Non-destructive evaluation of the physiochemical properties of milk drink flavored with date syrup utilizing NIR Spectroscopy and ANN analysis

2. Materials, Methods, and Production

2.1. Materials

Two of the most common dates varieties (Sukkary and Khlass) produced in Saudi Arabia, were obtained from a local date market in Riyadh and stored at a temperature of 5 °C until the start of the experiments.

Full-fat milk (both cow and camel) that was pasteurized by a brand-name dairy company was bought from a local market in Riyadh region. Milk samples were delivered in cold containers to the Food Engineering Laboratory (FEL) and kept refrigerated for a maximum of two days until the start of the experiments.

2.2. Methods

Date syrup production

Date syrup was produced utilizing a lab-scale level at FEL. The major unit operations include the removal of date pits, mechanical mincing to produce date paste, and mixing and heating of the date paste with water (at a w/w ratio of 2.5:1 (paste: water (weight/weight)) to produce a homogenized date suspension [40,41]. This was followed by press filtration of the date suspension to produce clarified date juice (Seitz Lab Filter Press, Model A20z, K150, Germany). Dates juice was then concentrated under vacuum using a lab-scale rising film natural convection evaporator (QVF Teaching system, CTSY Evaporation, Climbing Film and Natural Circulation Evaporator, QVF, Germany) to produce high-quality date syrup. Dates syrup can be preserved for several months at room temperature since sugar content reaches 80%.

Preparation of milk drinks flavored with date syrup

At the start of experiments, 16 batches of milk flavored with dates syrup were prepared as shown in Figure 1. Four amounts of date syrup (5, 10, 15, and 20 gm) from two date cultivars (Sukkary and Khlass) were added to milk (95, 90, 85, and 80 gm, respectively for cow and camel) so the total milk drink batch would be 100 gm. The initial sensory evaluation revealed that four batches were favorable from the sixteen mixes as reported in details by Elamshity and Alhamdan [41,42]. The chemical and physical measurements were then performed on those four favorable mixtures which were 15% milk drink flavored with Sukkary date syrup, and 10% milk drink flavored with Khlass date syrup for both cow and camel milk.

The drink samples were then pasteurized in a water bath (Kenwood, KM070 Series, and the UK) at 75 °C for 5 min [41,43]. The samples were then cooled in an ice-water bath with a mixer (Cofrimell & Coldream 2 M, Italy) to 5 °C. It was thus ready to conduct physiochemical experiments as well as sensory assessment.

Physiochemical Evaluation

a)

Physical properties

The standard method for measuring the moisture content was conducted for the four Date syrup-flavored milk drinks [44]. A vacuum oven (Vacutherm model VT 6025, Heraeus Instrument, D-63450. Hannover, Germany) was used to dry samples at a temperature of 70 °C under a vacuum of 200 mmHg for 48 hrs. Aqua Lab instrument (Model Series 3, Decagon Devices, Inc. Pullman, Washington 99163, and the USA) was used to measure water activity at room temperature (25 °C). The total soluble solids (TSS) of samples were measured using a refractometer (ABBE 5, Bellingham & Stanley Ltd., Longfield Rd, TunbridgeWells TN2 3EY, UK). The pH values of the samples were measured using a pH meter (Jenway, model 3510, Bibby Scientific Ltd., Stone, Staffordshire, UK) with measuring accuracy ± 0.01. After each measurement, the electrode was standardized using a pH 7.0 buffer. The total soluble solids and refraction indices of the samples were estimated using a refractometer (ABBA 5 (code 44-501), Bellingham and Stanley Ltd (BS), Jena, Germany) at lab temperature (25 ° C).

Figure 1. Preparation of milk and Dibb's drinks.

Figure 1. Preparation of milk and Dibb's drinks.

The densities of the sample drinks were determined at different temperatures (from 5 to 80 °C) using a density meter (DMA4100M, Anton Paar GmbH, Graz, Austria).

The basic color coefficients (L*, a*, and b*) of the samples were estimated using a color instrument (Color 45/0, Hunter Associates Laboratory, Inc., VA, USA). L* indicates whiteness or brightness/darkness, a* indicates redness/greenness, b* indicates yellowness/blueness, and L₀*, a₀*, and b₀* are the corresponding values at zero time. Color derivatives of Chroma, Hue Angle, and Browning Index (BI) were calculated from basic color coefficients [45,46,47]:

$$Chroma={\left({a^{\ast }}^2+{b^{\ast }}^2\right)}^{0.5}$$

(1)

$$Hueangle={\tan }^{-1}\left(\frac{b^{*}}{a^{*}}\right)$$

(2)

$$BI=\frac{\left[100\left(x-0.31\right)\right]}{0.17}$$

(3)

Where:

$$x=\frac{\left(a^{\ast }+1.75L^{\ast }\right)}{\left(5.645L^{\ast }+a^{\ast }-3.012b^{\ast }\right)}$$

b)

Chemical analysis

Chemical analysis was performed for the fresh milk(cow and camel), date syrup (Khlass and Sukkary), and the four date syrup-flavored milk drinks. The chemical analysis was conducted according to the standards of the Association of Official Analytical Chemists [44].

c)

Sensory evaluation

Sensory evaluation was carried out in two steps. The first was to evaluate the best drinks formulated from date syrup (5 to 20%) of the two date cultivars (Sukkary and Khlass) and add cow’s milk and camel's milk as described and detailed by [41,42]. A nine-point structured hedonic scale [48,49,50,51,52,53,54] was used, with a score of 9 indicating “like extremely”, and 1 meaning “dislike extremely”. The sensory characteristics were taste, flavor, texture, color, and general acceptance of the product. Thirty judges (professors, employees, and students from the departments of Agricultural Engineering and Food Science and Nutrition, Food Science and Agriculture College, King Saud University.

Evaluation of physicall properties of milk drinks utilizing NIR

The non-destructive assessment of samples properties was conducted with near-infrared spectroscopy (NIR) by a handheld NIR meter (F-750, Firmware v.1.2.0 build 7041, Felix Instruments, Camas, WA, USA)."

The F-750 system was equipped with a Zeiss MMS1 VIS-NIR spectrometer operating in the range of 310–1100 nm at 3 nm intervals. Prior to sample physical properties measurements, optical readings were taken for all samples. The F-750 device featured a reference shutter, allowing for the calculation of dark current and ambient light effects with each measurement, particularly when scanning with the lamp off. For each sample, 300 hundred scans were recorded and averaged. During the validation phase, spectra were acquired for a distinct set of samples under the same conditions at 5°C.

Following spectrum capture, the data was transferred from the F-750 SD-Card to a computer for analysis. The stored data was imported and saved as a comma-separated values file (CSV file) using Data Viewer Software. Spectra underwent pre-processing via the Savitzky–Golay second derivative. Calibration models were then established using a dataset comprising 1200 samples, 840 spectra (training), 240 spectra (test), and 120 spectra (validate). Two analysis tools were employed for calibration model development: partial least squares regression (PLSR) and artificial neural network (ANN).

PLSR entailed examining the spectra as a linear multivariate relationship [55]. This method involved identifying latent variables (LVs) that elucidate the most significant variance in the data. LVs were discerned by exploring sub-spaces enhancing covariance between predictor and response variables [56].

In parallel, artificial neural networks (ANNs) were employed, providing a robust nonlinear pattern recognition approach capable of modeling intricate diversities, environmental factors, and instrument variations [57]. The estimated data was analyzed using App-Builder v2.1.7 software (Felix Instruments, Camas, WA, USA). Evaluation of prediction performance relied on calibration and validation results, assessed with correlation coefficient (R²), root mean square error in calibration (RMSEC), and cross-validation (RMSECV) [11]."

2.3. Statistical analysis

All quantifiable properties were subjected to analysis using a statistical software package (SAS software, Version 9.2, SAS Institute Inc., Cary, NC, USA) [58]. Experimental data were utilized for the analysis of variance (ANOVA). The least significant difference (LSD) was calculated at P ≤ 0.05. The prediction performance was assessed based on calibration and validation results utilizing AppBuilder v2.1.7 software (Felix Instruments, Camas, WA, USA). Graphs, plots, and other calculations were performed using the Microsoft Office 365 package (Microsoft, Redmond, WA, USA).

3. Results

The approach of this study was to produce date syrup and then adding it to formulate milk drinks flavored with the syrup. The milk drinks would be evaluated for two cultivars of syrup, two types of milk, and at different added concentrations. From the objective and subjective assessments of the selected milk drinks, NIR models would be developed.

All data of the physicochemical properties and sensory evaluation of the date syrup, fresh milk, and the four preferred milk drinks are presented in the following sections.

3.1. Physical properties (MC, aw, TSS, color, density, pH)

Dates syrup was successfully produced at the lab scale level. Basic physical properties (moisture content, water activity, total soluble solids, and pH) were experimentally measured for the date syrup, fresh milk, and preferred milk drinks flavored with date syrup are shown in Table 1. Though values appeared to be similar within each group, the variations are significantly different within date syrup, fresh milk, and milk drinks except for TSS of dates syrup. There are variations of the properties of the four date syrup-flavored milk drinks. The initial values of the fresh milk and date syrup have an apparent effect on the milk drinks properties. It can be noticed that fresh milk has a notable effect on milk drinks properties due to the high % of milk (85 to 90%) compared to that of syrup (10 to 15%). The experimental results for the four drinks are summarized in Table 1 for mean values and variance analysis.

Color

Table 2 shows mean values of the basic color parameters (L*, a*, b*) and their derivatives parameters (Chroma, Hue Angle, and BI). They were measured at room temperature (25 °C) for the date Syrup, fresh milk, and preferred milk drinks.

It can be seen from Table 2 that there are variations and significantly difference within date syrup, fresh milk, and milk drinks due to nature of milk, dates, in addition to storage and processing parameters. It is apparent that (L*) values are way higher for fresh milk (whiteness) compared to syrup (darkness). This shows the importance of (L*) parameter compared to (a*) and (b*) parameters for the samples examined in this study.

Mean values of the basic parameter (L*) of the milk drinks which range between zero for darkness and 100 for whiteness (brightness) varied from 85.133 to 88.667. This indicated the effect of date’s syrup (dark brown) on darkening the color of the milk drinks. The mean value of (a*) varied from −0.075 to 0.418 whereas the mean value of (b*) varied from 13.383 to 15.262.

Table 2. Mean values of the basic and derivatives color parameters for the date syrup, fresh milk, and four preferred milk/Date syrup drinks.

Product type	Basic color parameters			Derivative color parameters
	L*	a*	b*	Chroma	Hue angle	BI
Date syrup Sukkary	4.444b	1.673b	5.348b	5.604b	51.730b	339.689a
Date syrup Khlass	6.892a	2.231a	7.588a	7.910a	52.103a	277.498b
Cow Milk	95.795a	-2.113a	9.064a	9.307a	-53.303a	8.064a
Camel Milk	94.912b	-1.274b	5.627b	5.770b	-53.432b	4.978b
Cow’s milk + Sukkary (15%)	86.128c	0.038c	13.991c	13.991c	57.474a	17.346c
Cow’s milk + Khlass (10%)	88.667a	−0.075d	13.383d	13.383d	−57.426d	15.915d
Camel milk + Sukkary (15%)	85.133d	0.379b	15.262a	15.267a	57.104b	19.630a
Camel milk + Khlass (10%)	87.873b	0.418a	14.444b	14.450b	57.034c	17.895b

* The similar letter in each column indicates that the average values are not significantly different at P<0.05.

Table 2. Mean values of the basic and derivatives color parameters for the date syrup, fresh milk, and four preferred milk/Date syrup drinks.

Product type	Basic color parameters			Derivative color parameters
	L*	a*	b*	Chroma	Hue angle	BI
Date syrup Sukkary	4.444b	1.673b	5.348b	5.604b	51.730b	339.689a
Date syrup Khlass	6.892a	2.231a	7.588a	7.910a	52.103a	277.498b
Cow Milk	95.795a	-2.113a	9.064a	9.307a	-53.303a	8.064a
Camel Milk	94.912b	-1.274b	5.627b	5.770b	-53.432b	4.978b
Cow’s milk + Sukkary (15%)	86.128c	0.038c	13.991c	13.991c	57.474a	17.346c
Cow’s milk + Khlass (10%)	88.667a	−0.075d	13.383d	13.383d	−57.426d	15.915d
Camel milk + Sukkary (15%)	85.133d	0.379b	15.262a	15.267a	57.104b	19.630a
Camel milk + Khlass (10%)	87.873b	0.418a	14.444b	14.450b	57.034c	17.895b

* The similar letter in each column indicates that the average values are not significantly different at P<0.05.

Density

Densities for date syrup, fresh milk, milk drinks samples were measured at a temperature range from 5 to 80 °C shown in Table 3. It is interesting to note that all samples' densities were higher than 1.00 except that of camel milk at 80 °C. Density values for all samples decreased with the increase of temperature.

Mean values of density values for the four milk drinks within a temperature range of 5 to 80 °C are shown in Figure 2. It is apparent that density values for all four samples decreased with temperature increase. Over the experimental temperature range, average density values ranged from 1.030 to 1.079 g/cm³ (Table 3.).

Densities of each sample of fresh milk, syrup, and milk drink were correlated linearly well with temperature (R²: 0.970 to 0.988) as shown in Table 4.

Table 3. Mean values of density (g/cm³) of the date syrup (for the two cultivars) at different temperatures (between 5 and 80 °C), fresh milk (for the two types), and four preferred milk/Date syrup drinks.*.

Temperature, °C	5	10	25	40	60	80
Date syrup Sukkary	1.373b	1.370b	1.364b	1.356a	1.346a	1.332a
Date syrup Khlass	1.378a	1.376a	1.367a	1.359a	1.345a	1.330a
Cow Milk	1.034a	1.033a	1.029a	1.023a	1.013a	1.010a
Camel Milk	1.033a	1.032a	1.028a	1.022a	1.012a	1.000a
Cow’s milk + Sukkary (15%)	1.077b	1.076b	1.070b	1.064b	1.054b	1.041a
Cow’s milk + Khlass (10%)	1.063d	1.062d	1.057d	1.051d	1.041d	1.031c
Camel milk + Sukkary (15%)	1.079a	1.078a	1.074a	1.067a	1.057a	1.041a
Camel milk + Khlass (10%)	1.068c	1.068c	1.063c	1.056c	1.046c	1.032c

* Similar letters in each column within a group indicates that the average values are not significantly different at P<0.05.

Table 3. Mean values of density (g/cm³) of the date syrup (for the two cultivars) at different temperatures (between 5 and 80 °C), fresh milk (for the two types), and four preferred milk/Date syrup drinks.*.

Temperature, °C	5	10	25	40	60	80
Date syrup Sukkary	1.373b	1.370b	1.364b	1.356a	1.346a	1.332a
Date syrup Khlass	1.378a	1.376a	1.367a	1.359a	1.345a	1.330a
Cow Milk	1.034a	1.033a	1.029a	1.023a	1.013a	1.010a
Camel Milk	1.033a	1.032a	1.028a	1.022a	1.012a	1.000a
Cow’s milk + Sukkary (15%)	1.077b	1.076b	1.070b	1.064b	1.054b	1.041a
Cow’s milk + Khlass (10%)	1.063d	1.062d	1.057d	1.051d	1.041d	1.031c
Camel milk + Sukkary (15%)	1.079a	1.078a	1.074a	1.067a	1.057a	1.041a
Camel milk + Khlass (10%)	1.068c	1.068c	1.063c	1.056c	1.046c	1.032c

* Similar letters in each column within a group indicates that the average values are not significantly different at P<0.05.

Figure 2. Density values for the four milk drinks at different temperatures.

Figure 2. Density values for the four milk drinks at different temperatures.

Table 4. Linear density prediction equations and their constants and correlation coefficients for the date syrup, fresh milk, and four milk drinks valid for temperature range of 5 to 80 °C.

Product type	$\mathit{\rho }$ = a T + b		R2
	a	b
Date syrup Sukkary	-0.0005	1.376	0.992
Date syrup Khlass	-0.0006	1.383	0.995
Cow Milk	-0.0004	1.038	0.978
Camel Milk	-0.0004	1.037	0.972
Cow’s milk + Sukkary (15%)	−0.0005	1.081	0.988
Cow’s milk + Khlass (10%)	−0.0004	1.067	0.985
Camel milk + Sukkary (15%)	−0.0005	1.084	0.970
Camel milk + Khlass (10%)	−0.0005	1.072	0.975

Table 4. Linear density prediction equations and their constants and correlation coefficients for the date syrup, fresh milk, and four milk drinks valid for temperature range of 5 to 80 °C.

Product type	$\mathit{\rho }$ = a T + b		R2
	a	b
Date syrup Sukkary	-0.0005	1.376	0.992
Date syrup Khlass	-0.0006	1.383	0.995
Cow Milk	-0.0004	1.038	0.978
Camel Milk	-0.0004	1.037	0.972
Cow’s milk + Sukkary (15%)	−0.0005	1.081	0.988
Cow’s milk + Khlass (10%)	−0.0004	1.067	0.985
Camel milk + Sukkary (15%)	−0.0005	1.084	0.970
Camel milk + Khlass (10%)	−0.0005	1.072	0.975

3.2. Sensory evaluation of all samples of milk drinks flavored with date syrup

The sensory evaluations of the milk drinks were conducted by sixty participants, using a nine-point structured hedonic scale for taste, flavor, texture, color, and overall acceptability. The tests were conducted for cow's and camel milk flavored with date syrup (Sukkary and Khlass cultivars) at different concentrations. Summary of the sensory evaluation results for the four milk drinks are illustrated in Figure 3.

3.3. Chemical analysis of fruits, milk, syrup, and milk drinks

The analysis data for the chemical composition of the fruit flesh of dates (Sukkary and Khlass) is shown in Table 5. Probably, the most noticeable observation in comparing dates of the two cultivars is Phosphorus content in which Sukkary is double that of Khlass. The second note is the % of sugars (7.8, 8.9, 63.4 gm/100gm dm) for Sukkary to (42.3, 54.5, 0.3) for Khlass of (Glucose, Fructose, and Sucrose) sugars; respectively.

Table 6 shows the chemical composition of the fresh milk, date syrup, and the four milk drinks. There were significant differences between the average experimental values of the chemical components of the four date syrup-flavored milk drinks. Vitamin (A) was in the range of 37.13 to 556.5 IU/100g and 10.00 IU/100g for vitamin D. Total energy varied between 78.50 to 99.00 kcal/100g. Concentrations of the most important metals ranged between 867 to 1002 ppm for calcium, 106 to 142 ppm for magnesium, 289 to 372 ppm for sodium, and 1702 to 2242 ppm for potassium.

Table 5. Chemical composition of dates fruits (flesh) for Sukkary and Khlass cultivars (Tamr stage of maturity)*.

Chemical Component	Sukkary	Khlass	Method/Ref.
Moisture	31.11±0.51c	15.21±0.71a	AOAC 2005-925.45
Units: (g/100g dm)** Crude Protein	3.37 ±0.05c	2.35±0.13b	AOAC 2005-920.152
Total Fat	0.14 ±0.01a	0.13±0.04a	AOAC 2005-989.05
Crude Fiber	4.13 ±0.23b	3.97±0.31b	AOAC 2005-962.09
Ash	1.65 ±0.18a	1.80±0.10a	AOAC 2005-930.30
Total Carbohydrate	90.70 ±0.36a	92.13±0.50b	CALCULATION
Total Sugars	79.83 ±1.46a	88.27±1.95b	AOAC 2005-977.20
Fructose	7.52 ±0.16a	42.36±0.16b	AOAC 2005-977.20
Glucose	8.90 ±0.59a	45.55±0.93c	AOAC 2005-977.20
Sucrose	63.40 ±0.75c	0.36±0.11a	AOAC 2005-977.20
Units: (kcal/100g)
Total energy	377.59 ±1.70a	379.11±2.55ab	CALCULATION
Units: (mg/100g dm)
Calcium	67.40 ±6.83c	52.38±11.28ab	AOAC 2005-985.35
Phosphorus	90.91 ±13.28b	54.15±1.40a	AOAC 2005-985.35
Sodium	9.27 ±2.71a	12.03±4.00a	AOAC 2005-985.35
Potassium	687.21±32.69a	682.58±55.85a	AOAC 2005-985.35
Magnesium	77.88±3.89b	60.35±1.96a	AOAC 2005-985.35
Iron	1.35 ±0.02a	1.27±0.03a	AOAC 2005-985.35
Total soluble solids (Brix)	76.23 ±0.55a	88.17±0.06c	AOAC 2005-983.17
pH- 10% @	7.70 ±0.03c	6.31±0.15a	AOAC 2005-981.12
Acidity as Citric Acid (mg/100g dm)	0.27 ±0.09a	0.34±0.04a	AOAC 2005-942.15

*The same letter in a row in same group means no significant differences at p<0.05.; **dm- dry matter.

Table 5. Chemical composition of dates fruits (flesh) for Sukkary and Khlass cultivars (Tamr stage of maturity)*.

Chemical Component	Sukkary	Khlass	Method/Ref.
Moisture	31.11±0.51c	15.21±0.71a	AOAC 2005-925.45
Units: (g/100g dm)** Crude Protein	3.37 ±0.05c	2.35±0.13b	AOAC 2005-920.152
Total Fat	0.14 ±0.01a	0.13±0.04a	AOAC 2005-989.05
Crude Fiber	4.13 ±0.23b	3.97±0.31b	AOAC 2005-962.09
Ash	1.65 ±0.18a	1.80±0.10a	AOAC 2005-930.30
Total Carbohydrate	90.70 ±0.36a	92.13±0.50b	CALCULATION
Total Sugars	79.83 ±1.46a	88.27±1.95b	AOAC 2005-977.20
Fructose	7.52 ±0.16a	42.36±0.16b	AOAC 2005-977.20
Glucose	8.90 ±0.59a	45.55±0.93c	AOAC 2005-977.20
Sucrose	63.40 ±0.75c	0.36±0.11a	AOAC 2005-977.20
Units: (kcal/100g)
Total energy	377.59 ±1.70a	379.11±2.55ab	CALCULATION
Units: (mg/100g dm)
Calcium	67.40 ±6.83c	52.38±11.28ab	AOAC 2005-985.35
Phosphorus	90.91 ±13.28b	54.15±1.40a	AOAC 2005-985.35
Sodium	9.27 ±2.71a	12.03±4.00a	AOAC 2005-985.35
Potassium	687.21±32.69a	682.58±55.85a	AOAC 2005-985.35
Magnesium	77.88±3.89b	60.35±1.96a	AOAC 2005-985.35
Iron	1.35 ±0.02a	1.27±0.03a	AOAC 2005-985.35
Total soluble solids (Brix)	76.23 ±0.55a	88.17±0.06c	AOAC 2005-983.17
pH- 10% @	7.70 ±0.03c	6.31±0.15a	AOAC 2005-981.12
Acidity as Citric Acid (mg/100g dm)	0.27 ±0.09a	0.34±0.04a	AOAC 2005-942.15

*The same letter in a row in same group means no significant differences at p<0.05.; **dm- dry matter.

Table 6. Mean values of the chemical components of the fresh milk, date syrup, and the four milk/Date syrup drinks.

Chemical components	Fresh Milk		Date syrup		Milk Drinks				Unit	Method/Ref.
	Cow	Camel	Sukkary	Khlass	Cow milk + Sukkary15%	Cow milk +Khlass10%	Camel milk +Sukkary15%	Camel milk +Khlass10%
Total Carbohydrate	15.6b	15.71a	75.76a	75.05b	15.95b	12.61d	16.09a	12.62c	(g/100g)	Calculation
Total Sugar	4.72b	4.83a	53.83a	53.05b	15.01	12.48	15.67	12.38	(g/100g)	AOAC 2005-977.20
Fructose	0.000	0.000	13.08a	26.54b	2.6d	3.95a	2.66c	3.65b	(g/100g)	AOAC 2005-977.20
Glucose	0.000	0.000	8.09b	26.51a	1.84d	4.18a	2.09c	4.07b	(g/100g)	AOAC 2005-977.20
Sucrose	0.000	0.000	29.09a	0.10b	5.91a	0.1c	5.84b	0.1c	(g/100g)	AOAC 2005-977.20
Maltose	0.000	0.000	3.57a	0.10b	1.26b	0.45d	1.41a	0.54c	(g/100g)	AOAC 2005-977.20
Lactose	4.72b	4.83a	0.000	0.000	3.40d	3.80 b	3.67 c	4.02 a	(g/100g)	AOAC 2005-977.20
Proteins	3.06b	3.10a	1.47a	0.88b	2.90c	2.92b	2.88d	2.93a	(g/100g)	FOSS-AN-300
Caseins	2.45a	2.25b	0.10a	0.10a	2.15b	2.30 a	1.87 d	2.03 c	(g/100g)	AOAC 2005-998.06
Crude Fiber	0.10a	0.10a	0.10a	0.10a	0.1	0.1	0.1	0.1	(g/100g)	AOAC 2005-962.09
Fat	2.95a	2.86b	0.10a	0.10a	2.64b	2.78a	1.75d	1.81c	(g/100g)	AOAC 2005-989.05
Ash	0.69b	0.82a	1.42a	1.49a	0.71c	0.60d	0.86a	0.83b	(g/100g)	AOAC 2005-930.30
Calcium	938b	1125a	494a	424b	867d	885c	965b	1002a	ppm	AOAC 2005-985.35
Magnesium	99a	78b	427a	420a	142a	123b	123b	106c	ppm	AOAC 2005-985.35
Sodium	293b	383a	212a	164b	297c	289d	357b	372a	ppm	AOAC 2005-985.35
Potassium	1382b	1827a	0.53a	0.54a	1967c	1702d	2242a	2082b	ppm	AOAC 2005-985.35
Standard acidity (Lactic acid)	0.08a	0.08a	1a	1a	0.26a	0.21c	0.22b	0.21c	(g/100g)	AOAC 2005-935.57
Vitamin A	56.8b	70.30a	1a	1a	430.44b	556.50a	43.17c	37.13d	IU/100 g	HPLC-LUNN
Vitamin D	45.4a	19.44b	10a	10a	10a	10a	10a	10a	IU/100 g	HPLC-LUNN
Total energy	58a	58a	309a	304b	99a	87c	91.63b	78.50d	kcal/100g	Calculation

*The same letter in a row means no significant differences based on the least square difference (LSD) test and a significance level at p<0.05.

Table 6. Mean values of the chemical components of the fresh milk, date syrup, and the four milk/Date syrup drinks.

Chemical components	Fresh Milk		Date syrup		Milk Drinks				Unit	Method/Ref.
	Cow	Camel	Sukkary	Khlass	Cow milk + Sukkary15%	Cow milk +Khlass10%	Camel milk +Sukkary15%	Camel milk +Khlass10%
Total Carbohydrate	15.6b	15.71a	75.76a	75.05b	15.95b	12.61d	16.09a	12.62c	(g/100g)	Calculation
Total Sugar	4.72b	4.83a	53.83a	53.05b	15.01	12.48	15.67	12.38	(g/100g)	AOAC 2005-977.20
Fructose	0.000	0.000	13.08a	26.54b	2.6d	3.95a	2.66c	3.65b	(g/100g)	AOAC 2005-977.20
Glucose	0.000	0.000	8.09b	26.51a	1.84d	4.18a	2.09c	4.07b	(g/100g)	AOAC 2005-977.20
Sucrose	0.000	0.000	29.09a	0.10b	5.91a	0.1c	5.84b	0.1c	(g/100g)	AOAC 2005-977.20
Maltose	0.000	0.000	3.57a	0.10b	1.26b	0.45d	1.41a	0.54c	(g/100g)	AOAC 2005-977.20
Lactose	4.72b	4.83a	0.000	0.000	3.40d	3.80 b	3.67 c	4.02 a	(g/100g)	AOAC 2005-977.20
Proteins	3.06b	3.10a	1.47a	0.88b	2.90c	2.92b	2.88d	2.93a	(g/100g)	FOSS-AN-300
Caseins	2.45a	2.25b	0.10a	0.10a	2.15b	2.30 a	1.87 d	2.03 c	(g/100g)	AOAC 2005-998.06
Crude Fiber	0.10a	0.10a	0.10a	0.10a	0.1	0.1	0.1	0.1	(g/100g)	AOAC 2005-962.09
Fat	2.95a	2.86b	0.10a	0.10a	2.64b	2.78a	1.75d	1.81c	(g/100g)	AOAC 2005-989.05
Ash	0.69b	0.82a	1.42a	1.49a	0.71c	0.60d	0.86a	0.83b	(g/100g)	AOAC 2005-930.30
Calcium	938b	1125a	494a	424b	867d	885c	965b	1002a	ppm	AOAC 2005-985.35
Magnesium	99a	78b	427a	420a	142a	123b	123b	106c	ppm	AOAC 2005-985.35
Sodium	293b	383a	212a	164b	297c	289d	357b	372a	ppm	AOAC 2005-985.35
Potassium	1382b	1827a	0.53a	0.54a	1967c	1702d	2242a	2082b	ppm	AOAC 2005-985.35
Standard acidity (Lactic acid)	0.08a	0.08a	1a	1a	0.26a	0.21c	0.22b	0.21c	(g/100g)	AOAC 2005-935.57
Vitamin A	56.8b	70.30a	1a	1a	430.44b	556.50a	43.17c	37.13d	IU/100 g	HPLC-LUNN
Vitamin D	45.4a	19.44b	10a	10a	10a	10a	10a	10a	IU/100 g	HPLC-LUNN
Total energy	58a	58a	309a	304b	99a	87c	91.63b	78.50d	kcal/100g	Calculation

*The same letter in a row means no significant differences based on the least square difference (LSD) test and a significance level at p<0.05.

3.4. Near Infrared Spectroscopy (NIR)

Mean second absorbance derivative spectra were generated for the fresh milk, date syrup, milk drinks consisting of 1200 samples within the wavelength range of 729–975 nm. Two analytical tools were utilized: Partial Least Squares Regression (PLSR) and Artificial Neural Networks (ANN).

PLSR performance of calibration and cross-validation for M.C., aw, TSS, pH, and BI, properties for milk drinks are shown in Table 7. In the calibration models, R² and RMSEC values were 0.988 and 0.777 for M.C.; 0.984 and 0.746 for aw; 0.941 and 0.727 for TSS; 0.957 and 0.755 for pH; 0.978 and 0.743 for BI; respectively.

The performance of ANN in calibrating and cross-validating for the properties of the favorable drink (cow’s milk with 10% Khlass) is summarized in Table 8. In the calibration models, the R² and RMSEC values were 0.989 and 0.745 for M.C.; 0.984 and 0.755 for aw; 0.946 and 0.715 for TSS; 0.955 and 0.740 for pH; 0.978 and 0.735 for BI; respectively. In the cross-validation assessments, R² and RMSECV values were 0.989 and 0.744 for M.C_D; 0.984 and 0.725 for aw; 0.946 and 0.754 for TSS; 0.955 and 0.711 for pH; 0.978 and 0.713 for BI; respectively.

Table 7. PLSR performance for M.C., aw, TSS, pH, and BI properties for the favored milk drink (FD), and TSS, BI properties for fresh milk (FM), and date syrup Khlass (DSK) for both calibration and cross-validation models.

Parameter	Calibration		Cross-Validation
	R2	RMSRC	R2	RMSECV
M.C.FD	0.988	0.777	0.982	0.788
AwFD	0.984	0.746	0.996	0.764
TSSFD	0.941	0.727	0.687	0.727
pHFD	0.957	0.755	0.955	0.723
BIFD	0.978	0.743	0.988	0.703
TSSFM	0.948	0.680	0.948	0.680
BIFM	0.978	0.762	0.946	0.643
TSSDSK	0.958	0.603	0.965	0.603
BIDSK	0.966	0.625	0.942	0.557

Table 7. PLSR performance for M.C., aw, TSS, pH, and BI properties for the favored milk drink (FD), and TSS, BI properties for fresh milk (FM), and date syrup Khlass (DSK) for both calibration and cross-validation models.

Parameter	Calibration		Cross-Validation
	R2	RMSRC	R2	RMSECV
M.C.FD	0.988	0.777	0.982	0.788
AwFD	0.984	0.746	0.996	0.764
TSSFD	0.941	0.727	0.687	0.727
pHFD	0.957	0.755	0.955	0.723
BIFD	0.978	0.743	0.988	0.703
TSSFM	0.948	0.680	0.948	0.680
BIFM	0.978	0.762	0.946	0.643
TSSDSK	0.958	0.603	0.965	0.603
BIDSK	0.966	0.625	0.942	0.557

Table 8. ANN performance for M.C., aw, TSS, pH, and BI properties for the favorable milk drink (FD), and TSS, BI properties for fresh milk (FM), and date syrup Khlass (DSK) for both calibration and cross-validation models.

Parameter	Calibration		Cross-Validation
	R2	RMSRC	R2	RMSECV
M.C.FD	0.989	0.745	0.989	0.744
AwFD	0.984	0.755	0.984	0.725
TSSFD	0.946	0.715	0.946	0.754
pHFD	0.955	0.740	0.955	0.711
BIFD	0.978	0.735	0.978	0.713
TSSFM	0.948	0.684	0.948	0.648
BIFM	0.978	0.715	0.978	0.633
TSSDSK	0.959	0.592	0.959	0.598
BIDSK	0.966	0.611	0.966	0.547

Table 8. ANN performance for M.C., aw, TSS, pH, and BI properties for the favorable milk drink (FD), and TSS, BI properties for fresh milk (FM), and date syrup Khlass (DSK) for both calibration and cross-validation models.

Parameter	Calibration		Cross-Validation
	R2	RMSRC	R2	RMSECV
M.C.FD	0.989	0.745	0.989	0.744
AwFD	0.984	0.755	0.984	0.725
TSSFD	0.946	0.715	0.946	0.754
pHFD	0.955	0.740	0.955	0.711
BIFD	0.978	0.735	0.978	0.713
TSSFM	0.948	0.684	0.948	0.648
BIFM	0.978	0.715	0.978	0.633
TSSDSK	0.959	0.592	0.959	0.598
BIDSK	0.966	0.611	0.966	0.547

The second derivative of NIR spectra was introduced to enhance data quality. Specifically, the mean second absorbance derivative spectra were generated for the fresh milk, date syrup Khlass, and the favorable milk drink (cow’s milk flavored with 10% Khlass) are consisting of 1200 samples within the wavelength range of 729–975 nm, as illustrated in Figure 4. It can be noted that the spectra behavior of both fresh milk and milk drink are closer compared to dates syrup apparently due to the low amount of syrup in the milk drink.

4. Discussion

4.1. Physical properties (MC, aw, TSS, color, density, pH)

It can be observed that the moisture content of Sukkary date syrup was higher than that of Khlass. This might be due to the initial moisture content of the Sukkary dates (9.5%wb) while it was (6.7%wb) for Khlass. A similar trend was observed for water activity. The average moisture content showed significant differences where the camel's milk flavored with Khlass date syrup (10%) was higher than that of the other three samples.

The water activity and pH of cow’s milk flavored with Khlass date syrup (10%) were higher than those of the other three samples. TSS was found to be higher in cow's milk flavored with Sukkary date syrup at 15%, which can be attributed to lower moisture content and higher amounts of date syrup.

From basic color parameters, derivative parameters can be obtained. The mean values of the derivative color parameters (Chroma, Hue angle, and BI) for the samples ranged from 13.383 to 15.267, −57.426 to 57.474, and 15.915 to 19.630, respectively. These data showed significant differences in the derivative color parameters of milk drinks. The differences might be attributed to the initial color of the raw dates fruit milk. BI values for the four milk drinks were higher than that of the raw milk but lower than that of date syrup (as shown in Table 2). The decrease in BI values of the four milk drinks was due to the high amount of milk present.

Density of all samples decreased with the increase of in temperature due to the expansion of sample volume. The elevated temperature leads to the weakening of the forces between molecules bonds and thus molecules of the sample expanded. Thus, the effect of temperature on density and volume should be considered in the design of pasteurization and sterilization processes of milk drinks flavored with date syrup.

4.2. Sensory evaluation of all samples of milk drinks flavored with date syrup

The results of the sensory evaluation revealed that the most favorable milk drink was cow milk flavored with Khlass date syrup (10%) followed by cow milk with Sukkary date syrup (15%). The third preference was camel milk with Sukkary date syrup (15%) and lastly, camel milk with 10% of Khlass date syrup. Details results of the sensory evaluation can be found in [41,42]. They showed that the most flavored milk drink was chosen from sixteen milk drinks (mix of 5 to 20%). The favorable drink was cow’s milk flavored with 10% Khlass as indicated by its taste, flavor, texture, color, and overall acceptability (7.200, 7.333, 7.467, 7.267, and 7.200, respectively) [42]. There is a need for further sensory investigation to include students from different grades, and additional sectors of the society (probably based on age, gender, location, and education). Furthermore, it is recommended to evaluate such milk drinks with sensory evaluation along the shelf-life of the pastoralized and sterilized milk drinks.

4.3. Chemical analysis of the milk drink with date syrup

The most pronounced differences of milk drinks were in total carbohydrates, fructose, glucose, sucrose, maltose, casein, fat, ash, and total energy. These differences are due to the chemical components of both date cultivar and milk type. Milk with Sukkary date syrup at a relatively higher concentration (15%) increased total carbohydrate, sucrose, maltose, and total energy compared with that of milk with Khlass date syrup at 10%. Mean values of the chemical components in the four milk drinks varied in the range of 12.61–16.09 gm/100g for total carbohydrates, 2.60–3.95 gm/100g for fructose, 1.84–4.18 gm/100g for glucose, 0.10–5.91 gm/100g for sucrose, 0.45–1.41 gm/100g for maltose, 3.40–4.02 gm/100g for lactose, 2.88–2.93 gm/100g for proteins, 1.87–2.30 gm/100g for Casein, 1.75–2.78 gm/100g for fat, 0.60–0.86 gm/100g for ash, and 0.21–0.26 gm/100g for standard acidity (lactic acid). These variations of milk drinks composition and sensory evaluation must be considered in marketing, nutritional values, and total cost for each selected milk drink.

4.4. Evaluating physical properties utilizing NIR technique

Recently, near-infrared spectroscopy (NIR) has gained more attention with the advancement and high speed computers. It has more wide applications in identifying food properties. One valuable technique for eliminating extraneous signals from the spectra involves the application of derivatives of NIR spectroscopy [59,60].

Several methods of pre-processing can be implemented prior to modeling [11,61]. After the completion of NIR experiments, two analytical tools can be utilized: PLSR and ANN.

In this study, PLSR revealed that R² and RMSECV values were 0.982 and 0.788 for M.C.; 0.996 and 0.764 for aw; 0.687 and 0.727 for TSS; 0.955 and 0.723 for pH; 0.988 and 0.703 for BI; respectively. For ANN, the correlation coefficient (R²) values fell within the range of 0.942 to 0.996, indicating a very good model performance. This range signifies an excellent model quality in which R² values exceeding 0.70 are generally deemed satisfactory in NIR modeling [62,63,64]. These findings underscore the effectiveness of the PLSR and ANN techniques as a robust statistical tool for accurately predicting both the objective properties and subjective evaluation of foods, here, milk drinks.

These results affirm the excellence of the ANN technique in predicting the properties of the milk drinks. It is evident that the correlation coefficients in the ANN model surpass those of PLSR. RMSEC serves as a measure indicating how well the calibration model aligns with the calibration set, typically decreasing as the number of factors increases. However, RMSECV, which represents the root mean square error in cross-validation may occasionally rise with the addition of more factors. RMSECV is considered a more reliable indicator of a model's future predictive performance compared to RMSEC [65]. Thus, both analytical techniques, PLSR and ANN, have demonstrated their effectiveness in modeling NIR data during the calibration and cross-validation phases in this study. Furthermore, the ANN model is preferred for the present data over PLSR due to the higher correlation coefficients. Therefore, these analyses validate the strong alignment between NIR and the properties of the preferred milk drink.

In practical applications, a non-destructive handheld NIR spectrophotometry meter can be successfully employed by food producers, processors, and regulatory authorities throughout the entire production, processing, transportation, storage, and retail chain to assess product quality. This technology holds the potential to serve as a foundational framework for further research and commercial applications.

5. Conclusion

Dates syrup was produced successfully on a lab scale level that can be utilized as a sweetener and a high nutritional value. The obtained date syrup (Sukkary and Khlass cultivars) was then added to cow's and camel's milk at different ratios (5, 10, 15, and 20%) constituting a combination of sixteen drinks (1200 samples) of milk flavored with date syrup. From the sixteen drinks, four mixes were selected based on sensory evaluation.

The study initially delved into the analysis of the physical and chemical composition of the four preferred milk drinks, which were all flavored with date syrup. These milk drinks exhibited noteworthy disparities in their chemical constituents, encompassing total carbohydrates, fructose, glucose, sucrose, maltose, casein, fat, ash, and total energy. Sensory evaluation discerned that the milk drink, combining cow's milk with 10% Khlass date syrup, outperformed the other variants.

The resulting date syrup-flavored milk drinks represent a natural and highly nutritious sweet product, highlighting the potential to establish a new market that leverages locally sourced date and milk products. It is an aspiration that the findings of this study will foster the production of distinctive, natural, and nutritionally rich products on an industrial scale.

The application of near-infrared spectroscopy (NIR) facilitated the correlation between reflectance/absorbance and the physiochemical attributes of food products. Notably, NIR enables the direct measurement and tracking of both sensory and objective assessments through NIR analysis, employing both partial least-square regression (PLSR) and artificial neural network (ANN) approaches.

NIR proved effective in accurately predicting physiochemical properties and aligning well with measured sample attributes (moisture content, water activity, total soluble solids, pH, Browning index properties). The coefficient of determination (R²) ranged from 0.987 to 0.996, underlining the competence of NIR technology in estimating the physiochemical properties of the favorable milk drink with date syrup. These predictions were affirmed in both the calibration and cross-validation phases.

Consequently, non-destructive NIR spectrophotometry stands as a robust tool for forecasting physiochemical properties and holds significant potential for practical implementation across the entire food production, processing, transportation, storage, and retail chain. This utilization can be instrumental in monitoring product 'quality' and 'shelf life,' aligning with the standards set forth by relevant authorities, such as SFDA.FD 150-1/2018 [66].