Incorporation of Acid Whey Yogurt By-Product in Novel Sauces Formulation: Quality and Shelf-Life Evaluation

Abstract

This study aimed to develop high quality, added value novel sauces with acid whey (AW) (liquid or powder) incorporation. Liquid pasteurized AW was substituted (partly 10%—totally 100%) for the water added in the tomato sauces. AW in powder, was partly substituted for the fat in white sauces and compared to conventional ones. Physicochemical (pH, Brix, viscosity, color), nutritional (proteins, lactose, minerals), microbiological and sensory evaluations were conducted for both developed sauces. Accelerated shelf-life tests were performed. Based on the quality and sensory characteristics deterioration, the optimal water substitution by AW was 70% w/w for tomato sauces and 10% w/w (AW in powder) for white sauces, without limiting their shelf life compared to the control ones for both cases. Both AW-substituted sauces were of high quality and of higher nutrients content compared to conventional products, improving their health promoting profile (tomato sauces: up to 3-fold increase; white sauces: up to 5-fold increase in calcium content; increase in essential amino acids content in both sauces due to AW addition).

1. Introduction

In the last decade, strained (Greek) yogurt production has increased significantly due to growing demand from consumers for its organoleptic characteristics and its health promoting profile [1]. However, to produce 1 kg Greek yogurt, approximately 3 kg of acid whey (AW) by-product needs to be discarded [2]. In 2018, it was estimated that the worldwide Greek yogurt production resulted in approximately 4 million tons of AW [3], creating several environmental concerns, and thus a challenge for the dairy industry [4,5]. AW is a dairy side stream, constituting approximately 95% water and 4% lactose with functional proteins (<3.71 mg/g), while being rich in several minerals, such as calcium (98–150 mg/100 g) [6,7]. Its composition mainly depends on the source of milk used and the type of yogurt produced [8]. Its high BOD (52,400 to 62,400 mg/L) and low pH (4.5–5.1) limit the options for cost-effective utilization or further use, also making its disposal a continuously studied issue [4]. Nowadays, its main current uses are as animal feed or in anaerobic digesters for energy production [2,9,10].

Manufacturers aim to unlock the potential of AW through its valorization as a source of high added-value compounds that could be incorporated into functional food systems [11,12]. The rapid growth of Greek-style yogurt sales and the technological advances in AW processing reveal its effective alternative applications. Several dairy companies have attempted to minimize the production of AW during Greek-style yogurt production. In addition, they have studied eco-friendly approaches for handling this by-product. For instance, a method has been developed to produce an AW with a pH equal to 6.0 [13] in order to replace the sweet whey used in food products as a bulking agent or nutrient fortifier [14]. The physicochemical characteristics of AW, along with high concentrations in minerals and organic acids, have been handled by using membrane technology strategy resulting in spray-dried powders with improved lactose crystallization properties and enhanced yields [15,16]. Its incorporation into food products, apart from serving as a solution in food waste reduction, simultaneously enhances the nutritional characteristics and flavor of the products, and could potentially partially or totally replace added sodium salts or/and sugars in final food products. AW contains a high water content and therefore can be used in the sauce manufacturing industry where water requirements are quite large. Furthermore, the inherent acidity and astringency of AW can benefit such food products, as it enhances their flavor by providing a dairy flavor profile [17]. When working on developing a product with a characteristic acid taste, AW could be used and incorporated into the food system as a clean label alternative or even as an added preservative, due to its low pH value between 4.21 and 4.48 [7]. The shelf-life of products incorporating AW is increased due to its high content of organic acids, such as lactic acid (0.65%), citric acid (0.18%) and glutamic acid (0.06%), which have proven antimicrobial properties [18]. Sodium chloride (table salt) is commonly added to sauce products to enhance their intense flavor. Therefore, the addition of the AW to sauces can reduce the sodium content while maintaining the pleasant sensory characteristics of the product, due to its high content in mineral salts such as potassium (>150 mg/100 g), calcium (>120 mg/100 g) and phosphorus (>60 mg/100 g) [17]. AW has 1.7–3.7 g/L of protein content [7], thus contributing to the increase of a product’s total protein content compared to the equivalent product prepared with plain water. AW sugars, mainly lactose and galactose, are useful in the sauce industry as they provide a sweet taste, allowing for reduced added sucrose in the final product. Therefore, the incorporation of AW into foods results in the development of products with high added value without the addition of sodium and sugars. In the literature, it is reported that AW has been used as a starting medium for the cultivation of lactic acid bacteria in fermented beverages [14,19,20,21] and as a food ingredient in new developed food products, mainly beverages or sport drinks, bakery products and salad dressings [17,22,23,24].

Sauces or dressings are in high demand and are convenient food products consumed worldwide [25]. Sauces are mainly used as toppings in various foods, increasing their attractiveness and tastiness. For the relevant industries, the production of sauces with high added value compounds is of increased interest, providing functionality to the final products [26].

The current research targeted the development of new food products by adding AW as a main food ingredient. There are no similar products available in the market. The development of two different widely consumed sauces was studied: a tomato-based sauce with the addition of pasteurized liquid AW, and a white sauce (oil–to–water emulsion) with the addition of AW powder (spray-dried AW). Thorough research was conducted, evaluating: i) the potential of using AW as a food ingredient, partially or fully substituting major ingredients that do not improve (i.e., water in tomato sauces) or act negatively (i.e., oil in white sauces) on the functionality of the products, and ii) the impact of AW addition on the quality, organoleptic characteristics, shelf life and nutritional profile of both novel sauces. The impact of this research is double-edged, since firstly it proposes the use of AW as an ingredient in the production of value-added food products at a higher scale, and secondly it offers an alternative solution for the valorization of a yoghurt production by-product with serious environmental concerns.

2. Materials and Methods

2.1. Raw Materials and Product Formulation

2.1.1. Novel Tomato Sauces Formulation

Tomato sauces were prepared based on a recipe provided by a sauce producing company, using concentrated tomato products and crushed concentrated tomato (~76.5%). Other ingredients such as dried vegetables, herbs and spices were added for the desired flavor and taste. For control samples, water was used for the formulation of the final products, up to 12.5 °Brix, while for the novel sauces, the water was substituted (by 30%, 70% and 100%) with a stabilized AW solution. Typical production conditions were used (Figure 1a).

Thermal pasteurization of novel tomato sauces at 100 °C in glass containers, assuring food safety and shelf-life extension for all studied samples, was conducted.

2.1.2. Novel White Sauces Formulation

The basic formulation of white sauces included 32% sunflower oil–olive oil (1:1 w/w), 42% water, 7% vinegar, 7% mustard, 3% honey, and emulsifiers (2.7% lecithin and 0.25% xanthan). For the novel sauces, part of the fat phase was substituted with AW powder at 10% and 20%. Herbs and spices (0.5% garlic powder, 0.5% parsley, 0.5% rosemary and 0.3% salt as a condiment) were also added for seasoning. High speed homogenization at 9500 rpm for 10 min was also carried out to create a stabilized oil in water (o/w) emulsion (Figure 1b).

2.1.3. Experimental Set Up

Thermal pasteurization of the novel sauces in glass containers assured food safety and shelf-life extension for all studied samples. For all developed sauces (novel tomato-based and white sauces), accelerated shelf-life testing protocol was applied and samples were stored at 20, 30, and 40 °C, for up to 8 months in high-precision incubators (Friocell 222-ECO line, MMM Group, Medcenter Einrichtungen GmbH), along with control samples (similar sauces produced by the typical recipe provided by the leading company, without any substitution by AW). Sampling (100 g for each one) at appropriate time intervals allowed kinetic analysis of quality deterioration indices. The shelf-life of all sauces was estimated by extrapolation, based on the quality degradation which occurred.

2.2. Evaluation of Quality Parameters of Sauces

The major physicochemical (pH, Brix, viscosity, texture, color, emulsion stability, oxidation), nutritional (proteins, carbohydrates, lactose, fat content, minerals), and microbiological parameters of AW and of developed sauces were determined and monitored during storage. All measurements for all studied samples were replicated four times.

2.2.1. Physicochemical Parameters

The pH value and total soluble solids (Brix) of tomato sauces were measured using an ORION pH-meter (ORION 188 ion analyzer model EA 940, ORION-scientific, Limena (PD), Italy) and a digital Refractometer (°Brix KERN Digital Refractometer, KERN & SOHN GmbH, Germany), respectively. Color quantification of novel sauces was determined based on CIE Lab coordinates (L: lightness, a: redness, b: yellowness) using a colorimeter Minolta CR-300 (Minolta Company, Chuo-Ku, Osaka, Japan). For each sample, the browning index (Equations (1) and (2)), chroma (Equation (3)), hue angle (Equation (4)) and the total color change ∆E (L₀, a₀, b₀ are the L, a and b values at zero time) (Equation (5)) were calculated:

$$\mathit{Browning\; Index}=\frac{\left[\mathbf{100}·\left(\mathit{X}-\mathbf{0.31}\right)\right]}{\mathbf{0.17}}$$

(1)

where

$$\mathit{X}=\frac{\left(\mathit{a}+\mathbf{1.75}·\mathit{L}\right)}{\mathbf{5.645}·\mathit{L}+\mathit{a}-\mathbf{3.012}·\mathit{b}}$$

(2)

$$\mathit{Chroma}=\sqrt{{\mathit{a}}^{\mathbf{2}}+{\mathit{b}}^{\mathbf{2}}}$$

(3)

$$\mathit{Hue\; angle}={\mathit{tan}}^{-\mathbf{1}}\left(\frac{\mathit{b}}{\mathit{a}}\right)$$

(4)

$$\mathit{∆}\mathit{{\rm E}}=\sqrt{{\left(\mathit{L}-{\mathit{L}}_{\mathbf{0}}\right)}^{\mathbf{2}}+{\left(\mathit{a}-{\mathit{a}}_{\mathbf{0}}\right)}^{\mathbf{2}}+{\left(\mathit{b}-{\mathit{b}}_{\mathbf{0}}\right)}^2}$$

(5)

The texture properties of sauces were measured using a TA. HD plus texture analyzer (Stable Micro Systems Ltd., UK). A two cycles compression test was carried out using a suitable probe (a forward extrusion cell/disk with 7 mm diameter, test speed: 0.5 mm/s, distance 1 mm). According to Yusof, Jaswir, Jamal, and Jami [27] and the obtained data from Texture Expert Exceed Software, the major texture properties of samples determined were the hardness (kg), cohesiveness (kg/s), adhesiveness (kg/s), chewiness and gumminess. Viscosity of the developed sauces was also measured using a rotary viscometer (Brookfield, DVII & Pro, USA). All measurements were replicated five times.

2.2.2. Nutritional Compounds

Novel sauces and AW used were analyzed in terms of total protein content, total carbohydrates, individual sugars and organic acids and major minerals content. The total protein content was determined according to the Kjeldahl method [28] using a Kjeldahl rapid distillation unit (Protein Nitrogen Distiller DNP-1500-MP, RAYPA, Spain). The total carbohydrates content was determined for all studied sauces using a modified protocol of the Debois assay [29] and was expressed as g lactose/100 g d.w. Individual sugars (fructose, glucose, lactose and glycerol) and organic acids (citric, mallic, tartaric and lactic) were determined by using the high performance liquid chromatography (HPLC) method as described by Andreou, Giannoglou, Thanou, Giannakourou and Katsaros [30]. Analysis of sugars and organic acids was carried out using a Repromer H column (300 mm, 7.8 mm; particle size: 9 μm) with a flow of 0.5 mL/min at 50 °C. Twenty (20) μL of the extracts were injected into the HPLC system. For the mobile phase, 1 mM sulfuric acid solution was used. Individual sugars and organic acids were quantified according to calibration curves performed with standards and the concentrations were expressed as g/100 g d.w. The major minerals, such as calcium, sodium, potassium, magnesium, iron, zinc, manganese and copper, were determined by means of atomic absorption spectrophotometry (AAS) based on the AOAC method [31]. Amino acids analysis was also performed for two different types of AW, using an Agilent 1200 series HPLC system (Agilent Technologies, Inc., USA) equipped with an Agilent ZORBAX Eclipse Plus C18 column. A diode array detector was programmed to detect the signal at wavelengths 338 nm/262 nm. Pre-column sample derivatization was performed using 9-fluorenyl-methyl chloroformate (FMOC-Cl), o-phthalaldehyde (OPA) and 3-Mercaptopropionic acid, all purchased by Merck (Sigma Aldrich). Mobile phase A contained 10 mM Na₂HPO₄, 10 mM Na₂B₄O₇, pH 8.2, and 5 mM NaN₃. Mobile phase B contained acetonitrile:methanol:water (45:45:10, v:v:v). The method was calibrated by a solution of 17 amino acids standards (aspartic acid, glutamic acid, serine, histidine, glycine, threonine, argigine, alanine, tyrosine, cysteine, valine, methionine, phenylalaline, isoleucine, leucine lysine, proline) (10 pmol/μL). All samples were analyzed in triplicate.

2.2.3. Microbiological Analysis

All studied sauces were microbiologically analyzed during storage. Total viable count (TVC) (Plate Count Agar-Biokar Diagnostics, Beauvais, France; incubation: 30 °C for 48 h) was determined using the pour plate method (ISO 15214:1998). Yeasts and molds (RBC, Biokar, Zac de Ther, France; incubation: 25 °C for 120 h) were also determined using the surface plating technique (ISO4833-2:2013). The measurements were performed twice.

2.2.4. Determination of Acidity of Tomato Sauces

The acidity of developed tomato sauces at all studied storage temperatures was measured according to Stadtman, Buhlert, and Marsh [32]. Five grams of the sample was mixed with 50 mL deionized water and then filtered. Twenty milliliters of the filtered sample were titrated with 0.1 N NaOH and phenolphthalein. The acidity of tomato-based sauces was expressed as g lactic acid/100 g product. Three replicates of each sample were performed.

2.2.5. Determination of Lipid Oxidation of White Sauces

Lipid oxidation of white sauces during shelf-life was also evaluated through peroxide value (PV) measurement. Five grams of samples were centrifuged at 10,000 rpm for 20 min to collect the upper fat phase—oil. PV value was expressed as meqO2/kg of oil extracted from white sauces. PV was determined according to the analytical method described in the Regulation EEC/2568/91 of the European Union Commission. Three replicates of each sample were performed.

2.2.6. Optical Microscopy

Microstructures of novel white sauces were observed through optical microscopy using an Olympus BX40 Clinical Microscope with magnification x100, equipped with an Olympus DP72 digital camera. All the images were taken on the same day of sample preparation and at the end of their storage. A drop of each sample was placed in the microscope glass slide and covered with a coverslip to avoid the mobilization of droplets. Then, the focus knob was adjusted to get a clear view field.

2.2.7. Determination of Volatile Compounds Using Headspace Gas Chromatography- Mass Spectrometry

A solid phase micro-extraction-gas chromatography-mass spectrometry (SPME-GC-MS) analysis was performed to identify the volatile compounds of AW and tomato sauces using a method (GC-MS Gas Chromatography) as proposed by Li, Di, and Bai [33]. An SPME fiber (Divinylbenzene/Carbon Wide Range/Polydimethylsiloxane Fiber; thickness: 50/30 μm; length 10 mm) was used to extract the volatile compounds of all studied samples. The fiber was put into the headspace vial with the sample for 40 min at 50 °C. After extraction, the fiber was inserted into the injector of the GC-MS (MSD Model 5972, Agilent Santa Clara, USA). Gas chromatography was carried out using an HP-5 column (50 m × 0.32 mm × 1.05 μm, J&W Scientific, Agilent, Santa Clara, CA, USA). Helium was used as the carrier gas at a flow rate of 1 mL/min. The chromatographic conditions were as follows: initial temperature 40 °C for 2 min; 40–250 °C at a rate of 5 °C min−1; 250 °C for next 2 min. An internal standard solution (2-octanol in 70% hydroalcoholic solution) was used for sample quantification. Three replicates of each sample were performed.

2.2.8. Emulsion Stability of White Sauces

Accelerated emulsion stability tests were performed in zero time (immediately after their production) by centrifugation as proposed by McClements [34]. Three milliliters of the sample were centrifuged at 10,000 rpm for 20 min and the emulsion “break” was observed, measuring (in cm) the fat phase above the residual sauce. This method allows for rapid evaluation and prediction of an emulsion stability during storage. All measurements were replicated three times.

2.2.9. Sensory Evaluation

Sensory evaluation was performed by an eight-member trained sensory panel, including individuals of both sexes (4 men and 4 women) from different ages ranging from 25 to 45 years old (average age was 31 years old). A typical sensory evaluation consent form was provided to the panelists to inform them of the products to be evaluated. According to ISO 8586:2012, a blind trial was performed for each studied sample in an accredited test room. Each panelist received approximately 20 g from each sample on a glass white plate, along with an organoleptic evaluation sheet featuring a variety of categories that the panel should use to review the products. These categories included appearance, taste, texture and smell and were scored while an overall rating and comments on comparison between the different samples were also requested. A 1–9 hedonic scale (1 the lowest quality score; 9 the highest quality score; 6 the organoleptically acceptable limit) was used and thoroughly explained to the panel before their evaluation (the way the panelists should score was also written in the evaluation sheet). Between each trial the panelists rinsed their mouths with tap water. The mean values were calculated for every characteristic scoring received.

2.3. Data Analysis

The results for total color change were measured and plotted versus storage time for all temperatures studied for both developed sauces. Based on the kinetic modeling, the experimental data were fitted to first order (Equation (6)) mathematical models for both sauces, respectively. The rate constants of color change k_∆Ε were calculated. Scores for the overall impression evaluated for white sauces were mathematically modeled by apparent zero-order kinetics (Equation (7)) and the rate constants of overall impression scores k_SE were calculated. The dependence of storage temperature on the rate constants was expressed through activation energy (E_a), calculated using the Arrhenius equation (Equation (8)). The shelf-life determination of novel sauces was calculated based on Equations (9) and (10) for the tomato sauces (based on organoleptic deterioration of overall impression) and white sauces (based on the increase of total color change), respectively:

$$\mathit{∆}\mathit{{\rm E}}=\mathit{∆}{\mathit{{\rm E}}}_{\mathit{max}}·(\mathbf{1}-{\mathit{e}}^{-{\mathit{k}}_{\mathit{∆}\mathit{{\rm E}}}·\mathit{t}})$$

(6)

$$\mathit{S}={\mathit{S}}_{\mathbf{0}}+{\mathit{k}}_{\mathit{S}\mathit{E}}·\mathit{t}$$

(7)

$$\mathrm{lnk}={\mathrm{lnk}}_{\mathrm{eff}\left(\mathrm{Tref}\right)}+\frac{{\mathrm{E}}_{\mathrm{a}}}{\mathrm{R}}·(\frac{1}{\mathrm{T}}-\frac{1}{{\mathrm{T}}_{\mathrm{ref}}})$$

(8)

$${\mathit{t}}_{\mathit{S}\mathit{L}}=\frac{{\mathit{S}}_{\mathbf{0}}-{\mathit{S}}_{\mathit{limit}}}{{\mathit{k}}_{\mathit{S}\mathit{E}}}$$

(9)

$${\mathit{t}}_{\mathit{S}\mathit{L}}=-\frac{\mathit{l}\mathit{n}\left(\mathbf{1}-\frac{\mathit{∆}{\mathit{{\rm E}}}_{\mathit{limit}}}{\mathit{∆}{\mathit{{\rm E}}}_{\mathit{max}}}\right)}{{\mathit{k}}_{\mathit{∆}\mathit{{\rm E}}}}$$

(10)

where ∆Ε is the total color change at storage time t, ∆Ε_max (=25 for tomato sauces and =27 for white sauces) is the maximum ∆Ε value that was achieved at the end of shelf-life, ∆Ε_limit (=20 for both sauces) is the accepted color change that was set as the average value for minimum acceptability, k_∆Ε is the rate constant of the total color change during storage (d⁻¹), S is the score of overall impression at storage time t, S₀ is the initial score of overall impression at zero storage time, S_limit is the organoleptically acceptable limit score of overall impression, k_SE is the rate constant of the overall impression score during storage (d⁻¹), t is the storage time (d), T and T_ref (22 °C) are storage temperatures (K), E_a is the activation energy (J/mol) and R is the universal gas constant (=8.314 J/mol K).

2.4. Statistical Analysis

Analysis of variance (ANOVA) and Duncan tests (α = 0.05) were used to determine statistically significant differences between the different storage temperatures and treatments, concerning physicochemical, nutritional and sensory parameters of studied samples, using Statistica 7 (Stat Soft, Tulsa, OK, USA).

3. Results and Discussion

3.1. Physicochemical and Nutritional Parameters of Acid Whey

The main physicochemical and nutritional parameters of liquid AW and AW powder that were provided from a leading dairy company are presented in

Table 1. Quality and nutritional characteristics of liquid AW and AW powder.

Quality Characteristics	Liquid Acid Whey	Acid Whey Powder
pH	4.26 ± 0.01	4.55 ± 0.03
Acidity (%)	0.28 ± 0.13	0.35 ± 0.22
Total soluble solids (°Brix)	8.72 ± 0.25	-
Water activity	-	0.215 ± 0.025
Total protein (%)	0.24 ± 0.02	3.87 ± 0.65
Total fat (%)	0.00 ± 0.00	0.00 ± 0.00
Moisture (%)	92.50 ± 0.98	3.01 ± 0.02
Ash (%)	0.78 ± 0.02	11.57 ± 0.12
Individual sugars	g/100 mL	g/100 g
Lactose (%)	3.72 ± 0.25	45.67 ± 2.65
Galactose (%)	0.82 ± 0.08	8.06 ± 1.57
Glucose (%)	0.04 ± 0.01	0.24 ± 0.02
Individual organic acids	g/100 mL	g/100 g
Citric acid (%)	0.26 ± 0.00	6.17 ± 0.56
Lactic acid (%)	1.00 ± 0.08	11.88 ± 1.45
Minerals	g/100 mL	g/100 g
Calcium	95.38 ± 2.25	1.22 ± 0.06
Potassium	159.1 ± 3.98	2.59 ± 0.36
Phosphorus	95.38 ± 4.22	1.22 ± 0.04
Magnesium	13.28 ± 0.25	0.27 ± 0.08
Sodium	58.47 ± 1.25	0.73 ± 0.04

± represents the standard deviation of triplicates.

.

The pH value of liquid AW was equal to 4.26 and the total soluble solids were 8.72 °Brix. It was rich in several minerals, such as calcium Ca²⁺ (95.4 mg/100 g), potassium K⁺ (58.5 mg/100 g) and sodium Na⁺ (159.1 mg/100 g). The lactose content was also high, and equal to 3.72 g/100 mL. The lactose content of the current AW was similar to that reported by other studies, ranging between 3.33 and 4.20% [7,15]. The protein content (0.24%) was lower than typical amounts of 0.80 % indicated by FAO (2013). It should be mentioned that significant differences have been observed about the protein content of the AW collected in different seasons from the same milk source under equal processing conditions [19]. The composition of AW depends on several factors, including the milk source, type of processed yogurt, milk treatment, storage etc. [8]. AW in a powder form was also produced by a series of steps including condensation by reverse osmosis, vacuum drying, crystallization and freeze drying of yoghurt production AW by-product. AW powder is considered a source of lactose (45.67 g/100 g) and lactic acid (11.88 g/100 g). AW had generally low protein content (<4 g/100 g d.m.). In this study, the moisture content of the AW powder was in the range reported by other studies (1.3–4.8%) [35]. The high ash and lactic acid contents in AW powder were similar to those found in the literature, while lactose content was lower (68.0–75.1) [36]. Liquid AW comes directly from the straining of yoghurts, while for AW in a powder form a series of steps including condensation by reverse osmosis, vacuum drying, crystallization and freeze drying were used. These processing steps might have a slight effect on the pH value (Table 1) of the product (AW in powder), since part of the acids might be retained in the pressurized part of the membrane. Another potential explanation could be that these AWs used in our study are coming from different yoghurt batches produced, thus giving slightly different pH values in the strained AW, and this is in accordance with the literature where similar differences have been reported between AW batches [7].

Whey proteins are widely known for their high bioactivity, leading to improved digestibility due to their structural properties and their contained amino acids. It was observed that the essential amino acids that have significant health benefits were almost 50% to 58% of the overall free amino acids (

Table 2. Free amino acids content of liquid AW and AW powder.

Free Amino Acids (mg/100 g)	Liquid Acid Whey	Acid Whey Powder
Aspartic acid	2.94 ± 0.01	106.29 ± 2.35
Glutamic acid	4.29 ± 0.07	145.38 ± 3.65
Serine	1.00 ± 0.09	40.08 ± 4.20
Histidine	0.54 ± 0.10	28.83 ± 2.65
Glycine	0.57 ± 0.15	28.98 ± 1.95
Threonine	1.26 ± 0.12	44.06 ± 3.65
Arginine	3.14 ± 0.35	81.11 ± 2.22
Alanine	0.50 ± 0.11	19.78 ± 0.98
Tyrosine	0.57 ± 0.01	18.77 ± 1.22
Cysteine	0.77 ± 0.03	22.72 ± 1.55
Valine	1.99 ± 0.22	62.37 ± 1.69
Methionine	0.78 ± 0.15	27.54 ± 2.47
Phenylalaline	1.27 ± 0.10	39.23 ± 3.85
Isoleucine	1.58 ± 0.07	46.41 ± 3.96
Leucine	3.87 ± 0.42	74.05 ± 4.12
Lysine	0.26 ± 0.08	42.11 ± 0.89
Essentials AA	58.6%	49.2%
Non-essentials AA	41.4%	50.8%

± represents the standard deviation of triplicates.

).

The results concerning the amino acid profiles of AW are in conformity with the findings of Yasmin et al. [37] and Ward [38], who also noticed leucine as the predominant essential amino acid followed by isoleucine and threonine. This proves that incorporating AW directly into food products may act as a potentially health promoting ingredient.

3.2. Case Study I: Incorporation of Liquid Acid Whey into Tomato Sauces

The tomato sauces were produced following the typical procedure for that kind of product, as advised by a leading company in Greece producing sauces. In more detail, tomato concentrate (32 °Brix), crushed tomato (12 °Brix) and whole tomatoes in tomato juice (8 °Brix) were well mixed in a ratio of 2:1:1 using appropriate equipment (mixer vessel of 30 L volume). The mix had a pH value of 4.2 and 20 °Brix. The total soluble solids (°Brix) for that kind of product (tomato sauce) are within the range of 11–14 °Brix. The total soluble solids were adjusted to the desired value (14 °Brix) by adding plain water (for the control samples), while for the AW samples, part or all of the water added was substituted with the AW solution in liquid form (substitution from 30% to 100%). Then, all other ingredients (sugar, garlic, oregano, basil, salt, pepper, oil) were added and the final mixture was well mixed and heated up to 70 °C. The packaging stage followed, using glass jars of 100 g each. The jar lids were closed in vacuum, using appropriate equipment. It was not possible to apply the hot-filling procedure in our case (no appropriate equipment available), so the batch pasteurization step was added for the final packaged samples. The temperature of the water bath was set to 100 °C and the jars were immersed for 20 min. The temperature in the center of the jar at 20 min processing time was measured as 92 °C, sufficient for that kind of product. After pasteurization, the samples were quickly cooled down to <50 °C.

3.2.1. Physicochemical Parameters and Nutritional Compounds of Tomato Sauces in Zero Time

The new sauces (tomato sauces with various substitution percentages of added water by AW) were evaluated in terms of quality properties, nutritional attributes and organoleptic parameters (

Table 3. Physicochemical parameters & nutritional compounds of tomato sauces immediately after production (t = 0).

	0% AW	30% AW	70% AW	100% AW
Physicochemical Characteristics of Tomato Sauces
pH	4.07 ± 0.00 a	4.08 ± 0.01 a	4.07 ± 0.01 a	4.05 ± 0.01 a
Brix	13.8 ± 0.1 c	14.5 ± 0.1 b	15.0 ± 0.1 a	15.1 ± 0.1 a
Color Parameters
L	25.7 ± 0.4 a	28.3 ± 1.6 a	26.8 ± 1.5 a	28.4 ± 1.3 a
a	14.4 ± 0.2 a	14.0 ± 2.4 a	13.7 ± 2.4 a	14.3 ± 1.9 a
b	13.5 ± 0.9 a	15.1 ± 1.5 a	14.4 ± 1.9 a	14.9 ± 2.2 a
a/b	1.06 ± 0.22 a	0.92 ± 0.15 a	0.95 ± 0.21 a	0.96 ± 0.17 a
Hue angle	0.55 ± 0.05 a	0.75 ± 0.15 a	0.71 ± 0.17 a	0.70 ± 0.06 a
Chroma	19.74 ± 1.95 a	20.59 ± 1.22 a	19.87 ± 1.32 a	20.65 ± 1.41 a
Texture Properties
Hardness (kg)	0.196 ± 0.032 a	0.216 ± 0.025 a	0.195 ± 0.036 a	0.186 ± 0.018 a
Cohesiveness (kg/s)	2.403 ± 0.032 a	2.241 ± 0.035 a	2.173 ± 0.022 a	1.979 ± 0.025 a
Adhesiveness (kg/s)	−0.032 ± 0.022 a	−0.035 ± 0.005 a	−0.036 ± 0.015 a	−0.038 ± 0.036 a
Chewiness	1.187 ± 0.122 a	1.193 ± 0.116 a	1.093 ± 0.114 a	1.181 ± 0.128 a
Gumminess	0.434 ± 0.216 a	0.533 ± 0.124 a	0.425 ± 0.116 a	0.491 ± 0.124 a
Nutritional Compounds of Tomato Sauces
Moisture (g/100 g)	84.32 ± 0.13 a	85.01 ± 0.11 a	84.75 ± 0.08 a	83.92 ± 0.09 a
Ash (g/100 g)	2.32 ± 0.05 a	2.27 ± 0.04 a	2.35 ± 0.01 a	2.40 ± 0.06 a
Total proteins (g/100 g)	11.37 ± 0.05 c	12.72 ± 0.07 b	12.98 ± 0.10 a	13.15 ± 0.02 a
Total carbohydrates (g lactose/100 g dm)	7.3 ± 0.1 d	7.6 ± 0.9 c	8.0 ± 0.6 b	8.3 ± 0.5 a
Minerals (mg/100 g)
Ca2+	9.04 ± 0.12 d	16.19 ± 2.51 c	25.73 ± 3.41 b	32.88 ± 2.98 a
Mg2+	29.00 ± 0.35 a	30.00 ± 0.09 a	31.32 ± 0.11 a	32.32 ± 0.12 a
K+	893.27 ± 1.52 d	905.20 ± 2.22 c	921.11 ± 1.47 b	933.05 ± 3.65 a
Na+	403.04 ± 0.98 d	410.20 ± 1.32 c	419.29 ± 2.65 b	429.86 ± 1.25 a

± represents the standard deviation of triplicates. Different superscript letters indicate significantly different means (p < 0.05) between tomato sauces with different AW substitution.

).

No significant differences between samples were observed for their pH value, measured approximately to 4.07 ± 0.01. The values of moisture content and ash ranged from 83.92 to 85.01 g/100 g and from 2.27 to 2.40 g/100 g, respectively, for all studied samples, indicating that no significant effect by the substitution was observed. With regards to color evaluation, all the parameters measured (including a/b ratio, typical for tomato products) were not significantly different (p < 0.05) between all samples. As was expected, the total soluble solids of new tomato sauces were slightly higher (15.1 °Brix for sample with 100% substitution) compared to the control tomato sauce (13.8%), due to the substitution of water by AW. Nutritionally, the consumption of such tomato sauces could contribute to intake of nutrients, such as minerals, lactose and proteins (Table 3). The total carbohydrates in tomato sauces with the highest substitution (100% AW) were 12.5% higher (8.3 g lactose/100 g d.m.) in lactose content compared to the control sample. Similarly, the calcium concentration was also more than three-fold higher (32.88 mg/100 g) than the corresponding value of control sample (9.04 mg/100 g).

The volatile compounds of novel tomato sauces were also determined (Figure 2).

The major groups of volatile compounds in novel sauces were those that provided a “fruity” (33.3%) and “cooked” (26.6%) aroma in final products. The “acidic” aroma was only 3% of the overall volatile compounds, which means that the substitution of AW did not cause any off-flavor in the new sauces.

Based mostly on the sensory evaluation of the newly developed products and by comparing them with the control samples, a substitution of water even up to 100% by AW is acceptable since it did not affect the flavor and taste of the products at zero time. The results agree with the study of Sady et al. [22], who reported that orange beverages with whey exhibited significantly higher intensity of ‘orange’, ‘sweet’ and ‘refreshing’ aromas than ‘sour’ and ‘whey’ tastes in their final products, leading to acceptable organoleptic beverages of that kind for consumers.

3.2.2. Shelf-Life Determination of New Tomato Sauces

Accelerated shelf-life testing at temperatures ranging from 20 to 40 °C was conducted to estimate the shelf-life of all tomato sauces with 0–100% water substitution. The novel sauces were stable throughout the whole shelf-life study, as in the case of control samples. Neither microbial load, nor nutritional composition alteration were detected, as expected for that kind of product. The acidity of the samples was increased during storage, presenting significant differences from their initial value (up to 25% for tomato sauces with 100% substitution by AW) after 7 months of storage at 40 °C (Figure 3).

The lactic acid content of AW could possibly act as seasoning, by providing a sour taste in the products used, allowing for the partial or total replacement of other added acids used such as acetic acid or citric acid, thus further reducing the production cost of these products. Flinois et al. [24] suggested that AW’s native acids can replace added acids for the activation of the chemical leavening agent favored in pancake preparation; the reaction of the AW native acids with the sodium bicarbonate led to the early release of carbon dioxide gas in the batter, enhancing the pancakes’ volume.

During storage, the color of the samples changed significantly, causing “browning”, attributed to the non-enzymatic Maillard reaction. This is the main deteriorative factor for these kinds of products, limiting their shelf-life to some months, due to the browning that occurs. The high lactose content of AW samples may accelerate browning through the Maillard reaction at the point of contact with the heat source. To solve that issue, ranch dressings made with AW should be processed appropriately, with a lower temperature, higher time, and more constant stirring to avoid direct contact with the heat source.

In all cases, increase in storage temperature led to increased color change, ∆Ε (Figure 4a). Based on data cited in the literature [39], Maillard reactions are always accelerated exponentially due to increased temperatures. This is attributed to the fact that an increase in temperature leads to a proportional increase in the reactivity between the sugars and the amino acids group, producing brown nitrogenous polymers and melanoidins. No differences were observed between the rate constants of color change for the AW-substituted tomato sauces and the control ones. A slight increase in the constant rate of the control sample was observed at 40 °C storage temperature (Figure 4b).

Ashoor and Zent [40] reported that amino acids may be divided in two different groups. The first group, which gives the most intense Maillard browning, includes lysine, glycine, tryptophan, and tyrosine, while the second group, with intermediate browning, produces amino acids includes alanine, valine, leucine, isoleucine, phenylalanine, proline, methionine, asparagine, and glutamine. In AW-substituted sauces, the second group of amino acids was present in significantly higher concentrations compared to the first group, indicating that the Maillard reaction could be delayed in higher storage temperatures and AW could be considered as a low browning-added ingredient.

Sensory evaluation of novel tomato sauces was also conducted during their shelf-life. Acidity and an unacceptable after-taste for tomato sauces with 100% substitution of water by AW was detected after 7 months of storage at 40 °C, justifying their lower score than the other ones. For that reason, the shelf-life of the samples was evaluated based on deterioration of organoleptic attributes. The scores of overall impression were fitted to Equation (7) and the rate constants were calculated. Based on the Arrhenius equation and through extrapolation of data, the shelf-life of the new tomato sauces at ambient temperatures was estimated to be approximately equal to 22 months (without showing significant differences between the samples with AW addition up to 70%), while the shelf-life of the 100% AW-substituted sauces was 3 months lower (

Table 4. Constant rates of the overall impression scores, k_SE (d⁻¹) of tomato sauces with 0 (control), 30, 70 and 100% water substitution by AW after 8 months of storage at 20, 30 and 40 °C. Shelf-life determination (d) of tomato sauces with 0 (control), 30, 70 and 100% water substitution by AW at ambient temperature (25 °C).

	kSE (d−1)
T (°C)	Control	30% AW	70% AW	100% AW
40	0.0112 ± 0.0008 b	0.0111 ± 0.0004 b	0.0114 ± 0.0006 b	0.0133 ± 0.0005 a
30	0.0049 ± 0.0004 b	0.0049 ± 0.0006 b	0.0050 ± 0.0007 b	0.0075 ± 0.0010 a
20	0.0030 ± 0.0006 b	0.0032 ± 0.0003 b	0.0038 ± 0.0004 b	0.0045 ± 0.0007 a
Shelf life at ambient temperature (d)	670 ± 15 a	646 ± 16 a	629 ± 11 a	509 ± 14 b

± represents the standard error estimated by fitting Equation (9). Different superscript letters indicate significantly different means (p < 0.05) between tomato sauces with different AW substitution at each storage temperature.

).

The effect of storage temperature on the rate constants of the overall impression scores was also expressed through the activation energy (E_a), which was calculated as 50.0, 47.2, 41.6 and 41.3 kJ mol⁻¹ for control, 30%, 70% and 100% AW incorporated tomato sauces, respectively. Finally, based on the obtained results of quality deterioration and the sensory characteristics of novel tomato sauces, the optimal water substitution by AW was selected to be the 70%. Similar findings have been reported by Flinois et al. [17], who concluded that AW concentrate at intermediate Brix degrees (15–17°) was the optimal replacement for buttermilk in a dressing, since the use of AW at the highest °Brix (25.2°) resulted in undesirable sensory characteristics and decreased lightness index and water activity.

3.3. Case Study II: Incorporation of Acid Whey Powder in White Sauces

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.

3.3.1. Physicochemical Parameters and Nutritional Compounds of White Sauces at Zero Time

The novel sauces (white sauces with substitution of fat phase with AW powder) were evaluated in terms of quality properties, nutritional attributes and organoleptic parameters as well (

Table 5. Physicochemical parameters & nutritional compounds of white sauces immediately after production (t = 0).

Physicochemical Properties	0% AW	10% AW	20% AW
pH value	3.68 ± 0.01 b	4.05 ± 0.02 a	4.10 ± 0.00 a
Brix	12.46 ± 0.31 c	23.5 ± 1.91 b	30.32 ± 2.01 a
Conductivity (μS/cm)	8.57 ± 0.01 c	13.79 ± 0.22 b	16.65 ± 0.81 a
L	57.65 ± 0.20 b	61.44 ± 0.28 a	63.52 ± 1.43 a
a	−3.79 ± 0.05 a	−3.78 ± 0.04 a	−4.07 ± 0.30 a
b	20.82 ± 0.35 c	21.76 ± 0.17 b	23.04 ± 0.68 a
Hue angle	100.34 ± 1.25 a	99.88 ± 0.15 a	100.02 ± 2.17 a
Chroma	21.16 ± 0.95 a	22.09 ± 0.22 a	23.4 ± 0.32 a
Viscosity (cp)	2800 ± 200 a	3000 ± 100 a	1950 ± 50 b
Nutrients (g/100 g)
Moisture	58.08 ± 0.13 a	57.43 ± 0.11 a	58.41 ± 0.08 a
Ash	0.75 ± 0.05 c	1.85 ± 0.04 b	2.99 ± 0.03 a
Proteins	0.63 ± 0.03 c	1.18 ± 0.02 b	1.52 ± 0.06 a
Lactose	1.12 ± 0.25 c	5.47 ± 0.32 b	7.66 ± 0.61 a
Minerals (mg/100 g)
Ca2+	18.7 ± 5.5 c	103.5 ± 2.51 b	149.6 ± 3.41 a
Mg2+	4.9 ± 0.35 c	36.3 ± 0.09 b	42.3 ± 0.11 a
K+	87.6 ± 8.5 c	504.4 ± 2.22 b	855.7 ± 1.47 a

± represents the standard deviation of triplicates. Different superscript letters indicate significantly different means (p < 0.05) between white sauces with different AW powder substitution.

).

The pH value of the white sauces was increased from 3.68 (control sample, no AW) up to 4.10 (20% AW) with the addition of AW. With regards to color evaluation, L* value was increased for the samples with incorporated AW (up to 63.52 for 20% AW substitution) compared to the control ones (57.65). All the other color parameters measured were not significantly different (p < 0.05) between all the samples. Total soluble solids of new sauces (20% AW) were significantly higher (by up to approximately 18 °Brix) compared to control (12.46 °Brix), due to AW powder incorporation. Increasing the AW powder substitution by up to 20% resulted in higher conductivity (from 8.57 to 16.65 μS/cm). Viscosity was decreased for 20% AW sauce compared to control, which might be attributed to their lower contained fat phase (20% decrease of fat phase compared to control white sauce).

The moisture content was approximately 58 g/100 g for all studied samples. The substitution of fat phase by AW powder affected the values of ash content, which increased from 0.75 to 2.99 g/100 g. The lactose content of sauces with the highest substitution (20% AW) was eight times higher (7.66 g lactose/100 g) compared to the control sample. The protein content of developed sauces saw a 2-fold and 4-fold increase compared to control ones, for 10 and 20% AW substitution, respectively. The calcium concentration of 20% AW sauce was equal to 149.6 mg/100 g, while the corresponding value of the control sample was only 18.7 mg/100 g. Similarly, the magnesium and potassium concentrations for the new sauces were up to 10 times higher compared to the control.

The incorporation of AW powder in the novel white sauces did not significantly affect the flavor and taste compared to the control samples at time t = 0 (immediately after production). The new samples were characterized by lower acidity according to the organoleptic panel. No differences were observed between samples in terms of emulsion stability immediately after their production. Nevertheless, it was expected that the incorporated white sauces with AW would have increased emulsion stability due to the smaller fat particles that were contained in the aqueous phase (Figure 5).

The average droplet size of fat particles was approximately 21.5, 17.5 and 7.2 μm for control, 10% AW- and 20% AW-substituted white sauces, respectively. According to the optical microscopic observations and the average diameter data, the droplet size of fat particles progressively decreased with the increasing substitution of AW from 0 to 20%, which is in accordance with the general consensus about the correlation of the emulsion stability with the dependence of particle concentration from their droplet size [41,42]. By increasing the AW substitution in the formed emulsion, the density of fat particles and the ratio of interfacial tension to their droplet size were increased resulting in improved emulsion strengthening [43].

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. Constant rates of the total color change ∆Ε, k_∆Ε (d⁻¹) of white sauces with 0 (control), 10 and 20% fat substitution by AW after storage at 20, 30 and 40 °C. Shelf-life determination at ambient temperature (d).

	k∆Ε (d−1)
T (°C)	Control	10% AW	20% AW
40	0.0123 ± 0.0011 b	0.0125 ± 0.0005 b	0.0151 ± 0.0009 a
30	0.0053 ± 0.0009 b	0.0056 ± 0.0010 b	0.0074 ± 0.0004 a
20	0.0041 ± 0.0008 b	0.0043 ± 0.0007 b	0.0063 ± 0.0009 a
Shelf Life at Ambient Temperature (d)	405 ± 14 a	384 ± 16 a	239 ± 10 b

± represents the standard error of fitted Equation (10). Different superscript letters indicate significantly different means (p < 0.05) between white sauces with different AW substitution at each storage temperature.

.

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 (E_a), 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 meqO₂/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.

4. Conclusions

The suggested products are ready-to-eat, safe, of high quality and nutritional value, and with a long shelf-life, fulfilling the current consumer demands associated with the consumption of healthy, low fat food products with added-value compounds. Based on the quality and sensory characteristics of the tomato sauces, the optimal water substitution by AW was 70% w/w (approximately 17% w/w of the total product formulation), resulting in increased lactose (10% increase) and calcium (three times higher) content, without causing any off-flavors and affecting their shelf-life. In the case of the developed white sauces, the optimal fat phase substitution by AW powder was 10% w/w of the total product formulation, which led to considerably higher lactose and calcium (both five times higher) content. AW incorporation mimicked the desired texture and mouth feel sensation that fat phase generally provides in typical white sauces, and no negative effect on the emulsion stability of samples during shelf-life was found. The proposed use of AW does not require complicated technological solutions and can be easily implemented even by small factories. Nevertheless, the effective use of AW directly in a food formulation should overcome several issues. The dairy industry should standardize the composition and quality characteristics of AW before its reuse in the food industry, thus providing a functionality in conventional products already available in market or even developing new ones. Finally, AW valorization could also benefit the dairy industry by solving the problem of AW disposal, considering the environmental awareness as well as the challenge for ‘zero food waste’.