Potential of a multiparametric optical sensor for determining in situ the maturity components of red and white Vitis vinifera wine grapes

Intrinsic Fluorescence Markers for Food Characteristics, Shelf Life, and Safety Estimation: Advanced Analytical Approach

Food is a complex matrix of proteins, fats, minerals, vitamins, and other components. Various analytical methods are currently used for food testing. However, most of the used methods require sample preprocessing and expensive chemicals. New analytical methods are needed for quick and economic measurement of food quality and safety. Fluorescence spectroscopy is a simple and quick method to measure food quality, without sample preprocessing. This technique has been developed for food samples due to the application of a front-face measuring setup. Fluorescent compounds-fluorophores in the food samples are highly sensitive to their environment. Information about molecular structure and changes in food samples is obtained by the measurement of excitation-emission matrices of the endogenous fluorophores and by applying multivariate chemometric tools. Synchronous fluorescence spectroscopy is an advantageous screening mode used in food analysis. The fluorescent markers in food are amino acids tryptophan and tyrosine; the structural proteins collagen and elastin; the enzymes and co-enzymes NADH and FAD; vitamins; lipids; porphyrins; and mycotoxins in certain food types. The review provides information on the principles of the fluorescence measurements of food samples and the advantages of this method over the others. An analysis of the fluorescence spectroscopy applications in screening the various food types is provided.

Non-destructive fluorescence sensing for assessing microclimate, site and defoliation effects on flavonol dynamics and sugar prediction in Pinot blanc grapes

In an era of growing international competition in modern viticulture, the study and implementation of innovative technologies to increase the production of high-quality grapes and wines are of critical importance. In this study, the non-destructive portable sensor Multiplex, based on fluorescence sensing technique, was applied to evaluate grape maturity parameters and flavonol content of the understudied Pinot blanc variety. The effects of environmental and agronomical factors on flavonol content of Pinot blanc grapes were investigated in eight vineyards characterised by different microclimatic and agronomic conditions. Furthermore, the direct impact of canopy management treatment on the flavonol dynamics of the grapes oriented in the four cardinal directions was assessed. Results highlight the positive role of moderate temperatures and direct sunlight exposure on Pinot blanc flavonol content; however, no direct vineyard-elevation effect was observed. The ability to modulate and evaluate the flavonol content in field represent crucial factors because of their potential effect on flavonoids-dependent wine characteristics, such as stability and ageing. In the present study, for the first time, two calibration curves were reported for pre- and post-veraison periods between flavonol indices and the berry skin flavonol content and a good correlation was observed between Multiplex measurement and the total polyphenolic content of grape juice. Moreover, the strong correlation between the chlorophyll index with grape juice sugar content and titratable acidity revealed the practical application of non-destructive sensors to predict the optimal harvest time for Pinot blanc grapes. In conclusion, the non-destructive fluorescence sensor Multiplex is a high-potential tool for innovative viticulture, for evaluating grape skin composition variables in white grape varieties.

Assessment of “Sugranineteen” Table Grape Maturation Using Destructive and Auto-Fluorescence Methods

The optimal harvesting of table grapes is commonly determined based on technological and phenolic indices analyzed over the course of its maturity. The classical techniques used for these analyses are destructive, time-consuming, and work for a limited number of samples that may not represent the heterogeneity of the vineyard. This study aimed to follow the ripening season of table grapes using non-destructive tools as a rapid and accurate alternative for destructive techniques. Grape samples were collected from a Sugranineteen vineyard during the ripening season to measure the basic maturity indices via wet chemistry, and total polyphenols, anthocyanins, and flavonoids were evaluated by spectrophotometry. Fluorescent readings were collected from intact clusters with a portable optical sensor (Multiplex^® 3, Force-A, France) that generates indices correlated to different maturity parameters. Results revealed strong relationships between the Multiplex^® indices ANTH_RG and FERARI and the skin anthocyanin content, with R² values equal to 0.9613 and 0.8713, respectively. The NBI_R index was also related to total anthocyanins (R² = 0.8032), while the SFR_R index was linked to the titratable acidity (R² = 0.6186), the sugar content (R² = 0.7954), and to the color index of red grapes (CIRG) (R² = 0.7835). Results demonstrated that Multiplex^® 3 can be applied on intact clusters as an effective non-destructive tool for a rapid estimation of table grapes’ anthocyanin content.

Multispectral fluorescence sensitivity to acidic and polyphenolic changes in Chardonnay wines - The case study of malolactic fermentation

In this study, stationary and time-resolvedfluorescence signatures, were statistically and chemometrically analyzed among three typologies of Chardonnay wines (A, B and C) with the objectives to evaluate their sensitivity to acidic and polyphenolic changes. For that purpose, a dataset was built using Excitation Emission Matrices of fluorescence (N = 103) decomposed by a Parallel Factor Analysis (PARAFAC), andfluorescence decays (N = 22), mathematically fitted, using the conventional exponential modeling and the phasor plot representation. Wine PARAFAC component C4 coupledwith its phasor plot g and s values enable the description of malolactic fermentation (MLF) occurrence in Chardonnay wines. Such proxies reflect wine concentration modifications in total acidity, malic/lactic and phenol acids.Lower g values among fresh MLF + wines compared to MLF- wines are explained by a quenching effect on wine fluorophores by both organic and phenolic acids.The combination of multispectral fluorescence parametersopens a novel routinely implementable methodology to diagnose fermentative processes.

Fruit ripening: dynamics and integrated analysis of carotenoids and anthocyanins

BACKGROUND

Fruits are vital food resources as they are loaded with bioactive compounds varying with different stages of ripening. As the fruit ripens, a dynamic color change is observed from green to yellow to red due to the biosynthesis of pigments like chlorophyll, carotenoids, and anthocyanins. Apart from making the fruit attractive and being a visual indicator of the ripening status, pigments add value to a ripened fruit by making them a source of nutraceuticals and industrial products. As the fruit matures, it undergoes biochemical changes which alter the pigment composition of fruits.

RESULTS

The synthesis, degradation and retention pathways of fruit pigments are mediated by hormonal, genetic, and environmental factors. Manipulation of the underlying regulatory mechanisms during fruit ripening suggests ways to enhance the desired pigments in fruits by biotechnological interventions. Here we report, in-depth insight into the dynamics of a pigment change in ripening and the regulatory mechanisms in action.

CONCLUSIONS

This review emphasizes the role of pigments as an asset to a ripened fruit as they augment the nutritive value, antioxidant levels and the net carbon gain of fruits; pigments are a source for fruit biofortification have tremendous industrial value along with being a tool to predict the harvest. This report will be of great utility to the harvesters, traders, consumers, and natural product divisions to extract the leading nutraceutical and industrial potential of preferred pigments biosynthesized at different fruit ripening stages.

Prediction of Sugar Content in Port Wine Vintage Grapes Using Machine Learning and Hyperspectral Imaging

The high quality of Port wine is the result of a sequence of winemaking operations, such as harvesting, maceration, fermentation, extraction and aging. These stages require proper monitoring and control, in order to consistently achieve the desired wine properties. The present work focuses on the harvesting stage, where the sugar content of grapes plays a key role as one of the critical maturity parameters. Our approach makes use of hyperspectral imaging technology to rapidly extract information from wine grape berries; the collected spectra are fed to machine learning algorithms that produce estimates of the sugar level. A consistent predictive capability is important for establishing the harvest date, as well as to select the best grapes to produce specific high-quality wines. We compared four different machine learning methods (including deep learning), assessing their generalization capacity for different vintages and varieties not included in the training process. Ridge regression, partial least squares, neural networks and convolutional neural networks were the methods considered to conduct this comparison. The results show that the estimated models can successfully predict the sugar content from hyperspectral data, with the convolutional neural network outperforming the other methods.

The Effect of Elevated CO2 on Berry Development and Bunch Structure of Vitis vinifera L. cvs. Riesling and Cabernet Sauvignon

Carbon dioxide (CO2) as one of the main factors driving climate change is known to increase grapevine growth and yield and could, therefore, have an impact on the fruit quality of vines. This study reports the effects of elevated CO2 (eCO2) on berry development and bunch structure of two grapevine cultivars (Vitis vinifera L. cvs. Riesling and Cabernet Sauvignon) within the VineyardFACE (Free-Air Carbon Dioxide enrichment) experiment, using must analysis and non-invasive fluorescence sensor technology. Berry development was examined on five dates over three consecutive years by analyzing total soluble solids (TSS), pH, total acidity, organic acids, nutrition status, and non-invasive Multiplex measurements. Before harvest, secondary bunches were collected to examine bunch and berry parameters. Results showed that eCO2 had little impact on berry composition of Riesling and Cabernet Sauvignon during berry development, which could be related to bunch structure or single berry weight within single seasons. Elevated CO2 (eCO2) did not result in modified TSS accumulation during ripening but was directly related to the chlorophyll index SFR_R. Higher single berry weights (SBW), higher malic acid (MA), and lower tartaric acid (TAA) were examined at some stages during development of berries under eCO2 levels. Our study provides evidence that eCO2 did alter some bunch and berry parameters without a negative impact on fruit quality.

Fluorescence-Sensor Mapping for the in Vineyard Non-Destructive Assessment of Crimson Seedless Table Grape Quality

Non-destructive tools for the in situ evaluation of vine fruit quality and vineyard management can improve the market value of table grape. We proposed a new approach based on a portable fluorescence sensor to map the ripening level of Crimson Seedless table grape in five different plots in the East, Central-North and South of the Macedonia Region of Greece. The sensor provided indices of ripening and color such as SFR_R and ANTH_RG correlated to the chlorophyll and anthocyanin berry contents, respectively. The mean ANTH_RG index was significantly different among all the plots examined due to the occurrence of different environmental conditions and/or asynchronous ripening processes. The indices presented moderate, poor in some cases, spatial variability, probably due to a significant vine-to-vine, intra-vine and intra-bunch variability. The cluster analysis was applied to the plot with the most evident spatial structure (at Kilkis). Krigged maps of the SFR_R, ANTH_RG and yield were classified by k-means clustering in two-zones that differed significantly in their mean values. ANTH_RG and SFR_R were inversely correlated over 64% of the plot. SFR_R appeared to be a potential useful proxy of yield since it was directly correlated to yield over 66% of the plot. The grape color (ANTH_RG) was slightly higher over the low-yield zones with respect to the high-yield zones. Our study showed that the combination of anthocyanins and chlorophyll indices detected in the field on Crimson Seedless table grape by a portable fluorescence sensor can help in defining the best harvest time and the best areas for harvesting.

Destructive and optical non-destructive grape ripening assessment: Agronomic comparison and cost-benefit analysis

Reliability and economic assessment of the Multiplex^® optical sensor employed for non-destructive grape parameters estimates was evaluated in 2017 against a wet chemistry approach in mature vineyards including five cultivars (two whites, two red and one pink colored) assuring a broad range of variation in both technological and phenolic maturity parameters. Among the five Multiplex (Mx) indices evaluated (SFR_R, FLAV, FLAV-UV, ANTH_RG and FERARI) in all cultivars with the exception of Barbera SFR_R showed a significant and linear correlation with total soluble solids (TSS) for TSS ≥ 10 °Brix. Conversely, no significant correlation was found between FLAV and total flavonols concentration, whereas a significant linear correlation was found in Barbera (R² = 0.66) and Ervi (R² = 0.63) when the FLAV index was replaced with the FLAV_UV index. Within each cultivar, both ANTH_RG and FERARI showed close correlations with total anthocyanins concentration determined by wet chemistry although under different model shapes. Expressing berry color accumulation on a per skin mass basis rather than for whole berry mass basis, allowed for better separation of behavior of single cultivars and improved accuracy of model fitting for the combination of Barbera and ANTH_RG. A strict linear correlation was always found, within each index, for Mx readings taken on the two opposite sides of the same cluster, implying no significant within-cluster differences in sugar, color and flavonol concentrations. Economic assessment of Mx by means of the Net Present Value (NPV) approach showed that Mx is economically viable for a two hectare vineyard cultivating three red grape varieties (90 samples per year) if its lifetime is at least 7 years. Conversely, if only two red varieties are grown Mx should be used at least 11 years to make it economic suitable. Bigger properties growing a higher number of red varieties are the more interested in Mx as the expected NPV assumes positive values with a Mx usage of minimum 3 years.

Suitability of fluorescence indices for the estimation of fruit maturity compounds in tomato fruits

BACKGROUND

We examined the suitability of chlorophyll fluorescence-based indices to monitor and predict concentrations of fruit maturity compounds during tomato ripening under different growing conditions in the greenhouse. The aim of this study was to evaluate the effects of chlorophyll concentration changes on fluorescence-based indices and to exploit the relation between fluorescence and reflectance indices with the corresponding maturity compounds determined analytically.

RESULTS

Fruits grown under water deficit matured faster than control fruits as recorded with fluorescence-based indices. The SFR_R index correlated well with the analytical determination of chlorophyll content, whereas the single-signal FRF_G correlated with lycopene content even if the sensor was unable to differentiate precisely between maturity stages 2 to 4. Neither the FLAV index nor the FLAV_UV index was suitable for flavonoid prediction in tomato fruits. Compared with fluorescence indices, the relation between the reflection index and pigment concentrations was lower for chlorophyll and higher for lycopene.

CONCLUSION

Chlorophyll and lycopene content in tomato fruits can be estimated by means of fluorescence indices during the pre-harvest phase. Since the chlorophyll decrease during tomato ripening is the driving force affecting all fluorescence signals, the methods are not reliable for estimation of other maturity compounds in tomato fruits. © 2018 Society of Chemical Industry.

Limitation of mineral supply as tool for the induction of secondary metabolites accumulation in tomato leaves

Agricultural residues are natural sources for secondary metabolites as high value ingredients for industrial uses. The present work aims to exploit the accumulation potential of rutin and solanesol in tomato leaves following nitrogen and general mineral deficiency in a commercial-like greenhouse. Physiological responses of tomato plants were monitored non-destructively with a multiparametric fluorescence sensor, and biochemical parameters were determined by means of HPLC analysis. Nitrogen and general mineral limitation led to an accumulation of rutin in young tomato leaves while solanesol concentration was higher in mature leaves. In young leaves, the fluorescence indices SFR_R and NBI_G showed lower values compared to control plants for both stress treatments. On the contrary, FLAV and ANTH_RG values increased during the experiment, but no differences could be recorded in mature leaves. However, correlation analysis indicates, that the FLAV index is not a reliable tool to estimate the concentration of rutin and solanesol tomato leaves. To monitor fruit yield/quality as primary objective of tomato production, fruits showing symptoms of blossom end rot (BER) were counted before and after stress treatments. BER was determined more frequently for plants grown under a general mineral deficiency, concluding that a practical applicability at the end of fruit production is advisable. Our results indicate that by-products from Solanaceae plants are promising resources for valuable bioactive leaf compounds. To achieve the highest concentrations, the seasonal variation, the optimal environmental conditions, the concentrations in different plant organs and varieties as well as different production systems are of high interest for commercial implementation.

Nutritional properties of Tempranillo grapevine leaves are affected by clonal diversity, mycorrhizal symbiosis and air temperature regime

Tempranillo grapevine is widely cultivated in Spain and other countries over the world (Portugal, USA, France, Australia, and Argentina, among others) for its wine, but leaves are scarcely used for human or animal nutrition. Since high temperatures affect quality of fruits and leaves in grapevine and the association of Tempranillo with arbuscular mycorrhizal fungi (AMF) enhances the antioxidant properties of berries and leaves, we assessed the effect of elevated air temperature and mycorrhization, separately or combined, on the nutritional properties of Tempranillo leaves at the time of fruit harvest. Experimental assay included three clones (CL-260, CL-1048, and CL-1089) and two temperature regimes (24/14 °C or 28/18 °C day/night) during fruit ripening. Within each clone and temperature regime there were plants not inoculated or inoculated with AMF. The nutritional value of leaves increased under warming climate: elevated temperatures induced the accumulation of minerals, especially in CL-1089; antioxidant capacity and soluble sugars also increased in CL-1089; CL-260 showed enhanced amounts of pigments, and chlorophylls and soluble proteins increased in CL-1048. Results suggested the possibility of collecting leaves together with fruit harvest with different applications of every clone: those from CL-1089 would be adequate for an energetic diet and leaves from CL-260 and CL-1048 would be suitable for culinary processes. Mycorrhization improved the nutritional value of leaves by enhancing flavonols in all clones, hydroxycinnamic acids in CL-1089 and carotenoids in CL-260.

Management Zone Delineation for Winegrape Selective Harvesting Based on Fluorescence-Sensor Mapping of Grape Skin Anthocyanins

We analyzed the potential of non-destructive optical sensing of grape skin anthocyanins for selective harvesting in precision viticulture. We measured anthocyanins by a hand-held fluorescence optical sensor on a 7 ha Sangiovese vineyard plot in central Italy. Optical indices obtained by the sensor were calibrated for the transformation in units of anthocyanins per berry mass, i.e., milligrams per gram of berry fresh weight. A full protocol for optimal data filtration, interpolation, and homogeneous zone delineation based on a very large number of optical measurements is proposed. Both the single signal-based fluorescence index (ANTH_R) and the two signal ratio-based index (ANTH_RG) can be used for Sangiovese grapes. Significant separations of grape-quality batches were obtained by several methods of data classification and zone delineations. Basic statistical criteria were as efficient as the K-means clustering. The best separations were obtained for three classes of grape skin anthocyanin.

Advances in Non-Destructive Early Assessment of Fruit Ripeness towards Defining Optimal Time of Harvest and Yield Prediction-A Review

Global food security for the increasing world population not only requires increased sustainable production of food but a significant reduction in pre- and post-harvest waste. The timing of when a fruit is harvested is critical for reducing waste along the supply chain and increasing fruit quality for consumers. The early in-field assessment of fruit ripeness and prediction of the harvest date and yield by non-destructive technologies have the potential to revolutionize farming practices and enable the consumer to eat the tastiest and freshest fruit possible. A variety of non-destructive techniques have been applied to estimate the ripeness or maturity but not all of them are applicable for in situ (field or glasshouse) assessment. This review focuses on the non-destructive methods which are promising for, or have already been applied to, the pre-harvest in-field measurements including colorimetry, visible imaging, spectroscopy and spectroscopic imaging. Machine learning and regression models used in assessing ripeness are also discussed.

Phenoliner: A New Field Phenotyping Platform for Grapevine Research

In grapevine research the acquisition of phenotypic data is largely restricted to the field due to its perennial nature and size. The methodologies used to assess morphological traits and phenology are mainly limited to visual scoring. Some measurements for biotic and abiotic stress, as well as for quality assessments, are done by invasive measures. The new evolving sensor technologies provide the opportunity to perform non-destructive evaluations of phenotypic traits using different field phenotyping platforms. One of the biggest technical challenges for field phenotyping of grapevines are the varying light conditions and the background. In the present study the Phenoliner is presented, which represents a novel type of a robust field phenotyping platform. The vehicle is based on a grape harvester following the concept of a moveable tunnel. The tunnel it is equipped with different sensor systems (RGB and NIR camera system, hyperspectral camera, RTK-GPS, orientation sensor) and an artificial broadband light source. It is independent from external light conditions and in combination with artificial background, the Phenoliner enables standardised acquisition of high-quality, geo-referenced sensor data.

Hyperspectral phenotyping of the reaction of grapevine genotypes to Plasmopara viticola

A major aim in grapevine breeding is the provision of cultivars resistant to downy mildew. As Plasmopara viticola produces sporangia on the abaxial surface of susceptible cultivars, disease symptoms on both leaf sides may be detected and quantified by technical sensors. The response of cultivars 'Mueller-Thurgau', 'Regent', and 'Solaris', which differ in resistance to P. viticola, was characterized under controlled conditions by using hyperspectral sensors. Spectral reflectance was suitable to differentiate between non-infected cultivars and leaf sides of the bicolored grapevine. Brown discoloration of tissue became visible on both leaf sides of resistant cultivars 2 days before downy mildew symptoms appeared on the susceptible 'Mueller-Thurgau' cultivar. Infection of this cultivar resulted in significant (P<0.05) reflectance changes 1-2 days prior to abaxial sporulation induced by high relative humidity, or the formation of adaxial oil spots. Hyperspectral imaging was more sensitive in disease detection than non-imaging and provided spatial information on the leaf level. Spectral indices provided information on the variability of chlorophyll content, photosynthetic activity, and relative water content of leaf tissue in time and space. On 'Mueller-Thurgau' downy mildew translated reflectance to higher values as detectable by the index DMI_3=(R₄₇₀+R₆₈₂+R₈₀₀)/(R₈₀₀/R₆₈₂) and affected reflectance at 1450nm. Tissue discoloration on 'Regent' and 'Solaris' cultivars was associated with lower reflectance between 750 and 900nm; blue and red reflectance demonstrated differences from leaf necroses. With high inoculum densities, P. viticola sporulated on even resistant cultivars. Hyperspectral characterization at the tissue level proved suitable for phenotyping plant resistance to pathogens and provided information on resistance mechanisms.

Nondestructive Optical Sensing of Flavonols and Chlorophyll in White Head Cabbage (Brassica oleracea L. var. capitata subvar. alba) Grown under Different Nitrogen Regimens

A multiparametric optical sensor was used to nondestructively estimate phytochemical compounds in white cabbage leaves directly in the field. An experimental site of 1980 white cabbages (Brassica oleracea L. var. capitata subvar. alba), under different nitrogen (N) treatments, was mapped by measuring leaf transmittance and chlorophyll fluorescence screening in one leaf/cabbage head. The provided indices of flavonols (FLAV) and chlorophyll (CHL) displayed the opposite response to applied N rates, decreasing and increasing, respectively. The combined nitrogen balance index (NBI = CHL/FLAV) calculated was able to discriminate all of the plots under four N regimens (0, 100, 200, and 400 kg/ha) and was correlated with the leaf N content determined destructively. CHL and FLAV were properly calibrated against chlorophyll (R(2) = 0.945) and flavonol (R(2) = 0.932) leaf contents, respectively, by using a homographic fit function. The proposed optical sensing of cabbage crops can be used to estimate the N status of plants and perform precision fertilization to maintain acceptable crop yield levels and, additionally, to rapidly detect health-promoting flavonol antioxidants in Brassica plants.

Fluorescence fingerprinting of bottled white wines can reveal memories related to sulfur dioxide treatments of the must

For the first time, Excitation Emission Matrix (EEM) fluorescence spectroscopy was combined with parallel factor statistical analysis (PARAFAC) and applied to a set of 320 dry white wines of the Chardonnay grape variety. A four component PARAFAC model (C1, C2, C3 and C4) best explained the variability of fluorescence signatures of white wines. Subtle changes were observed in EEMs of white wines from two different vintages (2006 and 2007), where different concentrations of sulfur dioxide (0, 4, and 8 g·hL(-1)) were added to the grape must at pressing. PARAFAC results clearly indicated that sulfur dioxide added to the must subsequently influenced white wine chemistry into three distinct sulfur dioxide dose-dependent aging mechanisms. For both vintages, C1 and C2 were the dominant components affected by sulfur dioxide and likely reacting with phenolic compounds associated with some presumably proteinaceous material. Distinct component combinations revealed either SO2 dependent or vintage-dependent signatures, thus, showing the extent of the complex versatile significance underlying such fluorescence spectra, even after several years of bottle aging.