Non-destructive method to predict Barhi dates quality at different stages of maturity utilising near-infrared (NIR) spectroscopy

Figures & data

Table 1. Physical properties of fresh Barhi dates.

Property	N	Minimum	Maximum	Mean	Standard Error
Mass (g)	135	8.18	12.16	10.17	0.25
Volume (cm^3)		8.52	11.52	10.12	0.20
Density (g cm^−3)		0.96	1.05	1.01	0.02
Length (mm)		30.12	36.79	33.46	0.26
Diameter (mm)		23.12	26.81	24.97	0.24
Surface Area (cm^2)		24.95	29.32	27.14	0.60

N: number of fruit samples.

Table 2. Maturity quality index for Barhi fruit at five stages of maturity**.

Stage #	Quality Index	TSS,%	b*	MC (wet basis),%
1	Green ‘ less than 80% Yellowish’	7–2^e	8–14^e	76–80^a
2	80% Yellowish	13–18^d	15–21^d	71–75^b
3	90% Yellowish	19–24^c	22–27^c	66–70^c
4	100% Yellowish	25–30^b	28–33^b	61–65^d
5	Rutab ‘more than 100%Yellowish’	31–36^a	34–39^a	56–60^e

TSS: total soluble solids, b*: CIE colour scale (the yellow/blue), and MC: moisture content

**Means of each column followed by the same letter are not significantly different at 95% confidence.

Figure 1. The mean second derivative of absorbance in wave length range (285-1200 nm) (A); absorbance for chlorophyll wave length range (660-690 nm) (B); and absorbance for water content wave length range (940-980 nm) (C) for each Barhi fruits stage of maturity.

Figure 2. The mean second derivative of absorbance in wave length range (285–1200 nm) (A); absorbance for chlorophyll wave length range (660–690 nm) (B); and absorbance for water content wave length range (940–980 nm) (C) for each Barhi fruits stage of maturity.

Table 3. PCR model for TSS, M.C, and b* in fresh Barhi dates.

			Calibration		Cross-validation
Property	Principle Components	Wave length range (nm)	R^2	RMSE	R^2	RMSE
TSS	12	285–981	0.99	0.69	0.97	1.00
b*	7	621–717	0.69	2.25	0.64	2.28
M.C.	11	732–972	0.97	1.26	0.94	1.90

TSS: total soluble solids, b*: CIE colour scale (the yellow/blue), and MC: moisture content (wet basis), R²: coefficient of determination, RMSE: Root Mean Square Error.

Table 4. Main statistical spectra for TSS, MC%, and b* in Barhi fruit samples.

Property	Items	Calibration	Validation	Prediction
TSS	No. of samples	996	996	100
	Range	7–35	9–32	10–34
	Mean value	21.22	21.29	22.31
	CV	3.52	2.60	2.81
M.C	No. of samples	1000	1000	100
	Range	56–79	60–78	52–80
	Mean value	67.5	69	66
	CV	3.80	2.95	3.08
b*	No. of samples	995	995	100
	Range	8–39	12.08–30.7	13.4–31.9
	Mean value	22.36	22.13	22.58
	CV	18.38	18.75	19.79

TSS: total soluble solids, b*: CIE colour scale (the yellow/blue), and MC: moisture content (wet basis), CV: coefficient of variation,

Figure 3. Predicted and measured values of TSS (A); b* (B); MC (C) models for Barhi fruit.