Assessment of the Performance of Electrodialysis in the Removal of the Most Potent Odor-Active Compounds of Herring Milt Hydrolysate: Focus on Ion-Exchange Membrane Fouling and Water Dissociation as Limiting Process Conditions

Abstract

Herring milt hydrolysate (HMH), like many fish products, presents the drawback to be associated with off-flavors. As odor is an important criterion, an effective deodorization method targeting the volatile compounds responsible for off-flavors needs to be developed. The potential of electrodialysis (ED) to remove the 15 volatile compounds identified, in the first part of this work, for their main contribution to the odor of HMH, as well as trimethylamine, dimethylamine and trimethylamine oxide, was assessed by testing the impact of both hydrolysate pH (4 and 7) and current conditions (no current vs. current applied). The ED performance was compared with that of a deaerator by assessing three hydrolysate pH values (4, 7 and 10). The initial pH of HMH had a huge impact on the targeted compounds, while ED had no effect. The fouling formation, resulting from electrostatic and hydrophobic interactions between HMH constituents and ion-exchange membranes (IEM); the occurrence of water dissociation on IEM interfaces, due to the reaching of the limiting current density; and the presence of water dissociation catalyzers were considered as the major limiting process conditions. The deaerator treatment on hydrolysate at pH 7 and its alkalization until pH 10 led to the best removal of odorant compounds.

Development of a New Deodorization Method of Herring Milt Hydrolysate: Impacts of pH, Stirring with Nitrogen and Deaerator Treatment on the Odorous Content

“…HMH solutions were then stirred overnight at 4 °C, while protected from light by being covered with aluminum foil, either with nitrogen or without depending on the tested conditions before being finally treated or not by a deaerator device model ERV2 (Koruma, Neuenburg, Germany) ( Figure 1 ). Treatment by deaerator was conducted for 30 min under 100 Torr in a closed circuit in accordance with the procedure described by Todeschini et al (2020) [ 12 ]. Before use, the deaerator was decontaminated with Oxygerm solution consisting in a mix of organic acids and powerful oxidizers.…”

“…To assess the DMA, TMA and TMAO contents, headspace (HS) gas chromatography (GC) with a nitrogen-phosphorus detector (NPD) was used. Samples were prepared as previously described by Todeschini et al (2020) [ 12 ]. Summarily, 2 mL of standards or samples were transferred into vials of 20 mL and alkalized to pH 10 with 0.1 M or 5 M NaOH solutions depending on their initial pH to avoid any dilution effect.…”

“…In the case of herring milt hydrolysate (HMH), antioxidant and anti-inflammatory activities were reported in vitro [ 7 , 8 ] while the ability of this latter to modulate diabetes pathology was demonstrated at both in vitro and in vivo levels [ 2 , 7 , 9 , 10 ]. However, HMH, like other fish hydrolysates and fish-related products, has the main disadvantage to be associated with unpleasant odors and this limits its use in spite of the aforementioned promising aspects [ 11 , 12 ]. Therefore, there is a real need to address this major issue.…”

“…In addition to these nitrogenous compounds, other compounds belonging to various chemical groups such as aldehydes, ketones or sulfur-containing compounds have been reported to be an important cause of off-flavors as well [ 11 ]. In the case of HMH more particularly, the presence of TMA, DMA and TMAO has recently been evidenced in addition to the major contribution to its odor of 15 compounds belonging mainly to the aldehyde chemical group [ 12 ]. Interestingly, among these 15 compounds, most of them have already been identified as being important contributors to the odor of other fish products except for 1-methyl-1H-tetrazole and (Z)-6-octen-2-one that would be more characteristic of the HMH smell [ 12 ].…”

“…Therefore, there is a real need to develop an effective deodorization method. Recently, Todeschini, et al (2020) showed that a deaerator treatment conducted on HMH at neutral pH preliminary stirred overnight with nitrogen as well as a simple alkalization of this latter could decrease its most potent odor-active compound contents as well as those of TMAO [ 12 ]. Nevertheless, this study neither analyzed the respective role of pH, overnight stirring with nitrogen and deaerator treatment nor the effect of a combination of these three factors with regards to the observed decrease in the targeted odorous compounds.…”