Microencapsulation of hop bioactive compounds by spray drying: Role of inlet temperature and wall material.

This study explores the effect of spray-drying (SD) inlet temperatures (Tinlet 120 and 150 °C) and wall material on the chemical and physico-chemical properties of microencapsulated hop extracts (MHE). Hop extract was formulated with maltodextrin (MD) and gum Arabic (GA) used in single or in combination with ß-cyclodextrin (ßCD). MHE were evaluated for physical properties, bitter acids (BA), total polyphenol content (TPC) and encapsulation efficiency (TPC EE), and antioxidant capacity (AOC). Powders produced at Tinlet 150 °C exhibited the highest flowability and generally higher TPC yield. Besides Tinlet, MD enabled the obtaining of MHE with the highest encapsulation efficiency. Other physico-chemical and antioxidant properties differently varied depending on the Tinlet. Overall, the ßCD addition positively affected α-acids, and ß-acids of MHE obtained at Tinlet 120 °C. ATR-FTIR analysis showed hydrogen bond formation between hop compounds and ßCD. Multifactorial ANOVA highlighted that Tinlet, W, and their interaction influenced almost all the chemical and physico-chemical properties of MHE.

Freeze-Drying Microencapsulation of Hop Extract: Effect of Carrier Composition on Physical, Techno-Functional, and Stability Properties.

In this study, freeze-drying microencapsulation was proposed as a technology for the production of powdered hop extracts with high stability intended as additives/ingredients in innovative formulated food products. The effects of different carriers (maltodextrin, Arabic gum, and their mixture in 1:1 w/w ratio) on the physical and techno-functional properties, bitter acids content, yield and polyphenols encapsulation efficiency of the powders were assessed. Additionally, the powders' stability was evaluated for 35 days at different temperatures and compared with that of non-encapsulated extract. Coating materials influenced the moisture content, water activity, colour, flowability, microstructure, and water sorption behaviour of the microencapsulates, but not their solubility. Among the different carriers, maltodextrin showed the lowest polyphenol load yield and bitter acid content after processing but the highest encapsulation efficiency and protection of hop extracts' antioxidant compounds during storage. Irrespective of the encapsulating agent, microencapsulation did not hinder the loss of bitter acids during storage. The results of this study demonstrate the feasibility of freeze-drying encapsulation in the development of functional ingredients, offering new perspectives for hop applications in the food and non-food sectors.

Conventional and innovative extraction technologies to produce food-grade hop extracts: Influence on bitter acids content and volatile organic compounds profile.

Hop extracts represent a natural alternative to synthetic food additives because of their high content of bitter acids and volatile organic compounds (VOCs) with bittering, flavoring, and antimicrobial properties. However, broader uses of hop extracts as natural techno-functional ingredients rely on the identification of sustainable and affordable extraction technologies allowing to diversify the processes and produce extracts characterized by different compositions and, consequently, qualitative properties. Thus, this study is aimed to evaluate and compare the effect of innovative and conventional extraction methods on the bitter acids content and VOCs pattern of food-grade ethanolic hop extracts for food applications. Innovative extractions were carried out by using two ultrasound systems (a laboratory bath [US] and a high-power ultrasound bath [HPUS]), and a high-pressure industrial process (high hydrostatic pressure [HHP]). Conventional extractions (CONV) were performed under dynamic maceration at 25 and 60°C; for ultrasound and conventional methods, the effect of the extraction time was also investigated. Among the extracts, the highest and lowest content of bitter acids was found in CONV 60°C extracts, and HHP and CONV 25°C extracts, respectively. Of the 34 VOCs identified in dry hops, ∼24 compounds were found in US, HPUS and CONV extracts, while only 18 were found in HHP. CONV extractions showed higher selectivity for sesquiterpenes, while US and HPUS showed higher selectivity for esters and monoterpenes. Hierarchical cluster analysis (HCA) and partial least squares-discriminant analysis (PLS-DA) allowed classifying hop extracts based on the extraction methods and also allowed highlighting the technological conditions to produce hop extracts with specific techno-functional and flavoring properties. PRACTICAL APPLICATION: The study showed that different extraction methods can lead to hop products with varying sensory and functional properties. By selecting the right extraction method, companies can produce hop extracts with specific compositions that meet their needs for clean label and sustainable food products, as well as new edible packaging or coatings.

Influence of Atmospheric Cold Plasma Exposure on Naturally Present Fungal Spores and Physicochemical Characteristics of Sundried Tomatoes (Solanum lycopersicum L.).

This research aimed to evaluate the impact of atmospheric cold plasma (ACP) treatment on the fungal spores naturally present in sundried tomatoes, as well as their influence on the physico-chemical properties and antioxidant activity. ACP was performed with a Surface Dielectric Barrier Discharge (SDBD), applying 6 kV at 23 kHz and exposure times up to 30 min. The results showed a significant reduction of mesophilic aerobic bacteria population and of filamentous fungi after the longer ACP exposure. In particular, the effect of the treatment was assessed on Aspergillus rugulovalvus (as sensible strain) and Aspergillus niger (as resistant strain). The germination of the spores was observed to be reliant on the species, with nearly 88% and 32% of non-germinated spores for A. rugulovalvus and A. niger, respectively. Fluorescence probes revealed that ACP affects spore viability promoting strong damage to the wall and cellular membrane. For the first time, the sporicidal effect of ACP against A. rugulovalvus is reported. Physicochemical parameters of sundried tomatoes such as pH and water activity (aw) were not affected by the ACP treatment; on the contrary, the antioxidant activity was not affected while the lycopene content was significantly increased with the increase in ACP exposure time (p ≤ 0.05) probably due to increased extractability.

Stinging Nettles as Potential Food Additive: Effect of Drying Processes on Quality Characteristics of Leaf Powders.

Stinging nettle (Urtica dioica L.) is a ubiquitous, multi-utility, and under-utilized crop with potential health benefits owing to its nutritional and bioactive components. The objective of the work is to produce powders by drying wild stinging nettle leaves as a storable, low-cost functional additive to be used in bakery and ready-to-cook products. Convective drying (CD) and freeze-drying (FD) were applied on unblanched (U) or blanched (B) leaves, which were then milled to nettle powders (NPs). The obtained NPs were evaluated for selected physicochemical (moisture, color), techno-functional (flow indices, hygroscopicity), and phytochemical (pigments, phenols) characteristics as well as mineral contents. Blanching improved mass transfer and reduced the oxidative degradation of pigments during drying, but it caused a loss of total phenols content, antioxidant activity, and potassium content. As for the drying method, CD resulted in better flow properties (i.e., Carr Index and Hausner Ratio), while FD retained better the color, pigments, magnesium content, phenolic, and antioxidant parameters. Overall, the evaluated processing methods resulted in different technological properties that can allow for better evaluation of NPs as a food additive or ingredient. Among the NPs, blanched and freeze-dried powders despite showing inferior technological properties can be recommended as more suitable ingredients targeted f or food enrichment owing to better retention of bio-active components.

Use of Conventional and Innovative Technologies for the Production of Food Grade Hop Extracts: Focus on Bioactive Compounds and Antioxidant Activity.

This study investigated the use of conventional and innovative extraction methods to produce food-grade hop extracts with high antioxidant capacity and content in bioactive compounds. Conventional extractions (CONV) were performed under dynamic maceration at 25 and 60 °C; innovative extractions were performed using two ultrasound systems, a laboratory bath (US) and a high-power ultrasound bath (HPUS), and a high-pressure industrial process. For CONV, US, and HPUS extractions the effect of the extraction time was also tested. Experimental results showed that extraction method, temperature, and time affect to a different extent the phenolic profile and have a significant effect (p < 0.05) on the total phenolic content, total flavonoid content, antiradical capacity (ABTS), chlorophyll α, and total carotenoids content. Overall, US and CONV 60 °C extractions showed the highest extraction efficiency for almost all the investigated compounds, however, the extraction method and time to be used strongly depends on the target compounds to extract.

Antioxidant Activity in Frozen Plant Foods: Effect of Cryoprotectants, Freezing Process and Frozen Storage.

The antioxidant activity (AOA) of plant foods is recognized as an index of the potential health benefits resulting from their consumption. Due to their high perishability and seasonality, plant foods are largely consumed or used as processed products and freezing is one of the technologies used for the production of high-quality foods. However, cell breakages occurring during freezing and frozen storage can lead to the release of antioxidant compounds and their degradation due to chemical and enzymatic oxidation reactions, and thus, they could present a lower antioxidant activity compared to the corresponding fresh product. In this context, process conditions, freezing pre-treatments and the use of cryoprotectants can limit the extent of freeze-induced damages and preserve the antioxidant activity of plant foods. This review collects and discusses the state-of-the-art knowledge on the single and combined effect of freezing and frozen storage conditions on the antioxidant activity of fruits and vegetables as well as the role of cryoprotectants. Classes of compounds responsible for the antioxidant activity of plant foods and the most common methods used for the evaluation of the antioxidant activity in vitro are also presented. The freezing principles and the effects of ice nucleation and crystallization on fruits, vegetables and their main derivatives (juices, pulps) have been addressed to highlight their impact on the AOA of plant foods. The effect of freezing and frozen storage on the AOA of plant foods resulted dependant on a series of intrinsic factors (e.g., composition and structure), while the role of extrinsic processing-related factors, such as freezing and storage temperatures, is ambiguous. In particular, many conflicting results are reported in the literature with a high variability depending on the method of analysis used for the AOA evaluation and data expression (fresh or dry weight). Other intrinsic raw material properties (e.g., cultivar, ripening degree), post-harvest conditions, as well as defrosting methods that in the majority of the studies are scarcely reported, contribute to the aforementioned discrepancies. Finally, due to the limited number of studies reported in the literature and the high variability in product processing, the effect of cryoprotectants on the AOA of plant foods remains unclear.

Physical and Sensory Properties of Mayonnaise Enriched with Encapsulated Olive Leaf Phenolic Extracts.

This work aimed to study the physical, structural, and sensory properties of a traditional full-fat mayonnaise (≈ 80% oil) enriched with an olive leaf phenolic extract, added as either free extract or encapsulated in alginate/pectin microparticles. Physical characterization of the mayonnaise samples was investigated by particle size, viscosity, lubricant properties, and color; a sensory profile was also developed by a quantitative descriptive analysis. The addition of the extract improved the dispersion degree of samples, especially when the olive leaf extract-loaded alginate/pectin microparticles were used. The encapsulated extract affected, in turn, the viscosity and lubricant properties. In particular, both of the enriched samples showed a lower spreadability and a higher salty and bitter perception, leading to a reduced overall acceptability. The results of this study could contribute to understanding the effects of the enrichment of emulsified food systems with olive by-product phenolic extracts, both as free and encapsulated forms, in order to enhance real applications of research outcomes for the design and development of healthy and functional formulated foods.

Response of organic and conventional apples to freezing and freezing pre-treatments: Focus on polyphenols content and antioxidant activity.

The effect of pre-treatment (dipping and vacuum impregnation in lemon juice solution), freezing and frozen storage (FS) on single and total polyphenols (free and conjugated) content and antioxidant activity (AOA) of organic and conventional apples, was investigated. Fresh organic and conventional fruits showed different profiles of free and conjugated polyphenols while their total phenolic content and AOA were similar. Organic and conventional apple tissues showed different physiological responses to physical stresses described by changes in phenolic profiles. Vacuum impregnation in lemon juice affected the polyphenols extractability of both the organic and conventional apples and favored their enrichment with bioactive compounds (AOA = +11.5%). FS decreased the single and conjugated polyphenols content of the pre-treated apple samples and the effect was different between organic and conventional fruits. After FS, not pre-treated organic apples showed a lower AOA reduction than the conventional ones (-13% vs -25%), while no differences were found on pre-treated samples.

From by-product to food ingredient: evaluation of compositional and technological properties of olive-leaf phenolic extracts.

BACKGROUND: Most olive by-products, like olive leaves, are still undervalued despite their strong potential as a source of healthy and functional components. To exploit their potential use as active ingredients in complex food systems, it is of primary importance the knowledge of their composition and technological functionality which represented the objective of this work. RESULTS: Phenolic extracts from olive leaves, obtained by extraction with pure water (Eth0) and two different water-ethanol solutions (Eth30, Eth70), were characterized for their composition and technological properties such as water- / oil- holding ability, air/water surface activity, and emulsifying capacity at pH 4.5 and 7. Their chemical stability over time, at constant temperature, was also investigated. The technological properties were affected by extraction media and pH. Phenolic extracts displayed significant surface activity, showing dose-dependent behavior. Surface properties were affected by pH and this result was confirmed by the emulsifying capacity. The extracts showed good oil-holding capacity but limited water-binding capacity. Eth70 showed the highest chemical stability, which was confirmed by the rate parameters obtained by modeling data using a Weibull model. CONCLUSION: The results of this study highlight that olive leaves extracts can represent a useful ingredient in acidic lipid-containing foods. © 2019 Society of Chemical Industry.

Effect of Dipping and Vacuum Impregnation Pretreatments on the Quality of Frozen Apples: A Comparative Study on Organic and Conventional Fruits.

The effect of dipping and vacuum impregnation (VI) pretreatments with lemon juice solution on the quality and stability of organic and conventional frozen apples was investigated. Fresh apples were characterized; organic apples showed, at equal starch and ripeness index, a lower sugar content, and higher acidity than conventional ones. The polyphenol content was slightly higher in organic apples than in conventional ones while polyphenoloxidase activity was similar. No differences in color and firmness were evidenced. Dipping affected organic and conventional apples' color by determining an increase of lightness (ΔL* ≈ 4) and h° (Δh° ≈ 6) parameters. VI reduced the lightness of apples (ΔL* ≈ -3) but the addition of lemon juice counterbalanced the lightness reduction by increasing ΔL* from 3 to 1.5 ca. Pretreatments did not affect the firmness of organic fruits while impaired that of the conventional ones ( 26% on average), likely due to different fruit matrix porosity and cell wall composition. Freezing (-40 °C) and frozen storage (up to 300 days) dramatically reduced the firmness of organic (42%) and conventional products (58%). At equal pretreatment and storage time (that is, 15, 30, 300 days), higher firmness retention was evidenced in organic apples than in conventional ones. All through frozen storage, VI was shown to better preserve the mechanical properties of organic apples than that of conventional ones. Both freezing and frozen storage reduced the hue of frozen apple products by up to 8% due to browning reactions. Lemon juice addition increased the hue of both frozen samples and thawed samples by about 2% all through storage time.

Silver and gold nanoparticles based colorimetric assays for the determination of sugars and polyphenols in apples.

In this work, the exploitability of rapid and easy to use methods for the evaluation of the antioxidant capacity (AOC) and sugars content (SC), through metal nanoparticles (MNPs) formation, has been proved and applied to apples. In particular, an AgNPs-based sugar quantification assays and an AuNPs-based polyphenols antioxidant capacity assay have been used as tools for the evaluation of apple extracts composition. Both assays are based on the ability of the analytes (sugars and polyphenols) to reduce the source of metal (Au3+ and Ag+), stabilizing, at the same time, the resulting MNPs colloidal suspensions. The AuNPs and AgNPs formation depends on the analyte structure and concentration, resulting in red (AuNPs) and yellow (AgNPs) colored suspensions. Both assays require an initial mixing step, followed by MNPs formation under mild conditions (10 min, room temperature or 45 °C), and the colorimetric response is easily acquired at a fixed wavelength (AgNPs: 430 nm and AuNPs: 540 nm). The analytical performance of both assays has been proven, obtaining good reproducibility (RSD ≤ 6%,), sensitivity (LODs ≤8.7 µmol L-1) and recoveries (91% -113.7%). The produced MNPs (AgNPs and AuNPs) have been characterized using UV-Vis spectroscopy and TEM, and the cross-reactivity between assays, as well as the possible endogenous interferents, studied. The assays have been tested on 42 apple samples, and the data obtained compared with those obtained by conventional methods (i.e. FC, ABTS, and ion chromatography). The proposed AgNPs-sugars assay gives results comparable (R = 0.915) to those determined by ion chromatography in terms of total sugars, and the AuNPs-polyphenols assay results able to assess the polyphenols antioxidant capacity, being correlated with those obtained by the ABTS method (R = 0.922). This MNPs-based approach demonstrated to be an excellent tool for rapid and facile analysis of sugars and polyphenols in apple samples.

Role of olive oil phenolics in physical properties and stability of mayonnaise-like emulsions.

The effect of olive oil phenolic content and pattern on the physical properties and stability of olive oil mayonnaise-like emulsions has been investigated. Mayonnaises were formulated with either naturally phenolic-rich extra virgin olive oils or purified olive oil artificially enriched with a phenolic-rich olive extract and pure oleuropein. Mayonnaises were characterized by droplet size distribution, microstructure, textural properties and flow behaviour. The addition of phenolic extracts significantly affected the dispersion degree of the corresponding mayonnaise-like emulsions, their microstructure and physical stability especially in the systems prepared with purified olive oil treated with pure oleuropein and the highest olive phenolic extract concentration. The viscosity and back-extrusion analyses evidenced that the systems characterized by a relatively high content of phenolics, either natural or by addition, presented lower yield stress and viscosity indices and were easier to deform and to break. This study confirms the main role of olive phenolic compounds, and in particular that of oleuropein, in the dispersion state, and physical properties of emulsions with main effects on their quality and stability.

Multidisciplinary approach to study the effect of water status and mobility on the activity of peroxidase in solutions.

The effect of water mobility on horseradish peroxidase (HRP) activity in solutions was investigated by measuring water activity (aw), freezable water content, (1)H proton transverse relaxation time and water self-diffusivity determined by nuclear magnetic resonance. The effect of system mobility as described by viscosity and glass transition temperature (T'g) was also studied. The aw and viscosity of aqueous solutions were modulated using ligands (glucose, sorbitol and trehalose) and a thickener (maltodextrin). The effectiveness of a solute in the inhibition of HRP activity was better related to its ability to reduce the mobility of the system than to its water mobility depleting effect. The relationship among viscosity and peroxidase activity was influenced by the type of enzyme but not by the substrate. Bovine lactoperoxidase activity was hindered by viscosity changes more than HRP activity (tested in the same system) due to the higher molecular weight of the former enzyme.

Mechanical properties and microstructure of frozen carrots during storage as affected by blanching in water and sugar solutions.

Raw carrots and carrots blanched in water and in 4% trehalose and maltose solutions at 75°C for 3 (A) and 10 min (C) and at 90°C for 3 (B) and 10 min (D) were frozen and stored at -18°C for eight months. The effects of heating conditions and exogenous added sugars on the mechanical properties and microstructure of the vegetable after blanching and during frozen storage were studied. By scanning electron microscopy (SEM) analysis no significant differences were observed among samples A and B water-blanched and raw carrot while a thermo-protective effect due to the sugars addition was evidenced in sample D, undergone to the most severe thermal treatment. Freezing and frozen storage determined several fractures on both raw and blanched carrots due to ice crystals formation and re-crystallisation. The cryo-protective effect of the sugars on the vegetable microstructure was observed only in the 'over-blanched' sample D. The mechanical properties of carrots were affected by blanching which caused a hardness decrease but after freezing and one month of frozen storage, all samples showed a further dramatic reduction of hardness. Only samples characterised by a pectinesterase residual activity showed a softening also after one month of frozen storage likely for a competitive effect of the thermo-protective ability of trehalose on this enzyme. The exogenous trehalose was able to limit the hardness loss of carrots undergone to B, C and D blanching pre-treatments.

Effect of blanching in water and sugar solutions on texture and microstructure of sliced carrots.

Thermal processing of vegetables has pronounced effects on the cell structure, often negatively affecting the final textural properties of the product. In order to study the effect of thermal processing and the protective effect of sugars on the tissue, sliced carrots were subjected to blanching treatments under different time and temperature combinations both in water and in 4% sugar solutions made of trehalose or maltose. The influence of these process conditions on mass transfer, texture, and microstructure (Cryo-scanning electron microscopy) was thus investigated. The total mass loss of all the samples blanched in water was associated to their cook value (C(100)(18)) except for the overprocessed one (90 °C, 10 min) that showed a total mass change significantly lower due to water uptake. The use of trehalose and maltose in the blanching solution reduced the solute loss while increasing the water loss. Microstructural analysis of the differently blanched carrots showed detachments between adjacent cell walls as well as plasmolysis phenomena as the time and temperature of the thermal treatment were increased. A protective effect of both sugars on cell structures was observed mostly in the sample treated at 90 °C. At macroscopic level, textural changes upon blanching were observed by a penetration test. As blanching time was increased, samples processed at 75 °C showed a hardness increase, while those processed at 90 °C showed a hardness decrease. However, both trehalose and maltose did not exert significant effects on the textural properties of blanched carrots when compared with those blanched in water. Practical Application: The results of this study could offer interesting perspectives in the optimization of the heat treatments in order to preserve the quality of semi-finished processed vegetables. Furthermore, the microstructural analysis is nowadays an important investigation tool that could contribute to a deeper understanding of both the effects of processing and ingredients on the vegetable microstructure and its relationship with the changes occurring on the quality properties at macroscopic level.