Chapter 12
Flavor Composition of Oil Obtained from Crude and Roasted Oats 1
S. M . Fors and P. Schlich
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Department of Food Science, Chalmers University of Technology, c/o SIK, Box 5401, S-402 29 Goteborg, Sweden Laboratoire de Recherches sur les Arômes, INRA, 17 rue Sully, BP 1540, F-21034 Dijon Cedex, France
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Twο oat varieties with different lipid content, Magne (7.4%) and Chiuauhua (8.3%), were studied before and after roasting. Oils were extracted by carbon dioxide and volatile fractions were isolated by molecular vacuum distillation. The samples obtained were analysed by GC-MS and by a panel. The lipid content and the preparation of the oats (heat or no heat, milling before and after roasting), influenced the flavor composition. More than 100 compounds were identified, isl and O-heterocycles were predominant in oils from roasted oats, especially in the Magne variety. Oils from whole roasted oats had larger amounts of volatiles than those from ground roasted oats. Aldehydes were highly correlated to heated oil from crude oats. Alcohols, ketones and hydrocar bons were present in all oils. Association between oils and chemical compounds was visualized by Principal Component Analysis and by using the RV coefficient. Oils from roasted oats had an aroma resembling of sesame oil and Swedish crispbread. Flavor formation in foods is a very complex process since it results from different phenomena often occuring simultaneously. Especially in heattreated food, the formation of flavor is often associated with the Maillard reaction. Reducing sugars and amino acids or peptides are constituents involved in this non-enzymatic browning reaction (1-3). The contribution of lipids and their role as flavor generators has also been extensively investi gated (fr-6). Despite a great deal of research effort, many questions remain concerning the above mentioned flavor precursors. Oat, Avena sativa, is a cereal which has been little studied, at least from a flavor point of view. Only a few investigations have been published, e.g. by Heydanek and McGorrin (7, 8). A review concerning oat flavor chemistry has also appeared quite recently (9). However, this cereal has attracted increased interest during the last few years, owing to the health benefits of oat. Examples are its cholesterol-lowering properties, the desirable physiological properties of fibre content and the favourable ratio of polyunsaturated to saturated fats in its lipid content (10). 0097-6156/89/0409-0121$06.00/0 ο 1989 American Chemical Society Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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T H E R M A L GENERATION OF AROMAS
New oat varieties are being studied with increasing interest in Sweden, e.g. varieties with a high lipid content. The present study deals with flavor compounds isolated from oils obtained from crude and roasted oats. The influence on the flavor composition of various parameters, such as heat and lipid content in the oat varieties are taken into account.
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Experimental Procedures Materials and Extraction Procedure. Two oat varieties, Magne and Chihuauhua, were used. They contained 7A and 8.3% lipids respectively. The oil fractions in batches of dehulled crude oats and roasted oats were extracted. Oat samples of 1.5 kg each were placed in glass vessels open to the air and dispersed in a layer 3-4 cm deep. The roasting was carried out in a domestic oven for 2 hours at 2 0 0 ° C , ±5°C. Lipid isolation was performed using supercritical carbon dioxide (SCCO2). The extraction was carried out at a pressure of 250 bar at 4 0 ° C for 5 hours. The oil samples obtained are presented in Figure 1. Details of the oat varieties and the extraction equipment have been given in an earlier paper (Fors and Eriksson, submitted for publication 1988). Isolation of Volatile Compounds from Oat Oil. Four oil samples were obtained from each oat variety, as shown in Figure 1. Each oil was isolated, in triplicate, for its volatile fraction by means of molecular vacuum distillation. The equipment used has been previously described (11, 12). Aliquots of 5.0 grams were used. The isolation was performed at room temperature and proceeded for 4 hours from the time secondary vacuum was
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12.
FORS AND SCHLICH
Flavor Composition of Oil from Oats
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methyl-2-furfural, 2-furanmethanol and 1-formylpyrrol were present in much greater amounts in MARM and MBRM (from oat with 7.4% lipids) compared with M A R C and MBRC (from oat with 8.3% lipids). This observation confirms of results obtained in a model system. When the medium was deprived of phospholipids and triglycerides, the amount of heterocyclic compounds increased (21). The preparation technique of the oats, whether or not heat was used and whether milling was carried out before or after roasting, also influenced the final volatile composition. Isolates from oats milled before roasting (MBRM, MBRC) had volatile compounds in lower concentrations compared with those milled after roasting (MARM, MARC). Despite a larger available surface area promoting the formation of heterocycles, for example, fewer volatiles were found. This was probably due to evaporation from the milled samples MBRM and MBRC. Volatiles formed in roasted whole oat seeds were retained and encapsulated, and gave a higher final amount. This observation concerns samples MARM and MARC which were isolated from oats milled after roasting. Sensory Analysis. Oils from the Magne variety were evaluated by a profile panel. Oil from crude oats (a), two oils from roasted oats (one part milled before roasting (b) and one milled after roasting (c) , and heated oil from crude oats (d) were subjected to the triangle test and descriptive analysis. No evaluations were performed of oils from the Chihuauhua variety, due to lack of material and also to similarities with the various Magne oils. A triangle test was performed in order to determine whether there was a significant difference between the oil samples studied. Results were as follows: * No significant difference was found between b and c (14 answers/+7R) * A large difference was found between a and d (12 answers/+12 R) * No comparisons were made between a-b and a-c, as there were very clearly marked differences. Descriptive analysis was made in order to obtain a detailed descriptive evaluation of a sample. A summary of attributes of Magne variety is presented below. Sample a: green, rancid, sourish, chemical (solvent, aldehyde, paint, petrol) Sample b
