Chapter 4 Results and Discussion
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CHAPTER 4 RESULTS AND DISCUSSION In this chapter the results obtained from the experiments described in chapter 3 are discussed in detail, to highlight the remarkable observations and to offer possible interpretation for those observations. The results are given in five sections. The first section describes the comparison of oil extractions from various types of rice bran. Second section deals with the mass transfer coefficient of rice bran oil extraction. The cross flow extraction of different bran types are explained in the third section and in the fourth section the oil extracted from raw and parboiled bran are compared. Finally the suitability of rice bran oil extracted from different varieties of bran available in Sri Lanka as a raw material for food items, pharmaceuticals and bio-fuel production is discussed. 4.1 COMPARISON OF OIL EXTRACTIONS FROM VARIOUS TYPES OF RICE BRAN 4.1.1 Yield of different varieties of bran Different varieties of bran were experimented for extracting oil using the soxhlet apparatus with 8 mm diameter and 5mm height pellets and the results are shown in table 4.1 in Annex II. The IPA extractable oil percentage is shown in Figure 4.1 and different varieties showed different extractable oil contents with highest percentage of oil in Red Samba LD356. 54 20 18 16 14 12 10 8 Yield(%) 6 4 2 0 LD356 BG450 BG360 BW364 BG352 AT307 Bran Type Figure 4.1: Extractable oil percentages of rice bran varieties available in Sri Lanka The yields are different in different varieties of bran. Due to the difference in degree of polishing and seeding times, the yields may differ. Different types were milled and polished in batch wise and since, polishing is partly done by humans; the degree of polishing can be different from one type to another (Taira, 1989). There is no clear distinction between the bran layer and endosperm. The harder the rice is polished, the more bran is generated. Some of the endosperm is going into the bran and so the properties unique to rice bran are diluted as the rice is polished harder. This will lead to differences in yield. Variation of oil percentage also depends on properties of different varieties such as oil content and porosity of the bran particle. Moreover, the difference in yield is due to the genetic variations of paddy (Fernando, et al., 2003). 55 4.1.2 Properties of oil from different varieties of bran 4.1.2.1 Free Fatty Acid (FFA) content of oil Oil extracted in section 4.1.1 was tested for the FFA content by the ASTM D1639 method and the results obtained are given in table 4.2 in Annex II. FFA content against the different varieties of bran is plotted in figure 4.2. 2.50 2.00 1.50 1.00 FFA (%) FFA 0.50 0.00 LD356 BG450 BG360 BW364 BG352 AT307 Bran Type Figure 4.2: FFA content of oil obtained from different varieties of rice bran The amount of free fatty acids depends on the nature of oil, method of extraction, storage conditions, humidity, temperature and lipase activity in rice bran. In this scenario, all the parameters except for the lipase activity in rice bran are the same for all these varieties. Type BW364 shows a significantly higher value of free fatty acids and this might be due to high initial free fatty acids as a result of lipase activity. 56 LD356, BG450 and BG352 show low and somewhat equal values, whereas BG360 and AT307 show average values. The acid value which is a measure of the free fatty acid content of oil, is an index of the measurement of freshness of oil. Humidity and high temperature result in an increase of the acid value due to hydrolysis of glycerides into free fatty acids. Higher values indicate undesirable changes as it not only results in greater refining losses but also increases susceptibility of oils to rancidity. It is thus very important in economics of oil refining. The oils intended for dietary purposes should not contain higher amounts of free fatty acids. The presence of free fatty acids in oils & fats is not desirable because they impart a sharp and unpleasant flavor to edible fats & oils. 4.1.2.2 Saponification value (SAP value) By following the ASTM D1962 method, the saponification values (SAP value) for the above extracted oil samples were found and the table 4.3 in Annex II shows the SAP values. The graph related to this table is shown in figure 4.3. 300 250 200 150 100 50 0 Saponification Value oil) (mg KOH/g Value Saponification LD356 BG450 BG360 BW364 BG352 AT307 Bran Type Figure 4.3: SAP value of oil obtained from different varieties of rice bran 57 Saponification value is a measure of the molecular weight of the fatty acids present in oil. Shorter the average chain length (C4-C12) the higher is the saponification number (Tamzid, et al., 2007). The oil with low molecular weight fatty acids has a higher saponification value (Adepoju, et al., 2013). LD356 and BW364 have the highest and relatively equal saponification values, whereas BG360 has the lowest value. 4.1.2.3 Unsaponifiable Matter The Unsaponifiable matter content was found using ASTM D1965 method and the values obtained for the oil extracted for the above mentioned rice varieties are given in table 4.4 in Annex II and the relevant graph is given figure 4.4. 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 Unsaponifiable MatterUnsaponifiable (%) 0.00 LD356 BG450 BG360 BW364 BG352 AT307 Bran Type Figure 4.4: Unsaponifiable matter content of oil obtained from different varieties of rice bran 58 Unsaponifiable matters are bioactive components with nutraceutical value, mainly composed of sterols, triterpene alcohols and less polar components such as squalene or tocotrienols. Recently, rice bran oil has gained attention because of its unique health claims attributed by its high level of unsaponifiable matter. Currently, efforts are being made to develop RBO with retained non-saponifiable components, while minimizing levels of problematic free fatty acids. There are several mechanisms by which unsaponifiables improve serum bio-chemical profile such as by interrupting the absorption of intestinal cholesterol rather increasing the excretion of fat and neutral sterols and increased fecal steroid excretion through interference with cholesterol absorption (Ginsberg, et al., 1998). 4.1.2.4 Iodine Value Oil extracted from different varieties of rice bran was tested for the Iodine value by the SLS313 Part II and the results obtained are given in table 4.5 in Annex II. Iodine value against the different varieties of rice bran is plotted in figure 4.5. 43.40 43.20 43.00 42.80 42.60 Iodine Value Iodine 42.40 42.20 LD356 BG450 BG360 BW364 BG352 AT307 Bran Type Figure 4.5: Iodine value of oil obtained from different varieties of rice bran 59 The iodine value is a measure of the degree of unsaturation of fatty acids and expressed in terms of the number of grams of iodine absorbed by 100g of oil. It also indicates the stability of oil towards oxidation. It is observed, higher the iodine value, greater the degree of unsaturation. Considerably high and low iodine values are seen in AT307 and BW364 respectively as 43.29 and 42.63. 4.1.2.5 Specific Gravity AOCS Official Method To 1a-64 was used to measure the specific gravity of the oil obtained from different varieties of rice bran and the results are shown in table 4.6 in Annex II. The graphical representation of the results is displayed in figure 4.6. 0.950 0.945 0.940 0.935 0.930 0.925 0.920 Specific Gravity Specific 0.915 0.910 0.905 LD356 BG450 BG360 BW364 BG352 AT307 Bran Type Figure 4.6: Specific Gravity of oil obtained from different varieties of rice bran 60 The presence of the number of double bonds and increase in chain length of the fatty acids tend to increase the specific gravity. It is evident from the results that the specific gravity of rice bran oil samples ranged from 0.919 to 0.944. For oils, the value of specific gravity is always <1 and normally ranges from 0.850 to 0.950. 4.1.2.6 Color of oil The oil obtained from different varieties of rice bran demonstrated different colors. Following are the colors of the oils and figure 4.7 is an image of the oil samples showing the colors. LD356 – Dark greenish, closer to black BG450 – In the middle of light and dark green, closer to dark green BG360 - In the middle of light and dark green, closer to light green BW364 – In the middle of light and dark brown, closer to dark brown BG352 – Light brownish AT307 – In the middle of light and dark brown, closer to light brown. AT307 BG450 BG352 LD356 BW364 Figure 4.7: Colors of oil obtained from different varieties of rice bran Color is mainly influenced by quality of bran, processing methods, storage conditions and method of extraction. 61 4.1.3 Reason for variation in properties of oil from different bran varieties The quality and the composition of each paddy variety are determined by a number of genetic and physiological characteristics. The genetic factors that can influence quality include genetic make-up, seed size and bulk density (International Rice Research Institute, 2009). The physical or environmental characteristics comprise of injury during planting and establishment, growing conditions during seed development, nutrition of the mother plant, physical damage during production or storage by machine or pest, moisture and temperature during storage and age or maturity of seed.