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. 2019 Aug 8;29(2):169–177. doi: 10.1007/s10068-019-00653-1

Effects of rendering and α-tocopherol addition on the oxidative stability of horse fat

Man Jae Cho 1, Hyun Jung Kim 2,✉
PMCID: PMC6992833  PMID: 32064125

Abstract

Oxidative stability of horse fat rendered at 70 °C, − 0.1 MPa under vacuum and 110 °C, 0.1 MPa from horse fatty tissues was investigated after the addition of α-tocopherol at 0, 30, 60, and 150 mg/kg during storage at 60 °C in the dark. Peroxide values of initial horse fat rendered at 70 °C under vacuum ranged from 6.10 to 7.40 meq/kg. After 14 days, those of horse fat with α-tocopherol at 0, 30, 60, and 150 mg/kg increased to 142.40, 34.10, 39.37, and 58.23 meq/kg, respectively. Acid values and thiobarbituric acid values of horse fat rendered at 70 °C were lower than those of horse fat at 110 °C. Unsaturated fatty acids contents of horse fat rendered at 70 °C and 110 °C were 58.04 and 57.15%, respectively. These results indicate that rendering at 70 °C under vacuum improved the oxidative stability of horse fat and the addition of α-tocopherol helped to prevent lipid oxidation.

Keywords: Horse fat, Oxidative stability, Rendering temperature, α-Tocopherol, Fatty acid

Introduction

Horse fat has long been used as a “folk medicine” in Asia. It is known to be a useful material with the great affinity to the human skin because it can be absorbed into the dermal layer of skin by similarity of unsaturated fatty acid composition (60–65%) and structure (Lee et al., 2013). Particularly, palmitoleic acid, a major component of sebum secreted from human skin, showed antimicrobial and anti-inflammatory effects on gram-positive bacteria in skin (Wille and Kydonieus, 2003). Horse fat is recently getting attention in cosmetics used as a skincare ingredient and its awareness has been gradually rising (Kim, 2015). Many cosmetic manufacturers have produced skincare creams and emulsions containing horse fat; however, the quality deterioration, such as off-flavor and discoloration of these cosmetic products, has become a problem (Kim, 2015). Lipid oxidation is known to cause quality losses of flavor, texture, consistency, and nutritive value. In particular, unsaturated fatty acids in lipid are easily oxidized and form hydroperoxides as primary oxidation products during processing and storage (Li et al., 2017). Horse fat which contains relatively high contents of unsaturated fatty acids is possibly oxidized faster than other animal fats (Kim, 2015).

One approach to reduce lipid oxidation is the use of antioxidants as an interferer to retard either chain propagation or initiation of lipid oxidation (Frankel, 2014). Tocopherol is a well-known lipid-soluble antioxidant and free radical scavenger (Azzi and Stocker, 2000). Its most common and biologically active form is α-tocopherol (Herrera and Barbas, 2001). α-Tocopherol prevented color changes in meat products and extended the shelf-life of animal fats (Wang et al., 2015). Uemura et al. (2016) reported that the addition of α-tocopherol to soybean oil, linseed oil, and fish oil completely inhibited volatile formation until 1400 h, 650 h, and 380 h of storage, respectively. The oxidation of soybean oil slowed down when contained 50–250 ppm α-tocopherol during storage at 60 °C; however, the antioxidant activity diminished at concentrations above 100 ppm (Evans et al., 2002). The cosmetic industries which manufacture the products with horse fat have used α-tocopherol as an antioxidant, which is cheaper than γ- or δ-tocopherol. Among tocopherol homologues, α-tocopherol is more concentration sensitive than others (Player et al., 2006). It is thus necessary to investigate the antioxidant activity of α-tocopherol with different conditions of the oil system.

The wet pressing method is the most common process to obtain crude oil from animal fat such as lard, fish, and tallow (Food and Agriculture Organization of the United Nations, 2018). The rendering condition, especially, temperature is a considerable factor to affect the quality of rendering lipid (Rosenthal et al., 1996). The lipid rendered at low temperature exhibited better quality than those rendered at high temperature (Rhee et al., 1972). Currently, there are not many studies on rendering horse fat and analysis of its oxidative stability during storage. Therefore, this study was conducted to compare refined horse fat from horse fatty tissues with different rendering conditions under vacuum and atmospheric pressure with low and high temperature. The oxidative stability of horse fat with or without α-tocopherol was investigated during storage as well.

Materials and methods

Materials

Fresh horse fatty tissues were provided from Jeju Specialized Agency (Jeju, Korea). Sodium hydroxide (Youngjin Chemistry, Bucheon, Korea) was used as a neutralizing agent. α-Tocopherol, 14% BF3-methanol, and triundecanoin were purchased from Sigma-Aldrich (St. Louis, MO, USA). Supelco® 37 component fatty acid methyl ester mixture as a fatty acid standard was obtained from Sigma-Aldrich. Chloroform and starch potato were purchased from OCI Company Ltd. (Seoul, Korea). Acetic acid, ethyl alcohol, ethyl ether, benzene, sodium thiosulfate, and potassium iodide were all purchased as analytical grade.

Rendering of horse fat

Horse fatty tissues (3 kg) were ground using a meat grinder (MN-22S, Hankook Fujee Industries, Hwaseong, Korea) and mixed with water (1:1, w/w). To optimize the fat extraction condition from fatty meat as a preliminary test, horse fat was extracted at temperature ranges of 60–110 °C under vacuum system. Among those conditions, the following extraction method was carried out based on the initial oxidation of horse fat. The primary rendering of horse fat was performed at either 70 °C at − 0.1 MPa (under vacuum) or 110 °C at 0.1 MPa (atmospheric pressure) for 3.5 h in liquid extraction equipment (Cosmos-660, Kyungseo E&P, Incheon, Korea). After the oil part was separated, the remaining fatty tissues with water (1:1) were rendered again for 3.5 h. The first and second rendered horse oil were mixed together and extracted with water (1:1) again for 3.5 h. The rendered horse oil was collected, filtered, and neutralized with 0.2% sodium hydroxide. The neutralized horse oil put in a stainless steel bucket which placed in a water bath (JSSB-30T, JS Research Inc., Gongju, Korea) at 100 °C for 30 min to precipitate impurities. After the final horse oil was collected, they were placed in serum bottles, sealed airtight, and stored in a freezer until use.

Analysis of tocopherol in horse fat

Tocopherol contents in horse fat extracted from horse fatty tissues were determined using a high performance liquid chromatography (HPLC, Agilent 1260, Agilent Technologies, Waldbronn, Germany) equipped with a diode array detector (Agilent Technology) on a Zorbax eclipse plus C18 rapid resolution column (4.6 × 100 mm, 3.5 μm, Agilent Technologies, Santa Clara, CA, USA) by the modified method of Joseph (2011). The mobile phase (75:25:5 = acetonitrile:methanol:0.035% acetic acid in tetrahydrofuran) was used after filtered through 0.45 μm filter (hydrophobic PTFE membrane filter, SciLab Korea Co., Ltd., Seoul, Korea) at the rate of 0.8 mL/min with a column temperature held at 45 °C. The sample was prepared as 1 g of horse fat in 1 mL ethanol. After dilution, 10 μL was injected to HPLC and detected at 220 nm. The tocopherol homologues in horse fat were quantified based on the peak areas and retention time of tocopherol standards (Merck Co., Darmstadt, Germany).

Preparation of horse fat added with α-tocopherol

Horse fat added with α-tocopherol (Sigma-Aldrich) at 0, 30, 60, and 150 mg/kg was prepared. All of the samples were sealed airtight and stored in a conventional oven (JSOF-150, JS Research, Gongju, Korea) at 60 °C in the dark to measure peroxide value, acid value, and thiobarbituric acid reactive substances (TBARS) for 14 days and fatty acid (FA) composition for 28 days.

Oxidative stability of horse fat

For the oxidative stability of horse fat, the peroxide value, acid value, and TBARS (thiobarbituric acid reactive substances) were determined by AOCS (2006), AOAC (1995), and Sidwell et al. (1945), respectively. Peroxide value and TBARS were calculated and expressed as milliequivalent of hydroperoxides per kilogram horse fat (meq/kg) and mg of malonaldehyde per kilogram horse far (mg MA/kg), respectively.

Analysis of fatty acids

For the analysis of fatty acid composition, fatty acid methyl esters (FAME) of horse fat were prepared by following AOCS method Ch 2a-94 (AOCS, 2006). The analysis of FAME was carried out on a gas chromatograph (QP2010Plus, Shimadzu, Kyoto, Japan) by AOCS method (AOCS, 2006). A fused silica capillary column (SP-2560, 100 m × 0.25 mm id., 0.2 µm, Sigma-Aldrich) was used. The column was operated at 100 °C to 225 °C at 3 °C/min and held for 15 min at 240 °C. The injector and flame ionization detector were kept at 285 °C. The carrier gas was helium at a flow rate of 0.75 mL/min. The split ratio was 200:1. The fatty acids were identified by comparison of their retention time with those of standards of FAME (Sigma-Aldrich). The percentage of fatty acid was calculated by the ratio of partial area to total peak area and only the peak areas over 0.2% were counted.

Statistical analysis

All of the experiments were performed in triplicate and were analyzed three times per a sample. Data were determined by one-way ANOVA followed by Duncan’s multiple range test for the comparison using SPSS 18.0 (SPSS Inc., Chicago, IL, USA). Significant differences were considered at p < 0.05.

Results and discussion

Tocopherol in horse fat

α-Tocopherol and γ-tocopherol were found in horse fat extracted from horse fatty tissues. They were 9.5 mg/kg and 6.5 mg/kg, respectively (data not shown). In animal fat, tallow contains 30.4 mg/kg of α-tocopherol and 3.8 mg/kg of γ-tocopherol and lard contains 18 mg/kg of α-tocopherol (Enig et al., 1983). The low concentration of tocopherol in horse fat was similar to those in a typical animal fat.

Oxidative stability of horse fat as determined by peroxide value

Changes in peroxide value (PV) of horse fat rendered at 110 °C under atmospheric pressure and 70 °C under vacuum condition with α-tocopherol at 0, 30, 60, and 150 mg/kg during storage of 14 days at 60 °C in the dark are shown in Fig. 1. As the storage time increased from 0 day to 14 days, the PVs of horse fats rendered at both conditions significantly increased (p < 0.05). The PVs of the horse fat rendered at 110 °C and 70 °C without α-tocopherol at 0 day were 20.97 and 6.73 meq/kg, respectively. These PVs greatly increased to 172.70 and 142.40 meq/kg, respectively, after 14 days at 60 °C. These results showed the same trends as reported by Kim et al. (2007) that the peroxide value increased along with the production of hydroperoxides as primary products of lipid oxidation.

Fig. 1.

Fig. 1

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Change in peroxide values of horse fat rendered at 110 °C under atmospheric pressure and 70 °C under vacuum condition with α-tocopherol at different concentration during storage of 14 days at 60 °C in the dark. Mean ± SD. Different small letters on the line indicate significantly different within storage days based on Duncan’s multiple range test at p < 0.05

The PVs of horse fat decreased by addition of α-tocopherol during storage of 14 days. As the concentration of α-tocopherol increased from 30 to 60 and 150 mg/kg, the PVs of horse fat rendered at 110 °C significantly decreased during storage (p < 0.05). Overall, the addition of α-tocopherol provided the highest inhibition of oxidation to reduce the formation of hydroperoxides in horse fat. The study of Kim (2014) showed the similar trend that α-tocotrienol, a homologue of tocols, effectively prevented the oxidation of lard. The rendering process of horse fat from horse fatty tissues at 70 °C under vacuum helped to retard the production of hydroperoxides during storage at 60 °C when compared to the horse fat rendered at 110 °C. The processing under vacuum at low temperature helped lowering the chance to contact oxygen during rendering and this prevented the lipid oxidation. These results indicate that the rendering at 70 °C under vacuum and addition of α-tocopherol significantly helped to reduce the formation of hydroperoxides in horse fat.

Oxidative stability of horse fat as determined by acid value

Changes in acid values (AV) of horse fat rendered at 110 °C under atmospheric pressure and 70 °C under vacuum condition with α-tocopherol at 0, 30, 60, and 150 mg/kg during storage of 14 days at 60 °C in the dark are shown in Fig. 2. As the storage time increased from 0 day to 14 days, the AVs of horse fats rendering at both conditions significantly increased (p < 0.05). The AVs of the horse fat rendered at 110 °C under atmospheric pressure and at 70 °C under vacuum without α-tocopherol at 0 day were 0.03 and 0.02 mg KOH/g, respectively. These AVs greatly increased to 0.53 and 0.43 mg KOH/g, respectively, after 14 days at 60 °C. As the concentration of α-tocopherol increased from 30 to 60 and 150 mg/kg, the AVs of horse fat rendered at 110 °C significantly decreased during storage (p < 0.05). The addition of α-tocopherol greatly inhibited oxidation and reduced the formation of free fatty acids (FFA) in horse fat. Bouaid et al. (2007) reported that the AVs of biodiesel oils increased with increasing storage period for 30 months. In addition, Sung et al. (2011) showed that the AVs of oils from brown rice and white rice significantly increased during the storage period and affected the quality of rice. The AV is not inherent characteristics of lipid and is measurement of FFA formed by the hydrolysis of lipid triacylglycerol molecules. Therefore, it exhibits the degree of refining and lipid acidification (Lee and Cho, 1998) which possibly gave a strong influence on the quality of horse fat.

Fig. 2.

Fig. 2

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Change in acid values of horse fat rendered at 110 °C under atmospheric pressure and 70 °C under vacuum condition with α-tocopherol at different concentration during storage of 14 days at 60 °C in the dark. Mean ± SD. Different small letters on the line indicate significantly different within storage days based on Duncan’s multiple range test at p < 0.05

The PVs and AVs of horse fat showed relatively high exponential relationships with the concentration of α-tocopherol during storage of 14 days (r2 = 0.78–0.96, data not shown). The rendering process of horse fat from horse fatty tissues at 70 °C under vacuum helped to retard the production of FFA during storage at 60 °C when compared to the horse fat rendered at 110 °C. After the extraction process, the AVs of initial horse fat were not significantly different between rendering at 110 °C and 70 °C; however, the AVs of horse fat rendered at 110 °C increased higher than those at 70 °C after storage of 14 days. These results indicate that the rendering at 70 °C under vacuum significantly helped to reduce the formation of FFA in horse fat.

Oxidative stability of horse fat as determined by TBA value

Figure 3 indicates the changes in TBA values of horse fat rendered at 110 °C under atmospheric pressure and 70 °C under vacuum condition with α-tocopherol at 0, 30, 60, and 150 mg/kg during storage of 14 days at 60 °C in the dark. Along with the results of PVs and AVs, TBA values of horse fats rendering at both conditions significantly increased (p < 0.05) as storage day increased. The TBA values of the horse fat rendered at 110 °C under atmospheric pressure and at 70 °C under vacuum without α-tocopherol at 0 day were 0.71 and 0.76 mg MA/kg, respectively. These TBA values greatly increased to 21.33 and 19.01 mg MA/kg, respectively, after 14 days at 60 °C. The PVs to the corresponding TBA values for horse fat obtained from rendering at two different conditions were highly correlated with r2 of 0.820–999 (data not shown). The TBA value determines malonaldehyde (MA) which is the most important secondary oxidized product as an indicator of lipid oxidation formed from 5-membered cyclic peroxides of linoleate and linolenate (Esterbauer et al., 1991). The TBA values of horse fat increased during storage, so meant to the increase of MA production from the decomposition of hydroperoxides with the progress of lipid oxidation. Capuano et al. (2010) also reported that TBA values of sunflower oil constantly increased during storage because of the decomposition of hydroperoxides formed as primary oxidation products.

Fig. 3.

Fig. 3

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Change in TBA values of horse fat rendered at 110 °C under atmospheric pressure and 70 °C under vacuum condition with α-tocopherol at different concentration during storage of 14 days at 60 °C in the dark. Mean ± SD. Different small letters on the line indicate significantly different within storage days based on Duncan’s multiple range test at p < 0.05

When α-tocopherol added to horse fat, the TBA values were lower than that of horse fat without α-tocopherol during storage of 14 days. As the concentration of α-tocopherol increased from 30 to 150 mg/kg, the TBA values of horse fat rendered at 110 °C significantly decreased during storage (p < 0.05). α-Tocopherol inhibited the formation of malondialdehyde in horse fat. These results showed the same trends as reported by Huang et al. (1994) who mentioned that tocopherol homologues greatly inhibited malondialdehyde formation as their concentration increased. The rendering process of horse fat from horse fatty tissues at 70 °C under vacuum helped to reduce the production of malondialdehyde during storage at 60 °C when compared to the horse fat rendered at 110 °C. These results indicate that the rendering at 70 °C under vacuum and addition of α-tocopherol helped to reduce the formation of malondialdehyde in horse fat.

Effect of α-tocopherol on the oxidation of horse fat

Table 1 showed high correlations (r2 > 0.80) between oxidation time and degree of horse fat oxidation during storage of 14 days at 60 °C. The equation for the hydroperoxide formation with oxidation time was formed as following: peroxide value (meq/kg) = a × oxidation time + b (Kim and Choe, 2016). The intercept is equal to ‘b’ and the slope is equal to ‘a’ from this equation. As the slope was increased, the oxidative stability of horse fat decreased. The rates of hydroperoxide production (a) in horse fat rendered at 110 °C with α-tocopherol at 30, 60, and 150 mg/kg were 7.46, 3.85, and 3.74 meq/kg/day, respectively, which were significantly lower (p < 0.05) than the rates of hydroperoxide production in horse fat without α-tocopherol rendered at 110 °C (11.04 meq/kg/day). The rates of hydroperoxide production in horse fat rendered at 70 °C under vacuum condition with α-tocopherol at 30, 60, and 150 mg/kg were 1.78, 2.24, and 3.58 meq/kg/day, respectively, which were significantly lower (p < 0.05) than that of horse fat rendered at 70 °C under vacuum condition (9.66 meq/kg/day). The oxidation time and hydroperoxide products showed relatively high correlations with the concentration of α-tocopherol during 14 days of storage (r2 = 0.86–0.99). In addition, Table 1 indicated that AVs and TBA values were similar to the trends of PVs as shown. These results strongly suggest that the addition of α-tocopherol effectively improved the oxidative stability of horse fat by decreasing the production of primary and secondary lipid oxidation products.

Table 1.

Regression analysis between oxidation time and peroxide value, acid value, or TBA value of horse fat added with α-tocopherol (α-T) at 0, 30, 60, and 150 mg/kg during storage of 28 days at 60 °C in the dark

α-T (mg/kg) Peroxide value Acid value TBA value
110 °C rendering 70 °C rendering under vacuum 110 °C rendering 70 °C rendering under vacuum 110 °C rendering 70 °C rendering under vacuum
a b r2 a b r2 a b r2 a b r2 a b r2 a b r2
0 11.04 12.52 0.99 9.66 − 1.28 0.98 0.038 − 0.02 0.93 0.031 − 0.04 0.87 1.54 − 1.52 0.94 1.28 − 1.47 0.91
30 7.46* 7.90 0.91 1.78* 6.83 0.96 0.021* 0.00 0.83 0.006* 0.00 0.90 0.97* − 1.40 0.90 0.15* 0.45 0.88
60 3.85* 15.98 0.86 2.24* 5.90 0.98 0.011* 0.00 0.88 0.007* 0.00 0.89 0.48* − 0.33 0.80 0.20* 0.40 0.93
150 3.74* 19.84 0.99 3.58* 6.93 0.99 0.015* − 0.01 0.93 0.007* 0.00 0.86 0.32* 0.61 0.98 0.24* 0.41 0.95
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Peroxide value (meq/kg), Acid value (mg KOH/g), or TBA value (mg MA/kg) = a × oxidation time + b, r2 = determination coefficient

Asterisk (*) in a value indicates significant difference between horse fat without α-tocopherol and horse fat with α-tocopherol by dummy variable regression analysis (p < 0.05)

Fatty acid composition of horse fat

Fatty acid compositions of horse fat with different rendering conditions and different α-tocopherol concentration when stored for 0 day and 28 days at 60 °C in the dark are shown in Table 2. The fatty acids of horse fat were classified as ten different fatty acids including lauric acid (C12:0), myristic acid (C14:0), myristoleic acid (C14:1), palmitic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3), and arachidic acid (C20:0). The major fatty acids were oleic acid, palmitic acid, linoleic acid, palmitoleic acid, stearic acid, and linolenic acid. The unsaturated fatty acids of horse fat rendered at 110 °C under atmospheric pressure and 70 °C under vacuum condition at 0 day were 57.15 and 58.04%, respectively, and reduced to 54.38% and 56.21% after 28 days of storage. Especially, the contents of linoleic acid (C18:2) in horse fat were reduced after 28 days. The content of linoleic acid in horse fat with α-tocopherol at 60 mg/kg was greater than that in horse fat without α-tocopherol after 28 days. The palmitoleic acid (C16:1, 7.3%) in horse fat is known as a main ingredient of skin sebum and its content was higher than that of beef tallow (1.8%) and lard (3.2%) (Enig et al., 1983).

Table 2.

Fatty acid composition (%) of horse fats rendered at 110 °C and 70 °C under vacuum with α-tocopherol (α-T) at 0, 30, 60, and 150 mg/kg stored at 60 °C in the dark for 0 day and 28 day

Fatty acid Rendering 110 °C 70 °C under vacuum
Storage 0 day 28 day 0 day 28 day
α-T 0 mg/kg 0 mg/kg 30 mg/kg 60 mg/kg 150 mg/kg 0 mg/kg 0 mg/kg 30 mg/kg 60 mg/kg 150 mg/kg
C12:0 1.57 ± 0.30a 1.68 ± 0.18a 1.71 ± 0.21a 1.63 ± 0.01a 1.60 ± 0.03a 1.68 ± 0.09a 1.66 ± 0.01a 1.58 ± 0.06a 1.47 ± 0.1a 1.75 ± 0.24a
C14:0 5.85 ± 0.43a 5.72 ± 0.88a 5.70 ± 0.40a 5.54 ± 0.57a 5.86 ± 0.26a 5.12 ± 0.12a 5.69 ± 0.70a 5.35 ± 0.40a 5.05 ± 0.18a 5.63 ± 0.25a
C14:0 0.45 ± 0.03a 0.38 ± 0.13a 0.30 ± 0.42a 0.38 ± 0.13a 0.48 ± 0.16a 0.32 ± 0.03a 0.40 ± 0.11a 0.36 ± 0.06a 0.36 ± 0.03a 0.21 ± 0.30a
C16:0 27.41 ± 0.18cde 29.19 ± 0.77a 28.68 ± 0.85ab 28.47 ± 0.20abcd 28.62 ± 0.73ab 27.36 ± 0.13de 28.18 ± 0.76abcde 27.26 ± 0.67bcde 27.17 ± 0.75e 27.89 ± 0.73bcde
C16:1 7.31 ± 0.23ab 7.05 ± 0.20ab 7.39 ± 0.01a 7.08 ± 0.47ab 7.15 ± 0.18ab 6.89 ± 0.01b 7.23 ± 0.40ab 7.01 ± 0.04ab 6.89 ± 0.07b 7.22 ± 0.01ab
C18:0 3.97 ± 0.19bc 4.38 ± 0.19a 4.18 ± 0.16abc 4.28 ± 0.22ab 4.28 ± 0.08ab 3.87 ± 0.04c 4.02 ± 0.22bc 4.10 ± 0.04abc 4.1 ± 0.01abc 3.97 ± 0.03bc
C18:1 33.59 ± 0.96a 34.93 ± 2.04a 34.91 ± 0.88a 34.48 ± 1.13a 34.51 ± 0.76a 34.10 ± 0.28a 34.45 ± 1.72a 34.66 ± 0.89a 34.83 ± 0.04a 34.25 ± 0.81a
C18:2 12.98 ± 0.26bc 10.19 ± 0.75f 10.94 ± 0.40ef 11.33 ± 0.02de 10.97 ± 0.02ef 14.04 ± 0.12a 11.95 ± 0.79 cd 12.80 ± 0.64bc 13.25 ± 0.37ab 12.68 ± 0.55bc
C18:3 2.09 ± 0.05a 1.03 ± 0.55a 1.16 ± 0.54a 1.20 ± 0.47a 1.12 ± 0.41a 1.74 ± 0.09a 1.37 ± 0.76a 1.55 ± 0.83a 1.56 ± 0.78a 1.50 ± 0.76a
C20:0 0.62 ± 0.06a 0.70 ± 0.14a 0.64 ± 0.03a 0.65 ± 0.03a 0.76 ± 0.01a 0.67 ± 0.03a 0.69 ± 0.14a 0.68 ± 0.10a 0.77 ± 0.06a 0.65 ± 0.04a
SFA 42.85 ± 0.20 45.62 ± 0.38 44.71 ± 0.45 44.46 ± 0.19 45.16 ± 0.22 41.96 ± 0.07 43.79 ± 0.29 42.65 ± 0.22 42.18 ± 0.19 43.46 ± 0.27
USFA 57.15 ± 0.38 54.38 ± 0.89 55.29 ± 0.51 55.54 ± 0.57 54.84 ± 0.34 58.04 ± 0.13 56.21 ± 0.92 57.35 ± 0.60 57.82 ± 0.32 56.54 ± 0.53
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Values are mean ± SD

Means with different letters within a row indicate significant difference at p < 0.05

α-T α-tocopherol, SA saturated fatty acids, USFA unsaturated fatty acids

As the storage time increased from 0 day to 28 days, the content of saturated fatty acid in horse fat increased. The contents of saturated fatty acid in horse fat rendered at 110 °C under atmospheric pressure with α-tocopherol at 0, 30, 60, and 150 mg/kg were increased from 42.85 to 45.62, 44.71, 44.46, and 45.16%, respectively, after 28 days at 60 °C. Also, the contents of saturated fatty acid in horse fat rendered at 70 °C under vacuum with α-tocopherol at 0, 30, 60, and 150 mg/kg were increased from 41.96 to 43.79, 42.65, 42.18, and 43.46%, respectively. Jung et al. (1994) reported that saturated fatty acids of fish oil were increased by reducing unsaturated fatty acids during storage of 20 weeks at 37 °C. These reductions were similarly observed by Lee et al. (1994) that the unsaturated fatty acid content of pork decreased during storage. These results showed that the apparent relationship between α-tocopherol concentration and oxidation stability of horse fat was observed during storage.

In conclusion, the peroxide value, acid value, and TBA value of the initial horse fat rendering at 70 °C under vacuum were kept in lower values than those of horse fat rendering at 110 °C under atmospheric pressure during storage of 14 days. Unsaturated fatty acids of horse fats were decreased with storage period. The peroxide value, acid value, and TBA value of horse fat were effectively improved by the addition of α-tocopherol. Particularly, α-tocopherol at 30 mg/kg was the most effective to prevent the oxidation of horse fat during storage at 60 °C. Therefore, when horse fat is rendering at 70 °C under vacuum and α-tocopherol is appropriately added, it can help to process horse fat by preventing lipid oxidation.

Acknowledgements

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2017R1C1B5016456).

Footnotes

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Contributor Information

Man Jae Cho, Email: marzzae@naver.com.

Hyun Jung Kim, Email: hyunjkim@jejunu.ac.kr.

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