Virgin coconut oil prepared by protease-assisted process : Characteristics and application

Abstract

Coconut milk and meat at three different maturity stages including immature coconut (IMC), mature coconut (MC) and overlay mature coconut (OMC) had varying proximate compositions. Compositions of coconut milk generally were in accordance with those found in coconut meat. Cocosin with molecular weight of 55 kDa was observed as the major protein in all coconut milks but its band intensity slightly decreased with increasing maturity stages. Oil droplet size increased as maturity stages increased. Nevertheless, virgin coconut oil (VCO) extracted from coconut with three different maturity stages had no impact on fatty acid composition and physicochemical properties. VCO separated using Alcalase showed the highest recovery (95.64%) when coconut milk from OMC was used as starting material. All VCO samples had waterlike appearance and contained medium chain fatty acid (MCFA), especially lauric acid as a major fatty acid, (49.74-51.18 g/100g). Myristic acid in the range of 18.70-19.84 g/100g was present in all VCO. All VCO samples had low lipid hydrolysis and oxidation, indicating that maturity stages had no influence on oil stability. Albumin and globulin were the predominant protein fractions in defatted coconut meat. Both fractions showed the differences in protein patterns and amino acid compositions. Varying emulsifying property was obtained between both fractions. Albumin, water-soluble protein fraction, exhibited lower emulsifying properties, compared to globulin (salt-soluble) counterpart. However, globulin fraction was more susceptible to hydrolysis by Alcalase, leading to the higher collapse of emulsion of coconut milk after being hydrolyzed. This contributed to the higher oil recovery from coconut milk. Difference was observed in degree of hydrolysis (DH), oil recovery, microstructure and protein pattern of coconut milk hydrolyzed by partially purified protease from seabass pyloric caeca (PPSP) and commercial trypsin (CT) at different proteolytic levels (5 and 10 units/g protein) at 60 °C for various hydrolysis times (0-150 min). The highest VCO yield (77.35%) was found when sample was hydrolyzed by PPSP (10 units/g protein) for 150 min. Based on DH and electrophoretic study, proteins in coconut milk were more prone to hydrolysis by PPSP, compared to CT. Therefore, PPSP could be used as an alternative processing aid and the efficiency was higher than CT. PPSP was further used in combination with different treatments including microfluidization, chill-thawing and freeze-thawing for extraction of VCO. Coconut milk hydrolyzed by PPSP at 10 units/g protein, followed by freeze-thawing showed the highest yield among other samples (p<0.05). Conversely, the lowest VCO yield was attained for coconut milk homogenized at 4000 psi, followed by hydrolysis using PPSP (5 units/ g protein). Hydrolysis by PPSP, followed by freeze-thawing of 5 cycle rendered the highest yield of VCO (98.6%). However, no marked difference was observed in fatty acid profile, moisture content, free fatty acid content (FFA) and oxidative stability among all VCO extracted from aforementioned methods. Because of high stability and various health benefits, VCO in combination with fish oil (FO) rich in n-3 fatty acids at different ratios (95:5, 90:10, 85:15, v/v) was used to prepare a functional mayonnaise. Chemical and physical changes were monitored during the storage of 30 days at room temperature (30-32 °C) in comparison with those of mayonnaise prepared using soybean oil (SO). Addition of FO up to 10% in VCO/FO blend could yield the mayonnaise with sensorial acceptability. Oxidative stability varied with mayonnaises containing different oils. Mayonnaise sample with VCO was less prone to lipid oxidation throughout storage of 30 days. Types of oil used for preparation of mayonnaise and storage time affected the color, textural and rheological properties of resulting mayonnaise. In general, mayonnaise containing VCO/FO (90:10) blend showed the property equivalent to that prepared using SO. Thus, VCO could be incorporated in combination with FO at appropriate level to prepare a functional mayonnaise with acceptability and oxidative stability. Therefore, VCO could be successfully produced with the aid of fish trypsin in conjunction with repeated freeze-thawing cycles. The resulting VCO could be employed as food ingredient or other applications.