impregnation, dried by hot air drying and stored during 30 days. Lactobacillus salivarius spp. salivarius was encapsulated with alginate as a coating by homogenization pressures at 70 MPa and it was added to mandarin juice. Juices with L. salivarius spp. salivarius encapsulated and non-encapsulated were used as impregnation liquid to incorporate the probiotic microorganisms in apple discs. Impregnated apple discs were dried at 40 °C during 24 h and water activity, moisture, counts of viable cells and survival during gastrointestinal simulation for the storage period of 30 days were evaluated. Dried apple discs with encapsulated L. salivarius spp. salivarius resulted with higher amount of viable cells than in those non-encapsulated. Gastrointestinal simulation results evidenced a protection of the microorganism due to the capsule effect.

Ultrasound-assisted vacuum impregnation on the fortification of fresh-cut apple with calcium and black carrot phenolics

This study evaluated the simultaneous effect of ultrasound on vacuum impregnation process to enhance infusion of calcium lactate and black carrot phenolics into ready to eat apple tissues. A vacuum – ultrasonic equipment was developed for this purpose and effects of different ultrasound powers (96–198 W) at 35 kHz and stage of ultrasound application at vacuum and restoration periods were investigated. The simultaneous application of 130 W ultrasound during vacuum impregnation did not rupture cellular integrity, but it led to increases in calcium content (13.8%), total phenolics (11.8%), total flavonoids (17.3%), total anthocyanins (24.6%) and antioxidant capacities (23.6%) of apple discs compared to non-ultrasound vacuum impregnation. In addition, total population of psychrophilic and mesophilic microorganisms were enumerated in both black carrot infused and non-infused samples and results showed that ultrasound-assisted vacuum impregnation treatment in the presence of black carrot phenolics were highly effective on inhibition of microorganisms growth in apple discs over storage period.

Synvina to extend PEF pilot phase

This work discusses the effects of pulsed electric field (PEF), ohmic heating (OH), and osmotic (O) treatments on the structure of apple tissue and its freezing/thawing behaviour. Apple discs were treated at electric field strength E = 800 V/cm (PEF, isothermal regime) and E = 40 V/cm (OH, non-isothermal regime) to a high level of tissue disintegration (conductivity disintegration index Z was ≈ 0.98) and then were subjected to osmotic (O) treatment in the aqueous solution of glycerol (20 wt.%). The distribution of osmotic solution was practically homogeneous inside the disc of PEF-treated tissue and highly inhomogeneous in untreated and OH-treated samples. The freezing–thawing (FT) experiments (+ 20 °C → − 40 °C → + 20 °C) were done in order to reveal the effects of combined modes of treatment on the structure of apple tissue. The most pronounced reducing of both freezing and thawing times and strengthening of the apple texture were observed for PEF treatment.Freezing-assisted preservation of plant materials in the most natural-looking state with near-original texture and colours requires thorough optimization of freezing operation. In this study, the research of the impact of pulsed electrotechnologies combined with osmotic pre-treatment on the structure of apple tissue, its freezing/thawing behaviour and texture quality, is provided.

Dynamic and static sensory methods to study the role of aroma on taste and texture: A multisensory approach to apple perception

To date very little research has been done on sensory interaction taking into account the temporal component. The objectives of this work were to better understand the influence of aroma perception on taste and texture perception in a real food matrix such as the apple, considering sensory perception both as a static and dynamic process. Another objective was to evaluate the suitability of Temporal Dominance of Sensations (TDS) for studying sensory interaction.A set of 9 apple samples, made up of apple discs modified with two distinct aromas (3-methylbutyl acetate and (E)-3-hexen-1-ol) and/or two tastants (fructose and dl-malic acid), was used for the experiment. Samples were analysed by Descriptive Analysis (DA) and TDS performed by two different panels. Samples were also analysed using instrumental measurement of texture, sugar and volatile content.Aroma addition modified perception of the apple in both a static and dynamic way. Some texture-aroma and taste-aroma interaction were highlighted. TDS showed that both aromas made perception of hardness and juiciness less dominant. In some cases, banana aroma modified sweet taste perception and when used without tastants, it tended to anticipate sweetness perception in time. DA evidenced different results: both aromas decreased crunchiness or flouriness intensities when used alone or with fructose respectively. They increased juiciness intensity when combined with malic acid.TDS confirmed well-known relations between taste and smell and showed its appropriateness for studying sensory interaction. Its combination with DA gathered complementary points of view enriching the analysis and revealing unexpected or time-related interaction, a new perspective for understanding the phenomena linked to perception.

Natural colorant enrichment of apple tissue with black carrot concentrate using vacuum impregnation

SummaryColoured apple discs containing black carrot concentrate (BCC), calcium lactate and lactic acid were formulated and produced as a new functional fresh fruit product using vacuum impregnation. Sensory test was conducted to select the most preferred impregnation formulation containing an addition of 0.0%, 0.4%, 0.8% and 1.2% BCC, 1.5%, 3.0% and 4.5% calcium lactate and 2.0%, 3.0% and 4.0% lactic acid. Results indicated that the formulation with the addition of 3% Ca‐lactate, 3% lactic acid and 0.8% BCC within 0.2 m mannitol solution was significantly preferred. The optimum vacuum pressure (211 mm Hg), vacuum time (3 min) and restoration time (20 min) according to highest colorant transfer, while the minimum cellular disruption occurs were estimated using response surface methodology. The use of Ca‐lactate and BCC contributed the treated apple to resemble untreated apple properties in terms of texture, total phenolic, total flavonoid contents and antioxidant capacity.

Acoustic emission as a tool to assess the changes induced by pulsed electric field in apple tissue

Abstract The aim of this work was to analyse the acoustic and mechanical properties of pulsed electric field treated solid-like plant tissue as exemplified by apple fruits. The electrical conductivity of the untreated and PEF treated samples was measured as well. Additionally, an attempt to use the acoustic emission as a tool to assess the electroporation efficiency was done. Subjecting the apple discs to PEF treatment resulted in altered mechanical, electrical and acoustic properties. The compressive force registered at 15% strain was reduced by the PEF application up to 72.7% in comparison to the intact material. The number of acoustic events obtained by the contact method was the most suitable acoustic emission descriptor among other ones to differentiate the PEF treated and intact materials. The results of experiment and especially the PCA point out that the acoustic emission measured by the contact method can be a useful tool to evaluate both the disintegration efficiency and texture changes caused by the PEF application.

Pulsed electric field assisted vacuum freeze-drying of apple tissue

Impact of apple treatment by pulsed electric field (PEF) on vacuum freeze-drying was studied. Apple discs were PEF treated at an electric field strength of E = 800 V/cm for the different values of disintegration index Z. Then vacuum cooling was applied to decrease the temperature to sub-zero level and freeze-drying experiments were done at a pressure of 10 mbar. Time evolution of temperature and moisture content were compared for the PEF treated and untreated apple samples. Acceleration of cooling and drying processes was observed for the PEF treated samples. The microscopic, macroscopic analysis and data of capillary impregnation test evidenced that the PEF treatment facilitates preservation of the shape of the dried samples, allows avoiding shrinking and results in increase of the tissue pores. The sample rehydration capacity strongly depends on Z. At Z = 0.96 a high level of rehydration capacity (≈ 1.3) was observed. Different methods of food drying are very popular for food processing and are widely used for food preservation. However, they are very energy intensive processes and can cause undesirable changes of colour, flavour, nutrient and textural properties of foods. Vacuum freeze-drying allows obtaining high-quality food products. On the other hand, this process is power consuming, requires long time and low pressure and can provoke the damage of final dried product. Thus, the development of efficient and optimal methodology for freeze-drying of foodstuff is relevant. Application of PEF as a pretreatment procedure may be useful for improving the efficiency of drying and the quality of dried products.

Effects of pulsed electric fields assisted osmotic dehydration on freezing-thawing and texture of apple tissue

The effects of pulsed electric fields (PEF) assisted partial dehydration of apple tissue on freezing-thawing processes and texture characteristics were studied. The apple disks were treated to a high level of tissue disintegration (electrical conductivity disintegration index Z was ≈0.98) and then were subjected to osmotic dehydration (OD) in the apple juice-glycerol solutions using different concentrations of glycerol and time of dehydration. PEF-assisted OD resulted in noticeable acceleration of the freezing/thawing processes as compared with those for untreated samples. The main characteristics of freezing-thawing processes (freezing and thawing time and freezing temperature) and texture of samples in dependence on intrinsic moisture content in the sample were evaluated. The differences in these characteristics were explained by the differences in spatial distributions of soluble solids and water inside the samples. For some optimum parameters of osmotic treatments (e.g., at t = 180 min, C ≈ 20 wt. %), the texture after defrosting was comparable to that of fresh apples.

“Ice” juice from apples obtained by pressing at subzero temperatures of apples pretreated by pulsed electric fields

Abstract The impact of apple pretreatment by pulsed electric field (PEF) on juice extraction using the freezing-assisted pressing was studied. Apple discs were PEF pretreated at electric field strength of E = 800 V/cm and then air blast frozen inside the freezer (− 40 °C). Then, pressing experiments in a laboratory-pressing chamber (2–5 bars) were started at sub-zero temperature (− 5 °C). Time evolution of juice yield and its nutritional qualities were compared for PEF and untreated apple samples. High improvements of juice yield were obtained for freeze-thawed (FT) and PEF + FT samples. The combination of PEF + pressing (5 bar) at sub-zero temperature gave optimum results for juice extraction with high levels of carbohydrates, and antioxidant bioactive compounds. At fixed value of extraction yield, Y , PEF pretreatment improved nutritional parameters. E.g., at Y = 0.6, an increase in °Brix (by ≈ 1.27), carbohydrates (by ≈ 1.42), total phenolic compounds (by ≈ 1.16), flavonoids (by ≈ 1.09) and antioxidant capacity (by ≈ 1.29) was observed after PEF pretreatment. Industrial relevance Pressing constitutes one of the most commonly used technologies at industrial scale to obtain fruit juices. However, during the pressing some undesirable chemical, physical and biological changes may occur in juices, thus reducing their nutritional and sensorial properties. For instance, the use of freezing-assisted pressing is a promising technique for the production of juice concentrates rich in sugars and other solids as the low temperature operation prevents undesirable modifications. But this method is rather expensive and requires strong control of the quality of “ice” juices, their sensory and compositional profiles. Thus, there is an increased search for obtaining new efficient methodologies for producing high quality juices. In this line, PEF-assisted pressing has been shown as a useful technology to increase juice yield. Therefore, the combination of PEF-assisted “ice” juice extraction by pressing of fruits at subzero temperatures may be a useful tool to improve the extraction yield of juices, thus improving their nutritional, physicochemical and sensorial properties. Keywords: “Ice” juice, Apple, Pulsed electric fields, Freezing-assisted pressing

Unfreezable Water in Apple Treated by Pulsed Electric Fields: Impact of Osmotic Impregnation in Glycerol Solutions

The effects of pulsed electric fields (PEF) and osmotic impregnation in glycerol solution on the amount of unfreezable water in apple were determined by means of low-temperature differential scanning calorimetry (DSC). The obtained data were compared with behaviour of pure water–glycerol solutions (sample WG). PEF treatment was applied using a near-rectangular monopolar generator with pulse duration of 100 μs at electric field strength of 800 V/cm. The osmotic impregnation of PEF-treated apple discs was done using water–glycerol (sample AWG) and apple juice–glycerol (sample AJG) osmotic solutions at different concentration of water or juice in glycerol, W = 30–100 wt%. The data evidenced that for the PEF-treated samples the glycerol was able to penetrate successfully inside apple tissue. The state diagrams for WG, AWG and AJG samples were rather similar. It was observed that free water existed only for moisture content above some minimum value. The unfreezable water content was the largest in AJG, followed by WG and AWG. The juice concentration in glycerol W ≈ 80 wt% was found to be optimal for preservation of the texture of PEF-treated samples.

Identification and characterization of serotonin as an anti-browning compound of apple and pear

Serotonin (5-hydroxytryptamine) is an indoleamine with important physiological functions in plants, including developmental processes and stress responses. In this study, a simple and rapid bioassay was developed to investigate the inhibition of the fruit browning enzyme, polyphenol oxidase (PPO) via serotonin, employing cut apple discs as well as apple tissue homogenate treated with serotonin. The present study demonstrated that serotonin is significantly effective in inhibiting browning compared to ascorbic acid. Serotonin reduced fruit browning in tissues as well as suppressed the activity of PPO enzyme in the browning model solutions containing epicatechin (Epi) and caffeoyl tartrate (CT) as polyphenol substrates. The determination of enzyme kinetic parameters also suggested that serotonin may act as a putative, non-competitive inhibitor of PPO. Apart from its anti-browning effect, the application of serotonin significantly increased total phenolics content and antioxidant capacity when applied to the apple homogenate. Furthermore, the analysis of MdPPOs showed that five (MdPPO2, MdPPO4, MdPPO6, MdPPO8 and MdPPO10) out of the nine MdPPOs expressed in apple fruits were down-regulated in apple tissues treated with serotonin. To the best of our knowledge, this is the first report documenting a role for serotonin in the biochemical and transcriptional regulation of PPO enzymes and a simple system to study the biochemical control of browning in pome fruits.

Vacuum impregnation and air drying temperature effect on individual anthocyanins and antiradical capacity of blueberry juice included into an apple matrix

Blueberries are an important source of bioactive compounds that can be consumed as fresh or processed fruit. The aim of this work was to study the addition of blueberry juice into apple discs by vacuum impregnation and further stabilization of the impregnated apple by air-drying and freeze-drying in order to produce a low-humidity fruit-like natural snack. The effect of processing operations was studied in terms of functional properties. Results indicated that it was possible to add blueberry juice into the structure of fresh apple slices without a negative effect on bioactive compounds. While air-drying operation implied a significant loss of the initial anthocyanin content, the final product stabilization by freeze-drying did not cause any loss of individual anthocyanin content. Results of the different analyses showed the best final product was obtained by freeze-drying or air-drying stabilization at 40 °C.

Effect of electric field and osmotic pre-treatments on quality of apples after freezing–thawing

Abstract This work discusses the effects of pulsed electric field (PEF), ohmic heating (OH), and osmotic (O) treatments on the structure of apple tissue and its freezing/thawing behaviour. Apple discs were treated at electric field strength E = 800 V/cm (PEF, isothermal regime) and E = 40 V/cm (OH, non-isothermal regime) to a high level of tissue disintegration (conductivity disintegration index Z was ≈ 0.98) and then were subjected to osmotic (O) treatment in the aqueous solution of glycerol (20 wt.%). The distribution of osmotic solution was practically homogeneous inside the disc of PEF-treated tissue and highly inhomogeneous in untreated and OH-treated samples. The freezing–thawing (FT) experiments (+ 20 °C → − 40 °C → + 20 °C) were done in order to reveal the effects of combined modes of treatment on the structure of apple tissue. The most pronounced reducing of both freezing and thawing times and strengthening of the apple texture were observed for PEF treatment. Industrial relevance Freezing-assisted preservation of plant materials in the most natural-looking state with near-original texture and colours requires thorough optimization of freezing operation. In this study, the research of the impact of pulsed electrotechnologies combined with osmotic pre-treatment on the structure of apple tissue, its freezing/thawing behaviour and texture quality, is provided.

Analysis by non-linear irreversible thermodynamics of compositional and structural changes occurred during air drying of vacuum impregnated apple (cv. Granny smith): Calcium and trehalose effects

Apple discs were impregnated with isotonic solutions of sucrose and trehalose with and without calcium addition and after air dried. In the vacuum impregnation experiments, the calcium and the replacement of sucrose by trehalose did not have significant effect on the final volumetric deformation of the samples. During air drying two stages of changes were considered. The first one lasted until the saturation of the intracellular liquid phase, and the second one from the saturation of the intracellular liquid phase until the end of the drying process. Mass transfer has been analysed applying nonlinear irreversible thermodynamics. Water flux, water chemical potential and tissue shrinkage have been taken into account in order to accurately describe the mass transfer phenomena during air drying. A precise definition of chemical potential allowed estimating the partial molar energy needed for breakages and the reversible and irreversible deformations of tissue structure coupled with mass transfer during air drying of apple.

Modelling of apple slice moisture content by optical methods

Experiments were performed to follow the moisture loss of apple slice samples (discs of 3 cm diameter and 1 cm thickness) during the drying process. Different optical methods were tested in order to find a model for prediction of the moisture content based on non-contact measurements. Apple discs were dried in a hot air drying chamber for different periods (0–7 hours). The mass of every individual sample was measured before drying (initial mass), after drying (actual mass), and after the optical tests at the end of a 24 h drying process (final mass). Both the wet base and the dry base moisture content were calculated from the actual mass and the final mass of the samples. The optical properties of the samples of different moisture content were measured by two different optical methods. Laser induced backscattering method, applying 3 mW laser modules of different wavelengths, was used to generate the diffuse reflection pattern (halo) on the surface of samples and evaluate the halo properties with a machine vision system. Near Infrared Reflection (NIR) technique was also used to collect/measure the log(1/R) spectra of the samples in the 740–1700 nm range.PLS method with full cross-validation was used to predict the moisture content of the samples based on the backscattering data (quantitative parameters of the halo profile) and on the NIR spectra (raw and transformed log(1/R) data). Effective models (r>0.98, RPD>5) were found for prediction of the dry base moisture content of the samples based on both optical methods.

How to deal with visco-elastic properties of cellular tissues during osmotic dehydration

In this work, vacuum impregnated apple discs with different isotonic solutions (sucrose and trehalose) were equilibrated during osmotic dehydration (55°Brix glucose at 40°C). Changes in sample composition (water and soluble solid contents), weight and volume are analysed. A mathematical model is proposed to describe and quantify the outflow of water from the protoplast as well as the visco-elastic behaviour of the cell. Good correspondence between simulated and measured data of non impregnated samples and samples impregnated with isotonic solutions of sucrose or trehalose during long term osmotic dehydration is obtained. Fitted values of the cell permeability correspond well with tabulated values. Furthermore, also the obtained values of the parameters describing the mechanical properties of the cell wall and Hectian strands seem to reflect the observed structural development of these structures for the different treated samples well.

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 ultraviolet-C light dose on quality of cut-apple: Microorganism, color and compression behavior

The present study was aimed to: (1) examine the effect of UV-C irradiation at different doses on the surface color of fresh-cut-apple discs stored in refrigeration for 7 days; (2) explore the use of some pretreatments (hot water blanching, dipping into a solution containing ascorbic acid and calcium chloride) to minimize browning of UV-C irradiated apple slices, (3) investigate the effect of UV-C light at different doses (with or without anti-browning pretreatment) on survival of some inoculated microorganisms and native flora, and (4) examine the compression behavior of apple discs subjected to UV-C irradiation with or without pretreatments. The color and compression parameters were found to be dependent on UV-C dose, storage time and type of pretreatment. At the end of storage, samples exposed to only UV-C light turned darker (lower L * values) and less green (higher a * value) when compared to fresh-cut-apple slices or to samples on day 0 and this effect was more pronounced at the greatest UV-C dose. Light microscopic images showed breakage of cellular membranes in UV-C treated samples which may explain the increase in browning of irradiated apples. Both pretreatments helped in maintaining the original color of apple slices after UV-C light exposure. Natural microflora counts were higher in untreated UV-C than in UV-C treated samples along the whole storage. Survival patterns of inoculated microorganisms ( Listeria innocua ATCC 33090; Escherichia coli ATCC 11229 and Saccharomyces cerevisiae KE 162) depended on the UV-C dose, the type of microorganism and the apple pretreatment.

PATULIN IN APPLE FRUITS: II. EFFECT OF APPLE TREATMENTS WITH SOME CHEMICAL SANITIZERS ON PATULIN PRODUCTION BY Penicillium expanusm

Penicillium expansum is a wide spread fungi found on apples that causes fruit decay and may lead to production of a toxic secondary metabolite, basically patulin. This study was carried out to evaluate the effectiveness of several chemical sanitizers against P. expansum NRRL 2304 and to establish sanitizing washing treatments that would inhibit P. expansum growth and subsequent patulin production on Anna apples destined for cider .Wash treatments with chemical sanitizers including NaOCl (100 to 200 ppm) , Potassium sorbate (0.1 to 0.5% ), SO2(100 to 300 ppm) and acetic acid (0.5 and 3% ) . The results showed that washing with NaOCl (200 ppm) delayed growth of P. expansum on inoculated apple discs but failed to completely inhibit patulin production. Acetic acid solutions (2 to 3%) were the most efficient chemical against P. expansum and subsequent patulin production on apple juices. While no significant effect in patulin production was found by SO­­2 and potassium sorbate. The effect of pressing on molded Anna apple discs fruits was studied. The pressing resulted in a partially elimination of patulin in apple juices. Patulin in the final juices is dependent on initial the concentrations.