Sheaolein-based cold-soluble powder fats with medium- and long-chain triacylglycerol: production via chemical interesterification using sheaolein and palm kernel stearin

Abstract

Medium- and long-chain triacylglycerol (MLCT) is increasingly popular because of its anti-obesity ability, and therefore it is considered as a healthy functional fat. Sheaolein (SO)-based cold soluble powder fats with high MLCT level were studied by chemical interesterification of SO and palm kernel stearin (PKST) (SO : PKST, 80 : 20; 60 : 40; 50 : 50; 40 : 60; 20 : 80). Physicochemical properties of interesterified products, mainly including fatty acid composition, triacylglycerol composition, solid fat content, melting point, melting and crystallization behavior, and sensory characteristics were comparatively analyzed with the original substrate mixture. In addition, some of the properties were compared with the traditional commercial powder fats. The interesterified fat of 40 : 60 (SO : PKST) showed ideal physicochemical properties for possible use as a cold soluble powder fat with healthy conception. In particular, the MLCT level increased from 12.3% to 53.0%, and the reduction of trisaturated triacylglycerol and the content of trans fatty acid (less than 1%) were also desirable.

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Introduction

Medium- and long-chain triacylglycerol (MLCT) is a type of modified lipid and consists of both medium-chain fatty acid (MCFA) and long-chain fatty acid (LCFA) attached to its glycerol backbone.¹ This structured lipid, with at least 12% of MCFA, can not only deliver essential fatty acids, especially polyunsaturated fatty acids, to the body, but most importantly it can also help to reduce weight and body fat accumulation in the body.^2–4

Powder fats are spray dried systems that deliver emulsified fat at a very high level to dry-based food products. Cold soluble powder fats, such as some kinds of milky tea and coffee, are usually solid at room temperature (15–25 °C) and can be drunk directly just by adding warm water (30–40 °C). These fat products are increasingly popular among Chinese due to the need for fast-paced life. Traditionally, tallow, lard, soybean oil, fractionated palm and palm kernel oil are commonly used to make powder fats. However, according to our market survey, the fully hydrogenated palm kernel oil or partially hydrogenated soybean oil are the most commonly used materials of above mentioned products. The former is characterized by a high level of trisaturated triacylglycerol with almost full of MCFA, such as trimyristic acid attached in one glycerol backbone that has a cholesterol level rising effect.¹ The later usually has high content of triacylglycerol with LCFA and especially of trans fatty acid (TFA) ranged 20–50%, which is considered to increase the low-density lipoprotein cholesterol and decrease the high-density lipoprotein cholesterol as well as it leads to the coronary heart disease.^5,6 Recently, Food and Drug Administration proposed eliminating artificial trans-fat from food products. Therefore, suitable processing techniques and materials should be applied to produce cold soluble powder fats with low trisaturated triacylglycerol and TFA content.

To decrease or eliminate the above mentioned undesirable fats in products, alternative technological approaches, especially interesterification and fractionation, have been developed to replace the conventional hydrogenation process.^7,8 In particular, interesterification has long been used to modify oils and fats into functional products.^9,10 A wide range of table trans-free margarines, spreads, and frying shortenings can be formulated by mixing interesterified blends and native oils in adequate proportions.^11,12 The oils widely used for interesterification are divided into two groups: common oils (e.g., palm stearin, palm olein, palm kernel oil and coconut oil) and special oils (e.g., olive oil, rice bran oil, sunflower oil and pine nut oil).^9,13–16

Sheaolein (SO), a byproduct of shea butter production, is obtained after the fractionation of shea butter. It mainly consists of LCFA including stearic and oleic, and also contains 8–10% diacylglycerol, which is usually used as an emulsifier for various applications.^17,18 Meanwhile, SO is a rich source of phytosterol, especially β-sitosterol.¹⁸ Depending on the fractionation condition, wide ranges of melting points (25–30 °C) can be obtained.^17,18 Compared with the high value of shea butter stearin fraction that usually used for cocoa butter equivalent in chocolate formulations, sheaolein is mostly predominantly used in bakery and pastry products, and is seldom treated as powder fats.¹⁹ Furthermore, the excessive supply of shea nut ensures a continuing need for expanding the application scope of shea butter.²⁰ Palm kernel stearin (PKST) is usually considered as an ideal trans free and MCFA source.¹ A interesterified mixture of SO and PKST might be a healthy product that consists of low trisaturated triacylglycerol level and high MLCT content, which possesses the ability to act as potential anti-obesity functional oil and to manage obesity problem through diet.¹

To our knowledge, there is very little published information about the SO-based powder fats. Therefore, the main objective of this study is to develop the potential industrial value of SO and PKST as the cold soluble powder fats with low TFA and trisaturated triacylglycerol levels and high MLCT content.

Experimental

Materials

SO (iodine value (IV) = 65.6 g I₂ per 100 g) and palm kernel stearin (PKST, IV = 6.2 g I₂ per 100 g) were used to perform the experiments. SO was from PGEO Group Sdn. Bhd (Singapore). PKST was from the factory of YiHai Kerry group (Shanghai, China). Two typical commercial powdered fats used in cold beverages, namely PHSBO-36 and FHPKOL-41, were collected from markets in China. Sodium methoxide used was from Sigma-Aldrich, other chemicals were from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). All chemicals used were of analytical grade.

Chemical interesterification and purification

400 g of each blend (SO : PKST = 80 : 20, 60 : 40, 50 : 50, 40 : 60, 20 : 80) was prepared in a round bottom flask (2000 mL) and dried under reduced pressure for 60 min at 105 °C. After lowering the temperature to 90 °C, 0.2% sodium methoxide was added as a catalyst and the temperature was increased to 105 °C. Interesterification was conducted under reduced pressure at 105 °C for 30 min until the appearance became dark brownish color. After completion of the reaction, 10% citric acid solution dosage was added to inactivate the catalyst, while the mixture was stirred for 10 min. The raw product was washed with hot water until the pH was equal to 7.0 and then dried at 105 °C for 1 h. Post-bleaching was performed with 2% of beaching earth under reduced pressure for 30 min at 90 °C. Filtration was done using a filter paper and then the free fatty acid was removed by deodorization carried out in a 2 L batch deodorizer. Interesterified fat was fed into the deodorizer, and the reduced pressure of the vacuum (Edward Technologies Trading Co. Ltd. Shanghai, China) was adjusted to less than 30–50 Pa. The temperature was raised to 240 °C and maintained for about 2 h or until the free fatty acid was completely removed. During the process, N₂ was continuously supplied into the reactants. The free fatty acid content of the oil samples was determined according to the AOCS Official Method Ca 5a-40.²¹ All the treatments were performed in triplicate, and the indices of each sample mentioned next was expressed as the mean of two determinations.

Fatty acid composition

The fatty acid composition (FAC) was determined on an Agilent 7820A gas chromatography equipped with an auto injector and a flame-ionization detector (Agilent Technologies, Little Falls, DE, USA) using a fused-silica Cp 6173 column (50 m × 0.25 mm × 0.2 μm, Agilent Technologies, Middelburg, Netherlands). After methylation, 0.2 μL of methyl esters were injected. The split ratio was 1/75. The initial temperature of oven was 80 °C and heating to 120 °C at 10 °C min⁻¹. Again, oven temperature was increased to 180 °C at 5 °C min⁻¹ and from 180 to 230 °C at 2 °C min⁻¹ and held for 5 min. The injector and detector temperatures were 250 and 280 °C, respectively. Hydrogen (purity 99.99%) was used as carrier gas at flow rate of 1.5 mL min⁻¹.

Triacylglycerol composition

Triacylglycerol compositions of samples were conducted using the above GC according to AOCS Official Methods Ce5-86 with a fused-silica cp column (30 m × 0.25 mm × 0.2 μm).²¹ The initial temperature of oven was 220 °C and held for 1 min before increasing to 340 °C at 5 °C min⁻¹, and then the oven temperature was increased to 350 °C at 2 °C min⁻¹ and held for 25 min. The injector and detector temperatures were 350 °C. Helium was used as carrier gas, and the total gas flow rate at the inlet was 50 mL min⁻¹. Triacylglycerol composition was analyzed before deacidification and identified using available standard as previously described.¹⁸

Solid fat content by NMR

Solid fat content (SFC) was determined using NMR analyzer MQ 20 (BukerOptik, Ettlingen, Germany) according to AOCS Official Methods Cd 16-81.²¹ Samples were filled into glass tubes to a depth of 4 ± 1 cm and completely melted at 60 °C for 30 min followed by 0 °C for 60 min. After that, the tubes were placed to 10, 20, 25, 30, 35 and 40 °C for 30 min, respectively. Then, the tubes were transferred as quickly as possible into the sample holder of the NMR instrument to record the SFC value.

Determination of slip melting point

The slip melting points (SMP) of the samples were determined according to AOCS Official Method Cc 3-25.²¹ Three clean capillary tubes (i.d. 1 mm) were filled with 10 mm high of oils, immediately chilled by holding the ends of the tubes that contain the test portion against a piece of ice until the fat solidified. Place the tubes in a beaker and hold in a refrigerator at 4 °C for 16 h before being immersed in a beaker of cold water. The water was stirred and heated gradually at about 1 °C min⁻¹. The temperature was recorded as the SMP when the fat in the tube started to rise due to hydrostatic pressure.

Differential scanning calorimetry

Thermal analysis for melting and crystallization thermograms was obtained using a differential scanning calorimetry (DSC, TA Q2000, USA). An empty aluminum pan was used as a reference, and sample was accurately weighed (5–6 ± 0.1 mg) for DSC analysis. The sample was heated to 80 °C and held for 10 min. Thereafter, the temperature was decreased at 5 °C min⁻¹ to −40 °C. After holding for 10 min at −40 °C, the melting curve was obtained by heating to 80 °C at 5 °C min⁻¹.

Sensory evaluation

Sensory evaluation of the interesterified blends and the two typical commercial powdered fats (PHSBO-36 and FHPKOL-41) was conducted by 12 professional staffs. The apparent characters of the abovementioned products were identified by visual judgments, and the tastes were distinguished by dissolving 30 g of the products mixed with 0.6 g of monoglyceride and 0.3 g of sodium stearyl lactate in 150 g of 30 °C drinking water.

Results and discussion

Fatty acid composition

The FAC of SO, PKST and their blends before and after interesterification were shown in Table 1. The fatty acid compositions before and after interesterification were similar, because chemical interesterification just altered the distribution of the fatty acid over the triacylglycerol molecules.²² The major fatty acid presented in PKST was MCFA, including lauric (59.1%) and myristic (21.6%), and the total MCFA and saturated fatty acid (SFA) were approximately 86% and 95%, respectively, while in terms of SO, the major was LCFA, especially stearic (30.3%), oleic (53.5%) and linoleic (7.0%), and the total LCFA and SFA were about 99% and 37% respectively. Therefore, as the ratio of SO increased in the blends, the content of MCFA and SFA significantly decreased, while the amount of total unsaturated fatty acid (C18 : 1 and C18 : 2) increased dramatically, which was most obviously in mono-unsaturated fatty acid. Furthermore, all blends were found to contain TFA less than 1.0%, except that the proportion of SO was 80%. Similar TFA level displayed characteristics suited to application as trans-free substrate, which was of considerable importance from the nutritional point of view.²³ Typical commercial powder fats have either high SFA content (e.g., 97.9% for FHPKOL-41) or TFA content (e.g., 37.6% for PHSBO-36), which is the shortcoming of current cold soluble powder fats. Compared with these commercial fats, interesterified blend with 40 : 60 of SO : PKST has lower SFA (<75%) and TFA (<1%), and especially a suitable level of MCFA (50.0%). This indicates that SFA which consisted mostly of MCFA should not be totally eliminated in this study as they are equally important to induce the fatty acid metabolism rate in the body which is vital for reducing the body fat accumulation and body weight gain.¹

Table 1 Fatty acid composition of commercial fats (PHSBO-36 and FHPKOL-51), interesterified blends and non-interesterified blends^a

Fatty acid composition (%)	Contrast		SO	PKST	Blends
	PHSBO-36	FHPKOL-41			SO : PKST (80 : 20)		SO : PKST (60 : 40)		SO : PKST (50 : 50)		SO : PKST (40 : 60)		SO : PKST (20 : 80)
					NIE	IE	NIE	IE	NIE	IE	NIE	IE	NIE	IE
a PHSBO-36 and FHPKOL-41 are commercial cold soluble powder fats; SO, sheaolein; PKST, palm kernel stearin; NIE, non-interesterification; IE, interesterification; MLFA, medium chain fatty acid; SFA, saturated fatty acid; UFA, unsaturated fatty acid; TFA, trans fatty acid; ND, not detected.
C8 : 0	0.1 ± 0.0	4.0 ± 0.8	ND	2.1 ± 0.3	0.4 ± 0.1	0.4 ± 0.1	0.8 ± 0.1	0.8 ± 0.2	1.0 ± 0.1	1.1 ± 0.2	1.2 ± 0.1	1.3 ± 0.2	1.7 ± 0.1	1.8 ± 0.2
C10 : 0	0.1 ± 0.0	3.4 ± 0.2	ND	2.9 ± 0.1	0.6 ± 0.1	0.6 ± 0.1	1.2 ± 0.0	1.2 ± 0.1	1.4 ± 0.3	1.7 ± 0.3	1.7 ± 0.3	2.0 ± 0.1	2.3 ± 0.3	2.0 ± 0.8
C12 : 0	1.1 ± 0.2	41.9 ± 2.71	ND	59.1 ± 1.5	11.8 ± 1.1	11.9 ± 1.3	23.6 ± 1.1	23.7 ± 1.2	29.5 ± 1.3	28.9 ± 1.7	35.4 ± 1.8	33.8 ± 2.1	47.3 ± 2.7	47.4 ± 2.1
C14 : 0	0.5 ± 0.1	12.9 ± 0.7	0.1 ± 0.0	21.6 ± 0.3	4.4 ± 0.6	4.4 ± 0.7	8.7 ± 0.9	8.8 ± 0.3	10.8 ± 0.2	11.7 ± 1.3	13.0 ± 0.9	13.0 ± 0.2	17.3 ± 1.3	17.3 ± 0.5
C16 : 0	11.1 ± 0.8	9.3 ± 1.1	5.5 ± 0.7	7.6 ± 1.1	5.9 ± 0.2	5.9 ± 0.8	6.4 ± 0.3	6.3 ± 0.2	6.6 ± 1.1	6.3 ± 0.2	6.8 ± 1.1	7.0 ± 1.1	7.2 ± 1.1	7.4 ± 0.5
C18 : 0	14.4 ± 0.6	26.1 ± 2.3	30.32 ± 1.8	1.6 ± 0.2	24.6 ± 1.0	25.0 ± 0.9	18.8 ± 1.6	18.7 ± 2.3	15.9 ± 1.0	16.1 ± 0.6	13.1 ± 0.2	13.0 ± 1.4	7.3 ± 0.4	7.0 ± 0.1
C18 : 1-T	32.4 ± 1.7	ND	0.5 ± 0.2	ND	0.4 ± 0.0	0.4 ± 0.1	0.3 ± 0.0	0.3 ± 0.2	0.3 ± 0.0	0.3 ± 0.1	0.2 ± 0.1	0.2 ± 0.0	0.1 ± 0.0	0.2 ± 0.1
C18 : 1	33.3 ± 1.1	1.6 ± 0.2	53.5 ± 2.7	4.3 ± 0.5	43.6 ± 1.1	43.9 ± 2.2	33.8 ± 1.2	33.9 ± 1.8	28.9 ± 0.5	28.6 ± 1.2	24.0 ± 2.0	25.0 ± 1.1	14.1 ± 0.9	14.0 ± 1.9
C18 : 2-T	5.2 ± 0.9	ND	0.8 ± 0.1	ND	0.7 ± 0.1	0.7 ± 0.0	0.5 ± 0.2	0.5 ± 0.1	0.4 ± 0.1	0.5 ± 0.1	0.3 ± 0.1	0.4 ± 0.2	0.2 ± 0.0	0.2 ± 0.0
C18 : 2	0.4 ± 0.2	0.3 ± 0.1	7.0 ± 0.2	0.3 ± 0.0	5.7 ± 0.8	5.7 ± 1.1	4.3 ± 0.8	4.3 ± 0.3	3.7 ± 0.2	3.8 ± 0.3	3.0 ± 0.3	3.0 ± 0.4	1.7 ± 0.2	1.9 ± 0.3
C20 : 0	0.4 ± 0.1	0.3 ± 0.1	1.4 ± 0.1	0.1 ± 0.0	1.1 ± 0.1	1.2 ± 0.1	0.9 ± 0.1	0.9 ± 0.1	0.7 ± 0.1	0.7 ± 0.2	0.6 ± 0.1	0.6 ± 0.1	0.3 ± 0.0	0.3 ± 0.1
MLFA	1.8 ± 0.3	62.2 ± 1.3	0.1 ± 0.0	85.6 ± 1.6	17.2 ± 1.1	17.2 ± 0.3	34.3 ± 1.6	34.4 ± 0.6	42.8 ± 2.9	43.3 ± 2.1	51.4 ± 2.8	50.0 ± 1.7	68.5 ± 1.5	68.5 ± 2.7
SFA	27.8 ± 1.2	97.9 ± 1.7	37.4 ± 1.5	94.9 ± 2.2	48.9 ± 2.3	49.2 ± 2.9	60.4 ± 2.7	60.3 ± 2.4	66.1 ± 1.3	66.5 ± 1.7	71.9 ± 1.4	70.6 ± 2.6	83.4 ± 1.7	84.1 ± 3.9
UFA	33.9 ± 1.9	1.9 ± 0.2	61.1 ± 1.9	4.7 ± 0.3	49.8 ± 1.5	49.7 ± 2.3	38.5 ± 1.0	38.2 ± 1.6	32.9 ± 1.8	32.3 ± 1.9	27.2 ± 0.9	28.3 ± 0.8	16.0 ± 0.8	16.0 ± 2.1
TFA	37.6 ± 2.1	ND	1.4 ± 0.2	ND	1.1 ± 0.2	1.1 ± 0.1	0.8 ± 0.1	0.8 ± 0.1	0.7 ± 0.2	0.7 ± 0.1	0.6 ± 0.3	0.6 ± 0.1	0.3 ± 0.1	0.4 ± 0.1

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Triacylglycerol composition

Triacylglycerol compositions of the non-interesterified and interesterified blends are presented in Table 2. The main triacylglycerol of SO mainly contained LCFA, including SOO, SOS, OOO and SLO, and SO also contained appreciable amounts of POS and POO. PKST mainly consisted of TAG with MCFA, especially LaLaLa, LaLaM, LaLaO, CN42-, CN44- and CN34-TAG, where CN is carbon atom number. Therefore, triacylglycerol containing MCFA, such as CN36- and CN38-TAG, was increased when the amount of SO decreased, while opposite results were observed when the PKST was decreased. In addition, chemical interesterification distributes fatty acids equally through in the three positions of the glycerol backbone, which result in the triacylglycerol profile of the interesterified blends showing a more balanced or even peak distribution than the starting blends.^24,25 This randomization distribution made the relative concentration of several triacylglycerol decrease, especially trisaturated triacylglycerol including LaLaM and LaLaLa, while others increased (e.g., MOP, MLP and MLO). It is worth noting that the MLCT increased dramatically after interesterification, especially in the interesterified blend with 40 : 60 (SO : PKST), the content of MPP, MOP, MLP, MLO CN42- and CN44-TAG increased from 12.3% to 53.0% due to the reaction. Such MCFA level presented in MLCT would pose a considerable reduction in body weight caused by fat accumulation and blood fat rise, and at the same time, lower the cholesterol contents.^3,26,27 Most importantly, incorporation of SO in the PKST for interesterification is beneficial as it helps to make the powder fats more nutritious due to the presence of monounsaturated fatty acid (mainly oleic), thereby reduces the triacylglycerol whose SFA level is high.

Table 2 Triacylglycerol composition of commercial fats (PHSBO-36 and FHPKOL-51), interesterified and blends and non-interesterified blends ^a

Triacylglycerol composition (%)	SO	PKST	Blends
			SO : PKST (80 : 20)		SO : PKST (60 : 40)		SO : PKST (50 : 50)		SO : PKST (40 : 60)		SO : PKST (20 : 80)
			NIE	IE	NIE	IE	NIE	IE	NIE	IE	NIE	IE
a PHSBO-36 and FHPKOL-41 are commercial cold soluble powder fats; SO, sheaolein; PKST, palm kernel stearin; NIE, non-interesterification; IE, interesterification; CN, carbon number; ND, not detected.
CN32	2.0 ± 0.1	3.1 ± 0.2	2.4 ± 0.2	2.4 ± 0.1	2.5 ± 0.2	2.3 ± 0.1	2.6 ± 0.1	1.9 ± 0.1	2.8 ± 0.6	2.1 ± 0.2	3.0 ± 0.9	1.9 ± 0.1
CN34-	ND	6.2 ± 0.3	1.8 ± 0.5	2.3 ± 0.3	3.3 ± 0.6	3.9 ± 0.3	3.7 ± 0.4	4.6 ± 0.3	4.4 ± 0.3	4.6 ± 0.3	5.4 ± 0.5	4.8 ± 0.7
CN36-LaLaLa	0.2 ± 0.0	26.8 ± 1.1	7.5 ± 1.1	6.9 ± 1.3	13.8 ± 1.1	10.7 ± 0.8	16.3 ± 1.5	6.3 ± 0.7	19.1 ± 1.4	9.0 ± 0.6	23.4 ± 0.1	15.1 ± 0.4
CN38-LaLaM	1.2 ± 0.2	25.3 ± 1.0	8.1 ± 0.9	7.8 ± 0.8	13.5 ± 1.3	11.1 ± 0.8	15.9 ± 1.3	7.1 ± 0.5	18.3 ± 2.1	9.4 ± 1.3	22.2 ± 0.7	16.1 ± 0.8
CN40	10.3 ± 0.5	15.5 ± 1.3	12.4 ± 1.1	12.2 ± 1.0	13.5 ± 0.4	11.1 ± 0.6	13.8 ± 1.1	8.5 ± 0.5	14.4 ± 1.7	9.9 ± 1.0	15.1 ± 0.3	13.2 ± 1.9
CN42	0.3 ± 0.1	9.3 ± 0.6	2.9 ± 0.3	3.1 ± 0.4	4.9 ± 0.8	6.9 ± 0.3	5.8 ± 0.7	18.3 ± 1.5	6.8 ± 0.9	20.6 ± 2.1	8.2 ± 0.1	20.5 ± 1.7
CN44	ND	4.9 ± 0.2	1.8 ± 0.2	1.8 ± 0.5	2.7 ± 0.5	4.4 ± 0.7	3.1 ± 0.6	13.5 ± 0.8	3.6 ± 0.6	14.6 ± 1.1	4.4 ± 0.6	13.1 ± 1.1
CN46-MPP	ND	1.4 ± 0.8	0.7 ± 0.2	1.1 ± 0.1	1.0 ± 0.3	1.0 ± 0.1	0.7 ± 0.1	5.2 ± 0.3	0.5 ± 0.1	5.0 ± 0.7	0.9 ± 0.1	3.9 ± 0.6
MOM	1.5 ± 0.2	1.6 ± 0.2	1.1 ± 0.1	0.1 ± 0.0	0.8 ± 0.2	1.8 ± 0.4	1.1 ± 0.2	0.6 ± 0.1	1.3 ± 0.2	0.4 ± 0.1	1.5 ± 0.3	0.2 ± 0.0
CN48-PPP	3.1 ± 0.7	1.1 ± 0.6	2.4 ± 0.3	2.5 ± 0.3	1.7 ± 0.1	2.8 ± 0.1	1.4 ± 0.1	2.9 ± 0.4	1.2 ± 0.1	2.2 ± 0.1	0.7 ± 0.1	1.5 ± 0.1
MOP	0.1 ± 0.0	0.6 ± 0.2	0.7 ± 0.1	0.7 ± 0.1	0.5 ± 0.0	2.3 ± 0.9	0.4 ± 0.1	8.0 ± 1.3	0.6 ± 0.2	6.3 ± 1.4	0.2 ± 0.0	3.0 ± 0.2
MLP	ND	1.2 ± 0.1	0.3 ± 0.1	0.1 ± 0.0	0.5 ± 0.1	1.8 ± 0.2	0.5 ± 0.1	8.0 ± 0.9	0.6 ± 0.2	4.8 ± 0.1	0.7 ± 0.1	2.5 ± 0.2
CN50-POP	1.8 ± 0.2	0.6 ± 0.1	1.5 ± 0.6	1.5 ± 0.4	1.1 ± 0.4	1.6 ± 0.3	0.1 ± 0.1	ND	0.8 ± 0.5	ND	0.6 ± 0.1	ND
CN52-MLO	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.1	0.2 ± 0.1	0.2 ± 0.0	0.3 ± 0.1	0.2 ± 0.0	2.2 ± 0.3	0.2 ± 0.1	1.7 ± 0.1	0.1 ± 0.0	0.2 ± 0.1
POS	5.0 ± 1.2	ND	3.3 ± 0.7	3.3 ± 0.7	2.3 ± 0.4	2.2 ± 0.9	1.8 ± 0.3	1.4 ± 0.6	1.5 ± 0.3	0.9 ± 0.3	ND	0.3 ± 0.1
POO	4.8 ± 0.7	0.5 ± 0.0	3.4 ± 1.1	3.4 ± 0.2	2.4 ± 0.6	2.3 ± 0.7	2.0 ± 0.2	1.1 ± 0.1	1.6 ± 0.1	0.8 ± 0.2	0.9 ± 0.1	0.3 ± 0.1
PLS	1.8 ± 0.2	ND	1.2 ± 0.1	1.2 ± 0.3	0.9 ± 0.1	0.8 ± 0.0	0.7 ± 0.2	0.2 ± 0.0	0.6 ± 0.1	0.1 ± 0.1	0.3 ± 0.1	0.1 ± 0.1
PLO	1.9 ± 0.2	0.2 ± 0.1	0.8 ± 0.2	0.8 ± 0.1	0.6 ± 0.1	0.6 ± 0.1	0.5 ± 0.2	0.2 ± 0.1	0.4 ± 0.0	0.1 ± 0.0	0.3 ± 0.0	ND
CN54-SOS	8.7 ± 0.7	ND	6.1 ± 0.9	6.1 ± 0.9	4.2 ± 0.3	3.7 ± 0.8	3.3 ± 0.7	1.2 ± 0.1	2.6 ± 0.7	0.7 ± 0.3	1.2 ± 0.2	0.2 ± 0.1
SOO	34.6 ± 1.1	0.1 ± 0.0	25.0 ± 1.1	24.1 ± 1.1	17.1 ± 0.1	14.2 ± 0.6	13.7 ± 0.9	2.2 ± 0.3	10.6 ± 0.9	1.2 ± 0.3	4.9 ± 1.1	0.3 ± 0.2
OOO	8.5 ± 0.2	0.3 ± 0.1	6.0 ± 0.2	6.3 ± 0.1	4.2 ± 0.3	3.8 ± 0.2	3.3 ± 0.4	1.3 ± 0.3	2.8 ± 0.7	0.7 ± 0.2	1.3 ± 0.2	0.1 ± 0.0
SLO	6.2 ± 0.3	ND	4.6 ± 1.1	4.6 ± 1.2	3.1 ± 0.1	2.7 ± 0.5	3.4 ± 0.7	0.6 ± 0.0	2.0 ± 0.1	0.3 ± 0.0	0.9 ± 0.2	0.2 ± 0.1
OLO	1.9 ± 0.5	0.2 ± 0.1	1.3 ± 0.2	2.1 ± 0.3	1.4 ± 0.2	0.9 ± 0.3	2.5 ± 1.1	0.4 ± 0.1	1.0 ± 0.1	ND	0.3 ± 0.1	ND
CN56-SOA	0.6 ± 0.1	ND	0.5 ± 0.1	0.4 ± 0.1	0.3 ± 0.1	0.2 ± 0.1	0.2 ± 0.1	0.1 ± 0.0	0.2 ± 0.1	0.1 ± 0.0	0.1 ± 0.0	ND
AOO	1.6 ± 0.2	ND	1.2 ± 0.2	1.1 ± 0.1	0.8 ± 0.2	0.7 ± 0.1	0.6 ± 0.1	0.1 ± 0.1	0.5 ± 0.2	0.1 ± 0.0	0.3 ± 0.0	ND

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Slip melting point

SMP is a parameter of significant importance for characterization and development of fats. As shown in the Fig. 1, SO showed medium SMP (28.4 °C) and PKST showed higher SMP (32.4 °C). Most blended fats had less SMP than that of SO or PKST only as the triacylglycerols of the blends suffered gradual melting according to their individual melting points.²⁸ The addition of PKST to SO slightly promoted the SMP increase of the blends, ranging from 22.1 to 30.9 °C. Interesterification caused a narrower SMP values for all blends evaluated, the value varied from 24.5 to 29.2 °C. In detail, the variation resulted from a decrease in the content of trisaturated triacylglycerol, such as LaLaM and LaLaLa, and a increase in the percentage of MLCT, especially within the oleic acid attached in the glycerol backbone. The results obtained were in accordance with those described by Ghotra.²⁹

Fig. 1 Slip melting point of commercial fats (PHSBO-36 and FHPKOL-51), interesterified blends and non-interesterified blends, the values represent mean of three replicates. PHSBO-36 and FHPKOL-41 are commercial cold soluble powder fats; SO, sheaolein; PKST, palm kernel stearin.

With higher SMP, such as 36.6 and 39.6 °C for PHSBO-36 and FHPKO-41, the dispersion and solubility of powder products were reduced, which lead to a poor taste.¹² On the other hand, lower SMP possesses poor heat resistance especially in South China, which is easily agglomerated and simultaneously accelerated the oxidation process due to the surface oil leakage. Therefore, in order to obtain expected application performance in cold soluble powder fats, proper SMP is required. Commonly, fats with SMP below that of body temperature (37 °C) can be directly used as shortenings, given that they completely melt in the mouth and produce no waxy sensation during consumption.²⁸ Meanwhile, the SMP of cold soluble powder fats should be higher than the room temperature (usually 25 °C), and is ideally not more than 30 °C, which thereby could be drunk directly just by adding the warm water. Hence, the 40 : 60 (SO : PKST) interesterified blend fits in this group.

Solid fat content

SFC affects physical properties such as spreadability, consistency and stability, besides influencing important sensorial properties.²⁸ Fig. 2 shows the SFC of the interesterified, non-interesterified and commercial powder fats. The SFC of the blends was proportional to the addition of PKST to SO, at all the temperatures analyzed. Usually, high SFC was required at a low temperature to get higher oxidation stability, but it should have a lower melting point than the human body (37 °C). Lower SFC was needed to obtain desirable oral taste. Compared with the commercial powder fats, interesterified blends with 40 : 60 possessed a more mild SFC profile and totally melted at 30 °C, which is lower than both commercial powder fats (>40 °C). Furthermore, FHPKOL-41 possessed a steep SFC profile, which is indicative of a narrow plastic range, and products of this type are high-stability shortenings and are more suitable for filler fat shortenings.^29,30 Therefore, interesterified blends with 40 : 60 of SO : PKST could be alternative to be ideally used as cold soluble powder fats.

Fig. 2 Solid fat content of commercial fats (PHSBO-36 and FHPKOL-51), interesterified blends (A) and non-interesterified blends (B), the values represent mean of three replicates. PHSBO-36 and FHPKOL-41 are commercial cold soluble powder fats; SO, sheaolein; PKST, palm kernel stearin; IE, interesterification.

Melting and crystallization thermograms

The melting and crystallization thermograms of interesterified and non-interesterified fats are shown in Fig. 3 and 4, respectively. All the non-interesterified blends showed higher melting peaks than interesterified mixtures where interesterified fats were found to broad peaks than non-interesterified ones. In particular, the melting points of the blends were decreased as a result of interesterification which has greatly altered the triacylglycerol composition of the mixtures. The more complicated melting profiles of the interesterified fats resulted from the more diversity triacylglycerol compositions with the modified technique. Adhikari et al. also reported that the broad melting peaks of interesterified fats represent the rearrangements of fatty acids within triacylglycerol molecules or the creation of new triacylglycerol species with close melting points.¹⁸ In this study, chemical interesterification reduced the content of both long chain and medium chain triacylglycerol, and increased the level of MLCT (Table 2), therefore the melting range of interesterified blend (SO : PKST = 40 : 60) was significantly narrower than blend before interesterification. These characteristics provide products with well heat resistance during storage and good solubility when brewing. The crystallization peaks of the all the observed blends exhibited the similar trend with the melting behavior.

Fig. 3 Melting thermograms of interesterified blends (A) and non-interesterified blends (B), the values represent mean of three replicates. PHSBO-36 and FHPKOL-41 are commercial cold soluble powder fats; SO, sheaolein; PKST, palm kernel stearin; IE, interesterification.

Fig. 4 Crystallization thermograms of interesterified blends (A) and non-interesterified blends (B), the values represent mean of three replicates. PHSBO-36 and FHPKOL-41 are commercial cold soluble powder fats; SO, sheaolein; PKST, palm kernel stearin; IE, interesterification.

Sensory characteristics

The apparent characters and tastes of the interesterified blends and the two typical commercial powdered fats are shown in Table 3. The products were displayed normal appearance except the blends with 60 : 40 and 80 : 20 of SO : PKST. Both of the two fats were found to melt at room temperature (20–26 °C) due to their relatively low melting points, i.e., 25.5 and 24.5 °C, respectively. In addition, the interesterified blend (SO : PKST = 20 : 80), PHSBO-36 and FHPKOL-41 left the waxiness in the mouth, for their higher SFC values (>0%) at the body temperature. Only the interesterified blends (SO : PKST = 50 : 50 and 40 : 60) were considered to be high quality products with normal appearance and silky taste.

Table 3 Sensory characteristics of commercial fats (PHSBO-36 and FHPKOL-51) and interesterified and blends

Products^a	Apparent characters	Tastes
a PHSBO-36 and FHPKOL-41 are commercial cold soluble powder fats; SO, sheaolein; PKST, palm kernel stearin; IE, interesterification.b —, not evaluate.
PHSBO-36	Normal	Waxiness
FHPKOL-41	Normal	Waxiness
IE (SO : PKST) = 20 : 80	Normal	Waxiness
IE (SO : PKST) = 40 : 60	Normal	Silky
IE (SO : PKST) = 50 : 50	Normal	Silky
IE (SO : PKST) = 60 : 40	Oil leakage	—^b
IE (SO : PKST) = 80 : 20	Oil leakage	—

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Conclusions

Commercial powder fats with either highly trans or highly saturated triacylglycerol content are the health risks to the customers. Alternative to traditional powder fats, i.e., fully or partially hydrogenated fats, chemical interesterification with SO and PKST could be an ideal choice to reduce the trans fat and trisaturated triacylglycerol content, and most importantly to increase MLCT level in the powder fats. MLCT is considered as a potential anti-obesity functional oil. In this study, sheaolein-based cold soluble powder fats obtained by the interesterification of SO and PKST (40 : 60) could be the ideal alternative fats, whose MLCT level increased from 12.3% to 53.0%, and trisaturated triacylglycerol and TFA content significantly decreased. Furthermore, the SFC, melting profile, thermal property and sensory characteristic of the selected blend are improved as powder fats. Therefore, this developed product could meet the healthy concept in cold beverage industry.

Acknowledgements

The research was financially supported by Projects in the National Science & Technology Pillar Program during the Twelfth Five-year Plan Period (No. 2011BAD02B03). The research was conducted in Wilmar (Shanghai) Biotechnology R&D Center, China. The first author gratefully acknowledges Jiangnan University and Wilmar Biotechnology Research and Development Center (Shanghai) Co., Ltd for their financial and professional support.

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