Ultrasound assisted low-temperature drying of kiwifruit: Effects on drying kinetics, bioactive compounds and antioxidant activity.

BACKGROUND: Low-temperature drying is considered to be a promising technique for food processing. It preserves thermolabile compounds and might be intensified by acoustic assistance. The effect of acoustic assistance (20.5 kW m-3 ) during low-temperature drying of kiwifruit (at 5, 10 and 15 °C, and 1 m s-1 ) on drying kinetics, bioactive compounds (such as ascorbic acid, vitamin E, and total polyphenols), and antioxidant activity was studied. RESULTS: Drying time was shortened by 55-65% when using power ultrasound. A diffusion model was used to evaluate the drying kinetics. The effective diffusion coefficient increased by 154 ± 30% and the external mass transfer coefficient increased by 158 ± 66% when ultrasound was applied during drying, compared with drying without ultrasound application. With regard to bioactive compounds and antioxidant activity, although samples dried at 15 °C presented significantly higher (P < 0.05) losses (39-54% and 57-69%, respectively) than samples dried at 5 °C (14-43% and 23-50%, respectively) when ultrasound was not applied, the application of ultrasound during drying at 15 °C significantly reduced (P < 0.05) those losses in all quality parameters (15-47% and 47-58%, respectively). CONCLUSION: Overall, low-temperature drying of kiwifruit was enhanced by acoustic assistance preserving bioactive compounds and antioxidant activity, especially at 15 °C. © 2018 Society of Chemical Industry.

Influence of freezing on the bioaccessibility of beetroot (Beta vulgaris) bioactive compounds during in vitro gastric digestion.

BACKGROUND: The effect of freezing (in liquid nitrogen at -196 °C , at -80 °C and at -20 °C) on the food matrix structure and the consequent effect on the bioaccessibility of total polyphenol content (TPC) and antioxidant activity (AA) of beetroot was investigated by an in vitro digestion method. The in vitro digestion involved incubation in simulated saliva followed by incubation in simulated gastric juice. Bioaccessibility of bioactive compounds was evaluated by measuring the TPC and the AA during in vitro digestion in both the beetroot matrix and the gastric juice. RESULTS: Release of TPC and AA of beetroot was higher in frozen samples (55 ± 5% for TPC and 68 ± 5% for AA) than in the fresh beetroot sample (∼46% for TPC and ∼53% for AA). The mass transfer kinetics were described by using a Weibull model with mean relative errors lower than 8.5% contributing to a better understanding of the influence of freezing on the bioaccessibility of bioactive compounds. CONCLUSIONS: From the treatments tested in this study, freezing with liquid nitrogen resulted in the greatest increase in bioaccessibility of the antioxidant and phenolic compounds of beetroots. © 2018 Society of Chemical Industry.

Application of power ultrasound on the convective drying of fruits and vegetables: effects on quality.

Drying gives rise to products with a long shelf life by reducing the water activity to a level that is sufficiently low to inhibit the growth of microorganisms, enzymatic reactions and other deteriorative reactions. Despite the benefits of this operation, the quality of heat sensitive products is diminished when high temperatures are used. The use of low drying temperatures reduces the heat damage but, because of a longer drying time, oxidation reactions occur and a reduction of the quality is also observed. Thus, drying is a method that lends itself to being intensified. For this reason, alternative techniques are being studied. Power ultrasound is considered as an emerging and promising technology in the food industry. The potential of this technology relies on its ability to accelerate the mass transfer processes in solid-liquid and solid-gas systems. Intensification of the drying process with power ultrasound can be achieved by modifying the product behavior during drying, using pre-treatments such as soaking in a liquid medium assisted acoustically or, during the drying process itself, by applying power ultrasound in the gaseous medium. This review summarises the effects of the application of the power ultrasound on the quality of different dried products, such as fruits and vegetables, when the acoustic energy is intended to intensify the drying process, either when the application is performed before pretreatment or during the drying process. © 2017 Society of Chemical Industry.

Evaluation of Different Pectic Materials Coming from Citrus Residues in the Production of Films.

This article explores the use of citrus residues as a source of different pectic materials for packaging film production: a water-soluble orange residue extract (WSE) (~5% pectin), semi-pure pectins extracted in citric acid (SP) (~50% pectin), and commercial pure citrus pectins (CP). First, these materials were characterized in terms of chemical composition. Then, films were produced using them pure or mixed with chitosan or glycerol through solvent-casting. Finally, antioxidant activity, functional properties (e.g., mechanical and gas barrier properties), and visual appearance of the films were assessed. WSE films showed the highest antioxidant activity but the lowest mechanical strength with the highest elongation at break (EB) (54%); incorporating chitosan increased the films' strength (Young's modulus 35.5 times higher). SP films showed intermediate mechanical properties, reinforced by chitosan addition (Young's modulus 4.7 times higher); they showed an outstanding dry O2 barrier. CP films showed a similar O2 barrier to SP films and had the highest Young's modulus (~29 MPa), but their brittleness required glycerol for improved pliability, and chitosan addition compromised their surface regularity. Overall, the type of pectic material determined the film's properties, with less-refined pectins offering just as many benefits as pure commercial ones.

High-Power Ultrasound in Gas Phase: Effects on the Bioactive Compounds Release from Red Bell Pepper during In Vitro Gastrointestinal Digestion.

High-power ultrasound in gas-phase (28.8 kW/m3 for 120 min at 17.5 ± 0.3 °C) has been evaluated as a pre-treatment to enhance the release of antioxidants and phenolic compounds from red bell pepper during digestion. The moisture content decreased (34 ± 4%) while both the antioxidant activity (between 4 ± 1% and 21 ± 1%) and the phenolic compounds content (37 ± 4%) increased after the treatment. Moreover, microstructural changes were observed in the treated sample, with the appearance of breaks in the plant tissue, cell shrinkage, and an increased number of cells per area unit (28 ± 2%). Bioaccessibility was determined by in vitro gastrointestinal digestion. The total release of antioxidants and phenolic compounds after gastrointestinal digestion was 22-55% higher and 45 ± 7% higher, respectively, in the sonicated sample, with cell swelling and a 9.2 ± 0.1% higher number of cells per area unit. Therefore, the ultrasound treatment caused microstructural changes in the red bell pepper tissue, which could help to explain the higher release of bioactive compounds.

Effect of Essential Oils from Lemongrass and Tahiti Lime Residues on the Physicochemical Properties of Chitosan-Based Biodegradable Films.

This work aimed to evaluate the impact of adding two essential oils (EO) from lemongrass (LEO) and Tahiti lime (TLEO) on the physical, mechanical, and thermal properties of chitosan-based biodegradable films. Six film formulations were prepared: two controls with chitosan concentrations of 1% and 1.5% v/w, two formulations combining the two chitosan concentrations with 1% LEO v/v, and two formulations combining the two chitosan concentrations with 1% TLEO v/v. The films' morphological, water affinity, barrier, mechanical, and thermal properties were evaluated. The films' surface showed a heterogeneous morphology without cracks, whereas the cross-section showed a porous-like structure. Adding EO to the films promoted a 35-50% decrease in crystallinity, which was associated with an increase in the elasticity (16-35%) and a decrease in the tensile strength (9.3-29.2 MPa) and Young's modulus (190-1555 MPa) on the films. Regarding the optical properties, the opacity of the films with TLEO increased up to 500% and 439% for chitosan concentrations of 1% and 1.5%, respectively. While the increase in opacity for the films prepared with LEO was 357% and 187%, the reduction in crystallinity also reduced the resistance of the films to thermal processes, which could be explained by the reduction in the enthalpy of fusion. The thermal degradation of the films using TLEO was higher than those where LEO was used. These results were indicative of the great potential of using TLEO and LEO in biodegradable films. Likewise, this work showed an alternative for adding value to the cultivation of Tahiti lime due to the use of its residues, which is in accordance with the circular economy model. However, it was necessary to deepen the study and the use of these essential oils in the preparation of biodegradable films.

Measurement of microstructural changes promoted by ultrasound application on plant materials with different porosity.

This research investigated the effects of ultrasound application (192 ± 6 W/L) on the microstructure of vegetables/fruits with different porosities, cell sizes and patterns (eggplants, beetroots, and apples), submitted to an immersion treatment in different liquids: distilled water, citric acid (1% w/v), and the vegetable/fruit juice, at 25 °C during 5 min. The ultrasound application did not significantly (p > 0.05) affect the size of the cells of the most porous material (eggplant) compared to the samples immersed without ultrasound assistance. The apple samples (with a middle-high porosity and the largest cells) were the most affected by ultrasound application. The median cell areas of samples treated with ultrasound in water and apple juice were 26 and 20% larger than those of samples treated without ultrasound, mainly because of cell wall disruption which caused the cells to merge into bigger clusters, but no effect was observed with the citric acid. Ultrasound application significantly (p < 0.05) increased the median cell area of the less porous raw matter (beetroot) only when the treatment was carried out in the vegetable juice (cells were 26% larger after treatment assisted with ultrasound than without it). Thus, the effects of ultrasound differ in materials with initially different characteristics.

Artificial Neural Networks to Optimize Oil-in-Water Emulsion Stability with Orange By-Products.

The use of artificial neural networks (ANNs) is proposed to optimize the formulation of stable oil-in-water emulsions (oil 6% w/w) with a flour made from orange by-products (OBF), rich in pectins (21 g/100 g fresh matter), in different concentrations (0.95, 2.38, and 3.40% w/w), combined with or without soy proteins (0.3 and 0.6% w/w). Emulsions containing OBF were stable against coalescence and flocculation (with 2.4 and 3.4% OBF) and creaming (3.4% OBF) for 24 h; the droplets' diameter decreased up to 44% and the viscosity increased up to 37% with higher concentrations of OBF. With the protein addition, the droplets' diameter decreased by up to 70%, and flocculation increased. Compared with emulsions produced with purified citrus pectins (0.2 and 0.5% w/w), OBF emulsions exhibited up to 32% lower viscosities, 129% larger droplets, and 45% smaller Z potential values. Optimization solved with ANNs minimizing the droplet size and the emulsion instability resulted in OBF and protein concentrations of 3.16 and 0.14%, respectively. The experimental characteristics of the optimum emulsion closely matched those predicted by ANNs demonstrating the usefulness of the proposed method.

Non-conventional starch from cubio tuber (Tropaeolum tuberosum): Physicochemical, structural, morphological, thermal characterization and the evaluation of its potential as a packaging material.

This work aimed to characterize the physicochemical, structural, morphological, and thermal properties of a non-conventional starch obtained from cubio (Tropaeolum tuberosum), as well as to evaluate the potential use of this native Andean tuber in the preparation of biodegradable packaging. The cubio starch (CUS) showed an intermediated apparent amylose content (31.2 %) accompanied by a high CIE whiteness index (90.8). About the morphology and particle size, the CUS exhibited irregular oval and round shapes and a smooth surface with a mean particle diameter of 14.04 ± 0.1 µm. Although it showed good stability regarding pasting properties, the final viscosity was low. Native CUS exhibits a typical B-type diffraction structure, with a relative crystallinity of 16 %. The resistant starch (RS) fraction of the CUS was 94 %, indicating a low susceptibility to enzymatic hydrolysis. The thermal analysis demonstrated that the CUS showed good thermal stability. Additionally, the films prepared using CUS as raw material showed continuous surfaces without porosities, good thermal stability, and high transparency. The results of this work demonstrate the industrial potential of the CUS as it presents characteristics comparable to commercial potato starch.

Organoleptic and Nutritional Traits of Lambs from Spanish Mediterranean Islands Raised under a Traditional Production System.

Our aim was to characterize the organoleptic and nutritional properties of meat from suckling (one-month-old) and light (around three-months-old) lambs in local breeds on the Spanish Mediterranean islands, using meat from male lambs of the Mallorquina and Roja Mallorquina breeds. The lambs were kept with their mother at all times under an extensive management system and fed on mother's milk until naturally weaned. In the Mallorquina breed, suckling lambs (n = 20) were slaughtered after weaning and the light lambs were bred using natural pasture (n = 20) or concentrate (n = 20), and the Roja Mallorquina light lambs were fed pasture and concentrate (n = 20). The pH, colour, texture, water-holding capacity, fatty acids, volatile compounds and sensorial attributes of the meat were analyzed. No differences in meat colour or texture were observed. The highest levels of non-desirable fatty acids were observed in lambs raised using concentrate. Light lambs showed a higher aldehydes content than suckling lambs. High notes of lactic acid and milk flavour were detected. Regardless of access to pasture or concentrate, continued access to mother's milk during rearing influences the sensorial meat traits of these lambs, so we consider this type of management an optimal way of obtaining the traditional 'Mediterranean lamb meat'.

Addition of a mushroom by-product in oil-in-water emulsions for the microencapsulation of sunflower oil by spray drying.

The by-product generated after ergosterol extraction from mushrooms (A. bisporus) is rich in polysaccharides (ß-glucans) and proteins. The usefulness of this mushroom's by-product (MC) in oil microencapsulation by spray drying was evaluated partially replacing maltodextrin (13.5% w/w dry matter) and totally substituting Tween®20 with MC. Ergosterol was investigated as antioxidant. Non-Newtonian stable emulsions with mono-modal droplet size distributions were obtained with MC. Oil encapsulation efficiency was high (≥89%) and oil within microcapsules containing MC exhibited higher (p < 0.05) oxidative stability during spray drying. Powders containing MC exhibited larger particles (d5027% larger), 12% lower solubility in water and perceptible color changes. During storage (35 °C 50% RH), conjugated dienes increased more slowly in microcapsules containing MC. Reductions up to 28% in linoleic acid were observed after 150 days. Ergosterol was 95% degraded after 150 days in powders with MC and totally degraded after 2 days in powders without MC.

Mathematical Modelling of Ultrasound-Assisted Extraction Kinetics of Bioactive Compounds from Artichoke By-Products.

Valorization of an artichoke by-product, rich in bioactive compounds, by ultrasound-assisted extraction, is proposed. The extraction yield curves of total phenolic content (TPC) and chlorogenic acid content (CAC) in 20% ethanol (v/v) with agitation (100 rpm) and ultrasound (200 and 335 W/L) were determined at 25, 40, and 60 °C. A mathematical model considering simultaneous diffusion and convection is proposed to simulate the extraction curves and to quantify both temperature and ultrasound power density effects in terms of the model parameters variation. The effective diffusion coefficient exhibited temperature dependence (72% increase for TPC from 25 °C to 60 °C), whereas the external mass transfer coefficient and the equilibrium extraction yield depended on both temperature (72% and 90% increases for TPC from 25 to 60 °C) and ultrasound power density (26 and 51% increases for TPC from 0 (agitation) to 335 W/L). The model allowed the accurate curves simulation, the average mean relative error being 5.3 ± 2.6%. Thus, the need of considering two resistances in series to satisfactorily simulate the extraction yield curves could be related to the diffusion of the bioactive compound from inside the vegetable cells toward the intercellular volume and from there, to the liquid phase.

Ultrasound-Assisted Aqueous Extraction of Biocompounds from Orange Byproduct: Experimental Kinetics and Modeling.

Orange byproduct (flavedo and albedo) from juice extraction, was used as raw material for this study. Kinetics of total phenolic and total flavonoid contents and antioxidant activity was experimentally determined during both conventional (agitation at 80 rpm) and ultrasound assisted (at 520 and 790 W/L) aqueous extraction from orange byproduct at 5, 15, and 25 °C. An extraction mathematical model was also developed. Significant increase of biocompounds extraction yields was observed as temperature and acoustic power density increased. Ultrasound assistance allowed higher yields at lower temperatures and shorter times. Yields of total phenolic and total flavonoid contents and antioxidant activity obtained with ultrasound extraction (790 W/L, 25 °C, 3 min) were 29%, 39%, and 197% higher, respectively, than those obtained by conventional extraction. The extraction kinetics curves were properly represented by the Weibull model for both conventional and acoustic extraction (mean relative error lower than 5%). Naringin, neohesperidin, and hesperidin were the main phenolic compounds found in the extracts, followed by ferulic, sinapic, and cuomaric acids. Neohesperidin, hesperidin, coumaric acid, and sinapic acid presented the highest yields, especially when extraction was assisted by ultrasound. Meanwhile, naringin and ferulic acid were extracted in a lesser extent, most likely due to their lipophilic character.

Ultrasound-assisted extraction of ergosterol and antioxidant components from mushroom by-products and the attainment of a ß-glucan rich residue.

Revalorization of mushroom by-product (stalks of A. bisporus) by extracting its components is proposed. The extraction kinetics at 25 °C of ergosterol, phenolic compounds and antioxidant activity by mechanical agitation (at 130 rpm) and ultrasound assistance (at 182 and 321 W/L) in 70 and 96% v/v ethanol/water solutions during 30 min were evaluated and satisfactorily modelled, using the Weibull model (mean relative error ≤ 7.8%). The effect of the ethanol concentration was high in the ergosterol extraction yield (2 times higher yields in 96% than in 70%) but slight in those of phenolic compounds and antioxidant activity. Ultrasound assistance promoted considerable yield increases (up to 2 times higher in ergosterol, 46% in phenolic compounds and 25% in antioxidant activity) depending on the ethanol concentration and ultrasound power density. The residues after extraction were characterized and constituted a potential source of high value polysaccharides as ß-glucans (average 12.2 ± 1.7g/100 g dm).

Effects of convective drying and freeze-drying on the release of bioactive compounds from beetroot during in vitro gastric digestion.

Drying may alter the microstructure of vegetables and influence the release of bioactive compounds during digestion. The effects of convective drying (at 60 °C and 2 m s-1; CD) and freeze-drying (at -50 °C and 30 Pa; FD) on the microstructure (evaluated using scanning electron microscopy (SEM) and image analyses with ImageJ software) of beetroot and the kinetics of biocompound release (total polyphenol content (TPC) and antioxidant activity (AA)) during 180 min of in vitro gastric digestion have been studied. Raw beetroot was used as the control. Drying promoted the collapse of cell walls causing volume shrinkage that resulted in a greater cell number per area unit; meanwhile in vitro digestion caused cell structure disruption, which resulted in a lower cell number per area unit. Drying promoted decreases of TPC (42% in CD and 29% in FD) and AA (66% in CD and 63% in FD) of beetroot. However, release of TPC and AA from dried samples during digestion was 82% (CD) and 76 (FD) % higher than from the raw sample. The Weibull model allowed the satisfactory modelling of the TPC and AA release kinetics (mean relative error of simulation lower than 8.5%).

Effects of addition of carrot dietary fibre on the ripening process of a dry fermented sausage (sobrassada).

Four formulations of a dry fermented sausage, known as sobrassada, containing different percentages of carrot dietary fibre (DF) [3% (S3), 6% (S6), 9% (S9) and 12% (S12) (w/w)] were analyzed for various physico-chemical and microbiological parameters and sensory attributes. The ripening process was monitored throughout storage. The pH of DF-supplemented sobrassadas was critically affected during ripening by the amount of DF incorporated, the values for sobrassada samples containing over 3% of DF suggested that the fermentation process in these samples was not successful. In addition, textural parameters, such as hardness and compression work, were significantly affected by the addition of over 3% of DF. The lipolytic process, one of the major biochemical events, was only affected when relatively large percentages of DF concentrate were incorporated. Thus, S3 and S6 samples exhibited similar free fatty acid profiles to the control throughout ripening.

Effects of freezing, freeze drying and convective drying on in vitro gastric digestion of apples.

The influence of processing (freezing at -196°C in liquid N2, FN sample; freeze-drying at -50°C and 30Pa, FD sample; and convective drying at 60°C and 2m/s, CD sample) on apple (var. Granny Smith) behavior during in vitro gastric digestion was investigated. Dried apples (FD and CD samples) were rehydrated prior to digestion. Changes in carbohydrate composition, moisture, soluble solids, acidity, total polyphenol content (TPC), and antioxidant activity (AA) of apple samples were measured at different times during digestion. Processing resulted in disruption of the cellular structure during digestion, as observed by scanning electron microscopy, light microscopy, and changes in carbohydrate composition. Moisture content increased (6-11% dmo), while soluble solids (55-78% dmo), acidity (44-72% dmo), total polyphenol content (30-61% dmo), and antioxidant activity (41-87%) decreased in all samples after digestion. Mathematical models (Weibull and exponential models) were used to better evaluate the influence of processing on apple behavior during gastric digestion.

Effect of acoustic frequency and power density on the aqueous ultrasonic-assisted extraction of grape pomace (Vitis vinifera L.) - a response surface approach.

Aqueous ultrasound-assisted extraction (UAE) of grape pomace was investigated by Response Surface Methodology (RSM) to evaluate the effect of acoustic frequency (40, 80, 120kHz), ultrasonic power density (50, 100, 150W/L) and extraction time (5, 15, 25min) on total phenolics, total flavonols and antioxidant capacity. All the process variables showed a significant effect on the aqueous UAE of grape pomace (p<0.05). The Box-Behnken Design (BBD) generated satisfactory mathematical models which accurately explain the behavior of the system; allowing to predict both the extraction yield of phenolic and flavonol compounds, and also the antioxidant capacity of the grape pomace extracts. The optimal UAE conditions for all response factors were a frequency of 40kHz, a power density of 150W/L and 25min of extraction time. Under these conditions, the aqueous UAE would achieve a maximum of 32.31mg GA/100g fw for total phenolics and 2.04mg quercetin/100g fw for total flavonols. Regarding the antioxidant capacity, the maximum predicted values were 53.47 and 43.66mg Trolox/100g fw for CUPRAC and FRAP assays, respectively. When comparing with organic UAE, in the present research, from 12% to 38% of total phenolic bibliographic values were obtained, but using only water as the extraction solvent, and applying lower temperatures and shorter extraction times. To the best of the authors' knowledge, no studies specifically addressing the optimization of both acoustic frequency and power density during aqueous-UAE of plant materials have been previously published.

Optimisation of the addition of carrot dietary fibre to a dry fermented sausage (sobrassada) using artificial neural networks.

An optimisation problem was formulated to maximise the amount of carrot dietary fibre (CDF) in a dry fermented sausage, while maintaining product quality, by using 0-12% CDF as the decision variable, and limiting values of several physico-chemical and textural parameters (moisture content, water activity, pH, colour, non-protein nitrogen, free fatty acid, compression work and hardness) as constraints. The evolution of each quality parameter during the ripening process was estimated by developing a multi-layer feed forward artificial neural network (ANN), taking into consideration the CDF concentration and the ripening time as independent variables. Results indicate an optimum CDF concentration of 4.9% with a good correlation between experimental and estimated values (mean relative error≤3.35%).