Patent Application
20230079687
This application is directed to antioxidant compositions comprising alkylresorcinol homologues in low-moisture foods, methods of their preparation, products and uses thereof.
The consumption of omega-3 fatty acids is associated with reducing the incidence of cardiovascular and inflammatory diseases, which has led to the food industry supplementing foods with omega-3s to confer these health benefits. One drawback to this is that these polyunsaturated fatty acids are highly labile to lipid oxidation, resulting in their breakdown and the loss of these health promoting benefits as well as the development of off-flavors. Antioxidants are often added to lipid-containing foods to slow the rate of oxidation, thus preserving omega-3s and their health benefits; however, concerns surrounding the toxicity and consumer acceptability of synthetic antioxidants has resulted in the need to identify and improve the efficacy of natural antioxidants.
Consumers of Western diets tend to overconsume saturated fats, which can have various detrimental effects on health including increasing the risk of developing coronary heart disease (Mozaffarian, Micha, & Wallace, 2010; Shan et al., 2019). Low-moisture foods (aw<0.5), such as cookies, crackers, and granola bars, are a major source of saturated fats in the diet with these grain-based snacks and desserts constituting one of the top three sources of saturated fats for children, aged 2-18 years, consuming Western diets (Huth, Fulgoni III, Keast, Park, & Auestad, 2013; Keast, Fulgoni III, Nicklas, & O'Neil, 2013; Reedy & Krebs-Smith, 2010).
Many foods are naturally prone to chemical degradation via lipid oxidation; however, this has only been exacerbated by the fact that the food industry has begun to reformulate various food products to replace saturated fatty acids with beneficial polyunsaturated fatty acids (Ganesan, Brothersen, & McMahon, 2014). One drawback to this is that polyunsaturated fatty acids are more prone to lipid oxidation due to their high degree of unsaturation. Lipid oxidation results in the loss of a food's nutritional value, the formation of toxic compounds, and the development of off-flavors associated with rancidity (Arab-Tehrany et al., 2012; Frankel, 1998; Jacobsen, Let, Nielsen, & Meyer, 2008; Kanner, 2007). One reported means to control lipid oxidation is through the addition of antioxidants that can rapidly react with prooxidants via a variety of mechanisms (Choe & Min, 2009).
While mechanisms of antioxidant action are well understood, the effect of a given food product's physical structure on antioxidant reactivity is less clear. Progress has been made to understand the effect of structure on lipid oxidation in oil-in-water emulsions and to a lesser extent in bulk oils; however, structural effects in low-moisture foods are not well studied. One important factor may be that prooxidants and antioxidants have reduced molecular mobility in low-moisture foods which limits their interactions, potentially impacting lipid oxidation (Barden & Decker, 2016). For example, many low-moisture foods are fortified with transition metals (e.g. iron) for nutritional purposes, despite this, these ions do not appear to be important prooxidants due to their low mobility (Barden & Decker, 2016; Barden, Vollmer, Johnson, & Decker, 2015).
A second structural factor that may be important in controlling lipid oxidation in low-moisture foods may be the nature of the interface between the lipid phase and other food components present. In bulk oils and high-moisture foods, lipid oxidation occurs at the lipid-water interface; however, this interface is not present in low-moisture foods. (Chen, McClements, & Decker, 2011; Waraho, McClements, & Decker, 2011).
In a low-moisture model cracker system, lipids were observed to form a continuous matrix that surrounds starch granules creating protein-starch-lipid, lipid-air, protein-lipid, and starch-lipid interfaces which may influence the progression of lipid oxidation (Barden, Vollmer, et al., 2015). These observations suggest that the antioxidant strategies required to extend the induction period of lipid oxidation and, thus, increase the shelf life of low-moisture foods, will differ greatly from those utilized in bulk oils and high-moisture foods.
Antioxidants that localize to lipid interfaces are thought to be more effective than antioxidants that localize to other phases because they are concentrated at the site where lipid oxidation occurs (Frankel, Huang, Kanner, & German, 1994). However, this approach is less clear in low-moisture systems where the nature of the interfaces is less well defined and antioxidants may become immobilized in the non-lipid matrix.
One strategy that has been used to enhance the effectiveness of polar antioxidants in oil-in-water emulsions is to graft them with alkyl moieties to increase their hydrophobicity and, thus, their surface activity, driving them to the lipid-water interface (Laguerre et al., 2015). A similar approach was taken using rosmarinic acid and a pair of rosmarinate alkyl esters in a low-moisture model cracker system, where it was found that the hydrophobic eicosyl ester displayed stronger antioxidant activity than rosmarinic acid and the dodecyl ester (Barden, Barouh, Villeneuve, & Decker, 2015). Based on these results, the lipid interfaces were hypothesized to be the sites of lipid oxidation in low-moisture foods, with hydrophobic antioxidants concentrating at the lipid phase, improving their efficacy (Barden, Barouh, et al., 2015).
Due to perceived consumer demand, the food industry is actively attempting to replace synthetic antioxidants with natural alternatives (Brewer, 2011; Gülçin, 2012). Therefore, while modulating hydrophobicity by modifying alkyl chain length has been shown to improve the efficacy of natural antioxidants, this strategy is unlikely to be implemented in the food industry because the resulting products are no longer considered to be “natural.”
Alkylresorcinols (ARs) are a naturally occurring homologous series of amphiphilic phenolipids derived from the bran layer of cereal grains (Bartfomiej, Justyna, & Ewa, 2012). ARs are meta-substituted dihydroxyl phenolics with an odd numbered alkyl chain ranging in length from 13 to 27 carbons (Bartlomiej et al., 2012). The alkyl chains are predominately saturated but can be monounsaturated, di-unsaturated, or contain hydroxyl or ketone groups.
Despite being present in many grain-based foods, the antioxidant activity of ARs in low-moisture foods has yet to be studied comprehensively. We report novel methods for use of alkylresorcinols as antioxidants. Some embodiments are directed to use of AR homologues of different alkyl chain lengths, either alone or in a mixture of two or more chain lengths (for example C17:0, C19:0, C21:0, C23:0, C25:0) as antioxidants in a low-moisture food, such as a low-moisture model cracker system.
Additionally, exemplary embodiments may relate to use of individual alkylresorcinol homologues and alpha-tocopherol used in unison, to determine if synergy exists between the two antioxidants, the possible underlying mechanism, and whether this combination improves the efficacy of these natural antioxidants.
According to an exemplary embodiment, there is provided an antioxidant composition comprising:
comprising an alkyl chain wherein n=12-26; and
wherein the low-moisture food has a water activity (aw) equal to or less than 0.85. In another exemplary embodiment the low-moisture food has a water activity equal to or less than 0.5.
In another exemplary embodiment is presented a method of preparing the compound of Formula (I) by winterization, comprising one or more of the following steps:
optionally repeating steps (i)-(vii) one or more times;
and optionally drying the pellet produced by step (vii).
In another exemplary embodiment is presented a method of preparing the compound of Formula (I) by winterization, comprising one or more of the following steps:
In another exemplary embodiment, there is provided a food product comprising an antioxidant composition disclosed herein.
Other aspects and advantages of the disclosure will be apparent from the following detailed description and the appended claims.
While the terms used herein are believed to be well understood by one of ordinary skill in the art, definitions are set forth herein to facilitate explanation of the subject matter disclosed herein.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter disclosed herein belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are described herein.
The terms “a,” “an,” and “the” refer to “one or more” when used in this application, including the claims. The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”
All references to singular characteristics or limitations of the present disclosure shall include the corresponding plural characteristic(s) or limitation(s) and vice versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made.
All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.
The methods and devices of the present disclosure, including components thereof, can comprise, consist of, or consist essentially of the essential elements and limitations of the embodiments described herein, as well as any additional or optional components or limitations described herein or otherwise useful.
The term “alkyl” includes branched, straight chain and cyclic, substituted or unsubstituted saturated aliphatic hydrocarbon groups. Alkyl groups can comprise about 1 to about 30 carbon atoms (“C1-C30”), about 16 to 20 carbon atoms, or about 1 to 24 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, cyclohexylmethyl, cyclopropylmethyl and neohexyl radicals.
The term “aryl” includes a 6- to 14-membered monocyclic, bicyclic or tricyclic aromatic hydrocarbon ring system. Examples of an aryl group include phenyl and naphthyl.
The term “aralkyl” refers to an aryl-alkyl group wherein aryl and alkyl are as previously described.
The term “low moisture food” refers to wherein the food has a water activity (aw) equal to or less than 0.85. Preferably, aw is between 0.6-0.85. In one aspect, aw is 0.6 or less. In a further aspect, aw is 0.6. Preferably, 0.5 or less. Low moisture foods are known to generally be less susceptible to microbial spoilage and growth of foodborne pathogens. Examples of foods that may be low moisture foods include but are not limited to cookies, crackers, granola bars, breakfast cereals, grains, confectionary such as chocolate and cocoa, dairy and egg powders, dried fruits, vegetables and meats, honey, seeds, nuts, peanut butter, chips and other snacks, and spices, for example.
Natural antioxidants normally include tocopherols, phospholipids, ascorbic acid (Vitamin C), phytic acid, phenolic acids, for example. Common synthetic antioxidants for edible use are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG), tertiary butyl hydroquinone (TBHQ), etc. In one embodiment, the composition disclosed herein further comprises any one or more of a natural antioxidant and/or a synthetic antioxidant.
Using a homologous series of ARs in bulk oils and oil-in-water emulsions, we observed that ARs were able to inhibit lipid oxidation reactions in both systems. In addition to this, ARs have been shown to function as free radical scavenging antioxidants but not metal chelating antioxidants.
According to an exemplary embodiment, there is provided an antioxidant composition comprising:
(i) a compound of Formula (I):
comprising an alkyl chain wherein n=12-26; and
(ii) a low-moisture food;
wherein the low-moisture food has a water activity (aw) equal to or less than 0.85.
In an exemplary aspect, the low-moisture food is manufactured.
In another exemplary aspect, the compound of Formula (I) is isolated, purified, and/or extracted.
In a further exemplary aspect, the compound of Formula (I) is obtained by a winterization process. For example, a forced crystallization process.
In yet another exemplary aspect, the natural abundance of the compound of Formula (I) is low. For example, between 0.004% to 0.32% alkylresorcinols per unit of dry matters low.
In an exemplary aspect, the composition comprises a mixture of compounds of Formula (I).
In a further exemplary aspect, the mixture comprises compounds of Formula (I) in which n=is 12, 14, 16, 18, 20, 22, 24, or 26.
In yet a further exemplary aspect, n=14-20, preferably, n=14, 16, 18, or 20, in the compound of Formula (I). In a yet still further aspect, n=16-24. In a further aspect n=14-24. In a yet still further exemplary aspect, n=16-20 and 22-24. In yet another aspect n=14-20 and 22-24.
In another exemplary aspect, the low moisture food is selected from any one or more of: cookies, crackers, granola bars, breakfast cereals, grains, confectionary such as chocolate and cocoa, dairy and egg powders, dried fruits, vegetables, meats, honey, seeds, nuts, peanut butter, chips, corn chips, potato chips, and other snacks, and spices.
In an exemplary aspect, the aw is 0.6 or less, for example 0.5 or less.
In another exemplary aspect, the composition comprises more than one compound of Formula (I), for example two, three, four, five compounds of Formula (I).
In an exemplary aspect, the alkyl chain length is C21-23. For example, C21 or C23. In another exemplary aspect, n, which is the alkyl chain length not including the terminal hydrocarbon, is 12-20 or 22-26.
In an exemplary embodiment, the composition of the application further comprises a second type of antioxidant, for example a synthetic or natural antioxidant, such as α-tocopherol and/or BHT.
In an exemplary aspect, the alkyl chain in the compound of Formula (I) is further substituted, for example by a further alkyl, aryl, araryl, unsaturated alkyl, or a carbonyl group.
The present application is also directed to the use of the compositions.
Thus, in another exemplary embodiment, there is provided iutilizing the composition as a preservative.
In another exemplary embodiment is presented a method of preparing the compound of Formula (I) by winterization, comprising one or more of the following steps:
In a further exemplary aspect, the (i) extracting step of the method disclosed herein uses acetone at a ratio of 1:40 (w/v) by continuous stirring at room temperature for 24 hours; and optionally the acetone is evaporated from the extract to dryness, for example under vacuum at 35° C. using a rotary evaporator. Those of skill in the art will recognize that other extraction and drying methods may be used. For example, rye bran is extracted with acetone using a sample to solvent ratio of 1:40 (w/v) for 24 h with continuous agitation. Insoluble bran components are removed by vacuum filtration, and the acetone is dried. The crude extract is then reconstituted using methanol, followed by centrifugation and recovery of supernatant. ARs are crystallized from the solubilized extract. The extract may be further centrifuged to afford a pellet, which can be solubilized in methanol, and winterization may be twice repeated to further purify the ARs. The final winterized extract can be brought to dryness.
In another exemplary aspect of the application, is provided a low-moisture food obtainable by the method disclosed herein, wherein the compound of formula (I) has a C17-25 alkyl chain, and is optionally further isolated from the winterized rye bran extract using preparative HPLC.
In an exemplary embodiment, there is provided a food product comprising the composition disclosed herein.
The following description is of further exemplary embodiments that are presently contemplated for carrying out exemplary embodiments reported herein. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of the present disclosure. The scope of the present disclosure is not limited by this description.
Typical embodiments are directed to compounds of Formula (I) and methods of making them.
Rye bran (Secale cereale) was donated by Snavely's Mill (Lititz, Pa., U.S.) and had a mean particle size of 1.41 mm or larger. Interesterified soybean oil (ISO) #762420 (Total Unsaturated Fatty Acid Content: 55.0%, Free Fatty Acid Content: 0.028%, Peroxide Value: 0.00 meq/kg) was donated by ADM (Chicago, Ill., U.S.). White rye flour (King Arthur Baking Company, Norwich, Vt., U.S.), iodized salt (Morton, Chicago, Ill., U.S.), and baking soda (Arm & Hammer, Ewing, N.J., U.S.) were purchased from a local grocery store (State College, Pa., U.S.). Dry goods were stored in resealable plastic freezer bags and kept refrigerated (4° C.) while ISO was kept frozen (−20° C.) until use. All other reagents were purchased from Sigma Chemical Company (St. Louis, Mo., U.S.) and were analytical grade or purer.
ARs were extracted from rye bran according to a method described previously (Elder, Coupland, & Elias, 2019). Briefly, rye bran (20 g) was extracted with acetone at a ratio of 1:40 (w/v) by continuous stirring at room temperature for 24 hours (Gunenc, HadiNezhad, Farah, Hashem, & Hosseinian, 2015). Bran solids were removed by vacuum filtration and the acetone extract was evaporated to dryness under vacuum at 35° C. using a rotary evaporator (Rotavapor R-210, Buchi, Flawil, Switzerland). The crude rye bran extract was reconstituted in methanol, centrifuged at 1700×g for 5 minutes at 20° C. (Centrifuge 5810 R, A-4-62 Rotor, Eppendorf, Hamburg, Germany), and the supernatant was retained. The supernatant was stored at −80° C. for 24 hours, causing the ARs to crystallize, then centrifuged at 1700×g for 3 minutes at −9° C. and the pellet was retained. The pellet was reconstituted in methanol and the winterization procedure of the partially purified rye bran extract was repeated twice to further purify the ARs. After the final winterization procedure, the winterized rye bran extract was dried under a stream of nitrogen and stored at −80° C. until use.
Individual AR homologues (C17:0, C19:0, C21:0, C23:0, C25:0) were isolated from the winterized rye bran extract using preparative HPLC. Dry, winterized rye bran extract was reconstituted in methanol at a concentration of 40 mg/mL. The preparative HPLC system consisted of a binary pumping system (PrepStar SD-1, Agilent, Santa Clara, Calif., U.S.) with high-pressure mixing and sample introduction by means of manual injection (1 mL). AR homologues were separated on a Viva C18 column (5 μm, 250×10 mm) (Restek, Bellefonte, Pa., U.S.) held at ambient temperature. The mobile phase consisted of water (A) and methanol (B). A gradient program was followed to separate the different AR homologues at a flow rate of 4.0 mL/min. The gradient program was as follows: 0 minutes, 90% B; 0-10 minutes, 100% B; 10-25 minutes, 100% B; 25-25.5 minutes, 90% B; 25.5-35 minutes, 90% B (Gunenc et al., 2015). Detection of the AR homologues was achieved using a UV-Vis detector (ProStar 325, Agilent, Santa Clara, Calif., U.S.) at 280 nm. Individual AR homologues were collected using a fraction collector (440-LC Fraction Collector, Agilent, Santa Clara, Calif., U.S.) with 0.5-minute fractions collected from 10-28 minutes. Chromatograms were reviewed after each run and fractions containing the same AR homologue were combined and stored at −80° C. until use.
The individual AR homologue fractions (C17:0, C19:0, C21:0, C23:0, C25:0) were evaporated to dryness under vacuum at 35° C. using a rotary evaporator (Rotavapor R-210, Buchi, Flawil, Switzerland). The individual AR homologues were reconstituted in methanol and stored at −80° C. for 24 hours, causing the ARs to crystallize, then centrifuged at 1700×g for 3 minutes at −9° C. (Centrifuge 5810 R, A-4-62 Rotor, Eppendorf, Hamburg, Germany) and the pellet was retained. The pellet was reconstituted in methanol and the winterization procedure of the partially purified individual AR homologues was repeated twice to further purify the ARs. After the final winterization procedure, the individual AR homologues were dried under a stream of nitrogen and stored at −80° C. until use.
A small mass of each dried AR homologue was dissolved in methanol to produce stock solutions and analyzed using HPLC to determine purity and concentration. Samples were prepared for HPLC analysis by filtering them over polytetrafluoroethylene (PTFE) syringe filter tips (0.45 μm). The HPLC system consisted of a binary pumping system (LC-10ADvp, Shimadzu, Kyoto, Japan) with high-pressure mixing and sample introduction by means of an autosampler (SIL 10ADvp, Shimadzu, Kyoto, Japan). AR homologues were separated on an Eclipse Plus C18 column (5 μm, 2.1×150 mm) (Agilent, Santa Clara, Calif., U.S.) held at 35° C. The mobile phase consisted of 0.1% (v/v) formic acid in water (A) and 0.1% (v/v) formic acid in methanol (B). A gradient program was followed to separate the different AR homologues at a flow rate of 0.2 mL/min. The gradient program was as follows: 0 minutes, 90% B; 0-10 minutes, 100% B; 10-25 minutes, 100% B; 25-25.5 minutes, 90% B; 25.5-35 minutes, 90% B (Gunenc et al., 2015). Detection and quantification of the AR homologues was achieved using a UV-Vis detector (SPD-10Avp, Shimadzu, Kyoto, Japan) at 280 nm and triple quadrupole mass spectrometer (Micromass Quattro Micro, Waters, Milford, Mass., U.S.) coupled to the HPLC. Mass spectra were collected in negative-ion mode using electrospray ionization (ESI). ESI capillary spray was held at 2.60 kV. Cone source voltage was set to 33 V and source temperature was set to 120° C. Desolvation gas (nitrogen) flow was 450 L/h. Selective ion monitoring was used to monitor ions with m/z of 123.0 (orcinol), 347.3 (C17:0), 375.3 (C19:0), 403.4 (C21:0), 431.4 (C23:0), and 459.4 (C25:0). AR homologues were quantified based on a standard curve prepared for orcinol using the integrated peak areas of the UV chromatograms as previous research has shown that absorbance at 280 nm is due only to the aromatic ring and not the alkyl chain of the AR homologue (Hengtrakul, Lorenz, & Mathias, 1991). The concentration of each individual AR homologue stock solution varied based on the mass used to prepare the stock solution, however, different volumes of the stock solutions were used to achieve the same final concentration of ARs in the ISO and hence in the crackers.
Based on the concentrations of the individual AR stock solutions previously determined, an appropriate volume, containing 153 μmol of the respective individual AR homologue, was measured into plastic centrifuge tubes to prepare individual AR homologue treatments. A treatment containing a mixture of the individual AR homologues, at their natural abundance in rye bran, was prepared by combining 25.3% of C17:0, 32.0% of C19:0, 22.6% of C21:0, 12.5% of C23:0, and 7.6% of C25:0. The same procedure was carried out with 10 mM stock solutions of orcinol, α-tocopherol, and butylated hydroxytoluene (BHT) and all treatments were dried under a stream of nitrogen. Ethanol (1.0 mL) was added to the dried treatments (and a control treatment containing no antioxidant) and mixed with 10 g of melted ISO. The antioxidant activity of each treatment was tested at 153 μmol because this corresponds to 500 ppm of C21:0 in the final cracker which is a typical antioxidant concentration used in bakery applications.
Crackers were prepared according to the procedure described by Barden, Vollmer, Johnson, & Decker (2015) (Table 1).
Antioxidant-treated ISO was melted at 90° C. for 10 minutes and mixed in a stand mixer (KSM95, KitchenAid, Benton Harbor, Mich., U.S.) using a beater blade for 1 minute (speed 2). Sifted flour, salt, and baking soda were added and mixed using a beater blade for 1 minute (speed 2). Water was added and mixed using a dough hook for 1 minute (speed 2). The additional flour was sprinkled onto the surface of a baking mat and incorporated into the dough by kneading by hand (30 folds). The dough was flattened by passing it through a pasta roller (KPSA, KitchenAid, Benton Harbor, Mich., U.S.) twice (thickness setting 2). The sheeted dough was cut into 2.5 cm×2.5 cm crackers and baked on an ungreased baking sheet for 9 minutes at 163° C. (FD 53-UL, Binder, Tuttlingen, Germany). After cooling to room temperature, crackers were coarsely crumbled using a mortar and pestle and weighed (0.5 g) into 10 mL amber glass headspace vials (Supelco Analytical, Bellefonte, Pa., U.S.), sealed with stainless steel screw caps with PTFE/silicone septa (Supelco Analytical, Bellefonte, Pa., U.S.), and allowed to autoxidize at 55° C. in the absence of light for up to 160 days. Crackers were analyzed for lipid hydroperoxides, headspace hexanal, and AR loss every 5 days for day 0-50, every 10 days for day 51-100, and every 20 days for the remainder of the storage time.
Lipid hydroperoxides were determined according to the method described by Shantha & Decker (1994) with slight modifications. Cracker samples (0.1 g) were finely ground using a mortar and pestle and mixed with 5.0 mL chloroform/methanol (2:1 (v/v)) by vortexing (10 seconds, 3 times). The hydroperoxide-containing lipid fraction was extracted and isolated by centrifugation at 2500×g for 10 minutes (Centrifuge 5702, A-4-38 Rotor, Eppendorf, Hamburg, Germany). To this extract (1.0 mL), 16.7 μL of an iron chloride solution (prepared by mixing 50 mL 66 mM FeSO4 in water with 50 mL 38 mM BaCl2 in 0.4 N HCl) was added followed by 16.7 μL of ammonium thiocyanate (3.9 M in water), and allowed to react at room temperature for 20 minutes. The absorbance of the samples was measured at 500 nm (GENESYS 180 UV-Vis Spectrophotometer, Thermo Fisher Scientific, Waltham, Mass., U.S.) and lipid hydroperoxides were quantified based on a standard curve prepared using cumene hydroperoxide.
Cracker samples were prepared for GC-MS analysis by adding 10 μL of 100 mg/L 2-methypentanal (internal standard) in methanol directly through the capped headspace vial's septum. The GC system consisted of a 7890B gas chromatograph (Agilent, Santa Clara, Calif., U.S.) with sample introduction by means of an autosampler (Robotic MultiPurpose Sampler, Gerstel, Mülheim, Germany). Samples were equilibrated for 10 minutes at 55° C. with continuous shaking. A 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) (1 cm) (Supelco Analytical, Bellefonte, Pa., U.S.) solid phase microextraction (SPME) fiber was exposed to the sample headspace for 2 minutes at 55° C. The SPME fiber was desorbed for 6 minutes at 250° C. in the injection port equipped with a SPME inlet liner at a split ratio of 10:1. Volatile aldehydes were separated on a Rtx-WAX capillary column (30 m, 0.25 mm i.d., 0.25 μm film thickness) (Restek, Bellefonte, Pa., U.S.). An oven program was followed to separate the different volatile aldehydes at a constant helium carrier gas flow rate of 1.22 mL/min. The oven program was as follows: hold at 40° C. for 1 minute; ramp at 10° C./min to 75° C.; ramp at 100° C./min to 250° C.; hold at 250° C. for 1.75 minutes. Detection and quantification of hexanal and 2-methylpentanal was achieved using a single quadrupole mass spectrometer (5977B, Agilent, Santa Clara, Calif., U.S.) coupled to the GC. The MS transfer line, quadrupole, and detector temperatures were set to 250° C., 230° C., 150° C., respectively. Mass spectra were collected in electron impact mode. Scan mode was used to monitor from 33 to 350 m/z with 8.1 scans/sec and selective ion monitoring was used to monitor ions with m/z of 56.0, 58.0, 71.0, and 82.0 with a dwell time of 60 msec each. Headspace hexanal was quantified based on a standard curve prepared by spiking cracker samples with known concentrations of hexanal. Hexanal was expressed relative to 2-methylpentanal using the integrated peak areas of the selected ion monitoring chromatograms.
ARs were extracted from the crackers that were treated with the mixture of individual AR homologues. Cracker samples (0.15 g) were finely ground using a mortar and pestle and mixed with 1.0 mL of 185 μM orcinol (internal standard) and 200 μM BHT (to inhibit sample degradation) in methanol. ARs were extracted by sonicating for 30 minutes (3510 Ultrasonic Cleaner, Branson Ultrasonics, Brookfield, Conn., U.S.).
Samples were prepared for HPLC analysis by filtering them over PTFE syringe filter tips (0.45 μm). The HPLC system consisted of a quaternary pumping system (G1311A, Agilent, Santa Clara, Calif., U.S.) with high-pressure mixing and sample introduction by means of an autosampler (G1329A, Agilent, Santa Clara, Calif., U.S.). AR homologues were separated on an Eclipse Plus C18 column (5 μm, 2.1×150 mm) (Agilent, Santa Clara, Calif., U.S.) held at 35° C. The mobile phase consisted of 0.1% (v/v) formic acid in water (A) and 0.1% (v/v) formic acid in methanol (B). A gradient program was followed to separate the different AR homologues at a flow rate of 0.2 mL/min. The gradient program was as follows: 0 minutes, 90% B; 0-10 minutes, 100% B; 10-25 minutes, 100% B; 25-25.5 minutes, 90% B; 25.5-35 minutes, 90% B (Gunenc et al., 2015). Detection and quantification of the AR homologues was achieved using a UV-Vis detector (G1315B, Agilent, Santa Clara, Calif., U.S.) at 280 nm and a fluorescence detector (G1321A, Agilent, Santa Clara, Calif., U.S.) with an excitation wavelength of 276 nm and emission wavelength of 306 nm. AR homologues were quantified relative to orcinol using the integrated peak areas of the fluorescence chromatograms. These relative peak areas were expressed relative to the relative peak area at time zero to plot the AR loss curves.
All experiments were performed in triplicate on separately prepared cracker samples. Statistical analysis was performed using a one-way ANOVA with Tukey's Honestly Significant Difference post-hoc test (Minitab, State College, Pa., U.S.) (α=0.05). All data was normally distributed as determined by a normality test (α=0.05).
An alternative explanation for the strong antioxidant activity of the AR Mix treatment is that the AR homologues might interact in a way that improves their overall efficacy as a mixture. When screening the antioxidant activity of a mixture of ARs (C15:0-C25:0) at their natural abundance in wheat bran, a synergistic effect was reported for the mixture given its higher radical scavenging capacity than the individual AR homologues (Gunenc, HadiNezhad, Tamburic-Ilincic, Mayer, & Hosseinian, 2013). While antioxidant interactions were not explicitly tested in either study, results from both suggest that individual AR homologues might behave in a synergistic manner when used in combination. Future work should formally test their interactions as antioxidants in a variety of foods and develop a model to explain this behavior.
Antioxidant Activities of Individual Alkylresorcinol Homologues in Crackers
Individual AR homologues (C17:0, C19:0, C21:0, C23:0, C25:0) were added separately and as a mixture (AR Mix) to ISO and subsequently incorporated into the cracker samples. The antioxidant activities of the AR homologues in crackers were compared to orcinol (a water-soluble AR), conventional antioxidants (i.e., α-tocopherol, BHT), and a control treatment (i.e., no added antioxidant). The crackers were allowed to autoxidize in the absence of light and primary (i.e., lipid hydroperoxides) and secondary products (i.e., headspace hexanal) of lipid oxidation were measured as a function of time.
The α-tocopherol-treated crackers began to accumulate lipid hydroperoxides immediately upon storage while the control crackers and other treatments remained in the lag phase of lipid oxidation indicating prooxidant activity of α-tocopherol (
Beginning on day 25, the orcinol, C17:0, C19:0, C21:0, and BHT-treated crackers showed an increase in the concentration of lipid hydroperoxides with the orcinol treatment oxidizing most rapidly followed by the C17:0 treatment and then the C19:0 and C21:0 treatments (
Hexanal was not detected in any of the cracker samples until day 5 (
The induction period before the onset of lipid oxidation in crackers was defined as the time to reach a critical threshold concentration of primary ([Hydroperoxides]=0.1 mM/g cracker) and secondary products ([Hexanal]=1.0 mM/g cracker) of lipid oxidation. For lipid hydroperoxides, the order of induction periods was AR Mix≈C23:0>C25:0>(C21:0≈C19:0)>(C19:0≈BHT)>(BHT≈orcinol)>(orcinol≈C17:0)>control>>α-tocopherol (
The antioxidant activity of ARs increased as alkyl chain length increased, with optimum activity at an alkyl chain length of C23:0. This follows the same general trend reported by Barden, Barouh, et al. (2015), who observed that antioxidant activity increased with increasing alkyl chain length for rosmarinic acid and a pair of rosmarinate alkyl esters in the same low-moisture model cracker system. The hydrophobic AR homologues derived from rye bran displayed stronger antioxidant activity than the hydrophilic homologue orcinol, which displayed weak to no antioxidant activity in the model cracker system. This is also in agreement with the results of the previous study by Barden, Barouh, et al., (2015) who observed that that the hydrophilic rosmarinic acid displayed weak antioxidant and prooxidant activity against the formation of lipid hydroperoxides and hexanal, respectively.
The Inventors have previously used an oxygen radical absorbance capacity assay to show that the radical scavenging capacity of AR homologues decreases as alkyl chain increases with orcinol displaying the strongest antiradical activity (Elder et al., 2021). However, the effect of alkyl chain length on the radical scavenging capacity does not align with the trend of the antioxidant activity of AR homologues seen in the low-moisture model cracker system indicating that another factor, presumably related to the effects of food physical structure, is responsible for the observed antioxidant activity of ARs in the model cracker system. Barden, Barouh, et al. (2015) used confocal microscopy to show that rosmarinic acid (i.e., an ineffective antioxidant) localized outside of the lipid phase in the model cracker system due to its low lipid solubility while the rosmarinate alkyl esters (i.e., effective antioxidants) were highly associated with the lipid phase. Similarly, the poor antioxidant activity of orcinol, despite its high radical scavenging capacity, is likely due to its hydrophilic nature resulting in it concentrating at phases other than the lipid phase. In contrast, the strong antioxidant activity of the AR homologues, especially C23:0 and C25:0, despite their low radical scavenging capacity, is likely due to their hydrophobic nature resulting in them concentrating at the lipid phase, the purported site of lipid oxidation in the model cracker system.
α-Tocopherol is a commonly used natural antioxidant but here it displayed strong prooxidant activity in the low-moisture model cracker system. This is in contrast to previous research which has shown that α-tocopherol is a more effective antioxidant than ARs in other food systems such as bulk oils and oil-in-water emulsions (Elder et al., 2021; Kamal-Eldin, Pouru, Eliasson, & Aman, 2001). The prooxidant activity of α-tocopherol in this work may be due to its usage level.
While α-tocopherol typically functions as an antioxidant, it has been shown to display prooxidant behavior at high concentrations. This is due to regeneration of α-tocopherol from tocopheroxyl radicals by lipid hydroperoxides which, in turn, forms peroxyl radicals that subsequently initiate further lipid oxidation reactions (Huang, Frankel, & German, 1994). In whole-wheat bread, loaves enriched with high levels of α-tocopherol (1 g/kg flour) had pronounced rancid aroma and rancid flavor according to sensory analysis and higher levels of lipid hydroperoxides and volatile secondary products of lipid oxidation compared to control loaves (i.e., without added antioxidant) (Jensen, Ostdal, Skibsted, & Thybo, 2011). This effect was also observed in cookies and puffed rice snacks when tocopherols were added at 100-200 ppm (Jensen et al., 2011; Ochi et al., 1993; Park, Kim, & Shin, 2002). In contrast, when used at low concentrations (˜18 ppm), α-tocopherol inhibited the formation of primary and secondary products of lipid oxidation in whole-wheat breads indicating antioxidant activity (Osuna, Romero, Romero, Judis, & Bertola, 2018). In this application, α-tocopherol was added to the crackers at 500 ppm; therefore, its prooxidant behavior is likely a result of its usage at a high concentration.
BHT is a commonly used synthetic antioxidant that displayed strong antioxidant activity in the low-moisture model cracker system which is in agreement with previous research (Barden, Barouh, et al., 2015). BHT was a more effective antioxidant than some of the individual AR homologues (i.e. C17:0, C19:0, C21:0) which has been observed in other food systems such as bulk oils and oil-in-water emulsions (Elder et al., 2021). The lower efficacy of ARs as compared to BHT has been attributed to the meta substitution of their phenolic ring (Sroka & Cisowski, 2003).
Loss of Individual Alkylresorcinol Homologues in Crackers
The loss of AR homologues was measured in the AR Mix-treated cracker samples over the course of the lipid oxidation study. The relative abundance of all of the AR homologues in the AR Mix-treated cracker samples decreased at a similar, constant rate over the entire storage time (
There is no effect of alkyl chain length on the rate of loss of ARs with ˜75% of each individual AR homologue remaining at day 120 when the AR Mix-treated crackers began to accumulate hexanal. This does not follow the general trend reported by Barden, Barouh, et al., (2015), who observed that rosmarinic acid and the rosmarinate alkyl esters were lost prior to hexanal formation and their rate of loss decreased with increasing alkyl chain length in the same low-moisture model cracker system. The authors hypothesized that differences in the rate of loss of the rosmarinate alkyl esters were due to differences in their localization and, thus, their availability to interact with other food components (e.g. transition metals) (Barden, Barouh, et al., 2015). Rosmarinic acid and the dodecyl ester were lost more rapidly because they localized to other phases than the lipid phase where they could readily interact with transition metals, degrading the antioxidants (Barden, Barouh, et al., 2015). In contrast, the eicosyl ester was lost more slowly because it was concentrated at the lipid phase making it unable to interact with transition metals, preserving the antioxidant to scavenge free radicals, thus improving its antioxidant activity (Barden, Barouh, et al., 2015).
The similar rate of loss of the AR homologues in the present work suggests that they are all localized to the same phase of the low-moisture model cracker system where they are susceptible to the same interactions and reactions. Moreover, the fact that such a large percentage of the AR homologues remained in their native, unoxidized state, even at advanced stages of lipid oxidation, suggests that only a small portion of the ARs were concentrated at the lipid phase and consumed as antioxidants while protecting the lipid while the remaining majority of ARs were localized in other, oxidatively inert phases where they could not prevent lipid oxidation reactions. This inert phase is presumably the non-lipid portions of the cracker where low molecular mobility limits the interaction of the ARs with transition metals and protects them from oxidative loss.
Differences in the antioxidant activity between the individual AR homologues could also be due to differences in the concentration of each homologue localized at the lipid phase. For the previously discussed rosmarinic acid and rosmarinate alkyl esters, it was hypothesized that the eicosyl ester displayed the strongest antioxidant activity because it had the highest solubility in the lipid phase due to its hydrophobicity (Barden, Barouh, et al., 2015). The eicosyl ester's greater hydrophobicity resulted in a higher concentration of this ester in the lipid phase, concentrating the antioxidant at the purported site of lipid oxidation (Barden, Barouh, et al., 2015). For the individual AR homologues, antioxidant activity increased as hydrophobicity increased (i.e., activity increased as alkyl chain length increased). Therefore, the more hydrophobic, long alkyl chain AR homologues (C23:0, C25:0) likely have higher solubility in the lipid phase, resulting in higher concentrations of these AR homologues at the purported site of lipid oxidation, thus, giving rise to stronger antioxidant activity than the less hydrophobic, shorter alkyl chain AR homologues (C17:0, C19:0, C21:0), despite their lower radical scavenging capacity.
This partitioning hypothesis could explain the strong antioxidant activity of the AR Mix treatment. It was expected that the AR Mix treatment would have similar antioxidant activity to the C17:0, C19:0, and C21:0 treatments since the mixture is predominately (˜80%) these three homologues. The AR Mix treatment displayed stronger antioxidant activity than these individual AR homologues and was comparable in activity to the C23:0 and C25:0 treatments despite having a fraction of these homologues in the mixture, these homologues only making up 12.5% and 7.6% of the AR Mix treatment, respectively. The stronger antioxidant activity of the AR Mix treatment could arise from the long alkyl chain homologues (C23:0, C25:0) that concentrate at the purported site of lipid oxidation, improving the antioxidant activity of the AR Mix treatment as a whole.
ARs (153 μmol) were found to be capable of inhibiting lipid oxidation reactions based on the delayed generation of lipid hydroperoxides and headspace hexanal compared to a control treatment, and were more effective than α-tocopherol which displayed prooxidant behavior.
This application shows AR homologues were able to slow the rate of lipid oxidation in a model low-moisture model food (i.e., a cracker). The antioxidant activity of ARs increased as their alkyl chain length increased, with optimum activity at an alkyl chain length of C23:0. ARs were consumed during the oxidation at a rate independent of alkyl chain length, however, a majority of ARs remained in the cracker even at advanced stages of lipid oxidation. These results suggest that only a fraction of the ARs were localized at the lipid phase in the model cracker system where they were able to inhibit oxidation while the remainder was inactive the oxidatively inert non-lipid portion of the cracker. Additionally, the more hydrophobic longer alkyl chain AR homologues (C23:0, C25:0) were likely more concentrated at the lipid phase giving rise to stronger antioxidant activity despite their lower radical scavenging capacity. All of the AR homologues were more effective than α-tocopherol which displayed prooxidant activity. The C23:0, C25:0, and AR Mix treatments displayed comparable antioxidant activities, and were also more effective than BHT at increasing the induction period before the onset of lipid oxidation, providing an effective alternative to synthetic antioxidants.
AR homologues have been shown to exert antioxidant activity in a variety of food systems with alkyl chain length affecting their activity differently depending on the system (i.e., bulk oils, emulsions, and low-moisture foods such as crackers) (Elder et al., 2021). This unique property of ARs provides versatility for the food industry to select homologues that exert optimal antioxidant activity for a given food application which cannot be achieved through the use of other conventional antioxidants. Additionally, a mixture of ARs, without isolation of the individual homologues, has been found to have the potential to be an alternative to synthetic antioxidants in low-moisture foods.
ARs are thus natural antioxidants, comprising a homologous series of phenolipids found in the bran layer of a variety of grains. Since ARs exist as a homologous series, certain homologues exhibit increased antioxidant activity in emulsified foods as they can partition to the lipid droplet surface (i.e. the site of oxidation) due to their amphiphilic nature.
All documents cited herein including those below are hereby incorporated by reference in their entirety. To the extent anything in these documents contradicts this written specification, this specification controls.
Although embodiments been described in terms of specific exemplary embodiments and examples, it will be appreciated that the embodiments disclosed herein are for illustrative purposes only and various modifications and alterations might be made by those skilled in the art without departing from the spirit and scope of the disclosure as set forth in the following claims.
This application claims the benefit of U.S. Provisional Patent Application No. 63/260,774, filed on Aug. 31, 2021, and U.S. Provisional Patent Application No. 63/263,483, filed on Nov. 3, 2021, both of which are incorporated by reference as if fully rewritten herein.
This invention was made with government support under Grant No. 2018-67011-28010 awarded by the United States Department of Agriculture/NIFA and under Hatch Act Project Nos. PEN04522 and PEN04708 awarded by the United States Department of Agriculture/NIFA. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63260774 | Aug 2021 | US | |
| 63263483 | Nov 2021 | US |
