Original Reports Yak Butter Lipid Composition and Vitamins In

Milk Science Vol. 52, No. 1 2003 Original Reports Yak butter lipid composition and vitamins in comparison with cow butter lipids Dhanapati Neupaney1), Shigefumi Sasaki2),Jin-boKim1), Makoto Ishioroshi1), and Kunihiko Samejima1) 1)Faculty of Dairy Science, Department of Food Science, Rakuno Gakuen University, Ebetsu-shi, Hokkaido, Japan 0698501 2)Hokkaido Food Processing Research Center, Ebetsu-shi, Hokkaido 0690836, Japan Abstract: Fatty acid compositions, vitamin A, and tocopherols in the butter lipid of the purebred of yak animal were determined by GLC and HPLC. The cholesterol content of yak butter and lipid oxidation kinetics were investigated by GLC and gravimetric methods. The butter produced from yak milk exhibited a strong ‰avor. This was caused due to the presence of a high concentration of short-chain saturated fatty acids in this butter. The major fatty acids in yak lipids were 160, 181, 140, 180, 40and80 in descending order. Retinol content in yak butter was 402.3 mg/100 gm fat. Alpha (a) tocopherol in yak butter was higher (2.6 mg/100 gm fat) than in cow butter (1.9 mg/100 gm fat), although g tocopherol was signiˆcant in cow butter (440 mg/100 gm fat). Tocopherols ( band dforms) were found in insigniˆcant amounts in yak and cow butter. Cholesterol content in yak butter was pronounced (325 mg/100 gm fat) than in cow butter (223 mg/100 gm fat). The cow milk lipid oxidation rate was faster and higher compared to the yak milk lipid. Polar lipid content in yak butter lipid was higher than in cow butter lipid. reported to be rich in fat (6～10),protein(5.5 Introduction: ),andminerals2). Yak milk fat comprises a major portion of the Himalayan people's food in- The yak is a large animal that looks like a walk- take. These people have been consuming yak but- ing shag rug and has been used for its milk since ter from ancient times as food, medicine to heal ancient times. People in the highlands of the wounds and they also use it to worship the gods Himalaya use yak milk for the production of due to its purity. In Himalayan areas there is no cheese, churpi, ghee, butter, buttermilk, and dahi regular supply of plant-originated oils, so the only (yogurt). oil utilized is yak butter and ghee in their daily diet. Yaks are found in the highlands of the Nepalese Yak butter is only deˆned by organoleptic Himalayas, Tibet, Indian Kasmir, Mongolia, and parameters such as taste, odor and color. Present- Bhutan up to the altitude of 5200 m above sea lev- ly, yak butter is being used in the Himalayas as a el. They can survive in temperatures as low as －40 primary ingredient to produce a variety of food °C with little atmospheric oxygen. The estimated items and diŠerent dairy products including butter yak population (Bos grunniens)1) in the world is tea. Thus, more emphasis must be given to the about 12 million. Their maximum life span is 25 study of yak milk fat and fatty acid composition for years. Yaks usually graze on grasses, herbs, and its wide range of use. lichens in meadows during summer season and Lipids serve as precursors for beneˆcial biologi- consume straw and dry leaves in the winter season. cally active compounds such as prostaglandins, Yaks have di‹culty ˆnding su‹cient dry grasses steroid hormones, and bile acids1). Although there during winter, so their milk production decreases. is controversy as to the role of saturated and trans The female yak gestation period is 9 months, and fatty acids in cardiovascular disease, the science she gives birth to a single calf. The female yak behind the eŠects of dietary fat on human health is yields a maximum of 1～2Lmilk/day. Its milk is so complex that there are no simple and compre- 第巻 hensive answers to the question in the êld at the present time. Yak milk fat has a unique taste and Preparation of fatty acid methyl esters (FAME). speciˆc ‰avor with a high nutritive value as claimed by the Himalayan people. Yak cheese and Lipids were saponiêd with 1 N alcoholic potas- butter are the major and most expensive milk sium hydroxide by heating at 90°C for 50 min. products sold in Nepalese market. Thousands of Saponiêd and unsaponiêd matters formed during Nepalese farmers are being engaged in yak milk heating were separated by diethyl ether and water. production due to the great market demand for yak Then the fatty acids were extracted from the mix- milk products. ture with diethyl ether. Fatty acid methyl ester The objective of this study is to investigate the (FAME) of yak or cow lipid was prepared by the fatty acid compositions and fat-soluble vitamins in addition of BF3 (7,v/v) in anhydrous methanol yak butter as well as yak lipid oxidation kinetics by heating at 100°Cfor15min.ThentheFAME and then compare with those of fresh cow butter was extracted, clariêd, dried, and stored at －30 lipids. °Cbeforeuse. Materials and Methods GLC of FAME The yak butter was produced in the Himalayas Fatty acid methyl ester preparations were inject- of Nepal and the cow butter was prepared at the ed (1 ml ) using the split mode. The carrier gas was experimental farm of Rakuno Gakuen University, helium, and the split ratio was 1001 at 250°C. Japan. Selected purebred of yaks at mid-lactation Oven temperature was programmed for 70°Cfor4 period were chosen for milking. Yaks were grazed min, then increased from 70 to 175°Cat13°C/min, on mature meadows when milked for butter held at 175°C for 27 min, raised to 215°Cat4°C/min production. No commercial feed or medical treat- and ˆnally held at this temperature for 31 min. ment had been used for these yaks. Yak and cow Chromatograms were documented with a comput- butter was produced by traditional technology, ing integrator (Turbochrom Work Station).Stan- churning the cream in a wooden butter churn. dard fatty acid methyl ester mixtures were used to HPLC and GLC-grade n-hexane, acetic acid, calibrate the gas chromatograph system using methanol, sodium chloride, pyrogallol acid, ethy- reference standards (GLCReference standard, lene acetate were purchased from Kanto Chemi- fatty acid methyl esters: GLC90). cals Industries, Ltd., Japan. Identiˆcation of fatty acids was made by com- paring the relative retention times of fatty acid Extraction of yak and cow butter lipids: methyl ester and peak areas from samples with those of the standards. The FAME standard con- Lipids were extracted from yak and cow butter tained C4 to C24 fatty acid methyl esters, which by a modiˆcation of the method of Bligh and were purchased from Nu-Chek Prep, Inc., USA. Dyer3). Yak or cow butter was dissolved in chloroform and methanol (21, v/v).Thechloroform HPLC method for tocopherols and vitamin A: was removed by rotary vacuum evaporator to ex- tract lipids. In the subsequent step the residual A measured amount of yak or cow lipid (1.5 gm) mass was mixed with chloroform, methanol and was mixed with 0.5 ml of (1,w/v) NaCl, 10 ml water (843, v/v). The composite mass was of (3,v/v) pyrogallol acid and 1 ml of (60,w/ sedimented and the lower phase containing lipids v) KOH. The mixture was heated at 70°Cina was collected. The chloroform portion was re- water bath for 30 min. Then the mix was cooled to moved from the lipid mass by a vacuum evaporator room temperature and combined with 22.5 ml of (1 and the extracted lipids were stored at －45°Cbe- ,w/v) NaCl and 15 ml of (19, v/v) ethylene fore use. acetate: n-hexane. The composite mix was cen- trifuged at 3000 rpm for 5 min and the upper layer 第号 was collected, evaporated, and concentrated. Fi- nally, the concentrated sample was dissolved with Polar and neutral lipid extraction n-hexane and used in the subsequent experiments. and identiˆcation The standard solutions of the vitamins for analyzing butter lipid samples were prepared to a The column chromatography technique was ap- concentration of 1 mg/ml. Normal-phase HPLC plied to separate the polar and neutral lipids in yak with UV detector (Hitachi, Co., Ltd),andcolumn and cow butter lipids. The TLC technique was ap- from Shimadzu, Co., Ltd, were used to analyze the plied to distinguish the quality of polar and neutral samples. The HPLC was set at 30°Candthe‰ow lipids. TLC plates were at ˆrst dried in hot air oven rate was ˆxed 1 ml/min using a mixture of at 110°C for 2 hrs. After heating, the plates were methanol and water (91, v/v) as an eluent. The cooled and 10 ml of each lipid was introduced onto eŒuent was monitored at 325 nm. Vitamin A, and the TLC plates and eluted with hexane, diethyl all trans-retinol (95) were purchased from Sigma ether, and acetic acid (80301, v/v). In the sub- Chemical Co., USA. Vitamin E which contained a sequent step, the plates were sprayed with 50 bgand dtocopherols was used as the standard. H2SO4 and heated indirectly at 180°Cfor30min. Tocopherols and retinol were quantiêd with an The polar and neutral lipid bands in the TLC plate external standard method in which quantiˆcation wereidentiêdbycomparisonwithstandard.Polar was based on peak areas. and nonpolar fatty acid standards were used from the stock of our laboratory chemical store. GLC procedure for yak and cow lipid cholesterol Fatty acid extraction and methylation of polar and neutral lipids were proceeded as mentioned el- Yakorcowlipidwassaponiêdwith1Nalcohol- sewhere.

Load more