Chemical composition and antioxidant capacity in strawberry cultivars (Fragaria x ananassa Duch.) by FT-MIR spectroscopy and chemometrics

Figures & data

Figure 1. (a) 3D scatter plot of the ten strawberry cultivars at seven ripeness stages, letters and numbers are codes: letters indicate the name of the cultivar and the number the degree of ripeness. (b) Principal components loading plot. TSS: total soluble solids, TA: total acidity, RS: reducing sugars, pH, AAC: ascorbic acid content, TPC: total phenolic content, TFC: total flavonoids content, TAC: total anthocyanins content, TEAC-ABTS: trolox equivalent antioxidant capacity with ABTS assay, TEAC-DPPH: trolox equivalent antioxidant capacity with DPPH assay.

Figura 1. (a) Gráfica de dispersión 3D de las puntuaciones del análisis de componentes principales de los diez cultivares de fresa en siete etapas de madurez, letras y números son códigos: las letras indican el nombre del cultivar y el número el grado de madurez. (b) Gráfico de cargas del análisis de componentes principales. TSS: sólidos solubles totales, TA: acidez total, RS: azúcares reductores, pH, AAC: contenido de ácido ascórbico, TPC: contenido fenólico total, TFC: contenido total de flavonoides, TAC: contenido total de antocianinas, TEAC-ABTS: capacidad antioxidante equivalente de trolox con ensayo ABTS, TEAC-DPPH: capacidad antioxidante equivalente de trolox con ensayo DPPH.

Table 1. Pearson’s correlation for the chemical composition, bioactive compounds, and antioxidant capacity in ten strawberry cultivars at seven ripeness stages.

Tabla 1. Correlación de Pearson para la composición química, los compuestos bioactivos y la capacidad antioxidante en diez cultivares de fresa en siete etapas de madurez.

Parameter	r
TSS	0.6561
TA	−0.4478
RS	0.6777
pH	0.3644
AAC	−0.0759
TPC	−0.2297
TFC	−0.3438
TAC	0.9108
TEAC-ABTS	−0.1659
TEAC-DPPH	−0.3486

TSS: total soluble solids, TA: total acidity, RS: reducing sugars, pH, AAC: ascorbic acid content, TPC: total phenolic content, TFC: total flavonoids content, TAC: total anthocyanins content, TEAC-ABTS: trolox equivalent antioxidant capacity with ABTS assay, TEAC-DPPH: trolox equivalent antioxidant capacity with DPPH assay.

TSS: sólidos solubles totales, TA: acidez total, RS: azúcares reductores, pH, AAC: contenido de ácido ascórbico, TPC: contenido fenólico total, TFC: contenido total de flavonoides, TAC: contenido total de antocianinas, TEAC-ABTS: capacidad antioxidante equivalente de trolox con ensayo ABTS, TEAC-DPPH: capacidad antioxidante equivalente de trolox con ensayo DPPH.

Figure 2. FT-MIR spectra of the ten strawberry cultivars at seven ripeness stages.

Figura 2. Espectros FT-MIR de los diez cultivares de fresa en siete etapas de madurez.

Table 2. Calibration data of the chemometric models to predict the chemical composition, bioactive compounds, and antioxidant capacity in ten strawberry cultivars at seven ripeness stages.

Tabla 2. Datos de calibración de los modelos quimiométricos para predecir la composición química, los compuestos bioactivos y la capacidad antioxidante en diez cultivares de fresa en siete etapas de madurez.

		UV-Vis spectroscopy				Multivariate analysis
						Calibration (n = 168)			Validation (n = 42)
Algorithm	Parameter (units)	Range	Mean	SD^a	SE^b	Factors^c	Rc^2 d	SEC^e	Rv^2 ^f	SEP^g	MD^h	RR ^i	RE^j	% RD^k	RPD^l
PLS1	TSS (%)	5.59–10.73	8.18	0.22	0.13	11	0.999	0.03	0.9844	0.03	0.25–0.31	1.58–1.82	0.98–1.08	0.69–3.78	7.33
	TA (% of citric acid)	0.53–0.94	0.80	0.49	0.06	10	0.999	0.06	0.9646	0.07	0.15–0.34	1.38–1.79	1.08–1.63	1.11–4.92	7.01
	RS (% glucose)	1.10–2.89	2.06	0.54	0.14	11	0.999	0.06	0.9442	0.08	0.08–0.37	1.55–2.78	1.64–1.78	0.45–6.17	6.75
	pH	2.87–3.89	3.40	0.78	0.09	11	0.999	0.08	0.9152	0.09	0.13–0.31	1.45–1.79	1.31–1.89	0.31–5.77	8.66
	AAC (mgAA/100 g FW)	31.87–143.30	90.68	0.89	0.11	12	0.999	0.06	0.9992	0.07	0.11–0.33	1.58–1.92	0.91–0.99	0.61–3.34	12.71
	TPC (mg EqGA/100 g FW)	46.30–358.02	169.64	14.11	1.69	13	0.999	0.08	0.9995	1.07	0.15–0.37	1.55–2.51	0.38–1.12	0.98–8.17	13.18
	TFC (mg EqC/100 g FW)	1.35–5.56	3.17	0.59	0.07	12	0.999	0.04	0.9993	0.06	0.14–0.36	1.41–1.88	0.96–1.67	1.53–4.76	9.83
	TAC (mg EqC-3-glc/100 g FW)	0.04–30.33	10.38	6.87	0.82	11	0.999	0.77	0.9720	0.85	0.13–0.35	1.69–2.09	1.12–1.54	0.23–5.46	8.09
	TEAC-ABTS (µmoles EqT/100 g FW)	553.82–1729.57	1150.41	8.73	1.04	14	0.999	0.86	0.9993	0.92	0.16–0.36	1.84–2.31	1.36–1.61	4.73–6.75	9.48
	TEAC-DPPH (µmoles EqT/100 g FW)	345.11–1371.60	775.12	9.45	1.13	15	0.999	1.05	0.9999	1.05	0.17–0.38	1.46–2.49	1.08–1.34	0.95–3.89	9.01
PLS2	TSS					8	0.823	0.49	-	0.54	-	-	-	-
	TA					8	0.861	0.04		0.05
	RS					8	0.888	0.12		0.14
	pH					8	0.897	0.06		0.08
	AAC					4	0.677	21.14		22.11
	TPC					4	0.635	44.71		46.12
	TFC					7	0.824	3.72		3.98
	TAC					8	0.825	0.29		0.34
	TEAC-ABTS					8	0.843	151.20		187.41
	TEAC-DPPH					6	0.889	315.73		670.01
PCR	TSS					6	0.695	0.63	-	0.71	-	-	-	-
	TA					11	0.921	0.04		0.05
	RS					9	0.770	0.18		0.21
	pH					10	0.929	0.05		0.06
	AAC					13	0.849	16.76		21.44
	TPC					8	0.700	43.08		50.71
	TFC					5	0.637	5.15		5.75
	TAC					1	0.108	0.61		0.63
	TEAC-ABTS					4	0.666	207.51		223.61
	TEAC-DPPH					12	0.971	175.92		516.63

TSS: total soluble solids, TA: total acidity, RS: reducing sugars, pH, AAC: ascorbic acid content, TPC: total phenolic content, TFC: total flavonoids content, TAC: total anthocyanins content, TEAC-ABTS: trolox equivalent antioxidant capacity with ABTS assay, TEAC-DPPH: trolox equivalent antioxidant capacity with DPPH assay. ^aSD: Standard deviation; ^bSE: Standard error; ^cFactors (PLS) or principal components (PCR); ^dRc²: determination coefficient in calibration, it must be as close as possible to 1; ^eSEC: standard error of calibration, must be as low as possible; ^fRv²: determination coefficient in validation, must be as close to 1 as possible; ^gSEP: standard error of prediction, must be as low as possible; ^hMD: Mahalanobis distance, must be lower than 1; ⁱRR: residuals relation, must be lower than 3; ^jRE: residual error, must be as low as possible; ^k% RD: relative difference, must be lower than 10%; ^lRPD: residual predicted deviation (SD/SEP), must be as high as possible.

TSS: sólidos solubles totales, TA: acidez total, RS: azúcares reductores, pH, AAC: contenido de ácido ascórbico, TPC: contenido fenólico total, TFC: contenido total de flavonoides, TAC: contenido total de antocianinas, TEAC-ABTS: capacidad antioxidante equivalente de trolox con ensayo ABTS, TEAC-DPPH: capacidad antioxidante equivalente de trolox con ensayo DPPH. ^aSD: desviación estándar; ^bFactores (PLS) o componentes principales (PCR); ^cRc²: coeficiente de determinación en la calibración, debe ser lo más cercano a 1; ^dSEC: error estándar de calibración, debe ser lo más bajo posible; ^eRv²: coeficiente de determinación en la validación, debe ser lo más cercano a 1; ^fSEP: error estándar de predicción, debe ser lo más bajo posible; ^gMD: distancia de Mahalanobis, debe ser inferior a 1; ^hRR: relación de residuos, debe ser inferior a 3; ⁱRE: error residual, debe ser lo más bajo posible; ^j% RD: diferencia relativa, debe ser inferior al 10%; ^kRPD: desviación residual predicha (SD/SEP), debe ser lo más alta posible.

Figure 3. 3D projection of the classes obtained with the SIMCA model.

Figura 3. Proyección 3D de las clases obtenidas con el modelo SIMCA.

Table 3. Interclass distance of the different classes derived from the SIMCA model.

Tabla 3. Distancia interclases de las clases derivadas del modelo SIMCA.

	Albión	Camino real	Celin	Dulce Ana	Dorado	Festival	Fortuna	Osceola	San Andreas	Spartan
Albión	0	59.20	26.50	86.40	92.30	50.20	60.40	56.30	16.30	42.60
Camino real		0	58.70	32.00	70.90	55.70	23.50	49.60	50.10	41.80
Celin			0	84.50	86.10	34.40	68.10	60.80	31.80	50.80
Dulce Ana				0	65.50	72.10	19.30	48.60	70.70	59.10
Dorado					0	68.30	55.80	43.40	87.00	80.70
Festival						0	62.70	55.40	49.00	59.60
Fortuna							0	41.60	51.50	38.50
Osceola								0	52.40	41.40
San Andreas									0	31.60
Spartan										0

Interclass distance must be as high as possible, minimum of 3.

Distancia interclase debe lo más alta possible, mínimo de 3.

Table 4. External validation data from the SIMCA model.

Tabla 4. Datos de validación externa del modelo SIMCA.

Specified material^a	Identified material^b	Result^c	Total distance^d	Residual distance^e
Albión	Albión	Identified	0.52–0.74	1.63–1.87
Camino real	Camino real	Identified	0.07–0.11	0.75–0.97
Celin	Celin	Identified	0.17–0.64	0.55–1.01
Dulce Ana	Dulce Ana	Identified	0.21–0.68	0.65–1.25
Dorado	Dorado	Identified	0.37–0.51	0.75–0.99
Festival	Festival	Identified	0.23–0.79	0.63–1.01
Fortuna	Fortuna	Identified	0.16–0.82	0.34–0.99
Osceola	Osceola	Identified	0.24–0.76	0.57–1.23
San Andreas	San Andreas	Identified	0.54–0.87	1.27–1.57
Spartan	Spartan	Identified	0.74–0.85	1.33–1.48

^aMaterial specified during validation; ^bMaterial identified by the SIMCA model; ^cResult indicates whether the sample was identified or rejected (does not pertain to the model); ^dTotal distance indicates whether the sample was correctly classified (must be lower than 1); ^eResidual distance high indicates that the sample contains a variation source not found previously, it must be lower than 3.

^aMaterial especificado durante la validación; ^bMaterial identificado por el modelo SIMCA; ^cEl resultado indica si la muestra fue identificada o rechazada (no pertenece al modelo); ^dLa distancia total indica si la muestra se clasificó correctamente (debe ser inferior a 1); ^eLa distancia residual alta indica que la muestra contiene una fuente de variación no encontrada anteriormente, debe ser inferior a 3.

Data availability statement

The data used to support the findings of this study are included within the article.