Thermal properties, triglycerides and crystal morphology of bambangan (Mangifera pajang) kernel fat and palm stearin blends as cocoa butter alternatives

LWT - Food Science and Technology 107 (2019) 64–71

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Thermal properties, triglycerides and crystal morphology of bambangan (Mangifera pajang) kernel fat and palm stearin blends as cocoa butter alternatives

T

M.H.A. Jahurula,∗, L.L. Pinga, M.S. Sharifudina, M. Hasmadia, A.H. Mansoora, J.S. Leea, B.W. Noorakmara, H.M.S. Amira, S. Jinapb,c, A.K. Mohd Omard, I.S.M. Zaidule a

Faculty of Food Science and Nutrition, Universiti Malaysia Sabah, 884000, Kota Kinabalu, Sabah, Malaysia Department of Food Science, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia Food Safety and Food Integrity (FOSFI), Institute of Tropical Agriculture and Food Security, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia d School of Industrial Technology, Universiti Sains Malaysia, 11800, Minden, Penang, Malaysia e Faculty of Pharmacy, International Islamic University Malaysia, Kuantan Campus, 25200, Pahang, Malaysia b c

A R T I C LE I N FO

A B S T R A C T

Keywords: Differential scanning calorimetry Melting Crystallization Enthalpy HPLC Crystallinity

The aim of this study was to investigate the thermal properties of bambangan kernel fat (BKF) and palm stearin (PS) blends and their possibility as cocoa butter alternatives. The triglycerides, thermal behaviors, and crystal morphology of the BKF and PS blends were determined using high performance liquid chromatography (HPLC), differential scanning calorimetry (DSC), and polarized light microscope (PLM). All the blends had three main triglycerides; namely, 1,3-dipalmitoyl-2-oleoyl-glycerol, 1-palmitoyl-2-oleoyl-3-stearoyl-glycerol, and 1,3-distearoyl-2-oleoyl-glycerol. The melting onset temperatures decreased for both non-stabilized (−8.81 to −16.80 °C) and stabilized fat blends (−14.04 to −22.16 °C), whereas the melting offset temperatures shifted toward high temperatures for both non-stabilized (35.94–50.21 °C) and stabilized fat blends (48.35–53.16 °C) with PS. The crystallization onset temperatures increased for both non-stabilized (14.66–23.78 °C) and stabilized fat blends (15.46–26.89 °C), whereas the offset temperatures decreased with the addition of PS for non-stabilized (−15.68 to −22.02 °C) and stabilized fat blends (−15.73 to −22.38 °C). The stabilized fat blends showed higher melting and crystallization peak temperatures than non-stabilized fat blends. In the study of crystal morphology, the fat blends showed small spherulites with the diameter of 10–100 μm.

1. Introduction Mangifera pajang is a species of plant in the mango group that grow only in the Borneo Island including Sabah, Sarawak, Brunei and Kalimantan. The uniqueness of the tree includes the fact that fruit is large in size, has a thicker peel and large seed compared to commercial mango (Mangifera indica) (Al-Sheraji et al., 2012). The bambangan fruit is nutritive and contains various phytochemicals such as phenolics, flavonoids, and carotenoids. The flesh is eaten fresh. However, the peel and seed which represents 40–50% of the total weight of the fruit are discarded (Bakar & Fry, 2013). The kernel of bambangan is about 27% of the total weight of the fruit that contains 9.9% of fat (Jahurul et al., 2018). Palm stearin (PS) comprises high melting solid fractions obtained by fractioning palm oil at controlled temperature and has a wide range of

∗

triglycerides with different melting profiles (Oliveira, Rodrigues, Bezerra, & Silva, 2017). Besides, PS has properties such as brittle texture and narrow melting range similar to cocoa butter (CB). Due to its versatile composition of fatty acids and triglycerides, PS can be used as a raw material for interesterification (Oliveira et al., 2017). Besides, it is a cost-saving ingredient in various applications because of its low price compared to other palm oil products (Jahurul et al., 2014a). Currently, global production of cocoa is declined because of crop failure, disease, and aging plantation. Besides, world demand for cocoa is increasing annually by 2–3% due to low productivity, price fluctuation, and shortage in supply of cocoa (Akhter, McDonald, & Marriott, 2016). Therefore, it is a necessity for the industries and researchers to search for high quality CB alternatives from other natural resources. Bambangan kernel fat (BKF) has the potential to provide a low-cost and high quality source of CB alternatives. It is rich sources of palmitic, stearic,

Corresponding author. E-mail addresses: [email protected], [email protected] (M.H.A. Jahurul).

https://doi.org/10.1016/j.lwt.2019.02.053 Received 25 July 2018; Received in revised form 2 January 2019; Accepted 17 February 2019 Available online 01 March 2019 0023-6438/ © 2019 Elsevier Ltd. All rights reserved.

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and oleic acids. These fatty acid profiles and other physicochemical and thermal properties of BKF make it ideal for use in formulations (blending components) as a CB alternatives (Jahurul et al., 2018). Blending is a method that helps to modify the thermal (melting and crystallization) and physicochemical properties as well as morphology of fats and oils in order to yield products with desired properties for food applications (Bahari & Akoh, 2018; Chiavaro, 2015; Jahurul et al., 2014b; Ramli, Said, Mizan, Tan, & Ayob, 2014). Besides, it is one of the cheapest processes for varying the fats and oils composition to improve nutritional quality by mixing two or more edible fats and oils (Chiavaro, 2015). Therefore, the products formed are new ingredients suitable for use in applications in which the original fats and oils could never use or would have performed poorly (Chiavaro, 2015). According to Jahurul et al. (2014b) and Biswas, Cheow, Tan, and Siow (2017a), chocolate products can be improved in solid fat content, inhibit fat bloom, and slightly reduce the tempering time by blending of fat or the addition of a small amount of SOS or SOS-rich fat in CB. The binary fat blend can be enhanced the oxidative and physical stability of soybean oil-based emulsions (Hayati, Man, Tan, & Aini, 2007). Besides, Ramli et al. (2014) reported that the ternary fat blend (palm oil mid-fraction, palm stearin, and olive oil) is found to exhibits better oxidative stability and may be suitable as a CB substitutes. The objective of this study was to determine the thermal properties of non-stabilized and stabilized BKF and PS blends. Moreover, the triglycerides and crystal morphology of these blends were also determined.

Table 1 Relative peak area (%) of triglycerides of bambangan kernel fat and palm stearin blends.

2. Material and methods

The melting and crystallization characteristics of the BKF and PS blends were determined by DSC (Pyris 4000 DSC; Perkin-Elmer, USA). The indium was used for the DSC calibration. To erase fat crystallographic memory, all the blends were melted at 90 °C. Molten samples (3–5 mg) were transferred to standard DSC aluminium pans and hermetically sealed. The pans were then placed in vials and melted at 90 °C for 30 min. For stabilization, the pans were kept in an incubator at 26 °C for 7 days. After 7 days of incubation at 26 °C, the pans were transferred to the DSC head. An empty hermetically sealed DSC aluminium pan was used as a reference. For the DSC experiments the following program was used: cooling to −40 °C and heating at 10 °C/min to 90 °C for 20 min to ensure a completely liquid state, cooling at 10 °C/min to −40 °C, holding at −40 °C for 2 min, heating at 10 °C/min to 90 °C (Jahurul et al., 2014b).

Blend no.

POP

POS

SOS

1 2 3 4 5 6 7 8 9 10 BKF PS CBa

7.37 ± 0.05ab 8.91 ± 0.29bc 10.03 ± 0.07cd 11.19 ± 0.01d 12.19 ± 0.43e 14.00 ± 0.16e 15.69 ± 0.03f 16.98 ± 0.41fg 17.05 ± 0.71g 18.55 ± 0.53h 5.40 ± 0.57a 71.82 ± 1.25i 13.8–16.4

11.48 ± 1.56a 12.90 ± 1.29ab 13.36 ± 0.06ab 13.87 ± 0.01ab 14.76 ± 0.66ab 15.43 ± 0.17ab 16.34 ± 0.24ab 17.01 ± 0.07abc 17.67 ± 0.16bc 18.66 ± 0.23bc 11.35 ± 1.00a 14.80 ± 1.09c 34.6–38.3

28.53 ± 1.56abc 27.71 ± 2.92bcd 26.45 ± 0.87cde 26.07 ± 0.01de 25.60 ± 1.03def 24.96 ± 1.31ef 24.90 ± 0.16ef 23.49 ± 0.37ef 22.97 ± 0.44ef 22.42 ± 0.13f 28.67 ± 0.43a 2.16 ± 1.29g 23.7–28.4

1

Mean value ± standard deviation (N = 2). Means for each sample sharing different lowercase letters in each column are significantly (P < 0.05) different. a Jahurul et al. (2018). 2

2014b). 2.5. Determination of melting and crystallization characteristics by differential scanning calorimetry (DSC)

2.1. Source of samples Matured bambangan fruit was collected from the farmers with the assistance of the local Agricultural Extension Officer. The bambangan kernel powder was prepared according to the method described in our previous study (Jahurul et al., 2018). 2.2. Extraction of bambangan kernel fat (BKF) The extraction of fat from bambangan kernel powder was carried out using Soxhlet method. The extraction involved the use of n-hexane and 8 h of heating time for achieving a fat percentage of 9.86 ± 0.85%. The extracted BKF was orange-yellow in color. The extracted fats were filled into glass tubes with nitrogen, and stored at −20 °C until further analyses.

2.6. Crystal morphological study by polarized light microscope (PLM) The crystal network microstructure of BKF and PS blends were observed using PLM (Olympus BX51, Olympus Optical Co., Ltd., Tokyo, Japan). The methodology established by Narine and Marangoni (1999) was used for crystallization of the samples with slight modification. The detailed procedure is described in our previous study (Jahurul et al., 2014b).

2.3. Preparation of fat blends BKF was blended with PS into various proportions which referred as blend 1 to blend 10. Total 10 blends with 5% increments of PS were taken into account: BKF/PS, 95:5 (Blend 1), 90:10 (Blend 2), 85:15 (Blend 3), 80:20 (Blend 4), 75:25 (Blend 5), 70:30 (Blend 6), 65:35 (Blend 7), 60:40 (Blend 8), 55:45 (Blend 9), 50:50 (Blend 10).

2.7. Statistical analysis 2.4. Determination of triglycerides by high performance liquid chromatography (HPLC)

Data were analyzed by one-way analysis of variance (one-way ANOVA) to test the variations in different blends. A P < 0.05 was considered statistically significant. Tukey's test was applied to detect the significant differences between the means. In addition, the pairedsamples t-test was used to compare the mean difference between paired observations. The SPSS software (version 20.0) was used to accomplish the analysis.

The triglycerides of BKF and PS blends were analyzed by HPLC (Series 1200; Agilent, USA) according to AOCS Official Method Ce 5b–89 (AOCS, 2003) with slight modification. The Agilent HPLC instrument with Quaternary Pump (Agilent HPLC Series 1200, Degasser Model G1322A, Quaternary Pump Model G1311A, RI Detector Model G1362A), and a Lichrospher 100 RP-18e HPLC column (4 mm i.d. × 250 mm length) was used to determine triglycerides of all blends. The column temperature of 30–35 °C, pressure of 5–6 MPa, acetone/ acetonitrile (70:30 v/v) as mobile phase, flow rate of 1 ml/min, and an injection volume of 10 μl were used. The triglycerides was determined by calculating the peak area of the chromatogram (Jahurul et al.,

3. Results and discussion 3.1. Triglycerides composition The triglycerides of BKF, PS and their blends in different ratios are 65

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Fig. 1. a DSC melting curves of non-stabilized BKF and PS blends. b: DSC melting curves of stabilized BKF and PS blends.

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Table 2 Melting profiles of non-stabilized and stabilized BKF and PS blends. Non-stabilized/stabilized Non-stabilized

Stabilized

Sample

Transition Temperature (oC) o

Enthalpy (J/g) o

Blend no.

Ton ( C)

1 2 3 4 5 6 7 8 9 10 BKF PS CBa

−8.81 ± 0.50 −9.91 ± 1.45abA −11.32 ± 0.20abcA −12.26 ± 0.35bcdA −13.21 ± 0.60cdeA −13.69 ± 0.14cdeA −14.32 ± 0.54defA −14.43 ± 0.67defA −15.51 ± 1.32efA −16.80 ± 0.30fA −12.38 ± 0.11bcdA −20.92 ± 0.05gA −3.50

35.94 37.91 41.17 43.13 43.45 45.55 46.79 48.73 49.82 50.21 40.18 61.87 40.18

−14.04 ± 1.60abB −14.45 ± 1.85abB −15.41 ± 2.13abB −15.49 ± 2.17abB −16.37 ± 1.97abcB −17.51 ± 0.40abcdeB −18.53 ± 0.83bcdeB −19.17 ± 1.09bcdeB −21.27 ± 0.54cdeB −22.16 ± 0.46deB −17.1 ± 0.65abcdB −22.50 ± 0.42eB −11.02

48.35 49.12 50.26 50.55 50.82 50.98 51.17 51.28 51.99 53.16 43.31 57.36 52.47

o

Toff ( C) aA

Tmax ( C)

± ± ± ± ± ± ± ± ± ± ± ±

ghA

1.14 0.21fgA 1.04efA 0.13deA 0.23deA 1.20cdA 0.27bcdA 2.31bcA 0.02bA 0.16bA 0.49 iA 0.56aA

14.01 16.11 17.27 18.13 19.06 20.17 21.29 24.25 24.27 24.60 35.66 46.05 –

± ± ± ± ± ± ± ± ± ± ± ±

0.78dA 0.35dA 0.08dA 1.38dA 0.77dA 0.27dA 0.58dA 1.76bA 0.38bA 0.13bA 0.71dA 0.78aA

39.40 42.32 44.46 46.70 46.97 48.69 49.49 50.48 51.14 54.24 54.28 61.64 80.02

± ± ± ± ± ± ± ± ± ± ± ±

1.67fA 2.64defA 3.31efA 4.92cdefA 1.38cdefA 1.52cdeA 0.61cdeA 1.93defA 0.91cdA 1.18bcA 3.02defA 0.11bA

± ± ± ± ± ± ± ± ± ± ± ±

0.91cdB 0.07bcB 1.05bcB 0.99bcB 0.72bcB 0.49bcB 1.65bcB 2.42bcB 2.60bcB 1.16abB 0.64dB 0.28aB

37.73 38.21 38.35 38.39 38.55 38.86 39.16 39.46 39.88 40.11 35.68 52.58

± ± ± ± ± ± ± ± ± ± ± ±

1.80bB 0.91bB 0.07bB 0.01bB 0.24bB 0.73bB 0.20bB 1.20cB 0.01bB 1.90bB 0.72bB 0.36aB

66.93 67.44 68.56 68.87 69.44 69.85 70.19 70.51 71.10 72.11 79.85 75.22 128.2

± ± ± ± ± ± ± ± ± ± ± ±

1.40cdB 2.09cdB 2.81cdB 1.92cdB 3.77cdB 0.34cdB 2.56cdB 3.04dB 1.75cdB 2.40dB 0.47bB 0.04bB

Blend no 1 2 3 4 5 6 7 8 9 10 BKF PS CBa

1

Mean value ± standard deviation (N = 2). Means for each sample sharing different lowercase letters in each column are significantly (P < 0.05) different. 3 Means for each sample sharing different uppercase letters in each column are significantly (P < 0.05) different. a Solís-Fuentes and Durán-de-Bazúa (2004). 2

high temperature resistant hard butter in hot climates countries (Jahurul et al., 2014b).

shown in Table 1. The triglycerides in BKF and PS blends were significantly affected by the blending ratios and they were significantly different (p < 0.05) within the blends. The contents of POP and POS increased proportionally whereas the contents of SOS decreased gradually with the addition of PS in the blends. For instance, the percentage of POP and POS increased from 7.37 ± 0.05 to 18.55 ± 0.53% and from 11.48 ± 1.56 to 18.66 ± 0.23%. At the same time, SOS decreased from 28.53 ± 1.56 to 22.42 ± 0.13%. This decreasing and increasing phenomena of triglycerides in the blends can be explained by the presence of decreasing amount of short-chain saturated fatty acids and increasing amounts of long-chain saturated and unsaturated fatty acids (Biswas, Cheow, Tan, Kanagaratnam, & Siow, 2017b). Moreover, the modification of triglycerides in mahua and kokum fat blends, milk fat and corn oil blends, and mango seed fat and palm stearin blends were observed by Jeyarani and Reddy (1999, 2010), Rodrigues and Gioielli (2003), and Jahurul et al. (2014b). The changes of physicochemical properties in fats and oils blends were also observed by Serjouie, Tan, Mirhosseini, and Che Man (2010), and Roiaini, Ardiannie, and Norhayati (2015). The POP, POS, and SOS of BKF and PS blends in the present study were comparable to the triglycerides of mango seed fat and PS blends which includes POP (8.6–17.7%), POS (12.5–19.6%) and SOS (37.2–31.4%) as reported by Jahurul et al. (2014b). Similar results were also reported by Zarringhalami, Sahari, Barzegar, and Hamidi-Esfehani (2010) that in enzymatic interesterification of hydrogenated and solid fraction of tea seed oil for preparing cocoa butter replacer, the amounts of POP, POS, and SOS were 10.73, 17.43, and 11.15%, respectively. PS had the potential to be used as a POP source as it contained the high level of POP, resulting in its incomplete melting at room temperature. Therefore, through the blending of BKF and PS, the triglycerides might be modified to become fat that could be used as suitable raw materials for the production of

3.2. Melting and crystallization characteristics 3.2.1. Melting profiles of BKF and PS blends The melting curves for non-stabilized and stabilized BKF, PS and their blends are shown in Fig. 1a, b and 1c. The measured parameters during melting of all blends were onset and offset temperatures, maximum peak height (temperature), and enthalpy (heat flow status) (Table 2). Non-stabilized BKF and PS blends showed two to four endothermic peaks whereas some stabilized fat blends exhibited two broad endothermic peaks (Fig. 1b and c). Basically, the presence of different endotherms indicated the existence of the fats in different polymorphic states (Sagiri, Sharma, Basak, & Pal, 2014). Triglycerides in a solid state showed a polymorphism phenomenon, which means that they can exist in a few crystalline forms. It is occurred in six distinct crystalline forms which includes I (γ), II (α), III (β′2), IV (β′1), V (β2), and VI (β1). Form I is the least stable polymorph, whereas Form VI the most stable polymorph (Talhat, Lister, Moggridge, Rasburn, & Wilson, 2015). The presence of the peak at ∼20 °C indicated the existence of the α-polymorphic state of triglycerides (Sagiri et al., 2014). Next to the α-polymorphic peaks, a peak corresponding to the β′ polymorphism observed, then followed by β-polymorphic peak (Sagiri et al., 2014). In the case of stabilized fat blends, they mainly crystallized in form V (β2) which was more stable and contributed a high melting peak temperature (Sullo, Arellano, & Norton, 2014). Moreover, the less stable forms such as α-form might be transformed into more stable forms after storage with sufficient time (Sullo et al., 2014). Therefore, stabilized fat blends were more preferred as CB alternative because of its sharp and narrow peaks which might not bring to waxy mouth-feel, more cooling 67

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Fig. 2. a DSC crystallization curves of non-stabilized BKF and PS blends. b: DSC crystallization curves of stabilized BKF and PS blends.

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Table 3 Crystallization profiles of non-stabilized and stabilized BKF and PS blends. Non-stabilized/Stabilized Samples Non-stabilized

Blend no. 1 2 3 4 5 6 7 8 9 10 BKF PS CBa

Stabilized

Transition Temperature (oC) o

Enthalpy (J/g) o

Ton ( C)

o

Toff ( C)

Tmax ( C)

14.66 16.42 17.69 18.84 19.89 20.40 21.17 22.47 23.31 23.78 14.32 30.96 12.17

± ± ± ± ± ± ± ± ± ± ± ±

0.12 0.21jA 0.09iA 0.10hA 0.44gA 0.11fgA 0.07efA 0.16cdA 0.09bcA 0.11bA 0.35kA 0.13aA

−15.68 −16.86 −17.51 −18.56 −18.73 −19.44 −19.89 −20.14 −21.03 −22.02 −13.24 −26.52 −26.17

± ± ± ± ± ± ± ± ± ± ± ±

0.11 0.03bcA 0.33cdA 0.08defA 0.09defA 0.21efgA 0.03fghA 0.09ghA 0.71hiA 0.01iA 0.06aA 0.06iA

10.09 10.12 10.13 12.17 17.08 18.01 19.07 20.32 20.91 21.72 10.33 25.33 –

± ± ± ± ± ± ± ± ± ± ± ±

0.76gA 0.53gA 0.49fgA 0.42efA 0.45dA 0.21dA 0.01cdA 0.16bcA 0.25bcA 0.24bA 0.53fgA 1.21aA

48.67 48.71 54.65 54.83 55.74 56.01 57.10 57.16 61.07 63.02 45.32 74.03 56.98

± ± ± ± ± ± ± ± ± ± ± ±

0.73dA 0.58dA 0.62cA 0.58cA 2.29cA 0.92cA 1.06cA 0.67cA 0.55bA 0.79bA 0.79dA 0.27aA

15.46 17.30 18.93 20.30 20.89 22.20 23.48 25.23 25.48 26.89 14.95 30.53

± ± ± ± ± ± ± ± ± ± ± ±

0.91fB 0.30efB 0.44defB 0.37cdefB 0.93bcdefB 0.91bcdeB 2.50bcdB 2.52abcB 2.26abcB 2.84abB 0.07fB 0.80aB

−15.73 −16.51 −17.07 −17.56 −18.47 −18.79 −20.06 −20.07 −21.04 −22.38 −13.33 −24.57

± ± ± ± ± ± ± ± ± ± ± ±

0.13abA 0.30bcA 0.75bcA 1.27bcdA 0.80bcdeA 0.81cdeA 0.34defA 0.72defA 1.42efA 0.10fgA 0.42aA 0.69gA

10.59 10.61 10.64 15.23 16.07 18.30 19.61 20.42 21.16 22.16 12.91 26.10

± ± ± ± ± ± ± ± ± ± ± ±

0.30jB 0.08ijB 0.31ijB 0.12fgB 1.30efB 0.03deB 0.98cdB 0.22bcdB 0.34bcB 0.80bB 0.52hiB 0.45aB

49.08 51.55 52.93 55.41 56.92 58.45 60.05 65.52 66.58 67.24 47.07 84.49

± ± ± ± ± ± ± ± ± ± ± ±

1.36hB 0.17ghB 1.07fghB 2.81efgB 0.30efgB 1.35efB 1.38deB 1.70cdB 2.59cB 2.11cB 0.69hB 0.89aB

kA

bA

Blend no 1 2 3 4 5 6 7 8 9 10 BKF PS

1 Mean value ± standard deviation (N = 2). 2 Means for each sample sharing different lowercase letters in each column are significantly (P < 0.05) different. 3 Means for each sample sharing different uppercase letters in each column are significantly (P < 0.05) different. a Solís-Fuentes and Durán-de-Bazúa (2004).

sensation, and more intense flavor release (Kadivar, Clercq, Mokbul, & Dewettinck, 2016). According to Sonwai, Kaphueakngam, and Flood (2014), mango seed fat and palm mid-fraction blends exhibited two maxima at 22.8 and 36.5 °C. Recently, Jin, Akoh, Jin, and Wang (2018) reported only one maxima at 39.2 °C for mango fat and palm oil mid fraction blends. Jahurul et al. (2014b) also reported that the melting profiles of mango seed fat and PS blends resemble to CB with two endotherms at 17.6 and 36.9 °C. The melting peak temperatures (14.01 ± 0.78 to 24.60 ± 0.13 °C) showed in the current study fall in the range of melting peak temperatures obtained from our previous study (Jahurul et al., 2014b). This could be explained by the similar family of fat sources extracted. The onset temperatures decreased gradually with the addition of PS in non-stabilized BKF and PS blends, however, opposite trends were observed for offset temperatures, where it is increased gradually (Table 2). For example, the melting peak began at −8.81 ± 0.50 °C and ended at 35.94 ± 1.14 °C for blend 1, whereas the melting peak started at −13.21 ± 0.60 °C and ended at 43.45 ± 0.23 °C for blend 5. In addition, maximum melting temperatures of non-stabilized BKF and PS blends increased gradually. The melting enthalpy of non-stabilized fat blends also followed the trend of increasing from blend 1 (39.40 ± 1.67 J/g) to blend 10 (54.24 ± 1.18 J/g). These mostly caused by the variation in fatty acid and triglyceride profiles in different fat blends of BKF and PS (Biswas et al., 2017b). Besides, these could be due to the formation of different polymorphic forms (α, β′, and β) in the fat blends (Fredrick, Foubert, Sype, & Dewettinck, 2008). The β′-form crystals crystallized if the temperature maintained slightly above the melting temperature of the α-form, whereas β-form can be crystallized slightly above the melting temperature of β′-form (Himawan, Starov, & Stapley, 2006). However, there were significantly different (p < 0.05) in transition temperatures and enthalpy

demonstrated among all the ten non-stabilized fat blends, which could be because of different blending ratios of BKF and PS. Stabilized fat blends that obtained through incubating were important in order to obtain the fine crystals in the correct form (βmodification). This aim was to make sure that the desired properties related to the melting in the mouth, glossiness, and snap achieved (Afoakwa, Paterson, Fowler, & Vieira, 2008). In the present study, the melting profiles of stabilized fat blends were significantly different (P < 0.05) than non-stabilized fat blends after one week of storage. The peak temperature of stabilized fat blends was shifted toward higher temperature. This can be explained by the high amounts of SOO present in the stabilized fat blends (Kadivar et al., 2016). In addition, the values of the peak temperature probably corresponded to a β-polymorph. The stabilized fat blends contained more β′-polymorph and β-polymorph after incubating at room temperature (Vereecken, Foubert, Smith, & Dewettinck, 2007). The β-polymorph was the most stable crystalline form and produced by incubating at slightly higher fusion temperature than that of α-form (Solís-Fuentes & Durán-de-Bazúa, 2004). In the current study, onset and offset temperatures of non-stabilized and stabilized blends (blends 1 to blend 4) were found more comparable to that of CB and indicated that these blends were more suitable as a CB alternatives.

3.2.2. Crystallization profiles of BKF and PS blends The crystallization curves for non-stabilized and stabilized BKF, PS and their blends are shown in Fig. 2a, b and 1c. The measured parameters during crystallization of BKF and PS blends were onset and offset temperatures, maximum temperatures, and enthalpy as shown in Table 3 (heat flow status). The crystallization profiles of non-stabilized and stabilized BKF and PS blends i.e. blends 1 and 2 were found to be different from those of blends 3 to 10 (Fig. 2b). DSC crystallization 69

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The non-stabilized blends corresponded to the formation of crystalline α form (low melting point), whereas the stabilized blends allowed the crystal formation of two other unstable polymorphs (β′ and other subforms) (Solís-Fuentes, Hernández-Medela, & Durán-de-Bazúab, 2005). Table 3 showed that with the addition of PS, the onset exothermic temperatures of non-stabilized fat blends increased gradually, however, offset temperatures follow the opposite trends where decreased gradually. For non-stabilized, crystallization of fat started at 14.66 ± 0.12 °C and continued up to −15.68 ± 0.11 °C, leading to a broad exotherm (blend 1). Evolution of this type of exotherm was a characteristic feature of packing of triglyceride chains in α form (Sagiri et al., 2014). The maxima crystallization peaks of non-stabilized fat blends were increased from 10.09 ± 0.76 to 21.72 ± 0.24 °C as well as the enthalpy increased from 48.67 ± 0.73 to 63.02 ± 0.79 J/g. There was significant difference (p < 0.05) in transition temperatures and enthalpy exhibited within all ten non-stabilized blends which could be due to different blending proportions of BKF and PS. After incubation, the onset crystallization temperature of stabilized fat blends varied from 15.46 ± 0.91 to 26.89 ± 2.84 °C, whereas the offset crystallization temperature ranged from −15.73 ± 0.13 to −22.38 ± 0.10 °C. In addition, the maximum crystallization temperature followed the trend which slightly shifted to the higher temperature. This could be due to polymorphism transition from α-form to β-form. Interestingly, onset and maximum crystallization temperatures of stabilized fat blends were significantly (P < 0.05) higher than nonstabilized fat blends. The onset and offset crystallization temperatures of non-stabilized and stabilized blends were found closed to that of CB and indicated that these blends were more suitable as the CB alternative. The cocoa butter equivalent developed through interesterification of mango seed oil and palm oil mid-faction by Momeny, Vafaei, and Ramli (2013). The authors reported that certain blends show similar melting and crystallization behavior to that of cocoa butter. 3.3. Crystal morphology Fig. 3 shows the crystal morphologies of BKF and PS blends which were studied using polarized light microscope. Based on Fig. 3, blends 2 to 7 with ratio 90: 10, 85:15, 80:20, 75:25, 70:30, and 65:35 of BKF and PS were more similar to each other with needle-shaped crystals branching outward from the middle nuclei under microscopic observation. These blends showed small spherulites with the diameter of 10–50 μm. However, the other blends were more closed to each other with bulky shaped and large spherulitic microstructures with diameter ranged from 60 to 100 μm. The diameter of crystals were fall in the ranges studied by Biswas et al. (2017b). They reported that the crystals of commercial CB were spherical in shape with 10–100 μm in diameter composed of needle-like crystals radiating outward from the middle nuclei. By comparing the shape and diameter, blends 2 to 7 were more compatible to commercial CB because of their smaller and more crystals. The small crystals had large surface area compared to bigger crystals (Devi & Khatkar, 2016). Therefore, small crystals can hold a massive amount of liquid oil and had superior creaming properties (Devi & Khatkar, 2016). The different blends exhibited different crystalline structures such as shape and size of fat crystal clusters. The shape and size of the individual fat crystals and crystal clusters changed with temperatures, polymorphism, and chemical compositions (McClements, 2007). This variation could be related to the differences in the fatty acids and triglycerides species (Biswas et al., 2017b). In this study, the samples required the temperature of 20–23 °C in order for proper crystallization (Solís-Fuentes & Durán-de-Bazúa, 2004). The triglycerides crystals of different polymorphs exhibited various morphologies. The α-form produces an amorphous mass of small crystals, the β′-form is usually a bulky shape or spherulitic, whereas the β-form is mostly a needle shape (Himawan et al., 2006). According to Biswas et al. (2017b), PS tends to crystallized in the stable β-form crystals. The β-form crystals found in

Fig. 3. Polarized light microphotographs (40 × lens) of BKF and PS blends.

curves of non-stabilized and stabilized blends 1 and 2 showed one exothermal peak with a shoulder before the peak maximum. The shoulder can possibly demonstrate a two-step crystallization where peaks cannot be completely separated due to the rapid crystallization (Fredrick et al., 2008). However, non-stabilized and stabilized blends (i.e blends 3 to 10) crystallized slowly and two crystallization peaks formed during cooling. The two crystallization peaks corresponding to high melting (hard) fraction and low melting (smooth) fraction (Fredrick et al., 2008). The high melting fraction (second exothermic peak) corresponded to the crystallization of the high melting saturated fatty acids which included disaturated and trisaturated triglycerides (Sagiri et al., 2014). However, the low melting fraction (first exothermic peak) was due to the transformation of monounsaturated triglycerides (Fredrick et al., 2008). The results showed that triglycerides were one of the primary factors which determined the crystallization behavior of fats and oils. Even the tiny changes in the triglycerides can have an impact on the crystallization and the final properties of fat blends (Gregersen, Miller, Hammershoj, Andersen, & Wiking, 2015). In addition, the multiple-step crystallization might due to the generation of non-identical polymorphic forms (α, βʹ, and β). The crystallization at 10–14 °C resulted in broad exotherm, it was expected that some of the α polymorphic fatty acids could be converted to β’ polymorphic state (Sagiri et al., 2014).

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blend 2 to 7 could more suitable for making chocolates and coatings because it's melted at high temperature. In addition, the small to medium of crystal size allowing for smooth mouth-feel products. Although it is usually found that fat crystals grew as spherulites, huge variations can be happened due to the changes in crystallization conditions, even for the same triglycerides (Himawan et al., 2006).

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4. Conclusion No research has been done on the thermal properties of BKF and PS blends. This is important in providing information such as triglycerides, melting and crystallization characteristics, and crystal morphology of fat blends. Besides, it is important to search for the CB alternative that has high availability and resemblance to characteristics as commercial CB. The BKF was blended with PS at different ratios and their triglycerides, thermal properties, and crystal morphology investigated. A total of ten blends (BKF: PS) were studied and found that the blend 3 (85:15), blend 4 (80:20), blend 5 (75:25), blend 6 (70:30), and blend 7 (65:35) were more resemble to CB and can be recommended as CB alternative. This recommendation was based on the overall results from triglycerides, melting and crystallization characteristics, and crystal morphology of BKF and PS blends. In addition, the stabilized fat blends were found to having characteristics more similar to CB as compared to non-stabilized fat blends. The storage stability of BKF and its blends with PS can be examined. It is suggested that BKF and its recommended blends with PS could be kept under accelerated condition. Acknowledgments This research was supported by the Centre for Research and Innovation, Universiti Malaysia Sabah (SBK0413-2018). References Afoakwa, E., Paterson, A., Fowler, M., & Vieira, J. (2008). Effects of tempering and fat crystallisation behaviour on microstructure, mechanical properties and appearance in dark chocolate systems. Journal of Food Engineering, 89, 128–136. Akhter, S., McDonald, M. A., & Marriott, R. (2016). Mangifera sylvatica (wild mango): A new cocoa butter alternative. Scientific Reports, 6, 32050. Al-Sheraji, S. H., Ismail, A., Manap, M. Y., Mustafa, S., Yusof, R. M., & Hassan, F. A. (2012). Fermentation and non-digestability of Mangifera pajang fibrous pulp and its polysaccharides. Journal of Functional Food, 4, 933–940. AOCS (2003). Official methods and recommended practices of the American Oil Chemists' Society (5th ed.). Champaign, Illinois, USA: American Oil Chemists' Society ((no. Ce5b-89) Part 1, A–C). Bahari, A., & Akoh, C. C. (2018). Texture, rheology and fat bloom study of ‘chocolates’ made from cocoa butter equivalent synthesized from illipe butter and palm midfraction. LWT – Food Science and Technology, 97, 349–354. Bakar, M. F., & Fry, J. R. (2013). A review on underutilized indigenous bambangan (Mangifera pajang) fruit as a potential novel source for functional food and medicine. Academic Journals, 7(45), 3292–3297. Biswas, N., Cheow, Y. L., Tan, C. P., Kanagaratnam, S., & Siow, L. F. (2017b). Cocoa butter substitute (CBS) produced from palm mid-fraction/palm kernel oil/palm stearin for confectionery fillings. Journal of the American Oil Chemists’ Society, 94, 235–245. Biswas, N., Cheow, Y. L., Tan, C. P., & Siow, L. F. (2017a). Physical, rheological and sensorial properties, and bloom formation of dark chocolate made with cocoa butter substitute (CBS). Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology, 82, 420–428. Chiavaro, E. (2015). Differential scanning calorimetry: Applications in fat and oil technology. Boca Raton: CRC Press. Devi, A., & Khatkar, B. S. (2016). Physicochemical, rheological and functional properties of fats and oils in relation to cookie quality: A review. Journal of Food Science & Technology, 53(10), 3633–3641. Fredrick, E., Foubert, I., Sype, J. V., & Dewettinck, K. (2008). Influence of monoglycerides on the crystallization behavior of palm oil. Crystal Growth & Design, 8(6), 1833–1839. Gregersen, S. B., Miller, R. L., Hammershoj, M., Andersen, M. D., & Wiking, L. (2015). Texture and microstructure of cocoa butter replacers: Influence of composition and cooling rate. Food Structure, 4, 2–15.

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