Micro-organisms growing on rapeseed during storage affect the profile of volatile compounds of virgin rapeseed oil.

BACKGROUND: Micro-organisms populate on rapeseed after harvest during storage depending on the growing conditions. The composition of the bacterial colonization is unknown, although its contribution to the profile of volatile aroma-active compounds determines the sensory quality of virgin cold-pressed rapeseed oil. RESULTS: From four rapeseed samples, 46 bacterial strains were isolated. By DNA-sequencing, the identification of four bacteria species and 17 bacteria genera was possible. In total, 22 strains were selected, based on their typical off-flavors resembling those of virgin sensory bad cold-pressed rapeseed oils. The cultivation of these strains on rapeseed meal agar and examination of volatile compounds by solid phase microextraction-gas chromatography-mass spectrometry allowed the identification of 29 different compounds, mainly degradation products of fatty acids such as alkanes, alkenes, aldehydes, ketones and alcohols and, in addition, sulfur-containing compounds, including one terpene and three pyrazines. From these compounds, 19 are described as aroma-active in the literature. CONCLUSION: Micro-organisms populating on rapeseed during storage may strongly influence the sensory quality of virgin rapeseed oil as a result of the development of volatile aroma-active metabolic products. It can be assumed that occurrence of off-flavor of virgin rapeseed oils on the market are the result of metabolic degradation products produced by micro-organisms populating on rapeseed during storage. © 2017 Society of Chemical Industry.

Bioactive compounds and "in vitro" antioxidant activity of some traditional and non-traditional cold-pressed edible oils from Macedonia.

The bioactive compounds and "in vitro" antioxidant activity measured by three antioxidant assays of some traditional and non-traditional cold-pressed edible oils from Macedonia were object of this study. The fatty acid composition showed dominance of monounsaturated oleic acid in "sweet" and "bitter" apricot kernel oils with percentages of 66.7 ± 0.5 and 57.8 ± 0.3%, respectively. The most dominant fatty acid in paprika seed oil was polyunsaturated linoleic acid with abundance of 69.6 ± 2.3%. The most abundant tocopherol was γ-tocopherol with the highest quantity in sesame seed oil (57.6 ± 0.1 mg/100 g oil). Paprika seed oil, sesame seed oil and sweet apricot oil were the richest source of phytosterols. DPPH assay was the most appropriate for the determination of the antioxidant activity of cold-pressed sunflower oil due to high abundance of α-tocopherol with a level of 22.8 ± 1.1 mg/100 g of oil. TEAC assay is the best for the determination of the antioxidant activity of sesame seed oil and paprika seed oils as the richest sources of phenolic compounds. ß-carotene assay was the most suitable assay for oils obtained from high pigmented plant material. Triacylglycerols and phytosterol profiles can be used as useful markers for the origin, variety and purity of the oils.

Optimization of sample clean-up for the determination of small amounts of MOSH and MOAH in edible oils - method DGF C-VI 22 (20).

Methods for determining MOSH and MOAH in edible oils showed major problems with interlaboratory comparability of analytical results, especially in the lower concentration range below 10 mg/kg. However, a method with improved sensitivity and reproducibility is urgently needed to obtain a valid data basis for minimization efforts. To cope this problem a new method was created in 2020. The method was established as the standard method DGF C-VI 22 (20) of the German Society for Fat Science e.V. (DGF). For the development of this method different sample epoxidation approaches have been performed, evaluated and improved. Additionally, a saponification, a decision tree for sample preparation, an upstream clean-up column and a system suitability test were introduced. The focus was on reliability and interlaboratory comparability over all edible oil matrices up to a LOQ of 1 mg/kg. The optimized method was validated in terms of trueness and precision in a collaborative trail with 11 laboratories. The achieved recovery rates of 89-105% MOSH and 70-105% MOAH met the JRC requirements. Method and validation results were obtained with HorRat values between 1.3 and 1.8 for MOSH and MOAH.

Determining MOSH and MOAH with High Sensitivity in Vegetable Oil─A New, Reliable, and Comparable Approach Using Online LC-GC-FID─Evaluation of Method Precision Data.

A method for the analysis of saturated mineral oil hydrocarbons (MOSH) and aromatic mineral oil hydrocarbons (MOAH) has been developed to improve interlaboratory precisions especially for amounts below 10 mg/kg. This approach was adopted as the standard method DGF C-VI 22 (20) of the German Society of Fat Sciences. Therefore, this method was evaluated on different edible oils containing a variety of interfering biogenic substances. The precision data were determined in an interlaboratory trial with an international group of 14 laboratories from Germany, Austria, and Italy. Good reproducible relative standard deviations for total MOSH (12.5-20.7%) and total MOAH (12.4-39.5%) as well as HorRat values ranging between 1.1 and 2.3 for total MOSH and between 0.9 and 2.6 for total MOAH have been achieved. As some matrices showed residual interferences in the MOAH fraction, these substances were further analyzed by online high-performance liquid chromatography-comprehensive two dimensional gas chromatography with time of flight mass detection.

Identification of bitter off-taste compounds in the stored cold pressed linseed oil.

Whereas freshly pressed linseed oil provides a delicate nutty flavor, a lingering bitter off-taste is developing upon storage at room temperature. Using a sensory guided fractionation approach, the key bitter compound was identified in stored linseed oil, and its structure was determined as the methionine sulfoxide-containing, cyclic octapeptide cyclo(PLFIM OLVF) by means of FTIR, LC-MS, NMR spectroscopy, and amino acid analysis. Although this peptide is known in the literature as cyclolinopeptide E, the bitter taste activity of this compound has not previously been described. Sensory evaluation revealed a recognition threshold concentration of 12.3 micromol/L water.

Metabolic Changes during Storage of Brassica napus Seeds under Moist Conditions and the Consequences for the Sensory Quality of the Resulting Virgin Oil.

Virgin rapeseed (Brassica napus) oil is a valuable niche product, if delivered with a high quality. In this study, the effects of moist storage of B. napus seeds for 1 to 4 days on the seed metabolome and the chemo-sensory properties of the produced oils were determined. The concentrations of several primary metabolites, including monosaccharides and amino acids, rapidly increased in the seeds, probably indicating the breakdown of storage compounds to support seed germination. Seed concentrations of indole glucosinolates increased with a slight time offset suggesting that amino acids may be used to modify secondary metabolism. The volatile profiles of the oils were pronouncedly influenced by moist seed storage, with the sensory quality of the oils decreasing. This study provides a direct time-resolved link between seed metabolism under moist conditions and the quality of the resulting oils, thereby emphasizing the crucial role of dry seed storage in ensuring high oil quality.

Quality of cold-pressed edible rapeseed oil in Germany.

Forty-eight cold-pressed edible rapeseed oils obtained from small- and medium-sized decentralized plants located all over Germany were characterized by different chemical parameters for their composition and by descriptive sensory evaluation. Between the different oils great differences could be noticed for each parameter. The results evidenced that additionally to the features given in the Guidelines for edible fats and oils of the German Food Codex, especially the sensory evaluation, the oxidation stability (Rancimat), content and the composition of tocopherols, the content of trans-fatty acids and the content of steradienes were crucial parameters to guarantee a high-quality product for the consumer.