Nectar Samples Research Articles

Abundance and diversity of the culturable nectar mycobiome in Rhododendron catawbiense varies with elevation

Abstract The nectar microbiome can influence pollinator choice and plant fitness. Previous research has shown that changes in environmental conditions at large spatial scales can influence nectar microbiome composition. However, little is known about how changes in climate with increasing elevation affect nectar microbiome abundance and composition. Here we describe the culturable nectar mycobiome of Rhododendron catawbiense (Ericaceae) by quantifying colony abundance, identity, and richness of fungal genera. We further evaluate how the culturable nectar mycobiome (CNMB) abundance, diversity, and composition (i.e., the fungal species within the nectar microbiome) varies at two different elevations. Nectar samples were collected from R. catawbiense individuals at a high and low elevation and were cultured on yeast agar with 0.01% chloramphenicol media. Fungal colonies were categorized morphologically, quantified, and then identified using DNA barcoding. In total, 2,822 fungal colonies were recorded belonging to six genera across both elevations. Elevation did not influence CNMB diversity (Simpson’s diversity index) or genera richness per flower, however only three genera were found at the high elevation while six were found at the low elevation. Elevation had a significant effect on colony abundance with a 95% increase in the number of colonies in nectar samples at low compared to the high elevation. Variation in abundance and overall genera composition of fungal colonies across elevations may have the potential to affect nectar quantity and quality and ultimately pollination success. This study adds to our understanding of the drivers of CNMB composition across spatial scales its potential implications for plant-pollinator interactions.

Sensory Analysis Performed within Augmented Virtuality System: Impact on Hedonic Scores, Engagement, and Presence Level.

Sensory analysis methodologies are performed in sensory booths designed to minimise external stimuli, lacking ecological validity. Immersive environments are used to introduce contextual cues, but there is a lack of studies using mixed reality systems. The main goal of this study was to evaluate an augmented virtuality (AV) system where participants are inserted into a virtual environment and evaluate a real product, being able to interact with both dimensions. A panel of 102 consumers evaluated five samples of commercial peach nectars in three sessions, each in a different environment: public food court, living room (AV environments), and laboratory (traditional sensory booth). Consumers rated overall liking, followed by open comments, and also answered an Engagement (EQ) and a Presence Questionnaire (PQ). The type of environment only affected hedonic discrimination among samples, with the laboratory setting being the only one with sample discrimination. Nonetheless, each sample was not evaluated differently across the different environments. Concerning engagement, the environment only significantly influenced the EQ's 'Affective Value' factor, being higher when using an AV system. The level of presence in the virtual environment was significantly higher in the public food court, being significantly correlated with the EQ factor scores.

Effect of Abiotic Factors on Nectar Quality and Secretion of Two Early Spring Species, Galanthus nivalis L. and Helleborus niger L.

Floral nectar is mainly a reward in the form of food for pollinators. In early spring, when snow can still be present, pollinators have trouble finding food. The composition and productivity of nectar in flowers play an important role in a pollinator’s life. It is known that low temperatures and lower humidity cause lower nectar secretion. Some studies have also shown that the quality of nectar can differ because of lower temperatures. In our research, we analysed whether abiotic factors affect nectar secretion, as well as the nectar composition of the early spring plant species Galanthus nivalis L. and Helleborus niger L. in February 2024. The study was conducted in two locations in nature. Nectar from H. niger was sampled in Tomišelj, Slovenia, whereas nectar from G. nivalis was sampled in Ljubljana, Slovenia. On four different days at three different times of day, we sampled nectar from flowers using microcapillaries. In total, we sampled 48 nectar samples from one species. We analysed soil humidity and temperature, air temperature and humidity, and UVB radiation. Our results show that nectar productivity is highest in the morning for both species. H. niger has sucrose-dominant nectar, while G. nivalis has hexose-dominant nectar. Proline, which is an important amino acid for bees, has the highest level in both species, as does the phenolic compound rutin. Environmental factors do affect nectar secretion. Soil and air temperature affect G. nivalis nectar secretion, while soil humidity affects H. niger nectar secretion. Soil and air temperature also have an effect on higher levels of sugars in both researched nectars. UVB, air humidity, and air and soil temperature seem to have an effect on phenolic compounds, but abiotic factors do not affect amino acids.

Characterization of near-field temporal and spatial variations of pesticide residues using honeybee specimens as bio-sensing matrices

This study was prompted by recent reports of the ubiquity of neonicotinoids (neonics) in environment and the likelihood of exposures and health hazards to non-target organisms. We aimed to quantify neonics levels in time- and location-match pollen and nectar samples foraged by honeybees (Apis mellifera) and characterized the temporal and spatial variations using a relative potency factor method to determine the total neonic levels, expressed as the imidacloprid-adjusted total neonics, IMIRPF (ng/g). Six pairs of pollen and nectar samples, a total of twelve samples, were collected from each of the thirty-two experimental hives during the active foraging months of March, April, and June and analyzed for eight neonics. We found 59% and 64% of pollen and nectar contained at least one neonic, respectively. Among those neonic-detected pollen and nectar samples, 45% and 77% of them contained more than one neonic, respectively. Imidacloprid and acetamiprid in pollen and clothianidin and thiamethoxam in nectar accounted for 60% and 83% detection, respectively. The highest 3-month average of IMIRPF in pollen (6.56 ng/g) and nectar (11.19 ng/g) were detected in a location with the predominant production of citrus fruit. The temporal and spatial variations of IMIRPF levels demonstrated the robustness of using paired pollen and nectar data as the bio-sensing matrices to facilitate the assessment of near-field exposure to total neonics and the delineation of risks.

Estrogenic Isoflavones in Clover Plants, Flower Nectar, Unripe Honeys and Mature Honeys: A Natural Biochemical Transformation of Isoflavones by Honeybees.

This study is the first to report on the presence of oestrogenic compounds in different clover flower nectar samples, in bee-deposited nectars collected from hive combs (unripe honey) and in mature honeys harvested from the same hives. The clover species investigated were two red clover (Trifolium pratense) cultivars, bred specifically for high isoflavone content, alongside a sainfoin (Onobrychis viciifolia) and a purple clover (T. purpureum) cultivar. A total of eight isoflavones, four of them non-glycosidic (biochanin A, formononetin, genistein and daidzein) the others glycosidic (sissotrin, ononin, genistin and daidzin), were targeted for identification and quantification in this study using high-performance thin-layer chromatography (HPTLC). Leaves and flower bracts of the clover samples were also investigated. Different isoflavone profiles were found across the four clover species and also in the different samples collected from each species indicating that, most likely due to the activity of honeybee (Apis mellifera) salivary enzymes, biochemical conversions take place when these bioactive compounds transition from flower nectar into ripe honey. Among the four investigated clover species, the two red clover cultivars, including their honeys, were found to contain higher levels of estrogenic compounds compared to other two cultivars.

Assessing the analytical reliability of traditional and novel sampling methods for the study of flower rewards quality

AbstractPollinator insects are declining worldwide also due to the alteration of their diet which plays a pivotal role in influencing their health status. Despite interspecific and intraspecific diversity in the diet, pollinators completely or partly rely on pollen and nectar as food sources. A precise characterization of the chemical composition of these flower resources represents a key step in the definition of pollinators' nutritional ecology. However, pollen and nectar represent challenging sources to collect and analyze, especially due to their small amounts per flower, and the application of suitable sampling and analysis tools is a pivotal step to perform dedicated studies and comparisons. Here, we compared a recently proposed tool based on a portable vacuum cleaner for floral pollen collection (E‐PoSa, i.e., Electronic Pollen Sampler) with traditional pollen sampling methods (i.e., anther collection and anther sieving) together with the evaluation of different nectar sampling techniques (i.e., centrifugation, microcapillaries, washing, and microrinsing) by looking at the differences in their quantitative recovery as well as their chemical profiling. Pollen and nectar were collected from three model flower species each. Our results demonstrated that different collection methods introduce biases in the nutritional profiling of floral rewards and specifically: (1) underestimation of the pollen protein and lipid content in the anther collection method; (2) reduction in the volume of recovered nectar by centrifugation; (3) overestimation of the glucose content in the nectar collected by flower washing and underestimation of the glucose content by microrinsing; and (4) relevant biases in the phytochemical profiles of pollen and nectar by analyzing the whole anthers and the nectar collected by washing the entire flower. Differences in methods were not directly related to the different productivity of pollen and nectar across species. The final goal of the study is to propose standardized, comparable, and easily accessible strategies for the study of flower resources that ultimately impact on pollinators' nutritional ecology. Acknowledging the potential influences of the sampling techniques and moving toward shared field protocols will advance the comprehension of species interactions, foraging patterns, and pollinators' nutritional needs.

Modern methods of assess- ing the resources of honeylands

An information review of innovative methods for assessing the resources of honey-bearing lands is presented. The relevance and problems of their use are noted. Alternative strategies for determining the resource potential of honey-bearing lands are shown. Scientific methods of identifying honey plants are described: the study of vegetation, analysis of the chemical composition of honey and its properties, the use of drones to survey honey grounds, and the use of artificial intelligence to process large amounts of data about honey grounds. GPS (global positioning system) technologies, which allow accurate geospatial mapping of homelands, are currently the most widespread. The identification of honey plants to improve the food supply is carried out by various methods: floral analysis of vegetation, pollen analysis, informational analysis of vegetation, and observation of the behaviour of bees in hives. New techniques for determining the land’s honey reserves and the flowering intensity of honey plants are presented: collecting nectar samples and sugar content in nectar, which helps collect data on nectar productivity and nectar quality with greater accuracy and efficiency. RFID tags are widely used for producing and managing honey stocks, monitoring the condition of hives, and determining bee colonies’ productivity. Thanks to advances in technology and scientific research, many new approaches allow for more accurate and efficient selection of resource aspects of honey lands.

Floral nectar and insect flower handling time change over the flowering season: Results from an exploratory study

In recent decades, hundreds of secondary metabolites have been found in floral nectar and many studies have demonstrated that they can play various roles in modulating the behaviour of floral visitors. However, temporal variations in nectar chemistry over extended flowering seasons have never been substantiated. Moreover, the effects of nectar chemicals on insect behaviour are often studied under laboratory conditions, focusing on few insect species under artificial conditions which may influence insect responses. The aim of this exploratory study was to compare nectar chemistry and the durations of pollinator visits in the early and late summer periods of the long-flowering species Echium vulgare L. in natural populations. Nectar samples were collected in the early and late summer periods and insects were observed for a total of 480 min. The biogenic amine octopamine, sugars and the protein to non-protein amino acid ratio increased as the season proceeded. It remains to clarify whether these changes are determined by biotic and abiotic factors or whether the plant expresses some chemical constraint, however it seems likely that changes in nectar chemistry may be the cause of the longer visits by bumblebees to single flowers at the end of the flowering season. Though not conclusive, these results set a baseline for future research and highlight an interesting question. Since long-flowering plants see changing contexts during their bloom period, do they express chemical constraints to regulate their attractiveness?

One-step pre-column derivatization method for HPLC-UV determination of organic acids in fruit juices

A simple and effective one-step pre-column derivatization method for reversed-phase HPLC-UV determination of the major organic acids (citric, malic, tartaric, and succinic acids) in fruit juices has been developed. The method is based on the coupling reaction of organic acids with 1-naphthylamine in the presence of N,N′-diisopropylcarbodiimide. The resulting organic acid amide derivatives were successfully separated on an AQ-C18 column and detected by a UV detector at 222 nm. Isocratic elution was performed using an acetonitrile-methanol-tetrahydrofuran-water (37:4:1:58; v/v) mixture as a mobile phase at a flow rate of 2.0 mL/min. Validation studies showed good recoveries ranging from 88.97 to 92.52% with RSD % between 2.95 and 4.56%. The detection limits obtained were 0.18, 0.48, 0.14, and 0.69 µg/mL for tartaric acid, malic acid, succinic acid, and citric acid, respectively. The method was successfully applied to three different commercial fruit juice and nectar samples with little or no clean-up procedures.

Comprehensive analysis of floral scent and fatty acids in nectar of Silene nutans through modern analytical gas chromatography techniques

The aim of this work was to show the potential of multidimensional gas chromatography combined with mass spectrometry and suitable chemometrics means based on untargeted and profiling data analysis to strengthen the information provided by floral scent and nectar fatty acids of four genetically differentiated lineages (E1, W1, W2, and W3) of the nocturnal moth-pollinated herb Silene nutans. Volatile organic compounds emitted by flowers were trapped for a total of 42 samples by in-vivo sampling dynamic head space for analysing floral scent by untargeted approach, while 37 samples of nectar were collected for analysing fatty acids through profiling analysis. The resulting data from floral scent analysis were aligned and compared using a tile-based methodology followed by data mining to access high-level information. Based on floral scent and nectar fatty acid results, it was possible to distinguish E1 from the W lineages, and W3 from W1 and W2. This work puts the bases for a larger study aiming to clarify the existence of prezygotic barriers involved in speciation among lineages of S. nutans, and thus the possible implication of different flower scents and nectar compositions in this phenomenon.

Temporal sweet taste dominance according to adult body mass index classification

Excess adipose tissue is associated with basic tastes perception change, which can negatively affect food choices. However, the effect of overweight and obesity on sensory perception is not clearly explained in the literature yielding heterogeneous results. The present investigation aimed to investigate the temporal dominance of sweet taste according to body mass index (BMI) classification in adults during the ingestion of five passion fruit nectar samples prepared with different sucrose concentrations. The temporal dominance of sensations methodology was applied, which allowed the representation of the stimuli assessed in dominance curves, considering a significant difference in Fisher's exact test (p≤0.05). The attributes evaluated were sweet taste, bitter taste, acidic taste, astringency, passion fruit flavor, metallic taste, or none of the previous options. The sensory analysis was performed with the participation of ninety adult consumers, divided into three groups: EG=eutrophic, WG=overweight, and OG=obesity group, according to the BMI classification. Between the groups a difference in the perception of the attribute "sweet taste" was observed: The EG demonstrated perception of the stimulus in food samples at lower sucrose concentrations, whereas WG and OG showed a higher rate of sweet taste dominance in the food samples with higher concentration of sucrose. Overweight and obese individuals have a lower sensory perception of sweet taste and require a greater amount of sucrose to producing sensory dominance of the attribute "sweet taste" when compared to eutrophic individuals. PRACTICAL APPLICATION: Overweight and obese individuals may experience taste perception in foods in a different way. This study investigated the dominance of sweet taste perception in a fruit beverage by adults with adequate weight and overweight. The results of the tests support the hypothesis that obese and nonobese individuals differ in the sweet taste perception, which can help to understand which factors are involved in sensory perception and food consumption, in addition to providing subsidies for the nonalcoholic beverage industry to elaborate products with new alternatives for concentration and/or replacement of sucrose.

Pesticide residues in nectar and pollen of melon crops: Risk to pollinators and effects of a specific pesticide mixture on Bombus terrestris (Hymenoptera: Apidae) micro-colonies

Residues detected in pollen collected by honey bees are often used to estimate pesticide exposure in ecotoxicological studies. However, for a more accurate assessment of pesticides effect on foraging pollinators, residues found directly on flowers are a more realistic exposure approximation. We conducted a multi-residue analysis of pesticides on pollen and nectar of melon flowers collected from five fields. The cumulative chronic oral exposure Risk Index (RI) was calculated for Apis mellifera, Bombus terrestris and Osmia bicornis to multiple pesticides. However, this index could underestimate the risk since sublethal or synergistic effects are not considered. Therefore, a mixture containing three of the most frequently detected pesticides in our study was tested for synergistic impact on B. terrestris micro-colonies through a chronic oral toxicity test. According to the result, pollen and nectar samples contained numerous pesticide residues, including nine insecticides, nine fungicides, and one herbicide. Eleven of those were not applied by farmers during the crop season, revealing that melon agroecosystems may be pesticide contaminated environments. The primary contributor to the chronic RI was imidacloprid and O. bircornis is at greatest risk for lethality resulting from chronic oral exposure at these sites. In the bumblebee micro-colony bioassay, dietary exposure to acetamiprid, chlorpyrifos and oxamyl at residue level concentration, showed no effects on worker mortality, drone production or drone size and no synergies were detected when pesticide mixtures were evaluated. In conclusion, our findings have significant implications for improving pesticide risk assessment schemes to guarantee pollinator conservation. In particular, bee pesticide risk assessment should not be limited to acute exposure effects to isolated active ingredients in honey bees. Instead, risk assessments should consider the long-term pesticide exposure effects in both pollen and nectar on a range of bees that reflect the diversity of natural ecosystems and the synergistic potential among pesticide formulations.

Lead determination in commercial juice samples by direct magnetic sorbent sampling flame atomic absorption spectrometry (DMSS-FAAS)

The direct magnetic sorbent sampling flame atomic absorption spectrometry (DMSS-FAAS), recently proposed by our research group, was applied to determine the lead in soy-based juice, whole grape juice, reconstituted grape juice, and orange nectar samples. A dispersive solid phase extraction (d-SPE) of lead was carried out using a magnetic orange peel powder, developed and optimized by Gupta et al (2012), that was inserted into flame by FAAS with a magnetic probe. The limits of quantification (<4.6 μg L-1) were smaller than maximum residue limits established in Brazil. Good precisions and accuracies were obtained. DMSS-FAAS presented a sensitivity at least 14 times greater than the d-SPE followed by conventional FAAS analysis, wherein the analytes were extracted and desorbed, and the eluate was introduced in FAAS via nebulization system. Lead was easily quantified in juice samples at very low concentrations, with satisfactory figures of merit, and without the need of a mineralization step.

Delayed self-fertilization and chemical analysis of floral nectar of a perennial relative of the tomato and potato from Mexico

We studied the floral reproductive biology and nectar chemistry of Jaltomata grandiflora (Solanaceae), an apparently rare perennial of Michoacán, Mexico. During day 1, flowers are pistillate (stigma receptive, anthers not yet presenting pollen); flowers close for the night. Early in the morning of day 2, the corolla re-opens, stamens elongate to five times their earlier length, and anthers dehisce; the dehisced anthers remain about 2 mm from the stigma for much of day 2. In the afternoon of day 2, the corolla again closes, the corolla–androecium abscises, and only then can pollen be seen on the stigma. Protogyny and herkogamy likely promote outcrossing during days 1 and 2, respectively. Autonomous self-pollination takes place at the end of the corolla's life and allows fruit and seed production in the absence of pollinators but results in fruits that are lighter and contain fewer seeds than fruits resulting from manual self-pollinations. Carbohydrates from floral nectar samples were separated and quantified using hydrophilic interaction liquid chromatography coupled with corona charged aerosol detection. In nectar, mean sucrose concentration (0.482 mg/mg nectar), is about 10 and five times higher than glucose (0.043 mg/mg nectar) and fructose (0.095 mg/mg nectar) concentrations.

Prediction of the potential colour stability of strawberry nectar by use of a Stability Prediction Value (SPV)

The colour stabilities of 169 different samples of strawberry nectars produced on a lab-scale were measured over 12 weeks. To find a prediction for consumer acceptance at set times, and therefore a shelf-life estimation, a Stability Prediction Value (SPV) was calculated using colour components L*, a* and b* on day of production. The SPV is the first easily measurable calculated value that can be used to predict the Acceptance Factor (AF) – a measure of how likely a strawberry nectar's colour is accepted by consumers – after 12 weeks. It also can predict how many days have elapsed for a nectar's colour to become unacceptable, giving a shelf-life prediction. The SPV values were also calculated for 21 samples produced industrially, and SPV was found to also predict AF after 12 and 36 weeks. SPV, for the first time, gives a quick and simple method to screen raw materials for nectar production, and so could be used by producers to make more colour stable nectars, and breeders to guide development of cultivars. Additionally the potential of the colour component L*, and the concentration of anthocyanins to predict colour stability was evaluated.

A Comparison of Springtime Pollen and Nectar Foraging in Honey Bees Kept in Urban and Agricultural Environments

Spring is an essential time for honey bee foraging in temperate climates. This is a period of increased brood rearing supporting colony growth and demands access to high-quality pollen and nectar resources. With the expansion of urban and agricultural landscapes, the availability of pollen and nectar producing flowers is declining in many areas. We aim to determine how patterns of spring pollen and nectar foraging differ between colonies surrounded by varying degrees of urban and agricultural intensity, as well as to assess the potential for nectar sampling to serve as a proxy for pollen collection. Thirteen apiaries in Central Ohio, along a gradient of urban and agricultural intensity, were monitored in spring of 2019 through the periodic collection of pollen and nectar samples and continuous colony weight monitoring. We found that spring honey bees in urban and agricultural areas gain comparable amounts of weight and use similar spring resources. Foraging was heavily focused on flowering trees and shrubs including Malus (apple), Salix (willow), and Prunus (cherry), until the beginning of clover bloom (Trifolium spp.). We also identified differences in pollen and nectar foraging within colonies, with nectar containing fewer species collected more evenly than matched pollen samples. These results demonstrate that honey bees in both agricultural and urban environments exhibit similar foraging patterns during the spring, and that plant species important for nectar collection are substantially different from plants important for pollen foraging, though limitations in nectar collection hinder our ability to draw definitive comparisons of pollen and nectar foraging in this region.

Comparison of the Effect of Hydrostatic and Dynamic High Pressure Processing on the Enzymatic Activity and Physicochemical Quality Attributes of 'Ataulfo' Mango Nectar.

The effects of hydrostatic (HHP) and dynamic (HPH) high-pressure treatments on the activity of pectin methylesterase (PME) and polyphenol oxidase (PPO) as well as the physicochemical quality attributes of ‘Ataulfo’ mango nectar were assessed. HHP reduced PME relative activity by 28% at 100 MPa for 5 min but increased PPO activity almost five-fold. Contrarily, HPH did not affect PME activity, but PPO was effectively reduced to 10% of residual activity at 300 MPa and at three passes. Color parameters (CIEL*a*b*), °hue, and chroma were differently affected by each type of high-pressure processing technology. The viscosity and fluid behavior were not affected by HHP, however, HPH changed the apparent viscosity at low dynamic pressure levels (100 MPa with one and three passes). The viscosity decreased at high shear rates in nectar samples, showing a shear-thinning effect. The results highlight how different effects can be achieved with each high-pressure technology; thus, selecting the most appropriate system for processing and preserving liquid foods like fruit beverages is recommended.

Is there a risk to honeybees from use of thiamethoxam as a sugar beet seed treatment?

The ban imposed by the European Union on the use of neonicotinoids as sugar beet seed treatments was based on the exposure of bees to residues of neonicotinoids in pollen and nectar of succeeding crops. To address this concern, residues of thiamethoxam (TMX) and clothianidin (CTD) were analyzed in soil collected from fields planted in at least the previous year with thiamethoxam‐treated sugar beet seed. This soil monitoring program was conducted at 94 sites across Germany in two separate years. In addition, a succeeding crop study assessed residues in soil, guttation fluid, pollen, and nectar sampled from untreated succeeding crops planted in the season after thiamethoxam seed‐treated sugar beet at eight field sites across five countries. The overall mean residues observed in soil monitoring were 8.0 ± 0.5 µg TMX + CTD/kg in the season after the use of treated sugar beet seed. Residue values decreased with increasing time interval between the latest thiamethoxam or clothianidin application before sugar beet drilling and with lower application frequency. Residues were detected in guttation fluid (2.0–37.7 µg TMX/L); however, the risk to pollinators from this route of exposure is likely to be low, based on the reported levels of consumption. Residues of thiamethoxam and clothianidin in pollen and nectar sampled from the succeeding crops were detected at or below the limit of quantification (0.5–1 µg a.i./kg) in 86.7% of pollen and 98.6% of nectar samples and, unlike guttation fluid residues, were not correlated with measured soil residues. Residues in pollen and nectar are lower than reported sublethal adverse effect concentrations in studies with honeybee and bumble bee individuals and colonies fed only thiamethoxam‐treated sucrose, and are lower than those reported to result in no effects in honeybees, bumble bees, and solitary bees foraging on seed‐treated crops. Integr Environ Assess Manag 2022;18:709–721. © 2021 SYNGENTA. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Development of synbiotic added sucrose-free mango nectar as a potential substrate for Lactobacillus casei: Physicochemical characterisation and consumer acceptability during storage

AbstractThe study was carried out to evaluate the viability of probiotic bacteria as well as physicochemical and sensory characteristics of synbiotic added sucrose-free mango nectar. The mango nectar samples were prepared incorporating different concentrations of inulin and stevia (0, 2 and 4% w/w) and stored for 45 days at 4 °C. The results indicated that the growth of Lactobacillus casei was strongly influenced by the beverage composition. Therefore, the addition of inulin and stevia had a positive effect on the viability of L. casei, especially with 2% w/w inulin or inulin in combination with stevia. However, bacterial viability reduced during storage. According to the results, pH and total soluble solid content of the samples decreased during storage; however, the viscosity values of mango nectars were elevated by the addition of inulin and stevia. Additionally, all beverages were considered a suitable medium to keep the L. casei survival above the minimum recommended value (106–107 CFU mL−1) during storage. In general, it can be concluded that the sample containing 2% inulin and 2% stevia in combination provided the best viability of L. casei with acceptable physicochemical properties and sensory characteristics that could be introduced as synbiotic and low-calorie mango nectar.

Effect of intermittent microwave vacuum concentration on quality parameters of apple juice and sour cherry nectar and mathematical modeling of concentration

In this study, sour cherry nectar and apple juice were concentrated using thermal concentration (75, 80, and 85 °C), and intermittent microwave concentration (180, 300, and 450 W) under vacuum condition (at 250 mbar). Thirteen different mathematical models were used to describe the concentration kinetics of the samples. The Midilli model exhibited the best fit to all experimental data (R2 ≥ 0.9972; χ2 ≤ 1.6724; RMSE ≤ 1.2932). The concentration time was reduced with increasing microwave power (from 180 W to 450 W) and thermal vacuum concentration temperature (from 75 °C to 85 °C). In addition, the main quality parameters of the concentrates were comparatively investigated after reconstitution. Generally, major differences were not observed in the physicochemical properties of samples concentrated by thermal and microwave methods. Total phenolic content of the apple juice and sour cherry nectar samples were ranged between 209.87-216.67 mg/L and 571.00-588.57 mg/L, respectively. Fructose was the main sugar in both juices, followed by glucose and sucrose. The particle size of the juice samples increased with concentration processing.