Mode of development of peroxides and attendant changes in vegetable oils on storage.
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Abstract:
It is well-known that fats and oils develop rancidity on storage. Under the
warm tropical conditions of India, they develop off-flavour at a comparatively rapid
rate. Method of extraction, conditions of storage, extent of exposure to heat, light
and air, presence of pro-oxidants, particularly, free fatty acids, moisture and metals
and metallic compounds and presence of natural antioxidants are some of the factors
affecting the keeping quality of fats and oils. The mechanism of the development
of rancidity, however, is not yet definitely known. In the present investigation,
attempts have been made to throw some light on the mode of formation of peroxides
and attendant changes in vegetable oils on storage. In the first instance, groundnut
and coconut oils have been selected for this study, because, these two oils differ
significantly with regard to the degree of unsaturation and also have their own
characteristic fatty acid composition.Keywords:
Degree of unsaturation
Flavour
Coconut oil
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Consumer expectations have been changing. Current consumer food trends emphasize naturalness and health. Fatty acid composition and mainly the unspecified constituents of vegetable oil such as tocopheols phytosterols, phenols, acting individually or exhibiting synergistic activity are contributors to good health. Chemical characteristics oxidative stability and processing procedures determine nutritional value of edible oil. The different chemical characteristics take part in oxidative stability of oils. Tocopherols and other components with antioxidant activity found in vegetable oil function as chain-breaking antioxidant that prevents the propagation of lipid oxidation. The successful production of canola, sunflower, olive, corn plants that produced oils with an increased monounsaturated (oleic) fat content and reduced polyunsaturated fat content has created a collection o f oils with enough stability to be used in demanding applications. Oil with high proportion of unsaturated ω-3 and ω-6 fatty acids has good nutritional value but poor oxidative stability. In view of new trends processing procedures should be more balanced, preserving the nutritional value of the oil, without jeopardizing the safety and quality of the product. The refining process depends on the quality of the crude oils, which may vary substantially. Severe processing conditions are therefore applied to guarantee the quality and food safety of the refined oils. Unwanted components that could either reduce the quality of the oil (such as flavor components, colorants, and pro-oxidants) or pose a significant risk to human health when consumed (such as pesticides polycyclic aromatic hydrocarbons, allergens) are removed during traditional refining. Quality of the refined oil decreases because of partial removal during process, of minor components with nutritional value, such as antioxidants (tocopherols, phenol acids and phytosterols). In contrast cold pressed oils are perceived to exhibit a natural image and to have a higher quality and stability. By utilizing lower expelling temperatures the oil quality improves with regard to nutritional components such as tocopherols, carotene, phospholipids and phytosterols. Unfortunately unwanted components such as prooxidant and pesticides, polycyclic aromatic hydrocarbons, allergens remain in expelled oils. To control the development of rancidity in the manufacture of top-quality cold pressed oils the following precautions must always be taken: high-quality raw material store the stock in a cool, dark and dry place, use stainless equipment to avoid trace metal contamination, strict quality control to avoid mixing old oils in any part of the process. Which oil is the best? Each, and every oil has its own virtues. Thus it is impossible to answer the question. Some oils are mostly composed of polyunsaturated acids, other are composed of monounsaturated fatty acids and their tocopherol content vary as well. So recommendation is to use different varieties of oils for different purpose at moderate quantity.
Vegetable oil
Edible oil
Ricinoleic acid
Sunflower oil
Lipid Oxidation
Phytosterol
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Abstract Crude edible fats and oils contain variable amounts of nonglyceride impurities, such as free fatty acids, non‐fatty materials generally classified as “gums”, and color pigments. Most of these impurities are detrimental to end product fresh and aged quality characteristics, hence must be eliminated by a purification process before the finished fats and oils are suitable for human consumption. The object of this process is to remove these objectionable impurities with the least possible loss of neutral oil and tocopherals. Key theoretical and practical factors for degumming and refining crude edible oils are discussed with particular reference to processes, flow charts, control systems and analytical testing requirements. In addition to typical large volume oils, such as soya and cotton, techniques are also reviewed for smaller volume oils, including palm, lauric and corm.
Refining (metallurgy)
Edible oil
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The resistance to oxidation of vegetable oils has been evaluated by means of a new instrument (Oxitest) able to obtain this parameter through the application of accelerated temperatures and oxygen absolute pressures (90°C and 6 bar) and the knowledge of the absolute pressure change in a closed and thermostatted room, assumed as the oxygen uptake by reactive substances. One of the advantages of this technique is that food stability against rancidity can be measured directly on whole foods (solid, liquid, doughy) without the need to perform preliminary separation of the fat. In the specific case of vegetable oils, the aim of this work has been the evaluation of the instrument ability in discriminating the oxidative stability of: a) vegetable oils of different botanic origins; b) soya oil stored at different temperatures; c) pesto sauce prepared both with extra virgin olive oil and sunflower oil. Finally the ability of Oxitest in revealing adulteration of vegetable oils has been also evaluated. The obtained data show the sensibility of this instrument and its accelerated conditions in evaluating the oxidative stability of different typologies of vegetable oils, of their mix and also of vegetable oils used in food preparations such as sauce. In the future, it should be of interest to evaluate the application of Oxitest to other foodstuffs.
Vegetable oil
Sunflower oil
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To analyze the difference of deterioration products in bio-waste oil and vegetable oils.The changes of species and abundance of deterioration products were analyzed through observing the differences in Raman spectra during the process of deterioration and refining.The deterioration contents produced during heating, cooking, frying and wasting, instead of storage, were significantly more abundant than normal contents. Through the refining process, the deterioration products abundance was reduced in vegetable oils while increased in bio-waste oils.Due to the distinct deteriorating processes, the species and abundance of deterioration products are remarkably different in bio-waste oil and vegetable oils. The deterioration products in vegetable oils would be mostly removed, but those in bio-waste oils are concentrated instead of eliminated during the refining procedure.
Refining (metallurgy)
Vegetable oil
Waste oil
Cooking oil
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Traditionally, mineral oils have been one of the most important quenchants used. However, their substantial deficiencies with respect to environment friendliness and toxicity as well as long-term, low-cost supply necessitate the search for alternative replacement media. Quenching performance of petroleum oils is limited by the oxidative degradation properties, which are composition dependent. Upon repeated exposure to the relatively high interfacial temperatures between the steel surface and the oil, petroleum oils undergo thermal and oxidative degradation leading to significant variation in their quenching performance. Therefore, this is a particularly important performance parameter that must be examined for any alternative quenching medium. One class of alternative fluids is vegetable oils, which are typically biodegradable and non-toxic. However, vegetable oils typically exhibit relatively poor oxidative stability properties, and therefore it is important to determine the potential impact of oxidation on quenching performance. The results reported here are the first step in a larger study. In this work, uninhibited vegetable oils were studied using a laboratory apparatus and procedure previously reported to promote premature oxidation of petroleum oils to approximate actual use conditions. Experimental fluids are examined and compared to typical petroleum quench oil compositions using viscosity, infrared spectroscopy, 13 CMR spectroscopy and cooling curve performance according to ASTM D 6200. The results obtained indicate that vegetable oils are promising alternatives to petroleum oils as quenchants but that to be commercially feasible, appropriate antioxidants must be used.
Vegetable oil
Degradation
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ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTConstituents of Fats and Oils Affecting the Development of Rancidity.H. S. Olcott and H. A. MattillCite this: Chem. Rev. 1941, 29, 2, 257–268Publication Date (Print):October 1, 1941Publication History Published online1 May 2002Published inissue 1 October 1941https://pubs.acs.org/doi/10.1021/cr60093a005https://doi.org/10.1021/cr60093a005research-articleACS PublicationsRequest reuse permissionsArticle Views309Altmetric-Citations48LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
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Abstract On the basis of the chemical, physical, and biological criteria used, all of which have been shown to be sensitive indicators of heat damage to oils, it must be concluded that the overall nutritional quality of an oil is not adversely affected by alkali refining, adsorptive decolorizing, or deodorization; that higher temperatures of deodorization (238C) produce oils nutritionally equivalent to those deodorized at lower temperatures (160C); and that the normal processes used in manufacturing edible oils improve the resistance of these oils to heat damage.
Refining (metallurgy)
Vegetable oil
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Peroxide value
Peroxide
Lipid Oxidation
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Processing of edible oils during refining of the crude oil, or when used in frying, often exposes the oils to thermal and oxidative stresses. However, because of weaknesses inherent in their chemical structure, oils subsequently undergo structural decomposition and transformation in response to thermooxidative stresses. Whereas some of the decomposition products from the processed oils confer some value additions to the oils and the foods prepared in them (e.g. flavor, color, texture, and even stability), a number of edible oils' degradation products are known to be potentially toxic, and at reasonably high quantity, can compromise the health and wellbeing of consumers. This article describes the sources and updated knowledge on major toxic compounds that are generated during high temperature processing and usage of vegetable oils.
Edible oil
Refining (metallurgy)
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Abstract The nuts are invariably sun‐dried in Pakistan, Iran, Afghanistan and adjoining areas of China and USSR. Their oils are generally kept in the unrefined form, being exposed to light during subsequent handling or marketing and consequently undergo changes in colour, flavour and chemical changes. Light induced reactions have been found to damage the quality and stability of edible oils, fats and fat containing food products [1, 2]. Oil characteristics of walnuts [3], and oxidation of almond and walnuts oils during heating have been studied [4]. Influence of clear flexible pouches and amber‐colour bottles on storage behaviour of groundnut oils was reported by Mahadevaiah et al. [5] and Nasirullah et al. [6]. Dry nut oils are generally sold in clear glass bottles in Pakistan and several other countries but their stability to fluorescent light in relation to different packages has not been tested, which is the object of these studies.
Flavour
Fluorescent light
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