Industrial Crops and Products 74 (2015) 784?791
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Industrial Crops and Products jo u r n al homep age: www.elsev ier .com/ locate / indcrop
Diffuse spe simulta an contain
Maria Ky seri
Department of 5 Athe a r t i c l
Received 28 Ja
Received in re
Accepted 4 Jun
Total phenolic content
Diffuse reflectance Fourier transform spectroscopy
Partial least sq n con spect onve nd de termi of calibration (RMSEC) 4.03, and the root-mean-square error of prediction (RMSEP) 6.49. For the condensed tannin content, the 2nd derivative of the spectral regions 1670?950 (R2 = 0.99; RMSEC = 7.01;
RMSEP = 10.13) and 3750?2125 cm?1 (R2 = 0.99; RMSEC = 2.65; RMSEP = 3.97) was correlated with the concentration estimated by means of methylcellulose and bovine serum albumin assays, respectively.
The proposed method in comparison with the conventional methods is simpler, less time consuming, more economical, and requires reduced quantities of chemical reagents and less sample processing prior 1. Introdu
Phenolic groups for located in g lization of due to thei
Under norm extracted, h seeds play a
Grape se are present tannins) co (?)-epicate (Souquet et the endosp
Singleton, 1 ? Correspon
E-mail add http://dx.doi.o 0926-6690/? uares to analysis. This might by a valuable tool for wine industry where the quantification of grape tannins in a large number of samples remains a priority. ? 2015 Elsevier B.V. All rights reserved. ction compounds represent one of the most important red wine as they affect directly wine quality. They are rape skins and seeds and are responsible for the stabithe color and the sensory characteristics of the wines r astringent and bitter properties (Sun et al., 2013). al winemaking practices, skin phenols are more readily owever as maceration increases (as with red wines) the n increasingly important role. eds are a rich source of flavan-3-ols. These structures as monomers, oligomers, and polymers (condensed mposed of flavan-3-ols subunits such as (+)-catechin, chin, (?)-epigallocatechin, and (?) epicatechin gallate al., 1996). They are located in the outer seed coat while erm contains little polymeric material (Thorngate and 994). ding author. Fax: +30 210 5294719. ress: email@example.com (S. Kallithraka).
The term tannin defines a very heterogeneous group of compounds that are identified by their function to complex with and precipitate proteins. It is precisely this capacity to precipitate proteins, in particular the salivary proteins in the oral cavity, which is believed to give them as astringent character easily recognized in red wines (Gawel, 1997).
Although, wine tannins are essential for astringency and bitterness (Gawel, 1997) there is lack of an efficient and reliable method for their quantification since the results depend on the analytical method employed and on sample composition.
The most widely adopted methods for tannin measurement are based on precipitation of these molecules by adding proteins (Hagerman and Butler, 1981; Harbertson et al., 2003). Bovine serum albumin (BSA) has been used as a precipitant to tannin solutions. In general, all protein precipitation assays are dependent on many variables including pH, isoelectric point, ionic strength, protein structure, and temperature. In addition to protein precipitation methods, there exist colorimetric assays based on reaction of tannins with a chemical to yield a colored complex, which can be measured spectrophotometrically (Somers and Evans, 1977;
Hagerman and Butler, 1994). rg/10.1016/j.indcrop.2015.06.016 2015 Elsevier B.V. All rights reserved. reflectance Fourier transform infrared neous quantification of total phenolics ed in grape seeds raleou, Christos Pappas, Eleni Voskidi, Yorgos Kot
Tarantilis, Stamatina Kallithraka ?
Food Science & Human Nutrition, Agricultural University of Athens, 75 Iera Odos, 1185 e i n f o nuary 2015 vised form 28 May 2015 e 2015 a b s t r a c t
Total phenolic and condensed tanni diffuse reflectance Fourier transform pared with those obtained using the c samples after freeze drying. The seco total phenolic determination. The dectroscopy for d condensed tannins dis, Marianthi Basalekou, ns, Greece tents of grape seeds were simultaneously quantified using roscopy and partial least squares (PLS). The results were comntional methods. Infrared spectra were recorder in solid state rivative of the 1560?1177 cm?1 spectral region was used for nation coefficient (R2) was 0.97, the root-mean-square error
M. Kyraleou et al. / Industrial Crops and Products 74 (2015) 784?791 785
However, these analyses are both time consuming and expensive. Therefore, cheap, rapid, and efficient methods to quantify grape and wine tannins remain a priority for wine research and industry.
Fourier have alread some of the phenols or s
Santos, 200 the signals the extracti plex data. P used model recently co ing the infra 2014; Talpu
Regardin tannins, the to the qua and Agosin (Cozzolino a suitable m in raw mate
Diffuse (DRIFTS) ha in food prod major adva a large sam representat
The obje ability of DR more econo in the prese nological im phenolic co ing to the c were correl 2. Materia 2.1. Plant m
To take i building the varieties (V harvested d different p islands-San
To ensur tive vines an were harve indices of su 2.2. Extract
Seeds of they were powder.
The extr viously rep obtained po tone/water methanol/w were combi remove org 2.3. Total phenolic content
A part of the crude extracts was re-dissolved in a model solution (12% ethanol; 5 g/L tartaric acid; pH 3.5 adjusted with NaOH otal in?C ed (A be, 0 ?Cio 0.15 e mix re in a Ray e tot n cu wer asure lues ?refe nnin rem c acid ntent t (TC
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