PhD Candidate, University of Massachusetts Amherst
Fundamental knowledge to develop technologies increasing food quality and reducing food waste
My research provides novel scientific knowledge on lipid oxidation in low moisture snacks which contributes a high saturated fat intake to American diet. Manufacturers can utilize my research findings to develop strategies to promote healthiness as well as increase shelf life of food products. Understanding oxidation mechanism allows manufacturers to reduce amount of saturated fat, which eventually reduce a risk of cardiovascular disease, and incorporate lipid bio active compounds into low moisture foods. In addition, increasing shelf life of food products is one of strategies to reduce food waste, which is currently a global challenge in sustainable development goals.
My study is the first one to address a relation between lipid physical properties and chemically oxidation stability in low moisture food system. A low moisture cracker is used as a model system. The chemical side of this story can be studied by many traditional lipid oxidation techniques such as gas chromatography and high performance liquid chromatography. However, the physical characterization is measured by cutting edge techniques, namedly spectrofluorometer and fluorescent molecular rotors. My findings indicated that the confinement of fat network inside low moisture cracker system impact on its chemically oxidative stability.
Interestingly, the oxidation fate of low moisture model cracker was different from those in oil-in-water emulsion and bulk oil. In low moisture cracker, fat was oxidized firstly into lipid hydroperoxides. It took these hydroperoxides up to several months to decompose into secondary oxidation products. Meanwhile, in emulsion or bulk oil systems, lipid hydroperoxides and secondary oxidation products were formed almost at the same time. Life time of lipid hydroperoxides in crackers depended on moisture and acidity of the cracker matrix.
Lastly, shelf life of crackers could be increased by using natural additives. Compared to protein, reducing sugars were found to increase oxidative stability of crackers. A good example of reducing sugar is maltose, which is also known as malt sugar or a product from starch hydrolysis. Hence, reducing sugars could be used as natural antioxidants to replace artificial compounds, such as butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ) which have been widely used as antioxidants in food industry.
Abstract: Proteins can inhibit lipid oxidation by biologically designed mechanisms (e.g. antioxidant enzymes and iron-binding proteins) or by nonspecific mechanisms. Both of these types of antioxidative proteins contribute to the endogenous antioxidant capacity of foods. Proteins also have excellent potential as antioxidant additives in foods because they can inhibit lipid oxidation through multiple pathways including inactivation of reactive oxygen species, scavenging free radicals, chelation of prooxidative transition metals, reduction of hydroperoxides, and alteration of the physical properties of food systems. A protein's overall antioxidant activity can be increased by disruption of its tertiary structure to increase the solvent accessibility of amino acid residues that can scavenge free radicals and chelate prooxidative metals. The production of peptides through hydrolytic reactions seems to be the most promising technique to form proteinaceous antioxidants since peptides have substantially higher antioxidant activity than intact proteins. While proteins and peptides have excellent potential as food antioxidants, issues such as allergenicity and bitter off-flavors as well as their ability to alter food texture and color need to be addressed.
Pub.: 09 May '08, Pinned: 08 Aug '17
Abstract: ABSTRACT Overly high intake of saturated fat is an international problem contributing to global health issues. Low-moisture snacks account for a nutritionally significant proportion of the saturated fat in the diet, making these foods a key target for improving consumers' health. However, it is not currently feasible to maintain the same oxidative shelf life when replacing saturated fats with unsaturated fats, which are generally perceived to be more heart-healthy. This article summarizes current theories and available research on lipid oxidation in low-moisture foods in order to lay the groundwork for new lipid oxidation rate-reduction strategies. Research deficits needing attention and new methods for assessing lipid oxidation in low-moisture foods are also discussed.
Pub.: 28 Nov '13, Pinned: 08 Aug '17
Abstract: The health benefits of long-chain (n-3) PUFA have been widely reported in the literature. Despite the potential benefits, consumption of these fatty acids continues to fall below recommendations from various health and regulatory agencies. Incorporation of long-chain PUFA in foods represents a considerable challenge due to the increased risk of lipid oxidation resulting in the development of off-flavors and reduced shelf life. As a result, new sources of (n-3) fatty acids are needed that are more efficiently converted to long-chain (n-3) fatty acids than α-linolenic acid (ALA) and can be more easily incorporated into food. Stearidonic acid [SDA, 18:4 (n-3)] is an intermediate in the desaturation of ALA to EPA. Soybeans have been modified to contain SDA. Clinical studies have demonstrated a significant increase in EPA levels when SDA is consumed. Being more stable, SDA has been added to a variety of foods and has demonstrated equal consumer acceptance compared to a regular soybean oil control. SDA-enhanced soybean oil can provide to food companies and consumers an option to increase (n-3) fatty acid consumption in foods consumers typically eat.
Pub.: 27 Jan '12, Pinned: 08 Aug '17
Abstract: Over the past few decades, the Dietary Guidelines for Americans has consistently recommended that consumers decrease consumption of saturated fatty acids due to the correlation of saturated fatty acid intake with coronary artery disease. This recommendation has not been easy to achieve because saturated fatty acids play an important role in the quality, shelf life, and acceptability of foods. This is because solid fats are critical to producing desirable textures (e.g., creaminess, lubrication, and melt-away properties) and are important in the structure of foods such as frozen desserts, baked goods, and confectionary products. In addition, replacement of saturated fats with unsaturated fats is limited by their susceptibility to oxidative rancidity, which decreases product shelf life, causes destruction of vitamins, and forms potentially toxic compounds. This article will discuss the fundamental chemical and physical properties in fats and how these properties affect food texture, structure, flavor, and susceptibility to degradation. The current sources of solid fats will be reviewed and potential replacements for solid fats will be discussed.
Pub.: 17 May '15, Pinned: 08 Aug '17
Abstract: Proteins can be used to produce cationic oil-in-water emulsion droplets at pH 3.0 that have high oxidative stability. This research investigated differences in the physical properties and oxidative stability of corn oil-in-water emulsions stabilized by casein, whey protein isolate (WPI), or soy protein isolate (SPI) at pH 3.0. Emulsions were prepared with 5% corn oil and 0.2-1.5% protein. Physically stable, monomodal emulsions were prepared with 1.5% casein, 1.0 or 1.5% SPI, and > or =0.5% WPI. The oxidative stability of the different protein-stabilized emulsions was in the order of casein > WPI > SPI as determined by monitoring both lipid hydroperoxide and headspace hexanal formation. The degree of positive charge on the protein-stabilized emulsion droplets was not the only factor involved in the inhibition of lipid oxidation because the charge of the emulsion droplets (WPI > casein > or = SPI) did not parallel oxidative stability. Other potential reasons for differences in oxidative stability of the protein-stabilized emulsions include differences in interfacial film thickness, protein chelating properties, and differences in free radical scavenging amino acids. This research shows that differences can be seen in the oxidative stability of protein-stabilized emulsions; however, further research is needed to determine the mechanisms for these differences.
Pub.: 06 Mar '03, Pinned: 08 Aug '17
Abstract: Linoleic acid oxidation in oil-in-water emulsions stabilized by a nonionic surfactant (Tween-20) was studied. The emulsion composition was varied at a constant oil droplet size. Lipid oxidation was measured as a function of time in the presence of a catalyst (FeSO4 corbic acid) by two methods: gas chromatographic determination of residual substrate and ultraviolet-visible spectrophotometric determination of conjugated dienes. Rate of oxidation was influenced by the emulsion composition (relative concentrations of substrate and emulsifier) and especially by the partition of the emulsifier between the interface and water phase. Concentrations of emulsifier exceeding the critical micelle concentration protected the fatty acid against oxidation. Excess surfactant formed micelles and mixed micelles with linoleic acid, which retarded oxidation by diluting the substrate or perhaps by replacing linoleic acid at the interface, making it less accessible to radical attack. The addition of sucrose also had a protective effect, but only up to a certain concentration, indicating the effect may involve factors other than viscosity.
Pub.: 01 Jan '99, Pinned: 12 Jul '17
Abstract: In the study of the oxidation rate of methyl linoleate in protein and cellulose systems, a prooxidant effect was found at intermediate moisture contents. At low water content, water hydrates metals and hydrogen bonds with peroxides, and an overall decrease in the rate of lipid oxidation results. With an increase in the water content to the region with a water activity of 0.6 to 0.7, the water predominantly acts as a solvent to dissolve and mobilize previously unavailable trace metals with the result of increased oxidation rates. Use of chelating agents such as ethylenediaminetetraacetic acid and citric acid reduced oxidation significantly although some antioxidant activity was also observed for butylated hydroxyanisole. These results have important implications in the preparation of intermediate moisture foods.
Pub.: 01 Feb '71, Pinned: 12 Jul '17
Abstract: The polarity and partitioning of antioxidants (AOX) in lipid dispersions and bulk oils have a large impact on efficacy, but this has not yet been studied in low-moisture foods. Using a homologous series of rosmarinic esters as AOX in crackers, we determined that efficacy increases with increasing hydrophobicity based on lipid hydroperoxide and hexanal generation. Confocal microscopy was used to determine the location of both lipids and AOX. Hydrophobic rosmarinic esters partitioned more closely with the lipid than rosmarinic acid, presumably placing the hydrophobic AOX at the site of oxidation reactions. Partitioning and efficacy of the intermediate polarity ester were affected by mode of incorporation (e.g., added to the water or to the lipid prior to dough formation). The synthetic AOXs propyl gallate, butylhydroxytoluene, and tert-butylhydroquinone gave similar results with the more hydrophobic BHT and TBHQ being more effective at reducing lipid hydroperoxide and hexanal generation than the more hydrophilic propyl gallate. These results provide important information on which AOX would be most effective in low-moisture foods.
Pub.: 04 Jun '15, Pinned: 12 Jul '17
Abstract: This research strove to understand the relationship between physical structure and oxidative stability in crackers since mechanisms of lipid oxidation are poorly understood in low-moisture foods. Confocal microscopy showed that lipids formed a continuous matrix surrounding starch granules, and starch-lipid, lipid-air, and protein-lipid interfaces were observed. Unlike bulk oils, meats, and emulsions, lipid hydroperoxides exhibited greater stability in low-moisture crackers as hexanal formation was delayed >20 d. Iron, added at 10 times the concentrations normally found in enriched flour, did not increase oxidation rates compared to the control. EDTA may reduce endogenous iron activity but not as greatly as in other matrices. Addition of fatty acids up to 1.0% of total lipid weight did not statistically affect lipid oxidation lag phases. The unique structure of low-moisture foods clearly affects their resistance to metal-promoted lipid oxidation.
Pub.: 03 Feb '15, Pinned: 12 Jul '17
Abstract: Fluorescent molecular rotors are compounds whose emission is modulated by segmental mobility; photoexcitation generates a locally excited (LE), planar state that can relax either by radiative decay (emission of a photon) or by formation of a twisted intramolecular charge transfer (TICT) state that can relax non-radiatively due to internal rotation. If the local environment around the probe allows for rapid internal rotation in the excited state, fast non-radiative decay can either effectively quench the fluorescence or generate a second, red-shifted emission band. Conversely, any environmental restriction to twisting in the excited state due to free volume, crowding or viscosity, slows rotational relaxation and promotes fluorescence emission from the LE state. The environmental sensitivity of molecular rotors has been exploited extensively in biological applications to sense microviscosity in biofluids, the stability and physical state of biomembranes, and conformational changes in macromolecules. The application of molecular rotors in food research, however, has been only marginally explored. In this review, we summarize the main characteristics of fluorescent molecular rotors, their current applications in biological research and their current and potential applications as sensors of physical properties in food science and engineering.
Pub.: 01 Jul '17, Pinned: 11 Jul '17
Abstract: Proteins dispersed in the continuous phase of oil-in-water emulsions are capable of inhibiting lipid oxidation reactions. The antioxidant activity of these proteins is thought to encompass both free radical scavenging by amino acid residues and chelation of prooxidative transition metals; however, the precise mechanism by which this occurs remains unclear. In this study, the oxidative stability of cysteine, tryptophan, and methionine residues in continuous phase beta-lactoglobulin (beta-Lg) in a Brij-stabilized menhaden oil-in-water emulsion was determined. The presence of low concentrations of continuous phase beta-Lg (250 and 750 microg/mL) significantly inhibited lipid oxidation as determined by lipid hydroperoxides and thiobarbituric acid reactive substances analysis. It was observed that cysteine oxidized before tryptophan in beta-Lg, and both residues oxidized before lipid oxidation could be detected. No oxidation of the methionine residues of beta-Lg was observed despite its reported high oxidative susceptibility. It is conceivable that surface exposure of amino acid residues greatly affects their oxidation kinetics, which may explain why some residues are preferentially oxidized relative to others. Further elucidation of the mechanisms governing free radical scavenging of amino acids could lead to more effective applications of proteins as antioxidants within oil-in-water food emulsions.
Pub.: 22 Dec '05, Pinned: 29 Aug '17
Abstract: Chelators are valuable ingredients used to improve the oxidative stability of food emulsions. Caseins and casein peptides have phosphoseryl residues capable of binding transition metals. Thus, the ability of enriched caseinophosphopeptides to inhibit lipid oxidation in corn oil-in-water emulsions was investigated. Enriched caseinophosphopeptides (25 microM) inhibited the formation of lipid oxidation at both pH 3.0 and 7.0 as determined by lipid hydroperoxides and hexanal. Calcium (0-100 mM) had no influence on the antioxidant activity of the enriched caseinophosphopeptides. Casein hydrolysates were more effective inhibitors of lipid oxidation than the enriched caseinophosphopeptides at equal phosphorus content. Thus, antioxidant properties might not be uniquely attributed to chelating metals by phosphoseryl residues but also by scavenging free radicals. Overall, the observed antioxidant activity of casein hydrolysates means they could be utilized to decrease oxidative rancidity in foods.
Pub.: 03 Apr '03, Pinned: 29 Aug '17
Abstract: The influence of three surface-active proteins on the oxidative stability and lipase digestibility of emulsified ω-3 oils was examined: deamidated wheat gliadin (gliadin); sodium caseinate (CN); whey protein isolate (WPI). Gliadin and WPI were more effective at inhibiting lipid oxidation (hydroperoxides and TBARS) of fish oil-in-water emulsions than CN. Protein oxidation during storage was determined by measuring the loss of tryptophan fluorescence. The CN-emulsions exhibited the highest loss of tryptophan fluorescence during aging, as well as the highest amount of lipid oxidation. Potential reasons for the differences in oxidative stability of the emulsions with different proteins include differences in interfacial film thickness, protein chelating ability, and antioxidant amino acids profiles. During in vitro digestion, gliadin-stabilized emulsions had the lowest digestion rate of the three proteins. These results have important implications for using proteins to fabricate emulsion-based delivery systems for ω-3 oils.
Pub.: 13 Jan '15, Pinned: 29 Aug '17