Color Parameters to Predict Moisture and Tannin Content in Yerba Mate Process

Frizon, Catia Nara Tobaldini; Nisgoski, Silvana

doi:10.1590/2179-8087.009818

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ORIGINAL ARTICLE, Wood Science and Technology • Floresta Ambient. 27 (2) • 2020 • https://doi.org/10.1590/2179-8087.009818 copy

Color Parameters to Predict Moisture and Tannin Content in Yerba Mate Process

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

This study evaluated color and reflectance spectra during industrial process of yerba mate leaves and tested the potential of these parameters to predict moisture and tannin content, to be applied as an auxiliary tool in quality control in industry. Two groups of yerba mate samples were evaluated: one grown under organic and another under conventional conditions. The results indicate an increase in lightness, loss of the green color, although less marked in the organic samples, an increase of yellow in both types of samples along processing due to moisture removal at high temperatures. For moisture content, reflectance curve can be applied with R² ≥ 0.9, and for tannin content the sum of b* parameter and spectra in region 590-700 nm are recommended. Color parameters and reflectance spectra can be applied for a preliminary evaluation of moisture and tannin content in the yerba mate industry, contributing for the quality control of samples.

Keywords:
Ilex paraguariensis; industrial processing; leaves characteristics and prediction

Processing stage	Conventional yerba mate			Organic yerba mate
Processing stage	L*	a*	b*	L*	a*	b*
Green leaves	30.97 ± 2.80^a	−4.48 ± 1.16^c	7.92 ± 2.05^a	32.94 ± 2.24^a	−8.50 ± 0.69^a	15.07 ± 2.55^a
Bleaching	39.64 ± 3.75^b	−6.04 ± 1.31^a	19.52 ± 2.93^c	47.82 ± 2.61^d	−7.96 ± 0.66^a	22.34 ± 2.44^c
Pre-drying	38.97 ± 2.59^b	−5.45 ± 0.83^b	17.87 ± 1.87^b	48.84 ± 2.29^e	−5.30 ± 1.13^c	31.59 ± 3.77^e
Drying	41.04 ± 2.60^c	−6.08 ± 0.81^a	20.96 ± 3.13^d	44.90 ± 0.89^c	−7.17 ± 0.22^b	26.57 ± 0.84^d
Crumbling	41.21 ± 1.42^c	−3.49 ± 0.65^d	19.09 ± 1.13^b	39.59 ± 2.37^b	−3.92 ± 1.74^d	18.13 ± 1.51^b
Natural Storage	45.76 ± 1.71^e	0.12 ± 0.47^e	21.06 ± 1.20^d	47.40 ± 0.87^d	−2.03 ± 0.19^e	21.38 ± 0.42^c
Forced Storage	44.13 ± 1.80^d	0.59 ± 0.54^e	20.15 ± 1.11^c	NR	NR	NR

Processing stage	Conventional yerba mate		Organic yerba mate
Processing stage	Moisture Content (%)	Standard deviation	Moisture Content (%)	Standard deviation
Green leaves	60.62	1.7	65.27	2.0
Bleaching	6.39	0.6	7.96	0.2
Pre-drying	7.11	0.5	8.15	0.8
Drying	6.08	0.1	7.89	0.6
Crumbling	7.06	0.3	6.45	0.5
Natural Storage	5.94	0.3	5.05	0.8
Forced Storage	5.21	0.4	Not applicable

Data	Number of PCs	Calibration			Validation
Data	Number of PCs	Correlation	R²	RMSEC	Correlation	R²	RMSEP
Spectra
Raw	7	0.95	0.90	6.56	0.89	0.79	9.69
1^st der.	7	0.96	0.93	5.43	0.94	0.89	6.74
2^nd der.	7	0.97	0.95	4.58	0.95	0.91	6.17
Lab*
Raw	2	0.78	0.61	12.71	0.75	0.58	13.49
Spectra + Lab*
Raw	6	0.97	0.95	4.68	0.95	0.91	6.14
1^st der.	7	0.97	0.95	4.69	0.96	0.91	5.96
2^nd der.	7	0.96	0.93	5.44	0.95	0.90	6.56

Processing stage	Conventional yerba mate		Organic yerba mate
Processing stage	Tannin Content (mg g^-1)	Standard deviation	Tannin Content (mg g^-1)	Standard deviation
Green leaves	5.58	1.1	3.85	0.4
Bleaching	23.46	2.0	9.67	2.2
Pre-drying	32.04	1.8	15.86	1.6
Drying	29.43	3.5	14.71	0.7
Crumbling	22.13	3.7	22.53	0.3
Natural Storage	22.54	3.2	19.57	2.5
Force d Storage	18.52	1.4	Not applicable

Data	PC number	Calibration			Validation
Data	PC number	Correlation	R²	RMSEC	Correlation	R²	RMSEP
Spectra
Raw	5	0.71	0.50	5.90	0.60	0.39	6.71
1^st der.	7	0.83	0.69	4.65	0.71	0.51	5.99
2^nd der.	7	0.85	0.72	4.43	0.75	0.59	5.57
Lab*
Raw	2	0.36	0.13	7.78	0.23	0.04	8.18
Spectra + Lab*
Raw	7	0.87	0.76	4.10	0.78	0.62	5.22
1^st der.	7	0.86	0.73	4.31	0.75	0.58	5.59
2^nd der.	7	0.80	0.64	4.99	0.70	0.49	6.05
Spectra (590-700 nm) + b*
Raw	7	0.68	0.90	6.10	0.55	0.86	7.31
1^st der.	7	0.80	0.93	5.08	0.75	0.92	5.63
2^nd der.	6	0.80	0.93	5.01	0.76	0.92	5.57

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