Recent advances in fishy odour in aquatic fish products,from formation to control

Aquatic products are one of the most important foods with plenty of high-quality protein, unsaturated fatty acids (EPA, DHA), a variety of minerals and other essential nutrients. However, the bad smell of fish, such as fishy smell and earthy smell, restricts its production and consumption. The main fishy odour substances from freshwater fish and marine fish are different. The geosmin and 2-methylisobomeol are the main compounds in freshwater fish, and aldehydes, alcohols and ketones are found in most marine fish. The odour compounds can come from environment like water, feed and alga, enzymolysis and oxidative reactions of protein and lipid. Thus, it is necessary to remove or inhibit odour by managing farming environment like improving water quality, using physical method like adding some substance to cover the bad smell and using some chemical or biological method to prevent enzymolysis or oxidation. Therefore, knowing the composition of fishy substances and understanding their production pathways will play an important role in suppressing fishy substances and improving the competitiveness of consumer production. Besides, it could provide new ideas for innovative deodorising methods.     

Deodorisation of fish oil by nanofiltration membrane process: focus on volatile flavour compounds and fatty acids composition

This study focuses on the investigations for the deodorisation of tuna oil and squid oil through n‐hexane extraction and nanofiltration membrane process with a molecular weight cut‐off of 360 Da. The change of the odour and the fatty acids composition were analysed. Volatile components analysed by monolithic material sorptive extraction (MMSE) combined with gas chromatography–mass spectrometry (GC‐MS) suggested that nanofiltration membrane process could remove the majority of the volatile components, and the removal rate was approximate to 80%. The odour activity values (OAVs) of the volatile components in tuna oil and squid oil were significantly reduced from 125.23 to 17.47 and 129.76 to 10.06 (P < 0.05), respectively. On the other hand, the contents of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were increased as expected. These results indicated that the organic solvent nanofiltration technique had obvious effects on deodorisation of fish oil, and it would be a promising deodorisation method in fish oil refining industry.     

Deodorisation of off-odour during sweet potato juice production by employing physical and chemical deodorants

The mechanism and efficiency of three types of deodorants, namely activated carbon (AC), maltosyl cyclodextrin (MCD) and apple polyphenol (AP), in reducing the “boiled heavy odour” of saccharified sweet potato juice was investigated. The highest deodorising efficiency of AC, followed by MCD and AP, was confirmed by using the electronic nose and sensory analysis. Furthermore, flavour compounds in the sweet potato juice were identified by GC–MS analysis. While AC decreased the peak intensities of all the compounds to below the minimum detection limit, MCD, which eliminated the odour components by the formation of enclosure compounds, did not reduce the peak intensities to a similar extent. The mechanisms of adsorption with AC and envelopment with MCD for the identified odour components of sweet potato juice was also clarified.     

Optimisation of sunflower oil deodorising: balance between oil stability and other quality attributes

The effect of deodorising on basic quality attributes of sunflower oil (free fatty acids, colour, oil stability, total tocopherols) was investigated. The results revealed that the levels of all these quality attributes decreased significantly during the deodorising step. The processing parameters of sunflower oil deodorisation were optimised using response surface methodology. The results revealed the effects of process parameters (temperature, time) on free fatty acids (FFA), colour (LCY and LCR), oil stability index (OSI) and total tocopherols (VE). These new models can be used as a tool to identify optimum deodorisation conditions within chosen constraints. Based on the optimisation of high oil stability with minimum retained FFA and colour, deodorisation parameters can be defined. At a constant vacuum, 3 mmHg vacuum, a temperature range of 200–250 °C and deodorisation time of 30–90 min were defined. An optimum temperature and time appear to be 218–224 °C and 59–64 min, respectively.     

Influence of chemical refining process and oil type on bound 3-chloro-1,2-propanediol contents in palm oil and rapeseed oil

The formation of bound 3-chloro-1,2-propanediol (3-MCPD-ester) in oils during chemical refining process was investigated for two palm oils and one rapeseed oil. Additionally, contents of mono- and diglycerides as well as total chlorine and chloride were determined. For all oils the deodorisation step representing one part of the refining process had the main impact on formation of 3-MCPD-esters whereas a direct effect of the other process steps could be neglected. 3-MCPD values in the range of 4–5 ppm for palm oil and 1 ppm for rapeseed oil were found. The chloride content was below detection limit. However, measurable amounts of total chlorine were found in palm oil with the highest 3-MCPD-ester contents. A considerable part of this total chlorine in the refined palm oil was embedded in the 3-MCPD-esters. On the other hand, content of diglycerides as the other potential pre-cursor was between 1% and 10% exceeding the 3-MCPD-ester contents by up to five magnitudes.     

除臭用陶瓷催化器的工艺初探

阐述了除臭用陶瓷催化器的催化机理 ,详细探讨了多孔陶瓷载体的研制、表层活性氧化铝的涂载技术 ,以及贵金属催化剂的浸渍工艺     

Deodorisation process variables for croaker (M. furnieri) oil

Fish oil is the major food source of the long-chain omega-3 polyunsaturated fatty acids. Deodorisation represents a critical step of the refining process since it involves high temperature that could induce degradation reactions which affect oil integrity and quality. The present study evaluated the effect of the deodorisation variables (temperature, time and steam) on the croaker (Micropogonias furnieri) oil refining process. The evaluated parameters were Lovibond color (LC), free fatty acids (FFA), peroxide (PV), Iodine (IV) and Saponification (SV) values. The best deodorisation conditions were at 220 °C, 60 min and 5% of steam (based in oil mass), resulting in oil with LC of 0.4 red and 30 yellow, FFA of 0.09%, PV of 0.53 meq/kg. IV and SV were not significantly affected. The obtained fish oil presented high quality and oxidative stability, as well as EPA and DHA contents of approximately 12% of total fatty acids.     

Glycidyl esters in refined palm (Elaeis guineensis) oil and related fractions. Part I: Formation mechanism

Glycidyl esters (GE) are process contaminants generated during the deodorisation step of edible oil refining. In particular, GE are found in high abundance in refined palm oil. Palm oil is unique in that it contains a high amount of diacylglycerols (DAG, 4-12%). In the present study, a series of model reactions mimicking palm oil deodorisation has been conducted with pure tri-, di- and mono-acylglycerols (MAG). Results showed that GE are formed from DAG and MAG, but not from TAG, at temperatures (T) above 200 °C. Our observations suggest that GE are formed predominantly by intramolecular elimination of a fatty acid from DAG. In addition, isomers of GE, formed from DAG heated at T > 140 °C, were identified as oxopropyl esters. These new isomers were found to represent approximately 10% of GE levels in refined palm oil. Based on these considerations, the final GE content of palm oil could be limited by reducing DAG levels before oil processing and minimising deodorisation temperatures.