Physicochemical Characteristics and Fatty Acid Composition
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Journal of Oleo Science Copyright ©2019 by Japan Oil Chemists’ Society doi : 10.5650/jos.ess19031 J. Oleo Sci. 68, (9) 827-835 (2019) Traditional Tibetan Ghee: Physicochemical Characteristics and Fatty Acid Composition Bingyu Jing1, Wenjie Chen2, Mengzhu Wang1, Xiaohui Mao1, Jia Chen1, and Xiuzhu Yu1* 1 College of Food Science and Engineering, Northwest A and F University, 22 Xinong Road, Yangling 712100, Shaanxi, P. R. CHINA 2 Hybrid Rape Research Center of Shaanxi Province, 6 West Gaogangqu Road,Yangling 712100, Shaanxi, P. R. CHINA Abstract: Fifty traditional Tibetan ghee (TTG) varieties were collected and analyzed their systematic characteristic indices, including physicochemical parameters, minerals, fatty acid composition, and thermal behavior. Results show that TTG contains a large amount of fat (71.68%–93.3%) and a small quantity of protein (0.51%–1.81%). The acid and peroxide values of TTG vary from 0.02 to 1.30 mg/g and 0.07 to 5.93 meq/kg, respectively. The content of minerals varied with altitude level and region significantly (p < 0.05), and the regional variations of fatty acids in TTG were also observed significantly, these differences may be due to the high unsaturated fatty acids level in the cow diets. Key words: traditional Tibetan ghee, physicochemical characteristics, minerals, fatty acid composition 1 Introduction logical properties, it indicated that ghee produced from Ghee is a traditional Tibetan dairy product that is pro- cows’ milk based on grass-feeding have a potentially duced from a series of fermentation, heat clarification, and healthier fat content and a desirable flavour5). Neupaney et desiccation of yak milk. The yak is placed under the sub- al. studied some functional properties of yak butter lipids family Bovine and belongs to the classification of Bos through analysis of conjugated linoleic acid(CLA)composi- grunniens, which is mainly found in the highlands of Nep- tion, differential scanning calorimetric(DSC)analysis, and alese Himalayas, Indian Kasmir, Tibet, Mongolia, and determination of tyrosine inhibition activity and antioxi- Bhutan1). The major constituents of yak milk are fat(6% dant property2). Orrashid et al. studied the fatty acid –10%), protein(5.5%), lactose(5%), and minerals(1.1%)2). content of both domesticated and stocked cheese, indicat- Yak milk is increasingly recognized for its nutritional bene- ing that cheese that grazed on Himalayan alpine pastures fits and is included in products such as cheese, butter milk has a more balanced fatty acid composition3), however, to tea, and yogurt. Due to the attractive appearance, grainy the best of our knowledge, the studies on characteristics of and semisolid texture, pleasant odor, excellent taste, and TTG were still lacking, while all of them are important pa- the high proportion of polyunsaturated fatty acids(PUFAs)3), rameters for processing and utilization. The main objec- traditional Tibetan ghee(TTG)has important culinary pur- tives of this study are to analyze the global character such poses, such as dressing, cooking, frying, and even in reli- as physicochemical characteristics, fatty acid composition gious rites. Many food manufacturers and research organi- and mineral content, Fourier transform infrared(FTIR) zations also consider TTG as PUFA resources to meet the spectra, and thermal characteristics, most importantly, the increased consumer demand of PUFA-rich oils. relationship of geographical location with the content of Over the past several years, various studies have been minerals and fatty acid also studied in the paper. focused on the characteristics of TTG. Chassaing et al. in- vestigated the European ghee with industrial ghee in terms of peroxide value, minerals, and vitamin A, but the numbers of samples are insufficient to determine the 2 Materials and Methods physico-chemical indicators in ghee varieties4). Moreover, 2.1 Samples many researches also focused on the functional properties The 50 ghee samples were collected from seven different in ghee. Silva et al. mainly studied the fatty acid composi- Tibetan regions, Sannan(n=12, 3700 m), Shigatse(n=12, tion, physicochemical characteristics, as well as microbio- 4000 m), Lhasa(n=9, 3650 m), Qamdo(n=11, 3500 m), *Correspondence to: Xiuzhu Yu, College of Food Science and Engineering, Northwest A and F University, 22 Xinong Road, Yangling 712100, Shaanxi, P. R. CHINA E-mail: [email protected] Accepted June 4, 2019 (received for review January 30, 2019) Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online http://www.jstage.jst.go.jp/browse/jos/ http://mc.manusriptcentral.com/jjocs 827 B. Jing, W. Chen, M. Wang et al. Nagqu(n=2, 3000 m)and Ngari(n=4, 4500 m)respective- cooling to -30℃, held for another 10 min, followed by ly. All the yak milk were collected during mid-April period, heating cycle to 80℃ at the same rate. The cooling and the samples were stored and frozen(-18℃)before further heating cycle were repeated. The onset, peak, end temper- analysis. The specific information of samples is presented atures, and the enthalpy of thermal transition(melting and in Table A. 3. crystallization)were determined through the acquired thermograms. 2.2 Physicochemical analysis The acid value(AV)and peroxide value(PV)were deter- 2.5 Mineral analysis mined according to the standard methods of American Oil The analytical wavelengths(nm)chosen were: Al, Ca, Fe, Chemist’s Society(AOCS Official Method Cd 8b-90) Mg Na, Zn. For the operating conditions of the equipment, (AOCS, 2003a). Briefly, the determination of PV mainly the radio frequency power(1.5 kW)and the plasma(15.0 L/ uses mixture of oil and chloroform/acetic acid, which was min), auxiliary(0.4 L/min), and nebulizer(0.7 L/min)gas left to react with a solution of potassium iodide indarkness; flow-rates were optimized from previous works. Single-ele- the free iodine then titrated with a sodium thiosulfate solu- ment standard stock solutions containing 1000 mg/L Cu, tion. The determination of AV mainly uses mixture of oil Fe, Mn, Mo, and Zn and 4000 mg/L Ca, K, Mg, Na, and P and diethyl ether/ethanol added with 2 mL phenolphtha- were suitably diluted to prepare analytical calibration solu- lein. The mixture was titrated with 0.01 M of potassium hy- tions. Elemental determination by ICP OES was performed droxide and shaken vigorously until the color was changed using external calibration. The standard solutions for the (from white to pink). calibration curves were prepared at the same acid concen- Moisture was determined according to AOCS Official tration for each digestion procedure. Method 926.12, briefly, moisture content was determined from the loss of mass of a specified quantity of oil heated at 2.6 Fatty acid composition analysis 105±1℃ in a hot-air oven for 1 h, and crude fat and The fatty acid composition of TTG was determined protein were determined according to the standard method through conventional saponification/methylation proce- of the Association of Official Analysis Chemists(AOAC Of- dure. First, 60 mg of sample was mixed with 200 μL of 2% ficial Methods of Analysis, 15th, 1990). Protein content was methanolic KOH in screw-capped glass tubes. The tubes calculated from nitrogen content as follows: N(%)×6.25 were stirred for 5 min and held at room temperature for 30 using Kjeldahl’s method. The fat content was measured by s. After acidification with 1 g of NaHSO4, the released fatty using a Soxhelt extraction apparatus with petroleum ether acids were extracted twice by using 4 mL of isooctane. as a solvent for 8 h. All analyses were carried out in tripli- Then, 2 mL of 5 mg/mL internal standard(C11: 0)was added cate. into the fatty acid mixture and vortexed for 1 min at ambient temperature. The fatty acid methyl esters 2.3 FTIR spectra analysis (FAMEs)were then extracted by the addition of 4mL of A Bruker VERTEX 70 series FTIR spectrometer(Bruker isooctane. This isooctane solution containing FAMEs was Optics, Germany)equipped with a deuterated detector was subjected to Gas chromatography–Flame Ionization used to obtain the FTIR spectra. At the ambient tempera- Detector(GC–FID)analysis to quantify the fatty acids. ture, a droplet of the sample was evenly smeared on the Under the same detection conditions, the retention time of screen of 100 meshes and placed in the sample chamber- mono-fatty acid methyl ester was compared with the stan- maid with at 50℃. The spectra were obtained from 6000 dard to identify the quality of fatty acids and with the area cm-1 to 400 cm-1 at a resolution of 8 cm-1 by using 64 co- of each peak for the quantitative analysis. GC measure- added scans. The background air spectrum was subtracted ments were carried out on a fused-silica capillary column before analyzing the sample spectra. (HP-INNOWAX, 0.25 mm×0.25 μL×30 m). The tempera- ture of the inlet was set at 250℃. After holding the sample 2.4 Thermal characteristic analysis at ambient temperature for 2 min, the oven temperature The thermal characteristics of samples were determined was increased to 240℃ at 10℃ min-1 and maintained for with a modulated differential scanning calorimeter(DSC, 10 min. High-purity nitrogen was used as carrier gas at flow TAQ20, USA). The instrument was calibrated using indium rate of 1.1 mL/min. One μL of sample was injected by the (156.6℃, 28.57 J/g)and zinc(419.5℃, 108 J/g). An empty split mode injection system. DSC-pan was used as a reference. N2 was used as the purge gas at a flow rate of 40 mL min-1. The sample(6–9 mg)was 2.7 Statistical analysis accurately weighed directly on the DSC-pan(SFI-Alumi- All experimental measurements were conducted at least num, TA Instrument T11024).