The white sauces were produced following the typical procedure to produce a food emulsion, as advised by a leading company in Greece producing those kinds of products. A liquid phase that contained vinegar (7%) and citric acid solution with a pH equal to 2.5 (45%) was heated up to 60 °C, and then the mustard (7%), honey (3%), lecithin (2.7%) and xanthan (0.25%) were added as emulsifiers and well mixed. An olive oil and sunflower oil (1:1) (33%) mix was added progressively in an aqueous phase, homogenizing them at 9500 rpm for 10 min in order to make the food emulsion using a high-speed homogenizer (Homogenizer HG-15D, Witeg, Germany). The final food emulsion had a pH value of 3.68 and 12.5 °Brix. In novel white sauces, AW powder was partly substituted for the fat phase (substitution 10 and 20%). Then, all flavorings (garlic, parsley, rosemary, salt) were added and the final mixture was well mixed. The packaging stage followed, using glass jars of 100 g each. The jar lids were closed in vacuum, using appropriate equipment, and the pasteurization step followed. The temperature of the water bath was set to 85 °C and the jars were immersed for 15 min. The temperature in the center of the jar at 15 min processing time was measured as 82 °C for 2 min, sufficient for those kinds of products. After pasteurization, the samples were quickly cooled down to <50 °C.
3.3.2. Shelf-Life Determination of New White Sauces
An accelerated shelf-life test at temperatures ranging from 20 to 40 °C was conducted to estimate the shelf-life of control, 10% and 20% AW-substituted white sauces. The total viable count load was below the detection limit (<2 logCFU/g) throughout the shelf-life study. The developed white sauces had no significant differences in nutritional and quality characteristics, such as pH value and °Brix, compared to the corresponded values at zero time for all studied temperatures for ~6 months shelf-life study.
Concerning the browning index of samples, it was increased significantly (
p < 0.05) during the shelf-life, ranging from −1.25 to 3.81 for control samples, from −1.00 to 5.31 for 10% AW-substituted sauces and from −1.10 to 13.97 for 20% AW-substituted sauces, potentially attributed to the
Maillard reactions. AW-substituted sauces had the most intense increase of BI due to their higher carbohydrate content. Chroma values ranged from 23.40 to 13.86 for all studied samples. During storage, the chroma was slightly decreased for all studied samples. The most pronounced decrease was observed for control samples (achieving approximately a 35% decrease, from 21.0 to 13.8), indicating that color strength was weaker during storage. Color change in white sauces was also reflected in hue angle values. No differences were observed in hue angle values between 10% AW-substituted sauces and the control ones, ranging from 100° to 89°. However, the hue angle of 20% AW-substituted sauces was 78° after 189 days at 40 °C storage temperature, while the corresponding values for 10% AW-substituted sauces and the control were approximately 89° for both (
Figure 6).
The high lactose content of the AW-substituted sauces may contribute to the acceleration of browning by the
Maillard reaction during storage at elevated temperatures. Sauces containing AW should be processed appropriately and stored at proper temperature conditions to avoid browning. Therefore, the incorporation of AW may affect the color parameters of final products due to the reaction of the components of AW to processing and storage conditions, as well as their interaction with other ingredients in the product. The obtained results are in accordance with the findings of other researchers on the effect of AW incorporation on the color change of value-added food products. Karwowska and Dolatowski [
44] and Flinois et al. [
17] reported that the addition of AW in fermented deer sausages and in dressings decreased their lightness (L*) and redness (a*).
The color of developed white sauces was the main quality index that was deteriorated through the shelf-life, thus it was used in order to determine the shelf-life of all samples. The total color difference
∆Ε of novel sauces was estimated at all studied storage temperatures. Experimental
∆Ε values fitted in a first-order model (
Figure 7) and the rate constants of total color change are presented in
Table 6.
As was expected, higher storage temperatures resulted in higher constant rates of the total color change ∆Ε. It was observed that the color altered with the same rate for control and 10% AW-substituted samples, while the color of 20% AW-substituted samples deteriorated in a shorter storage time, as the rate constant of these samples was 11–12% higher at all studied storage temperatures compared to the other ones.
Based on the Arrhenius equation and through extrapolation, the shelf-life of the control white sauces at ambient temperature was estimated to be approximately equal to 12 months (without showing significant differences between the 10% AW-substituted white sauces), while the shelf-life for the 20% AW-substituted ones was 5 months lower (
Table 6). The effect of storage temperature on the rate constants of the total color change was also expressed through the activation energy (
Ea), which was calculated as 40.4, 41.6, and 33.1 kJ mol
−1 for control, 10% and 20% AW incorporated white sauces, respectively.
Lipid oxidation in food emulsions is considered one of the major indices for their deterioration, producing undesirable components with off-flavors (rancidity) and potentially toxic reaction products, leading to rejection by the consumers [
45]. PV limit has been set as 30 meqO
2/kg, indicating the initial stage of fat oxidation in foods [
46]. The rate of lipid oxidation is influenced by many factors, such as the size and concentration of fat droplets, pH value and ingredient interactions of surrounding aqueous media [
34]. Lipid oxidation reactions mainly take place in the surface of the fat droplets, thus an increase in the droplet surface area (decrease of droplet size) could lead to increased rate of lipid oxidation, since a greater amount of fat is exposed to the aqueous phase [
47]. Moreover, the pH value of the aqueous phase has an important role in the acceleration of lipid oxidation. In the literature, lowering pH value results in a decreased rate of lipid oxidation [
48].
The PV value of all samples was slightly changed during shelf-life. After 5 months of storage at 40 °C, the PV value of control, 10% and 20% AW-substituted white sauces was increased from 6 to 15 meqO2/kg, from 5.5 to 21 meqO2/kg and 5.0 to 26 meqO2/kg, respectively. Nevertheless, all developed white sauces were considered as acceptable, since the PV values were below the lipid oxidation limit. This might be attributed to the low pH-value of the aqueous phase, which prevented the acceleration of oxidative reactions, as well as to the added ingredients of sauces, such as herbs and spices, that may have antioxidant properties, inhibiting oxidative reactions.
Food emulsion stability is also a main quality attribute that influences the texture, appearance and consumer acceptance of that kind of product [
49]. Emulsions can be easily destabilized during storage, causing “syneresis”; as a consequence, the fat and aqueous phases are separated from each other [
50]. According to the literature, food emulsions are more stable when their fat droplets are smaller [
51], but this also depends on many other factors and environmental conditions [
52]. Within this study, an emulsifier (~3%) was added into the developed white sauces [
53]. Thus, no emulsion “break” was observed at AW-substituted sauces at all studied temperatures after 3 months of storage. The samples were centrifuged to accelerate the destabilization of food emulsion [
54] in zero time (
Figure 8) and to predict whether the emulsions would be stable or not.
No emulsion destabilization was observed for 20% AW-substituted. More intense emulsion separation was achieved for the control samples, followed by 10% AW-substituted sauces. This phenomenon was expected, as the initial size of fat particles in the emulsion of control samples was significantly bigger than the one of novel sauces with fat phase substitution by AW powder. That difference in the destabilization rate confirmed that the presence of native ingredients (e.g., sugars) would greatly facilitate the formation of stabilized emulsions with smaller droplet sizes [
55]. Interestingly, it can be observed that the control sample was completely destabilized, releasing the whole fat phase, while all the other AW-substituted sauces were resistant to the accelerated stability test. The results are in agreement with the study of Zamani, Malchione, Selig, and Abbaspourrad [
56], who reported that the prepared emulsions using AW protein demonstrated higher stability than the control samples (without AW protein).
In
Figure 9, a microscope image for the developed sauces after 3 months storage at 40 °C is presented in order to monitor the progress of the droplet size increase.
It is known that the emulsion stability is affected by the concentration of particles and the fraction of fat volume. By decreasing the concentration of particles through the increase in the droplet size of the particles, the interfacial area of emulsion may not be sufficiently covered, resulting in decreased emulsion stability. In addition, by increasing the fraction of fat volume, the total area to be stabilized also increases, leading to increased fat droplet size and unstable emulsion systems [
57]. According to the literature, the bigger the fat droplets are, the shorter time in which destabilization of food emulsions is observed [
51]. This phenomenon may apply for the case of the control sauces; the increased fat droplet size resulted in lower particle concentration and in a higher fraction of fat volume, thus less stable formulation during storage as seen in
Figure 10. These observations are consistent with previously reported studies [
58,
59,
60]. The results were also confirmed by the accelerated emulsion stability test that was conducted at zero time by centrifugation. A slight fat accumulation was observed at the top of the emulsion for the 10% AW-substituted sauce related to its lower stability compared to the 20% AW-substituted one (
Figure 8), which is in agreement with the results obtained from the optical microscopy (
Figure 9).
The fat concentration and droplet size generally affect the viscosity and the texture of emulsions [
61]. Nevertheless, during storage, the texture properties of developed sauces were not affected compared to their initial values. Finally, sensory evaluation was carried out throughout the whole shelf-life. Trained panelists scored all sauces based on a hedonic scale (1–9 scores) in terms of appearance, texture in mouth, flavor, taste and overall impression (
Figure 10).
In zero time, the developed sauces had no differences in scores of all individual sensory attributes. The decreased fat content of AW-substituted sauces did not affect either the mouth feel texture or their taste. The incorporation of AW powder into the new sauces, substituting the fat phase, enhanced the organoleptic characteristics of samples and finally fulfilled the panelists. The high lactose content of AW powder resulted in approximately the same texture for the AW-substituted sauces compared to the control ones. These observations are consistent with previous studies, which reported that the addition of AW as replacement for milk powder improved the texture and mouthfeel of fermented dairy beverages [
62].
This result had also been confirmed by texture analysis, leading finally to the creation of reduced-fat sauces with the same quality and sensory characteristics as the control ones. During storage, as was expected, a deterioration of some organoleptic characteristics was observed, mainly for the 20% AW-substituted samples. These samples received the lowest scores from panelists, due to their unacceptable appearance (increase of browning from
Maillard reactions) and off-flavors (produced bitter components—melanoids from
Maillard reactions) after 3 months at 40 °C storage temperature. In the literature, the quality of foods substituted with AW was slightly decreased during the storage period, which was mainly associated with the increase in sour and bitter tastes and a decrease of flavor intensity linked to the increased content of lactic acid [
14,
63]. Control samples were rejected by the panelists, due to a more pronounced emulsion destabilization that was observed after 4 months’ storage at 40 °C. This phenomenon influenced the mouth feel texture of control sauces as well, finally receiving a score below 5.0, while at the same time the corresponding score for 10% AW sauces was 6.0.
It is worth pointing out that for overall sensory quality, 10% AW-substituted sauces obtained scores of up to 6 even at 4 months of storage period at 40 °C, which raises the possibility of these sauces being acceptable to consumers. The results are in agreement with the study of González-Martınez et al. [
64] who reported that the sensorial panel preferred the yoghurt samples fortified with the highest AW powder percentage (3.64–5.20%) to the control ones.
To conclude, based on the obtained results about the deterioration of quality and sensory characteristics in developed white sauces, the optimal fat substitution by AW powder was 10%. The addition of AW powder in the newly developed white sauces improved their nutrients content and their emulsion stability significantly. For the highest fat substitution (20%) by AW, an 8-fold increase in lactose and calcium content was observed, while simultaneously the food emulsion depicted stability throughout the shelf life of those sauces. Nevertheless, although the 20% AW-substituted white sauces had an improved nutritional profile, their shelf life was lower compared to the other samples mainly due to significant color alteration because of the Maillard reaction. This resulted in almost 5 months shorter shelf life compared to the 10% AW substitution. The high lactose content led to the acceleration of Maillard reactions and consequently to their unacceptable browning color, as well to off-flavors due to Maillard products in shorter time than the other ones.