Preparation of function-enhanced vegetable oils

Abstract

Background: Previously, we (HM) found that most commercially available edible oils, which were processed by hexane extraction followed by a number of purification steps, were extremely low in anti-peroxy radical (ROO^.), or radical scavenging activity.  This is a great contrast to the respective virgin oils as exemplified by extra-virgin olive oil or crude rape seed oil [1-4] (Figure 1).  Therefore, such highly purified oils will became prooxidant and less desirable food components in terms of health oriented diet. Oxidized oils may eventually cause DNA cleavages, modification of proteins, RNA, and lipids, as well as cellular damage, or promote inflammation and carcinogenesis at later time [5-9]. 

These commercial oils of low antioxidant activity may be improved by adding functionally effective antioxidative components, by using dried vegetable-waste such as tomato-juice-waste-residues and wine-ferment-waste-residues. Their antioxiative components will be transferred into the functionally poor grade edible oils, and consequently, one can improve the quality of such functionally poor oils and thereby contributing human health [2,8,9].   The purpose of this paper is to report a practical procedure to fortify functionally low grade conventional edible oils to functionally enriched edible oils using dried vegetable-waste residues such as tomato juice waste, and wine-ferment-residues, or other vegetable-waste residues.

Methods: 

(1) Preparation and measurements of lycopene and carotenoid enriched oils.  To 5.0g or 1.0g of the dried residue of tomato juice waste, 100ml of commercial rape seed (canola) oil was added respectively. Each mixture was incubated at room temperature in dark for several weeks.  Amount of lycopene and carotenoids extracted into the oil was monitored by increase of absorption (400-550nm) and fluorescence at 470nm of carotenoid.  Grape-juice ferment (wine) waste was similarly prepared after hot air drying, and immersed in canola oil.

(2) Evaluation of function-enriched edible oils: Preventive effect of lipid peroxidation;

(a)  Heat exposure: Commercial rape-seed oil and extra virgin oil were used as controls.  For preparation of the test samples (function fortified oils) of tomato-juice waste-residue and grape wine- ferment waste-residues, it is described in above section (1).  All oil preparations were exposed to high temperature at 150^oC and peroxide value (POV), acid value and TBARS were measured at various times as described.  The methods of measurements of POV, acid value and TBARS were adapted conventional standard method described elsewhere. 

(b)  Light exposure:  Similar to (a) they were exposed to excessive light using Nippon Ikaga Kikai (Tokyo), LH-200-RDS equipped with fluorescent light tube (x3), NEC FL40S-2XN, 3.2K lux at 390-730nm. 

Result and Discussions:

(1)  Extraction of carotenoids etc.

Modern edible oil refining processes are highly elaborated and efficient. The most of the commercial edible oils in the market are so purified that many important antioxidant components are mostly removed during refining process.  Oils became mostly colorless and odorless; and they lack are devoid of anti-oxidative or radical scavenging components.  We measured anti-alkyl peroxy radical (ROO^.)-scavenging activity, and found that many commercial oils have very little such activity (Figure 1).

Many disposal- of tomato juice or extraction waste-residues in wine making, yet contained significant amount of functionally useful components that may be recovered by immersing the dried waste residues in the functionally poor oil, ie., low grade oils.  Figure 2A, B shows it was indeed possible to recover such component like lycopene and carotenoids, and the spectrum of this oil exhibits multiple peaks correspond tomato lycopene.

(2) Antioxidation activity:

(a) Acid value after light and heat exposure. Commercial highly purified edible oils are vulnerable for oxidation and resulting in lipid or alkyl hydroperoxides formation (ROOH), which undergo formation lipid (alkyl) peroxyl radicals which (ROO^.) in the presence of heme or other metallic compounds (ROOH à ROO^.) (Figure 1) [5, 11].  This peroxyradical can break DNA/RNA or damage proteins and lead to cell death [4-7, 11].

Time course of carotenoids extraction into the purified canola oil, in which 1 or 5% (dry wt/wt) of tomato juice waste-residue yielded a significantly high carotenoid values, and extraction reached a plateau in about two to three weeks (Fig. 2A). The absorption spectrum shows multiple peaks corresponding lycopene (Fig. 2B).   

(b) Anti-POV after heat and light exposure. Upon exposure to oxidation condition, POV was significantly suppressed to 25% after 5 hrs at 150^oC and light exposure (above) to the 5% (w/w) tomato-residue-treated oil, and showed suppression of POV to about 25% (net) at 5 hrs (Fig. 3). 

(c) TBARS value after light and heat exposure. Figure 4C, D shows results of function fortified effect in oils treated with tomato- and wine ferment-waste-residues. They also showed significant suppression against the increase of acid value and POV (Figure 4A, B), which is consistent with absorption spectra.

These results indicate antioxidant components in dried tomato juice-waste-residues and wine ferment waste-residues were extracted into commercial low functional grade rapeseed oil. The results warrant a simple procedure to convert low quality edible oils to function-enriched high grade oils. The procedure not only prevents oxidation of oils, but also beneficial in providing various functional components such as polyphenolics, flavonoids, carotenoid, or lycopene.  This method and products thus obtained will ultimately benefit human health such as prevention of cancer and inflammation [8, 9, 11]. 

We have previously published that alkyl peroxyradical facilitates promotion step in carcinogenesis, and it was suppressed by various vegetable soup extracts, thus in suppressing promotion step in multistep carcinogenesis [2, 4, 10]. The step may be related to the suppression of inflammatory process as well via activation of cyclooxygenase I and i-NOS, as well as tumor necrosis factor [8, 9].

In the manufacturing traditional Japanese rape-seed (canola) oil, the seeds were roasted at high temperature.  We found during this heating process, new antioxidant component (canolol), which is a potent scavenger of alkylperoxyl radical and peroxinitrite (ONOO^-), was efficiently generated, and the oil became much healthier benefit than highly purified rape seed oil in the market, which are prepared by hexane extraction and other purification steps.

In these few decades’ vegetable oils are considered not healthy dietary components. This is probably due to preciously important antioxidants components, which originally did exist as intrinsic components in the seeds, were removed so effectively during manufacturing and purification processes. As a result, vegetable oils became prooxidant or procarcinogen, and thus unfavorable food staff. Now our method described herein provide easy enrichment procedure for functional components utilizing wasted residues of vegetable including wine and juice making.

Keywords: antioxidative components, enrichment of edible oils, lipid oxidation, dried vegetable-waste-residues.