About Gac Fruit in Vietnam

Fatty Acid and Carotenoid Composition of Gac (Momordica cochinchinensis Spreng) Fruit

 

BETTY K. ISHIDA,* CHARLOTTA TURNER, MARY H. CHAPMAN, AND THOMAS A. MCKEON

Western Regional Research Center, Agricultural Research Service, United States Department of

 

Agriculture, 800 Buchanan Street, Albany, California 94710

 

 

 

In this study, we analyzed fatty acid and carotenoid composition of fruit tissues, including seed ( which are surrounded by a bright red, oily aril) of Momordica cochinchinensis Spreng, known as gac in Vietnam. Carotenoid content was analyzed by reversed-phase HPLC, using a C30 column and a method separating cis- and trans-isomers of the major carotenoids in this fruit. Mean values obtained in aril tissues were 1342 µg trans-, 204 µg cis-, and 2227 µg total lycopene; 597 µg trans-, 39 µg cis-, and 718 µg total â-carotene; and 107 µg R-carotene/g FW. Mesocarp contained 11 µg trans-, 5 µg cis-â-carotene/g FW, trace amounts of R-carotene, and no lycopene. Gac aril contained 22 % fatty acids by weight, composed of 32% oleic, 29% palmitic, and 28% linoleic acids. Seeds contained primarily stearic acid (60.5%), smaller amounts of linoleic (20%), oleic (9%), and palmitic (5-6 % ) acids, and trace amounts of arachidic, cis-vaccenic, linolenic, and palmitoleic, eicosa-11-enoic acids, and eicosa-13-enoic (in one fruit only) acids.

 

Momordica cochinchinensis Spreng, a Cucurbitaceae, is indigenous throughout Asia and used as food and for medicinal purposes. The fruit, called gac in Vietnam, are only picked there at maturity from August through February when they are red and the seeds are hardened. Aril, the oily, red, fleshy pulp surrounding the seeds, has a palatable, bland to nutty taste and is cooked along with seeds to impart its red color and flavor to a rice dish, xoi gac, served at festive occasions (e.g., weddings) in Vietnam (1). Seeds are used in Chinese traditional medicine. Early recognition of the value of gac fruit focused on â-carotene concentration (2). West and Poortvliet (3) measured 188.10 µg of â-carotene and 891.50 µg total carotenoids/g fresh weight (FW) in gac aril. Chemical analyses by Vuong et al. (1) showed that gac aril contained 175 µg of â-carotene and 802 µg of lycopene/g FW (1). Lycopene concentration in gac aril is in marked contrast to the 40-60 µg lycopene/g FW found in fieldgrown tomatoes (4, 5), which is the major source of lycopene in the Western diet. Lycopene, of course, is of interest, because of the correlation of reduced risk of certain cancers, such as prostate (6-8) and lung (7, 9), with the consumption of tomato products, which is attributed to protection by free radicalquenching lycopene ([1], 11). In addition, studies on AfricanAmerican men having prostate cancer show that daily consumption of lycopene from tomato sauce significantly increased 

 

lycopene content of plasma and the prostate gland, decreased their prostate-specific antigen levels (a marker for prostate cancer), and showed significant clinical and metabolic improvements (12). Antioxidants seem to have protective effects against cardiovascular diseases (13-16) and a number of common eye diseases, such as cataracts and age-related macular degeneration (17-20). In addition, because â-carotene is a precursor to Vitamin A, gac fruit is a potentially valuable source of this vitamin and could be extremely useful in fighting Vitamin A deficiency, which is common in third world countries (1).

 

According to a report by Vuong et al. (1), gac aril also contains 102 mg oil/g of FW. These authors also found that, of the total fatty acids in gac aril, 69% are unsaturated, and 35 % of these are polyunsaturated (21). Vuong and King (21) reported that the oil in gac aril contains significant amounts of Vitamin E (334 µg/mL), as well as 3020 µg of lycopene and 2710 µg of â-carotene (and isomers)/mL, making gac aril with its oil a valuable potential source of antioxidants.

 

Gac seed composition is of interest because of its use in traditional Chinese medicine. Recently, a pentacyclic triterpenoid ester was isolated from the seed (22).

 

Since the completion of this study, a report on carotenoid pigments in gac fruit was published (23). Our study, in addition to identification of major carotenoids, includes carotenoid profiles, measuring both trans- and cis-isomers of lycopene and â-carotene. We also provide a detailed fatty acid analysis of gac seed and aril, as well as the weight distribution of anatomical components of the fruit.

 

MATERIALS AND METHODS

Fatty Acid Analysis. Materials. Gac fruit were purchased from two Asian markets (Vinh Phat and Shun Fat) in Sacramento, California. Fruit had been shipped frozen by commercial exporters from Vietnam to California (storage temperature during transport unknown) and were left frozen in a -20 °C freezer until ready for analyses. Gac fruit were divided carefully into its anatomical components: skin, mesocarp, connective tissue, aril, and seed. Most of the seeds used for analyses were taken from purchased, frozen fruit that had been shipped from Vietnam; a few were a gift from the Guangzhi Province in Western China.

 

Trifluoroacetic anhydride, 3-pyridyl carbinol, 4-(dimethyl amino) pyridine, and cyclohexane were obtained from Sigma-Aldrich (St. Louis, MO). Nonadecanoic acid methyl ester and GLC-68 fatty acid methyl ester (FAME) standard mixture were obtained from Nu-Chek Prep, Inc. (Elysian, MN). Heptadecanoic acid methyl ester and anhydrous acetyl chloride were purchased from Alltech (Deerfield, IL), and butylated hydroxytoluene (BHT) was obtained from Spectrum Chemical MFG Corp. (Gardena, CA). Anhydrous sodium sulfate was purchased from J. T. Baker Inc. (Philipsburg, NJ), and 2-propanol, methanol, hexane, toluene, diethyl ether, and dichloromethane were obtained from Fisher Scientific (Fair Lawn, NJ). Potassium hydroxide, sodium thiosulfate, sodium chloride, and potassium bicarbonate were obtained from Mallinckrodt Laboratory Chemicals (Philipsburg, NJ). Ethanol was purchased from AAPER Alcohol and Chemical Co. (Shelbyville, KY). The water used was double distilled, and all chemicals and solvents used were of reagent grade.

 

Method. Gac aril and mesocarp were thoroughly homogenized using a household-type coffee grinder (Mr. Coffee, Cleveland, OH; Model IDS59) and then dried using a vacuum centrifuge (7-8% dry weight). Gac seed was homogenized using a mortar and pestle. Gac sample (0.05 g) was accurately weighed into 10-mL glass tubes. The lipids were extracted using 2 mL of hexane/2-propanol (8:2, v/v) containing 50 µg/mL of BHT. Internal standard (nonadecanoic acid methyl ester) was added, and the extraction took place at 55 °C for 30 min with shaking every 10 min. Extracts were filtered and dried over sodium sulfate, and the solvent was evaporated under nitrogen. Oil weight was determined gravimetrically. Toluene (0.5 mL) was then added, and the lipids were methylated for 1 h at 80 °C using methanolic hydrogen chloride (3%), as described by Christie (24). Resulting FAMEs were dissolved in 10 mL of cyclohexane (0.01% BHT) for GC analysis.

 

Quantitative analysis was carried out by GC-FID using a HewlettPackard 6890 GC system with split injection connected to a 7673 automatic liquid sampler (Agilent Technologies, Palo Alto, CA).

 

Separation was achieved on a DB-WAX column (20-m × 0.12-mm i.d., 0.18-µm film thickness) purchased from J & W Scientific, Agilent Technologies. The injector and detector temperatures were 250 and 280 °C, respectively. The column temperature program was 100 °C for 1 min, then increased by 5 °C/min to 250 °C, and held at 250 °C for 1 min. Standard solutions of a mixture of FAMEs at three different concentrations in the range of 5 to 150 µg/mL were used for generating standard calibration curves. A 50-µL sample of methyl heptadecanoate (1 mg/mL) was added as internal standard to 1-mL aliquots of each standard sample. Injections of 1 µL were used, and duplicate determinations were performed.

 

Identification of peak components was achieved on a HewlettPackard 5890 GC system connected to a 5970A mass selective detector (Agilent Technologies). Split injection was applied, and the same type of column and temperature program as described above was used. Comparison to mass spectra of known FAMEs was used to identify each peak. In addition, double-bond locations for the unsaturated fatty acids were determined by interpreting spectra from picolinyl derivatives of free fatty acids (FFAs), employing the methodology described by Christie (24).

 

Carotenoid Analysis. Materials. Dichloromethane, 99.9%, HPLC grade and anhydrous tetrahydrofuran (THF), 99.9%, were purchased from Aldrich Chemical Co. (Milwaukie, WI). Methanol (MeOH), HPLC grade, methyl-tert-butyl ether (MTBE), and ethyl acetate (EtOAc), HPLC grade, were purchased from Fisher Scientific (Fair Lawn, NJ). Lycopene for standard solutions was extracted and purified from berries of autumn olive (Elaeagnus umbellata Thunberg) plants, which were a gift from Beverly A. Clevidence (Beltsville Human Nutrition Research Center, UDSA, ARS, Beltsville, MD). â-Carotene (type IV from carrots), mixed isomer carotene (from carrots), and lutein (from alfalfa) were purchased from Sigma Chemical Company (St Louis, MO).

 

Methods. Dry weights of gac aril and mesocarp tissues were determined using a Model AVC-80 microwave moisture/solids analyzer (CEM Corporation, Mathews, NC). Samples of tissue were placed between two tared glass-fiber pads and heated at 50% power for 4.5 min. Moisture content (or percent solids) was determined by difference in weight after drying.

 

Carotenoids were extracted from gac fruit tissues by the modification (25) of the method described by Ishida et al. (26). Tissues were excised carefully from gac fruit to avoid cross contamination, especially between aril and mesocarp, then homogenized, using an Omni-Mixer ( Sorvall/ DuPont Medical Products, Newtown, CT). Gac samples were first extracted, using 5 mL of ice-cold MeOH/homogenate, then the suspension was vacuum-filtered through two layers of Whatman No. 1 filter paper on a Bu¨chner funnel and washed with an additional volume of ice-cold MeOH. The filtrate was saved. The remaining dehydrated residue on the filter was carefully resuspended in 5 mL of dichloromethane and extracted by vacuum filtration three times to remove the red/orange color. The filtrate from the MeOH used to dehydrate the tissue homogenate was combined with dichloromethane extracts. Water (5 mL) was then added to the combined extracts and mixed thoroughly, using a vortex mixer. After phase separation, the bottom yellow layer was transferred to a small vial and dried under nitrogen gas. The residue was then resuspended in 2 mL of THF and passed through a 0.45-mm poly(tetrafluoroethylene) filter ( Alltech Associates, Inc., Deerfield, IL). Throughout these procedures, care was taken to keep samples ice-cold and protect them from exposure to light. Extracts of gac fruit tissue were analyzed for carotenoid content by separation followed by quantitation using a reversed-phase HPLC system, consisting of a Waters (Milford, MA) 2690 Separation Module, 996 Photodiode-Array Detector, auto injector, and column temperature regulator. Separations were accomplished using a reversed phase, analytical (250 × 4.6-mm I. D.), 3-µm particle diameter polymeric C30 column (YMC Inc. Wilmington, NC). The system was purged daily for 3 min each with MTBE, MeOH, and EtOAC. The C30 column was then conditioned with elution solvent at a flow rate of 1 mL/min for 10 min. Carotenoids were separated isocratically using a mobile phase of 40% MTBE 50%, MeOH, and 10% EtOAc (v/v). Injection volumes ranged from 5 to 20 µL. Column temperature was maintained at 28 °C. The photodiode array detector was set between 300 and 700 nm to detect all of the peaks of interest eluted from the column. Standard compounds: xanthophyll (Sigma; 70% pure from alfalfa); lycopene extracted from autumn olive (Elaeagnus umbellate Thunberg) (gift from B. A. Clevidence, USDA Beltsville Human Nutrition Research Center), purified and found to be 97% trans isomer, was used as a standard for quantitation; â-carotene (Sigma; synthetic, Type 1, 95% pure), and R-carotene (Sigma; from spinach, substantially free of â-carotene) were used to check retention times on the HPLC. Phytoene, phytofluene, zeaxanthin, and â-cryptoxanthin were detected by examining spectra of compounds under chromatographic peaks and comparing to known, published spectra of carotenoids to identify these compounds, which are found commonly in fruit such as tomato, guava, and citrus.

 

 

Some products from Vietnam Gac

 

 

Vietnam Gac oil