Optimization effects on the physicochemical properties of functional goat milk powder
Table 1 presents the experimental results for the physico-chemical properties of functional goat milk powder, including total phenolic content, antioxidant activity, solubility, hygroscopicity, bulk density and whiteness.
Influence of maltodextrin concentration and inlet temperature
The relationship between maltodextrin concentration (X1) and inlet temperature (X2) on total phenolic content (Y1), antioxidant activity (Y2), solubility (Y3), hygroscopicity (Y4), bulk density (Y5) and whiteness (Y6) follows a quadratic regression model. Analysis of variance (ANOVA) results indicate a significant influence (p≤0.05). These interactions are visually represented through contour plots (Fig 1a - 1f) and 3D surface plots (Fig 2a - 2f).
Effects on total phenolic content and antioxidant activity
The addition of maltodextrin during spray drying enhances total phenolic content by forming hydrogen bonds, which protect bioactive compounds (
Shishir and Chen, 2017;
Navarro-Flores et al., 2020). Higher inlet temperatures improve antioxidant activity due to water loss, which concentrates antioxidants
(Thakur et al., 2021). However, excessive temperatures can degrade bioactive compounds, reducing their effectiveness
(Thakur et al., 2021). A combination of 10% maltodextrin and 180
oC inlet temperature minimizes thermal degradation by forming a protective barrier
(Nadali et al., 2022). Additionally, pomegranate peel extract contributes significantly to the phenolic content, with key bioactive compounds including ellagitannins, ellagic acid and gallic acid
(Khan et al., 2017).
Effects on solubility and hygroscopicity
Solubility increases with maltodextrin concentration, as maltodextrin acts as a filler and enhances powder dispersibility (
Kalušević et al., 2017). Maltodextrin up to 15% maintains a non-hygroscopic nature in the powder (
Samsu and Zahir, 2020). It helps control moisture absorption, ensuring a drier product with stable texture (
Bednarska and Janiszewska-Turak, 2020). Higher drying temperatures result in lower moisture content, enhancing stability and reducing hygroscopicity (
Shishir and Chen, 2017). The formation of a protective maltodextrin layer further reduces exposure to humidity
(Sidlagatta et al., 2020). High-temperature drying reduces particle size, resulting in a finer powder with greater surface area for rehydration
(Masum et al., 2019; Leyva-Porras et al., 2019). However, protein aggregation due to β-lactoglobulin and casein interactions can negatively affect solubility
(Thakur et al., 2021).
Effects on bulk density
Bulk density increases with maltodextrin concentration as additional particles fill the matrix, reducing empty space
(Teo et al., 2021). Conversely, higher inlet temperatures reduce bulk density due to rapid water evaporation, leading to porous structures
(Thakur et al., 2021; Djaafar et al., 2018). The viscosity of the maltodextrin solution decreases at higher temperatures, allowing more efficient water removal and lower bulk density
(Saha et al., 2019).
Effects on color
Maltodextrin enhances whiteness by preventing Maillard reactions and oxidation during drying
(Sarabandi et al., 2019; Neves et al., 2019). However, at inlet temperatures above 140°C, the Maillard reaction between lactose and proteins causes browning
(Deshwal et al., 2020). Maltodextrin stabilizes pigment molecules, but excessive heat alters molecular interactions, reducing whiteness
(Chng et al., 2020; Thakur et al., 2021).
Characterization of optimized functional goat milk powder
Optimization and verification
The optimization of functional goat milk powder was conducted using a maltodextrin concentration of 12.10% and an inlet temperature of 178.98
oC, yielding a desirability value of 0.888. The verification results for total phenolic content, antioxidant activity, solubility, hygroscopicity, bulk density and whiteness are summarized in Table 2.
Fourier transform infrared spectroscopy (ftir) analysis
FTIR analysis identified distinct absorption bands in the optimized functional goat milk powder, particularly at 1680.73 cm
-1 and 480.38 cm
-1, indicating the presence of C=C bonds associated with alkenes and aromatic compounds (Table 3 and Fig 3). These spectral shifts suggest the successful incorporation of phenolic compounds from pomegranate peel extract, such as punicalagin and ferulic acid
(Bertolo et al., 2020; Sehari et al., 2022). Additionally, organic components, including minerals and oxygen-containing compounds, were detected, confirming the contribution of bioactive compounds from the extract (
Ben-Ali et al., 2018).
Microstructure analysis
SEM revealed that the addition of pomegranate peel extract led to the formation of agglomerates due to interactions between polyphenols, tannins and milk proteins (Fig 4). These interactions resulted in the formation of a matrix around the granules, influencing particle clustering. However, the slight variations in agglomerate shape did not significantly affect solubility, hygroscopicity, or bulk density. The presence of micropores in the agglomerates enhances water absorption, which can impact the bulk density of the powder
(Zhong et al., 2016; AlYammahi et al., 2023; Thakur et al., 2021).
Particle size distribution
Particle size analysis using PSA indicated an average particle size of 6.1755 μm for the control and 6.2293 ìm for the optimized functional goat milk powder (Fig 5). The slight increase in particle size is attributed to polyphenol-protein interactions, particularly with tannins, which promote protein aggregation. This results in the formation of larger, less water-soluble protein-tannin complexes, influencing the powder’s physical properties
(Slim et al., 2019; Trigueros et al., 2014). The observed particle sizes are comparable to those reported for spray-dried camel milk powder at an inlet temperature of 170
oC
(Deshwal et al., 2020).
These findings confirm that the optimization process successfully enhanced the functional properties of goat milk powder by incorporating bioactive compounds from pomegranate peel extract, leading to improved antioxidant activity, structural modifications and stable physical characteristics.