Evaluation of Alkylresorcinol-rich Extract as an Antioxidant in a Low-moisture Food
Open Access
- Author:
- Schmidt, Julia
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- May 30, 2023
- Committee Members:
- Robert Roberts, Program Head/Chair
Ryan John Elias, Thesis Advisor/Co-Advisor
Helene Hopfer, Committee Member
John Neil Coupland, Thesis Advisor/Co-Advisor - Keywords:
- Lipid Oxidation
Antioxidant
Alkylresorcinol
low-moisture food
crackers
shelf-life
stability
metabolomics
GC-MS
HPLC
Chromatography
sensory discrimination
oxidation
RapidOxy - Abstract:
- There is growing interest in reformulating a wide range of low moisture foods by replacing saturated fats with mono- polyunsaturated fats. However, unsaturated fats are more prone to lipid oxidation, resulting in product rancidity and a shortened shelf life. Shelf life can be extended with the use of antioxidants, but consumer demand for “clean label” foods has limited the use of synthetic antioxidants and necessitated the development of naturally derived alternatives. One class of antioxidant identified for this function is alkylresorcinols (ARs), a group of phenolipids comprised of an aromatic ring with meta-substituted hydroxyl groups and a long alkyl tail. ARs are found in the bran layer of many cereals but are most highly concentrated in rye (Secale cereale). Rye bran is currently an underutilized waste stream, so extracting a high-value food ingredient from such a low-cost input can be both economically profitable and environmentally sustainable. Previous research has shown that an extract of purified ARs from rye bran is capable of delaying lipid oxidation induction period in bulk oils, oil-in-water emulsions, and in crackers (Elder et al., 2019, 2021, 2022). ARs were particularly effective in delaying oxidation of crackers, and while the efficacy of individual homologs varied, antioxidative activity in an unseparated (i.e., less-processed) mixture was still comparable to that of more effective isolated homologs. However, these studies revealed many opportunities for future work. First, intrinsic antioxidants (mainly tocopherols) within the oils used were not considered in terms of either confounding effects or synergism. Second, comparison to established antioxidants in low-moisture food was limited to two antioxidants, one of which (-tocopherol) exhibited unexpected strong prooxidative activity. Third, the AR extract itself was not made in a food-safe manner or characterized beyond identification and quantification of AR homologs of interest. This thesis builds on previous research by comparing the antioxidative properties of ARs in low-moisture food at equimolar concentrations with other, commonly used antioxidants, and by further characterizing an AR extract as a potential food ingredient. Crackers were formulated with either an AR extract (15.3 mol/g oil, the oil was previously stripped to remove any intrinsic antioxidants) or equimolar concentrations of other widely used antioxidants (-tocopherol, carnosic acid, ascorbyl palmitate, tert-butylhydroquinone (TBHQ), and butylated hydroxytoluene (BHT)) and incubated for 185 days at 55 °C. The oxidative stability of the test crackers was measured in terms of a primary oxidation product (lipid hydroperoxides) and a secondary lipid oxidation product (hexanal). For lipid hydroperoxides, induction period was defined as time to reach 1 mM lipid hydroperoxides/g cracker. Antioxidative efficacy was as follows: BHT > TBHQ > carnosic acid > ARs > control > ascorbyl palmitate > -tocopherol. For headspace hexanal, induction period was defined as time to reach 10 mM/g cracker. Antioxidative efficiency was as follows: BHT > carnosic acid > control > ARs > TBHQ > -tocopherol > ascorbyl palmitate. In a second set of experiments, the consumption of headspace oxygen was measured in similar crackers using a rapid oxidation testing protocol (RapidOxy). The induction period was defined as time to achieve a 10% drop in oxygen pressure in the testing chamber. Antioxidative efficiency by this method was as follows: BHT > carnosic acid > TBHQ > ARs > ascorbyl palmitate > control >-tocopherol. It should be noted that induction period for ARs, ascorbyl palmitate, and -tocopherol were not significantly different from that of the control in this experiment (p>0.05). Broadly, ARs exhibited neutral to weak antioxidative activity in crackers, with induction periods longer than those of -tocopherol and ascorbyl palmitate and shorter than those of carnosic acid, TBHQ, and BHT. However, further RapidOxy experiments showed induction periods could be extended by increasing the amount of AR extract used. It was also shown that stripping the oil did not have a significant effect on cracker induction period for either crackers containing ARs or control treatments. Metabolomic profiling of the AR extract yielded 65 identifiable compounds in notable concentrations, including phospholipids, flavonoids, and metabolites related to linoleic and amino acid synthesis. Most metabolites present were associated with rye, but some fungal in origin, as is expected in cereal products. The AR extract was then characterized as a potential food ingredient. Residual acetone from the extraction of the bran was below quantifiable limits, but residual methanol was substantial (23,275 ppm), necessitating the development of a new, food-safe extraction procedure. Ethanol was selected as a replacement extraction and purification solvent as it had comparable yields and AR homolog distributions to acetone. The AR extract was shown to be stable under storage at frozen (-20 °C), room temperature (25 °C) and heated (55 °C) conditions over a 40-day period. Room temperature storage was shown to be the most stable, but even the heated extract retained 80% of its ARs at the end of the incubation time. In a triangle test, 51 of 111 participants were able to discriminate an AR-containing cracker from a control suggesting a significant difference (p<0.05). However, further analysis suggested that much of the difference between samples could be contributed to variability in cracker preparation, as textbox responses emphasized texture as a means of discrimination correlating with cracker presentation from different batches. No negative perceptions in terms of flavor, aroma, or aftertaste were reported. This work shows that, while not an effective antioxidant in a cracker model at the concentration used, a higher dose of AR extract may be viable option. The extract can be prepared using food-safe solvents and can be stored for extended periods without loss of efficacy. Preliminary sensory research suggests that the extract can be incorporated into foods without negative sensory outcomes.