Effect of homogenizer pressure and temperature on physicochemical, oxidative stability, viscosity, droplet size, and sensory properties of Sesame vegetable cream

Abstract In this study, the effects of homogenization pressure (125, 145, and 165 bars) and temperature (45, 60, and 75°C) on the properties of Sesame vegetable cream are investigated. The physical stability of cream was characterized by droplet size and syneresis, and chemical stability of it was evaluated by determining peroxide value and p‐anisidine. The results showed that the cream in the presence of high pressure and temperature treatment exhibits lower stability. At 75°C temperature and 165 bar, the vegetable cream had highest peroxide value (3.61) and p‐anisidine (2.16). However, pressure could protect the droplets against aggregation in the high pressure (165 bar) and greatly increased the physical stability. During increase in process parameters, the syneresis of cream was decreased with a rise of pressure and extension of temperature. The process condition in 145 bar and 60°C led to the high acceptability of vegetable cream.

Low-pressure homogenization cannot be able to increase the energy threshold necessary to break these clusters droplet. High-pressure homogenization increases the activity of surface of the emulsifying component, which may grow the efficiency of the emulsion (ability of coating or penetration action) (Floury, Desrumaux, & Lardieres, 2000).
Moreover, a considerable change in the oil droplets dispersion state would be the emulsification of some immiscible liquids (oil and water), which also results in a considerable state of the water-oil interface (McClements, 2015;Walstra, 1983), and mainly, two types of ingredient can be adsorbed: amphiphilic component (such as proteins) and emulsifiers with low molecular weight (monoglycerides, lecithins, spans, tweens, etc.) (Burgaud, Dickinson, & Nelson, 1990;Ozturk & McClements, 2016). Emulsifiers with low molecular weight and proteins help the production and the emulsions stabilization.
Proteins play two main roles: First, they lower surface tension between the interfaces that are applied during the process of emulsification, and second, they form a component layer surrounding the dispersed ingredient, which structurally stabilizes the emulsions by reducing the rate of coalescence (Walstra, 1983). In food emulsions, stability is usually received by the proteins application as the main stabilizer.
In the homogenizer, some processing conditions including shear stress, high pressure, and temperature can lead to a protein-stabilizing properties deterioration (Ozturk, Argin, Ozilgen, & McClements, 2015). However, when it is already established that structure of protein, it is susceptible to be modified by high-pressure method, and it is not known to what extent the new technology, such as homogenization with dynamic high pressure, allows systematic modification of the texture and rheology of protein-stabilized emulsions. Moreover, only the high hydrostatic pressure effects on the structure of the protein in aqueous solution have received considerable attention over the recent few years (Dickinson & Pawlowsky, 1996;Zhou et al., 2016).
Consequences on globular proteins are that disrupts of high pressure the quaternary structure and tertiary. It is also known that globular protein unfolding is partly due to secondary structure changes (β-sheets, α-helices). As with thermal treatment, the globular protein partial denaturation used of hydrostatic high pressure leads to aggregation (Dumay, Kalichevsky, & Cheftel, 1994;He, Mao, Gao, & Yuan, 2016). Dumay, Lambert, Funtenberger, and Cheftel (1996) have reported emulsion pressure-induced rheological modifications due to aggregation of β-lactoglobulin. Galazka, Dickinson, and Ledward (1996) showed that high-pressure process (up to 800 MPa) of the globular protein β-lactoglobulin leads to a reduction in the capacity of emulsifying and a decrease in the fine emulsion stability made at pH 7 with 20 vol.% oil and 0.4 w.w.b% protein. The author reported this result as a low of emulsifying efficiency due to pressure-induced unfolding followed by aggregation. Qualitatively similar effects of high-pressure process on emulsifying characterization were also showed when β-lactoglobulin was replaced with commercial WPC (Galazka, Ledward, Dickinson, & Langley, 1995).
The aim of this study was to evaluate the effect of homogenizer pressure (125, 145, and 165 bar) and temperature (45, 60, and 75°C) on physicochemical, oxidative stability, viscosity, droplet size, and sensory properties of vegetable cream.
Sesame oil was purchased from Narges Oil Company (Shiraz, Iran).

| Titratable Acidity and pH measurement
pH and total titratable acidity were determined by Bemer, Limbaugh, Cramer, Harper, and Maleky (2016) standard approach, and the acidity was expressed according to the lactic acid percentage.

| Serum loss measurement
Cream (10 ml) centrifuged at speed of 140 g for 5 min using a centrifuge (Phillips HR1565, China). Amount of Serum loss was reported according to the serum percentage.

| Peroxide value (PV) and P-Anisidine value measurement
Extraction of Lipid was performed and utilized to determine lipid oxidation and p-anisidine values as chemical indicator. Both panisidine value (AV) and peroxide value (PV) were determined according to the method described by Keramat, Golmakani, Aminlari, and Shekarforoush (2016). For PV evaluation, 5 g oil was added to 30 ml solvent (acetic acid and chloroform mixture), and then, approximately 5 ml potassium iodide was added. The mixture was mixed for 1 min. After that, 30 ml of double distilled water was mixed with mixture, and then, starch solution was also added.
Titration was carried out using 0.01 N sodium thiosulfate solution to appearance a transparent color. In AV, 0.2 g of oil was mixed with 10 ml of trimethylpentane. The A 1 absorbance was determined at 350 nm. One ml of 2.5 g/L p-anisidine in acetic acid was mixed with 5 ml of the oil-trimethylpentane dispersion. After 10 min, the A 2 absorbance was determined. AV was optioned from these absorbance, and the oil mass (m) previously calculated:

| Droplet size distribution
Droplet size and span were measured based on the method described by Nejadmansouri, Hosseini, Niakosari, Yousefi, and Golmakani (2016) with some modification. Static light scattering technique (at 20°C temperature) was used to evaluate the size of the droplet (Laser Diffraction Particle Size, SALD-2101, Shimadzu, Japan). The average droplet size (z-average) and span were reported.
The width of the droplet size distribution was shown as a span of distribution: span = (d90 − d10)/d50, where d × 0 is the diameter corresponding to ×0 intensity on a relative cumulative droplet size distribution curve.

| Sensory Evaluation
At least 20 members of a trained panelist group were selected from the department of food science and technology (Zarin Dasht Branch, Islamic Azad University, Fars, Iran) and performed sensory properties. This test was carried out based on 5-point Hedonic scale method (1 = dislike extremely, 2 = dislike moderately, 3 = neither like nor dislike, 4 = like moderately, and 5 = like extremely). The creams for organoleptic properties were coded and given to panelists in order to evaluate the acceptance rated of taste, aroma, texture, color, general acceptance. For this aim, the samples were kept in 4°C for 1 week (Bemer et al., 2016).

| Statistical analysis
All experiments were evaluated in the form of completely random blocks and repeated three times. Duncan test was used to compare means when the effect was significant. p < 0.05 was used as a level of significance. The data were shown in the form of mean and standard deviation. SAS software version 9.1 was applied for statistical analysis (SAS Institute Inc., 2000; Cary, NC, USA).

| Physicochemical properties
The effects of pressure and temperature on physicochemical change for the different sample were evaluated. As shown in Table 1, the acidity in all samples increased significantly by increasing the pressure, but temperature does not have any significant effect on acidity.
To increase homogenization level, O 2 amount in cream and oxidation rate and produce of fatty acids increased significantly. Marco-Molés, Hernando, Llorca, and Pérez-Munuera (2012)   Results showed that with an increase in homogenization, serum loss value significantly reduces to 40%. This phenomenon is due to increased amount of kappa casein on the surface droplet.

| Oxidative stability
The

| Color properties
The effects of different concentration of homogenizer pressure and temperature on the color changes (L* (lightness), a* (rednessgreenness) and b* (yellowness-blueness)) of vegetable cream treatments are shown in Table 2 and Fig 1. Comparison of L* values of treated samples showed a significant difference (p < 0.05).
According to the results, the L* value in all samples increased significantly with increasing homogenizer pressure, but the L* value in all samples decreased significantly with increasing temperature.
This change is due to the effect of pressure on droplet size distribution and viscosity. By increasing temperature and pressure, L value increases significantly (Quek, Chok, & Swedlund, 2007). (2003)

| Viscosity
The effects of homogenizer pressure and temperature on viscosity of cream are shown in Table 3. By evaluating the effect of temperature on K, the results showed treated sample in 60°C has the highest K. There was not any difference between 45 and 75°C

| Droplet size distribution
The effects of different homogenizer pressure and temperature on the droplet size distribution and span of treatments are shown in Table 3. The prepared samples were diluted for 10 times and then analyzed to determine particle size distribution. Generally, mixed systems that consist of both emulsifier and stabilizer could more prolong the aggregation of particle compared to single-type systems.
By an increase in homogenizer pressure and temperature, amount of droplet size significantly decreased. Yuan, Gao, Zhao, and Mao properties. They reported with an increase in pressure from 20 to 50 MPa droplet size decreased significantly, due to shear stress in high pressure.

| Sensorial attributes
Sensory attributes are one of the most efficient tests to evaluate the quality change of products (Abedi, Naseri, Ghanbarian, & Vazirzadeh, 2016

E TH I C A L S TATEM ENT
In this research, we used humans only for test panelist and I ensure this research conducted following the principles of the Institute of Standards and Industrial Research of Iran.

CO N FLI C T O F I NTE R E S T
None declared.