Comparison of the New Aqueous Method with Other Methods
Table 4 compares the performance of the NAM established, with other methods and the quality of oils obtained with that of the first class oil required by Chinese National Standard. The OR obtained by NAM was obviously better than that obtained by traditional enzyme-assisted aqueous method (EAAM) extraction. Although NAM had a significantly lower OEE (P < 0.05), it had a slightly higher OR without significant difference (P > 0.05) as compared to SE. NAM also had higher OR as compared with cold pressing (Scapinello et al., 2017). Since no national standard for pecan oil acid value (AV; mgKOH/g) or peroxide value (PV; mmol/kg) was found, it was compared to the national standard of walnut oil (GB/T 22327-2008). As can be seen from the table, the pecan oil extracted by the aqueous solution method met the national standard of walnut oil. The peroxide value and acid value of the product were better than that of first class walnut oil required by the national standard. The oils were transparent, clean and colored favorably.
The de-oiled pecan meal had 27.09% of water content when 1.40 mL water was added for extracting oil. The de-oiled meal was also colored favorably (L*=55.67, a*=7.64, b*=10.67), which should be able to be applied to food recipes or the food industry.
Although the NAM used a quite low centrifugation force, a satisfactory OR was achieved. This largely decreases the purchasing or operating cost of centrifuge machine although the improvement of OR by a further increasing in centrifugation force as comparing with 1435 g employed in this study may not be ruled out. It should be noted that other methods also need centrifugation or filtration to clarify oils.
The method of extracting oils from pecan kernels by NAM produces no waste water. Drying the de-oiled meal only discharges vapor of water to the air. Therefore, the NAM is more environmental friendly as compared to EAAM (using large quantities of water previously published in literature) and SE (releasing harmful solvent to the air).
The NAM produces the de-oiled pecan kernel meal with low water content whose drying cost is greatly reduced. This is currently not achieved when the EAAM using large amounts of water .
The NAM produces oil with high quality so that it is safe for consumption without refinement (Table 4). The quality of oil produced by the NAM is far better as comparing to the crude oil obtained by SE.
Although the established NAM had a slightly lower OER as compared to SE, crude oils obtained by SE was not edible without refinement. A significant amount of neutral oil can be lost during refining process (Stalker and Wilson, 2015). Therefore, the NAM had significant higher OR as compared with SE.