Cabernet Sauvignon Grapes Research Articles

Winter pruning timing, development and quality of Cabernet Sauvignon in Southern Brazil

The objective of this study was to evaluate the influence of winter pruning timing on phenology, productivity, and quality of Cabernet Sauvignon grapes and wines in 2022/2023 production cycle. The experimental design was randomized blocks, with 3 replications, each experimental unit consisted of 5 plants. The treatments involved four pruning timings (end of May, June, July and August). Phenology assessments were beginning and end of bud break, flowering, maturation and percentage of bud break. Production was evaluated by the number of clusters per plant, weight and size of clusters, productivity per plant and per hectare. The analyzes of must were pH, total acidity and soluble solids (°Brix). In wine, pH, total acidity, sugars, alcohol, volatile acidity and color were analyzed. In the end a wine sensory analysis was carried out. The results showed that the bud break of plants pruned early, in May, occurred at the same time as plants pruned in June and July. Early pruning resulted in lower productivity. The grape must from plants pruned late, in August, showed higher total acidity and lower values ​​of soluble solids and sugars. Early pruning did not change the duration of the cultivar's phenological subperiods, nor did it bring forward the harvest in relation to the control. The different pruning times influenced productivity more than the composition of grapes and wines, indicating that it is possible to extend the pruning period.

Late-season source limitation practices to cope with climate change: delaying ripening and improving colour of Cabernet-Sauvignon grapes and wine in a hot and arid climate

The current rise in temperatures is hastening grape ripening, resulting in unbalanced wines with high alcohol content but poor colour, aroma and phenolic composition. Late-season canopy manipulation practices aimed at reducing the size of the photosynthetic apparatus after veraison have been shown to delay ripening in cooler climates. However, these methods have not directly been compared in regions with high irradiance and temperature, where berry composition is negatively affected by late fruit exposure. In this two-year Cabernet-Sauvignon trial, we compared the application of pinolene (P) to late shoot topping (T) and late above-bunch zone leaf removal (LR), all performed during the late stages of ripening, with an untreated control (C). Vine water status was monitored weekly from the time of treatment application until harvest. Gas exchange was monitored only in 2021, from treatment application through to harvest. Berry samples were collected to measure berry weight, total soluble solids, pH, titratable acidity, and the anthocyanin profile. At harvest, we assessed yield components, rated sun damage on clusters, and produced experimental wines. Wine colour and chemical characteristics were evaluated. The application of P scarcely improved gas exchange and stem water potential. Conversely, LR and T increased water potential but did not affect leaf gas exchange. T was the only treatment that significantly decreased sugar accumulation, followed by P, which showed some effect although not significant. Grape yield was not altered, despite the use of P resulted in a lower berry weight in 2022. Canopy manipulation increased lighting conditions in the canopy and caused a significant presence of damaged fruits, especially in LR. Berry anthocyanins were not affected, but LR resulted in a lower concentration of total anthocyanins in the wine and altered the anthocyanin profile. P increased wine acidity, while LR and T improved wine colour. This study suggests that late-season canopy management can effectively control ripening speeds and improve the composition of grapes and wines. However, it is essential to avoid grape overexposure by employing the appropriate techniques to ensure grape quality is not compromised.

Manganese biofortification in grapevine by foliar spraying improves volatile profiles of Cabernet Sauvignon grapes and wine sensory traits.

Manganese (Mn) is involved in plant metabolism as an enzyme cofactor. However, the role of Mn in the formation of volatile compounds in grapes has rarely been studied. To address this gap, this study explored the effect of foliar Mn application on the aroma traits of grapes and wine. Mn nutrient solutions at different concentrations (0 (CK), 300, 1200, and 2400mg/L) were sprayed on grapevines in 2017 and 2018 and the volatile compounds, odor activity, and sensory features of grapes and wine were investigated. The results showed that Mn application significantly increased Mn content in grape leaves and fruits at harvest. Compared with CK, the total volatile content of grapes was significantly increased by Mn treatment in both years because of the promotion of the accumulation of alcohols and esters. Particularly, 1200mg/L Mn treatment resulted in a higher sensory score than CK, especially in terms of intensity, duration, and harmony. Multivariate analysis and odor activity values jointly identified eight volatile compounds (ethyl acetate, phenylethyl acetate, and phenylethyl alcohol, etc.) as key odorants that contribute to the floral and fruity flavors of Mn-treated wine. Overall, this study indicated that a moderate concentration of Mn is beneficial for improving the fragrance characteristics of grapes and wines. The results have implications for micronutrient management of grapevines to improve wine flavor quality.

Modelling the climate changing concentrations of key red wine grape quality molecules using a flexible modelling approach

Grape (Vitis vinifera) composition is a weather-dependent determiner of wine quality. With changing climates, we can expect variation in wine-quality. To understand the extent of this we built path models to create a generalised Cabernet-Sauvignon grape quality model focusing on the total concentrations of six important molecular groups (sugar, pH, phenols, tannins, flavanols, anthocyanins). Path models statistically connect factors from input to output using a series of dependent models. As such, this modelling approach takes the output from one model and puts it into the next model as a chain. By varying climate inputs, we can simulate how changes in climate impact the final composition of the grapes throughout their ripening. We explore the impact of changes in composition under several climate change scenarios namely: changes in light, temperature, and rainfall by changing the climatic inputs to the path model. We find that, under moderate-projected climatic changes (a combination of RCP4.5 and SRES A2 and B2), we expect higher concentrations of sugars, lower acidity (a more neutral pH), and higher total concentrations of aromatic compounds (tannins, phenols, flavanols, and anthocyanins). We also find that an earlier start of ripening leads to the same result. These two results combined suggest the potential for stronger red wines in future, with more flavour-related compounds and in particular tannins which often give greater ageing potential.

Development of a Process for Polyphenol Extraction and the Production of a Functional Powder for Food Fortification

The valorisation of co-products from food supply chains is consistent with the objectives of the national recovery and resilience plan (NRRP), which favours issues relating to the “green revolution and ecological transition”. The nutraceutical characteristics (antimicrobial, antiviral, anti-cancer, etc.) of grape pomace extracts are due to the presence of polyphenols. The objective of the following research was to develop an innovative extraction process in order to produce a special powder with high technological and nutraceutical value (polyphenols). For the experimentation, red grape pomace from Cabernet Sauvignon grapes was used. The first phase of the experimentation allowed the development of the extraction methods; the second involved the use of a pilot system for the extraction, filtration, and distillation phases. The result obtained is a powder with compositional characteristics suitable for the fortification of alcoholic and non-alcoholic food matrices, due to its colouring and antioxidant and nutraceutical properties.

Valorization of Mexican cabernet sauvignon grape pomace: A source of oil and lipophilic bioactive compounds

Valorization of Mexican cabernet sauvignon grape pomace: A source of oil and lipophilic bioactive compounds

Rootstock Influences Growth, Yield, Berry Physiochemical and Quality Wine Produced from Cabernet Sauvignon Grown in the Pune Region

The experiment was conducted to study the effect of rootstock on growth, yield, quality, and sensory evaluation of wine made from ‘Cabernet Sauvignon’ grapes. Among the rootstock’s, pruning weight was significantly higher in vines grafted on 110R rootstock. Days for buds sprout and days to veraison was early in Gravasec grafted rootstocks, while early days to harvest in Gravasec and SO4 rootstocks. Cabernet Sauvignon vines grafted on 110R rootstock recorded significantly higher fruit yield than other rootstocks studied. Wine composition like volatile acid, total acids and ethanol was higher in vines grafted on 140RU; malic acids in 1103P and colour intensity in SO4 grafted vines. The wine sensory attributes were also positively influenced using different rootstocks, wine prepared from Cabernet Sauvignon grapes grafted on 1103P recorded the highest overall wine quality which was followed by Fercal rootstock.

Evaluation of passive samplers as a cost-effective method to predict the impact of wildfire smoke in grapes and wines

Wildfire smoke exposure alters grape composition, potentially resulting in “smoke tainted” wines. This has been correlated with elevated levels of smoke-derived volatile phenols (VPs) in grapes and wines. This work sought to create a predictive tool that could correlate levels of VPs in smoke with concentrations in grapes and wines. Therefore, passive samplers and Cabernet Sauvignon grapes were intentionally exposed to various smoke intensities, and wines were made thereafter. As expected, concentrations of VPs in grapes and wines were positively associated with the intensity of smoke exposure. Interestingly, levels of guaiacol in the passive samplers had a strong positive correlation with concentrations in grapes (R2 = 0.9999) and wines (R2 = 0.9998). The passive samplers were able to accurately predict guaiacol levels in smoke exposed grapes and wines with percent errors ranging from 0.08 to 11.3 %. These results suggest the capability of passive samplers to act as a monitoring system in vineyards during smoke events.

Aggregation and assessment of grape quality parameters with visible-near-infrared spectroscopy: Introducing a novel quantitative index

Grape quality is generally assessed by measuring individual indicators rather than utilizing a comprehensive metric. A flexible approach to aggregating multiple quality-related parameters of grapes is introduced in this study, and an aggregative index was proposed for the synthetical evaluation of grape quality. First, visible-near-infrared (Vis-NIR) spectral data of two grape varieties were obtained, and the physical and chemical quality indicators were measured as reference standards. The variation trends and correlations of the indicators were analyzed, and an aggregative quality indicator (AQI) was proposed using the min-max normalization and factor analysis methods. The maturity stages of grapes were categorized by analyzing the AQI values. The spectral data underwent preprocessing using multiplicative scatter correction (MSC), Savitzky-Golay smoothing (SG), first-order derivative (FD), SG+FD and de-trending (DT) methods. Feature wavelengths were extracted using uninformative variable elimination (UVE), competitive adaptive reweighted sampling (CARS), and the UVE-CARS algorithms. Three regression models for the AQI were established based on partial least squares regression (PLSR), support vector machine regression (SVR) and convolutional neural network (CNN). Results indicated that the PLSR combined with the FD+SG preprocessing and CARS-selected feature wavelengths achieved optimal performance for Cabernet Sauvignon grapes, with the coefficient of determination for the prediction set (Rp2)=0.972, for the calibration set (Rc2)=0.995, the root mean square error of prediction (RMSEP)=0.040 and residual predictive deviation (RPD)=6.064. In addition, for the Muscat Kyoho grape, CNN combined with DT preprocessed full-spectrum data yielded the best prediction for the AQI, with Rp2=0.989, Rc2=0.981, RMSEP=0.103 and RPD=9.482. This research demonstrated that the non-destructive prediction of grape aggregative qualities can be achieved through the combination of Vis-NIR spectroscopy and a chemometric analysis, offering a practical and comprehensive metric for determining grape maturity stages and optimal harvest times. This approach is particularly valuable for the wine industry, as it facilitates better decision-making and quality control.

Enhancing bioactive phenolic extraction from unfermented Cabernet Sauvignon pomace through tailored synergies of pH, proteolysis, and microwave processing

The impact of enzyme-assisted (EAE), microwave-assisted (MAE), and microwave enzyme-assisted (MEAE) extractions using water were evaluated and compared to aqueous (AEP), conventional ethanolic (CSE), and microwave ethanolic (MSE) controls for the release of phenolics from Cabernet Sauvignon grape pomace. Optimization of extract total phenolic content (TPC) involved stepwise screening of time, temperature, slurry pH, solids-to-liquid ratio, and enzyme conditions. The use of 0.1 % alkaline protease in MEAE (1:10 g pomace/mL water, pH 11.5, 70 °C, 30 min) reduced extraction time by 50 % compared to AEP, EAE, and CSE methods, doubling the TPC of the extracts to 100.9 mg GAE/g dry weight pomace compared to ethanolic extractions. MAE and MEAE extracts exhibited in vitro antioxidant activities (ABTS and ORAC) similar to ethanolic extracts and had greater antioxidant activities than AEP/EAE extracts while boosting relative contents of catechins, procyanidins, trans-piceid, and malvidin-3,5-diglucoside as detected by untargeted metabolomics. Quantitation by HPLC showed increased levels of gallic acid, protocatechuic acid, syringic acid, p-coumaric acid, polymeric phenols, and polymeric pigments in MEAE compared to hydroethanolic methods. Scanning electron microscopy further supported the synergistic role of microwave processing and proteolysis in disrupting the grape cell structure to aid in releasing valuable bioactive phenolic compounds.

Volatilomics of Cabernet Sauvignon grapes and sensory perception of wines are affected by canopy side in vineyards with different row orientations

This study aimed to clarify how microclimate diversity altered volatilomics in Cabernet Sauvignon grapes and wines. Four row-oriented vineyards were selected, and metabolites of grapes and wines were determined from separate canopy sides. Results showed that shaded sides received 59% of the solar radiation and experienced 55% of the high-temperature days compared to the exposed sides on average. Grape primary metabolites were slightly affected by the canopy side. Herbaceous aromas were consistently more abundant in grapes and wines from shaded clusters. Heat-stressed canopy sides accelerated terpenoid loss and increased norisoprenoid levels in grapes, while β-damascenone in north-side wines was 13%–32% higher than that in south-side wines of the east-west vineyard. The northeast-southwest vineyard showed the most notable variation in taste and aroma sensory scores, with four parameters significantly different. There were 32 aroma series identified in wines, and banana, pineapple, and strawberry odors were highly correlated with aroma sensory score.

Impact of biodynamic and organic vineyard management on the microorganism community and aroma characteristics of cabernet sauvignon wine

Researchers and winemakers have recently paid more attention to biodynamic (BDN) and organic (ORG) vineyard management to produce more healthy and regional wines. However, little attention has been paid to the correlation between agricultural systems, microbiota, and wine quality in biodynamic and organic wines in Ningxia, China. In this study, volatiles of wine and microorganism diversities during the wine fermentation using Cabernet Sauvignon grapes from vineyards of biodynamic, non-dynamics (BNDc, i.e., conventional one which was close to BND, considered to be a control of BND), organic, and non-organic (ORGc, i.e., conventional one which was close to BND, considered to be a control of ORG) in Ningxia, China were investigated. Hanseniaspora uvarum, Cladosporium sp., and Alternaria alternata were the main three fungal species, and Lactobacillus kunkeei, Citrus maxima, and Tatumella ptyseos were the main three bacterial species. Surprisingly, BDNc and ORG showed a significantly higher diversity of fungal communities than BDN and ORGc. The network in BDNc was the most complex, with the highest average degree and density and a higher clustering coefficient. Managing biodynamic and organic vineyards could result in floral, herb, spice, and medium floral aromas with low temperate fruit, tropical fruit, and berry flavors to wines. The correlation between agricultural systems, microbiota, and wine sensory systems showed that lactic acid bacteria (Lactobacillus) played critical roles in ORG and BDN by offering pleasant sensory and nutritional benefits. Moreover, Nowamyces globulus, Hanseniaspora uvarum, Lactobacillus johnsonii, Fusarium sp., Microterricola viridarii, Citrus maxima, Sphingomonas faeni, Cladosporium sp., Cladosporium ramotenellum, Cladosporium cladosporioides, Kodamaea ohmeri and Lactobacillus plantarum were positively correlated with aroma compounds. This study improves our understanding of the influence of vineyard management on microorganism succession and wine characteristics, providing a reference and scientific basis for the development of BDN and ORG wines.

Hydrogen peroxide functioned as a redox signaling molecule in the putrescine-promoted drought tolerance in cabernet sauvignon

Drought stress poses a significantly constraint on grape growth, development, and yield. Increasing drought resistance is a critical goal of viticulture, especially in the context of global warming. In this study, exogenous putrescine (Put) significantly improved the photosynthetic and antioxidant capacity of drought-stressed Cabernet Sauvignon seedlings, stimulated the biosynthesis of endogenous polyamines, and reinforced the protective impact on organelle structure. Hydrogen peroxide scavenging agent (DMTU) severely undermined the drought resistance conferred by Put. The elimination of H2O2 using exogenous DMTU led to a dramatic reduction in the Fv/Fm value, antioxidant enzyme activity, and endogenous PAs content in the grape leaves. Our observations suggested that Put increased the expression of the nicotinamide adenine dinucleotide phosphate oxidase genes VvRBOHb and VvRBOHc2, which stimulated the synthesis of H2O2 in the cells. H2O2 functioned as signal molecules and contributed to the regulatory role of Put in enhancing the drought resistance of Cabernet Sauvignon grape seedlings.

Microbial Diversity Associated with the Cabernet Sauvignon Carposphere (Fruit Surface) from Eight Vineyards in Henan Province, China.

The microbial diversity on the carposphere (berry) surface of the grape cultivar Cabernet Sauvignon grown in eight different locations/vineyards of Henan Province was determined by high-throughput sequencing of the bacterial 16S rRNA gene and fungal 18S rRNA gene. The structure of bacterial and fungal communities varied according to the sampling sites, but with some common phyla. Proteobacteria and Ascomycota were dominant/common phyla for bacteria and fungi, respectively. A total of 27 and 20 bacterial and fungal families, respectively, and 39 and 20 bacterial and fungal genera, respectively, with statistically significant differences, were found among different sampling sites. The difference for metabolic pathways of bacteria among the sampling sites existed. In addition, various abundances of enzymes from different sites might indicate that different function patterns exist in microbiota from different sites. The results revealed that locations of grape vineyards might play a significant role in shaping the microbiome, as well as the fact that vineyards can be distinguished based on the abundance of several key bacterial and fungal taxa. Overall, these findings extend our understanding of the similarities and differences in microbial community and their metabolic function on Cabernet Sauvignon grape surfaces from different geographic locations.

The Influence of the Soil Profile on the Formation of the Elemental Image of Grapes and Wine of the Cabernet Sauvignon Variety.

The features for assessing the authenticity of wines by region of origin are studied, based on the relationship between the mineral composition of the wine, the grapes, and the soil profile (0 to 160 cm) from the place of growth of Cabernet Sauvignon grapes. Soil, grape, and wine samples were taken from the territories of six vineyards in the Anapa district of Krasnodar Territory, Russia. Using the methods of ICP-OES, thermal, and X-ray phase analysis, the soils were differentiated into three groups, differing in mineralogical and mineral compositions. The soil samples of the first group contained up to 31% quartz, the second group up to 25% quartz and 19% mixed calcite, and the third group up to 32% calcite and 15% quartz. The formation of the elemental image of the grapes was studied, taking into account the total content and mobile forms of metals in the soil. The territorial proximity of the vineyards did not affect the extraction of elements from the soil into the grape berry, and the migration of metals for each territory was selective. According to the values of the biological absorption coefficient, the degree of transition of metals from the soil to a berry was estimated. For K, Ti, Zn, Rb, Cu, and Fe in all berries, the coefficient was higher than 1.00, which means that the berry extracts contained not only mobile-form, but also difficult-to-dissolve metal compounds. The migration of macro-components from the soil to the berry was low, and amounted to 6-7% for Ca, 0.8-3.0% for Na, and 25-70% for Mg of the concentration of their mobile forms. For all territories, the maximum correlation between metal concentrations in grapes and soil was observed for samples from a depth of 0-40 cm. The discriminant model based on concentrations of Rb, Al, K, Sr, Co, Na, Pb, Ca, and Ni showed the formation of clusters in the territories of vineyard cultivation. The developed model allow the problems of identifying wines by region to be solved with high accuracy, using their elemental image.

Influences of Cluster Thinning on Fatty Acids and Green Leaf Volatiles in the Production of Cabernet Sauvignon Grapes and Wines in the Northwest of China.

Cluster thinning has been widely applied in yield management and its effect on green leaf volatiles (GLVs) in wines has seldom been studied. GLVs are important flavor compositions for grapes and wines. This work aimed to investigate the impact of cluster thinning on these volatiles and their precursors in grapes and wines. Severe cluster thinning (CT1) and medium cluster thinning (CT2) were performed on Cabernet Sauvignon (Vitis vinifera L.) vines in two sites (G-farm and Y-farm) from Xinjiang province in the Northwest of China. The impact of cluster thinning treatments on the accumulation of GLVs and their precursors, long chain fatty acids (LCFAs) of grape berries and C6 volatiles, in resulting wines was investigated. Multivariate analysis showed that cluster thinning treatments induced significant changes in fruit and wine composition in both farms. In Y-farm, medium cluster thinning (CT2) significantly increased the average cluster weight of harvested berries. Additionally, both cluster thinning treatments (CT1 and CT2) increased fatty acids in harvested berries and CT2 led to an increase in C6 esters and a decrease in C6 alcohols in the wines of Y-farm under the warmer and drier 2012 vintage. However, the effect of cluster thinning was likely negative in G-farm due to its wetter soil and excessive organic matter. The treatments may be applicable for local grape growers to improve viticultural practices for the more balanced vegetative and reproductive growth of Cabernet Sauvignon grapevines. This work also provided further knowledge on the regulation of fatty acids and the derived C6 volatiles through the lipoxygenase (LOX) pathway.

Abscisic acid reduced methoxypyrazines concentration and its derived unpleasant odors in Cabernet Sauvignon grapes and wines.

The influences of abscisic acid (ABA) applications on precursors and gene expression in 3-alkyl-2-methoxypyrazines (MPs) biosynthetic pathway, MPs concentration and sensory evaluation of its derived peculiar odors in Cabernet Sauvignon grapes and wines were investigated. At the vineyard, ABA solution with 25, 100 and 400 mg L-1 (AT1, AT2 and AT3, respectively) and an aqueous solution (control) were sprayed three times from veraison to pre-harvest. Higher concentration ABA applications (AT2 and AT3) in grapes could significantly reduce MPs concentration and its derived peculiar odors in grapes and wines compared to a lower concentration ABA application (AT1) and control, with AT2 application having the strongest effect. The changes in MPs were mainly a result of the downregulated expression of VvOMTs genes at higher concentration ABA applications, independent of the levels of their potential precursors. The present study reveals that ABA application had the potential to decrease production of MPs in Cabernet Sauvignon grapes and wines, and this result provides reference values for the removal of unpleasant vegetable odors from Cabernet Sauvignon wines in production. © 2024 Society of Chemical Industry.

Vineyard microclimate alterations induced by black inter-row mulch through transcriptome reshaped the flavoromics of cabernet sauvignon grapes

BackgroundWeed control is essential for agricultural floor management in vineyards and the inter-row mulching is an eco-friendly practice to inhibit weed growth via filtering out photosynthetically active radiation. Besides weed suppression, inter-row mulching can influence grapevine growth and the accumulation of metabolites in grape berries. However, the complex interaction of multiple factors in the field challenges the understanding of molecular mechanisms on the regulated metabolites. In the current study, black geotextile inter-row mulch (M) was applied for two vintages (2016–2017) from anthesis to harvest. Metabolomics and transcriptomics analysis were conducted in two vintages, aiming to provide insights into metabolic and molecular responses of Cabernet Sauvignon grapes to M in a semi-arid climate.ResultsUpregulation of genes related to photosynthesis and heat shock proteins confirmed that M weakened the total light exposure and grapes suffered heat stress, resulting in lower sugar-acid ratio at harvest. Key genes responsible for enhancements in phenylalanine, glutamine, ornithine, arginine, and C6 alcohol concentrations, and the downward trend in ε-viniferin, anthocyanins, flavonols, terpenes, and norisoprenoids in M grapes were identified. In addition, several modules significantly correlated with the metabolic biomarkers through weighted correlation network analysis, and the potential key transcription factors regulating the above metabolites including VviGATA11, VviHSFA6B, and VviWRKY03 were also identified.ConclusionThis study provides a valuable overview of metabolic and transcriptomic responses of M grapes in semi-arid climates, which could facilitate understanding the complex regulatory network of metabolites in response to microclimate changes.

How do in vitro digestion and cell metabolism affect the biological activity and phenolic profile of grape juice and wine

Cabernet Sauvignon grape juice and wine underwent in vitro digestion, resulting in a reduction of most phenolic compounds (10%–100% decline), notably impacting anthocyanins (82%–100% decline) due to pH variations. However, specific phenolics, including p–hydroxybenzoic, protocatechuic, vanillic, p-coumaric, gallic and syringic acids, and coumarin esculetin, increased in concentration (10%–120%). Grape juice and wine samples showed comparable polyphenolic profile during all phases of digestion. Antioxidant activity persisted, and inhibition of angiotensin-I converting enzyme was improved after the digestion process, likely because of increased concentrations of listed phenolic acids and esculetin. Digested grape juice displayed comparable or superior bioactivity to red wine, indicating it as a promising source of accessible grape polyphenols for a broader audience. Nevertheless, Caco-2 cell model metabolization experiments revealed that only 3 of 42 analyzed compounds passed to the basolateral compartment, emphasizing the significant impact of digestion on polyphenol bioactivity, suggesting potential yet unmeasurable and overlooked implications for human health.

Comparative analysis of the composition of Bayan Shirey, Rkatsiteli and Cabernet Sauvignon grape varieties for production of brandy wine materials

Comparative analysis of the composition of Bayan Shirey, Rkatsiteli and Cabernet Sauvignon grape varieties for production of brandy wine materials