Browsing by Subject "Glucosinolate"

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    Characterization of the aroma properties in fragrant rapeseed oil and aroma variation during critical roasting phase
    (2023) Zhang, Youfeng; Zhang, Yanyan
    Rapeseed oil is one of the third most-produced vegetable oil in the world, which is appreciated for its characteristic flavor and high nutritional value. Fragrant rapeseed oil (FRO) produced by a typical roasting process is popular for its characteristic aroma, which has an annual consumption exceeding 1.5 million tons. However, the changes in aroma blueprint of FRO during the typical roasting processing are still unclear, which challenges rapeseed oil quality and consumer acceptance. Accordingly, the aim of this work was to investigate the aroma characteristics and their precursors pyrolysis behavior of FRO to provide a basis and guidance for the control of FRO aroma quality during production processing. First, a systematic review on summarizing, comparing, and critiquing the literature regarding the flavor of rapeseed oil, especially about employed analysis techniques (i.e., extraction, qualitative, quantitative, sensorial, and chemometric methods), identified representative/off-flavor compounds, and effects of different treatments during the processes (dehulling, roasting, microwave, flavoring with herbs, refining, oil heating, and storage) was performed. One hundred and thirty-seven odorants found in rapeseed oil from literature are listed, including aldehydes, ketones, acids, esters, alcohols, phenols, pyrazines, furans, pyrrolines, indoles, pyridines, thiazoles, thiophenes, further S-containing compounds, nitriles, and alkenes, and possible formation pathways of some key aroma-active compounds are also proposed. Nevertheless, some of these compounds require further validation (e.g., nitriles) due to lack of recombination experiments in the previous work. To wrap up, advanced flavor analysis techniques should be evolved toward time-saving, portability, real-time monitoring, and visualization, which aims to obtain a “complete” flavor profile of rapeseed oil. Aparting from that, studies to elucidate the influence of key roasting processing on the formation of aroma-active compounds are needed to deepen understanding of factors resulting in flavor variations of rapeseed oil. Following, a systematic comparison among five flavor trapping techniques including solid-phase microextraction (SPME), SPME-Arrow, headspace stir bar sorptive extraction (HSSE), direct thermal desorption (DTD), and solvent-assisted flavor evaporation (SAFE) for hot-pressed rapeseed oil was conducted. Besides, methodological validation of these five approaches for 31 aroma standards found in rapeseed oil was conducted to compare their stability, reliability, and robustness. For the qualification of the odorants in hot-pressed rapeseed oil, SAFE gave the best performance, mainly due to the high sample volumes, but it performed worse than other methods regarding linearity, recovery, and repeatability. SPME-Arrow gave good performances in not only odorant extraction but also quantification, which is considered most suitable for quantifying odorants in hot-pressed rapeseed oil. Taking cost/performance ratio into account, SPME is still an efficient flavor extraction method. Multi-method combination of flavor capturing techniques might also be an option of aroma analysis for oil matrix. Afterwards, by application of the Sensomics approach the key odorants in representative commercial FRO samples were decoded. On the basis of the aroma blueprint, changes of overall aroma profiles of oils and their key odorants were studied and compared in different roasting conditions. To better simulate industrial conditions, high temperatures (150-200 ºC) were used in our roasting study, which was rarely studied before. Identification and quantitation of the key odorants in FRO were well performed by means of the Sensomics concept. Glucosinolate degradation products were a special kind of key odorants existing in rapeseed oil. Most of the odorants showed first rising and then decline trends as the roasting process progressed. Aroma profile results showed that high-temperature-short time and low-temperature-long time conditions could have similar effects on the aroma profiles of roasted rapeseed oils, which could provide a reference for the time cost savings in industrial production. To gain the fundamental knowledge of the aroma formation in FRO, the thermal degradation behavior of progoitrin (the main glucosinolate of rapeseed) and the corresponding generated volatile products were investigated in liquid (phosphate buffer at a pH value of 5.0, 7.0, or 9.0) and solid phase systems (sea sand and rapeseed powder). The highest thermal degradation rate of progoitrin at high temperatures (150-200 ºC) was observed at a pH value of 9.0, followed by sea sand and then rapeseed powder. It could be inferred that bimolecular nucleophilic substitution reaction (SN2) was mainly taken place under basic conditions. The highest degradation rate under basic conditions might result from the high nucleophilicity of present hydroxide ions. Under the applied conditions in this study, 2,4-pentadienenitrile was the major nitrile formed from progoitrin during thermal degradation at high temperature compared to l-cyano-2-hydroxy-3-butene, which might be less stable. The possible formation pathways of major S-containing (thiophenes) and N-containing (nitriles) volatile (flavor) compounds were proposed. Hydrogen sulfide, as a degradation product of glucosinolates, could act as a sulfur source to react further with glucose to generate thiophenes. Overall, the present work comprehensively documented the effects of thermal conditions and matrices on the aroma characteristics, aroma profiles, and key odorants of hot-pressed rapeseed oil, which could provide data and theoretical basis for the flavor control of FRO under thermal treatment at actual production temperatures (150-200 °C).
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    Evaluation of new open pollinating broccoli genotypes (Brassica oleracea convar. botrytis var. italica) specifically bred for organic farming conditions focusing on agronomic performance and glucosinolate content
    (2018) Sahamishirazi, Samira; Graeff-Hönninger, Simone
    Currently, a considerable share of varieties being used in the organic vegetable production are developed for conventional high-input production systems, and broccoli is no exception. In addition, F1 hybrids are cultivated in organic broccoli production to a great extent because of high quality and yield. Two main restrictions of cultivating the mentioned categories of varieties in organic farming are; 1) ban of using cytoplasmic male sterility (CMS) in organic agriculture for reproduction of F1 hybrids of broccoli and limitations of farmers to produce their own seeds, 2) absence of special traits of these varieties which result in weaker performance when being cultivated under organically low-input conditions. In contrast to hybrids, cultivation of open pollinating broccoli varieties gives the opportunity of reproducing seeds to organic farmers. Therefore, developing new open pollinating broccoli varieties, which have the same quality (agronomical, chemical and sensorial) as F1 hybrids, through organic breeding programs (on-farm breeding) would allow the organic broccoli farmers to replace the hybrids with varieties adapted to organic production conditions. With this in mind, the German Federal office for Agriculture and Food (BLE) initiated a project on “Breeding development of open pollinating cultivars of broccoli for organic farming in terms of agronomic characteristics, secondary and bioactive ingredients and sensory properties”. This was a joint project which was done through the cooperation of University of Hohenheim and Kultursaat e. V. (NGO of on-farm breeders) in two parts during six years (2011-2016). The present doctoral thesis, which was a part of the mentioned project, aims at 1) investigating the agronomic performance of the newly bred open pollinating genotypes of broccoli, 2) developing a Near-Infrared Spectroscopy (NIRS) method for fast analysis of total, indole, aliphatic and individual glucosinolates content of broccoli samples; and 3) determining the total and individual glucosinolate content of the newly bred open pollinating genotypes of broccoli. For investigations on agronomic performance, two field experiments were carried out by cultivating eleven newly bred open pollinating genotypes, two F1 hybrids and an open pollinating variety of broccoli over two growing seasons of fall 2015 and spring 2016. Evaluation of the effect of genotype, growing season and their interactions on agronomic parameters were targeted in this study. According to our findings, assessment of agronomic variables indicated that although there were distinctions in different parameters such as head firmness, head shape and total biomass fresh weight among the newly bred open pollinating genotypes, some genotypes performed similar to hybrid varieties in organic farming. However, most of the open pollinating genotypes had 16 % to 73 % lower yields compared to the hybrid varieties depending on growing season. Generally, the “marketable yield” of the genotypes was under the significant effect of “genotype × growing season interaction”. Head weight was significantly affected by growing season which resulted in significantly lower head weight of some genotypes in the spring compared to the fall season. Overall, cultivation of the genotypes in fall season led to significantly higher marketable yields, head weight and total biomass weight, as well as firmer heads in contrast to the spring season. Considering the performance of different agronomic parameters, we recommend genotypes “TH-CAN-SPB”, “Calinaro”, “CHE-GRE-G” for both fall and spring growing season. Other genotypes such as “CHE-GRE-A”, “CHE-BAL-A” and “CHE-MIC” and “Line 701” are also recommended for cultivation in spring growing season specifically due to the high marketable yield and share of marketable heads. In addition, this thesis aimed at testing a fast analytical technique for determination of glucosinolates content in order to help breeders to quickly test their most favorable genotypes during breeding procedures based on glucosinolates content. For this purpose, the accuracy of NIRS technic was tested, regardless of type of genotype, for fast analysis of the individual and total glucosinolates content of broccoli samples. NIRS calibration was developed by reference method of High Performance Liquid Chromatography (HPLC) based on modified partial least squares regression, to measure individual and total glucosinolates content of open pollinating genotypes of broccoli regardless of the type of genotype. The calibration was analyzed using coefficient of determination in prediction (R2) and ratio of preference of determination (RPD). Large variation occurred in the calibrations, R2 and RPD due to the variability of the samples. Derived calibrations for total glucosinolates (RPD = 1.36), aliphatic glucosinolates (RPD = 1.65), glucoraphanin (RPD = 1.63) and 4-methoxyglucobrassicin (RPD = 1.11) were quantitative with a high accuracy, while for indole glucosinolates (RPD = 0.95), glucosinigrin (RPD = 0.62), glucoiberin (RPD = 0.67), glucobrassicin (RPD = 0.81) and neoglucobrassicin (RPD = 0.56) they were more qualitative. Overall, the results showed a good potential of NIRS in determination of different glucosinolates in a large sample pool of broccoli quantitatively and qualitatively. The achieved calibration equations were used to measure glucosinolates content of the broccoli samples of following years. To evaluate the health beneficial value of the open pollinating genotypes, the glucosinolates content of them were determined. The determination was done by the tested NIRS technic. Six individual glucosinolates were detected in the broccoli samples similar to findings of the previous chapter. Glucoraphanin (1.44-1.69 µmol g-1 DW), glucobrassicin (0.63-0.77 µmol g-1 DW) and neoglucobrassicin (0.38-0.74 µmol g-1 DW) had the highest share and were the main individual glucosinolates. Total glucosinolates content ranged from 3.46 to 3.60 µmol g-1 DW across both growing season. Significant effect of genotype and growing season existed on the total glucosinolates content of broccoli samples. All individual glucosinolates were affected by genotype. The effect of growing season was significant on all individual glucosinolates, except for glucobrassicin. The interaction of genotype × growing season was significant on all indole glucosinolates, glucoraphanin and glucoiberin. Generally, the glucosinolates content of the samples were higher when broccoli genotypes were cultivated in the fall growing season, however the difference in the level of glucosinolates contents across seasons was significant only for glucoraphanin, neoglucobrassicin, 4-methoxyglucobrassicin and glucoiberin. The open pollinating genotypes showed a similar range of glucosinolates compared to the tested hybrids and performed as good as the hybrids. Since total glucosinolates were nearly similar in all open pollinating genotypes across seasons, all are recommended for cultivation in both growing seasons. It is important to note that this study only focused on a single health beneficial compound (glucosinolate) in broccoli heads. To provide a full insight into the nutritive and health benefiting compounds of broccoli such as vitamins and polyphenols, supplementary studies will have to be conducted. All in all, releasing new open pollinating broccoli varieties out of this pool of genotypes and replacing the present varieties with them seemed beneficial due to the well adapted agronomic performance and high health value with regard to glucosinolates content under organic farming conditions.