Formulation Optimization of Pistachio Oil Spreads by Characterization of the Instrumental Textural Attributes

Abstract

The influence of formulation variables pistachio oil (7.5 and 15% w/w), cocoa butter (7.5 and 15% w/w), xanthan gum (0 and 0.3% w/w), and distillated monoglyceride (0.5 and 1% w/w) on the important texture attributes of spreads based on pistachio oil was studied. The firmness, adhesiveness, cohesiveness, and compressibility attributes were evaluated as a function of different formulations. Results demonstrated that pistachio oil content, among all variables, had the most significant effect on these attributes. All the measured attributes were improved by adding xanthan gum to the spreads. Addition of distillated monoglyceride and pistachio oil components to various formulations considerably increased firmness and cohesiveness, respectively (p < 0.05). However, the firmness, adhesiveness, and compressibility of spreads were significantly declined by increasing the cocoa butter content. The spreads formulated with 15% pistachio oil, 7.5% cocoa butter, 0.3% xanthan gum, and 1% distillated monoglyceride showed the best texture attributes.

Keywords:

• Pistachio oil spreads
• Texture properties
• Xanthan gum
• Distillated monoglyceride (DMG)

INTRODUCTION

Spread is an edible paste put on other foods which is generally consumed on breads and toasts, or similar pastries such as pancakes and pitas. It is a model water/oil (W/O) emulsion with different formulation consisting fat (cocoa butter [CB]), water, emulsifiers, stabilizers, salt, antioxidants, and other ingredients.[1] One of the most important components in the spread manufacture is fat. It imparts shortening, richness, and tenderness, and improves mouthfeel, flavor (intensity), and perception.[2] Some researchers found that the partial replacement of used fat with vegetable oils can ameliorate the spreadability at refrigerator temperature (4°C) and enhance nutritional values, such as desirable fatty acid profile and lower cholesterol level in butter fat-vegetable oil blend spread products.[3, 4] Pistachio nut (Pistacia vera L.) as a unique nut generally has more than 55% oil. The predominant fatty acid of pistachio oil (PO) is oleic acid (56–64%). The oil also contains linoleic and linolenic acids that are essential in human diet.[5] Consumption of semi-solid foods prepared from PO to existence of high concentration of natural antioxidants has been reported as being protective against certain types of cancer and may also decrease the risk of cardiovascular diseases.[6] The liquid crystalline phase behavior between water and monoglyceride is called to mesomorphic phase behavior (MPB).[7] The MPB can change for certain ratios of monoglyceride and water, and under certain temperature conditions. Thus, these phases are characterized by behavior between the liquid and solid phase. Monoglyceride as a crucial emulsifier type in the spread production could also be used as solid fat providers in triglyceride systems, which is not specifically linked to its MPB.[8] A desired solid fat content (SFC)-profile could be obtained with selection of the correct blend of saturated and unsaturated monoglyceride.[7, 8] The SFC-profile is one of the principal indices to determine the suitable application of certain oils, fats, or fat blends.[8, 9] Moreover, the addition of small amounts of water to these components due to the MPB changes may have a significant effect on the functionality and structure of the systems.[10] Polyglycerol polyricinoleate (PGPR) also is a key ingredient for the spread manufacture which can form by polycondensation of castor oil and glycerol. It is a complex mixture with polyglycerol component dominated by di-, tri-, and tetraglycerols.[11] Schantz and Rohm[12] demonstrated that PGPR in some spreads increases the volume fraction of continuous phase and binds their residual water, making it unavailable to hydrate and swell the solid particles. There are at present a considerable number of polysaccharide biopolymers such xanthan gum (XG) and locust bean gum (LBG) which are used to provide structure to the aqueous phase of these food systems. Since no biopolymer on its own can provide the required structure alongside a “plastic” flow, mixtures have been applied to achieve the desired combination of characteristics.[13] XG is a non-linear anionic microbial heteropolysaccharide synthesized by aerobic fermentation of Xanthomonas campestris. Primary structure of XG is consisting of a cellulosic backbone of (1,4)-β-D-glucose residues, and a trisaccharide side chain consisting of β-D-mannose-(1,4)-β-D-glucuronic acid-(1,2)-β-D-mannose attached at C-3 to alternate glucose residues of the main chain.[14] It is widely used as an emulsion stabilizer and thickener due to its excellent viscosity and dispersion properties (such as reversible shear thinning and its ability to disperse in either hot or cold water).[15] LBG also is the refined endosperm of the seed of the carob tree (Ceratonia siliqua). The viscosity of the solutions by adding this gum considerably is enhanced. However, it is only slightly soluble in cold water and dispersions must be heated to about 80°C to attain full viscosity potential. This galactomannan has a backbone (1–4) linked to a β-D-mannopyranosyl unit having side stubs of (1–6)-linked α-D galactopyranosyl groups.[16] The interaction of XG is more pronounced with LBG than with any other polysaccharide or galactomannans to form mixed gels with high viscosity at low concentration.[16, 17] Nonetheless, the intermolecular interaction between XG and LBG has been previously displayed by Rock et al.[18] Understanding the correlation between food structure and its texture perception is of growing importance.[19, 20] Although texture examination via a sensory panel provides informative data, Radočaj et al.[21] found that the instrumental methods were better than sensory panel tests as they are more objective, reproducible, and require less time and cost. To accelerate their search process and the product texture evaluations, the food industry is looking for reliable instrumental determination and rapid methods that can help predict the texture attributes in the preliminary stages of product development.[22] The textural characteristics of spreads such as firmness, cohesiveness, adhesiveness, and compressibility commonly play a vital role in consumer appeal, buying decisions, and eventual consumption.[23 ⁻ 25] Moreover; optimization is an efficient solution to improve the research and development activity on new or existing products. Optimum formulation for the PO-based spreads production, with regard to suitable textural attributes, is necessary to the design of applicable apparatus and equipment, control of production process, storage, and shelf life.[26] It is believed that detailed measurements of principal textural attributes of PO-based spreads and optimization of their structural components have not been reported. Therefore, the objective of current study was to characterize and optimize the structure of novel functional spreads based on PO as a function of various practical formulations.

MATERIALS AND METHODS

Chemicals and Materials

Pistachio nuts were obtained from the local market during November–December, 2010 in a city located in Rafsanjan (Iran). They were manually cracked and shelled, and then chopped in a smooth corundum disk mill (Glen Mills, Clifton, NJ, USA). The oil expression was carried out with a screw press (Model NB 90, Kimiagaran Products Co., Kerman, Iran). The used oil in present study contained the following fatty acids (mol %): 0.6% C14:0, 11% C16:0, 0.7% C16:1, 1.7% C18:0, 59.5% C18:1, 25% C18:2, 0.2% C18:3, 0.3% C20:0, and 0.6% C20:1 as measured by gas chromatography of methyl esters. Other ingredients such as sugar, milk powder, CB, and salt powder were supplied by Gorji Biscuit Co. (Tehran, Iran). XG and LBG were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). PGPR 4110, PGPR 4175, distilled monoglycerides (DMG 0291) and DMG0295 were provided from Emulsion-Holland B.V., Zierikzee, Holland. According to the recommendation of the company, DMG0291 and PGPR4110 were applied in formulation with more than 20% oil and, DMG0295 and PGPR4175 were used to formulate spreads with less than 20% oil.

Sample Preparation

For the preparation of spreads, the method of Beckett[27] was adopted with minor modifications. A water-soluble mixture of sugar (45% w/w), milk powder (13.5% w/w), pistachio paste (10% w/w), XG (0 and 0.3% w/w), LBG (0.09% w/w), and salt (0.04% w/w) routinely refined to particle size <30 μm using a combination of two- and five-roll refiners. The fat-soluble ingredients including CB (7.5 and 15% w/w), PO (7.5 and 15% w/w), and surfactants (DMG [0.5 and 1% w/w] and PGPR [0.3% w/w]) were separately mixed and then added to the previous mixture at 50°C. The obtained mixture after refining for 2 h was moved into a laboratory-scale conch. The conching process is a necessary stage for achieving the suitable viscosity and satisfactory texture and flavor for spreads. This process as an endpoint for manufacture of PO-based spreads was determined by physico-chemical changes in the product mix. During the process, pistachio taste was developed and water content was reduced to less than 1%. Also, suitable control of temperature (50–60°C) during conching is necessary to produce a high-quality spread. Time of this process depends on the composition of the mass, but it is normally 8–10 h for the spread.[28] At the end stage of conching, interactions between disperse and continuous phase were promoted, and the different formulations were then hot-filled into special containers, cooled and kept at 25°C until the time of the tests.

Sixteen PO-based spreads (A-P samples) with different formulations were prepared according to the mentioned method (Table 1). Preliminary studies showed that the addition of the concentration levels studied to the spread formulation resulted in desirable textural changes of PO-based spreads. LBG and PGPR were used at optimal values 0.09 and 0.3% w/w, respectively.[11] Other ingredients such as pistachio paste and milk powder were used at recommended levels by the company. In this study, two commercial spreads also as a reference to compare with the prepared samples were used from the internal (sample Q) and external (sample R) producers.

Table 1  The combination of formulations based on different levels of independent variable

Sample	PO (% w/w)	CB (% w/w)	XG (% w/w)	DMG (% w/w)
A	15	7.5	0	0.5
B	7.5	7.5	0.3	0.5
C	7.5	15	0	1
D	15	15	0.3	0.5
E	7.5	15	0.3	0.5
F	7.5	7.5	0.3	1
G	7.5	15	0.3	1
H	15	7.5	0.3	1
I	15	7.5	0.3	0.5
J	7.5	7.5	0	0.5
K	15	7.5	0	1
L	7.5	15	0	0.5
M	15	15	0.3	1
N	15	15	0	1
O	15	15	0	0.5
P	7.5	7.5	0	1

Textural Attributes Measurement

The prepared samples were put into cylindrical steel containers 50 mm in diameter with particular notice to avoid bubble formation. One half of the containers were taken for analysis immediately, the other half were maintained at 5°C for 21 h and the texture was evaluated immediately after this storage. Texture profile analysis (TPA) method modified by Bonczar et al.[29] was applied to analyze the instrumental texture by two sequential compression events at the crosshead speed 1 mm/s on 25 mm depth, separated by a relaxation phase of 15 s using an Instron Universal Testing Machine (Testometric machine, M350-10CT, England) equipped with a 5 kg compression load cell and a cylindrical aluminum probe of 30 mm diameter with flat end. All of the samples were analyzed separately in triplicate and the results represented as a mean of the three values. The following attributes were measured by curves obtained from the texture analyzer machine (Figure 1): (a) firmness (or hardness, N): defined as the maximum peak force during the first compression cycle, (b) cohesiveness (%): defined as the ratio of the positive force area (A2) during the second compression to that during the first compression (A1), (c) compressibility (J): is equal to the sum of two areas A1 and A2, and (d) adhesiveness (J): defined as the negative force area for the first bite during the withdrawal of the compression plate (A3).[11]

Figure 1 A typical texture profile analysis diagram.

Experimental Design and Statistical Analysis

The textural properties of PO-based spreads prepared with various structural formulations were subjected to analysis of variance (ANOVA), applying full factorial design, using Minitab software (version 14 Minitab Ltd., USA). The factors studied were the concentration of emulsifying (DMG) and stabilizing (XG) agents, PO and CB. Significant differences (p < 0.05) for these variables, based on at least three individual measurements, were determined by the ANOVA procedure. Three dimensional (3D) graphs and interaction plots also obtained from this software. Moreover, correlation analysis was carried out employing Pearson's test using SPSS 13 (SPSS Inc., USA) software.

RESULTS AND DISCUSSION

Firmness

Table 2  Analysis of variance for the effect of the independent variables on the dependent variables

	Firmness (N)		Cohesiveness (%)		Adhesiveness (J)		Compressibility (J)
Textural Attributes Source	P value	T value	P value	T value	P value	T value	P value	T value
Constant	0.000	27.89	0.000	26.70	0.000	31.13	0.000	32.29
PO (Pistachio oil)	0.000	−18.66	0.000	10.16	0.000	−19.16	0.000	−21.81
XG (Xanthan gum)	0.001	3.55	0.000	10.27	0.011	2.70	0.015	2.56
CB (Cocoa butter)	0.000	−7.24	ns	1.96	0.000	−9.25	0.000	−5.13
DMG (Distillated monoglyceride)	0.001	−3.60	0.000	9.91	0.000	6.58	0.000	4.08
PO*XG	0.000	4.16	0.000	9.60	ns	1.43	0.000	5.80
PO*CB	0.000	5.02	0.000	−11.98	0.011	2.70	ns	0.27
PO*DMG	ns	1.99	ns	1.95	0.000	−4.04	0.023	−2.38
XG*CB	ns	1.17	0.000	−7.03	0.000	−4.34	0.014	−2.59
XG*DMG	ns	−1.16	0.000	19.05	0.000	−12.33	0.000	−12.8
CB*DMG	0.009	2.77	ns	0.62	0.000	−4.62	ns	0.94
PO*XG*CB	0.006	−2.93	0.000	−6.34	ns	−1.95	ns	−1.03
PO*XG*DMG	0.000	8.18	0.000	9.80	0.000	16.89	0.000	16.36
PO*CB*DMG	0.000	−3.95	0.000	−5.98	ns	0.38	0.017	−2.52
XG*CB*DMG	0.000	−5.93	0.001	3.55	0.001	−3.86	0.000	−5.65
ns: not significant (p > 0.05).

A higher firmness value indicates a lower spreadability of the test product. In other words, spreadability is related to the ability to apply a spread on a piece of bread or cracker. It is possibly the principal textural value of any spread, and is expressed as its hardness. As clearly exhibited in Table 2, the linear effect of all independent variables on firmness was highly significant (p < 0.0001; p < 0.01). The results also illustrated that among the interactions, PO–DMG, CB–XG, and XG–DMG had insignificant effects on firmness (Table 2). The most significant effect on firmness value was revealed to be the PO effect due to its highest T-value among the independent variables (Table 2). The results show that increasing PO concentration resulted in lower firmness. It may be due to the high concentrations of monounsaturated (oleic) and polyunsaturated (linoleic) fatty acid and followed by lower SFC values at higher PO levels. The instrumental firmness of dark chocolate spreads due to the changes of SFC values significantly decreased by increasing hazelnut oil content.[30] Full et al.[31] also determined that a strong positive correlation exists between instrumental firmness and SFC of chocolate spreads at 20°C. However, Radočaj et al.[21] reported that the firmness of hemp oil (HO)-spreads increased with the increase of the HO content. This discrepancy might be attributed to differences in the values of SFC among these spreads because of the higher content of the saturated fatty acids (SFAs) of HO can interact with the stabilizer crystals (a blend of saturated oils) to form a firmer structure. Variation in firmness of spreads as a function of DMG and XG concentrations, PO content and CB percentage is shown in Fig. 2. As can be considered, when the XG content increased from 0 to 0.3% w/w, the firmness increased in a parabolic manner (Figs. 2a and 2c). The increase of firmness might derive from an increased viscosity present for samples containing high XG concentration, which will harden the texture of the spread. Moreover, the interactions of XG with LBG due to association of XG double helicoidally structure with sequences of unsubstituted mannosyl residues in the galactomannan can increase the consistency and firmness.[16] Radočaj et al.[21] also showed that the addition of high amounts of a commercial stabilizer significantly lowered the samples spreadability. Gharibzahedi et al.[26] demonstrated that increase in XG concentration made droplet size distribution narrower and decreased the emulsion particle size. This fact is due to high viscosity of continuous phase, which gives enough time for the surfactant to adsorb and protect droplets.[15] It seems that the spreads with smaller particle size have more firmness values than those with bigger particle size. By measuring the texture of reduced-fat peanut butter, Lima et al.[32] found that the value of instrumental firmness was very dependent to the particles size, where the minimum hardness was achieved for a particle size of 0.3–0.33 mm. Narine and Marangoni[33] had also previously reported that fat systems with a larger crystal size were often characterized by a lower firmness. However, Dubost et al.[34] found that higher firmness of the peanut soy spreads may happen in the low level of used stabilizer (0.5%). They explained this amount cause more movement and interaction among the ingredients. Figures 2a and 2c show that the firmness respectively increased and decreased by increasing contents of DMG and CB. In this research, a blend of saturated and unsaturated monoglyceride was selected to provide a suitable SFC to triglyceride systems. Vernier[35] showed that these glycerol fatty acid esters increased plastic viscosity through less efficient coverage of sugar particles, thus leading to greater friction and firmness. CB has a distinct texture due to unique interactions of polymorphic lipid structures. Brunello et al.[36] found that polymorphism strongly influenced mechanical properties indirectly via its effects on the microstructure of the material. From the structural description, it seems that the interactions between the microstructural elements in molecular arrangement of spreads gradually weaken by increasing CB concentration in the different formulations and thus decreased the firmness.[33] Figure 2 reveals the lowest value for firmness was observed when the spread was formulated with the lowest levels of XG (0% w/w) and DMG (0.5% w/w), and the highest PO (15% w/w) and CB (15% w/w) amounts. According to these findings, F and O samples showed the highest firmness among all of the spreads (Table 3). From a technological point of view, it might be concluded that the H sample is an ideal spread due to its firmness similarity to two commercial spreads (Q and R samples) (Table 3).

Figure 2 Response surface curves for the correlative effect on firmness force of spreads of: (a) pistachio oil (PO) and xanthan gum (XG) concentration; (b) PO and cocoa butter (CB) concentration; (c) CB and distillated monoglyceride (DMG) concentration. In each plot, the other two factors were kept at low level.

Table 3  Instrumental evaluation of spreads with different formulation

	Structural Properties
Samples ^1 ^, ^2	Firmness (N)	Cohesiveness (%)	Adhesiveness (J)	Compressibility (J)
A	25.81 ± 1.99^ef	5.92 ± 0.44^b	43.40 ± 7.21^fgh	131.62 ± 20.14^gh
B	99.02 ± 2.65^c	Trace^e	237.35 ± 9.42^cd	1113.13 ± 51.94^c
C	116.60 ± 8.15^b	2.80 ± 0.07^cd	291.87 ± 38.55^b	1763.33 ± 66.16^a
D	11.15 ± 0.12^ghi	6.65 ± 0.46^b	9.85 ± 0.49^gh	123.19 ± 2.32^gh
E	113.22 ± 12.76^b	Trace^e	268.75 ± 46.73^bc	1130.19 ± 208.18^c
F	151.23 ± 5.65^a	Trace^e	71.20 ± 2.31^f	721.86 ± 27.77^d
G	7.70 ± 0.04^hi	Trace^e	30.59 ± 1.71^fgh	111.20 ± 2.29^gh
H	33.27 ± 2.04^e	12.10 ± 0.93^a	153.83 ± 26.84^e	498.90 ± 34.55^ef
I	10.63 ± 0.19^ghi	Trace^e	8.53 ± 1.38^gh	48.49 ± 2.81^h
J	15.02 ± 0.67^gh	6.10 ± 0.45^b	28.60 ± 3.18^fgh	158.09 ± 5.13^gh
K	24.29 ± 0.23^ef	3.30 ± 0.35^c	1.12 ± 0.37^h	158.48 ± 3.22^gh
L	18.09 ± 0.29^fg	3.08 ± 0.58^cd	51.70 ± 1.96^fg	228.58 ± 3.15^g
M	26.08 ± 0.06^ef	2.39 ± 0.29^d	33.861.08^fgh	166.82 ± 4.48^gh
N	61.58 ± 9.41^d	0.53 ± 0.13^e	206.34 ± 29.08^d	597.21 ± 105.42^e
O	4.53 ± 0.16^i	Trace^e	17.22 ± 0.51^gh	65.41 ± 2.40^h
P	111.37 ± 0.67^b	Trace^e	361.32 ± 36.26^a	1451.22 ± 21.51^b
Q ^3	33.30 ± 1.70^e	5.92 ± 0.21^b	133.36 ± 15.97^e	522.59 ± 51.08^ef
R ^3	29.62 ± 0.23^e	5.91 ± 0.57^b	114.72 ± 10.41^e	445.91 ± 3.04^f
^1Each value is expressed as the mean of three replications.
^2Means with the same letter within a column are not significantly different at p < 0.05.
^3Commercial samples.

Cohesiveness

Table 2 clearly shows that the main effects of PO, XG, and DMG were significant on the spread cohesiveness, whereas CB was not significant. The mutual interaction between PO and XG; PO and CB; XG and C; and XG and DMG was also found to be significant (p< 0.0001) (Table 2). This parameter increased significantly when PO and XG concentrations increased (Figs. 3a–3d). Glibowski et al.[37] also found that the fat partial replacement with oil content caused significant decrease in the spread cohesiveness. Cohesiveness is a determination of intermolecular strength. Thus, it seems that the strong interactions among solid particles such as sugar and CB, and PO, mainly via XG and XG-LBG as matrix-forming agents in the formulation of these spreads during conching were formed.[11, 16] The cohesiveness dramatically increased as the content of DMG emulsifier increased from 0.5 to 1% (Fig. 3d). The more cohesiveness for high DMG containing spreads can be explained by the denser structure because of the smaller size of spread particles.[38] Table 2 demonstrated that a significant interaction was among these critical structural components for the cohesiveness of PO-based spreads. Figure 3 also shows the highest value for cohesiveness was when the spreads were composed with the highest levels of PO (15% w/w), XG (0.3% w/w), and DMG (1% w/w). Therefore, H sample showed the maximum of cohesiveness because it had the high levels of PO, XG, and DMG (Table 3). Table 3 also shows that A, D, and J samples had rather similar cohesiveness to blank samples.

Figure 5 Response surface curves for the correlative effect on firmness force of spreads of: (a) PO and XG concentration; (b) DMG and PO concentration; (c) XG and DMG concentration; (d) CB and XG concentration. In each plot, the other two factors were kept at low level.

Figure 3 Response surface curves for the correlative effect on firmness force of spreads of: (a) PO and XG concentration; (b) PO and CB concentration; (c) XG and CB concentration; (d) CB and DMG concentration. In each plot, the other two factors were kept at low level.

Adhesiveness

As shown in Table 2, the adhesiveness was significantly influenced by the linear and mutual interaction effects of all independent variables studied except the interaction effect of PO-XG (p < 0.0001; p < 0.05). Moreover, among the independent variable effects, the linear effect of PO followed by interaction effect of PO-XG-DMG and XG-DMG had the most significant (p < 0.05) effect on the spread adhesiveness (Table 2). Figure 4 shows the adhesiveness increased as the content of XG and DMG was increased, but considerably decreased with increasing concentration of PO and CB. Adhesiveness or stickiness is described as the force required to overcome the attractive forces between the food surface and the surface in which the food sample comes in contact.[37] Radočaj et al.[21] also found that the spreads adhesiveness had lower values at higher levels of HO content. Increase of this parameter by increasing XG and DMG might be attributed to the high viscosity of the aqueous phase and low particle size of spreads, respectively. A decrease in particle size by increasing concentration of XG stabilizer has been previously reported by the literature.[26] Gharibzahedi et al.[39] showed that the additional emulsifier was able to coat the surface area and resulted in the formation of greater number of smaller particles. In other words, the overall surface area is generally increased as small particles are present, so the fat phase better disperses around the solid matrix, and this makes CB stickier as less oil is available.[32] Table 3 illustrated that P sample had the highest adhesiveness due to the lowest levels of PO and CB, and maximum of DMG. The lowest adhesiveness value was related to sample K because it had the maximum of PO and minimum of DMG (Table 3). However, sample H could be considered as an optimum spread comparing its adhesiveness (153.83 J) to that of two references commercial samples (114.72 and 133.36 J).

Figure 4 Response surface curves for the correlative effect on firmness force of spreads of: (a) PO and CB concentration; (b) PO and DMG concentration; (c) XG and CB concentration; (d) XG and DMG concentration; (e) CB and DMG concentration. In each plot, the other two factors were kept at low level.

Compressibility

Compressibility stands for the amount of work required to achieve deformation of internal strength of the structural bonds. This factor is very important in the sense that a moderately associated network would possibly maintain the product structure and its consistency during storage time.[40] Table 2 shows that the compressibility was influenced by all main independent variables and also the interaction effects of PO-XG, PO-DMG, XG-CB, and XG-DMG. In addition, a positive correlation was found between the compressibility and firmness values of spreads (r = 0.863, p < 0.0001). Figs. 5a and 5c show that the compressibility of PO-based spreads decreased rapidly with increases in PO concentration. This can be explained by the lower SFC of spreads containing high levels of unsaturated fatty acids. The compressibility increased with increasing the DMG from 0.5 to 1% (Figs. 5b and 5d). This may be due to the interactions between monoglycerides especially saturated monoglycerides in DMG and the used stabilizing agents (XG and LBG). These monoglycerides have strong emulsifying characteristics because of amphiphilic residues in their structure and thus can easily surround water droplets to compose a stable fine emulsion.[8] The compressibility attribute was found to significantly increase with higher amount of XG (Figs. 5a, 5c, and 5d). It demonstrates that the addition of XG widely enhanced the formation of a network matrix, thus increasing the system viscosity and the rate of compressibility. Moreover, this matrix can be complicated by the presence of LBG and its interaction with XG. The results showed that C sample had the highest compressibility with the low level of PO and the maximum of DMG content. In contrast, I and O samples had the lowest compressibility due to the maximum of PO and minimum of DMG (Table 3). However, the desirable level of compressibility was for H and N samples with a similar value to the reference samples.

CONCLUSION

Development and characterization of a low-fat spread based on PO was conducted using a full factorial design, consisting of varying levels of PO, CB, DMG, and XG. The current study revealed that textural attributes of these spreads were significantly influenced by different concentrations of their structural components. The correlation analysis showed that the firmness values of the spreads were positively associated with the compressibility. The results demonstrated that PO concentration had greater effect on the values of the firmness, adhesiveness, and compressibility whereas the XG content had a rather greater effect on the cohesiveness values. Optimum formulation to produce the spread with unique textural properties were based on 15% PO, 7.5% CB, 0.3% XG, and 1% DMG. Authors, of course, assume that further experiments are required to correlate sound prediction of these characteristics with perceived human senses.

ACKNOWLEDGEMENTS

This study has been partially supported by a grant provided by the Council for Research at the Campus of Agriculture and Natural Resources of the University of Tehran and the Research Council of the University of Tehran. Gratitude is expressed to the Gorji Biscuit Co. (Tehran, Iran) for providing the laboratory facilities and financial assistance.