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Shea olein based specialty fats: Preparation, characterization and potential application
LWT - Food Science and Technology 86 (2017) 492e500
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Shea olein based specialty fats: Preparation, characterization and potential application Zhen Zhang a, b, Xiang Ma c, Huihua Huang a, **, Yong Wang b, d, * a
School of Food Science and Engineering, South China University of Technology, Guangzhou 510641, China Guangdong Saskatchewan Oil Seed Joint Laboratory, Department of Food Science and Engineering, Jinan University, Guangzhou 510632, China c Research School of Chemistry, The Australian National University, Canberra 2601, Australia d Guangdong Engineering Technology Research Center for Oils and Fats Biorefinery, Guangzhou 510632, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 May 2017 Received in revised form 16 July 2017 Accepted 12 August 2017 Available online 14 August 2017
To expand low melting point “liquid” base oil categories of plastic fats, the soft fat named SheaOL25 as a byproduct of shea butter with a melting point of 25.5 C was achieved via solvent fractionating of shea butter, and abounded in oleic acid and stearic acid/oleic acid/oleic acid (SOO) type triacylglycerols. The compatibility test with palm-based oil and coconut oil showed the desirable linear relationship of isothermal curve. At temperatures above 25 C, SheaOL25 exhibits good compatibility and could serve as a blending base oil for preparing specialty fats. Compared with palm olein, blending SheaOL25 and palm stearin can significantly expedite crystallization rate and retard crystallization rate after interesterification, thereby stabilizing the b0 crystal form in the system. Further exploration of SheaOL25 as “liquid” oil in oil-in-water emulsion system revealed that SheaOL25 as the oil phase can significantly improve the system's stability compared with the control groups of soybean oil and palm olein towards maintaining the particle size and emulsion stability under high temperatures. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Shea olein Crystallization rate Compatibility Oil-in-water emulsion
1. Introduction Shea has become the second largest natural source of symmetrical stearic-rich triacylglycerols (TAGs) and is increasingly popular as a component of cosmetic formulations and a cocoa butter substitute in the chocolate industry (Alaba, Sani, Mohammed, Abakr, & Daud, 2017; Segman, Wiesman, & Yarmolinsky, 2012). However, only the hard fraction (shea stearin) is utilized by the food industry in past years. Shea olein, a byproduct of shea stearin production, is obtained after the fractionation of shea butter, and proves to be a rich source of bioactive compounds (Lovett, 2015). Depending on the fractionation condition, shea olein with melting points of 25e30 C can be obtained (Lovett, 2014) and these products hold much potential for applications. Adhikari and Hu (2012) modified the mixtures of rice bran
* Corresponding author. Department of Food Science and Engineering, Jinan University, 601 Huangpu Ave West, Guangzhou 510632, China. ** Corresponding author. College of Food Science and Engineering, South China University of Technology, 381 Wushan Road, Guangzhou 510641, China. E-mail addresses: [email protected] (H. Huang), [email protected] (Y. Wang). http://dx.doi.org/10.1016/j.lwt.2017.08.035 0023-6438/© 2017 Elsevier Ltd. All rights reserved.
oil, shea olein, and palm stearin by interesterification, and reported that margarine/shortening formulation with shea olein can enhance the whipping properties. Saturated fat is commonly used in food industry (Co & Marangoni, 2012) but its excessive consumption is considered highly unhealthy. As a consequence, a lot of research efforts have been focused on seeking functional liquid oil as alternatives (Floter, 2012). Particularly, compared with the conventional palm olein (POL) which abounds in palmitinic acid, shea olein is rich in unsaturated fatty acids (USFAs) including stearic acid and oleic acid. Therefore, shea olein, which is a kind of “liquid” oil, could be adopted in the oil-in-water (O/W) emulsion system to reduce saturated fats as a substitute for plastic fats. Xu et al. reported that shea olein based cold soluble powder fats obtained via the interesterification of shea olein and palm kernel stearin could be ideal alternative fats to the reduction of saturated TAGs, and shea olein could also be considered as a frying oil and confectionary fats (Xu et al., 2016). This study aims to prepare shea olein as a functional oil, explore its application in oil blends and oil chemical interesterification (CIE), and analyze its compatibility with traditional palm-based oil (PO) and medium-carbon chain oils. The rate of crystallization was
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recorded according to the solid fat content (SFC) method by p-NMR. CIE experiments using shea olein were introduced to study the SFC and crystal form changes. Besides, shea olein is used in an O/W emulsion system which was prepared by adding mono stearin emulsifying agent to mixtures of certain oil and water. The formed solid-fat-like product was featured by low contents of saturated fatty acid and fat compared with the existing margarine and shortening. To our knowledge, there is very little published information about the application of shea olein. Therefore, the findings in this work will contribute to the preparation of specialty fats based on shea olein as a new low melting point “liquid” base oil and raise its potential industrial application value.
The glycerolysis products were analyzed by a GC system equipped with a capillary column (DB-1HT, 15 m 0.25 mm i.d., 0.1 mm in film thickness, Agilent Technologies Inc., Palo Alto, CA, USA). The yields of acylglycerols were expressed as the percent content of the corresponding peak area response compared with the total peak area using a flame ionization detector (Wang, Wang, & Hu, 2011). TAGs compositions of samples were conducted using the above GC with column (Rtx-65TG, 30 m 0.25 mm i.d., 0.1 mm in film thickness, RESTEK, USA). TAGs composition was analyzed before deacidification and identified using available standard (Adhikari & Hu, 2012). All determinations were performed in three replicates and the means ± standard deviations were reported.
2. Materials and methods
2.6. Characterization of the samples
2.1. Materials
2.6.1. Solid fat contents (SFC) and crystallization rates SFC was determined according to the AOCS Official Method Cd 16-81 (AOCS, 2009d) on a Bruker PC/20 Series NMR analyzer, Minispec (Bruker Optics, Milton, On, Canada). Samples were tempered at 60 C for 30 min, followed by 0 C for 60 min and finally for 30 min at each temperature of measurement. SFC was measured at intervals of 5 C from 10 C up to 40 C. All determinations were performed in duplicate and the means were reported. Crystallization rates were measured at intervals of 2 min from 2 min up to 12 min according to the SFC value at 10 C. The increase rate of SFC value was defined as crystallization rate.
Shea butter, coconut oil (CNO), soybean oil (SBO), palm stearin (PST, Iodine value ¼ 33e35), and palm olein (POL, 24 C) were provided by PGEO Co., Ltd. (Pasir Gudang, Johor, Malaysia). Sodium methoxide (MeONa), oleic acids, n-hexane and acetone (>99.5%) were purchased from Fuyu Chemical Co., Ltd. (Tianjin, China). Sodium stearyl lactate (SSL) and monostearate (MS) were purchased from Danisco (China) Holding Co., Ltd. 2.2. Solvent fractionation of shea butter 300 g Shea butter was melted in a beaker followed by the addition of 1500 mL n-hexane. The beaker was put in a thermostatic water bath, and the temperature was set at 25 C. A mechanical impeller with a plastic paddle rotating at 200 r/min was used to stir the mixture. After 30 min, the mixture was filtered. The solid fat was collected and dried, and the filtrate was concentrated under vacuum to get the liquid oil. The solid fat and the liquid oil were marked as shea stearin (SheaST25) and shea olein (SheaOL25), respectively. 2.3. Chemical interesterification of SheaOL25 with palm-based oil 150 g of SheaOL25 and 150 g PST (or POL) were melted and added in a three-necked round-bottom flask (500 mL), and heated in a thermostatic oil bath, while being stirred at 400 r/min. When the temperature reached 105 C, 0.9 g MeONa (0.3 wt.% of the oil mass) was added. The reaction was conducted under vacuum (~2000 Pa) for 0.5 h. After reaction, the mixture was cooled, neutralized by citric acid, and then washed by hot water. The interesterified oils was then dried and analyzed by gas chromatography (GC). 2.4. O/W emulsion system preparation 120 mL deionized water (40.0 wt.%) was added in a beaker, immersed and heated to 80 C in a thermostatic water bath. 18.0 g MS (6.0 wt.%) and 1.5 g SSL (0.5 wt.%) were added to 160.5 g oil phase (53.5 wt.%) as emulsifiers in the other beaker, and then heated to melt. The O/W emulsion system was prepared by adding the melted oil phase to the water dropwise with a high-shear mulser to mix. 2.5. Fatty acid, acylglycerols analysis, and TAGs composition The composition of fatty acids (FAs) of samples was analyzed as fatty acid methyl esters (FAMEs) by a GC system with a capillary column (CP-Sil88, 100 m 0.250 mm i.d., 0.2 mm in film thickness, Agilent Technologies Inc., Palo Alto, CA, USA) (Zhang et al., 2015).
Crystallization rateðTÞ ¼
SFCðTÞð%Þ SFC ð10 CÞð%Þ
where SFC (T): SFC value of the melted sample at 10 C for a certain time, SFC (10 C): SFC value of the sample at 10 C. 2.6.2. Compatibility test The compatibility of dualistic mixtures of SheaOL25 with palmbased oil (PO) which contains 80%POLþ20%PST and with coconut oil (CNO) was studied by DSFC. DSFC ¼ practical SFC (PSFC) theoretical SFC (T-SFC), while T-SFC ¼ SFCx X% þ SFCy Y% which was calculated in computer according to the SFC value of single oil. X%, and Y% were the percentages in mixture total mass of x-oil and y-oil respectively. The closer to zero of DSFC, the better compatibility of oil blends. When the DSFC value is above zero, blends are monotectic, otherwise eutectic (Willimas, Ransom, & Hartel, 1997). 2.6.3. Melting and crystallization behaviors A differential scanning calorimetry (DSC) system was used to monitor the melting and crystallization behavior of the products. The exotherm was obtained by holding the samples for 5 min at 80 C followed by cooling to 40 C by 5 C/min. To obtain endotherm, the samples were heated to 80 C at 5 C/min (Bouzidi, Boodhoo, Humphrey, & Narine, 2005; Zhang et al., 2015). All determinations were performed in three replicates and the means ± standard deviations were reported. 2.6.4. Crystal structure Polarized light microscope (PLM) techniques were applied to characterize the structures of crystallization after smeared and 24 h ripening at 20 C. The products were characterized by X-ray diffraction (XRD) (Cerdeira, Martini, Candal, & Herrera, 2006). 2.6.5. Particle size analysis A laser particle size analyzer (LS13-320, Beckman Coulter) was used to measure the particle size changes of O/W samples during
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storage. O/W emulsion sample was diluted into 5% suspension to be analyzed, and the average particle size was recorded.
oil is commonly used to balance the SFC curve of the specialty fats system.
2.6.6. Emulsion system stability measurement TURBISCAN (LAB, Formulaction, France) was introduced to study the stability comparison of different O/W emulsion system under 60 C, scan every 10 min.
3.2. Compatibility of SheaOL25 with PO and CNO
2.7. Statistical analysis One-way ANOVA was performed using SPSS 16 statistical software (SPSS Inc., Chicago, IL). Differences were considered to be significant at p 0.05, according to Duncan's Multiple Range Test. 3. Results and discussion 3.1. Physicochemical profiles of SheaOL25 The FAs compositions of samples are shown in Table 1A. Traces of SFAs, including palmitic and stearic acids, were found in shea butter. The high contents of stearic (43.50 wt.%) and oleic (44.47 wt.%) acids demonstrate that shea butter was rich in C18 FAs. After solvent fractionation, the FAs compositions changed noticeably with increased content of oleic acids (50.15 wt.%) in SheaOL25 and stearic acid (58.24 wt.%) in SheaST25. This reveals that SheaOL25 abounded in heathier unsaturated FAs. In comparison, the olein and stearin from palm-based oil (POL, PST) contained much more saturated palmic acids (39.51 wt.% and 59.77 wt.%, respectively). Table 1B outlines the TAGs compositions of samples. It should be noted that shea-base oil has higher SOS and SOO contents and lower POP, PLP and PLS contents than palm-based oil, which is consistent with the FAs composition. In detail, shea butter contained 40.84 wt.% of SOS and 23.49 wt.% of SOO, while after solvent fractionation there were a decrease in SOS (7.03 wt.%) and increases in SOO and C40-TAGs (37.04 wt.% and 10.74 wt.% respectively) in SheaOL25. On the contrary, the content of SOS was increased to above 74 wt.% in SheaST25. In comparison, POL contained 33.20 wt.% POP, while 30.20 wt.% of PPP was in PST. Owing to the higher content of MUFA and SUU-type TAGs in SheaOL25 with lower melting point, it could be viewed as potential POL-substitutes “liquid” and healthier oil in specialty fats industry. The acylglycerols compositions of SheaOL25 are listed in Table 1C. Many batches of shea butter were analyzed in previous work, and a high content of diacylglycerols (DAGs) (9.70 wt.% to 19.41 wt.%) was found, which may be produced in the process of raw shea butter refining (Adhikari & Hu, 2012). The selected batch of shea butter contained 10.99 wt.% DAGs originally with 8.17 wt.% in SheaOL25 after fractionation. SFC is not only an important determinant of the texture of fats but responsible for various functional characteristics. The high SFC value at lower temperatures could provide the good shape maintenance ability around 37e40 C and the low SFC value allows a clear mouth feeling. Fig. 1A1 describes the SFC in samples under various temperatures. It shows that with regards to SFC values, SheaST25 and PST were superior to others while the trend of SFC changes of SheaST25 was sharper than that of PST. The SFC in SheaST25 decreased significantly from 92.70% to 15.91% along with the temperature from 10 C to 40 C. Due to such physical properties, fractionated stearin as suitable base oil is commonly used as confectionary and chocolate fats. It can be seen that POL has a much higher SFC value (33.12%) at 10 C, while at 25 C SFC of SheaOL25 decreased to 1.24% which is similar to POL (1.18%) and this indicates a lower melting point (SMP ¼ 25.5 C) of the fractionated olein phase. Such “liquid” base
The compatibility of oil blends refers to the degree of mutual consistency between TAGs and different oils. The compatibility among various stock oils directly influences processing course, quality and shelf life of plastic fats. The specialty fats products made by processing incompatible oil blends tend to have sand streaking, oil leaking, lowered caseation valence and so on (Lida & AIi, 1998). PO has extensive sources, while CNO is rich in medium-carbon chain FAs such as lauric acid (C12, 45.94 wt.%) and myristic acid (C14, 18.36 wt.%), which could be used to produce TAGs with less total carbon atoms (Table 1B). So they are commonly used in production of specialty fats. Investigation on the compatibility phenomenon with these two representative oils will be instructive to the application of SheaOL25 in specialty fats blends. The compatibility of binary mixtures with different ratios of SheaOL25 and PO, SheaOL25 and CNO were illustrated by DSFC (the practical SFC value theoretical SFC value) (Buning & Bartsch, 1989) and curves are shown in Fig. 2A and B, respectively. For the purpose of further analyzing specific compatibility and clarifying the acting degree of monotectic crystal and eutectic crystal, maps with temperature as X-coordinate and DSFC as Ycoordinate are shown in Fig. 2A and B. According to Fig. 2A, at temperatures below 25 C, eutectic crystal occurred in the blends system and thus the mixture system was in the initial stage of crystallization. The eutectic crystal phenomenon was most obvious at 10 C and 20 C, especially with 40%e70% of SheaOL25, where DSFC values were large, with D-value up to 10e14%. Since the content of high-melting point TAGs in compound system was high, its large difference from POL in thermodynamic property led to the partial incompatibility between them. As a consequence, the phenomenon of eutectic crystal presented. As the crystallization rate shown in Fig. 1A2, SheaOL25 crystallized rapidly and the rate reached 79% at 4 min. Since PO contains more POL, the crystallization rate is slower. The crystallization rate of 20%PST þ 80%POL at 2 min was only 23%. They differed significantly in terms of the conversion of crystal form and compatibility. During the same time, DSFC table and curve show that when the temperature was 25e40 C, eutectic crystal phenomenon of mixture system weakened, corresponding to the increased compatibility. The closer the DSFC was to 0, the better the compatibility blends were (Liu, Wu, & Yang, 2010). The SheaOL25 had lower SMP, and melted in this temperature range. Yet it still had some effects on the system. Fig. 2B shows that the eutectic crystal phenomenon of blended oil system of SheaOL25 and CNO was the most obvious when the temperature was 20 C with 10%e90% of SheaOL25, and the DSFC value was 6e16. The eutectic crystal phenomenon for the system was insignificant between 25 C and 40 C and the content of SheaOL25 was 10%e90% with DSFC values of between 0.1 and 2. These results suggest the good compatibility of the blends system. We speculate this may be because CNO contained high content of low temperature solid fat. At 10 C, the solid fat was around 80% in CNO, while SheaOL25 had only about 12%. In addition, CNO and SheaOL25 basically melted over 25 C. As a result, the phenomenon of eutectic crystal weakened and the compatibility increased. SheaOL25 demonstrated high compatibility with both of PO and CNO. The blends exhibited higher incompatibility with higher SheaOL25 proportion. However, when the temperature exceeded 25 C, the systems were highly compatible. In real production, the emulsification temperature exceeds the highest melting point of system's oils. Therefore, using SheaOL25 for blending could contribute to the practicable compatibility.
Table 1 Fatty acid, triacylglycerols and acylglycerols composition by GC analysis (wt.%).a,b (A) Fatty Acids
8:0
10:0
12:0
14:0
16:0
18:0
18:1
18:2
18:3
20:0
20:1
22:0
SFA
MUFA
Shea butter SheaOL 25 SheaST 25 POL PST CNO
e e e e e 7.48 ± 0.22
e e e e e 5.79 ± 0.59
0.09 ± 0.03 0.13 ± 0.01 0.03 ± 0.01 e e 45.94 ± 1.34
0.02 ± 0.01 0.09 ± 0.01 0.02 ± 0.01 1.01 ± 0.01 1.20 ± 0.06 18.36 ± 1.02
3.56 ± 0.27 4.24 ± 0.15 2.47 ± 0.01 39.51 ± 1.34 59.77 ± 1.91 9.75 ± 0.87
43.50 ± 2.11 35.59 ± 1.35 58.24 ± 2.09 4.70 ± 0.72 5.23 ± 0.72 3.11 ± 0.90
44.47 ± 1.83 50.15 ± 2.10 34.18 ± 1.38 42.01 ± 1.43 27.02 ± 1.11 6.95 ± 1.02
6.11 ± 0.19 6.95 ± 0.03 2.89 ± 0.79 11.14 ± 1.27 5.53 ± 0.53 1.61 ± 0.10
0.15 ± 0.02 1.44 ± 0.39 0.27 ± 0.04 0.16 ± 0.04 48.77 ± 2.85 44.74 ± 1.87 0.08 ± 0.01 1.46 ± 0.07 0.39 ± 0.07 0.17 ± 0.01 41.68 ± 1.60 50.54 ± 2.17 0.05 ± 0.01 1.65 ± 0.02 0.08 ± 0.01 0.17 ± 0.04 62.55 ± 2.15 34.26 ± 1.39 e e e e 45.22 ± 2.05 42.01 ± 1.43 e e e e 66.20 ± 2.69 27.02 ± 1.11 e e e e 90.43 ± 4.94 6.95 ± 1.02
PUFA 6.32 ± 0.21 7.12 ± 0.04 2.96 ± 0.80 11.14 ± 1.27 5.53 ± 0.53 1.61 ± 0.10
(B) Shea Butter
SheaOL25
SheaST25
POL
PST
CNO
C30 C32 C34 C36 C38 C40 C42 C44 MPP PPP MOP MLP PPS POP MOO PLP MLO PSS POS POO PLS PLO PLL SSS SOS SOO OOO SLO OLO OLL SOA AOO
e 1.02 ± 0.02 e e 0.45 ± 0.01 5.22 ± 0.65 e e 1.54 ± 0.12 e 1.72 ± 0.01 0.61 ± 0.01 0.04 ± 0.01 0.39 ± 0.01 0.03 ± 0.01 0.12 ± 0.01 e 0.31 ± 0.01 5.50 ± 0.03 2.27 ± 0.17 1.52 ± 0.02 0.85 ± 0.01 0.13 ± 0.01 1.25 ± 0.05 40.84 ± 1.21 23.49 ± 0.88 4.12 ± 0.19 4.21 ± 0.62 1.11 ± 0.33 0.79 ± 0.08 2.13 ± 0.11 1.12 ± 0.10
e 2.67 ± 0.37 e e 1.01 ± 0.01 10.74 ± 0.98 e e 2.56 ± 0.03 e 3.32 ± 0.01 1.20 ± 0.01 0.06 ± 0.01 e e 0.19 ± 0.01 e 0.09 ± 0.01 5.25 ± 0.02 3.80 ± 0.30 2.13 ± 0.02 1.18 ± 0.01 0.33 ± 0.01 0.86 ± 0.21 7.03 ± 0.75 37.04 ± 1.15 7.37 ± 0.53 7.37 ± 0.73 1.34 ± 0.17 2.14 ± 0.13 1.05 ± 0.04 1.65 ± 0.07
e 1.78 ± 0.13 e e 2.31 ± 0.02 2.91 ± 0.02 e e 0.08 ± 0.01 e 0.37 ± 0.01 0.10 ± 0.01 0.17 ± 0.01 0.40 ± 0.01 e 0.10 ± 0.01 e 0.56 ± 0.09 5.25 ± 0.17 0.44 ± 0.16 0.45 ± 0.01 0.15 ± 0.01 0.20 ± 0.01 1.71 ± 0.82 74.11 ± 2.10 4.57 ± 0.95 0.67 ± 0.25 0.71 ± 0.21 0.38 ± 0.07 0.13 ± 0.02 3.66 ± 0.32 0.23 ± 0.01
e e e e e e e e 0.34 ± 0.01 1.06 ± 0.31 2.11 ± 0.01 0.66 ± 0.01 e 33.20 ± 1.90 e 10.01 ± 0.83 0.59 ± 0.01 e 2.53 ± 0.01 5.89 ± 0.78 22.74 ± 1.19 9.22 ± 1.01 1.95 ± 0.02 e 0.59 ± 0.07 2.54 ± 0.20 3.25 ± 0.67 0.98 ± 0.34 1.69 ± 0.09 e e e
e e e e e e e e 2.35 ± 0.01 30.2 ± 1.78 1.20 ± 0.01 0.30 ± 0.01 6.20 ± 0.58 26.86 ± 1.55 e 5.73 ± 0.45 e 0.70 ± 0.12 4.50 ± 0.02 10.74 ± 0.99 1.15 ± 0.02 4.22 ± 0.19 0.86 ± 0.01 e 0.41 ± 0.07 1.17 ± 0.01 1.48 ± 0.41 0.53 ± 0.32 0.62 ± 0.03 0.15 ± 0.02 e e
2.82 ± 0.02 11.58 ± 0.57 15.79 ± 0.49 19.08 ± 1.01 17.26 ± 1.43 11.72 ± 0.89 8.42 ± 0.89 4.72 ± 0.64 2.85 ± 0.62 2.20 ± 0.10 e e 1.53 ± 0.01 e e e e e e e e e e e e e e e e e e e
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TAG
(C) Acylglycerols
SheaOL25
POL
SBO
MAG DAG TAG
ND 8.17 ± 0.58 91.83 ± 0.79
ND ND 100 ± 0
ND ND 100 ± 0
a
Values show the means ± standard deviations. Abbreviations used: SheaOL25, the liquid phase solvent-fractionated from shea butter under 25 C; SheaST25, the solid phase solvent-fractionated from shea butter under 25 C; POL, palm olein (slip melting point ¼ 24 C); PST, palm stearin (iodine value ¼ 33e35); CNO, coconut oil; SBO, soybean oil; 8:0, octanoic acid; 10:0, decanoic acid; 12:0, lauric acid; 14:0, myristic acid; 16:0, palmitic acid; 16:1t, trans-palmitoleic acid; 16:1c, palmitoleic acid; 18:0, stearic acid; 18:1, oleic acid; 18:2, linoleic acid; 18:3, linolenic acid; 20:0, arachidic acid; 20:1, eicosenoic acid; 22:0, behenic acid; SFA, saturated fatty acid; MUFA, mono-unsaturated fatty acid; PUFA, poly-unsaturated fatty acid; C30-44, TAG group of total carbon number ¼ 30e44; M, myristic acid; P, palmitic acid; O, oleic acid; L, linoleic acid; S, stearic acid; A, arachidic acid; MAGs, monoacylglycerols; DAGs, diacylglycerols; TAGs, triacylglycerols. b
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Fig. 1. SFC comparison of the samples and oil blends (A1 and B) and crystallization rate at 10 C (A2) by p-NMR analysis.
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Fig. 2. (A) SFC and Compatibility of SheaOL25 with PO. (B) SFC and Compatibility of SheaOL25 with CNO. (DSFC ¼ Practical solid fat content (P-SFC) e theoretical solid fat content (TSFC)).
3.3. CIE properties of SheaOL25 To explore the application of SheaOL25 in crystallization and CIE modified oil base, two common palm oil bases of PST and POL were selected for proportioning and CIE experiment. Crystallization rate was calculated by recording the SFC at 10 C within the first 12 min every 2 min. SFC results are listed in Fig. 1A1. The new base oils were prepared through CIE reactions under certain conditions and characterized by SFC. It is observed that the SFC trend markedly changed compared with non-interesterification (NIE) samples. All samples' profiles turn sharper than before for a notable increase in the SFC at 10 C. The crystallization rates (Fig. 1A2) of 50%PST þ 50% SheaOL25 at 2 min before and after CIE were 58% and 45% respectively, and this means the crystallization rate after CIE was retarded. 50%POL þ 50%SheaOL25 had faster crystallization rate and this rate was delayed slightly after CIE. It can also be observed that all oil base blended by 50% SheaOL25 underwent rapid increases in crystallization rate. To take interesterification specimen (50%POL þ 50%SheaOL25) for example, crystallization rate of POL itself is very slow (33% for 12 min). But crystallization rate at 6 min achieved 82% with the addition of 50% SheaOL25. To clarify if SheaOL25 could effectively change the crystallization rate of the oil blends system at 10 C, oil blends crystallization rates tests were conducted, and the results are also summarized in Fig. 1B. PST with
different ratios of SheaOL25 was mixed to test the SFC, and POL replaced SheaOL25 as the control. The results show that when the ratio of SheaOL25 to PST was 7:3, the rate increases significantly over 30% higher than the corresponding POL. When it comes to PST þ POL, with the increase of POL amount, the crystallization rate at 2 min exhibited a downtrend from 37.4% of 50%PST þ 50%POL to 23.6% of 20%PST þ 80%POL. The parallel comparison shows after the replacement of POL with SheaOL25, the crystallization rates were all higher than the case of adding POL in the same proportion. Meanwhile, the crystallization rate at the same time node was all above 56%. However, the crystallization rate did not always increase in proportion to the addition level of SheaOL25, which may be attributed to the increase of “liquid” phase amount. Nonetheless, parallel comparison demonstrates that when mixed with PST, SheaOL25 had better pro-crystallization than POL. In our efforts to verify this, a third experiment was conducted by mixing SheaOL25 and POL in a ratio of 1:1. It is observed that due to the addition of SheaOL25 which replaced parts of POL, the crystallization rate increased to above 41% at 2 min. The results could be explained from the different acyl-chain length structure between SheaOL25 and POL. The fat crystallization can vary in their chain length structure which provides the crystals with another dimension of variation (Sato, 2001). From the fatty acids composition analysis (Table 1A), SheaOL 25 contained 0.13 wt.% lauric acid, 1.46 wt.%
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Fig. 3. (A) DSC crystallization and melting thermograms of the samples. (B) Polymorphic forms of the SheaOL25-based interesterified samples at 25 C. (C) Images of SheaOL25based samples before and after interesterification at 25 C. Size bar ¼ 10 mm.
arachidic acid, and 0.39 wt.% eicosenoic acid, while they were not detected in POL. DSC is commonly adopted to evaluate the thermal behavior of oils. The DSC curves of samples are shown in Fig. 3A. Simultaneously, the transition temperatures of crystallization, melting points as well as the onset temperature (To), offset temperature (Tf), and temperature range (difference between To and Tf) are summarized in Table 2. General characteristics did not change greatly before and after CIE, with difference mainly in temperature. Thereinto, 50%PST þ 50%SheaOL25 had two primary crystallization peaks. The reason for the wider temperature range (51.06 C changed to 52.41 C) after CIE may derive from the slowed crystallization rate. From crystallization rate in Fig. 1A2, it is observed that the crystallization rate after CIE was lower by 14.4% than before and the beginning crystal temperature for NIE was about 26.51 C. After CIE, its crystallizing point rose to 31.28 C. 50%POL þ 50% SheaOL25 displayed one primary crystallization peak, but presented two crystallization peaks after CIE. The beginning crystal temperature increased from 14.08 C to 27.41 C. The analysis on melting characteristics of DSC show those general curve characteristics changed slightly after CIE. The general melting peak of 50% PST þ 50%SheaOL25 narrowed compared with that before ester interchange. Concurrently, end temperature of melting increased by about 6 C, and clearly the first melting peak was separated into two, indicating two substances with obvious melting point
differences appeared after CIE. The temperature range for 50% POL þ 50%SheaOL25 after CIE became narrower and changed from one primary melting peak into two. The initial melting temperature was postponed from 18.58 C to 15.74 C. High temperature melting peak appeared and augmented and this is in agreement with the increase of substances with high melting point after CIE. When producing food products containing fat or lipids it is important to be aware of the fact that the physicochemical and sensory properties of the end products will be influenced by the physical state of the fats or lipids (Damodaran, Parkin, & Fennema, 2008). The crystal forms before and after CIE reaction are shown in Fig. 3B. It can be seen that 50%PST þ 50%SheaOL25 had very strong diffraction peaks near 3.8 Å, 4.2 Å and 4.6 Å before CIE. The diffraction peak at around 4.6 Å disappeared after CIE, indicating the decrease of b crystal form which converts into b'. Similarly, more b0 crystal form existed in 50%POL þ 50%SheaOL25 after CIE, and there was also partial b crystal form. It can be inferred that CIE between SheaOL25 and hard oil can delay the translation of crystal form and stabilize b0 crystal form, which is consistent with its crystallization rate result. In detail, crystallization rate of CIE (50% POL þ 50%SheaOL25) was slowed and the transformation of crystal form to b was delayed. PLM picture (Fig. 3C) also demonstrates that the samples after CIE have finer crystalline state and was more uniform and smoother.
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Table 2 Comparison of DSC-measured onset, offset and transition temperatures for crystallization and melting curves of the samples.a,b Curve
Sample
To ( C)
Tf ( C)
Temperature range ( C)
Transition temperature ( C)
Crystallization
SheaOL25 NIE (50%PST þ 50%SheaOL25) CIE (50%PST þ 50%SheaOL25) NIE (50%POL þ 50%SheaOL25) CIE (50%POL þ 50%SheaOL25)
18.12 ± 0.21 26.51 ± 0.43
e 24.55 ± 0.22
e 51.06 ± 0.65
31.28 ± 0.16
21.13 ± 0.22
52.41 ± 0.38
14.08 ± 0.12
e
e
1: 6.85 ± 0.02 1:25.35 ± 0.66 2:6.14 ± 0.15 1:31.28 ± 0.34 2:14.74 ± 0.34 1:3.68 ± 0.12
27.41 ± 0.38
e
e
1:25.2 ± 0.18 2:11.76 ± 0.26
SheaOL25 NIE (50%PST þ 50%SheaOL25)
28.17 ± 0.25 18.05 ± 0.32
e 52.12 ± 0.61
e 70.17 ± 0.94
CIE (50%PST þ 50%SheaOL25)
17.11 ± 0.27
46.15 ± 0.12
63.26 ± 0.39
NIE (50%POL þ 50%SheaOL25) CIE (50%POL þ 50%SheaOL25)
18.58 ± 0.31
e
e
15.74 ± 0.23
e
e
1:7.85 ± 0.03 1:6.42 ± 0.02 2:25.58 ± 0.51 3:44.33 ± 0.45 1:7.01 ± 0.09 2:14.39 ± 0.30 3:28.34 ± 0.55 4:43.87 ± 0.38 1:6.98 ± 0.12 2:12.02 ± 0.16 1:12.44 ± 0.07 2:28.68 ± 0.14 3:40.01 ± 0.38
Melting
a
Values show the means ± standard deviations. Abbreviations used: SheaOL25, the liquid phase solvent-fractionated from shea butter under 25 C; PO, palm-based oil (80%POL, palm olein (slip melting point ¼ 24 C) þ 20%PST, palm stearin (iodine value ¼ 33e35)); CNO, coconut oil; P, practical value by p-NMR analysis; T, theoretical value in computer calculation; NIE, nonchemical interesterification; CIE, chemical interesterification. b
Fig. 4. (A) Particle size measurement of O/W emulsion samples during storage at 25 C. (B) Images of O/W emulsion samples stability after 2 h storage at 60 C. (Dynamic stability index: SBO-sample ¼ 30.55; POL-sample ¼ 12.20; SheaOL25-sample ¼ 3.90). The means ± standard deviation with different letters denote significant difference at p 0.05 (n ¼ 3).
3.4. Effects of SheaOL25 on O/W emulsion system The analysis result of particle size of O/W emulsion system in storage process is depicted in Fig. 4A. The curve demonstrates that the particle sizes of the three samples within the first day were very small, being 1.5e2.5 mm. Thereinto, SheaOL25-sample had the smallest particle size and kept at lower particle sizes during the storage of 30 days. This may be because the original presence of 8.17 wt.% DAGs in sheaolein (Table 1C) and DAGs usually act as an emulsifier for oil-water system (Mahmoud, Murad, & Murad, 2008; Yi, Cheng, & Dong, 2015). Adhikari and Hu (2012) reported that shea olein can be used for margarine/shortening formulation to enhance the whipping properties containing small amount of DAGs. Similarly, Kawai and Konishi (2006) reported that the O/W
system comprising DAGs displayed enhanced performance in terms of storage stability, appearance and taste. The particle sizes of POLsample and SBO-sample changed dramatically, undergoing an increasing trend after 24 h, and reaching the peak value of particle size (4.01 mm and 4.25 mm respectively) on the 15th day. The particle size of POL-sample and SBO-sample increased rapidly and fluctuated after being placed for 10 days, which may be due to the rearrangement of crystal network during storage (Cheong, Tan, & Long, 2009). High temperature stability test for O/W emulsion system was conducted. Fig. 4B illustrates that after SheaOL25sample was placed at 60 C for 2 h, the layering of oil phase and water phase was the least obvious, and the sample's dynamic stability index could reach 3.90. With regards to POL-sample and SBOsample, the oil and water were completely separated, and the
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dynamic stability index was up to 30.55. 4. Conclusion Solvent fractionated SheaOL25 was prepared and it is rich in oleic acid and SOO type TAGs. Compatibility testing with PO and CNO showed that the linear relationship of isothermal curve obtained was desirable. Moreover, at temperature above 25 C the SheaOL25 had good compatibility and could serve as blending base oil for preparing specialty fats. Compared with POL, SheaOL25 can significantly expedite crystallization rate of system, but retarded the crystallization rate of system after CIE, thereby stabilizing b0 crystal form of the system. O/W emulsion system with SheaOL25 as oil phase exhibited significantly improved stability compared with control groups of SBO and POL at high temperature. The findings will contribute to the application of shea olein as a novel base oil in the production of specialty fats and expand the low melting point “liquid” base oil categories of plastic fats. Acknowledgement The financial support from the National Natural Science Foundation of China under grant 31371785 and 31671781, the National Key Research and Development Program of China under grant 2017YFD0400200, the Department of Science and Technology of Guangdong Province under grant 2017B090907018, 2012B091100035 and 2013B090800009, and the Bureau of Science and Information of Guangzhou under grant 2014Y2-00192 are gratefully acknowledged. References Adhikari, P., & Hu, P. (2012). Enzymatic and chemical interesterification of rice bran oil, sheaolein, and palm stearin and comparative study of their physicochemical properties. Journal of Food Science, 77, 1284e1291. Alaba, P. A., Sani, Y. M., Mohammed, I. Y., Abakr, Y. A., & Daud, W. M. A. W. (2017). Synthesis and characterization of sulfated hierarchical nanoporous faujasite zeolite for efficient transesterification of shea butter. Journal of Cleaner Production, 142, 1987e1993. AOCS Official Method Cd 16-81. Bouzidi, L., Boodhoo, M., Humphrey, K. L., & Narine, S. S. (2005). Use of first and second derivatives to accurately determine key parameters of DSC
thermographs in lipid crystallization studies. Thermochimica Acta, 439, 94e102. Buning, P., & Bartsch, A. (1989). Investigation on the compatibility of milk fat fractions and lauric fat. Journal of Thermod Analysis, 35, 671e675. Cerdeira, M., Martini, S., Candal, R. J., & Herrera, M. L. (2006). Polymorphism and growth behavior of low-trans fat blends formulated with and without emulsifiers. Journal of the American Oil Chemists’ Society, 83, 489e496. Cheong, L. Z., Tan, C. P., & Long, K. (2009). Physicochemical textural and viscoelastic properties of palm diacylglycerol bakery margarine during storage. Journal of the American Oil Chemists’ Society, 86, 723e731. Co, E. D., & Marangoni, A. (2012). Organogels: An alternative edible oil-structuring method. Journal of the American Oil Chemists’ Society, 89, 749e780. Damodaran, S., Parkin, K. L., & Fennema, O. R. (2008). Fennema's food chemistry (4th ed.). Boca Raton: CRC Press/Taylor & Francis, 12, 1144. Floter, E. (2012). Structuring oils without highly saturated fats e how far are we? European Journal of Lipid Science and Technology, 114, 983e984. Kawai, S. & Konishi, Y. (2006) Acid oil-in-water emulsified composition. US Patent 7041328. Lida, H., & AIi, A. (1998). Physicochemical characteristics of palm based oil blends for production of reduced fat spreads. Journal of the American Oil Chemists’ Society, 75, 1625e1631. Liu, R. X., Wu, S. X., & Yang, W. F. (2010). Study on the compatibility of several kinds of palm oil. Grain Science and Technology and Economy, 35, 49e53. Lovett, P. N. (2014). Natural butters: Fractionation alternatives. Waxes and Butter, 49e52. Lovett, P. N. (2015). 5eShea butter: Properties and processing for use in food. Specialty Oils and Fats in Food and Nutrition, 125e158. Mahmoud, A. G., Murad, S., & Murad, A. H. (2008). Formulation and fuzzy modeling of emulsion stability and viscosity of a gum-protein emulsifier in a model mayonnaise system. Journal of Food Engineering, 84, 348e357. Sato, K. (2001). Crystallization behaviour of fats and lipids e a review. Chemical Engineering Science, 56, 2255e2265. Segman, O., Wiesman, Z., & Yarmolinsky, L. (2012). 17eMethods and technologies related to shea butter chemophysical properties and to the delivery of bioactives in chocolate and related products. Cocoa Butter and Related Compounds, 417e441. Wang, L. L., Wang, Y., & Hu, C. Y. (2011). Preparation of diacylglycerol-enriched oil from free fatty acid using lecitase ultra-catalyzed esterification. Journal of the American Oil Chemists’ Society, 88, 1557e1565. Willimas, S. D., Ransom, P. K. L., & Hartel, R. W. (1997). Mixtures of palm kernel oil with cocoa butter and milk fat in compound coatings. Journal of the American Oil Chemists’ Society, 74, 357e366. Xu, Z. B., Jin, J., Adhikari, P., Liang, J., Xu, X. B., Liu, Y. F., et al. (2016). Sheaolein-based cold-soluble powder fats with medium- and long-chain triacylglycerol: Production via chemical interesterification using sheaolein and palm kernel stearin. RSC Advance, 6, 18632e18640. Yi, J. H., Cheng, J. J., & Dong, W. B. (2015). Effect of pH emulsifier type and concentration on physical stability of oil-in-water emulsions. Science and Technology of Food Industry, 13, 266e270. Zhang, Z., Wang, Y., Ma, X., Wang, E. P., Liu, M. M., & Yan, R. A. (2015). Characterisation and oxidation stability of monoacylglycerols from partially hydrogenated corn oil. Food Chemistry, 173, 70e79.
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Shea olein based specialty fats: Preparation, characterization and potential application Zhen Zhang a, b, Xiang Ma c, Huihua Huang a, **, Yong Wang b, d, * a
School of Food Science and Engineering, South China University of Technology, Guangzhou 510641, China Guangdong Saskatchewan Oil Seed Joint Laboratory, Department of Food Science and Engineering, Jinan University, Guangzhou 510632, China c Research School of Chemistry, The Australian National University, Canberra 2601, Australia d Guangdong Engineering Technology Research Center for Oils and Fats Biorefinery, Guangzhou 510632, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 May 2017 Received in revised form 16 July 2017 Accepted 12 August 2017 Available online 14 August 2017
To expand low melting point “liquid” base oil categories of plastic fats, the soft fat named SheaOL25 as a byproduct of shea butter with a melting point of 25.5 C was achieved via solvent fractionating of shea butter, and abounded in oleic acid and stearic acid/oleic acid/oleic acid (SOO) type triacylglycerols. The compatibility test with palm-based oil and coconut oil showed the desirable linear relationship of isothermal curve. At temperatures above 25 C, SheaOL25 exhibits good compatibility and could serve as a blending base oil for preparing specialty fats. Compared with palm olein, blending SheaOL25 and palm stearin can significantly expedite crystallization rate and retard crystallization rate after interesterification, thereby stabilizing the b0 crystal form in the system. Further exploration of SheaOL25 as “liquid” oil in oil-in-water emulsion system revealed that SheaOL25 as the oil phase can significantly improve the system's stability compared with the control groups of soybean oil and palm olein towards maintaining the particle size and emulsion stability under high temperatures. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Shea olein Crystallization rate Compatibility Oil-in-water emulsion
1. Introduction Shea has become the second largest natural source of symmetrical stearic-rich triacylglycerols (TAGs) and is increasingly popular as a component of cosmetic formulations and a cocoa butter substitute in the chocolate industry (Alaba, Sani, Mohammed, Abakr, & Daud, 2017; Segman, Wiesman, & Yarmolinsky, 2012). However, only the hard fraction (shea stearin) is utilized by the food industry in past years. Shea olein, a byproduct of shea stearin production, is obtained after the fractionation of shea butter, and proves to be a rich source of bioactive compounds (Lovett, 2015). Depending on the fractionation condition, shea olein with melting points of 25e30 C can be obtained (Lovett, 2014) and these products hold much potential for applications. Adhikari and Hu (2012) modified the mixtures of rice bran
* Corresponding author. Department of Food Science and Engineering, Jinan University, 601 Huangpu Ave West, Guangzhou 510632, China. ** Corresponding author. College of Food Science and Engineering, South China University of Technology, 381 Wushan Road, Guangzhou 510641, China. E-mail addresses: [email protected] (H. Huang), [email protected] (Y. Wang). http://dx.doi.org/10.1016/j.lwt.2017.08.035 0023-6438/© 2017 Elsevier Ltd. All rights reserved.
oil, shea olein, and palm stearin by interesterification, and reported that margarine/shortening formulation with shea olein can enhance the whipping properties. Saturated fat is commonly used in food industry (Co & Marangoni, 2012) but its excessive consumption is considered highly unhealthy. As a consequence, a lot of research efforts have been focused on seeking functional liquid oil as alternatives (Floter, 2012). Particularly, compared with the conventional palm olein (POL) which abounds in palmitinic acid, shea olein is rich in unsaturated fatty acids (USFAs) including stearic acid and oleic acid. Therefore, shea olein, which is a kind of “liquid” oil, could be adopted in the oil-in-water (O/W) emulsion system to reduce saturated fats as a substitute for plastic fats. Xu et al. reported that shea olein based cold soluble powder fats obtained via the interesterification of shea olein and palm kernel stearin could be ideal alternative fats to the reduction of saturated TAGs, and shea olein could also be considered as a frying oil and confectionary fats (Xu et al., 2016). This study aims to prepare shea olein as a functional oil, explore its application in oil blends and oil chemical interesterification (CIE), and analyze its compatibility with traditional palm-based oil (PO) and medium-carbon chain oils. The rate of crystallization was
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recorded according to the solid fat content (SFC) method by p-NMR. CIE experiments using shea olein were introduced to study the SFC and crystal form changes. Besides, shea olein is used in an O/W emulsion system which was prepared by adding mono stearin emulsifying agent to mixtures of certain oil and water. The formed solid-fat-like product was featured by low contents of saturated fatty acid and fat compared with the existing margarine and shortening. To our knowledge, there is very little published information about the application of shea olein. Therefore, the findings in this work will contribute to the preparation of specialty fats based on shea olein as a new low melting point “liquid” base oil and raise its potential industrial application value.
The glycerolysis products were analyzed by a GC system equipped with a capillary column (DB-1HT, 15 m 0.25 mm i.d., 0.1 mm in film thickness, Agilent Technologies Inc., Palo Alto, CA, USA). The yields of acylglycerols were expressed as the percent content of the corresponding peak area response compared with the total peak area using a flame ionization detector (Wang, Wang, & Hu, 2011). TAGs compositions of samples were conducted using the above GC with column (Rtx-65TG, 30 m 0.25 mm i.d., 0.1 mm in film thickness, RESTEK, USA). TAGs composition was analyzed before deacidification and identified using available standard (Adhikari & Hu, 2012). All determinations were performed in three replicates and the means ± standard deviations were reported.
2. Materials and methods
2.6. Characterization of the samples
2.1. Materials
2.6.1. Solid fat contents (SFC) and crystallization rates SFC was determined according to the AOCS Official Method Cd 16-81 (AOCS, 2009d) on a Bruker PC/20 Series NMR analyzer, Minispec (Bruker Optics, Milton, On, Canada). Samples were tempered at 60 C for 30 min, followed by 0 C for 60 min and finally for 30 min at each temperature of measurement. SFC was measured at intervals of 5 C from 10 C up to 40 C. All determinations were performed in duplicate and the means were reported. Crystallization rates were measured at intervals of 2 min from 2 min up to 12 min according to the SFC value at 10 C. The increase rate of SFC value was defined as crystallization rate.
Shea butter, coconut oil (CNO), soybean oil (SBO), palm stearin (PST, Iodine value ¼ 33e35), and palm olein (POL, 24 C) were provided by PGEO Co., Ltd. (Pasir Gudang, Johor, Malaysia). Sodium methoxide (MeONa), oleic acids, n-hexane and acetone (>99.5%) were purchased from Fuyu Chemical Co., Ltd. (Tianjin, China). Sodium stearyl lactate (SSL) and monostearate (MS) were purchased from Danisco (China) Holding Co., Ltd. 2.2. Solvent fractionation of shea butter 300 g Shea butter was melted in a beaker followed by the addition of 1500 mL n-hexane. The beaker was put in a thermostatic water bath, and the temperature was set at 25 C. A mechanical impeller with a plastic paddle rotating at 200 r/min was used to stir the mixture. After 30 min, the mixture was filtered. The solid fat was collected and dried, and the filtrate was concentrated under vacuum to get the liquid oil. The solid fat and the liquid oil were marked as shea stearin (SheaST25) and shea olein (SheaOL25), respectively. 2.3. Chemical interesterification of SheaOL25 with palm-based oil 150 g of SheaOL25 and 150 g PST (or POL) were melted and added in a three-necked round-bottom flask (500 mL), and heated in a thermostatic oil bath, while being stirred at 400 r/min. When the temperature reached 105 C, 0.9 g MeONa (0.3 wt.% of the oil mass) was added. The reaction was conducted under vacuum (~2000 Pa) for 0.5 h. After reaction, the mixture was cooled, neutralized by citric acid, and then washed by hot water. The interesterified oils was then dried and analyzed by gas chromatography (GC). 2.4. O/W emulsion system preparation 120 mL deionized water (40.0 wt.%) was added in a beaker, immersed and heated to 80 C in a thermostatic water bath. 18.0 g MS (6.0 wt.%) and 1.5 g SSL (0.5 wt.%) were added to 160.5 g oil phase (53.5 wt.%) as emulsifiers in the other beaker, and then heated to melt. The O/W emulsion system was prepared by adding the melted oil phase to the water dropwise with a high-shear mulser to mix. 2.5. Fatty acid, acylglycerols analysis, and TAGs composition The composition of fatty acids (FAs) of samples was analyzed as fatty acid methyl esters (FAMEs) by a GC system with a capillary column (CP-Sil88, 100 m 0.250 mm i.d., 0.2 mm in film thickness, Agilent Technologies Inc., Palo Alto, CA, USA) (Zhang et al., 2015).
Crystallization rateðTÞ ¼
SFCðTÞð%Þ SFC ð10 CÞð%Þ
where SFC (T): SFC value of the melted sample at 10 C for a certain time, SFC (10 C): SFC value of the sample at 10 C. 2.6.2. Compatibility test The compatibility of dualistic mixtures of SheaOL25 with palmbased oil (PO) which contains 80%POLþ20%PST and with coconut oil (CNO) was studied by DSFC. DSFC ¼ practical SFC (PSFC) theoretical SFC (T-SFC), while T-SFC ¼ SFCx X% þ SFCy Y% which was calculated in computer according to the SFC value of single oil. X%, and Y% were the percentages in mixture total mass of x-oil and y-oil respectively. The closer to zero of DSFC, the better compatibility of oil blends. When the DSFC value is above zero, blends are monotectic, otherwise eutectic (Willimas, Ransom, & Hartel, 1997). 2.6.3. Melting and crystallization behaviors A differential scanning calorimetry (DSC) system was used to monitor the melting and crystallization behavior of the products. The exotherm was obtained by holding the samples for 5 min at 80 C followed by cooling to 40 C by 5 C/min. To obtain endotherm, the samples were heated to 80 C at 5 C/min (Bouzidi, Boodhoo, Humphrey, & Narine, 2005; Zhang et al., 2015). All determinations were performed in three replicates and the means ± standard deviations were reported. 2.6.4. Crystal structure Polarized light microscope (PLM) techniques were applied to characterize the structures of crystallization after smeared and 24 h ripening at 20 C. The products were characterized by X-ray diffraction (XRD) (Cerdeira, Martini, Candal, & Herrera, 2006). 2.6.5. Particle size analysis A laser particle size analyzer (LS13-320, Beckman Coulter) was used to measure the particle size changes of O/W samples during
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storage. O/W emulsion sample was diluted into 5% suspension to be analyzed, and the average particle size was recorded.
oil is commonly used to balance the SFC curve of the specialty fats system.
2.6.6. Emulsion system stability measurement TURBISCAN (LAB, Formulaction, France) was introduced to study the stability comparison of different O/W emulsion system under 60 C, scan every 10 min.
3.2. Compatibility of SheaOL25 with PO and CNO
2.7. Statistical analysis One-way ANOVA was performed using SPSS 16 statistical software (SPSS Inc., Chicago, IL). Differences were considered to be significant at p 0.05, according to Duncan's Multiple Range Test. 3. Results and discussion 3.1. Physicochemical profiles of SheaOL25 The FAs compositions of samples are shown in Table 1A. Traces of SFAs, including palmitic and stearic acids, were found in shea butter. The high contents of stearic (43.50 wt.%) and oleic (44.47 wt.%) acids demonstrate that shea butter was rich in C18 FAs. After solvent fractionation, the FAs compositions changed noticeably with increased content of oleic acids (50.15 wt.%) in SheaOL25 and stearic acid (58.24 wt.%) in SheaST25. This reveals that SheaOL25 abounded in heathier unsaturated FAs. In comparison, the olein and stearin from palm-based oil (POL, PST) contained much more saturated palmic acids (39.51 wt.% and 59.77 wt.%, respectively). Table 1B outlines the TAGs compositions of samples. It should be noted that shea-base oil has higher SOS and SOO contents and lower POP, PLP and PLS contents than palm-based oil, which is consistent with the FAs composition. In detail, shea butter contained 40.84 wt.% of SOS and 23.49 wt.% of SOO, while after solvent fractionation there were a decrease in SOS (7.03 wt.%) and increases in SOO and C40-TAGs (37.04 wt.% and 10.74 wt.% respectively) in SheaOL25. On the contrary, the content of SOS was increased to above 74 wt.% in SheaST25. In comparison, POL contained 33.20 wt.% POP, while 30.20 wt.% of PPP was in PST. Owing to the higher content of MUFA and SUU-type TAGs in SheaOL25 with lower melting point, it could be viewed as potential POL-substitutes “liquid” and healthier oil in specialty fats industry. The acylglycerols compositions of SheaOL25 are listed in Table 1C. Many batches of shea butter were analyzed in previous work, and a high content of diacylglycerols (DAGs) (9.70 wt.% to 19.41 wt.%) was found, which may be produced in the process of raw shea butter refining (Adhikari & Hu, 2012). The selected batch of shea butter contained 10.99 wt.% DAGs originally with 8.17 wt.% in SheaOL25 after fractionation. SFC is not only an important determinant of the texture of fats but responsible for various functional characteristics. The high SFC value at lower temperatures could provide the good shape maintenance ability around 37e40 C and the low SFC value allows a clear mouth feeling. Fig. 1A1 describes the SFC in samples under various temperatures. It shows that with regards to SFC values, SheaST25 and PST were superior to others while the trend of SFC changes of SheaST25 was sharper than that of PST. The SFC in SheaST25 decreased significantly from 92.70% to 15.91% along with the temperature from 10 C to 40 C. Due to such physical properties, fractionated stearin as suitable base oil is commonly used as confectionary and chocolate fats. It can be seen that POL has a much higher SFC value (33.12%) at 10 C, while at 25 C SFC of SheaOL25 decreased to 1.24% which is similar to POL (1.18%) and this indicates a lower melting point (SMP ¼ 25.5 C) of the fractionated olein phase. Such “liquid” base
The compatibility of oil blends refers to the degree of mutual consistency between TAGs and different oils. The compatibility among various stock oils directly influences processing course, quality and shelf life of plastic fats. The specialty fats products made by processing incompatible oil blends tend to have sand streaking, oil leaking, lowered caseation valence and so on (Lida & AIi, 1998). PO has extensive sources, while CNO is rich in medium-carbon chain FAs such as lauric acid (C12, 45.94 wt.%) and myristic acid (C14, 18.36 wt.%), which could be used to produce TAGs with less total carbon atoms (Table 1B). So they are commonly used in production of specialty fats. Investigation on the compatibility phenomenon with these two representative oils will be instructive to the application of SheaOL25 in specialty fats blends. The compatibility of binary mixtures with different ratios of SheaOL25 and PO, SheaOL25 and CNO were illustrated by DSFC (the practical SFC value theoretical SFC value) (Buning & Bartsch, 1989) and curves are shown in Fig. 2A and B, respectively. For the purpose of further analyzing specific compatibility and clarifying the acting degree of monotectic crystal and eutectic crystal, maps with temperature as X-coordinate and DSFC as Ycoordinate are shown in Fig. 2A and B. According to Fig. 2A, at temperatures below 25 C, eutectic crystal occurred in the blends system and thus the mixture system was in the initial stage of crystallization. The eutectic crystal phenomenon was most obvious at 10 C and 20 C, especially with 40%e70% of SheaOL25, where DSFC values were large, with D-value up to 10e14%. Since the content of high-melting point TAGs in compound system was high, its large difference from POL in thermodynamic property led to the partial incompatibility between them. As a consequence, the phenomenon of eutectic crystal presented. As the crystallization rate shown in Fig. 1A2, SheaOL25 crystallized rapidly and the rate reached 79% at 4 min. Since PO contains more POL, the crystallization rate is slower. The crystallization rate of 20%PST þ 80%POL at 2 min was only 23%. They differed significantly in terms of the conversion of crystal form and compatibility. During the same time, DSFC table and curve show that when the temperature was 25e40 C, eutectic crystal phenomenon of mixture system weakened, corresponding to the increased compatibility. The closer the DSFC was to 0, the better the compatibility blends were (Liu, Wu, & Yang, 2010). The SheaOL25 had lower SMP, and melted in this temperature range. Yet it still had some effects on the system. Fig. 2B shows that the eutectic crystal phenomenon of blended oil system of SheaOL25 and CNO was the most obvious when the temperature was 20 C with 10%e90% of SheaOL25, and the DSFC value was 6e16. The eutectic crystal phenomenon for the system was insignificant between 25 C and 40 C and the content of SheaOL25 was 10%e90% with DSFC values of between 0.1 and 2. These results suggest the good compatibility of the blends system. We speculate this may be because CNO contained high content of low temperature solid fat. At 10 C, the solid fat was around 80% in CNO, while SheaOL25 had only about 12%. In addition, CNO and SheaOL25 basically melted over 25 C. As a result, the phenomenon of eutectic crystal weakened and the compatibility increased. SheaOL25 demonstrated high compatibility with both of PO and CNO. The blends exhibited higher incompatibility with higher SheaOL25 proportion. However, when the temperature exceeded 25 C, the systems were highly compatible. In real production, the emulsification temperature exceeds the highest melting point of system's oils. Therefore, using SheaOL25 for blending could contribute to the practicable compatibility.
Table 1 Fatty acid, triacylglycerols and acylglycerols composition by GC analysis (wt.%).a,b (A) Fatty Acids
8:0
10:0
12:0
14:0
16:0
18:0
18:1
18:2
18:3
20:0
20:1
22:0
SFA
MUFA
Shea butter SheaOL 25 SheaST 25 POL PST CNO
e e e e e 7.48 ± 0.22
e e e e e 5.79 ± 0.59
0.09 ± 0.03 0.13 ± 0.01 0.03 ± 0.01 e e 45.94 ± 1.34
0.02 ± 0.01 0.09 ± 0.01 0.02 ± 0.01 1.01 ± 0.01 1.20 ± 0.06 18.36 ± 1.02
3.56 ± 0.27 4.24 ± 0.15 2.47 ± 0.01 39.51 ± 1.34 59.77 ± 1.91 9.75 ± 0.87
43.50 ± 2.11 35.59 ± 1.35 58.24 ± 2.09 4.70 ± 0.72 5.23 ± 0.72 3.11 ± 0.90
44.47 ± 1.83 50.15 ± 2.10 34.18 ± 1.38 42.01 ± 1.43 27.02 ± 1.11 6.95 ± 1.02
6.11 ± 0.19 6.95 ± 0.03 2.89 ± 0.79 11.14 ± 1.27 5.53 ± 0.53 1.61 ± 0.10
0.15 ± 0.02 1.44 ± 0.39 0.27 ± 0.04 0.16 ± 0.04 48.77 ± 2.85 44.74 ± 1.87 0.08 ± 0.01 1.46 ± 0.07 0.39 ± 0.07 0.17 ± 0.01 41.68 ± 1.60 50.54 ± 2.17 0.05 ± 0.01 1.65 ± 0.02 0.08 ± 0.01 0.17 ± 0.04 62.55 ± 2.15 34.26 ± 1.39 e e e e 45.22 ± 2.05 42.01 ± 1.43 e e e e 66.20 ± 2.69 27.02 ± 1.11 e e e e 90.43 ± 4.94 6.95 ± 1.02
PUFA 6.32 ± 0.21 7.12 ± 0.04 2.96 ± 0.80 11.14 ± 1.27 5.53 ± 0.53 1.61 ± 0.10
(B) Shea Butter
SheaOL25
SheaST25
POL
PST
CNO
C30 C32 C34 C36 C38 C40 C42 C44 MPP PPP MOP MLP PPS POP MOO PLP MLO PSS POS POO PLS PLO PLL SSS SOS SOO OOO SLO OLO OLL SOA AOO
e 1.02 ± 0.02 e e 0.45 ± 0.01 5.22 ± 0.65 e e 1.54 ± 0.12 e 1.72 ± 0.01 0.61 ± 0.01 0.04 ± 0.01 0.39 ± 0.01 0.03 ± 0.01 0.12 ± 0.01 e 0.31 ± 0.01 5.50 ± 0.03 2.27 ± 0.17 1.52 ± 0.02 0.85 ± 0.01 0.13 ± 0.01 1.25 ± 0.05 40.84 ± 1.21 23.49 ± 0.88 4.12 ± 0.19 4.21 ± 0.62 1.11 ± 0.33 0.79 ± 0.08 2.13 ± 0.11 1.12 ± 0.10
e 2.67 ± 0.37 e e 1.01 ± 0.01 10.74 ± 0.98 e e 2.56 ± 0.03 e 3.32 ± 0.01 1.20 ± 0.01 0.06 ± 0.01 e e 0.19 ± 0.01 e 0.09 ± 0.01 5.25 ± 0.02 3.80 ± 0.30 2.13 ± 0.02 1.18 ± 0.01 0.33 ± 0.01 0.86 ± 0.21 7.03 ± 0.75 37.04 ± 1.15 7.37 ± 0.53 7.37 ± 0.73 1.34 ± 0.17 2.14 ± 0.13 1.05 ± 0.04 1.65 ± 0.07
e 1.78 ± 0.13 e e 2.31 ± 0.02 2.91 ± 0.02 e e 0.08 ± 0.01 e 0.37 ± 0.01 0.10 ± 0.01 0.17 ± 0.01 0.40 ± 0.01 e 0.10 ± 0.01 e 0.56 ± 0.09 5.25 ± 0.17 0.44 ± 0.16 0.45 ± 0.01 0.15 ± 0.01 0.20 ± 0.01 1.71 ± 0.82 74.11 ± 2.10 4.57 ± 0.95 0.67 ± 0.25 0.71 ± 0.21 0.38 ± 0.07 0.13 ± 0.02 3.66 ± 0.32 0.23 ± 0.01
e e e e e e e e 0.34 ± 0.01 1.06 ± 0.31 2.11 ± 0.01 0.66 ± 0.01 e 33.20 ± 1.90 e 10.01 ± 0.83 0.59 ± 0.01 e 2.53 ± 0.01 5.89 ± 0.78 22.74 ± 1.19 9.22 ± 1.01 1.95 ± 0.02 e 0.59 ± 0.07 2.54 ± 0.20 3.25 ± 0.67 0.98 ± 0.34 1.69 ± 0.09 e e e
e e e e e e e e 2.35 ± 0.01 30.2 ± 1.78 1.20 ± 0.01 0.30 ± 0.01 6.20 ± 0.58 26.86 ± 1.55 e 5.73 ± 0.45 e 0.70 ± 0.12 4.50 ± 0.02 10.74 ± 0.99 1.15 ± 0.02 4.22 ± 0.19 0.86 ± 0.01 e 0.41 ± 0.07 1.17 ± 0.01 1.48 ± 0.41 0.53 ± 0.32 0.62 ± 0.03 0.15 ± 0.02 e e
2.82 ± 0.02 11.58 ± 0.57 15.79 ± 0.49 19.08 ± 1.01 17.26 ± 1.43 11.72 ± 0.89 8.42 ± 0.89 4.72 ± 0.64 2.85 ± 0.62 2.20 ± 0.10 e e 1.53 ± 0.01 e e e e e e e e e e e e e e e e e e e
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TAG
(C) Acylglycerols
SheaOL25
POL
SBO
MAG DAG TAG
ND 8.17 ± 0.58 91.83 ± 0.79
ND ND 100 ± 0
ND ND 100 ± 0
a
Values show the means ± standard deviations. Abbreviations used: SheaOL25, the liquid phase solvent-fractionated from shea butter under 25 C; SheaST25, the solid phase solvent-fractionated from shea butter under 25 C; POL, palm olein (slip melting point ¼ 24 C); PST, palm stearin (iodine value ¼ 33e35); CNO, coconut oil; SBO, soybean oil; 8:0, octanoic acid; 10:0, decanoic acid; 12:0, lauric acid; 14:0, myristic acid; 16:0, palmitic acid; 16:1t, trans-palmitoleic acid; 16:1c, palmitoleic acid; 18:0, stearic acid; 18:1, oleic acid; 18:2, linoleic acid; 18:3, linolenic acid; 20:0, arachidic acid; 20:1, eicosenoic acid; 22:0, behenic acid; SFA, saturated fatty acid; MUFA, mono-unsaturated fatty acid; PUFA, poly-unsaturated fatty acid; C30-44, TAG group of total carbon number ¼ 30e44; M, myristic acid; P, palmitic acid; O, oleic acid; L, linoleic acid; S, stearic acid; A, arachidic acid; MAGs, monoacylglycerols; DAGs, diacylglycerols; TAGs, triacylglycerols. b
495
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Fig. 1. SFC comparison of the samples and oil blends (A1 and B) and crystallization rate at 10 C (A2) by p-NMR analysis.
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497
Fig. 2. (A) SFC and Compatibility of SheaOL25 with PO. (B) SFC and Compatibility of SheaOL25 with CNO. (DSFC ¼ Practical solid fat content (P-SFC) e theoretical solid fat content (TSFC)).
3.3. CIE properties of SheaOL25 To explore the application of SheaOL25 in crystallization and CIE modified oil base, two common palm oil bases of PST and POL were selected for proportioning and CIE experiment. Crystallization rate was calculated by recording the SFC at 10 C within the first 12 min every 2 min. SFC results are listed in Fig. 1A1. The new base oils were prepared through CIE reactions under certain conditions and characterized by SFC. It is observed that the SFC trend markedly changed compared with non-interesterification (NIE) samples. All samples' profiles turn sharper than before for a notable increase in the SFC at 10 C. The crystallization rates (Fig. 1A2) of 50%PST þ 50% SheaOL25 at 2 min before and after CIE were 58% and 45% respectively, and this means the crystallization rate after CIE was retarded. 50%POL þ 50%SheaOL25 had faster crystallization rate and this rate was delayed slightly after CIE. It can also be observed that all oil base blended by 50% SheaOL25 underwent rapid increases in crystallization rate. To take interesterification specimen (50%POL þ 50%SheaOL25) for example, crystallization rate of POL itself is very slow (33% for 12 min). But crystallization rate at 6 min achieved 82% with the addition of 50% SheaOL25. To clarify if SheaOL25 could effectively change the crystallization rate of the oil blends system at 10 C, oil blends crystallization rates tests were conducted, and the results are also summarized in Fig. 1B. PST with
different ratios of SheaOL25 was mixed to test the SFC, and POL replaced SheaOL25 as the control. The results show that when the ratio of SheaOL25 to PST was 7:3, the rate increases significantly over 30% higher than the corresponding POL. When it comes to PST þ POL, with the increase of POL amount, the crystallization rate at 2 min exhibited a downtrend from 37.4% of 50%PST þ 50%POL to 23.6% of 20%PST þ 80%POL. The parallel comparison shows after the replacement of POL with SheaOL25, the crystallization rates were all higher than the case of adding POL in the same proportion. Meanwhile, the crystallization rate at the same time node was all above 56%. However, the crystallization rate did not always increase in proportion to the addition level of SheaOL25, which may be attributed to the increase of “liquid” phase amount. Nonetheless, parallel comparison demonstrates that when mixed with PST, SheaOL25 had better pro-crystallization than POL. In our efforts to verify this, a third experiment was conducted by mixing SheaOL25 and POL in a ratio of 1:1. It is observed that due to the addition of SheaOL25 which replaced parts of POL, the crystallization rate increased to above 41% at 2 min. The results could be explained from the different acyl-chain length structure between SheaOL25 and POL. The fat crystallization can vary in their chain length structure which provides the crystals with another dimension of variation (Sato, 2001). From the fatty acids composition analysis (Table 1A), SheaOL 25 contained 0.13 wt.% lauric acid, 1.46 wt.%
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Fig. 3. (A) DSC crystallization and melting thermograms of the samples. (B) Polymorphic forms of the SheaOL25-based interesterified samples at 25 C. (C) Images of SheaOL25based samples before and after interesterification at 25 C. Size bar ¼ 10 mm.
arachidic acid, and 0.39 wt.% eicosenoic acid, while they were not detected in POL. DSC is commonly adopted to evaluate the thermal behavior of oils. The DSC curves of samples are shown in Fig. 3A. Simultaneously, the transition temperatures of crystallization, melting points as well as the onset temperature (To), offset temperature (Tf), and temperature range (difference between To and Tf) are summarized in Table 2. General characteristics did not change greatly before and after CIE, with difference mainly in temperature. Thereinto, 50%PST þ 50%SheaOL25 had two primary crystallization peaks. The reason for the wider temperature range (51.06 C changed to 52.41 C) after CIE may derive from the slowed crystallization rate. From crystallization rate in Fig. 1A2, it is observed that the crystallization rate after CIE was lower by 14.4% than before and the beginning crystal temperature for NIE was about 26.51 C. After CIE, its crystallizing point rose to 31.28 C. 50%POL þ 50% SheaOL25 displayed one primary crystallization peak, but presented two crystallization peaks after CIE. The beginning crystal temperature increased from 14.08 C to 27.41 C. The analysis on melting characteristics of DSC show those general curve characteristics changed slightly after CIE. The general melting peak of 50% PST þ 50%SheaOL25 narrowed compared with that before ester interchange. Concurrently, end temperature of melting increased by about 6 C, and clearly the first melting peak was separated into two, indicating two substances with obvious melting point
differences appeared after CIE. The temperature range for 50% POL þ 50%SheaOL25 after CIE became narrower and changed from one primary melting peak into two. The initial melting temperature was postponed from 18.58 C to 15.74 C. High temperature melting peak appeared and augmented and this is in agreement with the increase of substances with high melting point after CIE. When producing food products containing fat or lipids it is important to be aware of the fact that the physicochemical and sensory properties of the end products will be influenced by the physical state of the fats or lipids (Damodaran, Parkin, & Fennema, 2008). The crystal forms before and after CIE reaction are shown in Fig. 3B. It can be seen that 50%PST þ 50%SheaOL25 had very strong diffraction peaks near 3.8 Å, 4.2 Å and 4.6 Å before CIE. The diffraction peak at around 4.6 Å disappeared after CIE, indicating the decrease of b crystal form which converts into b'. Similarly, more b0 crystal form existed in 50%POL þ 50%SheaOL25 after CIE, and there was also partial b crystal form. It can be inferred that CIE between SheaOL25 and hard oil can delay the translation of crystal form and stabilize b0 crystal form, which is consistent with its crystallization rate result. In detail, crystallization rate of CIE (50% POL þ 50%SheaOL25) was slowed and the transformation of crystal form to b was delayed. PLM picture (Fig. 3C) also demonstrates that the samples after CIE have finer crystalline state and was more uniform and smoother.
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Table 2 Comparison of DSC-measured onset, offset and transition temperatures for crystallization and melting curves of the samples.a,b Curve
Sample
To ( C)
Tf ( C)
Temperature range ( C)
Transition temperature ( C)
Crystallization
SheaOL25 NIE (50%PST þ 50%SheaOL25) CIE (50%PST þ 50%SheaOL25) NIE (50%POL þ 50%SheaOL25) CIE (50%POL þ 50%SheaOL25)
18.12 ± 0.21 26.51 ± 0.43
e 24.55 ± 0.22
e 51.06 ± 0.65
31.28 ± 0.16
21.13 ± 0.22
52.41 ± 0.38
14.08 ± 0.12
e
e
1: 6.85 ± 0.02 1:25.35 ± 0.66 2:6.14 ± 0.15 1:31.28 ± 0.34 2:14.74 ± 0.34 1:3.68 ± 0.12
27.41 ± 0.38
e
e
1:25.2 ± 0.18 2:11.76 ± 0.26
SheaOL25 NIE (50%PST þ 50%SheaOL25)
28.17 ± 0.25 18.05 ± 0.32
e 52.12 ± 0.61
e 70.17 ± 0.94
CIE (50%PST þ 50%SheaOL25)
17.11 ± 0.27
46.15 ± 0.12
63.26 ± 0.39
NIE (50%POL þ 50%SheaOL25) CIE (50%POL þ 50%SheaOL25)
18.58 ± 0.31
e
e
15.74 ± 0.23
e
e
1:7.85 ± 0.03 1:6.42 ± 0.02 2:25.58 ± 0.51 3:44.33 ± 0.45 1:7.01 ± 0.09 2:14.39 ± 0.30 3:28.34 ± 0.55 4:43.87 ± 0.38 1:6.98 ± 0.12 2:12.02 ± 0.16 1:12.44 ± 0.07 2:28.68 ± 0.14 3:40.01 ± 0.38
Melting
a
Values show the means ± standard deviations. Abbreviations used: SheaOL25, the liquid phase solvent-fractionated from shea butter under 25 C; PO, palm-based oil (80%POL, palm olein (slip melting point ¼ 24 C) þ 20%PST, palm stearin (iodine value ¼ 33e35)); CNO, coconut oil; P, practical value by p-NMR analysis; T, theoretical value in computer calculation; NIE, nonchemical interesterification; CIE, chemical interesterification. b
Fig. 4. (A) Particle size measurement of O/W emulsion samples during storage at 25 C. (B) Images of O/W emulsion samples stability after 2 h storage at 60 C. (Dynamic stability index: SBO-sample ¼ 30.55; POL-sample ¼ 12.20; SheaOL25-sample ¼ 3.90). The means ± standard deviation with different letters denote significant difference at p 0.05 (n ¼ 3).
3.4. Effects of SheaOL25 on O/W emulsion system The analysis result of particle size of O/W emulsion system in storage process is depicted in Fig. 4A. The curve demonstrates that the particle sizes of the three samples within the first day were very small, being 1.5e2.5 mm. Thereinto, SheaOL25-sample had the smallest particle size and kept at lower particle sizes during the storage of 30 days. This may be because the original presence of 8.17 wt.% DAGs in sheaolein (Table 1C) and DAGs usually act as an emulsifier for oil-water system (Mahmoud, Murad, & Murad, 2008; Yi, Cheng, & Dong, 2015). Adhikari and Hu (2012) reported that shea olein can be used for margarine/shortening formulation to enhance the whipping properties containing small amount of DAGs. Similarly, Kawai and Konishi (2006) reported that the O/W
system comprising DAGs displayed enhanced performance in terms of storage stability, appearance and taste. The particle sizes of POLsample and SBO-sample changed dramatically, undergoing an increasing trend after 24 h, and reaching the peak value of particle size (4.01 mm and 4.25 mm respectively) on the 15th day. The particle size of POL-sample and SBO-sample increased rapidly and fluctuated after being placed for 10 days, which may be due to the rearrangement of crystal network during storage (Cheong, Tan, & Long, 2009). High temperature stability test for O/W emulsion system was conducted. Fig. 4B illustrates that after SheaOL25sample was placed at 60 C for 2 h, the layering of oil phase and water phase was the least obvious, and the sample's dynamic stability index could reach 3.90. With regards to POL-sample and SBOsample, the oil and water were completely separated, and the
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dynamic stability index was up to 30.55. 4. Conclusion Solvent fractionated SheaOL25 was prepared and it is rich in oleic acid and SOO type TAGs. Compatibility testing with PO and CNO showed that the linear relationship of isothermal curve obtained was desirable. Moreover, at temperature above 25 C the SheaOL25 had good compatibility and could serve as blending base oil for preparing specialty fats. Compared with POL, SheaOL25 can significantly expedite crystallization rate of system, but retarded the crystallization rate of system after CIE, thereby stabilizing b0 crystal form of the system. O/W emulsion system with SheaOL25 as oil phase exhibited significantly improved stability compared with control groups of SBO and POL at high temperature. The findings will contribute to the application of shea olein as a novel base oil in the production of specialty fats and expand the low melting point “liquid” base oil categories of plastic fats. Acknowledgement The financial support from the National Natural Science Foundation of China under grant 31371785 and 31671781, the National Key Research and Development Program of China under grant 2017YFD0400200, the Department of Science and Technology of Guangdong Province under grant 2017B090907018, 2012B091100035 and 2013B090800009, and the Bureau of Science and Information of Guangzhou under grant 2014Y2-00192 are gratefully acknowledged. References Adhikari, P., & Hu, P. (2012). Enzymatic and chemical interesterification of rice bran oil, sheaolein, and palm stearin and comparative study of their physicochemical properties. Journal of Food Science, 77, 1284e1291. Alaba, P. A., Sani, Y. M., Mohammed, I. Y., Abakr, Y. A., & Daud, W. M. A. W. (2017). Synthesis and characterization of sulfated hierarchical nanoporous faujasite zeolite for efficient transesterification of shea butter. Journal of Cleaner Production, 142, 1987e1993. AOCS Official Method Cd 16-81. Bouzidi, L., Boodhoo, M., Humphrey, K. L., & Narine, S. S. (2005). Use of first and second derivatives to accurately determine key parameters of DSC
thermographs in lipid crystallization studies. Thermochimica Acta, 439, 94e102. Buning, P., & Bartsch, A. (1989). Investigation on the compatibility of milk fat fractions and lauric fat. Journal of Thermod Analysis, 35, 671e675. Cerdeira, M., Martini, S., Candal, R. J., & Herrera, M. L. (2006). Polymorphism and growth behavior of low-trans fat blends formulated with and without emulsifiers. Journal of the American Oil Chemists’ Society, 83, 489e496. Cheong, L. Z., Tan, C. P., & Long, K. (2009). Physicochemical textural and viscoelastic properties of palm diacylglycerol bakery margarine during storage. Journal of the American Oil Chemists’ Society, 86, 723e731. Co, E. D., & Marangoni, A. (2012). Organogels: An alternative edible oil-structuring method. Journal of the American Oil Chemists’ Society, 89, 749e780. Damodaran, S., Parkin, K. L., & Fennema, O. R. (2008). Fennema's food chemistry (4th ed.). Boca Raton: CRC Press/Taylor & Francis, 12, 1144. Floter, E. (2012). Structuring oils without highly saturated fats e how far are we? European Journal of Lipid Science and Technology, 114, 983e984. Kawai, S. & Konishi, Y. (2006) Acid oil-in-water emulsified composition. US Patent 7041328. Lida, H., & AIi, A. (1998). Physicochemical characteristics of palm based oil blends for production of reduced fat spreads. Journal of the American Oil Chemists’ Society, 75, 1625e1631. Liu, R. X., Wu, S. X., & Yang, W. F. (2010). Study on the compatibility of several kinds of palm oil. Grain Science and Technology and Economy, 35, 49e53. Lovett, P. N. (2014). Natural butters: Fractionation alternatives. Waxes and Butter, 49e52. Lovett, P. N. (2015). 5eShea butter: Properties and processing for use in food. Specialty Oils and Fats in Food and Nutrition, 125e158. Mahmoud, A. G., Murad, S., & Murad, A. H. (2008). Formulation and fuzzy modeling of emulsion stability and viscosity of a gum-protein emulsifier in a model mayonnaise system. Journal of Food Engineering, 84, 348e357. Sato, K. (2001). Crystallization behaviour of fats and lipids e a review. Chemical Engineering Science, 56, 2255e2265. Segman, O., Wiesman, Z., & Yarmolinsky, L. (2012). 17eMethods and technologies related to shea butter chemophysical properties and to the delivery of bioactives in chocolate and related products. Cocoa Butter and Related Compounds, 417e441. Wang, L. L., Wang, Y., & Hu, C. Y. (2011). Preparation of diacylglycerol-enriched oil from free fatty acid using lecitase ultra-catalyzed esterification. Journal of the American Oil Chemists’ Society, 88, 1557e1565. Willimas, S. D., Ransom, P. K. L., & Hartel, R. W. (1997). Mixtures of palm kernel oil with cocoa butter and milk fat in compound coatings. Journal of the American Oil Chemists’ Society, 74, 357e366. Xu, Z. B., Jin, J., Adhikari, P., Liang, J., Xu, X. B., Liu, Y. F., et al. (2016). Sheaolein-based cold-soluble powder fats with medium- and long-chain triacylglycerol: Production via chemical interesterification using sheaolein and palm kernel stearin. RSC Advance, 6, 18632e18640. Yi, J. H., Cheng, J. J., & Dong, W. B. (2015). Effect of pH emulsifier type and concentration on physical stability of oil-in-water emulsions. Science and Technology of Food Industry, 13, 266e270. Zhang, Z., Wang, Y., Ma, X., Wang, E. P., Liu, M. M., & Yan, R. A. (2015). Characterisation and oxidation stability of monoacylglycerols from partially hydrogenated corn oil. Food Chemistry, 173, 70e79.