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Sweet potato lipids
CHAPTER 6
Sweet potato lipids Tai-Hua Mu and Miao Zhang Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences; Key Laboratory of Agro-Products Processing, Ministry of Agriculture and Rural Affairs, Beijing, People’s Republic of China
Overview of lipids Definition of lipids Lipids, as a potential functional ingredient, are present in almost all foods and play an important role in nutrition and the sensory aspects of food. Lipids are mainly divided into neutral lipids (NLs), glycolipids (GLs), and phospholipids (PLs). It was reported that the contents of NLs, GLs, and PLs in total lipids (TLs) of potato tubers were 21%, 22%, and 47%, respectively (Ramadan and Oraby, 2016). The NLs, GLs, and PLs contents in the major Indian Garcinia fruit, which has different varieties, range from 37.6% to 95.8%, 3.2% to 55.9%, and 0.8% to 6.8%, respectively (Patil et al., 2016). Fatty acids (FAs) play an important role in lipids, such as linoleic acid (C18:2), linolenic acid (C18:3), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), showing effects on diverse physiological processes and thus have an impact on normal health and chronic diseases (Benatti et al., 2004).
Extraction methods of lipids Mechanical squeezing method Mechanical squeezing is one of the most long-standing methods for obtaining lipids. Lipids are obtained by being squeezed out, mainly by mechanical force, and this process mainly involves physical changes, such as friction heating, material deformation, oil separation, water evaporation, etc. At present, this method is still widely used by some enterprises. The advantages of the mechanical squeezing method are that it is convenient to operate and requires less investment. However, there are still some shortcomings, such as the low content of bioactive substances in the oil and the low yield of oil. At the same time, due to the effects of changes in water and temperature, some biochemical reactions will Sweet Potato DOI: https://doi.org/10.1016/B978-0-12-813637-9.00006-5
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occur, for example, the oil is easily oxidized, and the protein is prone to denaturation. Bligh-Dyer method The Bligh-Dyer method is a widely used method for lipid determination in biologics and food. The outstanding advantages of this method are the high extraction rate of oil, low residual rate, and high production efficiency—it can achieve continuous processing with low energy consumption. However, some dangerous flammable solvents are used in this method, and the health problems caused by residual solvents in oil meal are also serious (Radin, 1988). Other novel lipid extraction methods Some novel lipid extraction methods have been investigated, for example, simultaneous distillation and extraction (Tanzi et al., 2013), ultrasoundassisted extraction (Adam et al., 2012), microwave-assisted extraction (Cheng et al., 2013), and supercritical fluid extraction (Halim et al., 2011). However, the methods above still require high energy inputs, high temperature, and take a long time, and are currently limited at the laboratory scale. Yang et al. (2014) extracted lipids from wet microalga Picochlorum sp. by using ethanol at room temperature, and indicated that the yield of lipids could be comparable to that by the Bligh-Dyer method without significant differences in FA composition and lipid classes distribution.
Physiological functions of lipids Lipids present different physiological functions, including improvements in the bioavailability of functional components, as well as having hypolipidemic, antiatherosclerosis, antimicrobial, antiinflammatory, memory improving, diabetes prevention, and anticancer properties, which have been summarized here. Improvement on the bioavailability of functional components It has been reported that some kinds of lipids could improve the bioavailability of some functional components. PLs are the major carriers for active molecules of plants; they interact with plant constituents, protect plant active components from degradation, and increase their bioavailability by imparting lipid solubility to them (Khan and Krishnaraj, 2014).
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PLs and glyceroglycolipids could markedly affect the uptake of carotenoids by human intestinal Caco-2 cells by solubilizing in mixed micelles via decreasing intercellular barrier integrity, suggesting their potential to modify the intestinal uptake of carotenoids (Kotake-Nara et al., 2015). The stability and biological availability of carotenoid fucoxanthin was improved when encapsulated in chitosan-glycolipid nanogels (Ravi and Baskaran, 2015). Hypolipidemic effect Yang and Jiao (2008) investigated the effects of soy lecithin on blood lipids in patients with hyperlipidemia. According to the blood lipid levels, 100 patients with hyperlipidemia were divided into the control and experimental groups, with 50 cases in each group. The patients in the experimental group took soy lecithin 20 g per day, and the control group received the same dose of placebo for 8 weeks. Serum total cholesterol (STC) and triglyceride (TG) levels were measured before and after taking soy lecithin or placebo. The results showed that no significant difference was observed in levels of STC and TG between the experimental group and control group before taking. However, after taking soy lecithin for 8 weeks, STC and TG levels in the experimental group were significantly lower than the starting levels and the levels in the control group, suggesting that soybean lecithin could significantly decrease the serum lipid level in the hyperlipidemic population. The lipid regulation function might be through inhibiting TG synthesis and eliminating cholesterol in vivo and in TC emulsions. Waststrate and Meijer (1998) found that STC and TC levels decreased significantly with an intake of 1.6 2 g/person/day of plant sterols. Nyugen et al. (1999) studied TC lowering effects of plant stanol esters, and the results showed that the total STC and low-density lipoprotein (LDL) cholesterol decreased by 6.4% and 10.1% after intake of 2 3 g/ person/day of plant stanol esters, respectively. Gylling and Miettinen (2005) indicated that plant sterols and stanols could inhibit the absorption of cholesterol that was endogenous and produced by diet in the small intestine. The authors indicated that the main reason is that free sterols and stanols could replace cholesterol from microcapsules mixed with bile acid, thus reducing the intestinal absorption of cholesterol, and also could compete with cholesterol during its absorption in the microvillous membrane.
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Antiatherosclerosis effect Karantonis et al. (2002) separated the TLs of oils from corn, olive, soybean, sunflower, and sesame into PLs and NLs by using a new extraction technique, which were further separated into different components by high-performance liquid chromatography. Among the different components of lipids, PL showed strong inhibitory effects on the plateletactivating factor, suggesting the preventive effects of PL on atherosclerosis. Volger et al. (2001) found that plant sterols had inhibitory effects on atherosclerosis, and its mechanism of action was mainly by reducing the STC. LDL oxidation was a major cause of atherosclerosis, and there was a positive correlation between the oxidation degree of LDL and STC content, so reducing STC content could inhibit the occurrence of atherosclerosis effects. Antimicrobial effect Jing and Qi (2001) isolated three kinds of glyceroglycolipids from Serratula strangulate, and determined their antibacterial activities. The results showed that three kinds of glyceroglycolipids had significant inhibitory effects on Bacillus subtilis, Escherichia coli, and Staphylococcus aureus. Zhang et al. (2013) used Candida albicans and E. coli as the tested bacteria, and determined the antibacterial activities of 10 saturated fatty acids (SFAs), 6 unsaturated fatty acids (UFAs), 2 FA methyl ester, 3 FAs, 4 fatty alcohols, and 9 FA monoglycerides. It was suggested that the antimicrobial activity of FAs and their derivatives was related to the carbon chain length of FAs, the number and position of double bonds in UFAs, and the types of substituent groups. Qian et al. (2012) found that the minimum inhibitory concentration of dirhamnoside derivative compound 7 (DDC7) and cleistrioside-5 (C5) on S. aureus (MIC) is 16 μg/mL, and the mechanism might be due to DDC7 and C5 having a similar chemical structure with the sugar chain of the β-1,4 glycosidic bond of the S. aureus peptidoglycan, which could destroy the biosynthesis or glycosidic linkage of bacterial polysaccharides. Hu et al. (2012) indicated that sophorolipids could effectively inhibit the growth of S. aureus in a concentration-dependent manner, even in acidic and high temperature conditions. Antiinflammatory effect GLs from spinach could suppress lipopolysaccharides-induced vascular inflammation through endothelial nitric oxide synthase and NK-κB signaling in human umbilical vein endothelial cells, suggesting that GLs from
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spinach might have a potential therapeutic utilization for inflammatory vascular diseases (Ishii et al., 2017). Milo et al. (2002) investigated the effects of short-chain FAs on the levels of proinflammatory cytokines in miniature pigs, and indicated that short-chain FAs could increase the intestinal proinflammatory cytokines IL-1 and lL-6 level to inhibit inflammation. Larsen et al. (2003) isolated monogalactosyl diacylglycerol (MGDG) from rose hip through active tracking detection technology, and found that MGDG presented an antiinflammatory effect without cell toxicity in an in vitro experiment. Bruno et al. (2005) isolated MGDG, digalactosyl diglyceride (DGDG), and sulfoquinovosyl diacylglycerol (SQDG) from thermophilic cyanobacteria, and showed that MGDG, DGDG, and SQDG could inhibit the swelling of mouse ear in a dosedependent manner. In addition, some clinical trials showed that a diet containing cod liver oil could significantly reduce the joint swelling in patients with rheumatoid arthritis, while the intake of an ordinary diet had no effect (James et al., 2000; Kremer, 2000). The mechanism of antiinflammation activities of cod liver oil was as follows: (1) through influencing the metabolism of peanut arachidonic acid (Simopoulos, 2002); (2) by changing the structure of PLs in the cell membrane (Calder and Grimble, 2002); and (3) by acting on the mediators of inflammation and immunity (Adam et al., 2003). Memory improving effect It was well known that EPA and DHA could improve memory and eyesight, especially to promote the growth and development of infant brain cells. Avrova et al. (2002) found that ganglioside GM1 could improve the memory function, and the mechanism was that GM1 improved the neuroprotective effects of the glial cell line and brain-derived neurotrophic factor, decreased the concentration of free radicals, thereby reducing the generation of nitric oxide, and then decreased the death of nerve cells. Chung et al. (1995) indicated that egg yolk lecithin could improve the memory of mice with dementia, and improve the concentration of acetylcholine in the brain of mice. Diabetes prevention effect Suresh and Das (2001, 2003) found that cooking oils rich in n-3 PUFA (EPA and DHA) and n-6 PUFA (GLA and AA) could prevent diabetes, and alleviate oxidative stress induced by diabetes. Delarue et al. (2004) indicated that the mechanism of n-3 PUFA on diabetes protection was as
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follows: (1) inhibiting the activity decrease of phosphatidylinositol 3kinase (PI3-K) and the failure of glucose transporter (GLUT4) in muscle; (2) preventing the decrease of GLUT4 expression in adipose tissue; and (3) inhibiting the activity of hepatic 6-glucokinase. Anticancer effect The anticarcinogenic effect of lipids was shown in several types of cancers including skin, melanoma, colon, and breast cancers. The addition of n-3 PUFAs in the diet could reduce the number of epithelial degeneration crypt lesions in mice induced by reactive oxygen species, thus preventing the development of colon cancer (Murray et al., 2002). DHA could reduce the positioning function of sarcoma protein (RSP) in epithelial cells of rats, inhibit the activation of RSP, reduce the binding level of RSP by guanosine triphosphate, and thus reduce the incidence of colon cancer in rats (Collett et al. 2001). It had been proved that the GLs components from plants could inhibit the proliferation and promote the differentiation of cancer cells. Morimoto et al. (1995) found that MGDG isolated from green algae had a strong inhibitory effect on lymph cancer cells. Maeda et al. (2008) indicated that GLs isolated from spinach presented a strong inhibitory effect on cervical cancer cells with the median lethal dose (LD50) of 57.2 μg/ mL. In addition, it was reported that MGDG, DGDG, and SQDG from freshwater cyanobacterium showed a certain inhibition effect on lymph cancer cells, among which MGDG and DGDG showed a higher inhibition effect than SQDG; and DGDG also presented a strong inhibitory effect on skin papilloma (Tokuda et al., 1996).
Lipids and fatty acid composition of different varieties of sweet potato Overview of sweet potato Sweet potato (Ipomoea batatas (L.) Lam.) is an important economic crop that can successfully adapt to a wide range of habitats, including marginal regions. It is a dicotyledonous plant belonging to the family Convolvulaceae with approximately 50 genera and over 1000 species (Woolfe, 1992). Artificial selection of sweet potatoes, as well as the occurrence of natural hybrids and mutations, has resulted in the existence of a very large number of cultivars, which differ in many of their properties, including physical appearance and texture of the tuber (Zhang and Oates,
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1999). Sweet potatoes are widely cultured in China, which has the highest production in the world with approximately 71.54 million tons produced annually, resulting in 68% of the world’s production, and sweet potatoes are the fifth most common food crop after rice, wheat, maize, and potato (FAOSTAT, 2017). Sweet potato has unique nutritional and functional properties (Wang et al., 2016), and is a valuable source of food, animal feed, and industrial raw materials.
Composition of sweet potato lipids To better understand the lipids and FA composition of different varieties of sweet potato, sweet potatoes from 11 representative cultivars were obtained from Zhejiang (Xinxiang No.1, Zheshu 7518), Hebei (Beijing 553, Jishu 98, Wutang No.1), Jiangsu (Xushu 18, Xushu 22, Xushu 27, Xushu 28, Shangshu 19), and Beijing (Mixuan No. 1), respectively, of which the proximate composition, lipids, and FA composition were determined. Table 6.1 shows the proximate composition of sweet potatoes. The moisture content ranged from 60.13% to 78.43%. The moisture content in Xushu 27 (78.43%) and Beijing 553 (75.28%) was significantly higher than those in Zheshu 7518 (60.13%) and Mixuan No.1 (61.21%). Starch was the main component of sweet potato, and the starch content ranged from 54.59% to 76.95%, which was similar to the values reported by Ravindran, Sivakanesan, and Rajaguru (1995). Xushu 27 had the highest starch content (76.95%), whereas Jishu 98 had the lowest starch content (54.59%). Protein content ranged from 3.53% to 9.13%. Woolfe et al. (1992) reported that the protein content in sweet potato was higher than cassava, plantain, and taro, but lower than potato and yam. Crude fiber content ranged from 1.80% to 3.65%, which was similar to the report by Zakir et al. (2006), where Xushu 27 had the highest crude fiber content (3.65%) and Wutang No.1 had the lowest (1.80%). Similarly, there were significant differences in ash content among the sweet potato cultivars (P , .05), and the content ranged from 2.32% (Zheshu 7518) to 3.95% (Shangshu 19). Ash content is an important indicator in evaluating mineral element content, and the minerals in sweet potato have been identified as Ca, P, Mg, Na, K, Fe, Zn, and Cu (Bouwkamp, 1985). The TLs content of sweet potatoes of different cultivars ranged from 0.72% to 1.44%, and these results were similar to those of Ravindran et al. (1995). Fat is involved in the insulation of body organs and in the maintenance of body
Table 6.1 Proximate composition of 11 sweet potato cultivars (%, DW). Cultivar
Moisturea
Starch
Protein
Crude fiber
Ash
Crude lipid
NLs
GLs
PLs
Xushu 28 Xushu 27 Mixuan No.1 Jishu 98 Xushu 22 Xushu 18 Shangshu 19 Beijing 553 Xinxiang No.1 Zheshu 7518 Wutang No.1
67.29 6 0.14def 78.43 6 0.13a 61.21 6 0.07g
72.25 6 1.39ab 76.95 6 1.53a 65.43 6 1.02b
6.23 6 0.26e 5.42 6 0.07f 7.00 6 0.01d
2.64 6 0.79c 3.65 6 1.19a 2.27 6 0.68d
2.46 6 0.81g 3.83 6 0.65b 2.41 6 0.14g
0.97 6 0.11cd 0.93 6 0.06d 1.06 6 0.04c
54.18 6 1.82ab 56.76 6 2.23ab 55.26 6 6.67ab
37.65 6 0.88cde 36.10 6 0.54e 36.08 6 4.32ef
8.17 6 0.13bc 7.14 6 0.26c 8.69 6 7.15bc
67.94 6 0.13de 72.3 6 0.67c 68.94 6 0.13d 72.40 6 0.50c 75.28 6 0.44b 65.15 6 0.17f
54.59 6 0.49c 66.33 6 0.53b 71.47 6 0.23ab 67.47 6 0.58ab 66.87 6 0.67b 73.88 6 0.72ab
9.13 6 0.35a 7.90 6 0.33b 3.72 6 0.26h 4.27 6 0.11g 5.32 6 0.13f 3.65 6 0.19hi
2.17 6 0.72d 3.51 6 0.76a 2.35 6 0.49cd 3.13 6 0.35b 3.76 6 1.29a 3.05 6 1.80b
2.73 6 0.22e 3.63 6 1.02c 2.33 6 1.16h 3.95 6 0.62a 3.15 6 0.87d 2.60 6 0.20f
0.72 6 0.08e 0.99 6 0.10cd 1.00 6 0.01cd 1.44 6 0.03a 0.98 6 0.12cd 1.25 6 0.07b
36.74 6 0.42d 61.04 6 1.87a 50.95 6 1.19bc 52.96 6 7.13b 55.79 6 0.21ab 44.90 6 0.12c
45.49 6 0.34ab 31.24 6 0.18g 42.00 6 0.22bc 31.30 6 0.10fg 36.38 6 3.06ed 41.03 6 4.44bcd
17.79 6 2.98a 7.72 6 0.16c 7.05 6 0.22c 15.73 6 2.49ab 7.85 6 2.19c 14.07 6 7.89abc
60.13 6 2.29g 66.42 6 3.53ef
68.59 6 0.35ab 72.71 6 0.68ab
3.53 6 0.06i 7.88 6 0.08c
2.08 6 0.67de 1.80 6 0.58e
2.32 6 0.34h 2.79 6 0.19e
0.95 6 0.16d 0.91 6 0.03d
55.56 6 0.50ab 33.70 6 5.15d
30.29 6 0.74g 49.25 6 1.62a
14.14 6 0.66abc 17.07 6 0.53a
Values within columns with different letters are significantly different (P , .05). NLs, Neutral lipids; GLs, glycolipids; PLs, phospholipids. a Moisture content was expressed in g/100 g FW.
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temperature and cell function, and sources of fats such as omega-3 and omega-6 FAs are required for the digestion, absorption, and transport of vitamins A, D, E, and K. To further understand the differences of lipids composition of sweet potatoes of different varieties, the TLs were separated into NLs, GLs, and PLs using silica gel column chromatography. The composition of lipid classes is shown in Table 6.1. NLs were the main component of sweet potato TLs, and TGs were most abundant in NLs (Walter, Hansen and Purcell, 1971); these play an important role in maintaining energy metabolism. The content of NLs in sweet potatoes ranged from 36.74% to 61.04%. Wutang No.1 had the highest content of NLs (61.04%), while Jishu 98 had the lowest (36.74%). The content of GLs ranged from 30.29% to 49.25%, and Zhushu 7518 had the highest content of GLs (49.25%) and Jishu 98 had the lowest (30.29%). It has been reported that GLs have significant antiproliferative, antimicrobial, antiviral, and antiinflammatory effects (Da Costa et al., 2016; Varamini et al., 2017). The content of PLs in sweet potato was limited, and ranged from 7.05% (Xushu 27) to 17.07% (Zheshu 7518). PLs from milk reduced plasma cholesterol concentrations, but did not change the low-density lipoprotein/high-density lipoprotein (LDL/HDL) ratio (Keller et al., 2013). Previous research indicated that the lipid composition of sweet potato was 42.1% NLs, 30.8% GLs, and 27.1% PLs (Walter et al., 1971). It has been reported that the composition of lipids in rice bran consists of 88.1% 89.2% NLs, 6.3% 7.0% GLs, and 4.5% 4.9% PLs (Hemavathy and Prabhakar, 1989). The composition of lipids extracted from millet seeds consisted of 85% NLs, 3% GLs, and 12% PLs (Osagie and Kates, 1984). Hemavathy and Prabhakar (1987) also reported that the TLs in fenugreek seeds consisted of 84.1% NLs, 5.4% GLs, and 10.5% PLs. Thus sweet potatoes are a good source of essential GLs and PLs.
Fatty acid composition of total lipids The composition of FAs in TLs is presented in Table 6.2. The FAs in sweet potatoes include palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3), and arachidic acid (C20:0), of which C16:0, C18:2, and C18:3 are abundant. The content of C16:0 ranged from 35.92% to 42.57%, and Xushu 27 had the highest C16:0 content (42.57%), whereas Jishu 98 had the lowest content (35.92%). C18:2 was the most abundant FA in sweet potato TLs, which
Table 6.2 Fatty acids composition of TLs from 11 sweet potato cultivars (%). Cultivar
Palmitic acid C16:0
Stearic acid C18:0
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20:0
SFA
UFA
SFA/ UFA
Xushu 18 Mixuan No.1 Xinxiang No.1 Wutang No.1 Xushu 28 Xushu 27 Xushu 22 Jishu 98 Shangshu 19 Beijing 553 Zheshu 7518
38.53 6 0.07de 41.34 6 1.62ab 40.42 6 0.25bc 39.78 6 0.25cd 38.34 6 0.20e 42.57 6 0.10a 39.96 6 0.12c 35.92 6 0.39g 37.55 6 0.88ef 38.4 6 0.18e 36.52 6 0.25fg
2.54 6 0.03de 2.62 6 0.14d 3.43 6 0.03a 2.38 6 0.03gf 2.61 6 0.01d 2.74 6 0.03c 2.95 6 0.00b 2.3 6 0.04g 2.47 6 0.01ef 2.12 6 0.01h 3.04 6 0.01b
1.68 6 0.01b 1.18 6 0.04d 1.36 6 0.01c 0.69 6 0.22f 1.27 6 0.01cd 1.21 6 0.14cd 1.2 6 0.01d 0.62 6 0.01f 2.11 6 0.02a 0.92 6 0.00e 1.63 6 0.04b
37.78 6 0.18d 37.96 6 0.78d 39.67 6 0.13c 38.43 6 0.02d 41.45 6 0.08a 35.2 6 0.28f 36.73 6 0.07e 39.48 6 0.20c 41.67 6 0.50a 40.48 6 0.15b 40.61 6 0.19b
18.95 6 0.25b 16.28 6 1.01e 14.54 6 0.16f 18.16 6 0.04cd 15.88 6 0.12e 17.7 6 0.28d 18.57 6 0.03bc 21.21 6 0.19a 15.65 6 0.32e 17.54 6 0.04d 17.73 6 0.01d
0.30 6 0.01cd 0.36 6 0.02a 0.35 6 0.00a 0.31 6 0.03bcd 0.26 6 0.01e 0.31 6 0.04bcd 0.36 6 0.01a 0.28 6 0.03de 0.33 6 0.03abc 0.35 6 0.01ab 0.29 6 0.01de
41.61 6 0.09de 44.61 6 1.74ab 44.45 6 0.28b 42.74 6 0.25cd 41.43 6 0.21de 45.87 6 0.17a 43.53 6 0.11bc 38.71 6 0.40g 40.59 6 0.86ef 41.09 6 0.17ef 40.06 6 0.23fg
58.41 6 0.08cd 55.42 6 1.75fg 55.57 6 0.28f 57.28 6 0.23de 58.6 6 0.21cd 54.11 6 0.71g 56.5 6 0.11ef 61.31 6 0.38a 59.43 6 0.84bc 58.94 6 0.18bc 59.97 6 0.23ab
0.71 0.80 0.80 0.75 0.71 0.85 0.77 0.63 0.68 0.70 0.67
Values within columns with different letters are significantly different (P , .05). SFA, Saturated fatty acid; UFA, unsaturated fatty acid.
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ranged from 35.2% to 41.45%, and Xushu 28 had the highest content (41.45%) and Xushu 27 had the lowest content (35.2%). The content of C18:3 ranged from 14.54% to 21.21%, and Jishu 98 had the highest content (21.21%) and Xinxiang No.1 had the lowest content (14.54%). The content of C18:0, C18:1, and C20:0 were relatively low, and ranged from 2.12% (Beijing 553) to 3.43% (Xinxiang No.1), 0.62% (Jishu 98) to 2.11% (Shangshu 19), and 0.26% (Xushu 28) to 0.36% (Xushu 22), respectively. The content of UFAs in sweet potatoes was greater than SFAs. Jishu 98 had the highest content of UFA (61.31%), while Xushu 27 had the lowest content (54.11%). It was reported that the FAs in rice mainly consisted of C16:0, C18:2, and C18:3 (Yoshida et al., 2012), and the FA composition was very similar to that of sweet potatoes.
Fatty acids composition of neutral lipids The FAs composition of TLs is presented in Table 6.3. The UFA in sweet potato TLs primarily consisted of palmitic acid (C16:0), linoleic acid (C18:2), and linolenic acid (C18:3). C18:2 was the most abundant UFA in sweet potato NLs, which ranged from 43.79% to 54.47%. Xushu 28 had the highest UFA content (54.47%), while Xinxiang No.1 had the lowest content (43.79%). The contents of C18:1 and C18:3 ranged from 0.50% (Wutang No.1) to 1.43% (Mixuan No.1) and 7.35% (Wutang No.1) to 15.57% (Jishu 98), respectively. The SFA in sweet potato NLs primarily consisted of C16:0, C18:0, and C20:0. C16:0 was the most abundant SFA in sweet potato NLs, which ranged from 26.90% (Jishu 98) to 36.84% (Xushu 18). The contents of C18:0 and C20:0 ranged from 3.11% (Jishu 98) to 4.52% (Xushu 18) and 1.02% (Xushu 27) to 1.57% (Xushu 18), respectively. Compared with the TLs (Table 6.2), the UFA contents in NLs were significantly higher. The contents of UFA in NLs ranged from 55.89% (Xushu 18) to 66.18% (Xushu 28). UFA has positive effects on reducing blood cholesterol and fat contents, and in the prevention of cardiovascular diseases and the protection of the brain and nervous system (Torres et al., 2000).
Fatty acids composition of glycolipids The FAs composition of GLs is shown in Table 6.4. The content of GLs in sweet potato was approximately 8 10 times that in rice bran, fenugreek seeds, and Perilla seed (Hemavathy and Prabhakar, 1987, 1989; Shin
Table 6.3 Fatty acids composition of NLs from 11 sweet potato cultivars (%). Cultivar
Palmitic acid C16:0
Stearic acid C18:0
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20:0
SFA
UFA
SFA/ UFA
Xushu 28 Shangshu 19 Xinxiang No.1 Xushu 18 Wutang No.1 Xushu 27 Xushu 22 Mixuan No.1 Beijing 553 Jishu 98 Zheshu 7518
27.50 6 7.26d 31.35 6 0.17bcd 29.88 6 0.03cd 36.84 6 0.27a 31.39 6 0.22bcd 33.11 6 0.04abc 35.45 6 0.02ab 30.81 6 0.29bcd 34.26 6 2.03abc 26.90 6 0.24d 30.32 6 0.11cd
4.26 6 0.36abc 3.22 6 0.00f 4.41 6 0.00ab 4.52 6 0.01a 4.03 6 0.04cd 3.26 6 0.010f 4.56 6 0.03a 3.46 6 0.00ef 3.78 6 0.39de 3.11 6 0.04f 4.08 6 0.04bcd
1.14 6 0.12c 0.90 6 0.00e 1.17 6 0.01c 1.18 6 0.03c 0.50 6 0.06f 1.61 6 0.02a 1.07 6 0.00cd 1.43 6 0.07b 0.97 6 0.17de 0.65 6 0.04f 1.39 6 0.05b
54.47 6 5.46a 53.43 6 0.22ab 52.12 6 0.17abc 43.79 6 0.45d 54.00 6 0.10a 48.96 6 0.06c 44.56 6 0.10d 49.46 6 0.31c 48.95 6 1.30c 52.08 6 0.02abc 49.85 6 0.19bc
10.57 6 1.13ef 8.42 6 0.14h 9.96 6 0.12fg 10.91 6 0.16de 7.35 6 0.08i 11.40 6 0.08cde 11.49 6 0.04cd 13.11 6 0.06b 9.50 6 0.44g 15.57 6 0.33a 11.84 6 0.08c
1.23 6 0.08ab 1.36 6 0.00ab 1.36 6 0.06ab 1.57 6 0.01a 1.10 6 0.07b 1.02 6 0.00b 1.29 6 0.05ab 1.34 6 0.02ab 1.16 6 0.65ab 1.07 6 0.00b 1.40 6 0.04ab
32.98 6 6.82de 35.93 6 0.17cde 35.65 6 0.09cde 42.93 6 0.25a 36.52 6 0.33bcd 37.39 6 0.05bcd 41.31 6 0.06ab 35.61 6 0.27cde 39.20 6 3.07abc 31.08 6 0.28e 35.80 6 0.03cde
66.18 6 6.72ab 62.75 6 0.36bc 63.26 6 0.30bc 55.89 6 0.58d 61.86 6 0.09bc 61.97 6 0.03bc 57.13 6 0.07d 64.00 6 0.32abc 59.43 6 1.92cd 68.31 6 0.31a 63.08 6 0.06bc
0.50 0.57 0.56 0.77 0.59 0.60 0.72 0.56 0.66 0.45 0.57
Values within columns with different letters are significantly different (P , .05). SFA, Saturated fatty acid; UFA, unsaturated fatty acid.
Table 6.4 Fatty acids composition of GLs from 11 sweet potato cultivars (%). Cultivar
Palmitic acid C16:0
Stearic acid C18:0
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20:0
SFA
UFA
SFA/ UFA
Xushu 28 Shangshu 19 Xinxiang No.1 Xushu 18 Wutang No.1 Xushu 27 Xushu 22 Mixuan No.1 Beijing 553 Jishu 98 Zheshu 7518
28.04 6 0.09c 20.09 6 0.01e 24.06 6 4.88de 32.39 6 0.04ab 23.37 6 0.85de 29.46 6 0.18bc 31.04 6 0.19abc 24.08 6 0.28d 33.42 6 2.39a 21.37 6 0.51de 21.24 6 0.26de
5.43 6 0.06ab 3.13 6 0.01f 4.28 6 0.76def 5.04 6 0.06abc 4.81 6 0.36bcd 4.38 6 0.01cde 5.90 6 0.04a 4.37 6 0.10cde 3.78 6 1.25ef 3.94 6 0.03def 4.90 6 0.08abcd
0.49 6 0.01cdef 0.56 6 0.03cde 0.52 6 0.22def 0.85 6 0.07ab 0.25 6 0.01f 1.02 6 0.11a 0.72 6 0.01bc 1.00 6 0.26a 0.67 6 0.08bcd 0.37 6 0.01ef 0.57 6 0.08cde
57.72 6 0.02abc 65.20 6 0.41a 61.46 6 1.36ab 50.47 6 0.26bc 64.20 6 0.67a 54.28 6 0.06abc 50.54 6 0.30bc 52.80 6 0.01bc 52.46 6 3.48bc 59.18 6 0.20ab 61.35 6 0.12ab
8.04 6 0.04ef 10.58 6 0.06cd 9.31 6 3.47f 10.59 6 0.02cd 7.01 6 0.26f 10.23 6 0.05cde 11.36 6 0.16c 17.47 6 0.09a 8.28 6 1.03def 14.55 6 0.31b 11.66 6 0.14c
ND 0.22 6 0.31a 0.11 6 0.35a 0.31 6 0.44a 0.21 6 0.30a ND ND ND 0.47 6 0.67a ND ND
33.46 6 0.03a 23.44 6 0.32c 25.38 6 6.00bc 37.75 6 0.34a 28.39 6 0.91bc 33.84 6 0.19a 36.95 6 0.15a 28.45 6 0.18b 37.67 6 4.31a 25.32 6 0.54bc 26.14 6 0.17bc
66.25 6 0.03c 76.34 6 0.32a 71.02 6 1.19b 61.92 6 0.31e 71.46 6 0.91b 65.52 6 0.09cd 62.62 6 0.13de 71.27 6 0.18b 61.41 6 4.44e 74.10 6 0.50ab 73.58 6 0.19ab
0.51 0.31 0.36 0.61 0.40 0.52 0.59 0.40 0.61 0.34 0.36
Data are means 6 SD (n $ 2). Values within columns with different letters are significantly different (P , .05). SFA, Saturated fatty acid; UFA, unsaturated fatty acid; ND, not detected.
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and Kim, 1994). The most abundant FA in sweet potato GLs was C18:2, which ranged from 50.47% (Xushu 18) to 65.20% (Shangshu 19), followed by C16:0, which ranged from 20.09% (Shangshu 19) to 33.42% (Beijing 553). The contents of C18:0 and C18:3 ranged from 3.13% (Shangshu 19) to 5.90% (Xushu 22) and 9.31% (Xinxiang No.1) to 17.47% (Mixuan No.1), respectively. The contents of C18:1 and C20:0 were relatively low; C18:1 ranged from 0.25% (Wutang No.1) to 1.02% (Xushu 27), and C20:0 was not detected in some sweet potato cultivars, including Xushu 22, Mixuan No.1, Jishu 98, and Beijing 553. GLs derived from plants exhibit various biological properties in vitro and/or in vivo, including antitumor activity (Kuriyama et al., 2005; Hou et al., 2007) and antiinflammatory activity (Leth-Larsen et al., 2003). The GLs in sweet potatoes consisted mainly of MGDGs and DGDGs (Walter et al., 1971). Plant GLs are characterized by one or two UFAs with chain lengths typically varying from C16 to C20 linked to the glycerol moiety, and this is why the UFAs in GLs increased significantly.
Fatty acids composition of phospholipids The composition of FAs in PLs was similar to the other lipid classes (Table 6.5). The UFA content in sweet potato PLs was much higher than the SFA content. The content of UFA ranged from 56.53% (Beijing 553) to 75.37% (Shang 19). The UFAs mainly consisted of C18:1, C18:2, and C18:3, and their contents ranged from 0.59% (Wutang No.1) to 3.08% (Beijing 553), 48.02% (Mixuan No.1) to 67.74% (Shang 19), and 4.40% (Wutang No.1) to 8.84% (Xushu 22), respectively. The contents of SFA in sweet potato PLs primarily consisted of C16:0, C18:0, and C20:0. C16:0 was the most abundant SFA in sweet potato PLs, and ranged from 21.92% (Shangshu 19) to 39.33% (Beijing 553). The content of C18:0 ranged from 1.82% (Shangshu 19) to 4.53% (Xinxiang No.1). C20:0 was not found in Xushu 27 and Mixuan No.1. PLs were the predominant lipid class in biological membranes, although the content of PLs was limited.
Anticancer effects of sweet potato lipids As mentioned in the first section, lipids from different sources exhibited certain anticancer effects. However, reports on the anticancer effects of sweet potato lipids were rare. Thus the antiproliferative effects and cell migration inhibition on cancer cells of sweet potato lipids were studied,
Table 6.5 Fatty acids composition of PLs from 11 sweet potato cultivars (%). Cultivar
Palmitic acid C16:0
Stearic acid C18:0
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20:0
SFA
UFA
SFA/ UFA
Xushu 28 Shangshu 19 Xinxiang No.1 Xushu 18 Wutang No.1 Xushu 27 Xushu 22 Mixuan No.1 Beijing 553 Jishu 98 Zheshu 7518
34.48 6 0.92e 21.92 6 0.25h 31.76 6 1.25g 36.29 6 0.34cd 37.08 6 0.26bc 34.66 6 0.56e 33.36 6 0.32f 37.74 6 0.23b 39.33 6 0.66a 35.30 6 0.13de 32.60 6 0.06fg
3.45 6 0.20b 1.82 6 0.08c 4.53 6 0.99a 3.51 6 0.07b 3.57 6 0.07b 3.23 6 0.10b 3.63 6 0.09b 3.62 6 0.00b 3.36 6 0.30b 3.22 6 0.06b 3.70 6 0.16b
1.12 6 0.09d 1.10 6 0.15de 1.17 6 0.14d 1.27 6 0.09d 0.59 6 0.16g 2.11 6 0.05b 0.92 6 0.00ef 1.83 6 0.06c 3.08 6 0.73a 0.74 6 0.06fg 1.20 6 0.00d
53.16 6 1.06d 67.74 6 0.40a 56.38 6 1.23b 49.51 6 0.26g 53.15 6 0.11de 51.81 6 0.30f 52.30 6 0.02ef 48.02 6 0.64h 47.00 6 0.63i 51.92 6 0.06f 54.92 6 0.02c
6.76 6 0.16d 6.53 6 0.10d 5.62 6 0.33e 8.37 6 0.25b 4.40 6 0.18f 8.18 6 0.11bc 8.84 6 0.02a 8.21 6 0.01bc 5.89 6 0.58e 7.89 6 0.09c 6.91 6 0.05d
1.03 6 0.07a 0.72 6 0.01ab 0.55 6 0.78ab 0.98 6 0.01a 1.14 6 0.01a ND 0.87 6 0.07a ND 1.34 6 0.06a 0.93 6 0.02a 0.67 6 0.07ab
39.41 6 0.65d 24.46 6 0.35f 36.84 6 1.04e 40.78 6 0.29c 41.79 6 0.34bc 37.89 6 0.47e 37.86 6 0.16e 41.94 6 0.58b 43.73 6 0.42a 39.45 6 0.21d 36.97 6 0.03e
61.75 6 0.99cd 75.37 6 0.35a 63.16 6 1.04b 59.14 6 0.42e 58.14 6 0.45e 62.11 6 0.46bc 62.06 6 0.05bc 58.06 6 0.59e 56.53 6 0.78f 60.55 6 0.21d 63.03 6 0.03bc
0.64 0.32 0.58 0.69 0.72 0.61 0.61 0.72 0.77 0.65 0.59
Data are means 6 SD (n $ 2). Values within columns with different letters are significantly different (P , .05). SFA, Saturated fatty acid; UFA, unsaturated fatty acid; ND, not detected.
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to provide basic information for sweet potato lipids potentially to be used in functional foods.
Antiproliferative effect of sweet potato lipids on cancer cells Cancer is proposed to be an aftereffect of the accumulation of multiple genetic alterations, of which the developing risk could be regulated by bioactive components from food (Kim and Milner, 2011). Colorectal cancer is one of the commonest malignancies of the gastrointestinal tract, which ranks as the fourth and third most common cause of cancer deaths in the world and the United States, respectively, while breast cancer is the main cause of cancer deaths among women (Greenlee et al., 2000; Faghfoori et al., 2015; Brosens et al., 2015). Two cancer cells, HT-29 colon cancer cells and Bcap-37 breast cancer cells, then were chosen to study the antiproliferative effect of sweet potato lipids. At the same time, since GLs from other sources showed significant antiproliferative effect on different cancer cells, GLs from sweet potato lipids were separated by macroporous resin using different proportions of ethanol solutions into GLs (I, II, III) to better understand their antiproliferative effect. As shown in Figs. 6.1 and 6.2, both TLs and GLs (I, II, III) showed dose-dependent antiproliferative effects on HT-29 and Bcap-37 cells as shown using the MTT assay. Stronger inhibitory effects were observed on HT-29 than Bcap-37 cells. Compared with TLs, GLs I, II, and III had greater antiproliferative effects on HT-29 cells, of which GL III exhibited the highest effects (Fig. 6.1A, P , .05). The antiproliferative effects of GL III on HT-29 cells were 59.66%, 68.66%, 78.12%, 82.33%, 88.23%, and 92.21% at concentrations of 50, 100, 200, 400, 800, and 1000 μg/mL, respectively (Fig. 6.1A, P , .05). In the crystal violet study, dosedependent inhibitory effects of TLs and GLs (I, II, III) on HT-29 cells were also observed (Fig. 6.1B). In the case of Bcap-37 cells, GL III also exhibited the highest antiproliferative effects, which were 18.83%, 30.48%, 46.62%, 58.26%, 66.87%, and 76.42% at concentrations of 50, 100, 200, 400, 800, and 1000 μg/mL, respectively (Fig. 6.2A). And dosedependent inhibitory effects of TLs and GLs (I, II, III) on Bcap-37 cells were also observed in the crystal violet study (Fig. 6.2B). In addition, the maximum effects were seen in HT-29 and Bcap-37 cells treated with GLs III when concentrations reached 1000 μg/mL (Figs. 6.1B and 6.2B), which was in accordance with the results of the MTT assay (Figs. 6.1A and 6.2A). When the GLs fraction from spinach was incubated with
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Figure 6.1 Antiproliferative effects of sweet potato lipids on HT-29 cancer cells. (A) MTT assay; (B) crystal violet study.
mouse colon-26 cell lines for 24 h, the growth inhibition rate of colon-26 cells decreased to 75.7% at 100 μg/mL (Maeda et al., 2008), which was similar to the antiproliferative effect of sweet potato GLs on HT-29 cells. The treatment of cardiovascular diseases and cancers with natural food ingredients, such as GLs, has gained increased research attention. GLs are a class of metabolites and mainly comprise MGDG, DGDG, and SQDG, which have numerous biological properties, such as antitumor, antimicrobial, antimicrofouling, and antiinflammatory activities (Da Costa et al., 2016). MGDG and DGDG have shown potential anticancer activities due
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Figure 6.2 Antiproliferative effects of sweet potato lipids on Bcap-37 cancer cells. (A) MTT assay; (B) crystal violet study.
to DNA polymerase inhibition, antiproliferation of cancer cells, and antitumor growth (Maeda et al., 2008). SQDG has also shown antiproliferative effects on gastric cancer cells (Quasney et al., 2001).
Cell metastasis inhibition of sweet potato lipids on cancer cells Metastasis of cancer cells is the process of tumor cells transferring from primary tumor blocks to distant target tissues. It is a difficult point in tumor therapy and is also the main cause of cancer-related morbidity and
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mortality. The cell metastasis inhibition of sweet potato lipids on cancer cells was studied via their effects on the adhesion and migration of cancer cells to provide the basic data for the application of sweet potato lipids in functional foods. Effect of total lipids and glycolipids on adhesion of HT-29 and Bcap-37 cells The effects of TLs on the adhesion of HT-29 and Bcap-37 cells are shown in Fig. 6.3A. Compared with the untreated cells, the adhesion time for cells treated with phorbol 12-myristate 13-acetate (PMA) increased significantly, that is, 1.7 times that of untreated cells. With the increase of TLs concentration (100, 400, and 1000 μg/mL), the adhesion effect of cancer cells decreased significantly (P , .05). The cell adhesion time for cells treated with TLs at 100 and 400 μg/mL was higher than that of untreated cells, but lower than that of cells treated with PMA
Figure 6.3 Cell adhesion inhibition effects of sweet potato lipids on HT-29 and Bcap37 cancer cells. (A) TLs; (B) GLs I; (C) GLs II; (D) GLs III.
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(P , .05). The cell adhesion time for HT-29 and Bcap-37 cells treated with TLs at 1000 μg/mL is 7.5 and 7.0 min, separately, showing no significant difference with untreated cells (P..05). The effects of GLs I, II, and III on the adhesion of HT-29 and Bcap37 cells were shown in Fig. 6.3B, C, and D. The cell adhesion time of both HT-29 and Bcap-37 cells by adding PMA without GLs was significantly higher than those of the untreated cells and the cells with GLs (P , .05). Among the cells treated with GLs, the cell adhesion time decreased significantly with the increase of GLs concentration (100, 400, and 1000 μg/mL), of which GLs III showed the highest effect, followed by GLs II (P , .05). Compared with the untreated cells, adhesion time of cells treated with GLs was higher with the concentration less than 400 μg/mL. When the concentration of GLs increased up to 1000 μg/ mL, there was no significant difference between the adhesion time between the untreated cells and cells treated with GLs I, while the adhesion time of cells treated with GLs II and III was much lower than that of untreated ones (P , .05). For HT-29 cells, when the concentration of GLs was 1000 μg/mL, the adhesion time of cells treated with GLs I, II, and III were 7.1, 6.1, and 5.3 min, which reduced by 42.7%, 50.8%, and 57.3% compared with that of the PMA-treated cells, respectively. For Bcap-37 cells, when the concentration of GLs was 1000 μg/mL, the adhesion time of cells treated with GLs I, II, and III were 6.1, 5.5, and 4.7 min, which reduced by 45.0%, 50.5%, and 57.7% compared to the PMA-treated cells, respectively. Compared with TLs, the adhesion time of HT-29 cells treated with GLs I, II, and III decreased by 4.7%, 12.8%, and 19.3%; and the adhesion time of Bcap-37 cells was shortened by 8.1%, 13.6%, and 20.8%, respectively. The results suggested that GLs I, II, and III could reduce the adhesion of cancer cells, of which the effect was better than TLs, particularly for Bcap-37 cells. Effects of total lipids and glycolipids on the migration of HT-29 and Bcap-37 cells The effects of TLs on the migration of HT-29 and Bcap-37 cells are shown in Fig. 6.4. The cell migration of both HT-29 and Bcap-37 cells by adding PMA without TLs was significantly higher than those of the untreated cells and cells with TLs (P , .05). Among the cells treated with TLs, the cell migration decreased significantly with the increase of TLs concentration (100, 400, and 1000 μg/mL). For HT-29 cells, when the concentration of TLs was 1000 μg/mL, the cell migration of cells treated with TLs was 23.03%, which was reduced by 17.32% compared to
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Figure 6.4 Cell migration inhibition effects of sweet potato lipids on HT-29 (A) and Bcap-37 (B) cancer cells.
Figure 6.5 Cell adhesion inhibition effects of sweet potato lipids on HT-29 (A, GLs I; B, GLs II; C, GLs III) and Bcap-37 (D, GLs I; E, GLs II; F, GLs III) cancer cells.
PMA-treated cells (Fig. 6.4A). For Bcap-37 cells, when the concentration of TLs was 1000 μg/mL, the cell migration of cells treated with TLs was 35.83%, which was decreased by 18.36% compared with that of the PMA-treated cells (Fig. 6.4B). The effects of GLs I, II, and III on the migration of HT-29 and Bcap37 cells are shown in Fig. 6.5. The cell migration of HT-29 and Bcap-37 cells by adding PMA without GLs was significantly higher than those of the untreated cells and cells with GLs (P , .05). Among the cells treated with GLs, the cell migration decreased significantly with the increase of GLs concentration (100, 400, and 1000 μg/mL), of which GLs III showed the highest effect, followed by GLs II (P , .05). For HT-29 cells, when
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the concentration of GLs was 1000 μg/mL, the cell migrations of cells treated with GLs I, II, and III were 10.35%, 8.06%, and 6.04%, which reduced by 30%, 32.29%, and 34.31% compared to the PMA-treated cells, respectively. For Bcap-37 cells, when the concentration of GLs was 1000 μg/mL, the cell migrations of cells treated with GLs I, II, and III were 22.35%, 20.04%, and 16.72%, which reduced by 31.84%, 34.15%, and 37.47% compared to the PMA-treated cells, respectively.
Anticancer effects confirmation of sweet potato lipids To confirm the anticancer effects of TLs, GLs I, II, and III in sweet potato, the MGDG and DGDG contents were determined. Compared with TLs, GLs I, and II, GL III showed the highest level of MGDG, which was 35.84% (Fig. 6.6A, P , .05). There were significant differences
Figure 6.6 MGDG and DGDG in sweet potato lipids. (A) MGDG percentage; (B) DGDG percentage.
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in the percentages of DGDG in TLs and GLs (I, II, III), which followed the order GL III . TLs . GL I . GL II (Fig. 6.6B, P , .05). Thus GL III showed the highest percentage of DGDG compared with TLs, GLs I and II, which was 89.16% (Fig. 6.6B, P , .05). Napolitano et al. (2007) indicated that 16 novel and 10 known galactolipids identified from sweet potato leaves cultivated in Japan contained MGDG and DGDG. Roberts and Moreau (2016) showed that GLs in spinach leaves included MGDG, DGDG, and SQDG, which exhibited antiproliferative activity in many different cancer cell lines. MGDG from spinach also inhibited the proliferation of colon-26 cells, and oral administration suppressed colon tumor growth in mice (Maeda et al., 2013). In addition, further studies on the relationship between the molecular mechanisms and the structures of sweet potato lipids should be performed, as well as animal experiments.
Application prospect of sweet potato lipids Sweet potato lipids are rich in GLs and PLs, and could be a good source of essential GLs and PLs. The UFA content in sweet potato lipids is greater than the content of SFA, showing potential utilization in the prevention of cardiovascular diseases and the protection of the brain and nervous system. In addition, sweet potato lipids present certain anticancer effects, especially for GLs with the contribution of MGDG and DGDG. Thus sweet potato lipids could be potentially used in functional foods, health care products, and pharmaceuticals in the near future.
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Radin, N.S., 1988. Lipid extraction. Lipids Relat. Compounds 7, 1 61. Ramadan, M.F., Oraby, H.F., 2016. Fatty acids and bioactive lipids of potato cultivars: an overview. J. Oleo Sci. 65, 459 470. Ravi, H., Baskaran, V., 2015. Biodegradable chitosan-glycolipid hybrid nanogels: a novel approach to encapsulate fucoxanthin for improved stability and bioavailability. Food Hydrocolloid. 2015 (43), 717 725. Ravindran, V., Ravindran, G., Sivakanesan, R., Rajaguru, S.B., 1995. Biochemical and nutritional assessment of tubers from 16 cultivars of sweet potato (Ipomoea batatas L.). J. Agr. Food Chem. 43, 2646 2651. Roberts, J.L., Moreau, R., 2016. Functional properties of spinach (Spinacia oleracea L.) phytochemicals and bioactives. Food Funct. 7, 3337 3353. Shin, H.S., Kim, S.W., 1994. Lipid composition of perilla seed. J. Am. Oil Chem. Soc. 71, 619 622. Simopoulos, A.P., 2002. Omega-3 fatty acids in inflammation and autoimmune diseases. J. Am. Coll. Nutr. 21, 495 505. Suresh, Y., Das, U.N., 2001. Protective action of arachidonic acid against alloxan-induced cytotoxicity and diabetes mellitus. Prostag. Leukotr. ESS 64, 37 52. Suresh, Y., Das, U.N., 2003. Long-chain polyunsaturated fatty acids and chemically induced diabetes mellitus: effect of omega-6 fatty acids. Nutrition 19, 93 114. Tanzi, C.D., Vian, M.A., Chemat, F., 2013. New procedure for extraction of algal lipids from wet biomass: a green clean and scalable process. Bioresour. Technol. 134, 271 275. Tokuda, H., Nishino, H., Shirahashi, H., Sakakibara, J., 1996. Inhibition of 12- O-tetradecanoylphorbol-13- acetate promoted mouse skin papilloma by digalactosyl diacylglycerols from the fresh water cyanobacterium Phormidium tenue. Cancer Lett. 104, 91 95. Torres, I.C., Mira, L., Ornelas, C.P., Melim, A., 2000. Study of the effects of dietary fish intake on serum lipids and lipoproteins in two populations with different dietary habits. Br. J. Nutr. 83, 371 379. Varamini, P., Mansfeld, F.M., Giddam, A.K., Steyn, F., Toth, I., 2017. New gonadotropin-releasing hormone glycolipids with direct antiproliferative activity and gonadotropin-releasing potency. Int. J. Pharm. 521, 327 336. Volger, O.L., Mensink, R.P., Plat, J., Hornstra, G., Havekes, L.M., Princen, H.M., 2001. Dietary vegetable oil and wood derived plant stanol esters reduce atherosclerotic lesion size and severity in apoE 3-Leiden transgenic mice. Atherosclerosis 157, 375 381. Walter, W.M., Hansen, A.P., Purcell, A.E., 1971. Lipids of cured centennial sweet potatoes. J. Food Sci. 36, 795 797. Wang, S., Nie, S., Zhu, F., 2016. Chemical constituents and health effects of sweet potato. Food Res. Int. 89, 90 116. Weststrate, J.A., Meijer, G.W., 1998. Plant sterol-enriched margarines and reduction of plasma total-and LDL-cholesterol concentrations in normocholesterolaemic and mildly hypercholesterolaemic subjects. Eur. J. Clin. Nutr. 52, 334 343. Woolfe, J.A., 1992. Sweet Potato: An Untapped Food Resource. Cambridge University Press, New York. Yang, Y.H., Jiao, G.Y., 2008. Effect of soybean lecithin on serum lipid in hyperlipidemia population. Chin. J. Clin. Nutr. 16, 172 174. in Chinese. Yang, F., Xiang, W., Sun, X., Wu, H., Li, T., Long, L., 2014. A novel lipid extraction method from wet microalga picochlorum sp. at room temperature. Mar. Drugs 12, 1258 1270. Yoshida, H., Mizushiria, Y., Yoshida, N., 2012. Profiles of fatty acid distribution of different acyl lipids from red and black rices. J. Food Res. 1, 46 53.
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Zakir, S., Sarwar, M., Allen, J., Khan, M.N., Butt, M.S., 2006. Variation in physiochemical characteristics of some cultivars of sweet potato. Pak. J. Bot. 38, 283. Zhang, T., Oates, C.G., 1999. Relationship between α-amylase degradation and physico-chemical properties of sweet potato starches. Food Chem. 65, 157 163. Zhang, X., Yang, M., Song, F., Zhang, H., Feng, F., 2013. Antimicrobial activity of selected fatty acids and their derivatives. J. Zhejiang Univ. (Agri. Life Sci.) 39, 155 160. in Chinese.
Sweet potato lipids Tai-Hua Mu and Miao Zhang Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences; Key Laboratory of Agro-Products Processing, Ministry of Agriculture and Rural Affairs, Beijing, People’s Republic of China
Overview of lipids Definition of lipids Lipids, as a potential functional ingredient, are present in almost all foods and play an important role in nutrition and the sensory aspects of food. Lipids are mainly divided into neutral lipids (NLs), glycolipids (GLs), and phospholipids (PLs). It was reported that the contents of NLs, GLs, and PLs in total lipids (TLs) of potato tubers were 21%, 22%, and 47%, respectively (Ramadan and Oraby, 2016). The NLs, GLs, and PLs contents in the major Indian Garcinia fruit, which has different varieties, range from 37.6% to 95.8%, 3.2% to 55.9%, and 0.8% to 6.8%, respectively (Patil et al., 2016). Fatty acids (FAs) play an important role in lipids, such as linoleic acid (C18:2), linolenic acid (C18:3), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), showing effects on diverse physiological processes and thus have an impact on normal health and chronic diseases (Benatti et al., 2004).
Extraction methods of lipids Mechanical squeezing method Mechanical squeezing is one of the most long-standing methods for obtaining lipids. Lipids are obtained by being squeezed out, mainly by mechanical force, and this process mainly involves physical changes, such as friction heating, material deformation, oil separation, water evaporation, etc. At present, this method is still widely used by some enterprises. The advantages of the mechanical squeezing method are that it is convenient to operate and requires less investment. However, there are still some shortcomings, such as the low content of bioactive substances in the oil and the low yield of oil. At the same time, due to the effects of changes in water and temperature, some biochemical reactions will Sweet Potato DOI: https://doi.org/10.1016/B978-0-12-813637-9.00006-5
© 2019 Elsevier Inc. All rights reserved.
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occur, for example, the oil is easily oxidized, and the protein is prone to denaturation. Bligh-Dyer method The Bligh-Dyer method is a widely used method for lipid determination in biologics and food. The outstanding advantages of this method are the high extraction rate of oil, low residual rate, and high production efficiency—it can achieve continuous processing with low energy consumption. However, some dangerous flammable solvents are used in this method, and the health problems caused by residual solvents in oil meal are also serious (Radin, 1988). Other novel lipid extraction methods Some novel lipid extraction methods have been investigated, for example, simultaneous distillation and extraction (Tanzi et al., 2013), ultrasoundassisted extraction (Adam et al., 2012), microwave-assisted extraction (Cheng et al., 2013), and supercritical fluid extraction (Halim et al., 2011). However, the methods above still require high energy inputs, high temperature, and take a long time, and are currently limited at the laboratory scale. Yang et al. (2014) extracted lipids from wet microalga Picochlorum sp. by using ethanol at room temperature, and indicated that the yield of lipids could be comparable to that by the Bligh-Dyer method without significant differences in FA composition and lipid classes distribution.
Physiological functions of lipids Lipids present different physiological functions, including improvements in the bioavailability of functional components, as well as having hypolipidemic, antiatherosclerosis, antimicrobial, antiinflammatory, memory improving, diabetes prevention, and anticancer properties, which have been summarized here. Improvement on the bioavailability of functional components It has been reported that some kinds of lipids could improve the bioavailability of some functional components. PLs are the major carriers for active molecules of plants; they interact with plant constituents, protect plant active components from degradation, and increase their bioavailability by imparting lipid solubility to them (Khan and Krishnaraj, 2014).
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PLs and glyceroglycolipids could markedly affect the uptake of carotenoids by human intestinal Caco-2 cells by solubilizing in mixed micelles via decreasing intercellular barrier integrity, suggesting their potential to modify the intestinal uptake of carotenoids (Kotake-Nara et al., 2015). The stability and biological availability of carotenoid fucoxanthin was improved when encapsulated in chitosan-glycolipid nanogels (Ravi and Baskaran, 2015). Hypolipidemic effect Yang and Jiao (2008) investigated the effects of soy lecithin on blood lipids in patients with hyperlipidemia. According to the blood lipid levels, 100 patients with hyperlipidemia were divided into the control and experimental groups, with 50 cases in each group. The patients in the experimental group took soy lecithin 20 g per day, and the control group received the same dose of placebo for 8 weeks. Serum total cholesterol (STC) and triglyceride (TG) levels were measured before and after taking soy lecithin or placebo. The results showed that no significant difference was observed in levels of STC and TG between the experimental group and control group before taking. However, after taking soy lecithin for 8 weeks, STC and TG levels in the experimental group were significantly lower than the starting levels and the levels in the control group, suggesting that soybean lecithin could significantly decrease the serum lipid level in the hyperlipidemic population. The lipid regulation function might be through inhibiting TG synthesis and eliminating cholesterol in vivo and in TC emulsions. Waststrate and Meijer (1998) found that STC and TC levels decreased significantly with an intake of 1.6 2 g/person/day of plant sterols. Nyugen et al. (1999) studied TC lowering effects of plant stanol esters, and the results showed that the total STC and low-density lipoprotein (LDL) cholesterol decreased by 6.4% and 10.1% after intake of 2 3 g/ person/day of plant stanol esters, respectively. Gylling and Miettinen (2005) indicated that plant sterols and stanols could inhibit the absorption of cholesterol that was endogenous and produced by diet in the small intestine. The authors indicated that the main reason is that free sterols and stanols could replace cholesterol from microcapsules mixed with bile acid, thus reducing the intestinal absorption of cholesterol, and also could compete with cholesterol during its absorption in the microvillous membrane.
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Antiatherosclerosis effect Karantonis et al. (2002) separated the TLs of oils from corn, olive, soybean, sunflower, and sesame into PLs and NLs by using a new extraction technique, which were further separated into different components by high-performance liquid chromatography. Among the different components of lipids, PL showed strong inhibitory effects on the plateletactivating factor, suggesting the preventive effects of PL on atherosclerosis. Volger et al. (2001) found that plant sterols had inhibitory effects on atherosclerosis, and its mechanism of action was mainly by reducing the STC. LDL oxidation was a major cause of atherosclerosis, and there was a positive correlation between the oxidation degree of LDL and STC content, so reducing STC content could inhibit the occurrence of atherosclerosis effects. Antimicrobial effect Jing and Qi (2001) isolated three kinds of glyceroglycolipids from Serratula strangulate, and determined their antibacterial activities. The results showed that three kinds of glyceroglycolipids had significant inhibitory effects on Bacillus subtilis, Escherichia coli, and Staphylococcus aureus. Zhang et al. (2013) used Candida albicans and E. coli as the tested bacteria, and determined the antibacterial activities of 10 saturated fatty acids (SFAs), 6 unsaturated fatty acids (UFAs), 2 FA methyl ester, 3 FAs, 4 fatty alcohols, and 9 FA monoglycerides. It was suggested that the antimicrobial activity of FAs and their derivatives was related to the carbon chain length of FAs, the number and position of double bonds in UFAs, and the types of substituent groups. Qian et al. (2012) found that the minimum inhibitory concentration of dirhamnoside derivative compound 7 (DDC7) and cleistrioside-5 (C5) on S. aureus (MIC) is 16 μg/mL, and the mechanism might be due to DDC7 and C5 having a similar chemical structure with the sugar chain of the β-1,4 glycosidic bond of the S. aureus peptidoglycan, which could destroy the biosynthesis or glycosidic linkage of bacterial polysaccharides. Hu et al. (2012) indicated that sophorolipids could effectively inhibit the growth of S. aureus in a concentration-dependent manner, even in acidic and high temperature conditions. Antiinflammatory effect GLs from spinach could suppress lipopolysaccharides-induced vascular inflammation through endothelial nitric oxide synthase and NK-κB signaling in human umbilical vein endothelial cells, suggesting that GLs from
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spinach might have a potential therapeutic utilization for inflammatory vascular diseases (Ishii et al., 2017). Milo et al. (2002) investigated the effects of short-chain FAs on the levels of proinflammatory cytokines in miniature pigs, and indicated that short-chain FAs could increase the intestinal proinflammatory cytokines IL-1 and lL-6 level to inhibit inflammation. Larsen et al. (2003) isolated monogalactosyl diacylglycerol (MGDG) from rose hip through active tracking detection technology, and found that MGDG presented an antiinflammatory effect without cell toxicity in an in vitro experiment. Bruno et al. (2005) isolated MGDG, digalactosyl diglyceride (DGDG), and sulfoquinovosyl diacylglycerol (SQDG) from thermophilic cyanobacteria, and showed that MGDG, DGDG, and SQDG could inhibit the swelling of mouse ear in a dosedependent manner. In addition, some clinical trials showed that a diet containing cod liver oil could significantly reduce the joint swelling in patients with rheumatoid arthritis, while the intake of an ordinary diet had no effect (James et al., 2000; Kremer, 2000). The mechanism of antiinflammation activities of cod liver oil was as follows: (1) through influencing the metabolism of peanut arachidonic acid (Simopoulos, 2002); (2) by changing the structure of PLs in the cell membrane (Calder and Grimble, 2002); and (3) by acting on the mediators of inflammation and immunity (Adam et al., 2003). Memory improving effect It was well known that EPA and DHA could improve memory and eyesight, especially to promote the growth and development of infant brain cells. Avrova et al. (2002) found that ganglioside GM1 could improve the memory function, and the mechanism was that GM1 improved the neuroprotective effects of the glial cell line and brain-derived neurotrophic factor, decreased the concentration of free radicals, thereby reducing the generation of nitric oxide, and then decreased the death of nerve cells. Chung et al. (1995) indicated that egg yolk lecithin could improve the memory of mice with dementia, and improve the concentration of acetylcholine in the brain of mice. Diabetes prevention effect Suresh and Das (2001, 2003) found that cooking oils rich in n-3 PUFA (EPA and DHA) and n-6 PUFA (GLA and AA) could prevent diabetes, and alleviate oxidative stress induced by diabetes. Delarue et al. (2004) indicated that the mechanism of n-3 PUFA on diabetes protection was as
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follows: (1) inhibiting the activity decrease of phosphatidylinositol 3kinase (PI3-K) and the failure of glucose transporter (GLUT4) in muscle; (2) preventing the decrease of GLUT4 expression in adipose tissue; and (3) inhibiting the activity of hepatic 6-glucokinase. Anticancer effect The anticarcinogenic effect of lipids was shown in several types of cancers including skin, melanoma, colon, and breast cancers. The addition of n-3 PUFAs in the diet could reduce the number of epithelial degeneration crypt lesions in mice induced by reactive oxygen species, thus preventing the development of colon cancer (Murray et al., 2002). DHA could reduce the positioning function of sarcoma protein (RSP) in epithelial cells of rats, inhibit the activation of RSP, reduce the binding level of RSP by guanosine triphosphate, and thus reduce the incidence of colon cancer in rats (Collett et al. 2001). It had been proved that the GLs components from plants could inhibit the proliferation and promote the differentiation of cancer cells. Morimoto et al. (1995) found that MGDG isolated from green algae had a strong inhibitory effect on lymph cancer cells. Maeda et al. (2008) indicated that GLs isolated from spinach presented a strong inhibitory effect on cervical cancer cells with the median lethal dose (LD50) of 57.2 μg/ mL. In addition, it was reported that MGDG, DGDG, and SQDG from freshwater cyanobacterium showed a certain inhibition effect on lymph cancer cells, among which MGDG and DGDG showed a higher inhibition effect than SQDG; and DGDG also presented a strong inhibitory effect on skin papilloma (Tokuda et al., 1996).
Lipids and fatty acid composition of different varieties of sweet potato Overview of sweet potato Sweet potato (Ipomoea batatas (L.) Lam.) is an important economic crop that can successfully adapt to a wide range of habitats, including marginal regions. It is a dicotyledonous plant belonging to the family Convolvulaceae with approximately 50 genera and over 1000 species (Woolfe, 1992). Artificial selection of sweet potatoes, as well as the occurrence of natural hybrids and mutations, has resulted in the existence of a very large number of cultivars, which differ in many of their properties, including physical appearance and texture of the tuber (Zhang and Oates,
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1999). Sweet potatoes are widely cultured in China, which has the highest production in the world with approximately 71.54 million tons produced annually, resulting in 68% of the world’s production, and sweet potatoes are the fifth most common food crop after rice, wheat, maize, and potato (FAOSTAT, 2017). Sweet potato has unique nutritional and functional properties (Wang et al., 2016), and is a valuable source of food, animal feed, and industrial raw materials.
Composition of sweet potato lipids To better understand the lipids and FA composition of different varieties of sweet potato, sweet potatoes from 11 representative cultivars were obtained from Zhejiang (Xinxiang No.1, Zheshu 7518), Hebei (Beijing 553, Jishu 98, Wutang No.1), Jiangsu (Xushu 18, Xushu 22, Xushu 27, Xushu 28, Shangshu 19), and Beijing (Mixuan No. 1), respectively, of which the proximate composition, lipids, and FA composition were determined. Table 6.1 shows the proximate composition of sweet potatoes. The moisture content ranged from 60.13% to 78.43%. The moisture content in Xushu 27 (78.43%) and Beijing 553 (75.28%) was significantly higher than those in Zheshu 7518 (60.13%) and Mixuan No.1 (61.21%). Starch was the main component of sweet potato, and the starch content ranged from 54.59% to 76.95%, which was similar to the values reported by Ravindran, Sivakanesan, and Rajaguru (1995). Xushu 27 had the highest starch content (76.95%), whereas Jishu 98 had the lowest starch content (54.59%). Protein content ranged from 3.53% to 9.13%. Woolfe et al. (1992) reported that the protein content in sweet potato was higher than cassava, plantain, and taro, but lower than potato and yam. Crude fiber content ranged from 1.80% to 3.65%, which was similar to the report by Zakir et al. (2006), where Xushu 27 had the highest crude fiber content (3.65%) and Wutang No.1 had the lowest (1.80%). Similarly, there were significant differences in ash content among the sweet potato cultivars (P , .05), and the content ranged from 2.32% (Zheshu 7518) to 3.95% (Shangshu 19). Ash content is an important indicator in evaluating mineral element content, and the minerals in sweet potato have been identified as Ca, P, Mg, Na, K, Fe, Zn, and Cu (Bouwkamp, 1985). The TLs content of sweet potatoes of different cultivars ranged from 0.72% to 1.44%, and these results were similar to those of Ravindran et al. (1995). Fat is involved in the insulation of body organs and in the maintenance of body
Table 6.1 Proximate composition of 11 sweet potato cultivars (%, DW). Cultivar
Moisturea
Starch
Protein
Crude fiber
Ash
Crude lipid
NLs
GLs
PLs
Xushu 28 Xushu 27 Mixuan No.1 Jishu 98 Xushu 22 Xushu 18 Shangshu 19 Beijing 553 Xinxiang No.1 Zheshu 7518 Wutang No.1
67.29 6 0.14def 78.43 6 0.13a 61.21 6 0.07g
72.25 6 1.39ab 76.95 6 1.53a 65.43 6 1.02b
6.23 6 0.26e 5.42 6 0.07f 7.00 6 0.01d
2.64 6 0.79c 3.65 6 1.19a 2.27 6 0.68d
2.46 6 0.81g 3.83 6 0.65b 2.41 6 0.14g
0.97 6 0.11cd 0.93 6 0.06d 1.06 6 0.04c
54.18 6 1.82ab 56.76 6 2.23ab 55.26 6 6.67ab
37.65 6 0.88cde 36.10 6 0.54e 36.08 6 4.32ef
8.17 6 0.13bc 7.14 6 0.26c 8.69 6 7.15bc
67.94 6 0.13de 72.3 6 0.67c 68.94 6 0.13d 72.40 6 0.50c 75.28 6 0.44b 65.15 6 0.17f
54.59 6 0.49c 66.33 6 0.53b 71.47 6 0.23ab 67.47 6 0.58ab 66.87 6 0.67b 73.88 6 0.72ab
9.13 6 0.35a 7.90 6 0.33b 3.72 6 0.26h 4.27 6 0.11g 5.32 6 0.13f 3.65 6 0.19hi
2.17 6 0.72d 3.51 6 0.76a 2.35 6 0.49cd 3.13 6 0.35b 3.76 6 1.29a 3.05 6 1.80b
2.73 6 0.22e 3.63 6 1.02c 2.33 6 1.16h 3.95 6 0.62a 3.15 6 0.87d 2.60 6 0.20f
0.72 6 0.08e 0.99 6 0.10cd 1.00 6 0.01cd 1.44 6 0.03a 0.98 6 0.12cd 1.25 6 0.07b
36.74 6 0.42d 61.04 6 1.87a 50.95 6 1.19bc 52.96 6 7.13b 55.79 6 0.21ab 44.90 6 0.12c
45.49 6 0.34ab 31.24 6 0.18g 42.00 6 0.22bc 31.30 6 0.10fg 36.38 6 3.06ed 41.03 6 4.44bcd
17.79 6 2.98a 7.72 6 0.16c 7.05 6 0.22c 15.73 6 2.49ab 7.85 6 2.19c 14.07 6 7.89abc
60.13 6 2.29g 66.42 6 3.53ef
68.59 6 0.35ab 72.71 6 0.68ab
3.53 6 0.06i 7.88 6 0.08c
2.08 6 0.67de 1.80 6 0.58e
2.32 6 0.34h 2.79 6 0.19e
0.95 6 0.16d 0.91 6 0.03d
55.56 6 0.50ab 33.70 6 5.15d
30.29 6 0.74g 49.25 6 1.62a
14.14 6 0.66abc 17.07 6 0.53a
Values within columns with different letters are significantly different (P , .05). NLs, Neutral lipids; GLs, glycolipids; PLs, phospholipids. a Moisture content was expressed in g/100 g FW.
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temperature and cell function, and sources of fats such as omega-3 and omega-6 FAs are required for the digestion, absorption, and transport of vitamins A, D, E, and K. To further understand the differences of lipids composition of sweet potatoes of different varieties, the TLs were separated into NLs, GLs, and PLs using silica gel column chromatography. The composition of lipid classes is shown in Table 6.1. NLs were the main component of sweet potato TLs, and TGs were most abundant in NLs (Walter, Hansen and Purcell, 1971); these play an important role in maintaining energy metabolism. The content of NLs in sweet potatoes ranged from 36.74% to 61.04%. Wutang No.1 had the highest content of NLs (61.04%), while Jishu 98 had the lowest (36.74%). The content of GLs ranged from 30.29% to 49.25%, and Zhushu 7518 had the highest content of GLs (49.25%) and Jishu 98 had the lowest (30.29%). It has been reported that GLs have significant antiproliferative, antimicrobial, antiviral, and antiinflammatory effects (Da Costa et al., 2016; Varamini et al., 2017). The content of PLs in sweet potato was limited, and ranged from 7.05% (Xushu 27) to 17.07% (Zheshu 7518). PLs from milk reduced plasma cholesterol concentrations, but did not change the low-density lipoprotein/high-density lipoprotein (LDL/HDL) ratio (Keller et al., 2013). Previous research indicated that the lipid composition of sweet potato was 42.1% NLs, 30.8% GLs, and 27.1% PLs (Walter et al., 1971). It has been reported that the composition of lipids in rice bran consists of 88.1% 89.2% NLs, 6.3% 7.0% GLs, and 4.5% 4.9% PLs (Hemavathy and Prabhakar, 1989). The composition of lipids extracted from millet seeds consisted of 85% NLs, 3% GLs, and 12% PLs (Osagie and Kates, 1984). Hemavathy and Prabhakar (1987) also reported that the TLs in fenugreek seeds consisted of 84.1% NLs, 5.4% GLs, and 10.5% PLs. Thus sweet potatoes are a good source of essential GLs and PLs.
Fatty acid composition of total lipids The composition of FAs in TLs is presented in Table 6.2. The FAs in sweet potatoes include palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3), and arachidic acid (C20:0), of which C16:0, C18:2, and C18:3 are abundant. The content of C16:0 ranged from 35.92% to 42.57%, and Xushu 27 had the highest C16:0 content (42.57%), whereas Jishu 98 had the lowest content (35.92%). C18:2 was the most abundant FA in sweet potato TLs, which
Table 6.2 Fatty acids composition of TLs from 11 sweet potato cultivars (%). Cultivar
Palmitic acid C16:0
Stearic acid C18:0
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20:0
SFA
UFA
SFA/ UFA
Xushu 18 Mixuan No.1 Xinxiang No.1 Wutang No.1 Xushu 28 Xushu 27 Xushu 22 Jishu 98 Shangshu 19 Beijing 553 Zheshu 7518
38.53 6 0.07de 41.34 6 1.62ab 40.42 6 0.25bc 39.78 6 0.25cd 38.34 6 0.20e 42.57 6 0.10a 39.96 6 0.12c 35.92 6 0.39g 37.55 6 0.88ef 38.4 6 0.18e 36.52 6 0.25fg
2.54 6 0.03de 2.62 6 0.14d 3.43 6 0.03a 2.38 6 0.03gf 2.61 6 0.01d 2.74 6 0.03c 2.95 6 0.00b 2.3 6 0.04g 2.47 6 0.01ef 2.12 6 0.01h 3.04 6 0.01b
1.68 6 0.01b 1.18 6 0.04d 1.36 6 0.01c 0.69 6 0.22f 1.27 6 0.01cd 1.21 6 0.14cd 1.2 6 0.01d 0.62 6 0.01f 2.11 6 0.02a 0.92 6 0.00e 1.63 6 0.04b
37.78 6 0.18d 37.96 6 0.78d 39.67 6 0.13c 38.43 6 0.02d 41.45 6 0.08a 35.2 6 0.28f 36.73 6 0.07e 39.48 6 0.20c 41.67 6 0.50a 40.48 6 0.15b 40.61 6 0.19b
18.95 6 0.25b 16.28 6 1.01e 14.54 6 0.16f 18.16 6 0.04cd 15.88 6 0.12e 17.7 6 0.28d 18.57 6 0.03bc 21.21 6 0.19a 15.65 6 0.32e 17.54 6 0.04d 17.73 6 0.01d
0.30 6 0.01cd 0.36 6 0.02a 0.35 6 0.00a 0.31 6 0.03bcd 0.26 6 0.01e 0.31 6 0.04bcd 0.36 6 0.01a 0.28 6 0.03de 0.33 6 0.03abc 0.35 6 0.01ab 0.29 6 0.01de
41.61 6 0.09de 44.61 6 1.74ab 44.45 6 0.28b 42.74 6 0.25cd 41.43 6 0.21de 45.87 6 0.17a 43.53 6 0.11bc 38.71 6 0.40g 40.59 6 0.86ef 41.09 6 0.17ef 40.06 6 0.23fg
58.41 6 0.08cd 55.42 6 1.75fg 55.57 6 0.28f 57.28 6 0.23de 58.6 6 0.21cd 54.11 6 0.71g 56.5 6 0.11ef 61.31 6 0.38a 59.43 6 0.84bc 58.94 6 0.18bc 59.97 6 0.23ab
0.71 0.80 0.80 0.75 0.71 0.85 0.77 0.63 0.68 0.70 0.67
Values within columns with different letters are significantly different (P , .05). SFA, Saturated fatty acid; UFA, unsaturated fatty acid.
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ranged from 35.2% to 41.45%, and Xushu 28 had the highest content (41.45%) and Xushu 27 had the lowest content (35.2%). The content of C18:3 ranged from 14.54% to 21.21%, and Jishu 98 had the highest content (21.21%) and Xinxiang No.1 had the lowest content (14.54%). The content of C18:0, C18:1, and C20:0 were relatively low, and ranged from 2.12% (Beijing 553) to 3.43% (Xinxiang No.1), 0.62% (Jishu 98) to 2.11% (Shangshu 19), and 0.26% (Xushu 28) to 0.36% (Xushu 22), respectively. The content of UFAs in sweet potatoes was greater than SFAs. Jishu 98 had the highest content of UFA (61.31%), while Xushu 27 had the lowest content (54.11%). It was reported that the FAs in rice mainly consisted of C16:0, C18:2, and C18:3 (Yoshida et al., 2012), and the FA composition was very similar to that of sweet potatoes.
Fatty acids composition of neutral lipids The FAs composition of TLs is presented in Table 6.3. The UFA in sweet potato TLs primarily consisted of palmitic acid (C16:0), linoleic acid (C18:2), and linolenic acid (C18:3). C18:2 was the most abundant UFA in sweet potato NLs, which ranged from 43.79% to 54.47%. Xushu 28 had the highest UFA content (54.47%), while Xinxiang No.1 had the lowest content (43.79%). The contents of C18:1 and C18:3 ranged from 0.50% (Wutang No.1) to 1.43% (Mixuan No.1) and 7.35% (Wutang No.1) to 15.57% (Jishu 98), respectively. The SFA in sweet potato NLs primarily consisted of C16:0, C18:0, and C20:0. C16:0 was the most abundant SFA in sweet potato NLs, which ranged from 26.90% (Jishu 98) to 36.84% (Xushu 18). The contents of C18:0 and C20:0 ranged from 3.11% (Jishu 98) to 4.52% (Xushu 18) and 1.02% (Xushu 27) to 1.57% (Xushu 18), respectively. Compared with the TLs (Table 6.2), the UFA contents in NLs were significantly higher. The contents of UFA in NLs ranged from 55.89% (Xushu 18) to 66.18% (Xushu 28). UFA has positive effects on reducing blood cholesterol and fat contents, and in the prevention of cardiovascular diseases and the protection of the brain and nervous system (Torres et al., 2000).
Fatty acids composition of glycolipids The FAs composition of GLs is shown in Table 6.4. The content of GLs in sweet potato was approximately 8 10 times that in rice bran, fenugreek seeds, and Perilla seed (Hemavathy and Prabhakar, 1987, 1989; Shin
Table 6.3 Fatty acids composition of NLs from 11 sweet potato cultivars (%). Cultivar
Palmitic acid C16:0
Stearic acid C18:0
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20:0
SFA
UFA
SFA/ UFA
Xushu 28 Shangshu 19 Xinxiang No.1 Xushu 18 Wutang No.1 Xushu 27 Xushu 22 Mixuan No.1 Beijing 553 Jishu 98 Zheshu 7518
27.50 6 7.26d 31.35 6 0.17bcd 29.88 6 0.03cd 36.84 6 0.27a 31.39 6 0.22bcd 33.11 6 0.04abc 35.45 6 0.02ab 30.81 6 0.29bcd 34.26 6 2.03abc 26.90 6 0.24d 30.32 6 0.11cd
4.26 6 0.36abc 3.22 6 0.00f 4.41 6 0.00ab 4.52 6 0.01a 4.03 6 0.04cd 3.26 6 0.010f 4.56 6 0.03a 3.46 6 0.00ef 3.78 6 0.39de 3.11 6 0.04f 4.08 6 0.04bcd
1.14 6 0.12c 0.90 6 0.00e 1.17 6 0.01c 1.18 6 0.03c 0.50 6 0.06f 1.61 6 0.02a 1.07 6 0.00cd 1.43 6 0.07b 0.97 6 0.17de 0.65 6 0.04f 1.39 6 0.05b
54.47 6 5.46a 53.43 6 0.22ab 52.12 6 0.17abc 43.79 6 0.45d 54.00 6 0.10a 48.96 6 0.06c 44.56 6 0.10d 49.46 6 0.31c 48.95 6 1.30c 52.08 6 0.02abc 49.85 6 0.19bc
10.57 6 1.13ef 8.42 6 0.14h 9.96 6 0.12fg 10.91 6 0.16de 7.35 6 0.08i 11.40 6 0.08cde 11.49 6 0.04cd 13.11 6 0.06b 9.50 6 0.44g 15.57 6 0.33a 11.84 6 0.08c
1.23 6 0.08ab 1.36 6 0.00ab 1.36 6 0.06ab 1.57 6 0.01a 1.10 6 0.07b 1.02 6 0.00b 1.29 6 0.05ab 1.34 6 0.02ab 1.16 6 0.65ab 1.07 6 0.00b 1.40 6 0.04ab
32.98 6 6.82de 35.93 6 0.17cde 35.65 6 0.09cde 42.93 6 0.25a 36.52 6 0.33bcd 37.39 6 0.05bcd 41.31 6 0.06ab 35.61 6 0.27cde 39.20 6 3.07abc 31.08 6 0.28e 35.80 6 0.03cde
66.18 6 6.72ab 62.75 6 0.36bc 63.26 6 0.30bc 55.89 6 0.58d 61.86 6 0.09bc 61.97 6 0.03bc 57.13 6 0.07d 64.00 6 0.32abc 59.43 6 1.92cd 68.31 6 0.31a 63.08 6 0.06bc
0.50 0.57 0.56 0.77 0.59 0.60 0.72 0.56 0.66 0.45 0.57
Values within columns with different letters are significantly different (P , .05). SFA, Saturated fatty acid; UFA, unsaturated fatty acid.
Table 6.4 Fatty acids composition of GLs from 11 sweet potato cultivars (%). Cultivar
Palmitic acid C16:0
Stearic acid C18:0
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20:0
SFA
UFA
SFA/ UFA
Xushu 28 Shangshu 19 Xinxiang No.1 Xushu 18 Wutang No.1 Xushu 27 Xushu 22 Mixuan No.1 Beijing 553 Jishu 98 Zheshu 7518
28.04 6 0.09c 20.09 6 0.01e 24.06 6 4.88de 32.39 6 0.04ab 23.37 6 0.85de 29.46 6 0.18bc 31.04 6 0.19abc 24.08 6 0.28d 33.42 6 2.39a 21.37 6 0.51de 21.24 6 0.26de
5.43 6 0.06ab 3.13 6 0.01f 4.28 6 0.76def 5.04 6 0.06abc 4.81 6 0.36bcd 4.38 6 0.01cde 5.90 6 0.04a 4.37 6 0.10cde 3.78 6 1.25ef 3.94 6 0.03def 4.90 6 0.08abcd
0.49 6 0.01cdef 0.56 6 0.03cde 0.52 6 0.22def 0.85 6 0.07ab 0.25 6 0.01f 1.02 6 0.11a 0.72 6 0.01bc 1.00 6 0.26a 0.67 6 0.08bcd 0.37 6 0.01ef 0.57 6 0.08cde
57.72 6 0.02abc 65.20 6 0.41a 61.46 6 1.36ab 50.47 6 0.26bc 64.20 6 0.67a 54.28 6 0.06abc 50.54 6 0.30bc 52.80 6 0.01bc 52.46 6 3.48bc 59.18 6 0.20ab 61.35 6 0.12ab
8.04 6 0.04ef 10.58 6 0.06cd 9.31 6 3.47f 10.59 6 0.02cd 7.01 6 0.26f 10.23 6 0.05cde 11.36 6 0.16c 17.47 6 0.09a 8.28 6 1.03def 14.55 6 0.31b 11.66 6 0.14c
ND 0.22 6 0.31a 0.11 6 0.35a 0.31 6 0.44a 0.21 6 0.30a ND ND ND 0.47 6 0.67a ND ND
33.46 6 0.03a 23.44 6 0.32c 25.38 6 6.00bc 37.75 6 0.34a 28.39 6 0.91bc 33.84 6 0.19a 36.95 6 0.15a 28.45 6 0.18b 37.67 6 4.31a 25.32 6 0.54bc 26.14 6 0.17bc
66.25 6 0.03c 76.34 6 0.32a 71.02 6 1.19b 61.92 6 0.31e 71.46 6 0.91b 65.52 6 0.09cd 62.62 6 0.13de 71.27 6 0.18b 61.41 6 4.44e 74.10 6 0.50ab 73.58 6 0.19ab
0.51 0.31 0.36 0.61 0.40 0.52 0.59 0.40 0.61 0.34 0.36
Data are means 6 SD (n $ 2). Values within columns with different letters are significantly different (P , .05). SFA, Saturated fatty acid; UFA, unsaturated fatty acid; ND, not detected.
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and Kim, 1994). The most abundant FA in sweet potato GLs was C18:2, which ranged from 50.47% (Xushu 18) to 65.20% (Shangshu 19), followed by C16:0, which ranged from 20.09% (Shangshu 19) to 33.42% (Beijing 553). The contents of C18:0 and C18:3 ranged from 3.13% (Shangshu 19) to 5.90% (Xushu 22) and 9.31% (Xinxiang No.1) to 17.47% (Mixuan No.1), respectively. The contents of C18:1 and C20:0 were relatively low; C18:1 ranged from 0.25% (Wutang No.1) to 1.02% (Xushu 27), and C20:0 was not detected in some sweet potato cultivars, including Xushu 22, Mixuan No.1, Jishu 98, and Beijing 553. GLs derived from plants exhibit various biological properties in vitro and/or in vivo, including antitumor activity (Kuriyama et al., 2005; Hou et al., 2007) and antiinflammatory activity (Leth-Larsen et al., 2003). The GLs in sweet potatoes consisted mainly of MGDGs and DGDGs (Walter et al., 1971). Plant GLs are characterized by one or two UFAs with chain lengths typically varying from C16 to C20 linked to the glycerol moiety, and this is why the UFAs in GLs increased significantly.
Fatty acids composition of phospholipids The composition of FAs in PLs was similar to the other lipid classes (Table 6.5). The UFA content in sweet potato PLs was much higher than the SFA content. The content of UFA ranged from 56.53% (Beijing 553) to 75.37% (Shang 19). The UFAs mainly consisted of C18:1, C18:2, and C18:3, and their contents ranged from 0.59% (Wutang No.1) to 3.08% (Beijing 553), 48.02% (Mixuan No.1) to 67.74% (Shang 19), and 4.40% (Wutang No.1) to 8.84% (Xushu 22), respectively. The contents of SFA in sweet potato PLs primarily consisted of C16:0, C18:0, and C20:0. C16:0 was the most abundant SFA in sweet potato PLs, and ranged from 21.92% (Shangshu 19) to 39.33% (Beijing 553). The content of C18:0 ranged from 1.82% (Shangshu 19) to 4.53% (Xinxiang No.1). C20:0 was not found in Xushu 27 and Mixuan No.1. PLs were the predominant lipid class in biological membranes, although the content of PLs was limited.
Anticancer effects of sweet potato lipids As mentioned in the first section, lipids from different sources exhibited certain anticancer effects. However, reports on the anticancer effects of sweet potato lipids were rare. Thus the antiproliferative effects and cell migration inhibition on cancer cells of sweet potato lipids were studied,
Table 6.5 Fatty acids composition of PLs from 11 sweet potato cultivars (%). Cultivar
Palmitic acid C16:0
Stearic acid C18:0
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20:0
SFA
UFA
SFA/ UFA
Xushu 28 Shangshu 19 Xinxiang No.1 Xushu 18 Wutang No.1 Xushu 27 Xushu 22 Mixuan No.1 Beijing 553 Jishu 98 Zheshu 7518
34.48 6 0.92e 21.92 6 0.25h 31.76 6 1.25g 36.29 6 0.34cd 37.08 6 0.26bc 34.66 6 0.56e 33.36 6 0.32f 37.74 6 0.23b 39.33 6 0.66a 35.30 6 0.13de 32.60 6 0.06fg
3.45 6 0.20b 1.82 6 0.08c 4.53 6 0.99a 3.51 6 0.07b 3.57 6 0.07b 3.23 6 0.10b 3.63 6 0.09b 3.62 6 0.00b 3.36 6 0.30b 3.22 6 0.06b 3.70 6 0.16b
1.12 6 0.09d 1.10 6 0.15de 1.17 6 0.14d 1.27 6 0.09d 0.59 6 0.16g 2.11 6 0.05b 0.92 6 0.00ef 1.83 6 0.06c 3.08 6 0.73a 0.74 6 0.06fg 1.20 6 0.00d
53.16 6 1.06d 67.74 6 0.40a 56.38 6 1.23b 49.51 6 0.26g 53.15 6 0.11de 51.81 6 0.30f 52.30 6 0.02ef 48.02 6 0.64h 47.00 6 0.63i 51.92 6 0.06f 54.92 6 0.02c
6.76 6 0.16d 6.53 6 0.10d 5.62 6 0.33e 8.37 6 0.25b 4.40 6 0.18f 8.18 6 0.11bc 8.84 6 0.02a 8.21 6 0.01bc 5.89 6 0.58e 7.89 6 0.09c 6.91 6 0.05d
1.03 6 0.07a 0.72 6 0.01ab 0.55 6 0.78ab 0.98 6 0.01a 1.14 6 0.01a ND 0.87 6 0.07a ND 1.34 6 0.06a 0.93 6 0.02a 0.67 6 0.07ab
39.41 6 0.65d 24.46 6 0.35f 36.84 6 1.04e 40.78 6 0.29c 41.79 6 0.34bc 37.89 6 0.47e 37.86 6 0.16e 41.94 6 0.58b 43.73 6 0.42a 39.45 6 0.21d 36.97 6 0.03e
61.75 6 0.99cd 75.37 6 0.35a 63.16 6 1.04b 59.14 6 0.42e 58.14 6 0.45e 62.11 6 0.46bc 62.06 6 0.05bc 58.06 6 0.59e 56.53 6 0.78f 60.55 6 0.21d 63.03 6 0.03bc
0.64 0.32 0.58 0.69 0.72 0.61 0.61 0.72 0.77 0.65 0.59
Data are means 6 SD (n $ 2). Values within columns with different letters are significantly different (P , .05). SFA, Saturated fatty acid; UFA, unsaturated fatty acid; ND, not detected.
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to provide basic information for sweet potato lipids potentially to be used in functional foods.
Antiproliferative effect of sweet potato lipids on cancer cells Cancer is proposed to be an aftereffect of the accumulation of multiple genetic alterations, of which the developing risk could be regulated by bioactive components from food (Kim and Milner, 2011). Colorectal cancer is one of the commonest malignancies of the gastrointestinal tract, which ranks as the fourth and third most common cause of cancer deaths in the world and the United States, respectively, while breast cancer is the main cause of cancer deaths among women (Greenlee et al., 2000; Faghfoori et al., 2015; Brosens et al., 2015). Two cancer cells, HT-29 colon cancer cells and Bcap-37 breast cancer cells, then were chosen to study the antiproliferative effect of sweet potato lipids. At the same time, since GLs from other sources showed significant antiproliferative effect on different cancer cells, GLs from sweet potato lipids were separated by macroporous resin using different proportions of ethanol solutions into GLs (I, II, III) to better understand their antiproliferative effect. As shown in Figs. 6.1 and 6.2, both TLs and GLs (I, II, III) showed dose-dependent antiproliferative effects on HT-29 and Bcap-37 cells as shown using the MTT assay. Stronger inhibitory effects were observed on HT-29 than Bcap-37 cells. Compared with TLs, GLs I, II, and III had greater antiproliferative effects on HT-29 cells, of which GL III exhibited the highest effects (Fig. 6.1A, P , .05). The antiproliferative effects of GL III on HT-29 cells were 59.66%, 68.66%, 78.12%, 82.33%, 88.23%, and 92.21% at concentrations of 50, 100, 200, 400, 800, and 1000 μg/mL, respectively (Fig. 6.1A, P , .05). In the crystal violet study, dosedependent inhibitory effects of TLs and GLs (I, II, III) on HT-29 cells were also observed (Fig. 6.1B). In the case of Bcap-37 cells, GL III also exhibited the highest antiproliferative effects, which were 18.83%, 30.48%, 46.62%, 58.26%, 66.87%, and 76.42% at concentrations of 50, 100, 200, 400, 800, and 1000 μg/mL, respectively (Fig. 6.2A). And dosedependent inhibitory effects of TLs and GLs (I, II, III) on Bcap-37 cells were also observed in the crystal violet study (Fig. 6.2B). In addition, the maximum effects were seen in HT-29 and Bcap-37 cells treated with GLs III when concentrations reached 1000 μg/mL (Figs. 6.1B and 6.2B), which was in accordance with the results of the MTT assay (Figs. 6.1A and 6.2A). When the GLs fraction from spinach was incubated with
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Figure 6.1 Antiproliferative effects of sweet potato lipids on HT-29 cancer cells. (A) MTT assay; (B) crystal violet study.
mouse colon-26 cell lines for 24 h, the growth inhibition rate of colon-26 cells decreased to 75.7% at 100 μg/mL (Maeda et al., 2008), which was similar to the antiproliferative effect of sweet potato GLs on HT-29 cells. The treatment of cardiovascular diseases and cancers with natural food ingredients, such as GLs, has gained increased research attention. GLs are a class of metabolites and mainly comprise MGDG, DGDG, and SQDG, which have numerous biological properties, such as antitumor, antimicrobial, antimicrofouling, and antiinflammatory activities (Da Costa et al., 2016). MGDG and DGDG have shown potential anticancer activities due
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Figure 6.2 Antiproliferative effects of sweet potato lipids on Bcap-37 cancer cells. (A) MTT assay; (B) crystal violet study.
to DNA polymerase inhibition, antiproliferation of cancer cells, and antitumor growth (Maeda et al., 2008). SQDG has also shown antiproliferative effects on gastric cancer cells (Quasney et al., 2001).
Cell metastasis inhibition of sweet potato lipids on cancer cells Metastasis of cancer cells is the process of tumor cells transferring from primary tumor blocks to distant target tissues. It is a difficult point in tumor therapy and is also the main cause of cancer-related morbidity and
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mortality. The cell metastasis inhibition of sweet potato lipids on cancer cells was studied via their effects on the adhesion and migration of cancer cells to provide the basic data for the application of sweet potato lipids in functional foods. Effect of total lipids and glycolipids on adhesion of HT-29 and Bcap-37 cells The effects of TLs on the adhesion of HT-29 and Bcap-37 cells are shown in Fig. 6.3A. Compared with the untreated cells, the adhesion time for cells treated with phorbol 12-myristate 13-acetate (PMA) increased significantly, that is, 1.7 times that of untreated cells. With the increase of TLs concentration (100, 400, and 1000 μg/mL), the adhesion effect of cancer cells decreased significantly (P , .05). The cell adhesion time for cells treated with TLs at 100 and 400 μg/mL was higher than that of untreated cells, but lower than that of cells treated with PMA
Figure 6.3 Cell adhesion inhibition effects of sweet potato lipids on HT-29 and Bcap37 cancer cells. (A) TLs; (B) GLs I; (C) GLs II; (D) GLs III.
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(P , .05). The cell adhesion time for HT-29 and Bcap-37 cells treated with TLs at 1000 μg/mL is 7.5 and 7.0 min, separately, showing no significant difference with untreated cells (P..05). The effects of GLs I, II, and III on the adhesion of HT-29 and Bcap37 cells were shown in Fig. 6.3B, C, and D. The cell adhesion time of both HT-29 and Bcap-37 cells by adding PMA without GLs was significantly higher than those of the untreated cells and the cells with GLs (P , .05). Among the cells treated with GLs, the cell adhesion time decreased significantly with the increase of GLs concentration (100, 400, and 1000 μg/mL), of which GLs III showed the highest effect, followed by GLs II (P , .05). Compared with the untreated cells, adhesion time of cells treated with GLs was higher with the concentration less than 400 μg/mL. When the concentration of GLs increased up to 1000 μg/ mL, there was no significant difference between the adhesion time between the untreated cells and cells treated with GLs I, while the adhesion time of cells treated with GLs II and III was much lower than that of untreated ones (P , .05). For HT-29 cells, when the concentration of GLs was 1000 μg/mL, the adhesion time of cells treated with GLs I, II, and III were 7.1, 6.1, and 5.3 min, which reduced by 42.7%, 50.8%, and 57.3% compared with that of the PMA-treated cells, respectively. For Bcap-37 cells, when the concentration of GLs was 1000 μg/mL, the adhesion time of cells treated with GLs I, II, and III were 6.1, 5.5, and 4.7 min, which reduced by 45.0%, 50.5%, and 57.7% compared to the PMA-treated cells, respectively. Compared with TLs, the adhesion time of HT-29 cells treated with GLs I, II, and III decreased by 4.7%, 12.8%, and 19.3%; and the adhesion time of Bcap-37 cells was shortened by 8.1%, 13.6%, and 20.8%, respectively. The results suggested that GLs I, II, and III could reduce the adhesion of cancer cells, of which the effect was better than TLs, particularly for Bcap-37 cells. Effects of total lipids and glycolipids on the migration of HT-29 and Bcap-37 cells The effects of TLs on the migration of HT-29 and Bcap-37 cells are shown in Fig. 6.4. The cell migration of both HT-29 and Bcap-37 cells by adding PMA without TLs was significantly higher than those of the untreated cells and cells with TLs (P , .05). Among the cells treated with TLs, the cell migration decreased significantly with the increase of TLs concentration (100, 400, and 1000 μg/mL). For HT-29 cells, when the concentration of TLs was 1000 μg/mL, the cell migration of cells treated with TLs was 23.03%, which was reduced by 17.32% compared to
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Figure 6.4 Cell migration inhibition effects of sweet potato lipids on HT-29 (A) and Bcap-37 (B) cancer cells.
Figure 6.5 Cell adhesion inhibition effects of sweet potato lipids on HT-29 (A, GLs I; B, GLs II; C, GLs III) and Bcap-37 (D, GLs I; E, GLs II; F, GLs III) cancer cells.
PMA-treated cells (Fig. 6.4A). For Bcap-37 cells, when the concentration of TLs was 1000 μg/mL, the cell migration of cells treated with TLs was 35.83%, which was decreased by 18.36% compared with that of the PMA-treated cells (Fig. 6.4B). The effects of GLs I, II, and III on the migration of HT-29 and Bcap37 cells are shown in Fig. 6.5. The cell migration of HT-29 and Bcap-37 cells by adding PMA without GLs was significantly higher than those of the untreated cells and cells with GLs (P , .05). Among the cells treated with GLs, the cell migration decreased significantly with the increase of GLs concentration (100, 400, and 1000 μg/mL), of which GLs III showed the highest effect, followed by GLs II (P , .05). For HT-29 cells, when
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the concentration of GLs was 1000 μg/mL, the cell migrations of cells treated with GLs I, II, and III were 10.35%, 8.06%, and 6.04%, which reduced by 30%, 32.29%, and 34.31% compared to the PMA-treated cells, respectively. For Bcap-37 cells, when the concentration of GLs was 1000 μg/mL, the cell migrations of cells treated with GLs I, II, and III were 22.35%, 20.04%, and 16.72%, which reduced by 31.84%, 34.15%, and 37.47% compared to the PMA-treated cells, respectively.
Anticancer effects confirmation of sweet potato lipids To confirm the anticancer effects of TLs, GLs I, II, and III in sweet potato, the MGDG and DGDG contents were determined. Compared with TLs, GLs I, and II, GL III showed the highest level of MGDG, which was 35.84% (Fig. 6.6A, P , .05). There were significant differences
Figure 6.6 MGDG and DGDG in sweet potato lipids. (A) MGDG percentage; (B) DGDG percentage.
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in the percentages of DGDG in TLs and GLs (I, II, III), which followed the order GL III . TLs . GL I . GL II (Fig. 6.6B, P , .05). Thus GL III showed the highest percentage of DGDG compared with TLs, GLs I and II, which was 89.16% (Fig. 6.6B, P , .05). Napolitano et al. (2007) indicated that 16 novel and 10 known galactolipids identified from sweet potato leaves cultivated in Japan contained MGDG and DGDG. Roberts and Moreau (2016) showed that GLs in spinach leaves included MGDG, DGDG, and SQDG, which exhibited antiproliferative activity in many different cancer cell lines. MGDG from spinach also inhibited the proliferation of colon-26 cells, and oral administration suppressed colon tumor growth in mice (Maeda et al., 2013). In addition, further studies on the relationship between the molecular mechanisms and the structures of sweet potato lipids should be performed, as well as animal experiments.
Application prospect of sweet potato lipids Sweet potato lipids are rich in GLs and PLs, and could be a good source of essential GLs and PLs. The UFA content in sweet potato lipids is greater than the content of SFA, showing potential utilization in the prevention of cardiovascular diseases and the protection of the brain and nervous system. In addition, sweet potato lipids present certain anticancer effects, especially for GLs with the contribution of MGDG and DGDG. Thus sweet potato lipids could be potentially used in functional foods, health care products, and pharmaceuticals in the near future.
References Adam, F., Vian, M.A., Peltier, G., Chemat, F., 2012. “Solvent-Free” ultrasound assisted extraction of lipids from fresh microalgae cells: a green, clean and scalable process. Bioresour. Technol. 114, 457 465. Adam, O., Beringer, C., Kless, T., Lemmen, C., Adam, A., Wiseman, M., et al., 2003. Anti-inflammatory effects of a low arachidonic acid diet and fish oil in patients with rheumatoid arthritis. Rheumatol. Int. 23, 27 36. Avrova, N.F., Zakharova, I.O., Tyurin, V.A., Tyurina, Y.Y., Gamaley, I.A., Schepetkin, I.A., 2002. Different metabolic effects of ganglioside GM1 in brain synaptosomes and phagocytic cells. Neurochem. Res. 27, 751 759. Benatti, P., Peluso, G., Nicolai, R., Calvani, M., 2004. Polyunsaturated fatty acids: biochemical, nutritional and epigenetic properties. J. Am. Coll. Nutr. 23, 281 302. Bouwkamp, J.C., 1985. Sweet Potato Products: A Natural Resource for the Tropics. CRC Press. Brosens, L.A.A., Offerhaus, G.J.A., Giardiello, F.M., 2015. Hereditary colorectal cancer: genetics and screening. Surg. Clin. N. Am. 95, 1067 1080.
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