Lipoxidase deactivation to improve stability,odor and flavor of full-fat soy flours

Oxidation of soybean lipids catalyzed by lipoxidase was prevented by heat treatment of soybean meats, which were then ground to give a full-fat soy flour free of rancid odor and flavors. Our previous studies showed that lipids in cracked, dehulled, soybeans rapidly oxidized after the lipoxidase system was activated by increasing moisture content to 20%. A series of experiments are reported in which various heat treatments were evaluated for effectiveness of lipoxidase deactivation. Dry heat to 212 F, steaming, or both, deactivated lipoxidase to give flours that had low values of peroxide, conjugated diene and free fatty acid and had good flavors after 2 years’ storage. Wet heat alone was also an effective treatment, whereas wet heat preceded by dry heat at 180 F gave poor flavor stability after 2 years. Gas liquid chromatography studies gave evidence that the rapid formation of volatiles in full-fat soy flours was catalyzed by an enzyme system. A 10 member taste panel was able to detect significant flavor and odor differences between oxidized and nonoxidized samples. Presented at the AOCS Meeting, Chicago, October 1967. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Interaction of flavor compounds with soy protein

The addition of flavors to soy protein products often results in a loss or change of the flavor. Processing parameters and especially the specific sorption properties of soy protein for many organic compounds strongly influence the flavor performance in such products. A systematic study on the interactions of individual classes of flavor compounds (alcohols, carbonyls, etc.) has been conducted in our laboratory. We will report on the methods used and the results obtained and will discuss the practical consequences for flavoring soy products. The discussion also will include the influence of processing conditions during texturization of soy protein on the flavors.     

Edible oil evaluation by room odor tests: A preliminary report

Room odors developed on heating edible fats in open vessels were evaluated and characterized by a 20 member odor panel. Edible fats tested were: special soybean salad and cooking oils, hydrogenated soybean oil and some commercial salad and cooking oils. Factors were investigated that affect reliability and reproducibility of the test and the acuity of the panel members. The effects of fry temperature and size of sample were investigated. The method has been applied to a study of hydrogenated and unhydrogenated soybean oil samples. Presented at the AOCS Meeting, Chicago, September 1970. No. Market. Nutr. Res. Div., ARS, USDA.     

Analysis of flavor quality and residual solvent of soy protein products

A simple, direct, gas Chromatographic technique is described for eluting and resolving residual solvent and flavor-related volatile components from soy products such as flour and protein isolates. No prior enrichment of volatiles is necessary. A sample, together with a small amount of water, is secured in a glass liner and placed in the heated injection port of a gas Chromatograph. The volatiles are rapidly steam distilled from the sample by the heat, moisture, and flow of carrier gas and are adsorbed on the chromatographic column in situ. Residual solvent and other volatiles adsorbed on the column are resolved by temperature-programmed gas chromatography and identified by combined gas chromatography-mass spectrometry. The correlation between taste panel flavor score and concentration of volatile components is significant at the 1% level. Presented at the AOCS Meeting, New York, May 1977.     

Minor components responsible for flavor reversion of soybean oil

Edible refined, bleached and deodorized (RBD) soybean oil was fractionated by silicic acid column chromatography to identify minor components responsible for flavor reversion. Minor components from oil eluted with diethyl ether/n-hexane (1:1) were compared with those from corn and canola oils. All vegetable oils contain free fatty acids, diglycerides and sterols as major ingredients in this fraction. However, unusual triglycerides consisting of 10-oxo-8-octadecenoic acid and 10-and 9-hydroxy octadecanoic acids were detected in RBD and crude soybean oils.     

Improving soy bean oil color

Summary 1. Increased heat developed in the Expeller barrel as the capacity and efficiency have been increased in the modern types of Expellers has resulted in increasing the color of crude soya bean oil to a point where it is objectionable for some uses. 2. Reducing and controlling the barrel temperature by spraying cool oil over it resulted in materially reducing the color of crude soya bean oil.     

Phosphatides in American soy beans and oil

Summary It has been found that the precipitate separating from clarified expressed crude oil from soy beans grown in North Carolina and Virginia is composed chiefly of phosphatides. Methods have been described for the determination of phosphatide phosphorus in soy beans which is applicable to seeds in general and in the oil. Soy beans of the more important varieties used by the oil mills both in the Eastern and Middle West States have been examined for their respective phosphatide content. With but few exceptions it was found that the beans grown in the East contained less phosphatides than those from the West, which indicated that the quantity of these substances present is not a factor in causing a partial separation of them in some oils but not in others. Regardless of whether or not a separation of phosphatides takes place, all the crude soy bean oils which have been examined so far have contained notable quantities of them.     

A review of soybean oil reversion flavor

Crude soybean oil has a characteristic “greenbeany” flavor, which during refining, bleaching and deodorization is eliminated to produce a bland tasting, light colored oil. However, flavor returns during storage and has been characteristically called the “reversion flavor” of soybean oil. This deleterious characteristics flavor has influenced the utilization of soybean oil and its fatty acids. Several theories for the cause of reversion flavor include: (a) oxidation of linolenic acid; (b) oxidation of isolinoleic acid of the 9,15-diene structure; (c) phosphatide reactions; (d) unsaponifiables; and (e) oxidative polymers. References are presented that support or contradict these theories. Recent publications concerning the isolation and characterization of the components of reversion flavor indicate slight oxidation of the fatty acids is the major cause. Techniques that are effective in increasing the flavor stability of soybean oil are presented.     

History of the development of soy oil for edible uses

In the early 1940s, soybean oil was considered neither a good industrial paint oil nor a good edible oil. The history of soybean oil is a story of progress from a minor, little-known, problem oil to a major source of edible oil proudly labeled on premium products in the 1980s. It is also a story of cooperative government research and industrial implementation of research findings. After 3-1/2 decades, soybean oil, “the number one problem of the soybean industry,” has become the source of choice for edible oil products in the U.S., moreover, increasing outlets appear to be assured in the world markets of the future.     

Room odor evaluation of oils and cooking fats

Panel evaluations have been made of room odors developed by edible oils and cooking fats heated to frying temperatures. Vegetable and mixed fat shortenings, as well as oils of different iodine value and from special processing, were investigated with and without added stabilizers. When silicones were added to frying fats, room odor scores improved markedly. Certain added autoxidative cleavage products had little effect on odor scores at levels where they were detected easily in taste tests. To be discernible in room odors, these additives had to be present at levels ca. 100-fold greater than their taste thresholds. Panel results show that the undesirable frying odors contributed by unhydrogenated soybean oil in mixtures with other oils could be detected readily at 25% levels. As the level of soybean oil was lowered further, the room odor scores of oil mixtures improved perceptibly. One of 13 papers presented in the symposium “Flavor Research in Fats and Fat Bearing Foods,” AOCS Meeting, Atlantic City, October 1971. N. Market. Nutr. Res. Div., ARS, USDA.     

Oxidation-derived flavor compounds as quality indicators for packaged olive oil

Aroma compounds in packaged extra virgin olive oil can be present naturally or be derived through oxidative degradation under favorable conditions of temperature, light, and oxygen availability. In this study, the identity and quantity of flavor compounds were determined for extra virgin olive oil packaged in 0.5-L glass, poly(ethylene terephthalate), and poly(vinyl chloride) bottles and stored at 15,30, and 40°C under fluorescent light or in the dark for 1 yr. A set of mathematical equations concerning the rates of the most fundamental oxidation reactions in the oil was prepared and numerically solved, and the reaction constants were estimated for specific temperature values. Mainly, the presence of fluorescent light, followed by elevated temperature, stimulated oxidative alterations in the olive oil. Separated and identified flavor compounds were recorded for all the olive oil samples. Based on their abundance and evolution in the oil samples, those most clearly describing oxidation were hexanal, nonanal, (E)-2-decenal, (E)-2-heptenal, and 2-pentyl furan. These compounds could be used as markers of the oxidation process to monitor and describe the quality of packaged olive oil quantitatively.     

Adsorption of soy oil phospholipids on silica

An experimental method for adsorption of phospholipids from soybean oil was developed based on chromatographic properties of the oil components. The traditional method for removing phospholipids involves hydrating the gums. However, when crude oil in hexane is applied to thin layers or columns of silica, the phospholipids irreversibly adsorb. The triglycerides can be eluted with non-polar solvents and phospholipids with a polar solvent system. Hence, there is a basis for a selective adsorption of phospholipids on silica. The system involved stirring one hundred milliliters of oil in solvent (i.e., miscella) with one gram of silica for 15 min. The phosphorus content, before and after the reaction, was analyzed by wet ashing and Fiske-Subbarow colorimetric reaction. Addition of isopropanol (at least 1%) to the hexane miscella caused an increase in phosphorus adsorption, most likely due to liberating triglyceride from adsorption sites. Increased adsorption was achieved by deactivating the silica. Oil concentration did not appear to affect the adsorption. The amount of phosphorus adsorbed depended on the concentration of the phospholipid. When phospholipid adsorbed per gram of silica is plotted vs the residual phospholipid, the plot resembles a Freundlich isotherm for reversible adsorption. Yet the adsorption is irreversible. Possible explanations for this type of adsorptive behavior are explored.     

Components of the hardening flavor present in hardened linseed oil and soybean oil

The characteristic hardening flavor which develops in hardened linseed and soybean oils during storage has been coned from hardened linseed oil by stripping with nitrogen. After separating the volatile substances by adsorption chromatography on silica, the fraction containing the hardening flavor has been converted into 2,4-dinitrophenylhydrazones (DNPHs) and separated by means of partition chromatography. On regeneration of the fractions of DNPSs obtained, the characteristic hardening flavor was observed in one specific band. Both by hydrogenation and by oxidation of the free carbonyl the carrier of the flavor was found to be an unsaturated aldehyde; however, not of the α-β unsaturated type. Further separation of the regenerated carbonyls by means of gas-liquid chromatography (GLC) points to a C₉-aldehyde. After synthesis of the 4-,5- and 6-cis- andtrans-nonenals, comparison made it probable that the carrier of the hardening flavor is a mixture of 6-cis and 6-trans-nonenal, the latter of which has the greatest share in the hardening flavor. In order to confirm the location of the double bond in the carrier of the hardening flavor a recent isolation technique was applied. The volatile substances from hardened linseed oil were first separated via GLC. After conversion of the carbonyls in question into their DNPHs, the latter have been separated by means of thin-layer chromatography (TLC). By means of IR-analysis and oxidation with osmium tetroxide of the pure derivative, the principal carrier of the hardening flavor has been identified as 6-trans-nonenal.     

Oxidative and flavor stability of oil from lipoxygenase-free soybeans

Soybeans that lack or contain three lipoxygenase (LOX) isozymes, LOX-1, LOX-2, and LOX-3, were evaluated for oxidative and flavor stability at 60°C in the dark and at 35°C in the light. Although the two types of soybeans had a similar genetic background, there were significant differences (P ≤ 0.01) in fatty acid percentages between the lipoxygenase-free and normal oils before and after storage at both temperatures. The linolenic acid content of oil from LOX-free germplasm before storage averaged 7.2%, while normal lines averaged 6.6%. The linoleic acid content after storage averaged 6.9% for LOX-free and 6.6% for normal oils. LOX-free oil was not significantly different from normal oil in flavor, as judged by a sensory panel, or in concentrations of volatiles during storage at either storage condition. LOX-free oil had less hexanal than normal oil before storage, but had significantly greater (P ≤ 0.05) levels after storage for two weeks at 35°C. Peroxide values of oil from LOX-free soybeans were significantly greater (P ≤ 0.01) than oil from the normal soybean after storage at 60 and 35°C. LOX-free oil had significantly greater (P ≤ 0.01) levels of α-, β-, and γ-tocopherols. In general, oil from LOX-free soybeans did not have improved flavor or oxidative stability. Differences between the two oil types in peroxide value and in production of a few volatiles were probably a result of the differences in initial fatty acid composition.     

Oxidative and flavor stability of oil from lipoxygenase-free soybeans

Soybeans that lack or contain three lipoxygenase (LOX) isozymes, LOX-1, LOX-2, and LOX-3, were evaluated for oxidative and flavor stability at 60°C in the dark and at 35°C in the light. Although the two types of soybeans had a similar genetic background, there were significant differences (P≤0.01) in fatty acid percentages between the lipoxygenase-free and normal oils before and after storage at both temperatures. The linolenic acid content of oil from LOX-free germplasm before storage averaged 7.2%, while normal lines averaged 6.6%. The linoleic acid content after storage averaged 6.9% for LOX-free and 6.6% for normal oils. LOX-free oil was not significantly different from normal oil in flavor, as judged by a sensory panel, or in concentrations of volatiles during storage at either storage condition. LOX-free oil had less hexanal than normal oil before storage, but had significantly greater (P≤0.05) levels after storage for two weeks at 35°C. Peroxide values of oil from LOX-free soybeans were significantly greater (P≤0.01) than oil from the normal soybean after storage at 60 and 35°C. LOX-free oil had significantly greater (P≤0.01) levels of α-, β-, and γ-tocopherols. In general, oil from LOX-free soybeans did not have improved flavor or oxidative stability. Differences between the two oil types in peroxide value and in production of a few volatiles were probably a result of the differences in initial fatty acid composition.     

Processing and utilization of by-products from soy oil processing

Crude soybean oil contains a number of materials which must be removed to produce a neutral, bland-flavored and light-colored refined oil. While at times these materials may have been considered waste constituting a disposal problem, they are, in fact, valuable byproducts when efficiently recovered and processed. Methods of recovery and processing lecithin, soapstock and deodorizer distillate at the refinery level are reviewed. Process and analytical control are discussed. Some of the important end uses are listed.